Modifications of mitochondria in human tumor cells during anthracycline-induced apoptosis

Adriamycin (ADR), one of the major antitumor agents used for the clinical t reatment of a wide variety of human cancers and its glutathione(GSH)-conjug ated adduct, ADRIGLU, induced apoptosis in K562 erythroleukemia and TVM-A12 clone 2 melanoma human cell lines. We have previously reported that ADA ha s nuclear localization and that ADRIGLU localizes exclusively in the cytopl asm. During ADR or ADRIGLU treatment, significant depletion of the cell Ene rgy state, demonstrated by a reduction in high-energy phosphates (ATP and G TP) and a decrease in energy charge potential (ECP), were recorded between 2 hours and 24 hours, by HPLC analysis. Transmission electron microscopy al so revealed that between 2 hours and 24 hours of ADR or ADRIGLU treatment, mitochondria underwent evident morphological changes, from an initial "high amplitude swelling state" to a "shrinkage state" and finally, in early apo ptotic cells, to an "abnormal shrinkage state" in which a marked accumulati on of pycnotic mitochondria was also observed. Confocal microscopic analysi s, using the potential-sensitive dye JC-I, showed that inhibition of cell e nergy metabolism was preceded by a rapid decrease in mitochondrial transmem brane potential (Delta Psi (m)). With the progression of exposure time, the early depolarization of the mitochondrial membrane was followed by a trans ient reversion to normal Delta Psi (m) until, in apoptotic cells, almost al l mitochondrial subpopulations appeared to be hyperpolarized. Our results i ndicated that mitochondria are actively involved in anthracycline-induced p rogrammed cell death, suggesting a novel mechanism that may be common to al l forms of apoptosis.