Objective:

To develop a population PBPK model that integrates plasma and intracranial pharmacokinetics (PK) along with CDK4/6 target occupancy parameters to optimize the dosing regimen of ribociclib (RIB) for patients with breast cancer and brain metastases, ultimately enhancing therapeutic outcomes.

Key Findings:

• Ribociclib has a CSF/unbound plasma concentration ratio of 1.29, indicating significant penetration into the cerebrospinal fluid, which may enhance treatment efficacy.
• Current studies primarily focus on plasma PK, with limited data on intracranial drug distribution and CDK4/6 occupancy, highlighting a critical gap in knowledge.
• Physiologically based pharmacokinetic modeling can predict intracranial drug concentrations and optimize dosing strategies for CNS-targeted therapies, potentially improving patient outcomes.

Interpretation:

The ability of RIB to penetrate the blood-brain barrier and achieve effective concentrations in the CSF suggests potential for improved treatment outcomes in patients with brain metastases, warranting further clinical exploration.

Limitations:

• Limited clinical studies on RIB efficacy in patients with brain metastases, which restricts the applicability of findings.
• Challenges in accurately predicting drug penetration into the brain and integrating intracranial PK data into clinical decision-making, necessitating further research.

Conclusion:

The study highlights the utility of PBPK modeling in personalizing cancer therapy and optimizing ribociclib dosing regimens for patients with breast cancer and brain metastases, with the potential to significantly improve clinical outcomes.