Preclinical antitumor activity of an anti-HER2/Trop-2 bispecific antibody-drug conjugate with a new DNA topoisomerase I inhibitor.

e15013 Background: In recent years, antibody-drug conjugates (ADCs) have made significant progress in cancer therapy and show a promising future. Among the approved ADCs, Enhertu, the HER2 directed ADC and Trodelvy, the Trop-2 directed ADC, have shown considerable clinical benefits. Bispecific antibody-drug conjugate represents a fast-growing class of next generation ADC due to its potentials in enhancing specificity, improving efficacy, and reducing toxicity. Additionally, targeting more than one molecule can be useful to avoid resistance to treatment and broaden the patient population. Methods: We generated a novel bispecific ADC (BIO-201) co-targeting HER2 and Trop-2 which are the two clinically validated tumor-associated antigens that are expressed on a wide variety of tumors. BIO-201 is consisted of a novel bispecific anti-HER2/Trop-2 antibody conjugated with a potent DNA topoisomerase I inhibitor (TOPO Ii) via a cleavable linker. TOPO Ii is a proprietary payload platform developed in house that exhibits similar characteristics including in vitro and in vivo anti-tumor activities and safety profile to DXd. The bispecific antibody was fully characterized and in vitro and in vivo anti-tumor activity of BIO-201 was assessed using preclinical models. Results: The bispecific antibody showed comparable or increased cell binding and internalization compared with the parental antibodies in various tumor cells that express different surface levels of HER2 and Trop-2. In the in vitro cytotoxicity assay, the bispecific ADC BIO-201 effectively killed cancer cells with IC50 in the sub nM range with BIO-201 being most potent against cancer cells that co-express HER2 and Trop-2. The anti-tumor activity of BIO-201 was further demonstrated in vivo in several tumor xenograft models. Treatment of BIO-201 induced significant tumor regression in HER2 or Trop-2 positive tumors, suggesting broader coverage of tumor types than conventional HER2 and Trop-2 ADCs. BIO-201 also showed similar anti-tumor activity to Herceptin-DXd. Conclusions: Taken together, these findings suggest that anti-HER2/Trop-2 bispecific ADC has potential as an effective therapy for a variety of cancers that co-express HER2/Trop-2 or express either of the targets. BIO-201 may be expected to have a similar clinical activity to Enhertu or Trodelvy but treat more patient sub-populations and indications.