TY - JOUR
T1 - Chemical Analysis of Drug Biocrystals
T2 - A Role for Counterion Transport Pathways in Intracellular Drug Disposition
AU - Keswani, Rahul K.
AU - Baik, Jason
AU - Yeomans, Larisa
AU - Hitzman, Chuck
AU - Johnson, Allison M.
AU - Pawate, Ashtamurthy S.
AU - Kenis, Paul J.A.
AU - Rodriguez-Hornedo, Nair
AU - Stringer, Kathleen A.
AU - Rosania, Gus R.
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/7/6
Y1 - 2015/7/6
N2 - 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.
AB - 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.
KW - bioaccumulation
KW - chloride channels
KW - clofazimine
KW - intracellular crystals
KW - pharmacokinetics
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U2 - 10.1021/acs.molpharmaceut.5b00032
DO - 10.1021/acs.molpharmaceut.5b00032
M3 - Article
C2 - 25926092
AN - SCOPUS:84936805464
SN - 1543-8384
VL - 12
SP - 2528
EP - 2536
JO - Molecular pharmaceutics
JF - Molecular pharmaceutics
IS - 7
ER -