Involvement of UDP-glucuronosyltransferase activity in irinotecan-induced delayed-onset diarrhea in rats

Fecal SN-38 Content as a Surrogate Predictor of Intestinal SN-38 Exposure and Associated Irinotecan-induced Severe Delayed-Onset Diarrhea by a Novel Use of the Spectrofluorimetric Method

BACKGROUND

Irinotecan administration can lead to severe delayed-onset diarrhea (SDOD) in clinical practice. Currently, there is no reliable surrogate predictor of intestinal exposure to SN-38 and subsequent diarrhea incidence.

METHODS

The relationship between fecal 7-ethyl-10-hydroxycamptothecin (SN-38) content and SDOD was investigated in Fisher 344 rats using a novel spectrofluorimetric method. Additionally, a pharmacokinetic study of irinotecan was performed to evaluate the biodistribution of SN-38 to establish the relationship between tissue and fecal SN-38 exposure.

RESULTS

The spectrofluorimetric method was successfully employed to measure fecal SN-38 and CPT-11 content from Day 3 to Day 6 post-irinotecan administration. Only fecal SN-38 content on Day 3 exhibited a significantly positive correlation with SDOD incidence on Days 4 and 5. A cutoff value of SN-38 ≥ 0.066 mg/g in feces was identified, predicting severe diarrhea incidence with 81% accuracy and 80% specificity. The positive correlation between fecal SN-38 content and SN-38 exposure in the ileum on Day 3 was also reflected in the changes of indicators during intestinal injury, such as prostaglandin E2 level and antioxidant activity.

CONCLUSION

Fecal SN-38 content proves to be representative of intestinal exposure to SN-38, indicative of intestinal injury, and predictive of SDOD incidence in rats, while the spectrofluorimetric method demonstrates the translational potential.

Optimized rat models better mimic patients with irinotecan-induced severe diarrhea

Irinotecan-induced severe diarrhea (IISD) not only limits irinotecan's application but also significantly affects patients' quality of life. However, existing animal models often inadequately represent the dynamics of IISD development, progression, and resolution across multiple chemotherapy cycles, yielding non-reproducible and highly variable response with limited clinical translation. Our studies aim to establish a reproducible and validated IISD model that better mimics the pathophysiology progression observed in patients, enhancing translational potential. We investigated the impact of dosing regimens (including different dose, infusion time, and two cycles of irinotecan administration), sex, age, tumor-bearing conditions, and irinotecan formulation on the IISD incidence and severity in mice and rats. Lastly, we investigated above factors' impact on pharmacokinetics of irinotecan, intestinal injury, and carboxylesterase activities. In summary, we successfully established a standard model establishment procedure for an optimized IISD model with highly reproducible severe diarrhea incidence rate (100%) and a low mortality rate (11%) in F344 rats. Additionally, the rats tolerated at least two cycles of irinotecan chemotherapy treatment. In contrast, the mouse model exhibited suboptimal IISD incidence rates (60%) and an extremely high mortality rate (100%). Notably, dosing regimen, age and tumor-bearing conditions of animals emerged as critical factors in IISD model establishment. In conclusion, our rat IISD model proves superior in mimicking pathophysiology progression and characteristics of IISD in patients, which stands as an effective tool for mechanism and efficacy studies in future chemotherapy-induced gut toxicity research.

A modular ROS-responsive platform co-delivered by 10-hydroxycamptothecin and dexamethasone for cancer treatment

Traditional and single treatment strategies are difficult to achieve good results due to tumor resistance and complex mechanisms. Combination therapy through co-delivery systems is one of the methods to improve the effectiveness of cancer treatment. The polyprodrug platform has inherent advantages such as high drug loading and strong stability. Herein, a new reactive oxygen species (ROS)-responsive micelle composed of poly 10-hydroxycamptothecin (pHCPT) and PEG is reported, which loaded dexamethasone (DEX) as synergistic drugs. The micelles collapse in the complex microenvironment of tumor cells to release DEX. The first released DEX can increase the ROS level of tumor cells, thereby facilitating the cleavage of thioketal bonds to release intact HCPT molecules. Meanwhile, DEX can normalize tumor blood vessels, reduce adverse reactions, and further improve the efficacy of HCPT. This co-delivery system shows an ideal tumor suppressive effect in vivo and in vitro. Designing drugs into a modular multi-drug platform and selecting appropriate synergistic drugs according to the treatment plan provides a convenient strategy for future clinical treatment.

PLX038: a PEGylated prodrug of SN-38 independent of UGT1A1 activity

PURPOSE

The purpose of this study was to determine the importance of UGT1A1 activity on the metabolism and pharmacokinetics of a releasable PEG ~ SN-38 conjugate, PLX038A. Irinotecan (CPT-11) is converted to the topoisomerase 1 inhibitor SN-38 by first-pass hepatic metabolism and is converted to its glucuronide SN-38G by UGT1A1. With diminished UGT1A1 activity, the high liver exposure to SN-38 can cause increased toxicity of CPT-11. In contrast, releasable PEG ~ SN-38 conjugates-such as PLX038-release SN-38 in the vascular compartment, and only low levels of SN-38 are expected to enter the liver by transport through the OATP1B1 transporter.

METHODS

We measured CPT-11 and PLX038A metabolites in plasma and bile, and determined pharmacokinetics of PLX038A in UGT1A-deficient and replete rats.

RESULTS

Compared to CPT-11, treatment of rats with PLX038A results in very low levels of biliary SN-38 and SN-38G, a low flux through UGT1A, and a low SN-38G/SN-38 ratio in plasma. Further, the pharmacokinetics of plasma PLX038A and SN-38 in rats deficient in UGT1A is unchanged compared to normal rats.

CONCLUSIONS

The disposition of PEGylated SN-38 is independent of UGT1A activity in rats, and PLX038 may find utility in full-dose treatment of patients who are UGT1A1*28 homozygotes or have metastatic disease with coincidental or incidental liver dysfunction.

A Pilot Study of Irinotecan Combined with 5-Fluorouracil and Leucovorin for the Treatment of Chinese Patients with Locally Advanced and Metastatic Gastric Cancer

Aims and background

The FOLFIRI regimen was evaluated for its anti-tumor activity and toxicity in Chinese patients with locally advanced and metastatic gastric cancer.

Methods and study design

Treatment consisted of irinotecan, 180 mg/m2 (90-min infusion), leucovorin, 200 mg/m2 (2-h infusion), followed by 5-fluorouracil, 400 mg/m2 (bolus), and then 5-fluorouracil, 600 mg/m2 (22-h continuous infusion) on days 1 and 2, every 14 days.

Results

Twenty-six patients, of whom 17 were pretreated, were included in the study. Partial response was observed in 9 patients (37.5%). The overall disease control rate was 83.3%. Median progression-free and overall survival was 6.8 and 11.2 months, respectively. Grade 3–4 neutropenia was observed in 6 patients (23.1%) and grade 2–3 diarrhea in 5 (19.2%). No treatment-related deaths occurred.

Conclusions

The results demonstrate that the FOLFIRI regimen is an active regimen with acceptable toxicity for Chinese patients with advanced and metastatic gastric cancer that merits further investigation in comparative trials.

Comparative intestinal bacteria-associated pharmacokinetics of 16 components of Shengjiang Xiexin decoction between normal rats and rats with irinotecan hydrochloride (CPT-11)-induced gastrointestinal toxicity in vitro using salting-out sample preparation and LC-MS/MS

Comparative intestinal bacteria-associated pharmacokinetics of SXD components between normal and model rats in vitro using salting-out preparation and LC-MS/MS.

[Effect of tacrolimus on the pharmacokinetics and glucuronidation of SN-38, an active metabolite of irinotecan]

The present study has investigated the effect of tacrolimus on the pharmacokinetics of an active metabolite of irinotecan (CPT-11), 7-ethyl-10-hydroxy-camptothecin (SN-38) and SN-38 glucuronide (SN-38G) in rats. The effect of tacrolimus on SN-38 glucuronidation was also investigated in human and rat liver microsomes. When tacrolimus (0.5 mg/kg) was intravenously injected in rats 15 min before intravenous injection of CPT-11 (5 mg/kg), tacrolimus decreased the plasma concentration of SN-38G. Tacrolimus significantly decreased the area under plasma concentration-time curve (AUC) of SN-38G without change in the mean residence time. On the contrary, significant changes in the pharmacokinetic parameters of SN-38 were not observed. SN-38 glucuronidation in human and rat liver microsomes was inhibited dose-dependently by the presence of tacrolimus and the 50% inhibition concentration (IC50) values of tacrolimus in rat and human liver microsomes were 10.33 μM and 3.58 μM, respectively. When the inhibition type was determined by Lineweaver-Burk and Dixon plots, the inhibition was noncompetitive and the calculated inhibition constant (Ki) values for rat and human liver microsomes were 12.57 μM and 3.88 μM, respectively. These findings suggest that tacrolimus inhibits UGT1A1-mediated SN-38 glucuronidation. Considering the IC50 and Ki values for tacrolimus, it is likely that tacrolimus does not alter the pharmacokinetics of SN-38 and SN-38G at the clinically used dosages, suggesting the possibility that tacrolimus can use safely for cancer patients with irinotecan chemotherapy.

Kampo medicine "Dai-kenchu-to" prevents CPT-11-induced small-intestinal injury in rats

PURPOSE

The key anticancer agent, CPT-11 (irinotecan hydrochloride), induces severe diarrhea clinically. We investigated the effect of a Kampo medicine, Dai-kenchu-to (DKT), on CPT-11-induced intestinal injuries in rats.

METHODS

Twenty-four male Wistar rats were divided into three groups: a control group; a CPT-11 group, given CPT-11 150 mg/kg intraperitoneally for 2 days; and a DKT group, given DKT 300 mg/kg orally for 5 days with CPT-11 150 mg/kg intraperitoneally on days 4 and 5. The rats were killed on day 6.

RESULTS

Interleukin (IL)-1β, IL-12, interferon (IFN)-γ, and tumor necrosis factor-α expression in the small intestine of the CPT-11 group was significantly higher than that of the control group. Interleukin-1β and IFN-γ expression was improved significantly by DKT (P < 0.05). The number and height of jejuna villi, injury score, and apoptosis index in the CPT-11 group were improved significantly by DKT (P < 0.05).

CONCLUSIONS

DKT suppressed CPT-11 induced inflammatory cytokines and apoptosis in the intestinal mucosa and maintained the mucosal integrity.

Streptomycin alleviates irinotecan-induced delayed-onset diarrhea in rats by a mechanism other than inhibition of β-glucuronidase activity in intestinal lumen

Irinotecan hydrochloride (CPT-11) is a useful drug for cancer chemotherapy but sometimes induces severe diarrhea clinically. CPT-11 is mainly activated to SN-38 by carboxylesterase (CES) and then detoxified to SN-38 glucuronide (SN-38G) by UDP-glucuronosyltransferase (UGT) in the liver. SN-38G is excreted via bile and de-conjugated to SN-38 by β-glucuronidase (β-GLU) in the intestinal content. In order to clarify the alleviative effect of antibiotics on CPT-11-induced diarrhea, we examined whether penicillin G and streptomycin (SM) alleviate CPT-11-induced delayed-onset diarrhea using three diarrheal models, i.e., Wistar rats with repeated dosing of CPT-11 (60 mg/kg/day i.v. for 4 consecutive days) and Wistar and Gunn rats with a single dosing of CPT-11 (200 and 20 mg/kg i.v., respectively). Gunn rats have an inherited deficiency of UGT1A and cannot conjugate SN-38 to SN-38G. Therefore, onset of CPT-11-induced diarrhea in Gunn rats is not affected by β-GLU activity. SM alleviated diarrhea in all three diarrheal models. The alleviation of diarrhea by SM in Gunn rats indicated that the effect of SM occurred by a mechanism other than the inhibition of β-GLU activity. SM decreased CPT-11 and/or SN-38 concentrations in intestinal tissues and alleviated epithelial damage from the ileum to colon. SM did not inhibit β-GLU activity in the cecal content. SM also inhibited the intestinal absorption of CPT-11 and decreased CES activity and increased UGT activity in the intestinal epithelium. These findings indicated that SM decreased the exposure of CPT-11 and SN-38 to the intestinal epithelium by inhibiting the absorption of CPT-11 from the intestinal lumen and the change of CES and UGT activities in the intestinal epithelium and alleviated delayed-onset diarrhea.

Irinotecan and its active metabolite, SN-38: review of bioanalytical methods and recent update from clinical pharmacology perspectives

The introduction of irinotecan has revolutionized the applicability of camptothecins as predominant topoisomerase I inhibitor for anti-cancer therapy. The potent anti-tumor activity of irinotecan is due to rapid formation of an in vivo active metabolite, SN-38. Therefore, irinotecan is considered as a pro-drug to generate SN-38. Over the past decade, side-by-side with the clinical advancement of the use of irinotecan in the oncology field, a plethora of bioanalytical methods have been published to quantify irinotecan, SN-38 and other metabolites. Because of the availability of HPLC, LC-MS and LC-MS/MS methods, the pharmacokinetic profiling of irinotecan and its metabolites has been accomplished in multiple species, including cancer patients. The developed assays continue to find use in the optimization of newly designed delivery systems with regard to pharmacokinetics to promote safe and effective use of either irinotecan or SN-38. This review intends to: firstly, provide an exhaustive compilation of the published assays for irinotecan, SN-38 and other metabolite(s) of irinotecan, as applicable; secondly, to enumerate the validation parameters and applicable conclusions; and thirdly, provide some recent perspectives in the clinical pharmacology arena pertaining to efflux transporters, pediatric profiling, role of kidney function in defining toxicity, drug-drug interaction potential of irinotecan, etc.

Comparative and veterinary pharmacogenomics

Pharmacogenomics is the study of the impact of genetic variation on drug effects, with the ultimate goal of achieving "personalised medicine". Since the completion of the Human Genome Project, great strides have been made towards the goal of personalised dosing of drugs in people, as exemplified by the development of gene-guided dosing of the anticoagulant drug, warfarin. Although the pharmacogenomics of domestic animals is still at an early stage of development, there is great potential for advances in the coming years as the direct result of complete genome sequences currently being derived for many of the species of significance to veterinary and comparative medicine. This sequence information is being used to discover sequence variants in candidate genes associated with altered drug response, as well as to develop whole genome high density single nucleotide polymorphism arrays for genotype-phenotype linkage analysis. This review summarises the current state of veterinary pharmacogenomics research, including drug response variability phenotypes with either known genetic aetiology or strong circumstantial evidence for genetic involvement. Polymorphisms and rarer gene variants affecting drug disposition (pharmacokinetics) and drug effect (pharmacodynamics) are discussed. In addition to providing the veterinary clinician with useful information for the practise of therapeutics, it is envisaged that the increasing knowledge base will also provide a resource for individuals involved in veterinary and comparative biomedical research.