In vitro plasma stability, permeability and solubility of mercaptoacetamide histone deacetylase inhibitors

Abstract

Histone deacetylase inhibitors (HDACIs) are emerging as a new class of therapeutic agents with potent antitumor activities in a broad spectrum of human cancers. In this study, the in vitro plasma stability, permeability, solubility, and lipophilicity (log D) of two mercaptoacetamide-based HDACIs (coded as W2 and S2) were evaluated and compared to Vorinostat (SAHA). The results demonstrated that the compounds manifested high solubility in HCl (pH 1.2) but lower in PBS (pH 7.4) than SAHA. Moreover, mercaptoacetamide-based HDACIs exhibited higher lipophilicity values compared to SAHA. The permeability of these compounds was evaluated using the Caco-2 cell monolayer as a model of the intestinal mucosa. The Caco-2 studies revealed that the compounds S2 and W2 are highly permeable with apparent permeability coefficients (P(app)) in the apical to basolateral direction of 7.33 x 10(-6) and 15.0 x 10(-6)cm/s, respectively. The in vitro stability was determined in human, mouse, porcine and rat plasma. Data showed that the compound W2 is more stable in human and rat plasma and the S2 is more stable in all plasma species than SAHA. Taken together, these results indicate that the mercaptoacetamide-based HDACIs possess favorable solubility, lipophilicity, permeability and plasma stability features.

Figure 1

Chemical Structures of Compounds. ^a taken from Chen et al., 2005.

Figure 2

Solubility profiles of the mercaptoacetamide-based HDACIs and SAHA over a period of 24 h in (A) PBS pH 7.4 at 37°C and (B) HCl pH 1.2 at 37°C. Both compounds demonstrated higher solubility in HCl (pH 1.2) and lower in PBS (pH 7.4) compared to SAHA (paired Student’s t -test, <0.05).

Figure 3

Time dependent transport of the compounds and SAHA across Caco-2 cells grown on inserts. Transport is expressed as nmol/ml. Data points represent both basolateral to apical (BL to AP) and apical to basolateral (AP to BL) transport. BL to AP transport of W2 (closed circles), S2 (closed squares) and SAHA (closed triangles) is illustrated. AP to BL transport of W2 (open circles), S2 (open squares) and SAHA (open triangles) is displayed. The data points represent the mean values ± S.E.M. of three independent experiments. Statistical analysis was carried out by the paired Student’s t-test (p<0.05). Upper panel, *, BL to AP transport of the compounds and SAHA is significantly higher than AP to BL; p<0.05. Lower panel, ‡, the transport of W2 is significant different from SAHA at a level of p<0.05.

Figure 4

Stability profiles of the compounds and SAHA obtained in human, mouse, porcine and rat plasma. The values represent the mean ± S.E.M. of three independent experiments. Statistical analysis was performed by using the paired Student’s t-test at p<0.05 level of significance.