Induction of tumor-specific cytotoxicity and apoptosis by doxorubicin

Doxorubicin (adriamycin), an anthracycline antibiotic, showed higher cytotoxic activity against human tumor cell lines (oral squamous cell carcinoma HSC-2, HSC-3, submandibular gland carcinoma HSG, promyelocytic leukemia HL-60) than against normal human cells (gingival fibroblast HGF, pulp cell HPC, periodontal ligament fibroblast HPLF). Doxorubicin activated caspases 3, 8 and 9 in both HSC-2 and HL-60 cells, but induced internucleosomal DNA fragmentation only in HL-60 cells. Western blot analysis showed that doxorubicin did not significantly change the intracellular concentration of Bcl-2, Bax and Bad in HL-60 cells. Real-time PCR analysis showed that HPC cells expressed the highest amount of mdr1 mRNA, followed by HSC-2 > HGF > HSC-3 > HPLF > HSG > HL-60. ESR spectroscopy showed that doxorubicin produced no discernible radical under alkaline conditions (pH 7.4 to 10.5) except at pH 12.5, and it did not scavenge O2-, NO and DPPH radicals. The present study demonstrates that doxorubicin induces the tumor-specific cytotoxicity and some, but not all, apoptosis markers possibly by a radical-independent mechanism, and that mdr1 expression in the tumor cells is not related to the tumor specificity of doxorubicin.