[Study on the mechanisms of diarrhea induced by a new anticancer camptothecin derivative, irinotecan hydrochloride (CPT-11), in rats]

Multiple roles of baicalin and baicalein in the regulation of colorectal cancer

The prevalence of colorectal cancer is increasing worldwide, and despite advances in treatment, colorectal cancer (CRC) remains in the top three for mortality due to several issues, including drug resistance and low efficiency. There is increasing evidence that baicalin and baicalein, novel small molecule inhibitor extracts of the Chinese herb Scutellaria baicalensis, have better anti-colorectal cancer effects and are less likely to induce drug resistance in cancer cells. The present review article explains the anti-proliferative properties of baicalin and baicalein in the context of against CRC. Additionally, it explores the underlying mechanisms by which these compounds modulate diverse signaling pathways associated with apoptosis, cell proliferation, tumor angiogenesis, invasion, metastasis, and tumor microenvironment. Moreover, this review article highlights the inhibitory effect of colorectal inflammatory-cancer transformation and the near-term therapeutic strategy of using them as adjuvant agents in chemotherapy.

Irinotecan-induced gastrointestinal damage impairs the absorption of dabigatran etexilate

Irinotecan causes serious gastrointestinal damage. Dabigatran etexilate (DABE), an oral anticoagulant and substrate of P-glycoprotein (P-gp), is poorly absorbed and exhibits low bioavailability in humans. The aim of this study was to evaluate the effects of irinotecan-induced gastrointestinal damage on the pharmacokinetics/pharmacodynamics (PK/PD) of DABE. Irinotecan was administered intravenously to rats for 4 days to induce gastrointestinal damage. To investigate the PK profile of dabigatran (DAB), an active moiety of DABE, DABE was administered orally on day 5, and then DAB was administered intravenously on day 6. To evaluate the PD profile of DAB, the activated partial thromboplastin time (APTT) was measured. The protein expression level of intestinal P-gp was evaluated. In the irinotecan-treated rats, the area under the concentration-time curve of DAB after the oral administration of DABE and the bioavailability of DABE were decreased significantly. The APTT ratio also decreased, suggesting that the impaired efficacy of DABE was attributable to a reduction in its bioavailability. The expression of intestinal P-gp was higher in the irinotecan-treated rats. Taking into consideration the histological damage caused to the intestinal epithelium, both the increased P-gp expression and the reduced passive diffusion were considered to be responsible for the reduction in the bioavailability of DABE.

Carbon monoxide breath test assessment of mild hemolysis in Gilbert's syndrome

BACKGROUND

Mild hemolysis is difficult to determinate by traditional methods, and its role in Gilbert's syndrome (GS) is unclear. The main aims were to inspect the erythrocyte (RBC) survival in GS by using Levitt's carbon monoxide (CO) breath test and to assess its contribution to unconjugated hyperbilirubinemia.

METHODS

Fifty subjects with GS and 1 with type-II Crigler-Najjar syndrome (CN2) received RBC lifespan measurement with Levitt's CO breath test. Mean RBC lifespan was compared with normal referral value. Correlations of serum total bilirubin (TB) with RBC lifespan, blood panel data, demographic factors, and uridine diphosphate glucuronosyltransferase (UGT1A1) mutation load were calculated by Spearman analysis. Susceptibility factors for mild hemolysis were analyzed by multivariate regression analysis.

RESULTS

The mean RBC lifespan of the GS subjects was significantly shorter than the normal reference value (95.4 ± 28.9 days vs 126 days; t = -7.504, P < .01), with 30.0% below the lower limit of the normal reference range (75 days). The RBC lifespan of the participant with CN2 was 82 days. Serum TB correlated positively with UGT1A1 mutation load (γ = 0.281, P = .048), hemoglobin (γ = .359, P = .010) and hematocrit (γ = 0.365, P = .010), but negatively with RBC lifespan (γ = -0.336, P = .017). No significant susceptibility factors for mild hemolysis were found.

CONCLUSIONS

The results indicate that mild hemolysis indeed, exists in a portion of patients with GS and might serve as an important contributor to unconjugated hyperbilirubinemia in addition to UGT1A1 polymorphism. Further studies on the mechanism and the potential risks in various medical treatments might be wanted.

Herbal Medicines for Irinotecan-Induced Diarrhea

Irinotecan (CPT-11), a water-soluble derivative of camptothecin, belongs to the class of DNA topoisomerase I inhibitors and has been approved worldwide for the treatment of advanced colorectal cancer, lung cancer, and malignant lymphoma. Although CPT-11-based chemotherapy is widely used, severe gastrointestinal (GI) toxicity, especially late-onset diarrhea, is a common adverse reaction, limiting clinical application of the drug. The incidence of grade 3 or 4 diarrhea is high, with 20-40% of CPT-11-treated patients experiencing this adverse effect. High-dose loperamide and octreotide are generally recommended for treatment of CPT-11-induced diarrhea. However, in clinical practice, loperamide is associated with a significant failure rate and the beneficial effects of octreotide are controversial. An accumulating number of recent studies have suggested that medicinal herbs and their derived phytocompounds may be effective complementary treatments for CPT-11-induced diarrhea. In this mini-review, we briefly summarize currently available literatures regarding the formulae and herbs/natural products used as adjuvants in animal and clinical studies for the treatment of diarrhea caused by CPT-11.

Gilbert Syndrome with Concomitant Hereditary Spherocytosis Presenting with Moderate Unconjugated Hyperbilirubinemia

We experienced a case of a 19-year-old man with Gilbert syndrome with concomitant hereditary spherocytosis. The patient presented with moderate unconjugated hyperbilirubinemia, and inherited etiology was strongly suspected. The diagnosis of Gilbert syndrome was confirmed by the genetic analysis of the UGT1A1 gene, demonstrating UGT1A1*28 and compound heterozygote UGT1A1*6. In addition, since the laboratory findings and imaging studies revealed lysemia as well as gallstone and splenomegaly, a diagnosis of hereditary spherocytosis was made as a comorbidity. Both Gilbert syndrome and hereditary spherocytosis are hereditary diseases with a high frequency, and the hyperbilirubinemia may be exacerbated when these two diseases are concomitant.

Effect of genistein, a natural soy isoflavone, on the pharmacokinetics and intestinal toxicity of irinotecan hydrochloride in rats

Objectives

The effect of genistein, a natural soy isoflavone, on pharmacokinetics and intestinal toxicity, or late-onset diarrhoea, of irinotecan hydrochloride (CPT-11) was examined in rats.

Methods

Probenecid, a typical inhibitor of multidrug resistance-associated protein (MRP) 2, was also employed for comparison with genistein. Plasma concentration, biliary excretion and intestinal secretion of CPT-11, 7-ethyl-10-hydroxycamptothecin (SN-38) and SN-38 glucuronide (SN-38G) were determined in untreated, genistein-treated and probenecid-treated rats. CPT-11 was administered repeatedly by intravenous injection (60 mg/kg/day for 4 days), and the effects of genistein and probenecid on CPT-11-induced intestinal toxicity were evaluated by measuring body weight, induction of diarrhoea, and alkaline phosphatase (ALP) activity in the intestinal mucosal membranes.

Key findings

Genistein, as well as probenecid, significantly suppressed the MRP2-mediated biliary and intestinal secretion of CPT-11 and its metabolites and increased their plasma concentrations. Multiple administration of CPT-11 reduced body weight and ALP activity, and induced watery diarrhoea. Genistein, as well as probenecid, significantly suppressed the loss in body weight and the reduced mucosal ALP activity in the ileum, and ameliorated the symptoms of diarrhoea induced by CPT-11.

Conclusions

Intravenous genistein was effective in ameliorating CPT-11-induced late-onset diarrhoea, by suppressing MRP2-mediated biliary excretion of CPT-11 and its metabolites.

Chemotherapy-induced diarrhea: pathophysiology, frequency and guideline-based management

Diarrhea is one of the main drawbacks for cancer patients. Possible etiologies could be radiotherapy, chemotherapeutic agents, decreased physical performance, graft versus host disease and infections. Chemotherapy-induced diarrhea (CID) is a common problem, especially in patients with advanced cancer. The incidence of CID has been reported to be as high as 50-80% of treated patients (≥30% CTC grade 3-5), especially with 5-fluorouracil bolus or some combination therapies of irinotecan and fluoropyrimidines (IFL, XELIRI). Regardless of the molecular targeted approach of tyrosine kinase inhibitors and antibodies, diarrhea is a common side effect in up to 60% of patients with up to 10% having severe diarrhea. Furthermore, the underlying pathophysiology is still under investigation. Despite the number of clinical trials evaluating therapeutic or prophylactic measures in CID, there are just three drugs recommended in current guidelines: loperamide, deodorized tincture of opium and octreotide. Newer strategies and more effective agents are being developed to reduce the morbidity and mortality associated with CID. Recent research focusing on the prophylactic use of antibiotics, budesonide, probiotics or activated charcoal still have to define the role of these drugs in the routine clinical setting. Whereas therapeutic management and clinical work-up of patients presenting with diarrhea after chemotherapy are rather well defined, prediction and prevention of CID is an evolving field. Current research focuses on establishing predictive factors for CID like uridine diphosphate glucuronosyltransferase-1A1 polymorphisms for irinotecan or dihydropyrimidine-dehydrogenase insufficiency for fluoropyrimidines.

Effect of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) micelles on pharmacokinetics and intestinal toxicity of irinotecan hydrochloride: potential involvement of breast cancer resistance protein (ABCG2)

Objectives

Intestinal toxicity and low levels of systemic drug exposure are among the major problems associated with tumour therapy. We have developed poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) micelles loaded with irinotecan hydrochloride (CPT-11) hoping to decrease CPT-11-induced intestinal toxicity while increasing its systemic exposure. In addition, we have investigated the potential involvement of breast cancer resistance protein (BCRP) in biliary excretion, pharmacokinetics, and intestinal toxicity of CPT-11.

Methods

PEO-PPO-PEO micelles were prepared using PEO20-PPO70-PEO20 and lecithin. The effect of PEO-PPO-PEO micelles on BCRP-mediated cellular accumulation and transport efflux of CPT-11 was evaluated in MDCKII/BCRP cells. The biliary excretion, intestinal damage, and pharmacokinetic study of CPT-11-loaded PEO-PPO-PEO micelles were investigated in rats.

Key findings

The obtained micelles could effectively inhibit BCRP-mediated CPT-11 efflux in MDCKII/BCRP cells, and significantly decrease the drug biliary excretion in rats. Moreover, intestinal toxicity, assessed by microscopic examination of pathological damage, was ameliorated in rats injected with PEO-PPO-PEO micelles compared with rats injected with CPT-11 alone. Treatment with PEO-PPO-PEO micelles resulted in prolonged circulation time in blood and increased bioavailability of CPT-11 and SN-38 (7-ethyl-10-hydroxycamptothecin).

Conclusions

PEO-PPO-PEO micelles were identified as promising carriers able to reduce intestinal toxicity and increase antitumour therapeutic effect of CPT-11. The study indicated a potential involvement of BCRP in CPT-11 pharmacokinetics and CPT-11-induced intestinal toxicity.

Effects of breast cancer resistance protein inhibitors and pharmaceutical excipients on decreasing gastrointestinal toxicity of camptothecin analogs

AIM

To investigate the effect of breast cancer resistance protein (BCRP) inhibitors and pharmaceutical excipients on reducing the biliary excretion of camptothecins (CPT), ameliorating delayed-type diarrhea and intestinal mucosa damage induced by CPT.

METHODS

The cumulative biliary excretion of irinotecan (CPT-11) and hydroxycamptothecin (HCPT) with or without BCRP inhibitors and excipients was investigated in rats. The gastrointestinal toxicity, assessed as the diarrheal score, body weight change and microscopic pathological damage was also determined in rats.

RESULTS

Breast cancer resistance protein (BCRP) exhibited important effects on the biliary excretion of CPT. Coadministration of BCRP inhibitors such as GF120918 and cyclosporin A reduced the biliary excretion of CPT-11 and HCPT. Pharmaceutical excipients such as Pluronic F68 and PEG 2000 stearate also showed inhibitory effects on BCRP and similarly reduced CPT biliary excretion. The observed gastrointestinal toxicity was ameliorated by coadministration of BCRP inhibitors and excipients compared with injection of CPT-11 and HCPT alone.

CONCLUSION

The use of excipients as inhibitors of BCRP is safe and relatively non-toxic, and may lead to important pharmacotherapeutic benefits by decreasing the gastrointestinal toxicity of CPT.

Optimal antidiarrhea treatment for antitumor agent irinotecan hydrochloride (CPT-11)-induced delayed diarrhea

PURPOSE

An antitumor camptothecin derivative CPT-11 has proven a broad spectrum of solid tumor malignancy, but its severe diarrhea has often limited its more widespread use. We have demonstrated from a rat model that intestinal beta-glucuronidase may play a key role in the development of CPT-11-induced delayed diarrhea by the deconjugation of the luminal SN-38 glucuronide, and the elimination of the intestinal microflora by antibiotics or dosing of TJ-14, a Kampo medicine that contains beta-glucuronidase inhibitor baicalin, exerted a protective effect. In the present study, we assessed the efficacy of several potential treatments in our rat model to clarify which is the most promising treatment for CPT-11-induced delayed diarrhea.

METHODS AND RESULTS

Oral dosing (twice daily from days -1 to 4) of streptomycin 20 mg/kg and penicillin 10 mg/kg (Str/Pen), neomycin 20 mg/kg and bacitracin 10 mg/kg (Neo/Bac), both of which inhibited almost completely the fecal beta-glucuronidase activity, or TJ-14 1,000 mg/kg improved the decrease in body weight and the delayed diarrhea symptoms induced by CPT-11 (60 mg/kg i.v. from days 1 to 4) to a similar extent. The efficacy was less but significant in activated charcoal (1,000 mg/kg p.o. twice daily from days -1 to 4). In a separate experiment using rats bearing breast cancer (Walker 256-TC), TJ-14, Neo/Bac, and charcoal at the same dose regimen improved CPT-11-induced intestinal toxicity without reducing CPT-11's antitumor activity. In contrast, oral dosing (twice a day) of cyclosporin A (50 mg/kg), a P-glycoprotein and cMOAT/MRP2 inhibitor or valproic acid (200 mg/kg), a UDP-glucuronosyltranferase inhibitor, exacerbated the intestinal toxicity without modifying CPT-11's antitumor activity.

CONCLUSIONS

The result clearly demonstrated the ability of Neo/Bac, Str/Pen, and TJ-14, less but significant ability of activated charcoal, to ameliorate CPT-11-induced delayed-onset diarrhea, suggesting the treatments decreasing the exposure of the intestines to the luminal SN-38 are valuable for improvement of CPT-11-induced intestinal toxicity. In contrast, the treatments affecting the biliary excretion of CPT-11 and its metabolites might have undesirable results.

Activation and antitumor activity of CPT-11 in plasma esterase-deficient mice

PURPOSE

To examine the antitumor activity and the pharmacokinetics of CPT-11 (irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) in a plasma esterase-deficient scid mouse model, bearing human tumor xenografts.

EXPERIMENTAL DESIGN

Plasma carboxylesterase (CE)-deficient mice were bred with scid animals to develop a strain that would allow growth of human tumor xenografts. Following xenotransplantation, the effect of the plasma esterase on antitumor activity following CPT-11 administration was assessed. In addition, detailed pharmacokinetic studies examining plasma and biliary disposition of CPT-11 and its metabolites were performed.

RESULTS

In mice lacking plasma carboxylesterase, the mean SN-38 systemic exposures were approximately fourfold less than that observed in control animals. Consistent with the pharmacokinetic data, four to fivefold more CPT-11 was required to induce regressions in human Rh30 xenografts grown in esterase-deficient scid mice, as opposed to those grown in scid animals. Additionally, the route of elimination of CPT-11, SN-38, and SN-38 glucuronide (SN-38G) was principally in the bile.

CONCLUSIONS

The pharmacokinetic profile for CPT-11 and its metabolites in the esterase-deficient mice more closely reflects that seen in humans. Hence, these mice may represent a more accurate model for antitumor studies with this drug and other agents metabolized by CEs.

Phase II Study of Activated Charcoal to Prevent Irinotecan-Induced Diarrhea

Purpose

The dose-limiting toxicity of irinotecan (CPT-11; Camptosar) is delayed-onset diarrhea, with an incidence at the grade 3 to 4 level of 20% to 35%. SN38, its active moiety, is responsible by a direct effect on mucosal topoisomerase-I. The aim of this study was to assess whether activated charcoal (AC), possibly by adsorbing free lumenal SN38, can reduce irinotecan-induced diarrhea (CID) and optimize its dose-intensity.

Patients and Methods

Patients with advanced colorectal cancer receiving irinotecan 125 mg/m2intravenously once a week for 4 weeks every 6 weeks were studied. In cycle 1, patients received irinotecan plus AC (5 mL aqueous Charcodote [1,000 mg AC] plus 25 mL water) given the evening before the irinotecan dose and then tid for 48 hours after the dose. In cycle 2, no AC was given. National Cancer Institute Common Toxicity Criteria diarrhea grade, irinotecan dose-intensity, and loperamide consumption were recorded prospectively in both cycles.

Results

Twenty-eight patients had completed cycle 1 with AC; 24 subsequently completed cycle 2 without AC. Grade 3 to 4 diarrhea was 7.1% v 25%, and grade 0 diarrhea was 46.4% v 20.8% in cycles 1 and 2, respectively. Median percent planned dose delivered was 98% v 70% in cycles 1 and 2, respectively. In cycles 1 and 2, respectively, 25% v 54% patients took more than 10 loperamide tablets. AC was well tolerated with excellent compliance.

Conclusion

The administration of AC with irinotecan reduced the incidence of grade 3 to 4 diarrhea and antidiarrheal medication consumption and increased irinotecan dose-intensity. Prophylactic AC may have a role in reducing dose-limiting CID and optimizing irinotecan therapy.

UGT1A1*28 polymorphism as a determinant of irinotecan disposition and toxicity

The metabolism of irinotecan (CPT-11) involves sequential activation to SN-38 and detoxification to the pharmacologically inactive SN-38 glucuronide (SN-38G). We have previously demonstrated the role of UGT1A1 enzyme in the glucuronidation of SN-38 and a significant correlation between in vitro glucuronidation of SN-38 and UGT1A1 gene promoter polymorphism. This polymorphism (UGT1A1*28) is characterized by the presence of an additional TA repeat in the TATA sequence of the UGT1A1 promoter, ((TA)7TAA, instead of (TA)6TAA). Here we report the results from a prospective clinical pharmacogenetic study to determine the significance of UGT1A1*28 polymorphism on irinotecan disposition and toxicity in patients with cancer. Twenty patients with solid tumors were treated with a 90 min i.v. infusion of irinotecan (300 mg m(-2)) once every 3 weeks. The frequency of UGT1A1 genotypes was as follows: 6/6--45%, 6/7--35% and 7/7--20%, with allele frequencies of 0.375 and 0.625 for (TA)7TAA and (TA)6TAA, respectively. Patients with the (TA)7TAA polymorphism had significantly lower SN-38 glucuronidation rates than those with the normal allele (6/6>6/7>7/7, P = 0.001). More severe grades of diarrhea and neutropenia were observed only in patients heterozygous (grade 4 diarrhea, n = 1) or homozygous (grade 3 diarrhea/grade 4 neutropenia, n = 1 and grade 3 neutropenia, n = 1) for the (TA)7TAA sequence. The results suggest that screening for UGT1A1*28 polymorphism may identify patients with lower SN-38 glucuronidation rates and greater susceptibility to irinotecan induced gastrointestinal and bone marrow toxicity.

Reduced gastrointestinal toxicity following inhibition of the biliary excretion of irinotecan and its metabolites by probenecid in rats

PURPOSE

To ameliorate the late-onset of severe gastrointestinal toxicity provoked by irinotecan (CPT-11), which may be related to the biliary excretion of CPT-11 and/or its metabolites.

METHODS

Effects of probenecid, an inhibitor of MRP2/ABCC2, on the biliary excretion and mucosal intestinal tissue concentration of CPT-11 and its metabolites were examined in rats. CPT-11-induced late-onset gastrointestinal toxicity was also evaluated.

RESULTS

Coadministration of probenecid reduced the biliary excretion of CPT-11, an active metabolite (SN-38) and its glucuronide by half with a concomitant increase in their plasma concentration. When the dose of CPT-11, in the presence of probenecid, was set at half that in its absence, the plasma SN-38 concentration was maintained at the same level as the control, whereas the mucosal intestinal tissue concentration of SN-38 was reduced. Under this condition, CPT-11-induced watery diarrhea, changes in intestinal marker enzymes and body weight reduction were much less in the probenecid-treated group, although the degree of bone marrow suppression was almost the same as that in the control.

CONCLUSIONS

Coadministration of probenecid with a reduced dose of CPT-11 potently reduces both SN-38 exposure and CPT-11-induced late-onset toxicity in gastrointestinal tissues, possibly by inhibiting the biliary excretion of CPT-11 and/or its metabolites.

The Potential for an Interaction between MRP2 (ABCC2) and Various Therapeutic Agents: Probenecid as a Candidate Inhibitor of the Biliary Excretion of Irinotecan Metabolites

Irinotecan hydrochloride (CPT-11) is an anticancer agent with unpredictable bouts of diarrhea as a dose-limiting toxic side-effect. Since the biliary excretion of its active metabolite (SN-38) and SN-38 glucuronide (SN38-Glu), which are mediated by the multidrug resistance associated protein-2 (MRP2/ABCC2), has been proposed to be related to this gastrointestinal toxicity, we have attempted here to examine the potential of various therapeutic agents to interact with the biliary excretion in order to identify MRP2 inhibitors to prevent this toxicity. The inhibition constants (K(i)) of 26 compounds were examined for the transport of a typical MRP2 substrate in isolated canalicular membrane vesicles. Of these, 13 compounds inhibited the transport with K(i) values from 0.0461 to 281 microM. Three inhibitors (probenecid, sulfobromophthalein and glycyrrhizin) were also found to inhibit the biliary excretion of SN-38 and SN38-Glu in rats in vivo, and the degrees of inhibition were compatible with the estimated values based on the ratios of K(i) and unbound concentrations in circulating plasma. A similar estimation of the potential inhibitory effect in human was also examined by considering both the K(i) of each therapeutic agent and its unbound concentration both in circulating plasma and the inlet to the liver. The predicted degrees of inhibition by most compounds were minimal whereas approximately 75% inhibition was predicted for probenecid. Thus, probenecid may be a candidate which can be used clinically to inhibit the biliary excretion of CPT-11 metabolites, whereas an interaction between most of the other compounds and MRP2 is more unlikely.

Fish oil supplementation enhanced CPT-11 (irinotecan) efficacy against MCF7 breast carcinoma xenografts and ameliorated intestinal side-effects

The cancer chemotherapeutic efficacy of the topoisomerase I inhibitor, CPT-11 (irinotecan) is often limited by the induction of severe delayed diarrhoea. In animal studies, CPT-11 use is associated with histopathological damage to the mucosa of the small and large intestines. Results from the present study demonstrate that 60 mg CPT-11 per kg body weight (i.v. q4d x 6) halted the growth, but did not cause significant regression, of MCF7 human breast carcinoma xenografts in mice fed a diet containing 7% corn oil. However, when the diet of the MCF7-bearing mice was supplemented with 3% or 6% fish oil, the same CPT-11 treatment caused significant regression of the MCF7 xenograft. Histomorphometric analyses of intestinal mucosa of mice treated with CPT-11 and fed the diet containing 7% com oil indicated that treatment with CPT-11 induced structural changes in the intestinal mucosa which persisted at least 5 days after the last dose of CPT-11. The intestinal mucosal architecture of mice that were treated with CPT-11 and fed the diets containing fish oil was largely unchanged from the architecture of the group of mice which did not receive CPT-11. These findings indicate that fish oil supplements may be a useful adjunct to CPT-11 treatment.

Genetic predisposition to the metabolism of irinotecan (CPT-11). Role of uridine diphosphate glucuronosyltransferase isoform 1A1 in the glucuronidation of its active metabolite (SN-38) in human liver microsomes

Irinotecan (CPT-11) is a promising antitumor agent, recently approved for use in patients with metastatic colorectal cancer. Its active metabolite, SN-38, is glucuronidated by hepatic uridine diphosphate glucuronosyltransferases (UGTs). The major dose-limiting toxicity of irinotecan therapy is diarrhea, which is believed to be secondary to the biliary excretion of SN-38, the extent of which is determined by SN-38 glucuronidation. The purpose of this study was to identify the specific isoform of UGT involved in SN-38 glucuronidation. In vitro glucuronidation of SN-38 was screened in hepatic microsomes from normal rats (n = 4), normal humans (n = 25), Gunn rats (n = 3), and patients (n = 4) with Crigler-Najjar type I (CN-I) syndrome. A wide intersubject variability in in vitro SN-38 glucuronide formation rates was found in humans. Gunn rats and CN-I patients lacked SN-38 glucuronidating activity, indicating the role of UGT1 isoform in SN-38 glucuronidation. A significant correlation was observed between SN-38 and bilirubin glucuronidation (r = 0.89; P = 0.001), whereas there was a poor relationship between para-nitrophenol and SN-38 glucuronidation (r = 0.08; P = 0.703). Intact SN-38 glucuronidation was observed only in HK293 cells transfected with the UGT1A1 isozyme. These results demonstrate that UGT1A1 is the isoform responsible for SN-38 glucuronidation. These findings indicate a genetic predisposition to the metabolism of irinotecan, suggesting that patients with low UGT1A1 activity, such as those with Gilbert's syndrome, may be at an increased risk for irinotecan toxicity.

Relevance of irinotecan hydrochloride-induced diarrhea to the level of prostaglandin E2 and water absorption of large intestine in rats

For characterization of the mechanism(s) of severe diarrhea due to the anticancer agent, irinotecan hydrochloride (CPT-11), examination was made of the relation of CPT-11-related diarrhea to colonic prostaglandin E2 (PGE2) and water absorption in rats. Acute diarrheal symptoms were observed within 1 hr after the administration of CPT-11 to rats, with increased PGE2 and decreased water absorption in the colon. Treatment with atropine at 1 mg/kg, s.c. was noted to inhibit intestinal PGE2 and the CPT-11-related acute diarrheal symptoms, indicating that these diarrheal symptoms were mediated through the cholinergic nervous system accelerated functionally by CPT-11. On the other hand, daily treatment of CPT-11 at the same dose resulted in chronic diarrheal symptoms in all animals 3 days after CPT-11 treatment. Histopathological changes observed in the descending colon and ileum of the rats included degeneration and necrosis of villi and cryptal cells and a decrease in the number of the goblet cells. Significantly increased PGE2 and impaired water absorption of the descending colon were also observed during the chronic diarrheal stage. It can be considered that the chronic diarrheal symptoms appear as a consequence of the gastrointestinal injury characterized by significant increase in PGE2 accompanied by impaired water absorption.

Preventive effects of Hange-shashin-to on irinotecan hydrochloride-caused diarrhea and its relevance to the colonic prostaglandin E2 and water absorption in the rat

The possible preventive effect of Kampo medicine Hange-shashin-to (TJ-14) on chronic diarrheal symptoms induced by the administration of the anticancer agent irinotecan hydrochloride (CPT-11) was investigated in the rat. Repeated oral administrations of TJ-14 at 125 and 500 mg/kg significantly prevented the reduction in body weight and the onset of chronic diarrheal symptoms due to CPT-11 in a dose-dependent manner, even though it failed to show a definite effect on acute diarrheal symptoms. In addition, treatment with TJ-14 accelerated the healing of the intestinal tract injured by repeated dosing of CPT-11 and inhibited significantly the increase of colonic prostaglandin E2 (PGE2) which is closely related to the onset of diarrhea. TJ-14 also improved colonic water absorption impaired by repeated dosing of CPT-11 in rats. These results demonstrate that TJ-14 is an effective medicine for the prevention and/or treatment of CPT-11-induced chronic diarrheal symptoms.

Protective effects of kampo medicines and baicalin against intestinal toxicity of a new anticancer camptothecin derivative, irinotecan hydrochloride (CPT-11), in rats

In clinical use, irinotecan hydrochloride (CPT-11; 7-ethyl-10-[4-(piperidino)-1-piperidino]carbonyloxycamptothecin), a novel antitumor agent, causes a relatively high incidence of severe forms of diarrhea. We investigated whether baicalin, an inhibitor of beta-glucuronidase, which deconjugates the glucuronide of the active metabolite of CPT-11, SN-38 (7-ethyl-10-hydorxycamptothecin), and Japanese herbal medicines (Kampo medicines) which contain baicalin can ameliorate CPT-11-induced intestinal toxicity in rats. CPT-11 (60 mg/kg i.v. once daily for 4 consecutive days) induced intestinal toxicity characterized by diarrhea, loss of body weight, anorexia and disruption of intestinal epithelium. Treatment with baicalin (25 mg/kg p.o. twice daily) or Kampo medicines (TJ-14 and TJ-114; 1 g/kg p.o. twice daily) from the day before to 4 or 10 days after the start of CPT-11 administration resulted in significantly decreased weight loss, improved anorexia and delayed onset of diarrheal symptoms. Histological examination revealed that Kampo medicine-treated animals had less damage to the intestinal epithelium and that damage was repaired more rapidly than in control rats. These results suggest that the prophylactic use of Kampo medicines (TJ-14 and TJ-114) may be of value against CPT-11-induced intestinal toxicity.