Novel (1S,3R)-RSL3-Encapsulated Polyunsaturated Fatty Acid Rich Liposomes Sensitise Multiple Myeloma Cells to Ferroptosis-Mediated Cell Death

Background: Multiple myeloma (MM) is an incurable malignancy of plasma cells that accounts for 10% of all haematological malignancies diagnosed worldwide. The poor outcome of patients with MM highlights the ongoing need for novel treatment strategies. Ferroptosis is a recently-characterised form of non-apoptotic programmed cell death. Phospholipids (PLs) containing polyunsaturated fatty acids (PUFA) play a crucial role as ferroptosis substrates when oxidised to form toxic lipid reactive oxygen species (ROS). Methods: Using a range of scientific techniques, we demonstrate a strong correlation between the PL profile of MM and diffuse large B cell lymphoma (DLBCL) cells with their sensitivity to ferroptosis. Using this PL profiling, we manufacture liposomes that are themselves composed of PL-PUFA ferroptosis substrates relatively deficient in MM cells, with and without the GPX4 inhibitor, RSL3, for investigation of their ferroptosis-inducing potential. Results: PL-PUFA were more abundant in DLBCL than MM cell lines, consistent with greater ferroptosis sensitivity. In contrast, MM cells generally contained a significantly higher proportion of PLs containing monounsaturated fatty acids. Altering the lipid composition of MM cells through exogenous supplementation with PL-PUFAs induced ferroptosis-mediated cell death and further sensitised these cells to RSL3. Liposomes comprised predominantly of PL-PUFAs were subsequently manufactured and loaded with RSL3. Uptake, cytotoxicity and lipid ROS studies demonstrated that these novel liposomes were readily taken up by MM cells. Those containing RSL3 were more effective at inducing ferroptosis than empty liposomes or free RSL3, resulting in IC ₅₀ values an average 7.1-fold to 14.5-fold lower than those for free RSL3, from micromolar to nanomolar range. Conclusions: We provide a better understanding of the mechanisms associated with ferroptosis resistance of MM cells and suggest that strategies such as liposomal delivery of relatively deficient ferroptosis-inducing PL-PUFAs together with other targeted agents could harness ferroptosis for the personalised treatment of MM and other cancers.