Human tissue molecular determinants

Tissue cross-reactivity studies, although burdensome, provide a rational in vitro assay to determine the range and intensity of distribution of potential epitopes reactive with a monoclonal antibody test article prior to its administration to humans. In addition, cross-reactivity studies provide a useful tool to identify animal species for safety assessment. The cross-reactivity profiles of different species can be compared to the profiles obtained in human tissues. The predictive value of the assay lies in incorporating the characteristics of the monoclonal antibody (isotype, subtype, and other molecular modifications) with the biological activity of the molecule itself, and the potential in vivo distribution of it. 

Methods for Determining Biomarkers of Exposure and Effect. Analytical methods with satisfactory sensitivity and precision are available to determine the levels of strontium in human tissues and body fluids. Strontium and radiostrontium are found in essentially all food, water, and air, so everyone is exposed to some levels. Recently, Sutherland et al. (2000a, 2000b) developed a molecular biological strategy to identify clustered lesions in DNA resulting from in vitro cellular exposure to gamma radiation. 

Perera, F.P., Poirier, M.C., Yuspa, S.H., Nakayama, J., Jaretski, A., Curnen, M.M., Knowles, D.M., and Weinstein, I.B., A pilot project in molecular cancer epidemiology Determination of benzo [a] pyrene-DNA adducts in animal and human tissues by immunoassays. Carcinogenesis, 3, 1405, 1982. 

While many researchers have focused on the tools of molecular biology and genetics to determine biochemical mechanisms of nutrient action in animal models, a few have focused on mathematical modeling of kinetic data to achieve a quantitative understanding of the dynamics of nutrient metabolism in vivo (for recent symposia, see Abumrad, 1991 Coburn, 1992). Three recent developments stimulated interest in mathematical modeling. First, there is an opportunity to integrate quantitative characteristics of the dynamics of nutrient metabolism with knowledge of nutrient action mechanisms and health status. Second, it appears that some animal models do not mimic nutrient metabolism and health status of humans. Third, stable isotope tracers and reliable methods to measure minute amounts of them in human tissues have become more readily available. 

Antiproliferative assay, flow cytometry studies, in vivo activities and biomarkers determination represent key tools for profiling the phenotypic response to molecular or pharmacologic perturbation at cellular or tissue levels the study enables therapeutic response irrespective of target activity of topi and taken together, these results suggest that there is a strong potential for edotecarin in clinical [36, 37] development for treatment of human tumors. 

Once a chemical is in systemic circulation, the next concern is how rapidly it is cleared from the body. Under the assumption of steady-state exposure, the clearance rate drives the steady-state concentration in the blood and other tissues, which in turn will help determine what types of specific molecular activity can be expected. Chemicals are processed through the liver, where a variety of biotransformation reactions occur, for instance, making the chemical more water soluble or tagging it for active transport. The chemical can then be actively or passively partitioned for excretion based largely on the physicochemical properties of the parent compound and the resulting metabolites. Whole animal pharmacokinetic studies can be carried out to determine partitioning, metabolic fate, and routes and extent of excretion, but these studies are extremely laborious and expensive, and are often difficult to extrapolate to humans. To complement these studies, and in some cases to replace them, physiologically based pharmacokinetic (PBPK) models can be constructed [32, 33]. These are typically compartment-based models that are parameterized for particular... 

The applicability of the APCI interface is restricted to the analysis of compounds with lower polarity and lower molecular mass compared with ESP and ISP. An early demonstration of the potential of the APCI interface is the LC-APCI-MS-MS analysis of phenylbutazone and two of its metabolites in plasma and urine (128). Other applications include the LC-APCI-MS analysis of steroids in equine and human urine and plasma (129-131), the determination of six sulfonamides in milk samples after a simple solid-phase extraction and LC separation (132), of tetracyclines in muscle at the 100 ppb level (133), of fenbendazole, oxfendazole, and the sulfone metabolite in muscle at the 10 ppb level, and of five thyreostats in thyroid tissue at the 1 ppm level (134). 

---