Program 3 long-term goal is to discover novel anti cancer drugs based on inhibiting the function of persistently activated Rho GTPases in cancer. Rho GTPases are frequently found aberrantly activated in human cancers. For example, RhoC overexpression is common in many cancers such as breast cancer and is associated with metastasis and poor prognosis. Furthermore, many guanine nucleotide exchange factors (GEFs) which activate Rho induce malignant transformation and some such as Tiaml (RaclGEF) and LARG (RhoA and RhoC GEF) have been implicated in human cancer. Rho proteins such as RhoA, RhoC and Rac 1 require prenylation by geranylgeranyltransferase I (GGTase I) for their ability to induce uncontrolled growth, invasion and transformation. Finally, RhoA and RhoC require Rho kinase (ROCK) for their transforming activity. The hypothesis upon which this program of the NCDDG is based is that inhibitors of GGTase I, RhoGEFs and ROCK will reverse malignant transformation of human cancers with aberrant Rho function. Program 3 will interact very closely with Programs 1 and 2 as well as Cores A and B to test this hypothesis. To this end, the specific aims of Program 3 are:
Specific Aim 1; To determine the potency and selectivity in vitro and in cultured cells of GGTase I, RhoGEF and ROCK inhibitors from Program 1 and Core B. We will determine whether GGTase I inhibitors are selective for GGTase I over farnesyltransferase;whether RhoGEF inhibitors are selective for Tiaml or LARG over ITSN, Dbs and m-SOS-1 and whether ROCK inhibitors are selective for ROCK I or ROCK II over other ser/thr kinases as well as tyr kinase.
Specific Aim 2; To determine the effects of GGTase I, RhoGEF and ROCK inhibitors on signaling, proliferation, cell cycle progression and apoptosis. We will determine whether cancer cells where Rho function is aberrantly activated are more sensitive to inhibitors of GGTase I, RhoGEF and ROCK (i.e. whether cancer cells that overexpress RhoC or activated Tiaml or LARG are more sensitive to inhibition of proliferation and induction of apoptosis by these inhibitors). We will also determine if aberrant activation of Rho function by overexpression of RhoC or activated Tiaml or LARG result in activation of PI3K/Akt pathway, induction of survivin expression and/or suppression of the expression of Bax, p21waf and p27kip;and whether the inhibitors antagonize this.
Specific Aim 3 : To determine the anti tumor efficacy, pharmacodynamics, pharmacokinetics and toxicity of GGTase I, RhoGEF and ROCK inhibitors. We will use murine and human cells that overexpress RhoA, RhoC, Racl, activated Tiaml and LARG as well as other genes that activate Rho such as EGFR and Ras to determine if tumor cells with aberrantly activated Rho GTPases are more sensitive to inhibition of tumor growth in animal models. We will also determine if inhibition of tumor growth in animal models correlates with inhibition of Rho function in tumors and whether the selected inhibitors have favorable pharmacokinetic and pharmacodynamic properties and lack toxicity. The proposed studies, coupled with those of Programs 1 and 3 and Core B will lead to the identification of potent and selective inhibitors of GGTase I, RhoGEF and ROCK that will thwart the aberrant activation of Rho protein and inhibit malignant transformation of cancer cells.
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