A phase I study of highly potent oral ATR inhibitor (ATRi) tuvusertib plus oral PARP inhibitor (PARPi) niraparib in patients with solid tumors.

3018 Background: Ataxia telangiectasia and Rad3-related (ATR) protein kinase and poly-ADP ribose polymerases (PARPs) are crucial components in the DNA damage response (DDR). Combining tuvusertib and niraparib may synergistically enhance synthetic lethality and increase apoptosis. Part B1 of the DDRiver Solid Tumors 301 study (NCT04170153) assessed this combination. Methods: Part B1 of this open-label multicenter dose-escalation phase Ib trial enrolled unselected patients with metastatic or locally advanced unresectable solid tumors refractory to standard treatment. The primary objective was to determine safety (including maximum tolerable dose and recommended dose(s) for expansion RDE). Secondary and tertiary objectives included determination of the pharmacokinetics (PK), pharmacodynamics (PD), and preliminary efficacy of different dosing regimens of tuvusertib plus niraparib. Multiple continuous and intermittent schedules were explored with tuvusertib doses ranging from 90–180 mg once-daily (QD) and niraparib doses from 100–200 mg QD. A partial ordering continual reassessment method was used to identify the RDEs. Results: As of 02 January 2024, 43 patients had been enrolled (all with baseline body weight <77kg or platelet count <150,000/mm 3 ); 13 patients remained on treatment. Ten (26.3%) patients had dose-limiting toxicities (DLTs). The most common DLT was grade 3 anemia requiring blood transfusion (n=4; 10.5%); the most frequent grade ≥3 treatment-emergent adverse events were anemia (n=18; 41.9%), platelet count decrease (n=6; 14.0%) and fatigue (n=4; 9.3%). The PK of tuvusertib when combined with niraparib was consistent with that of tuvusertib monotherapy, suggesting a lack of any clinically meaningful mutual drug–drug interactions. Dose-dependent ɣ-H2AX inhibition (proximal PD marker) was observed at tuvusertib doses ≥130 mg QD. Preliminary efficacy data show 5 (15.6%) responses (3 confirmed) by RECIST v1.1 in 32 evaluable patients: 2 in patients with epithelial ovarian cancer (EOC; 1 with BRCA1-mutant BRCA1m PARPi-resistant EOC, 1 with BRCA-wild type homologous recombination deficiency-positive EOC) and 1 each in patients with non-small cell lung cancer, estrogen receptor-positive HER2-negative BRCA1m breast cancer, and BRCA1m PARPi-resistant pancreatic cancer. Tuvusertib 180 mg QD and niraparib 100 mg QD or tuvusertib 90 mg QD and niraparib 200 mg QD, both given in a 1 week on/1 week off schedule, were identified as RDEs. Conclusions: The combination of tuvusertib plus niraparib, each administered on a 1 week on/1 week off schedule, has a manageable safety profile and is suitable for further investigation. A combination study in patients with PARPi-resistant EOC is planned. Clinical trial information: NCT04170153 .