On April 17, 2016 Medivation, Inc. (NASDAQ: MDVN) reported that Phase I data from its investigational agent talazoparib, a highly-potent PARP inhibitor, was presented at the American Association for Cancer Research (AACR) (Free AACR Whitepaper) Annual Meeting 2016 in New Orleans by the study’s lead investigator Zev A. Wainberg, M.D., Associate Professor of Medicine at the University of California Los Angeles (UCLA) and Co-Director of the UCLA GI Oncology Program, during a Clinical Trials Mini-Symposium (Press release, Medivation, APR 17, 2016, View Source [SID:1234510958]). The primary objective of the study was to determine the maximum tolerated dose (MTD) of talazoparib in combination with either low-dose temozolomide or low-dose irinotecan in heavily pretreated patients with advanced malignancies.
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The data from the 40 patient trial demonstrated that combination treatment with talazoparib and low-dose chemotherapy resulted in stable disease or an objective response in 23 of 40 heavily pretreated patients with a variety of advanced cancers (clinical benefit rate of 58%). Most notably, objective responses were seen in four of seven (57%) heavily pre-treated non-BRCA-mutated ovarian cancer patients when talazoparib was used in combination with either low-dose temozolomide or low-dose irinotecan. Six of seven individuals (86%) with non-BRCA ovarian cancer had clinical benefit (four partial responses and two stable disease) and had a reduction in CA 125 levels by 50% or greater.
Importantly, the overall study demonstrated responses to combination talazoparib/low-dose chemotherapy in patients with multiple tumor types in which specific deleterious mutations in certain DNA repair genes extended beyond BRCA deficiency, including one patient who did not meet the criteria of having homologous recombination deficiency (HRD). These effects may be mediated through PARP inhibition, as well as enhanced PARP trapping, which interferes with the tumor cell’s ability to replicate DNA by locking PARP molecules onto the DNA strand.
"In non-clinical studies, talazoparib has been shown to have high potency specifically against PARP 1 and 2, and antitumor effects in various solid tumors. With these new results, we now have evidence in humans that suggests talazoparib in combination with low-dose chemotherapy is active in tumors with defects in DNA repair beyond BRCA deficiency, and possibly in patients without evidence of HRD. We feel these data are consistent with talazoparib’s potent PARP trapping ability, which we believe makes talazoparib a unique and exciting product candidate with the potential to be used in combination with DNA damaging therapies across a wide variety of tumor types," said David Hung M.D., Founder, President and Chief Executive Officer of Medivation. "With more than half of the ovarian cancer patients demonstrating an objective response, particularly in a heavily pre-treated patient population with advanced disease, these findings are encouraging and support further evaluation of the safety and efficacy of talazoparib."
Talazoparib currently is in Phase III development for patients with locally advanced and/or metastatic breast cancer who harbor a germline BRCA1/2 mutation. It is also being studied in several investigator-sponsored trials across multiple tumor types.
The Phase I investigator-sponsored study evaluated escalating doses of talazoparib ( ≥ 0.5 mg given orally once daily) with either temozolomide ( ≥ 25 mg/m2 given orally on days 1-5; Arm A) or irinotecan ( ≥ 25 mg/m2 given by intravenous infusion every two weeks; Arm B) every 28 days in patients with advanced malignancies. Study participants ranged in age from 21 to 77 years (median: 57 years) and had received one to 15 prior chemotherapy regimens (median: 6). The primary endpoint of the study was the determination of the MTD. Secondary endpoints included pharmacokinetics, tumor response and biomarkers.
A total of 40 patients received escalating doses of talazoparib (0.5-1.0 mg) and either temozolomide or irinotecan (18 patients in Arm A and 22 in Arm B). Results showed the MTD for talazoparib was 1.0 mg. and 37.5 mg/m2 for either temozolomide or irinotecan when combined with 1.0 mg talazoparib. Partial responses were seen in four of seven (57%) germline BRCA wild type ovarian cancer patients who were platinum-resistant. Additional responses were seen in one patient each with Ewing’s Sarcoma, cervical adenocarcinoma, small cell lung cancer, and triple negative breast cancer. An association was observed between response and the presence of deleterious somatic mutations in DNA repair genes (PALB2 and RAD51D) distinct from BRCA mutations.
The most common grade 3/4 adverse events ( ≥ 5%) observed in patients treated with talazoparib plus temozolomide were neutropenia (28%), anemia (33%), and thrombocytopenia (33%). Among those treated with talazoparib plus irinotecan, the most common adverse events were thrombocytopenia (13%), anemia (27%) and neutropenia (31%). No significant pharmacokinetic interactions were observed between talazoparib and either temozolomide or irinotecan.
About Talazoparib
Talazoparib is a potent and specific inhibitor of PARP 1 and 2(i) that is being developed by Medivation for the treatment of selected solid tumors. In pre-clinical studies, talazoparib has shown single-agent anti-tumor activity, as well as synergy in combination with lowered doses of DNA-damaging agents, due to its dual mechanisms of cytotoxicity, PARP trapping, and inhibition of PARP enzyme activity. Trapping of PARP on DNA impairs DNA replication resulting in tumor cell death. Talazoparib currently is in Phase III development for patients with locally advanced and/or metastatic breast cancer who harbor a germline BRCA1/2 mutation.