Phase I Study of Single-Agent AZD1775 (MK-1775), a Wee1 Kinase Inhibitor, in Patients With Refractory Solid Tumors

Abstract

Purpose: Wee1 tyrosine kinase phosphorylates and inactivates cyclin-dependent kinase (Cdk) 1/2 in response to DNA damage. AZD1775 is a first-in-class inhibitor of Wee1 kinase with single-agent antitumor activity in preclinical models. We conducted a phase I study of single-agent AZD1775 in adult patients with refractory solid tumors to determine its maximum-tolerated dose (MTD), pharmacokinetics, and modulation of phosphorylated Tyr15-Cdk (pY15-Cdk) and phosphorylated histone H2AX (γH2AX) levels in paired tumor biopsies.

Patients and methods: AZD1775 was administered orally twice per day over 2.5 days per week for up to 2 weeks per 21-day cycle (3 + 3 design). At the MTD, paired tumor biopsies were obtained at baseline and after the fifth dose to determine pY15-Cdk and γH2AX levels. Six patients with BRCA-mutant solid tumors were also enrolled at the MTD.

Results: Twenty-five patients were enrolled. The MTD was established as 225 mg twice per day orally over 2.5 days per week for 2 weeks per 21-day cycle. Confirmed partial responses were observed in two patients carrying BRCA mutations: one with head and neck cancer and one with ovarian cancer. Common toxicities were myelosuppression and diarrhea. Dose-limiting toxicities were supraventricular tachyarrhythmia and myelosuppression. Accumulation of drug (t1/2 approximately 11 hours) was observed. Reduction in pY15-Cdk levels (two of five paired biopsies) and increases in γH2AX levels (three of five paired biopsies) were demonstrated.

Conclusion: This is the first report of AZD1775 single-agent activity in patients carrying BRCA mutations. Proof-of-mechanism was demonstrated by target modulation and DNA damage response in paired tumor biopsies.

Trial registration: ClinicalTrials.gov NCT01748825.

Fig 1.

Best response in patients with BRCA1/2 mutations. Two patients had partial responses.

Fig 2.

Computed tomography scan results of a patient with squamous cell carcinoma of the head and neck who had a BRCA1 germline mutation. This patient had a confirmed partial response with more than 30% reduction in target lesions noted after two cycles, persisting through four cycles of treatment with AZD1775. (A) Baseline, (B) after two cycles, and (C) after four cycles.

Fig 3.

Mean plasma concentration curves for AZD1775 after multiple dosing. Blood samples were collected predose and during cycle 1 at 1, 2, 4, 6, and 8 hours after the first dose; before the third dose; and before and at 1, 2, 4, 6, and 8 hours after the fifth dose. Plasma concentrations increased after each dose to an average maximum serum concentration of 1,650 nmol/L after the fifth dose. Area under the serum concentration-time curve on day 3 was two- to three-fold higher than on day 1.

Fig 4.

Quantitation of pY15-Cdk and γH2AX signaling based on the percentage of the nuclear area positive for the marker. Three of five patients had a demonstrable decrease in pY15-Cdk levels post-treatment. All five patient biopsies had some increase in γH2AX level post-treatment, with four patients having substantial increases. Postdose (*) or predose (†) biopsy levels less than the lower limit of quantitation did not allow quantitation of the percentage change in marker level after treatment.

Fig 5.

Immunofluorescence assay for pY15-Cdk (phosphorylated Tyr15-Cdk), γH2AX (phosphorylated histone H2AX), and pHH3 (phosphorylated histone H3) in paired tumor biopsies from a patient with nonsquamous non–small-cell lung carcinoma. Post-treatment biopsies were obtained 2 to 5 hours after the fifth dose on day 3 of cycle 1. Hematoxylin and eosin staining demonstrates adequate tumor content. A decrease in pY15-Cdk signal in the post-treatment biopsy is consistent with the downstream effect of Wee1 inhibition. Increases in γH2AX and pHH3 levels were observed in the post-treatment biopsy. (A) Hematoxylin and eosin, (B) pY15-Cdk, (C) γH2AX, and (D) pHH3.