Abstract A22: Effectiveness of ErbB inhibitors in the treatment of bladder cancer

Background: It is estimated that close to 70,000 men and women will be diagnosed with bladder cancer every year and, of those, close to 15,000 will die from the disease. This makes bladder cancer the ninth most common cancer among women and the fourth most common cancer amongst men. Current treatments focus on surgery and radiation with total bladder removal being common with more advanced disease. Chemotherapy including cisplatin offers an alternative treatment for patients who do not want to undergo such a drastic, life-changing operation. While these treatments are initially effective, chemoresistance is common, thereby increasing the need for newer therapies. Recent studies indicated the efficacy of epidermal growth factor receptors, alone or in combination with ErbB2 inhibitors in bladder cancer cell lines – hence we investigated the efficacy of these inhibitors in cisplatin-resistant and -sensitive cells. Methods: We used the cisplatin-resistant T24 bladder cancer cell line along with the cisplatin-sensitive TCCSUP bladder cancer cell line to evaluate the use of the single ErbB inhibitors Herceptin (trastuzumab) and Tarceva (erlotinib), which was purchased from LC Laboratories, along with the dual ErbB inhibitors Tykerb (lapatinib), which was purchased from LC Laboratories, and dacomitinib (PF00299804). Cells were plated into 24-well plates and treated as indicated. Cell growth was estimated by MTT assay. Protein expression was determined by Western blotting after incubation with the indicated treatment for 72 hours. Results: MTTs with varying concentrations of Herceptin indicated that this drug was an ineffective growth inhibitor in both cell lines while Tarceva treatment was more effective, especially in TCCSUP cells. Literature suggests that dual-ErbB inhibition in various cancers is more effective than single target therapy and so we opted to explore drugs that target multiple ErbB family members. Lapatinib, which targets ErbB2 at low doses along with EGFR at higher doses, was relatively ineffective in inhibiting growth of bladder cancer cells, especially at low doses. On the other hand, dacomitinib, which targets EGFR at low doses in addition to ErbB2 at higher doses, was effective at inhibiting growth of bladder cancer cells at a much lower dose. Upon examination of the relative levels of ErbB expression we discovered that both cell lines had increased expression of EGFR but much lower expression of ErbB3 when compared to an androgen-independent prostate cancer cell line. However, treatment with lapatinib, dacomitinib, and Tarceva, alone or in combination, showed dephosphorylation of EGFR and AKT when cells were stimulated with EGF. Furthermore, treatment with Lapatinib increased expression of EGFR and ErbB2. Finally, we assayed the growth of both cell lines when treated with these drugs, alone or in combination, and found that the combination of Tarceva and dacomitinib was most effective at inhibiting the growth of bladder cancer cells while lapatinib had little effect on its own or in any combination. Conclusions: Herceptin was ineffective as a bladder cancer treatment while dacomitinib and Tarceva, in combination, have a synergistic effect which inhibits growth of cisplatin-resistant as well as sensitive bladder cancer cell lines. These studies indicate the efficacy of EGFR inhibitors, but not ErbB2 inhibitors in cisplatin-resistant bladder cancer lines. Acknowledgements: We would like to thank Dr. deVere White for the gift of T24 and TCCSUP cells. We would also like to thank Pfizer Inc. for the gift of dacomitinib and Genentech Inc. for the gift of Herceptin.