Ribociclib, a CDK4/6 inhibitor used in the treatment of hormone receptor-positive, HER2-negative metastatic breast cancer, exhibits significant pharmacokinetic variability in Black patients based on their CYP3A5 genotype, according to a study published in Nature. The LEANORA trial (NCT04657679) assessed the pharmacokinetics and pharmacogenomics of ribociclib in a cohort of Black women with previously untreated HR+/HER2- metastatic or locally advanced breast cancer.
The study, a prospective, observational, multicenter cohort, administered ribociclib at 600 mg daily (3 weeks on, 1 week off) plus letrozole 2.5 mg daily or fulvestrant 500 mg on days 1 and 15. Researchers collected serial blood samples for pharmacokinetic (PK) and pharmacogenetic (PGx) analyses to determine drug concentrations and genetic influences.
Impact of CYP3A5 Genotype on Ribociclib Exposure
The primary endpoint was the area under the concentration-time curve (AUCtau) of ribociclib between days 8 and 16 of cycle 1, comparing CYP3A5 poor metabolizers (PM) and CYP3A5 intermediate/normal metabolizers (IM/NM). The results indicated a notable difference in ribociclib exposure based on CYP3A5 genotype. Patients with CYP3A5 PM exhibited higher ribociclib AUCtau compared to CYP3A5 IM/NM.
Specifically, the study found that individuals with the CYP3A5 poor metabolizer phenotype had significantly increased exposure to ribociclib. This suggests that genetic variations in CYP3A5, a key enzyme involved in ribociclib metabolism, can lead to altered drug concentrations in Black patients.
Clinical Implications and Future Directions
These pharmacokinetic differences may have implications for both the efficacy and toxicity of ribociclib. Higher drug exposure in CYP3A5 poor metabolizers could potentially increase the risk of adverse events or necessitate dose adjustments. The study also explored the association of other variants with ribociclib AUCTAU, using an exact Wilcoxon rank sum test or a Kruskal-Wallis test.
"The findings underscore the importance of considering pharmacogenomics in optimizing cancer treatment for diverse populations," said the lead author of the study. "Further research is needed to determine whether CYP3A5 genotype-guided dosing of ribociclib can improve patient outcomes."
The study's limitations include a small sample size (n=14) and the lack of a comparator group of non-Hispanic White participants due to enrollment challenges. However, the results provide valuable insights into the pharmacokinetics of ribociclib in Black patients and highlight the need for more inclusive research in cancer drug development.
Study Details
The LEANORA trial enrolled women with previously untreated HR+/HER2- metastatic or locally advanced breast cancer who self-identified as African American/Black. The primary endpoint was ribociclib AUCtau. Secondary endpoints included additional ribociclib pharmacokinetic properties and adverse events. Statistical analysis included the exact Wilcoxon rank-sum test and multiple regression analysis.
