Correlation between endogenous DPD substrate concentrations and the pharmacokinetics and toxicity of 5-fluorouracil in patients with colorectal or pancreas cancer

The anticancer drug 5-fluorouracil (5-FU) is widely used in the treatment of
amongst others early and advanced colorectal, gastric, pancreas and breast
cancer. 5-FU is mainly metabolized by the enzyme dihydropyrimidine
dehydrogenase (DPD), an enzyme encoded by the DPYD gene. Genetic polymorphism
in this gene may lead to DPD deficiency and thereby an increased risk of
drug-induced severe toxicity. In the Caucasian population, 3 to 5% has a
partial DPD-deficiency and 0.1 to 0.2% has a complete deficiency.(1,2) DPD
deficiency can lead to severe toxicity (grade 3 to 5, according to CTC-AE
version 4.03), such as myelosuppression, mucositis, diarrhoea and hand-foot
syndrome. Measuring the DPYD genotype prior 5-FU-based chemotherapy has shown
to be able to prevent drug-induced severe toxicity of 5-FU. The clinical
utility has thus far been demonstrated for four polymorphisms, i.e. DPYD*2A;
*13; 2846A>T; 1236G>A, which are therefore routinely determined prior to start
of chemotherapy. Despite the use of genotyping, a significant proportion of
patients still develop 5-FU-related severe toxicity. Since both endogenous
uracil (U) and thymine (T) are being converted by DPD into dihydrouracil (DHU)
and dihydrothymine (DHT), respectively, patients with a low DHU/U and/or a low
DHT/T plasma ratio before start of 5-FU based therapy have higher risk of 5-FU
induced severe toxicity. It is not known what the correlation of the DHU/U
and/or DHT/T plasma ratios is compared to the actual DPD enzyme activity within
the white blood cells. The DPD enzyme activity will not only be compared to the
plasma ratios DHU/U and/or DHT/T but also to pharmacokinetics of 5-FU. As the
DPD enzyme activity test is a more time consuming, labour intense, complex and
expensive test to perform, the use of endogenous biomarkers such as uracil and
thymine might favour over the DPD enzyme activity test.
In this study we will investigate the correlation between the endogenous DPD
substrates uracil and thymine as well as the DPD enzyme activity with the
pharmacokinetics and toxicity of 5-FU in patients with colorectal or pancreas
cancer treated with prolonged infusions of 5-FU. The ultimate goal is to
develop an easy to measure additional predictive marker besides DPYD genotype
in order to prevent 5-FU induced severe toxicity.

Primary objective:
To determine the correlation between the baseline endogenous DPD substrate
plasma ratios of DHU/U and DHT/T with the pharmacokinetics of 5-FU in patients
with pancreas or colorectal cancer treated with intravenous 5-FU-based
chemotherapy.

Secondary objectives:
- To determine the potential changes in U, DHU, T and DHT concentrations over
time during the prolonged 5-FU infusion
- To determine the DHU/U, DHT/T and DHFU/FU ratios over time during 5-FU
prolonged infusion
- To establish a cut-off concentration in a daily Dutch patient population for
all measured analytes, their metabolites and ratios, including 5-FU, DHFU, U,
DHU, T and DHT
- To determine the effect of DPYD genotype on the U, DHU, T and DHT
concentrations and on the pharmacokinetics of 5-FU
- To determine the correlation between serious adverse events or 5-FU toxicity
to AUC of 5-FU, DHU/U or DHT/T ratio or DPD enzyme activity
- To determine the effect of other genetic polymorphisms on the
pharmacokinetics of 5-FU (if applicable)
- To determine the correlation between the DPD enzyme activity and the DHU/U,
DHT/T of DHFU/FU plasma ratios, and 5-FU pharmacokinetics.

Prospective, non-randomized, pharmacokinetic study

To determine the DPD enzyme activity a sample of 12mL whole blood (2x 6mL EDTA)
is obtained after connecting the port-a-cath. Since connecting the port-a-cath
is needed to administer the chemotherapy there is no need for a puncture.
At t=0, prior starting the 5-FU infusion, 4mL of whole blood (EDTA tube) is
obtained by using a venflon. This sample is used to determine the
concentrations of uracil, DHU, T and DHT.
During treatment the samples at t=0.5 and 2 hours are retracted by the same
venflon so there is no need for another puncture. The sample at t=44 hours is
taken by the port-a-cath, this way another puncture is not needed. At each time
point during treatment 8mL of whole blood (2x 4mL EDTA) will be retracted to
determine the concentrations of uracil, DHU, T, DHT, 5-FU and DHFU.
The risk of drawing blood from a vein include discomfort at the site of
puncture and possible redness and swelling around the puncture site. Since the
prolonged 5-FU infusion is routinely administered within the hospital the
intervention does not require additional or prolonged hospital visits.