[DNA Turnover in the Whole Body of Tumour Bearing Mice (author's transl)].

Abstract

Unlabelled: During the last 3 decades several authors have found in tumour-bearing animals an increase of synthesis and content of DNA in various organs which were free from neoplastic cells (Griffin, 1957;Kelly and Jones, 1950; Morgan and Cameron, 1973; Cerecedo et al., 1951; Lombardo et al., 1952). 5-iodo-2'-deoxyuridine (IUdR) is a thymidine analogue and specifically incorporated into DNA. When it is labelled with 125I or 131I it permits to reinvestigate these findings by measuring the rate of precursor incorporation into DNA and the rate of loss of labelled DNA in the living animal by means of counting the gamma emission from the incorporated iodine isotopes. In this paper, therefore, an attempt is made to analyse the DNA turnover in the whole body of liver tumour-bearing mice.

Material and methods: 5-iodo-2'-deoxyuridine (IUdR) labelled with 125iodine was used as DNA precursor. It is a thymidine analogue 5% of which is specifically incorporated into the DNA of those proliferating cells which are in the phase of DNA synthesis at the moment of tracer application. Non-incorporated IUdR (about 95% of the injected amount) is rapidly degraded and excreted within 24 hours. The tracer remains bound to the cellular DNA druing the life span of the labelled cells. After cell death only about 5% of IUdR from DNA breakdown is reutilized. 125I has a half live of 60 days and therefore allows, over periods of weeks, external measurements of the DNA turnover in the living animal without disturbing the physiological environment. The measured loss of DNA-bound 125I reflects almost exclusively the turnover of the labelled cells. Female albino NMRI mice, 2 months old, bearing sarcoma-180 implanted into the right hind leg were intraveneously injected with 2 muCi 125I-UdR. At the time of injection, the tumour had reached in one group of mice an average volume of about 25 mm3 and in another group an average volume of nearly 850 mm3. When implanted into subcutaneous tissue sarcoma-180 rarely produces metastases in parenchymal organs, never in the spleen and--within the first 30 days after implantation--only in ca. 10% of the animals a small metastasis in a single lymphnode (Deodhar and Crile, 1969; Franchi et al., 1968). Whole body measurements were carried out immediately after tracer injection and then daily during the first week and every second or third day in the following 2 weeks in a NaI well counter with a single channel pulse height analyser. The tumour activity was also determined in vivo by a special counting device.

Results: In the normal mouse 4 to 6% of injected 125I-UdR is retained in the whole body 24 hours after tracer injection. During the following five days the 125I activity rapidly declines to 0.8% of that of day O immediately after injection. Thereafter the rate of loss of activity greatly diminishes (Fig. I). The first component of the turnover curve reflects an average daily cell loss of approximately 30% and involves about 90% of the incorporated activity...