A Phase I Study Investigating AZD8186, a Potent and Selective Inhibitor of PI3Kβ/δ, in Patients with Advanced Solid Tumors

Advanced Solid Tumors; PI3K beta/delta inhibitorTumores sólidos avanzados; Inhibidor de PI3K beta/deltaTumors sòlids avançats; Inhibidor de PI3K beta/deltaPurpose: To characterize safety and tolerability of the selective PI3Kβ inhibitor AZD8186, identify a recommended phase II dose (RP2D), and assess preliminary efficacy in combination with abiraterone acetate or vistusertib. Patients and Methods: This phase I open-label study included patients with advanced solid tumors, particularly prostate cancer, triple-negative breast cancer, and squamous non–small cell lung cancer. The study comprised four arms: (i) AZD8186 monotherapy dose finding; (ii) monotherapy dose expansion; (iii) AZD8186/abiraterone acetate (with prednisone); and (iv) AZD8186/vistusertib. The primary endpoints were safety, tolerability, and identification of the RP2D of AZD8186 monotherapy and in combination. Secondary endpoints included pharmacokinetics (PK), pharmacodynamics, and tumor and prostate-specific antigen (PSA) responses. Results: In total, 161 patients were enrolled. AZD8186 was well tolerated across all study arms, the most common adverse events being gastrointestinal symptoms. In the monotherapy dose-finding arm, four patients experienced dose-limiting toxicities (mainly rash). AZD8186 doses of 60-mg twice daily [BID; 5 days on, 2 days off (5:2)] and 120-mg BID (continuous and 5:2 dosing) were taken into subsequent arms. The PKs of AZD8186 were dose proportional, without interactions with abiraterone acetate or vistusertib, and target inhibition was observed in plasma and tumor tissue. Monotherapy and combination therapy showed preliminary evidence of limited antitumor activity by imaging and, in prostate cancer, PSA reduction. Conclusions: AZD8186 monotherapy had an acceptable safety and tolerability profile, and combination with abiraterone acetate/prednisone or vistusertib was also tolerated. There was preliminary evidence of antitumor activity, meriting further exploration of AZD8186 in subsequent studies in PI3Kβ pathway–dependent cancers.This study was sponsored by AstraZeneca. We thank the patients and their doctors and caregivers who participated in this study. We acknowledge support in Cambridge from Cancer Research UK, Experimental Cancer Medicine Center, NIHR Biomedical Research Center, and NIHR Cambridge Clinical Research Center. Research at the Christie NHS Foundation Trust was supported by the NIHR Manchester Clinical Research Facility and Manchester Experimental Cancer Medicine Center award. We also thank Martine Roudier (AstraZeneca) for providing analysis data of tumor tissue biopsies, and Wolfram Brugger and Caroline Kennedy (AstraZeneca, Cambridge, UK). Abiraterone acetate was kindly provided by Janssen. Medical writing and editorial assistance were provided by Bioscript Medical, Macclesfield, UK, and funded by AstraZeneca