Showing papers in "Molecular Cancer Therapeutics in 2021"

Small Molecule Inhibitors of TEAD Auto-palmitoylation Selectively Inhibit Proliferation and Tumor Growth of NF2-deficient Mesothelioma

Abstract: Mutations in the neurofibromatosis type 2 (NF2) gene that limit or abrogate expression of functional Merlin are common in malignant mesothelioma. Merlin activates the Hippo pathway to suppress nuclear translocation of YAP and TAZ, the major effectors of the pathway that associate with the TEAD transcription factors in the nucleus and promote expression of genes involved in cell proliferation and survival. In this article, we describe the discovery of compounds that selectively inhibit YAP/TAZ-TEAD promoted gene transcription, block TEAD auto-palmitoylation, and disrupt interaction between YAP/TAZ and TEAD. Optimization led to potent analogs with excellent oral bioavailability and pharmacokinetics that selectively inhibit NF2-deficient mesothelioma cell proliferation in vitro and growth of subcutaneous tumor xenografts in vivo These highly potent and selective TEAD inhibitors provide a way to target the Hippo-YAP pathway, which thus far has been undruggable and is dysregulated frequently in malignant mesothelioma and in other YAP-driven cancers and diseases.

The KRASG12C Inhibitor MRTX849 Reconditions the Tumor Immune Microenvironment and Sensitizes Tumors to Checkpoint Inhibitor Therapy.

Abstract: KRASG12C inhibitors, including MRTX849, are promising treatment options for KRAS-mutant non-small cell lung cancer (NSCLC). PD-1 inhibitors are approved in NSCLC; however, strategies to enhance checkpoint inhibitor therapy (CIT) are needed. KRASG12C mutations are smoking-associated transversion mutations associated with high tumor mutation burden, PD-L1 positivity, and an immunosuppressive tumor microenvironment. To evaluate the potential of MRTX849 to augment CIT, its impact on immune signaling and response to CIT was evaluated. In human tumor xenograft models, MRTX849 increased MHC class I protein expression and decreased RNA and/or plasma protein levels of immunosuppressive factors. In a KrasG12C -mutant CT26 syngeneic mouse model, MRTX849 decreased intratumoral myeloid-derived suppressor cells and increased M1-polarized macrophages, dendritic cells, CD4+, and CD8+ T cells. Similar results were observed in lung KrasG12C -mutant syngeneic and a genetically engineered mouse (GEM) model. In the CT26 KrasG12C model, MRTX849 demonstrated marked tumor regression when tumors were established in immune-competent BALB/c mice; however, the effect was diminished when tumors were grown in T-cell-deficient nu/nu mice. Tumors progressed following anti-PD-1 or MRTX849 single-agent treatment in immune-competent mice; however, combination treatment demonstrated durable, complete responses (CRs). Tumors did not reestablish in the same mice that exhibited durable CRs when rechallenged with tumor cell inoculum, demonstrating these mice developed adaptive antitumor immunity. In a GEM model, treatment with MRTX849 plus anti-PD-1 led to increased progression-free survival compared with either single agent alone. These data demonstrate KRAS inhibition reverses an immunosuppressive tumor microenvironment and sensitizes tumors to CIT through multiple mechanisms.

CSF1/CSF1R Signaling Inhibitor Pexidartinib (PLX3397) Reprograms Tumor-Associated Macrophages and Stimulates T-cell Infiltration in the Sarcoma Microenvironment.

Abstract: Colony-stimulating factor 1 (CSF1) is a primary regulator of the survival, proliferation, and differentiation of monocyte/macrophage that sustains the protumorigenic functions of tumor-associated macrophages (TAMs) Considering current advances in understanding the role of the inflammatory tumor microenvironment, targeting the components of the sarcoma microenvironment, such as TAMs, is a viable strategy Here, we investigated the effect of PLX3397 (pexidartinib) as a potent inhibitor of the CSF1 receptor (CSF1R) PLX3397 was recently approved by the Food and Drug Administration (FDA) to treat tenosynovial giant cell tumor and reprogram TAMs whose infiltration correlates with unfavorable prognosis of sarcomas First, we confirmed by cytokine arrays of tumor-conditioned media (TCM) that cytokines including CSF1 are secreted from LM8 osteosarcoma cells and NFSa fibrosarcoma cells The TCM, like CSF1, stimulated ERK1/2 phosphorylation in bone marrow-derived macrophages (BMDMs), polarized BMDMs toward an M2 (TAM-like) phenotype, and strikingly promoted BMDM chemotaxis In vitro administration of PLX3397 suppressed pERK1/2 stimulation by CSF1 or TCM, and reduced M2 polarization, survival, and chemotaxis in BMDMs Systemic administration of PLX3397 to the osteosarcoma orthotopic xenograft model significantly suppressed the primary tumor growth and lung metastasis, and thus improved metastasis-free survival PLX3397 treatment concurrently depleted TAMs and FOXP3+ regulatory T cells and, surprisingly, enhanced infiltration of CD8+ T cells into the microenvironments of both primary and metastatic osteosarcoma sites Our preclinical results show that PLX3397 has strong macrophage- and T-cell-modulating effects that may translate into cancer immunotherapy for bone and soft-tissue sarcomas

Effects of MTX-23, a Novel PROTAC of Androgen Receptor Splice Variant-7 and Androgen Receptor, on CRPC Resistant to Second-Line Antiandrogen Therapy

Abstract: Although second-line antiandrogen therapy (SAT) is the standard of care in men with castration-resistant prostate cancer (CRPC), resistance inevitably occurs. One major proposed mechanism of resistance to SAT involves the emergence of androgen receptor (AR) splice variant-7, AR-V7. Recently, we developed MTX-23 using the principle of proteolysis targeting chimera (PROTAC) to target both AR-V7 and AR-full length (AR-FL). MTX-23 has been designed to simultaneously bind AR's DNA binding domain (DBD) and the Von Hippel-Lindau (VHL) E3 ubiquitin ligase. Immunoblots demonstrated that MTX-23's degradation concentration 50% (DC50) for AR-V7 and AR-FL was 0.37 and 2 μmol/L, respectively. Further studies revealed that MTX-23 inhibited prostate cancer cellular proliferation and increased apoptosis only in androgen-responsive prostate cancer cells. The antiproliferative effect of MTX-23 was partially reversed when either AR-V7 or AR-FL was overexpressed and was completely abrogated when both were overexpressed. To assess the potential therapeutic value of MTX-23, we next generated 12 human prostate cancer cell lines that are resistant to the four FDA-approved SAT agents-abiraterone, enzalutamide, apalutamide, and darolutamide. When resistant cells were treated with MTX-23, decreased cellular proliferation and reduced tumor growth were observed both in vitro and in mice. These results collectively suggest that MTX-23 is a novel PROTAC small molecule that may be effective against SAT-resistant CRPC by degrading both AR-V7 and AR-FL.

The Glutaminase Inhibitor CB-839 (Telaglenastat) Enhances the Antimelanoma Activity of T-Cell–Mediated Immunotherapies

Abstract: Immune-checkpoint inhibitors and adoptive tumor-infiltrating lymphocyte (TIL) therapies have profoundly improved the survival of patients with melanoma. However, a majority of patients do not respond to these agents, and many responders experience disease relapse. Although numerous innovative treatments are being explored to offset the limitations of these agents, novel therapeutic combinations with immunotherapies have the potential to improve patient responses. In this study, we evaluated the antimelanoma activity of immunotherapy combinations with Telaglenastat (CB-839), a potent glutaminase inhibitor (GLSi) that has favorable systemic tolerance. In in vitro TIL:tumor coculture studies, CB-839 treatment improved the cytotoxic activity of autologous TILs on patient-derived melanoma cells. CB-839 treatment decreased the conversion of glutamine to alpha-ketoglutarate (αKGA) more potently in tumor cells versus TILs in these cocultures. These results suggest that CB-839 may improve immune function in a tumor microenvironment by differentially altering tumor and immune cell metabolism. In vivo CB-839 treatment activated melanoma antigen-specific T cells and improved their tumor killing activity in an immune-competent mouse model of adoptive T-cell therapy. Additionally, the combination of CB-839 with anti-PD1 or anti-CTLA4 antibodies increased tumor infiltration by effector T cells and improved the antitumor activity of these checkpoint inhibitors in a high mutation burden mouse melanoma model. Responsiveness to these treatments was also accompanied by an increase of interferon gamma (IFNγ)-associated gene expression in the tumors. Together, these results provide a strong rationale for combining CB-839 with immune therapies to improve efficacy of these treatments against melanoma.

Innate Immune Checkpoint Inhibitors: The Next Breakthrough in Medical Oncology?

Abstract: While immunotherapy has revolutionized the treatment of many types of advanced cancer, most patients still do not derive benefit. The currently available immune checkpoint inhibitors target the adaptive immune system, generating a T-cell antitumor response. However, an antitumor immune response depends on a complex interplay of both innate and adaptive immune cells. The innate immune system is a promising new target, and innate immune checkpoint inhibitors can disrupt inhibitory interactions ("don't eat me" signals) between tumor and both phagocytes and natural killer cells. The checkpoint inhibitor may also provide a stimulatory interaction ("eat me" signal), or this can be achieved through use of combination therapy. This generates antitumor effector functions including phagocytosis, natural cytotoxicity, antibody-dependent effects, and synergistic activation of the adaptive immune system via antigen presentation. This is a rapidly expanding area of drug development, either alone or in combination (with anticancer antibodies or adaptive immune checkpoint inhibitors). Here, we comprehensively review the mechanism of action and up-to-date solid tumor clinical trial data of the drugs targeting phagocytosis checkpoints (SIRPα/CD47, LILRB1/MHC-I, and LILRB2/MHC-I) and natural killer-cell checkpoints (TIGIT/CD112 + CD155, PVRIG/CD112, KIRs/MHC-I, and NKG2A-CD94/HLA-E). Innate immune checkpoint inhibitors could once again revolutionize immune-based cancer therapies.

Novel and Highly Potent ATR Inhibitor M4344 Kills Cancer Cells With Replication Stress, and Enhances the Chemotherapeutic Activity of Widely Used DNA Damaging Agents

Abstract: Although several ATR inhibitors are in development, there are unresolved questions regarding their differential potency, molecular signatures of patients with cancer for predicting activity, and most effective therapeutic combinations Here, we elucidate how to improve ATR-based chemotherapy with the newly developed ATR inhibitor, M4344 using in vitro and in vivo models The potency of M4344 was compared with the clinically developed ATR inhibitors BAY1895344, berzosertib, and ceralasertib The anticancer activity of M4344 was investigated as monotherapy and combination with clinical DNA damaging agents in multiple cancer cell lines, patient-derived tumor organoids, and mouse xenograft models We also elucidated the anticancer mechanisms and potential biomarkers for M4344 We demonstrate that M4344 is highly potent among the clinically developed ATR inhibitors Replication stress (RepStress) and neuroendocrine (NE) gene expression signatures are significantly associated with a response to M4344 treatment M4344 kills cancer cells by inducing cellular catastrophe and DNA damage M4344 is highly synergistic with a broad range of DNA-targeting anticancer agents It significantly synergizes with topotecan and irinotecan in patient-derived tumor organoids and xenograft models Taken together, M4344 is a promising and highly potent ATR inhibitor It enhances the activity of clinical DNA damaging agents commonly used in cancer treatment including topoisomerase inhibitors, gemcitabine, cisplatin, and talazoparib RepStress and NE gene expression signatures can be exploited as predictive markers for M4344

Exosome Surface Display of IL12 Results in Tumor-Retained Pharmacology with Superior Potency and Limited Systemic Exposure Compared with Recombinant IL12.

Abstract: The promise of IL12 as a cancer treatment has yet to be fulfilled with multiple tested approaches being limited by unwanted systemic exposure and unpredictable pharmacology. To address these limitations, we generated exoIL12, a novel, engineered exosome therapeutic that displays functional IL12 on the surface of an exosome. IL12 exosomal surface expression was achieved via fusion to the abundant exosomal surface protein PTGFRN resulting in equivalent potency in vitro to recombinant IL12 (rIL12) as demonstrated by IFNγ production. Following intratumoral injection, exoIL12 exhibited prolonged tumor retention and greater antitumor activity than rIL12. Moreover, exoIL12 was significantly more potent than rIL12 in tumor growth inhibition. In the MC38 model, complete responses were observed in 63% of mice treated with exoIL12; in contrast, rIL12 resulted in 0% complete responses at an equivalent IL12 dose. This correlated with dose-dependent increases in tumor antigen-specific CD8+ T cells. Rechallenge studies of exoIL12 complete responder mice showed no tumor regrowth, and depletion of CD8+ T cells completely abrogated antitumor activity of exoIL12. Following intratumoral administration, exoIL12 exhibited 10-fold higher intratumoral exposure than rIL12 and prolonged IFNγ production up to 48 hours. Retained local pharmacology of exoIL12 was further confirmed using subcutaneous injections in nonhuman primates. This work demonstrates that tumor-restricted pharmacology of exoIL12 results in superior in vivo efficacy and immune memory without systemic IL12 exposure and related toxicity. ExoIL12 is a novel cancer therapeutic candidate that overcomes key limitations of rIL12 and thereby creates a therapeutic window for this potent cytokine.

Belantamab Mafodotin (GSK2857916) Drives Immunogenic Cell Death and Immune-Mediated Anti-Tumor Responses In Vivo

Abstract: B-cell maturation antigen (BCMA) is an attractive therapeutic target highly expressed on differentiated plasma cells in multiple myeloma (MM) and other B-cell malignancies. GSK2857916 (belantamab mafodotin, BLENREP) is a BCMA-targeting antibody-drug-conjugate approved for the treatment of relapsed/refractory MM. We report that GSK2857916 induces immunogenic cell death in BCMA-expressing cancer cells and promotes dendritic cell activation in vitro and in vivo. GSK2857916 treatment enhances intra-tumor immune cell infiltration and activation, delays tumor growth and promotes durable complete regressions in immune-competent mice bearing EL4 lymphoma tumors expressing human BCMA (EL4-hBCMA). Responding mice are immune to re-challenge with EL4 parental and EL4-hBCMA cells, suggesting engagement of an adaptive immune response, immunologic memory, and tumor antigen spreading, which are abrogated upon depletion of endogenous CD8+ T-cells. Combinations with OX40/OX86, an immune agonist antibody, significantly enhance anti-tumor activity and increase durable complete responses, providing a strong rationale for clinical evaluation of GSK2857916 combinations with immunotherapies targeting adaptive immune responses, including T-cell-directed checkpoint modulators.

TPX-0131, a Potent CNS-penetrant, Next-generation Inhibitor of Wild-type ALK and ALK-resistant Mutations

Abstract: Since 2011, with the approval of crizotinib and subsequent approval of four additional targeted therapies, anaplastic lymphoma kinase (ALK) inhibitors have become important treatments for a subset of patients with lung cancer. Each generation of ALK inhibitor showed improvements in terms of central nervous system (CNS) penetration and potency against wild-type (WT) ALK, yet a key continued limitation is their susceptibility to resistance from ALK active-site mutations. The solvent front mutation (G1202R) and gatekeeper mutation (L1196M) are major resistance mechanisms to the first two generations of inhibitors while patients treated with the third-generation ALK inhibitor lorlatinib often experience progressive disease with multiple mutations on the same allele (mutations in cis, compound mutations). TPX-0131 is a compact macrocyclic molecule designed to fit within the ATP-binding boundary to inhibit ALK fusion proteins. In cellular assays, TPX-0131 was more potent than all five approved ALK inhibitors against WT ALK and many types of ALK resistance mutations, e.g., G1202R, L1196M, and compound mutations. In biochemical assays, TPX-0131 potently inhibited (IC50 <10 nmol/L) WT ALK and 26 ALK mutants (single and compound mutations). TPX-0131, but not lorlatinib, caused complete tumor regression in ALK (G1202R) and ALK compound mutation-dependent xenograft models. Following repeat oral administration of TPX-0131 to rats, brain levels of TPX-0131 were approximately 66% of those observed in plasma. Taken together, preclinical studies show that TPX-0131 is a CNS-penetrant, next-generation ALK inhibitor that has potency against WT ALK and a spectrum of acquired resistance mutations, especially the G1202R solvent front mutation and compound mutations, for which there are currently no effective therapies.

Dolaflexin: A Novel Antibody-Drug Conjugate Platform Featuring High Drug Loading and a Controlled Bystander Effect.

Abstract: After significant effort over the last 30 years, antibody-drug conjugates (ADC) have recently gained momentum as a therapeutic modality, and nine ADCs have been approved by the FDA to date, with additional ADCs in late stages of development. Here, we introduce dolaflexin, a novel ADC technology that overcomes key limitations of the most common ADC platforms with two key features: a higher drug-to-antibody ratio and a novel auristatin with a controlled bystander effect. The novel, cell permeable payload, auristatin F-hydroxypropylamide, undergoes metabolic conversion to the highly potent, but less cell permeable auristatin F to balance the bystander effect through drug trapping within target cells. We conducted studies in mice, rats, and cynomolgus monkeys to complement in vitro characterization and contrasted the performance of dolaflexin with regard to antitumor activity, pharmacokinetic properties, and safety in comparison with the ADC platform utilized in the approved ADC ado-trastuzumab emtansine (T-DM1). A HER2-targeted dolaflexin ADC was shown to have a much lower threshold of antigen expression for potent cell killing in vitro, was effective in vivo in tumors with low HER2 expression, and induced tumor regressions in a xenograft model that is resistant to T-DM1.

HDP-101, an Anti-BCMA Antibody-Drug Conjugate, Safely Delivers Amanitin to Induce Cell Death in Proliferating and Resting Multiple Myeloma Cells.

Abstract: Despite major treatment advances in recent years, patients with multiple myeloma inevitably relapse. The RNA polymerase II complex has been identified as a promising therapeutic target in both proliferating and dormant cancer cells. Alpha-amanitin, a toxin so far without clinical application due to high liver toxicity, specifically inhibits this complex. Here, we describe the development of HDP-101, an anti-B-cell maturation antigen (BCMA) antibody conjugated with an amanitin derivative. HDP-101 displayed high efficacy against both proliferating and resting myeloma cells in vitro, sparing BCMA-negative cells. In subcutaneous and disseminated murine xenograft models, HDP-101 induced tumor regression at low doses, including durable complete remissions after a single intravenous dose. In cynomolgus monkeys, HDP-101 was well tolerated with a promising therapeutic index. In conclusion, HDP-101 safely and selectively delivers amanitin to myeloma cells and provides a novel therapeutic approach to overcome drug resistance in this disease.

Restoration of T-cell Effector Function, Depletion of Tregs, and Direct Killing of Tumor Cells: The Multiple Mechanisms of Action of a-TIGIT Antagonist Antibodies.

Abstract: TIGIT is an immune checkpoint inhibitor expressed by effector CD4+ and CD8+ T cells, NK cells, and regulatory T cells (Tregs). Inhibition of TIGIT-ligand binding using antagonistic anti-TIGIT mAbs has shown in vitro potential to restore T-cell function and therapeutic efficacy in murine tumor models when combined with an anti–PD(L)-1 antibody. In the current work, we demonstrate broader TIGIT expression than previously reported in healthy donors and patients with cancer with expression on γδ T cells, particularly in CMV-seropositive donors, and on tumor cells from hematologic malignancies. Quantification of TIGIT density revealed tumor-infiltrating Tregs as the population expressing the highest receptor density. Consequently, the therapeutic potential of anti-TIGIT mAbs might be wider than the previously described anti–PD(L)-1-like restoration of αβ T-cell function. CD155 also mediated inhibition of γδ T cells, an immune population not previously described to be sensitive to TIGIT inhibition, which could be fully prevented via use of an antagonistic anti-TIGIT mAb (EOS-448). In PBMCs from patients with cancer, as well as in tumor-infiltrating lymphocytes from mice, the higher TIGIT expression in Tregs correlated with strong antibody-dependent killing and preferential depletion of this highly immunosuppressive population. Accordingly, the ADCC/ADCP–enabling format of the anti-TIGIT mAb had superior antitumor activity, which was dependent upon Fcγ receptor engagement. In addition, the anti-TIGIT mAb was able to induce direct killing of TIGIT-expressing tumor cells both in human patient material and in animal models, providing strong rationale for therapeutic intervention in hematologic malignancies. These findings reveal multiple therapeutic opportunities for anti-TIGIT mAbs in cancer therapeutics.

SAR439859, a Novel Selective Estrogen Receptor Degrader (SERD), Demonstrates Effective and Broad Antitumor Activity in Wild-Type and Mutant ER-Positive Breast Cancer Models.

Abstract: Primary treatment for estrogen receptor-positive (ER+) breast cancer is endocrine therapy. However, substantial evidence indicates a continued role for ER signaling in tumor progression. Selective estrogen receptor degraders (SERD), such as fulvestrant, induce effective ER signaling inhibition, although clinical studies with fulvestrant report insufficient blockade of ER signaling, possibly due to suboptimal pharmaceutical properties. Furthermore, activating mutations in the ER have emerged as a resistance mechanism to current endocrine therapies. New oral SERDs with improved drug properties are under clinical investigation, but the biological profile that could translate to improved therapeutic benefit remains unclear. Here, we describe the discovery of SAR439859, a novel, orally bioavailable SERD with potent antagonist and degradation activities against both wild-type and mutant Y537S ER. Driven by its fluoropropyl pyrrolidinyl side chain, SAR439859 has demonstrated broader and superior ER antagonist and degrader activities across a large panel of ER+ cells, compared with other SERDs characterized by a cinnamic acid side chain, including improved inhibition of ER signaling and tumor cell growth. Similarly, in vivo treatment with SAR439859 demonstrated significant tumor regression in ER+ breast cancer models, including MCF7-ESR1 wild-type and mutant-Y537S mouse tumors, and HCI013, a patient-derived tamoxifen-resistant xenograft tumor. These findings indicate that SAR439859 may provide therapeutic benefit to patients with ER+ breast cancer, including those who have resistance to endocrine therapy with both wild-type and mutant ER.

Targeting Oncogene mRNA Translation in B-Cell Malignancies with eFT226, a Potent and Selective Inhibitor of eIF4A.

Abstract: The PI3K/AKT/mTOR pathway is often activated in lymphoma through alterations in PI3K, PTEN, and B-cell receptor signaling, leading to dysregulation of eIF4A (through its regulators, eIF4B, eIF4G, and PDCD4) and the eIF4F complex. Activation of eIF4F has a direct role in tumorigenesis due to increased synthesis of oncogenes that are dependent on enhanced eIF4A RNA helicase activity for translation. eFT226, which inhibits translation of specific mRNAs by promoting eIF4A1 binding to 5'-untranslated regions (UTR) containing polypurine and/or G-quadruplex recognition motifs, shows potent antiproliferative activity and significant in vivo efficacy against a panel of diffuse large B-cell lymphoma (DLBCL), and Burkitt lymphoma models with ≤1 mg/kg/week intravenous administration. Evaluation of predictive markers of sensitivity or resistance has shown that activation of eIF4A, mediated by mTOR signaling, correlated with eFT226 sensitivity in in vivo xenograft models. Mutation of PTEN is associated with reduced apoptosis in vitro and diminished efficacy in vivo in response to eFT226. In models evaluated with PTEN loss, AKT was stimulated without a corresponding increase in mTOR activation. AKT activation leads to the degradation of PDCD4, which can alter eIF4F complex formation. The association of eFT226 activity with PTEN/PI3K/mTOR pathway regulation of mRNA translation provides a means to identify patient subsets during clinical development.

Targeting Radiation-Resistant Prostate Cancer Stem Cells by B7-H3 CAR T Cells.

Abstract: Radiotherapy (RT) is a key treatment for prostate cancer. However, RT resistance can contribute to treatment failure. Prostate cancer stem cells (PCSCs) are radioresistant. We recently found that fractionated irradiation (FIR) upregulates expression of the immune checkpoint B7-H3 (CD276) on PCSCs and bulk cells in each prostate cancer cell line tested. These findings prompted us to investigate whether B7-H3 targeting chimeric antigen receptor (CAR) T cells, which may abrogate function of an immune checkpoint and mediate lysis of targeted cells, can target RT-resistant PCSCs in vitro and in vivo. B7-H3 expression is naturally higher on PCSCs than bulk prostate cancer cells and cytotoxicity of B7-H3 CAR T cells to PCSCs is more potent than to bulk prostate cancer cells. Furthermore, FIR significantly upregulates B7-H3 expression on PCSCs and bulk prostate cancer cells. The duration of FIR or single-dose irradiation-induced further upregulation of B7-H3 on bulk prostate cancer cells and PCSCs lasts for up to 3 days. B7-H3 CAR T-cell cytotoxicity against FIR-resistant PCSCs at a low effector to target ratio of 1:1 was assessed by flow cytometry and sphere formation assays. Further upregulation of B7-H3 expression by FIR made PCSCs even more sensitive to B7-H3 CAR T-cell-mediated killing. Consequently, the FIR and B7-H3 CAR T-cell therapy combination is much more effective than FIR or CAR T cells alone in growth inhibition of hormone-insensitive prostate cancer xenografts in immunodeficient mice. Our work provides a sound basis for further development of this unique combinatorial model of RT and B7-H3 CAR T-cell therapy for prostate cancer. SIGNIFICANCE: We demonstrate that FIR significantly upregulates B7-H3 expression by RT-resistant PCSCs and bulk cells; cytotoxicity of B7-H3 CAR T cells to FIR-treated PCSCs is potent and results in significantly improved antitumor efficacy in mice.

First-in-Human, Phase 1 Dose-Escalation Study of Biparatopic Anti-HER2 Antibody-Drug Conjugate MEDI4276 in Patients with HER2-positive Advanced Breast or Gastric Cancer.

Abstract: MEDI4276 is a biparatopic tetravalent antibody targeting two nonoverlapping epitopes in subdomains 2 and 4 of the HER2 ecto-domain, with site-specific conjugation to a tubulysin-based microtubule inhibitor payload. MEDI4276 demonstrates enhanced cellular internalization and cytolysis of HER2-positive tumor cells in vitro This was a first-in-human, dose-escalation clinical trial in patients with HER2-positive advanced or metastatic breast cancer or gastric cancer. MEDI4276 doses escalated from 0.05 to 0.9 mg/kg (60- to 90-minute intravenous infusion every 3 weeks). Primary endpoints were safety and tolerability; secondary endpoints included antitumor activity (objective response, progression-free survival, and overall survival), pharmacokinetics, and immunogenicity. Forty-seven patients (median age 59 years; median of seven prior treatment regimens) were treated. The maximum tolerated dose was exceeded at 0.9 mg/kg with two patients experiencing dose-limiting toxicities (DLTs) of grade 3 liver function test (LFT) increases, one of whom also had grade 3 diarrhea, which resolved. Two additional patients reported DLTs of grade 3 LFT increases at lower doses (0.4 and 0.6 mg/kg). The most common (all grade) drug-related adverse events (AEs) were nausea (59.6%), fatigue (44.7%), aspartate aminotransferase (AST) increased (42.6%), and vomiting (38.3%). The most common grade 3/4 drug-related AE was AST increased (21.3%). Five patients had drug-related AEs leading to treatment discontinuation. In the as-treated population, there was one complete response (0.5 mg/kg; breast cancer), and two partial responses (0.6 and 0.75 mg/kg; breast cancer)-all had prior trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1). MEDI4276 has demonstrable clinical activity but displays intolerable toxicity at doses >0.3 mg/kg.

Characterization of KRAS Mutation Subtypes in Non-small Cell Lung Cancer.

Abstract: KRAS is the most commonly mutated oncogene in NSCLC and development of direct KRAS inhibitors has renewed interest in this molecular variant. Different KRAS mutations may represent a unique biologic context with different prognostic and therapeutic impact. We sought to characterize genomic landscapes of advanced, KRAS-mutated non–small cell lung cancer (NSCLC) in a large national cohort to help guide future therapeutic development. Molecular profiles of 17,095 NSCLC specimens were obtained using DNA next-generation sequencing of 592 genes (Caris Life Sciences) and classified on the basis of presence and subtype of KRAS mutations. Co-occurring genomic alterations, tumor mutational burden (TMB), and PD-L1 expression [22C3, tumor proportion score (TPS) score] were analyzed by KRAS mutation type. Across the cohort, 4,706 (27.5%) samples harbored a KRAS mutation. The most common subtype was G12C (40%), followed by G12V (19%) and G12D (15%). The prevalence of KRAS mutations was 37.2% among adenocarcinomas and 4.4% in squamous cell carcinomas. Rates of high TMB (≥10 mutations/Mb) and PD-L1 expression varied across KRAS mutation subtypes. KRAS G12C was the most likely to be PD-L1 positive (65.5% TPS ≥ 1%) and PD-L1 high (41.3% TPS ≥ 50%). STK11 was mutated in 8.6% of KRAS wild-type NSCLC but more frequent in KRAS-mutant NSCLC, with the highest rate in G13 (36.2%). TP53 mutations were more frequent in KRAS wild-type NSCLC (73.6%). KRAS mutation subtypes have different co-occurring mutations and a distinct genomic landscape. The clinical relevance of these differences in the context of specific therapeutic interventions warrants investigation.

Preclinical Characterization of Linrodostat Mesylate, a Novel, Potent, and Selective Oral Indoleamine 2,3-Dioxygenase 1 Inhibitor

Abstract: Tumors can exploit the indoleamine 2,3-dioxygenase 1 (IDO1) pathway to create an immunosuppressive microenvironment. Activated IDO1 metabolizes tryptophan into immunosuppressive kynurenine, leading to suppressed effector T-cell (Teff) proliferation, allowing for tumor escape from host immune surveillance. IDO1 inhibition counteracts this immunosuppressive tumor microenvironment and may improve cancer outcomes, particularly when combined with other immunotherapies. Linrodostat mesylate (linrodostat) is a potent, selective oral IDO1 inhibitor that occupies the heme cofactor binding site to prevent further IDO1 activation and is currently in multiple clinical trials for treatment of patients with advanced cancers. Here, we assess the in vitro potency, in vivo pharmacodynamic (PD) activity, and preclinical pharmacokinetics (PK) of linrodostat. Linrodostat exhibited potent cellular activity, suppressing kynurenine production in HEK293 cells overexpressing human IDO1 and HeLa cells stimulated with interferon gamma (IFNɣ), with no activity against tryptophan 2,3-dioxygenase (TDO2) or murine indoleamine 2,3-dioxygenase 2 (IDO2) detected. Linrodostat restored T-cell proliferation in a mixed-lymphocyte reaction of T cells and allogeneic IDO1-expressing dendritic cells. In vivo, linrodostat reduced kynurenine levels in human tumor xenograft models, exhibiting significant PD activity. Linrodostat demonstrated a PK/PD relationship in the xenograft model, preclinical species, and samples from patients with advanced cancers, with high oral bioavailability in preclinical species and low to moderate systemic clearance. Our data demonstrate that linrodostat potently and specifically inhibits IDO1 to block an immunosuppressive mechanism that could be responsible for tumor escape from host immune surveillance with favorable PK/PD characteristics that support clinical development.

Repurposing the Antidepressant Sertraline as SHMT Inhibitor to Suppress Serine/Glycine Synthesis-Addicted Breast Tumor Growth

Abstract: Metabolic rewiring is a hallmark of cancer that supports tumor growth, survival, and chemotherapy resistance. Although normal cells often rely on extracellular serine and glycine supply, a significant subset of cancers becomes addicted to intracellular serine/glycine synthesis, offering an attractive drug target. Previously developed inhibitors of serine/glycine synthesis enzymes did not reach clinical trials due to unfavorable pharmacokinetic profiles, implying that further efforts to identify clinically applicable drugs targeting this pathway are required. In this study, we aimed to develop therapies that can rapidly enter the clinical practice by focusing on drug repurposing, as their safety and cost-effectiveness have been optimized before. Using a yeast model system, we repurposed two compounds, sertraline and thimerosal, for their selective toxicity against serine/glycine synthesis-addicted breast cancer and T-cell acute lymphoblastic leukemia cell lines. Isotope tracer metabolomics, computational docking, enzymatic assays, and drug-target interaction studies revealed that sertraline and thimerosal inhibit serine/glycine synthesis enzymes serine hydroxymethyltransferase and phosphoglycerate dehydrogenase, respectively. In addition, we demonstrated that sertraline's antiproliferative activity was further aggravated by mitochondrial inhibitors, such as the antimalarial artemether, by causing G1-S cell-cycle arrest. Most notably, this combination also resulted in serine-selective antitumor activity in breast cancer mouse xenografts. Collectively, this study provides molecular insights into the repurposed mode-of-action of the antidepressant sertraline and allows to delineate a hitherto unidentified group of cancers being particularly sensitive to treatment with sertraline. Furthermore, we highlight the simultaneous inhibition of serine/glycine synthesis and mitochondrial metabolism as a novel treatment strategy for serine/glycine synthesis-addicted cancers.

In Like a Lamb; Out Like a Lion: Marching CAR T Cells Toward Enhanced Efficacy in B-ALL.

Abstract: Combining synthetic biology with adoptive T-cell transfer has led to promising advances in the treatment of relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL), diffuse large B-cell lymphoma (DLBCL), and mantle cell lymphoma (MCL). Chimeric antigen receptors (CARs) are synthetic receptors that redirect T-cell specificity against cancer. CARs include “built-in” signaling domains that reprogram T-cell metabolism, enhance effector function, and support long-term persistence. Despite their success in blood-based malignancies, relapse can occur in CD19-redirected CAR T-cell therapies for several reasons, including poor engraftment, impaired in vivo proliferation, and T-cell senescence. Herein, we explain how subtle alterations in CAR design may overcome barriers to effective adoptive immunotherapy. We also discuss how the physiochemical properties of the single-chain variable fragment (scFv) affect differentiation and persistence. Moreover, we describe innovative advances in CAR engineering and provide insight into the development of humanized scFvs whose proposed benefits include increased persistence and improved clinical outcomes. Tumor cells can evade CAR T-cell–mediated detection and elimination due to the emergence or presence of CD19-negative leukemic cell subpopulations. We also discuss the opportunities and challenges in targeting other B-ALL–associated antigens. Identifying alternate targets is fundamentally necessary to restore the success of CAR T-cell therapies in CD19-negative patients with B-ALL.

Discovery and Pharmacological Characterization of JNJ-64619178, a Novel Small Molecule Inhibitor of PRMT5 with Potent Anti-Tumor Activity.

Abstract: The protein arginine methyltransferase 5 (PRMT5) methylates a variety of proteins involved in splicing, multiple signal transduction pathways, epigenetic control of gene expression, and mechanisms leading to protein expression required for cellular proliferation. Dysregulation of PRMT5 is associated with clinical features of several cancers including lymphomas, lung cancer, and breast cancer. Here, we describe the characterization of JNJ-64619178, a novel, selective, and potent PRMT5 inhibitor, currently in clinical trials for patients with advanced solid tumors, non-Hodgkin's lymphoma, and lower risk myelodysplastic syndrome. JNJ-64619178 demonstrated a prolonged inhibition of PRMT5 and potent anti-proliferative activity in subsets of cancer cell lines derived from various histologies, including lung, breast, pancreatic, and hematological malignancies. In primary acute myeloid leukemia samples, the presence of splicing factor mutations correlated with a higher ex vivo sensitivity to JNJ-64619178. Furthermore, the potent and unique mechanism of inhibition of JNJ-64619178, combined with highly optimized pharmacological properties, led to efficient tumor growth inhibition and regression in several xenograft models in vivo, with once-daily or intermittent oral dosing schedules. An increase in splicing burden was observed upon JNJ-64619178 treatment. Overall, these observations support the continued clinical evaluation of JNJ-64619178 in patients with aberrant PRMT5 activity driven tumors.

Activity of Combined Androgen Receptor Antagonism and Cell Cycle Inhibition in Androgen Receptor Positive Triple Negative Breast Cancer.

Abstract: Triple-negative breast cancer (TNBC) is an aggressive subtype, with a peak recurrence rate within the first few years after diagnosis. Few targeted therapies are available to treat this breast cancer subtype, defined by the lack of estrogen receptor (ER) and progesterone receptor and without amplification of human epidermal growth factor receptor 2 (HER2). Although cell cycle cyclin-dependent kinase (CDK) 4/6 inhibitors are approved for treatment of ER-positive (ER+) breast cancer, they have not proven effective as monotherapy in patients with TNBC. The androgen receptor (AR) has emerged as a therapeutic target in a subset of TNBCs and with significant clinical benefit observed in multiple trials. The purpose of this study was to investigate the preclinical activity of the CDK4/6 inhibitor, abemaciclib, in combination with an agent that targets both androgen biosynthesis and AR activity, seviteronel, using TNBC cell lines expressing high AR, cell line xenografts, and an AR-positive (AR+), androgen-responsive TNBC patient-derived xenograft (PDX). Single-cell RNA sequencing demonstrated heterogeneity in AR levels, even in a highly AR+ cell line, and identified cell cycle pathway activation in ARHigh- versus ARLow-expressing cells. Combination treatment with the cell cycle CDK4/6 inhibitor, abemaciclib, and seviteronel showed synergy in an AR+ TNBC model compared with each drug alone. Although cell cycle inhibitors are FDA approved for use in ER+ breast cancer, our studies suggest that they may also be effective in AR+ TNBC, perhaps combined with AR-targeted agents.

Shaping Functional Avidity of CAR T Cells: Affinity, Avidity, and Antigen Density That Regulate Response.

Abstract: Chimeric antigen receptors (CARs) are immunoreceptors that redirect T cells to selectively kill tumor cells. Given their clinical successes in hematologic malignancies, there is a strong aspiration to advance this immunotherapy for solid cancers; hence, molecular CAR design and careful target choice are crucial for their function. To evaluate the functional significance of the biophysical properties of CAR binding (i.e., affinity, avidity, and antigen density), we generated an experimental system in which these properties are controllable. We constructed and characterized a series of CARs, which target the melanoma tumor-associated antigen Tyr/HLA-A2, and in which the affinity of the single-chain Fv binding domains ranged in KD from 4 to 400 nmol/L. These CARs were transduced into T cells, and each CAR T-cell population was sorted by the level of receptor expression. Finally, the various CAR T cells were encountered with target cells that present different levels of the target antigen. We detected nonmonotonic behaviors of affinity and antigen density, and an interrelation between avidity and antigen density. Antitumor activity measurements in vitro and in vivo corroborated these observations. Our study contributes to the understanding of CAR T-cell function and regulation, having the potential to improve therapies by the rational design of CAR T cells.See related article on p. 946.

EMT-Induced Gemcitabine Resistance in Pancreatic Cancer Involves the Functional Loss of Equilibrative Nucleoside Transporter 1.

Abstract: Epithelial-mesenchymal transition (EMT) in cancer cells drives cancer chemoresistance, yet the molecular events of EMT that underpin the acquisition of chemoresistance are poorly understood. Here, we demonstrate a loss of gemcitabine chemosensitivity facilitated by human equilibrative nucleoside transporter 1 (ENT1) during EMT in pancreatic cancer and identify that cadherin switching from the epithelial (E) to neuronal (N) type, a hallmark of EMT, contributes to this loss. Our findings demonstrate that N-cadherin decreases ENT1 expression, membrane localization, and gemcitabine transport, while E-cadherin augments each of these. Besides E- and N-cadherin, another epithelial cell adhesion molecule, EpCAM, played a more prominent role in determining ENT1 membrane localization. Forced expression of EpCAM opposed cadherin switching with restored ENT1 expression, membrane localization, and gemcitabine transport in EMT-committed pancreatic cancer cells. In gemcitabine-treated mice, EpCAM-positive tumors had high ENT1 expression and reduced metastasis, whereas tumors with N-cadherin expression resisted gemcitabine treatment and formed extensive secondary metastatic nodules. Tissue microarray profiling and multiplexed IHC analysis of pancreatic cancer patient-derived primary tumors revealed EpCAM and ENT1 cell surface coexpression is favored, and ENT1 plasma membrane expression positively predicted median overall survival times in patients treated with adjuvant gemcitabine. Together, our findings identify ENT1 as an inadvertent target of EMT signaling mediated by cadherin switching and provide a mechanism by which mesenchymal pancreatic cancer cells evade gemcitabine therapy during EMT.

Vimseltinib: A Precision CSF1R Therapy for Tenosynovial Giant Cell Tumors and Diseases Promoted by Macrophages.

Abstract: Macrophages can be co-opted to contribute to neoplastic, neurologic, and inflammatory diseases. Colony-stimulating factor 1 receptor (CSF1R)-dependent macrophages and other inflammatory cells can suppress the adaptive immune system in cancer and contribute to angiogenesis, tumor growth, and metastasis. CSF1R-expressing osteoclasts mediate bone degradation in osteolytic cancers and cancers that metastasize to bone. In the rare disease tenosynovial giant cell tumor (TGCT), aberrant CSF1 expression and production driven by a gene translocation leads to the recruitment and growth of tumors formed by CSF1R-dependent inflammatory cells. Small molecules and antibodies targeting the CSF1/CSF1R axis have shown promise in the treatment of TGCT and cancer, with pexidartinib recently receiving FDA approval for treatment of TGCT. Many small-molecule kinase inhibitors of CSF1R also inhibit the closely related kinases KIT, PDGFRA, PDGFRB, and FLT3, thus CSF1R suppression may be limited by off-target activity and associated adverse events. Vimseltinib (DCC-3014) is an oral, switch control tyrosine kinase inhibitor specifically designed to selectively and potently inhibit CSF1R by exploiting unique features of the switch control region that regulates kinase conformational activation. In preclinical studies, vimseltinib durably suppressed CSF1R activity in vitro and in vivo, depleted macrophages and other CSF1R-dependent cells, and resulted in inhibition of tumor growth and bone degradation in mouse cancer models. Translationally, in a phase I clinical study, vimseltinib treatment led to modulation of biomarkers of CSF1R inhibition and reduction in tumor burden in TGCT patients.

The Dolaflexin-based Antibody-Drug Conjugate XMT-1536 Targets the Solid Tumor Lineage Antigen SLC34A2/NaPi2b.

Abstract: Target selection for antibody-drug conjugates (ADC) frequently focuses on identifying antigens with differential expression in tumor and normal tissue, to mitigate the risk of on-target toxicity. However, this strategy restricts the possible target space. SLC34A2/NaPi2b is a sodium phosphate transporter expressed in a variety of human tumors including lung and ovarian carcinoma, as well as the normal tissues from which these tumors arise. Previous clinical trials with a NaPi2b targeting MMAE-ADCs have shown objective durable responses. However, the protein-based biomarker assay developed for use in that study was unable to discern a statistically significant relationship between NaPi2b protein expression and the probability of response. XMT-1536 is a NaPi2b targeting ADC comprised of a unique humanized antibody conjugated with 10-15 auristatin F- hydroxypropylamide (AF-HPA) payload molecules via the Dolaflexin platform. AF-HPA is a cell-permeable, antimitotic compound that is slowly metabolized intratumorally to an active, very low-permeable metabolite, auristatin F (AF), resulting in controlled bystander killing. We describe the preclinical in vitro and in vivo antitumor effects of XMT-1536 in models of ovarian and lung adenocarcinoma. Pharmacokinetic analysis showed approximately proportional increases in exposure in rat and monkey. Systemic free AF-HPA and AF concentrations were observed to be low in all animal species. Finally, we describe a unique IHC reagent, generated from a chimeric construct of the therapeutic antibody, that was used to derive a target expression and efficacy relationship in a series of ovarian primary xenograft cancer models.

Hallmarks of RET and Co-occuring Genomic Alterations in RET-aberrant Cancers

Abstract: Activating receptor-tyrosine kinase rearranged during transfection (RET) mutations and fusions are potent drivers of oncogenesis. The recent FDA approvals of highly potent and selective RET inhibitors, selpercatinib and pralsetinib, has altered the therapeutic management of RET aberrant tumors. There is ample evidence of the role of RET signaling in certain cancers. RET aberrations as fusions or mutations occur in multiple cancers, however, there is considerable phenotypic diversity. There is emerging data on the lack of responsiveness of immunotherapy in RET-altered cancers. Herein, we review the registrational data from the selective RET-inhibitor trials, and comprehensively explore RET alterations in pan-cancer adult malignancies and their co-alterations. These co-occuring alterations may define the future of RET inhibition from specific selective targeting to customized combination therapies as data are rapidly emerging on both on-target and off-target acquired resistance mechanisms. Fascinatingly, oncogenic RET fusions have been reported to mediate resistance to EGFR inhibition and KRASG12C inhibition.

ABBV-085, Antibody-Drug Conjugate Targeting LRRC15, Is Effective in Osteosarcoma: A Report by the Pediatric Preclinical Testing Consortium.

Abstract: Membrane protein leucine-rich repeat containing 15 (LRRC15) is known to be expressed in several solid tumors including osteosarcoma. ABBV-085, an antibody-drug conjugate against LRRC15, conjugated to monomethyl auristatin E (MMAE), was studied in osteosarcoma patient-derived xenografts (PDXs) by the Pediatric Preclinical Testing Consortium (PPTC). LRRC15 expression data were obtained from PPTC RNA-sequencing data for the PDX models. The TARGET database was mined for LRRC15 expression in human osteosarcoma. Protein expression was confirmed via IHC in three PDX models. Seven osteosarcoma PDX models (OS1, OS9, OS33, OS34, OS42, OS55, and OS60) with varying LRRC15 gene expression were studied. ABBV-085 was administered at 3 mg/kg (OS33), 6 mg/kg (all seven PDXs), and 12 mg/kg (OS60) weekly for 4 consecutive weeks via intraperitoneal injection. Control cohorts included vehicle and an isotype MMAE-linked antibody. Tumor volumes and responses were reported using PPTC statistical analysis. OS1, OS33, OS42, OS55, and OS60 had high LRRC15 expression while OS9 and OS34 had low LRRC15 expression. ABBV-085 inhibited tumor growth in six of seven PDX models as compared with vehicle control and significantly improved event-free survival in five of seven models as compared with isotype controls. Two models showed maintained complete responses while all others showed progressive disease. Response correlated with LRRC15 expression. ABBV-085's antitumor activity against osteosarcoma PDX suggests LRRC15 may be a rational target for pursuing clinical trials in patients with this disease.

Heat Shock Protein-90 Inhibition Alters Activation of Pancreatic Stellate Cells and Enhances the Efficacy of PD-1 Blockade in Pancreatic Cancer

Abstract: Pancreatic ductal adenocarcinoma (PDAC) has a prominent fibrotic stroma, which is a result of interactions between tumor, immune and pancreatic stellate cells (PSC), or cancer-associated fibroblasts (CAF). Targeting inflammatory pathways present within the stroma may improve access of effector immune cells to PDAC and response to immunotherapy. Heat shock protein-90 (Hsp90) is a chaperone protein and a versatile target in pancreatic cancer. Hsp90 regulates a diverse array of cellular processes of relevance to both the tumor and the immune system. However, to date the role of Hsp90 in PSC/CAF has not been explored in detail. We hypothesized that Hsp90 inhibition would limit inflammatory signals, thereby reprogramming the PDAC tumor microenvironment to enhance sensitivity to PD-1 blockade. Treatment of immortalized and primary patient PSC/CAF with the Hsp90 inhibitor XL888 decreased IL6, a key cytokine that orchestrates immune changes in PDAC at the transcript and protein level in vitro XL888 directly limited PSC/CAF growth and reduced Jak/STAT and MAPK signaling intermediates and alpha-SMA expression as determined via immunoblot. Combined therapy with XL888 and anti-PD-1 was efficacious in C57BL/6 mice bearing syngeneic subcutaneous (Panc02) or orthotopic (KPC-Luc) tumors. Tumors from mice treated with both XL888 and anti-PD-1 had a significantly increased CD8+ and CD4+ T-cell infiltrate and a unique transcriptional profile characterized by upregulation of genes associated with immune response and chemotaxis. These data demonstrate that Hsp90 inhibition directly affects PSC/CAF in vitro and enhances the efficacy of anti-PD-1 blockade in vivo.