CR011, a potent fully human monoclonal antibody-auristatin E conjugate for the treatment of melanoma

Abstract

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Metastatic melanoma is an incurable disease whose incidence has increased dramatically over the past three decades. Since current therapies are mostly ineffective, additional therapeutic options are desperately needed. To address this unmet medical need, we employed transcriptional profiling to identify a gene, CG56972 that is highly expressed in human melanoma tissues and cell lines. A fully human monoclonal antibody, designated CR011, generated to the CG56972 gene product showed specific binding to the surface of melanoma cell lines by FACS analysis. Immunohistochemical analysis revealed significant CG56972 expression in 83% of metastatic melanoma clinical samples, with restricted distribution in normal tissues. Several other types of cancers also expressed CG56972, although in an antibody inaccessible compartment. Therefore, CG56972 may represent a suitable target for monoclonal antibody-based therapy of metastatic melanoma. In support of this hypothesis, CR011 was found to internalize and kill CG56972-expressing melanoma cell lines in a secondary antibody-saporin based screening assay. Based upon these results, a fully human monoclonal antibody-drug conjugate (ADC) was generated by directly coupling CR011 to the potent cytotoxic agent monomethylauristatin E via the highly serum-stable yet intracellular protease-sensitive valine-citrulline peptide linker (vcMMAE). This antibody, CR011-vcMMAE, retained binding to cell surface CG56972 and potently inhibited the growth of CG56972-positive melanoma cell lines (IC₅₀ < 200 ng/ml) but was inactive on antigen-negative cell lines. An isotype-control antibody conjugated with vcMMAE demonstrated no binding to or activity against CG56972-positive cell lines. In an athymic mouse melanoma xenograft model, established after subcutaneously implantation of a CG56972-positive melanoma cell line, CR011-vcMMAE induced significant and substantial dose-proportional anti-tumor effects in mice. Tumor free-survivors were noted at doses as low as 2.5 mg/kg. No overt toxicity was observed in mice at doses up to 20 mg/kg (cumulative dose of 80 mg/kg). These data indicate that CR011-vcMMAE directed against CG56972 may be a highly potent and selective agent for the treatment of melanoma.