Galectin-1 suppression delineates a new therapeutic strategy for myeloma-induced angiogenesis

Galectin-1 (Gal-1) is a lectin, involved in several processes related to cancer, including immunosuppression, angiogenesis, hypoxia, and metastases. Actually, the Gal-1 expression profile in multiple myeloma (MM) and its pathophysiological role in MM–induced angiogenesis and tumoral growth is unknown. Firstly, we found that Gal-1 was expressed by malignant plasma cells in MM patients and that its expression was up-regulated upon hypoxic treatment (1% of O2). Moreover the stable knock-down of Hypoxia Inducible Factor-1α (HIF-1α) in MM cells significantly downregulated Gal-1 expression. Thereafter, we performed Gal-1 inhibition by lentivirus shRNA anti-Gal-1 in human myeloma cell lines (HMCLs) showing that its suppression did not affect cell proliferation and survival but modified their transcriptional profiles either in hypoxia or hypoxia condition. Interestingly pro-angiogenic genes including MMP9 and CCL2 were downregulated and those anti-angiogenic SEMA3A and CXCL10 were up-regulated by Gal-1 inhibition in MM cells. Data were also validated by Real time PCR and at protein level. Consistently we found that Gal-1 suppression in MM cells significantly decreased their pro-angiogenic proprieties by an in vitro assay. These evidences were confirmed in mice injected either subcutaneously or intratibially with HMCLs carrying a stable infection with shRNA anti-inhibition of Gal-1 or with the control vector cell line. Gal-1 suppression in both models showed a significant reduction in the tumoral burden and microvascular density compared to the control mice. Moreover, Gal-1 suppression induced smaller lytic lesions on x-ray in the intratibially model. Overall, our data indicate that Gal-1 is a new potential therapeutic target in MM. Total RNA samples from JJN3 anti-Gal-1 and JJN3 scramble, after 48h of normoxic or hypoxic conditions and 48h of re-oxygenation process were analyzed on GeneChip® HG-U133 Plus 2.0 arrays (Affymetrix; Santa Clara, CA). Anti-Gal-1 was compared to scramble JJN3 sample in normoxic, hypoxic or re-oxygenation conditions, respectively, to find specific differentially expressed genes in each experimental condition.