Membrane transporters can be major determinants of the pharmacokinetic, safety and efficacy profiles of drugs. This presents several key questions for drug development, including which transporters are clinically important in drug absorption and disposition, and which in vitro methods are suitable for studying drug interactions with these transporters. In addition, what criteria should trigger follow-up clinical studies, and which clinical studies should be conducted if needed. In this article, we provide the recommendations of the International Transporter Consortium on these issues, and present decision trees that are intended to help guide clinical studies on the currently recognized most important drug transporter interactions. The recommendations are generally intended to support clinical development and filing of a new drug application. Overall, it is advised that the timing of transporter investigations should be driven by efficacy, safety and clinical trial enrolment questions (for example, exclusion and inclusion criteria), as well as a need for further understanding of the absorption, distribution, metabolism and excretion properties of the drug molecule, and information required for drug labelling.

https://www.njacs.org/wp-content/docs/2010-10-DrugMet-R-Evers.pdf

Membrane transporters in drug development.

Synthesis of 3d metallic single-molecule magnets

We have obtained, for the first time, a quantitative protein expression profile of membrane transporters and receptors in human brain microvessels, that is, the blood-brain barrier (BBB). Brain microvessels were isolated from brain cortexes of seven males (16-77 years old) and protein expression of 114 membrane proteins was determined by means of a liquid chromatography-tandem mass spectrometric quantification method using recently established in-silico peptide selection criteria. Among drug transporters, breast cancer resistance protein showed the most abundant protein expression (8.14 fmol/μg protein), and its expression level was 1.85-fold greater in humans than in mice. By contrast, the expression level of P-glycoprotein in humans (6.06 fmol/μg protein) was 2.33-fold smaller than that of mdr1a in mice. The organic anion transporters reported in rodent BBB, that is, multidrug resistance-associated protein, organic anion transporter and organic anion-transporting polypeptide family members, were under limit of quantification in humans, except multidrug resistance-associated protein 4 (0.195 fmol/μg protein). Among detected transporters and receptors for endogenous substances, the glucose transporter 1 level was similar to that of mouse, while the L-type amino acid transporter 1 level was fivefold smaller than that of mouse. These findings should be useful for understanding human BBB function and its differences from that in mouse.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1471-4159.2011.07208.x

Quantitative targeted absolute proteomics of human blood–brain barrier transporters and receptors

Despite scientific advances in understanding the causes and treatment of human malignancy, a persistent challenge facing basic and clinical investigators is how to adequately treat primary and metastatic brain tumors. The blood-brain barrier is a physiologic obstruction to the delivery of systemic chemotherapy to the brain parenchyma and central nervous system (CNS). A number of physiologic properties make the endothelium in the CNS distinct from the vasculature found in the periphery. Recent evidence has shown that a critical aspect of this barrier is composed of xenobiotic transporters which extrude substrates from the brain into the cerebrospinal fluid and systemic circulation. These transporters also extrude drugs and toxins if they gain entry into the cytoplasm of brain endothelial cells before they enter the brain. This review highlights the properties of the blood-brain barrier, including the location, function, and relative importance of the drug transporters that maintain this barrier. Primary and metastatic brain malignancy can compromise this barrier, allowing some access of chemotherapy treatment to reach the tumor. The responsiveness of brain tumors to systemic treatment found in past clinical research is discussed, as are possible explanations as to why CNS tumors are nonetheless able to evade therapy. Finally, strategies to overcome this barrier and better deliver chemotherapy into CNS tumors are presented.

https://clincancerres.aacrjournals.org/content/clincanres/13/6/1663.full.pdf

The blood-brain barrier and cancer: transporters, treatment, and Trojan horses.

3.2. Other Potential in vivo Functions of Pgp 2992 3.3. Physiological Role of ABCG2 2992 3.4. Physiological Role of MRP1 2992 4. Structure of ABC Superfamily Drug Efflux Pumps 2992 4.1. Domain Structure of ABC Proteins 2992 4.2. Structure of Entire Bacterial ABC Proteins 2993 4.3. Structure of Pgp, MRP1, and ABCG2 2994 5. Substrate Specificity of ABC Drug Efflux Pumps 2995 5.1. MDR Spectrum Substrates 2995 5.2. Binding and Transport of Drugs 2998 5.3. Multidrug-Binding Pockets 2998 6. Catalytic Cycle of ABC Drug Efflux Pumps 3000 6.1. ATP Binding and Hydrolysis 3000 6.2. Occluded Nucleotide Conformation of Pgp 3000 6.3. Role of NBD Dimerization and the Occluded Conformation in the Catalytic Cycle of Pgp 3000

ABC efflux pump-based resistance to chemotherapy drugs.

Background

Numerous knockout mouse studies have revealed that P-glycoprotein (P-gp) significantly limits drug distribution across the mouse blood-brain barrier (BBB). To determine the importance of P-gp at the human BBB, we developed a state-of-the-art, noninvasive, quantitative imaging technique to measure P-gp activity by use of carbon 11-labeled verapamil as the P-gp substrate and cyclosporine (INN, ciclosporin) as the P-gp inhibitor.



Methods

In brief, 11C-verapamil (approximately 0.2 mCi/kg) was administered to healthy volunteers (n = 12 [6 women and 6 men]) as an intravenous infusion over a period of approximately 1 minute before and after at least a 1-hour infusion of cyclosporine (2.5 mg · kg−1 · h−1). Arterial blood samples and brain positron emission tomography images were obtained at frequent intervals for 45 minutes. Both blood and plasma radioactivity contents were determined in each verapamil sample. The content of verapamil and its metabolites in the 20- and 45-minute plasma samples was determined by a rapid solid-phase extraction method. The brain uptake of 11C-radioactivity (brain area under the curve [AUCbrain]/blood area under the curve [AUCblood]) was determined in the presence and absence of cyclosporine.



Results

The AUCbrain/AUCblood ratio of 11C-radioactivity was increased by 88% ± 20% (1.02 ± 0.18 versus 0.55 ± 0.10, P < .001) in the presence of cyclosporine (mean blood concentration, 2.8 ± 0.4 μmol/L) without affecting 11C-verapamil metabolism or plasma protein binding. The corresponding increases for the brain white and gray matter were 84% ± 13% and 84% ± 18%, respectively.



Conclusions

This is the first time that P-gp activity at the human BBB has been measured. The modest inhibition of human BBB P-gp by cyclosporine has implications for P-gp-based drug interactions at the human BBB. Our method for imaging P-gp activity can be used to identify multidrug-resistant tumors or to determine the contribution of P-gp polymorphism, inhibition, or induction to interindividual variability in drug response.



Clinical Pharmacology & Therapeutics (2005) 77, 503–514; doi: 10.1016/j.clpt.2005.01.022

Imaging P-glycoprotein transport activity at the human blood-brain barrier with positron emission tomography.

The X-ray structural characterization of the iron (II) amides [Fe{N(SiMe 3 ) 2 } 2 ] 2 (1) and [Fe(NPh 2 ) 2 ] 2 (2) and the Lewis base adduct Fe[N(SiMe 3 ) 2 ] 2 (THF) (3), as well as the syntheses of the last two compounds, is described. These complexes are rare examples of the coordination number 3 for iron. Compounds 1 and 2 are both dimeric in the solid state, with each trigonal-planar ion bound to one terminal and two bridging amides. They closely resemble the corresponding Mn(II) and Co(II) compounds. Compound 3 is monomeric in the solid state, with one THF and two amides arranged in a trigonal-planar fashion

Three-coordinate iron complexes: x-ray structural characterization of the iron amide-bridged dimers [Fe(NR2)2]2 (R = SiMe3, C6H5) and the adduct Fe[N(SiMe3)2]2(THF) and determination of the association energy of the monomer Fe{N(SiMe3)2}2 in solution

Series of two-coordinate and quasi-two-coordinate transition-metal complexes: synthesis, structural, and spectroscopic studies of sterically demanding borylamide ligands -NRBR'2 (R = Ph, R' = Mes, Xyl; R = R' = Mes), their lithium salts, Li(Et2O)2NRBR'2, and their transition-metal derivatives, M(NPhBMes2)2 (M = Cr, Co, Ni), Co(NPhBXyl2)2 and M(NMesBMes2)2 (M = Cr .fwdarw. Ni)

The synthesis and structural characterization of several alkylzinc alkoxides, aryloxides, and thiolates, many of which have unusual structures, are described. The compounds were synthesized by the simple reaction of the zinc dialkyl, ZnR 2 (R=Ch 2 SiMe 3 ), with 1 equiv of an aocohol or thiol to afford the products [RZnOR'] n

Synthesis and characterization of novel quasiaromatic zinc-sulfur aggregates and related zinc-oxygen complexes

Synthesis and characterization of the homoleptic aryloxides [M{O(2,4,6-tert-Bu3C6H2)}2]2 (M = manganese, iron), the adducts [Mn(OCPh3)2(py)2] and [Fe(OCPh3)2(THF)2], and the mixed complex [Fe{N(SiMe3)2}{.mu.-O(2,4,6-tert-Bu3C6H2)}]2: evidence for primarily ionic metal-oxygen bonding

Steven C. Shoner

Papers

Imaging P-glycoprotein transport activity at the human blood-brain barrier with positron emission tomography.

Three-coordinate iron complexes: x-ray structural characterization of the iron amide-bridged dimers [Fe(NR2)2]2 (R = SiMe3, C6H5) and the adduct Fe[N(SiMe3)2]2(THF) and determination of the association energy of the monomer Fe{N(SiMe3)2}2 in solution

Synthesis and characterization of novel quasiaromatic zinc-sulfur aggregates and related zinc-oxygen complexes

Synthesis and characterization of the homoleptic aryloxides [M{O(2,4,6-tert-Bu3C6H2)}2]2 (M = manganese, iron), the adducts [Mn(OCPh3)2(py)2] and [Fe(OCPh3)2(THF)2], and the mixed complex [Fe{N(SiMe3)2}{.mu.-O(2,4,6-tert-Bu3C6H2)}]2: evidence for primarily ionic metal-oxygen bonding