James P. Rizzi

Topology of the pore-region of a K+ channel revealed by the NMR-derived structures of scorpion toxins

The architecture of the pore-region of a voltage-gated K+ channel, Kv1.3, was probed using four high affinity scorpion toxins as molecular calipers. We established the structural relatedness of these toxins by solving the structures of kaliotoxin and margatoxin and comparing them with the published structure of charybdotoxin; a homology model of noxiustoxin was then developed. Complementary mutagenesis of Kv1.3 and these toxins, combined with electrostatic compliance and thermodynamic mutant cycle analyses, allowed us to identify multiple toxin-channel interactions. Our analyses reveal the existence of a shallow vestibule at the external entrance to the pore. This vestibule is approximately 28-32 A wide at its outer margin, approximately 28-34 A wide at its base, and approximately 4-8 A deep. The pore is 9-14 A wide at its external entrance and tapers to a width of 4-5 A at a depth of approximately 5-7 A from the vestibule. This structural information should directly aid in developing topological models of the pores of related ion channels and facilitate therapeutic drug design.

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.

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.

A novel product from Beckmann rearrangement of erythromycin A 9(E)-oxime

Abstract Beckmann rearrangement of erythromycin A 9(E)-oxime with toluenesulfonyl chloride in ethyl ether at −45°C generates 9,11-imino ether IV which leads to azithromycin. The 9,11-imino ether can also be readily obtained from isomerization of its isomer 6,9-imino ether III .

Nuclear variations of quinuclidine substance P antagonists: 2-diphenylmethyl-1-azabicyclo[3.2.2]nonan-3-amines

Abstract The synthesis and SAR of a series of 1-azabicyclo[3.2.2] analogues of the nonpeptide substance P antagonist CP-96,345 are described. The results demonstrate the sensitivity of the substance P receptor toward alterations in the nuclear structure of CP-96,345.

Pexmetinib: A Novel Dual Inhibitor of Tie2 and p38 MAPK with Efficacy in Preclinical Models of Myelodysplastic Syndromes and Acute Myeloid Leukemia.

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) suppress normal hematopoietic activity in part by enabling a pathogenic inflammatory milieu in the bone marrow. In this report, we show that elevation of angiopoietin-1 in myelodysplastic CD34(+) stem-like cells is associated with higher risk disease and reduced overall survival in MDS and AML patients. Increased angiopoietin-1 expression was associated with a transcriptomic signature similar to known MDS/AML stem-like cell profiles. In seeking a small-molecule inhibitor of this pathway, we discovered and validated pexmetinib (ARRY-614), an inhibitor of the angiopoietin-1 receptor Tie-2, which was also found to inhibit the proinflammatory kinase p38 MAPK (which is overactivated in MDS). Pexmetinib inhibited leukemic proliferation, prevented activation of downstream effector kinases, and abrogated the effects of TNFα on healthy hematopoietic stem cells. Notably, treatment of primary MDS specimens with this compound stimulated hematopoiesis. Our results provide preclinical proof of concept for pexmetinib as a Tie-2/p38 MAPK dual inhibitor applicable to the treatment of MDS/AML. Cancer Res; 76(16); 4841-9. ©2016 AACR.

Inhibitors of MMP-1: an examination of P1′ Cα gem-disubstitution in the N-carboxyalkylamine and glutaramide carboxylate series

Abstract Modification of the N-carboxyalkylamine 3 by independent replacement of the P1′ NH group for CH2 and introduction of P1′ gem-cyclohexyl substitution affords compounds 5 and 6a which retain appreciable activity against MMP-1 (IC50s = 0.023 μM and 0.09 μM, respectively). The glutaramide 7a which incorporates both these structural changes also retains potent activity (IC50 = 0.038 μM).

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

Abstract 551: A potent and selective cFMS inhibitor regulates the tumor macrophage microenvironment leading to tumor growth inhibition

Increasing evidence suggests that interactions between tumor cells, stromal cells, macrophages and the extracellular matrix are pivotal to the processes of tumorigenesis, metastasis, and neovascularization. Macrophages within the tumor microenvironment are thought to facilitate cancer progression, making them intriguing targets for therapy. Colony stimulating factor 1 (CSF-1) and its receptor, cFMS, play a central role in the development of mononuclear phagocytes, recruitment of macrophages to tumors, and differentiation and function of osteoclasts. We have developed an orally active, selective small-molecule cFMS inhibitor for cFMS. This molecule inhibits cFMS cellular activity (IC 50 = 9 nM) in vitro and inhibits cFMS phosphorylation in a transfected cell line grown in nude mice (ED 50 = 3 mg/kg). Our compound also inhibits CSF-1-mediated osteoclast differentiation and function (IC 50 values of = 4 nM and 58 nM, respectively). To further explore the potential of our selective inhibitor for the treatment of cancer, we evaluated anti-tumor activity in several preclinical models. We first explored the effect on the murine ovarian cancer cell line, ID8. ID8 cells injected intraperitoneally into nude mice form multiple peritoneal tumor deposits and abundant ascites. Macrophage infiltration in the ID8 ascites was markedly lowered in mice treated with a cFMS inhibitor. Using MCF-7, a human breast adenocarcinoma cell line that has been shown to produce M-CSF, a daily oral dose with 100 mg/kg of our inhibitor for 21 days significantly reduced tumor growth and was accompanied by a marked reduction in tumor-associated macrophages. These findings support the potential of a selective inhibitor of cFMS to favorably impact human cancers by modulating tumor-associated macrophage functions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 551. doi:10.1158/1538-7445.AM2011-551