The use of pharmacogenetics to increase the safety of colorectal cancer patients treated with fluoropyrimidines

Pharmacogenomic-guided dosing of fluoropyrimidines beyond DPYD: time for a polygenic algorithm?

Fluoropyrimidines are chemotherapeutic agents widely used for the treatment of various solid tumors. Commonly prescribed FPs include 5-fluorouracil (5-FU) and its oral prodrugs capecitabine (CAP) and tegafur. Bioconversion of 5-FU prodrugs to 5-FU and subsequent metabolic activation of 5-FU are required for the formation of fluorodeoxyuridine triphosphate (FdUTP) and fluorouridine triphosphate, the active nucleotides through which 5-FU exerts its antimetabolite actions. A significant proportion of FP-treated patients develop severe or life-threatening, even fatal, toxicity. It is well known that FP-induced toxicity is governed by genetic factors, with dihydropyrimidine dehydrogenase (DPYD), the rate limiting enzyme in 5-FU catabolism, being currently the cornerstone of FP pharmacogenomics. DPYD-based dosing guidelines exist to guide FP chemotherapy suggesting significant dose reductions in DPYD defective patients. Accumulated evidence shows that additional variations in other genes implicated in FP pharmacokinetics and pharmacodynamics increase risk for FP toxicity, therefore taking into account more gene variations in FP dosing guidelines holds promise to improve FP pharmacotherapy. In this review we describe the current knowledge on pharmacogenomics of FP-related genes, beyond DPYD, focusing on FP toxicity risk and genetic effects on FP dose reductions. We propose that in the future, FP dosing guidelines may be expanded to include a broader ethnicity-based genetic panel as well as gene*gene and gender*gene interactions towards safer FP prescription.

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.

DPYD and UGT1A1 Pharmacogenetic Testing in Patients with Gastrointestinal Malignancies: An Overview of the Evidence and Considerations for Clinical Implementation

Gastrointestinal (GI) malignancies are among the most commonly diagnosed cancers worldwide. Despite the introduction of targeted and immunotherapy agents in the treatment landscape, cytotoxic agents, such as fluoropyrimidines and irinotecan, remain as the cornerstone of chemotherapy for many of these tumors. Pharmacogenetics (PGx) is a rapidly evolving field that accounts for interpatient variability in drug metabolism to predict therapeutic response and toxicity. Given the significant incidence of severe treatment-related adverse events associated with cytotoxic agents, utilizing PGx can allow clinicians to better anticipate drug tolerability while minimizing treatment interruptions or delays. In this review, the PGx profiles of drug-gene pairs with potential impact in GI malignancy therapy - DPYD-5-fluorouracil/capecitabine and UGT1A1-irinotecan - and the available clinical evidence of their roles in reducing severe adverse events are discussed. Considerations for clinical implementation, such as optimal laboratory workflows, electronic health record integration, and stakeholder engagement, as well as provider education, are addressed. Last, exploratory PGx markers in GI malignancy treatment are described. As the PGx knowledge base rapidly evolves, pharmacists will be vital in leveraging their pharmacology knowledge and clinical skills to implement PGx testing in the clinic.