Cancer chemotherapy administered by activated carbon particles and liposomes

Targeting doxorubicin encapsulated in stealth liposomes to solid tumors by non thermal diode laser

BACKGROUND

The use of liposomes as drug delivery systems is the most promising technique for targeting drug especially for anticancer therapy.

METHODS

In this study sterically stabilized liposomes was prepared from DPPC/Cholesterol/PEG-PE encapsulated doxorubicin. The effect of lyophilization on liposomal stability and hence expiration date were studied. Moreover, the effect of diode laser on the drug released from liposomesin vitro and in vivo in mice carrying implanted solid tumor were also studied.

RESULTS

The results indicated that lyophilization of the prepared liposomes encapsulating doxorubicin led to marked stability when stored at 5 °C and it is possible to use the re-hydrated lyophilized liposomes within 12 days post reconstitution. Moreover, the use of low energy diode laser for targeting anticancer drug to the tumor cells is a promising method in cancer therapy.

CONCLUSION

We can conclude that lyophilization of the liposomes encapsulating doxorubicin lead to marked stability for the liposomes when stored at 5 °C. Moreover, the use of low energy diode laser for targeting anticancer drug to the tumor cells through the use of photosensitive sterically stabilized liposomes loaded with doxorubicin is a promising method. It proved to be applicable and successful for treatment of Ehrlich solid tumors implanted in mice and eliminated toxic side effects of doxorubicin.

Clinical pharmacology of anticancer agents in relation to formulations and administration routes

In the past years, alternative administration routes and pharmaceutical formulations of anticancer agents have been investigated in order to improve conventional chemotherapy treatment. The impact of these adjustments on the pharmacokinetics and pharmacodynamics is discussed. A review of the literature shows many examples of alternative administration forms of anticancer agents with improved pharmacokinetics. Local administration routes have been investigated in order to reduce the systemic toxicity and to enhance the local efficacy of conventional chemotherapy. Oral administration of anticancer agents is preferred by patients for its convenience and its potential for outpatient treatment. In addition, oral administration facilitates a prolonged exposure to the cytotoxic agent. However, poor bioavailability and substantial interpatient variability are noted as limitations for oral chemotherapy. Increased tumour selectivity can also be achieved by the use of specific pharmaceutical formulations, such as liposomes and macromolecular drug conjugates. The composition of these formulations often determine the pharmacokinetic behaviour of the formulated drug. In conclusion, several alternative administration forms of anticancer agents have been designed in the past years, with the potential for improvement of conventional chemotherapy, however, more extensive clinical evaluation of these novel strategies is warranted to prove their real clinical value.

Liposomal Arg-Gly-Asp analogs effectively inhibit metastatic B16 melanoma colonization in murine lungs

Analogs of a synthetic peptide having the L-arginine-L-glycine-L-aspartic acid (RGD) sequence have been found to decrease metastatic colonization. To enhance the metastasis-suppressing efficacy of these analogs, we sought to stabilize these analogs and to prolong their circulation time by incorporating them into a liposomal formulation. Various structures of RGD analogs grafted to hydrophobic groups were synthesized and then incorporated into liposomes. Liposomes composed of distearoylphosphatidylcholine, cholesterol, dipalmitoylphosphatidylglycerol and appropriate RGD analogs were injected intravenously along with B16BL6 murine melanoma cells into mice. Liposomal RGD (0.6 mumol of the analog equivalent to ca. 200 micrograms RGD peptides) inhibited lung colonization up to 76%. This dose is an order of magnitude lower than that for comparable inhibition reported for free RGD. Multi-dose administration of liposomal RGD (0.15 mumol of the analog) also inhibited the spontaneous lung metastasis of cells from a primary tumor site of B16BL6 cells subcutaneously implanted into the footpad of mice. Taken together, our data indicate that liposomal RGD may serve as a useful anti-metastatic agent.

Antitumor activity of vincristine encapsulated in glucuronide-modified long-circulating liposomes in mice bearing Meth A sarcoma

Liposomes modified with the uronic acid derivative palmityl-D-glucuronide (PGlcUA) have a long circulation time and tend to accumulate in the tumors of tumor-bearing mice. Taking advantage of this character, we investigated the therapeutic effect of vincristine (VCR) encapsulated in liposomes containing PGlcUA (dipalmitoylphosphatidylcholine/cholesterol/PGlcUA = 4:4:1 as a molar ratio) on tumor-bearing mice. VCR was loaded into liposomes by a remote loading method, and then free or liposomal VCR was injected intravenously into BALB/c mice bearing Meth A sarcoma implanted subcutaneously 5 days before hand. Single-dose administration of VCR (3.0 mg/kg) in PGlcUA-liposomes significantly suppressed tumor growth, and prolonged the survival time (T/C = 1.37). Furthermore, two-dose administration of the liposomes cured one third of the animals. The therapeutic effect of PGlcUA-liposomes was greater than that of control liposomes containing dipalmitoylphosphatidylglycerol instead of PGlcUA. PGlcUA-liposomes might thus be a useful tool for delivering antitumor agents to tumor tissues.

Real-time analysis of liposomal trafficking in tumor-bearing mice by use of positron emission tomography

Long-circulating liposomes are known to accumulate passively in tumor tissues of tumor-bearing animals. To evaluate the in vivo behavior of such liposomes, we investigated the real-time liposomal trafficking by a non-invasive method using position emission tomography (PET). Liposomes composed of dipalmitoylphosphatidylcholine, cholesterol, and palmityl-D-glucuronide (PGlcUA) in a molar ratio of 4:4:1 were prepared in the presence of 2-[18F]fluoro-2-deoxyglucose ([2-18F]FDG). [2-18F]FDG-labeled liposomes sized by extrusion through a filter with various-sized pores were administered to mice bearing Meth A sarcoma, and a PET scan was performed for 120 min. Small-sized, long-circulating liposomes (100 nm in diameter) constructed with PGlcUA tended to accumulate in the tumor tissues. On the contrary, control liposomes (100 nm in diameter) containing dipalmitoylphosphatidylglycerol instead of PGlcUA accumulated in the liver. Large-sized PGlcUA-containing liposomes (> 300 nm) also accumulated in the liver, as well as in the spleen. Time-activity curves indicated that the small long-circulating liposomes (< 200 nm) transiently accumulated in the liver right after the injection but that the accumulation there decreased time-dependently. These data suggest that, although the majority of small long-circulating liposomes remain in the bloodstream, some extravasate once into the interstitial spaces in the liver re-enter the bloodstream again, and finally accumulate in the tumor tissues. This PET technique might be useful for studying real-time liposomal trafficking and for tumor imaging.

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.

Potential usage of thermosensitive liposomes for macromolecule delivery

Since transient swelling during phase transition of liposomes with hyper-osmotic internal aqueous phase may cause permeation of large molecules through the lipid bilayer, this type of liposomes can be useful for delivering macromolecules. In fact, thermosensitive liposomes containing an internal solution with osmotic pressure 2-fold higher than the physiologic level and sized through 200-nm pore, released encapsulated macromolecules such as dextran (M(r) 144,000) effectively when they were incubated at 40-42 degrees C. These liposomes were stable in the presence of serum compared to the liposomes with internal osmotic pressure more than 3-fold higher than the physiologic level.

Tumor imaging with technetium-99m-DTPA encapsulated in RES-avoiding liposomes

For passive targeting of liposomes to tumor tissues, we earlier developed reticuloendothelial system (RES)-avoiding liposomes modified with a uronic acid derivative, palmityl-D-glucuronide (PGlcUA). In the present study, we encapsulated technetium-99m (99mTc)-diethylenetriaminepentaacetic acid (DTPA) in PGlcUA-liposomes (dipalmitoylphosphatidylcholine:cholesterol:PGlcUA = 40:40:20 as a molar ratio) and studied the biodistribution of the liposomes in tumor-bearing mice. 99mTc-DTPA encapsulated in liposomes effectively accumulated in tumor tissues after intravenous administration. Corresponding to these results, tumor was strongly imaged by a gamma-camera when 99mTc-DTPA-encapsulated PGlcUA-liposomes were used.