Significance of Thymidine Kinase Activity in Renal Cell Carcinoma

Final results of a phase II study of S-1 in patients with cytokine-refractory metastatic renal cell carcinoma

OBJECTIVE

A planned primary analysis of a Phase II study of S-1 demonstrated that the drug was active and tolerable in Japanese patients with cytokine-refractory metastatic renal cell carcinoma. Furthermore, pharmacogenomic analysis suggested that low expression of thymidylate synthase mRNA may have been associated with clinical outcome in terms of overall response rate and progression-free survival. Here, we report the results of the final analysis assessing the efficacy and safety of S-1 including overall survival.

METHODS

Patients with renal cell carcinoma were eligible if they had had at least one regimen of cytokine for metastatic disease. S-1 was orally administered on Days 1-28 of a 42-day cycle until disease progression. The primary endpoint was the overall response rate, and the secondary endpoint included progression-free survival, overall survival and safety.

RESULTS

A total of 45 patients were treated with S-1 and were fully assessable for efficacy and safety. At the final analysis, a response was seen in 11 patients (overall response rate, 24.4%; 95% confidence interval: 12.9-39.5%), including two patients who achieved a complete response. The final median progression-free and overall survival were 9.2 and 42.8 months, respectively. The safety profile of S-1 was favorable. It was suggested that there was no relation between overall survival and the expression level of thymidylate synthase.

CONCLUSION

This final analysis confirms that S-1 treatment is effective and safe in patients with cytokine-refractory renal cell carcinoma.

Multicenter Phase II Trial of S-1 in Patients With Cytokine-Refractory Metastatic Renal Cell Carcinoma

Purpose

This phase II multicenter trial was conducted to evaluate the activity and safety of S-1 in Japanese patients with metastatic renal cell carcinoma (mRCC). We also examined the relation between response and mRNA expression levels of enzymes involved in the metabolism of fluorouracil (FU).

Methods

Patients with mRCC who had received nephrectomy in whom cytokine-based immunotherapy was ineffective or contraindicated were studied. S-1 was administered orally at 80-, 100-, or 120-mg daily, assigned according to body surface area, on days 1 to 28 of a 42-day cycle. The primary end point was the objective response rate. The mRNA expression levels of FU-related enzymes were measured by reverse-transcriptase polymerase chain reaction in formalin-fixed, paraffin-embedded specimens of tumors obtained at nephrectomy.

Results

A total of 45 eligible patients were enrolled. Eleven (24.4%) of 45 patients had partial responses to S-1, and 28 (62.2%) had stable disease. Median progression-free survival was 9.2 months. The severity of most adverse events was mild to moderate. The most common grade 3/4 drug-related adverse events were neutropenia (8.9%) and anorexia (8.9%). The expression level of thymidylate synthase (TS) mRNA was significantly lower in patients who responded to treatment (t-test, P = .048), and progression-free survival was significantly longer in patients whose TS mRNA expression levels were below the median value, as compared with those with higher levels (log-rank test, P = .006).

Conclusion

S-1 is active against cytokine-refractory mRCC. Quantification of TS mRNA levels in tumors before treatment may facilitate prediction of the response of mRCC to S-1.

The proliferation marker thymidine kinase 1 level is high in normal kidney tubule cells compared to other normal and malignant renal cells

The activity of the proliferation related enzyme thymidine kinase 1 (TK1) was reported to be 3-fold higher in extracts from normal kidney tissue as compare to renal carcinoma extracts [3]. To verify these unexpected results, determinations of the protein levels of TK1 in normal kidney and in samples from different types of renal cell carcinoma (RCC) were done with immunohistochemistry and Western blot analysis. Two anti-TK1 peptide antibodies reacting with different TK1 epitops were used. TK1 levels were high in tubule cells as compared to glomerulus cells and connective tissue cells, while an intermediary TK1 was observed in renal cell carcinoma (RCC) cells. Western blot analysis demonstrated high levels of TK1 in extract from normal kidney, and lower levels of TK1 in the RCC extracts. The specificity of TK1 staining was demonstrated in competition experiments with excess TK1 antigen. The high TK1 levels in normal kidney tubule cells suggest that they are in a form of activated G1-state. The relatively low TK1 level in RCC, representing TK1 expression in S-phase cells, is in accordance with the low overall proliferation rate of these tumors. These results suggest that cell cycle regulation of TK1 in normal tubule cells differ from that in other type of normal and malignant renal cells.

Thymidine kinase activity in serum of renal cell carcinoma patients is a useful prognostic marker

It is known that the concentration and activity of the DNA precursor enzyme thymidine kinase 1 (TK1) in serum is significantly elevated in patients with malignancies, as compared with levels in patients with benign tumours and those in healthy individuals. For the first time, the use of serum TK1 as a prognostic marker for patients with renal cell carcinoma (RCC) was examined. Serum TK1 protein (STK1p) concentration and serum TK1 activity (STK1a) were determined by a dot blot chemoluminescence assay and a radio enzyme assay, respectively. There was no correlation between STK1p and STK1a in the same sera from 27 RCC patients. Only one STK1p value as compared with 15 STK1a values was clearly above the cut-off values (2 pmol/l and 6 U/l, respectively) for healthy individuals. STK1a values did not correlate with the level of TK1 expression in tumour sections from the RCC patients, estimated by immunohistochemistry staining. However, there was a significant correlation between STK1a levels and the grade, stage and size of the RCC tumours. The discrepancy between the STK1p and the STK1a results is likely to be because of reduced ability of the TK1 antibody to recognize the STK1 in sera from RCC patients. We conclude that the activity of STK1 is a useful tool for evaluating the prognosis of patients with RCC.

Prognostic significance of orotate phosphoribosyltransferase activity in bladder carcinoma

BACKGROUND

5-Fluorouracil (5-FU), an antitumor agent, is used clinically against a variety of malignancies, including bladder carcinoma. 5-FU is a prodrug, and orotate phosphoribosyltransferase (OPRT) is the principal enzyme that converts 5-FU directly into an active antitumor metabolite, 5-fluoro-2'-deoxyuridine 5'-monophosphate. In addition, OPRT is the key enzyme in the de novo DNA and RNA synthetic process. To the authors' knowledge, little is known regarding the significance of OPRT in various malignancies, including bladder carcinoma. The authors analyzed the activity levels of OPRT in 60 bladder carcinomas and evaluated the association between the level of OPRT activity and the stage and grade status of bladder carcinoma. They also examined the prognostic significance of OPRT activity in patients with bladder carcinoma and the correlation between OPRT activity levels in bladder carcinoma cells and the sensitivity of those cells to 5-FU.

METHODS

OPRT activity levels in nonfixed, fresh-frozen specimens of bladder carcinoma and normal bladder were determined enzymatically using a 5-FU phosphorylation assay. The sensitivity of bladder cells to 5-FU was assessed using a microculture tetrazolium dye assay.

RESULTS

The activity levels of OPRT were approximately 7.5-fold higher in bladder carcinoma specimens compared with the activity levels in normal bladder specimens. OPRT activity in muscle-invasive bladder carcinoma was 2-fold higher compared with the activity in superficial bladder carcinoma (classified as Ta and T1). In addition, the activity of OPRT in T1 bladder carcinoma was 2-fold higher compared with the activity in Ta bladder carcinoma. The level of OPRT activity in Grade 3 bladder carcinoma was 6-fold and 2-fold higher compared with the activity in Grade 1 and Grade 2 bladder carcinoma, respectively. Patients who had Ta and T1 bladder carcinoma with low OPRT activity had a longer postoperative tumor free period compared with patients who had bladder carcinoma with high OPRT activity in the 3-year follow-up. There was a positive association between the activity levels of OPRT and thymidylate synthase/thymidine kinase, which are the key enzymes in the de novo/salvage DNA synthetic process. OPRT activity in bladder carcinoma cells was correlated positively with their sensitivity to 5-FU.

CONCLUSIONS

to the authors' knowledge, the current study is the first to demonstrate that OPRT activity levels in bladder carcinoma were higher compared with its activity in the normal bladder tissues and that OPRT activity levels were correlated positively with the stage and grade of bladder carcinoma. In addition, high OPRT activity levels in patients with superficial bladder carcinoma predicted early recurrence and high sensitivity to 5-FU. These results suggest that the level of OPRT activity may be used both as a prognostic parameter and as a predictive indicator for 5-FU efficacy in patients with bladder carcinoma and that OPRT may be a molecular therapeutic target in bladder carcinoma.

Significance of Orotate Phosphoribosyltransferase Activity in Renal Cell Carcinoma

PURPOSE

The anticancer agent 5-fluorouracil (5-FU) is clinically used against various cancers, including renal cell carcinoma (RCC). It is a prodrug and orotate phosphoribosyltransferase (OPRT) is the principal enzyme that directly converts 5-FU to the active anticancer metabolite 5-fluoro-2'-deoxyuridine 5'-monophosphate. In addition, OPRT is the key enzyme in the de novo DNA and RNA synthetic process. Little is known about the significance of OPRT in various cancers, including RCC. We investigated the activity of OPRT in 83 RCCs and evaluated the association between the level of OPRT activity and the stage/grade of RCC. The relationship between OPRT activity in RCC cells and their sensitivity to 5-FU was also examined.

MATERIALS AND METHODS

OPRT activity in nonfixed, fresh frozen RCC and normal kidney was determined enzymatically by the 5-FU phosphorylation assay. The sensitivity of RCC cells to 5-FU was assessed by the microculture tetrazolium dye assay.

RESULTS

The activity of OPRT was approximately 8.5-fold higher in RCC than in normal kidney. OPRT activity in stage III/IV RCC was 3-fold higher than in stage I/II RCC. The level of OPRT activity in grade 3 RCC was 3-fold higher than that in grade 1/2 cancer. Patients with RCC with low OPRT activity had longer postoperative disease specific survival than those with high activity at 5-year followup. OPRT activity in RCC cells positively correlated with their sensitivity to 5-FU.

CONCLUSIONS

To our knowledge this is the first study to demonstrate that OPRT activity in RCC was higher than that in normal kidney and OPRT activity positively correlated with RCC stage/grade. In addition, higher OPRT activity in RCC predicted worse prognosis and higher sensitivity to 5-FU. These results suggest that the level of OPRT activity may be used as a prognostic parameter and predictive indicator for 5-FU efficacy in RCC and OPRT may be a molecular therapeutic target in RCC.