Abstract A5: Lenalidomide Inhibits Hypoxia-Induced HIF-1α Production and Prevents the Invasive Phenotype in Epithelial Solid Tumor Cells

Abstract Background: In hematological malignancies lenalidomide (len) exerts tumoricidal and immunomodulatory effects and may also influence the tumor cell microenvironment by blocking the proangiogenic and proinvasive effects of growth factors and/or hypoxia. In solid tumor models len is antimetastatic but lacks overt tumoricidal activity. These observations led us to explore the effect of len on hypoxic solid tumor cells, in particular the expression of HIF-α and its upstream regulators p53 and HDM-2. Methods: Eighteen solid tumor cell lines were tested for the effect of len on the response to hypoxia (1 % O2, 5% CO2, 94% N2; Invivo2 400 hypoxic workstation). Cell lysates from three cell lines (HCT-15, MDA-MB-231 and SKOV-2) were assessed for HIF-1α, p53 and HDM-2 proteins by immunoblot. We also performed immunoprecipitation studies to explore the effect of len on the interaction of these proteins. The effect of len on HIF-1α was assessed in p53 siRNA transfected HCT-15 cells and on HIF-1 α mRNA in transfected Luc-HIF NIH 3T3 cells. Len effects on hypoxia-induced trans-well invasion of three cell lines were also assessed. Results: Len (1 µM) significantly inhibited hypoxia-induced HIF-1 a protein levels dose-dependently in the majority of tumor cell lines tested; breast (by 68%, MDA-MB-231; 65%, MCF-7), colorectal (76%, HCT-116; 65%, HCT-15; 82% HT-29), ovarian (71%, OVCAR-3; 66%, SKOV-3), renal (83%, 786-O; 57%, HEK293), prostate (54%, DU- 145) and pancreatic (45%, MiaPaca-3)(all p<0.05). Len had no effect on HIF-1 α in SW480 (colorectal), Panc-1, BxPC3 (pancreatic), SW579 (thyroid), NCI-H446 (SCLC) or Caki-1 (Renal) cell lines or on HCT-15 cells transfected with p53 siRNA. In addition to inhibition of HIF-1 α protein len also inhibited hypoxia-induced HIF-1α mRNA expression (p< 0.01). Len enhanced p53 levels in hypoxic HCT-15 cells (by 2-fold; p<0.05), SKOV-3 cells (by 4-fold; p<0.01) and MDA-MB-231 cells (by almost 2-fold; p<0.05) but had little apparent effect on the interaction of these proteins. Len totally inhibited the 2-fold hypoxic induction of HDM-2 levels in HCT-15 (p<0.05) and SKOV-3 (p<0.01) cells but had no effect on HDM-2 in p53 mutant MDA-MB-231 cells. Tumor cell invasiveness was enhanced in response to hypoxia by ~3- fold in all three lines and was blocked by 50-80% by len treatment (all p < 0.05). Conclusions: These results suggest that len inhibits the proinvasive hypoxic response in multiple, diverse tumor lines and may exert antimetastatic effects within the hypoxic solid tumor microenvironment. Citation Information: Clin Cancer Res 2010;16(14 Suppl):A5.