The induction of partial resistance to photodynamic therapy by the protooncogene BCL-2.
Photodynamic therapy (PDT) is an efficient inducer of apoptosis, an active form of cell death that can be inhibited by the BCL-2 oncoprotein. The ability of BCL-2 to modulate PDT-induced apoptosis and overall cell killing has been studied in a pair of Chinese hamster ovary cell lines that differ from one another by a transfected human BCL-2 gene in one of them (Bissonnette et al, Nature 359, 552-554, 1992). Cells were exposed to the phthalocyanine photosensitizer Pc 4 and various fluences of red light. Pc 4 uptake was identical in the two cell lines. The parental cells displayed a high incidence of apoptosis after PDT, whereas at each fluence there was a much lower incidence of apoptosis in the BCL-2-expressing cells. Apoptosis was monitored by (a) observation of 50 kbp and oligonucleosome-size DNA fragments by gel electrophoresis, (b) flow cytometry of cells labeled with fluorescently tagged dUTP by terminal deoxynucleotidyl transferase and (c) fluorescence microscopy of acridine orange-stained cells. The time course of apoptosis varied with the PDT dose, suggesting that only after moderately high doses (> 99% loss of clonogenicity) was there a relatively synchronous and rapid entry of many cells into apoptosis. At PDT doses reducing cell survival by 90 or 99%, significant increases in apoptotic cells were found in the population after 6-12 h. Clonogenic assays showed that BCL-2 protein inhibited not only apoptosis but overall cell killing as well, effecting a two-fold resistance at the 10% survival level. Thus, BCL-2-expressing cells may be relatively resistant to PDT.
He
J
J
Division of Radiation Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4942, USA. nlo@po.cwru.edu
Agarwal
M L
ML
Larkin
H E
HE
Friedman
L R
LR
Xue
L Y
LY
Oleinick
N L
NL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells / Q000187:drug effects / Q000502:physiology; D006224:Cricetinae; D004351:Drug Resistance; D015870:Gene Expression; D019254:Genes, bcl-2; D006801:Humans; D010778:Photochemotherapy; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology*; D014162:Transfection
D019253:Proto-Oncogene Proteins c-bcl-2