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New chemotherapeutics are urgently needed to combat malaria. We previously reported on a novel series of antimalarial, ethylenediamine-based inhibitors of protein farnesyltransferase (PFT). In the current study, we designed and synthesized a series of second generation inhibitors, wherein the core ethylenediamine scaffold was varied in order to examine both the homology model of Plasmodium falciparum PFT (PfPFT) and our predicted inhibitor binding mode. We identified several PfPFT inhibitors (PfPFTIs) that are selective for PfPFT versus the mammalian isoform of the enzyme (up to 136-fold selectivity), that inhibit the malarial enzyme with IC50 values down to 1 nM, and that block the growth of P. falciparum in infected whole cells (erythrocytes) with ED50 values down to 55 nM. The structure−activity data for these second generation, ethylenediamine-inspired PFT inhibitors were rationalized by consideration of the X-ray crystal structure of mammalian PFT and the homology model of the malarial enzyme.

A potent class of anticancer, human farnesyltransferase (hFTase) inhibitors has been identified by “piggy-backing” on potent, antimalarial inhibitors of Plasmodium falciparum farnesyltransferase (PfFTase). On the basis of a 4-fold substituted ethylenediamine scaffold, the inhibitors are structurally simple and readily derivatized, facilitating the extensive structure–activity relationship (SAR) study reported herein. Our most potent inhibitor is compound 1f, which exhibited an in vitro hFTase IC50 value of 25 nM and a whole cell H-Ras processing IC50 value of 90 nM. Moreover, it is noteworthy that several of our inhibitors proved highly selective for hFTase (up to 333-fold) over the related prenyltransferase enzyme geranylgeranyltransferase-I (GGTase-I). A crystal structure of inhibitor 1a co-crystallized with farnesyl pyrophosphate (FPP) in the active site of rat FTase illustrates that the para-benzonitrile moiety of 1a is stabilized by a π–π stacking interaction with the Y361β residue, suggesting a structural explanation for the observed importance of this component of our inhibitors.

SummaryProtein farnesyltransferase (FTase) catalyzes an essential posttranslational lipid modification of more than 60 proteins involved in intracellular signal transduction networks. FTase inhibitors have emerged as a significant target for development of anticancer therapeutics and, more recently, for the treatment of parasitic diseases caused by protozoan pathogens, including malaria (Plasmodium falciparum). We present the X-ray crystallographic structures of complexes of mammalian FTase with five inhibitors based on an ethylenediamine scaffold, two of which exhibit over 1000-fold selective inhibition of P. falciparum FTase. These structures reveal the dominant determinants in both the inhibitor and enzyme that control binding and selectivity. Comparison to a homology model constructed for the P. falciparum FTase suggests opportunities for further improving selectivity of a new generation of antimalarial inhibitors.

Third world nations require immediate access to inexpensive therapeutics to counter the high mortality inflicted by malaria. Here, we report a new class of antimalarial protein farnesyltransferase (PFT) inhibitors, designed with specific emphasis on simple molecular architecture, to facilitate easy access to therapies based on this recently validated antimalarial target. This novel series of compounds represents the first Plasmodium falciparum selective PFT inhibitors reported (up to 145-fold selectivity), with lead inhibitors displaying excellent in vitro activity (IC50 < 1 nM) and toxicity to cultured parasites at low concentrations (ED50 < 100 nM). Initial studies of absorption, metabolism, and oral bioavailability are reported.

Inhibition of mutant H-Ras farnesylation with farnesyltransferase inhibitors (FTIs) blocks its binding to membranes and its ability to activate oncogenic signaling. In contrast, inhibition of K-Ras farnesylation with FTIs leads to its prenylation by geranylgeranyltransferase I (GGT-1), and therefore, inhibition of K-Ras prenylation and oncogenic function requires blocking both FT and GGT-1. Furthermore, several proteins downstream of K-Ras that mediate its malignant transforming activity also require farnesylation (e.g.Rheb) or gernaylgeranylation (e.g. Ral). In addition, the ability of mutant K-Ras to induce lung cancer in mouse models is severely hampered when both FT and GGT-1 are conditionally deficient. These observations prompted us to design small molecule dual FT and GGT-1 inhibitors. In this presentation, the development of FGTI-2734 as a novel therapeutic for K-Ras dependent cancers will be described. The presentation will focus on the effect of this dual inhibitor as compared to the selective FTI-2148 and GGTI-2418 on K-ras prenylation, oncogenic signaling and malignant transformation in cancer cells that depend on K-Ras. Citation Format: Kazi Aslamuzzaman, Xiaolei Zhang, Yunting Luo, Ronil Patel, Steven Fletcher, Christopher Cummings, Harshani Lawrence, Andrew Hamilton, Said M. Sebti. Dual inhibitors of FT and GGT-1 as novel therapeutic agents for K-Ras-dependent tumors. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B35. doi: 10.1158/1557-3125.RASONC14-B35

Many low molecular weight GTPases such as Ras, Ral and Rho require posttranslational farnestylation or geranylgeranylation for mediating malignant transformation. This prompted the development of farnesyltransferase (FT) inhibitors (FTI) and geranylgeranyltransferase-I (GGT-1) inhibitors (GGTI) as potential anticancer agents. However, when cancer cells are treated with FTIs, K-Ras becomes geranylgeranylated suggesting that inhibition of both FT and GGT-1 may be required to inhibit tumors harboring K-Ras mutations. Recently our group has developed a series of dual FT and GGT-1 inhibitors based on an ethylenediamine scaffold. Among these dual inhibitors FGTI-2734 was most potent in vitro (FT IC50 = 250±190 nM and GGT-1 IC50 = 520±90 nM). In human cancer cells FGTI-2734 inhibits potently HDJ-2 farnesylation, Rap 1A geranylgeranylation and K-Ras prenylation. Furthermore, FGTI-2734 inhibits the phosphorylation of Erk1/2, Akt and S6K, induces p27 accumulation and inhibits potently tumor cell growth. Finally, FGTI-2734 significantly reduces survivin protein levels, and reduction of survivin levels is associated with induction of apoptosis. Thus, this single molecule with dual FT and GGT-1 inhibitory activities may have distinct advantage over selective FTIs and GGTIs and warrants further advanced pre-clinical studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 620. doi:10.1158/1538-7445.AM2011-620