Targeting Multiple EGFR Expressing Tumors with a Highly Potent Tumor-Selective Antibody Drug Conjugate

ABBV-321 (serclutamab talirine), a next-generation epidermal growth factor receptor (EGFR)-targeted antibody-drug conjugate (ADC) incorporates a potent pyrrolobenzodiazepine (PBD) dimer toxin conjugated to the EGFR-targeting ABT-806 affinity matured AM1 antibody. ABBV-321 follows the development of related EGFR targeted ADCs including depatuxizumab mafodotin (depatux-m, ABT-414), ABT-806 conjugated to monomethyl auristatin F (MMAF), and ABBV-221 (losatuxizumab vedotin), AM1 antibody conjugated to monomethyl auristatin E (MMAE). The distinct tumor selectivity of ABBV-321 differentiates it from many previous highly active antibody PBD conjugates that lack a therapeutic window. Potency of the PBD dimer, combined with increased binding of AM1 to EGFR-positive tumor cells, opens the possibility to target a wide array of tumors beyond those with high levels of EGFR overexpression or amplification, including those insensitive to auristatin-based ADCs. ABBV-321 exhibits potent anti-tumor activity in cellular and in vivo studies including xenograft cell line and patient-derived xenograft (PDX) glioblastoma (GBM), colorectal, lung, head & neck and malignant mesothelioma tumor models which are less sensitive to depatux-m or ABBV-221. Combination studies with ABBV-321 and depatux-m suggest a promising treatment option permitting suboptimal, and potentially better tolerated, doses of both ADCs while providing improved potency. Collectively, these data suggest that ABBV-321 may offer an extended breadth of efficacy relative to other EGFR ADCs while extending utility to multiple EGFR-expressing tumor indications. Despite its highly potent PBD dimer payload, the tumor selectivity of ABBV-321 - coupled with its pharmacology, toxicology and pharmacokinetic profiles - support continuation of ongoing Phase 1 clinical trials in patients with advanced EGFR-expressing malignancies.