Comparison of Anti-Angiogenic Activities of Thalidomide and Lenalidomide In Vitro.

Inhibition of angiogenesis is currently perceived as one of the promising strategies in the cancer therapy. Thalidomide (Thalomid®) and its Immunomodulatory Drug (IMiD®) analogs have entered into clinical trials for the treatment of various types of cancers. Lenalidomide (Revlimid®, CC-5013) is currently being assessed in oncology clinical trials worldwide. In this study we have compared the anti-angiogenic mechanisms of thalidomide and lenalidomide in a variety of experimental systems representing distinct events of the angiogenic process. Endothelial cell (EC) proliferation is stimulated by growth factors. Neither thalidomide nor lenalidomide have an appreciable inhibitory effect on growth factor-induced proliferation of human umbilical vein endothelial cells (HUVEC). In both the HUVEC and B16-F10 mouse melanoma tube formation assays, lenalidomide appears to be at least 10-fold more potent than thalidomide, the latter indicating that effects extend to vessels lined by tumor cells. However, in endothelial cell migration assays, thalidomide is more active than lenalidomide; in both the HUVEC and B16-F10 monolayer scratch migration assays, thalidomide is clearly more potent than lenalidomide in preventing the migration of cells into the wounded/scratched region. In assays of HUVEC migration towards specific angiogenic factors, such as VEGF, bFGF, and TNF-α, thalidomide is also more potent than lenalidomide. Interestingly, assays where the whole physiological process of angiogenesis can be studied show differential sensitivities. Lenalidomide is more potent in the rat aorta assay, whereas thalidomide is more potent in the human umbilical explant assay. Mechanistic studies on signal transduction events triggered by VEGF show that both thalidomide and lenalidomide partially inhibit Akt phosphorylation in VEGF-induced HUVEC. Furthermore, inhibitory effects on the phosphorylation of Gab1, a scaffolding protein upstream of Akt activation, have been observed. In summary, our data indicate that both thalidomide and lenalidomide interfere with key events in the angiogenic process and that they can be differentiated qualitatively depending on which component part is studied.