The preclinical activity of lenalidomide in urothelial carcinoma (UC).
e15002 Background: Lenalidomide is approved for multiple myeloma and deletion 5q myelodysplastic syndromes (MDS) and demonstrates immune modulation, anti-angiogenic activity and direct anti-tumor cytotoxicity. A rationale can be made to evaluate the preclinical activity of lenalidomide in urothelial carcinoma (UC) based on the importance of these pathways. Methods: The in vitro anti-tumor activity of lenalidomide was evaluated in 4 human (5637, TCC-SUP, RT4, RT112) and 1 murine (MB49) cell line. Anti-proliferative activity activity (MTT assay), apoptosis (Annexin-FITC immunohistochemistry [IHC], flow cytometry) and cell viability by colony forming assay were measured. In vivo examination of activity of daily oral lenalidomide 10 mg/kg orally once daily or placebo for 4 weeks is examined in a syngeneic immunocompetent mouse model employing MB49-Luc25 cells injected subcutaneously in C57BL/6 mice. Murine tumors will be studied for anti-tumor activity. Results: In vitro activity of lenalidomide was detected at low ~1 µM concentrations (attainable in human subjects) against a non-invasive human UC cell line (RT4). Long-term cultures of RT4 cells for 10 days with daily repletion of lenalidomide reduced cell viability and colony forming ability to 75.6% of controls. Induction of apoptosis in RT4 was demonstrated by Annexin-FITC IHC and flow cytometry compared to control (30.11 vs. 14.74%). Invasive human UC cells and murine MB49 cells did not demonstrate apoptosis with lenalidomide exposure in vitro. Futher, lenalidomide did not inhibit overall tumor growth in the syngeneic immunocompetent murine model; immune activity and stem cell directed activity will be presented. Conclusions: Lenalidomide demonstrated preclinical anti-tumor activity against non-invasive human UC cells. Given its favorable toxicity profile compared to cytotoxic chemotherapy, clinical evaluation in patients with non-muscle-invasive bladder cancer and recurrence after BCG therapy may be warranted.