EGFR activity addiction facilitates anti-ERBB based combination treatment of squamous bladder cancer

Recent findings suggested a benefit of anti-EGFR therapy for basal-like muscle invasive bladder cancer (MIBC). However, impact on bladder cancer with substantial squamous differentiated (Sq-BLCA) and especially pure squamous cell carcinoma (SCC) remains unknown. Therefore, we comprehensively characterized pure and mixed Sq-BLCA (n=125) on genetic and protein expression level, and performed functional pathway and drug-response analyses with cell line models and isolated primary SCC (p-SCC) cells of the human urinary bladder. We identified abundant EGFR expression in 95% of Sq-BLCA without evidence for activating EGFR mutations. Both SCaBER and p-SCC cells were sensitive to EGFR tyrosine kinase inhibitors (TKIs: erlotinib and gefitinib). Combined treatment with anti-EGFR TKIs and varying chemotherapeutics led to a concentration-dependent synergism in SCC cells according to the Chou-Talalay method. In addition, siRNA knockdown of EGFR impaired SCaBER viability suggesting a putative ‘‘Achilles heel’’ of Sq-BLCA. The observed effects seem Sq-BLCA-specific since non-basal urothelial cancer cells were characterized by poor TKI sensitivity associated with a short-term feedback response by upregulating EGFR and ERBB3 expression. Hence, our findings give novel insights into a crucial, Sq-BLCA-specific role of the ERBB signaling pathway proposing improved effectiveness of combined anti-EGFR and chemotherapeutic regimens in squamous bladder cancers with wild-type EGFR-overexpression. Tumor tissue of an individual diagnosed with a pure SCC was obtained from the RWTH centralized biomaterial bank (RWTH cBMB) for SCC-tumor cell (p-SCC) isolation. Primary cells derived from pure SCC (p-SCC) tissue were established as a cell culture ex vivo model. p-SCC cells (n=1) were characterized and compared with the original tumor tissue (n=1) by whole transcriptomic analysis. SCaBER (n=1) and J82 cell lines (n=1) served as squamous and urothelial-like controls.