Knock-down of P-glycoprotein reverses taxol resistance in ovarian cancer multicellular spheroids.

We previously established that multicellular ovarian cancer spheroids develop intrinsic multidrug resistance with the appearance of quiescent cell areas. p27 protein is a determinant of such resistance. However, the precise molecular basis of such resistance remains unknown. We demonstrated herein that these multicellular ovarian cancer spheroids expressed high levels of p27 and P-gp protein. Compared with monolayer cells, there is a significant increase in the resistance of spheroids cells to anticancer reagent Taxol. Antisense oligodeoxynucleotide not only mediated down-regulation of p27, but also P-gp expression in multicellular spheroids. Selective small interfering RNAs (siRNA) of P-gp with MDR1-targeted short hairpin RNAs (shRNA) expression vector sensitized the cells to Taxol. These results suggest that both p27 and P-gp can modulate Taxol sensitivity respectively, while p27 requires P-gp for its full function. Increased P-gp protein expression through p27 mediation is one of the major mechanisms of Taxol resistance in ovarian cancer multicellular spheroids.