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Invest New Drugs. 2012 Dec;30(6):2096-102. doi: 10.1007/s10637-011-9767-5. Epub 2011 Nov 17.

Plasma protein binding of sorafenib, a multi kinase inhibitor: in vitro and in cancer patients.

Author information

1
The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Bunting-Blaustein Cancer Research Bldg, Room 1M52, Baltimore, MD 21231-1000, USA.

Abstract

Sorafenib is an orally administered multikinase inhibitor that exhibits antiangiogenic and antitumor activity. Few investigators have been able to correlate cumulative sorafenib dose or total exposure to pharmacodynamic effects. This discrepancy may be in part due to poorly understood protein binding characteristics. Since unbound drug concentrations are believed to be more relevant to pharmacological and toxicological responses than total drug, an equilibrium dialysis method using 96-well microdialysis plates was optimized and validated for determining the fraction unbound (F(u)) sorafenib in human plasma and in isolated protein solutions. Unbound sorafenib concentrations were determined in cancer patients receiving the drug orally at a dose of 400 mg and 600 mg twice daily. Sorafenib was extensively bound with mean F(u) value of 0.3% in both non-cancer and cancer patient's plasma. The binding in plasma was concentration independent, indicating a low-affinity, possibly nonspecific and nonsaturable process. In isolated protein solutions, 99.8% and 79.3% of sorafenib was bound to human serum albumin (HSA) (4 g/dL) and α(1)-acid glycoprotein (AAG) (0.1 g/dL) with binding constants of 1.24 × 10(6) M(-1) and 1.40 × 10(5) M(-1), respectively. In cancer patients receiving sorafenib, unbound sorafenib was not correlated with patient characteristics or laboratory values. In conclusion, sorafenib is highly protein bound in human plasma with a higher affinity towards albumin and limited free drug may be partly responsible for its borderline clinical activity.

PMID:
22089297
PMCID:
PMC3652000
DOI:
10.1007/s10637-011-9767-5
[Indexed for MEDLINE]
Free PMC Article

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