Gedatolisib Plus Talazoparib in Advanced Triple Negative or BRCA1/2 Positive, HER2 Negative Breast Cancers

Triple negative breast cancers (TNBC) are tumors that lack the hormone receptors and the human epidermal growth factor receptor-2 (HER2). TNBC represents about 15% of all invasive breast cancers diagnosed in the United States each year. This aggressive breast cancer subtype has the lowest overall survival rate of all advanced breast cancers with median survival of 12-13 months. Due to the lack of expression of the hormone receptors and HER2,chemotherapy remains the current treatment for women with advanced TNBC.

A subset of breast cancers have defects in homologous recombination (HR) DNA repair due to germline BRCA mutations, and these cases are often triple negative. Poly(ADP-ribose) polymerase (PARP) enzymes are involved in DNA repair and are activated by DNA strand breaks. PARP function is particularly critical in tumors with BRCA1/2 mutations, making PARP inhibition a rationale therapeutic strategy.

Two PARP inhibitors, Talazoparib and Olaparib, were approved by the FDA in 2018 for patients who have advanced HER2 negative breast cancer and a germline BRCA 1/2 mutation. These approvals were based on results from the EMBRACA and OLYMPIAD trials, respectively, which both showed an improvement in progression-free survival (PFS) versus physician choice chemotherapy.

Gedatolisib is an intravenously administered PI3K and mTOR inhibitor which has been shown to be safe in patients with metastatic breast cancer, either alone or in combination with oral therapies. Previous research has shown that PI3K inhibitors lower nucleotide pools required for DNA synthesis and S-phase progression. Additionally, inhibition of PI3K/mTOR could impede PI3K interaction with the homologous recombination complex, increasing dependency on PARP enzymes for DNA repair. Based on this data, the combination of a PI3K inhibitor and PARP inhibitor could potentially lead to a new, non-chemotherapy treatment option for TNBC with wild-type BRCA and improve the modest PFS seen with the PARP inhibitors as single agents in BRCA1/2 mutant advanced breast cancer. The hypothesis for this trial is that the gedatolisib will sensitize advanced TNBC or BRCA1/2 mutant breast cancers to PARP inhibition with talazoparib. This study is thus designed to determine the recommended phase 2 dose of gedatolisib in combination with talazoparib and to evaluate the efficacy of this combination in advanced HER2 negative breast cancer that is triple negative or BRCA1/2 positive (mutated/deficient).