Development of solid lipid nanoparticles for sustained release of anticancer agents

A brief introduction to solid lipid nanoparticles (SLN) is provided and the reasoning behind the use of SLN over other colloidal carriers, such as emulsions and liposomes, are discussed. SLN has many advantageous such as controlled drug release, non-biotoxicity of the carrier, increased bioavailability of drug and lower overall cost. Techniques for the production of SLN, drug incorporation, loading capacity and drug release mechanisms are reviewed. The potential of SLN in anti-cancer drug delivery systems is highlighted. SLN formulations of two different lipids (tristearin, stearic acid), used as carriers for the encapsulation of the anticancer drug substance curcumin (CRC), have been investigated. The physicochemical characteristics of the CRC-SLNs were investigated by particle size, zeta potential and stability measurements. In addition transmission electron microscopy was used to study the morphology of the SLNs and differential scanning calorimetry (DSC) as well as X- ray diffraction (XRD) were used to evaluate the physical state of the drug in the SLN formulations after freeze drying. The release pattern of CRC-SLN showed sustained release over five days, Moreover, encapsulation efficiency at the range of 92-95% indicated the loosely ordered crystal lattice of lipid matrix, which facilitated a higher drug payload. The anti-cancer effects of CRC encapsulated SLN formulations (both loaded and unloaded) were evaluated using a human prostate cancer cell line (LNCaP). Blank SLN (BL-SLN) did not show any anti-tumour activity; CRC encapsulated SLN (CRC-SLN) displayed anti-tumour activity. Both lipid based CRC loaded SLNs reduced the LNCaP cell viability to almost 0% at a CRC concentration of 100 μg/ml. Cellular uptake studies confirmed the internalisation of CRC-SLN which was found to be localized in the cytoplasm around the nucleus. Flow cytometric studies confirmed the early and late apoptosis inducing ability of CRC-SLNs. Retinoic acid (RTA) loaded SLN, optimized by tuning the process parameters (pressure and temperature) and using various lipid grades to produce nano-dispersions, displayed enhanced anticancer activity. The RTA-SLN dispersions were produced by high-pressure homogenization and characterized in terms of particle size, zeta potential, drug entrapment efficiency, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and in vitro drug release. Anticancer efficiency was evaluated by incubating RTA-SLN with LNCaP cells, and demonstrated reduced cell viability with increasing drug concentrations (9.5% at 200 ug/ml) while blank SLN showed negligible cytotoxicity. Cellular uptake studies of SLNs showed localization within the cytoplasm of the cell and flow cytometry analysis showed an increase in the fraction of cells expressing early apoptotic markers, suggesting that the RTA-SLN is able to induce apoptosis in LNCaP cells. Both empty and loaded (curcumin) nanostructured lipid carriers (NLC) were characterized in relation to their size, zeta potential and polydispersity index. The drug entrapment efficiency and in vitro drug release behaviour of these NLC formulations were also investigated. Analysis of the shape and morphology (using transmission electron microscopy (TEM) and laser diffraction) revealed spherical shaped NLC with a uniform particle size distribution. Cellular uptake studies revealed the internalisation of CRC-NLC, which appear to be localized in the cytoplasm around the nucleus. Flow cytometry studies were performed to evaluate apoptosis inducing abilities of CRC-NLC, as at a CRC concentration of 100 μg/ml, the CRC-NLC treated cells showed 12.2% (early) and 76.9% (late) apoptotic cells. Nude mice bearing prostate cancer xenografts exhibited significant suppression upon administering CRC loaded NLC formulations, with no significant weight loss. The efficacy of CRC-NLC treatment group with CRC only group in comparison with the CRC group showed 40% tumour volume suppression. Unconjugated SLN were conjugated with transferrin for specific (active) delivery of CRC into LNCaP prostate cancer cells. SLNs prepared by high-pressure homogenization were characterised for particle size, zeta potential and drug loading. The transferrin conjugated to SLN was quantified by the Bradford assay. In vitro and in vivo studies of SLN for passive and active delivery of CRC to LNCaP prostate cancer cells were evaluated. In vivo studies of tumour regression efficiency showed CRC-SLN formulations to be more effective in suppressing tumour growth compared to the free drug. In addition the transferrin conjugated SLN also demonstrated a higher anti-tumour activity in tumour bearing mice compared to the non-conjugated formulation. The tumour mass was significantly suppressed by 61% and 79% for CRC-SLN and Tf-CRC-SLN, respectively, when compared with the control group