Phase Ib trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy and a CDK4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC).

Abstract

1066 Background: The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), with an anti-estrogen, are the standard of care for HR+/HER2- MBC. Insights from patient biopsies and preclinical analysis suggest that AKT1 activation can provoke CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may provide clinical benefit. Methods: TAKTIC is an open-label phase Ib trial exploring the combination of the AKT1 inhibitor, ipatasertib (ipat), with an aromatase inhibitor (Arm A), fulvestrant (Arm B), or the triplet combination (Arm C) of fulvestrant + ipat + palbociclib (palbo). The primary objective is to evaluate the safety and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an interim analysis from the triplet combination (Arm C). Results: As of 1/31/2020, 25 pts have enrolled, including 12 on Arm C, all of whom received prior CDK4/6i (median no of prior lines = 5.5, range 2-7). Along with fulvestrant, 3 pts received ipat at 200mg + 125mg palbo, 7 pts received 300mg + 125mg palbo, and 2 pts received 400mg + 100mg palbo. To date, 8/12 pts remain on treatment including 2 with partial response, 3 with stable disease, 3 with restaging studies pending and 4 with progressive disease. The triplet combination was well tolerated. Grade 3 toxicities included reduced WBC (8/12), reduced neutrophil count (11/12), reduced lymphocyte count (2/12) and single instances of transaminitis, rash, and reduced platelet count. The only grade 4 toxicity was reduced neutrophil count (4/12). There were no DLTs observed and no discontinuations due to toxicity. Mean steady state pharmacokinetic parameters for ipat were similar to historical data from single agent trials suggesting that combined treatment with palbo + fulvestrant did not affect the pharmacokinetics of ipat. Updated analysis will be presented at the meeting. Conclusions: The triplet combination of endocrine therapy with CDK 4/6i and AKTi appears to be well tolerated in heavily pre-treated pts, with a subset demonstrating signs of clinical benefit. The trial demonstrates how insights into the molecular mechanisms of CDK4/6i resistance could be leveraged into actionable therapeutic regimens for HR+/HER2- MBC. Clinical trial information: NCT03959891 .

AKT Inhibitors: New Weapons in the Fight Against Breast Cancer?

“…Preliminary results on the first 12 patients enrolled in cohort C (ipatasertib + fulvestrant + palbociclib) were reported at ASCO 2020. The triplet showed signals of clinical activity in this heavily pretreated population with proven resistance to CDKIs, with two partial responses and three stable disease registered ( Wander et al, 2020 ). IPATunity150 is a phase III randomized trial with a preliminary safety run-in cohort, which will compare the combination of ipatasertib + fulvestrant + palbociclib and placebo + fulvestrant + palbociclib in a population of endocrine resistant HR + BC, naïve to CDK4/6 inhibitors.…”

Nexus between PI3K/AKT and Estrogen Receptor Signaling in Breast Cancer

“…Everolimus in combination with Exemestane (BOLERO-2 trial) [87,88] Ipatasertib in combination with endocrine therapy and a CDK4/6 inhibitor (TAKTIC trial) [89] Concurrent inhibition of ERα, CCND1-CDK4/6-RB pathway and the PI3K-AKT-mTOR pathways…”

Clinical Development of AKT Inhibitors and Associated Predictive Biomarkers to Guide Patient Treatment in Cancer Medicine

“…Preliminary results of the triplet combination have shown two partial responses amongst 12 patients, and the combination was well tolerated with no dose limiting toxicities at reported dose levels. 96 A phase Ib trial of cobimetinib and ipatasertib was however poorly tolerated and all 66 patients who received study drug reported an adverse event, with 53% experiencing drug-related AE of grade 3 or worse severity, though none were dose-limiting toxicities. Although biomarker analyses indicated blockade of combined RAS/MEK/ ERK and pI3K/AKT/mTOR pathways in paired tumor biopsies, objective responses were only observed in two patients with endometrial cancer and one with ovarian cancer.…”

“…Preliminary results of the triplet combination have shown two partial responses amongst 12 patients, and the combination was well tolerated with no dose limiting toxicities at reported dose levels. 96 …”