Delivery and Metabolic Fate of Doxorubicin and Betulin Nanoformulations In Vivo: A Metabolomics Approach

Background: Betulins (betulin, betulinic acid and lupeol) demonstrated antitumor and chemopreventive activity but showed low bioavailability due to their self-aggregation in hydrophilic environments. To overcome these disadvantages, their incorporation into lipid nanoformulations (PEGylated liposomes and Lipid Nanostructured Carriers (NLCs)) has proven to represent a viable solution. Objectives: The purpose of this study is to evaluate the size and incorporation rate of these molecules in nanoformulations, as well as their delivery and metabolic fate (pure betulinic acid versus a standardized extract, TT) relative to Doxorubicin using an in vivo protocol. The investigation extended our previous in vitro investigations towards an in vivo evaluation of antitumor activity, metabolic fate and toxicity in Wistar rats bearing Walker 256 carcinoma tumors over 21 days. Since previous studies used oral or intratumor administration, this exploratory study applied intravenous administration via microbubble-assisted sonoporation, considering its higher relevance for translational studies. Methods: The delivery and metabolic fate of the parent molecules, the identification of their fragments and metabolites using UHPLC-QTOF-ESI⁺MS were investigated, along with the identification of some toxicity biomarkers in rat plasma, tumor tissues and urine. Results: Preferential accumulation of Doxorubicin in tumors was observed compared to betulinic acid and TT components, as well as their persistence in plasma or elimination in urine. Compared to PEGylated liposomes, NLC formulations (especially NLC Doxo) induced a lower survival rate, a decreased bioavailability and increased toxicity by around 20%. Conclusions: These data are a starting point and complement the contrast-enhanced imaging and histology evaluations, which may contribute to the actual knowledge about the in vivo fate of betulins.