Association of ceramide accumulation with photodynamic treatment-induced cell death.
Ceramide, a stress-induced second messenger, has been associated with apoptosis in several malignant and non-malignant cell lines. We have shown that photodynamic treatment (PDT), using the phthalocyanine photosensitizer Pc 4 (HOSiPcOSi[CH3]2[CH2]3N[CH3]2), causes increased ceramide generation and subsequent induction of apoptosis in L5178Y-R (LY-R) mouse lymphoma cells. To test further if ceramide generation accompanies photocytotoxicity, we treated various cell lines with a PDT dose producing a 99-99.9% loss of clonogenicity. Like LY-R cells, human leukemia (U937) cells underwent rapid DNA fragmentation initiating within 1 h after PDT. Similarly, Chinese hamster ovary (CHO) cells showed rapid DNA laddering, beginning 1 h following the treatment. In contrast, mouse radiation-induced fibrosarcoma (RIF-1) cells showed no apoptosis within 24 h post-PDT, as judged by the absence of 50 kbp and oligonucleosome size DNA fragments, as well as no annexin V binding to cells with preserved membrane integrity. Using the same doses of PDT, we observed a time-dependent ceramide accumulation in all three cell lines. While a significant increase in ceramide levels was reached within 1 and 10 min in U937 and CHO cells, respectively, elevated ceramide production was measured only after 30 min in RIF-1 cells. In addition, exogenous N-acetyl-sphingosine was able to mimic PDT-induced apoptosis in U937 and CHO cells. We suggest that ceramide accumulation is associated with PDT-induced apoptosis and photocytotoxicity.
Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4942, USA. dxs66@po.cwru.edu
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Separovic
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Mann
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Oleinick
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D016466:CHO Cells; D002518:Ceramides / Q000378:metabolism* / Q000494:pharmacology; D006224:Cricetinae; D006801:Humans; D007211:Indoles / Q000493:pharmacokinetics; D051379:Mice; D018462:Photobiology; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured
D002518:Ceramides; D007211:Indoles; D017319:Photosensitizing Agents; C107448:phthalocyanine Pc 4