The aim of this work was to use the quality-by-design (QbD) approach in the development of long-circulating liposomes co-loaded with curcumin (CUR) and doxorubicin (DOX) and to evaluate the cytotoxic potential of these liposomes in vitro using C26 murine colon carcinoma cell line. Based on a risk assessment, six parameters, namely the phospholipid, CUR and DOX concentrations, the phospholipid:cholesterol molar ratio, the temperature during the evaporation and hydration steps and the pH of the phosphate buffer, were identified as potential risk factors for the quality of the final product. The influence of these variables on the critical quality attributes of the co-loaded liposomal CUR and DOX was investigated: particle size, zeta potential, drug loading and entrapment efficiency. For this, a 26−2 factorial design was employed to establish a proper regression model and to generate the contour plots for the responses. The obtained data served to establish the design space for which different combinations of variables yielded liposomes with characteristics within predefined specifications. The validation of the model was carried out by preparing two liposomal formulations corresponding to the robust set point from within the design space and one outside the design space and calculating the percentage bias between the predicted and actual experimental results. The in vitro antiproliferative test showed that at higher CUR concentrations, the liposomes co-encapsulating CUR and DOX had a greater cytotoxic effect than DOX-loaded liposomes. Overall, this study showed that QbD is a useful instrument for controlling and optimizing the manufacturing process of liposomes co-loaded with CUR and DOX and that this nanoparticulate system possesses a great potential for use in colon cancer therapy.

Quality by design principles (QbD) were used to assist the formulation of prednisolone-loaded long-circulating liposomes (LCL-PLP) in order to gain a more comprehensive understanding of the preparation process. This approach enables us to improve the final product quality in terms of liposomal drug concentration, encapsulation efficiency and size, and to minimize preparation variability. A 19-run D-optimal experimental design was used to study the impact of the highest risk factors on PLP liposomal concentration (Y- μg/ml), encapsulation efficiency (Y-%) and size (Y-nm). Out of six investigated factors, four of them were identified as critical parameters affecting the studied responses. PLP molar concentration and the molar ratio of DPPC to MPEG-2000-DSPE had a positive impact on both Y and Y, while the rotation speed at the formation of the lipid film had a negative impact. Y was highly influenced by prednisolone molar concentration and extrusion temperature. The accuracy and robustness of the model was further on confirmed. The developed model was used to optimize the formulation of LCL-PLP for efficient accumulation of the drug to tumor tissue. The cytotoxicity of the optimized LCL-PLP on C26 murine colon carcinoma cells was assessed. LCL-PLP exerted significant anti-angiogenic and anti-inflammatory effects on M2 macrophages, affecting indirectly the C26 colon carcinoma cell proliferation and development.

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LCL-CURC-DOX demonstrated enhanced cytotoxicity on C26 murine colon cancer cells by inhibiting the production of the majority of factors involved in tumor-associated angiogenesis and inflammation and is now being evaluated in vivo regarding its efficacy towards tumor growth in colon cancer.

The effect of lyoprotectant type and concentration on the stability of freeze-dried prednisolone sodium phosphate-loaded long-circulating liposomes was investigated. Trehalose at a 5:1 carbohydrate to lipid molar ratio proved to be superior in maintaining the structural integrity and the permeability properties of the liposome bilayers, assuring the desired characteristics of the final product: a cake with a porous structure and easy to reconstitute, a similar size to the liposomes before freeze-drying, a high percent of encapsulated drug, and a low residual moisture content. Further on, the study demonstrated the possibility of near-infrared spectroscopy to provide valuable insights for detecting critical changes in acyl chain packing of the liposome bilayer. By visualizing the spectra after principal component analysis, one can predict if any harm has occurred to liposome integrity during the process. Moreover, near-infrared spectroscopy enabled us to determine the end points of primary and secondary drying without disturbing the normal freeze-drying procedure, which allowed us to gain a better understanding of the process and to improve process efficiency by optimizing the primary and secondary drying time.