P-glycoprotein expression in human major and minor salivary glands

Human ABC and SLC Transporters: The Culprit Responsible for Unspecific PSMA-617 Uptake?

[177Lu]Lu-PSMA-617 has recently been successfully approved by the FDA, the MHRA, Health Canada and the EMA as Pluvicto®. However, salivary gland (SG) and kidney toxicities account for its main dose-limiting side-effects, while its corresponding uptake and retention mechanisms still remain elusive. Recently, the presence of different ATP-binding cassette (ABC) transporters, such as human breast cancer resistance proteins (BCRP), multidrug resistance proteins (MDR1), multidrug-resistance-related proteins (MRP1, MRP4) and solute cassette (SLC) transporters, such as multidrug and toxin extrusion proteins (MATE1, MATE2-K), organic anion transporters (OAT1, OAT2v1, OAT3, OAT4) and peptide transporters (PEPT2), has been verified at different abundances in human SGs and kidneys. Therefore, our aim was to assess whether [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are substrates of these ABC and SLC transporters. For in vitro studies, the novel isotopologue ([α,β-3H]Nal)Lu-PSMA-617 was used in cell lines or vesicles expressing the aforementioned human ABC and SLC transporters for inhibition and uptake studies, respectively. The corresponding probe substrates and reference inhibitors were used as controls. Our results indicate that [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are neither inhibitors nor substrates of the examined transporters. Therefore, our results show that human ABC and SLC transporters play no central role in the uptake and retention of [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 in the SGs and kidneys nor in the observed toxicities.

Tacrolimus Concentration in Saliva of Kidney Transplant Recipients: Factors Influencing the Relationship with Whole Blood Concentrations

OBJECTIVE

The objective of this study was to examine the association between tacrolimus concentration in oral fluids and in whole blood and to investigate the various factors that influence this relationship.

PATIENTS AND METHODS

Forty-six adult kidney transplant recipients were included in the study. Study A (ten patients) included the collection of several paired oral fluid samples by passive drool over a 12-h post-dose period. Study B (36 patients) included the collection of oral fluids pre-dose and at 2 h after the tacrolimus dose under three conditions: un-stimulated, after stimulation with a tart candy, and after mouth rinsing. The tacrolimus concentration in oral fluids was measured by a specially developed sensitive and specific liquid chromatography mass spectrometry method. A salivary transferrin concentration of >1 mg/dL was used as a cut-off value for oral fluid blood contamination.

RESULTS

Rinsing the oral cavity before sampling proved to provide the most suitable sampling strategy giving a correlation coefficient value of 0.71 (p = 0.001) between the tacrolimus concentration in oral fluids and the tacrolimus concentration in whole blood at trough. Mean and 95% confidence interval of tacrolimus concentration in oral fluids at the pre-dose concentration for samples collected after mouth rinsing was 584 (436, 782) pg/mL. The ratio of the tacrolimus concentration in oral fluids to the tacrolimus concentration in whole blood (*100) was 11% (95% confidence interval 9-13) for all sampling times. Oral fluid pH or weight of a saliva sample did not influence the tacrolimus concentration in oral fluids. Tacrolimus distribution into oral fluids exhibited a delay with a pronounced counter-clockwise hysteresis with respect to the time after dose. A multivariate analysis of variance revealed that the tacrolimus concentration in oral fluids is related to the tacrolimus concentration in whole blood and tacrolimus plasma-binding proteins including albumin and cholesterol.

CONCLUSION

An optimal sampling strategy for the determination of the tacrolimus concentration in oral fluids was established. Measuring the tacrolimus concentration in oral fluids appears to be a feasible and non-invasive method for predicting the concentration of tacrolimus in whole blood.

Membrane Transporters in Human Parotid Gland-Targeted Proteomics Approach

Salivary glands provide secretory functions, including secretion of xenobiotics and among them drugs. However, there is no published information about protein abundance of drug transporters measured using reliable protein quantification methods. Therefore, mRNA expression and absolute protein content of clinically relevant ABC (n = 6) and SLC (n = 15) family member transporters in the human parotid gland, using the qRT-PCR and liquid chromatography‒tandem mass spectrometry (LC−MS/MS) method, were studied. The abundance of nearly all measured proteins ranged between 0.04 and 0.45 pmol/mg (OCT3 > MRP1 > PEPT2 > MRP4 > MATE1 > BCRP). mRNAs of ABCB1, ABCC2, ABCC3, SLC10A1, SLC10A2, SLC22A1, SLC22A5, SLC22A6, SLC22A7, SLC22A8, SLCO1A2, SLCO1B1, SLCO1B3 and SLCO2B1 were not detected. The present study provides, for the first time, information about the protein abundance of membrane transporters in the human parotid gland, which could further be used to define salivary bidirectional transport (absorption and secretion) mechanisms of endogenous compounds and xenobiotics.

Polyspecific organic cation transporters and their impact on drug intracellular levels and pharmacodynamics

Most drugs are intended to act on molecular targets residing within a specific tissue or cell type. Therefore, the drug concentration within the target tissue or cells is most relevant to its pharmacological effect. Increasing evidences suggest that drug transporters not only play a significant role in governing systemic drug levels, but are also an important gate keeper for intra-tissue and intracellular drug concentrations. This review focuses on polyspecific organic cation transporters, which include the organic cation transporters 1-3 (OCT1-3), the multidrug and toxin extrusion proteins 1-2 (MATE1-2) and the plasma membrane monoamine transporter (PMAT). Following an overview of the tissue distribution, transport mechanisms, and functional characteristics of these transporters, we highlight the studies demonstrating the ability of locally expressed OCTs to impact intracellular drug concentrations and directly influence their pharmacological and toxicological activities. Specifically, OCT1-mediated metformin access to its site of action in the liver is impacted by genetic polymorphisms and chemical inhibition of OCT1. The impact of renal OCT2 and MATE1/2-K in cisplatin intrarenal accumulation and nephrotoxicity is reviewed. New data demonstrating the role of OCT3 in salivary drug accumulation and secretion is discussed. Whenever possible, the pharmacodynamic response and toxicological effects is presented and discussed in light of intra-tissue and intracellular drug exposure. Current challenges, knowledge gaps, and future research directions are discussed. Understanding the impact of transporters on intra-tissue and intracellular drug concentrations has important implications for rational-based optimization of drug efficacy and safety.

Measurement of saliva tacrolimus levels in pediatric renal transplant recipients

The aim of this study was to investigate whether a strong and clinically applicable correlation exists between saliva and whole-blood tacrolimus levels measured by high-performance liquid chromatography-tandem mass spectrometry. A high degree of correlation would potentially allow pain-free saliva sample collection to replace blood sampling for the measurement of tacrolimus levels. Enrolled in the study were 37 children (24 boys) aged 8-18 years [median (IQR) 16.2 (12.9-17.5) years] attending the renal transplant clinic at the Royal Manchester Children's Hospital and 77 paired blood saliva samples were collected. The mean (SD) saliva tacrolimus level was 0.14 (0.16), range 0-0.7 μg/l. In ten cases, tacrolimus was not detected in the saliva despite being present in blood. The ratio of blood-to-saliva tacrolimus levels varied from 2.6 to 550. The Pearson product-moment correlation suggested a weak linear relationship between tacrolimus levels in blood and saliva with a coefficient 0.36. Individual patients did not demonstrate consistent tacrolimus blood/saliva ratios with a mean correlation of 0.08. Additional experiments excluded saliva contamination with blood and sample collection and storage conditions as causes of poor correlation. The measurement of saliva tacrolimus levels in place of or as an adjunct to blood sampling therefore cannot be recommended.

Pharmacokinetics of pradofloxacin and doxycycline in serum, saliva, and tear fluid of cats after oral administration

The pharmacokinetic properties of pradofloxacin and doxycycline were investigated in serum, saliva, and tear fluid of cats. In a crossover study design, six cats were treated orally with a single dose of pradofloxacin (Veraflox Oral Suspension 2.5%) and doxycycline (Ronaxan 100 mg) at 5 mg/kg body weight. Following administration, samples of serum, saliva, and tear fluid were taken in regular intervals over a period of 24 h and analysed by turbulent flow chromatography/tandem mass spectrometry. All values are given as mean +/- SD. Pradofloxacin reached a mean maximum serum concentration (C(max)) of 1.1 +/- 0.5 microg/mL after 1.8 +/- 1.3 h (t(max)). In saliva and tear fluid, mean C(max) was 6.3 +/- 7.0 and 13.4 +/- 20.9 microg/mL, respectively, and mean t(max) was 0.5 +/- 0 and 0.8 +/- 0.3 h, respectively. Doxycycline reached a mean C(max) in serum of 4.0 +/- 0.8 microg/mL after 4.3 +/- 3.2 h. Whilst only at two time-points doxycycline concentrations close to the limit of quantification were determined in tear fluid, no detectable levels were found in saliva. The high concentrations of pradofloxacin in saliva and tear fluid are promising to apply pradofloxacin for the treatment of conjunctivitis and upper respiratory tract infections in cats. As doxycycline is barely secreted into these fluids after oral application the mechanisms of its clinical efficacy remain unclear.

ABCB1 genetic polymorphism and risk of upper aerodigestive tract cancers among smokers, tobacco chewers and alcoholics in an Indian population

BACKGROUND AND OBJECTIVE

Upper aerodigestive tract (UADT) cancers are associated with the tobacco use and alcohol consumption. Certain toxins and carcinogens causing UADT cancers are found to be substrates of polymorphic ABCB1 gene encoded P-glycoprotein efflux pump. This study investigates the association between ABCB1 gene polymorphism at exon 26 (3435C>T) and risk to UADT cancers in Tamilians, a population of south India.

METHODS

The study included 219 unrelated histopathologically confirmed cases and 210 population-based controls. Genomic DNA was extracted from peripheral leukocytes and genotyped for ABCB1 3435C>T polymorphism by PCR-restriction fragment length polymorphism method.

RESULTS

The multivariate logistic regression analyses demonstrated that the homozygous ABCB1 TT genotype was significantly associated with an overall increased risk for developing UADT cancers [odds ratio (OR): 2.53; 95% confidence interval (CI): 1.28-5.02]. Further, the determination of gene-environment interaction by stratified analyses have revealed a significant interaction between the smoking and homozygous TT genotype [(OR: 7.52; CI: 1.50-37.70) and (OR: 16.89; CI: 3.87-73.79) for 11-20 and >20 pack-years, respectively]. The strongest interaction was observed among the regular tobacco chewers (OR: 45.29; CI: 8.94-130.56) homozygous for TT genotype. No suggestion, however, of an interaction between the genotypes and the alcohol consumption on the multiplicative scale was made.

CONCLUSION

The ABCB1 gene polymorphism at exon 26 (3435C>T) may be one of the risk factors for susceptibility to UADT cancers. Furthermore, the significant interaction among habitual smokers and tobacco chewers, homozygous for TT genotype modulates the risk to UADT cancers in the Tamilian population of south India.

Evaluation of acetaminophen P-glycoprotein-mediated salivary secretion by rat submandibular glands

The constant ratio between saliva and plasma acetaminophen concentrations (S/P) during the elimination phase is assumed to result from the equilibrium established among the free-drug concentrations in the arterial blood, venous blood and saliva. Salivary secretion of acetaminophen is assumed to result from a passive diffusion of the drug to saliva from the blood that supplies the salivary glands. However, the constant S/P ratio during acetaminophen disposition and the finding that P-glycoprotein (P-gp), a protein recognized to pump substrates out of the cell, is expressed in duct cells of the submandibular glands questions the mechanisms involved in acetaminophen salivary secretion. Thus, we intended to evaluate the existence of a P-glycoprotein-mediated transport of acetaminophen in rat submandibular glands. Acetaminophen (30 mg/kg, i.v.) pharmacokinetics was assessed in controls and in rats pre-treated with erythromycin (100 mg/kg) as a P-glycoprotein inhibitor. Acetaminophen pharmacokinetic parameters were calculated from saliva and plasma levels considering a non-compartmental analysis. Mean plasma and salivary profiles of control and pre-treated animals were almost superimposable. No difference could be found in S/P ratios in control and erythromycin pre-treated animals (P > 0.05). Moreover, no statistical difference could be found in the kinetic parameters calculated from saliva or plasma drug level (P > 0.05). These observations indicate that acetaminophen salivary secretion in rat submandibular glands is not related to P-glycoprotein-mediated transport under the experimental conditions of the present work.

P-glycoprotein drug transporter MDR1 gene polymorphism in renal transplant patients with and without gingival overgrowth

OBJECTIVE

To determine whether there is association between genotypes of drug transporter multidrug resistant (MDR)1 gene coding drug transporter P-glycoprotein and gingival overgrowth in kidney transplant patients.

METHODS

Fifty-four unrelated kidney transplant patients suffering from gingival overgrowth as well 120 control transplant patients without overgrowth were enrolled into the study. Gingival overgrowth was assessed by two independent periodontal specialists at 6 months after transplantation. During the post-transplant period all patients were given medication, which included cyclosporine A, diltiazem or verapamil, prednisone, azathioprine. MDR1 C3435T polymorphism was determined using the polymerase chain reaction-restriction fragment length polymorphism assay.

RESULTS

In kidney transplant patients suffering from gingival overgrowth mean score of gingival overgrowth was 1.43 +/- 0.63, whereas in control subjects was 0.0. Patients with gingival overgrowth induced by immunosuppressive medication were characterized by similar distribution of MDR1 genotypes. There were no significant differences of 3435CC, 20.4% and 22.5%, 3435CT, 61.1% and 54.2% and 3435TT, 18.5% and 23.3% genotypes (frequencies) between patients with and without gingival overgrowth. The risk of gingival overgrowth was the highest among patients carrying 3435CT genotype (OD 1.33), but did not differ markedly from the other genotypes, i.e. 3435CC (OD 0.88) and 3435TT (OD 0.75). Likewise to genotypes, distribution of alleles was similar in patients with gingival overgrowth and healthy gingiva. The wild-type allele 3435C was found in 50.9% and 49.6% of subjects whereas the mutated allele 3435T was revealed in 49.1% and 50.4% of patients with and without gingival overgrowth, respectively. The evaluated risk of gingival overgrowth in patients with 3435C allele was 1.06 versus 0.95 in those with healthy gingiva. The medication regimen administered in both groups of the study was comparable. Immunohistochemical studies revealed expression of P-glycoprotein in ducts of the salivary gland.

CONCLUSION

No association between the MDR1 gene polymorphism and gingival overgrowth was revealed in kidney transplant patients administered cyclosporine A as a principal immunosuppressive agent. Further studies are needed to elucidate the role of P-glycoprotein in drug transport in salivary glands.

Expression of ATP-binding cassette transporter in human salivary ducts

P-glycoprotein expression has been observed in normal tissues as well as malignant tumours and thus does not appear to be induced by anticancer drugs. Knowledge of the distribution of ATP-binding cassette (ABC) transporters other than P-glycoprotein in normal salivary tissue is essential for understanding the physiological secretion or excretion of potentially toxic substances. Here the expression of ABC transporters was studied immunohistochemically in normal salivary gland tissue from nine patients. In striated duct cells, staining was strong for P-glycoprotein, multidrug resistance-associated protein (MRP) 1, MRP 2/canalicular multispecific organic anion transporter (cMOAT), and lung resistance-related protein (LRP). The staining intensity of acinar and intercalated duct cells for MRP 1 expression was distinct from that for MRP2/cMOAT, but was similar to that for P-glycoprotein. LRP was observed as particles between the nuclear and luminal membranes in the cytoplasm of intercalated duct cells. The expression of ABC transporters suggests that numerous transporters other than those studied might be isolated from normal salivary tissues. These observations indicate that these ABC transporters may not arise from any previous contact with anticancer drugs but are expressed physiologically. The achieved drug resistance as well as the physiological secretory function of ABC transporters could contribute to the responsiveness to chemotherapy of malignant salivary tumours.

Evidence of P-glycoprotein mediated apical to basolateral transport of flunisolide in human broncho-tracheal epithelial cells (Calu-3)

1. Transepithelial transport of flunisolide was studied in reconstituted cell monolayers of Calu-3, LLC-PK1 and the MDR1-P-glycoprotein transfected LLC-MDR1 cells. 2. Flunisolide transport was polarized in the apical (ap) to basolateral (bl) direction in Calu-3 cells and was demonstrated to be ATP-dependent. In LLC-MDR1 cells, flunisolide was transported in the bl to ap direction and showed no polarization in LLC-PK1 cells. 3. Non-specific inhibition of cellular metabolism at low temperature (4 degrees C) or by 2-deoxy-D-glucose (2-d-glu) and sodium azide (NaN(3)) abolished the polarized transport. Polarized flunisolide transport was also inhibited by the specific Pgp inhibitors verapamil, SDZ PSC 833 and LY335979. 4. Under all experimental conditions and in the presence of all used inhibitors, no decrease in the TransEpithelial Electrical Resistance (TEER) values was detected. From all inhibitors used, only the general metabolism inhibitors 2-deoxy-D-glucose and NaN(3), decreased the survival of Calu-3 cells. 5. Western blotting analysis and confocal laser scanning microscopy demonstrated the presence of MDR1-Pgp at mainly the basolateral side of the plasma membrane in Calu-3 cells and at the apical side in LLC-MDR1 cells. Mass spectroscopy studies demonstrated that flunisolide is transported unmetabolized across Calu-3 cells. 6. In conclusion, these results show that the active ap to bl transport of flunisolide across Calu-3 cells is facilitated by MDR1-Pgp located in the basolateral plasma membrane.