Zentalis's Early WEE1 Inhibitor Data Shows 'Exceptional' Response In Solid Tumor Study, Plans Combination Trials

Zentalis Pharmaceuticals Inc ZNTL has announced initial efficacy and safety data from the Phase 1 dose-escalation portion of its ongoing Phase 1/2 trial evaluating ZN-c3 in patients with advanced solid tumors who are refractory to or ineligible for standard therapy or for whom no standard therapy is available.
Data were presented at the American Association of Cancer Research (AACR) Annual Meeting.
Zentalis’ WEE1 inhibitor, ZN-c3, posted partial responses across a slate of tumor types with a tolerable safety profile as monotherapy for solid tumor patients.
The drug shrank tumors in two patients: One patient had stage 4 ovarian cancer and had tried 18 lines of treatment, while the other patient had stage 4 colorectal cancer and had undergone five prior lines of treatment.
The ovarian cancer patient saw targeted tumors shrink by about 56%. Four weeks into treatment, it saw a “large rapid drop” in blood levels of CA-125, an antigen used to monitor certain cancers.
As for the colorectal cancer patient, tumors shrank by 42%, and the patient remained on treatment for about six months before the disease progressed.
Three other patients had their tumors shrink, too—including one with Stage IV non-small cell lung cancer (NSCLC) and two with uterine serous carcinoma.
The NSCLC patient had received three prior lines of therapy and, after ZN-c3 treatment, achieved an unconfirmed partial response with a 50% reduction in overall target lesions.
On the safety front, side effects were mostly mild to moderate, with nausea affecting about half of the 55 patients evaluated for safety, diarrhea, fatigue, and vomiting, afflicting less than one-third of them.
Blood-related side effects struck less than 10% of patients: 1.8% of patients suffered a low white blood cell count, 7.2% of patients had a low platelet count, and 7.2% of patients developed anemia.
The company initiated the Phase 1 expansion portion of the trial with the 300 mg dose earlier in 2021 and is exploring ZN-c3’s potential in combination trials, including in ovarian cancer and osteosarcoma.
Separately, the company has collaborated with GlaxoSmithKline plc GSK to evaluate the combination of ZN-c3 and Zejula (niraparib) in patients with advanced epithelial ovarian cancer.
Under the terms of the non-exclusive collaboration, Zentalis is responsible for conducting the study with GSK supplying niraparib. Zentalis maintains full ownership of ZN-c3.
The company will host a webcast event with key opinion leaders today at 4:00 p.m. ET.
Price Action: ZNTL shares are up 7.53% at $40.22 on the last check Monday.

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