Cognate RNA-Binding Modes by the Alternative-Splicing Regulator MBNL1 Inferred from Molecular Dynamics.

The muscleblind-like protein family (MBNL) plays a prominent role in the regulation of alternative splicing. Consequently, the loss of MBNL function resulting from sequestration by RNA hairpins triggers the development of a neuromuscular disease called myotonic dystrophy (DM). Despite the sequence and structural similarities between the four zinc-finger domains that form MBNL1, recent studies have revealed that the four binding domains have differentiated splicing activity. The dynamic behaviors of MBNL1 ZnFs were simulated using conventional molecular dynamics (cMD) and steered molecular dynamics (sMD) simulations of a structural model of MBNL1 protein to provide insights into the binding selectivity of the four zinc-finger (ZnF) domains toward the GpC steps in YGCY RNA sequence. In accordance with previous studies, our results suggest that both global and local residue fluctuations on each domain have great impacts on triggering alternative splicing, indicating that local motions in RNA-binding domains could modulate their affinity and specificity. In addition, all four ZnF domains provide a distinct RNA-binding environment in terms of structural sampling and mobility that may be involved in the differentiated MBNL1 splicing events reported in the literature.

Recent advances in the pharmacological targeting of ubiquitin-regulating enzymes in cancer.

As a post-translational modification that has pivotal roles in protein degradation, ubiquitination ensures that intracellular proteins act in a precise spatial and temporal manner to regulate diversified cellular processes. Perturbation of the ubiquitin system contributes directly to the onset and progression of a wide variety of diseases, including various subtypes of cancer. This highly regulated system has been for years an active research area for drug discovery that is exemplified by several approved drugs. In this review, we will provide an update of the main breakthrough scientific discoveries that have been leading the clinical development of ubiquitin-targeting therapies in the last decade, with a special focus on E1 and E3 modulators. We will further discuss the unique challenges of identifying new potential therapeutic targets within this ubiquitous and highly complex machinery, based on available crystallographic structures, and explore chemical approaches by which these challenges might be met.

Pharmacological modulation of CXCR4 cooperates with BET bromodomain inhibition in diffuse large B-cell lymphoma.

Constitutive activation of the chemokine receptor CXCR4 has been associated with tumor progression, invasion, and chemotherapy resistance in different cancer subtypes. Although the CXCR4 pathway has recently been suggested as an adverse prognostic marker in diffuse large B-cell lymphoma, its biological relevance in this disease remains underexplored. In a homogeneous set of 52 biopsies from patients, an antibody-based cytokine array showed that tissue levels of CXCL12 correlated with high microvessel density and bone marrow involvement at diagnosis, supporting a role for the CXCL12-CXCR4 axis in disease progression. We then identified the tetra-amine IQS-01.01RS as a potent inverse agonist of the receptor, preventing CXCL12-mediated chemotaxis and triggering apoptosis in a panel of 18 cell lines and primary cultures, with superior mobilizing properties in vivo than those of the standard agent. IQS-01.01RS activity was associated with downregulation of p-AKT, p-ERK1/2 and destabilization of MYC, allowing a synergistic interaction with the bromodomain and extra-terminal domain inhibitor, CPI203. In a xenotransplant model of diffuse large B-cell lymphoma, the combination of IQS-01.01RS and CPI203 decreased tumor burden through MYC and p-AKT downregulation, and enhanced the induction of apoptosis. Thus, our results point out an emerging role of CXCL12-CXCR4 in the pathogenesis of diffuse large B-cell lymphoma and support the simultaneous targeting of CXCR4 and bromodomain proteins as a promising, rationale-based strategy for the treatment of this disease.

Molecular basis of the selective binding of MDMA enantiomers to the alpha4beta2 nicotinic receptor subtype: synthesis, pharmacological evaluation and mechanistic studies.

The α4ß2 nicotinic acetylcholine receptor (nAChR) is a molecular target of 3,4-methylenedioxymethamphetamine (MDMA), a synthetic drug also known as ecstasy, and it modulates the MDMA-mediated reinforcing properties. However, the enantioselective preference of the α4ß2 nAChR subtype still remains unknown. Since the two enantiomers exhibit different pharmacological profiles and stereoselective metabolism, the aim of this study is to assess a possible difference in the interaction of the MDMA enantiomers with this nAChR subtype. To this end, we report a novel simple, yet highly efficient enantioselective synthesis of the MDMA enantiomers, in which the key step is the diastereoselective reduction of imides derived from optically pure tert-butylsulfinamide. The enantioselective binding to the receptor is examined using [(3)H]epibatidine in a radioligand assay. Even though the two enantiomers induced a concentration-dependent binding displacement, (S)-MDMA has an inhibition constant 13-fold higher than (R)-MDMA, which shows a Hill's coefficient not significantly different from unity, implying a competitive interaction. Furthermore, when NGF-differentiated PC12 cells were pretreated with the compounds, a significant increase in binding of [(3)H]epibatidine was found for (R)-MDMA, indicating up-regulation of heteromeric nAChR in the cell surface. Finally, docking and molecular dynamics studies have been used to identify the binding mode of the two enantiomers, which provides a structural basis to justify the differences in affinity from the differential interactions played by the substituents at the stereogenic centre of MDMA. The results provide a basis to explore the distinct psychostimulant profiles of the MDMA enantiomers mediated by the α4ß2 nAChR subtype.