Abstract 3195: SHR-4602, next generation of HER2-targeting ADC with potent anti-tumor efficacy overcoming the resistance of HER2 ADC with Topo I inhibitor payload in xenograft models

Abstract Background: Current clinical HER2-targeting ADCs (i. e. DS-8201) have shown promising clinical efficacy in HER2 expressing or mutant cancer patients. However, most of them will ultimately experience disease progression due to different mechanisms. Herein, we presented a novel HER2 ADC, SHR-4602, which demonstrated good in vitro and in vivo anti-tumor activities and could overcome the resistance caused by HER2 ADC including DS-8201 analogue (synthesized using DS-8201 structure) and SHR-A1811 (composed of trastuzumab, a cleavable linker, and a Topo I inhibitor payload, in phase III clinical trials) in xenograft models. Method: We used a stable enzyme-cleavable linker technology to conjugate the HER2 ADC using the amino acid sequence of pertuzumab and ER300 (eribulin derivative). The in vitro biological and anti-tumor activities were assessed by a series of assays. The in vivo anti-tumor efficacies were evaluated in the JIMT-1 (HER2 low expressing) as well as the SHR-A1811 and DS-8201 analogue induced JIMT-1 resistance (caused by treating with SHR-A1811 followed by DS-8201 analogue for a long-term) xenograft models in BALB/c nude mice. Results: Through the SPR assay, SHR-4602 exerted single nanomolar binding affinity to human and rhesus monkey HER2, but no binding activity against rat HER2. It demonstrated varying inhibitory activity on the proliferation of cancer cell lines with various HER2 expression levels, with the IC50 at the range of 0. 007 nM to 8. 21 nM. SHR-4602 showed highly efficient internalization in NCI-N87 HER2 expressing cells and could be translocated to the lysosome followed by releasing ER300. The cytotoxic activity of SHR-4602 was predominantly mediated by released ER300 through microtubule dynamics inhibition, G2/M arrest and apoptosis induction. Furthermore, SHR-4602 showed a strong in vitro bystander effect in the co-culture of HER2 positive/negative cells. SHR-4602 showed significant anti-tumor efficacy in JIMT-1, SHR-A1811 and DS-8201 analogue both-resistant JIMT-1 xenograft models. In SHR-A1811 and DS-8201 analogue both-resistant xenograft models, treatment with 10 mg/kg SHR-A1811 or DS-8201 analogue exerted negligible anti-tumor activity (TGI% 17%), whereas SHR-4602 at 2. 5, 5 and 10 mg/kg significantly inhibited the tumor growth (p 0. 001, vs. vehicle), with TGI% of 84. 96%, 101. 64% and 113. 11% on Day 42, respectively, which indicated a superior anti-tumor efficacy against SHR-A1811 and DS-8201 analogue both-resistant xenograft models. Conclusion: SHR-4602 represents a new generation HER2-targeting ADC to deliver a potent cytotoxin to HER2 expressing tumor cells and may be more efficacious to the tumors in which current anti-HER2 therapies are ineffective. SHR-4602 is now in the phase I clinical development stage for advanced malignant solid tumors (NCT05819684). Citation Format: Yunan Tian, Xing Sun, Changyong Yang, Cheng Liao. SHR-4602, next generation of HER2-targeting ADC with potent anti-tumor efficacy overcoming the resistance of HER2 ADC with Topo I inhibitor payload in xenograft models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3195.