Inhibition of protein phosphatases by Michael adducts of ascorbic acid analogues with alpha,beta-unsaturated carbonyl compounds

By investigating the stereospecific Michael reaction of derivatives of ascorbic acid with acrolein we obtained a novel class of protein Ser/Thr phosphatase inhibitors. The inhibitory effect of the Michael adducts was examined using the canonical protein phosphatases type 1, 2A and 2B. Of the isozymes examined the type 1 isoform was strongly inhibited.     

Calyculin A and okadaic acid: inhibitors of protein phosphatase activity

Calyculin A and okadaic acid induce contraction in smooth muscle fibers. Okadaic acid is an inhibitor of phosphatase activity and the aims of this study were to determine if calyculin A also inhibits phosphatase and to screen effects of both compounds on various phosphatases. Neither compound inhibited acid or alkaline phosphatases, nor the phosphotyrosine protein phosphatase. Both compounds were potent inhibitors of the catalytic subunit of type-2A phosphatase, with IC50 values of 0.5 to 1 nM. With the catalytic subunit of protein phosphatase type-1, calyculin A was a more effective inhibitor than okadaic acid, IC50 values for calyculin A were about 2 nM and for okadaic acid between 60 and 500 nM. The endogenous phosphatase of smooth muscle myosin B was inhibited by both compounds with IC50 values of 0.3 to 0.7 nM and 15 to 70 nM, for calyculin A and okadaic acid, respectively. The partially purified catalytic subunit from myosin B had IC50 values of 0.7 and 200 nM for calyculin A and okadaic acid, respectively. The pattern of inhibition for the phosphatase in myosin B therefore is similar to that of the type-1 enzyme.     

Fumonisins and fumonisin analogs as inhibitors of ceramide synthase and inducers of apoptosis

Sphingoid bases are growth inhibitory and pro-apoptotic for many types of cells when added to cells exogenously, and can be elevated to toxic amounts endogenously when cells are exposed to inhibitors of ceramide synthase. An important category of naturally occurring inhibitors are the fumonisins, which inhibit ceramide synthase through structural similarities with both the sphingoid base and fatty acyl-CoA co-substrates. Fumonisins cause a wide spectrum of disease (liver and renal toxicity and carcinogenesis, neurotoxicity, induction of pulmonary edema, and others), and most-possibly all-of the pathophysiologic effects of fumonisins are attributable to disruption of the sphingolipid metabolism. The products of alkaline hydrolysis of fumonisins (which occurs during the preparation of masa flour for tortillas) are aminopentols that also inhibit ceramide synthase, but more weakly. Nonetheless, the aminopentols (and other 1-deoxy analogs of sphinganine) are acylated to derivatives that inhibit ceramide synthase, perhaps as product analogs, elevate sphinganine, and kill the cells. Somewhat paradoxically, fumonisins sometimes stimulate growth and inhibit apoptosis, possibly due to elevation of sphinganine 1-phosphate, which is known to have these cellular effects. These findings underscore the complexity of sphingolipid metabolism and the difficulty of identifying the pertinent mediators unless a full profile of the potentially bioactive species is evaluated.     

Synthesis of substituted biphenyl methylene indolinones as apoptosis inducers and tubulin polymerization inhibitors

A new series of biphenyl methylene indolinones has been designed, synthesized and evaluated for their in vitro antiproliferative activity against various cancer cell lines like DU-145 (prostate cancer cell line), 4T1 (mouse breast cancer cell line), MDA-MB-231 (human breast cancer cell line), BT-549 (human breast cancer cell line), T24 (human urinary bladder carcinoma cell line), and HeLa (cervical cancer cell line). Among the series, compound 10e showed potent in vitro cytotoxic activity against HeLa and DU-145 cancer cell lines with IC₅₀ value of 1.74 ± 0.69 µM and 1.68 ± 1.06 µM respectively. To understand the underlying mechanism of most potent cytotoxic compound 10e, various mechanistic studies were carried out on DU-145 cell lines. Cell cycle analysis results revealed that these conjugates affect both G0/G1 and G2/M phase of the cycle, tubulin binding assay resulted that compound 10e interrupting microtubule network formation by inhibiting tubulin polymerization with IC₅₀ value of 4.96 ± 0.05 μM. Moreover, molecular docking of 10e on colchicine binding site of the tubulin explains the interaction of 10e with tubulin. Clonogenic assay indicated inhibition of colony formation by compound 10e in a dose dependent manner. In addition, morphological changes were clearly observed by AO/EB and DAPI staining studies. Moreover, ROS detection using DCFDA, JC-1, and annexin V-FITC assays demonstrated the significant apoptosis induction by 10e.     

Chemopreventive effects of NSAIDs as inhibitors of cyclooxygenase-2 and inducers of apoptosis in experimental lung carcinogenesis

Roles of cyclooxygenase (COX) enzyme and intrinsic pathway of apoptosis have been explored for the chemopreventive effects of non-steroidal anti-inflammatory drugs (NSAIDs) on 9,10-dimethyl benz(a)anthracene (DMBA)-induced lung cancer in rat model. 16 weeks after the administration of DMBA, morphological analysis revealed the occurrences of tumours and lesions, which were regressed considerably with the co-administration of indomethacin and etoricoxib, the two NSAIDs under investigation. DMBA group was marked by hyperplasia and dysplasia as observed by histological examination, and these features were corrected to a large extent by the two NSAIDs. Elevated levels of COX-2 were seen in the DMBA group, the enzyme responsible for prostaglandin synthesis during inflammation and cancer, whilst the expression of the constitutive isoform, COX-1, was equally expressed in all the groups. Apoptosis was quantified by studying the activities of apaf-1, caspase-9, and 3 by immunofluorescence and western blots. Their activities were found to diminish in the DMBA-treated animals as compared to the other groups. Fluorescent co-staining of the isolated broncho-alveolar lavage cells showed reduced number of apoptotic cells in the DMBA group, indicating decrease in apoptosis after carcinogen administration. The present results thus suggest that the mechanism of cancer chemoprevention of NSAIDs may include the suppression of COX-2 and the induction of apoptosis.     

Involvement of histone phosphorylation in thymocyte apoptosis by protein phosphatase inhibitors

Incubation of rat thymocytes with the inhibitors of protein phosphatase such as calyculin A and okadaic acid resulted in an increase in DNA fragmentation. These effects were dependent on the concentration of the inhibitors and the incubation time. Analyses of the fragmented DNA revealed the production of approximately 50 kbp of DNA and a 180 bp DNA ladder. In addition, a laser scanning-microscopic analysis showed that these compounds caused nuclear condensation. Thus, these results demonstrated that protein phosphatase inhibitors induced thymocyte apoptosis. The inhibitors of protein phosphatase increased the phosphorylation of proteins of approximately 15 kDa. The phosphorylation of proteins preceded the DNA fragmentation induced by these inhibitors. Judging from acetic acid-urea-Triton X-100 gel electrophoresis, the phosphorylated proteins were histone H1 and H2A/H3. Therefore, these results suggest that phosphorylation of histones triggers the DNA fragmentation of thymocytes undergoing apoptosis.     

Biaryls and heterobiaryls as alpha-glucosidase and protein tyrosine phosphatase inhibitors

Various 6-aryl-4-substituted-2H-pyran-2-one-3-carbonitriles (1a-d) have been synthesized as precursor for the synthesis of 3,4-dihydro-1H-isothiochroman (2a) and benzocycloalkanes (2b-e). Highly functionalized 9-thiaphenanthrene (3b) and phenanthrene (3a) have also been obtained from the reaction of 1c with thiochroman-4-one and 1-tetralone separately. Similarly 4 has been obtained by the ring transformation of 1d by 4-trifluoromethylacetophenone. Most of the synthesized compounds were evaluated for alpha-glucosidase and protein tyrosine phosphatase inhibitory activities. Some of the compounds, 2a, 3a and b and 4 displayed better alpha-glucosidase inhibitory activity compared to standard drug acarbose.     

Steroidal derived acids as inhibitors of human Cdc25A protein phosphatase

A group of steroidal derived acids were synthesized and found to be human Cdc25A inhibitors. Their potency ranged from 1.1 to > 100 microM; the best ones compare very favorably with that of the novel cyano-containing 5,6-seco-cholesteryl acid 1 (IC50=2.2microM) reported by us recently (Peng, H.; Zalkow, L. H.; Abraham, R. T.; Powis, G. J. Med. Chem. 1998, 41, 4677). Structure-activity relationships of these compounds revealed that a hydrophobic cholesteryl side chain and a free carboxyl group are crucial for activity. The distance between these two pharmacophores is also important for the potency of these compounds. Several of the compounds showed selective growth inhibition effects in the NCI in vitro cancer cell line panel.     

The structure of protein phosphatase 2A is as highly conserved as that of protein phosphatase 1

cDNA coding for protein phosphatase 2A (PP2A) has been isolated from Drosophila head and eye imaginal disc libraries. Drosophila PP2A mRNA is expressed throughout development, but is most abundant in the early embryo. The cDNA hybridises to a single site on the left arm of the second chromosome at position 28D2-4. The deduced amino acid sequence (309 residues) of Drosophila PP2A shows 94% identity with either rabbit PP2A alpha or PP2A beta, indicating that PP2A may be the most conserved of all known enzymes.     

Discovery of novel and potent heterocyclic carboxylic acid derivatives as protein tyrosine phosphatase 1B inhibitors

A series of novel heterocyclic carboxylic acid based protein tyrosine phosphatase 1B (PTP1B) inhibitors with hydrophobic tail have been synthesized and characterized. Structure-activity relationship (SAR) optimization resulted in identification of several potent, selective (over the highly homologous T-cell protein tyrosine phosphatase, TCPTP) and metabolically stable PTP1B inhibitors. Compounds 7a, 19a and 19c showed favorable cell permeability and pharmacokinetic properties in mouse with moderate to very good oral (% F=13-70) bio-availability.     

Evans Blue and other dyes as protein tyrosine phosphatase inhibitors

Commonly used dyes including Evans Blue and Trypan Blue were examined for their inhibitory activities against protein tyrosine phosphatases (PTPases), all of them showed inhibition of PTPases with different potencies. Of the 13 dyes tested, four exhibited IC(50) value of less than 10 microM, Evans Blue lowest IC(50) of 1.3 microM against PTP1B. Care must be taken in the use of dyes for clinical or biochemical experiments to avoid unwanted side effects. Some of the low molecular weight dyes might be useful as lead compounds for the development of potent and selective PTPase inhibitors.     

Synthesis of tripeptides as potent Yersinia protein tyrosine phosphatase inhibitors

We report the synthesis of a series of monoanionic phosphotyrosyl (pTyr) mimetic-containing tripeptides based on 'Fmoc-Glu(OBn)-Xxx-Leu-amide' (where Xxx = pTyr mimetic) and their N-terminally modified derivatives. The inhibitory potencies of compounds were tested against YopH and human PTP1B enzymes. Several compounds exhibited noteworthy activity against both YopH and PTP1B. Among the N-terminally modified analogues, 5-methylindole derivative 30 was found to be the best moiety to replace base-labile Fmoc group. A mode of binding with YopH is proposed for tripeptides 21, 30, and 31.     

Characterization of alkaline phosphatase inactivation by ascorbic acid

Ascorbic acid, isoascorbic acid and dehydroascorbic acid inhibit bovine kidney alkaline phosphatase activity. Ascorbic acid free radicals seem not to be involved. Dialysis does not make the inactivation reversible. A competitive mechanism can be inferred from experiments with phosphate and substrates, which block the activity decay. The influence of temperature, pH, other inhibitors and tertiary structure modifications on the inactivation process is also investigated.     

Synthesis,biological evaluation,and molecular docking of new series of antitumor and apoptosis inducers designed as VEGFR-2 inhibitors

Based on quinazoline, quinoxaline, and nitrobenzene scaffolds and on pharmacophoric features of VEGFR-2 inhibitors, 17 novel compounds were designed and synthesised. VEGFR-2 IC₅₀ values ranged from 60.00 to 123.85 nM for the new derivatives compared to 54.00 nM for sorafenib. Compounds 15_a, 15_b, and 15_d showed IC₅₀ from 17.39 to 47.10 µM against human cancer cell lines; hepatocellular carcinoma (HepG2), prostate cancer (PC3), and breast cancer (MCF-7). Meanwhile, the first in terms of VEGFR-2 inhibition was compound 15_d which came second with regard to antitumor assay with IC₅₀ = 24.10, 40.90, and 33.40 µM against aforementioned cell lines, respectively. Furthermore, Compound 15_d increased apoptosis rate of HepG2 from 1.20 to 12.46% as it significantly increased levels of Caspase-3, BAX, and P53 from 49.6274, 40.62, and 42.84 to 561.427, 395.04, and 415.027 pg/mL, respectively. Moreover, 15_d showed IC₅₀ of 253 and 381 nM against HER2 and FGFR, respectively.     

Identification of mono- and bisubstrate inhibitors of protein farnesyltransferase and inducers of apoptosis from a pepticinnamin E library

A library of 51 analogues of the naturally occurring protein farnesyltransferase inhibitor pepticinnamin E was investigated biologically. Several compounds with pronounced inhibitory activity were discovered with the lowest IC(50) value reaching 1 microM. The library contains inhibitors which are competitive to either farnesylpyrophosphate or the peptide substrate and a bisubstrate inhibitor. This activity is supported and rationalized by molecular modelling experiments and different binding modes of the inhibitors deduced from them. Several compounds induced apoptosis in a Ras-transformed tumour cell line, and in one case this correlated with farnesyltransferase-inhibiting activity.     

Bicyclic benzofuran and indole-based salicylic acids as protein tyrosine phosphatase inhibitors

Protein tyrosine phosphatases (PTPs) constitute a large and structurally diverse family of signaling enzymes that control the cellular levels of protein tyrosine phosphorylation. Malfunction of PTP activity has significant implications in many human diseases, and the PTP protein family provides an exciting array of validated diabetes/obesity (PTP1B), oncology (SHP2), autoimmunity (Lyp), and infectious disease (mPTPB) targets. However, despite the fact that PTPs have been garnering attention as novel therapeutic targets, they remain largely an untapped resource. The main challenges facing drug developers by the PTPs are inhibitor specificity and bioavailability. Work over the last ten years has demonstrated that it is feasible to develop potent and selective inhibitors for individual members of the PTP family by tethering together small ligands that can simultaneously occupy both the active site and unique nearby peripheral binding sites. Recent results with the bicyclic salicylic acid pharmacophores indicate that the new chemistry platform may provide a potential solution to overcome the bioavailability issue that has plagued the PTP drug discovery field for many years. Structural analysis of PTP-inhibitor complexes reveals molecular determinants important for the development of more potent and selective PTP inhibitors, thus offering hope in the medicinal chemistry of a largely unexploited protein class with a wealth of attractive drug targets.     

Bicyclic and tricyclic thiophenes as protein tyrosine phosphatase 1B inhibitors

A novel pyridothiophene inhibitor of PTP1B was discovered by rational screening of phosphotyrosine mimics at high micromolar concentrations. The potency of this lead compound has been improved significantly by medicinal chemistry guided by X-ray crystallography and molecular modeling. Excellent consistency has been observed between structure-activity relationships and structural information from PTP1B-inhibitor complexes.     

Chemical modification of ascorbic acid and evaluation of its lipophilic derivatives as inhibitors of secretory phospholipase A2 with anti-inflammatory activity

This investigation aims to evaluate the antitumor and antioxidant potential of Chrysaora quinquecirrha (sea nettle) nematocyst venom on Ehrlich ascites carcinoma (EAC) tumor model. Tumor was induced in mice by intraperitoneal injection of EAC cells. The antitumor effect of sea nettle nematocyst venom (SNV) peptide was evaluated by assessing in vitro cytotoxicity, survival time, hematological, and antioxidant parameters. Intraperitoneal injection of SNV peptide increased the survival time of the EAC-bearing mice. The SNV peptide brought back the altered levels of the hematological and antioxidant parameters in a dose dependent manner in EAC-bearing mice. The results were comparable to that of the result obtained from the animals treated with the standard drug 5-fluorouracil (20 mg/kg bw). Thus, present study revealed that SNV peptide possessed significant antitumor and antioxidant activity.     

Cathepsin D-mediated yolk protein degradation is blocked by acid phosphatase inhibitors

Vitellin (VT) is a lipoglycophosphoprotein stored inside the eggs of every oviparous organism during oogenesis. In the blood-sucking bug Rhodnius prolixus, VT is deposited inside growing oocytes together with two acid hydrolases: acid phosphatase (AP) and cathepsin D (CD). Egg fertilization triggers AP activity and VT proteolysis in vivo [Insect Biochem. Mol. Biol. 2002 (32) 847]. Here, we show that CD is the main protease targeting VT proteolysis during egg development. CD activity in total egg homogenates is blocked by the classical aspartyl protease inhibitor, pepstatin A. Surprisingly, AP inhibitors such as NaF, Na+/K+ tartrate, and inorganic phosphate also block VT proteolysis, whereas this effect is not observed when tyrosine phosphatase inhibitors such as vanadate and phenylarsine oxide or an inhibitor of alkaline phosphatases such as levamisole are used in a VT proteolysis assay. NaF concentrations that block isolated AP activity do not affect the activity of partially purified CD. Therefore, a specific repressor of VT proteolysis must be dephosphorylated by AP in vivo. In conclusion, these results demonstrate for the first time that acid hydrolases act cooperatively to promote yolk degradation during egg development in arthropods.