Proffered Papers— Basic Science/Biology

WILD-TYPE P53 SENSITIZES SOFT TISSUE SARCOMA CELLS TO DOXORUBICIN BY DOWNREGULATION OF MDR1 EXPRESSION

Zhan M; Yu D; Lang A; Li L; Pollock RE

p53 mutations occur in almost half of all soft issue sarcomas (STS) and may be a contributing factor in their chemoresistance to most of chemotherapeutic agents including Doxorubicin (Dox), the most active single agent in this disease. To examine whether introduction of wild type (wt) p53 might increase chemosensitivity of STS cells harboring p53 mutations, two wt p53 stable transfectants of SKLMS-1 sarcoma cells, SKp53-1, SKp53-3, and a p53 temperature-sensitive mutant transfectant of SKLMS-1 cells, SKAla-14 were used and compared with parental cells SKLMS-1 for their sensitivity to Dox. MTT assays showed that the IC50 of Dox decreased fr om 2.5 mm for SKLMS-1 to 0.25 mm for SKp53-1 and 0.18 mm for SKp53-3 cells. Clonogenetic assays showed that the IC50 decreased from 27.5 mg/ml for SKLMS-1 to 2.4 mg/ml for SKp53-1 and SKp53-3 cells. In tumorigenic assays, cells were injected s.c. into SCID mice. When the resulting tumor volume reached 62.5 mm3, mice were given Dox (1 mg/kg) s.c. weekly. Consequently, Dox treatment inhibited tumor growth more effectively in mice bearing SKp53-1 and SKp53-3 tumors than in mice bearing SKLMS-1 tumors. Western blot, northern blot, and immunohistochemical analyses showed that mdr1 gene encoded p-glycoprotein (P-gp) expression decreased in wt p53 transfectants compared with SKLMS-1 cells. Higher levels of intracellular accumulations of Dox were found in wt p53 transfectants than that in SKLMS-1 cells. No difference in DNA fragmentation, Bax or Bcl-2 expression was detected. Taken together these results suggest that introduction of wt p53 into STS cells harboring p53 mutation can enhance their chemosensitivity to Dox by inhibiting mdr1 expression. These results also suggest that combination of p53 gene therapy and chemotherapy might increase the therapeutic efficacy in the treatment of STS.