Zentalis®Pharmaceuticals, Inc. announced positive data from the Phase 1b trial of azenosertib, the Company's potentially first-in-class WEE1 inhibitor, in combination with chemotherapy in patients with platinum-resistant ovarian cancer. Azenosertib was well tolerated in combination with multiple types of chemotherapy and demonstrated encouraging clinical activity, with noteworthy improvements in objective response rates (ORRs) and median progression free survival (mPFS) in all patients, especially those with Cyclin E1+ tumors, a subgroup recognized to have a poor prognosis and be refractory to chemotherapy. A total of 115 patients were enrolled in the study across all chemotherapy combination groups.

At the data cut-off of April 10, 2023, 94 were efficacy evaluable. Across all dosing schedules, azenosertib plus paclitaxel demonstrated the higher ORR of 50.0% (mPFS of 7.4m), followed by an ORR of 38.5% (mPFS of 8.3m) for azenosertib plus gemcitabine. Azenosertib plus carboplatin demonstrated an ORR of 35.7% (mPFS of 10.4m), and azenosertib plus PLD demonstrated an ORR of 19.4% (mPFS of 6.3m).

A total of 82 response-evaluable patients had available Cyclin E1 expression data by immunohistochemistry (IHC). Cyclin E1+ status (H-score >50) was associated with a superior ORR and a longer mPFS across the total patient population (ORR of 40.0% vs 8.3%; mPFS of 9.86 vs 3.25 months, HR = 0.37; P = 0.0078), showcasing the potential synergy of WEE1 inhibition with chemotherapy in this patient population. Overall, the tolerability of azenosertib dosed intermittently in combination with either paclitaxel or carboplatin compares favorably to historical data from standard of care chemotherapy doublets of either paclitaxel-carboplatin or PLD-carboplatin.

Frequent Grade =3 treatment-related adverse events (%) across all azenosertib intermittent dosing groups were thrombocytopenia (27.5%), neutropenia (25.5%), anemia (15.7%), and fatigue (9.8%). A recommended Phase 2 dose was determined for each of the azenosertib combinations with paclitaxel, carboplatin, and PLD. Based on these results, the Company is planning to initiate a Phase 3 study comparing azenosertib dosed intermittently in combination with either carboplatin or paclitaxel in patients with Cyclin E1+ platinum-sensitive ovarian cancer.

The Company expects to initiate the Phase 3 study in the first quarter of 2024.