DR319-DP: A Nectin-4/Trop-2 bispecific ADC with an avidity-driven VHH design and dual-MOA payloads

Trop-2 and Nectin-4 have emerged as attractive targets for the development of next-generation antibody-drug conjugates (ADCs). However, the emergence of drug resistance remains a critical challenge in ADC therapy. Combination strategies represent a promising approach to enhance therapeutic efficacy and mitigate resistance. Notably, Trop-2 and Nectin-4 exhibit high and frequent co-expression across multiple solid tumors, while showing limited or moderate expression in normal tissues. In clinical attempts, the combination of sacituzumab govitecan (SG) and enfortumab vedotin (EV) has demonstrated substantially improved efficacy in early-phase trials for metastatic urothelial carcinoma. However, toxicities arising from both “off-target, off-tumor” and “on-target, off-tumor” effects remain a major concern. To maximize antitumor efficacy while minimizing systemic toxicity, we developed an avidity-driven bispecific antibody, DR319, featuring a “1+1” bispecific format that incorporates a low-affinity but high-avidity anti-Trop-2 VHH arm. We demonstrated that DR319 enables potent, high-avidity binding to Nectin-4/Trop-2 dual-positive tumor cells in our diverse cell line panel, while minimizing binding to Trop-2 single-positive cells, thereby mechanistically reducing on-target toxicities. We then conjugated DR319 to a novel Topoisomerase I inhibitor (TopoI) linker-payload (CPD3) featuring improved plasma stability, generating DR319-CPD3 (DAR 6). Our results showed that DR319-CPD3 exhibited superior antitumor efficacy in CDX models compared with benchmark mono-targeting ADCs with TopoI payloads, even those using the same CPD3. Furthermore, we generated a dual-payloads ADC, DR319-DP, with a DAR of 4 TopoI + 2 microtubule inhibitor (MTI), through a one-step glyco-conjugation strategy. This construct is designed to deliver synergistic, orthogonal mechanisms of action (MOA) to address tumor heterogeneity and therapeutic resistance. In our studies, DR319-DP demonstrated excellent target and bystander killing and achieved more potent and durable tumor suppression than mono-targeting ADCs (with either TopoI or MTI payloads) and DR319-CPD3, across multiple CDX and PDX models. Additionally, our characterization confirmed that DR319-DP displayed excellent thermal and plasma stability, along with a favorable pharmacokinetic (PK) profile in mice and cynomolgus monkeys. DR319 is precision-engineered with an avidity-driven backbone to minimize the on-target toxicities that limit current Nectin-4 and Trop-2 therapies. The incorporation of synergistic dual-MOA payloads (DP) into DR319 provides a comprehensive strategy to maximize efficacy and overcome resistance. These preclinical data strongly support the clinical development of DR319 ADCs as a potential best-in-class therapeutic for solid tumors.