Cell physiology, biochemistry, and molecular biology of 5-aminolevulinic acid-induced protoporphyrin IX in normal, immortalized, transfected, and malignant cells

It is widely accepted that substantially more 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PPIX) accumulates in cancer cells than in the normal cells from which they were derived. This phenomenon is the ALA-phenotype. Based on this phenotype, ALA-associated photodynamic therapy (ALA-PDT) was developed and became a modality for the treatment of cancer. However, the mechanisms responsible for the ALA-phenotype are still unclear. In this thesis, we describe investigations of the relationship between the ALA-phenotype and several factors including cell physiology (proliferation and differentiation), biochemistry (alterations of enzymatic metabolism), and molecular biology (oncogene transfection). The significant results and clinical implications are summarized as follows. (1) Murine and rat fibroblasts at different stages during malignant transformation appear to provide a good model for studies of ALA-phenotype. The cells included Balb/c mouse embryonic fibroblasts (MEFs) (normal), Balb/c mouse and rat immortalized but not malignant fibroblasts, immortalized fibroblasts transfected with selected oncogenes (transformed), and Balb/c mouse fibrosarcoma cell lines (neoplastic). ALA-PDT may be useful modality for the treatment of fibrosarcoma. (2) There is no correlation between cell proliferation and ALA-induced PPIX accumulation. In contrast, cell differentiation has apparent effects on ALA-induced PPIX accumulation. The impact of cell differentiation on ALA-phenotype is cell type dependent. The induced differentiation of human promyelocytic leukemia HL 60 decreased ALA-induced PPIX accumulation, while the induction of differentiation of mouse preadipocytes 3T3 L1 increased ALA-induced PPIX accumulation. The ALA-phenotype might be used as a marker for the detection of leukemic cells and for monitoring the effects of treatment of leukemia during differentiation therapy. (3) A model was proposed for studies of enzymatic alterations in the heme biosynthetic pathway. According to this model, enzymes responsible for the ALA phenotype are located upstream from PPIX rather than downstream. A decrease in protoporphyrinogen oxidase is suspected, but an increase in some other enzyme (especially porphobilinogen deaminase) cannot be excluded from playing an important role in the ALA-induced PPIX accumulation. Once the specific enzyme responsible for the ALA phenotype is discovered, it may be possible to develop techniques based on this enzyme to diagnosis and treat cancer. (4) There is a correlation between oncogene activity and the ALA-phenotype. Antisense oligodeoxynucleotide therapy that blocks the oncogene responsible for malignant transformation can be monitored by following the ALA-phenotype.