Methotrexate Used in Combination With Aminolaevulinic Acid for Photodynamic Killing of Prostate Cancer Cells

Br J Cancer. 2006 Aug 21;95(4):485-95. doi: 10.1038/sj.bjc.6603273. Epub 2006 Jul 25.

Abstract

Photodynamic therapy (PDT) using 5-aminolaevulinic acid (ALA) to drive production of an intracellular photosensitiser, protoporphyrin IX (PpIX), is a promising cancer treatment. However, ALA-PDT is still suboptimal for thick or refractory tumours. Searching for new approaches, we tested a known inducer of cellular differentiation, methotrexate (MTX), in combination with ALA-PDT in LNCaP cells. Methotrexate alone promoted growth arrest, differentiation, and apoptosis. Methotrexate pretreatment (1 mg l(-1), 72 h) followed by ALA (0.3 mM, 4 h) resulted in a three-fold increase in intracellular PpIX, by biochemical and confocal analyses. After exposure to 512 nm light, killing was significantly enhanced in MTX-preconditioned cells. The reverse order of treatments, ALA-PDT followed by MTX, yielded no enhancement. Methotrexate caused a similar relative increase in PpIX, whether cells were incubated with ALA, methyl-ALA, or hexyl-ALA, arguing against a major effect upon ALA transport. Searching for an effect among porphyrin synthetic enzymes, we found that coproporphyrinogen oxidase (CPO) was increased three-fold by MTX at the mRNA and protein levels. Transfection of LNCaP cells with a CPO-expressing vector stimulated the accumulation of PpIX. Our data suggest that MTX, when used to modulate intracellular production of endogenous PpIX, may provide a new combination PDT approach for certain cancers.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aminolevulinic Acid / pharmacology*
  • Apoptosis
  • Cell Differentiation
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Survival
  • Coproporphyrinogen Oxidase / metabolism
  • Humans
  • Male
  • Methotrexate / administration & dosage
  • Methotrexate / pharmacology*
  • Metribolone / pharmacology
  • Models, Biological
  • Photochemotherapy*
  • Photosensitizing Agents / pharmacology
  • Prostatic Neoplasms / therapy*
  • Protoporphyrins / metabolism
  • Up-Regulation

Substances

  • Photosensitizing Agents
  • Protoporphyrins
  • Metribolone
  • Aminolevulinic Acid
  • protoporphyrin IX
  • Coproporphyrinogen Oxidase
  • Methotrexate