Emergence of nitrosourea resistant sublines of Lewis lung tumour following MeCCNU treatment in vivo

Cimetidine administration decreases radiogenic damage on the thyroid gland in mice

PURPOSE

To study if Cimetidine administration could ameliorate the thyroid damage in external radiation.

MATERIALS AND METHODS

Forty healthy male adult mice were used in the present study. The animals were randomized into four groups. Untreated mice (Group 1) that received 1 mg/kg saline intraperitoneally (IP). Group 2 received a single 10 Gy gamma radiation dose with 1 mg/kg saline IP and group 3 were treated with Cimetidine IP. Group 4 was irradiated 1 hour after treatment with Cimetidine. The serum were assayed for the contents of triiodothyronine (T3), tetraiodothyronine (T4), thyroid stimulating hormone (TSH), Free T4 (FT4) and Cortisol using a radioimmunological technique 7 days following radiation. The thyroid tissue was processed and stained with hematoxylin and eosin (H&E), and periodic acid-Schiff (PAS) for histological examination. Data were statistically analyzed using Tukey's post-hoc test and were considered significant at p < 0.05.

RESULTS

External radiation resulted in weight loss and reduction of serum thyroid hormone levels. However, Cimetidine administration prevented marked changes. Histological study showed that Cimetidine injection to irradiated mice minimized the thyroid damage.

CONCLUSIONS

These findings suggested that Cimetidine administration 1 hour before radiation exposure was potent in ameliorating the thyroid damages.

DNA adducts from chemotherapeutic agents

The guiding principle of early work was the hypothesis that the anti-cancer alkylating drugs acted through their ability to cross-link macromolecules essential for cell division. Not long afterwards, DNA was specified as the essential target, and support for the hypothesis came from evidence that the archetypal agent, mustard gas, could link guanine bases in DNA through their N-7 atoms. Quantitative correlations between alkylation of DNA and its inactivation as a template followed, with bacteriophage as a simple test object, showing that the mean lethal dose was close to a single cross-link in the genome. This conclusion applied to either mustard gas or the more recently introduced platinum drugs. Although both inter- and intra-strand cross-links were effective, it was thought that in cells the inter-strand cross-link would, by preventing the separation of the strands necessary for cell division, and by being more difficult to repair, constitute the more effectively lethal lesion. With repair-deficient bacteria, it also emerged that a single cross-link in the genome was lethal, but proficient bacteria could remove about 20 cross-links through excision repair. Mono-7-alkylguanines were not removed and were evidently inert. Thus, only a few percent of the total alkylation products were the most effective lesions. Parallel studies with cultured mammalian cells gave a rather different picture, in that the mean lethal doses of even hypersensitive cell lines were around 20 or more cross-links per genome, about the same as for resistant strains of bacteria. Most cells could withstand several hundreds of cross-links per genome, and although adducts were removed, there was incomplete removal of cross-links. Some, but not all, sensitive cell lines were deficient in excision repair. Methods were devised for measuring the extents of alkylation of DNA in cells of patients treated with chemotherapeutic drugs; these are mainly immunoassays, and were applied generally to peripheral blood leukocytes, although some tumours were studied. Extents of alkylation of leukocyte DNA were generally of the same order as, or rather less than the mean lethal doses of cultured cells of the 'normal' type, but in some reports for cisplatin-treated patients, very wide variability between individuals was found. A positive correlation between adduct levels, and particularly a very minor adduct recognised specifically by one antibody, and favourable therapeutic outcome was discerned, and suggested to have a pharmacogenetic basis. In several instances, extents of alkylation of tumours were significantly higher than the average for leukocytes; for ovarian and a testicular tumour for cisplatin, and for a plasma cell tumour for melphalan. Nevertheless, these favourable examples would not constitute more than three or four mean lethal doses in the tumour cells, assuming that they had the same sensitivity as 'normal' cell lines: the therapeutic effect would of course be much more favourable if the tumour cells resembled 'sensitive' cell lines. This lack of a favourable difference between extents of alkylation in DNA of patients and the mean lethal dose for normal cells was particularly obvious with the methylating drugs dacarbazine and procarbazine. These considerations stress the need for higher extents of alkylation to be achieved in target tumour DNA for successful chemotherapy. One approach is to give a higher overall dose, and to 'rescue' the bone marrow (known from the earliest report on mustard gas to be the most susceptible tissue) by autologous transplantation. The second, which has yet to reach the clinic, is to convert unreactive prodrugs through enzymic activation into alkylating agents specifically in tumours (see Bagshawe, 1994).

Antitumor activity of Ilmofosine (BM 41.440) in the 3Lewis-lung carcinoma model

Ilmofosine (1-hexadecylthio-2-methoxymethyl-1,3-propanediol-phosphocholine, BM 41.440) is a thioether phospholipid with cytostatic/cytotoxic properties. The antineoplastic activity of this compound was investigated in vivo in the 3Lewis-lung carcinoma system. 3Lewis lung tumor-bearing C57Bl/6 mice were treated with 0.625 to 40 mg Ilmofosine/kg per day p.o. either from days 1 to 9 or from days 11 to 28 after intrafoot-pad tumor cell inoculation. Ilmofosine caused a significant dose-related response on tumor growth and metastases, expressed in terms of tumor diameter, tumor weight, survival time and number of metastases-free animals as compared to sham-treated and positive (cyclophosphamide) controls. The results suggest that direct cytostatic/cytotoxic effects, rather than immune-modulatory mechanisms, preferentially contribute to the antitumor activity of Ilmofosine in vivo.

In vivo emergence of a highly metastatic tumour cell line from a rat rhabdomyosarcoma after treatment with an alkylating agent

Rats bearing a transplanted nickel-induced rhabdomyosarcoma (RMS 9-4/0), treated with chlorozotocin (CZT), an alkylating agent, showed an amplified metastatic invasion of the lung (median of 165 lung tumour nodules, compared to 3 for untreated controls). A higher level of metastatic invasion (200 nodules) was reached spontaneously after the grafting of the S4T line, which was obtained by successive in vivo passages of RMS 9-4/0 cells in CZT treated rats. S4T tumour cells also invaded the liver and a considerable proportion of the lymph nodes. The NT4T line, obtained by successive in vivo passages in untreated rats, showed a lesser degree of enhancement of metastatic capacity (57 nodules). Both derived lines proved to be more aggressive than the parental, proliferated more rapidly, and were resistant to CZT toxicity. Only the non-treated lineage became more resistant to NK lysis. The S4T line lost its myogenic differentiation and was best described as a fibrohistiosarcoma, whereas NT4T did not. Chromosome analysis demonstrated a reduced range of chromosome number per cell in both lines. We conclude that both S4T and NT4T tumours became more metastatic than RMS 9-4/0 as the result of tumour progression through in vivo passages, and that in addition S4T acquired a spontaneously higher metastatic potential, similar to that which occurred in rats grafted with RMS 9-4/0 or NT4T tumours and treated by CZT. This suggests an inheritable mutation in the S4T line.

Drug resistance and DNA repair

DNA repair confers resistance to anticancer drugs which kill cells by reacting with DNA. A review of our current information on the topic will be presented here. Our understanding of the molecular biology of repair of 0(6)-alkylguanine adducts in DNA has advanced as a result of the molecular cloning of the E. coli ada gene but the precise role of this lesion in the cytotoxic effects of alkylating agents in mammalian cells is not completely understood. Less progress has been made in understanding the enzymology and molecular biology of DNA cross-link repair even though such lesions are important for the cytotoxic effects of the widely used bifunctional alkylating agents and platinum compounds. It is evident that drug sensitive or resistant phenotypes are as highly complex as are the effects of DNA damage on cell metabolism and various aspects of these effects are discussed. Few clear correlations have been made between quantitative differences in DNA repair capacity and cellular sensitivity but assays which were developed to measure fidelity and intragenomic heterogeneity in DNA repair are beginning to be applied. Such studies may reveal subtle differences between sensitive and resistant cell lines. The molecular cloning of human DNA repair genes by transfection into drug sensitive rodent cells has been attempted. Some success has been achieved in this area but the functions of the cloned genes have yet to be identified.

Development of MeCCNU-resistance in clonally derived lines of Lewis lung carcinoma

The development of resistance to MeCCNU in four clonal lines of Lewis lung carcinoma derived from lung colonies has been examined. Treatment of the clones with 15 mg/kg MeCCNU once in each in vivo passage resulted in a rapid reduction in tumour responsiveness to this drug. This shows that MeCCNU resistance can arise at rates which may be applicable in spontaneous tumours and their metastases. Karyotypic heterogeneity was evident very early after isolation of the clones and this has potentially important implications for the experimental use of clones and for the features of metastatic disease. Karyotype analysis of one of the clones at each passage suggested that development of resistance was associated with the selection of a single sub-population of tumour cells but the kinetics of resistance development cannot be totally explained in terms of this simple selection.