IDEAYA Enrolls First Patient In Phase 1 Trial Of IDE034 Bispecific TOP1 Antibody-Drug Conjugate (ADC),Triggers $5M Biocytogen Milestone

IDEAYA Biosciences, Inc. announced the enrollment of the first patient in its Phase 1 dose-escalation and expansion study of IDE034, an investigational PTK7/B7H3 bispecific TOP1 antibody-drug conjugate (ADC). The trial will evaluate the safety, tolerability, and pharmacokinetics of IDE034 as a monotherapy, with planned combination cohorts assessing its use alongside DNA damage response (DDR) pathway agents, including IDEAYA’s proprietary PARG inhibitor, IDE161. The initial patient dosing has triggered a $5 million milestone payment from IDEAYA to Biocytogen Pharmaceuticals under their Option and License Agreement.

IDE034 is designed as a potentially first-in-class bispecific ADC targeting both B7H3 and PTK7. The therapy is engineered to be internalized only when both antigens are co-expressed on the same tumor cell, a mechanism intended to improve tumor selectivity and tolerability compared to conventional monovalent antibody approaches.

"This is an important milestone for IDE034 as well as our broader ADC/DDR portfolio focused on exploring combinations of highly selective TOP1 ADCs with agents targeting the DDR pathway.  We are excited to begin dosing patients with IDE034, a B7H3/PTK7 bispecific ADC that has demonstrated promising signs of efficacy as a monotherapy and synergy in combination with IDE161 across several preclinical tumor cell models. IDE034 is our second proprietary TOP1 ADC, building on the progress we have made with IDE849, our DLL3 TOP1 ADC currently in Phase 1 for SCLC and NEC, and represents another potentially first-in-class therapy for cancer patients in need of new and improved treatment options," said Yujiro S. Hata, President and Chief Executive Officer of IDEAYA Biosciences.

According to IDEAYA, co-expression of B7H3 and PTK7 occurs in approximately 30–40% of certain major solid tumors, including lung, breast, ovarian, and colorectal cancers, while dual expression appears minimal in normal tissues. This differential expression profile supports the rationale for a targeted bispecific strategy.

Preclinical tumor models have also shown promising synergy when IDE034 is combined with IDE161, an oral PARG inhibitor. The company believes that targeting DNA repair pathways alongside a TOP1 ADC payload may enhance both the efficacy and durability of treatment responses in selected solid tumors.