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

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 duration of treatment Other inclusion and exclusion criteria as defined in the study protocol