Shunji Futagawa

Prognostic impact of orotate phosphoribosyl transferase among 5‐fluorouracil metabolic enzymes in resectable colorectal cancers treated by oral 5‐fluorouracil‐based adjuvant chemotherapy

Orotate phosphoribosyl transferase (OPRT) is the main enzyme that involves in phosphoribosylation of 5‐fluorouracil (5‐FU), an essential step that leads to tumor growth inhibition. In our study, the prognostic relevance of OPRT, thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) in resectable colorectal cancer (CRC) patients treated by oral 5‐FU were compared to further clarify the prognostic value of OPRT. Tumor tissue was collected from 90 CRC patients and the patients were followed for 5.2 years (Median). TS, DPD and OPRT activities in the extract of tumor tissue were determined enzymatically. The cut‐off value of OPRT (0.147 nmol/(min mg), TS (0.044 pmol/mg) and DPD (72.10 pmol/(min mg) were determined by maximal χ2 method. Among these 5‐FU metabolic enzymes, only high OPRT group demonstrated significantly better disease‐free survival (DFS) (p = 0.0152) and better overall survival (p = 0.0078). In Cox regression analysis, node status (p < 0.0005) and OPRT (p = 0.044) were significant factors for DFS. OPRT activity in tumor tissue was a predictor of prognosis in resectable CRC patients treated by oral 5‐FU‐based adjuvant chemotherapy, and was useful to pick‐up high risk patients independent from known prognosis factors.

Evaluation of the individual 50% inhibitory area under the concentration curve of 5-fluorouracil based on the collagen gel droplet embedded culture drug sensitivity test in colorectal cancer

We have previously reported the 5-fluorouracil (5-FU) sensitivity of cancer cells from colorectal cancer (CRC) patients using the collagen gel droplet embedded culture-drug sensitivity test (CD-DST) under multiple drug concentrations and contact durations. Moreover, the area under the concentration curve (AUC) and growth inhibition rate (IR) were combined, resulting in the AUC-IR curve, which was approximated to the logarithmic curve. In the present study, we used the AUC-IR curve to calculate the individualized AUCIR50, the AUC value that imparts 50% growth inhibition. Individual AUCIR50 was calculated in CRC patients, and its distribution was evaluated. The cumulative distribution of individual AUCIR50 was regressed over two lines (logarithmic scale). Among the 45 resectable CRC patients, those who achieved more than the individual AUCIR50 during post-operative 5-FU-based chemotherapy demonstrated a trend towards better disease-free survival compared to those who did not achieve AUCIR50. Of the Dukes D patients (n=10), those who achieved more than twice the individual AUCIR50 during post-operative 5-FU-based chemotherapy demonstrated significantly better survival rates (p=0.05) than those who did not. In this study, the distribution of the individual AUCIR50 suggested that approximately 6% of patients demonstrated very low 5-FU sensitivity. Therefore, the individual AUCIR50 was useful in classifying good, intermediate and poor 5-FU response. Achievement of the individual AUCIR50 may be a prerequisite for individualized 5-FU-based adjuvant chemotherapy. As well, the early achievement of twice the individual AUCIR50 may indicate an improved prognosis in Dukes D patients. The individual AUCIR50 using CD-DST is useful in determining the individualized chemotherapy of CRC patients, thus CD-DST has the potential to facilitate the establishment of individualized chemotherapy for CRC.