Liposomal pemetrexed: formulation, characterization and in vitro cytotoxicity studies for effective management of malignant pleural mesothelioma

Our plain-English summary of Liposomal pemetrexed: formulation, characterization and in vitro cytotoxicity studies for effective management of malignant pleural mesothelioma, by N. Essam Eldin, H.M. Elnahas, M.A. Mahdy, et al (Biological & Pharmaceutical Bulletin, 2015).

The study

• Authors: N. Essam Eldin, H.M. Elnahas, M.A. Mahdy, T. Ishida
• Journal: Biological & Pharmaceutical Bulletin
• Published: 2015;38(3):461-9
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Pemetrexed (PMX) is a newly developed multi-targeted anti-folate with promising clinical activity in many solid tumors including malignant pleural mesothelioma (MPM). However, PMX does not show sufficient anti-tumor activity in vivo when used alone either due to inefficient delivery of adequate concentrations to tumor tissue or dose-limiting side effects. In order to overcome these problems and to achieve potent anti-tumor activity, PMX was encapsulated into a liposomal delivery system. In the present study, various formulations of liposomal PMX were prepared. The effect of formulation parameters on the encapsulation efficiency of PMX within liposomes was evaluated. In addition, the influence of drug release rate on the in vitro cytotoxicity was investigated. Encapsulation of PMX within liposomes was remarkably increased by the incorporation of cholesterol within liposomal membranes and by increasing the total lipid concentration. Encapsulation efficiency was found to be unaffected by the type of phospholipid used or the inclusion of a cation lipid, DC-6-14. Interestingly, encapsulation of PMX within "fluid" liposomes was found to allow efficient release of PMX from liposomes resulting in a potent in vitro cytotoxicity against MPM MSTO-211H cell line. On the other hand, entrapment of PMX within "solid" liposomes substantially hindered PMX release from liposomes, and thus PMX failed to exert any in vitro cytotoxicity. These results suggest that encapsulation of PMX within "fluid" liposomes might represent a novel strategy to enhance the therapeutic efficacy of PMX while minimizing the side effect encountered by the non selective delivery of free PMX to various body tissues.

In plain English

This was a laboratory study of a drug formulation. It did not study people or asbestos exposure. The authors made nine versions of liposomes (tiny fat-based capsules) carrying pemetrexed, a drug for malignant pleural mesothelioma. They tested free pemetrexed and the three positively charged liposome versions (HSPC, POPC and DOPC) on MSTO-211H, a human malignant pleural mesothelioma cell line grown in the lab. Adding cholesterol raised the share of drug captured, as did using more lipid. Adding the positively charged lipid DC-6-14 changed neither capture nor release. No release was seen from "solid" HSPC liposomes even after 24 hours, and cholesterol slowed release from "fluid" DOPC liposomes. The fluid POPC and DOPC versions showed a cytotoxic effect, with IC50 values (the concentration giving 50% inhibition) of 61.46 and 129.55 ng/mL. The HSPC version showed no effect at the concentrations tested. All the liposomal versions tested were significantly less toxic to the cells than free pemetrexed (p less than 0.001). The authors suggested fluid liposomes might outperform free pemetrexed in living animals. They said such studies were still under way.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) drug-formulation study: preparation and characterization of liposomal pemetrexed and cell-culture cytotoxicity testing
• Who was studied: No human subjects. A human malignant pleural mesothelioma cell line, MSTO-211H, obtained from the American Type Culture Collection
• Exposure: No asbestos exposure was studied. Nine liposomal pemetrexed (PMX) formulations (F-1 to F-9) were prepared, differing in phospholipid (HSPC, POPC/DOPE, DOPC/DOPE), cholesterol and the cationic lipid DC-6-14. In the cell assay, free PMX and the cationic liposomal formulations (HSPC, POPC and DOPC) were tested at 0.01 to 10 µg/mL PMX
• Main results:
  • Encapsulation efficiency of PMX was increased significantly by adding cholesterol to the liposome membrane, rather than by the type of phospholipid (for example, HSPC liposomes 14.8 with cholesterol vs 10.2 without, in percent, Table 3)
  • For HSPC liposomes, entrapment efficiency rose from 4.2 plus or minus 0.7% to 14.8 plus or minus 2.8% as total lipid concentration increased from 10 to 50 µmol/mL; POPC and DOPC liposomes showed similar increases
  • Including the cationic lipid DC-6-14 did not affect entrapment of PMX
  • Including DC-6-14 did not affect the release profile of PMX from any of the liposomal formulations
  • No PMX release was observed from solid-phase HSPC liposomes even after 24 hours
  • Cholesterol in fluid DOPC liposomes significantly reduced PMX release compared with cholesterol-free DOPC liposomes (13% vs. 65%)
  • After storage at 4°C for 7 and 14 days, liposome sizes were similar to initial sizes, with some significant differences, especially in DOPC formulations
  • Against MSTO-211H cells (MTT assay), IC50 was 61.46 plus or minus 2.1 ng/mL for PMX in cationic POPC liposomes and 129.55 plus or minus 3.2 ng/mL for PMX in cationic DOPC liposomes
  • PMX in solid-phase cationic HSPC liposomes showed no cytotoxic effect on MSTO-211H cells at the concentrations tested
  • The liposomal PMX formulations tested in the cell assay were all significantly less cytotoxic to MSTO-211H cells than free PMX (p less than 0.001)
• The authors' conclusion: The authors concluded that PMX in fluid (POPC or DOPC) liposomes had a superior in vitro cytotoxic effect against MSTO-211H cells compared with solid (HSPC) liposomes. They suggested that fluid liposomal PMX might be more effective than free PMX when used in vivo, while reducing side effects.
• Limitations the authors state:
  • The work was done only in cell culture; the authors state that studies of the formulation's potential in vivo were still being conducted

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pemetrexed (Alimta), Pleural Mesothelioma, Encapsulation, Cation.

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