C22:0- and C24:0-dihydroceramides confer cytotoxicity in T-cell acute lymphoblastic leukemia cell lines
Holliday, Michael W.
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The synthetic retinoid N-(4-hydroxyphenyl)-retinamide (fenretinide, 4-HPR) is an anti-cancer agent under clinical evaluation in a variety of cancers, including in pediatric acute lymphoblastic leukemia (ALL). We have previously reported that 4-HPR induces cell death in association with an increase of dihydroceramides in multiple cancer cell lines in vitro. However, exogenous, very short acyl chain dihydroceramides are not cytotoxic. We, therefore, hypothesized that the cytotoxic potential of dihydroceramides may depend on the length and saturation status of their acyl chains. Using a novel method that selectively increased the de novo synthesis of specific acyl chain dihydroceramides and ceramides in cell culture, we report the first comprehensive assessment of the cytotoxic potentials of individual native acyl chain dihydroceramides. Correlation analyses in four pediatric T- cell ALL cell lines (including a p53-null cell line) revealed strong positive correlations between cytotoxicity and levels of C22:0-dihydroceramide (ρ = 0.75 – 0.88, P ≤ 0.01) and C24:0-dihydroceramide (ρ = 0.83 – 0.88, P ≤ 0.005), but not with total or other individual dihydroceramides, total or individual ceramides, sphingoid bases or phosphorylated derivatives, and in the absence of an increase of reactive oxygen species. C22:0-dihydroceramide induced cytotoxicity via apoptosis that was coincident with increased autophagic vacuolization. Furthermore, supplementing 4-HPR-treated cells with C22:0- fatty acid (but not C18:0-fatty acid) increased both C22:0-dihydroceramide levels (P < 0.01) and cytotoxicity (P < 0.05). These data provide first-in-field evidence that, contrary to current literature, specific acyl chain dihydroceramides are cytotoxic and can mediate 4-HPR-induced killing in T-cell ALL cell lines. The targeted increase of specific dihydroceramides may constitute a novel anticancer approach.