A Phase 1/2 Trial of SRA737 in Subjects With Advanced Cancer

The purpose of this clinical study is to establish the safety profile, determine the maximum tolerated dose (MTD) and recommend a Phase 2 dose and schedule of SRA737; and to evaluate the efficacy of SRA737 in prospectively-selected subjects with genetically-defined tumors that harbor genomic alterations linked to increased replication stress and that are hypothesized to be more sensitive to checkpoint kinase 1 (Chk1) inhibition via synthetic lethality. Specific cancer indications that frequently harbor these genetic mutations will be studied.

SRA737 is a potent, highly selective, orally bioavailable small molecule inhibitor of Chk1, a key regulator of cell cycle progression and the DNA Damage Response (DDR) replication stress response. In cancer cells, intrinsic replication stress (RS) is induced by factors such as oncogenes (e.g., CCNE1 or MYC), genetic mutations in DNA repair machinery (e.g. BRCA1 or FANCA), genetic mutations leading to a dysregulated cell cycle (e.g., TP53 or RAD50) or other genomic alterations. This replication stress results in persistent DNA damage and genomic instability, leading to an increased dependency on Chk1 for survival. Targeted inhibition of Chk1 by SRA737 may therefore be synthetically lethal to cancer cells with elevated intrinsic RS. This study has been designed to: establish the safety profile; determine the pharmacokinetic profile; identify the optimal dose, schedule, and MTD; obtain preliminary evidence of activity; and evaluate SRA737's efficacy in prospectively-selected subjects with tumors that harbor genomic alterations linked to increased replication stress and that are hypothesized to be more sensitive to Chk1 inhibition via synthetic lethality. This clinical study consists of two phases, a Dose Escalation Phase 1 portion and a Cohort Expansion Phase 2 portion. In the Dose Escalation Phase 1 portion, cohorts consisting initially of a single subject will receive escalating doses of SRA737, administered orally on a continuous daily dosing schedule in 28-day cycles. Once an SRA737-related Grade 2 toxicity is observed in a dose escalation cohort during Cycle 1, that cohort will be expanded to 3 to 6 subjects, and subsequent dose level cohorts will follow a rolling 6 design until the MTD has been identified. In the Cohort Expansion Phase 2 portion, subjects with genetically-defined tumors that harbor genomic alterations linked to increased replication stress and that are hypothesized to be more sensitive to Chk1 inhibition will be prospectively enrolled into six indication-specific cohorts to explore the preliminary efficacy of SRA737. Subjects must have advanced or metastatic disease of one of the following types: * castration-resistant prostate cancer (mCRPC); * high grade serous ovarian cancer (HGSOC) without CCNE1 gene amplification; * HGSOC with CCNE1 gene amplification (or alternative genetic alteration with similar functional effect); * non-small cell lung cancer (NSCLC); * head and neck squamous cell carcinoma (HNSCC) or squamous cell carcinoma of the anus (SCCA); and * colorectal cancer (mCRC). To qualify for enrolment in the Cohort Expansion Phase 2 portion, the subject's tumor must have a confirmed combination of mutations which are expected to confer sensitivity to Chk1 inhibition, determined by the Sponsor's review of genetic abnormalities detected in the following categories: * Oncogenic drivers such as CCNE1 or MYC, etc. * Genes involved in the DNA repair process including BRCA1, BRCA2, FANC genes, mismatch repair (MMR) genetic alterations and/or high microsatellite instability. * Key tumor suppressor genes regulating G1 cell cycle progression/arrest such as TP53, RAD50, etc. For patients with HNSCC or SCCA, positive human papilloma virus (HPV) status is also considered for eligibility. * Genetic indicators of replicative stress such as gain of function/amplification of CHEK1, ATR or other related genes. Tumor genetics will be prospectively determined using Next-Generation Sequencing.