Prediction of Tumour Tissue Diffusion Coefficients of Hypoxia-Activated Prodrugs from Physicochemical Parameters

Abstract

The therapeutic activity of anticancer agents depends critically on their ability to penetrate through tumour tissue to reach their target cells, a requirement that is especially important for hypoxia-activated prodrugs. Here we use multicellular layers (MCL) grown in vitro from HT29 colon carcinoma cells to measure tissue diffusion coefficients (D mcl ) of 67 structurally diverse benzotriazine di-N-oxides (analogues of the hypoxia-activated prodrug tirapazamine) plus four miscellaneous compounds. An algorithm was developed to predict D mcl from physicochemical parameters (molecular weight, octanol/water partition coefficient at pH 7.4, number of hydrogen bond donors and acceptors); the fitted multivariate relationship had an explained variance (R 2 ) of 0.907 and predictive power (Q 2 ) of 0.879. Using a subset of nine compounds tested as a single cassette, the algorithm was shown to apply, with some adjustment of coefficients, to MCLs from three other tumour cell lines with differing cell packing densities (SiHa, HCT8-Ea, and HCT8-Ra). The demonstrated relationships provide tools for optimizing extravascular transport of anticancer agents during lead optimization.

Pharmacokinetic modeling of ascorbate diffusion through normal and tumor tissue

“…Two radiolabeled internal standards, [ 14 C]urea (Amersham Pharmacia Biotech, Piscataway, NJ, USA) and [ 3 H]mannitol (ICN Pharmaceuticals, Waltham, MA, USA), were added together with fresh sodium L-ascorbate (Sigma-Aldrich) to the donor compartment. The flux of [ 14 C]urea was used to determine the thickness of each MCL and [ 3 H]mannitol flux was measured as marker of paracellular diffusion and MCL integrity [31]. A schematic of the diffusion chamber experimental setup is given in Fig.…”

The extravascular penetration of tirapazamine into tumours: a predictive model of the transport and efficacy of hypoxia specific cytotoxic analogues and the potential use of cucurbiturils to facilitate delivery

“…Figures 2(a),(b), and (c) show the TPZ analogues examined by Hicks, Pruijn and Hay [21][22][23][24] with a diverse range of 3-NH(R) substituents, with properties given in Table 1. All molecular properties in Table 1 were calculated using DFT/B3LYP/6-311 + G(d,p) (6d, 7f) quantum mechanical methods as given in the experimental section.…”

“…The D MCL equation shows a negative increased dependency on the desolvation, lipophilicity and dipole moment compared to the D S equation 2 but no change in dependency on molecular volume. Eq 2 represents Fickian diffusion behaviour as shown by Pruijn 22,23 so the some degree of desolvation occurs as the TPZ drugs pass through the support membrane and the MCL, and hydrophobic (or lipophilic) and polar (dipole moment) interactions are of almost equal importance in determining the diffusion rates, whilst the influence of molecular volume has positive dependency on diffusion.…”

“…The object of this study is to develop a quantum mechanical model based on identifying linear free energy relationships based on equation 1 which supplement the extensive multicellular layer pharmacokinetic/pharmacodynamic or structure activity modelling studies of Hicks, Pruijn and Hay [21][22][23][24] but may be more amenable to drug design by using in silico methods to examine molecular changes and their effects on biological activities. A secondary object is to see if TPZ can form inclusion complexes with CB [7] as a precursor to proof of principle of enhanced TPZ delivery to tumours which might be warrant further investigation.…”

“…TPZ appears to undergo significant metabolic conversion before reaching its cellular DNA target based on the large change in efficacy between in vitro conditions (50-300 fold) and the observed 3-5 fold found in preclinical in vivo studies. [20][21][22][23][24] [Denny 2009, Hicks 2006, Pruijn 2005, 2008, Hay 2003] The activity of TPZ in tumours is known to be compromised by its inefficient penetration into the hypoxic tissue. Hypoxic cells are the most distant from the functional oxygen supplying vasculature, so efficient extravascular transport is required for optimal TPZ efficacy.…”