Triethyl phosphine decorated cerium oxide nanoparticles exhibit selective killing of the unicellular protozoan parasite Leishmania donovani.

Globally, Leishmaniasis affects underprivileged communities of the nations and chemotherapy remains one of the preferred treatment options. However, the cytotoxicity, side effects, and cost of the present chemotherapies limit their utilization. Auranofin [an organogold compound having significant structural similarity with triethyl-phosphine (TEP)] has been reported as an effective therapy for Leishmaniasis treatment. Considering the high cost of gold and the strong affinity of cerium oxide nanoparticles (CeNPs) to phosphine ligands, we designed TEP-decorated CeNPs (CeNPs-TEP) and used them as a novel antileishmanial agent. The hydrodynamic size of synthesized CeNPs and CeNPs-TEP was observed to be 22.2 ± 3.7 nm and 92.11 ± 6.2 nm, respectively. CeNPs-TEP provided aqueous stability to TEP as TEP alone is extremely unstable in water. Exposure of CeNPs-TEP showed ~ 60 and ~ 82% cell death in Leishmania donovani Ag83 promastigotes after 24 and 48 h, respectively. The same concentration of CeNPs-TEP did not affect the cellular viability of RAW 264.7 macrophage cells significantly. The oxidative stress and depolarization of the mitochondrial membrane were also observed after the treatment of CeNPs-TEP. Exposure of CeNPs-TEP induced a ~ 2.2-fold increase in ROS generation inside Leishmania donovani Ag83 cells. Dual staining with ethidium bromide and acridine orange reveals that these processes ultimately result in cell death. The results conclude that a combination of CeNPs and TEP could open the door for developing novel antileishmanial therapeutics in the future. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03813-7.

ZnO nanoparticles-associated mitochondrial stress-induced apoptosis and G2/M arrest in HaCaT cells: a mechanistic approach.

Zinc oxide nanoparticles (ZnO NPs) with their wide range of consumer applications in day-to-day life received great attention to evaluate their effects in humans. This study has been attempted to elucidate the DNA damage response mechanism in a dermal model exposed to ZnO NPs through Ataxia Telangiectasia Mutated (ATM)-mediated ChK1-dependent G2/M arrest. Further, viability parameters and mechanism involved in the cell death with special reference to the consequences arising due to DNA damage were explored. Our study showed that ZnO NPs at concentrations 5 and 10 µg/ml induced significant cytotoxic effect in skin cell line. Moreover, the results confirmed generation of reactive oxygen species (ROS) induces the cell death by genotoxic insult, leading to mitochondrial membrane depolarisation and cell cycle arrest. Subsequently, ZnO NPs treatment created DNA damage as confirmed via Comet assay (increase in olive tail moment), micronucleus assay (increase in micronucleus formation), double-strand breaks (increase in ATM and Ataxia Telangiectasia and Rad3 related (ATR) expression), DNA fragmentation and cell cycle (G2/M arrest) studies. Finally, marker proteins analysis concluded the mechanistic approach by demonstrating the key marker expressions HMOX1 and HSP60 (for oxidative stress), cytochrome c, APAF1, BAX, Caspase 9, Caspase 3 and decrease in BCL2 (for activating apoptotic pathway), pATM, ATR and γH2AX (for double-strand breaks), DNA-PK (involved in DNA repair) and decrease in cell cycle regulators. In together, our data revealed the mechanism of ROS generation that triggers apoptosis and DNA damage in HaCaT cell lines exposed to ZnO NPs.

Neutral Porphyrin Derivative Exerts Anticancer Activity by Targeting Cellular Topoisomerase I (Top1) and Promotes Apoptotic Cell Death without Stabilizing Top1-DNA Cleavage Complexes.

Camptothecin (CPT) selectively traps topoisomerase 1-DNA cleavable complexes (Top1cc) to promote anticancer activity. Here, we report the design and synthesis of a new class of neutral porphyrin derivative 5,10-bis(4-carboxyphenyl)-15, 20-bis(4-dimethylaminophenyl)porphyrin (compound 8) as a potent catalytic inhibitor of human Top1. In contrast to CPT, compound 8 reversibly binds with the free enzyme and inhibits the formation of Top1cc and promotes reversal of the preformed Top1cc with CPT. Compound 8 induced inhibition of Top1cc formation in live cells was substantiated by fluorescence recovery after photobleaching (FRAP) assays. We established that MCF7 cells treated with compound 8 trigger proteasome-mediated Top1 degradation, accumulate higher levels of reactive oxygen species (ROS), PARP1 cleavage, oxidative DNA fragmentation, and stimulate apoptotic cell death without stabilizing apoptotic Top1-DNA cleavage complexes. Finally, compound 8 shows anticancer activity by targeting cellular Top1 and preventing the enzyme from directly participating in the apoptotic process.

Linked Patient-Reported Outcomes Data From Patients With Multiple Sclerosis Recruited on an Open Internet Platform to Health Care Claims Databases Identifies a Representative Population for Real-Life Data Analysis in Multiple Sclerosis.

BACKGROUND: An enormous amount of information relevant to public health is being generated directly by online communities. OBJECTIVE: To explore the feasibility of creating a dataset that links patient-reported outcomes data, from a Web-based survey of US patients with multiple sclerosis (MS) recruited on open Internet platforms, to health care utilization information from health care claims databases. The dataset was generated by linkage analysis to a broader MS population in the United States using both pharmacy and medical claims data sources. METHODS: US Facebook users with an interest in MS were alerted to a patient-reported survey by targeted advertisements. Eligibility criteria were diagnosis of MS by a specialist (primary progressive, relapsing-remitting, or secondary progressive), ≥12-month history of disease, age 18-65 years, and commercial health insurance. Participants completed a questionnaire including data on demographic and disease characteristics, current and earlier therapies, relapses, disability, health-related quality of life, and employment status and productivity. A unique anonymous profile was generated for each survey respondent. Each anonymous profile was linked to a number of medical and pharmacy claims datasets in the United States. Linkage rates were assessed and survey respondents' representativeness was evaluated based on differences in the distribution of characteristics between the linked survey population and the general MS population in the claims databases. RESULTS: The advertisement was placed on 1,063,973 Facebook users' pages generating 68,674 clicks, 3719 survey attempts, and 651 successfully completed surveys, of which 440 could be linked to any of the claims databases for 2014 or 2015 (67.6% linkage rate). Overall, no significant differences were found between patients who were linked and not linked for educational status, ethnicity, current or prior disease-modifying therapy (DMT) treatment, or presence of a relapse in the last 12 months. The frequencies of the most common MS symptoms did not differ significantly between linked patients and the general MS population in the databases. Linked patients were slightly younger and less likely to be men than those who were not linkable. CONCLUSIONS: Linking patient-reported outcomes data, from a Web-based survey of US patients with MS recruited on open Internet platforms, to health care utilization information from claims databases may enable rapid generation of a large population of representative patients with MS suitable for outcomes analysis.

Poly(ADP-ribose) polymers regulate DNA topoisomerase I (Top1) nuclear dynamics and camptothecin sensitivity in living cells.

Topoisomerase 1 (Top1) is essential for removing the DNA supercoiling generated during replication and transcription. Anticancer drugs like camptothecin (CPT) and its clinical derivatives exert their cytotoxicity by reversibly trapping Top1 in covalent complexes on the DNA (Top1cc). Poly(ADP-ribose) polymerase (PARP) catalyses the addition of ADP-ribose polymers (PAR) onto itself and Top1. PARP inhibitors enhance the cytotoxicity of CPT in the clinical trials. However, the molecular mechanism by which PARylation regulates Top1 nuclear dynamics is not fully understood. Using live-cell imaging of enhanced green fluorescence tagged-human Top1, we show that PARP inhibitors (Veliparib, ABT-888) delocalize Top1 from the nucleolus to the nucleoplasm, which is independent of Top1-PARP1 interaction. Using fluorescence recovery after photobleaching and subsequent fitting of the data employing kinetic modelling we demonstrate that ABT-888 markedly increase CPT-induced bound/immobile fraction of Top1 (Top1cc) across the nuclear genome, suggesting Top1-PARylation counteracts CPT-induced stabilization of Top1cc. We further show Trp205 and Asn722 of Top1 are critical for subnuclear dynamics. Top1 mutant (N722S) was restricted to the nucleolus in the presence of CPT due to its deficiency in the accumulation of CPT-induced Top1-PARylation and Top1cc formation. This work identifies ADP-ribose polymers as key determinant for regulating Top1 subnuclear dynamics.

Flavone-resistant Leishmania donovani overexpresses LdMRP2 transporter in the parasite and activates host MRP2 on macrophages to circumvent the flavone-mediated cell death.

In parasites, ATP-binding cassette (ABC) transporters represent an important family of proteins related to drug resistance and other biological activities. Resistance of leishmanial parasites to therapeutic drugs continues to escalate in developing countries, and in many instances, it is due to overexpressed ABC efflux pumps. Progressively adapted baicalein (BLN)-resistant parasites (pB(25)R) show overexpression of a novel ABC transporter, which was classified as ABCC2 or Leishmania donovani multidrug resistance protein 2 (LdMRP2). The protein is primarily localized in the flagellar pocket region and in internal vesicles. Overexpressed LdABCC2 confers substantial BLN resistance to the parasites by rapid drug efflux. The BLN-resistant promastigotes when transformed into amastigotes in macrophage cells cannot be cured by treatment of macrophages with BLN. Amastigote resistance is concomitant with the overexpression of macrophage MRP2 transporter. Reporter analysis and site-directed mutagenesis assays demonstrated that antioxidant response element 1 is activated upon infection. The expression of this phase II detoxifying gene is regulated by NFE2-related factor 2 (Nrf2)-mediated antioxidant response element activation. In view of the fact that the signaling pathway of phosphoinositol 3-kinase controls microfilament rearrangement and translocation of actin-associated proteins, the current study correlates with the intricate pathway of phosphoinositol 3-kinase-mediated nuclear translocation of Nrf2, which activates MRP2 expression in macrophages upon infection by the parasites. In contrast, phalloidin, an agent that prevents depolymerization of actin filaments, inhibits Nrf2 translocation and Mrp2 gene activation by pB(25)R infection. Taken together, these results provide insight into the mechanisms by which resistant clinical isolates of L. donovani induce intracellular events relevant to drug resistance.

PARP1-TDP1 coupling for the repair of topoisomerase I-induced DNA damage.

Poly(ADP-ribose) polymerases (PARP) attach poly(ADP-ribose) (PAR) chains to various proteins including themselves and chromatin. Topoisomerase I (Top1) regulates DNA supercoiling and is the target of camptothecin and indenoisoquinoline anticancer drugs, as it forms Top1 cleavage complexes (Top1cc) that are trapped by the drugs. Endogenous and carcinogenic DNA lesions can also trap Top1cc. Tyrosyl-DNA phosphodiesterase 1 (TDP1), a key repair enzyme for trapped Top1cc, hydrolyzes the phosphodiester bond between the DNA 3'-end and the Top1 tyrosyl moiety. Alternative repair pathways for Top1cc involve endonuclease cleavage. However, it is unknown what determines the choice between TDP1 and the endonuclease repair pathways. Here we show that PARP1 plays a critical role in this process. By generating TDP1 and PARP1 double-knockout lymphoma chicken DT40 cells, we demonstrate that TDP1 and PARP1 are epistatic for the repair of Top1cc. The N-terminal domain of TDP1 directly binds the C-terminal domain of PARP1, and TDP1 is PARylated by PARP1. PARylation stabilizes TDP1 together with SUMOylation of TDP1. TDP1 PARylation enhances its recruitment to DNA damage sites without interfering with TDP1 catalytic activity. TDP1-PARP1 complexes, in turn recruit X-ray repair cross-complementing protein 1 (XRCC1). This work identifies PARP1 as a key component driving the repair of trapped Top1cc by TDP1.

Disuccinyl betulin triggers metacaspase-dependent endonuclease G-mediated cell death in unicellular protozoan parasite Leishmania donovani.

The unicellular organism Leishmania undergoes apoptosis-like cell death in response to external stress or exposure to antileishmanial agents. Here, we showed that 3-O,28-O-disuccinyl betulin (DiSB), a potent topoisomerase type IB inhibitor, induced parasitic cell death by generating oxidative stress. The characteristic feature of the death process resembled the programmed cell death (PCD) seen in higher eukaryotes. In the current study, the generation of reactive oxygen species (ROS), followed by the depolarization of mitochondrial membrane potential (ΔΨm), caused a loss in ATP production in Leishmania parasites. This further gave positive feedback to produce a large amount of ROS, which in turn caused oxidative DNA lesions and genomic DNA fragmentation. The treatment of promastigotes with DiSB induced high expression levels of metacaspase protein that led to cell death in this unicellular organism. The PCD was insensitive to benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk), suggesting that the death process was not associated with the activation of caspases. DiSB treatment translocated Leishmania donovani endonuclease G (LdEndoG) from mitochondria to the nucleus, which was responsible for the DNA degradation process. Conditional antisense knockdown of L. donovani metacaspase (LdMC), as well as EndoG, -subverted death of the parasite and rescued cell cycle arrest in G1 phase. The present study on the effector molecules associated with the PCD pathway of the parasite should help to manifest the mechanisms of PCD and also might be exploited in antileishmanial chemotherapy.

The lignan niranthin poisons Leishmania donovani topoisomerase IB and favours a Th1 immune response in mice.

Niranthin, a lignan isolated from the aerial parts of the plant Phyllanthus amarus, exhibits a wide spectrum of pharmacological activities. In the present study, we have shown for the first time that niranthin is a potent anti-leishmanial agent. The compound induces topoisomerase I-mediated DNA-protein adduct formation inside Leishmania cells and triggers apoptosis by activation of cellular nucleases. We also show that niranthin inhibits the relaxation activity of heterodimeric type IB topoisomerase of L. donovani and acts as a non-competitive inhibitor interacting with both subunits of the enzyme. Niranthin interacts with DNA-protein binary complexes and thus stabilizes the 'cleavable complex' formation and subsequently inhibits the religation of cleaved strand. The compound inhibits the proliferation of Leishmania amastigotes in infected cultured murine macrophages with limited cytotoxicity to the host cells and is effective against antimony-resistant Leishmania parasites by modulating upregulated P-glycoprotein on host macrophages. Importantly, besides its in vitro efficacy, niranthin treatment leads to a switch from a Th2- to a Th1-type immune response in infected BALB/c mice. The immune response causes production of nitric oxide, which results in almost complete clearance of the liver and splenic parasite burden after intraperitoneal or intramuscular administration of the drug. These findings can be exploited to develop niranthin as a new drug candidate against drug-resistant leishmaniasis.

Development of derivatives of 3, 3'-diindolylmethane as potent Leishmania donovani bi-subunit topoisomerase IB poisons.

BACKGROUND: The development of 3, 3'-diindolyl methane (DIM) resistant parasite Leishmania donovani (LdDR50) by adaptation with increasing concentrations of the drug generates random mutations in the large and small subunits of heterodimeric DNA topoisomerase I of Leishmania (LdTOP1LS). Mutation of large subunit of LdTOP1LS at F270L is responsible for resistance to DIM up to 50 µM concentration. METHODOLOGY/PRINCIPAL FINDINGS: In search of compounds that inhibit the growth of the DIM resistant parasite and inhibit the catalytic activity of mutated topoisomerase I (F270L), we have prepared three derivatives of DIM namely DPDIM (2,2'-diphenyl 3,3'-diindolyl methane), DMDIM (2,2'-dimethyl 3,3'-diindolyl methane) and DMODIM (5,5'-dimethoxy 3,3'-diindolyl methane) from parent compound DIM. All the compounds inhibit the growth of DIM resistant parasites, induce DNA fragmentation and stabilize topo1-DNA cleavable complex with the wild type and mutant enzyme. CONCLUSION: The results suggest that the three derivatives of DIM can act as promising lead molecules for the generation of new anti-leishmanial agents.

Cryptolepine-Induced Cell Death of Leishmania donovani Promastigotes Is Augmented by Inhibition of Autophagy.

Leishmania donovani are the causative agents of visceral leishmaniasis worldwide. Lack of vaccines and emergence of drug resistance warrants the need for improved drug therapy and newer therapeutic intervention strategies against leishmaniasis. In the present study, we have investigated the effect of the natural indoloquinoline alkaloid cryptolepine on L. donovani AG83 promastigotes. Our results show that cryptolepine induces cellular dysfunction in L. donovani promastigotes, which leads to the death of this unicellular parasite. Interestingly, our study suggest that cryptolepine-induced cell death of L. donovani is counteracted by initial autophagic features elicited by the cells. For the first time, we show that autophagy serves as a survival mechanism in response to cryptolepine treatment in L. donovani promastigotes and inhibition of autophagy causes an early increase in the amount of cell death. This study can be exploited for designing better drugs and better therapeutic strategies against leishmaniasis in future.

Novel betulin derivatives as antileishmanial agents with mode of action targeting type IB DNA topoisomerase.

Toward developing antileishmanial agents with mode of action targeted to DNA topoisomerases of Leishmania donovani, we have synthesized a large number of derivatives of betulin. The compound, a natural triterpene isolated from the cork layer of Betula spp. plants exhibits several pharmacological properties. Three compounds (disuccinyl betulin, diglutaryl dihydrobetulin, and disuccinyl dihydrobetulin) inhibit growth of the parasite as well as relaxation activity of the enzyme type IB topoisomerase [Leishmania donovani topoisomerase I (LdTOP1LS)] of the parasite. Mechanistic studies suggest that these compounds interact with the enzyme in a reversible manner. The stoichiometry of these compounds binding to LdTOP1LS is 1:1 (mole/mole) with a dissociation constant on the order of ∼10(-6) M. Unlike CPT, these compounds do not stabilize the cleavage complex; rather, they abrogate the covalent complex formation. In processive mode of relaxation assay condition, these compounds slow down the strand rotation event, which ultimately affects the relaxation of supercoiled DNA. It is noteworthy that these compounds reduce the intracellular parasite burden in macrophages infected with wild-type L. donovani as well as with sodium antimony gluconate resistant parasite (GE1). Taken together, our data suggest that these betulin derivatives can be exploited as potential drug candidates against threatening drug resistant leishmaniasis.

ATP independent type IB topoisomerase of Leishmania donovani is stimulated by ATP: an insight into the functional mechanism.

Most type IB topoisomerases do not require ATP and Mg(2+) for activity. However, as shown previously for vaccinia topoisomerase I, we demonstrate that ATP stimulates the relaxation activity of the unusual heterodimeric type IB topoisomerase from Leishmania donovani (LdTOP1L/S) in the absence of Mg(2+). The stimulation is independent of ATP hydrolysis but requires salt as a co-activator. ATP binds to LdTOP1L/S and increases its rate of strand rotation. Docking studies indicate that the amino acid residues His93, Tyr95, Arg188 and Arg190 of the large subunit may be involved in ATP binding. Site directed mutagenesis of these four residues individually to alanine and subsequent relaxation assays reveal that the R190A mutant topoisomerase is unable to exhibit ATP-mediated stimulation in the absence of Mg(2+). However, the ATP-independent relaxation activities of all the four mutant enzymes remain unaffected. Additionally, we provide evidence that ATP binds LdTOP1L/S and modulates the activity of the otherwise ATP-independent enzyme. This study establishes ATP as an activator of LdTOP1L/S in the absence of Mg(2+).

Mutational studies reveal lysine 352 on the large subunit is indispensable for catalytic activity of bi-subunit topoisomerase I from Leishmania donovani.

From the vanadate complex crystal structure of Leishmania donovani topoisomerase I, several amino acid residues have been implicated to be involved in the catalytic reaction. Although several predictions and propositions have been made, the exact role of these amino acids has not yet been clearly demonstrated in vitro. Among these residues, lysine 352 and arginine 314 stand as potential candidates for playing the role of a general acid during the cleavage step. In this study, we have characterized the role of lysine 352 on the large subunit, by site-directed mutagenesis and have tried to identify the general acid that can protonate the 5?-O atom of the leaving strand. Studies with the mutant enzymes reveal that, relaxation activity was severely affected when Lys352 was mutated to arginine or alanine (K352R or K352A). Mutation of Arg314 to Lys (R314K) has very little effect on the relaxation activity. Detailed study reveals that, both cleavage and religation steps are severely affected in case of K352R and K352A and the cleavage religation equilibrium is shifted towards the cleavage. On the contrary, the R314K mutant exhibits only a slightly slower rate of cleavage compared to wild-type enzyme. Cleavage assays with an oligonucleotide containing 5?-bridging phosphorothiolate indicate that Lys352 acts as a general acid in the cleavage step. Altogether, this study establishes the indispensable role of lysine 352 in the catalytic reaction of L. donovani topoisomerase I.

Antileishmanial activity mediated by apoptosis and structure-based target study of peganine hydrochloride dihydrate: an approach for rational drug design.

OBJECTIVES: The aim of this study was to resolve the putative pathway responsible for death induced by peganine hydrochloride dihydrate isolated from Peganum harmala seeds at cellular, structural and molecular level in Leishmania donovani, a causative agent of fatal visceral leishmaniasis. METHODS: The mode of action was assessed using various biochemical approaches including phosphatidylserine exposure, estimation of mitochondrial transmembrane potential and in situ dUTP nick end labelling staining of nicked DNA in the parasite. Molecular modelling and molecular dynamics studies were conducted with DNA topoisomerase I to identify the target of peganine hydrochloride dihydrate mediating apoptosis. Further, DNA topoisomerase I inhibition by peganine hydrochloride dihydrate was also assessed using an L. donovani topoisomerase I relaxation assay. RESULTS: Peganine hydrochloride dihydrate, besides being safe, was found to induce apoptosis in both the stages of L. donovani via loss of mitochondrial transmembrane potential. Molecular docking studies suggest that a binding interaction with DNA topoisomerase I of L. donovani (binding energy of -79 kcal/mol) forms a stable complex, indicating a possible role in apoptosis. The compound also inhibits L. donovani topoisomerase I. CONCLUSIONS: The compound induces apoptosis in L. donovani and inhibits DNA topoisomerase I.

Amino acids 39-456 of the large subunit and 210-262 of the small subunit constitute the minimal functionally interacting fragments of the unusual heterodimeric topoisomerase IB of Leishmania.

The unusual, heterodimeric topoisomerase IB of Leishmania shows functional activity upon reconstitution of the DNA-binding large subunit (LdTOPIL; or L) and the catalytic small subunit (LdTOPIS; or S). In the present study, we generated N- and C-terminal-truncated deletion constructs of either subunit and identified proteins LdTOPIL(39-456) (lacking amino acids 1-39 and 457-635) and LdTOPIS(210-262) (lacking amino acids 1-210) as the minimal interacting fragments. The interacting region of LdTOPIL lies between residues 40-99 and 435-456, while for LdTOPIS it lies between residues 210-215 and 245-262. The heterodimerization between the two fragments is weak and therefore co-purified fragments showed reduced DNA binding, cleavage and relaxation properties compared with the wild-type enzyme. The minimal fragments could complement their respective wild-type subunits inside parasites when the respective subunits were down-regulated by transfection with conditional antisense constructs. Site-directed mutagenesis studies identify Lys455 of LdTOPIL and Asp261 of LdTOPIS as two residues involved in subunit interaction. Taken together, the present study provides crucial insights into the mechanistic details for understanding the unusual structure and inter-subunit co-operativity of this heterodimeric enzyme.