Chemical Analysis of Drug Biocrystals: A Role for Counterion Transport Pathways in Intracellular Drug Disposition.
In mammals, highly lipophilic small molecule chemical agents can accumulate as inclusions within resident tissue macrophages. In this context, we characterized the biodistribution, chemical composition, and structure of crystal-like drug inclusions (CLDIs) formed by clofazimine (CFZ), a weakly basic lipophilic drug. With prolonged oral dosing, CFZ exhibited a significant partitioning with respect to serum and fat due to massive bioaccumulation and crystallization in the liver and spleen. The NMR, Raman, and powder X-ray diffraction (p-XRD) spectra of CLDIs isolated from the spleens of CFZ-treated mice matched the spectra of pure, CFZ hydrochloride crystals (CFZ-HCl). Elemental analysis revealed a 237-fold increase in chlorine content in CLDIs compared to untreated tissue samples and a 5-fold increase in chlorine content compared to CFZ-HCl, suggesting that the formation of CLDIs occurs through a chloride mediated crystallization mechanism. Single crystal analysis revealed that CFZ-HCl crystals had a densely packed orthorhombic lattice configuration. In vitro, CFZ-HCl formed at a pH of 4-5 only if chloride ions were present at sufficiently high concentrations (>50:1 Cl(-)/CFZ), indicating that intracellular chloride transport mechanisms play a key role in the formation of CLDIs. While microscopy and pharmacokinetic analyses clearly revealed crystallization and intracellular accumulation of the drug in vivo, the chemical and structural characterization of CLDIs implicates a concentrative, chloride transport mechanism, paralleling and thermodynamically stabilizing the massive bioaccumulation of a weakly basic drug.
Rahul K
RK
Keswani
Jason
J
Baik
Larisa
L
Yeomans
∥Stanford Nano Center, Stanford University, 476 Lomita Mall, McCullough Building, Stanford, California 94305, United States.
Chuck
C
Hitzman
Allison M
AM
Johnson
Ashtamurthy S
AS
Pawate
Paul J A
PJ
Kenis
Nair
N
Rodriguez-Hornedo
Kathleen A
KA
Stringer
Gus R
GR
Rosania
D000818:Animals; D001692:Biological Transport / Q000187:drug effects*; D002712:Chlorides / Q000378:metabolism; D002991:Clofazimine / Q000378:metabolism* / Q000494:pharmacology*; D003460:Crystallization / Q000379:methods; D002479:Inclusion Bodies; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D013154:Spleen / Q000378:metabolism; D014018:Tissue Distribution
D002712:Chlorides; D002991:Clofazimine
bioaccumulation; chloride channels; clofazimine; intracellular crystals; pharmacokinetics