Prognostic signs and the role of operative management in acute pancreatitis

Nox4-dependent ROS modulation by amino endoperoxides to induce apoptosis in cancer cells

Tumor metastasis is the main cause of death in cancer patients. Anoikis resistance is one critical malefactor of metastatic cancer cells to resist current clinical chemotherapeutic treatments. Although endoperoxide-containing compounds have long been suggested as anticancer drugs, few have been clinically employed due to their instability, complex synthesis procedure or low tumor cell selectivity. Herein, we describe a one-pot strategy to synthesize novel amino endoperoxides and their derivatives with good yields and stabilities. In vitro cell-based assays revealed that 4 out of the 14 amino endoperoxides selectively induce metastatic breast carcinoma cells but not normal breast cells to undergo apoptosis, in a dose-dependent manner. Mechanistic studies showed that the most potent amino endoperoxide, 4-Me, is selective for cancer cells expressing a high level of Nox4. The anticancer effects are further shown to be associated with reduced O₂⁻:H₂O₂ ratio and increased ·OH level in the cancerous cells. Animal study showed that 4-Me impairs orthotopic breast tumor growth as well as tumor cell metastasis to lymph nodes. Altogether, our study suggests that anticancer strategies that focus on redox-based apoptosis induction in tumors are clinically viable.

pH-responsive artemisinin derivatives and lipid nanoparticle formulations inhibit growth of breast cancer cells in vitro and induce down-regulation of HER family members

Artemisinin (ART) dimers show potent anti-proliferative activities against breast cancer cells. To facilitate their clinical development, novel pH-responsive artemisinin dimers were synthesized for liposomal nanoparticle formulations. A new ART dimer was designed to become increasingly water-soluble as pH declines. The new artemisinin dimer piperazine derivatives (ADPs) remained tightly associated with liposomal nanoparticles (NPs) at neutral pH but were efficiently released at acidic pH's that are known to exist within solid tumors and organelles such as endosomes and lysosomes. ADPs incorporated into nanoparticles down regulated the anti-apoptotic protein, survivin, and cyclin D1 when incubated at low concentrations with breast cancer cell lines. We demonstrate for the first time, for any ART derivative, that ADP NPs can down regulate the oncogenic protein HER2, and its counterpart, HER3 in a HER2+ cell line. We also show that the wild type epidermal growth factor receptor (EGFR or HER1) declines in a triple negative breast cancer (TNBC) cell line in response to ADP NPs. The declines in these proteins are achieved at concentrations of NP109 at or below 1 µM. Furthermore, the new artemisinin derivatives showed improved cell-proliferation inhibition effects compared to known dimer derivatives.

Antiproliferative effects of artemisinin on human breast cancer cells requires the downregulated expression of the E2F1 transcription factor and loss of E2F1-target cell cycle genes

Artemisinin, a sesquiterpene phytolactone derived from Artemisia annua, is a potent antimalarial compound with promising anticancer properties, although the mechanism of its anticancer signaling is not well understood. Artemisinin inhibited proliferation and induced a strong G1 cell cycle arrest of cultured MCF7 cells, an estrogen-responsive human breast cancer cell line that represents an early-stage cancer phenotype, and effectively inhibited the in-vivo growth of MCF7 cell-derived tumors from xenografts in athymic nude mice. Artemisinin also induced a growth arrest of tumorigenic human breast cancer cell lines with preneoplastic and late stage cancer phenotypes, but failed to arrest the growth of a nontumorigenic human mammary cell line. Concurrent with the cell cycle arrest of MCF7 cells, artemisinin selectively downregulated the transcript and protein levels of the CDK2 and CDK4 cyclin-dependent kinases, cyclin E, cyclin D1, and the E2F1 transcription factor. Analysis of CDK2 promoter-luciferase reporter constructs showed that the artemisinin ablation of CDK2 gene expression was accounted for by the loss of CDK2 promoter activity. Chromatin immunoprecipitation revealed that artemisinin inhibited E2F1 interactions with the endogenous MCF7 cell CDK2 and cyclin E promoters. Moreover, constitutive expression of exogenous E2F1 prevented the artemisinin-induced cell cycle arrest and downregulation of CDK2 and cyclin E gene expression. Taken together, our results demonstrate that the artemisinin disruption of E2F1 transcription factor expression mediates the cell cycle arrest of human breast cancer cells and represents a critical transcriptional pathway by which artemisinin controls human reproductive cancer cell growth.

Menthol induces cell-cycle arrest in PC-3 cells by down-regulating G2/M genes, including polo-like kinase 1

Menthol, a naturally occurring monoterpene, is used in foods, cosmetic products, and topical therapeutic preparations. It also exerts cytotoxic activity against several cancer cell types, including prostate cancer cells. However, little is known about the mechanism of menthol action against prostate cancer cells. In this study, we investigated the effect of menthol on the gene expression profile of PC-3 prostate cancer cells using DNA microarray analyses. Gene set enrichment analysis revealed that menthol primarily affects the expression of cell cycle-related genes. Subsequent experimental analyses validated that menthol induces G2/M arrest. Particularly, menthol markedly down-regulated polo-like kinase 1 (PLK1), a key regulator of G2/M phase progression and inhibited its downstream signaling. Our computational analyses and experimental validation provide a basis for future investigations that are aimed at elucidating the action of menthol on cell cycle control in prostate cancer cells.

Antitumor activity of artemisinin and its derivatives: from a well-known antimalarial agent to a potential anticancer drug

Improvement of quality of life and survival of cancer patients will be greatly enhanced by the development of highly effective drugs to selectively kill malignant cells. Artemisinin and its analogs are naturally occurring antimalarials which have shown potent anticancer activity. In primary cancer cultures and cell lines, their antitumor actions were by inhibiting cancer proliferation, metastasis, and angiogenesis. In xenograft models, exposure to artemisinins substantially reduces tumor volume and progression. However, the rationale for the use of artemisinins in anticancer therapy must be addressed by a greater understanding of the underlying mechanisms involved in their cytotoxic effects. The primary targets for artemisinin and the chemical base for its preferential effects on heterologous tumor cells need yet to be elucidated. The aim of this paper is to provide an overview of the recent advances and new development of this class of drugs as potential anticancer agents.

Identification of the Schistosoma mansoni molecular target for the antimalarial drug artemether

Plasmodium falciparum and Schistosoma mansonii are the parasites responsible for most of the malaria and schistosomiasis cases in the world. Notwithstanding their many differences, the two agents have striking similarities in that they both are blood feeders and are targets of an overlapping set of drugs, including the well-known artemether molecule. Here we explore the possibility of using the known information about the mode of action of artemether in Plasmodium to identify the molecular target of the drug in Schistosoma and provide evidence that artemether binds to SmSERCA, a putative Ca²⁺-ATPase of Schistosoma . We also predict the putative binding mode of the molecule for both its Plasmodium and Schistosoma targets. Our analysis of the mode of binding of artemether to Ca²⁺-ATPases also provides an explanation for the apparent paradox that, although the molecule has no side effect in humans, it has been shown to possess antitumoral activity.

Characterization of dihydroartemisinin-resistant colon carcinoma HCT116/R cell line

Dihydroartemisinin (DHA) is an important artemisinin derivative and presents profound anti-tumor potential. A DHA-resistant cell line named HCT116/R derived from colon carcinoma cell line HCT116 was established in our previous study. Herein, we found that HCT116/R cells were much more resistant to DHA- or artesunate-induced proliferation inhibition and more tolerant to DHA-induced cell cycle arrest and apoptosis compared with those of the parent HCT116 cells. The protein levels of P-glycoprotein and MDR-associated protein 1 and the accumulation of doxorubicin in cells were similar in both cell lines. Moreover, HCT116/R cells were still sensitive to camptothecin- and doxorubicin-induced cell growth inhibition. To further explore the characterization of HCT116/R cell line, a proteomic study employing two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was performed. Eight different expressed proteins between the two cell lines were identified including some heat shock proteins, annexins, etc. This study not only indicates that exposure to DHA may not induce a tumor multi-drug-resistant phenotype but also affords new clues for the further investigation of the anti-cancer mechanisms of DHA and other artemisinin derivatives.

Anti-cancer natural products isolated from chinese medicinal herbs

In recent years, a number of natural products isolated from Chinese herbs have been found to inhibit proliferation, induce apoptosis, suppress angiogenesis, retard metastasis and enhance chemotherapy, exhibiting anti-cancer potential both in vitro and in vivo. This article summarizes recent advances in in vitro and in vivo research on the anti-cancer effects and related mechanisms of some promising natural products. These natural products are also reviewed for their therapeutic potentials, including flavonoids (gambogic acid, curcumin, wogonin and silibinin), alkaloids (berberine), terpenes (artemisinin, β-elemene, oridonin, triptolide, and ursolic acid), quinones (shikonin and emodin) and saponins (ginsenoside Rg3), which are isolated from Chinese medicinal herbs. In particular, the discovery of the new use of artemisinin derivatives as excellent anti-cancer drugs is also reviewed.

Anti-cancer natural products isolated from chinese medicinal herbs

In recent years, a number of natural products isolated from Chinese herbs have been found to inhibit proliferation, induce apoptosis, suppress angiogenesis, retard metastasis and enhance chemotherapy, exhibiting anti-cancer potential both in vitro and in vivo. This article summarizes recent advances in in vitro and in vivo research on the anti-cancer effects and related mechanisms of some promising natural products. These natural products are also reviewed for their therapeutic potentials, including flavonoids (gambogic acid, curcumin, wogonin and silibinin), alkaloids (berberine), terpenes (artemisinin, β-elemene, oridonin, triptolide, and ursolic acid), quinones (shikonin and emodin) and saponins (ginsenoside Rg₃), which are isolated from Chinese medicinal herbs. In particular, the discovery of the new use of artemisinin derivatives as excellent anti-cancer drugs is also reviewed.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

The redox antimalarial dihydroartemisinin targets human metastatic melanoma cells but not primary melanocytes with induction of NOXA-dependent apoptosis

Recent research suggests that altered redox control of melanoma cell survival, proliferation, and invasiveness represents a chemical vulnerability that can be targeted by pharmacological modulation of cellular oxidative stress. The endoperoxide artemisinin and semisynthetic artemisinin-derivatives including dihydroartemisinin (DHA) constitute a major class of antimalarials that kill plasmodium parasites through induction of iron-dependent oxidative stress. Here, we demonstrate that DHA may serve as a redox chemotherapeutic that selectively induces melanoma cell apoptosis without compromising viability of primary human melanocytes. Cultured human metastatic melanoma cells (A375, G361, LOX) were sensitive to DHA-induced apoptosis with upregulation of cellular oxidative stress, phosphatidylserine externalization, and activational cleavage of procaspase 3. Expression array analysis revealed DHA-induced upregulation of oxidative and genotoxic stress response genes (GADD45A, GADD153, CDKN1A, PMAIP1, HMOX1, EGR1) in A375 cells. DHA exposure caused early upregulation of the BH3-only protein NOXA, a proapototic member of the Bcl2 family encoded by PMAIP1, and genetic antagonism (siRNA targeting PMAIP1) rescued melanoma cells from apoptosis indicating a causative role of NOXA-upregulation in DHA-induced melanoma cell death. Comet analysis revealed early DHA-induction of genotoxic stress accompanied by p53 activational phosphorylation (Ser 15). In primary human epidermal melanocytes, viability was not compromised by DHA, and oxidative stress, comet tail moment, and PMAIP1 (NOXA) expression remained unaltered. Taken together, these data demonstrate that metastatic melanoma cells display a specific vulnerability to DHA-induced NOXA-dependent apoptosis and suggest feasibility of future anti-melanoma intervention using artemisinin-derived clinical redox antimalarials.

Artesunate mitigates proliferation of tumor cells by alkylating heme-harboring nitric oxide synthase

Artesunate (ART), a semi-synthetic derivative of antimalarial artemisinin, kills cancer cells with uncertain mechanisms. Here, we report for the first time that ART may exert the anti-tumor activity by conjugating the prosthetic heme of hemoproteins in a hepatoma cell line, HepG2, which was evident by monitoring the shift of absorbance from heme (A₄₁₅) to the ART-heme adduct (A₄₇₆). Accordingly, a transient elevation of A₄₁₅ was observed with a synchronous burst of nitric oxide (NO) and a high rate of survival following incubation of HepG2 with 50 μM ART. In contrast, ART at above 100 μM led to an abrogation of NO generation and a decline of the survival rate in HepG2. These data implied that heme-containing nitric oxide synthase (NOS) may represent a major cellular target of ART in killing tumor cells.

Heme as trigger and target for trioxane-containing antimalarial drugs

Heme is not only just the binding site responsible for oxygen transport by hemoglobin, but it is also the prosthetic group of many different heme-containing enzymes, such as cytochromes P450, peroxidases, catalase, and several proteins involved in electron transfer. Heme plays a key role in the mechanism of action of many different antimalarial drugs. In degrading the host's hemoglobin, the malaria parasite Plasmodium and several other heme-eating parasites are faced with this redox-active metal complex. Heme is able to induce the toxic reductive cascade of molecular oxygen, which leads to the production of destructive hydroxyl radicals. Plasmodium detoxifies heme by converting it into a redox-inactive iron(III) polymer called hemozoin. Artemisinin, a natural drug containing a biologically important 1,2,4-trioxane structure, is now the first-line treatment for multidrug-resistant malaria. The peroxide moiety in artemisinin reacts in the presence of the flat, achiral iron(II)-heme; the mechanism does not reflect the classical "key and lock" paradigm for drugs. Instead, the reductive activation of the peroxide function generates a short-lived alkoxy radical, which quickly rearranges to a C-centered primary radical. This radical alkylates heme via an intramolecular process to produce covalent heme-drug adducts. The accumulation of non-polymerizable redox-active heme derivatives, a consequence of heme alkylation, is thought to be toxic for the parasite. The alkylation of heme by artemisinin has been demonstrated in malaria-infected mice, indicating that heme is acting as the trigger and target of artemisinin. The alkylation of heme by artemisinin is not limited to this natural compound: the mechanism is invoked for a large number of antimalarial semisynthetic derivatives. Synthetic trioxanes or trioxolanes also alkylate heme, and their alkylation ability correlates well with their antimalarial efficacy. In addition, several reports have demonstrated the cytotoxicity of artemisinin derivatives toward several tumor cell lines. Deoxy analogues were just one-fiftieth as active or less, showing the importance of the peroxide bridge. The involvement of heme in anticancer activity has thus also been proposed. The anticancer mechanism of endoperoxide-containing molecules, however, remains a challenging area, but one that offers promising rewards for research success. Although it is not a conventional biological target, heme is the master piece of the mechanism of action of peroxide-containing antimalarial drugs and could well serve as a target for future anticancer drugs.

Investigations into the role of the Plasmodium falciparum SERCA (PfATP6) L263E mutation in artemisinin action and resistance

Artemisinin-based combination therapies (ACTs) are highly effective for the treatment of Plasmodium falciparum malaria, yet their sustained efficacy is threatened by the potential spread of parasite resistance. Recent studies have provided evidence that artemisinins can inhibit the function of PfATP6, the P. falciparum ortholog of the ER calcium pump SERCA, when expressed in Xenopus laevis oocytes. Inhibition was significantly reduced in an L263E variant, which introduced the mammalian residue into a putative drug-binding pocket. To test the hypothesis that this single mutation could decrease P. falciparum susceptibility to artemisinins, we implemented an allelic-exchange strategy to replace the wild-type pfatp6 allele by a variant allele encoding L263E. Transfected P. falciparum clones were screened by PCR analysis for disruption of the endogenous locus and introduction of the mutant L263E allele under the transcriptional control of a calmodulin promoter. Expression of the mutant allele was demonstrated by reverse transcriptase (RT) PCR and verified by sequence analysis. Parasite clones expressing wild-type or L263E variant PfATP6 showed no significant difference in 50% inhibitory concentrations (IC(50)s) for artemisinin or its derivatives dihydroartemisinin and artesunate. Nonetheless, hierarchical clustering analysis revealed a trend toward reduced susceptibility that neared significance (artemisinin, P approximately = 0.1; dihydroartemisinin, P = 0.053 and P = 0.085; and artesunate, P = 0.082 and P = 0.162 for the D10 and 7G8 lines, respectively). Notable differences in the distribution of normalized IC(50)s provided evidence of decreased responsiveness to artemisinin and dihydroartemisinin (P = 0.02 for the D10 and 7G8 lines), but not to artesunate in parasites expressing mutant PfATP6.

The anti-cancer activity of dihydroartemisinin is associated with induction of iron-dependent endoplasmic reticulum stress in colorectal carcinoma HCT116 cells

Dihydroartemisinin (DHA), the main active metabolite of artemisinin derivatives, is among the artemisinin derivatives possessing potent anti-malarial and anti-cancer activities. In the present study, we found that DHA displayed significant anti-proliferative activity in human colorectal carcinoma HCT116 cells, which may be attributed to its induction of G1 phase arrest and apoptosis. To further elucidate the mechanism of action of DHA, a proteomic study employed two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was performed. Glucose-regulated protein 78 (GRP78), which is related with endoplasmic reticulum stress (ER stress), was identified to be significantly up-regulated after DHA treatment. Further study demonstrated that DHA enhanced expression of GRP78 as well as growth arrest and DNA-damage-inducible gene 153 (GADD153, another ER stress-associated molecule) at both mRNA and protein levels. DHA treatment also led to accumulation of GADD153 in cell nucleus. Moreover, pretreatment of HCT116 cells with the iron chelator deferoxamine mesylate salt (DFO) abrogated induction of GRP78 and GADD153 upon DHA treatment, indicating iron is required for DHA-induced ER stress. This result is consistent with the fact that the anti-proliferative activity of DHA is also mediated by iron. We thus suggest the unbalance of redox may result in DHA-induced ER stress, which may contribute, at least in part, to its anti-cancer activity.

Subcellular localization of a fluorescent artemisinin derivative to endoplasmic reticulum

A cytotoxic artemisinin derivative conjugated with a fluorescent dansyl moiety was synthesized and its subcellular localization in Hep3B cells was examined. Comparison of the localization signals of the fluorescent artemisinin derivative with organelle specific dyes revealed that endoplasmic reticulum (ER) is the main site of its accumulation.

Effect of artemisinin derivatives on apoptosis and cell cycle in prostate cancer cells

Artemisinin is a plant-derived anti-malarial drug that has relatively low toxicity in humans and is activated by heme and/or intracellular iron leading to intracellular free radical formation. Interestingly, artemisinin has displayed anti-cancer activity, with artemisinin dimers being more potent than monomeric artemisinin. Intracellular iron uptake is regulated by the transferrin receptor (TfR), and the activity of artemisinin depends on the availability of iron. We examined the level of TfR in prostate cancer (PCa) tumor cells, synthesized two new artemisinin dimers, and evaluated the effect of dihydroartemisinin and artemisinin dimers, ON-2Py and 2Py, on proliferation and apoptosis in PCa cells. TfR was expressed in the majority of PCa bone and soft tissue metastases, all 24 LuCaP PCa xenografts, and PCa cell lines. After treatment with dihydroartemisinin, ON-2Py, or 2Py all PCa cell lines displayed dose-dependent decrease in cell number. 2Py was most effective in decreasing cell number. An increase in apoptotic events and growth arrest was observed in the C4-2 and LNCaP cell lines. Growth arrest was observed in PC-3 cells, but no significant change was observed in DU 145 cells. Treatment with 2Py resulted in a loss of the anti-apoptotic protein survivin in all four cell lines. 2Py treatment also decreased androgen receptor and prostate-specific antigen expression in C4-2 and LNCaP cells, with a concomitant loss of cell cycle regulatory proteins cyclin D1 and c-Myc. This study shows the potential use of artemisinin derivatives as therapeutic candidates for PCa and warrants the initiation of preclinical studies.

Purified E255L mutant SERCA1a and purified PfATP6 are sensitive to SERCA-type inhibitors but insensitive to artemisinins

The antimalarial drugs artemisinins have been described as inhibiting Ca(2+)-ATPase activity of PfATP6 (Plasmodium falciparum ATP6) after expression in Xenopus oocytes. Mutation of an amino acid residue in mammalian SERCA1 (Glu(255)) to the equivalent one predicted in PfATP6 (Leu) was reported to induce sensitivity to artemisinin in the oocyte system. However, in the present experiments, we found that artemisinin did not inhibit mammalian SERCA1a E255L either when expressed in COS cells or after purification of the mutant expressed in Saccharomyces cerevisiae. Moreover, we found that PfATP6 after expression and purification from S. cerevisiae was insensitive to artemisinin and significantly less sensitive to thapsigargin and 2,5-di(tert-butyl)-1,4-benzohydroquinone than rabbit SERCA1 but retained higher sensitivity to cyclopiazonic acid, another type of SERCA1 inhibitor. Although mammalian SERCA and purified PfATP6 appear to have different pharmacological profiles, their insensitivity to artemisinins suggests that the mechanism of action of this class of drugs on the calcium metabolism in the intact cell is complex and cannot be ascribed to direct inhibition of PfATP6. Furthermore, the successful purification of PfATP6 affords the opportunity to develop new antimalarials by screening for inhibitors against PfATP6.

Heme synthesis increases artemisinin-induced radical formation and cytotoxicity that can be suppressed by superoxide scavengers

Artemisinin (ART) is a sesquiterpene lactone natural product that is widely used to treat multi-drug resistant strains of malaria. Artemisinin and its derivatives are also selectively cytotoxic to cancer cells, which can be modulated by altering heme synthesis. Cytotoxicity to cancer cells is thought to involve generation of oxidative stress, although conflicting data exist. We have analyzed reactive oxygen species (ROS) generation using the fluorescent probes 2',7'-dichlorodihydrofluorescein diacetate (DCF) and dihydroethidine (HET) upon exposure to dihydroartemisinin (DHA) in Molt-4 leukemia cells. HET fluorescence correlated with dose-dependent DHA-induced cytotoxicity, increased within 30 min of DHA exposure, and was significantly enhanced by increasing heme synthesis. Protein levels of copper, zinc-superoxide dismutase (CuZnSOD), manganese-superoxide dismutase (MnSOD), catalase, and glutathione peroxidases 1/2 were also found to increase with DHA exposure. 4-hydroxy-tempol (TEMPOL) and DF-Mn, MnSOD mimetics, could significantly inhibit ROS generation and reduce cell death. Production of superoxide appears to be a central mediator of cytotoxicity from DHA.

The molecular mechanism of action of artemisinin--the debate continues

Despite international efforts to 'roll back malaria' the 2008 World Malaria Report revealed the disease still affects approximately 3 billion people in 109 countries; 45 within the WHO African region. The latest report however does provide some 'cautious optimism'; more than one third of malarious countries have documented greater than 50% reductions in malaria cases in 2008 compared to 2000. The goal of the Member States at the World Health Assembly and 'Roll Back Malaria' (RBM) partnership is to reduce the numbers of malaria cases and deaths recorded in 2000 by 50% or more by the end of 2010. Although malaria is preventable it is most prevalent in poorer countries where prevention is difficult and prophylaxis is generally not an option. The burden of disease has increased by the emergence of multi drug resistant (MDR) parasites which threatens the use of established and cost effective antimalarial agents. After a major change in treatment policies, artemisinins are now the frontline treatment to aid rapid clearance of parasitaemia and quick resolution of symptoms. Since artemisinin and its derivatives are eliminated rapidly, artemisinin combination therapies (ACT's) are now recommended to delay resistance mechanisms. In spite of these precautionary measures reduced susceptibility of parasites to the artemisinin-based component of ACT's has developed at the Thai-Cambodian border, a historical 'hot spot' for MDR parasite evolution and emergence. This development raises serious concerns for the future of the artemsinins and this is not helped by controversy related to the mode of action. Although a number of potential targets have been proposed the actual mechanism of action remains ambiguous. Interestingly, artemisinins have also shown potent and broad anticancer properties in cell lines and animal models and are becoming established as anti-schistosomal agents. In this review we will discuss the recent evidence explaining bioactivation and potential molecular targets in the chemotherapy of malaria and cancer.

Dihydroartemisinin accelerates c-MYC oncoprotein degradation and induces apoptosis in c-MYC-overexpressing tumor cells

Artemisinin and its derivatives (ARTs) are effective antimalarial drugs and also possess profound anticancer activity. However, the mechanism accounted for its distinctive activity in tumor cells remains unelucidated. We computed Pair wise Pearson correlation coefficients to identify genes that show significant correlation with ARTs activity in NCI-55 cell lines using data obtained from studies with HG-U133A Affymetrix chip. We found c-myc is one of the genes that showed the highest positive correlation coefficients among the probe sets analyzed (r=0.585, P<0.001). Dihydroartemisinin (DHA), the main active metabolite of ARTs, induced significant apoptosis in HL-60 and HCT116 cells that express high levels of c-MYC. Stable knockdown of c-myc abrogated DHA-induced apoptosis in HCT116 cells. Conversely, forced expression of c-myc in NIH3T3 cells sensitized these cells to DHA-induced apoptosis. Interestingly, DHA irreversibly down-regulated the protein level of c-MYC in DHA-sensitive HCT116 cells, which is consistent to persistent G1 phase arrest induced by DHA. Further studies demonstrated that DHA accelerated the degradation of c-MYC protein and this process was blocked by pretreatment with the proteasome inhibitor MG-132 or GSK 3beta inhibitor LiCl in HCT116 cells. Taken together, ARTs might be useful in the treatment of c-MYC-overexpressing tumors. We also suggest that c-MYC may potentially be a biomarker candidate for prediction of the antitumor efficacies of ARTs.

Antiprotozoal, anticancer and antimicrobial activities of dihydroartemisinin acetal dimers and monomers

Nine dihydroartemisinin acetal dimers (6-14) with diversely functionalized linker units were synthesized and tested for in vitro antiprotozoal, anticancer and antimicrobial activity. Compounds 6, 7 and 11 [IC(50): 3.0-6.7 nM (D6) and 4.2-5.9 nM (W2)] were appreciably more active than artemisinin (1) [IC(50): 32.9 nM (D6) and 42.5 nM (W2)] against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of the malaria parasite, Plasmodium falciparum. Compounds 10, 13 and 14 displayed enhanced anticancer activity in a number of cell lines compared to the control drug, doxorubicin. The antifungal activity of 7 and 12 against Cryptococcus neoformans (IC(50): 0.16 and 0.55 microM, respectively) was also higher compared to the control drug, amphotericin B. The antileishmanial and antibacterial activities were marginal. A number of dihydroartemisinin acetal monomers (15-17) and a trimer (18) were isolated as byproducts from the dimer synthesis and were also tested for biological activity.