Tumor metastasis causes the majority of cancer deaths. Dysregulation of small GTPases such as K-Ras and Rho family GTPases (RhoA, RhoC, Rac1 and Cdc42) is critical to drive the invasion and metastasis of a variety of cancers including breast carcinomas. In order to fulfill their biological functions, these GTPases must properly localize subcellularly and associate with cellular membrane. The association of these proteins to membranes is regulated by a series of post-translational modifications including either farnesylation or geranylgeranylation of the C-terminal CaaX motif, thus providing the rationale to target the farnesyltransferase (FTase) and geranylgeranyltransferases (GGTase) as the potential anti-cancer drugs. However, FTase inhibitors (FTIs) failed in clinic due to alternative prenylation, which causes K-Ras to be geranylgeranylated, and their inability to target geranylgeranylated proteins such as Rho family GTPases. As an alternative, we have developed a unique class of potential anti-cancer therapeutics called Prenyl Function Inhibitors (PFIs), which are synthetic farnesol or geranylgeraniol analogs that act as alternative substrates for FTase or GGTase but do not support normal prenyl function. Here, we test the ability of our lead PFIs anilinogeraniol (AGOH; farnesol analog) and anilinofarnesol (AFOH; geranylgeraniol analog) to impact the migratory and invasive capacities of breast carcinoma cells. We found that AGOH treatment effectively decreased the invasion of MDA-MBA-231 in a two-dimensional invasion assay at 100 mM while it blocked invasive growth in three-dimensional (3D) culture model in as little as 20 μM. Notably, the effect of AGOH on 3D invasive growth was phenocopied by electroporation of cells with C3 exotransferase, which ribosylates and inactivates Rho proteins. The results demonstrate that Rho proteins are essential for the invasive growth of MDA-MB-231 cells. To determine how AGOH impacts Rho signaling, we performed RhoA and RhoC activity assays in MDA-MB-231 and MDA-MB-468 cells. We determined that AGOH blocked RhoA and RhoC activation in response to LPA and EGF stimulation. Notably, the geranylgeraniol analog AFOH was more potent than AGOH in inhibiting RhoA/C activation and invasive growth where it inhibited RhoA and RhoC activation completely at 20 μM and blocked the invasive growth of MDA-MB-231 cells at ≤ 5 μM. Interestingly, both AGOH and AFOH had no effect on the growth of MCF10A cells in 3D culture. Collectively, this study demonstrates that our lead PFI compounds dramatically inhibited breast cancer invasion, at least in part, through affecting RhoA and RhoC function; thus, suggesting that targeting the function of Rho prenylation by PFIs will offer a promising mechanism for the treatment of breast cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-04-11.