Showing papers by "Robert H. Shoemaker published in 2018"
TL;DR: 4A6 is a novel specific inhibitor of the β5 subunit-associated chymotrypsin-like proteasome activity of the 26S proteasomes.
Abstract: Background The hexapeptide 4A6 (Ac-Thr(tBu)-His(Bzl)-Thr(Bzl)-Nle-Glu(OtBu)-Gly-Bza) was isolated from a peptide library constructed to identify peptide-based transport inhibitors of multidrug resistance (MDR) efflux pumps including P-glycoprotein and Multidrug Resistance-associated Protein 1. 4A6 proved to be a substrate but not an inhibitor of these MDR efflux transporters. In fact, 4A6 and related peptides displayed potent cytotoxic activity via an unknown mechanism. Objective To decipher the mode of cytotoxic activity of 4A6. Methods Screening of 4A6 activity was performed against the NCI60 panel of cancer cell lines. Possible interactions of 4A6 with the 26S proteasome were assessed via proteasome activity and affinity labeling, and cell growth inhibition studies with leukemic cells resistant to the proteasome inhibitor bortezomib (BTZ). Results The NCI60 panel COMPARE analysis revealed that 4A6 had an activity profile overlapping with BTZ. Consistently, 4A6 proved to be a selective and reversible inhibitor of β5 subunit (PSMB5)-associated chymotrypsin-like activity of the 26S proteasome. This conclusion is supported by several lines of evidence: (i) inhibition of chymotrypsin-like proteasome activity by 4A6 and related peptides correlated with their cell growth inhibition potencies; (ii) 4A6 reversibly inhibited functional β5 active site labeling with the affinity probe BodipyFL-Ahx3L3VS; and (iii) human myeloid THP1 cells with acquired BTZ resistance due to mutated PSMB5 were highly (up to 287-fold) cross-resistant to 4A6 and its related peptides. Conclusion 4A6 is a novel specific inhibitor of the β5 subunit-associated chymotrypsin-like proteasome activity. Further exploration of 4A6 as a lead compound for development as a novel proteasome-targeted drug is warranted.
7 citations
TL;DR: It was found that strongly positive results were highly reproducible in the preclinical models evaluated, and testing multiple agents of the same mechanistic class found this to be the case.
Abstract: Because of the importance of testing reproducibility of results, we present our findings regarding screening agents in preclinical chemoprevention studies in rodent models performed by the Chemopreventive Agent Development Research Group (CADRG) of the Division of Cancer Prevention of the NCI These studies were performed via contracts to various commercial and academic laboratories Primarily, results with positive agents are reported since positive agents may progress to the clinics In testing reproducibility, a limited number of direct repeats of our standard screening assays were performed; which entailed initiating treatment shortly after carcinogen administration or in young transgenic mice and continuing treatment until the end of the study However, three additional protocols were employed relating to reproducibility: (a) testing agents at lower doses to determine efficacy and reduced toxicity; (b) testing agents later in tumor progression when microscopic lesions existed and, (c) testing multiple agents of the same mechanistic class Data with six models that were routinely employed are presented: MNU-induced ER positive mammary cancer in rats; MMTV-Neu ER negative mammary cancers in transgenic mice; AOM-induced colon tumors in rats; intestinal adenomas in Min mice; OH-BBN-induced invasive rat urinary bladder cancers in rats; and UV-induced skin squamous carcinomas in mice It was found that strongly positive results were highly reproducible in the preclinical models evaluated
4 citations
TL;DR: Two studies demonstrate that in protocols meant to reduce the toxicity of agents (weekly erlotinib or intermittent dosing with naproxen), high chemopreventive efficacy was achieved and reduced the size of the urinary bladder cancers without showing observable toxicity.
Abstract: Inflammation and epidermal growth factor receptor (EGFR) signaling dysregulation plays an important role in urinary bladder cancer development. We have previously shown that single agent regimens with erlotinib (EGFR inhibitor) or naproxen (nonsteroidal anti-inflammatory drug; NSAID) when given continuously were highly effective in the prevention of OH-BBN-induced urinary bladder cancers in rats. Better tolerated chemoprevention regimens can be obtained by reducing doses and frequency of administration. Low dose combinations may also achieve substantial efficacy with minimal toxicity by targeting complementary pathways. Female Fischer-344 rats were obtained at 28 days of age, placed on Teklad (4% fat) diet, and received OH-BBN (150 mg/gavage) 2x/week for 8 weeks beginning at 56 days of age. In the first study, beginning one week after the final OH-BBN treatment the rats (25/group) received either: Group 1, erlotinib (42 mg/kg BW, 1x/week); Group 2, naproxen (30 mg/kg BW/day, 3 weeks on/ 3 weeks off); Group 3, the combination of erlotinib and naproxen (using the same treatment regimens), and Group 4, vehicle. The rats were palpated for urinary bladder tumors, weighed 1x/week and observed daily for signs of toxicity. At the end of the study (10 months after the initial OH-BBN), the average weights of the urinary bladders (bladder plus tumors combined) were determined. The weights in Groups 1-4 were: 194*, 186*, 136* and 354 mg (*P 200 mg). The second study used the same treatment regimens, but administration of the agents was delayed until three months after the final OH-BBN treatment, at which point microscopic transitional cell carcinomas were present. At the end of the study (11 months after the initial OH-BBN), the weights of the individual bladders in Groups 1-4 were: 584, 234*, 138* and 779 mg (*P 200 mg). These studies demonstrate that in protocols meant to reduce the toxicity of agents (weekly erlotinib or intermittent dosing with naproxen), high chemopreventive efficacy was achieved. Of importance, starting erlotinib and/or naproxen intermittent treatments at the time microscopic cancers were present still reduced the size of the urinary bladder cancers without showing observable toxicity. The latter is of particular interest based on the clinical FAP trial showing great efficacy of erlotinib and sulindac. Supported by NCI contract number HHSN261201500036I, Task Order HHSN26100002. Citation Format: Altaf Mohammed, Mark S. Miller, Ronald A. Lubet, Chen Suen, Shizuko Sei, Robert H. Shoemaker, Clinton J. Grubbs. Efficacy of erlotinib and/or naproxen when administered by intermittent dosing schedules in the prevention of chemically induced urinary bladder cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4989.
1 citations