First-in-Human Study of ATX-559, an Oral Inhibitor of DHX9, in Patients With Advanced or Metastatic Solid Tumors, and Molecularly Defined Cancers

Key Inclusion Criteria: * Patients with histologically confirmed solid tumors who have locally recurrent or metastatic disease * Refractory to or relapsed after all standard therapies with proven clinical benefit, unless as deemed by the Investigator, the subject is not a candidate for standard treatment, there is no standard treatment, or the subject refuses standard treatment after expressing an understanding of all available therapies with proven clinical benefit * For the expansion cohorts, participants must have histological confirmation of the specified tumor types: * BRCA1 or BRCA2 deficient, HER2 negative metastatic breast cancer * dMMR or MSI-H with unresectable or metastatic solid tumors * There is no limit to the number of prior treatment regimens * Have measurable or evaluable disease * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 Key Exclusion Criteria: * Clinically unstable central nervous system (CNS) tumors or brain metastasis * Any other concurrent anti-cancer treatment * Has undergone a major surgery within 3 weeks of starting study treatment * Medical issue that limits oral ingestion or impairment of gastrointestinal function that is expected to significantly reduce the absorption of ATX-559 * Clinically significant (ie, active) or uncontrolled cardiovascular disease * Unable to transition off strong or moderate CYP2C8 inhibitors or inducers * Pregnancy or intent to breastfeed or conceive a child within the projected dur…