Loperamide potentiates doxorubicin sensitivity in triple-negative breast cancer cells by targeting MDR1 and JNK and suppressing mTOR and Bcl-2: In vitro and molecular docking study.

Multidrug resistance (MDR) is the leading cause of treatment failure in triple-negative breast cancer (TNBC) patients treated with doxorubicin (DXR). We aimed to investigate the potential of the antidiarrheal drug Loperamide (LPR) in sensitizing TNBC cells to DXR and elucidate the underlying molecular mechanisms. Therefore, we examined the effects of DXR alone or in combination with LPR on MDA-MD-231 cells viability using MTT assay, cell cycle, and apoptosis by flow cytometry, and the expression of the MDR-related genes (MDR1 and JNK1) and cell cycle/survival genes (p21, mTOR, and Bcl-2) by quantitative reverse transcription polymerase chain reaction. Results showed that adding LPR to DXR potentiated its antiproliferation effect and reduced its IC50 by twofolds compared with DXR alone. The value of the combination index of LPR/DXR was <1 indicating a synergistic effect. Combined DXR/LPR treatment also caused G1 arrest and potentiated apoptosis more than DXR-single treatment. At the molecular levels, LPR/DXR treatment downregulated the mRNA of MDR1 (1.35-folds), JNK1 (2.5-folds), mTOR (6.6-folds), Bcl-2 (9.5-folds); while upregulated p21 gene (8-folds) compared with DXR alone. Molecular docking analyses found LPR antagonizes MDR1 and JNK1 proteins, and hence supports the in vitro studies. In conclusion, the results confirmed the potential of LPR in sensitizing TNBCs to DXR by targeting MDR1 and JNK1 and suppressing Bcl-2 and mTOR genes, while upregulating the cell cycle inhibitor gene p21. Additionally, LPR could be repurposed to reduce the therapeutic doses of DXR as indicated by the dose reduction index (DRI) and subsequently decrease its side effects.

Cardiac Electropharmacological Effects of Antidiarrheal Drug Loperamide and Its Antidote Naloxone in Anesthetized Guinea Pigs.

Cardiac electropharmacological effects of an antidiarrheal drug loperamide and its antidote naloxone were assessed in isoflurane-anesthetized guinea pigs. Intravenous administration of loperamide at 0.01-0.1 mg/kg did not affect parameters of electrocardiogram (ECG) or monophasic action potential (MAP) of the right ventricle. Additional administration of loperamide at 1 mg/kg prolonged the QT interval and MAP duration of the ventricle accompanied with increments of the PQ interval and QRS width. The potency of loperamide for QT-interval prolongation was about 100-times lower than that of dofetilide, in spite that similar inhibitory effects on the human Ether-a-go-go Related Gene (hERG) K+ channels have been reported between loperamide and dofetilide, implying lower accessibility of loperamide to the K+ channels. Intravenous administration of naloxone at 0.003-0.3 mg/kg, which effectively inhibits µ-opioid receptors, did not affect ECG parameters including QT interval or MAP duration. Furthermore, the loperamide-induced cardiac electrophysiological changes were not modified in the presence of naloxone at 0.3 mg/kg. These results suggest that loperamide has a potential to delay cardiac conduction and repolarization in the in vivo condition. Since naloxone did not modify ECG parameters and loperamide-induced ECG changes, naloxone is confirmed to possess acceptable cardiac safety when used as an antidote.

In Silico Drug Repurposing Approach: Investigation of Mycobacterium tuberculosis FadD32 Targeted by FDA-Approved Drugs.

Background: Despite the enormous efforts made towards combating tuberculosis (TB), the disease remains a major global threat. Hence, new drugs with novel mechanisms against TB are urgently needed. Fatty acid degradation protein D32 (FadD32) has been identified as a promising drug target against TB, the protein is required for the biosynthesis of mycolic acids, hence, essential for the growth and multiplication of the mycobacterium. However, the FadD32 mechanism upon the binding of FDA-approved drugs is not well established. Herein, we applied virtual screening (VS), molecular docking, and molecular dynamic (MD) simulation to identify potential FDA-approved drugs against FadD32. Methodology/Results: VS technique was found promising to identify four FDA-approved drugs (accolate, sorafenib, mefloquine, and loperamide) with higher molecular docking scores, ranging from -8.0 to -10.0 kcal/mol. Post-MD analysis showed that the accolate hit displayed the highest total binding energy of -45.13 kcal/mol. Results also showed that the accolate hit formed more interactions with FadD32 active site residues and all active site residues displayed an increase in total binding contribution. RMSD, RMSF, Rg, and DCCM analysis further supported that the presence of accolate exhibited more structural stability, lower bimolecular flexibility, and more compactness into the FadD32 protein. Conclusions: Our study revealed accolate as the best potential drug against FadD32, hence a prospective anti-TB drug in TB therapy. In addition, we believe that the approach presented in the current study will serve as a cornerstone to identifying new potential inhibitors against a wide range of biological targets.

Loperamide exerts a direct bactericidal effect against M. tuberculosis, M. bovis, M. terrae and M. smegmatis.

Tuberculosis (TB) is caused by Mycobacterium tuberculosis. TB is highly prevalent, characterized by the constant occurrence of drug-resistant cases, and confounded by the incidence of respiratory disease caused by non-tuberculous mycobacteria (NTB). Expanding the spectrum of drugs for the treatment of TB is indispensable. Loperamide, an antidiarrhoeal drug, enhances immune-driven antimycobacterial activity, and we aimed to evaluate its bactericidal activity against M. tuberculosis, Mycobacterium bovis BCG, Mycobacterium terrae and Mycobacterium smegmatis. Loperamide exhibited an inhibitory effect against all mycobacterial species tested, with MICs of 100 and 150 µg ml-1 . Thus, loperamide is a mycobactericidal drug with potential as adjunctive therapy for TB and NTB infections.

Cucumis sativus extract elicits chloride secretion by stimulation of the intestinal TMEM16A ion channel.

CONTEXT: Cucumber (Cucumis sativus Linn. [Cucurbitaceae]) is widely known for its purgative, antidiabetic, antioxidant, and anticancer therapeutic potential. However, its effect on gastrointestinal (GI) disease is unrecognised. OBJECTIVE: This study investigated the effect of C. sativus fruit extract (CCE) on intestinal chloride secretion, motility, and motor function, and the role of TMEM16A chloride channels. MATERIALS AND METHODS: CCE extracts were obtained from commercially available cucumber. Active fractions were then purified by HPLC and analysed by high resolution mass spectrometry. The effect of CCE on intestinal chloride secretion was investigated in human colonic T84 cells, ex vivo mouse intestinal tissue using an Ussing chamber, and the two-electrode voltage-clamp technique to record calcium sensitive TMEM16A chloride currents in Xenopus laevis oocytes. In vivo, intestinal motility was investigated using the loperamide-induced C57BL/6 constipation mouse model. Ex vivo contractility of mouse colonic smooth muscles was assessed by isometric force measurements. RESULTS: CCE increased the short-circuit current (ΔIsc 34.47 ± µA/cm2) and apical membrane chloride conductance (ΔICl 95 ± 8.1 µA/cm2) in intestinal epithelial cells. The effect was dose-dependent, with an EC50 value of 0.06 µg/mL. CCE stimulated the endogenous TMEM16A-induced Cl- current in Xenopus laevis oocytes. Moreover, CCE increased the contractility of smooth muscle in mouse colonic tissue and enhanced small bowel transit in CCE treated mice compared to loperamide controls. Mass spectrometry suggested a cucurbitacin-like analogue with a mass of 512.07 g/mol underlying the bioactivity of CCE. CONCLUSION: A cucurbitacin-like analog present in CCE activates TMEM16A channels, which may have therapeutic potential in cystic fibrosis and intestinal hypodynamic disorders.

Laxative Effects of a Standardized Extract of Dendropanax morbiferus H. Léveille Leaves on Experimental Constipation in Rats.

Background and Objectives: This study aimed at investigating the laxative effects of a standardized aqueous extract of Dendropanax morbiferus H. Lév. on two different constipation rat models. Materials and Methods: Animal studies were conducted with low-fiber diet-induced and loperamide-induced constipation animal models, and isolated colons were used in ex vivo analysis to determine the changes in colonic motility caused by D. morbiferus H. Lév. leaf extract (DPL). Results: The results showed that DPL administration significantly improved certain reduced fecal parameters (number, weight, and water content of the stools) in a both low-fiber diet and loperamide-induced constipation models without adverse effects of diarrhea. The laxative effect of DPL was confirmed to improve the charcoal excretion time upon DPL treatment in a low-fiber diet or loperamide-induced constipation model through gastrointestinal (GI) motility evaluation using the charcoal meal test. In addition, when DPL was administered to RAW264.7 cells and loperamide-induced constipation model rats, the production of prostaglandin E2 (PGE2) increased significantly in cells and tissue. Furthermore, DPL dose-dependently stimulated the spontaneous contractile amplitude and frequency of the isolated rat colon. Conclusion: Although our study did not provide information on the acute or chronic toxicity of DPL, our results demonstrated that DPL can effectively promote defecation frequency and rat colon contraction, providing scientific evidence to support the use of DPL as a therapeutic application. However, further toxicity studies of DPL are needed prior to the initiation of clinical trials and clinical applications.

Ileocecal Valve Removal Reverses the Constipating Effects of Loperamide in Rats.

BACKGROUND: Previous evidence associating ileocecal valve removal (ICVR) with a reduced risk of fecal impaction of the ileocecum in cystic fibrosis indicated possible benefits from ileocecal valve loss in disorders with inhibited proximal colon transit caused by fecal dehydration and hypoperistalsis. We aimed to investigate the ability of ICVR in reversing fecal impaction in a loperamide-induced model of a similar pattern of inhibited proximal colon transit in rats. MATERIALS AND METHODS: Thirty pubertal Sprague-Dawley rats were rendered constipated with subcutaneous loperamide treatment (1 mg/kg/d) for 7 d. On day four, rats were allocated to groups: ICVR (n = 12), total colectomy (TC, n = 9), and sham operation (SO, n = 9). Fecal pellet number and consistency were assessed daily. On day seven, all rats were gavaged with barium. Two hours later, intestinal transit ratio (distance of barium head from the pylorus adjusted for small intestine length) and adjusted (for total intestine length) barium-to-anus distance were assessed. RESULTS: ICVR showed higher transit ratio and shorter barium-to-anus distance, that is, faster transit, than SO (P < 0.0001); differences between ICVR and TC were not significant (P > 0.06). Furthermore, ICVR and TC showed similar reduction in hard feces, compared with SO (P < 0.0001). TC showed higher diarrhea rate than ICVR (P < 0.0001). CONCLUSIONS: ICVR led to an effective, similar to TC, reversal of the constipating effects of loperamide and, unlike TC, was not associated with diarrhea. Our findings support the idea that ICVR might be beneficial in disorders with inhibited proximal colon transit resulting from fecal dehydration and hypoperistalsis, such as refractory cystic fibrosis-related intestinal obstruction. Potential clinical implications merit further study.

Pharmacological Aspects of Over-the-Counter Opioid Drugs Misuse.

Several over-the-counter (OTC) drugs are known to be misused. Among them are opioids such as codeine, dihydrocodeine, and loperamide. This work elucidates their pharmacology, interactions, safety profiles, and how pharmacology is being manipulated to misuse these common medications, with the aim to expand on the subject outlined by the authors focusing on abuse prevention and prevalence rates. The reviewed literature was identified in several online databases through searches conducted with phrases created by combining the international non-proprietary names of the drugs with terms related to drug misuse. The results show that OTC opioids are misused as an alternative for illicit narcotics, or prescription-only opioids. The potency of codeine and loperamide is strongly dependent on the individual enzymatic activity of CYP2D6 and CYP3A4, as well as P-glycoprotein function. Codeine can also be utilized as a substrate for clandestine syntheses of more potent drugs of abuse, namely desomorphine ("Krokodil"), and morphine. The dangerous methods used to prepare these substances can result in poisoning from toxic chemicals and impurities originating from the synthesis procedure. OTC opioids are generally safe when consumed in accordance with medical guidelines. However, the intake of supratherapeutic amounts of these substances may reveal surprising traits of common medications.

Molecular determinants of loperamide and N-desmethyl loperamide binding in the hERG cardiac K+ channel.

Abuse of the common anti-diarrheal loperamide is associated with QT interval prolongation as well as development of the potentially fatal arrhythmia torsades de pointes. The mechanism underlying this cardiotoxicity is high affinity inhibition of the human ether-a-go-go-related gene (hERG) cardiac K+ channel. N-Desmethyl loperamide is the major metabolite of loperamide and is a close structural relative of the parent molecule. To date no information is available regarding the affinity of N-desmethyl loperamide for human cardiac ion channels. The effects of N-desmethyl loperamide on various cloned human cardiac ion channels including hERG, KvLQT1/mink and Nav1.5 were studied and compared to that of the parent. N-Desmethyl loperamide was a much weaker (7.5-fold) inhibitor of hERG compared to loperamide. However, given the higher plasma levels of the metabolite relative to the parent, it is likely that N-desmethyl loperamide can contribute, at least secondarily, to the cardiotoxicity observed with loperamide abuse. We used the recently solved cryo-EM structure of the hERG channel together with previously published inhibitors, to understand the basis of the interactions as well as the difference that a single methyl plays in the hERG channel blocking affinities of these two compounds.

Mu-Opioid Receptors in Ganglia, But Not in Muscle, Mediate Peripheral Analgesia in Rat Muscle Pain.

BACKGROUND: Previous studies have demonstrated the participation of peripheral µ-opioid receptors (MOR) in the antinociceptive effect of systemically administered morphine and loperamide in an orofacial muscle pain model, induced by hypertonic saline, but not in a spinally innervated one, in rats. In this study, we determine whether this peripheral antinociceptive effect is due to the activation of MOR localized in the muscle, ganglia, or both. METHODS: To determine the local antinociceptive effect of morphine and loperamide, 2 models of acute muscle pain (trigeminal and spinal) were used. Also, to study the MOR expression, protein quantification was performed in the trigeminal and spinal ganglia, and in the muscles. RESULTS: The behavioral results show that the intramuscular injection of morphine and loperamide did not exert an antinociceptive effect in either muscle (morphine: P = .63, loperamide: P = .9). On the other hand, MOR expression was found in the ganglia but not in the muscles. This expression was on average 44% higher (95% confidence interval, 33.3-53.9) in the trigeminal ganglia than in the spinal one. CONCLUSIONS: The peripheral antinociceptive effect of systemically administered opioids may be due to the activation of MOR in ganglia. The greater expression of MOR in trigeminal ganglia could explain the higher antinociceptive effect of opioids in orofacial muscle pain than in spinal muscle pain. Therefore, peripheral opioids could represent a promising approach for the treatment of orofacial pain.

Enhanced intestinal 2-deoxy-2-[18F]fluoro-D-glucose uptake under metformin is not fully suppressed by loperamide.

OBJECTIVE: This study investigated whether the metformin (Met)-induced enhanced intestinal uptake of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) is reduced by loperamide, a long-acting anti-diarrheal agent. METHODS: Mean 18F-FDG uptake in the mouse small intestine and colon with Met exposure was compared with that in control mice. In the Met group, high-dose (1.0 mg/kg body weight) and low-dose (0.1 mg/kg body weight) loperamide were introduced, and 18F-FDG uptake in the small intestine and colon was compared with that of control mice administered high-dose loperamide. The percent injected dose of 18F-FDG per gram of tissue (%ID/g) in the extracted tissues was then determined. RESULTS: 18F-FDG uptake increased significantly in the small intestine (0.64±0.06 vs. 1.01±0.15, p=0.040) and, especially, the colon (0.46±0.13 vs. 2.16±0.51, p<0.001) after Met exposure. Neither high-dose nor low-dose loperamide significantly reduced 18F-FDG uptake in the small intestine (0.82±0.31 vs. 0.84±0.22, p=0.93 and 0.78±0.25 vs. 0.70±0.15, p=0.13, respectively) or colon (2.13±0.41 vs. 1.67±0.55, p=0.063 and 1.77±0.39 vs. 1.80±0.25, p=0.56, respectively). The colonic %ID/g was significantly higher in Met groups irrespective of loperamide introduction than in control group, whereas the significant difference in the small intestine was observed only between Met and control groups. CONCLUSION: Metformin increased 18F-FDG uptake in intestines especially in colon. Loperamide administration partially, but not sufficiently, suppresses the Met-induced increased colonic uptake of 18F-FDG.

Loperamide cardiotoxicity: "A Brief Review".

Loperamide is a popular antidiarrheal medication that has been used for many years. It is currently gaining more attention among healthcare professionals due to its increasing potential for side effects. At present, it is considered safe enough to be sold over the counter. In contrast with other opioid agonists, loperamide is a peripherally acting µ-receptor agonist exerting its effects mainly on the myenteric plexus of the gastrointestinal longitudinal muscle layer. It decreases peristalsis and fluid secretion resulting in longer gastrointestinal transit time. The bioavailability of the drug is extremely low. Moreover, it is actively excluded from the central nervous system; hence, it lacks the central effects of euphoria and analgesia at the recommended dosages. Loperamide abuse has been steadily increasing in the United States. Abusers typically ingest high doses in desire to achieve a satisfactory central nervous system drug penetration. This has made it a potential over the counter substitute for self-treating opioid withdrawal symptoms and achieving euphoric effects.

Inhibitory Effects of Gastrointestinal Drugs on CYP Activities in Human Liver Microsomes.

OTC drugs have an important role in self-medication. However, the pharmacokinetic properties of some OTC drugs have not been fully investigated and reports concerning their drug interactions are insufficient. Several gastrointestinal drugs are available as OTC drugs. Because of their pharmacological properties, these drugs are often used concomitantly with other drugs. Therefore, it is important to predict the possible drug interactions among these drugs. In the current study, we investigated the inhibitory effects of five gastrointestinal drugs, namely loperamide, oxethazaine, papaverine, pirenzepine, and trimebutine, on CYP activities in human liver microsomes. Furthermore, we calculated the ratio of the intrinsic clearance of each CYP substrate in the presence or absence of the gastrointestinal drugs. The possibility of drug interactions in vivo was predicted by cut-off criteria. CYP3A4 activity was markedly inhibited by trimebutine, papaverine, and oxethazaine. Their inhibitory properties were competitive and the Ki values were 6.56, 12.8, and 3.08 µM, respectively. Alternative R values of CYP3A4 exceeded the cut-off level. These results suggested that drug interactions mediated by CYP3A4 may occur during treatment with these gastrointestinal drugs, necessitating the confirmation of the clinical significance of these drug interactions to prevent unexpected adverse effects.

Loperamide Restricts Intracellular Growth of Mycobacterium tuberculosis in Lung Macrophages.

New approaches for improving tuberculosis (TB) control using adjunct host-directed cellular and repurposed drug therapies are needed. Autophagy plays a crucial role in the response to TB, and a variety of autophagy-inducing drugs that are currently available for various medical conditions may serve as an adjunct treatment in pulmonary TB. Here, we evaluated the potential of loperamide, carbamazepine, valproic acid, verapamil, and rapamycin to enhance the antimicrobial immune response to Mycobacterium tuberculosis (Mtb). Human monocyte-derived macrophages (MDMs) and murine alveolar cells (MACs) were infected with Mtb and treated with loperamide, carbamazepine, valproic acid, verapamil, and rapamycin in vitro. Balb/c mice were intraperitoneally administered loperamide, valproic acid, and verapamil, and MACs were infected in vitro with Mtb. The induction of autophagy, the containment of Mtb within autophagosomes and the intracellular Mtb burden were determined. Autophagy was induced by all of the drugs in human and mouse macrophages, and loperamide significantly increased the colocalization of microtubule-associated protein 1 light chain 3 with Mtb in MDMs. Carbamazepine, loperamide, and valproic acid induced microtubule-associated protein 1 light chain 3 and autophagy related 16- like protein 1 gene expression in MDMs and in MACs. Loperamide also induced a reduction in TNF-α production. Loperamide and verapamil induced autophagy, which was associated with a significant reduction in the intracellular growth of Mtb in MACs and alveolar macrophages. The intraperitoneal administration of loperamide and valproic acid induced autophagy in freshly isolated MACs. The antimycobacterial activity in MACs was higher after loperamide treatment and was associated with the degradation of p62. In conclusion, loperamide shows potential as an adjunctive therapy for the treatment of TB.

G9a inhibits CREB-triggered expression of mu opioid receptor in primary sensory neurons following peripheral nerve injury.

Neuropathic pain, a distressing and debilitating disorder, is still poorly managed in clinic. Opioids, like morphine, remain the mainstay of prescribed medications in the treatment of this disorder, but their analgesic effects are highly unsatisfactory in part due to nerve injury-induced reduction of opioid receptors in the first-order sensory neurons of dorsal root ganglia. G9a is a repressor of gene expression. We found that nerve injury-induced increases in G9a and its catalyzed repressive marker H3K9m2 are responsible for epigenetic silencing of Oprm1, Oprk1, and Oprd1 genes in the injured dorsal root ganglia. Blocking these increases rescued dorsal root ganglia Oprm1, Oprk1, and Oprd1 gene expression and morphine or loperamide analgesia and prevented the development of morphine or loperamide-induced analgesic tolerance under neuropathic pain conditions. Conversely, mimicking these increases reduced the expression of three opioid receptors and promoted the mu opioid receptor-gated release of primary afferent neurotransmitters. Mechanistically, nerve injury-induced increases in the binding activity of G9a and H3K9me2 to the Oprm1 gene were associated with the reduced binding of cyclic AMP response element binding protein to the Oprm1 gene. These findings suggest that G9a participates in the nerve injury-induced reduction of the Oprm1 gene likely through G9a-triggered blockage in the access of cyclic AMP response element binding protein to this gene.

Distribution and trafficking of the µ-opioid receptor in enteric neurons of the guinea pig.

The µ-opioid receptor (MOR) is a major regulator of gastrointestinal motility and secretion and mediates opiate-induced bowel dysfunction. Although MOR is of physiological and therapeutic importance to gut function, the cellular and subcellular distribution and regulation of MOR within the enteric nervous system are largely undefined. Herein, we defined the neurochemical coding of MOR-expressing neurons in the guinea pig gut and examined the effects of opioids on MOR trafficking and regulation. MOR expression was restricted to subsets of enteric neurons. In the stomach MOR was mainly localized to nitrergic neurons (∼88%), with some overlap with neuropeptide Y (NPY) and no expression by cholinergic neurons. These neurons are likely to have inhibitory motor and secretomotor functions. MOR was restricted to noncholinergic secretomotor neurons (VIP-positive) of the ileum and distal colon submucosal plexus. MOR was mainly detected in nitrergic neurons of the colon (nitric oxide synthase positive, 87%), with some overlap with choline acetyltransferase (ChAT). No expression of MOR by intrinsic sensory neurons was detected. [d-Ala(2), MePhe(4), Gly(ol)(5)]enkephalin (DAMGO), morphiceptin, and loperamide induced MOR endocytosis in myenteric neurons. After stimulation with DAMGO and morphiceptin, MOR recycled, whereas MOR was retained within endosomes following loperamide treatment. Herkinorin or the δ-opioid receptor agonist [d-Ala(2), d-Leu(5)]enkephalin (DADLE) did not evoke MOR endocytosis. In summary, we have identified the neurochemical coding of MOR-positive enteric neurons and have demonstrated differential trafficking of MOR in these neurons in response to established and putative MOR agonists.

Biotransformation Capacity of Carboxylesterase in Skin and Keratinocytes for the Penta-Ethyl Ester Prodrug of DTPA.

The penta-ethyl ester prodrug of the chelating agent diethylene triamine pentaacetic acid (DTPA), referred to as C2E5, effectively accelerated clearance of americium after transdermal delivery. Carboxylesterases (CESs) play important roles in facilitating C2E5 hydrolysis. However, whether CESs in human skin hydrolyze C2E5 remains unknown. We evaluated the gene and protein expression of CESs in distinctive human epidermal cell lines: HEKa, HEKn, HaCaT, and A431. The substrates p-nitrophenyl acetate (pNPA) and 4-nitrophenyl valerate (4-NPV) were used to access esterase and CES activity. C2E5 hydrolysis was measured by radiometric high-performance liquid chromatography after incubation of [(14)C]C2E5 with supernatant fractions after centrifugation at 9000g (S9) prepared from skin cell lines. CES-specific inhibitors were used to access metabolism in human skin S9 fractions with analysis by liquid chromatography-tandem mass spectrometry. We identified the human carboxylesterase 1 and 2 (CES1 and CES2) bands in a Western blot. The gene expression of these enzymes was supported by a real-time polymerase chain reaction (qPCR). pNPA and 4-NPV assays demonstrated esterase and CES activity in all the cell lines that were comparable to human skin S9 fractions. The prodrug C2E5 was hydrolyzed by skin S9 fractions, resulting in a primary metabolite, C2E4. In human skin S9 fractions, inhibition of C2E5 hydrolysis was greatest with a pan-CES inhibitor (benzil). CES1 inhibition (troglitazone) was greater than CES2 (loperamide), suggesting a primary metabolic role for CES1. These results indicate that human keratinocyte cell lines are useful for the evaluation of human cutaneous metabolism and absorption of ester-based prodrugs. However, keratinocytes from skin provide a small contribution to the overall metabolism of C2E5.

Identification of novel small-molecule inhibitors targeting menin-MLL interaction, repurposing the antidiarrheal loperamide.

Leukemia with a mixed lineage leukemia (MLL) rearrangement, which harbors a variety of MLL fusion proteins, has a poor prognosis despite the latest improved treatment options. Menin has been reported to be a required cofactor for the leukemogenic activity of MLL fusion proteins. Thus, the disruption of the protein-protein interactions between menin and MLL represents a very promising strategy for curing MLL leukemia. Making use of menin-MLL inhibitors with a shape-based scaffold hopping approach, we have discovered that the antidiarrheal loperamide displays previously unreported mild inhibition for the menin-MLL interaction (IC50 = 69 ± 3 µM). In an effort to repurpose this drug, a series of chemical modification analyses was performed, and three of the loperamide-based analogues, DC_YM21, DC_YM25 and DC_YM26 displayed better activities with IC50 values of 0.83 ± 0.13 µM, 0.69 ± 0.07 µM and 0.66 ± 0.05 µM, respectively. Further treatment with DC_YM21 demonstrated potent and selective blockage of proliferation and induction of both cell cycle arrest and differentiation of leukemia cells harboring MLL translocations, which confirmed the specific mechanism of action. In conclusion, molecules of a novel scaffold targeting menin-MLL interactions were reported and they may serve as new potential therapeutic agents for MLL leukemia.

Loperamide-induced expression of immune and inflammatory genes in Collies associated with ivermectin sensitivity.

This study evaluated the impact of the ABCB1-1Δ mutation in Collies which exhibited toxicity toward ivermectin, on changes in gene expression when given the unrelated ABCB1 substrate loperamide, to identify potential biomarkers predictive of drug safety. Thirty-two healthy intact Collies consisting of dogs with either a wild-type, heterozygous mutant, or homozygous mutant genotype were used. Whole blood samples were collected from Collies at 0 or 5 h following administration of loperamide at a dose of 0.10 mg/kg. Whole-genome gene expression microarray was conducted to examine for changes in gene expression. Microarray analysis identified loperamide-induced changes in gene expression which were specifically associated with ivermectin-sensitive phenotypes in Collies possessing the ABCB1-1Δ mutation. Gene pathway analysis further demonstrated that the altered genes are involved in immunological disease, cell death and survival, and cellular development. Thirteen genes, including CCL8 and IL-8, were identified. Collie dogs harboring ABCB1-1Δ mutation which also exhibited toxicity toward ivermectin demonstrated systematic responses following loperamide treatment exhibited by altered expression of genes involved in immune and inflammatory signaling pathways. Genes such as CCL8 and IL-8 are potential biomarkers in whole blood that may predict the safety of loperamide in dogs with ABCB1-1∆ mutation associated with ivermectin sensitivity.

Influence of ABCB1 Genotype in Collies on the Pharmacokinetics and Pharmacodynamics of Loperamide in a Dose-Escalation Study.

Thirty-three Collies (14 male and 19 female) were used in a dose-escalation study to determine the impact of ABCB1 genotype on loperamide pharmacokinetics (PK) and pharmacodynamics (PD). Loperamide was orally administered in four ascending doses (0.01, 0.05, 0.1, or 0.2 mg/kg) over a 4-wk period to fasted Collies. Comparisons were made within each dose to genotype, phenotype, and whether Collies received three (3D) or four (4D) loperamide doses. The 3D and 4D groupings had statistically significant differences in systemic drug exposure (defined by the area under the concentration-versus-time profile estimated from time zero to the last quantifiable drug concentration, AUC0-last). In contrast, statistical differences in AUC0-last only occurred in the comparison between wild-type (WT) Collies versus homozygous mutant (Mut) Collies administered 0.1 mg/kg. Statistical differences in the proportionality relationship were observed when comparing 3D to 4D Collies, and the WT to Mut Collies. Intersubject variability in drug exposure tended to be twice as high between Mut and WT Collies. Associations were observed between systemic drug exposure and ataxia or depression but not between systemic drug exposure and mydriasis or salivation. Thus, Collies expressing the greatest sensitivity to CNS-associated effects of loperamide (Mut) tended to have higher drug exposure compared with those less sensitive to the adverse effects of loperamide. Genotype and phenotype only partially explained differences in loperamide PK and PD, suggesting this relationship may not be straightforward and that other factors need to be considered. Accordingly, the PD and PK of one P-glycoprotein substrate only partially predicted the likelihood of adverse responses to unrelated substrates.