Liposome co-encapsulation of synergistic combination of irinotecan and doxorubicin for the treatment of intraperitoneally grown ovarian tumor xenograft.

Liposome co-encapsulation of synergistic anti-cancer drug combination is an emerging area that has demonstrated therapeutic benefit in clinical trials. Remote loading of two or more drugs into a single liposome constitutes a new challenge that calls for a re-examination of drug loading strategies to allow the loading of the drug combination efficiently and with high drug content. In this study, the Mn(2+) gradient coupled with A23187 ionophore was applied in the sequential co-encapsulation of doxorubicin and irinotecan, as this drug loading method is capable of remotely loading drugs by apparently two different mechanisms, namely, coordination complexation and pH gradient. Doxorubicin and irinotecan could be co-encapsulated into liposomes in a wide range of drug-to-drug ratios, with encapsulation efficiencies of > 80%. The total encapsulated drug content was non-linearly correlated with increases in the intraliposomal Mn(2+) concentration, with a maximum total drug-to-lipid molar ratio of 0.8:1 achieved with 600 mM Mn(2+). This high encapsulated drug content did not affect the stability of the co-encapsulated liposomes upon storage for six months. Regardless of the encapsulated drug amount, the liposomes did not exhibit the fiber bundle precipitate morphology but rather an undefined structural organization in the aqueous core. The co-encapsulated liposome formulation was further tested in an intraperitoneally grown, human ovarian tumor xenograft model, and was shown to significantly improve the survival of the tumor-bearing animals. The improvement in therapeutic efficacy was possibly due to the increase in systemic drug exposure, with the maintenance of the synergistic molar drug ratio of 1:1 in circulation.

Lipid-based nanoparticulate systems for the delivery of anti-cancer drug cocktails: Implications on pharmacokinetics and drug toxicities.

The use of drug cocktails has become a widely adopted strategy in clinical cancer therapy. Cytotoxic drug cocktails are often administered based on maximum tolerated dose (MTD) of each agent, with the belief of achieving maximum cell kill through tolerable toxicity level. Yet, MTD administration may not have fully captured the therapeutic synergism that exists among the individual agents in the drug cocktail, as the response to a cocktail regimen, that is, whether the effect is synergistic or not, could be highly sensitive to the concentration ratios of the individual drugs at the site of action. It is important to realize that the inherently different pharmacokinetic profiles of the individual agents could have significant influence on the response to an anti-cancer drug cocktail by dictating the amount of the individual agents reaching the tumor site and therefore the concentration ratios. Furthermore, the individual agents may have unfavorable pharmacokinetic interactions that add to the difficulty in determining the therapeutic and/or toxicological effects of the drug cocktail. In this review, we will focus on how lipid-based nanoparticulate systems could address the above issues associated with anti-cancer drug cocktails. Specifically, we will highlight the use of liposome systems as the means to control and coordinate the delivery of various anti-cancer drug cocktails, encompassing conventional chemotherapeutics, chemosensitizing agents and molecularly targeted agents.