Expanding control of the tumor cell cycle with a CDK2/4/6 inhibitor

The CDK4/6 inhibitor, palbociclib (PAL), significantly improves progression-free survival in HR⁺/HER2^- breast cancer when combined with anti-hormonals. We sought to discover PAL resistance mechanisms in preclinical models and through analysis of clinical transcriptome specimens, which coalesced on induction of MYC oncogene and Cyclin E/CDK2 activity. We propose that targeting the G₁ kinases CDK2, CDK4, and CDK6 with a small-molecule overcomes resistance to CDK4/6 inhibition. We describe the pharmacodynamics and efficacy of PF-06873600 (PF3600), a pyridopyrimidine with potent inhibition of CDK2/4/6 activity and efficacy in multiple in vivo tumor models. Together with the clinical analysis, MYC activity predicts (PF3600) efficacy across multiple cell lineages. Finally, we find that CDK2/4/6 inhibition does not compromise tumor-specific immune checkpoint blockade responses in syngeneic models. We anticipate that (PF3600), currently in phase 1 clinical trials, offers a therapeutic option to cancer patients in whom CDK4/6 inhibition is insufficient to alter disease progression.

Discovery of PF-06873600, a CDK2/4/6 Inhibitor for the Treatment of Cancer

Control of the cell cycle through selective pharmacological inhibition of CDK4/6 has proven beneficial in the treatment of breast cancer. Extending this level of control to additional cell cycle CDK isoforms represents an opportunity to expand to additional tumor types and potentially provide benefits to patients that develop tumors resistant to selective CDK4/6 inhibitors. However, broad-spectrum CDK inhibitors have a long history of failure due to safety concerns. In this approach, we describe the use of structure-based drug design and Free-Wilson analysis to optimize a series of CDK2/4/6 inhibitors. Further, we detail the use of molecular dynamics simulations to provide insights into the basis for selectivity against CDK9. Based on overall potency, selectivity, and ADME profile, PF-06873600 (22) was identified as a candidate for the treatment of cancer and advanced to phase 1 clinical trials.

Structure-Based Drug Design and Synthesis of PI3Kα-Selective Inhibitor (PF-06843195)

The phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway is a frequently dysregulated pathway in human cancer, and PI3Kα is one of the most frequently mutated kinases in human cancer. A PI3Kα-selective inhibitor may provide the opportunity to spare patients the side effects associated with broader inhibition of the class I PI3K family. Here, we describe our efforts to discover a PI3Kα-selective inhibitor by applying structure-based drug design (SBDD) and computational analysis. A novel series of compounds, exemplified by 2,2-difluoroethyl (3S)-3-{[2'-amino-5-fluoro-2-(morpholin-4-yl)-4,5'-bipyrimidin-6-yl]amino}-3-(hydroxymethyl)pyrrolidine-1-carboxylate (1) (PF-06843195), with high PI3Kα potency and unique PI3K isoform and mTOR selectivity were discovered. We describe here the details of the design and synthesis program that lead to the discovery of 1.

Abstract B25: Development of a nanoparticle containing the PI3K/mTOR dual Inhibitor, gedatolisib, for cancer therapy

Gedatolisib, a PI3K/mTOR dual inhibitor delivered intravenously, is in early clinical trials in women with metastatic ER+ breast cancer. We reasoned that the therapeutic index could be further maximized by encapsulation of gedatolisib in nanoparticles (NP), thereby providing longer half-life, sustained release, blunting of Cmax and associated toxicity, asymmetric distribution to leaky tumor vasculature and the possibility of less frequent dosing. PF-07034663 is a polymeric NP encapsulating gedatolisib, targeted to prostate-specific membrane antigen (PSMA), a clinically validated tumor antigen expressed on prostate cancer cells and the neovasculature of some nonprostate solid tumors. Studies in mice, rats, and cynomolgus monkeys demonstrated that the terminal half-life of PF-07034663 following intravenous administration increased by ~1.5 fold and the Cmax of released gedatolisib from PF-07034663 decreased by ~75 fold compared to gedatolisib delivered by the same route. Gedatolisib released from PF-07034663 exhibited markedly enhanced intratumoral accumulation compared to gedatolisib (~40 fold), indicating enhanced tissue delivery and/or prolonged retention. In exploratory toxicology studies, PF-07034663 caused no hyper-insulinemic spike in rats, in contrast to gedatolisib. To evaluate the antitumor activity of PF-07034663, we performed tumor growth inhibition (TGI) studies in PSMA-positive C4-2 prostate and in PSMA-negative MDAMB361 ER+ breast and A549 lung xenograft tumor models. In the C4-2 model, PF-07034663 showed dose-dependent antitumor efficacy as a single agent, and, in combination with enzalutamide, exhibited enhanced activity leading to tumor regressions. PF 07034663 also exhibited prolonged, dose-dependent inhibition of phosphorylation of S6 (pS6) in the C4-2 model compared to gedatolisib. Interestingly, increased pharmacodynamics (PD) responses compared to gedatolisib were not restricted to PSMA-positive tumors. Moreover, TGI responses were increased in the PSMA-negative A549 lung cancer model, relative to those observed with gedatolisib. PF 07034663 treatment in spontaneous prostate tumors in PTENnullp53mut GEM mice and in subcutaneous allografts of these spontaneous tumors in wild-type mice showed that treatment of PF-07034663 caused similar pS6 inhibition in both models, suggesting that PD modulation is independent of tumor origin or milieu and is less likely due to altered enhanced permeability and retention (EPR) effect. Taken together, PF-07034663 exhibits potential for improved tolerability, sustained tumor PK, prolonged PD modulation, and less frequent dosing schedule compared to gedatolisib. These results support further exploration of gedatolisib in tumor-targeted or non-tumor-targeted nanoparticles in clinical trials as a promising vehicle for delivery of PI3K/mTOR inhibitors to advanced cancer patients.

Citation Format: Lianglin Zhang, Gabriel Troche, Ravi Visswanathan, Wenhu Huang, Young-Ho Song, Mary E. Spilker, Zhenxiong Wang, Hui Wang, Anand Giddabasappa, Louise Cadzow, Susan Low, Greg Troiano, Jennifer Lafontaine, Valeria Fantin, Robert T. Abraham, Shubha Bagrodia. Development of a nanoparticle containing the PI3K/mTOR dual Inhibitor, gedatolisib, for cancer therapy [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B25.

Bioanalysis of Targeted Nanoparticles in Monkey Plasma via LC-MS/MS

This work represents the first reporting of a comprehensive bioanalytical GLP methodology detailing the mass spectrometric quantitation of PF-05212384 dosed as a targeted polymeric encapsulated nanoparticle (PF-07034663) to monkeys. Polymeric nanoparticles are a type of drug formulation that enables the sustained release of an active therapeutic agent (payload) for targeted delivery to specific sites of action such as cancer cells. Through the careful design and engineering of the nanoparticle formulation, it is possible to improve the biodistribution and safety of a given therapeutic payload in circulation. However, the bioanalysis of nanoparticles is challenging due to the complexity of the nanoparticle drug formulation itself and the number of pharmacokinetic end points needed to characterize the in vivo exposure of the nanoparticles. Gedatolisib, also known as PF-05212384, was reformulated as an encapsulated targeted polymeric nanoparticle. The bioanalytical assays were validated to quantitate both total and released PF-05212384 derived from the encapsulated nanoparticle (PF-07034663). Assay performance calculated from quality control samples in three batch runs demonstrated intraday precision and accuracy within 10.3 and 12.2%, respectively, and interday precision and accuracy within 9.1 and 8.5%, respectively. This method leveraged automation to ease the burden of a laborious and complicated sample pretreatment and extraction procedure. The automated method was used to support a preclinical safety study in monkeys in which both released and total PF-05212384 concentrations were determined in over 1600 monkey plasma study samples via LC-MS/MS.

Abstract P6-20-06: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Dann S, Chionis J, Eisele K, Zhang Q, Liu C, Yuan J, Miller N, Murray B, Xu M, Solowiej J, Wei P, Weinrich S, Sutton S, Behenna D, Ninkovic S, Hoffman R, Freeman-Cook K, Jessen B, Huser N, Zhang C, Visswanathan R, Boras B, VanArsdale T, White MA. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-06.

Found in Translation: Maximizing the Clinical Relevance of Nonclinical Oncology Studies

Purpose: The translation of nonclinical oncology studies is a subject of continuous debate. We propose that translational oncology studies need to optimize both pharmacokinetic (drug exposure) and pharmacodynamic (xenograft model) aspects. While improvements in pharmacodynamic translatability can be obtained by choosing cell lines or patient-derived xenograft models closer to the clinical indication, significant ambiguity and variability exists when optimizing the pharmacokinetic translation of small molecule and biotherapeutic agents.Experimental Design and Results: In this work, we propose a pharmacokinetic-based strategy to select nonclinical doses for approved drug molecules. We define a clinically relevant dose (CRD) as the dosing regimen in mice that most closely approximates the relevant pharmacokinetic metric in humans. Such metrics include area under the time-concentration curve and maximal or minimal concentrations within the dosing interval. The methodology is applied to six drugs, including targeted agents and chemotherapeutics, small and large molecules (erlotinib, dasatinib, vismodegib, trastuzumab, irinotecan, and capecitabine). The resulting efficacy response at the CRD is compared with clinical responses.Conclusions: We conclude that nonclinical studies designed with the appropriate CRDs of approved drug molecules will maximize the translatability of efficacy results, which is critical when testing approved and investigational agents in combination. Clin Cancer Res; 23(4); 1080-90. ©2016 AACR.

Leveraging model-based study designs and serial micro-sampling techniques to understand the oral pharmacokinetics of the potent LTB4 inhibitor, CP-105696, for mouse pharmacology studies

1. Leukotriene B4 (LTB4) is a proinflammatory mediator important in the progression of a number of inflammatory diseases. Preclinical models can explore the role of LTB4 in pathophysiology using tool compounds, such as CP-105696, that modulate its activity. To support preclinical pharmacology studies, micro-sampling techniques and mathematical modeling were used to determine the pharmacokinetics of CP-105696 in mice within the context of systemic inflammation induced by a high-fat diet (HFD). 2. Following oral administration of doses > 35 mg/kg, CP-105696 kinetics can be described by a one-compartment model with first order absorption. The compound's half-life is 44-62 h with an apparent volume of distribution of 0.51-0.72 L/kg. Exposures in animals fed an HFD are within 2-fold of those fed a normal chow diet. Daily dosing at 100 mg/kg was not tolerated and resulted in a >20% weight loss in the mice. 3. CP-105696's long half-life has the potential to support a twice weekly dosing schedule. Given that most chronic inflammatory diseases will require long-term therapies, these results are useful in determining the optimal dosing schedules for preclinical studies using CP-105696.