Abstract 4743: Using genome-wide CRISPR screen to understand resistance mechanisms to PCA062, a P-cadherin targeting antibody-drug conjugate

P-cadherin (PCAD) is a member of the cadherin family that mediates calcium dependent cell-cell contacts in adherens-type junctions of epithelium. Expression of P-cadherin is high in malignant tumors of epithelial origin, such as breast, esophagus, head and neck cancers, but low in normal tissues. This expression pattern makes P-cadherin a potential good target for antibody-drug conjugates (ADCs). PCA062 is a first-in-class antibody drug conjugate targeting P-cadherin. PCA062 consists of a fully human anti-P-cadherin antibody of the IgG1/κ subtype, a non-cleavable bi-functional linker (SMCC) and a maytansine-derived cytotoxic payload (DM1, with a target average drug to antibody ratio (DAR) of 3.8). PCA062 activity was examined in a collection of cell lines expressing high level of PCAD. A subset of these PCAD high cell lines are resistant to PCA062 treatment while they remain sensitive to DM1, suggesting defects in the process of PCA062 uptake or the processing and release of DM1 into the cytoplasmic compartment. PCA062 internalization rate was measured by the uptake of a fluorescent dye labeled anti-PCAD antibody (CQY684, the Ab portion of PCA062) in both PCA062 sensitive and resistant lines. PCA062 resistant lines show slower CQY684 internalization as compared to PCA062 sensitive lines, indicating a defect in ADC internalization may contribute to PCA062 resistance. To explore additional resistance mechanisms to PCA062 as well as to find critical components for PCA062 internalization, a genome wide CRISPR screen was performed in PCA062 sensitive HCC1954 and in PCA062 resistant KYSE510 cell line in the presence and absence of PCA062 and DM1 to look for genes that when knocked out may specifically modulate PCA062 sensitivity. The multi-drug resistant gene MRP1 is a strong hit for PCA062 sensitization in both PCA062 resistant KYSE510 and PCA062 sensitive HCC1954 cells. Lysosomal transporter SLC46A3 and Saga transcription complex components are strong rescue hits for PCA062 in HCC1954. These data suggest that in addition to target expression level and cell intrinsic sensitivity to payload, genes involved in ADC internalization and payload cytoplasmic accumulation will also impact tumor cell sensitivity to ADCs. Citation Format: Angela Tam, Mark Zambrowski, Katherine Seiss, Si-Qi Liu, Tinya Abrams, Giordano Caponigro, William Tschantz, Jennifer Campbell, Tony DAlessio, Qing Sheng. Using genome-wide CRISPR screen to understand resistance mechanisms to PCA062, a P-cadherin targeting antibody-drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4743.