Development of 11-DGA-3-O-Gal-Modified Cantharidin Liposomes for Treatment of Hepatocellular Carcinoma.

BACKGROUND: Liver cancer is a common malignant tumor worldwide, and its morbidity and mortality increase each year. The disease has a short course and high mortality, making it a serious threat to human health. PURPOSE: The objective of this study was to create novel liver-targeting nanoliposomes to encapsulate cantharidin (CTD) as a potential treatment for hepatic carcinoma. METHODS: 3-Galactosidase-30-stearyl deoxyglycyrrhetinic acid (11-DGA-3-O-Gal)-modified liposomes (11-DGA-3-O-Gal-CTD-lip) for the liver-targeted delivery of CTD were prepared via the film-dispersion method and characterized. In vitro analyses of the effects on cellular cytotoxicity, cell migration, cell cycle, and cell apoptosis were carried out and an in vivo pharmacokinetics study and tissue distribution analysis were performed. RESULTS: Compared with unmodified liposomes (CTD-lip), 11-DGA-3-O-Gal-CTD-lip showed higher cytotoxicity and increased the inhibition of HepG2 cell migration, but they did not increase the apoptotic rate of cells. The inhibition mechanism of 11-DGA-3-O-Gal-CTD-lip on hepatocellular carcinoma was partly through cell cycle arrest at the S phase. Analysis of pharmacokinetic parameters indicated that 11-DGA-3-O-Gal-CTD-lip were eliminated more rapidly than CTD-lip. Regarding tissue distribution, the targeting efficiency of 11-DGA-3-O-Gal-CTD-lip to the liver was (41.15 ± 3.28)%, relative targeting efficiency was (1.53 ± 0.31)%, relative uptake rate was( 1.69 ± 0.37)%, and peak concentration ratio was (2.68 ± 0.12)%. CONCLUSION: 11-DGA-3-O-Gal-CTD-lip represent a promising nanocarrier for the liver-targeted delivery of antitumor drugs to treat hepatocellular carcinoma.

Asialoglycoprotein receptor-targeted liposomes loaded with a norcantharimide derivative for hepatocyte-selective targeting.

In order to overcome the shortcomings associated with the clinical application of norcantharidin (NCTD), including intense irritation and a short half-life, and to obtain a hepatocyte-selective liposome system with high encapsulation efficiency (EE) and low leakage, we synthesized a C14 alkyl chain norcantharimide derivative of NCTD (2-tetradecylhexahydro-1H-4,7-epoxyisoindole-1,3(2H)-dione, N-14NCTDA). Asialoglycoprotein receptor-targeted, galactosylated liposomes loaded with N-14NCTDA (GAL-Lipo) were prepared by the lipid film hydration method. GAL-Lipo with a satisfactory particle size of approximately 120nm has a higher encapsulation efficiency of more than 98.0%, which is markedly increased compared with NCTD loaded liposomes (EE%=47.6%). In addition, GAL-Lipo remained stable for at least 1 month at 4°C. In cytotoxicity assays, GAL-Lipo demonstrated stronger cytotoxicity effects (IC50=24.58µmolL-1) on Hep G2 cells than free N-14NCTDA (100µmol/L) and conventional liposomes (Con-Lipo, 39.49µmol/L) without the GAL modification. GAL-Lipo can continuously accumulate in Hep G2 cells and be internalized into cells via two pathways, namely caveolin-dependent endocytosis and clathrin-dependent asialoglycoprotein receptors (ASGP-R) mediated endocytosis and produces considerably more significant cellular apoptosis. The results of vivo toxicity studies showed that GAL-Lipo dramatically reduced renal toxicity. In addition, GAL-Lipo has a markedly improved pharmacokinetic profile in vivo and a longer circulation time (AUC=6.700±2.964mgL-1h, t1/2z=1.347±0.519h) than Con-Lipo (AUC=2.319±0.121mgL-1h, t1/2z=0.413±0.238h). In conclusion, N-14NCTDA with an ideal logP is a better alternative for the treatment of primary hepatic carcinoma. GAL-Lipo offers an attractive strategy to specifically target hepatocytes via caveolin-dependent and clathrin-dependent asialoglycoprotein receptor-mediated endocytosis resulting in higher anticancer activity and fewer side-effects.

Synthesis of Canthardin Sulfanilamides and Their Acid Anhydride Analogues via a Ring-Opening Reaction of Activated Aziridines and Their Associated Pharmacological Effects.

The cantharidinimide derivatives, 5a-h, including sulfanilamides containing pyrimidyl, pyrazinyl, hydrogen, thiazolyl, and oxazolyl groups were synthesized. Modification of cantharidinimide by means of the reaction of activated aziridine ring opening led to the discovery of a novel class of antitumor compounds. The analogues 10i-k, 11l-n, 12o-p, and 16q-s were obtained from treating cantharidinimide 6 and analogues (7, 8, and 13) with activated aziridines, which produced a series of ring-opened products including normal and abnormal types. Some of these compounds showed cytotoxic effects in vitro against HL-60, Hep3B, MCF7, and MDA-MB-231 cancer cells. The most potent cytostatic compound, N-cantharidinimido-sulfamethazine (5a), exhibited anti-HL-60 and anti-Hep3B cell activities. Two compounds 5g and 5h displayed slight effects on the Hep3B cell line, while the other compounds produced no response in these four cell lines.

A simple procedure for preparation of N-thiazol, thiadiazol, pyridyl and sulfanylamidocantharidinimines analogues and evaluation of their cytotoxicities against human HL-60, MCF7, Neuro-2a and A549 carcinoma cell.

The lab made an effort to prepare some biological active cantharidinimines by heating the reactant 1 and 2a-g, 5h-i and 7j-r amines to suitable temperature with ethanol to provide 18 N-thiazolyl-, sulfanyl-, aminopyridyl-, bromopyridyl-, alkylpyridyl- and hydroxypyridylcantharidinimines 3a-g, 4a-c, 6h-i and 8j-r in yield of 4-77% (Chart 1). These cantharidinimine derivatives were tested for their capabilities to suppress growth of the human carcinoma cell lines, HL-60, MCF7, Neuro-2a and A549, because the incidence rate is more prominent in Asian countries than western countries. Compounds 3c-d and 6h-i were found to have some antitumor activity in HL-60 but less activity in MCF cell and compounds 8j-l displayed some inhibition effects to A549 cell line, but less effect to Neuro-2a cell line. Compounds 8m-r had no cytotoxic effect against both cell lines. The cytotoxic effects of these cantharidinimine compounds seemed to be better than the cantharidinimide compounds which we had mentioned several years ago.

Cantharidin and its anhydride-modified derivatives: relation of structure to insecticidal activity.

Cantharidin is a natural compound of novel structure with ideal insecticidal activity. However, the relationship of structure to insecticidal activity of cantharidin and its derivatives has not been ever clarified. To explore what determines the insecticidal activity structurally of cantharidin-related compounds, two series target compounds 6 and 7 were synthesized by replacing the anhydride ring of norcantharidin with an aromatic amine or fatty amine with different electron density, respectively. The structures of these compounds were characterized by 1H NMR, 13C NMR and HRMS-ESI. A bioassay showed that compounds 6 (a-m) lacked any larvicidal activity against Plutella xylostella; whereas their ring-opened partners 7 (a-m) provided a variety of larvicidal activities against P. xylostella, and compound 7f indicated the highest larvicidal activity with LC(50) value of 0.43 mM. The present work demonstrated that the form of the compound (cyclic or ring-opened) or their ability to hydrolyze facilely was the key to determine whether it exhibits larvicidal activity. Moreover, it revealed that the improvement of insecticidal activity required a reasonable combination of both aliphatic amide and aromatic amide moieties, and the type of substituent Y on the aniline ring was critical.

Synthesis and biological activity of Delta-5,6-norcantharimides: importance of the 5,6-bridge.

Cantharidin (1) and norcantharidin (2) are potent protein phosphatase 1 and 2A inhibitors that also display high levels of anticancer activity against a broad range of tumor cells lines. Surprisingly, Delta-5,6-ethyl norcantharidin (3, cis-tetrahydrofurano[3,4-c]furan-1,3-dione) displays neither phosphatase inhibition nor anticancer activity. This suggests that the 5,6-ethyl bridge is pivotal to both anti-cancer and protein phosphatase activity. Additionally bioisosteric replacement of the ethereal oxygen has no effect on biological activity nor does modification of the anhydride moiety. Unlike the parent norcantharidin, anhydride ring opening has no effect on either protein phosphatase inhibition or anti-cancer activity. Additionally, this work highlights the discovery of the octyl substituted, cis-5-benzyl-2-hexyltetrahydro-2H,3aH-pyrrolo[3,4-c]pyrrole-1,3-dione, 9p, and the octyl substituted, cis-octyltetrahydro-5H-furo[3,4-c]pyrrole-4,6-dione, 8p, as two new cytotoxic agents which are equipotent (9p) with, and more potent (8p) than norcantharidin.

Norcantharidin analogues: synthesis, anticancer activity and protein phosphatase 1 and 2A inhibition.

Cantharidin (1) and its derivatives are of significant interest as serine/threonine protein phosphatase 1 and 2A inhibitors. Additionally, compounds of this type have displayed growth inhibition of various tumour cell lines. To further explore both of these inhibition pathways, a number of amide-acid norcantharidin analogues (15-26) were prepared. Compounds 23 and 24, containing two carboxylic acid residues, showed good PP1 and PP2A activity, with IC(50) values of approximately 15 and approximately 3 mum, respectively. Substituted aromatic amide analogues 45, 48, 49, 52, 53, and 54 also displayed good PP1 and PP2A inhibition, with IC(50) values in the range of 15-10 microM (PP1) and 11-5 microM (PP2A). However, bulky ortho substituents on the aromatic ring caused the aromatic ring to be skewed from the NCO planarity, leading to a decrease in PP1 and PP2A inhibition. A number of analogues, 20, 22, 25 and 46, showed excellent tumour growth inhibition, with 46 in particular being more potent than the lead, norcantharidin 2.

Heterocyclic substituted cantharidin and norcantharidin analogues--synthesis, protein phosphatase (1 and 2A) inhibition, and anti-cancer activity.

Norcantharidin (3) is a potent PP1 (IC(50)=9.0+/-1.4 microM) and PP2A (IC(50)=3.0+/-0.4 microM) inhibitor with 3-fold PP2A selectivity and induces growth inhibition (GI(50) approximately 45 microM) across a range of human cancer cell lines including those of colorectal (HT29, SW480), breast (MCF-7), ovarian (A2780), lung (H460), skin (A431), prostate (DU145), neuroblastoma (BE2-C), and glioblastoma (SJ-G2) origin. Until now limited modifications to the parent compound have been tolerated. Surprisingly, simple heterocyclic half-acid norcantharidin analogues are more active than the original lead compound, with the morphilino-substituted (9) being a more potent (IC(50)=2.8+/-0.10 microM) and selective (4.6-fold) PP2A inhibitor with greater in vitro cytotoxicity (GI(50) approximately 9.6 microM) relative to norcantharidin. The analogous thiomorpholine-substituted (10) displays increased PP1 inhibition (IC(50)=3.2+/-0 microM) and reduced PP2A inhibition (IC(50)=5.1+/-0.41 microM), to norcantharidin. Synthesis of the analogous cantharidin analogue (19) with incorporation of the amine nitrogen into the heterocycle further increases PP1 (IC(50)=5.9+/-2.2 microM) and PP2A (IC(50)=0.79+/-0.1 microM) inhibition and cell cytotoxicity (GI(50) approximately 3.3 microM). These analogues represent the most potent cantharidin analogues thus reported.

Synthesis and structure evaluation of a novel cantharimide and its cytotoxicity on SK-Hep-1 hepatoma cells.

A remarkable control of the potency of cantharimide is described based on the electronic properties of functional group and it exhibits a relatively less toxic effect to the non-malignant hematological disorder bone marrow cells.

Apoptogenic activity of a synthetic cantharimide in leukaemia: implication on its structural activity relationship.

Cantharidin isolated from Mylabris caraganae and other insects has been used as an anti-cancer drug in China for many years. However, its toxicity on the renal system and suppression effect on bone marrow limits its usage clinically. A synthetic analogue of cantharidin (CAN 037) has been shown to have cytotoxic effect on the SK-Hep 1 hepatoma cell line but its underlying working principle remains undefined. Here we further report the action of CAN 037 on an acute myelogenous leukaemia (AML) cell line, KG1a. [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) assay was used to demonstrate the cytotoxicity of CAN 037 on KG1a cells. Morphological changes of CAN 037-treated leukaemia cells were recorded under an inverted microscope. Possible activation of caspase 3, 8 and 9 from KG1a cells was also investigated. KG1a AML cells were sensitive to CAN 037. Morphological changes including cell shrinkage and loss of colony formation ability were observed. Caspase 3, 8 and 9 activity was elevated, whereas pre-incubating the KG1a cells with the generic caspase inhibitor z-VAD-fmk could only partially reverse the CAN 037-induced cell death. In addition to the SK-Hep-1 hepatoma cell line, CAN 037 is also effective in inducing the death of KG1a AML cells in vitro. Apoptosis is involved in the action of CAN 037 including the activation of the caspase family. Caspase-dependent cell death pathway may be necessary but not essential in CAN 037-induced apoptosis of KG1a cells. Further consideration of the structural activity relationship of CAN 037 may provide opportunities to improve its therapeutic value.

Cytotoxicity of cantharidin analogues targeting protein phosphatase 2A.

Cantharidin is a natural toxin that possesses potent anti-tumor properties. Its clinical application, however, is limited due to severe side-effects. Its cytotoxicity is believed to be mediated by the inhibition of serine/threonine protein phosphatase 2A. In order to identify new compounds with potential clinical therapeutic use, a series of cantharidin analogues, including those with skeletal modifications at 1-C position (analogues 1-6) and those with anhydride modifications (analogues 7-13), were synthesized, and tested for their inhibitory effects on protein phosphatase 2A and their cytotoxicity to a panel of cancer cell lines. In addition, the mode of inhibition of cantharidin and analogue 13 on protein phosphatase 2A was determined by enzymatic kinetics assay. The data indicated that analogue 13 exhibited potent cytotoxicity to all cancer cell lines, and analogues 9, 11 and 12 showed relatively weak cytotoxicity to one or more cell lines, while other analogues showed little cytotoxicity. Accordingly, analogue 13 exhibited potent inhibitory activity on protein phosphatase 2A, and analogues 9, 11 and 12 showed weak inhibitory activity, while other analogues did not show any inhibitory activity. The findings indicate that the cytotoxicity of synthetic cantharidin analogues is likely to be associated with their protein phosphatase 2A inhibitory activity. The mode of inhibition of cantharidin and analogue 13 on protein phosphatase 2A is identified as noncompetitive inhibition by the Lineweaver-Burk plot.

Mechanistic insight into a novel synthetic cantharidin analogue in a leukaemia model.

Cantharidin isolated from Mylabris caraganae and other insects is used traditionally as an anti-cancer drug especially on hepatoma and leukaemia. Previously, we demonstrated that the novel synthetic cantharidin analogue CAN 032 possessed apoptotic activity on two human hepatoma cell lines Hep3B hepatocellular carcinoma and SK-Hep-1 liver adenocarcinoma. However, its underlying mechanistic action on cancer cells remained unclear. Herein, we furthered our work by making use of KG1a acute myelogenous leukaemia (AML) and K562 chronic myelogenous leukaemia (CML) as experimental models. As anticipated, both leukaemia cell lines were sensitive to the cytotoxic action of CAN 032. The activity of CAN 032 was both dose- and time-course-dependent. CAN 032 readily inhibited the colony formation potential of both leukaemia cell lines. KG1a AML treated with CAN032 decreased G1 phase cell population, mitochondrial membrane potential collapse, caspase 3 activation and hence DNA fragmentation. Pre-incubation of leukaemia cells with the general caspase inhibitor Z-VAD-FMK could partially reversed the apoptotic action of CAN 032. This result suggested that the caspase- dependent pathway is necessary for the apoptotic action of CAN 032. CAN 032 provides a new direction for novel drug discovery in experimental cancer therapy.

Apoptotic activity of a novel synthetic cantharidin analogue on hepatoma cell lines.

Cantharidin isolated from Mylabris caraganae and other insects is used traditionally as an anti-cancer drug. However, its toxicity on the renal system and suppression effect on bone marrow limits its clinical usage. Recently, we have synthesized two cantharidin analogues, CAN 029 (compound 2) and CAN 030 (compound 3). Although both showed an apoptotic induction ability on cancer cells, they were still relatively toxic towards non-malignant haematological disordered bone marrow. Based on the principle structure of cantharidin, we have further chemically synthesized another analogue, CAN 032. The cytotoxic activity of this analogue was screened on both Hep3B hepatocellular carcinoma and SK-Hep-1 liver adenocarcinoma cell lines by [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) assay. Morphological changes of hepatoma cell lines were recorded under an inverted microscope. The possible tolerance of these analogues was further investigated using non-malignant haematological bone marrow primary culture. CAN 032 showed a significant cytotoxic response on both hepatoma cell lines in which the potencies were comparable to that of cantharidin. Further screening on the bone marrow tolerance revealed that compound CAN 032 showed a relatively less toxic effect. Phase contrast microscopy demonstrated that cell shrinkage, rounding, loss of adherent property and loss of colony-formation ability were induced. The dose-dependence of the response of CAN 032 on Hep3B was further assayed by DNA fragmentation gel electrophoresis. The G1 peak of Hep3B cells was reduced. Chemically synthesized CAN 032 may provide an improved therapeutic advantage over traditional cantharidin.

Induction of apoptosis on carcinoma cells by two synthetic cantharidin analogues.

Cantharidin isolated from Mylabris caraganae and other insects has been used as an anti-cancer drug in China for many years. However, its toxicity on the renal system and suppression effect on bone marrow limits its usage clinically. Based on the core structure of cantharidin, we have chemically synthesized two cantharidin analogues (compounds 2 and 3). The cytotoxic activity of these analogues was demonstrated on the Hep3B hepatocellular carcinoma, MDA-MB231 breast cancer, A549 non-small cell lung carcinoma and KG1a acute myelogenous leukaemia (AML) cell lines by monitoring the intracellular adenosine triphosphate level. Morphological changes in these cancer cell lines, including cell shrinkage and loss of adherent potential, were readily observed. By making use of the KG1a AML cells as a test model, we further found that mitochondrial membrane potential depolarization and reduction of intracellular bcl-2 anti-apoptotic protein level were involved. These resulted in the activation of caspase 3 protease activity and oligonucleosomal length DNA fragment formation as detected by both time resolved fluorescence technology-based caspase activity assay and TdT-mediated dUTP nick end-labelling assay.

Structure-based design of a highly selective catalytic site-directed inhibitor of Ser/Thr protein phosphatase 2B (calcineurin).

Protein serine/threonine phosphatases (PP1, PP2A and PP2B) play important roles in intracellular signal transductions. The immunosuppressant drugs FK506 and cyclosporin A (CsA) bind to immunophilins, and these complexes selectively inhibit PP2B (calcineurin), leading to the suppression of T-cell proliferation. Both FK506 and CsA must, however, form complexes with immunophilins to exert their inhibitory action on PP2B. Thus, it is of interest to find a direct and selective inhibitor of PP2B that does not involve the immunophilins as a biological tool for studies of PP2B and also as a candidate therapeutic agent. We selected the simple natural product cantharidin, a known PP2A-selective inhibitor, as a lead compound for this project. Primary SAR indicated that norcantharidin (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride) inhibits not only PP1 and PP2A but also PP2B, and a binding model of norcantharidin carboxylate to the PP2B catalytic site was computationally constructed. Based on this binding model, we designed and synthesized several cantharidin derivatives. Among these compounds, 1,5-dibenzoyloxymethyl-substituted norcantharidin was found to inhibit PP2B without inhibiting PP1 or PP2A. To our knowledge, this is the first highly selective catalytic site-directed inhibitor of PP2B.

Cantharidin analogues: synthesis and evaluation of growth inhibition in a panel of selected tumour cell lines.

Diels-Alder addition of furans (furan, furfuryl alcohol, and 3-bromofuran) to maelic anhydride yields three distinct 5,6-dehydronorcantharidins. Hydrogenation of (4,10-dioxatricyclo[5.2.1.0]decane-3,5-dione) (4a), in dry ethanol affords the monoester (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic aid monoethyl ester) (6). Subsequent transesterification affords a series of monoesters (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid monomethyl ester (7)), 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid monopropyl ester (8), (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid monohexyl ester (9)) and differentially substituted diesters (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid 2-ethyl ester 3-isopropyl ester) (10), and (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid 2-ethyl ester 3-phenyl ester) (11). Analogues were firstly screened for their ability to inhibit protein phosphatases 1 (PP1) and 2A (PP2A) as the lead compounds cantharidin (1) and norcantharidin (2) are known PP1 and PP2A inhibitors. Only analogues 4a, 6-8 displayed good PP1 and PP2A inhibition (PP1 IC(50)'s=2.0, 2.96, 4.71, and 4.82 microM, respectively; PP2A IC(50)'s=0.2, 0.45, 0.41, and 0.47 microM, respectively). All analogues were also screened for their anti-cancer potential against a panel of tumour cell lines, HL60, L1210, SW480, WiDr, HT29, HCT116, A2780, ADDP, and 143B, producing GI(50) values ranging from 6 microM to >1000 microM. Analogues possessing good PP1 and/or PP2A inhibition also returned moderate to good anti-cancer activity. Analogues with substituents directly attached to the intact bicyclo[2.2.1]heptane skeleton were poor to moderate anti-cancer agents. This correlates well with their lack of PP1 or PP2A activity. Analogues capable of undergoing a facile ring opening of the anhydride or with a single carboxylate were good PP1 and PP2A inhibitors, largely correlating to the observed anti-cancer activity in all cases, except 11. Analogue 11, whist neither a PP1 nor a PP2A inhibitor shows anti-cancer activity comparable to 1 and 2. We believe that intracellular esterases generate the corresponding dicarboxylate, which is a potent PP1 and PP2A inhibitor, and that it is this species which is responsible for the observed anti-cancer activity.

The first two cantharidin analogues displaying PP1 selectivity.

High pressure Diels-Alder reactions of furan and dimethylmaleate, and thiophene and maleimide resulted in two cantharidin analogues, 3 and 6 possessing PP1 selectivity (>40- and >30-fold selectivity) over PP2A. Both compounds exhibited moderate PP1 activity, 3 IC(50) 50 microM and 6 IC(50) 12.5 microM. Interestingly, the corresponding mono-ester derivatives of 3 showed no such selectivity.

Cantharimides: a new class of modified cantharidin analogues inhibiting protein phosphatases 1 and 2A.

Cantharidin and its analogues have been of considerable interest as potent inhibitors of the serine/threonine protein phosphatases 1 and 2A (PP1 and PP2A). However, limited modifications to the parent compounds is tolerated. As part of an on-going study we have developed a new series of cantharidin analogues, the cantharimides. Inhibition studies indicate that cantharimides possessing a D- or L-histidine, are more potent inhibitors of PP1 and PP2A (PP1 IC(50)=3.22+/-0.7 microM; PP2A IC(50)=0.81+/-0.1 microM and PP1 IC(50)=2.82+/-0.6 microM; PP2A IC(50)=1.35+/-0.3 microM, respectively) than norcantharidin (PP1 IC(50)=5.31+/-0.76 microM; PP2A IC(50)=2.9+/-1.04 microM) and essentially equipotent with cantharidin (PP1 IC(50)=3.6+/-0.42 microM; PP2A IC(50)=0.36+/-0.08 microM). Cantharimides with non-polar or acidic amino acid residues are only poor inhibitors of PP1 and PP2A.

The inhibition of protein phosphatases 1 and 2A: a new target for rational anti-cancer drug design?

Recent investigations in our laboratories have highlighted that the inhibition of the serine/threonine protein phosphatases 1 and 2A (PP1 and PP2A) is an excellent target for the development of novel anti-cancer agents. Using a combination of the known crystal structure of PP1 and the modelled structure of PP2A, we have rationally designed a new class of protein phosphatase inhibitors, cantharimides, which exhibit broad-spectrum anti-cancer activity. Synthetic modifications of the simplest known PP1 and PP2A inhibitor, norcantharidin, has led to the development of potent PP1 and PP2A inhibitors.