Evaluation of a novel irreversible pan-HER inhibitor in bladder cancer models.

253 Background: Human epidermal receptors (HER) are overexpressed and HER signaling is biologically relevant in bladder cancer and may mediate chemotherapy resistance. Dacomitinib is a novel, potent, irreversible pan-HER inhibitor with activity against several solid tumors, currently in a phase III clinical trial in NSCLC. We hypothesized that dacomitinib has antitumor activity in bladder cancer models. Methods: Expression level of EGFR and HER2 protein was measured semi-quantitatively in 8 bladder cancer cell lines. We treated UM-UC-3, UM-UC-6, UM-UC-9 cell lines with dacomitinib (1nM-10uM) for 24-72 hours, and measured cell viability, proliferation, apoptosis, and cell cycle effects. Correlations between dose and cell viability were measured by two-way ANOVA (GraphPad Prism 5.0). We injected age-matched male NOD/SCID mice SC with 1x106 UM-UC-6 and UM-UC-9 cells, respectively, generating xenografts. Mice were randomized and treated with dacomitinib, 6mg/kg p.o. daily, starting 1 day or 1 week after cell injection; controls were treated with vehicle. Mice were monitored daily, weighed weekly, sacrificed at 4 weeks and tumors weighed. Results: In vitro, significant cytostatic effect was noted with as low as 50nM in UM-UC6 cells and 100nM in UM-UC9 cells. UM-UC3 cells did not exhibit cytostatic effect even with 1000nM, corresponding to differential target protein (HER) expression. Dacomitinib (2uM) induced apoptosis (UM-UC-6), and G1 cell cycle arrest in both cell lines. These effects corresponded to dacomitinib-mediated inhibition of EGFR, ERK, AKT phosphorylation. In vivo, xenograft weights in both cell lines were significantly lower in dacomitinib-treated mice vs control (p<0.001), corresponding to pharmacodynamic effects (decreased E-cadherin, p-EGFR, p-ERK, mitotic count). Dacomitinib 6mg/kg p.o. daily resulted in significantly lower tumor weights vs lapatinib 50 mg/kg p.o. daily in UM-UC-9 xenograft model (p=0.0052). Conclusions: Dacomitinib demonstrated single-agent activity in bladder cancer cell lines and xenografts. Induction of apoptosis and G1 phase arrest are the suggested mechanisms for anti-tumor activity. Further investigation of this inhibitor in bladder cancer models is being pursued.