Abstract 3148: ABBV-706 is a novel SEZ6-targeted topoisomerase 1 inhibitor ADC for SCLC and other neuroendocrine cancers

Abstract Lung cancer has the highest rates of incidence (2. 1 million cases/year) and mortality (1. 8 million deaths/year) among all cancers worldwide. Approximately 15% of lung cancers are small cell lung cancer (SCLC). SCLC is typically diagnosed at late stages, with approximately 70% of patients having extensive stage disease at time of diagnosis. Unfortunately, these patients have a dismal 5-year survival rate of approximately 3%. In contrast to non-small cell lung cancer (NSCLC), there has been little advancement in the treatment of SCLC, with no biomarker directed therapies available for patients. SEZ6 is overexpressed in most SCLC’s and other neuroendocrine tumor types. This overexpression and limited normal tissue expression suggest SEZ6 would be a good target for the development of an antibody drug conjugate (ADC). Validation of SEZ6 as an ADC target was supported by signs of clinical activity for ABBV-011, a SEZ6-targeting calicheamicin ADC. Preclinical and clinical data suggest an increased therapeutic index for Top1i ADCs relative to calicheamicin ADCs. Furthermore, Top1i inhibition is an effective mechanism of action in SCLC with topotecan approved in 2L, although significant toxicity limits broad utility. As such, we hypothesized that a SEZ6-Top1i ADC would enable effective Top1 inhibition in tumor cells and reduce toxicity relative to ABBV-011 or systemic chemotherapy, driving increased therapeutic benefit. ABBV-706 is an ADC comprised of the same SEZ6 targeting antibody as ABBV-011 conjugated to AbbVie’s topoisomerase-1 (Top1) inhibitor. ABBV-706 is a potent anti-proliferative agent in SEZ6 positive SCLC cell lines, with sub- to low-nanomolar activity. SEZ6 dependence was demonstrated by the correlation of SEZ6 mRNA expression to ABBV-706 growth inhibition. On-target Top1i activity was confirmed in cells treated with ABBV-706 as measured by dose-dependent induction of γ-H2AX, a marker of DNA damage, and G2/M arrest. ABBV-706 possessed superior anti-tumor activity compared to ABBV-011 in a panel of SCLC cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models with a range of SEZ6 expression levels. In addition, ABBV-706 had activity in the setting of resistance to cisplatin/etoposide (1L SoC in SCLC), in combination with cisplatin, and in SEZ6-expressing neuroendocrine liver and cervical PDX models. ABBV-706 has favorable pharmacokinetics and is well-tolerated in cynomolgus monkeys with bone marrow and gastrointestinal tract toxicities common to other Top1 inhibitors. ABBV-706 shows promise as an agent for the treatment of SCLC and other difficult to treat SEZ6 expressing neuroendocrine tumors. ABBV-706 has completed dose escalation, and dose expansion is currently ongoing in a Phase 1 FIH clinical study (NCT05599984). Citation Format: Emily J. Faivre, Marybeth A. Pysz, Eoghainín Ó hAinmhire, Laura Kreckler, Kelly Doyle, Aloma D'Souza, Zhiyong Ding, Trusha Sondkar, Dolonchampa Maji, Fan Zhao, Andrew Phillips. ABBV-706 is a novel SEZ6-targeted topoisomerase 1 inhibitor ADC for SCLC and other neuroendocrine cancers 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 3148.