A combination of pre-screening for DPD deficiency by genotyping/phenotyping methods and pharmacokinetics-guided dosing of 5-FU for precision treatment to prevent severe toxicity in gastrointestinal cancer patients

Rationale:
Fluorouracil (5-FU) are broadly used in chemotherapeutic regimens for the treatment of cancers. Dihydropyrimidine dehydrogenase (DPD) is a major enzyme in the 5-FU metabolism pathway. Patients with a partial or complete DPD deficiency have a strongly reduced capacity to metabolize 5-FU which may result in severe or life-threatening toxicity when treated with a standard dose of fluoropyrimidines. A partial DPD deficiency is present in 3–5% of the North American and European population. DPD deficiency is most often caused by genetic variants in the gene encoding DPD (DPYD). The four DPYD variants considered most clinically relevant and with statistically significant association with severe toxicity are DPYD*2A (rs3918290, c.1905+1G>A, IVS14+1G>A), c.2846A>T (rs67376798, D949V), c.1679T>G (rs55886062, DPYD*13, I560S), and c.1236G>A (rs56038477, E412E, in haplotype B3). Prospective testing for DPD deficiency can prevent severe toxicity or mortality. Several methods have been proposed for detection of DPD deficiency, based on either genotyping of DPYD or measurement of the DPD phenotype. However, DPD deficiency is not the only factor associated with variable concentrations of 5-FU. 5-FU displays an exposure-response relationship between systemic exposure and clinical events. Therapeutic Drug Monitoring (TDM) or pharmacokinetics (PK)-guided dosing of 5-FU is also considered as an alternative to ensure an acceptable exposure of 5-FU. Upfront DPD screening combined with PK guided 5-FU dosing as a tool to personalize treatment has never been studied before. In this study, we aim to investigate the PK of 5-FU for the 4 most common DPYD genetic variants, in order to better define a safe starting dose for 5-FU in DPD deficient patients.

Objectives:
The primary objective of this study is to investigate the clearance of 5-FU for the 4 most common DPYD gene variants compared to the clearance of 5-FU in DPYD wild-type patients. The secondary objectives of this study are to determine the toxicity incidence and the extent of DPD deficiency as measured by Uracil Loading Test (ULT) for the 4 most common DPYD variants, to evaluate the safety and tolerability of reduced starting dose of 5-FU in patients with DPD deficiency, to demonstrate the ability to achieve a target AUC range , to establish that PK-guided 5-FU dosing decreases the incidence of 5-FU related toxicities, and to establish the sensitivity, specificity and predictive values of the DPYD genotyping test.

Study design:
The study is designed as a single-centre prospective inception cohort study. All patients will be screened for DPD deficiency by DPYD genotyping and separated into two groups; DPYD common variants and control group. Patients with DPYD wild-type but who experience CTC grade 3-4 toxicity will also be included in this study as a toxicity group. Patients will be tested with an oral ULT to identify their DPD phenotype and measured an endogenous U/DHU ratio. Therapeutic drug monitoring will be performed to follow-up patients’ 5-FU plasma concentration after start chemotherapy treatment. 5-FU plasma concentrations will be monitored until a steady state AUC of 20-30 mg.h/L is reached or maximum 4 treatment cycles is reached.

Study population:
All gastrointestinal cancer patients aged 18 years and older who are scheduled to receive treatment with fluoropyrimidine based chemotherapy.
Treatment:
All patients will be treated with a standard chemotherapy regimen for their respective gastrointestinal cancer. Only 5-FU based regimens will be considered for this study. Patients will receive adjusted 5-FU doses based on their condition, including body surface area, gene activity score or DPD status, and steady state AUC from the previous dose, until their AUC reaches a target range. Patients will continue to receive regular treatment, as long as needed and/or tolerated.

Main study parameters:
The primary outcome of the study is the clearance of 5-FU at steady state (Clss) measured in ml/min. Among cancer patients treated with 5-FU, we will compare the variation in clearance between the four common DPYD variant allele carriers and DPYD wild-type carriers. The secondary study parameters are the incidence of 5-FU related toxicities, U/DHU ratio, DPD phenotype (EM, IM, and PM), 5-FU doses, dosage adjustment and time to reach target AUC (cycle number).

Nature and extent of the burden and the risk-benefit analysis and group relatedness:

The burden associated with participation:
Patients have to participate in this study for a maximum of 5 study visits.
Pre-screening: Physical examination and DPYD genotyping (1 blood sample (3 mL))
Visit 1*: ULT + endogenous U/DHU ratio (3 blood sample, total 9 mL)
Visit 2*: 5-FU TDM (1 blood sample 3 mL)
Visit 3**: 5-FU TDM (1 blood sample 3 mL)
Visit 4**: 5-FU TDM (1 blood sample 3 mL)
Visit 5**: 5-FU TDM (1 blood sample 3 mL)
* These 2 visits can be switched around, according to the physicians’ discretion.
** If AUCss of previous cycle does not reach target AUC.

The risk-benefit analysis:
The possible risks of this study are additional blood measurements and adverse reactions that might occur from ULT. Uracil is one of chemical bases that are part of RNA and previous studies show absence of unfavorable effect from uracil consumption. Therefore, excess risks are considered to be low. According to previous studies, patients who receive adjusted 5-FU dose based on their DPD activity and 5-FU previous dose are more likely to achieve an optimum AUC target range and experience less 5-FU related toxicity. Thus, patients who will participate in this study have greater benefits than risks.
Group relatedness:
5-FU based chemotherapy regimens are the first-line therapy for gastrointestinal cancer patients. Therefore, this group of patients is related to this study.

We expect that patients who are screened for DPYD deficiency and receive adjusted 5-FU dose based on their gene activity score and PK-guided 5-FU dosing will experience less 5-FU related grade 3-4 toxicities and reach a target AUC (20-30 mg.h/L) within 4 treatment cycles.

Patients have to participate in this study for a maximum of 5 study visits.
Pre-screening: Physical examination and DPYD genotyping (1 blood sample (3 mL))
Visit 1*: ULT + endogenous U/DHU ratio (3 blood sample, total 9 mL)
Visit 2*: 5-FU TDM (1 blood sample 3 mL)
Visit 3**: 5-FU TDM (1 blood sample 3 mL)
Visit 4**: 5-FU TDM (1 blood sample 3 mL)
Visit 5**: 5-FU TDM (1 blood sample 3 mL)
* These 2 visits can be switched around, according to the physicians’ discretion.
** If AUCss of previous cycle does not reach target AUC.

5-FU dose adaptation according to IATDMCT guideline