IDEAYA Biosciences has announced the enrolment of the first patient in its Phase I dose-escalation and expansion trial evaluating IDE034, an investigational PTK7/B7H3 bispecific topoisomerase 1 (TOP1) Antibody-Drug Conjugate (ADC).

The Phase I study will assess the safety, tolerability and pharmacokinetics (PK) of IDE034 as a monotherapy. The company also plans to explore combination strategies with agents targeting the DNA damage response pathway, including its proprietary PARG inhibitor, IDE161. The dosing of the first patient has triggered a USD 5 million milestone payment from Biocytogen under an existing Option and License Agreement.

According to Yujiro S. Hata, President and Chief Executive Officer of IDEAYA, the milestone marks important progress for the company’s broader ADC/DDR portfolio. IDE034 is designed as a potentially first-in-class B7H3/PTK7 bispecific TOP1 ADC that is internalised only when both target antigens are co-expressed on the same tumour cell. This mechanism is expected to enhance selectivity and improve tolerability compared to traditional monovalent antibody formats.

IDEAYA estimates that B7H3 and PTK7 are co-expressed in approximately 30–40 percent of certain major solid tumours, including lung, breast, ovarian and colorectal cancers, while demonstrating minimal dual expression in normal tissues. Preclinical studies have shown promising monotherapy activity and synergistic potential when combined with IDE161, suggesting improved efficacy and durability of response.

IDE034 represents the company’s second proprietary TOP1 ADC, following IDE849, currently in Phase I development for Small Cell Lung Cancer (SCLC) and Neuroendocrine Carcinoma (NEC).

IDEAYA continues to advance its precision medicine approach, integrating small-molecule drug discovery, structural biology, bioinformatics and biomarker-driven development to deliver potentially first-in-class targeted therapies aligned with the genetic drivers of cancer.