Role of the monocarboxylic acid transport system in the intestinal absorption of an orally active beta-lactam prodrug: carindacillin as a model

A facile di-acid mono-amidation strategy to prepare cyclization-activating mono-carboxylate transporter 1-targeting gemcitabine prodrugs for enhanced oral delivery

Intestinal mono-carboxylate transporter 1 (MCT1) plays an important role in the oral absorption of short-chain fatty acids that were used as oxidative metabolite. However, the prodrug strategy targeting intestinal MCT1 for oral delivery is rarely exploited. The oral bioavailability of Gemcitabine (Gem) is low mainly due to its poor intestinal permeability and rapid metabolism. Herein, a facile di-acid mono-amidation strategy was firstly developed to target MCT1 for oral chemotherapy. The N4-amino group of Gem is mono-amidated with di-acids containing different carbon chain lengths, which could recognize intestinal MCT1 and are bio-activated at physiological pH independent of the hydrolysis enzymes. The adipic acid-Gem shows higher MCT1 affinity, better gastrointestinal tract stability (3-fold), improved oral bioavailability (8.8-fold), and less gastrointestinal toxicity in comparison to Gem. Moreover the bio-activation rate of the prodrugs decreases with the increased fatty acid chain length of the linkage under physiological conditions. In summary, we present the first evidence that MCT1 could act as a new target for oral prodrug delivery, and that the linkage could modify the bio-activation rate for achieving optimal oral bioavailability. Our findings provide novel knowledge to rationally design intestinal transporter-targeting oral carrier prodrug.

Identification of genes with universally upregulated or downregulated expressions in colorectal cancer

BACKGROUND AND AIM

Differentially expressed (DE) genes detected at the population-level through case-control comparison provide no information on the dysregulation frequencies of DE genes in a cancer. In this work, we aimed to identify the genes with universally upregulated or downregulated expressions in colorectal cancer (CRC).

METHODS

We firstly clarified that DE genes in an individual cancer tissue should be the disease-relevant genes, which are dysregulated in the cancer tissue in comparison with its own previously normal state. Then, we identified DE genes at the individual level for 2233 CRC samples collected from multiple data sources using the RankComp algorithm.

RESULTS

We found 26 genes that were upregulated or downregulated in almost all the 2233 CRC samples and validated the results using 124 CRC tissues with paired adjacent normal tissues. Especially, we found that two genes (AJUBA and EGFL6), upregulated universally in CRC tissues, were extremely lowly expressed in normal colorectal tissues, which were considered to be oncogenes in CRC oncogenesis and development. Oppositely, we found that one gene (LPAR1), downregulated universally in CRC tissues, was silenced in CRC tissues but highly expressed in normal colorectal tissues, which were considered to be tumor suppressor genes in CRC. Functional evidences revealed that these three genes may induce CRC through deregulating pathways for ribosome biogenesis, cell proliferation, and cell cycle.

CONCLUSIONS

In conclusion, the individual-level DE genes analysis can help us find genes dysregulated universally in CRC tissues, which may be important diagnostic biomarkers and therapy targets.

Multidrug resistant Acinetobacter baumannii--the role of AdeABC (RND family) efflux pump in resistance to antibiotics

Acinetobacter baumannii is an opportunistic pathogen which play the more and more greater role in the pathogenicity of the human. It is often attached with the hospital environment, in which is able easily to survive for many days even in adverse conditions. Acinetobacter baumannii is the species responsible for a serious nosocomial infections, especially in the intensive care units. Option of surviving in natural niches, and in the hospital environment could also be associated with the efflux pump mechanisms. Mechanisms of efflux universally appear in all cells (eukaryotic and prokaryotic) and play the physiological important role. In prokaryote, the main functions are evasion of such naturally produced molecules, removal of metabolic products and toxins. These pumps could also be involved in an early stage of infection, such as adhesion to host cells and the colonization. Importantly, they remove commonly used antibiotics from the cell in therapy of infections caused by these bacteria. Efflux pumps exemplify a unique phenomenon in drug resistance: a single mechanism causing resistance against several different classes of antibiotics. In Acinetobacter baumannii, the AdeABC efflux pump, a member of the resistance-nodulation-cell division family (RND), has been well characterized. Aminoglicosides, tetracyclines, erythromycin, chloramphenicol, trimethoprim, fluoroquinolones, some beta-lactams, and also recently tigecycline, were found to be substrates for this pump. Drugs, as substrates for the AdeABC pump, can increase the expression of the AdeABC genes, leading to multidrug resistance (MDR). From this reason, treatment failure and death caused by Acinetobacter baumannii infections or underlying diseases are common. Because the AdeABC pump is widespread in Acinetobacter baumannii, similarly to other pumps in Gram-negative and Gram-positive bacteria, exists a need of searching a new therapeutic solutions. Specific efflux inhibitors of pumps (EPIs), including AdeABC inhibitors, could be suppress the activity of pumps and restore the sensitivity of such important bacteria as Acinetobacter baumannii to commonly used antibiotic.

Overview of the proton-coupled MCT (SLC16A) family of transporters: characterization, function and role in the transport of the drug of abuse gamma-hydroxybutyric acid

The transport of monocarboxylates, such as lactate and pyruvate, is mediated by the SLC16A family of proton-linked membrane transport proteins known as monocarboxylate transporters (MCTs). Fourteen MCT-related genes have been identified in mammals and of these seven MCTs have been functionally characterized. Despite their sequence homology, only MCT1-4 have been demonstrated to be proton-dependent transporters of monocarboxylic acids. MCT6, MCT8 and MCT10 have been demonstrated to transport diuretics, thyroid hormones and aromatic amino acids, respectively. MCT1-4 vary in their regulation, tissue distribution and substrate/inhibitor specificity with MCT1 being the most extensively characterized isoform. Emerging evidence suggests that in addition to endogenous substrates, MCTs are involved in the transport of pharmaceutical agents, including gamma-hydroxybuytrate (GHB), 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins), salicylic acid, and bumetanide. MCTs are expressed in a wide range of tissues including the liver, intestine, kidney and brain, and as such they have the potential to impact a number of processes contributing to the disposition of xenobiotic substrates. GHB has been extensively studied as a pharmaceutical substrate of MCTs; the renal clearance of GHB is dose-dependent with saturation of MCT-mediated reabsorption at high doses. Concomitant administration of GHB and L: -lactate to rats results in an approximately two-fold increase in GHB renal clearance suggesting that inhibition of MCT1-mediated reabsorption of GHB may be an effective strategy for increasing renal and total GHB elimination in overdose situations. Further studies are required to more clearly define the role of MCTs on drug disposition and the potential for MCT-mediated detoxification strategies in GHB overdose.

Carrier-mediated cellular uptake of pharmaceutical drugs: an exception or the rule?

It is generally thought that many drug molecules are transported across biological membranes via passive diffusion at a rate related to their lipophilicity. However, the types of biophysical forces involved in the interaction of drugs with lipid membranes are no different from those involved in their interaction with proteins, and so arguments based on lipophilicity could also be applied to drug uptake by membrane transporters or carriers. In this article, we discuss the evidence supporting the idea that rather than being an exception, carrier-mediated and active uptake of drugs may be more common than is usually assumed - including a summary of specific cases in which drugs are known to be taken up into cells via defined carriers - and consider the implications for drug discovery and development.

Intestinal solute carriers: an overview of trends and strategies for improving oral drug absorption

A large amount of absorptive intestinal membrane transporters play an important part in absorption and distribution of several nutrients, drugs and prodrugs. The present paper gives a general overview on intestinal solute carriers as well as on trends and strategies for targeting drugs and/or prodrugs to these carriers in order to increasing oral bioavailability and distribution. A number of absorptive intestinal transporters are described in terms of gene and protein classification, driving forces, substrate specificities and cellular localization. When targeting absorptive large capacity membrane transporters in the small intestine in order to increase oral bioavailabilities of drug or prodrug, the major influence on in vivo pharmacokinetics is suggested to be dose-dependent increase in bioavailability as well as prolonged blood circulation due to large capacity facilitated absorption, and renal re-absorption, respectively. In contrast, when targeting low-capacity transporters such as vitamin transporters, dose independent saturable absorption kinetics are suggested. We thus believe that targeting drug substrates for absorptive intestinal membrane transporters could be a feasible strategy for optimizing drug bioavailability and distribution.

Membrane transporter/receptor-targeted prodrug design: strategies for human and veterinary drug development

The bioavailability of drugs is often severely limited due to the presence of biological barriers in the form of epithelial tight junctions, efflux proteins and enzymatic degradation. Physicochemical properties, such as lipophilicity, molecular weight, charge, etc., also play key roles in determining the permeation properties of drug candidates. As a result, many potential drug candidates may be dropped from the initial screening portfolio. Prodrug derivatization targeting transporters and receptors expressed on mammalian cells holds tremendous potential. Enhanced cellular delivery can significantly improve drug absorption. Such approaches of drug targeting and delivery have been the subject of intense research. Various prodrugs have been designed that demonstrate enhanced bioavailability and tissue specificity. This approach is equally applicable to human and veterinary pharmaceuticals since most of the transporters and receptors expressed by human tissues are also expressed in animals. This review highlights studies conducted on the use of transporters and receptors in an effort to improve drug bioavailability and to develop targeted drug delivery systems.

Transepithelial Permeation of Tolbutamide across the Human Intestinal Cell Line, Caco-2

Sulfonylurea hypoglycemic agents have interindividual variability in the gastrointestinal absorption rate. However, the absorption mechanism at the intestinal epithelium has not yet been clarified. To elucidate contribution of the specific mechanism for transepithelial transport of sulfonylureas, the apical-to-basolateral and basolateral-to-apical transport studies of tolbutamide were carried out using Caco-2 cell monolayers cultured on the polycarbonate membrane. The transported amounts of the substrate were measured by HPLC to estimate the apparent permeability coefficients (P(app)). In the apical-to-basolateral flux, the transport activity of tolbutamide was facilitated when the pH of the apical medium was more acidic than the basolateral one. ATP-depletion decreased the P(app) of tolbutamide. The kinetic analysis of the permeation rate indicated that the saturable process largely contributed to the tolbutamide flux. The P(app) of tolbutamide was lowered by an ionophore and monocarboxylic acids, while dicarboxylic acids and the inhibitor for the anion exchanger had no effect. In addition, mutual inhibition with benzoic acid was observed in transepithelial transport of tolbutamide. On the other hand, the permeation rate of tolbutamide from the basolateral to apical side was concentration-independent and neither affected by metabolic inhibitors, probenecid nor inhibitors for P-glycoprotein. In conclusion, these results suggest that apical-to-basolateral transport of tolbutamide across the Caco-2 cell monolayers is mediated by the pH-dependent specific system, presumably shared with other organic anions such as benzoic acid.

Prodrug based optimal drug delivery via membrane transporter/receptor

The carrier-mediated absorption of drugs and prodrugs across epithelial and endothelial barriers is emerging as a novel trend in biotherapeutics. This review examines the important advances in this field in the past decade. The feasibility of drug absorption of the parent drug or the appropriately modified prodrug via these transporters is discussed in detail. Several successful examples of synthesis of prodrugs recognised by the targeted transporters are described. The applicability of this approach in translocating drugs across the almost impenetrable blood-brain barrier (BBB) has also been examined.