Enhancement of the cytotoxicity of liposomal ricin by the carboxylic ionophore monensin and the lysosomotropic amine NH4Cl in Chinese hamster ovary cells

Preparation, characterization, and evaluation of eosin B-loaded nano-liposomes for growth inhibition of Plasmodium falciparum

Malaria is a deadly disease in humans caused by the Plasmodium parasite. High prevalence of malaria and resistance of malaria parasite to currently proposed drugs have increased the need to introduce and use new and effective antimalarial agents. In this study, eosin B was used as an effective antimalarial agent, the efficacy of which has already been confirmed by in vitro models. Also, for efficacy and safety improvement of eosin B, liposomal nanocarrier was used because of diversity and adaptability in controlled drug delivery and targeting. Eosin B was trapped inside liposomal nanocarriers by thin layer hydration method and its optimization was performed based on size, polydispersity index, and drug entrapment efficiency. Finally, the eosin B-loaded liposomes were tested on Plasmodium falciparum in culture to evaluate its anti-plasmodial effect. According to the results, the formulation with DSPC:cholesterol 8:1 (molar ratio) and drug concentration of 3 mg/ml was selected as the optimal form. The optimal nano-liposomes showed a size of 163.3 nm, a polydispersity index of 0.250, and an encapsulation efficiency of 69.94%. The process of drug release from nanocarriers was also obtained about 63% at the end of 72 h. Stability studies over 2 months at 25 °C and 4 °C on the optimum sample showed that the samples stored in the refrigerator were more stable in terms of size characteristics, polydispersity index, and drug entrapment efficiency. The results indicate a greater effect of liposomal-formulated eosin B on inhibiting parasite growth compared to the free eosin B.

Ricin and Ricinus communis in pharmacology and toxicology-from ancient use and "Papyrus Ebers" to modern perspectives and "poisonous plant of the year 2018"

While probably originating from Africa, the plant Ricinus communis is found nowadays around the world, grown for industrial use as a source of castor oil production, wildly sprouting in many regions, or used as ornamental plant. As regards its pharmacological utility, a variety of medical purposes of selected parts of the plant, e.g., as a laxative, an anti-infective, or an anti-inflammatory drug, have been described already in the sixteenth century BC in the famous Papyrus Ebers (treasured in the Library of the University of Leipzig). Quite in contrast, on the toxicological side, the native plant has become the "poisonous plant 2018" in Germany. As of today, a number of isolated components of the plant/seeds have been characterized, including, e.g., castor oil, ricin, Ricinus communis agglutinin, ricinin, nudiflorin, and several allergenic compounds. This review mainly focuses on the most toxic protein, ricin D, classified as a type 2 ribosome-inactivating protein (RIP2). Ricin is one of the most potent and lethal substances known. It has been considered as an important bioweapon (categorized as a Category B agent (second-highest priority)) and an attractive agent for bioterroristic activities. On the other hand, ricin presents great potential, e.g., as an anti-cancer agent or in cell-based research, and is even explored in the context of nanoparticle formulations in tumor therapy. This review provides a comprehensive overview of the pharmacology and toxicology-related body of knowledge on ricin. Toxicokinetic/toxicodynamic aspects of ricin poisoning and possibilities for analytical detection and therapeutic use are summarized as well.

Di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) overcomes multidrug resistance by a novel mechanism involving the hijacking of lysosomal P-glycoprotein (Pgp)

Multidrug resistance (MDR) is a major obstacle in cancer treatment. More than half of human cancers express multidrug-resistant P-glycoprotein (Pgp), which correlates with a poor prognosis. Intriguingly, through an unknown mechanism, some drugs have greater activity in drug-resistant tumor cells than their drug-sensitive counterparts. Herein, we investigate how the novel anti-tumor agent di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) overcomes MDR. Four different cell types were utilized to evaluate the effect of Pgp-potentiated lysosomal targeting of drugs to overcome MDR. To assess the mechanism of how Dp44mT overcomes drug resistance, cellular studies utilized Pgp inhibitors, Pgp silencing, lysosomotropic agents, proliferation assays, immunoblotting, a Pgp-ATPase activity assay, radiolabeled drug uptake/efflux, a rhodamine 123 retention assay, lysosomal membrane permeability assessment, and DCF (2',7'-dichlorofluorescin) redox studies. Anti-tumor activity and selectivity of Dp44mT in Pgp-expressing, MDR cells versus drug-sensitive cells were studied using a BALB/c nu/nu xenograft mouse model. We demonstrate that Dp44mT is transported by the lysosomal Pgp drug pump, causing lysosomal targeting of Dp44mT and resulting in enhanced cytotoxicity in MDR cells. Lysosomal Pgp and pH were shown to be crucial for increasing Dp44mT-mediated lysosomal damage and subsequent cytotoxicity in drug-resistant cells, with Dp44mT being demonstrated to be a Pgp substrate. Indeed, Pgp-dependent lysosomal damage and cytotoxicity of Dp44mT were abrogated by Pgp inhibitors, Pgp silencing, or increasing lysosomal pH using lysosomotropic bases. In vivo, Dp44mT potently targeted chemotherapy-resistant human Pgp-expressing xenografted tumors relative to non-Pgp-expressing tumors in mice. This study highlights a novel Pgp hijacking strategy of the unique dipyridylthiosemicarbazone series of thiosemicarbazones that overcome MDR via utilization of lysosomal Pgp transport activity.

Efficacy of Liposomal Monensin on the Enhancement of the Antitumour Activity of Liposomal Ricin in Human Epidermoid Carcinoma (KB) Cells

The monensin, known to enhance the cytotoxicity of ricin and ricin-based immunotoxins is a very hydrophobic molecule and this limits its administration in optimum doses under in vivo conditions. In order to realise its full potential, monensin was intercalated into various liposomal formulations and its ability to potentiate the cytotoxicity of ricin liposomes in human epidermoid carcinoma (KB) cells was studied. It was observed that ricin cytotoxicity enhancing ability of monensin liposome depends on the surface charge as well as density and chain length of distearoyl phosphatidylethanolamine-methoxy polyethylene glycol present on the surface of liposomal monensin. Maximum potentiation on the cytotoxicity of liposomal ricin was observed by monensin entrapped in neutral liposome (106.5 fold) followed by negatively charged (94.2 fold) and positively charged liposome (90 fold). Studies on the effect of variation of density and chain length of distearoyl phosphatidylethanolamine-methoxy polyethylene glycol showed that neutral monensin liposomes having 2.5 mol% distearoyl phosphatidylethanolamine-methoxy polyethylene glycol with chain length of 2000 exhibits maximum potentiation (117.6 fold) on the cytotoxicity of ricin liposomes when the cellular uptake of monensin liposome was maximum (42.0%) and the zeta potential value on the surface of liposomes was -0.645. The present study has clearly shown that liposomal monensin is very effective in enhancing the cytotoxicity of liposomal ricin in human cancer cells and liposome can be used as in vivo deliver vehicle for monensin to potentiate the cytotoxicity of liposomal ricin to eliminate cancer cells.

Inhibition of the Growth of Plasmodium falciparum in Culture by Stearylamine-Phosphatidylcholine Liposomes

We have examined the effect of stearylamine (SA) in liposomes on the viability of Plasmodium falciparum in culture by studying the inhibition of incorporation of [³H]-hypoxanthine in the nucleic acid of parasites. Stearylamine in liposomes significantly inhibits the growth of the parasites depending on the phospholipids composition. The maximum inhibition was observed when SA was delivered through Soya phosphatidylcholine (SPC) liposomes. The chain length of alkyl group and density of SA in liposomes play a significant role in inhibiting the growth of the parasites. Incorporation of either cholesterol or Distearylphosphatidylethanolamine−Methoxy-Polyethylene glycol-2000 (DSPE-mPEG-2000) in Soya phosphatidylcholine-stearylamine (SPC-SA) liposomes improves the efficacy. Intraerythrocytic entry of intact SPC-SA liposomes into infected erythrocytes was visualized using fluorescent microscopy. No hemolysis was observed in uninfected erythrocytes, and slight hemolysis was noted in infected erythrocytes at high concentrations of SPC-SA liposomes. Overall, our data suggested SA in SPC-liposomes might have potential application in malaria chemotherapy.

Folate receptor mediated targeted delivery of ricin entrapped into sterically stabilized liposomes to human epidermoid carcinoma (KB) cells: effect of monensin intercalated into folate-tagged liposomes

Ricin was encapsulated into various sterically stabilized liposomes having different density of folate on the surface and the cytotoxicity of ricin in these liposomes was examined in KB cells. The effect of monensin in free and various sterically stabilized liposomal forms having different density of folate on the surface on the enhancement of cytotoxicity of ricin entrapped in these liposomes was also examined. It was observed that liposomal ricin having 0.5 mol% folate-PEG on the surface exhibits maximum cytotoxicity (IC(50)=1274 ng/ml) in KB cells as compared to non-targeted liposomes (IC(50)=3274 ng/ml). Monensin either in free form (266.2-fold) or liposomal form (291.5-fold) enhances the cytotoxicity of this targeted liposomal ricin significantly. This enhancement of the cytotoxicity of ricin entrapped in folate-targeted liposomes is further enhanced to 557.7-fold by monensin when it was delivered through folate-targeted (0.5 mol% folate-PEG) liposomes. The present study has clearly demonstrated that ricin entrapped in folate-tagged-sterically stabilized liposomes in combination with monensin intercalated in folate-tagged-sterically stabilized liposomes may have potential application for the treatment of cancer cells over-expressing folate receptors on the cell surface.

Enhanced killing of human epidermoid carcinoma (KB) cells by treatment with ricin encapsulated into sterically stabilized liposomes in combination with monensin

Ricin was encapsulated in various charged liposomes having 5 mol% PEG of different chain length on the surface. The cytotoxicity of ricin entrapped in these liposomal formulations was examined in human epidermoid carcinoma (KB) cells with a view to develop an optimum delivery system for ricin in vivo. It was observed that the cytotoxicity of ricin entrapped in various charged liposomes was significantly dependent on the surface charge as well as chain length of PEG. The maximum cytotoxicity of ricin was observed when it was delivered through negatively charged liposomes having 5 mol% PEG-2000 on the surface. Monensin enhances the cytotoxicity of ricin entrapped in various charged liposomes depending on the surface charge. Maximum potentiation of cytotoxicity of ricin was observed when it was delivered through negatively charged liposomes having 5 mol% PEG-2000 on the surface. Studies on the kinetics of inhibition of protein synthesis by ricin revealed that the lag period of inhibition of protein synthesis is significantly lengthened following its delivery through various charged liposomes. Monensin significantly reduced the lag period of action of ricin. It was also observed that the efficacies of monensin on the enhancement of cytotoxicity of ricin entrapped in various charged PEG-liposomes were highly related to their amount of cell association. The current study has demonstrated that by suitable adjustment of charge, density, and chain length of PEG on the surface of liposomes it would be possible to direct liposomal ricin to human tumor cells for their selective elimination in combination with monensin.

Effect of surface charge and density of distearylphosphatidylethanolamine-mPEG-2000 (DSPE-mPEG-2000) on the cytotoxicity of liposome-entrapped ricin: Effect of lysosomotropic agents

Ricin was encapsulated in various liposomes having neutral, negatively and positively charged and different density of DSPE-mPEG-2000 on the surface and cytotoxicity of ricin entrapped in these different charged liposomal formulations was studied in CHO pro(-) cells and compared with free ricin with a view to develop an optimum delivery system for ricin in vivo. It was observed that the cytotoxicity of ricin entrapped in various charged liposomes was significantly dependent on the charge on the surface of liposomes. The maximum cytotoxicity of ricin was observed when it was delivered through negatively charged liposomes. Monensin enhances the cytotoxicity of ricin entrapped in various charged liposomes and the extent of enhancement of the cytotoxicity is significantly dependent on the charge on the surface of liposomes. Maximum potentiation (213.14-fold) of cytotoxicity of ricin was observed when it was delivered through positively charged liposomes followed by negatively charged (83.36-fold) and neutral (71.30-fold) liposomes, respectively. Studies on the kinetics of inhibition of protein synthesis by ricin entrapped in various charged liposomes revealed that lag period of inhibition of protein synthesis is significantly lengthened following delivery through various charged liposomes. However, in the presence of monensin, the lag period was reduced. There is a marginal variation in the cytotoxicity of ricin entrapped in various charged liposomes after incorporation of 5mol% of DSPE-mPEG-2000 on the surface. However, there is a significant variation in the enhancing potency of monensin on the cytotoxicity of ricin entrapped in various charged liposomes in CHO pro(-) cells following incorporation of 5mol% DSPE-mPEG-2000 on the surface. Studies on the effect of variation of density of DSPE-mPEG-2000 on the surface of various charged liposomes on the enhancement of cytotoxicity of entrapped ricin by monensin in CHO pro(-) cells showed that the enhancing potency of monensin on the cytotoxicity of ricin entrapped in various charged liposomes is significantly dependent on the density of DSPE-mPEG-2000 on their surface. It was also observed that the efficacies of monensin on the enhancement of cytotoxicity of ricin entrapped in various charged PEG-liposomes in CHO pro(-) cells was highly related to their amount of cell-association. The present study has clearly shown that by suitable alteration of liposomal lipid composition, charge and density of hydrophilicity it would be possible to direct liposomal ricin to specific cells for their selective elimination in combination with monensin.