Exploring the Potential of CS5001: A Tumor-Selective ROR1-Targeted ADC for Cancer Therapy

RORC1, a protein predominantly found in various cancers but not in normal adult tissues, is a promising target for antibody drug conjugates (ADCs). CS5001/ABL202/LCB71 is an innovative ADC that utilizes a human monoclonal antibody to target RORC1, linked to a PBD dimer prodrug through a cleavable β-glucuronide linker. The conjugate is designed to be selectively cleaved by lysosomal β-glucuronidase, an enzyme overexpressed in cancer cells, to release the PBD dimer and crosslink DNA in tumor cells.

The in vitro and in vivo pharmacological properties of CS5001 were assessed and compared to those of CS5001-BMK1, an ADC based on monomethyl auristatin E (MMAE). The binding specificity, affinity, and internalization of CS5001 were measured using Octet, ELISA, and flow cytometry techniques. The cytotoxicity and predictive biomarkers were evaluated across 20 different human cancer cell lines with varying levels of RORC1 expression. The in vivo efficacy of CS5001 was investigated in xenograft models of Jeko-1 mantle cell lymphoma and MDA-MB-231 triple-negative breast cancer.

CS5001 showed high binding specificity to human RORC1 with a KD of 1.38 nM and demonstrated cross-reactivity with the RORC1 of mouse, rat, and cynomolgus monkeys. The ADC was rapidly internalized by RORC1-expressing cancer cells at body temperature. It exhibited potent cytotoxicity against RORC1-expressing cell lines such as Jeko-1 and MDA-MB-231, with IC50 values significantly lower than those of CS5001-BMK1. The growth inhibition activity of CS5001 was strongly correlated with RORC1 expression levels.

In terms of mechanism, CS5001 induced DNA damage, increased apoptosis, and caused a concentration-dependent G2-M cell cycle arrest in MDA-MB-231 cells, consistent with the cytotoxic effects of the PBD payload. In xenograft models, CS5001 displayed significant antitumor activity in a dose-dependent manner. Notably, a single administration of CS5001 at 1mg/kg resulted in complete regression in Jeko-1 xenografts, a response not achieved by CS5001-BMK1 even at the highest dose. Furthermore, CS5001 showed superior tumor growth inhibition compared to CS5001-BMK1 when administered at a fraction of their respective maximum tolerated doses.

The study concludes that CS5001 exhibits potent and selective cytotoxicity against RORC1-expressing cells and has shown remarkable in vivo antitumor activity. The density of RORC1 as measured by cytometry predicts sensitivity to CS5001 in vitro. As such, CS5001 is a promising therapeutic candidate for the treatment of RORC1-expressing malignancies and has the potential for precision medicine.