Liposomal Tumor Targeting in Drug Delivery Utilizing MMP-2- and MMP-9-Binding Ligands

Abstract

Nanotechnology offers an alternative to conventional treatment options by enabling different drug delivery and controlled-release delivery strategies. Liposomes being especially biodegradable and in most cases essentially nontoxic offer a versatile platform for several different delivery approaches that can potentially enhance the delivery and targeting of therapies to tumors. Liposomes penetrate tumors spontaneously as a result of fenestrated blood vessels within tumors, leading to known enhanced permeability and subsequent drug retention effects. In addition, liposomes can be used to carry radioactive moieties, such as radiotracers, which can be bound at multiple locations within liposomes, making them attractive carriers for molecular imaging applications. Phage display is a technique that can deliver various high-affinity and selectivity peptides to different targets. In this study, gelatinase-binding peptides, found by phage display, were attached to liposomes by covalent peptide-PEG-PE anchor creating a targeted drug delivery vehicle. Gelatinases as extracellular targets for tumor targeting offer a viable alternative for tumor targeting. Our findings show that targeted drug delivery is more efficient than non-targeted drug delivery.

Figure 1

Chemical structure of ¹²⁵I-CTT2-peptide. CTT2-peptide is a 17-amino acid peptide with a disulphide bridge between the two cysteines. The amino terminal end of the peptide is amidated to increase its stability. Upon iodination, peptide labeling occurs on the aromatic ring of the tyrosine amino acid.

Figure 2

Chemical structure of CTT2-PEG3400-DSPE. CTT2-PEG3400-DSPE was synthesized by coupling CTT2-peptide to PEG3400-DSPE, followed by purification of the reaction product from the initial mixture.

Figure 3

Schematic illustration of CTT2-PEG-3400-DSPE liposome [22].

Figure 4

Hepatic accumulation of ¹²⁵I-CTT2-peptides in normal mice. Liver accumulation of peptides per gram of tissue in normal mice (n = 5) relative to muscle (control). All values are expressed as the percentage of the control (% control) ± SD.

Figure 5

Tissue distribution of a single dose of ¹²⁵I-CTT2-peptide in immunosuppressed OV-90 xenograft mice. Blood and major organs/tissues were collected at 0.5 hr and 3 hrs p.i. ¹²⁵I-CTT2-peptide (40 μg/mouse, n = 5) and their radioactivities were measured. Results are expressed as percentage of injected dose per gram tissue (%ID/g). All values are given as mean ± SD.

Figure 6

Tissue distribution of ¹²⁵I-CTT2-micelle in OV-90 tumor mice. %ID/g values after i.v. injection of CTT2-micelles (200 μg/mouse, n = 5). All values are expressed as mean ± SD.

Figure 7

Comparison of doxorubicin concentrations in tumors after a single i.v. injection of CTT2-SL liposome or Caelyx. A2780 xenografts (n = 6) were collected at 2, 6, 24, 48, 72, and 96 hours after CTT2-liposome or Caelyx injection, and their doxorubicin content was measured using spectrophotometry. Results are shown as μg drug per gram of dry tissue. All values are expressed as the mean ± SD. The differences in each time point are near significant. The overall difference in the AUC is significant.

Figure 8

Kaplan-Meier plot of the survival of tumor bearing mice. Mice were treated with doxorubicin (9 mg/kg), administered either as CTT2-SL liposome or Caelyx. Controls were injected with doxorubicin (9 mg/kg) or saline dilution buffer. Injections for each treatment group were made at day 0, day 3 and day 6, respectively.

Figure 9

Mouse body weight changes in each treatment group during the first 32 days of the trial. Mice were treated with 9 mg/kg doxorubicin (calculated doxorubicin equivalents) or saline dilution buffer at day 0, 3 and 6. All values are expressed as mean of 9 mice.

Figure 10

Concentrations of doxorubicin in (a) serum and (b) OV-90 xenografts in mice treated with CTT2-SL liposome and Caelyx at 0.5 and 6 hours. Data are represented as a mean of 5 mice ± SD.

Figure 11

Serum doxorubicin levels. Concentration of doxorubicin in (a) serum and (b) OV-90 xenograft mice (n = 3) treated with CTT2-SL-DSPE-PEG3400. Data are represented as a mean ± SEM.