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PROTAC target-engagement and degradation dynamics

A mechanistic pharmacodynamic model connecting PROTAC concentration, target and E3-ligase binding, catalytic degradation, protein turnover, and the high-concentration hook effect.

A Mechanistic Pharmacodynamic Modeling Framework for the Assessment and Optimization of Proteolysis Targeting Chimeras (PROTACs) ↗

Pharmaceutics

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MODEL IN MOTION 18 sec

How do the two empirical PROTAC response descriptions evolve?

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Eq. 14 hook-model 6 h to 24 h RIPK2 degradation

How do binding affinity, catalytic rate, and PROTAC concentration determine target degradation and the hook effect? Explore this biological starting configuration through Mechanistic relative target protein, Hook-model relative target protein, Simplified target engagement, Steady-state maximum degradation.

0–96 hour

Scenario details

Eq. 14 hook-model 6 h to 24 h RIPK2 degradation

How do binding affinity, catalytic rate, and PROTAC concentration determine target degradation and the hook effect? Explore this biological starting configuration through Mechanistic relative target protein, Hook-model relative target protein, Simplified target engagement, Steady-state maximum degradation.

Readouts

Relative mechanistic degradation · dimensionless
Relative mechanistic degradation over the selected simulation window.
Relative hook-effect response · dimensionless
Relative hook-effect response over the selected simulation window.
Simplified target engagement · Unit unavailable
Simplified target engagement over the selected simulation window.
Steady state maximum degradation · Unit unavailable
Steady state maximum degradation over the selected simulation window.

Study purpose

  • How do binding affinity, catalytic rate, and PROTAC concentration determine target degradation and the hook effect?

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Model parameter

PROTAC concentration coefficient used by the released system of model equations.

nM

Suggested: 34.5–103. You can explore beyond this range.

68.9 → —

Target–PROTAC dissociation constant describing equilibrium binding affinity in the modeled interaction.

nM

Suggested: 69–207. You can explore beyond this range.

138 → —

PROTAC–E3 ligase dissociation constant describing equilibrium binding affinity in the modeled interaction.

nM

Suggested: 1,550–4,650. You can explore beyond this range.

3100 → —

Catalytic degradation rate coefficient used by the released system of model equations.

1/h

Suggested: 0.25–0.75. You can explore beyond this range.

0.5 → —

Target-protein half-life controlling the time required for the corresponding quantity to decrease by half.

h

Suggested: 22.5–67.5. You can explore beyond this range.

45 → —
Simulation time
h
h
96 → 168

Time between reported samples.

h

1 change · Variation 1

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Biology

A fixed PROTAC concentration drives two independent reduced pharmacodynamic lanes. In the mechanistic lane, algebraic target engagement adds catalytic protein loss while basal turnover restores target protein. In the hook lane, concentration sets an empirical hook-shaped steady state toward which a separate target-protein state relaxes.

How do constant PROTAC concentration and two reduced PD formulations change target protein?A fixed PROTAC concentration drives two independent reduced pharmacodynamic lanes. In the mechanistic lane, algebraic target engagement adds catalytic protein loss while basal turnover restores target protein. In the hook lane, concentration sets an empirical hook-shaped steady state toward which a separate target-protein state relaxes.BIOLOGY OVERVIEWHow do constant PROTAC concentration and two reduced PD formulations change targetprotein?Fixed PROTAC level: Scenario-defined concentrationFixed PROTAC levelScenario-defined concentrationSimplified engagement: Algebraic target/E3 termSimplifiedengagementAlgebraic target/E3 termCatalytic degradation: Engagement-driven target lossCatalyticdegradationEngagement-driven target lossBasal recovery: Protein turnover toward baselineBasal recoveryProtein turnover towardbaselineMechanistic target protein: Relative target-protein stateMechanistic targetproteinRelative target-protein stateHook-shaped steady state: Independent empirical laneHook-shaped steadystateIndependent empirical laneHook-model target protein: Relaxes toward hook predictionHook-model targetproteinRelaxes toward hook predictionPRIMARY READOUTSMechanistic relative target proteinMechanistic relative targe…Hook-model target proteinHook-model target proteinSimplified engagementSimplified engagementHook-shaped degradationHook-shaped degradation

Solid arrows show modeled movement or change; two-headed arrows show reversible exchange; dashed arrows show modulation without material transfer.

Model scope: PROTAC PK or dosing, explicit binary or ternary-complex states, ubiquitin chains, proteasome states, and a causal connection between the two prediction lanes are not represented.

Modeled relationships (7)
  • Fixed PROTAC level → Simplified engagement: algebraic engagement (modulation)
  • Simplified engagement → Catalytic degradation: sets degradation (modulation)
  • Catalytic degradation → Mechanistic target protein: target loss (loss)
  • Mechanistic target protein → Basal recovery: baseline deficit (modulation)
  • Basal recovery → Mechanistic target protein: restoration (production)
  • Fixed PROTAC level → Hook-shaped steady state: biphasic curve (modulation)
  • Hook-shaped steady state → Hook-model target protein: relaxation target (modulation)

Modeled relationships: Fixed PROTAC level to Simplified engagement: algebraic engagement (modulation); Simplified engagement to Catalytic degradation: sets degradation (modulation); Catalytic degradation to Mechanistic target protein: target loss (loss); Mechanistic target protein to Basal recovery: baseline deficit (modulation); Basal recovery to Mechanistic target protein: restoration (production); Fixed PROTAC level to Hook-shaped steady state: biphasic curve (modulation); Hook-shaped steady state to Hook-model target protein: relaxation target (modulation).

Primary readouts: Mechanistic relative target protein; Hook-model target protein; Simplified engagement; Hook-shaped degradation.

Model details

10 parameters · 3 states · 3 equations · 6 derived outputs

Classification & API access
Therapeutic
Parameterized PROTAC
Modality
Targeted protein degrader
Target
generic POI, E3 ligase
Disease / scope
Mechanistic target-degradation pharmacology
ParameterDefaultUnitDescription
Alphaalpha1.34—Alpha coefficient used by the released system of model equations.
E0e0_nm203nME0 coefficient used by the released system of model equations.
Hook DC50hook_dc50_nm0.29nMHook DC50 at which the corresponding modeled effect reaches half of its maximum.
Hook dcmaxhook_dcmax_nm68.9nMHook dcmax coefficient used by the released system of model equations.
Hook dmax sshook_dmax_ss0.949—Hook dmax ss coefficient used by the released system of model equations.
Catalytic degradation ratekcat_h0.51/hCatalytic degradation rate coefficient used by the released system of model equations.
PROTAC–E3 ligase dissociation constantkd_e_nm3100nMPROTAC–E3 ligase dissociation constant describing equilibrium binding affinity in the modeled interaction.
Target–PROTAC dissociation constantkd_p_nm138nMTarget–PROTAC dissociation constant describing equilibrium binding affinity in the modeled interaction.
PROTAC concentrationprotac_conc_nm68.9nMPROTAC concentration coefficient used by the released system of model equations.
Target-protein half-lifet_half_p_h45hTarget-protein half-life controlling the time required for the corresponding quantity to decrease by half.

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