Patients with VHL-positive renal cell carcinoma (RCC) have very few treatment options. Indeed, these patients are most often told by their oncologists that experimental treatments are their best option, since there are no biologically rational treatments for them. The lack of therapeutic targets to treat VHL-positive RCC is a critical unmet need in cancer treatment. We recently demonstrated in human VHL-positive RCC cancer cells and patient tumors that the oncogenic Src kinase signaling pathway was elevated. Moreover, we found that the Src inhibitor, dasatinib reduced the proliferation of VHL-positive cells both in vitro and in mouse models. Together, our studies represent the first breakthrough for the molecularly targeted treatment of VHL-positive RCC. While dasatinib alone did slow cell proliferation, however, it failed to kill VHL-positive RCC in vitro and in vivo. We hypothesize tha the response observed with Src inhibition by dasatinib alone resulted from bypass pathways present in kidney cancer that override the therapeutic benefit of inhibiting a single target. Consistent with this possibility, VHL-positive RCC contains elevated levels of Signal Transducer and Activator of Transcription-3 (STAT3) and activated Src homology phosphotyrosine phosphatase (Shp2). Indeed, dasatinib alone failed to block oncogenic STAT3 activation. We further hypothesize that the STAT3 and Shp2 signaling pathways represent new therapeutic targets for treatment of VHL-positive RCC. This is because STAT3 plays a pivotal role in activating genes responsible for survival and chemoresistance, and Shp2 can activate downstream effectors of cell transformation in the face of Src inhibition. To address this hypothesis we will pursue the following:
Aim 1 : Determine the role of STAT3 in overriding Src inhibition;
Aim 2 : Determine the role and requirement of Shp2 signaling in VHL-positive RCC pathogenesis;
and Aim 3 : Identify kinase inhibitors that work synergistically with dasatinib to kil VHL-positive RCC cells. We will use human cancer cell lines and tumor specimens to establish the biological rationale for inhibiting survival and tumor-specific bypass pathways in VHL-Positive RCC and leverage this insight into novel drug combinations and biomarkers for a disease that is incurable. This proposed research, which builds on our published work, will comprehensively determine the role of transcription factors, tyrosine phosphatases and kinases in mediating resistance to Src inhibitors-and ultimately is expected to deliver more effective therapies. Importantly, this is not an incremental advance in treatment since it shifts from a reliance on monotherapy to evidence-based combination therapies that override resistance from the get-go, and thereby deliver sustained clinical responses.
Cancers that occur in the kidney frequently recur despite surgery and rarely respond to chemotherapy and radiation and subsequently the outlook for patients with advanced kidney cancer is very poor. Thus there is a great need to improve the therapy for these patients in order to increase cure rates and improve their quality of life. We recently discovered that the protein kinase Src, when blocked can stop the growth of certain types of kidney cancer and so the goal of the proposed research is to determine combination therapies targeting Src that can maximize the initial treatment response to deliver sustained clinical benefit.
