Encapsulation, controlled release, and antitumor efficacy of cisplatin delivered in liposomes composed of sterol-modified phospholipids

Abstract

We employed a recently introduced class of sterol-modified lipids (SML) to produce m-PEG-DSPE containing liposome compositions with a range of cis-platinum content release rates. SML have a cholesterol succinate attached to the phosphatidylglycerol head group and a fatty acid at the 2 position. These compositions were compared to the well-studied liposome phospholipid compositions: mPEG-DSPE/Hydrogenated Soy PC/cholesterol or mPEG-DSPE/POPC/cholesterol to determine the effect of the cis-platinum release extent on C26 tumor proliferation in the BALB/c colon carcinoma mouse model. The release rates of cis-platinum from liposomes composed of SML are a function of the acyl chain length. SML-liposomes with shorter acyl chain lengths C-8 provided more rapid cisplatin release, lower in vitro IC50, and were easier to formulate compared to liposomes using traditional phospholipid compositions. Similar to other liposome cis-platinum formulations, the half-life of m-PEG-DSPE SML liposome cisplatin is substantially longer than the free drug. This resulted in a higher tumor cisplatin concentration at 48h post-dosing compared to the free drug and higher Pt-DNA adducts in the tumor. Moreover, the maximum tolerated dose of the liposome formulations where up to four fold greater than the free drug. Using X-ray fluorescence spectroscopy on tumor sections, we compared the location of platinum, to the location of a fluorescence lipid incorporated in the liposomes. The liposome platinum co-localized with the fluorescent lipid and both were non-uniformly distributed in the tumor. Non-encapsulated Cis-platinum, albeit at a low concentration, was more uniformly distributed thorough the tumor. Three liposome formulations, including the well-studied hydrogenated HSPC composition, had better antitumor activity in the murine colon 26 carcinoma model as compared to the free drug at the same dose but the SML liposome platinum formulations did not perform better than the HSPC formulation.

Keywords: C26 colon carcinoma; Cisplatin; Liposome; Sterol-modified phospholipid; X-ray fluorescence microscopy.

Fig. 1

Retention of body weight after single injection of cisplatin and cisplatin liposomes in healthy, tumor free mice. The lines are not a fit and are only provided to enable the identification of the weight change with the formulation.

Fig. 2

Blood circulation of C8Chems and HSPC liposomes in healthy, tumor free mice. Each time included three samples from individual mice (n = 3).

Fig. 3

Localization of liposome-associated fluorescent dye, encapsulated platinum or non-encapsulated platinum in tumor sections at 54 h post dosing. Microfluorescence of platinum in C26 tumor the scale inserted into the images represents 1 mm. Maximum and minimum threshold values are given which correspond with the rainbow color scale at the bottom of the image.

Fig. 4

A) Average change in body weight from day of injection. B) Survival probability for mice treated with cisplatin and liposomal cisplatin. Mice (n = 10 per group) dosed on day 8 and day 15 at 6 mg/kg cis-platinum.

Fig. 5

A) Average weight change following treatment at days 8 and 15. B) Survival plot of mice treated with four leaky formulations and the less leaky HSPC formulation. Mice (n=10/group) were dosed on day 8 and 15 at 6 mg/kg.