Selection Criteria

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Selection Criteria
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Gold Compound Selection Criteria

Standard to Meet Acceptance Criteria
In Vivo Data
1. Adverse events
When drugs are specified as reference standards, we are generally interested in repeated dose toxicants and one or more of the following adverse events
  • cytotoxicity
  • cholestasis
  • steatosis
  • phospholipidosis
  • fibrosis
  • Cardiac
  • cytotoxicity
  • long QT syndrome
  • Renal
  • cytotoxicity
  • 2. Toxicity mechanism
    Toxicity should map to one (or more) of the following major cellular pathways:
  • Energy metabolism (e.g. mitochondrial disruption or fatty acid oxidation)
  • Lipid metabolism (resulting in steatosis, cholestasis, or phospholipidosis)
  • Inflammatory response (e.g. resulting in fibrosis)
    Reactive compounds should be selected so that together they represent a range of chemical reactivities (e.g. thiol alkylation, lysine alkylation, free radical, oxidation, or redox cycling).
    Reversible inhibitors should be selected for especially promiscuous receptors (e.g. the hERG ion channel or nuclear hormone receptors) or for profiling specific elements of the above cellular pathways (e.g. the bile salt export pump in lipid metabolism or complex IV of the electron transport chain in energy metabolism).
  • 3. Therapeutic target
    For reference standards that are drugs, this data is provided for

    information. Ideally, the pharmacological activity of the drug should not be targeted to the organ for which adverse events are observed. This is desirable in order to minimize cellular responses that are extraneous to the toxicity response.

    4. PK parameters:
    In vivo PK parameters are used to evaluate the relevance of in vitro results to in vivo adverse events. For reversible inhibition, the in vitro concentration should be comparable to or less than Cmax. For hepatotoxins, a factor of 10 higher can be applied to in vitro concentrations to account for increased first pass exposure. For idiosyncratic toxicity, a factor of 10 higher can be applied to in vitro concentrations if idiosyncrasy is believed to be related to variations in metabolism. These considerations are not quantitative rules but if violated will indicate that a more detailed analysis may be required to rationalize in vitro effects to in vivo adverse events.

    A high volume of distribution (Vd) is an indicator of extensive non-selective binding, commonly to lipids but possibly to cellular protein or DNA. Thus a high Vd would be consistent with a promiscuous mechanism of toxicity due to lipid disruption.

    5. Therapeutic window.
    When available for standards that are drugs, the in vivo therapeutic window can be applied as a factor to IC50s for in vitro efficacy to estimate the concentration that is relevant to in vitro toxicity assays.
    6. Metabolically activated (optional), active metabolite known and available for testing.
    For hepatotoxins, we prefer compounds that require metabolic activation, although standards that are active in themselves will be accepted if they have otherwise valuable properties. We require knowing the active metabolite, and we prefer compounds where the metabolite is stable and has been or can be independently tested in order to verify the mechanism of toxicity.
    Omics and IC50 Data
    Literature data for at least one, but not necessarily all, of the 'omics datasets is desired.
    7. Gene expression profiles known.
    8. Proteomics profiles known.
    9. Metabonomics/Fluxomics profiles known.
    10. Epigenomics profiles known.
    11. Observed IC50 for in vitro cellular efficacy.
    Data are provided here for the pharmacological activity (not toxicity) in cell culture. This data can be used in conjunction with in vivo PK and therapeutic window data to evaluate the relevance of in vitro toxicity studies to in vivo adverse events.
    12. Observed IC50 for in vitro cellular toxicity studies.
    Representative in vitro studies of cellular toxicity are referenced here, along with observed IC50’s. The relevance of the in vitro results to mechanism of toxicity may be discussed here.
    Physical Properties
    In cases where criteria for physical properties are not met,

    compensating handling procedures should be identified.

    13. ToxCast/Tox21
    It is not a requirement that the compound is accepted as a standard in the EPA testing programs, but compounds utilized in these programs can be assumed to have physical properties verified to be suitable for in vitro cellular assays.
    14. Structure
    Structure and isomeric form are defined and confirmed.
    15. Stability
    If the compound is not stable to light, freeze thaw, and storage in

    solution, precautions required to ensure stability will be identified.

    16. Solubility in buffer
    The compound should be soluble in buffer at 30 times the in vitro IC50 for toxicity to allow accurate determination of IC50s. Sparingly soluble compounds may be assayed for solubility in serum, and the percent serum to be used to achieve the desired solubility will be specified here. References provided for "'Omics and IC50 Data" can also be consulted to determine appropriate compound handling procedures.
    17. Solubility in DMSO
    Solubility in DMSO should be 100 times desired buffer solubility to allow for dilution of stock solutions to 1% DMSO or less in cell culture. If this condition is not met, then an alternative configuration for stock solutions should be identified.
    18. Binding to plasticware/vessel
    Binding to plasticware should be insignificant at the concentrations

    used in cell culture. This property will be measured when a sample of compound becomes available.

    19. Availability
    The compound should be available commercially at >95% purity (>99%

    preferred). A preferred supplier and specific product number will be specified so that the same product may be used in all studies.

    20. Volatility
    The compound should be nonvolatile primarily to ensure consistent

    concentrations in stock solutions over time.

    Authors of this ToxBank wiki page

    David Bower
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