Drug-tolerant persisting polyploid giant cancer cells mediate resistance to HER2-targeting antibody-drug conjugates.

Polyploid giant cancer cells (PGCCs) contribute to resistance against various cancer therapies. This study investigates whether HER2-directed antibody-drug conjugates (ADC) induce PGCCs and their role in drug resistance. HER2-positive breast cancer (JIMT-1) and gastric cancer (MKN7, SNU-216) cells were treated with HER2-directed ADCs, trastuzumab emtansine, trastuzumab deruxtecan, XMT-1522, and disitamab vedotin (DV). The induced persister cells were characterized using live cell imaging, confocal microscopy, immunohistochemistry, flow cytometry, gene expression analysis, SNP genotyping, and next-generation sequencing. Drug sensitivity was assessed using the AlamarBlue assay and SCID mouse xenografts. All 4 ADCs induced PGCCs, with XMT-1522 and DV being the most effective. The induced giant cells were drug-resistant and exhibited drug-tolerant persister cell characteristics. HER2 protein levels were downregulated in persisting drug-tolerant PGCCs and their daughter cells. JIMT-1 cells lost HER2 amplification following XMT-1522 treatment, along with the loss of extrachromosomal DNA containing HER2. However, XMT-1522-treated MKN7 and SNU-216 cells, and DV-treated JIMT-1 cells, retained the amplicon. Drug-tolerant PGCCs upregulated nectin-4, and treatment with enfortumab vedotin, a nectin-4-targeted ADC, inhibited the regrowth of JIMT-1 xenografts. ADC treatment induces PGCCs that contribute to drug resistance. ADC-induced drug-tolerant PGCCs express nectin-4, which may serve as a potential therapeutic target.