Hyperactivities of polyisoprenylated proteins are currently the principal drivers of some of the most difficult to treat cancers. Monomeric G-proteins such as Ras mutate and lose their ability to act as molecular switches and remain constitutively active. The hyperactivities of other family members such Rho is due to overexpression. Developing effective drugs for cancers with hyperactivities of these proteins has been very challenging. Despite numerous efforts, there are no effective therapies for cancers with these aberrations. This proposal adopts a hitherto unexplored approach to address this problem using an entirely novel class of compounds targeting polyisoprenylated protein metabolism and function. This is based on previous studies showing that polyisoprenylation pathway modifications are essential for polyisoprenylated protein effects on cell proliferation, differentiation, apoptosis and the cytoskeletal organization. The studies will address the hypothesis that polyisoprenylated methylated protein methyl esterase (PMPMEase) is overexpressed in lung cancer and that polyisoprenylated cysteinyl amide inhibitors (PCAIs) of PMPMEase will inhibit cancer cell proliferation and tumor growth as well as the cell migration that promotes metastasis. This is rationalized by the vast evidence in the scientific literature showing that hyperactivities of monomeric G-proteins drive a large number of lung cancer cases and our own preliminary results clearly showing an overexpression of PMPMEase in 83% of lung cancer cases. Furthermore, our other findings reveal that lung cancer cells overexpress the enzyme and when exposed to specific inhibitors (L-28 and PCAIs) undergo apoptosis while non-cytotoxic concentrations disrupt F-actin organization and inhibit cell migration. A member of the PCAIs family of compounds prevents the growth of lung cancer A549 xenograft tumors in the athymic nude mouse model. The proposed studies are therefore aimed at broadening these studies by (1) further studying the expression and enzymatic activities of PMPMEase in different stages of lung cancer and normal adjacent tissues as a novel strategy for early/companion diagnosis and/or screening for lung cancer, (2) determining the role of PMPMEase on the biology of lung cancer cells and (3) determining the effect of the specific PMPMEase inhibitors on lung cancer xenograft model. It is anticipated that upon the completion of the proposed studies, a clear rationale for the continuous development of an entirely new class of drugs and therapeutic management of lung cancer will be evident.