Timothy J Brown, Aileen M. Garcia, Lindsey N Kissinger, Sriram S Shanmugavelandy, Xujung Wang1, Myles C Cabot, Mark Kester, David F Claxton1 and Brian M BarthNovel approaches to enhancing the efficacy of ceramide-based therapeutics are of interest for the treatment of acute myeloid leukemia (AML). Ceramide is a bioactive sphingolipid that has long been established as an inducer of apoptosis. We have pioneered the effort to develop nanoliposomal C6-ceramide (Lip-C6) as an anticancer therapeutic and recently have engaged in efforts to enhance its therapeutic efficacy. Ceramide catabolism by acid ceramidase and subsequently sphingosine kinase 1 yields the metabolite oncogenic sphingosine-1-phosphate (S1P). Therefore, in the present study we hypothesized that targeting of this metabolic pathway with the sphingosine kinase 1 inhibitor safingol would augment the anti-AML efficacy of Lip-C6. We generated and evaluated nanoliposomes encapsulating safingol (Lip-Saf), in combination with Lip-C6 using AML cell lines and primary AML patient samples. This combination exerted synergistic therapeutic efficacy using HL-60 and KG-1 cells, and additive efficacy using HL-60/VCR cells. In contrast, the combination of Lip-C6 and Lip-Saf yielded an antagonistic effect using the murine AML cell line C1498 and this effect was correlated with an increase in autophagy as a potent leukemia survival mechanism. Intriguingly, by using an inhibitor of ceramide glycosylation, nanoliposomal tamoxifen, we observed synergistic anti-AML efficacy using the C1498 cell line demonstrating that unique manipulations of ceramide metabolism may be prevalent in different AMLs. Lastly, we evaluated both favorable prognosis and poor prognosis primary patient AML samples and observed combinatorial efficacy of Lip-C6 and Lip-Saf. This was reflected by a decrease in autophagy and concomitant increase in apoptosis, as well as the ability to block colony forming capacity. Altogether, these results demonstrated that the efficacy of Lip-C6 as an experimental anti-AML therapy can be dramatically enhanced through combination with inhibitors of ceramide metabolism.