Reversible grade 4 hyperbilirubinemia in a patient with UGT1A1 7/7 genotype treated with irinotecan and cetuximab

Induction of Mild Hyperbilirubinemia: Hype or Real Therapeutic Opportunity?

Observational epidemiological studies showed that mild hyperbilirubinemia has beneficial effects on the prevention of cardiovascular disease, type 2 diabetes mellitus, and metabolic syndrome. In mammals, bilirubin plays a major role as a potent antioxidant. Uridine 5'-diphospho-glucuronosyl transferase (UGT)1A1 variants coding for bilirubin UDP-glucuronosyl transferase resulting in mild hyperbilirubinemia (as in Gilbert syndrome (GS)) may confer a strong genetic advantage. Strategies to boost bioavailability of bilirubin or to mimic GS represent an attractive approach to prevent many oxidative stress and inflammation-mediated diseases. Even a tiny, micromolar increase in serum bilirubin concentrations substantially decreases the risk of oxidative stress-mediated diseases. There are several possible ways to achieve this, including lifestyle changes, changes in dietary patterns, regular physical activities, or use of chemical drug or of specific plant products either in the form of regular food items or nutraceuticals. Further basic and experimental research is required to fully uncover this promising therapeutic field.

Relationship between UGT1A1*27 and UGT1A1*7 polymorphisms and irinotecan-related toxicities in patients with lung cancer

Background

The objective of this study was to evaluate the effects of gene polymorphisms, including UGT1A1*7, *27, and *29, on the safety of irinotecan therapy.

Methods

The eligibility criteria were: lung cancer patients scheduled to undergo irinotecan therapy, aged ≥ 20 years, with a performance status of 0–2. Thirty‐one patients were enrolled and their blood was collected and used to examine the frequency of UGT1A1*6, *7, *27, *28, and *29 polymorphisms and the concentrations of irinotecan, SN‐38, and SN‐38G after irinotecan therapy.

Results

The patients’ characteristics were as follows: male/female 25/6, median age 71 years (range 55–84), stage IIB/IIIA/IIIB/IV 2/6/11/12, and adenocarcinoma/squamous cell carcinoma/small cell carcinoma/other 14/10/3/4, respectively. The −/−, *6/−, *7/−, *27/−, *28/−, and *29/− UGT1A1 gene polymorphisms were observed in 10 (32%), 10 (32%), 2 (6%), 2 (6%), 7 (23%), and 0 (0%) cases, respectively. The UGT1A1*27 polymorphism occurred separately from the UGT1A1*28 polymorphism. The lowest leukocyte counts of the patients with the UGT1A1*27 and UGT1A1*6 gene polymorphisms were lower than those observed in the wild‐type patients. SN‐38 tended to remain in the blood for a prolonged period after the infusion of irinotecan in patients with UGT1A1*27 or UGT1A1*28 polymorphisms. No severe myelotoxicity was seen in the patients with UGT1A1*7.

Conclusion

UGT1A1*27 can occur separately from UGT1A1*28 and is related to leukopenia during irinotecan treatment. UGT1A1*7 is less relevant to irinotecan‐induced toxicities, and UGT1A1*29 seems to have little clinical impact.

Colorectal cancer patients with liver metastases and severe hyperbilirubinemia: A consecutive series that explores the benefits and risks of chemotherapy

Background:

Do colorectal cancer patients with hyperbilirubinemia and liver metastases benefit from chemotherapy?

Methods/Results:

This study entailed a review of 3,019 consecutive patients with colorectal cancer. Within this cohort, 20 met the study’s a priori selection criteria, which included a new diagnosis of colorectal cancer, no prior therapy, and a total bilirubin of ≥3.0 mg/dL. All 20 patients had liver metastases, and as a whole the group had a median serum bilirubin of 6.4 mg/dL (range 3.1, 28 mg/dL). Six patients received chemotherapy with an oxaliplatin-containing regimen, and four subsequently sustained a drop in their bilirubin. In one instance, a drop from 27.2 to 2.5 mg/dL occurred. These six patients lived a median of 71 days (range 23+, 283 days), but one treatment-related death occurred. In contrast, patients who received only supportive care lived a median of 28 days.

Conclusion:

Chemotherapy appears to provide modest benefit to newly diagnosed colorectal cancer patients with severe hyperbilirubinemia.

Correlation between bilirubin glucuronidation and estradiol-3-gluronidation in the presence of model UDP-glucuronosyltransferase 1A1 substrates/inhibitors

Inhibition of UDP-glucuronosyltransferase (UGT) 1A1-catalyzed bilirubin glucuronidation by drug compounds may potentially be of clinical concern. However, in drug discovery and development settings, bilirubin is less than an ideal in vitro probe for assessing the potential of a chemical entity to inhibit bilirubin glucuronidation. In part, this is due to the propensity of bilirubin to photodegrade and to the instability of its metabolites. To this end, the utility of estradiol-3-glucuronidation as a surrogate in vitro predictor for interactions with bilirubin was evaluated. The glucuronidation kinetics of bilirubin and estradiol were carefully characterized with recombinant UGT1A1 expressed in human embryonic kidney 293 cells. Consistent with previous reports, estradiol-3-glucuronidation displayed sigmoidal kinetics, whereas bilirubin glucuronidation exhibited typical hyperbolic kinetics. The two compounds also mutually inhibited the metabolism of the other. Sixteen UGT1A1 substrates/inhibitors were evaluated as effectors of each reaction. Fourteen compounds inhibited both bilirubin and estradiol glucuronidation. However, two compounds (ethinylestradiol and daidzein) exhibited mixed effects (concentration-dependent activation and inhibition) on estradiol-3-glucuronidation, whereas bilirubin glucuronidation was inhibited by both compounds. In addition, 7-ethyl-10-hydroxycamptothecin, a substrate of UGT1A1 (reported K(m) = 24 μM) seemed to be a weak inhibitor of bilirubin glucuronidation (IC(50) = 356.4 μM) but a partial inhibitor of estradiol-3-glucuronidation. The IC(50) values of the inhibitors against estradiol-3-glucuronidation were strongly correlated with IC(50) values against bilirubin glucuronidation, resulting in an R(2) value of 0.9604 (activator excluded) or 0.8287 (activator included). Thus, estradiol-3-glucuronidation can serve as a good surrogate for predicting inhibition of bilirubin glucuronidation with the caveat that occasionally compounds may demonstrate activation of estradiol-3-glucuronidation.

Bilirubin glucuronidation revisited: proper assay conditions to estimate enzyme kinetics with recombinant UGT1A1

Bilirubin, an end product of heme catabolism, is primarily eliminated via glucuronic acid conjugation by UGT1A1. Impaired bilirubin conjugation, caused by inhibition of UGT1A1, can result in clinical consequences, including jaundice and kernicterus. Thus, evaluation of the ability of new drug candidates to inhibit UGT1A1-catalyzed bilirubin glucuronidation in vitro has become common practice. However, the instability of bilirubin and its glucuronides presents substantial technical challenges to conduct in vitro bilirubin glucuronidation assays. Furthermore, because bilirubin can be diglucuronidated through a sequential reaction, establishment of initial rate conditions can be problematic. To address these issues, a robust high-performance liquid chromatography assay to measure both bilirubin mono- and diglucuronide conjugates was developed, and the incubation conditions for bilirubin glucuronidation by human embryonic kidney 293-expressed UGT1A1 were carefully characterized. Our results indicated that bilirubin glucuronidation should be assessed at very low protein concentrations (0.05 mg/ml protein) and over a short incubation time (5 min) to assure initial rate conditions. Under these conditions, bilirubin total glucuronide formation exhibited a hyperbolic (Michaelis-Menten) kinetic profile with a K(m) of ∼0.2 μM. In addition, under these initial rate conditions, the relative proportions between the total monoglucuronide and the diglucuronide product were constant across the range of bilirubin concentration evaluated (0.05-2 μM), with the monoglucuronide being the predominant species (∼70%). In conclusion, establishment of appropriate incubation conditions (i.e., very low protein concentrations and short incubation times) is necessary to properly characterize the kinetics of bilirubin glucuronidation in a recombinant UGT1A1 system.

Pharmacogenetic testing for uridine diphosphate glucuronosyltransferase 1A1 polymorphisms: are we there yet?

Recent changes to the labels of three prescription drugs--irinotecan, 6-mercaptopurine, and warfarin--include recommendations for pharmacogenetic testing in patients. Thus, clinicians are faced with determining the utility and practicality of pharmacogenetic testing in clinical practice. We illustrate the clinical implications that this testing may have using irinotecan, an agent approved for the treatment of metastatic colorectal cancer, as an example. A clinical association between the drug's active metabolite and toxicity has been found. By performing uridine diphosphate glucuronosyltransferase (UGT) 1A1 genetic testing, some studies have been able to predict which patients receiving irinotecan will experience the toxicity. Thus, irinotecan's package insert was revised to include a recommendation for such testing. In addition, the United States Food and Drug Administration approved a clinical test for the UGT1A1*28 allele. These events demonstrate that pharmacogenetics has entered the realm of clinical practice. However, the transition from bench to bedside of these tests has distinct challenges such as population differences, test sensitivity, and the role of other genetic and nongenetic factors that influence drug toxicity. In addition, ethical and logistic implications of pharmacogenetic testing exist.