Drug administration via feeding tubes-a procedure that carries risks: systematic identification of critical factors based on commonly administered drugs in a cohort of stroke patients.

PURPOSE: Drug administration via feeding tubes is considered a process with many uncertainties. This review aimed to give a comprehensive overview of data available on feeding tube application and to carry out risk assessments for drug substances commonly administered to stroke patients. METHODS: Drugs frequently administered via feeding tubes were identified through a retrospective analysis of discharge letters from a stroke unit. Physicochemical, pharmacokinetic, and stability properties of these drugs and data on drug-enteral nutrition interactions were systematically searched for in the European Pharmacopoeia, Hagers Handbook of Pharmaceutical Practice, Birchers clinical-pharmacological data compilation, and the Martindale Complete Drug Reference, as well as from databases including DrugBank, DrugDex, PubChem, Google Scholar, and PubMed. RESULTS: Of the drugs most commonly administered via feeding tubes in the present stroke patient cohort, bisoprolol, candesartan, and ramipril could be considered the least critical due to their overall favourable properties. Acetylsalicylic acid, amlodipine, hydrochlorothiazide, omeprazole and esomeprazole, simvastatin, and torasemide pose risks based on pH or light-dependent instability or proposed food effects. The most critical drugs to be administered via feeding tubes are considered to be furosemide, levodopa, and levothyroxine as they show relevant instabilities under administration conditions and substantial food effects; the latter two even possess a narrow therapeutic index. However, little information is available on drug-tube and drug-formula interactions. CONCLUSION: Feeding tube administration of medications turned out to be a highly complex process with several unmet risks. Therefore, investigations that systematically assess these risk factors using clinically relevant model systems are urgently needed.

Loss of Key EMT-Regulating miRNAs Highlight the Role of ZEB1 in EGFR Tyrosine Kinase Inhibitor-Resistant NSCLC.

Despite recent advances in the treatment of non-small cell lung cancer (NSCLC), acquired drug resistance to targeted therapy remains a major obstacle. Epithelial-mesenchymal transition (EMT) has been identified as a key resistance mechanism in NSCLC. Here, we investigated the mechanistic role of key EMT-regulating small non-coding microRNAs (miRNAs) in sublines of the NSCLC cell line HCC4006 adapted to afatinib, erlotinib, gefitinib, or osimertinib. The most differentially expressed miRNAs derived from extracellular vesicles were associated with EMT, and their predicted target ZEB1 was significantly overexpressed in all resistant cell lines. Transfection of a miR-205-5p mimic partially reversed EMT by inhibiting ZEB1, restoring CDH1 expression, and inhibiting migration in erlotinib-resistant cells. Gene expression of EMT-markers, transcription factors, and miRNAs were correlated during stepwise osimertinib adaptation of HCC4006 cells. Temporally relieving cells of osimertinib reversed transition trends, suggesting that the implementation of treatment pauses could provide prolonged benefits for patients. Our results provide new insights into the contribution of miRNAs to drug-resistant NSCLC harboring EGFR-activating mutations and highlight their role as potential biomarkers and therapeutic targets.

Novel Symmetrical Cage Compounds as Inhibitors of the Symmetrical MRP4-Efflux Pump for Anticancer Therapy.

Within the last decades cancer treatment improved by the availability of more specifically acting drugs that address molecular target structures in cancer cells. However, those target-sensitive drugs suffer from ongoing resistances resulting from mutations and moreover they are affected by the cancer phenomenon of multidrug resistance. A multidrug resistant cancer can hardly be treated with the common drugs, so that there have been long efforts to develop drugs to combat that resistance. Transmembrane efflux pumps are the main cause of the multidrug resistance in cancer. Early inhibitors disappointed in cancer treatment without a proof of expression of a respective efflux pump. Recent studies in efflux pump expressing cancer show convincing effects of those inhibitors. Based on the molecular symmetry of the efflux pump multidrug resistant protein (MRP) 4 we synthesized symmetric inhibitors with varied substitution patterns. They were evaluated in a MRP4-overexpressing cancer cell line model to prove structure-dependent effects on the inhibition of the efflux pump activity in an uptake assay of a fluorescent MRP4 substrate. The most active compound was tested to resentisize the MRP4-overexpressing cell line towards a clinically relevant anticancer drug as proof-of-principle to encourage for further preclinical studies.

Herb-drug interactions: a novel algorithm-assisted information system for pharmacokinetic drug interactions with herbal supplements in cancer treatment.

PURPOSE: To develop a system to estimate the risk of herb-drug interactions that includes the available evidence from clinical and laboratory studies, transparently delineates the algorithm for the risk estimation, could be used in practice settings and allows for adaptation and update. METHODS: We systematically searched Drugbank, Transformer, Drug Information Handbook, European and German Pharmacopoeia and MEDLINE for studies on herb-drug interactions of five common medicinal plants (coneflower, ginseng, milk thistle, mistletoe and St. John's wort). A diverse set of data were independently extracted by two researchers and subsequently analysed by a newly developed algorithm. Results are displayed in the form of interaction risk categories. The development of the algorithm was guided by an expert panel consensus process. RESULTS: From 882 publications retrieved by the search, 154 studies were eligible and provided 529 data sets on herbal interactions. The developed algorithm prioritises results from clinical trials over case reports over in vitro investigations and considers type of study, consistency of study results and study outcome for clinical trials as well as identification, permeability, bioavailability, and interaction potency of an identified herbal perpetrator for in vitro investigations. Risk categories were assigned to and dynamically visualised in a colour-coded matrix format. CONCLUSIONS: The novel algorithm allows to transparently generate and dynamically display herb-drug interaction risks based on the available evidence from clinical and laboratory pharmacologic studies. It provides health professionals with readily available and easy updatable information about the risk of pharmacokinetic interactions between herbs and oncologic drugs.

Package delivered: folate receptor-mediated transporters in cancer therapy and diagnosis.

Neoplasias pose a significant threat to aging society, underscoring the urgent need to overcome the limitations of traditional chemotherapy through pioneering strategies. Targeted drug delivery is an evolving frontier in cancer therapy, aiming to enhance treatment efficacy while mitigating undesirable side effects. One promising avenue utilizes cell membrane receptors like the folate receptor to guide drug transporters precisely to malignant cells. Based on the cellular folate receptor as a cancer cell hallmark, targeted nanocarriers and small molecule-drug conjugates have been developed that comprise different (bio) chemistries and/or mechanical properties with individual advantages and challenges. Such modern folic acid-conjugated stimuli-responsive drug transporters provide systemic drug delivery and controlled release, enabling reduced dosages, circumvention of drug resistance, and diminished adverse effects. Since the drug transporters' structure-based de novo design is increasingly relevant for precision cancer remediation and diagnosis, this review seeks to collect and debate the recent approaches to deliver therapeutics or diagnostics based on folic acid conjugated Trojan Horses and to facilitate the understanding of the relevant chemistry and biochemical pathways. Focusing exemplarily on brain and breast cancer, recent advances spanning 2017 to 2023 in conjugated nanocarriers and small molecule drug conjugates were considered, evaluating the chemical and biological aspects in order to improve accessibility to the field and to bridge chemical and biomedical points of view ultimately guiding future research in FR-targeted cancer therapy and diagnosis.

Investigation of real-life drug intake behaviour in older adults and geriatric patients in Northern Germany - A biopharmaceutical perspective.

Dosing conditions (type and amount of accompanying fluid, the type of food, the time of administration, and dosage form modifications such as crushing tablets) are critical and affect the performance of oral dosage forms in the gastrointestinal tract and thus bioavailability. Because older adults are the primary users of medications and are more susceptible to adverse effects, it is important to understand how they take their medications in order to reduce risks and increase benefits of the pharmacotherapy. The aim of the study was to investigate the real-life drug intake behaviour in geriatric patients and older adults and discuss their influence on drug absorption after oral administration. The data from two settings home vs. hospital and genders women vs. men were presented. A questionnaire study was performed among people aged at least 65 years from two settings (hospital vs. home), recruited mostly from community pharmacies and a regional hospital in Mecklenburg - Western Pomerania. The obtained data demonstrates that older adults and geriatric patients take their medications in the same way regardless of the setting and gender. There were no significant differences. Interviewed participants were mostly adherent to the doctor's recommendations and mostly took their medications in the same way every day. Medications are most commonly taken with a small (100 mL) or large (200 mL) glass of noncarbonated water, after food (during or after breakfast 64 % of intakes in the morning and during or after dinner 81 % of intakes in the evening). Meal usually consisted of bread, either with jam or honey (breakfast), or ham and cheese (dinner). All reported dosage form modifications were made to tablets. In almost all cases it was splitting the tablet, which was performed due to doctor's indication.

Characterization of the EGFR interactome reveals associated protein complex networks and intracellular receptor dynamics.

Growth factor receptor mediated signaling is meanwhile recognized as a complex signaling network, which is initiated by recruiting specific patterns of adaptor proteins to the intracellular domain of epidermal growth factor receptor (EGFR). Approaches to globally identify EGFR-binding proteins are required to elucidate this network. We affinity-purified EGFR with its interacting proteins by coprecipitation from lysates of A431 cells. A total of 183 proteins were repeatedly detected in high-resolution MS measurements. For 15 of these, direct interactions with EGFR were listed in the iRefIndex interaction database, including Grb2, shc-1, SOS1 and 2, STAT 1 and 3, AP2, UBS3B, and ERRFI. The newly developed Cytoscape plugin ModuleGraph allowed retrieving and visualizing 93 well-described protein complexes that contained at least one of the proteins found to interact with EGFR in our experiments. Abundances of 14 proteins were modulated more than twofold upon EGFR activation whereof clathrin-associated adaptor complex AP-2 showed 4.6-fold enrichment. These proteins were further annotated with different cellular compartments. Finally, interactions of AP-2 proteins and the newly discovered interaction of CIP2A could be verified. In conclusion, a powerful technique is presented that allowed identification and quantitative assessment of the EGFR interactome to provide further insight into EGFR signaling.

Drug-induced pancreatitis.

Drugs are thought to be a rare cause for acute pancreatitis; however 525 different drugs are listed in the World Health Organization (WHO) database suspected to cause acute pancreatitis as a side effect. Many of them are widely used to treat highly prevalent diseases. The true incidence is not entirely clear since only few systematic population based studies exist. The majority of the available data are derived from case reports or case control studies. Furthermore, the causality for many of these drugs remains elusive and for only 31 of these 525 dugs a definite causality was established. Definite proof for causality is defined by the WHO classification if symptoms reoccur upon rechallenge.In the actual algorithm the diagnosis is confirmed if no other cause of acute pancreatitis can be detected, and the patient is taking one of the suspected drugs.

Antineoplastic agent busulfan regulates a network of genes related to coagulation and fibrinolysis.

Purpose Hepatic veno-occlusive disease (HVOD) is one of the major complications following hematopoietic stem cell transplantation (HSCT). Although high-dose busulfan is associated with the development of HVOD, the underlying molecular mechanisms are still unknown.Methods Transcriptional gene regulation by busulfan was profiled using Affymetrix GeneChip® Human Genome U133 Plus 2.0 arrays. Messenger RNA (mRNA) expression of regulated genes was assessed by TaqMan real-time polymerase chain reaction (PCR), and protein expression and secretion was determined by enzyme-linked immunosorbent assay (ELISA)in cell supernatants, lysates, and patient plasma.Results Plasma levels of plasminogen activator inhibitor(PAI)-1 significantly increased 48 h after starting busulfan treatment IV in children preconditioned for HSCT. In vitro,busulfan significantly induced plasminogen activator inhibitor-1 (PAI-1) expression in endothelium-like ECV304 cells in a concentration- and time-dependent manner. Comparative transcriptional profiling of busulfan-treated and control ECV304 cells identified differential expression of genes related to coagulation and fibrinolysis, including tissue factor, tissue factor pathway inhibitor-1, protein S, thrombospondin-1, urokinase receptor, and PAI-1, as well as activin A and transforming growth factor beta 1 (TGF-ß1). Ingenuity pathway analysis (IPA) suggested TGF-ß1 as a central modulator of gene regulation by busulfan. Consequently, expression of tissue factor, urokinase receptor, and PAI-1 mRNA and PAI-1 protein secretion induced by busulfan were significantly reduced by the activin A/TGF-ß1 inhibitor SB 431542 in ECV304 and primary endothelial cells.Conclusions This is the first report that directly relates busulfan exposure to antifibrinolytic activity by PAI-1 and hypercoagulation possibly mediated by members of the TGF-ß1 family. This suggests further research to evaluate activin A and TGF-ß1 as potential targets for HVOD treatment.

[Medication review for dementia patients]. / Medikationsreview in der psychiatrischen Institutsambulanz.

Due to demographic changes we are faced with several challenges as an increasing prevalence of dementia patients. We report on a medication review of a patient with Alzheimer's disease as well as Lewy body dementia. The intake of risperidone was interrupted instead of a dose reduction which was recommended by the psychiatrist to improve mobility. As an adverse event the patient developed serious psychiatric symptoms which were treated in an acute care facility. We discussed several alternative treatment options (pipamperon, melperon, haloperidol, risperidone, clozapine, olanzapine, aripiprazol, and quetiapin) in a case conference. Due to a short half life period and insignificant anticholinergic effects we decided to choose quetiapin. Despite a small number of taken drugs we identified several potential drug related problems which were solved in a multipartite health care professional team.

Gas Plasma Exposure of Glioblastoma Is Cytotoxic and Immunomodulatory in Patient-Derived GBM Tissue.

Glioblastoma multiforme (GBM) is the most common primary malignant adult brain tumor. Therapeutic options for glioblastoma are maximal surgical resection, chemotherapy, and radiotherapy. Therapy resistance and tumor recurrence demand, however, new strategies. Several experimental studies have suggested gas plasma technology, a partially ionized gas that generates a potent mixture of reactive oxygen species (ROS), as a future complement to the existing treatment arsenal. However, aspects such as immunomodulation, inflammatory consequences, and feasibility studies using GBM tissue have not been addressed so far. In vitro, gas plasma generated ROS that oxidized cells and led to a treatment time-dependent metabolic activity decline and G2 cell cycle arrest. In addition, peripheral blood-derived monocytes were co-cultured with glioblastoma cells, and immunomodulatory surface expression markers and cytokine release were screened. Gas plasma treatment of either cell type, for instance, decreased the expression of the M2-macrophage marker CD163 and the tolerogenic molecule SIGLEC1 (CD169). In patient-derived GBM tissue samples exposed to the plasma jet kINPen ex vivo, apoptosis was significantly increased. Quantitative chemokine/cytokine release screening revealed gas plasma exposure to significantly decrease 5 out of 11 tested chemokines and cytokines, namely IL-6, TGF-ß, sTREM-2, b-NGF, and TNF-α involved in GBM apoptosis and immunomodulation. In summary, the immuno-modulatory and proapoptotic action shown in this study might be an important step forward to first clinical observational studies on the future discovery of gas plasma technology's potential in neurosurgery and neuro-oncology especially in putative adjuvant or combinatory GBM treatment settings.

Drug efflux transporter multidrug resistance-associated protein 5 affects sensitivity of pancreatic cancer cell lines to the nucleoside anticancer drug 5-fluorouracil.

Pancreatic adenocarcinoma is one of the malignancies that is highly resistant to therapy and among the leading causes of cancer-related death. Several factors may influence pancreatic cancer resistance, and expression of ATP-binding cassette transport proteins is one of the major mechanisms of drug resistance. Members of this family's C-branch, also referred to as multidrug resistance-associated proteins (MRPs), might be of particular interest because they are able to efflux nucleoside analogs used in the treatment of pancreatic cancer. Expression of MRP1, MRP3, MRP4, and MRP5 in human pancreas and pancreatic carcinoma has been reported. However, contributions of MRPs to chemoresistance of pancreatic cancer are not fully understood. MRP5 mRNA expression in pancreatic adenocarcinoma cell lines correlated significantly with cellular sensitivity to 5-fluorouracil (5-FU) (r = 0.738, p < 0.05). Long-term treatment with 5-FU increased expression of MRP5 by 2.4-fold and was associated with significant drug resistance [IC(50) values for control and 5-fluorouracil (5-FU)-resistant Patu-T cell lines were 11.3 ± 5.3 and 33.2 ± 6.9 µM, respectively (p < 0.05)]. Consequently, overexpression of MRP5 in Colo-357 cells resulted in significantly reduced accumulation of 5-FU related radioactivity and 5-FU cytotoxicity. Knockdown of MRP5 significantly increased cellular cytotoxicity of 5-FU to Patu-02 cells and enhanced accumulation of radioactivity related to 5-FU and its metabolites. Our results suggest that MRP5 is expressed and functionally active and contributes to variable sensitivities of pancreatic adenocarcinoma cell lines to 5-FU. Further investigations using models that resemble human pancreas tumors are necessary to prove a causative relation between expression and activity of MRP5 and tumor resistance to 5-FU.

Constitutive Cell Proliferation Regulating Inhibitor of Protein Phosphatase 2A (CIP2A) Mediates Drug Resistance to Erlotinib in an EGFR Activating Mutated NSCLC Cell Line.

Exploring mechanisms of drug resistance to targeted small molecule drugs is critical for an extended clinical benefit in the treatment of non-small cell lung cancer (NSCLC) patients carrying activating epidermal growth factor receptor (EGFR) mutations. Here, we identified constitutive cell proliferation regulating inhibitor of protein phosphatase 2A (CIP2A) in the HCC4006rErlo0.5 NSCLC cell line adapted to erlotinib as a model of acquired drug resistance. Constitutive CIP2A resulted in a constitutive activation of Akt signaling. The proteasome inhibitor bortezomib was able to reduce CIP2A levels, which resulted in an activation of protein phosphatase 2A and deactivation of Akt. Combination experiments with erlotinib and bortezomib revealed a lack of interaction between the two drugs. However, the effect size of bortezomib was higher in HCC4006rErlo0.5, compared to the erlotinib-sensitive HCC4006 cells, as indicated by an increase in Emax (0.911 (95%CI 0.867-0.954) vs. 0.585 (95%CI 0.568-0.622), respectively) and decrease in EC50 (52.4 µM (95%CI 46.1-58.8 µM) vs. 73.0 µM (95%CI 60.4-111 µM), respectively) in the concentration-effect model, an earlier onset of cell death induction, and a reduced colony surviving fraction (0.38 ± 0.18 vs. 0.95 ± 0.25, respectively, n = 3, p < 0.05). Therefore, modulation of CIP2A with bortezomib could be an interesting approach to overcome drug resistance to erlotinib treatment in NSCLC.

Proteomic analysis of doxorubicin-induced changes in the proteome of HepG2cells combining 2-D DIGE and LC-MS/MS approaches.

HepG-2 cells are widely used as a cell model to investigate hepatocellular carcinomas and the effect of anticancer drugs such as doxorubicin, an effective antineoplastic agent, which has broad antitumoral activity against many solid and hematological malignancies. To investigate the effect of doxorubicin on the protein pattern, we used complementary proteomic workflows including 2-D gel-based and gel-free methods. The analysis of crude HepG2 cell extracts by 2-D DIGE provided data on 1835 protein spots which was then complemented by MS-centered analysis of stable isotope labeling by amino acids in cell culture-labeled cells. The monitoring of more than 1300 distinct proteins, including proteins of the membrane fraction provides the most comprehensive overview on the proteome of the widely used model cell line HepG2. Of the proteins monitored in total, 155 displayed doxorubicin-induced changes in abundance. Functional analysis revealed major influences of doxorubicin on proteins involved in protein synthesis, DNA damage control, electron transport/mitochondrial function, and tumor growth. The strongest decrease in level was found for proteins involved in DNA replication and protein synthesis, whereas proteins with a function in DNA damage control and oxidative stress management displayed increased levels following treatment with doxorubicin compared with control cells. Furthermore, the doxorubicin-associated increase in levels of multiple forms of keratins 8, 18, and 19 and other structural proteins revealed an influence on the cytoskeleton network.

Expression of ABCC-type nucleotide exporters in blasts of adult acute myeloid leukemia: relation to long-term survival.

PURPOSE: Successful treatment of acute myeloid leukemia (AML) remains a therapeutic challenge, with a high percentage of patients suffering from persistent or relapsed disease. Resistance to drug therapy can develop from increased drug export and/or altered intracellular signaling. Both mechanisms are mediated by the efflux transporters ABCC4 (MRP4), ABCC5 (MRP5), and ABCC11 (MRP8), which are involved in cellular efflux of endogenous signaling molecules (e.g., cyclic adenosine 3', 5'-monophosphate and cyclic guanosine 3',5'-monophosphate) and nucleoside analogues. The nucleoside analogue cytosine arabinoside (AraC) is administered to all patients with AML. EXPERIMENTAL DESIGN: Expression of ABCC transporters MRP4, MRP5, and MRP8 in blast samples from 50 AML patients was investigated by real-time reverse transcription-PCR analysis and correlated with clinical outcome measures. Accumulation of radiolabeled AraC, transport of AraC metabolites, and AraC cytotoxicity were analyzed in MRP8-transfected LLC-PK1 cells. RESULTS: Regression analysis revealed that high expression of MRP8 is associated with a low probability of overall survival assessed over 4 years (P<0.03). MRP8-transfected LLC-PK1 cells accumulated reduced intracellular levels of AraC (63% of the parental vector-transfected LLC-PK1 control cells) as well as AraC metabolites. Furthermore, AraC monophosphate was transported by MRP8-enriched membrane vesicles (116+/-6 versus 65+/-13 pmol/mg/10 minutes by control vesicles), and MRP8-transfected cells were resistant to AraC. CONCLUSION: These data suggest that MRP8 is differentially expressed in AML blasts, that expression of MRP8 serves as a predictive marker for treatment outcome in AML, and that efflux of AraC metabolites by MRP8 is a mechanism that contributes to resistance of AML blasts.

Novel Nonsymmetrical 1,4-Dihydropyridines as Inhibitors of Nonsymmetrical MRP-Efflux Pumps for Anticancer Therapy.

Cancer is a strong global burden with increasing numbers of diseases and ongoing anticancer drug resistance. The number of structurally novel anticancer drugs is strongly limited. They cause high costs for the social health systems. Most critical so-called multidrug resistances (MDR) are caused by transmembrane efflux pumps that transport drugs with various structures out of the cancer cells. Multidrug resistance proteins (MRPs) type 1 and 2 are found overexpressed in various kinds of cancer. There is a strong need for inhibitors of those efflux pumps. We developed novel nonsymmetrical 1,4-dihydropyridines as novel inhibitors of cancer relevant MRP types 1 and 2. The structure-dependent activities of the differently substituted derivatives were evaluated in cellular assays of respective cancer cells and are discussed. Promising candidates were identified. One candidate was demonstrated to resensitize a cisplatin resistant cancer cell line and thus to overcome the anticancer drug resistance.

Process of translation and cross-cultural adaptation of two Australian instruments to evaluate the physician-pharmacist collaboration in Germany.

BACKGROUND: Building interprofessional working relationships between physicians and pharmacists is essential to ensure high-quality patient care. To assess which factors influence the performance and success of their collaboration, validated instruments should be used, such as the Australian "Attitudes Toward Collaboration Instrument (ATCI)" and the "Frequency of Interprofessional Collaboration Instrument (FICI)". Both instruments were already translated in a previous German study, but not pretested for comprehensibility or cultural appropriateness to ensure that the target group is able to adequately answer the translated items. OBJECTIVES: To translate and particularly cross-culturally adapt two Australian instruments measuring physicians' and pharmacists' attitudes towards interprofessional collaboration and the frequency of their interactions for use in Germany. METHODS: The ATCI and FICI were translated following internationally recognised guidelines. Two-step cognitive interviewing was performed with physicians and pharmacists working in ambulatory care in Germany. The "Standards for Reporting Qualitative Research" were used to report this study. RESULTS: Overall, 2 forward and 2 back translations, and 38 cognitive interviews, i.e. cognitive probing (N = 10) and behaviour observation (N = 28), with 18 physicians and 20 pharmacists were performed. Experts discussed all potential changes. The ATCI and FICI were translated introducing 15 minor (e.g. paraphrasing, item order) and 6 major (e.g. 2 more items in FICI, additional response options) adaptations. The ATCI-P/GP-German and FICI-P/GP-German were found to be easy to answer and clearly-phrased. CONCLUSION: This study shows the importance of using recognised methods to translate and adapt questionnaires, consisting of at least four steps: forward translation, back translation, cognitive interviewing and finalisation (each reviewed by an expert panel making their decisions by consensus). A profoundly pretested German-speaking instrument is now available to evaluate and describe interprofessional collaboration between physicians and pharmacists. However, collecting further sociodemographic and contextual information seems necessary for enhanced interpretation of future results.

Hematopoietic stem cell differentiation affects expression and function of MRP4 (ABCC4), a transport protein for signaling molecules and drugs.

Several types of peripheral blood cells express ABC transporters. ABCC4 (MRP4) and ABCC5 (MRP5) localize to different cellular sites and fulfill lineage-specific functions such as mediator storage in platelets' dense granules. All mature blood cells originate from the same precursor and specific functionalities arise during differentiation. To characterize this process, expression, localization and function of MRP4 and MRP5 were assessed in differentiating human CD34+ progenitors and leukemia cell lines using real time polymerase chain reaction (PCR), immunofluorescence microscopy and cell viability assays. Median MRP4 mRNA copy numbers were significantly enhanced by megakaryocytic differentiation from 7.9 x 10(3) to 5.8 x 10(4) copies per nanograms of total RNA (p < 0.05) in CD34+ progenitors and in M-07e cells (MRP4 mRNA/18S rRNA ratios: 5.4 +/- 3.8 x 10(-4) vs. 2.7 +/- 0.9 x 10(-3) for native and differentiated cells, respectively, p < 0.05), and MRP4 protein was localized to granular structures and to the plasma membrane both in differentiated progenitors and bone marrow megakaryocytes. In contrast, expression of MRP4 decreased during maturation to leukocytes (MRP4 mRNA/18S rRNA ratios: 5.2 x 10(-3) for native vs. 3.5 x 10(-3) for CD34+ cells in the presence of G-CSF, p < 0.05) and was significantly reduced in mature monocytes and granulocytes compared with progenitors (MRP4 mRNA/18S rRNA ratios: 8.1 +/- 5.4 x 10(-5) and 2.8 +/- 1.6 x 10(-4) vs. 1.2 +/- 0.7 x 10(-3), respectively, p < 0.05). Expression of MRP5 was not significantly altered under all differentiation conditions. These results indicate that MRP4 expression is differentially regulated during hematopoiesis. The increase of MRP4 together with its specific localization during differentiation toward megakaryocytes supports the concept of platelet specific functions whereas decreased transporter expression in leukocyte differentiation may have implications for chemotherapy.