Relevance of CYP3A4*20, UGT1A1*37 and UGT1A1*28 variants in irinotecan-induced severe toxicity

Irinotecan dosing and pharmacogenomics: a comprehensive exploration based on UGT1A1 variants and emerging insights

Irinotecan is a critical anticancer drug used to treat metastatic colorectal cancer and advanced pancreatic ductal adenocarcinoma by obstructing topoisomerase 1; however, it can cause minor-to-severe and life-threatening adverse effects. UDP glucuronosyltransferase family 1 member A1 (UGT1A1) polymorphisms increase the risk of irinotecan-induced neutropenia and diarrhea. Hence, screening for UGT1A1 polymorphisms before irinotecan-based chemotherapy is recommended to minimize toxicity, whereas liposomes offer the potential to deliver irinotecan with fewer side effects in patients with pancreatic ductal adenocarcinoma. This review presents a comprehensive overview of the effects of genotype-guided dosing of irinotecan on UGT1A1*28 and UGT1A1*6 variants, incorporating pharmacogenomic research, optimal regimens for metastatic colorectal and pancreatic cancer treatment using irinotecan, guidelines for toxicity reduction, and an evaluation of the cost-effectiveness of UGT1A1 genotype testing.

Gene Polymorphisms and Drug-Drug Interactions Determine the Metabolic Profile of Blonanserin

This study aimed to evaluate the effects of cytochrome P450 3A4 (CYP3A4) gene polymorphism and drug interaction on the metabolism of blonanserin. Human recombinant CYP3A4 was prepared using the Bac-to-Bac baculovirus expression system. A microsomal enzyme reaction system was established, and drug-drug interactions were evaluated using Sprague-Dawley rats. Ultra-performance liquid chromatography-tandem mass spectrometry was used to detect the concentrations of blonanserin and its metabolite. Compared with wild type CYP34A, the relative clearance of blonanserin by CYP3A4.29 significantly increased to 251.3%, while it decreased notably with CYP3A4.4, 5, 7, 8, 9, 10, 12, 13, 14, 16, 17, 18, 23, 24, 28, 31, 33, and 34, ranging from 6.09% to 63.34%. Among 153 tested drugs, nimodipine, felodipine, and amlodipine were found to potently inhibit the metabolism of blonanserin. Moreover, the inhibitory potency of nimodipine, felodipine, and amlodipine varied with different CYP3A4 variants. The half-maximal inhibitory concentration and enzymatic kinetics assay demonstrated that the metabolism of blonanserin was noncompetitively inhibited by nimodipine in rat liver microsomes and was inhibited in a mixed manner by felodipine and amlodipine in both rat liver microsomes and human liver microsomes. When nimodipine and felodipine were coadministered with blonanserin, the area under the blood concentration-time curve (AUC)(0-t), AUC(0-∞), and C max of blonanserin increased. When amlodipine and blonanserin were combined, the C max of blonanserin C increased remarkably. The vast majority of CYP3A4 variants have a low ability to catalyze blonanserin. With combined administration of nimodipine, felodipine, and amlodipine, the elimination of blonanserin was inhibited. This study provides the basis for individualized clinical use of blonanserin. SIGNIFICANCE STATEMENT: The enzyme kinetics of novel CYP3A4 enzymes for metabolizing blonanserin were investigated. Clearance of blonanserin by CYP3A4.4, 5, 7-10, 12-14, 16-18, 23-24, 28, 31, 33, and 34 decreased notably, but increased with CYP3A4.29. Additionally, we established a drug interaction spectrum for blonanserin, in which nimodipine, felodipine, and amlodipine kinetics exhibited mixed inhibition. Moreover, their inhibitory potencies decreased with CYP3A4.4 and 5 compared to CYP3A4.1. This study provides essential data for personalized clinical use of blonanserin.

Predicting drug response and toxicity in metastatic colorectal cancer: the role of germline markers

INTRODUCTION

Despite the introduction of targeted agents leading to therapeutic advances, clinical management of patients with metastatic colorectal cancer (mCRC) is still challenged by significant interindividual variability in treatment outcomes, both in terms of toxicity and therapy efficacy. The study of germline genetic variants could help to personalize and optimize therapeutic approaches in mCRC.

AREAS COVERED

A systematic review of pharmacogenetic studies in mCRC patients published on PubMed between 2011 and 2021, evaluating the role of germline variants as predictive markers of toxicity and efficacy of drugs currently approved for treatment of mCRC, was perfomed.

EXPERT OPINION

Despite the large amount of pharmacogenetic data published to date, only a few genetic markers (i.e., DPYD and UGT1A1 variants) reached the clinical practice, mainly to prevent the toxic effects of chemotherapy. The large heterogeneity of available studies represents the major limitation in comparing results and identifying potential markers for clinical use, the role of which remains exploratory in most cases. However, the available published findings are an important starting point for future investigations. They highlighted new promising pharmacogenetic markers within the network of inflammatory and immune response signaling. In addition, the emerging role of previously overlooked rare variants has been pointed out.

Why We Need to Take a Closer Look at Genetic Contributions to CYP3A Activity

Cytochrome P450 3A (CYP3A) subfamily enzymes are involved in the metabolism of 40% of drugs in clinical use. Twin studies have indicated that 66% of the variability in CYP3A4 activity is hereditary. Yet, the complexity of the CYP3A locus and the lack of distinct drug metabolizer phenotypes has limited the identification and clinical application of CYP3A genetic variants compared to other Cytochrome P450 enzymes. In recent years evidence has emerged indicating that a substantial part of the missing heritability is caused by low frequency genetic variation. In this review, we outline the current pharmacogenomics knowledge of CYP3A activity and discuss potential future directions to improve our genetic knowledge and ability to explain CYP3A variability.

Microbiota-Host-Irinotecan Axis: A New Insight Toward Irinotecan Chemotherapy

Irinotecan (CPT11) and its active metabolite ethyl-10-hydroxy-camptothecin (SN38) are broad-spectrum cytotoxic anticancer agents. Both cause cell death in rapidly dividing cells (e.g., cancer cells, epithelial cells, hematopoietic cells) and commensal bacteria. Therefore, CPT11 can induce a series of toxic side-effects, of which the most conspicuous is gastrointestinal toxicity (nausea, vomiting, diarrhea). Studies have shown that the gut microbiota modulates the host response to chemotherapeutic drugs. Targeting the gut microbiota influences the efficacy and toxicity of CPT11 chemotherapy through three key mechanisms: microbial ecocline, catalysis of microbial enzymes, and immunoregulation. This review summarizes and explores how the gut microbiota participates in CPT11 metabolism and mediates host immune dynamics to affect the toxicity and efficacy of CPT11 chemotherapy, thus introducing a new concept that is called "microbiota-host-irinotecan axis". Also, we emphasize the utilization of bacterial β-glucuronidase-specific inhibitor, dietary interventions, probiotics and strain-engineered interventions as emergent microbiota-targeting strategies for the purpose of improving CPT11 chemotherapy efficiency and alleviating toxicity.

Elucidating the role of pharmacogenetics in irinotecan efficacy and adverse events in metastatic colorectal cancer patients

INTRODUCTION

Irinotecan is a cytotoxic agent that is widely used in the treatment of several types of solid tumors. However, although it is generally well tolerated, approximately 20% to 35% of patients develop severe toxicity, particularly delayed-type diarrhea and neutropenia. As the incidence of such toxicities is often associated with the UGT1A1 *28/*28, *6/*28 and *6/*6 genotypes, individualized dosing could reduce these adverse events. Furthermore, prospective trials have shown that patients harboring the UGT1A1 *1/*1 and *1/*28 genotypes can tolerate higher doses of irinotecan, which may in turn impact on a better outcome. Upfront UGT1A1 genotyping could therefore be a usefulness strategy in order to individualize irinotecan dosing, but consensus on the recommended dose based on the UGT1A1 genotype is still lacking.

AREAS COVERED

This review summarizes the results of the main pharmacogenetic studies focused on irinotecan. We provide an overview of current evidence and recommendations for individualized dosing of irinotecan in metastatic colorectal cancer patients.

EXPERT OPINION

Implementation of UGT1A1*28 and UGT1A1*6 genotyping in clinical practice is a first step toward personalizing irinotecan therapy. This approach is likely to improve patient care and reduce healthcare costs. Future large and prospective studies will help to clarify the clinical value of other genetic markers in irinotecan treatment personalization.

TaqMan real time PCR for the Detection of the Gilbert's Syndrome Markers UGT1A1*28; UGT1A1*36 and UGT1A1*37

Gilbert's syndrome is characterized by mild unconjugated hyperbilirubinemia. The key of this disease is a diminished activity of UDP-glucuronosyltransferase 1A1 (UGT1A1). TA insertion into the TATA box promoter region of the UGT1A1 gene on chromosome 2 is the genetic basis of Gilbert's syndrome (UGT1A1*28). An extra TA insert leads to eight (TA)8 repeats (UGT1A1*37) resulting in a further reduction of glucuronidation activity. A variant lacking one TA repeat (TA)5 (UGT1A1*36) has been identified. (TA)8 repeats (UGT1A1*37) and (TA)5 (UGT1A1*36) have been detected in Africans (frequency up to 0.07 and 0.08 respectively). We present a real time PCR method for genotyping the UGT1A1 (TA)n polymorphism (UGT1A1*28, UGT1A1*36, UGT1A1*37) using Taqman PCR on 7500 and cfx96 Real-Time PCR System. We present a real time PCR method for genotyping the UGT1A1 (TA)n polymorphism (UGT1A1*28, UGT1A1*36, UGT1A1*37) using Taqman PCR. About clinical validation, all 53 samples collected from patients referred for suspected Gilbert's syndrome were analyzed. We found 21 on the 53 patients (39.6%) were homozygotes (UGT1A1-TATA (TA)6) and referred as wild-type, 13 on the 53 patients (24.5%) were homozygotes (UGT1A1-TATA (TA)7) and referred as mutated, 1 on the 53 patients (1.9%) were homozygotes (UGT1A1-TATA (TA)8) and referred as mutated, 1 on the 53 patients (1.9%) were heterozygotes (UGT1A1-TATA (TA)7/8) and referred as mutated, 1 on the 53 patients (1.9%) were heterozygotes (UGT1A1-TATA (TA)5/6) and referred as mutated, and 16 on the 53 patients (30.2%) were heterozygotes (UGT1A1-TATA (TA)6/7). None were homozygotes UGT1A1-TATA (TA)5, homozygotes UGT1A1-TATA (TA)8, or heterozygotes with (TA)5 or (TA)8 alleles. The newly described technique represents a valid alternative method to sequencing, mainly due to its rapidity, easiness, and minor costs.

The Road so Far in Colorectal Cancer Pharmacogenomics: Are We Closer to Individualised Treatment?

In recent decades, survival rates in colorectal cancer have improved greatly due to pharmacological treatment. However, many patients end up developing adverse drug reactions that can be severe or even life threatening, and that affect their quality of life. These remain a limitation, as they may force dose reduction or treatment discontinuation, diminishing treatment efficacy. From candidate gene approaches to genome-wide analysis, pharmacogenomic knowledge has advanced greatly, yet there is still huge and unexploited potential in the use of novel technologies such as next-generation sequencing strategies. This review summarises the road of colorectal cancer pharmacogenomics so far, presents considerations and directions to be taken for further works and discusses the path towards implementation into clinical practice.

ABCB1 Genetic Variants as Predictors of Irinotecan-Induced Severe Gastrointestinal Toxicity in Metastatic Colorectal Cancer Patients

Irinotecan is widely used in the treatment of metastatic colorectal cancer (mCRC) despite its severe toxicities. Toxicity is often associated with the UGT1A1*28/*28 genotype. An explanation for idiopathic toxicity beyond the UGT1A1 biomarker, however, remains a major concern for clinicians. One of the main irinotecan transporters is P-glycoprotein (P-gp), which is a hepatic efflux pump encoded by ABCB1. P-gp is involved in the biliary excretion of irinotecan and its active metabolite SN-38. We aimed to assess whether functional variants in ABCB1 also contribute to identifying patients at risk of toxicity. A cohort of 308 mCRC patients treated with irinotecan-based regimens were genotyped for polymorphisms in ABCB1 (rs1128503, rs2032582, and rs1045642). The effect of these variants and their haplotypes on irinotecan-induced severe toxicity (diarrhea, neutropenia, asthenia, nausea, and mucositis) was assessed. After adjusting for the relevant clinical and pathological parameters in the multivariate analysis, we found rs1128503 was significantly associated with severe diarrhea and mucositis (P=0.014 and P=0.002, respectively). Additionally, rs2032582 was associated with severe mucositis (P<0.001). Our results show that rs1128503 genotyping could help to predict severe gastrointestinal toxicity induced by irinotecan.

Sacituzumab Govitecan-hziy in Refractory Metastatic Triple-Negative Breast Cancer

BACKGROUND

Standard chemotherapy is associated with low response rates and short progression-free survival among patients with pretreated metastatic triple-negative breast cancer. Sacituzumab govitecan-hziy is an antibody-drug conjugate that combines a humanized monoclonal antibody, which targets the human trophoblast cell-surface antigen 2 (Trop-2), with SN-38, which is conjugated to the antibody by a cleavable linker. Sacituzumab govitecan-hziy enables delivery of high concentrations of SN-38 to tumors.

METHODS

We conducted a phase 1/2 single-group, multicenter trial involving patients with advanced epithelial cancers who received sacituzumab govitecan-hziy intravenously on days 1 and 8 of each 21-day cycle until disease progression or unacceptable toxic effects. A total of 108 patients received sacituzumab govitecan-hziy at a dose of 10 mg per kilogram of body weight after receiving at least two previous anticancer therapies for metastatic triple-negative breast cancer. The end points included safety; the objective response rate (according to Response Evaluation Criteria in Solid Tumors, version 1.1), which was assessed locally; the duration of response; the clinical benefit rate (defined as a complete or partial response or stable disease for at least 6 months); progression-free survival; and overall survival. Post hoc analyses determined the response rate and duration, which were assessed by blinded independent central review.

RESULTS

The 108 patients with triple-negative breast cancer had received a median of 3 previous therapies (range, 2 to 10). Four deaths occurred during treatment; 3 patients (2.8%) discontinued treatment because of adverse events. Grade 3 or 4 adverse events (in ≥10% of the patients) included anemia and neutropenia; 10 patients (9.3%) had febrile neutropenia. The response rate (3 complete and 33 partial responses) was 33.3% (95% confidence interval [CI], 24.6 to 43.1), and the median duration of response was 7.7 months (95% CI, 4.9 to 10.8); as assessed by independent central review, these values were 34.3% and 9.1 months, respectively. The clinical benefit rate was 45.4%. Median progression-free survival was 5.5 months (95% CI, 4.1 to 6.3), and overall survival was 13.0 months (95% CI, 11.2 to 13.7).

CONCLUSIONS

Sacituzumab govitecan-hziy was associated with durable objective responses in patients with heavily pretreated metastatic triple-negative breast cancer. Myelotoxic effects were the main adverse reactions. (Funded by Immunomedics; IMMU-132-01 ClinicalTrials.gov number, NCT01631552.).

Relevance of CYP3A4*20, UGT1A1*37 and UGT1A1*28 variants in irinotecan-induced severe toxicity

Severe irinotecan-induced toxicity is associated with UGT1A1 polymorphisms. However, some patients develop side-effects despite harbouring a normal UGT1A1 genotype. As CYP3A4 is also an irinotecan-metabolizing enzyme, our study aimed to elucidate the influence of the CYP3A4*20 loss-of-function allele in the toxicity profile of these patients. Three-hundred and eight metastatic colorectal cancer patients treated with an irinotecan-containing chemotherapy were studied. The presence of CYP3A4*20, UGT1A1*37 and UGT1A1*28 alleles was tested. Associations between these genetic variants and toxicity were evaluated. UGT1A1*28 was significantly associated with severe diarrhoea, neutropenia and asthenia (P = 0.002, P = 0.037 and P = 0.041, respectively). One patient with the UGT1A1*28/*37 genotype presented with grade IV neutropenia and lethal septic shock. One heterozygous UGT1A1 (*1/*28) patient also carried the CYP3A4*20 allele but did not develop toxicity. We confirm that UGT1A1*37 and UGT1A1*28 are associated with severe toxicity and suggest that the CYP3A4*20 allele does not play a role in irinotecan-induced toxicity.