Molecular and pharmacokinetic properties associated with the therapeutics of Bcl-2 antisense oligonucleotide G3139 combined with free and liposomal doxorubicin

Bcl-2 is a key apoptosis-regulating protein that has been implicated in mec hanisms of chemoresistance for a variety of malignancies by blocking progra mmed cell death, This study investigated the activity of the Bcl-2 antisens e oligodeoxynucleotide (AS ODN) G3139 combined with free doxorubicin (F-DOX ) or sterically stabilized liposomal doxorubicin (SL-DOX) to determine the role that drug pharmacodistribution properties may have on antitumor activi ty using a Bcl-2-expressing human breast solid tumor xenograft model. Admin istration of G3139 was able to delay the growth of MDA435/LCC6 cells compar ed with control ODN-treated animals; however, in all of the cases, tumors r eestablished after AS ODN treatment. Western blot analyses of Bcl-2 levels of solid tumors showed a sequence-specific down-regulation of the Bcl-2 pro tein after four daily doses of G3139, which correlated with histological ev idence of tumor cell death. Interestingly, the expression of Bcl-2 returned to pretreatment levels during the course of subsequent ODN administration, which suggested the development of resistance to continued Bcl-2 ODN treat ment. The antitumor activity of ODN given in conjunction with either F-DOX or SL-DOX was also examined. The combination of G3139 and F-DOX was able to suppress the growth of MDA435/LCC6 cells beyond that obtained with either of the treatments given alone, indicative of synergistic action. Examinatio n of the pharmacokinetics of F-DOX with systemic G3139 administration revea led that elevated tumor drug DOX levels were obtained compared with DOX tre atment in the absence of G3139, This effect was sequence-specific and plasm a DOX levels were unaffected by G3139 treatment, which indicated possible p ositive ODN-drug interactions at the tumor site. Combining G3139 with SL-DO X further increased the degree of antitumor activity. The improved efficacy of this combination was attributed to increased tumor drug levels that ari se from the ability of SL-DOX to passively accumulate in solid tumors. Thes e results suggest that additional benefits of Bcl-2 antisense ODN may be ob tained when it is combined with liposomal formulations of anticancer drugs such as DOX.