Category: Clinical Pharmacology
Purpose: RON receptor, a member of the MET family of tyrosine kinase, is overexpressed in a wide range of solid tumors; tumor overexpression has been correlated with disease severity and poor outcome in several cancer types. H-Zt/g4-MMAE is an antibody-drug conjugate (ADC) targeted against RON and comprised of the cleavable linker-MMAE payload, conjugated to an anti-RON humanized IgG1/kappa monoclonal antibody through reduced interchain disulfides, with an average drug-to-antibody ratio of ~3.67. Our previous studies indicated H-Zt/g4-MMAE exhibited a favorable preclinical profile, with strong reactivity toward tumor cells and limited normal tissue reactivity, potent cytotoxicity in vitro and antitumor activity in vivo toward a range of RON-expressing tumor cell lines representing several cancer types. Based on these preliminary results, expanded development of H-Zt/g4-MMAE was undertaken to support clinical development.
Methods: Antibody humanization was achieved by grafting sequences of complementarity-determining regions from mouse monoclonal antibody Zt/g4 into human IgG1/κ acceptor frameworks. The selected humanized Zt/g4 subclone H1L3 was conjugated with monomethyl auristatin E using a dipeptide linker to form H-Zt/g4-MMAE. Single- and repeated-dose in vivo efficacy studies were conducted in nude mice with human tumor xenografts that express RON to explore the relationship between Cmax, exposure and anti-tumor activity, and to define the minimal efficacious dose in these models. A toxicology study was conducted in cynomolgus monkeys in which H-Zt/4-MMAE was administered at dose levels of 10 and 30 mg/kg.
Results: H-Zt/g4-MMAE demonstrated specific, dose-dependent in vivo antitumor activity toward RON-positive tumor xenografts representing breast, colon, lung and pancreatic cancers. H-Zt/g4-MMAE had a drug to antibody ratio of 3.77:1 and was highly stable in human plasma with a dissociation rate of less than 5% within a 20 day period. H-Zt/g4-MMAE displayed a favorable pharmacokinetic profile in both mouse and cynomolgus monkey. In vivo, H-Zt/g4-MMAE inhibited pancreatic cancer xenograft growth with tumoristatic concentrations at 1~3 mg/kg body weight. Significantly, H-Zt/g4-MMAE eradicated tumors across multiple xenograft models regardless of their chemoresistant and metastatic statuses. Moreover, H-Zt/g4-MMAE inhibited and eradicated xenografts mediated by pancreatic cancer stem-like cells and by primary cells from patient-derived tumors. Toxicologically, H-Zt/g4-MMAE is well tolerated in mice up to 60 mg/kg. In cynomolgus monkey, H-Zt/g4-MMAE up to 30 mg/kg had a manageable and reversible toxicity profile.
Conclusion: H-Zt/g4-MMAE, a preclinical candidate comprised of a humanized mAb targeting RON, conjugated to the potent microtubule disrupting payload MMAE via a cleavable peptide linker, exhibited a favorable preclinical profile. H-Zt/g4-MMAE demonstrated potent antitumor activity in vivo towards RON-expressing tumor xenografts at clinically relevant dose levels. H-Zt/g4-MMAE was tolerated in cynomolgus monkeys, a relevant toxicology model, at exposure levels in excess of those required for antitumor activity. Our findings support the clinical development of H-Zt/g4-MMAE to evaluate its potential as an ADC therapeutic for RON-expressing solid cancers.