Safety evaluation of combination treatment of drug-eluting bead transarterial chemoembolization and immune checkpoint inhibitors for hepatocellular carcinoma: An increased risk of liver abscess with treatment interval less than one month

PURPOSE

To analyze the safety of combination treatment comprising drug-eluting bead transarterial chemoembolization (DEB-TACE) and immune checkpoint inhibitors (ICIs) in hepatocellular carcinoma (HCC).

METHOD

In total, 208 HCC patients receiving DEB-TACE were enrolled for this retrospective single-institution study. Among them, 50 patients who received ICIs at an interval less than one month from DEB-TACE were categorized into the DEB-ICI group; the remaining 158 patients were categorized into the DEB group. Albumin-bilirubin (ALBI) score before and at three months after DEB-TACE were recorded to evaluate liver function changes. Adverse events within three months after DEB-TACE were considered TACE-related and were compared between the two groups.

RESULTS

The DEB-ICI group had significantly higher incidence of liver abscess than the DEB group (14.0 % versus 5.1 %, p-value = 0.0337). No significant difference in the other TACE-related adverse events and change of ALBI score between the groups. Univariate logistic regression confirmed that combination with ICIs was an independent risk factor for liver abscess after DEB-TACE (odds ratio = 3.0523, 95 % confidence interval: 1.0474-8.8947, p-value = 0.0409); other parameters including subjective angiographic chemoembolization endpoint scale and combined targeted therapy were nonsignificant risk factors in this study population. In the DEB-ICI group, patients who received ICIs before DEB-TACE exhibited a trend toward liver abscess formation compared with those who received DEB-TACE before ICIs (23.8 % versus 6.9 %, p-value = 0.0922).

CONCLUSIONS

Combination treatment involving DEB-TACE and ICIs at an interval less than one month increased the risk of liver abscess after DEB-TACE. Greater caution is therefore warranted for HCC patients who receive ICIs and DEB-TACE with this short interval.

Cholecystoenteric fistula in a patient with advanced gallbladder cancer: A case report and review of literature

BACKGROUND

Cholecystoenteric fistula (CEF) involves the formation of a spontaneous anomalous tract between the gallbladder and the adjacent gastrointestinal tract. Chronic gallbladder inflammation can lead to tissue necrosis, perforation, and fistulogenesis. The most prevalent cause of CEF is chronic cholelithiasis, which rarely results from malignancy. Because the symptoms and laboratory findings associated with CEF are nonspecific, the condition is often misdiagnosed, presenting a challenge to the surgeon when detected intraoperatively. Therefore, a preoperative diagnosis of CEF is crucial.

CASE SUMMARY

We present the case of a 57-year-old male with advanced gallbladder cancer (GBC) who arrived at the emergency room with persistent vomiting, abdominal pain, and diarrhea. An abdominopelvic computed tomography scan revealed a contracted gallbladder with bubbles in the fundus connected to the second portion of the duodenum and transverse colon. We suspected that GBC had invaded the adjacent gastrointestinal tract through a cholecystoduodenal fistula (CDF) or a cholecystocolonic fistula (CCF). He underwent multiple examinations, including esophagogastroduodenoscopy, an upper gastrointestinal series, colonoscopy, and magnetic resonance cholangiopancreatography; the results of these tests confirmed a diagnosis of synchronous CDF and CCF. The patient underwent a Roux-en-Y gastrojejunostomy and loop ileostomy to address the severe adhesions that were previously observed to cover the second portion of the duodenum and hepatic flexure of the colon. His symptoms improved with supportive treatment while hospitalized. He initiated oral targeted therapy with lenvatinib for further anticancer treatment.

CONCLUSION

The combination of imaging and surgery can enhance preoperative diagnosis and alleviate symptoms in patients with GBC complicated by CEF.

Drug-eluting beads loaded with irinotecan to treat synchronous liver-only metastases of colorectal cancer non-responsive to bevacizumab-based chemotherapy

OBJECTIVE

To evaluate the efficacy of drug-eluting beads loaded with irinotecan (DEBIRI) in colorectal cancer (CRC) patients with synchronous liver-only metastases non-responsive to bevacizumab-based chemotherapy (BBC).

METHODS

Fifty-eight patients were enrolled in this study. Treatment response to BBC and DEBIRI were determined by the morphological criteria and Choi's criteria, respectively. Progression-free survival (PFS) and overall survival (OS) were recorded. The correlation between pre-DEBIRI CT parameters and treatment response to DEBIRI was analyzed.

RESULTS

CRC patients were divided into the BBC responsive group (R group) (n = 16) and the non-responsive group (n = 42), which was further divided into the NR group (23 patients who did not receive DEBIRI) and the NR+DEBIRI group (19 patients who received DEBIRI after failing BBC). Among the R, NR and NR+DEBIRI groups, the median PFS were 11, 12, and 4 months, respectively (p < 0.01); median OS were 36, 23, and 12 months, respectively (p = 0.01). In the NR+DEBIRI group, 33 metastatic lesions were treated with DEBIRI, of which 18 (54.5%) reached objective response. The receiver operating characteristic curve showed that the contrast enhancement ratio (CER) before DEBIRI could predict objective response (AUC = 0.737, p < 0.01).

CONCLUSION

In CRC patients, DEBIRI can achieve acceptable objective response for liver metastases non-responsive to BBC. However, this locoregional control does not prolong survival. The pre-DEBIRI CER can predict OR in these patients.

ADVANCES IN KNOWLEDGE

DEBIRI can act as an acceptable locoregional management in CRC patients with liver metastases non-responsive to BBC, and the pre-DEBIRI CER is a potential indicator of locoregional control.

Safety of drug-eluting beads transarterial chemoembolization under the combination therapy with immune checkpoint inhibitors in unresectable hepatocellular carcinoma

556

Background: To analyze the safety of drug-eluting beads transarterial chemoembolization (DEB-TACE) under the combination treatment with immune checkpoint inhibitors (ICI) in unresectable hepatocellular carcinoma (HCC). Methods: In this retrospective single-institution study, 208 HCC patients (152 male and 56 female; mean age, 64.70±11.46 years) who received DEB-TACE between 2018.Nov and 2021.Dec were enrolled. There were 74.0% patients had Barcelona Clinic Liver Cancer stage B HCC, 90.4% were Child-pugh A patients, 63.0% patients had albumin-bilirubin (ALBI) grade 2, and 51.0% patients were up-to-seven out. Among them, 50 patients (24.0%) who received ICI with interval less than 30 days with DEB-TACE were categorized as DEB-ICI group; the remaining 158 patients (76.0%) were categorized as DEB group. ALBI grade before and 90 days after DEB-TACE were recorded to evaluate liver function change. Complications within 90 days after DEB-TACE were considered as TACE-related and were compared between two groups. Results: DEB-ICI group had significant higher incidence rate of liver abscess than DEB group (14.0% versus 5.1%, p=0.0337); other TACE-related complications showed no difference between two groups. There were 23.9% patients in DEB-ICI group had elevated ALBI grade after DEB-TACE, which revealed no difference in comparison with 22.4% in DEB group ( p=0.8460). Univariate analysis confirmed that combination with ICI was an independent risk factor of liver abscess formation after DEB-TACE (odds ratio = 3.0523, 95% confidence interval: 1.0474-8.8947, p=0.0409). Among DEB-ICI group, patients received ICI before DEB-TACE had a trend to have higher risk of liver abscess formation than those who received DEB-TACE before ICI (23.8% versus 6.9%, p-value=0.0922). Conclusions: Combination treatment of ICI with DEB-TACE with interval less than 30 days increased risk of liver abscess formation after DEB-TACE.

Combination therapy of sorafenib and drug-eluting bead transarterial chemoembolization for advanced hepatocellular carcinoma with and without hepatic arteriovenous shunt

BACKGROUND

To compare the efficacy and safety of combination therapy with sorafenib and drug-eluting bead transarterial chemoembolization (DEB-TACE) in advanced hepatocellular carcinoma (HCC) with or without hepatic arteriovenous shunt (HAVS).

METHODS

This retrospective, single-center study enrolled 59 advanced HCC patients treated with combination therapy, of whom 33 (55.9%) patients had HAVS. Tumor response according to the mRECIST criteria was evaluated based on the CT images 1 month after TACE, and changes in the arterial enhancement ratio (AER) of tumors and portal vein tumor thrombosis were also documented. Time-to-progression (TTP), overall survival (OS), and prognostic factors were analyzed. Safety was evaluated with the incidence of TACE-related complications within 6 weeks after TACE.

RESULTS

The tumor response between the two groups showed no significant difference in the objective response rate (69.2% in the group without HAVS vs 60.6% in the group with HAVS, p = 0.492) or disease control rate (92.3% vs 87.9%, p = 0.685). The two groups showed comparable TTP (4.23 vs 2.33 months, p = 0.235) and OS (12.77 vs 12.97 months, p = 0.910). A drop in the AER of tumors of more than 20% on post-TACE CT independently predicted better OS. With regard to safety, there was no significant difference between the two groups.

CONCLUSION

For advanced HCC, combination therapy had equal efficacy and safety in patients with HAVS compared to those without HAVS, indicating that DEB-TACE is an optional and effective treatment in these patients.

Transcatheter Arterial Chemoembolization with Drug-Eluting Beads for the Treatment of Hepatocellular Carcinoma: Recommended Selection for Small-Caliber (<100 μm) Beads

Drug-eluting beads transarterial chemoembolization (DEB-TACE) is an alternative to conventional lipiodol-based TACE (cTACE) to treat hepatocellular carcinoma (HCC). With the advancement in pharmacology, small-caliber DEB-TACE (<100 μm) has been introduced since 2016. For the treatment of hepatic neoplasms or HCC, there is a tendency to use smaller beads by DEB-TACE to achieve more extensive tumor necrosis and a significant reduction in liver toxicity in comparison with that caused by cTACE. However, the indications and potential complications of small-caliber DEB-TACE remain uncertain and have not been well established, due to lack of randomized phase III clinical trials. Instead of systematic or meta-analysis review, this narrative review article describes the suggested indications and contraindications of DEB-TACE with small DEBs, benefit of super-selective embolization of the feeding arteries and the recommended selection of small-caliber DEB. This review was approved by the institutional review board (File Number: 1-105-05-158).

Combined immune checkpoint inhibitors of CTLA4 and PD-1 for hepatic melanoma of unknown primary origin: A case report

BACKGROUND

Melanoma is uncommonly found in lymph nodes, subcutaneous tissue, or visceral organs without a primary lesion, where it is identified as metastatic melanoma with unknown primary (MUP). Hepatic MUP is extremely rare and has a poor prognosis. There is limited information on its pathogenesis, clinical and imaging features, and pathological findings. There are no guidelines for the use of immune checkpoint inhibitors (ICIs) in hepatic MUP, and the treatment outcome has rarely been reported.

CASE SUMMARY

A 42-year-old woman presented to our hospital with hepatic tumors found incidentally during a routine check-up. Contrast-enhanced abdominal com-puterized tomography showed multiple mass lesions in the liver. Pathological results revealed melanoma, which was confirmed by immunohistochemical staining for HMB-45(+), Melan-A(+), S-100(+), and SOX10(+). There was no evidence of primary cutaneous, ocular, gastrointestinal, or anal lesion on a comprehensive examination. The patient was diagnosed with hepatic MUP. She received combined antibodies against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4, ipilimumab) and programmed death protein-1 (PD-1, nivolumab). She died of hepatic failure 9 mo after hepatic MUP was diagnosed. This the first case of hepatic MUP treated with combined ipilimumab and nivolumab, who showed better outcome than previous cases.

CONCLUSION

Combined ICIs of PD-1 and CTLA-4 may be considered as the first-line therapy for patients with hepatic MUP.

Efficacy and Safety of Supplemental Transarterial Chemoembolization Through Extrahepatic Collateral Arteries with Drug-eluting Beads: Treatment for Unresectable Hepatocellular Carcinoma

Purpose

To evaluate the therapeutic efficacy and safety of supplement transarterial chemoembolization (TACE) with drug-eluting beads TACE (DEB-TACE) through extrahepatic collateral (EHC) arteries for the treatment of hepatocellular carcinoma (HCC).

Patients and Methods

In this retrospective study, 61 unresectable HCC patients with treatment-naïve EHC blood supplies who received TACE from January 2016 to March 2019 were enrolled; of these patients, 42 (68.9%) received DEB-TACE, and 19 (31.1%) received cTACE. The hepatic tumor feeding arteries were treated in the same TACE session if it presented. The tumor response, time-to-progression (TTP), and overall survival (OS) were analyzed. Safety was assessed based on the occurrence of liver function deterioration and major complications within three months after TACE.

Results

DEB-TACE showed better efficacy than cTACE in the disease control rate (p=0.001), overall response rate (p=0.005), the TTP (eight months vsthree months, p=0.002) and the OS (23.8 months vs nine months, p=0.045). Nine patients in the DEB-TACE group and one patient in the cTACE group were downstaged to resection or liver transplantation (21.4% vs 5.3%, p=0.151). DEB-TACE and cTACE have no difference in the acute and chronic liver toxicity. With regard to complications, there was no significant difference in the occurrence of both major (16.7% vs 21.1%, p=0.72) and minor (57.1% vs 47.4%, p=0.48) complications between DEB-TACE and cTACE.

Conclusion

DEB-TACE through EHC arteries has a potential therapeutic effect in the treatment of unresectable HCC, with comparable safety compared with cTACE.

Post-operative assessment in patients after liver transplantation: imaging parameters associated with 1-year graft failure

PURPOSE

To identify post-liver transplant CT findings which predict graft failure within 1 year.

MATERIALS AND METHODS

We evaluated the CT scans of 202 adult liver transplants performed in our institution who underwent CT within 3 months after transplantation. We recorded CT findings of liver perfusion defect (LPD), parenchymal homogeneity, and the diameters and attenuations of the hepatic vessels. Findings were correlated to 1-year graft failure, and interobserver variability was assessed.

RESULTS

Forty-one (20.3%) of the 202 liver grafts failed within 1 year. Graft failure was highly associated with LPD (n = 18/25, or 67%, versus 15/98, or 15%, p < 0.001), parenchymal hypoattenuation (n = 20/41, or 48.8% versus 17/161, or 10.6%, p < 0.001), and smaller diameter of portal veins (right portal vein [RPV], 10.7 ± 2.7 mm versus 14.7 ± 2.2 mm, and left portal vein [LPV], 9.8 ± 3.0 mm versus 12.4 ± 2.2 mm, p < 0.001, respectively). Of these findings, LPD (hazard ratio [HR], 5.43, p < 0.001) and small portal vein diameters (HR, RPV, 3.33, p < 0.001, and LPV, 3.13, p < 0.05) independently predicted graft failure. All the measurements showed fair to moderate interobserver agreement (0.233~0.597).

CONCLUSION

For patients who have CT scan within the first 3 months of liver transplantation, findings of LPD and small portal vein diameters predict 1-year graft failure.

KEY POINTS

•Failed grafts are highly associated with liver perfusion defect, hypoattenuation, and small portal vein. •Right portal vein < 11.5 mm and left portal vein < 10.0 mm were associated with poor graft outcome. •Liver perfusion defect and small portal vein diameter independently predicted graft failure.

Contact behavior of focused ion beam deposited Pt on p-type Si nanowires

Pt contact on p-Si nanowires (NWs) using Ga-ion-induced deposition by a focused ion beam was formed with a specific contact resistance (rho(c)) of 1.54 x 10(-6) Omega cm(2). Ohmic behavior is caused by Ga-ion-induced amorphization of Si NWs underneath the Pt contact. A very low Schottky barrier height associated with interface states raised from Pt-amorphized Si junction and with an image force induced by the applied bias can be implemented to elucidate ultralow rho(c). The value of rho(c) lower than that of any known contact to Si NWs demonstrates a practical method for integrating NWs in devices and circuits.

Mycobacterium immunogenum sp. nov., a novel species related to Mycobacterium abscessus and associated with clinical disease, pseudo-outbreaks and contaminated metalworking fluids: an international cooperative study on mycobacterial taxonomy

PCR-restriction enzyme pattern analysis of a 439 bp hsp65 gene segment identified 113 unique isolates among non-pigmented rapidly growing mycobacteria (RGM) from clinical and environmental sources that failed to match currently recognized species patterns. This group represented 40% of isolates recovered from bronchoscope contamination pseudo-outbreaks, 0% of disease-associated nosocomial outbreaks and 4% of routine clinical isolates of the Mycobacterium abscessus/Mycobacterium chelonae group submitted to the Mycobacteria/Nocardia laboratory for identification. It is grouped within the Mycobacterium fortuitum complex, with growth in less than 7 d, absence of pigmentation, positive 3-d arylsulfatase reaction and growth on MacConkey agar without crystal violet. It exhibited overlapping biochemical, antimicrobial susceptibility and HPLC characteristics of M. abscessus and M. chelonae. By 16S rRNA gene sequencing, these isolates comprised a homogeneous group with a unique hypervariable region A sequence and differed by 8 and 10 bp, respectively, from M. abscessus and M. chelonae. Surprisingly, this taxon contained two copies of the ribosomal operon, compared with single copies in the two related species. By DNA-DNA hybridization, this new group exhibited <30% homology with recognized RGM species. The name Mycobacterium immunogenum sp. nov. is proposed for this new taxon.

Use of on-line hydrogen/deuterium exchange to facilitate metabolite identification

Biotransformation studies performed on an investigational compound (I, represented by R1-CH(NH(2))-CO-N(R2)-CH(2)-S-R3) led to the identification of five metabolites (M1-M5). Based on LC/MS (liquid chromatography/mass spectrometry) analysis which included the use of H(2)O and D(2)O in the mobile phases, they were identified as the sulfoxide (M1), sulfone (M2), carbamoyl glucuronide (M3), N-glucuronide (M4), and N-glucoside (M5) metabolites, respectively. The structure of M3, a less commonly seen carbamoyl glucuronide metabolite, was established using on-line H/D (hydrogen/deuterium) exchange experiments conducted by LC/MS. H/D exchange experiments were also used to distinguish the S-oxidation structures of M1 and M2 from hydroxylation. Herein, the application of deuterium oxide as the LC/MS mobile phase for structural elucidation of drug metabolites in biological matrices is demonstrated.

Parallel extraction columns and parallel analytical columns coupled with liquid chromatography/tandem mass spectrometry for on-line simultaneous quantification of a drug candidate and its six metabolites in dog plasma

A method with parallel extraction columns and parallel analytical columns (PEC-PAC) for on-line high-flow liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for simultaneous quantification of a drug candidate and its six metabolites in dog plasma. Two on-line extraction columns were used in parallel for sample extraction and two analytical columns were used in parallel for separation and analysis. The plasma samples, after addition of an internal standard solution, were directly injected onto the PEC-PAC system for purification and analysis. This method allowed the use of one of the extraction columns for analyte purification while the other was being equilibrated. Similarly, one of the analytical columns was employed to separate the analytes while the other was undergoing equilibration. Therefore, the time needed for re-conditioning both extraction and analytical columns was not added to the total analysis time, which resulted in a shorter run time and higher throughput. Moreover, the on-line column extraction LC/MS/MS method made it possible to extract and analyze all seven analytes simultaneously with good precision and accuracy despite their chemical class diversity that included primary, secondary and tertiary amines, an alcohol, an aldehyde and a carboxylic acid. The method was validated with the standard curve ranging from 5.00 to 5000 ng/mL. The intra- and inter-day precision was no more than 8% CV and the assay accuracy was between 95 and 107%.

A rotaxane-like complex with controlled-release characteristics

A rotaxane-like complex, based on a dumbbell-shaped component containing an NH(2)(+) recognition site for a [25]crown-8 ring component and a slippage stopper in the form of a p-(tert-butyl)phenyl group, has been synthesized by a "threading-followed-by-stoppering" approach. The half-life for dissociation of this complex, which is very sensitive to its environment, can be varied from minutes to months by changing the temperature and the polarity of the solvent.

Phosphorylated morpholine acetal human neurokinin-1 receptor antagonists as water-soluble prodrugs

The regioselective dibenzylphosphorylation of 2 followed by catalytic reduction in the presence of N-methyl-D-glucamine afforded 2-(S)-(1-(R)-(3, 5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluoro)phenyl-4-(5-(2- phosphoryl-3-oxo-4H,-1,2,4-triazolo)methylmorpholine, bis(N-methyl-D-glucamine) salt, 11. Incubation of 11 in rat, dog, and human plasma and in human hepatic subcellular fractions in vitro indicated that conversion to 2 would be expected to occur in vivo most readily in humans during hepatic circulation. Conversion of 11 to 2 occurred rapidly in vivo in the rat and dog with the levels of 11 being undetectable within 5 min after 1 and 8 mg/kg doses iv in the rat and within 15 min after 0.5, 2, and 32 mg/kg doses iv in the dog. Compound 11 has a 10-fold lower affinity for the human NK-1 receptor as compared to 2, but it is functionally equivalent to 2 in preclinical models of NK-1-mediated inflammation in the guinea pig and cisplatin-induced emesis in the ferret, indicating that 11 acts as a prodrug of 2. Based in part on these data, 11 was identified as a novel, water-soluble prodrug of the clinical candidate 2 suitable for intravenous administration in humans.

Substance P receptor antagonist I: conversion of phosphoramidate prodrug after i.v. administration to rats and dogs

A water-soluble phosphoramidate prodrug (L-758,298, compound I) of the potent and selective human Substance P receptor antagonist L-754, 030 (compound II) is under development as an i.v. drug for treatment of emesis, migraine, and chronic pain. Compound I undergoes hydrolysis readily to II under acidic conditions. In the studies reported herein, we investigated the stability of I in blood and hepatic subcellular fractions from rats, dogs, and humans as well as the conversion of I to II in rats and dogs after i.v. dosing. Compound I was converted to II rapidly in rat blood but was stable in dog and human blood. However, the conversion was rapid in liver microsomes prepared from dogs and humans. As expected from the results of in vitro studies, the in vivo conversion of I to II was rapid after i.v. dosing of I to rats and dogs. The relative extent of exposure of II after i.v. dosing of I was estimated by comparing the dose-adjusted area under the plasma concentration versus time curve values of II after i.v. dosing of I with those after i.v. dosing of II. In rats, the extent of exposure was estimated to be approximately 90 and approximately 100% at 1 and 8 mg/kg, respectively; in dogs, that was approximately 59% at 0.5 mg/kg. A nonproportional increase in the area under the concentration versus time curve value of II with dose was observed after i.v. administration of I in dogs from 0.5 to 32 mg/kg, suggesting that the elimination of II might have been saturated at higher doses.

Mycobacterium wolinskyi sp. nov. and Mycobacterium goodii sp. nov., two new rapidly growing species related to Mycobacterium smegmatis and associated with human wound infections: a cooperative study from the International Working Group on Mycobacterial Taxonomy

Previous investigations demonstrated three taxonomic groups among 22 clinical isolates of Mycobacterium smegmatis. These studies were expanded to 71 clinical isolates, of which 35 (49%) (group 1) were identical to five ATCC reference strains including the type strain ATCC 19420T. Twenty-eight isolates (39%) were group 2, and eight isolates (11%) were group 3. Isolates of groups 2 and 3 were most often associated with post-traumatic or post-surgical wound infections including osteomyelitis, were susceptible to sulfamethoxazole, amikacin, imipenem and the tetracyclines, variably resistant to clarithromycin, and susceptible (group 1), intermediately resistant (group 2) or resistant (group 3) to tobramycin. The three groups were similar by routine biochemical and growth characteristics, but had different mycolic acid dimethoxy-4-coumarinylmethyl ester elution patterns by HPLC and different PCR-restriction enzyme patterns of a 439 bp fragment of the hsp-65 gene. Group 3 isolates differed from group 1 by 18 bp by 16S rRNA sequencing and exhibited < 25% homology by DNA-DNA hybridization, being most closely related to Mycobacterium mageritense. The 16S rRNA of group 1 and group 2 isolates differed by only 3 bp, but by DNA-DNA hybridization they exhibited only 40% homology. The following names are proposed: Mycobacterium goodii sp. nov. for group 2 isolates (type strain ATCC 700504T = MO69T), Mycobacterium wolinskyi sp. nov. for group 3 isolates (type strain ATCC 700010T = MO739T) and Mycobacterium smegmatis sensu stricto for group 1 isolates.

Mycophenolic acid increases apoptosis, lysosomes and lipid droplets in human lymphoid and monocytic cell lines

BACKGROUND

Mycophenolic acid (MPA), a selective inhibitor of inosine monophosphate dehydrogenase, is the active agent of the immunosuppressive drug, mycophenolate mofetil (MMF). Previous studies have shown that MPA inhibits DNA synthesis in T and B lymphocytes by blocking de novo guanosine synthesis, and that MPA induces monocyte differentiation. MMF is being used for prevention of organ graft rejection and has also shown efficacy in rheumatoid arthritis trials. This study was designed to determine if apoptosis also plays a role in the immunosuppressive and anti-inflammatory effects of MMF.

METHODS

Cultured human T lymphocytic (MOLT-4) and monocytic (THP-1 and U937) cell lines were treated with MPA. Apoptosis, cell viability, DNA content, lipid content, cell volume, and lysosomes were measured by a variety of microscopic, flow cytometric, and biochemical techniques.

RESULTS

MPA inhibits proliferation, arrests cell cycle in S phase, and increases apoptosis in all three cell lines. Exogenous guanosine added within 24 hr of MPA treatment, but not later, partially reversed MPA-induced apoptosis in MOLT-4 cells. MPA increased lipid droplets in all three cell lines and increased both cell volumes and numbers of lysosomes in the monocytic cell lines. In both monocytic cell lines, MPA also reduced the number of nuclei containing nucleoli and greatly increased neutral lipids, primarily triacylglycerols, suggesting that these cells were differentiating.

CONCLUSIONS

Increased apoptosis and terminal differentiation of both lymphocytes and monocytes may promote the antiproliferative, immunosuppressive, and anti-inflammatory effects of MMF seen clinically in transplantation and rheumatoid arthritis.

L-770,644: a potent and selective human beta3 adrenergic receptor agonist with improved oral bioavailability

L-770,644 (9c) is a potent and selective agonist of the human beta3 adrenergic receptor (EC50 = 13 nM). It shows good oral bioavailability in both dogs and rats (%F = 27), and is a full agonist for glycerolemia in the rhesus monkey (ED50 = 0.21 mg/kg). Based on its desirable in vitro and in vivo properties, L-770,644 was chosen for further preclinical evaluation.

Studies on cytochrome P-450-mediated bioactivation of diclofenac in rats and in human hepatocytes: identification of glutathione conjugated metabolites

The nonsteroidal anti-inflammatory drug diclofenac causes a rare but potentially fatal hepatotoxicity that may be associated with the formation of reactive metabolites. In this study, three glutathione (GSH) adducts, namely 5-hydroxy-4-(glutathion-S-yl)diclofenac (M1), 4'-hydroxy-3'-(glutathion-S-yl)diclofenac (M2), and 5-hydroxy-6-(glutathion-S-yl)diclofenac (M3), were identified by liquid chromatography-tandem mass spectrometry analysis of bile from Sprague-Dawley rats injected i.p. with a single dose of diclofenac (200 mg/kg). These adducts presumably were formed via hepatic cytochrome P-450 (CYP)-catalyzed oxidation of diclofenac to reactive benzoquinone imines that were trapped by GSH conjugation. In support of this hypothesis, M1, M2, and M3 were generated from diclofenac in incubations with rat liver microsomes in the presence of NADPH and GSH. Increases in adduct formation were observed when incubations were performed with liver microsomes from phenobarbital- or dexamethasone-treated rats. Adduct formation was inhibited by polyclonal antibodies against CYP2B, CYP2C, and CYP3A (40-50% inhibition at 5 mg of IgG/nmol of CYP) but not by an antibody against CYP1A. Maximal inhibition was obtained when the three inhibitory antibodies were used in a cocktail fashion (70-80% inhibition at 2.5 mg of each IgG/nmol of CYP). These data suggest that diclofenac undergoes biotransformation to reactive metabolites in rats and that CYP isoforms of the 2B, 2C, and 3A subfamilies are involved in this bioactivation process. With respect to CYP2C isoforms, rat hepatic CYP2C7 and CYP2C11 were implicated as mediators of the bioactivation based on immunoinhibition studies using antibodies specific to CYP2C7 and CYP2C11. Screening for GSH adducts also was carried out in human hepatocyte cultures containing diclofenac, and M1, M2, and M3 again were detected. It is possible, therefore, that reactive benzoquinone imines may be formed in vivo in humans and contribute to diclofenac-mediated hepatic injury.

Roles of human hepatic cytochrome P450s 2C9 and 3A4 in the metabolic activation of diclofenac

Recently, it was shown that diclofenac was metabolized in rats to reactive benzoquinone imines via cytochrome P450-catalyzed oxidation. These metabolites also were detected in human hepatocyte cultures in the form of glutathione (GSH) adducts. This report describes the results of further studies aimed at characterizing the human hepatic P450-mediated bioactivation of diclofenac. The reactive metabolites formed in vitro were trapped by GSH and analyzed by LC/MS/MS. Thus, three GSH adducts, namely, 5-hydroxy-4-(glutathion-S-yl)diclofenac (M1), 4'-hydroxy-3'-(glutathion-S-yl)diclofenac (M2), and 5-hydroxy-6-(glutathion-S-yl)diclofenac (M3), were identified in incubations of diclofenac with human liver microsomes in the presence of NADPH and GSH. The formation of the adducts was taken to reflect the intermediacy of the corresponding putative benzoquinone imines. While M2 was the dominant metabolite over a substrate concentration range of 10-50 microM, M1 and M3 became equally important products at >/=100 microM diclofenac. The formation of M2 was inhibited by sulfaphenazole or an anti-P450 2C9 antibody (5-10% of control values). The formation of M1 and M3 was inhibited by troleandomycin, ketoconazole, or an anti-P450 3A4 antibody (30-50% of control values). In studies in which recombinant P450 isoforms were used, M2 was generated only by P450 2C9-catalyzed reaction, while M1 and M3 were produced by P450 3A4-catalyzed reaction. Good correlations were established between the extent of formation of M2 and P450 2C9 activities (r = 0.93, n = 10) and between the extent of formation of M1 and M3 and P450 3A4 activities (r = 0.98, n = 10) in human liver microsomal incubations. Taken together, the data suggest that the biotransformation of diclofenac to M2 is P450 2C9-dependent, whereas metabolism of the drug to M1 and M3 involves mainly P450 3A4. Although P450s 2C9 and 3A4 both catalyze the bioactivation of diclofenac, P450 2C9 is capable of producing the benzoquinone imine intermediate at lower drug concentrations which may be more clinically relevant.

Disposition of L-732,531, a potent immunosuppressant, in rats and baboons

L-732,531 is a semi-synthetic analog of the macrolide tacrolimus (Prograf(R)). Like tacrolimus, L-732,531 is a potent immunosuppressant. In this study, its absorption, distribution, metabolism, and excretion were studied in rats and baboons. In rats, its blood and plasma levels were similar, whereas in baboons, its blood levels were, on average, twice as high as those in plasma. This was consistent with the in vitro blood-to-plasma ratio of L-732, 531, which in these two species, as well as in humans, was much lower than that of tacrolimus and showed a minimal concentration dependence. After iv administration to rats, the blood and plasma clearance of L-732,531 decreased from approximately 60 ml/min/kg at 0.2 mg/kg to 30 ml/min/kg when dosed at 1 and 3 mg/kg. After oral administration, plasma area under the concentration vs. time curve (AUC) and maximal plasma concentration (Cmax) increased more than proportionally to the dose. At 1, 5, and 15 mg/kg, plasma AUC was 29, 466, and 2832 ng.hr/ml, respectively, and Cmax was 10, 129, and 304 ng/ml, respectively. Bioavailability, although compromised by nonlinear kinetics, was estimated to be between 8% and 18%. In baboons, the clearance of L-732,531 was lower than that in rats, especially when calculated from blood concentrations (12 ml/min/kg at 0.2 mg/kg and 8 ml/min/kg at 1 mg/kg). After oral dosing, baboon plasma AUC and Cmax were much lower than those in rats, but as in rats, they increased more than proportionally with increasing doses. The bioavailability of L-732,531 in baboons was estimated at 3%, 9%, and 24% when animals were dosed at 5, 15, and 26 mg/kg po, respectively. After oral administration of [3H]L-732,531 at 5 mg/kg, approximately 32% of the radioactivity was recovered in bile and urine of rats, compared with 9% in baboons. High-performance liquid chromatography profiles of rat and baboon plasma, bile, urine, and feces indicated that L-732,531 was metabolized extensively to a complex mixture of products. Some intact parent drug was observed in feces of orally dosed animals, indicating incomplete absorption. In vitro, L-732,531 was metabolized more extensively by baboon liver microsomes than rat or human microsomes. Its metabolism in human liver microsomes was shown to be catalyzed primarily by cytochrome P450 3A isozymes.

The saturation characteristics of glucose transport in bovine retinal pigment epithelium

PURPOSE

To study the saturation characteristics of the glucose transport across the bovine retinal pigment epithelium(RPE).

METHODS

The bovine RPE preparations were munted with a modified Ussing chamber. The L-[3H]-glucose and 3-O-methyl-D-[14C]-glucose fluxes across the RPE from the choroid to retina were studied at different glucose concentrations.

RESULTS

The glucose transport was found to be stereospecific, with 3-O-methyl-D-glucose (MDG) being transported about three times faster than L-glucose. The glucose transport showed typical saturation characteristics in Michaelis-Menten fashion. The Vmax and the Km of corrected MDG were 2452 nmol cm-2h-1 and 30.8 mM respectively. It was shown that the glucose transport system was saturated at 61.6 mM.

CONCLUSIONS

The saturation characteristics of the corrected MDG flux suggested that the capacity of glucose transport through the bovine RPE is immense.

Species differences in N-glucuronidation

Glucuronidation of amines has been shown to exhibit species differences in vitro and in vivo. Substrates for N-glucuronidation can be classified according to the chemical structures of the resulting glucuronides into two groups: compounds that form non-quaternary N-conjugates, and those that form the quaternary counterparts. For compounds of the former class-such as sulfonamides, arylamines, and alicyclic, cyclic, and heterocyclic amines-species differences appear to be less striking and are of a quantitative nature. No one common laboratory animal species used routinely in metabolism research (e.g. rat, mouse, dog, non-human primate, rabbit, and guinea pig) has been shown to be deficient in N-glucuronidation when all of the substrates studied and reported are taken into consideration. The ability of a species to form N-glucuronides is compound-dependent, although rabbit and guinea pig appear to exhibit the highest capacity for this bioconjugation among preclinical species. For tertiary amines, most notably the tricyclic antidepressant and antihistamine drugs, N-glucuronidation is commonly observed in non-human primates and man. There are examples, however, of quaternary glucuronidation occurring in lower animal species. In exploring species differences in amine conjugation in vivo, it is noted that the apparent absence of N-glucuronides in animal urine may not reflect the inability of that species to form such conjugates, since the N-glucuronides may be excreted in bile. Problems such as degradation or low recoveries commonly encountered in isolation and identification of in vivo metabolites further complicate the interpretation of data. Because of the wide range of pKa values exhibited by various classes of amines, caution also should be exercised for in vitro studies since incubation conditions for N-glucuronidation often are substrate- and species-dependent. Explanations for the species differences observed in N-glucuronidation appear to be emerging as rapid advances are made in the understanding of the glucuronosyltransferases at the molecular level. More information, however, remains to be gathered from the glucuronosyltransferase genes of animal species other than humans before a better understanding of species differences in N-glucuronidation can be achieved.

3-Pyridyloxypropanolamine agonists of the beta 3 adrenergic receptor with improved pharmacokinetic properties

Pyridyloxypropanolamines L-749,372 (8, beta 3 EC50 = 3.6 nM) and L-750,355 (29, beta 3 EC50 = 13 nM) are selective partial agonists of the human receptor, with 33% and 49% activation, respectively. Both stimulate lipolysis in rhesus monkeys (ED50 = 2 and 0.8 mg/kg, respectively), with minimal effects on heart rate. Oral bioavailability in dogs, 41% for L-749,372 and 47% for L-750,355, is improved relative to phenol analogs.

A selective human beta3 adrenergic receptor agonist increases metabolic rate in rhesus monkeys

Activation of beta3 adrenergic receptors on the surface of adipocytes leads to increases in intracellular cAMP and stimulation of lipolysis. In brown adipose tissue, this serves to up-regulate and activate the mitochondrial uncoupling protein 1, which mediates a proton conductance pathway that uncouples oxidative phosphorylation, leading to a net increase in energy expenditure. While chronic treatment with beta3 agonists in nonprimate species leads to uncoupling protein 1 up-regulation and weight loss, the relevance of this mechanism to energy metabolism in primates, which have much lower levels of brown adipose tissue, has been questioned. With the discovery of L-755,507, a potent and selective partial agonist for both human and rhesus beta3 receptors, we now demonstrate that acute exposure of rhesus monkeys to a beta3 agonist elicits lipolysis and metabolic rate elevation, and that chronic exposure increases uncoupling protein 1 expression in rhesus brown adipose tissue. These data suggest a role for beta3 agonists in the treatment of human obesity.

Pharmacokinetics and disposition of the oxytocin receptor antagonist L-368,899 in rats and dogs

L-368,899 is a potent, orally-active oxytocin antagonist that completed phase I clinical trials for the prevention of preterm labor. The pharmacokinetics and disposition of L-368,899 were studied in rats (female and male) and dogs (female), the two species used in the toxicology studies. L-368,899 exhibited similar pharmacokinetics in rats and dogs. After iv dosing at 1, 2.5, and 10 mg/kg, the compound had a t1/2 of approximately 2 hr and plasma clearance between 23 and 36 ml/min/kg at all doses and in both species. The exception was female rats at the 10 mg/kg dose where plasma clearance decreased to 18 ml/min/kg. The Vdss was between 2.0 and 2.6 liters/kg for rats and 3.4 to 4.9 liters/kg for dogs. After oral doing, L-368,899 was rapidly absorbed. Mean Cmax values were achieved at <1 hr at the low doses (25 mg/kg in rats and 5 mg/kg in dogs) and between 1 and 4 hr at the higher doses (100 mg/kg in rats and 33 mg/kg in dogs). In bile duct-cannulated female rats, approximately 70% of a radioactive 28 mg/kg dose was recovered in bile and urine within 72 hr post dose. Plasma drug concentrations were higher in female than in male rats especially at the 25 mg/kg dose, where mean AUC values were 4.5-fold higher in the females. In both rats and dogs, plasma drug levels increased more than proportionally with increasing oral dose. In female rats, the mean AUC increased by approximately 8-fold between 25 and 100 mg/kg, while in female dogs, the mean AUC at the 33 mg/kg dose was 12-fold higher than that at 5 mg/kg. Oral bioavailability was estimated at 14% and 18% for the 5 mg/kg dose in female and male rats, respectively, 41% for the 25 mg/kg dose in male rats and 17% and 41%, respectively, for the 5 and 33 mg/kg doses in dogs. Owing to nonlinear kinetics, bioavailability could not be calculated for the other oral doses. L-368,899 was metabolized extensively in both species after iv and oral dosing, with <10% of the dose excreted unchanged. The main route of elimination was via the feces, which contained >70% of the radioactive dose by 48 hr, primarily as metabolites. The gender and dose dependence of the pharmacokinetics of L-389,899 in rats were attributed to gender differences in metabolizing capacity and saturation of hepatic metabolism, respectively. This conclusion was based primarily on results from experiments comparing the rate of in vitro metabolism of L-368,899 in liver microsomes, which showed that the Vmax and KM values for L-368,899 were 4-fold lower in female than in male rat liver microsomes.

Orally active inhibitors of human leukocyte elastase. II. Disposition of L-694,458 in rats and rhesus monkeys

The disposition of L-694,458, a potent monocyclic beta-lactam inhibitor of human leukocyte elastase, was studied in male Sprague-Dawley rats and rhesus monkeys. After iv dosing, L-694,458 exhibited similar pharmacokinetic parameters in rats and rhesus monkeys. The mean values for its plasma clearance, terminal half-life, and volume of distribution at steady state were 27 ml/min/kg, 1.8 hr, and 4.0 liters/kg in rats and 34 ml/min/kg, 2.3 hr, and 5 liters/kg in rhesus monkeys. The bioavailability of a 10 mg/kg oral dose was higher in rats (65%) than in rhesus monkeys (39%). In both species, concentrations of L-694,458 in plasma increased more than proportionally when the oral dose was increased from 10 mg/kg to 40 mg/kg. In monkeys a protracted plasma concentration-time profile was observed at 40 mg/kg, characterized by a delayed T(max) (8-24 hr) and a long terminal half-life (6 hr). [3H]L-694,458 was well absorbed after oral dosing to rats at 10 mg/kg, as indicated by the high recovery of radioactivity in bile (83%) and urine (6%) of bile duct-cannulated rats. Only approximately 5% or less of the radioactivity in bile, urine, and feces was a result of intact L-694,458, indicating that the compound was being eliminated by metabolism, followed by excretion of the metabolites in feces, via bile. Demethylenation of the methylenedioxyphenyl group resulting in the catechol was the primary metabolic pathway in human and rhesus monkey liver microsomes. In rat liver microsomes, the major metabolite was the N-oxide of the methyl-substituted piperazine nitrogen. In rats dosed iv and orally with [3H]L-694,458, concentrations of radioactivity were highest in the lung (the primary target tissue), adrenals, and liver. L-694,458 was unstable in rat blood and plasma, degrading via a pathway believed to be catalyzed by B-esterases and to involve cleavage of the beta-lactam ring and loss of the methylpiperazine phenoxy group. In vitro studies indicated that in human liver, L-694,458 was metabolized by CYP3A and 2C isozymes, and in both monkey and human liver microsomes the compound acted as an inhibitor of testosterone 6beta-hydroxylation.

Orally active inhibitors of human leukocyte elastase. III. Identification and characterization of metabolites of L-694,458 by liquid chromatography-tandem mass spectrometry

The in vitro and in vivo metabolism of N-[1(R)-(1,3-benzodioxol-5-yl)butyl]-3,3-diethyl-2(S)-[4-[(4-methy l-1-piperazinyl)carbonyl]phenoxy]-4-oxo-1-azetidinecarboxamide (L-694,458) was studied in male Sprague-Dawley rats and rhesus monkeys. Analysis by LC-MS/MS and NMR revealed that the major metabolite generated in incubations with rat liver microsomes resulted from N-oxidation of the piperazine group, while the major metabolite generated in monkey liver microsomes was the catechol that resulted from O-dealkylation of the methylenedioxyphenyl group. Other metabolites observed in these incubations include the piperazine N-desmethyl, several monohydroxylated derivatives of the parent compound, and three products that resulted from cleavage of the beta-lactam ring. Incubations of parent compound with rat hepatocytes in culture generated two major metabolites that resulted from cleavage of the piperazine ring with the loss of an ethylene group from one side of the ring; one of these metabolites retained the piperazine N-methyl group, while the other did not. The metabolite profiles in vivo were similar to those observed in vitro, but they were much more complex owing to secondary and, in some cases, tertiary biotransformations of many of the primary metabolites. Bile obtained from orally dosed rats contained more than 40 parent-related components, and many of these metabolites had arisen from piperazine ring cleavage.

Disposition and metabolism of finasteride in dogs

Finasteride (FIN) is a potent 5 alpha-reductase inhibitor that has shown clinical success in treating men with benign prostatic hyperplasia. In the study of biological effects and metabolism of FIN in animals, the dog serves as the primary modality. This study was conducted to determine the pharmacokinetics and fate of FIN after oral administration of single doses of [14C]FIN to dogs at 10 and 80 mg/kg (N = 2 and 3, respectively), and also after intravenous infusion at 5 mg/kg (N = 2). Plasma, urine, and feces were analyzed for total 14C content. Parent drug and metabolites in plasma and excreta were measured by HPLC/UV/radioassay and identified by NMR spectroscopy and MS, FIN was subject to extensive biotransformation before excretion. Structures were determined for the major metabolites in plasma, urine, and feces. The primary metabolic events for FIN were hydroxylation of the t-butyl side chain to give hydroxymethyl-FIN (metabolite I), which is oxidized further to form the carboxylic acid derivative (metabolite IV), and hydroxylation at positions B alpha and 15. Terminal half-life of FIN after the intravenous dose was 3.4 hr. Plasma clearance and volume of distribution at steady-state were 4.8 ml/min/kg and 1.1 liter/kg. Dogs showed rapid absorption after oral administration of the low dose, with Cmax reached in the 1-2 hr, bioavailability was estimated to be > 90%. After either dosing route, 45% of the plasma radioactivity (as represented by AUC) was parent drug, 43% was metabolite I, and 1% was metabolite IV. After oral administration, the 80 mg/kg dose was absorbed slowly, with the highest levels of radioactivity in plasma reached in 4-30 hr. Average Cmax value for FIN and metabolite I increased in a dose-related, but nonproportional, manner. Compared with the 10 mg/kg dose, it seems the higher dose was reasonably well-absorbed, as indicated by the nearly proportional increase of AUC values of total radioactivity and FIN. Composition of plasma metabolites observed at the 80 mg/kg dose level was similar to that observed previously for the low dose, suggesting that an increase in plasma exposure was effected in dogs receiving FIN at 80 mg/kg in toxicity studies. Most of the administered radioactivity was recovered in feces after all doses. Little of the intravenous and low oral doses, but > 50% of the 80 mg/kg oral dose, was excreted as intact FIN, suggesting that metabolism might have been saturated at the high dose.

Orally active inhibitors of human leukocyte elastase. I. Disposition of L-683,845 in rats and rhesus monkeys

L-683,845 is an orally active inhibitor of human leukocyte elastase. Its disposition was studied in rats and rhesus monkeys after dosing with a 3H- or 14C-labeled compound intravenously at 5 mg/kg and orally at 10 mg/kg. L-683,845 exhibited different pharmacokinetics in these two species. In rats, L-683,845 was well-absorbed after oral dosing, with a maximum concentration of 6 microg/ml at 2 hr and bioavailability of approximately 100%. After intravenous dosing, it was cleared slowly at approximately 3 ml/min/kg, with a terminal half-life of approximately 7 hr and a volume of distribution at steady-state of 1 liter/kg. After both intravenous and oral dosing, L-683,845 comprised 50-95% of plasma radioactivity. About 75% of the intravenous and 87% of the oral dose were recovered in the feces as parent and/or conjugates, with the remaining fraction recovered in the urine as polar components. In rhesus monkeys, maximum concentration after oral dosing was only 0.25 microg/ml, and bioavailability was 50%. Plasma clearance was 8-fold higher, at 23 ml/min/kg, and volume of distribution at steady-state larger, at 2 liters/kg, than in rats. The terminal half-life of L-683,845 could not be determined accurately after intravenous dosing, but seemed to be long in orally dosed animals, approximately 13 hr. Intact L-683,845 was a minor component in plasma comprising only approximately 20% of the radioactivity at most time points. Moreover, persistent levels of radioactivity were detected in plasma and urine of rhesus monkeys even at 1-month postdose, and > or = 25% of the radioactivity in plasma was irreversibly bound to proteins at the later time points. Recovery of the radioactivity was incomplete, with only 77% of the intravenous and 43% of the oral dose recovered over a 4-day period. L-683,845-derived radioactivity distributed to all major rat tissues, with highest levels in the liver followed by the small intestine, adrenals, kidneys, and lungs. Radioactivity concentrations in the liver were high even at 24 hr, 22.7 microg eq/g. A large portion of the intravenous dose was recovered in the small intestine, approximately 40% at 2 hr, indicating rapid and extensive biliary excretion. L-683,845 was metabolized primarily to the acyl glucuronide, which was very unstable in rat plasma, and was subject to hydrolysis to L-683,845 and rearrangement. The glucuronide and L-683,845 were degraded in rat plasma by opening the beta-lactam ring and loss of the C4 substituent followed by decarboxylation to give an olefin and/or decomposition to the monosubstituted urea. Based on inhibition by organophosphorus compounds, it is speculated that their degradation is catalyzed by a type B esterase.

Pharmacokinetics and disposition of L-692,429. A novel nonpeptidyl growth hormone secretagogue in preclinical species

L-692,429 is a novel nonpeptidyl growth hormone secretagogue that has been demonstrated to stimulate growth hormone secretion in rats, dogs, and humans after intravenous administration. We have examined the pharmacokinetics and disposition of L-692,429 in male Sprague-Dawley rats, beagle dogs, and chimpanzees. Plasma clearance (CLp) of L-692,429 in dogs after intravenous dosing was approximately 18 ml/min/kg and was constant between the doses of 0.1 and 0.9 mg/kg. In rats, CLp after intravenous dosing increased from 3 to 12 ml/min/kg in a dose-dependent manner between 0.1 and 5 mg/kg. In chimpanzees, CLp after an intravenous dose of L-692,429 at 0.5 mg/kg was 5.7 ml/min/kg. In vitro binding of L-692,429 to plasma proteins of dogs, chimpanzees, and humans was approximately 87%, 94%, and 93.5%, respectively, and was independent of concentration. In contrast, plasma binding of L-692,429 was concentration-dependent in rats and decreased from 98.5% to 90.6% between 0.01 and 10 micrograms/ml. Metabolism of L-692,429 was minimal in rats, but moderate in dogs, with the major metabolite being a derivative monohydroxylated at the benzolactam moiety. Thus, the faster clearance of L-692,429 in dogs likely is caused by less extensive plasma protein binding and higher metabolic clearance. The nonlinear pharmacokinetics in rats probably is the result of concentration-dependence in plasma binding. The results of these studies suggest that plasma protein binding plays a major role in determining the values of CLp of L-692,429 among the species. After an intravenous dose of [3H]L-692,429 to rats, liver, kidney, lung, and heart had the highest levels of radioactivity at the early time points, but the gastrointestinal tract had increasing concentrations at later time points. Most of the radioactivity was cleared from all tissues by 24 hr, indicating that L-692,429 did not accumulate in tissues. After intravenous dosing of [3H]L-692,429 to rats and dogs, recoveries of total radioactivity in urine and feces corresponded to approximately 10% and 90%, respectively. Greater than 70% of radioactivity was recovered in bile of rats within 24 hr after intravenous dosing of [3H]L-692,429, indicating that biliary excretion was the primary route of elimination. Based on the combined recoveries of the radioactive dose in bile and urine after an oral dose of L-692,429, oral absorption in rats was approximately 3%. The poor absorption may be the result of the zwitterionic nature of this compound.

Identification of human cytochrome P450 isozymes responsible for the in vitro oxidative metabolism of finasteride

Finasteride, a prescription drug for the treatment of benign prostatic hypertrophy and alleviation of symptoms associated with benign prostatic hypertrophy and alleviation of symptoms associated with benign prostatic hypertrophy, has been shown to be metabolized in rat hepatic microsomes by hydroxylation at the t-butyl group (omega-OH finasteride), followed by further oxidation to the corresponding acid (omega-oic acid finasteride), with omega-aldehyde finasteride as an intermediate. In this study, we identified specific human cytochrome P450 (CYP) isozyme(s) involved in the in vitro metabolism of [14C]finasteride using CYP isozyme-selective inhibitors and microsomes containing specific recombinant human CYP isozymes (expressed in human AHH-1 TK+/-cells). Each of the three steps of the oxidative pathway was examined separately by using [14C]finasteride and its consecutive metabolites (omega-OH finasteride and omega-aldehyde finasteride) as substrates, and human liver microsomes or expressed recombinant CYP isozymes as the enzyme source. Gestodene, a mechanism-based inhibitor of CYP3A isozymes, showed a concentration-dependent inhibition of the oxidative metabolism of [14C]finasteride. In addition, the respective omega-OH finasteride and omega-oic acid finasteride metabolites were generated only by microsomes containing recombinant CYP3A4, but not the other isozymes (CYP1A1, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP2E1). Similar results were obtained for the oxidation of omega-OH finasteride to omega-aldehyde finasteride, suggesting that human CYP3A isozymes were involved in the oxidation of omega-OH finasteride. When omega-aldehyde finasteride was incubated with human liver microsomes in the presence of an NADPH regenerating system, both the omega-oic acid finasteride and the omega-OH finasteride were detected, suggesting that oxidative and reductive reactions were occurring simultaneously and that they were NADPH- or NADP-dependent. Inhibitors of CYP3A isozymes inhibited the oxidation of omega-aldehyde finasteride in a concentration-dependent manner; an increase in the reduction was also observed, presumably caused by inhibition of the competitive oxidative reaction. Other selective CYP inhibitors for CYP1A1/2 (alpha-naphthoflavone), CYP2C8-10 (sulfaphenazole), CYP2D6 (quinidine), and CYP2E1 (diallylsulfone) showed minor or no effects on both reactions. Consistent with these results, only microsomes containing human recombinant CYP3A4 catalyzed the oxidation of omega-aldehyde finasteride to omega-oic acid finasteride. These results indicate that the oxidation of omega-aldehyde finasteride was NADPH-dependent and was mediated at least in part by CYP3A4. In addition, NAD-dependent enzymes in cytosolic, microsomal, and mitochondrial fractions were capable of oxidizing omega-aldehyde finasteride to omega-oic acid finasteride. Other cellular fractions, particularly mitochondria, were shown to convert finasteride to omega-oic acid finasteride in a similar fashion.

Mechanism of bioactivation and covalent binding of 2,4,6-trinitrotoluene

Studies were undertaken to investigate the mechanism of bioactivation and covalent binding of TNT. Incubation of [14C]TNT with rat liver microsomes in the presence of an NADPH generating system resulted in metabolism and covalent binding to microsomal proteins. Time-dependence studies showed that TNT was rapidly reduced to yield 4-hydroxylamino-2,6-dinitrotoluene (4HA), 4-amino-2,6-dinitrotoluene (4A) and 2-amino-4,6-dinitrotoluene (2A) as intermediates which were further metabolized to form 2,4-diamino-6-nitrotoluene (2,4DA) and 2,6-diamino-4-nitrotoluene (2,6DA). In contrast to the rapid disappearance of TNT, formation of covalent protein adducts increased with time, suggesting that the reactive intermediate was likely to be formed not directly from TNT but from proximal intermediates such as 4HA. The hypothesis that 4HA was more readily converted to the reactive intermediate than TNT was further supported by the increased levels of covalent adduct formation when [14C]4HA was incubated directly with liver microsomes. Covalent binding of TNT and 4HA was dependent on oxygen concentration. Higher levels of covalent adducts were formed when TNT was incubated aerobically (up to 50% oxygen concentration) than under anaerobic conditions. Covalent binding of [14C]4HA also increased with increasing oxygen concentrations. These results suggest that the reactive intermediate is likely to be an oxidized metabolite of 4HA, e.g. 4-nitroso-2,6-dinitrotoluene. Compounds containing a free sulfhydryl group (cysteine, N-acetylcysteine, GSH or 3,4-dichlorobenzenethiol) decreased the amount of covalent binding to various degrees, suggesting the involvement of the sulfhydryl group in adduct formation with TNT following bioactivation. Metabolic activation of TNT by liver microsomes required NADPH but not NADH as the cofactor. Incubation of [14C]TNT with purified rat liver NADPH cytochrome P450 reductase under either aerobic or anaerobic conditions yielded exclusively 4HA. In contrast, 2A and 4A were formed following incubation of TNT with the reconstituted system containing cytochrome P450, NADPH cytochrome P450, reductase and dilauroyl phosphatidylcholine. These observations suggest that the initial reduction of the nitro group can be catalyzed by NADPH cytochrome P450 reductase alone but cytochrome P450 is needed in the reduction of the hydroxylamine to the amine.

The role of drug metabolism in drug discovery: a case study in the selection of an oxytocin receptor antagonist for development

Drug discovery is a process involving multiple disciplines and interests. During the research phase of drug discovery, usually a large number of compounds are evaluated for biological activity and toxicological potential in animal species. Various types of problems with respect to pharmacodynamics, pharmacokinetics, and toxicity are commonly encountered at this stage. Drug metabolism, as a discipline participating in a drug discovery team, can play an important role in identifying factors underlying the problems, facilitate the optimal selection of compounds for further development, provide information on metabolites for possible improvement in drug design, and contribute to the identification of the appropriate animal species for subsequent toxicity testing. During the process of evaluating oxytocin receptor antagonists for further development for treatment of preterm labor, in vivo and in vitro drug metabolism studies conducted in rats, dogs, and monkeys contributed to the selection of L-368,899 as the development candidate on the basis of pharmacokinetic and metabolism observations. The presence of active N-demethylated metabolites of two other equipotent compounds in rats and dogs was found to be the major factor responsible for the discrepancy between oral bioavailability and efficacies observed for these 2 compounds. For L-368,899, a compound that demonstrated 20-40% oral bioavailability in rats, dogs, and chimpanzees, extensive first-pass metabolism rather than absorption was determined as the major factor responsible for the poor bioavailability (< 1%) in rhesus monkeys. In vitro metabolism studies with hepatic microsomes from rats, dogs, monkeys, and humans substantiated the conclusion that the rate of hepatic metabolism of L-368,899 in monkeys is faster than in the other species.

Biotransformation of losartan to its active carboxylic acid metabolite in human liver microsomes. Role of cytochrome P4502C and 3A subfamily members

Losartan is a 4-chloro-5-hydroxymethylimidazole derivative that is a potent and highly selective angiotensin II receptor antagonist. Losartan is metabolized in vivo in rats, monkeys, and humans to a carboxylic acid derivative E3174 that is pharmacologically more active than the parent compound. We have investigated the mechanism of this biotransformation in human liver preparations. The oxidation of both losartan and the putative aldehyde intermediate E3179 was catalyzed by the microsomal fraction, required both NADPH and molecular oxygen, and was inhibited by SKF 525-A, implicating cytochrome P450 (CYP). When incubations with each substrate were performed under an atmosphere of 18O2, the extent of 18O incorporation into the carboxylic acid product was consistent with a mechanism for losartan oxidation involving an aldehyde intermediate. To substantiate the involvement of CYP in these reactions, incubations with losartan and the aldehyde E3179 were performed in the presence of isoform-selective inhibitors. Inhibitors of CYP3A4/5 (gestodene and ketoconazole) and CYP2C9/10 (sulfaphenazole) attenuated the oxidation of both substrates. It was then demonstrated that microsomes containing either recombinant human liver CYP2C9 or CYP3A4 were capable of oxidizing both losartan and the aldehyde E3179 to the carboxylic acid E3174. Subsequently, it was shown that rabbit anti-CYP2C9 and anti-CYP3A3/4 inhibited the oxidation of losartan to E3174 in incubations with human liver microsomes. These studies support the hypothesis that the aldehyde E3179 is an intermediate in the oxidation of losartan and that this two-step reaction is catalyzed in human liver microsomes by members of the CYP3A and CYP2C subfamilies.

N-glucuronidation reactions. II. Relative N-glucuronidation reactivity of methylbiphenyl tetrazole, methylbiphenyl triazole, and methylbiphenyl imidazole in rat, monkey, and human hepatic microsomes

The relative intrinsic in vitro N-glucuronidation reactivity of three classes of heterocyclic compounds was compared using model compounds incubated with UDP-glucuronic acid-enriched liver microsomes from rats, monkeys, and humans. These compounds, all methylbiphenyl (MB) derivatives, represent three classes of N-containing heterocycles commonly used in the design of new drug entities [i.e MB-tetrazole, MB-triazole, (1,2,3- and 1,2,4-), and MB-imidazole (C2- and C4-substituted)]. The structures of all respective N-glucuronides generated from microsomal incubations were determined by Nuclear Overhauser Effect difference NMR spectroscopy. The chemical and enzymic stabilities of N-glucuronides were also studied. In general, relatively low reactivity was found at nitrogens located next to substituted carbons in heterocycles such as N3 in MB-C4-imidazole, N3 in MB-1,2,3-triazole, N2 (or N4) in MB-1,2,4-triazole, and N1 (or N4) in MB-tetrazole. MB-C2-imidazole, in which both nitrogens are in immediate neighboring positions of the substituted carbon, was unreactive toward N-glucuronidation. When the rate of N-glucuronidation was compared under optimal reaction conditions for each compound, most compounds showed higher reactivity with liver microsomes from monkeys than those from rats, except for N2-glucuronidation of MB-tetrazole and MB-1,2,3-triazole. However, the trend for the relative N-glucuronidation reactivity of these compounds by liver microsomes from humans is quite different from those by monkeys and rats.(ABSTRACT TRUNCATED AT 250 WORDS)

1-((7,7-Dimethyl-2(S)-(2(S)-amino-4-(methylsulfonyl)butyramido)bicyclo [2.2.1]-heptan-1(S)-yl)methyl)sulfonyl)-4-(2-methylphenyl)piperaz ine (L-368,899): an orally bioavailable, non-peptide oxytocin antagonist with potential utility for managing preterm labor

Modifications to the previously reported spiroindenylpiperidine camphor-sulfonamide oxytocin (OT) antagonist L-366,509 have produced a new series of o-tolylpiperazine (TP) camphor-sulfonamides. A number of analogues in the TP series that incorporate a modified or unmodified L-methionine sulfone amide at the C2 endo position on the camphor ring exhibit high affinity for OT receptors (IC50 = 1.3-15 nM) and good selectivity for binding to OT versus arginine vasopressin V1a and V2 receptors. Several of these analogues were additionally characterized as potent antagonists of OT-stimulated contractions of the isolated and/or in situ rat uterus. Compound 7 (L-368,899) exhibited the best overall profile of OT receptor affinity (IC50 = 8.9 nM, rat uterus; 26 nM, human uterus), potency for inhibition of OT-stimulated contractions of the isolated rat uterus (pA2 = 8.9) and in situ rat uterus (AD50 = 0.35 mg/kg after intravenous (i.v.) administration and 7.0 mg/kg after intraduodenal administration), aqueous solubility (3.7 mg/mL at pH 5.0), and oral bioavailability in several species (35% (rat), 25% (dog), and 21% (chimpanzee) as estimated from radioreceptor determination of drug levels in plasma after oral and i.v. dosing). On the basis of these favorable properties, 7 has begun clinical testing for use as an oral and i.v. tocolytic agent. Molecular modeling alignment studies have provided support for the hypothesis that the TP camphor-sulfonamide portion of the non-peptide structures may serve as a mimetic of the important D-AA2-Ile3 dipeptide (AA = aromatic amino acid) found in many potent OT antagonists from the cyclic hexapeptide and OT analogue structural classes.

N-glucuronidation reactions. I. Tetrazole N-glucuronidation of selected angiotensin II receptor antagonists in hepatic microsomes from rats, dogs, monkeys, and humans

In vitro conditions for the preparation of tetrazole N2-glucuronides using liver microsomes (enriched with UDP-glucuronic acid) from rats, dogs, monkeys, and humans have been developed and optimized. The structures of tetrazole N2-glucuronides of 3 biphenyl tetrazole-containing angiotensin II (AII) receptor antagonists MK-954 (I), L-158,338 (II), and L-158,809 (III), and a model compound methyl biphenyl tetrazole (IV) were determined either by NMR and mass spectrometry or by comparison of HPLC retention times with that from authentic compounds. The species difference as well as gender difference in the rate of the in vitro reaction were compared. The optimal pH for the reaction was determined to be 5.0 with liver microsomes from monkeys and humans, and 6.2 with those from rats and dogs. For the model compound IV, the rate of N2-glucuronidation by liver microsomes from rats, dogs, and monkeys was approximately 10-fold faster than that by humans. For the AII receptor antagonists I, II, and III, the rate of the same reaction by liver microsomes from dogs and monkeys was much faster than that by humans. The relative intrinsic rate of this reaction for these three substrates ranked similarly in rats and humans as II > III > I. With compound I, a biphenyl tetrazole-containing imidazole derivative that has potential sites for both O- (primary hydroxyl) and N2-(tetrazole) glucuronidation, both O- and tetrazole N2-glucuronides were formed by liver microsomes from rats and monkeys (at neutral pH), whereas N2-glucuronide was the only product from dogs and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a 1,2-hydride shift in the microsomal metabolism of the heterocycle L-158,338, a nonpeptide angiotensin II receptor antagonist

L-158,338 is an imidazo[4,5-b]pyridine derivative that is a potent and highly selective angiotensin II receptor antagonist. Rat liver microsomal metabolism of [C6-3H]L-158,338 gave a major metabolite that was monohydroxylated at the C6 position of the imidazo-pyridine but showed partial retention of the radiolabel. This biotransformation necessitated a shift of the radiolabel from the C6 position to another site within the molecule. We have investigated the mechanism of this biotransformation using 3H-, 3H/14C-, and 2H-labeled L-158,338. Metabolites were identified by FAB/MS, LC/MS, and 1H-NMR. Results of these studies show that the microsomal metabolism of L-158,338 to its C6-monohydroxylated derivative was mediated by a 1,2 hydride shift.

The use of in vitro metabolism studies in the understanding of new drugs

In vitro models derived from various animal species are routinely used for the evaluation of pharmacological potency and toxicological potential of new drug candidates. It is well known that metabolism of the drug molecule often contributes to the efficacy and toxicity observed in vivo. In vitro metabolism studies conducted in biological matrixes ranging from intact organ, tissue slice to subcellular fraction offer the advantage of reduced complexity of the study system, and allow the evaluation of intrinsic metabolic potential or mechanism with respect to a specific reaction. In addition, in vitro systems derived from various animal species offer the possibility of comparing metabolic pathways among species, including humans, before a compound can be tested clinically. Two areas of particular interest for the use of in vitro studies in the understanding of new drugs are 1) the relationship of metabolic pathway and pharmacodynamics and 2) the prediction of drug interaction potential in humans. To illustrate these aspects, I review metabolism studies on losartan, an angiotensin-II receptor antagonist currently in phase-III clinical development for hypertension, and cyclosporin A, a widely prescribed immunosuppressant.

Determination of enantiomeric concentrations of a 2,5-diaryltetrahydrofuran (L-668,750), a platelet-activating factor receptor antagonist, in rat plasma using a chiral alpha 1-acid glycoprotein high-performance liquid chromatographic column

Racemic sulfonylated 2,5-diaryltetrahydrofuran [L-668,750, (+-)-trans-2-[3-methoxy-5-(2-hydroxy)ethylsulfonyl-4-n-propoxy]-p henyl-5-(3,4,5-trimethoxyphenyl)-tetrahydrofuran, I] is a potent, specific and orally active platelet-activating factor (PAF) receptor antagonist. Its (-)-(2S,5S) enantiomer [L-680,573, (S)-I] exhibited higher PAF antagonistic potency than the (+)-(2R,5R) enantiomer [L-680,574, (R)-I] in vitro and in animal models. For assay of drug concentrations in plasma of rats dosed intravenously or orally with tritium-labeled I, we have developed a high-performance liquid chromatographic (HPLC) method which directly resolved the two enantiomers. The column contained alpha 1-acid glycoprotein as the chiral stationary phase and was eluted with phosphate buffer, methanol and ethanol at neutral pH. The concentration of each enantiomer in the plasma was then determined by reverse isotope dilution assay. Results showed that the plasma clearance rate of the more potent (S)-I enantiomer was more than ten-fold faster than that of the (R)-I enantiomer; the enantioselective clearance resulted in nearly ten-fold higher concentrations of the latter in plasma at all time points regardless of the dosing route. This paper describes the HPLC chiral resolution method and its application in plasma analysis.