Dasatinib enhances tumor growth in gemcitabine-resistant orthotopic bladder cancer xenografts

Background

Systemic chemotherapy with gemcitabine and cisplatin is standard of care for patients with metastatic urothelial bladder cancer. However, resistance formation is common after initial response. The protein Src is known as a proto-oncogene, which is overexpressed in various human cancers. Since there are controversial reports about the role of Src in bladder cancer, we evaluated the efficacy of the Src kinase inhibitor dasatinib in the urothelial bladder cancer cell line RT112 and its gemcitabine-resistant sub-line RT112^rGEMCI²⁰ in vitro and in vivo.

Methods

RT112 urothelial cancer cells were adapted to growth in the presence of 20 ng/ml gemcitabine (RT112^rGEMCI²⁰) by continuous cultivation at increasing drug concentrations. Cell viability was determined by MTT assay, cell growth kinetics were determined by cell count, protein levels were measured by western blot, and cell migration was evaluated by scratch assays. In vivo tumor growth was tested in a murine orthotopic xenograft model using bioluminescent imaging.

Results

Dasatinib exerted similar effects on Src signaling in RT112 and RT112^rGEMCI²⁰ cells but RT112^rGEMCI²⁰ cells were less sensitive to dasatinib-induced anti-cancer effects (half maximal inhibitory concentration (IC₅₀) of dasatinib in RT112 cells: 349.2 ± 67.2 nM; IC₅₀ of dasatinib in RT112^rGEMCI²⁰ cells: 1081.1 ± 239.2 nM). Dasatinib inhibited migration of chemo-naive and gemcitabine-resistant cells. Most strikingly, dasatinib treatment reduced RT112 tumor growth and muscle invasion in orthotopic xenografts, while it was associated with increased size and muscle-invasive growth in RT112^rGEMCI²⁰ tumors.

Conclusion

Dasatinib should be considered with care for the treatment of urothelial cancer, in particular for therapy-refractory cases.

Enzastaurin shows preclinical antitumor activity against human transitional cell carcinoma and enhances the activity of gemcitabine

Enzastaurin, an oral serine/threonine kinase inhibitor, suppresses signaling through protein kinase C (PKC)-beta and the phosphatidylinositol 3-kinase/AKT pathways. We preclinically evaluated enzastaurin alone and in combination with gemcitabine for transitional cell cancer (TCC). Immunohistochemistry (IHC) was done on 105 human samples from a microarray to show the expression of PKC-beta. The preclinical antitumor activity of enzastaurin and gemcitabine as single agents and in combination against aggressive human -lines (-SUP and 5637) and murine subcutaneous xenografts bearing 5637 cells was determined. Western Blot was done on tumor cells in vitro to detect signaling through PKC-beta, GSK-3beta, and AKT. The effect on cell migration was determined in vitro. Modulation of proliferation (Ki-67), apoptosis (cleaved caspase-3), and angiogenesis (CD31) in vivo was determined by IHC. IHC done on human TCC samples from a microarray showed the expression of PKC-beta in 33% of tumors. Enzastaurin induced significant apoptosis and inhibited proliferation in vitro at low micromolar concentrations. The in vitro inhibitory activity of combination enzastaurin and gemcitabine by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay seemed synergistic. Western Blotting revealed down-regulation of Akt, PKC-beta, and GSK-3 beta phosphorylation. Enzastaurin inhibited migration at an earlier time point independent of antiproliferative activity. Combination therapy had significantly superior antitumor activity in murine xenografts compared with untreated controls, whereas single agents did not. IHC showed reduced Ki-67 and CD31 and increased cleaved caspase-3 with combination therapy compared with controls. Enzastaurin showed preclinical antitumor activity against human TCC and enhanced the activity of gemcitabine.

Systemic therapy for unresectable and metastatic transitional cell carcinoma of the urothelium: first-line and beyond

PURPOSE OF REVIEW

The review aims to provide an overview of recent advances and future research direction in the management of patients with advanced transitional cell carcinoma.

RECENT FINDINGS

Early data of the randomized phase III study comparing paclitaxel, cisplatin, and gemcitabine with gemcitabine plus cisplatin for advanced urothelial cancer detected no survival difference. A phase II study investigated the safety and efficacy of trastuzumab, carboplatin, gemcitabine, and paclitaxel in human epidermal growth factor receptor-2/neu-positive advanced urothelial carcinoma and reported promising results. Renal-sparing regimens are under active development. A nonrandomized comparison of the 3-week with the 4-week schedule for gemcitabine and cisplatin showed that the 3-week schedule had less hematological toxicity and better dose intensity. Potential molecular markers such as excision repair cross-complementation group 1, emmprin, and survivin for survival and/or platinum resistance in patients with transitional cell carcinoma showed promise.

SUMMARY

Recent data do not support change in the current standard of care for advanced transitional cell carcinoma. Clinical testing of emerging anticancer therapies using new agents, new combinations, and new approaches is under active investigation. Rational combination and new strategy in clinical trial design are critical for new drug development for transitional cell carcinoma.