Molecular flux rates through critical pathways measured by stable isotope labeling in vivo, as biomarkers of drug action and disease activity

A method for evaluating an action of one or more compounds on a molecular flux rate through a solid or liquid tumor formation pathway in a living system, said method comprising:

• a) administering a first isotope-labeled substrate to a first living system, not exposed to said one or more compounds, for a period of time sufficient for said first isotope-labeled substrate to enter into and label at least one DNA molecule derived from the solid or liquid tumor to produce at least one first isotope-labeled DNA molecule derived from the solid or liquid tumor within said solid or liquid tumor formation pathway in said first living system;
• b) obtaining one or more samples from said first living system, wherein said one or more samples comprise said at least one first isotope-labeled DNA molecule derived from the solid or liquid tumor;
• c) measuring an isotopic content, rate of incorporation, and/or pattern or rate of change in isotopic content and/or pattern of isotope labeling of said at least one first isotope-labeled DNA molecule derived from the solid or liquid tumor;
• d) calculating a molecular flux rate through said solid or liquid tumor formation pathway based on the isotopic content, rate of incorporation, and/or pattern or rate of change of isotopic content and/or pattern of isotopic labeling in said at least one first isotope-labeled DNA molecule derived from the solid or liquid tumor;
• e) exposing a second living system to said one or more compounds;
• administering a second isotope-labeled substrate to said second living system for a period of time sufficient for said second isotope-labeled substrate to enter into and label at least one DNA molecule derived from the solid or liquid tumor to produce at least one second isotope-labeled DNA molecule derived from the solid or liquid tumor;
• g) obtaining one or more samples from said second living system, wherein said one or more samples comprise said at least one second isotope-labeled DNA molecule derived from the solid or liquid tumor;
• h) measuring an isotopic content, rate of incorporation, and/or pattern or rate of change in isotopic content and/or pattern of isotope labeling of said at least one second isotope-labeled DNA molecule derived from the solid or liquid tumor;
• i) calculating a molecular flux rate through said solid or liquid tumor formation pathway in said second living system based on the isotopic content, rate of incorporation, and/or pattern or rate of change in isotopic content and/or pattern of isotope labeling of said at least one second isotope-labeled DNA molecule derived from the solid or liquid tumor;
• and
• j) comparing said molecular flux rate through said solid or liquid tumor formation pathway in said first living system to said molecular flux rate through said solid or liquid tumor formation pathway in said second living system to evaluate the action of said one or more compounds on said molecular flux rate through the solid or liquid tumor formation pathway in said second living system.