Targeting phosphatases: From molecule design to clinical trials.

Phosphatase is a kind of enzyme that can dephosphorylate target proteins, which can be divided into serine/threonine phosphatase and tyrosine phosphatase according to its mode of action. Current evidence showed multiple phosphatases were highly correlated with diseases including various cancers, demonstrating them as potential targets. However, currently, targeting phosphatases with small molecules faces many challenges, resulting in no drug approved. In this case, phosphatases are even regarded as "undruggable" targets for a long time. Recently, a variety of strategies have been adopted in the design of small molecule inhibitors targeting phosphatases, leading many of them to enter into the clinical trials. In this review, we classified these inhibitors into 4 types, including (1) molecular glues, (2) small molecules targeting catalytic sites, (3) allosteric inhibition, and (4) bifunctional molecules (proteolysis targeting chimeras, PROTACs). These molecules with diverse strategies prove the feasibility of phosphatases as drug targets. In addition, the combination therapy of phosphatase inhibitors with other drugs has also entered clinical trials, which suggests a broad prospect. Thus, targeting phosphatases with small molecules by different strategies is emerging as a promising way in the modulation of pathogenetic phosphorylation.

Identification of potential therapeutic and diagnostic characteristics of Alzheimer disease by targeting the miR-132-3p/FOXO3a-PPM1F axis in APP/PS1 mice.

Alzheimer disease (AD) is a neurodegenerative disorder, which is characterized by progressive impairment of memory and cognition. Early diagnosis and treatment of AD has become a leading topic of research. In this study, we explored the effects of the miR-132-3p/FOXO3a-PPM1F axis on the onset of AD for possible early diagnosis and therapy. We found that miR-132-3p levels in the hippocampus and blood were drastically decreased in APP/PS1 mice from 9 months of age, and bi-directional manipulation of miR-132-3p levels induced magnified effects on learning memory behaviors, and manifestation of AD-related pathological characteristics and inflammatory cytokines in APP/PS1 mice of relevant ages. The hippocampal PPM1F expression levels were significantly elevated in APP/PS1 mice from 3 months of age, which was correlated with miR-132-3p levels at different ages. Overexpression of PPM1F remarkably accelerated the progression of learning memory deficits and associated pathological factors in APP/PS1 mice. Further, we showed that miR-132-3p modulated the expression of PPM1F via FOXO3a in HT22 cells. Finally, using peripheral blood samples of human study participants, we found that the miR-132-3p and PPM1F expression levels in patients with AD were also altered with prominent correlations. In conclusion, miR-132-3p indirectly regulates PPM1F expression by targeting FOXO3a, which could play an extensive role in contributing to the establishment of early diagnosis, treatment, and pathogenesis of AD.

Meeting Report Europhosphatase 2015: Phosphatases as Drug Targets in Cancer.

Phosphatases are key regulators of cellular signaling and as such play an important role in nearly all cellular processes governing diseases, including cancer. However, due to their highly conserved structure and highly charged and reactive catalytic site, they have been regarded as "undruggable." Fortunately, during the recent Europhosphatase meeting (Turku, Finland), it became clear that phosphatases can no longer be ignored as potential targets in cancer therapy. As reactivation of tumor-suppressor phosphatases or direct inhibition of phosphatases acting as oncogenes is becoming available, this class of enzymes can now be considered as feasible drug targets. Cancer Res; 76(2); 193-6. ©2016 AACR.

Standardised extract of Bacopa monniera (CDRI-08) improves contextual fear memory by differentially regulating the activity of histone acetylation and protein phosphatases (PP1α, PP2A) in hippocampus.

Contextual fear conditioning is a paradigm for investigating cellular mechanisms involved in hippocampus-dependent memory. Earlier, we showed that standardised extract of Bacopa monniera (CDRI-08) improves hippocampus-dependent learning in postnatal rats by elevating the level of serotonin (5-hydroxytryptamine, 5-HT), activate 5-HT3A receptors, and cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein. In this study, we have further examined the molecular mechanism of CDRI-08 in hippocampus-dependent memory and compared to the histone deacetylase (HDACs) inhibitor sodium butyrate (NaB). To assess the hippocampus-dependent memory, wistar rat pups were subjected to contextual fear conditioning (CFC) following daily (postnatal days 15-29) administration of vehicle solution (0.5 % gum acacia + 0.9 % saline)/CDRI-08 (80 mg/kg, p.o.)/NaB (1.2 g/kg in PBS, i.p.). CDRI-08/NaB treated group showed enhanced freezing behavior compared to control group when re-exposed to the same context. Administration of CDRI-08/NaB resulted in activation of extracellular signal-regulated kinase ERK/CREB signaling cascade and up-regulation of p300, Ac-H3 and Ac-H4 levels, and down-regulation of HDACs (1, 2) and protein phosphatases (PP1α, PP2A) in hippocampus following CFC. This would subsequently result in an increased brain-derived neurotrophic factor (Bdnf) (exon IV) mRNA in hippocampus. Altogether, our results indicate that CDRI-08 enhances hippocampus-dependent contextual memory by differentially regulating histone acetylation and protein phosphatases in hippocampus.

sMEK1 enhances gemcitabine anti-cancer activity through inhibition of phosphorylation of Akt/mTOR.

Recently, we reported that sMEK1 is down-regulated in cancer cells and tissues, and that it enhances the pro-proliferative effect as a novel pro-apoptotic protein. However, the biological mechanism of the sMEK1 tumor suppressor in the cellular signal pathway has not been well understood. In our current work, we examined whether sMEK1 could promote the cytotoxic activity of gemcitabine in the human ovarian carcinoma system. Initially, we attempted to use a treatment of gemcitabine traditional chemotherapeutic agent and over-expression of sMEK1 in OVCAR-3 cancer cells. The combined treatment of sMEK1 and gemcitabine was more effective at inhibiting cell proliferation than either chemotherapeutic agent treatment alone. In addition, sMEK1 actively contributes to cell migration through its ability to promote gemcitabine-inhibited cell migration in tumorigenesis. Cell cycle-related proteins are highly associated with the down-regulation of cyclin D1 and CDK4, and the promotion of p16 and p27 as a cyclin-dependent kinase inhibitor. At the same time, sMEK1 arrests cell cycle progression in the G(1)-G(0) phase, and activates p53 and p21 expression, whereas Bcl-2 and Bcl-xL protein expression is reduced. Additionally, sMEK1 and gemcitabine suppresses the phosphorylation of signaling modulators downstream of PI3K, such as PDK1 and Akt. The p53 and p21 promoter luciferase activities were promoted by either sMEK1 or gemcitabine, and sMEK1 and gemcitabine combined additively activated the promoter further. Furthermore, as expected, sMEK1 plus gemcitabine markedly reduced the phosphorylation of p70S6K and the phosphorylation of 4E-BP1, which is one of the best characterized targets of the mTOR complex cascade. Taken together, these results provide evidence that sMEK1 can effectively regulate the pro-apoptotic activity of gemcitabine through the up-regulation of p53 expression.

Organizing glucose disposal: emerging roles of the glycogen targeting subunits of protein phosphatase-1.

Glucose is stored in mammalian tissues in the form of glycogen. Glycogen levels are markedly reduced in liver or muscle cells of patients with insulin-resistant or insulin-deficient forms of diabetes, suggesting that impaired glycogen synthesis may contribute to development of hyperglycemia. Recently, interest in this area has been further stimulated by new insights into the spatial organization of metabolic enzymes within cells and the importance of such organization in regulation of glycogen metabolism. It is now clear that a four-member family of glycogen targeting subunits of protein phosphatase-1 (PP1) plays a major role in coordinating these events. These proteins target PP1 to the glycogen particle and also bind differentially to glycogen synthase, glycogen phosphorylase, and phosphorylase kinase, thereby serving as molecular scaffolds. Moreover, the various glycogen-targeting subunits have distinct tissue expression patterns and can influence regulation of glycogen metabolism in response to glycogenic and glycogenolytic signals. The purpose of this article is to summarize new insights into the structure, function, regulation, and metabolic effects of the glycogen-targeting subunits of PP1 and to evaluate the possibility that these molecules could serve as therapeutic targets for lowering of blood glucose in diabetes.