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Purpose: Hypoxic cells in tumours are resistant to 5-fluorouracil (5-FU). This in vivo study investigated the ability of hypoxia to regulate the gene expression of thymidylate synthase (TS), the target enzyme of 5-FU. Materials and methods: C3H mammary carcinomas, grown in the feet of female CDF1 mice, were used for all experiments. Mice were placed in a 10% oxygen environment for various time periods and the tumour oxygen status was determined with an Eppendorf oxygen electrode. The animals were then injected with BrdU (100mg/kg, i.p.). Tumours were excised and immediately frozen (-80 C) until isolation of total RNA. The mRNA was reversibly transcribed to complementary DNA and the resulting cDNA amplified in a multiplex PCR reaction, with beta-actin as the internal reference gene. Results: One hour of low oxygen breathing made tumours significantly more hypoxic. This increase was maintained for a maximum incubation period of 48h. In the same tumours, no change in TS gene expression was seen with up to 3h of low oxygen breathing. At longer times it decreased, reaching significance at 12-24h and remaining at this lower level for up to 48h. BrdU labelling was significantly reduced after breathing low O2 for 24h (p=0.001). Conclusion: Hypoxia-induced down-regulation of TS gene expression was observed. This would be expected to make hypoxic tumour cells more sensitive to 5-FU. Other mechanisms must be responsible for the previously reported resistance to this drug. [ABSTRACT FROM AUTHOR]

The rate of reduction in the concentration of serum human chorionic gonadotrophin (hCG) following chemotherapy for germ cell tumours may follow a complex pattern, with longer apparent half-life during later stages of chemotherapy, even in patients treated successfully. The commonly used half-life of less than 3 days for hCG to monitor the effect of chemotherapy in patients with germ cell tumours of the testis may represent too simple a model. [SUP125]I-labelled hCG was injected intravenously in 27 patients with germ cell tumours and elevated hCG during chemotherapy. The plasma radioactivity and hCG concentrations were followed. During chemotherapy, the plasma disappearance of hCG showed a biphasic pattern, with an initial fast and a later slow component in all patients. Using the steep part of the hCG plasma disappearance curve, five patients who achieved long-term remission had half-lives longer than 3 days (3.6-6.8 days), whereas four out of five patients not achieving long-term remission had half-lives shorter than 3 days. After the third treatment cycle, eight patients who achieved long-term remission had hCG half-lives longer than 3 days (7.4-17.0 days). In these patients, the plasma disappearance of [[SUP125]I]hCG was equivalent to that of hCG. Thus, the slow decline of hCG represented a slow plasma disappearance rather than a hCG production from vital tumour cells and could, consequently, not be used to select patients for additional or intensified chemotherapy. The concept of a fixed half-life for plasma hCG during treatment of hCG-producing germ cell tumours is inappropriate and should be revised. Difficulties in interpreting a slow decline of hCG may be overcome by comparing the plasma disappearance of total hCG with the plasma disappearance of [[SUP125]I]hCG. [ABSTRACT FROM AUTHOR]

We have recently introduced [SUP125]I-hCG as an elimination marker in patients with human chorionic gonadotrophin (hCG) producing testicular cancer.[SUP125]I-hCG is a well-known reagent in clinical biochemistry and is used extensively in hCG assays. Previous studies have shown that the iodination process leaves the hCG molecule mainly intact. The iodination, purification and stability of[SUP125]I-hCG tracer are described. The aim of the present study was to determine whether or not [SUP125]I is associated with hCG after the injection of [SUP125]I-hCG intravenously (i.v.) in humans. Three different methods were used. Following injection of[SUP125]I-hCG, the plasma disappearance of radioactivity and hCG were followed for a period of 28 days in 13 normal subjects. Serum from a normal healthy male following injection of[SUP125]I-hCG was analysed using a double antibody direct binding radioimmunoassay specific for holo-hCG and high performance liquid chromatography (HPLC). Following injection of[SUP125]I-hCG in eight normal healthy males and five normal healthy females, the disappearance of radioactivity and hCG showed identical paths in the 28 days follow-up period. The bindable radioactive fraction of immunologically active hCG in serum of a normal healthy male following injection of[SUP125]I-hCG was between 57.0% and 72.1%, and was constant over time. HPLC showed similar elution pattern of serum from a normal healthy male injected i.v. with[SUP125]I-hCG and[SUP125]I-hCG. Using three different methods, we were able concurrently to demonstrate the association of[SUP125]I with hCG in humans up to 28 days after injection of radiolabelled hCG i.v. Thus, information about the expected elimination of hCG can be obtained by following the elimination of activity in plasma after injection of[SUP125]I-hCG. [ABSTRACT FROM AUTHOR]