We are studying the molecular mechanisms involved in the pathogenesis of rhabdomyosarcoma (RMS). This neoplasm probably arises due to a developmental disturbance during muscle formation. Since much has be learned recently about the molecular mechanisms underlying the commitment to muscle lineage and the mechanisms involved in normal muscle development, the study of rhabdomyosarcoma offers a unique opportunity to evaluate the relationship between differentiation arrest and the development of this pediatric embryonal tumor. For example, the activation of genes such as MyoD and myogenin have been shown to be required for the commitment of stem cells to myogenic differentiation. Additionally, several growth factors including TGF-beta and insulin-like growth factors have been implicated in the normal growth and maturation of muscle tissue Finally, alterations of the tumor suppressor gene p53 have recently been demonstrated to play a role in hereditary cancer syndrome (Li - Fraumini) of which rhabdomyosarcoma is a component. Our current focus has therefore been aimed at identifying the roles that such growth factors and the tumor suppressor gene p53 may play in the development of the striated muscle tumor, rhabdomyosarcoma. In particular we have focused on the role of insulin-like growth factor II in the development of this tumor since previous work has shown that this growth factor is expressed at abnormally high levels in these tumors compared to normal muscle. We have identified IGF II as an autocrine growth factor in this set of tumors and have initiated a Phase II study aimed at disrupting this autocrine loop. We have also characterized p53 mutations in cell lines and tumor samples and found that the majority of tumors have mutations in those tumor suppressor gene. We are currently attempting to define the precise role that each of these alterations play in the development of childhood RMS. We have also been evaluating various agents in an attempt to in vitro differentiate tumor cell lines. These studies are aimed at identifying particular lesions within the normal differentiation pathway that may occur in the development of rhabdomyosarcoma. One such agent was identified that was able to both differentiate tumor cell lines as well as reverse the transformed phenotype. This work led to the initiation of a second Phase II study. We are also using CDNA cloning approaches to identify potential molecular mechanisms which may distinguish between the unregulated continual growth of the embryonal tumor, rhabdomyosarcoma, compared to the normal regulated growth of normal embryonal human muscle.
