Discovery of a potent and dual-selective bisubstrate inhibitor for protein arginine methyltransferase 4/5.

Protein arginine methyltransferases (PRMTs) have been implicated in the progression of many diseases. Understanding substrate recognition and specificity of individual PRMT would facilitate the discovery of selective inhibitors towards future drug discovery. Herein, we reported the design and synthesis of bisubstrate analogues for PRMTs that incorporate a S-adenosylmethionine (SAM) analogue moiety and a tripeptide through an alkyl substituted guanidino group. Compound AH237 is a potent and selective inhibitor for PRMT4 and PRMT5 with a half-maximal inhibition concentration (IC50) of 2.8 and 0.42 nmol/L, respectively. Computational studies provided a plausible explanation for the high potency and selectivity of AH237 for PRMT4/5 over other 40 methyltransferases. This proof-of-principle study outlines an applicable strategy to develop potent and selective bisubstrate inhibitors for PRMTs, providing valuable probes for future structural studies.

A new class of cytotoxic agents targets tubulin and disrupts microtubule dynamics.

Despite the advances in treatment strategies, cancer is still the second leading cause of death in the USA. A majority of the currently used cancer drugs have limitations in their clinical use due to poor selectivity, toxic side effects and multiple drug resistance, warranting the development of new anticancer drugs of different mechanisms of action. Here we describe the design, synthesis and initial biological evaluation of a new class of antimitotic agents that modulate tubulin polymerization. Structurally, these compounds are chalcone mimics containing a 1-(1H-imidazol-2-yl)ethan-1-one moiety, which was initially introduced to act as a metal-binding group and inhibit histone deacetylase enzymes. Although several analogues selectively inhibited purified HDAC8 with IC50 values in low micromolar range, tissue culture studies suggest that HDAC inhibition is not a major mechanism responsible for cytotoxicity. The compounds demonstrated cell growth inhibition with GI50 values of upper nanomolar to low micromolar potency with significant selectively for cancer over normal cells. Interestingly, several compounds arrested HeLaM cells in mitosis and seem to target tubulin to cause mitotic arrest. For example, when combined with inhibitors of Aurora B kinase, they led to dramatic disassembly of the mitotic spindle. In-vitro tubulin polymerization studies showed that the compounds reduced the rate of polymerization of microtubules during the elongation phase and lowered the amount of polymerized tubulin during the plateau phase. Finally, in silico docking studies identified binding of IPE-7 to the colchicine site with similar affinity as the test compound D64131. These compounds represent a new antimitotic pharmacophore with limited HDAC inhibitory activity.

A Pan-Inhibitor for Protein Arginine Methyltransferase Family Enzymes.

Protein arginine methyltransferases (PRMTs) play important roles in transcription, splicing, DNA damage repair, RNA biology, and cellular metabolism. Thus, PRMTs have been attractive targets for various diseases. In this study, we reported the design and synthesis of a potent pan-inhibitor for PRMTs that tethers a thioadenosine and various substituted guanidino groups through a propyl linker. Compound II757 exhibits a half-maximal inhibition concentration (IC50) value of 5 to 555 nM for eight tested PRMTs, with the highest inhibition for PRMT4 (IC50 = 5 nM). The kinetic study demonstrated that II757 competitively binds at the SAM binding site of PRMT1. Notably, II757 is selective for PRMTs over a panel of other methyltransferases, which can serve as a general probe for PRMTs and a lead for further optimization to increase the selectivity for individual PRMT.

Non-Histone Arginine Methylation by Protein Arginine Methyltransferases.

Protein arginine methyltransferase (PRMT) enzymes play a crucial role in RNA splicing, DNA damage repair, cell signaling, and differentiation. Arginine methylation is a prominent posttransitional modification of histones and various non-histone proteins that can either activate or repress gene expression. The aberrant expression of PRMTs has been linked to multiple abnormalities, notably cancer. Herein, we review a number of non-histone protein substrates for all nine members of human PRMTs and how PRMT-mediated non-histone arginine methylation modulates various diseases. Additionally, we highlight the most recent clinical studies for several PRMT inhibitors.

A Bioactive Resveratrol Trimer from the Stem Bark of the Sri Lankan Endemic Plant Vateria copallifera.

A new resveratrol trimer, vateriferol (1), having four cis-oriented methine protons and constituting four contiguous stereocenters, was isolated from the bark extract of Vateria copallifera by bioassay-guided fractionation using a combination of normal, reversed phase, and size exclusion column chromatography. The structure was established based on its spectroscopic data. Vateriferol (1) was evaluated in vitro for its antioxidant capacity, enzyme inhibitory activity, growth inhibitory activity on a number of cancer cell lines, neuroprotective activity, and anti-inflammatory activity. Vateriferol (1) exhibited AChE inhibitory activity (IC50 8.4 ± 0.2 µM), ORAC activity (2079 ± 0.20 TE/g), and neuroprotective activity at 1.5 µM using PC12 cells deprived of oxygen and glucose and lowered NO levels in lipopolysaccharide-stimulated SIM-A9 microglial cells at 14.7 and 73.6 µM. Vateriferol (1) exhibited weak cytotoxic potency (<50% growth inhibition) against the tested cell lines at 147.2 µM.

Small-molecule anticancer agents kill cancer cells by harnessing reactive oxygen species in an iron-dependent manner.

In the course of generating a library of open-chain epothilones, we discovered a new class of small molecule anticancer agents that has no effect on tubulin but instead kills selected cancer cell lines by harnessing reactive oxygen species in an iron-dependent manner. Results of the preliminary studies are consistent with the recently described cell death mechanism ferroptosis. Studies are in progress to confirm ferroptosis as the cell death mechanism and to identify the specific molecular targets of these small molecule anticancer agents.

Largazole Analogues Embodying Radical Changes in the Depsipeptide Ring: Development of a More Selective and Highly Potent Analogue.

A number of analogues of the marine-derived histone deacetylase inhibitor largazole incorporating major structural changes in the depsipeptide ring were synthesized. Replacing the thiazole-thiazoline fragment of largazole with a bipyridine group gave analogue 7 with potent cell growth inhibitory activity and an activity profile similar to that of largazole, suggesting that conformational change accompanying switching hybridization from sp3 to sp2 at C-7 is well tolerated. Analogue 7 was more class I selective compared to largazole, with at least 464-fold selectivity for class I HDAC proteins over class II HDAC6 compared to a 22-fold selectivity observed with largazole. To our knowledge 7 represents the first example of a potent and highly cytotoxic largazole analogue not containing a thiazoline ring. The elimination of a chiral center derived from the unnatural amino acid R-α-methylcysteine makes the molecule more amenable to chemical synthesis, and coupled with its increased class I selectivity, 7 could serve as a new lead compound for developing selective largazole analogues.