Pharmacokinetic and biodistribution studies of N-(2-hydroxypropyl)methacrylamide copolymer-dexamethasone conjugates in adjuvant-induced arthritis rat model

Abstract

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer has been found to be arthrotropic (joint-targeting) in the adjuvant-induced arthritis (AA) rat model using magnetic resonance imaging (MRI). In this manuscript, we report the quantitative pharmacokinetics and biodistribution (PK/BD) of (125)I-labeled HPMA copolymer-dexamethasone conjugate (P-Dex) in AA rats. Structural parameters of the prodrug such as the molecular weight (MW) and Dex content were found to have strong impact on the PK/BD profiles of P-Dex. The increase of MW (14,000, 24,000, and 42,000 g/mol) and Dex content (0, 151, and 313 micromol/g) enhances the arthrotropism of P-Dex. For the conjugate with highest MW and Dex content (P-H-M(W)/Dex), the percentage of injected doses per gram (ID/g) of ankle synovial tissue at day seventh postadministration is 1% g(-1), which confirms P-Dex as an arthrotropic macromolecular prodrug. For liver and spleen, the ID/g values are 0.51 and 3.64% g(-1), respectively. As an antigen-presenting organ, the sequestration of the prodrug by spleen may be explained by its abnormal enlargement associated with the systemic inflammatory disease model. Gradual reduction of spleen weight due to the inflammation resolution effect of P-Dex may also contribute to the high ID/g values. Increase of Dex content and reduction of MW would increase P-Dex distribution to kidney. The highest ID/g value for kidney at day seventh postadministration (0.91% g(-1)) was found with P-L-M(w) (MW = 14,000 g/mol, Dex content =288 micromol/g), which may suggest kidney tubuli reabsorption of the conjugates. The P-Dex's distribution to heart and lung is minimum.

Figure 1

The general structure of dexamethasone-containing HPMA copolymer conjugates. For all conjugates used in PK/BD and plasma stability studies, x = 0; For all conjugates used in cell culture study, y = 0.

Figure 2

The release of dexamethasone from P-Dex conjugates in murine plasma.

Figure 3

In vitro internalization of HPMA copolymer conjugates in Raw 264.7 cell cultures (n = 3). (A) Internalization of HPMA copolymer conjugates with different molecular weight; (B) Internalization of HPMA copolymer conjugates with different Dex content. * indicates significant difference (p < 0.05, one-way ANOVA).

Figure 4

The pharmacokinetics profiles of HPMA copolymer conjugates with different molecular weights and Dex contents in blood and major organs/tissues over the time course of 7 days post i.v. administration.

Figure 5

The change of AA rats’ spleen weight after the treatment with different HPMA copolymer conjugates. The average spleen weight of healthy male Lewis rats of matching age is ∼ 0.5 g.