Cisplatin preferentially binds mitochondrial DNA and voltage-dependent anion channel protein in the mitochondrial membrane of head and neck squamous cell carcinoma: possible role in apoptosis.
OBJECTIVE
Cisplatin adducts to nuclear DNA (nDNA) are felt to be the molecular lesions that trigger apoptosis, but the mechanism linking nDNA adduct formation and cell death is unclear. Some literature in the last decade has suggested a possible direct effect of cisplatin on mitochondria independent of nDNA interaction. In this study, we define separately the sequelae of cisplatin interactions with nDNA and with mitochondria in head and neck squamous cell carcinoma (HNSCC) cell lines.


METHODS
Cisplatin binding to mitochondrial DNA (mtDNA) and proteins was analyzed by atomic absorption spectroscopy and other methods.


RESULTS
Following 1 hour of exposure to cisplatin, platinum adducts to mtDNA were 300- to 500-fold more abundant than adducts to nDNA; these differences were not due to differences in rates of adduct repair. Whereas HNSCC cell cytoplasts free of nDNA retained the same dose-dependent cisplatin sensitivity as parental cells, HNSCC rho(0) cells free of mtDNA were 4- to 5-fold more resistant to cisplatin than parental cells. Isolated mitochondria released cytochrome c within minutes of exposure to cisplatin, and ultrastructural analysis of intact HNSCC cells by electron microscopy showed marked mitochondrial disruption after 4 hours of cisplatin treatment, whereas the nucleus and other cellular structures remain intact. The very prompt release of cytochrome c from isolated mitochondria implies that apoptosis does not require alteration in mitochondrial gene transcription. Further, cisplatin binds preferentially to mitochondrial membrane proteins, particularly the voltage-dependent anion channel.


CONCLUSIONS
Cisplatin binding to nDNA is not necessary for induction of apoptosis in HNSCC, which can result from direct action of cisplatin on mitochondria.
Yang
Zejia
Z
University of Maryland Marlene and Stewart Greenebaum Cancer Center, 22 South Greene Street, Baltimore, MD 21201, USA.
Schumaker
Lisa M
LM
Egorin
Merrill J
MJ
Zuhowski
Eleanor G
EG
Guo
Zhongmin
Z
Cullen
Kevin J
KJ
D000970:Antineoplastic Agents / Q000378:metabolism; D017209:Apoptosis; D002467:Cell Nucleus / Q000378:metabolism; D002945:Cisplatin / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D018736:DNA Adducts; D004260:DNA Repair; D004272:DNA, Mitochondrial / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D051336:Mitochondrial Membranes / Q000378:metabolism*; D018307:Neoplasms, Squamous Cell / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D014407:Tumor Cells, Cultured; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism*
D000970:Antineoplastic Agents; D018736:DNA Adducts; D004272:DNA, Mitochondrial; D050994:Voltage-Dependent Anion Channels; D045304:Cytochromes c; D002945:Cisplatin