KdMAX

Complete quantitative affinity (Kd) profile using the scanMAX kinase assay panel

Quantitate compound binding affinity against the entire panel of KINOMEscan kinase assays.  Inhibitor binding constants (Kd values) are calculated from duplicate 11-point dose-response curves (plus DMSO control).  Measurements are made under optimized conditions that generate true thermodynamic Kd values and facilitate direct comparison of inhibitor affinity across kinases.

KdMAX is a powerful screening tool and ideally suited for later stage compounds in preclinical & clinical development.  KdMAX is employed to provide a robust kinome-wide affinity profile which may reveal unanticipated opportunities that could extend the therapeutic potential or potential off-target liabilities.

Panel Highlights and Benefits

  • Reveal unanticipated opportunities & potential liabilities
  • 11-point dose response curve in duplicate
  • Sensitivity & dynamic range: <100 pM to >10 mM
  • Quantify binding to inactive or low activity kinases
True thermodynamic constant unaffected by ATP or enzyme concentration
Assay sensitivity and dynamic range

Binding constant (Kd) determinations for the indicated compounds against LOK demonstrate the broad range (> 5 logs) of interaction affinities quantitatively measured using the KINOMEscan assay platform. Assays are performed at low kinase concentrations (<0.1 nM), which enables the measurement of accurate Kd values in the pM range [click graph to enlarge].

Frequently Asked Questions About Kd determinations (dissociation constants)

What is the difference between a Kd and an IC50?

Activity-based assays provide IC50 values, which are defined as a measure of a compound's effectiveness in inhibiting a kinase, and an indication of the inhibitor concentration required to reduce kinase activity by 50%. In other words it is the half maximal (50%) inhibitory concentration (IC) of a substance (50% IC, or IC50).  In contrast, KINOMEscan competition binding assays do not measure kinase activity.  Instead, compound affinity for a kinase is measured at a range of compound concentrations to calculate potency, expressed as a dissociation constant, and is a true thermodynamic constant used to describe binding affinity.  The formula used to describe this:

  Kd = ([K][I]/[C])


    [K] = molar concentration of non-inhibitor bound kinase at equilibrium
     [I] = molar concentration of the free inhibitor at equilibrium
    [C] = molar concentration of kinase-inhibitor complex at equilibrium



How are IC50 and KD values correlated?

IC50 is not a direct indicator of affinity, nor is Kd a direct indicator of inhibition.  However, the two can be related using the Cheng-Prusoff equation:

  Ki = (IC50)/(1+([S]/[Km]))


       Ki = binding affinity of the inhibitor; an absolute value or inhibition constant
  IC50 = the inhibitory strength of the compound
     [S] = substrate concentration
  [Km] = substrate concentration where kinase activity is at half maximal



How do the two values correlate for measured interactions?

Since 2005, KINOMEscan scientists have extensively assessed and characterized binding interactions against a panel of over 100 reference compounds, and have published on over 40 of them.  This set of compounds includes approved therapeutics, clinical candidates and tool compounds against a growing panel of kinase assays.  A list of profiled compounds, links to publications and supplementary data may be found in our Reference Compound Data page.  This body of data collectively validates the correlation and agreement between published IC50 literature values and corresponding Kd values for most compound-kinase interactions.  In general, good agreement between IC50 values of small molecule kinase inhibitors described in literature and corresponding Kd values for those interactions can be seen.  In cases of data divergence, there are often revealing explanations and may provide additional knowledge and context around compound characterization efforts.