A phase Ib study of BKM120 combined with abiraterone acetate for castrate-resistant, metastatic prostate cancer.

Abstract

274 Background: There is cross-talk between PI3-kinase (PI3K) pathway and androgen receptor (AR) signaling pathways, respectively, which are both critical for cell survival in castrate-resistant prostate cancer (CRPC). The primary study objective is to determine the safety profile and MTD of BKM120 (B, pan-PI3K inhibitor) in combination with abiraterone/prednisone (A/P) in CRPC patients. The secondary objectives are to assess the impact of PTEN status on duration of response/time to progression in the expansion cohort, and to evaluate the impact of B on a PI3-kinase activation fingerprint in metastatic bone or lymph node tissue samples. An exploratory objective is to assess the effect of B on transcription of a set of AR-regulated genes in metastatic bone biopsy samples. Methods: The trial design involves a 14 day lead-in phase with B alone, to assess single-agent toxicity and perform correlative studies. A/P is combined with B at the end of 14 days using the standard 3+3 dose-escalation design with 3 dose levels of B, and participants are assessed for safety and MTD on the combination therapy. To determine PD impact of single agent B on the PI3K activation signature at a metastatic site, a mandatory CT-guided bone or lymph node biopsy is performed prior to B initiation and at the end of 2 weeks on B single-agent therapy. Immunohistochemical (IHC) stains for three markers (p-AKT, p-S6 and PTEN) are used to obtain a semi-quantitative PI3K activation score, based on the quartile levels of continuous staining scores of each marker. Results: Patient 1 had symptomatic bone pain improvement, marked decline in narcotic pain requirements and a biochemical decline in PSA from 156.5 to a PSA nadir of 9.2 within 4 weeks of combination therapy. Patient 3 had a symptomatic and >90% biochemical improvement and has currently completed 15 cycles on treatment, and remains on study to date. RT-PCR analysis showed that the feedback circuitry between PI3K and AR signaling is heterogeneous in the metastatic prostate cancer-bone microenvironment, and dependent on tumor PTEN status. Conclusions: Preliminary data shows promising anti-tumor activity in CRPC patients from dual targeting of PI3K and AR pathways with B and A/P, respectively. Clinical trial information: NCT01741753.