PF-06952229

The development of transforming growth factor βreceptor inhibitors (TGFβRi) as new medicines has been affected by cardiac valvulopathy and arteriopathy toxicity findings in nonclinical toxicology studies. PF-06952229 (MDV6058) selected using rational drug design is a potent and selective TGFβRI inhibitor with a relatively clean off-target selectivity profile and good pharmacokinetic properties across species. PF-06952229 inhibited clinically translatable phospho-SMAD2 biomarker (≥60%) in human and cynomolgus monkey peripheral blood mononuclear cells, as well as in mouse and rat splenocytes. Using an optimized, intermittent dosing schedule (7-day on/7-day off/cycle; 5 cycles), PF-06952229 demonstrated efficacy in a 63-day syngeneic MC38 colon carcinoma mouse model. In the pivotal repeat-dose toxicity studies (rat and cynomolgus monkey), PF-06952229 on an intermittent dosing schedule (5-day on/5-day off cycle; 5 cycles, 28 doses) showed no cardiac-related adverse findings. However, new toxicity findings related to PF-06952229 included reversible hepatocellular (hepatocyte necrosis with corresponding clinically monitorable transaminase increases) and lung (hemorrhage with mixed cell inflammation) findings at ≥ targeted projected clinical efficacious exposures. Furthermore, partially reversible cartilage hypertrophy (trachea and femur in rat; femur in monkey) and partially to fully reversible, clinically monitorable decreases in serum phosphorus and urinary phosphate at ≥ projected clinically efficacious exposures were observed. Given the integral role of TGFβ in endochondral bone formation, cartilage findings in toxicity studies have been observed with other TGFβRi classes of compounds. The favorable cumulative profile of PF-06952229 in biochemical, pharmacodynamic, pharmacokinetic, and nonclinical studies allowed for its evaluation in cancer patients using the intermittent dosing schedule (7-day on/7-day off) and careful protocol-defined monitoring. SIGNIFICANCE STATEMENT: Only a few TGFβRi have progressed for clinical evaluation due to adverse cardiac findings in pivotal nonclinical toxicity studies. The potential translations of such findings in patients are of major concern. Using a carefully optimized intermittent dosing schedule, PF-06952229 has demonstrated impressive pharmacological efficacy in the syngeneic MC38 colon carcinoma mouse model. Additionally, a nonclinical toxicology package without cardiovascular liabilities and generally monitorable toxicity profile has been completed. The compound presents an acceptable International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use S9-compliant profile for the intended-to-treat cancer patients.

PF-06952229 is a selective small-molecule inhibitor of transforming growth factor-β (TGF-β) receptor 1. We evaluated its antitumor activity in preclinical studies and its safety, tolerability, pharmacokinetics, and pharmacodynamics in a phase I study (NCT03685591).

In vitro and in vivo preclinical studies were conducted. Patients (aged ≥18 years) received PF-06952229 monotherapy [20-500 mg, oral b.i.d., 7 days on/7 days off, 28-day cycles, Part 1A (P1A)] for advanced/metastatic solid tumors and combination therapy [250/375 mg with enzalutamide, Part 1B (P1B)] for metastatic castration-resistant prostate cancer (mCRPC). Primary endpoints were dose-limiting toxicity (DLT), adverse events (AEs), and laboratory abnormalities. Efficacy, pharmacokinetic parameters, and biomarker modulation were assessed.

PF-06952229 showed activity in preclinical murine tumor models including pSMAD2 modulation in tumors. The study (NCT03685591) enrolled 49 patients (P1A, n = 42; P1B, n = 7). DLTs were reported in 3/35 (8.6%) P1A patients receiving PF-06952229 375 mg (anemia, intracranial tumor hemorrhage, and anemia and hypertension, all grade 3, n = 1 each). The most frequent grade 3 treatment-related AEs (TRAEs) were alanine aminotransferase increased and anemia (9.5% each). There were no grade 4-5 TRAEs. Plasma PF-06952229 exposures were dose proportional between 80 and 375 mg. Pharmacodynamic studies confirmed target modulation of pSMAD2/3 (peripheral monocytes). One P1A patient with prostate cancer receiving PF-06952229 375 mg monotherapy achieved confirmed partial response (31-month duration of response). A total of 8 patients (P1A, n = 6; P1B, n = 2) achieved stable disease.

Antitumor activity of PF-06952229 was observed in preclinical studies. PF-06952229 was generally well tolerated with manageable toxicity; a small group of patients achieved durable responses and/or disease stabilization.