Macromolecular drugs have great promises for cancer treatment, such as the pro-apoptotic peptide D-(KLAKLAK)2 and the bcl-2 antisense oligodeoxynucleotide G3139. However, these macromolecules require efficient drug carriers, like liposomes, to deliver them inside cells. Also, if these macromolecules can be combined in a single liposome, the cancer cell killing will be greater than using just one. With this possibility in mind, cationic liposomes (CLs) were elaborated to encapsulate both macromolecules and deliver them inside cells. Later, surface modification of CLs was investigated through the addition of polyethylene glycol (PEG) to obtain long-circulating liposomes.
CLs were prepared through charge alternation among D-(KLAKLAK)2 , G3139 and DOTAP. These liposomes were characterized with particle size and zeta-potential measurements, antisense entrapment and peptide loading efficiency. The in vitro effects of CL formulations were tested with B16(F10) cells through viability studies, uptake assay and detection of apoptosis. CL formulations were also applied in vivo in B16(F10) tumor-bearing mice through intratumoral injections, and tumor growth inhibition and detection of apoptosis were evaluated. Next, the mechanism of action of the CL formulations was investigated by Western blotting. Later, PEG was incorporated at increasing amounts to the liposomes to determine which concentration can better prevent interactions between PEG-cationic liposomes (PCL) and B16(F10) cells. Next, pH-cleavable PEG was prepared and then added to the liposomes in the same amount that PEG in PCL could decrease interaction with cells. Finally, cell viability studies were performed with CL, PCL and pH-sensitive PCL (pH-PCL) formulations after pre-incubation at pH 7.4 or at pH 5.0.
Positively charged CL particles were obtained after encapsulation of negatively charged D-(KLAKLAK)2/G3139 complexes. In vitro , CLs containing D-(KLAKLAK)2/G3139 complexes could reduce B16(F10) cell viability with half of the concentration needed for G3139 alone in CL to reduce the cell viability by 40%. Also, it was found greater apoptotic signal in cells treated with CLs containing D-(KLAKLAK)2/G3139 complexes than CLs with G3139 only. In vivo, D-(KLAKLAK) 2/G3139 complexes in CL significantly inhibited tumor growth compared to the saline treated group, through apoptosis induction. However, the mechanism involved in cell death by apoptosis seems to be independent of reduction of bcl-2 protein levels. PEG2000 at 1% mol could significantly reduce activity of PCL formulation towards B16(F10) cells compared to CLs. After pre-incubation at pH 7.4, PCL and pH-PCL had decreased activity compared to CL towards B16(F10) cells. After pre-incubation at pH 5.0, while CL and PCL had the same activity with the cells as in neutral pH, pH-PCL formulation had its PEG cleaved and its cytotoxicity was restored against the melanoma cells.
Thus, D-(KLAKLAK)2/G3139 complexes in CL had enhanced anti-cancer therapy, through apoptosis, than G3139 alone in CL in vitro and in vivo. In vitro, PCL and pH-PCL particles obtained can have a prolonged blood residence time, and, once a tumor tissue is reached, pH-PCL can have its cytotoxicity restored because of hydrolysis of cleavable PEG at a lowered pH.