Targeted delivery of doxorubicin via sterically stabilized immunoliposomes: Pharmacokinetics and biodistribution in tumor-bearing mice

Purpose. To evaluate benefits in tumor localization, availability, and noncancerous organ distribution of doxorubicin (DOX) delivered via small (≤120 nm) sterically stabilized immunoliposomes targeted against a tumor-associated antigen in fibrosarcoma-bearing mice. Methods. DOX-loaded liposomes were prepared with (i) specific monoclonal IgG₃ antibody (32/2, D-SSIL-32/2); (ii) non-specific IgG₃ (D-SSIL-IgG); or (iii) no IgG (D-SSL) on their surface. Equal DOX amounts were injected intravenously via each type of liposome into BALB/c mice carrying experimental lung metastases of a polyoma virus-induced fibrosarcoma (A9 ctc 220) expressing a polyoma virus-induced tumor-associated antigen (PAA) on their surface. Metastases occurred mainly in lung. Mice were treated at 3 stages of tumor development (micrometastases, medium-size metastases, and large, necrotic metastases). Performance evaluation was based on time-dependent quantification of DOX and DOX metabolites (DOX-M) in lung tumor, noncancerous organs, and plasma. Results. (i) DOX delivered via both SSIL retained the prolonged circulation time typical of DOX delivered via D-SSL. (ii) DOX accumulation in noncancerous organs was similar for all preparations. Low levels of DOX-M were obtained for all three preparations in all organs except liver, suggesting a similar processing. (iii) Preparations differed in behavior in lung tumor depending on tumor size and microanatomy. Only at the micrometastases stage were the specifically targeted DSSIL-32/2 superior to D-SSL and D-SSIL-IgG, delivering 2-4 times more drug into the tumor. (iv) DOX-M level in all three tumor stages was in the following order: D-SSIL-32/2 >> D-SSL >> D-SSIL-IgG suggesting that DOX delivered as D-SSIL-32/2 is most available to tumor cells. Conclusions. The advantage of specific targeting of sterically stabilized liposomes is expressed mainly in increasing availability of DOX to tumor cells in a way which is dependent on tumor microanatomy. The impact of this advantage to therapeutic efficacy remains to be determined.