MTX-13, a novel PTK7-directed antibody-drug conjugate with widened therapeutic index shows sustained tumor regressions for a broader spectrum of PTK7-positive tumors.

Protein tyrosine kinase 7 (PTK7) is a Wnt signaling pathway protein implicated in cancer development and metastasis. When using a potent microtubule inhibitor (Aur0101), PTK7-targeting antibody-drug conjugate (ADC), h6M24-vc0101 (PF-06647020/Cofetuzumab pelidotin) is efficacious only in limited tumor types with low response rates in a phase I trial. To improve patient response and to expand responding tumor types, we designed MTX-13, a PTK7-targeting ADC consisting of a novel antibody (Ab13) conjugated to eight molecules of Topoisomerase I inhibitor exatecan through T1000, a novel self-immolative moiety. MTX-13 exhibited PTK7-specific cell binding, efficient internalization and exatecan release to cause cytotoxic activity through DNA damage and apoptosis induction, and a strong bystander killing. MTX-13 displayed potent antitumor activities on CDX and PDX models from a wide range of solid tumors, significantly outperforming h6M24-vc0101. PTK7 was shown to be an actionable target in small cell lung cancer for which MTX-13 showed complete and durable responses. With a consistent overexpression of PTK7 in squamous cell carcinomas derived from diverse anatomic sites, strong potency of MTX-13 in this group of heterogenous tumors suggested a common treatment strategy. Finally, MTX-13 inhibited tumor growth and metastasis in an orthotopic colon cancer xenograft model. MTX-13 displayed a favorable pharmacokinetic and safety profile in monkey with a highest non-severely toxic dose (HNSTD) of >30 mg/kg, significantly higher than 3-5 mg/kg of HNSTD for h6M24-vc0101. The higher therapeutic index of MTX-13 bodes well for its clinical translation with a potential to expand responding patient population beyond that of current PTK7-targeting ADCs.