HSP90 antagonist, geldanamycin, inhibits proliferation, induces apoptosis and blocks migration of rhabdomyosarcoma cells in vitro and seeding into bone marrow in vivo

In this study, geldanamycin (GA) was found to have an antiproliferative effect on both embryonal and alveolar rhabdomyosarcoma (RMS) cell lines. The maximum level of inhibition reached 80% for both embryonal and alveolar RMS. After GA treatment, cells also became apoptotic as judged by Annexin V-positive staining, activation of caspase-3 pathway and poly(ADP ribose) polymerase cleavage. GA was responsible for the arrest of RMS cells in both G1 and G2/M phases of the cell cycle. G1 blockade, however, was transient and was seen only in the first 24 h of GA treatment. RMS often gives distant metastases to various organs including bone marrow. RMS cells express high levels of MET receptor and respond to hepatocyte growth factor with increased motility. In our study, we found that GA decreased the level of MET expression and inhibited the chemotaxis of RMS cells toward the hepatocyte growth factor gradient. GA also blocked the homing of RMS cells into bone marrow of severe combined immune deficient mice. In all our experiments embryonal RMS cell lines were significantly more sensitive, and lower concentrations of GA were sufficient to block embryonal RMS cell proliferation, induce apoptosis and inhibit motility. Our data show that the HSP90 inhibitor GA has the potential to become a new drug in RMS treatment. It blocks RMS proliferation, decreases cell survival and inhibits motility of RMS cells.