Amit Kumar

Bio: Amit Kumar is an academic researcher from University of Colorado Denver. The author has contributed to research in topics: Medicarpin & Michael reaction. The author has an hindex of 12, co-authored 26 publications receiving 586 citations. Previous affiliations of Amit Kumar include Anschutz Medical Campus & Indian Institute of Technology Kanpur.

Methoxylated isoflavones, cajanin and isoformononetin, have non-estrogenic bone forming effect via differential mitogen activated protein kinase (MAPK) signaling.

Abstract: Following a lead obtained from stem-bark extract of Butea monosperma, two structurally related methoxyisoflavones; cajanin and isoformononetin were studied for their effects in osteoblasts. Cajanin had strong mitogenic as well as differentiation-promoting effects on osteoblasts that involved subsequent activation of MEK-Erk and Akt pathways. On the other hand, isoformononetin exhibited potent anti-apoptotic effect in addition to promoting osteoblast differentiation that involved parallel activation of MEK-Erk and Akt pathways. Unlike genistein or daidzein, none of these two compounds appear to act via estrogen receptors in osteoblast. Once daily oral (by gavage) treatment for 30 consecutive days was given to recently weaned female Sprague-Dawley rats with each of these compounds at 10.0 mg kg(-1) day(-1) dose. Cajanin increased bone mineral density (BMD) at all skeletal sites studied, bone biomechanical strength, mineral apposition rate (MAR) and bone formation rate (BFR), compared with control. BMD levels at various anatomic positions were also increased with isoformononetin compared with control however, its effect was less potent than cajanin. Isoformononetin had no effect on the parameters of bone biomechanical strength although it enhanced MAR and BFR compared with control. Isoformononetin had very mild uterotrophic effect, whereas cajanin was devoid of any such effect. Our data suggest that cajanin is more potent than isoformononetin in accelerating peak bone mass achievement. To the best of our knowledge, this work represents the first attempt to elucidate structure-activity relationship between the two methoxylated isoflavones regarding their effects in osteoblasts and bone formation.

ATM/G6PD-driven redox metabolism promotes FLT3 inhibitor resistance in acute myeloid leukemia

Abstract: Activating mutations in FMS-like tyrosine kinase 3 (FLT3) are common in acute myeloid leukemia (AML) and drive leukemic cell growth and survival. Although FLT3 inhibitors have shown considerable promise for the treatment of AML, they ultimately fail to achieve long-term remissions as monotherapy. To identify genetic targets that can sensitize AML cells to killing by FLT3 inhibitors, we performed a genome-wide RNA interference (RNAi)-based screen that identified ATM (ataxia telangiectasia mutated) as being synthetic lethal with FLT3 inhibitor therapy. We found that inactivating ATM or its downstream effector glucose 6-phosphate dehydrogenase (G6PD) sensitizes AML cells to FLT3 inhibitor induced apoptosis. Examination of the cellular metabolome showed that FLT3 inhibition by itself causes profound alterations in central carbon metabolism, resulting in impaired production of the antioxidant factor glutathione, which was further impaired by ATM or G6PD inactivation. Moreover, FLT3 inhibition elicited severe mitochondrial oxidative stress that is causative in apoptosis and is exacerbated by ATM/G6PD inhibition. The use of an agent that intensifies mitochondrial oxidative stress in combination with a FLT3 inhibitor augmented elimination of AML cells in vitro and in vivo, revealing a therapeutic strategy for the improved treatment of FLT3 mutated AML.

Tyrosine Kinase Inhibition in Leukemia Induces an Altered Metabolic State Sensitive to Mitochondrial Perturbations

Abstract: Purpose: Although tyrosine kinase inhibitors (TKI) can be effective therapies for leukemia, they fail to fully eliminate leukemic cells and achieve durable remissions for many patients with advanced BCR-ABL + leukemias or acute myelogenous leukemia (AML). Through a large-scale synthetic lethal RNAi screen, we identified pyruvate dehydrogenase, the limiting enzyme for pyruvate entry into the mitochondrial tricarboxylic acid cycle, as critical for the survival of chronic myelogenous leukemia (CML) cells upon BCR-ABL inhibition. Here, we examined the role of mitochondrial metabolism in the survival of Ph + leukemia and AML upon TK inhibition. Experimental Design: Ph + cancer cell lines, AML cell lines, leukemia xenografts, cord blood, and patient samples were examined. Results: We showed that the mitochondrial ATP-synthase inhibitor oligomycin-A greatly sensitized leukemia cells to TKI in vitro . Surprisingly, oligomycin-A sensitized leukemia cells to BCR-ABL inhibition at concentrations of 100- to 1,000-fold below those required for inhibition of respiration. Oligomycin-A treatment rapidly led to mitochondrial membrane depolarization and reduced ATP levels, and promoted superoxide production and leukemia cell apoptosis when combined with TKI. Importantly, oligomycin-A enhanced elimination of BCR-ABL + leukemia cells by TKI in a mouse model and in primary blast crisis CML samples. Moreover, oligomycin-A also greatly potentiated the elimination of FLT3-dependent AML cells when combined with an FLT3 TKI, both in vitro and in vivo . Conclusions: TKI therapy in leukemia cells creates a novel metabolic state that is highly sensitive to particular mitochondrial perturbations. Targeting mitochondrial metabolism as an adjuvant therapy could therefore improve therapeutic responses to TKI for patients with BCR-ABL + and FLT3 ITD leukemias. Clin Cancer Res; 21(6); 1360–72. ©2014 AACR .

ROS and the DNA damage response in cancer.

Abstract: Reactive oxygen species (ROS) are a group of short-lived, highly reactive, oxygen-containing molecules that can induce DNA damage and affect the DNA damage response (DDR). There is unequivocal pre-clinical and clinical evidence that ROS influence the genotoxic stress caused by chemotherapeutics agents and ionizing radiation. Recent studies have provided mechanistic insight into how ROS can also influence the cellular response to DNA damage caused by genotoxic therapy, especially in the context of Double Strand Breaks (DSBs). This has led to the clinical evaluation of agents modulating ROS in combination with genotoxic therapy for cancer, with mixed success so far. These studies point to context dependent outcomes with ROS modulator combinations with Chemotherapy and radiotherapy, indicating a need for additional pre-clinical research in the field. In this review, we discuss the current knowledge on the effect of ROS in the DNA damage response, and its clinical relevance.

Physiology and pathophysiology

Abstract: Chapter 1 Transmissible Spongiform Encephalopathy: from the High Middle Ages to Daniel Carlton Gajdusek Paul Brown Chapter 2 The Rich Chemistry of the Copper and Zinc Sites in Cellular Prion Protein Glenn L. Millhauser Chapter 3 Role of Cellular Prion Protein in the Amyloid-ss Oligomer Pathophysiology of Alzheimer's Disease Adam C. Kaufman, Stephen M. Strittmatter Chapter 4 Cellular Prion Protein and Cancers Wei Xin, Man-sun Sy, Chaoyang Li Chapter 5 Insoluble Cellular Prion Protein Wen-Quan Zou Chapter 6 Protein Misfolding Cyclic Amplification Fabio Moda, Sandra Pritzkow, Claudio Soto Chapter 7 Cofactor Involvement in Prion Propagation Surachai Supattapone, Michael B. Miller Chapter 8 Prion Protein Conversion and Lipids Jiyan Ma Chapter 9 New Perspectives on Prion Conversion: Introducing a Mechanism of Deformed Templating Ilia V. Baskakov Chapter 10 Infectious and Pathogenic Forms of Prion Protein Emiliano Biasini, David A. Harris Chapter 11 Cellular Mechanisms of Propagation and Clearance Hermann M. Schatzl Chapter 12 Molecular Mechanisms Encoding Quantitative and Qualitative Traits of Prion Strains Jiri G. Safar Chapter 13 Modeling the Cell Biology of Prions Richard Rubenstein, Robert B. Petersen Chapter 14 Prion Strain Interference Charles R. Schutt, Ronald A. Shikiya, Jason C. Bartz Chapter 15 Introduction to Yeast and Fungal Prions Reed B. Wickner Chapter 16 Yeast Prions are Pathogenic, in-register Parallel Amyloids Reed B. Wickner, Herman K. Edskes, David A. Bateman, Amy C. Kelly, Anton Gorkovskiy

Sex steroid deficiency–associated bone loss is microbiota dependent and prevented by probiotics

Abstract: A eubiotic microbiota influences many physiological processes in the metazoan host, including development and intestinal homeostasis. Here, we have shown that the intestinal microbiota modulates inflammatory responses caused by sex steroid deficiency, leading to trabecular bone loss. In murine models, sex steroid deficiency increased gut permeability, expanded Th17 cells, and upregulated the osteoclastogenic cytokines TNFα (TNF), RANKL, and IL-17 in the small intestine and the BM. In germ-free (GF) mice, sex steroid deficiency failed to increase osteoclastogenic cytokine production, stimulate bone resorption, and cause trabecular bone loss, demonstrating that the gut microbiota is central in sex steroid deficiency-induced trabecular bone loss. Furthermore, we demonstrated that twice-weekly treatment of sex steroid-deficient mice with the probiotics Lactobacillus rhamnosus GG (LGG) or the commercially available probiotic supplement VSL#3 reduces gut permeability, dampens intestinal and BM inflammation, and completely protects against bone loss. In contrast, supplementation with a nonprobiotic strain of E. coli or a mutant LGG was not protective. Together, these data highlight the role that the gut luminal microbiota and increased gut permeability play in triggering inflammatory pathways that are critical for inducing bone loss in sex steroid-deficient mice. Our data further suggest that probiotics that decrease gut permeability have potential as a therapeutic strategy for postmenopausal osteoporosis.