Abstract P2-16-22: A dose-finding phase lb study of BEZ235 in combination with paclitaxel in patients with HER2-negative, locally advanced or metastatic breast cancer

Abstract

Abstract Background: The PI3K/Akt/mTOR pathway is the most frequently activated signaling pathway in breast cancer (BC). Activation of this pathway promotes tumor growth and progression, and resistance to anticancer therapies, including paclitaxel (PTX). BEZ235 is an oral, ATP-competitive inhibitor that targets class l PI3K and downstream effectors mTORC1/2. BEZ235 has shown antiproliferative, proapoptotic, and antiangiogenic activity in multiple preclinical cancer models. In a Ph I study, single-agent BEZ235 given twice daily (BID) showed preliminary signs of clinical activity. Methods: This was a multicenter, open-label Ph Ib/II study of daily, oral BEZ235 given BID in combination with weekly (QW) intravenous PTX in women with HER2-, metastatic or locally advanced BC (NCT01495247). For the Ph Ib part, the primary objective was to determine the maximum tolerated dose (MTD)/recommended Ph II dose (RP2D) of BEZ235 in combination with PTX based on dose-limiting toxicities (DLTs) using a 5-parameter adaptive Bayesian logistic regression model with overdose control. MTD was defined as the highest dose not causing medically unacceptable DLTs in >35% of pts during Cycle 1 (28 days). Secondary objectives included safety, preliminary activity, and PK. Safety was monitored by physical exams, vital signs, laboratory tests, weight, and cardiac health. AEs were assessed continuously by CTCAE v4.03. Tumor evaluations were performed at screening and every 8 wks after starting treatment, and assessed locally by RECIST v1.1. Results: As of April 12, 2013, 18 pts (mean age: 50 yr; 67% ≥4 prior lines of antineoplastic therapy) had been enrolled into Ph Ib. 13 pts received BEZ235 200 mg BID + PTX 80 mg/m2 QW. The dose level was then reduced to BEZ235 100 mg BID + PTX 80 mg/m2 QW (n = 5). Of 17 evaluable pts (12 at the 200-mg BID dose; 5 at the 100-mg BID dose), 6 (35%) developed ≥1 DLTs (5 [42%] at the 200-mg BID dose; 1 [20%] at the 100-mg BID dose): neutropenia (n = 3 [1 at the 100-mg BID dose]), stomatitis (n = 3), nausea (n = 2), and vomiting (n = 1). Of 18 pts, 12 have discontinued (6 due to disease progression; 4 AEs; 1 physician decision; 1 pt/guardian decision). Median duration of exposure to BEZ235 and PTX was 76 days each. The most common suspected study drug-related AEs included asthenia (78%), nausea (72%), neutropenia (72%), diarrhea (67%), stomatitis (61%), and decreased appetite (56%). Among 13 pts receiving BEZ235 200 mg BID, 2 (15%) achieved a PR, 4 (31%) had SD, and 4 (31%) had PD; all 5 pts receiving BEZ235 100 mg BID had SD. PK results showed large interpatient variability at both dose levels. Analysis of pAKT and p4EBP1 was performed on peripheral blood mononuclear cells collected from pts before treatment and 4 h following treatment (Cmax). PK/PD analysis did not provide evidence of a strong and consistent correlation between BEZ235 plasma concentrations and pAKT inhibition. Conclusions: The MTD/RP2D of BEZ235 in combination with PTX in pts with locally advanced or metastatic HER2- BC was not reached. Based on the observed overall safety profile, efficacy, variable PK, and PD data from the Ph Ib part of this study, further enrollment has stopped. The Ph II part of the study will not be conducted. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-22.