Stephen T. Schlachter

A Small-Molecule Antagonist of HIF2α Is Efficacious in Preclinical Models of Renal Cell Carcinoma

More than 90% of clear cell renal cell carcinomas (ccRCC) exhibit inactivation of the von Hippel-Lindau (pVHL) tumor suppressor, establishing it as the major underlying cause of this malignancy. pVHL inactivation results in stabilization of the hypoxia-inducible transcription factors, HIF1α and HIF2α, leading to expression of a genetic program essential for the initiation and progression of ccRCC. Herein, we describe the potent, selective, and orally active small-molecule inhibitor PT2385 as a specific antagonist of HIF2α that allosterically blocks its dimerization with the HIF1α/2α transcriptional dimerization partner ARNT/HIF1β. PT2385 inhibited the expression of HIF2α-dependent genes, including VEGF-A, PAI-1, and cyclin D1 in ccRCC cell lines and tumor xenografts. Treatment of tumor-bearing mice with PT2385 caused dramatic tumor regressions, validating HIF2α as a pivotal oncogenic driver in ccRCC. Notably, unlike other anticancer agents that inhibit VEGF receptor signaling, PT2385 exhibited no adverse effect on cardiovascular performance. Thus, PT2385 represents a novel class of therapeutics for the treatment of RCC with potent preclincal efficacy as well as improved tolerability relative to current agents that target the VEGF pathway. Cancer Res; 76(18); 5491-500. ©2016 AACR.

Non-oxime inhibitors of B-Raf V600E kinase

The development of inhibitors of B-Raf(V600E) serine-threonine kinase is described. Various head-groups were examined to optimize inhibitor activity and ADME properties. Several of the head-groups explored, including naphthol, phenol and hydroxyamidine, possessed good activity but had poor pharmacokinetic exposure in mice. Exposure was improved by incorporating more metabolically stable groups such as indazole and tricyclic pyrazole, while indazole could also be optimized for good cellular activity.

Discovery of a Novel Class of Imidazo[1,2-a]Pyridines with Potent PDGFR Activity and Oral Bioavailability.

The in silico construction of a PDGFRβ kinase homology model and ensuing medicinal chemistry guided by molecular modeling, led to the identification of potent, small molecule inhibitors of PDGFR. Subsequent exploration of structure-activity relationships (SAR) led to the incorporation of a constrained secondary amine to enhance selectivity. Further refinements led to the integration of a fluorine substituted piperidine, which resulted in significant reduction of P-glycoprotein (Pgp) mediated efflux and improved bioavailability. Compound 28 displayed oral exposure in rodents and had a pronounced effect in a pharmacokinetic-pharmacodynamic (PKPD) assay.

The Discovery of furo[2,3-c]pyridine-based indanone oximes as potent and selective B-Raf inhibitors.

Virtual and high-throughput screening identified imidazo[1,2-a]pyrazines as inhibitors of B-Raf. We describe the rationale, SAR, and evolution of the initial hits to a series of furo[2,3-c]pyridine indanone oximes as highly potent and selective inhibitors of B-Raf.

Anti-inflammatory/antiarthritic ketonic bisphosphonic acid esters

Bisphosphonate ester 2 is an inhibitor of inflammation, but is devoid of antiarthritic effects. SAR studies on a series of related bisphosphonate esters resulted in compounds 6e, 6i, 6j, and 6m, which exhibited excellent inhibition of an arthritis model, in addition to potent anti-inflammatory effects.

New Anti-Inflammatory/Anti-Arthritic Heterocyclic Bisphosphonates

Abstract. In the course of research toward a safe and effective treatment for rheumatoid arthritis, we identified new pyrazolo[1,5-a]pyrimidine and 4-pyrimidinone bisphosphonate esters, which are potent inhibitors of a murine model of chronic, cutaneous inflammation (delayed type hypersensitivity granuloma) and a murine antigen induced arthritis model. 9a has EC30 values of 0.01 and 0.005 mg/kg respectively and represents a new class of antiinflammatory/antiarthritic bisphosphonate ester.

Design and Activity of Specific Hypoxia-Inducible Factor-2α (HIF-2α) Inhibitors for the Treatment of Clear Cell Renal Cell Carcinoma: Discovery of Clinical Candidate (S)-3-((2,2-Difluoro-1-hydroxy-7-(methylsulfonyl)-2,3-dihydro-1H-inden-4-yl)oxy)-5-fluorobenzonitrile (PT2385)

HIF-2α, a member of the HIF family of transcription factors, is a key oncogenic driver in cancers such as clear cell renal cell carcinoma (ccRCC). A signature feature of these cancers is the overaccumulation of HIF-2α protein, often by inactivation of the E3 ligase VHL (von Hippel-Lindau). Herein we disclose our structure based drug design (SBDD) approach that culminated in the identification of PT2385, the first HIF-2α antagonist to enter clinical trials. Highlights include the use of a putative n → π*Ar interaction to guide early analog design, the conformational restriction of an essential hydroxyl moiety, and the remarkable impact of fluorination near the hydroxyl group. Evaluation of select compounds from two structural classes in a sequence of PK/PD, efficacy, PK, and metabolite profiling identified 10i (PT2385, luciferase EC50 = 27 nM) as the clinical candidate. Finally, a retrospective crystallographic analysis describes the structural perturbations necessary for efficient antagonism.

Abstract DDT01-01: PT2385: First-in-class HIF-2α antagonist for the treatment of renal cell carcinoma

Hypoxia-inducible factors (HIFs), including HIF-1α and HIF-2α, are transcription factors that mediate cellular response to changes of oxygen supply. These proteins become stabilized under hypoxia and subsequently activate the expression of genes to facilitate cell survival and proliferation. HIF proteins are activated in many types of cancers due to the tumor hypoxic microenvironment and have been implicated in cancer initiation, progression and metastasis. The oncogenic role of HIF-2α is pertinent in clear cell renal carcinoma (ccRCC). In the majority of ccRCC tumors, the von Hippel-Lindau protein (VHL) that targets HIF-2α for degradation is inactivated, leading to the accumulation of HIF-2α and the activation of genes that drive kidney cancer tumorigenesis. We have identified small molecules that bind to the PAS-B domain of HIF-2α protein and block it9s dimerization with ARNT (aryl hydrocarbon receptor nuclear translocator, HIF-1β), a prerequisite for its transcriptional activities. Specifically, we describe PT2385, a selective, orally active HIF-2α antagonist with potent anti-cancer activity in mouse models of ccRCC. PT2385 is currently under evaluation in Phase I clinical trials for the treatment of ccRCC. Citation Format: Eli M. Wallace, Zhaodan Cao, Tzuling Cheng, Robert Czerwinski, Darryl D. Dixon, Xinlin Du, Barry Goggin, Jonas Grina, Megan Halfmann, Guangzhou Han, Heli Huang, John A. Josey, Melissa A. Maddie, Sarah Olive, James Rizzi, Stephen T. Schlachter, Hui-Ling Tan, Bin Wang, Keshi Wang, Paul M. Wehn, Shanhai Xie, Rui Xu, Hanbiao Yang. PT2385: First-in-class HIF-2α antagonist for the treatment of renal cell carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr DDT01-01. doi:10.1158/1538-7445.AM2015-DDT01-01