For decades, oncology drug development followed a simple principle: administer the highest dose patients could tolerate. With today's therapies, this principle no longer holds.
The highest tolerated dose is not always the optimal dose
The Maximum Tolerated Dose (MTD) approach was well suited for traditional chemotherapies, where increased exposure generally led to greater tumor cell killing. Today's oncology therapies are fundamentally different.
Targeted therapies, antibody-drug conjugates (ADCs), bispecific antibodies, and immunotherapies act through highly specific biological mechanisms. In many cases, efficacy reaches a plateau once sufficient target engagement is achieved, while toxicity continues to increase with dose.
This shift has transformed dose optimization into one of the most important—and often underestimated—challenges in oncology development.
Project Optimus : A New Regulatory Expectation
Recognizing the limitations of the traditional MTD paradigm, the FDA launched project Optimus to improve dose selection in oncology and encourage a more comprehensive understanding of the relationship between dose, exposure, efficacy, and safety.
The initiative challenges sponsors to move beyond identifying the highest tolerable dose and instead determine the dose that delivers the best overall benefit-risk profile for patients.
The optimal dose is not necessarily the maximum tolerated dose.
Efficacy quickly reaches a plateau, while toxicity continues to increase with dose. The OBD zone (Optimal Biological Dose) lies before the MTD, where clinical benefit is maximal at a level of toxicity that remains manageable.
Why oncology dose optimization is more complex than ever
Modern therapies introduce biological complexities that traditional dose-escalation studies often fail to capture:
Receptor saturation and target engagement plateaus
Nonlinear exposure-response relationships, difficult to extrapolate through classical dose escalation
Complex immune system dynamics, specific to immunotherapies
Delayed and cumulative toxicities, which does not appear in the early cycles
Tumor evolution and resistance mechanisms over the course of treatment
Long-term treatment requiring sustained tolerability
These factors make dose optimization far more challenging than simply identifying a toxicity threshold.
Why MIDD is central to project Optimus
Model Informed Drug Development (MIDD) provides the quantitative framework needed to understand how dose, exposure, efficacy, biomarkers, and safety interact throughout development.
By integrating pharmacokinetic (PK), pharmacodynamic (PD), biomarker, efficacy, and safety data, MIDD enables sponsors to evaluate multiple dosing strategies before large-scale clinical trials are conducted..
This represents the fundamental shift that Project Optimus seeks to achieve.
From Maximum Tolerated Dose to Optimal Biological Dose
One of the primary goals of MIDD is identifying the Optimal Biological Dose (OBD) — the exposure range where several conditions are met simultaneously.
The OBD zone: four conditions to meet
To support OBD selection, MIDD can be used for:
A roadmap aligned with FDA expectations
By structuring the development strategy around the OBD rather than the MTD, sponsors directly address project Optimus requirements — and strengthen their regulatory dialogue from the earliest stages.
Optimize your dose strategy in oncology?
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