Molecular Therapeutics of Kidney Cancer-VHL Gene and Fumarate Hydratase Gene Understanding the genes that cause kidney cancer provides the opportunity to develop approaches for molecular therapeutics for this disease. We have identified 3 genes that cause cancer of the kidney: the VHL gene (clear cell renal cell carcinoma); the c-Met gene (papillary type 1 renal carcinoma); and the BHD gene (chromophobe renal carcinoma). Targeting the VHL Clear Cell Kidney Cancer Gene Pathway Urologic Oncology Branch scientists are studying intensively how damage (mutation) to the VHL gene leads to the manifestations in VHL and sporadic renal carcinoma patients. Recently, it is has been shown that the VHL protein forms a complex with other proteins, including elongin C and B and the CUL-2 protein, and this complex targets the alpha subunit of hypoxia inducible factors (HIF1-alpha and HIF2-alpha) for ubiquitin-mediated degradation. This is a hypoxia-mediated process normally, i.e., under hypoxic conditions HIF is not degraded by the VHL complex. HIF is a transcription factor that regulates the transcription of a number of downstream genes important for cancer, such as VEGF, Glut 1, TGF-alpha and PDGF. When the VHL gene is mutated, in the germline of VHL patients or in tumor tissue from patients with clear cell renal carcinoma, the HIFs cannot be degraded and the result is the over-transcription of VEGF, Glut1, TGF-alpha and PDGF. One approach to evaluating the role of agents targeting the VHL pathway in VHL and clear cell renal carcinoma is to determine the activity of agents which block the VEGF and TGF-alpha/EGFr pathways in-vitro and in-vivo. Another approach for molecular therapeutics of clear cell RCC is by use of agents such as geldanamycin analogues, which disrupt the binding of HIF to HSP-90. In-vitro studies have shown that the 17AAG geldanamycin analogues can degrade HIF even in VHL -/- cell lines. In-vitro and in-vivo studies are underway in kidney cancer models that we have developed from human material to evaluate the role of agents which block this cancer gene pathway as a potential approach for the treatment of clear cell kidney cancer. Clinical trials evaluating the role of geldanamycin analogues as well as agents which target the VEGF/EGFr receptors and other parts of the VHL pathway are currently in progress. Targeting the Fumarate Hydratase Gene: Type 2 Papillary Kidney Cancer The Krebs cycle enzyme, fumarate hydratase (FH), is the gene for Hereditary Leiomyomatosis Renal Cell Carcinoma (HLRCC). HLRCC patients are at risk for the development of cutaneous and uterine leiomyomas as well as a very aggressive form of type 2 papillary kidney cancer. We have found mutations of the FH gene in the germline of 95% of our HLRCC families and loss of heterozygosity of the FH gene in HLRCC-associated kidney cancer. In order to understand how mutation of a Krebs cycle enzyme could cause kidney cancer we stained HLRCC-associated kidney tumors for the presence of hypoxia induced factor 1-alpha (HIF1-alpha) and hypoxia induced factor 2-alpha (HIF2-alpha). We found both HIF1-alpha and HIF2-alpha to be elevated in the HLRCC kidney tumors. We are developing novel in-vitro models from human tumors and evaluating growth in in-vitro and in-vivo systems. In in-vitro models we found that when fumarate hydratase was inactivated (with SiRNA), fumarate increased and the increase in fumarate inhibited prolyl hydroxylase. The inhibition of prolyl hydroxylase prevented normoxic VHL-mediated HIF degradation, providing a VHL-independent mechanism for dysregulation of HIF degradation in HLRCC kidney cancer. These studies provided the rationale for the development of a targeted therapeutic approach for the treatment of HLRCC-associated kidney cancer. In-vitro and in-vivo studies are underway to evaluate the role of agents which block this cancer gene pathway as a potential approach for the treatment of HLRCC-associated as well as sporadic type 2 papillary kidney cancer.
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