ASN004 is an Antibody Drug Conjugate (ADC) that targets the 5T4 oncofetal antigen (trophoblast glycoprotein). High expression of 5T4 is observed in a wide range of malignant tumors, while very limited expression is found in normal tissues. ASN004 incorporates a novel single-chain homo-dimer antibody, Fleximer® linker technology (Mersana Therapeutics), and several cytotoxic dolastatin (auristatin) analog warheads per ADC molecule with a drug/antibody ratio of ~15:1. ASN004 shows high affinity for the 5T4 antigen (Kd < 30 pM) and 5T4-expressing tumor cells; rapid cellular internalization; and potent, selective cytotoxicity. ASN004 provides complete tumor regressions and tumor-free survivors in multiple tumor xenograft models, derived from human tumor cell lines having both high and low 5T4 expression levels. Tumor-free survivors were achieved at doses that are well-tolerated, based on xenograft body weight measures and exploratory toxicology studies in pharmacologically-relevant non-human primates. As well, tumor-free survivors were achieved in xenograft tumor models following administration of a single dose of ASN004, as low as 1 mg/kg iv. The broad activity of ASN004 has been demonstrated by its superior efficacy in a head-to-head study against trastuzumab-DM1, in a low-5T4, high-HER2 expressing tumor xenograft model. Finally, tumor xenografts that initially responded to ASN004 and later showed tumor regrowth, had not developed resistance and responded well to subsequent treatment with ASN004. Overall, ASN004 is demonstrated to be an ADC with high therapeutic potential in multiple tumor types, encompassing a wide range of 5T4-expression levels. IND-enabling toxicology studies are ongoing, in preparation for advancement to clinical studies in patients with solid tumors.

Citation Format: Roger A. Smith, David J. Zammit, Sanjeeva P. Reddy. ASN004, a novel 5T4-targeted Dolaflexin ADC, achieves complete regressions and tumor-free survivors in a broad variety of solid tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 43. doi:10.1158/1538-7445.AM2017-43