Niemann-Pick human lymphoblasts are resistant to phthalocyanine 4-photodynamic therapy-induced apoptosis

Duska Separovic, John J. Pink, Nancy A. Oleinick, Mark Kester, David A. Boothman, Maureen McLoughlin, Louis A. Peña, Adriana Haimovitz-Friedman

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Stress-induced activation of sphingomyelinase (SMase) leading to generation of ceramide, a lipid mediator, has been associated with apoptosis in several malignant and nonmalignant cell lines. Photodynamic therapy (PDT), with the phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N(CH3)2], is an oxidative stress associated with increased ceramide generation and subsequent induction of apoptosis in various cell types. We assessed the role of SMase in photocytotoxicity. Normal human lymphoblasts accumulated ceramide and underwent apoptosis after Pc 4-PDT. In contrast, Niemann-Pick disease (NPD) lymphoblasts, which are deficient in acid sphingomyelinase (ASMase) activity, failed to respond to Pc 4-PDT with ceramide accumulation and apoptosis, suggesting that ASMase may be a Pc 4-PDT target. NPD lymphoblasts were exposed to exogenous bacterial sphingomyelinase (bSMase) to test whether these defects are reversible. Treatment of NPD cells with bSMase itself led to elevated ceramide formation, which did not translate into induction of apoptosis. However, a combination of Pc 4-PDT + bSMase induced a significant apoptotic response. Thus, the combined treatment of Pc 4-PDT + bSMase, rather than bSMase alone, was required to restore apoptosis in NPD cells. These data support the hypothesis that SMase is a proapoptotic factor determining responsiveness of cells to Pc 4-PDT.

Original languageEnglish (US)
Pages (from-to)506-512
Number of pages7
JournalBiochemical and Biophysical Research Communications
Issue number3
StatePublished - May 19 1999


  • Acid sphingomyelinase
  • Apoptosis
  • Ceramide
  • Pc 4
  • Phthalocyanine

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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