Effect of intratumoral injection on the biodistribution and the therapeutic potential of HPMA copolymer-based drug delivery systems

Abstract

The direct intratumoral (i.t.) injection of anticancer agents has been evaluated extensively in the past few decades. Thus far, however, it has failed to become established as an alternative route of administration in routine clinical practice. In the present report, the impact of i.t. injection on the biodistribution and the therapeutic potential of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-based drug delivery systems was investigated. It was found that, compared to intravenous injection, both the tumor concentrations and the tumor-to-organ ratios of carriers improved substantially. In addition, compared to intravenously and intratumorally applied free doxorubicin and to intravenously applied poly(HPMA)-glycylphenylalanylleucylglycine-doxorubicin, intratumorally injected poly(HPMA)-glycylphenylalanylleucylglycine-doxorubicin presented a significantly increased antitumor efficacy, as well as an improved therapeutic index. Based on these findings, we propose intratumorally injected carrier-based chemotherapy as an interesting alternative to routinely used chemotherapy regimens and routes of administration.

Figures

Figure 1

Effect of i.t. injection on the circulation kinetics of HPMA copolymers. The blood concentrations of 31-kDa poly(HPMA) (A) and 65-kDa poly(HPMA) (B) after i.v. and i.t. injection are plotted against time. Values represent the average ± SD of four to six animals per experimental group. *P

Figure 2

Effect of i.t. injection on the biodistribution of HPMA copolymers. (A) Scintigraphic analysis of the effect of i.t. injection on the biodistribution of 31-kDa and 65-kDa poly(HPMA) in rats bearing subcutaneously transplanted AT1 tumors. In the images obtained 0.5 hour after i.v. administration, the accumulation of the radiolabeled copolymers was most prominent in the heart (i.e., circulation) (1) and bladder (2). In the images obtained at 4 and 24 hours, the highest amounts of the copolymers were found in the heart/lungs (1), spleen (3), liver (4), and tumor (5). In addition, at the two latter time points, released radioactive iodine was found to accumulate in the thyroid (T). On i.t. injection, only localization to the tumor (5) could be observed over the first 24 hours after administration. (B and C) Quantification of the effect of i.t. injection on the tumor and organ concentrations of 31-kDa poly(HPMA) (B) and 65 kDa-poly(HPMA) (C) at 24 hours p.i. Values represent the average ± SD of four to six animals per experimental group. *P

Figure 3

Effect of i.t. injection on the biodistribution of poly(HPMA)-GFLG-doxorubicin. (A) Scintigraphic analysis of the effect of i.t. injection on the biodistribution of poly(HPMA)-GFLG-doxorubicin (PK1) in rats bearing subcutaneously transplanted AT1 tumors. In the images obtained 0.5 hour after i.v. injection, the accumulation of the radiolabeled conjugate was most prominent in the heart (i.e., circulation) (1) and bladder (2). At 4 and 24 hours, most of the conjugate was found in the kidneys (3) and tumor (4). Released radioactive iodine was again found to accumulate in the thyroid (T). On i.t. injection, the highest amounts of poly(HPMA)-GFLG-doxorubicin were found in the kidneys (3) and tumor (4). (B) Quantification of the effect of i.t. injection on the tumor and organ concentrations of poly(HPMA)-GFLG-doxorubicin (PK1) at 24 hours p.i. Values represent the average ± SD of three to four animals per experimental group. *P

Figure 4

In vitro efficacy of free and HPMA copolymer-bound doxorubicin. The cytotoxicity of free doxorubicin, poly(HPMA)-GFLG-doxorubicin, and control copolymer (lacking doxorubicin) was assessed by investigating the ability of agents to inhibit the colony formation of AT1 rat prostate carcinoma cells. Values represent the average ± SD of three independent experiments.

Figure 5

Effect of i.t. injection on the efficacy and toxicity of free and HPMA copolymer-bound doxorubicin. (A) Growth inhibition of subcutaneous AT1 tumors induced by a single i.v. injection of saline (Control; n = 12), a single i.v. injection of 5 mg/kg free doxorubicin (Dox i.v.; n = 9), a single i.t. injection of 5 mg/kg doxorubicin (Dox i.t.; n = 4), a single i.v. injection of 5 mg/kg (doxorubicin-equivalent) poly(HPMA)-GFLG-doxorubicin (PK1 i.v.; n = 7), and a single i.t. injection of 5 mg/kg (doxorubicin-equivalent) poly(HPMA)-GFLG-doxorubicin (PK1 i.t.; n = 4). *P