BackgroundMany cancers show aberrant silencing of gene expression and overexpression of histone methyltransferases. The histone methyltransferases (HKMT) EZH2 and EHMT2 maintain the repressive chromatin histone methylation marks H3K27me and H3K9me, respectively, which are associated with transcriptional silencing. Although selective HKMT inhibitors reduce levels of individual repressive marks, removal of H3K27me3 by specific EZH2 inhibitors, for instance, may not be sufficient for inducing the expression of genes with multiple repressive marks.ResultsWe report that gene expression and inhibition of triple negative breast cancer cell growth (MDA-MB-231) are markedly increased when targeting both EZH2 and EHMT2, either by siRNA knockdown or pharmacological inhibition, rather than either enzyme independently. Indeed, expression of certain genes is only induced upon dual inhibition. We sought to identify compounds which showed evidence of dual EZH2 and EHMT2 inhibition. Using a cell-based assay, based on the substrate competitive EHMT2 inhibitor BIX01294, we have identified proof-of-concept compounds that induce re-expression of a subset of genes consistent with dual HKMT inhibition. Chromatin immunoprecipitation verified a decrease in silencing marks and an increase in permissive marks at the promoter and transcription start site of re-expressed genes, while Western analysis showed reduction in global levels of H3K27me3 and H3K9me3. The compounds inhibit growth in a panel of breast cancer and lymphoma cell lines with low to sub-micromolar IC50s. Biochemically, the compounds are substrate competitive inhibitors against both EZH2 and EHMT1/2.ConclusionsWe have demonstrated that dual inhibition of EZH2 and EHMT2 is more effective at eliciting biological responses of gene transcription and cancer cell growth inhibition compared to inhibition of single HKMTs, and we report the first dual EZH2-EHMT1/2 substrate competitive inhibitors that are functional in cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-015-0118-9) contains supplementary material, which is available to authorized users.

l Current antimalarials are under continuous threat due to the relentless development of drug resistance by malaria parasites. We previously reported promising in vitro parasite-killing activity with the histone methyltransferase inhibitor BIX-01294 and its analogue TM2-115. Here, we further characterize these diaminoquinazolines for in vitro and in vivo efficacy and pharmacokinetic properties to prioritize and direct compound development. BIX-01294 and TM2-115 displayed potent in vitro activity, with 50% inhibitory concentrations (IC 50 s) of <50 nM against drug-sensitive laboratory strains and multidrug-resistant field isolates, including artemisinin-refractory Plasmodium falciparum isolates. Activities against ex vivo clinical isolates of both P. falciparum and Plasmodium vivax were similar, with potencies of 300 to 400 nM. Sexual-stage gametocyte inhibition occurs at micromolar levels; however, mature gametocyte progression to gamete formation is inhibited at submicromolar concentrations. Parasite reduction ratio analysis confirms a high asexual-stage rate of killing. Both compounds examined displayed oral efficacy in in vivo mouse models of Plasmodium berghei and P. falciparum infection. The discovery of a rapid and broadly acting antimalarial compound class targeting blood stage infection, including transmission stage parasites, and effective against multiple malaria-causing species reveals the diaminoquinazoline scaffold to be a very promising lead for development into greatly needed novel therapies to control malaria.T he continuous evolution of antimalarial drug resistance by Plasmodium parasites is a major impediment to the elimination of this devastating disease. Artemisinin combination therapies (ACTs) are the current mainstay of malaria chemotherapy, but the development of artemisinin resistance in parasites was reported in 2008 and 2009 along the Thai-Cambodian border (1). This underscores the need to validate new antimalarial targets within the parasite and to develop new antimalarial treatments based on novel scaffolds with desirable characteristics, such as fast killing activity against multiple parasite life stages; efficacy against multidrug-resistant strains and multiple species of human malaria parasites, including Plasmodium vivax; and favorable pharmacokinetics to allow oral administration.Epigenetic gene regulation mediated by histone-modifying enzymes has been shown to play an important role in malaria parasite transcriptional regulation, including the control of virulence genes involved in immune evasion (2, 3). Histone lysine methyltransferase (HKMT) enzymes present a novel potential target class for the development of antimalarials due to the association of histone methylation at distinct lysine positions with both overall transcriptional activation (H3K4me) and multicopy gene family transcriptional repression (H3K9me) (4, 5). Indeed, half of the identified Plasmodium falciparum HKMT enzymes were recently shown to be refractory to genetic disruption (6). The essential and important re...

Modulating epigenetic mechanisms in malarial parasites is an emerging avenue for the discovery of novel antimalarial drugs. Previously we demonstrated the potent in vitro and in vivo antimalarial activity of BIX01294 (1), a known human G9a inhibitor, together with its dose-dependent effects on histone methylation in the malarial parasite. This work describes our initial medicinal chemistry efforts to optimize the diaminoquinazoline chemotype for antimalarial activity. A variety of analogues were designed by substituting the 2 and 4 positions of the quinazoline core and these molecules were tested against Plasmodium falciparum (3D7 strain). Several analogues with IC50 values as low as 18.5 nM and with low mammalian cell toxicity (HepG2) were identified. Certain pharmacophoric features required for the antimalarial activity were found to be analogous to the previously published SAR of these analogues for G9a inhibition, thereby suggesting potential similarities between the malarial and the human HKMT targets of this chemotype. Physiochemical, in vitro activity, and in vitro metabolism studies were also performed for a select set of potent analogues to evaluate their potential as anti-malarial leads.

A series of new lipid prodrugs of paclitaxel, which can be formulated as nanoassemblies, are described. These prodrugs which are designed to overcome the limitations due to the systemic toxicity and low water solubility of paclitaxel consist of a squalene chain bound to the 2'-OH of paclitaxel through a 1,4-cis,cis-dienic linker. This design allows the squalene-conjugates to self-assemble as nanoparticular systems while preserving an efficient release of the free drug, thanks to the dienic spacer. The size, steric hindrance, and functional groups of the spacer have been modulated. All these prodrugs self-assemble into nanosized aggregates in aqueous solution as characterized by dynamic light scattering and transmission electron microscopy and appear stable in water for several days as determined by particle size measurement. In vitro biological assessment shows that these squalenoyl-paclitaxel nanoparticles display notable cytotoxicity on several tumor cell lines including A549 lung cell line, colon cell line HT-29, or KB 3.1 nasopharyngeal epidermoid cell line. The cis,cis-squalenyl-deca-5,8-dienoate prodrug show improved activity over simple 2'-squalenoyl-paclitaxel prodrug highlighting the favourable effect of the dienic linker. The antitumor efficacy of the nanoassemblies constructed with the more active prodrugs has been investigated on human lung (A549) carcinoma xenograft model in mice. The prodrug bearing the cis,cis-deca-5,8-dienoyl linker shows comparable antitumor efficacy to the parent drug, but reveals a much lower subacute toxicity as seen in body weight loss. Thus, nanoparticles with the incorporated squalenoyl paclitaxel prodrug may prove useful for replacement of the toxic Cremophor EL.

A new paclitaxel (Ptx) prodrug was designed by coupling a single terpene unit (MIP) to the hydroxyl group in position 2' of the drug molecule. Using a squalene derivative of polyethylene glycol (SQ-PEG) as surface active agent, the resulting bioconjugate (PtxMIP) self-assembled in water leading to the formation of stable nanoparticles (PtxMIP_SQ-PEG NPs) with an impressively high drug loading (82%). In vivo, the anticancer activity of this novel Ptx nanoassembled prodrug was compared to the conventional Cremophor-containing formulation (Taxol) on a murine model of breast cancer lung metastasis induced by intravenous injection of 4T1 tumor cells, genetically modified to stably express firefly luciferase. Cell growth was assessed noninvasively by bioluminescence imaging (BLI) which enabled monitoring tumor metastatic burden in the same animals. PtxMIP_SQ-PEG nanoparticles slowed metastatic spread and were better tolerated than the Cremophor-containing formulation (i.e., free drug), thus demonstrating the potential of terpene-based nanoassembled prodrugs in the improvement of the therapeutic index of Ptx in balb/c mice.