Etiological profile of diarrhea in solid organ transplant recipients at a tertiary care center in Southern India.

BACKGROUND: Diarrhea is one of the common gastrointestinal (GI) adverse events after solid organ transplantation. Diarrhea may be caused by infectious or non-infectious etiology. The infectious etiology of diarrhea varies according to the location and duration of diarrhea. Non-infectious etiologies include drugs, inflammatory bowel disease, neoplasia. The objective of this study was to evaluate the etiological profile of diarrhea in solid organ transplant recipients presenting to a tertiary care center in Southern India. METHODS: This was a retrospective analysis of prospectively collected data of all solid organ transplantation recipients referred to the Department of Medical Gastroenterology for evaluation of diarrhea from April 2012 till May 2014. All patients had stool evaluated by wet mount examination, modified acid fast (AFB) stain, trichrome stain, culture, and Clostridium difficile toxin assay. EDTA plasma was collected for quantitative Cytomegalovirus (CMV) detection by real-time PCR. If the diarrhea was acute (<2 wk), and no etiological agent was identified, empirical antibiotic therapy was instituted and followed up. If persistent or chronic diarrhea (>2-4 wk), endoscopic evaluation (upper GI endoscopy and/or colonoscopy with biopsies), depending on the clinical type of diarrhea was done. If no specific etiological diagnosis was established after endoscopic evaluation, breath test for SIBO and celiac serology were done. If no specific etiology was identified after the above investigations, dose of immunosuppressive drugs was reduced. If diarrhea responded to dose reduction, it was considered to be drug related. RESULTS: Fifty-eight episodes of diarrhea occurred in 55 solid organ transplant recipients during the study period. Renal transplant recipients constituted the majority (70%). Most (79%) of patients included in the study had their transplant > 6 mo ago. Infective diarrhea was the etiology in 46%, drug-related diarrhea in 29.3%. No specific etiology was identified in 22.4% of patients. Parasites accounted for 69% of all infective diarrhea. Stool evaluation was the main investigation in establishing diagnosis in acute diarrhea. Endoscopic evaluation was required in two thirds of patients to establish diagnosis in chronic diarrhea. CONCLUSION: GI infections and drug-related diarrhea were the common causes of diarrhea in solid organ transplant recipients. Parasites were the most common infectious etiology of diarrhea. Step-wise evaluation was able to identify the etiology in ~ 77% of patients. Overall, 98% of diarrheal episodes resolved.

Per rectal endoscopic myotomy for the treatment of adult Hirschsprung's disease: First human case (with video).

Hirschsprung's disease (HD) is a congenital disorder characterized by the absence of intrinsic ganglion cells in submucosal and myenteric plexuses of the hindgut; and presents with constipation, intestinal obstruction and/or megacolon. HD commonly involves the rectosigmoid region (short segment HD), although shorter and longer variants of the disease are described. Standard treatment involves pull-through surgery for short segment HD or posterior anorectal myotomy in selected ultrashort segment candidates. Third space endoscopy has evolved during the past few years. Per oral endoscopic myotomy and per oral pyloromyotomy are described for treatment of achalasia cardia and refractory gastroparesis, respectively. Using the same philosophy of muscle/sphincter disruption for spastic bowel segments, per rectal endoscopic myotomy could be considered as a treatment option for short segment HD. A 24-year-old male patient presented with refractory constipation since childhood, and habituated to high-dose laxative combinations. Diagnosis was confirmed as adult short segment HD by barium enema, colonoscopic deep suction mucosal biopsies and anorectal manometry. Histopathology confirmed aganglionosis in the distal 15 cm. By implementing principles of third space endoscopy, per rectal endoscopic myotomy 20 cm in length was successfully carried out. At 24-week follow up, the patient reported significant relief of constipation and associated symptoms. Sigmoidoscopy, anorectal manometry and barium enema confirm improved rectal distensibility and reduced rectal pressures. The present case report describes the first human experience of per rectal endoscopic myotomy for successful treatment of adult short segment HD.

N-aryl-oxazolidin-2-imine muscle selective androgen receptor modulators enhance potency through pharmacophore reorientation.

A novel selective androgen receptor modulator (SARM) scaffold was discovered as a byproduct obtained during synthesis of our earlier series of imidazolidin-2-ones. The resulting oxazolidin-2-imines are among the most potent SARMs known, with many analogues exhibiting sub-nM in vitro potency in binding and functional assays. Despite the potential for hydrolytic instability at gut pH, compounds of the present class showed good oral bioavailability and were highly active in a standard rodent pharmacological model.

Pharmacokinetics of the dipeptidyl peptidase 4 inhibitor saxagliptin in rats, dogs, and monkeys and clinical projections.

Saxagliptin is a potent, selective, reversible dipeptidyl peptidase 4 (DPP4) inhibitor specifically designed for extended inhibition of the DPP4 enzyme and is currently under development for the treatment of type-2 diabetes. The pharmacokinetics of saxagliptin were evaluated in rats, dogs, and monkeys and used to predict its human pharmacokinetics. Saxagliptin was rapidly absorbed and had good bioavailability (50-75%) in the species tested. The plasma clearance of saxagliptin was higher in rats (115 ml/min/kg) than in dogs (9.3 ml/min/kg) and monkeys (14.5 ml/min/kg) and was predicted to be low to moderate in humans. The plasma elimination half-life was between 2.1 and 4.4 h in rats, dogs, and monkeys, and both metabolism and renal excretion contributed to the overall elimination. The primary metabolic clearance pathway involved the formation of a significant circulating, pharmacologically active hydroxylated metabolite, M2. The volume of distribution values observed in rats, dogs, and monkeys (1.3-5.2 l/kg) and predicted for humans (2.7 l/kg) were greater than those for total body water, indicating extravascular distribution. The in vitro serum protein binding was low (< or =30%) in rats, dogs, monkeys, and humans. After intra-arterial administration of saxagliptin to Sprague-Dawley and Zucker diabetic fatty rats, higher levels of saxagliptin and M2 were observed in the intestine (a proposed major site of drug action) relative to that in plasma. Saxagliptin has prolonged pharmacodynamic properties relative to its plasma pharmacokinetic profile, presumably due to additional contributions from M2, distribution of saxagliptin and M2 to the intestinal tissue, and prolonged dissociation of both saxagliptin and M2 from DPP4.

Prediction of human oral pharmacokinetics using nonclinical data: examples involving four proprietary compounds.

The oral pharmacokinetics (concentration-time profile) of four proprietary compounds in humans were predicted using the C(vss)-MRT method. The first step was to demonstrate superposition of intravenous (i.v.) pharmacokinetic profiles of preclinical species following mathematical transformation of their respective concentration-time curves using the corresponding C(vss) (where C(vss)=dose/Vss; Vss is the volume of distribution at steady state) and mean residence time (MRT) values. The resultant profiles were then back-transformed to estimate human i.v. plasma concentration-time profiles using human C(vss) and MRT values. Human C(vss) and MRT values were estimated from projected human Vss and CL values. Projection of CL was based on scaled (in vitro) metabolic clearance, simple allometry with and without various correction factors and the unbound fraction corrected intercept method. Vss values were estimated by allometric scaling with and without correction for interspecies differences in plasma protein binding. The predicted human i.v. profiles, in combination with the estimated mean absorption rate constants and bioavailability, were then used to simulate the oral pharmacokinetics in human using one- or multi-compartment kinetic models. Overall, with this approach, key oral pharmacokinetic parameters such as AUC, C(max), C(min) and oral plasma T((1/2)) were projected to be within two-fold of the actual values in humans.

Discovery of potent and muscle selective androgen receptor modulators through scaffold modifications.

A novel series of imidazolin-2-ones were designed and synthesized as highly potent, orally active and muscle selective androgen receptor modulators (SARMs), with most of the compounds exhibiting low nM in vitro potency in androgen receptor (AR) binding and functional assays. Once daily oral treatment with the lead compound 11a (AR Ki = 0.9 nM, EC50 = 1.8 nM) for 14 days induced muscle growth with an ED50 of 0.09 mg/kg, providing approximately 50-fold selectivity over prostate growth in an orchidectomized rat model. Pharmacokinetic studies in rats demonstrated that the lead compound 11a had oral bioavailability of 65% and a plasma half-life of 5.5 h. On the basis of their preclinical profiles, the SARMs in this series are expected to provide beneficial anabolic effects on muscle with minimal androgenic effects on prostate tissue.

Discovery and preclinical studies of (R)-1-(4-(4-fluoro-2-methyl-1H-indol-5-yloxy)-5- methylpyrrolo[2,1-f][1,2,4]triazin-6-yloxy)propan- 2-ol (BMS-540215), an in vivo active potent VEGFR-2 inhibitor.

A series of substituted 4-(4-fluoro-1H-indol-5-yloxy)pyrrolo[2,1-f][1,2,4]triazine-based inhibitors of vascular endothelial growth factor receptor-2 kinase is reported. Structure-activity relationship studies revealed that a methyl group at the 5-position and a substituted alkoxy group at the 6-position of the pyrrolo[2,1-f][1,2,4]triazine core gave potent compounds. Biochemical potency, kinase selectivity, and pharmacokinetics of the series were optimized and in vitro safety liabilities were minimized to afford BMS-540215 (12), which demonstrated robust preclinical in vivo activity in human tumor xenograft models. The l-alanine prodrug of 12, BMS-582664 (21), is currently under evaluation in clinical trials for the treatment of solid tumors.

Design, synthesis, and evaluation of orally active 4-(2,4-difluoro-5-(methoxycarbamoyl)phenylamino)pyrrolo[2,1-f][1,2,4]triazines as dual vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 inhibitors.

A series of substituted 4-(2,4-difluoro-5-(methoxycarbamoyl)phenylamino)pyrrolo[2,1-f][1,2,4]triazines was identified as potent and selective inhibitors of the tyrosine kinase activity of the growth factor receptors VEGFR-2 (Flk-1, KDR) and FGFR-1. The enzyme kinetics associated with the VEGFR-2 inhibition of compound 50 (K(i) = 52 +/- 3 nM) confirmed that the pyrrolo[2,1-f][1,2,4]triazine analogues are competitive with ATP. Several analogues demonstrated low-nanomolar inhibition of VEGF- and FGF-dependent human umbilical vein endothelial cell (HUVEC) proliferation. Replacement of the C6-ester substituent of the pyrrolo[2,1-f][1,2,4]triazine core with heterocyclic bioisosteres, such as substituted 1,3,5-oxadiazoles, afforded compounds with excellent oral bioavailability in mice (i.e., 50 F(po) = 79%). Significant antitumor efficacy was observed with compounds 44, 49, and 50 against established L2987 human lung carcinoma xenografts implanted in athymic mice. A full account of the synthesis, structure-activity relationships, pharmacology, and pharmacokinetic properties of analogues within the series is presented.

Synthesis and SAR of 4-(3-hydroxyphenylamino)pyrrolo[2,1-f][1,2,4]triazine based VEGFR-2 kinase inhibitors.

A versatile synthesis of the suitably functionalized pyrrolo[2,1-f][1,2,4]triazine nucleus is described. SAR at the C-5 and C-6 positions of the 4-(3-hydroxy-4-methylphenylamino)pyrrolo[2,1-f][1,2,4]triazine template led to compounds with good in vitro potency against VEGFR-2 kinase. Glucuronidation of the phenol group is mitigated by incorporation of a basic amino group on the C-6 side chain of the pyrrolotriazine nucleus.

A novel calcium-sensing receptor antagonist transiently stimulates parathyroid hormone secretion in vivo.

Circulating calcium (Ca(2+)) is a primary regulator of bone homeostasis through its action on PTH secretion. Extracellular Ca(2+) modulates PTH secretion through a cell surface G protein-coupled receptor, the calcium-sensing receptor (CaR). The expression of the CaR suggests a critical role in cellular regulation by calcium in various organs, including parathyroid gland, bone, and kidney. Despite an obvious pharmacological utility for CaR antagonists in the treatment of disease, only a limited number of such classes of compounds exist. We have identified a novel class of small molecules with specific activity at the CaR. This class of compounds is represented by compound 1. It possesses potent antagonist activity at the human CaR with IC(50) values of 64 nm and 230 nm in inhibiting intracellular Ca(2+) flux and inositol phosphate generation in vitro, respectively. When administered to male rats in vivo, compound 1 robustly increased serum PTH levels. The stimulation of PTH secretion was rapid and transient when administered either iv or orally. The pharmacokinetic profile of compound 1 after oral administration revealed that maximal plasma levels of compound were reached within 1 h and the half-life of the compound to be approximately 2 h in rats. These data describe a representative compound of a novel chemical class than previously described allosteric modulators that offer a new avenue for the development of improved treatments of osteoporosis.

Membrane transport of camptothecin: facilitation by human P-glycoprotein (ABCB1) and multidrug resistance protein 2 (ABCC2).

BACKGROUND: The purpose of the present study was to continue the investigation of the membrane transport mechanisms of 20-(S)-camptothecin (CPT) in order to understand the possible role of membrane transporters on its oral bioavailability and disposition. METHODS: The intestinal transport kinetics of CPT were characterized using Caco-2 cells, MDCKII wild-type cells and MDCKII cells transfected with human P-glycoprotein (PGP) (ABCB1) or human multidrug resistance protein 2 (MRP2) (ABCC2). The effects of drug concentration, inhibitors and temperature on CPT directional permeability were determined. RESULTS: The absorptive (apical to basolateral) and secretory (basolateral to apical) permeabilities of CPT were found to be saturable. Reduced secretory CPT permeabilities with decreasing temperatures suggests the involvement of an active, transporter-mediated secretory pathway. In the presence of etoposide, the CPT secretory permeability decreased 25.6%. However, inhibition was greater in the presence of PGP and of the breast cancer resistant protein inhibitor, GF120918 (52.5%). The involvement of additional secretory transporters was suggested since the basolateral to apical permeability of CPT was not further reduced in the presence of increasing concentrations of GF120918. To investigate the involvement of specific apically-located secretory membrane transporters, CPT transport studies were conducted using MDCKII/PGP cells and MDCKII/MRP2 cells. CPT carrier-mediated permeability was approximately twofold greater in MDCKII/PGP cells and MDCKII/MRP2 cells than in MDCKII/wild-type cells, while the apparent Km values were comparable in all three cell lines. The efflux ratio of CPT in MDCKII/PGP in the presence of 0.2 microM GF120918 was not completely reversed (3.36 to 1.49). However, the decrease in the efflux ratio of CPT in MDCKII/MRP2 cells (2.31 to 1.03) suggests that CPT efflux was completely inhibited by MK571, a potent inhibitor of the Multidrug Resistance Protein transporter family. CONCLUSIONS: The current results provide evidence that PGP and MRP2 mediate the secretory transport of CPT in vitro. However, the involvement of other transporters cannot be ruled out based on these studies. Since these transporters are expressed in the intestine, liver and kidney variations in their expression levels and/or regulation may be responsible for the erratic oral absorption and biliary excretion of CPT observed in human subjects.

A phase I and pharmacologic study of the combination of marimastat and paclitaxel in patients with advanced malignancy.

BACKGROUND: Marimastat is a potent inhibitor of matrix metalloproteinases and in preclinical studies enhances the anti-tumor activity of certain chemotherapeutics. We performed a phase I clinical evaluation of the combination of oral marimastat and intravenous paclitaxel, to determine if these drugs could be co-administered safely, and to determine whether marimastat alters paclitaxel pharmacokinetics. MATERIAL/METHODS: Marimastat was administered twice daily and paclitaxel as a three hour infusion every three weeks. Doses of both marimastat and paclitaxel were escalated in cohorts of patients up to maximal doses of 10 mg for marimastat and 175 mg/m2 for paclitaxel. Paclitaxel plasma pharmacokinetic parameters were assessed in the absence (cycle 1) and presence (cycle 2) of marimastat. Trough marimastat plasma levels were evaluated during cycle 2. RESULTS: A total of 19 patients were treated at three different dose levels. There were no dose-limiting toxicities during the first cycle of therapy, resulting in dose escalation up to the planned maximal dose for each drug. Neutropenia was the most common significant toxicity at the highest dose level, with grade 3 or higher neutropenia occurring in 38% of patients. There were no complete or partial responses. Pharmacokinetic analyses indicate that marimastat does not alter paclitaxel clearance. At the 10 mg dose, the mean trough marimastat level was 14.8 Kg/L. CONCLUSIONS: Marimastat and paclitaxel can be co-administered safely at doses equivalent to those recommended for single-agent administration. Additional studies are necessary to determine whether this combination is more effective in controlling tumor progression than paclitaxel alone.

Phase I evaluation of sequential topoisomerase targeting with irinotecan/cisplatin followed by etoposide in patients with advanced malignancy.

PURPOSE: To investigate pharmacologically guided addition of etoposide to a weekly irinotecan/cisplatin chemotherapy. PATIENTS AND METHODS: Patients with advanced nonhematologic malignancies were eligible. Treatment consisted of i.v. administration of 50 mg/m(2) irinotecan and 20 mg/m(2) cisplatin on days 1, 8, 15, and 22 of a 42-day cycle or on days 1 and 8 of a 21-day cycle. Etoposide was administered in a dose-escalating fashion 2 days after each dose of irinotecan/cisplatin, either i.v. as a single dose or p.o. as two doses administered 12 h apart. Pharmacologic analyses included measurement of plasma concentrations of irinotecan, SN-38, and SN-38 glucuronide, as well as quantitation of topoisomerase protein levels in peripheral blood mononuclear cells (PBMNCs). RESULTS: A total of 40 patients with a variety of malignancies received 122 cycles of therapy. Dose-limiting toxicities included neutropenia and diarrhea, with the 21-day cycle tolerated better than the 42-day cycle. For the 21-day cycle, the maximum tolerated dose was 75 mg/m(2) for i.v. etoposide and 85 mg/m(2) for oral etoposide. Objective responses were observed in four patients with previously treated mesothelioma, gastric, breast, and ovarian cancer, respectively. PBMNC levels of topoisomerase IIalpha were increased at the time of etoposide administration in two patients, with these patients having the highest SN-38 glucuronide peak-plasma-concentration and area-under-the-curve values among 15 patients with available pharmacokinetic data. One of these patients had a partial response to therapy. CONCLUSIONS: Pharmacologically guided administration of etoposide in combination with irinotecan/cisplatin using a 21-day cycle is associated with acceptable toxicity and significant antitumor activity. The finding that PBMNC topoisomerase IIalpha protein levels increased after irinotecan/cisplatin treatment in two of six patients supports the continued development of sequential topoisomerase targeting in the treatment of malignancy.