Introduction

Although prior clinical trials testing trastuzumab in urothelial carcinoma of the bladder (UCB) have failed, recent genomic studies suggest that UCB could potentially respond to HER2-targeted therapy if patients are selected optimally. T-DM1 is an antibody-drug conjugate consisting of trastuzumab linked to the cytotoxic agent DM1. It showed a significant survival advantage in breast cancer patients refractory to trastuzumab. Our previous study demonstrated that T-DM1 has significant anti-tumor effects in pre-clinical models of HER2-overexpressing UCB. These effects were superior to trastuzumab and depended on level of HER2 expression. Here, we studied the potential anti-metastatic function and optimal patients of T-DM1 in UCB.

Methods

HER2 expression in bladder cancer treated by radical cystectomy was examined by the same immunohistochemistry (IHC) criteria as for breast cancer. HER2 expression level in UCB cell lines was examined by western blotting (WB), qRT-PCR, FISH and FACS in adherent (AD) and anchorage independent (AI) culture conditions.

Results

HER2 over-expression (score 2+ or 3+) in IHC was detected in 59 of 159 (37%) bladder cancer patients. HER2 expression was higher in lymph node metastases than in primary tumors. Higher HER2 expression was detected in all cell lines cultured in AI conditions, compared to those in AD conditions. Furthermore, T-DM1 significantly inhibited colony formation in soft agar compared to control IgG or trastuzumab. Since anoikis is a pre-requisite for metastasis, these results suggest that HER2 expression contributes to the establishment of metastasis and T-DM1 could have anti-metastatic potential. The bladder cancer cell line with the highest HER2 expression (BOY) was equivocal HER2 amplification by FISH (HER2/CEP17 ratio: 1.8, HER2 copy number: 4.7), which is known to correspond to HER2 IHC score 2+ in patient tissue. BOY responded most sensitively to T-DM1, and low concentration (10nM) T-DM1 induced apoptosis only in BOY. This suggests T-DM1 could be effective in patients with HER2 over-expression (IHC score 2+/3+).

Conclusions

Our pre-clinical results suggest that T-DM1 could have anti-metastatic potential and be a promising targeted therapy for patients with HER2 score 2+/3+ UCB. T-DM1 warrants clinical evaluation in these patients.

Funding

none