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Low-dose methotrexate enhances aminolevulinate-based photodynamic therapy in skin carcinoma cells in vitro and in vivo
Clinical Cancer Research, 05/22/09

Anand S et al. - In a study to improve treatment efficacy and tumor cell selectivity of δ-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) via pretreatment of cells and tumors with methotrexate to enhance intracellular photosensitizer levels, it was shown that combination therapy using short-term exposure to low-dose methotrexate followed by ALA-PDT should be further investigated as a new combination modality to enhance efficacy and selectivity of PDT for epithelial carcinomas.

• Skin carcinoma cells, in vitro and in vivo, served as the model system.
• Cultured human SCC13 and HEK1 cells, normal keratinocytes, and in vivo skin tumor models were preconditioned with methotrexate for 72 h and then incubated with ALA for 4 h.
• Changes in protoporphyrin IX (PpIX) levels and cell survival after light exposure were assessed.

• Methotrexate preconditioning of monolayer cultures preferentially increased intracellular PpIX levels 2- to 4-fold in carcinoma cells vs normal keratinocytes.
• Photodynamic killing was synergistically enhanced by the combined therapy vs PDT alone.
• Methotrexate enhancement of PpIX levels was achieved over a broad methotrexate concentration range (0.0003-1.0 mg/L; 0.6 nmol/L-2 mmol/L).
• PpIX enhancement correlated with changes in protein expression of key porphyrin pathway enzymes, 4-fold increase in coproporphyrinogen oxidase and stable or slightly decreased expression of ferrochelatase.
• Differentiation markers (E-cadherin, involucrin, and filaggrin) were also selectively induced by methotrexate in carcinoma cells.
• In vivo relevance was established by showing that methotrexate preconditioning enhances PpIX accumulation in 3 models: organotypic cultures of immortalized keratinocytes, chemically induced skin tumors in mice; and human A431 squamous cell tumors implanted subcutaneously in mice.

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