Purpose: To evaluate the pharmacokinetic (PK) properties of Bcl-2 antisense oligodeoxynucleotide G3139 when combined with the anthracycline anticancer drug doxorubicin (DOX) in a model of MDA435/LCC6 human breast cancer in severely compromised immunodeficient (SCID) mice. Methods: An orthotopic model of MDA435/LCC6 solid breast tumors was developed by bilateral implantation of passaged cells in female SCID-RAG2 mice. The G3139 plasma profile was compared for two common routes of administration (i.v. or i.p.) in single and multiple dose treatment regimens of 5 mg/kg G3139 alone or with simultaneous DOX (5 mg/kg) administration. At selected times, plasma and major organs were assayed for [H-3]G3139 using scintillation counting and DOX determined using HPLC. The molecular integrity of G3139 was analyzed using SDS-PAGE. The PKs of G3139 and DOX were evaluated using a two-compartment model. Results: G3139 administered i.v. at 5 mg/kg revealed a biexponential plasma concentration-time curve with a Cmax of 99.9 mug/ml and elimination half-lives of 0.03 h and 9.8 h, respectively, which resulted in an area under the concentration-time curve (AUC) of 15.9 mug(.)h/ml. G3139 administered i.p. showed a plasma absorption, distribution and elimination profile typical of this route of administration, characterized by half-lives of 0.03 h, 0.2 h and 8.9 h, respectively and a Cmax of 8.6 mug/ml. Based on AUC comparisons, the bioavailability of G3139 injected i.p. was 84% compared to i.v. administration. Subtle changes were observed in G3139 PKs after three prior i.p. doses of G3139. Specifically, a sixfold slower absorption rate, lower Cmax (6.9 mug/ml), increased Tmax (0.2 h), and an AUC of 17.4 mug(.)h/ml were observed, consistent with concentrations approaching saturation levels in tissue sites to which G3139 distributes. Coadministration of DOX had significant effects on the PK properties of G3139, manifested by an increased Cmax (11.2 mug/ml), higher AUC (19.7 mug(.)h/ml), and ninefold lower plasma clearance for single-dose G3139 administration. G3139 in plasma remained largely intact (< 17% degraded in plasma over 4 h), and increased plasma protein association occurred as a function of time. G3139 was detected in both healthy and tumor tissue after i.v. and i.p. administration. The highest tissue levels of G3139 were observed in the kidneys (40 mug/g), and low levels (< 2 mug/g) were detected in lung, heart and muscle. The rate of accumulation of G3139 in organs was dependent upon G3139 levels in plasma and the presence of coadministered DOX. Significant accumulation of G3139 was observed in solid tumors, with peak levels of approximately 5 mug G3139/g tumor, and approximately a two-to threefold tumor/muscle AUC ratio. The kinetics of G3139 accumulation in tumor tissue increased with increasing circulating G3139 concentration. The tissue distribution properties of DOX were also altered in the presence of coadministered G3139: in the presence of G3139, tumor exposure to DOX increased two-to threefold without alteration in plasma DOX PKs. Conclusions: These findings indicate that drug-drug interactions between G3139 and DOX are modest and favorable in that elevated tumor DOX levels are achieved without compromising G3139 tumor uptake or significantly altering plasma drug concentrations.
