Beyond reversible: unlocking covalent & time-dependent kinase inhibition
A single-timepoint IC50 can misrepresent a covalent or slow-binding inhibitor entirely. See the workflow that gets the kinetics right.
Potency that changes over time breaks the standard playbook
Covalent inhibitors and reversible compounds with slow off rates demonstrate time-dependent inhibition (TDI) and don't behave like classical non-TDI inhibitors. Their apparent potency shifts with incubation time — so the parameters that predict efficacy are Ki and residence time for reversible TDI compounds, and kinact/KI, kinact and KI, for irreversible compounds. Compounds with TDI should not be evaluated with a single IC50 value.
Topics covered in this session
Why TDI breaks classical IC50 assumptions, and how to spot it directly in your own progress-curve data.
How free-compound-clearance and jump dilution distinguish reversible slow-binders from true covalent inhibitors, without rebinding artifacts.
How to determine kinact/KI correctly via global fit analysis — including when a one-step versus two-step model applies.
Why compounds with near-identical IC50 values can carry very different inactivation efficiencies, and what that means for SAR ranking.
How kinact/KI correlates with cellular potency, shown against real Ba/F3 CellTiter-Glo data.
Kinome-wide selectivity profiling for covalent inhibitors, and how ATP concentration shifts apparent selectivity.
How AssayQuant enables this
The kinetic workflow in this session — progress-curve analysis, free-compound-clearance, global kinact/KI fitting — depends on continuous, real-time activity measurement. That's exactly what our PhosphoSens® activity assay kits are built for.
Run continuous, real-time kinase activity assays in your own lab — the same assay format used throughout this webinar.
A proven three-step path to the right kinetic parameters
Demonstrated live on five well-known EGFR inhibitors — Gefitinib, Lapatinib, Osimertinib, Lazertinib, and Staurosporine — each with a distinct mechanism.
Inhibitor characterization
Determine whether TDI is present at all, using progress-curve linearity and IC50 shift with pre-incubation.
Reversibility characterization
Free-compound-clearance or jump dilution establishes whether inhibition is reversible or irreversible.
TDI characterization
Extract final kinetic parameters — off-rate and residence time, or kinact/KI via global progress-curve fitting.
Working on a covalent or slow-binding inhibitor program?
Get direct scientific support characterizing your compounds — plus access to our Excel-Fit templates for streamlined kinact/KI and residence-time analysis.
TDI detection.
Reversibility assessment.
Global kinact/KI fitting.
Get the full 45-minute session
Standard IC₅₀ assays can seriously mislead when a compound shows time-dependent inhibition — and that's common for covalent kinase inhibitors and slow-binding reversible ones alike. This session walks through a proven three-step kinetic workflow for getting it right, demonstrated on five real EGFR inhibitors spanning fast-reversible to fully covalent mechanisms, with a close look at how to correctly determine kinact/KI, distinguish reversible from irreversible binding without rebinding artifacts, and interpret kinome-wide selectivity data for covalent compounds.

