Heme mediates cytotoxicity from artemisinin and serves as a general anti-proliferation target

New hydrazide derivatives of N-amino-11-azaartemisinin as promising epidermal growth factor receptor inhibitors for therapeutic development in triple-negative breast cancer

Triple-negative breast cancer (TNBC) treatments, such as DNA-damaging agents like carboplatin, pose considerable human toxicity and may contribute to cancer relapse. Artemisinin derivatives offer a less toxic alternative; however, their specific role in TNBC management remains to be established. To address this gap, computational models were employed to design and evaluate artemisinin-based prototypes as potential TNBC therapeutics, aiming to provide safer and more effective treatment options for this aggressive cancer subtype. Among the series of hydrazide derivatives of azaartemisinin (10a-l) reported herein, compound 10j emerged as the most promising, exhibiting notable cytotoxicity with IC50 values of 1.74 and 1.64 µM against MDA-MB-231 and MDA-MB-468 cells, respectively. The clinically useful drug doxorubicin provided IC50 values of 0.29 and 0.29 µM against MDA-MB-231 and MDA-MB-468 cells, while artemisinin provided IC50 values of 107.30 and 116.60 µM, respectively. Furthermore, putative interactions between the synthesized compounds and the epidermal growth factor receptor (EGFR) were identified using molecular docking studies, suggesting a possible mechanism for their anticancer effect. Additionally, to determine the thermodynamic parameters of the interactions between artemisinin, azaartemisinin, and biomolecules, isothermal titration calorimetry experiments were performed. The binding constant value on the order of 104 indicates a comparatively stronger binding affinity of azaartemisinin with human serum albumin (HSA) compared to artemisinin with HSA. These findings support the potential of azaartemisinin derivatives as promising EGFR inhibitors for therapeutic development in TNBC, offering a new avenue for less toxic and more effective cancer treatments.

Diversified Synthesis of N-Benzoyl Piperidine Tetraoxane Analogues Using Molybdenum Trioxide as a Newer Catalyst and Its Antiplasmodial Activity

Molybdenum trioxide has been proven to be an efficient catalyst in synthesizing mixed N-benzoyl piperidine dispiro-1,2,4,5-tetraoxane analogues using a one-pot reaction. This catalyst facilitated the synthesis of 21 tetraoxanes using cyclic, acyclic, and aromatic ketones. The structure and methodology of this reaction have been validated by single-crystal X-ray analysis of compound ″3g″. The nature of dispiro-1,2,4,5-tetraoxane being synthesized has an impact on the overall yield of tetraoxanes such as symmetric dispiro-1,2,4,5-tetraoxanes ranging from 53 to 82%, while yields of N-benzoyl piperidine dispiro-1,2,4,5-tetraoxanes ranged from 26 to 51%. Additionally, the in vitro antiplasmodial activity of the newly developed tetraoxanes against Plasmodium falciparum was assessed, which exhibited significantly higher activity in the nanomolar range, with values ranging from 6.35 to 44.65 nM. Molecular docking studies revealed that newer tetraoxane derivatives bind to the active site of the falcipain-2 enzyme through H-bonding and hydrophobic contacts, which are the primary indicators of the effectiveness of the synthesized compounds. Findings suggest that these peculiar compounds may act as antiplasmodial agents, which spur further study and advancement in the battle against malaria.

GPX4 inhibition synergistically boosts mitochondria targeting nanoartemisinin-induced apoptosis/ferroptosis combination cancer therapy

Artemisinin, originally used for its antimalarial activity, has received much attention in recent years for cancer therapy. The anticancer mechanisms of artemisinin are complicated and debatable. Challenges in the delivery of artemisinin also persist because the anticancer effect of artemisinin alone is often not satisfactory when used with traditional nanocarriers. We herein report the mitochondrial delivery of artemisinin with extremely high anticancer capacity. The action mode of artemisinin in the mitochondria of cancer cells includes heme-participating and oxygen-independent conversion of artemisinin into a carbon-centered radical, which is partly converted into ROS in the presence of molecular oxygen. We reveal that artemisinin alone in the mitochondria can induce strong cancer cell apoptosis. In addition, due to the weak inhibition of GPX4 activity by artemisinin, weak ferroptosis is also observed. We further discover that GPX4 activity in MCF-7 cells is greatly inhibited by RSL3 to synergistically enhance the anticancer capacity of artemisinin via enhancing ferroptosis. The synergistic anticancer activity of artemisinin and RSL3 in the mitochondria not only improves cancer cell-killing ability, but also inhibits the re-proliferation of residual cancer cells. This study provides a new insight into developing highly efficient and practical artemisinin nanomedicines for cancer therapy.

Zinc Protoporphyrin-9 Potentiates the Anticancer Activity of Dihydroartemisinin

Besides the clinically proven superior antimalarial activity, artemisinins (ARTs) are also associated with anticancer properties, albeit at much lower potency. Iron and heme have been proposed as possible activators of ARTs against cancer cells. Here we show that zinc protoporphyrin-9 (ZnPPIX), a heme homolog and a natural metabolite for heme synthesis during iron insufficiency, greatly enhanced the anticancer activity of dihydroartemisinin (DHA) in multiple cell lines. Using melanoma B16 and breast cancer 4T1 cells, we demonstrated ZnPPIX dramatically elevated intracellular free heme levels, accompanied by heightened reactive oxidative species (ROS) production. The tumor-suppression activity of ZnPPIX and DHA is mitigated by antioxidant vitamin E or membrane oxidation protectant ferrostatin. In vivo xenograft animal models confirmed that ZnPPIX significantly potentiated the tumor-inhibition capability of DHA while posing no apparent toxicity to the mice. The proliferating index and growth of tumors after the combinatory treatment of DHA and ZnPPIX were evidently reduced. Considering the clinical safety profiles of both DHA and ZnPPIX, their action synergy offers a promising strategy to improve the application of ARTs in our fight against cancer.

The antimalarial artemisinin is a non-electrophilic agonist of the transient receptor potential ankyrin type 1 receptor-channel

Artemisinin and its derivatives are the main therapeutic drugs against Plasmodium protists, the causative agents of malaria. While several putative mechanisms of action have been proposed, the precise molecular targets of these compounds have not been fully elucidated. In addition to their antimalarial properties, artemisinins have been reported to act as anti-tumour agents and certain antinociceptive effects have also been proposed. We investigated the effect of the parent compound, artemisinin, on a number of temperature-gated Transient Receptor Potential ion channels (so called thermoTRPs), given their demonstrated roles in pain-sensing and cancer. We report that artemisinin acts as an agonist of the Transient Receptor Potential Ankyrin type 1 (TRPA1) receptor channel. Artemisinin was able to evoke calcium transients in HEK293T cells expressing recombinant human TRPA1, as well as in a subpopulation of mouse dorsal root ganglion (DRG) neurons which also responded to the selective TRPA1 agonist allyl isothiocyanate (AITC) and these responses were reversibly abolished by the selective TRPA1 antagonist A967079. Artemisinin also triggered whole-cell currents in HEK293T cells transiently transfected with human TRPA1, as well as in TRPA1-expressing DRG neurons, and these currents were inhibited by A967079. Interestingly, using human TRPA1 mutants, we demonstrate that artemisinin acts as a non-electrophilic agonist of TRPA1, activating the channel in a similar manner to carvacrol and menthol. These results may provide a better understanding of the biological actions of the very important antimalarial and anti-tumour agent artemisinin.

Artesunate Inhibits the Growth Behavior of Docetaxel-Resistant Prostate Cancer Cells

Novel therapeutic strategies are urgently needed for advanced metastatic prostate cancer (PCa). Phytochemicals used in Traditional Chinese Medicine seem to exhibit tumor suppressive properties. Therefore, the therapeutic potential of artesunate (ART) on the progressive growth of therapy-sensitive (parental) and docetaxel (DX)-resistant PCa cells was investigated. Parental and DX-resistant PCa cell lines DU145, PC3, and LNCaP were incubated with artesunate (ART) [1-100 µM]. ART-untreated and 'non-cancerous' cells served as controls. Cell growth, proliferation, cell cycle progression, cell death and the expression of involved proteins were evaluated. ART, dose- and time-dependently, significantly restricted cell growth and proliferation of parental and DX-resistant PCa cells, but not of 'normal, non-cancerous' cells. ART-induced growth and proliferation inhibition was accompanied by G0/G1 phase arrest and down-regulation of cell cycle activating proteins in all DX-resistant PCa cells and parental LNCaP. In the parental and DX-resistant PC3 and LNCaP cell lines, ART also promoted apoptotic cell death. Ferroptosis was exclusively induced by ART in parental and DX-resistant DU145 cells by increasing reactive oxygen species (ROS). The anti-cancer activity displayed by ART took effect in all three PCa cell lines, but through different mechanisms of action. Thus, in advanced PCa, ART may hold promise as a complementary treatment together with conventional therapy.

Ferroptosis: A Novel Mechanism of Artemisinin and its Derivatives in Cancer Therapy

BACKGROUND

Artemisinin is a sesquiterpene lactone compound with a special peroxide bridge that is tightly linked to the cytotoxicity involved in fighting malaria and cancer. Artemisinin and its derivatives (ARTs) are considered to be potential anticancer drugs that promote cancer cell apoptosis, induce cell cycle arrest and autophagy, inhibit cancer cell invasion and migration. Additionally, ARTs significantly increase intracellular Reactive Oxygen Species (ROS) in cancer cells, which result in ferroptosis, a new form of cell death, depending on the ferritin concentration. Ferroptosis is regarded as a cancer suppressor and as well as considered a new mechanism for cancer therapy.

METHODS

The anticancer activities of ARTs and reference molecules were compared by literature search and analysis. The latest research progress on ferroptosis was described, with a special focus on the molecular mechanism of artemisinin-induced ferroptosis.

RESULTS

Artemisinin derivatives, artemisinin-derived dimers, hybrids and artemisinin-transferrin conjugates, could significantly improve anticancer activity, and their IC50 values are lower than those of reference molecules such as doxorubicin and paclitaxel. The biological activities of linkers in dimers and hybrids are important in the drug design processes. ARTs induce ferroptosis mainly by triggering intracellular ROS production, promoting the lysosomal degradation of ferritin and regulating the System Xc-/Gpx4 axis. Interestingly, ARTs also stimulate the feedback inhibition pathway.

CONCLUSION

Artemisinin and its derivatives could be used in the future as cancer therapies with broader applications due to their induction of ferroptosis. Meanwhile, more attention should be paid to the development of novel artemisinin-related drugs based on the mechanism of artemisinininduced ferroptosis.

pH-dependent rearrangement determines the iron-activation and antitumor activity of artemisinins

The action mechanisms of artemisinins remains elusive for decades, and one long-standing question is whether the indispensable peroxide group is activated by iron or heme. Although heme usually reacts faster with artemisinins than iron does, we have found that rearrangement of dihydroartemisinin (DHA) into monoketo-aldehyde-peroxyhemiacetal (MKA) under physiological conditions can significantly enhance its reaction towards iron. The rearrangement is pH-dependent and the derived MKA is identified by LC-MS in the cellular metabolites of DHA in cancer cells. MKA reacts quickly with ferrous irons to afford reactive carbon-centered radicals and can inhibit enzyme activities in vitro. Moreover, MKA oxidizes ferrous irons to ferric irons, which may explain the effect of DHA on decreasing cellular labile iron pool (LIP). Both addition of exogenous iron and increase in LIP via triggering ferroptosis can enhance the cytotoxicity of DHA against cancer cells. While artesunate (ATS) can also decompose to MKA after hydrolyzing into DHA, the other artemisinins of lower antitumor activity, e.g. artemisinin (ART), artemether (ATM) and arteether (ATE), exhibit negligible hydrolysis and rearrangement under the same conditions. Our study reveals the vital role of molecular rearrangement to the activation and activity of artemisinins and provides a new strategy for designing antitumor molecules containing endoperoxide group.

Advances in the research on the targets of anti-malaria actions of artemisinin

Malaria has been a global epidemic health threat since ancient times. It still claims roughly half a million lives every year in this century. Artemisinin and its derivatives, are frontline antimalarial drugs known for their efficacy and low toxicity. After decades of wide use, artemisinins remain our bulwark against malaria. Here, we review decades of efforts that aim to understand the mechanism of action (MOA) of artemisinins, which help explain the specificity and potency of this anti-malarial drug. We summarize the methods and approaches employed to unravel the MOA of artemisinin over the last three decades, showing how the development of advanced techniques can help provide mechanistic insights and resolve some long-standing questions in the field of artemisinin research. We also provide examples to illustrate how to better repurpose artemisinins for anti-cancer therapies by leveraging on MOA. These examples point out a practical direction to engineer artemisinin for broader applications beyond malaria.

Genetic screens reveal a central role for heme metabolism in artemisinin susceptibility

Artemisinins have revolutionized the treatment of Plasmodium falciparum malaria; however, resistance threatens to undermine global control efforts. To broadly explore artemisinin susceptibility in apicomplexan parasites, we employ genome-scale CRISPR screens recently developed for Toxoplasma gondii to discover sensitizing and desensitizing mutations. Using a sublethal concentration of dihydroartemisinin (DHA), we uncover the putative transporter Tmem14c whose disruption increases DHA susceptibility. Screens performed under high doses of DHA provide evidence that mitochondrial metabolism can modulate resistance. We show that disrupting a top candidate from the screens, the mitochondrial protease DegP2, lowers porphyrin levels and decreases DHA susceptibility, without significantly altering parasite fitness in culture. Deleting the homologous gene in P. falciparum, PfDegP, similarly lowers heme levels and DHA susceptibility. These results expose the vulnerability of heme metabolism to genetic perturbations that can lead to increased survival in the presence of DHA.

Heme-Dependent ER Stress Apoptosis: A Mechanism for the Selective Toxicity of the Dihydroartemisinin, NSC735847, in Colorectal Cancer Cells

Colorectal cancer (CRC) is a leading cause of cancer death in the United States. Artemisinin derivatives, including the dihydroartemisinin (DHA) monomers, are widely used as clinical agents for the treatment of malaria. Numerous studies demonstrate that these molecules also display antineoplastic activity with minimal toxicity. Of interest, dimeric DHA molecules are more active than their monomeric counterparts. Our previous data showed that the DHA dimer, NSC735847, was a potent inducer of death in different cancer cell types. However, the mechanism of action and activity of NSC735847 in colon cancer cells was not explored. The present study investigated the anticancer activity of NSC735847 and four structurally similar analog in human tumorigenic (HT-29 and HCT-116) and non-tumorigenic (FHC) colon cell lines. NSC735847 was more cytotoxic toward tumorigenic than non-tumorigenic colonocytes. In addition, NSC735847 exhibited greater cytotoxicity and tumor selectivity than the NSC735847 derivatives. To gain insight into mechanisms of NSC735847 activity, the requirement for endoplasmic reticulum (ER) stress and oxidative stress was tested. The data show that ER stress played a key role in the cytotoxicity of NSC735847 while oxidative stress had little impact on cell fate. In addition, it was observed that the cytotoxic activity of NSC735847 required the presence of heme, but not iron. The activity of NSC735847 was then compared to clinically utilized CRC therapeutics. NSC735847 was cytotoxic toward colon tumor cells at lower concentrations than oxaliplatin (OX). In addition, cell death was achieved at lower concentrations in colon cancer cells that were co-treated with folinic acid (Fol), 5-FU (F), and NSC735847 (FolFNSC), than Fol, F, and OX (FolFOX). The selective activity of NSC735847 and its ability to induce cytotoxicity at low concentrations suggest that NSC735847 may be an alternative for oxaliplatin in the FolFOX regimen for patients who are unable to tolerate its adverse effects.

DHA Affects Microtubule Dynamics Through Reduction of Phospho-TCTP Levels and Enhances the Antiproliferative Effect of T-DM1 in Trastuzumab-Resistant HER2-Positive Breast Cancer Cell Lines

Trastuzumab emtansine (T-DM1) is an anti-human epidermal growth factor receptor 2 (HER2) antibody-drug conjugated to the microtubule-targeting agent emtansine (DM1). T-DM1 is an effective agent in the treatment of patients with HER2-positive breast cancer whose disease has progressed on the first-line trastuzumab containing chemotherapy. However, both primary and acquired tumour resistance limit its efficacy. Increased levels of the phosphorylated form of Translationally Controlled Tumour Protein (phospho-TCTP) have been shown to be associated with a poor clinical response to trastuzumab therapy in HER2-positive breast cancer. Here we show that phospho-TCTP is essential for correct mitosis in human mammary epithelial cells. Reduction of phospho-TCTP levels by dihydroartemisinin (DHA) causes mitotic aberration and increases microtubule density in the trastuzumab-resistant breast cancer cells HCC1954 and HCC1569. Combinatorial studies show that T-DM1 when combined with DHA is more effective in killing breast cells compared to the effect induced by any single agent. In an orthotopic breast cancer xenograft model (HCC1954), the growth of the tumour cells resumes after having achieved a complete response to T-DM1 treatment. Conversely, DHA and T-DM1 treatment induces a severe and irreversible cytotoxic effect, even after treatment interruption, thus, improving the long-term efficacy of T-DM1. These results suggest that DHA increases the effect of T-DM1 as poison for microtubules and supports the clinical development of the combination of DHA and T-DM1 for the treatment of aggressive HER2-overexpressing breast cancer.

Activation of artemisinin and heme degradation in Leishmania tarentolae promastigotes: A possible link

Endoperoxides (EPs) appear to be promising drug candidates against protozoal diseases, including malaria and leishmaniasis. Previous studies have shown that these drugs need an intracellular activation to exert their pharmacological potential. The efficiency of these drugs is linked to the extensive iron demand of these intracellular protozoal parasites. An essential step of the activation mechanism of these drugs is the formation of radicals in Leishmania. Iron is a known trigger for intracellular radical formation. However, the activation of EPs by low molecular iron or by heme iron may strongly depend on the structure of the EPs themselves. In this study, we focused on the activation of artemisinin (Art) in Leishmania tarentolae promastigotes (LtP) in comparison to reference compounds. Viability assays in different media in the presence of different iron sources (hemin/fetal calf serum) showed that IC50 values of Art in LtP were modulated by assay conditions, but overall were within the low micromolar range. Low temperature electron paramagnetic resonance (EPR) spectroscopy of LtP showed that Art shifted the redox state of the labile iron pool less than the EP ascaridole questioning its role as a major activator of Art in LtP. Based on the high reactivity of Art with hemin in previous biomimetic experiments, we focused on putative heme-metabolizing enzymes in Leishmania, which were so far not well described. Inhibitors of mammalian heme oxygenase (HO; tin and chromium mesoporphyrin) acted antagonistically to Art in LtP and boosted its IC50 value for several magnitudes. By inductively coupled plasma methods (ICP-OES, ICP-MS) we showed that these inhibitors do not block iron (heme) accumulation, but are taken up and act within LtP. These inhibitors blocked the conversion of hemin to bilirubin in LtP homogenates, suggesting that an HO-like enzyme activity in LtP exists. NADPH-dependent degradation of Art and hemin was highest in the small granule and microsomal fractions of LtP. Photometric measurements in the model Art/hemin demonstrated that hemin requires reduction to heme and that subsequently an Art/heme complex (λmax 474 nm) is formed. EPR spin-trapping in the system Art/hemin revealed that NADPH, ascorbate and cysteine are suitable reductants and finally activate Art to acyl-carbon centered radicals. These findings suggest that heme is a major activator of Art in LtP either via HO-like enzyme activities and/or chemical interaction of heme with Art.

Artemisinin and its derivatives target mitochondrial c-type cytochromes in yeast and human cells

Artemisinin and its derivatives kill malaria parasites and inhibit the proliferation of cancer cells. In both processes, heme was shown to play a key role in artemisinin bioactivation. We found that artemisinin and clinical artemisinin derivatives are able to compensate for a mutation in the yeast Bcs1 protein, a key chaperon involved in biogenesis of the mitochondrial respiratory complex III. The equivalent Bcs1 variant causes an encephalopathy in human by affecting complex III assembly. We show that artemisinin derivatives decrease the content of mitochondrial cytochromes and disturb the maturation of the complex III cytochrome c1. This last effect is likely responsible for the compensation by decreasing the detrimental over-accumulation of the inactive pre-complex III observed in the bcs1 mutant. We further show that a fluorescent dihydroartemisinin probe rapidly accumulates in the mitochondrial network and targets cytochromes c and c1 in yeast, human cells and isolated mitochondria. In vitro this probe interacts with purified cytochrome c only under reducing conditions and we detect cytochrome c-dihydroartemisinin covalent adducts by mass spectrometry analyses. We propose that reduced mitochondrial c-type cytochromes act as both targets and mediators of artemisinin bioactivation in yeast and human cells.

Vitamin and cofactor acquisition in apicomplexans: Synthesis versus salvage

The Apicomplexa phylum comprises diverse parasitic organisms that have evolved from a free-living ancestor. These obligate intracellular parasites exhibit versatile metabolic capabilities reflecting their capacity to survive and grow in different hosts and varying niches. Determined by nutrient availability, they either use their biosynthesis machineries or largely depend on their host for metabolite acquisition. Because vitamins cannot be synthesized by the mammalian host, the enzymes required for their synthesis in apicomplexan parasites represent a large repertoire of potential therapeutic targets. Here, we review recent advances in metabolic reconstruction and functional studies coupled to metabolomics that unravel the interplay between biosynthesis and salvage of vitamins and cofactors in apicomplexans. A particular emphasis is placed on Toxoplasma gondii, during both its acute and latent stages of infection.

Ozonide Antimalarials Alkylate Heme in the Malaria Parasite Plasmodium falciparum

The mechanism of action of ozonide antimalarials involves activation by intraparasitic iron and the formation of highly reactive carbon-centered radicals that alkylate malaria parasite proteins. Given free intraparasitic heme is generally thought to be the iron source responsible for ozonide activation and its likely close proximity to the activated drug, we investigated heme as a possible molecular target of the ozonides. Using an extraction method optimized for solubilization of free heme, untargeted LC-MS analysis of ozonide-treated parasites identified several regioisomers of ozonide-alkylated heme, which resulted from covalent modification of the heme porphyrin ring by an ozonide-derived carbon-centered radical. In addition to the intact alkylated heme adduct, putative ozonide-alkylated heme degradation products were also detected. This study directly demonstrates ozonide modification of heme within the malaria parasite Plasmodium falciparum, revealing that this process may be important for the biological activity of ozonide antimalarials.

Drug Repurposing in the Development of Anticancer Agents

BACKGROUND

Research into repositioning known drugs to treat cancer other than the originally intended disease continues to grow and develop, encouraged in part, by several recent success stories. Many of the studies in this article are geared towards repurposing generic drugs because additional clinical trials are relatively easy to perform and the drug safety profiles have previously been established.

OBJECTIVE

This review provides an overview of anticancer drug development strategies which is one of the important areas of drug restructuring.

METHODS

Repurposed drugs for cancer treatments are classified by their pharmacological effects. The successes and failures of important repurposed drugs as anticancer agents are evaluated in this review.

RESULTS AND CONCLUSION

Drugs could have many off-target effects, and can be intelligently repurposed if the off-target effects can be employed for therapeutic purposes. In cancer, due to the heterogeneity of the disease, often targets are quite diverse, hence a number of already known drugs that interfere with these targets could be deployed or repurposed with appropriate research and development.

Synergistic antitumor activity of artesunate and HDAC inhibitors through elevating heme synthesis via synergistic upregulation of ALAS1 expression

Artemisinin and its derivatives (ARTs) were reported to display heme-dependent antitumor activity. On the other hand, histone deacetylase inhibitors (HDACi) were known to be able to promote heme synthesis in erythroid cells. Nevertheless, the effect of HDACi on heme homeostasis in non-erythrocytes remains unknown. We envisioned that the combination of HDACi and artesunate (ARS) might have synergistic antitumor activity through modulating heme synthesis. In vitro studies revealed that combination of ARS and HDACi exerted synergistic tumor inhibition by inducing cell death. Moreover, this combination exhibited more effective antitumor activity than either ARS or HDACi monotherapy in xenograft models without apparent toxicity. Importantly, mechanistic studies revealed that HDACi coordinated with ARS to increase 5-aminolevulinate synthase (ALAS1) expression, and subsequent heme production, leading to enhanced cytotoxicity of ARS. Notably, knocking down ALAS1 significantly blunted the synergistic effect of ARS and HDACi on tumor inhibition, indicating a critical role of ALAS1 upregulation in mediating ARS cytotoxicity. Collectively, our study revealed the mechanism of synergistic antitumor action of ARS and HDACi. This finding indicates that modulation of heme synthesis pathway by the combination based on ARTs and other heme synthesis modulators represents a promising therapeutic approach to solid tumors.

Synthesis of artemisinin derived glycoconjugates inspired by click chemistry

Cu(i)-catalysed click reactions between β-propargylated dihydroartemisinin and azido sugars were carried out to furnish artemisinin based glycoconjugates.

Dihydroartemisinin-Ferriprotoporphyrin IX Adduct Abundance in Plasmodium falciparum Malarial Parasites and the Relationship to Emerging Artemisinin Resistance

Previously (Heller, L. E., and Roepe, P. D. Quantification of Free Ferriprotoporphyrin IX Heme and Hemozoin for Artemisinin Sensitive versus Delayed Clearance Phenotype Plasmodium falciparum Malarial Parasites. Biochemistry, DOI: 10.1021/acs.biochem.8b00959, preceding paper in this issue), we quantified free ferriprotoporphyrin IX (FPIX) heme abundance for control versus delayed clearance phenotype (DCP) intraerythrocytic Plasmodium falciparum malarial parasites. Because artemisinin drugs are activated by free FPIX, these data predict that the abundance of long-hypothesized toxic artemisinin drug-FPIX covalent adducts might differ for control versus DCP parasites. If so, this would have important repercussions for understanding the mechanism of the DCP, also known as emerging artemisinin resistance. To test these predictions, we studied in vitro formation of FPIX-dihydroartemisinin (DHA) adducts and then for the first time quantified the abundance of FPIX-DHA adducts formed within live P. falciparum versus the stage of intraerythrocytic development. Using matched isogenic parasite strains, we quantified the adduct for DCP versus control parasite strains and found that mutant PfK13 mediates lower adduct abundance for DCP parasites. The results suggest improved models for the molecular pharmacology of artemisinin-based antimalarial drugs and the molecular mechanism of the DCP.

Synthesis of novel 1,2,3-triazole based artemisinin derivatives and their antiproliferative activity

Novel artemisinin-1,2,3-triazole derivatives show significant antiproliferative activity, and induce apoptosis and ROS generation and arrest the cell cycle at the G2/M phase.

Artemisinin as an anticancer drug: Recent advances in target profiling and mechanisms of action

Artemisinin and its derivatives (collectively termed as artemisinins) are among the most important and effective antimalarial drugs, with proven safety and efficacy in clinical use. Beyond their antimalarial effects, artemisinins have also been shown to possess selective anticancer properties, demonstrating cytotoxic effects against a wide range of cancer types both in vitro and in vivo. These effects appear to be mediated by artemisinin-induced changes in multiple signaling pathways, interfering simultaneously with multiple hallmarks of cancer. Great strides have been taken to characterize these pathways and to reveal their anticancer mechanisms of action of artemisinin. Moreover, encouraging data have also been obtained from a limited number of clinical trials to support their anticancer property. However, there are several key gaps in knowledge that continue to serve as significant barriers to the repurposing of artemisinins as effective anticancer agents. This review focuses on important and emerging aspects of this field, highlighting breakthroughs in unresolved questions as well as novel techniques and approaches that have been taken in recent studies. We discuss the mechanism of artemisinin activation in cancer, novel and significant findings with regards to artemisinin target proteins and pathways, new understandings in artemisinin-induced cell death mechanisms, as well as the practical issues of repurposing artemisinin. We believe these will be important topics in realizing the potential of artemisinin and its derivatives as safe and potent anticancer agents.

A mitochondria-targeting artemisinin derivative with sharply increased antitumor but depressed anti-yeast and anti-malaria activities

The potent anti-malarial drug artemisinins are additionally anti-tumorigenic and inhibitory to yeast growth. The action mechanism of artemisinins, however, is not well understood. Heme and mitochondrial membrane are both suggested to be involved in the action of artemisinins. Because heme is also synthesized in the mitochondrion, mitochondria appear to be a critical organelle for artemisinins' activities. In this study, we synthesized a mitochondria-targeting artemisinin derivative by conjugating triphenylphosphonium (TPP) to artelinic acid (ARTa). ARTa-TPP displays far more potent anti-tumorigenic activity than its parent compound. In contrast, ARTa-TPP is much less active against yeast respiration growth and malarial parasites. Notably, ARTa-TPP is also associated with increased toxicity to other kinds of control mammalian cells. These results suggest divergent action modes for artemisinins against cancer cells and malaria or yeast cells. We conclude that mitochondrial targeting could substantially elevate the anticancer potency of artemisinins, but the accompanied increased toxicity to normal cells raises an alert. The mechanism regarding the opposing effects of TPP conjugation to ARTa on its anticancer and anti-malarial/anti-yeast potencies is discussed based on our current understandings of artemisinins' action.

Development of Anticancer Agents from Plant-Derived Sesquiterpene Lactones

Sesquiterpene lactones are of considerable interest due to their potent bioactivities, including cancer cell cytotoxicity and antineoplastic efficacy in in vivo studies. Among these compounds, artesunate, dimethylaminoparthenolide, and L12ADT peptide prodrug, a derivative of thapsigargin, are being evaluated in the current cancer clinical or preclinical trials. Based on the structures of several antitumor sesquiterpene lactones, a number of analogues showing greater potency have been either isolated as natural products or partially synthesized, and some potential anticancer agents that have emerged from this group of lead compounds have been investigated extensively. The present review focuses on artemisinin, parthenolide, thapsigargin, and their naturally occurring or synthetic analogues showing potential anticancer activity. This provides an overview of the advances in the development of these types of sesquiterpene lactones as potential anticancer agents, including their structural characterization, synthesis and synthetic modification, and antitumor potential, with the mechanism of action and structure-activity relationships also discussed. It is hoped that this will be helpful in stimulating the further interest in developing sesquiterpene lactones and their derivatives as new anticancer agents.

Strategies to enhance biologically active-secondary metabolites in cell cultures of Artemisia - current trends

The genus Artemisia has been utilized worldwide due to its immense potential for protection against various diseases, especially malaria. Artemisia absinthium, previously renowned for its utilization in the popular beverage absinthe, is gaining resurgence due to its extensive pharmacological activities. Like A. annua, this species exhibits strong biological activities like antimalarial, anticancer and antioxidant. Although artemisinin was found to be the major metabolite for its antimalarial effects, several flavonoids and terpenoids are considered to possess biological activities when used alone and also to synergistically boost the bioavailability of artemisinin. However, due to the limited quantities of these metabolites in wild plants, in vitro cultures were established and strategies have been adopted to enhance medicinally important secondary metabolites in these cultures. This review elaborates on the traditional medicinal uses of Artemisia species and explains current trends to establish cell cultures of A. annua and A. absinthium for enhanced production of medicinally important secondary metabolites.

Interactions between 4-aminoquinoline and heme: Promising mechanism against Trypanosoma cruzi

Chagas disease is a neglected tropical disease caused by the flagellated protozoan Trypanosoma cruzi. The current drugs used to treat this disease have limited efficacy and produce severe side effects. Quinolines, nitrogen heterocycle compounds that form complexes with heme, have a broad spectrum of antiprotozoal activity and are a promising class of new compounds for Chagas disease chemotherapy. In this study, we evaluated the activity of a series of 4-arylaminoquinoline-3-carbonitrile derivatives against all forms of Trypanosoma cruzi in vitro. Compound 1g showed promising activity against epimastigote forms when combined with hemin (IC50<1 μM), with better performance than benznidazole, the reference drug. This compound also inhibited the viability of trypomastigotes and intracellular amastigotes. The potency of 1g in combination with heme was enhanced against epimastigotes and trypomastigotes, suggesting a similar mechanism of action that occurs in Plasmodium spp. The addition of hemin to the culture medium increased trypanocidal activity of analog 1g without changing the cytotoxicity of the host cell, reaching an IC50 of 11.7 μM for trypomastigotes. The mechanism of action was demonstrated by the interaction of compound 1g with hemin in solution and prevention of heme peroxidation. Compound 1g and heme treatment induced alterations of the mitochondrion-kinetoplast complex in epimastigotes and trypomastigotes and also, accumulation of electron-dense deposits in amastigotes as visualized by transmission electron microscopy. The trypanocidal activity of 4-aminoquinolines and the elucidation of the mechanism involving interaction with heme is a neglected field of research, given the parasite's lack of heme biosynthetic pathway and the importance of this cofactor for parasite survival and growth. The results of this study can improve and guide rational drug development and combination treatment strategies.

Treatment of a chemoresistant neuroblastoma cell line with the antimalarial ozonide OZ513

BACKGROUND

Evaluate the anti-tumor activity of ozonide antimalarials using a chemoresistant neuroblastoma cell line, BE (2)-c.

METHODS

The activity of 12 ozonides, artemisinin, and two semisynthetic artemisinins were tested for activity against two neuroblastoma cell-lines (BE (2)-c and IMR-32) and the Ewing's Sarcoma cell line A673 in an MTT viability assay. Time course data indicated that peak effect was seen 18 h after the start of treatment thus 18 h pre-treatment was used for all subsequent experiments. The most active ozonide (OZ513) was assessed in a propidium iodide cell cycle flow cytometry analysis which measured cell cycle transit and apoptosis. Metabolic effects of OZ513 in BE (2)-c cells was evaluated. Western blots for the apoptotic proteins cleaved capase-3 and cleaved PARP, the highly amplified oncogene MYCN, and the cell cycle regulator CyclinD1, were performed. These in-vitro experiments were followed by an in-vivo experiment in which NOD-scid gamma immunodeficient mice were injected subcutaneously with 1 × 10⁶ BE (2)-c cells followed by immediate treatment with 50-100 mg/kg/day doses of OZ513 administered IP three times per week out to 23 days after injection of tumor. Incidence of tumor development, time to tumor development, and rate of tumor growth were assessed in DMSO treated controls (N = 6), and OZ513 treated mice (N = 5).

RESULTS

It was confirmed that five commonly used chemotherapy drugs had no cytotoxic activity in BE (2)-c cells. Six of 12 ozonides tested were active in-vitro at concentrations achievable in vivo with OZ513 being most active (IC50 = 0.5 mcg/ml). OZ513 activity was confirmed in IMR-32 and A673 cells. The Ao peak on cell-cycle analysis was increased after treatment with OZ513 in a concentration dependent fashion which when coupled with results from western blot analysis which showed an increase in cleaved capase-3 and cleaved PARP supported an increase in apoptosis. There was a concentration dependent decline in the MYCN and a cyclinD1 protein indicative of anti-proliferative activity and cell cycle disruption. OXPHOS metabolism was unaffected by OZ513 treatment while glycolysis was increased. There was a significant delay in time to tumor development in mice treated with OZ513 and a decline in the rate of tumor growth.

CONCLUSIONS

The antimalarial ozonide OZ513 has effective in-vitro and in-vivo activity against a pleiotropic drug resistant neuroblastoma cell-line. Treatment with OZ513 increased apoptotic markers and glycolysis with a decline in the MYCN oncogene and the cell cycle regulator cyclinD1. These effects suggest adaptation to cellular stress by mechanism which remain unclear.

Phytomedicine-Modulating oxidative stress and the tumor microenvironment for cancer therapy

In spite of the current advances and achievements in systems biology and translational medicinal research, the current strategies for cancer therapy, such as radiotherapy, targeted therapy, immunotherapy and chemotherapy remain palliative or unsatisfactory due to tumor metastasis or recurrence after surgery/therapy, drug resistance, adverse side effects, and so on. Oxidative stress (OS) plays a critical role in chronic/acute inflammation, carcinogenesis, tumor progression, and tumor invasion/metastasis which is also attributed to the dynamic and complex properties and activities in the tumor microenvironment (TME). Re-educating or reprogramming tumor-associated stromal or immune cells in the TME provides an approach for restoring immune surveillance impaired by disease in cancer patients to increase overall survival and reduce drug resistance. Herbal medicines or plant-derived natural products have historically been a major source of anti-cancer drugs. Delving into the lore of herbal medicine may uncover new leads for anti-cancer drugs. Phytomedicines have been widely documented to directly or indirectly target multiple signaling pathways and networks in cancer cells. A combination of anti-cancer drugs and polypharmacological plant-derived extracts or compounds may offer a significant advantage in sensitizing the efficacy of monotherapy and overcoming drug-induced resistance in cancer patients. This review introduces several phytochemicals and phytoextracts derived from medicinal plants or dietary vegetables that have been studied for their efficacy in preclinical cancer models. We address the underlying modes of action of induction of OS and deregulation of TME-associated stromal cells, mediators and signaling pathways, and reference the related clinical investigations that look at the single or combination use of phytochemicals and phytoextracts to sensitize anti-cancer drug effects and/or overcome drug resistance.

The molecular and cellular action properties of artemisinins: what has yeast told us?

Artemisinin (ART) or Qinghaosu is a natural compound possessing superior anti-malarial activity. Although intensive studies have been done in the medicinal chemistry field to understand the structure-effect relationship, the biological actions of artemisinin are poorly understood and controversial. Due to the current lack of a genetic amiable model to address this question, and an accidental finding made more than a decade ago during our initial exploratory efforts that yeast Saccharomyces cerevisiae can be inhibited by artemisinin, we have since been using the baker's yeast as a model to probe the molecular and cellular properties of artemisinin and its derivatives (ARTs) in living cells. ARTs were found to possess potent and specific anti-mitochondrial properties and, to a lesser extent, the ability to generate a relatively general oxidative damage. The anti-mitochondrial effects of artemisinin were later confirmed with purified mitochondria from malaria parasites. Inside some cells heme appears to be a primary reducing agent and reduction of ARTs by heme can induce a relatively nonspecific cellular damage. The molecular basis of the anti-mitochondrial properties of ARTs remains not well elucidated yet. We propose that the anti-mitochondrial and heme-mediated ROS-generating properties constitute two cellcidal actions of ARTs. This review summarizes what we have learned from yeast about the basic biological properties of ARTs, as well as some key unanswered questions. We believe yeast could serve as a window through which to peek at some of the biological action secrets of ARTs that might be difficult for us to learn otherwise.

Phospho-TCTP as a therapeutic target of Dihydroartemisinin for aggressive breast cancer cells

Upregulation of Translationally Controlled Tumor Protein (TCTP) is associated with poorly differentiated aggressive tumors, including breast cancer, but the underlying mechanism(s) are still debated. Here, we show that in breast cancer cell lines TCTP is primarily localized in the nucleus, mostly in the phosphorylated form.

The effects of Dihydroartemisinin (DHA), an anti-malaria agent that binds TCTP, were tested on breast cancer cells. DHA decreases cell proliferation and induces apoptotic cell death by targeting the phosphorylated form of TCTP. Remarkably, DHA enhances the anti-tumor effects of Doxorubicin in triple negative breast cancer cells resulting in an increased level of apoptosis. DHA also synergizes with Trastuzumab, used to treat HER2/neu positive breast cancers, to induce apoptosis of tumor cells.

Finally, we present new clinical data that nuclear phospho-TCTP overexpression in primary breast cancer tissue is associated with high histological grade, increase expression of Ki-67 and with ER-negative breast cancer subtypes. Notably, phospho-TCTP expression levels increase in trastuzumab-resistant breast tumors, suggesting a possible role of phospho-TCTP as a new prognostic marker.

In conclusion, the anti-tumor effect of DHA in vitro with conventional chemotherapeutics suggests a novel therapeutic strategy and identifies phospho-TCTP as a new promising target for advanced breast cancer.

Haem-activated promiscuous targeting of artemisinin in Plasmodium falciparum

The mechanism of action of artemisinin and its derivatives, the most potent of the anti-malarial drugs, is not completely understood. Here we present an unbiased chemical proteomics analysis to directly explore this mechanism in Plasmodium falciparum. We use an alkyne-tagged artemisinin analogue coupled with biotin to identify 124 artemisinin covalent binding protein targets, many of which are involved in the essential biological processes of the parasite. Such a broad targeting spectrum disrupts the biochemical landscape of the parasite and causes its death. Furthermore, using alkyne-tagged artemisinin coupled with a fluorescent dye to monitor protein binding, we show that haem, rather than free ferrous iron, is predominantly responsible for artemisinin activation. The haem derives primarily from the parasite's haem biosynthesis pathway at the early ring stage and from haemoglobin digestion at the latter stages. Our results support a unifying model to explain the action and specificity of artemisinin in parasite killing.

The mechanism of action of artemisinin, an antimalarial drug, is not well understood. Here, the authors use a labelled artemisinin analogue to show that the drug is mainly activated by haem and then binds covalently to over 120 proteins in the malaria parasite, affecting many of its cellular processes.

Artesunate overcomes drug resistance in multiple myeloma by inducing mitochondrial stress and non-caspase apoptosis

Although novel drugs have contributed immensely to improving outcomes of patients with multiple myeloma (MM), many patients develop drug resistance and ultimately succumb to MM. Here, we show that artesunate, an anti-malarial drug, reliably induces cell death in vitro in naïve as well as drug-resistant MM cells at concentrations shown to be safe in humans. Artesunate induced apoptosis predominantly through the non-caspase mediated pathway by primarily targeting mitochondria and causing outer mitochondrial membrane permeabilization that led to cytosolic and subsequent nuclear translocation of mitochondrial proteins apoptosis inducing factor (AIF) and endonuclease G (EndoG). Nuclear translocation of AIF and EndoG was accompanied by low levels of reactive oxygen species (ROS) and increased mitochondrial production of superoxide. These effects were present before apoptosis was evident and were related to intracellular levels of bivalent iron (Fe+2). Artesunate's unique mechanism probably was at least partially responsible for, its ability to act synergistically with multiple anti-myeloma agents. Our findings suggest that artesunate acts through iron to affect the mitochondria and induce low ROS and non-caspase-mediated apoptosis. Its potency, toxicity profile, and synergism with other drugs make it an intriguing new candidate for MM treatment.

Anticancer Effect of AntiMalarial Artemisinin Compounds

The anti-malarial drug artemisinin has shown anticancer activity in vitro and animal experiments, but experience in human cancer is scarce. However, the ability of artemisinins to kill cancer cells through a variety of molecular mechanisms has been explored. A PubMed search of about 127 papers on anti-cancer effects of antimalarials has revealed that this class of drug, including other antimalarials, have several biological characteristics that include anticancer properties. Experimental evidences suggest that artemisinin compounds may be a therapeutic alternative in highly aggressive cancers with rapid dissemination, without developing drug resistance. They also exhibit synergism with other anticancer drugs with no increased toxicity toward normal cells. It has been found that semisynthetic artemisinin derivatives have much higher antitumor activity than their monomeric counterparts via mechanisms like apoptosis, arrest of cell cycle at G₀/G₁, and oxidative stress. The exact mechanism of activation and molecular basis of these anticancer effects are not fully elucidated. Artemisinins seem to regulate key factors such as nuclear factor-kappa B, survivin, NOXA, hypoxia-inducible factor-1α, and BMI-1, involving multiple pathways that may affect drug response, drug interactions, drug resistance, and associated parameters upon normal cells. Newer synthetic artemisinins have been developed showing substantial antineoplastic activity, but there is still limited information regarding the mode of action of these synthetic compounds. In view of the emerging data, specific interactions with established chemotherapy need to be further investigated in different cancer cells and their phenotypes and validated further using different semisynthetic and synthetic artemisinin derivatives.

Artemisinin mimics calorie restriction to trigger mitochondrial biogenesis and compromise telomere shortening in mice

Calorie restriction is known to extend lifespan among organisms by a debating mechanism underlying nitric oxide-driven mitochondrial biogenesis. We report here that nitric oxide generators including artemisinin, sodium nitroprusside, and L-arginine mimics calorie restriction and resembles hydrogen peroxide to initiate the nitric oxide signaling cascades and elicit the global antioxidative responses in mice. The large quantities of antioxidant enzymes are correlated with the low levels of reactive oxygen species, which allow the down-regulation of tumor suppressors and accessory DNA repair partners, eventually leading to the compromise of telomere shortening. Accompanying with the up-regulation of signal transducers and respiratory chain signatures, mitochondrial biogenesis occurs with the elevation of adenosine triphosphate levels upon exposure of mouse skeletal muscles to the mimetics of calorie restriction. In conclusion, calorie restriction-triggered nitric oxide provides antioxidative protection and alleviates telomere attrition via mitochondrial biogenesis, thereby maintaining chromosomal stability and integrity, which are the hallmarks of longevity.

Artemisinin mimics calorie restriction to extend yeast lifespan via a dual-phase mode: a conclusion drawn from global transcriptome profiling

Calorie restriction (CR) promotes longevity among distinct organisms from yeast to mammals. Although CR-prolonged lifespan is believed to associate with enhanced respiratory activity, it is apparently controversial for accelerated energy consumption regardless of insufficient nutrient intake. In reconciling the contradiction of less food supply versus much metabolite dispense, we revealed a CR-based mode of dual-phase responses that encompass a phase of mitochondrial enhancement (ME) and a phase of post-mitochondrial enhancement (PME), which can be distinguished by the expression patterns and activity dynamics of mitochondrial signatures. ME is characterized by global antioxidative activation, and PME is denoted by systemic metabolic modulation. CR-mediated aging-delaying effects are replicated by artesunate, a semi-synthetic derivative of the antimalarial artemisinin that can alkylate heme-containing proteins, suggesting artesunate-heme conjugation functionally resembles nitric oxide-heme interaction. A correlation of artesunate-heme conjugation with cytochrome c oxidase activation has been established from adduct formation and activity alteration. Exogenous hydrogen peroxide also mimics CR to trigger antioxidant responses, affect signaling cascades, and alter respiratory rhythms, implying hydrogen peroxide is engaged in lifespan extension. Conclusively, artesunate mimics CR-triggered nitric oxide and hydrogen peroxide to induce antioxidative networks for scavenging reactive oxygen species and mitigating oxidative stress, thereby directing metabolic conversion from anabolism to catabolism, maintaining essential metabolic functionality, and extending life expectancy in yeast.

Two distinct and competitive pathways confer the cellcidal actions of artemisinins

The biological actions of artemisinin (ART), an antimalarial drug derived from Artemisia annua, remain poorly understood and controversial. Besides potent antimalarial activity, some of artemisinin derivatives (together with artemisinin, hereafter referred to as ARTs), in particular dihydroartemisinin (DHA), are also associated with anticancer and other antiparasitic activities. In this study, we used baker’s yeast Saccharomyces cerevisiae as cellular and genetic model to investigate the molecular and cellular properties of ARTs. Two clearly separable pathways exist. While all ARTs exhibit potent anti-mitochondrial actions as shown before, DHA exerts an additional strong heme-dependent, likely mitochondria-independent inhibitory action. More importantly, heme antagonizes the mitochondria-dependent cellcidal action. Indeed, when heme synthesis was inhibited, the mitochondria-dependent cellcidal action of ARTs could be dramatically strengthened, and significant yeast growth inhibition at as low as 100 nM ART, an increase of about 25 folds in sensitivity, was observed. We conclude that ARTs are endowed with two major and distinct types of properties: a potent and specific mitochondria-dependent reaction and a more general and less specific heme-mediated reaction. The competitive nature of these two actions could be explained by their shared source of the consumable ARTs, so that inhibition of the heme-mediated degradation pathway would enable more ARTs to be available for the mitochondrial action. These properties of ARTs can be used to interpret the divergent antimalarial and anticancer actions of ARTs.

Artesunate induces cell death in human cancer cells via enhancing lysosomal function and lysosomal degradation of ferritin

Artesunate (ART) is an anti-malaria drug that has been shown to exhibit anti-tumor activity, and functional lysosomes are reported to be required for ART-induced cancer cell death, whereas the underlying molecular mechanisms remain largely elusive. In this study, we aimed to elucidate the molecular mechanisms underlying ART-induced cell death. We first confirmed that ART induces apoptotic cell death in cancer cells. Interestingly, we found that ART preferably accumulates in the lysosomes and is able to activate lysosomal function via promotion of lysosomal V-ATPase assembly. Furthermore, we found that lysosomes function upstream of mitochondria in reactive oxygen species production. Importantly, we provided evidence showing that lysosomal iron is required for the lysosomal activation and mitochondrial reactive oxygen species production induced by ART. Finally, we showed that ART-induced cell death is mediated by the release of iron in the lysosomes, which results from the lysosomal degradation of ferritin, an iron storage protein. Meanwhile, overexpression of ferritin heavy chain significantly protected cells from ART-induced cell death. In addition, knockdown of nuclear receptor coactivator 4, the adaptor protein for ferritin degradation, was able to block ART-mediated ferritin degradation and rescue the ART-induced cell death. In summary, our study demonstrates that ART treatment activates lysosomal function and then promotes ferritin degradation, subsequently leading to the increase of lysosomal iron that is utilized by ART for its cytotoxic effect on cancer cells. Thus, our data reveal a new mechanistic action underlying ART-induced cell death in cancer cells.

DJ-1 mediates the resistance of cancer cells to dihydroartemisinin through reactive oxygen species removal

Dihydroartemisinin (DHA), one of the main metabolites of artemisinin and its derivatives, presents anti-cancer potential in vitro and in vivo. To explore the mechanisms of resistance toward DHA, a DHA-resistant cell line, HeLa/DHA, was established with a resistance factor of 7.26 in vitro. Upon DHA treatment, apoptotic cells were significantly elicited in parental HeLa cells but minimally induced in HeLa/DHA cells. HeLa/DHA cells also displayed much less sensitivity to DHA-induced tumor suppression in cancer xenograft models than HeLa cells. Intriguingly, DHA-resistant cells did not display a multidrug-resistant phenotype. Based on a proteomic study employing LC-ESI-MS/MS together with pathway analysis, DJ-1 (PARK7) was found to be highly expressed in HeLa/DHA cells. Western blot and immunofluorescence assays confirmed the higher expression of DJ-1 in HeLa/DHA cells than in parental cells in both cell line and xenograft models. DJ-1 is translocated to the mitochondria of HeLa/DHA cells and oxidized, providing DJ-1 with stronger cytoprotection activity. Further study revealed that DJ-1 knockdown in HeLa/DHA cells abolished the observed resistance, whereas overexpression of DJ-1 endowed the parental HeLa cells with resistance toward DHA. Reactive oxygen species (ROS) were also significantly induced by either DHA or hydrogen peroxide in HeLa cells but not in resistant HeLa/DHA cells. When the cells were pretreated with N-acetyl-l-cysteine, the effect of DJ-1 knockdown on sensitizing HeLa/DHA cells to DHA was significantly attenuated. In summary, our study suggests that overexpression and mitochondrial translocation of DJ-1 provides HeLa/DHA cells with resistance to DHA-induced ROS and apoptosis.

Anticancer properties of distinct antimalarial drug classes

We have tested five distinct classes of established and experimental antimalarial drugs for their anticancer potential, using a panel of 91 human cancer lines. Three classes of drugs: artemisinins, synthetic peroxides and DHFR (dihydrofolate reductase) inhibitors effected potent inhibition of proliferation with IC50s in the nM- low µM range, whereas a DHODH (dihydroorotate dehydrogenase) and a putative kinase inhibitor displayed no activity. Furthermore, significant synergies were identified with erlotinib, imatinib, cisplatin, dasatinib and vincristine. Cluster analysis of the antimalarials based on their differential inhibition of the various cancer lines clearly segregated the synthetic peroxides OZ277 and OZ439 from the artemisinin cluster that included artesunate, dihydroartemisinin and artemisone, and from the DHFR inhibitors pyrimethamine and P218 (a parasite DHFR inhibitor), emphasizing their shared mode of action. In order to further understand the basis of the selectivity of these compounds against different cancers, microarray-based gene expression data for 85 of the used cell lines were generated. For each compound, distinct sets of genes were identified whose expression significantly correlated with compound sensitivity. Several of the antimalarials tested in this study have well-established and excellent safety profiles with a plasma exposure, when conservatively used in malaria, that is well above the IC50s that we identified in this study. Given their unique mode of action and potential for unique synergies with established anticancer drugs, our results provide a strong basis to further explore the potential application of these compounds in cancer in pre-clinical or and clinical settings.

Erythrophagocytosis enhances heme-dependent cytotoxicity of antimalarial drugs in canine histiocytic sarcoma cell line DH82

Antimalarial drugs, dihydroartemisinin (DHA) and artesunate (ATS), exhibit iron-dependent cytotoxicity in tumor cells. We hypothesized that erythrophagocytic uptake of heme-iron enhances the cytotoxicity of DHA and ATS. Erythrophagocytic (EP) treatment of the canine histiocytic sarcoma cell line DH82 markedly increased the cytotoxicity of DHA and ATS compared to controls. Succinyl acetone, an inhibitor of intracellular heme synthesis, decreased the cytotoxicity of DHA and ATS in normal cells, but this change was not observed in EP cells. These results suggest that exogenous heme derived from erythrocytes can enhance the cytotoxicity of DHA and ATS. Furthermore, our study suggests that heme could be a novel component of tumor treatment in veterinary medicine.

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.

New approaches for the identification of drug targets in protozoan parasites

Antiparasitic chemotherapy is an important issue for drug development. Traditionally, novel compounds with antiprotozoan activities have been identified by screening of compound libraries in high-throughput systems. More recently developed approaches employ target-based drug design supported by genomics and proteomics of protozoan parasites. In this chapter, the drug targets in protozoan parasites are reviewed. The gene-expression machinery has been among the first targets for antiparasitic drugs and is still under investigation as a target for novel compounds. Other targets include cytoskeletal proteins, proteins involved in intracellular signaling, membranes, and enzymes participating in intermediary metabolism. In apicomplexan parasites, the apicoplast is a suitable target for established and novel drugs. Some drugs act on multiple subcellular targets. Drugs with nitro groups generate free radicals under anaerobic growth conditions, and drugs with peroxide groups generate radicals under aerobic growth conditions, both affecting multiple cellular pathways. Mefloquine and thiazolides are presented as examples for antiprotozoan compounds with multiple (side) effects. The classic approach of drug discovery employing high-throughput physiological screenings followed by identification of drug targets has yielded the mainstream of current antiprotozoal drugs. Target-based drug design supported by genomics and proteomics of protozoan parasites has not produced any antiparasitic drug so far. The reason for this is discussed and a synthesis of both methods is proposed.