Plasma membrane targeting by short chain sphingolipids inserted in liposomes improves anti-tumor activity of mitoxantrone in an orthotopic breast carcinoma xenograft model.

Mitoxantrone (MTO) is clinically used for treatment of various types of cancers providing an alternative for similarly active, but more toxic chemotherapeutic drugs such as anthracyclines. To further decrease its toxicity MTO was encapsulated into liposomes. Although liposomal drugs can accumulate in target tumor tissue, they still face the plasma membrane barrier for effective intracellular delivery. Aiming to improve MTO tumor cell availability, we used short chain lipids to target and modulate the tumor cell membrane, promoting MTO plasma membrane traversal. MTO was encapsulated in liposomes containing the short chain sphingolipid (SCS), C8-Glucosylceramide (C8-GluCer) or C8-Galactosylceramide (C8-GalCer) in their bilayer. These new SCS-liposomes containing MTO (SCS-MTOL) were tested in vivo for tolerability, pharmacokinetics, biodistribution, tumor drug delivery by intravital microscopy and efficacy, and compared to standard MTO liposomes (MTOL) and free MTO. Liposomal encapsulation decreased MTO toxicity and allowed administration of higher drug doses. SCS-MTOL displayed increased clearance and lower skin accumulation compared to standard MTOL. Intratumoral liposomal drug delivery was heterogeneous and rather limited in hypoxic tumor areas, yet SCS-MTOL improved intracellular drug uptake in comparison with MTOL. The increased MTO availability correlated well with the improved antitumor activity of SCS-MTOL in a MDAMB-231 breast carcinoma model. Multiple dosing of liposomal MTO strongly delayed tumor growth compared to free MTO and prolonged mouse survival, whereas among the liposomal MTO treatments, C8-GluCer-MTOL was most effective. Targeting plasma membranes with SCS improved MTO tumor availability and thereby therapeutic activity and represents a promising approach to improve MTO-based chemotherapy.

C8-glycosphingolipids preferentially insert into tumor cell membranes and promote chemotherapeutic drug uptake.

Insufficient drug delivery into tumor cells limits the therapeutic efficacy of chemotherapy. Co-delivery of liposome-encapsulated drug and synthetic short-chain glycosphingolipids (SC-GSLs) significantly improved drug bioavailability by enhancing intracellular drug uptake. Investigating the mechanisms underlying this SC-GSL-mediated drug uptake enhancement is the aim of this study. Fluorescence microscopy was used to visualize the cell membrane lipid transfer intracellular fate of fluorescently labeled C6-NBD-GalCer incorporated in liposomes in tumor and non-tumor cells. Additionally click chemistry was applied to image and quantify native SC-GSLs in tumor and non-tumor cell membranes. SC-GSL-mediated flip-flop was investigated in model membranes to confirm membrane-incorporation of SC-GSL and its effect on membrane remodeling. SC-GSL enriched liposomes containing doxorubicin (Dox) were incubated at 4°C and 37°C and intracellular drug uptake was studied in comparison to standard liposomes and free Dox. SC-GSL transfer to the cell membrane was independent of liposomal uptake and the majority of the transferred lipid remained in the plasma membrane. The transfer of SC-GSL was tumor cell-specific and induced membrane rearrangement as evidenced by a transbilayer flip-flop of pyrene-SM. However, pore formation was measured, as leakage of hydrophilic fluorescent probes was not observed. Moreover, drug uptake appeared to be mediated by SC-GSLs. SC-GSLs enhanced the interaction of doxorubicin (Dox) with the outer leaflet of the plasma membrane of tumor cells at 4°C. Our results demonstrate that SC-GSLs preferentially insert into tumor cell plasma membranes enhancing cell intrinsic capacity to translocate amphiphilic drugs such as Dox across the membrane via a biophysical process.