The interaction between doxorubicin (DOX), an anthracycline antibiotic frequently used in chemotherapy, and zwitterionic dipalmitoylphosphatidylcholine (DPPC) was investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and rheological measurements. FTIR results showed that DOX shifted the wavenumber of the PO(2)(-) band for pure DPPC to a higher wavenumber. This may have been because of the strong interactions between the NH(3)(+) group in DOX and the phosphate (PO(2)(-)) group in the polar head of DPPC. The main transition temperature of DPPC liposomes was slightly shifted to a lower temperature for DPPC liposome-encapsulated DOX. This suggested that DOX had a significant effect on the acyl chains in the DPPC bilayers, and that its presence decreased the transition cooperativity of lipid acyl chains. There was also the appearance of an additional transition peak at nearly 136 °C for the DPPC/DOX sample. These interactions between DOX and DPPC phospholipid would cause a decrease in the DPPC liposomes plastic viscosity and increase membrane fluidity. A better understanding of the interactions between DOX and lipid bilayers could help in the design and development of improved liposomal drug delivery systems.
In order to improve liposomal doxorubicin stability, differentiation between Heparin and Polyethylene Glycol (PEG) as biofunctionalization for liposomal doxorubicin has been investigated by measuring the entrapment efficiency, size distribution, zeta potential, evaluating the in vitro potential cytotoxicity against MCF-7 (Breast cancer cell) and stability in serum by measuring the drug release rate. We synthesized Four liposomal formulations: (A) Conventional liposomes; DPPC:DOX, (B) Positively charged PEGylated liposomes; DPPC:CHOL:SA:PEG:DOX (C) Negatively charged PEGylated liposomes: DPPC:CHOl:DCP:PEG:DOX (D) positively charged liposomes to conjugate heparin; DPPC:CHOL:SA:DOX. Entrapment efficiency of doxorubicin dramatically increased after PEGylation and conjugation with heparin. In addition, zeta potential was changed upon the encapsulation of doxorubicin into conventional and PEGylated liposomes which indicates that DOX encapsulated completely into liposomes. For heparin conjugated liposomes, zeta potential was slightly changed. Sulphorhodamine-B (SRB) assay showed a greater cytotoxic effect of the liposomal doxorubicin formulations at different concentrations with respect to free drug against MCF-7 cell lines. The anticancer activity order was observed between the various liposome formulations, especially those observed with conjugated heparin liposomes. Slower drug release rate showed an order of D > C > B > A that means stability showed an order of D > C > B > A. From above results, the most stable liposomal doxorubicin formulation was the liposomal formulation D. The results optimized using heparin than PEG as biofunctionalization. Further studies are suggested for better understanding why heparin improves the stability of liposomal doxorubicin.
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