Molecular characterization of bladder cancer patient-derived xenografts with whole-exome sequencing. Homo sapiens

The objective of this project was to establish a patient-derived bladder cancer xenograft (PDX) platform annotated with molecular features/aberrations and patient clinical information to improve molecularly guided targeted therapy (MTT) and chemotherapy, and study resistance mechanisms in bladder cancer. Towards these goals, twenty-two PDXs with annotated clinical information were established from uncultured unselected clinical bladder cancer specimens in immunodeficient NSG mice. The morphology fidelity was maintained in PDXs. Whole-exome sequencing (WES) was performed for each PDX in order to determine the entire repertoire of single nucleotide variants and insertions/deletions in each tumor. This revealed that PDXs and parental patient cancers shared 92–97% of genetic aberrations, including multiple druggable targets. For drug re-purposing, an EGFR/HER2 dual inhibitor lapatinib was effective in PDX BL0440 (progression-free survival or PFS of 25.4 days versus 18.4 days in the control, p=0.007), but not in PDX BL0269 (12 days versus 13 days in the control, p=0.16) although both expressed HER2. To screen for the most effective MTT, we evaluated three drugs (lapatinib, ponatinib, and BEZ235) matched with aberrations in PDX BL0269; but only a PIK3CA inhibitor BEZ235 was effective (p<0.0001). To study the mechanisms of secondary resistance, a fibroblast growth factor receptor 3 inhibitor BGJ398 prolonged PFS of PDX BL0293 from 9.5 days of the control to 18.5 days (p<0.0001), and serial biopsies revealed that the MAPK/ERK and PIK3CA-AKT pathways were activated upon resistance. Inhibition of these pathways significantly prolonged PFS from 12 day of the control to 22 days (p=0.001). To screen for effective chemotherapeutic drugs, four of the first six PDXs were sensitive to the cisplatin/gemcitabine combination, and chemoresistance to one drug could be overcome by the other drug. In conclusion, the PDX platform allows screening for multiple targeted therapy, chemotherapy, or combinations simultaneously for the most efficacious drugs or combination, serial biopsies during treatment to study drug resistance and for drug development, a task not possibly replicable at the clinical setting.