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

ATX-559 is an oral drug that inhibits a protein called DHX9, a multi-functional RNA helicase that is involved in the maintenance of genomic stability by resolving DNA/RNA secondary structures that may lead to DNA replication stress and DNA damage in certain molecularly defined cancers. ATX-559 has been shown preclinically to induce robust anti-tumor activity of a variety of different solid tumors, including models with BRCA deficiency and microsatellite instability-high (MSI-H) and/or deficient mismatch repair (dMMR).

This is a first-in-human, Phase 1, open-label, single-arm, dose-escalation and expansion study to:

Evaluate the safety profile of ATX-559 and determine the recommended phase 2 dose (RP2D). In addition, the study aims to characterize the PK, PD, and preliminary anti-tumor activity of orally administered ATX-559. Exploratory objectives include examination of biomarker responses in relationship to ATX-559 exposure.

Patients with molecularly selected locally advanced or metastatic solid tumors (for example, BRCA1- or BRCA2-deficient breast cancer and solid tumors with microsatellite instability (MSI-H) and/or deficient mismatch repair (dMMR) will be enrolled to preliminarily assess the anti-tumor effect, and further examine the safety and PK of ATX-559 at the RP2D.