TY - JOUR
T1 - The non-specific binding of tyrosine kinase inhibitors to human liver microsomes
AU - Burns, Kushari
AU - Nair, Pramod
AU - Rowland, Andrew
AU - Mackenzie, Peter
AU - Knights, Kathleen
AU - Miners, John
PY - 2015/12/1
Y1 - 2015/12/1
N2 - Drugs and other chemicals frequently bind nonspecifically to the constituents of an in vitro incubation mixture, particularly the enzyme source [e.g., human liver microsomes (HLM)]. Correction for nonspecific binding (NSB) is essential for the accurate calculation of the kinetic parameters Km, Clint, and Ki. Many tyrosine kinase inhibitors (TKIs) are lipophilic organic bases that are nonionized at physiologic pH. Attempts to measure the NSB of several TKIs to HLM by equilibrium dialysis proved unsuccessful, presumably due to the limited aqueous solubility of these compounds. Thus, the addition of detergents to equilibrium dialysis samples was investigated as an approach to measure the NSB of TKIs. The binding of six validation set nonionized lipophilic bases (felodipine, isradipine, loratidine, midazolam, nifedipine, and pazopanib) to HLM (0.25 mg/ml) was shown to be unaffected by the addition of CHAPS (6 mM) to the dialysis medium. This approach was subsequently applied to measurement of the binding of axitinib, dabrafenib, erlotinib, gefitinib, ibrutinib, lapatinib, nilotinib, nintedanib, regorafenib, sorafenib, and trametinib to HLM (0.25 mg/ml). As with the validation set drugs, attainment of equilibrium was demonstrated in HLM-HLM and buffer-buffer control dialysis experiments. Values of the fraction unbound to HLM ranged from 0.14 (regorafenib and sorafenib) to 0.93 (nintedanib), and were generally consistent with the known physicochemical determinants of drug NSB. The extensive NSB of many TKIs to HLM underscores the importance of correction for TKI binding to HLM and, presumably, other enzyme sources present in in vitro incubation mixtures.
AB - Drugs and other chemicals frequently bind nonspecifically to the constituents of an in vitro incubation mixture, particularly the enzyme source [e.g., human liver microsomes (HLM)]. Correction for nonspecific binding (NSB) is essential for the accurate calculation of the kinetic parameters Km, Clint, and Ki. Many tyrosine kinase inhibitors (TKIs) are lipophilic organic bases that are nonionized at physiologic pH. Attempts to measure the NSB of several TKIs to HLM by equilibrium dialysis proved unsuccessful, presumably due to the limited aqueous solubility of these compounds. Thus, the addition of detergents to equilibrium dialysis samples was investigated as an approach to measure the NSB of TKIs. The binding of six validation set nonionized lipophilic bases (felodipine, isradipine, loratidine, midazolam, nifedipine, and pazopanib) to HLM (0.25 mg/ml) was shown to be unaffected by the addition of CHAPS (6 mM) to the dialysis medium. This approach was subsequently applied to measurement of the binding of axitinib, dabrafenib, erlotinib, gefitinib, ibrutinib, lapatinib, nilotinib, nintedanib, regorafenib, sorafenib, and trametinib to HLM (0.25 mg/ml). As with the validation set drugs, attainment of equilibrium was demonstrated in HLM-HLM and buffer-buffer control dialysis experiments. Values of the fraction unbound to HLM ranged from 0.14 (regorafenib and sorafenib) to 0.93 (nintedanib), and were generally consistent with the known physicochemical determinants of drug NSB. The extensive NSB of many TKIs to HLM underscores the importance of correction for TKI binding to HLM and, presumably, other enzyme sources present in in vitro incubation mixtures.
UR - http://www.scopus.com/inward/record.url?scp=84948991000&partnerID=8YFLogxK
U2 - 10.1124/dmd.115.065292
DO - 10.1124/dmd.115.065292
M3 - Article
SN - 0090-9556
VL - 43
SP - 1934
EP - 1937
JO - Drug Metabolism and Disposition
JF - Drug Metabolism and Disposition
IS - 12
ER -