Summary.-The antitumour effects of ICRF-159 and related analogues were evaluated using the B16 melanoma. Treatment of mice with ICRF-159 inhibited tumour growth, while each of the analogues, trans-4,41-(1,2-cyclopropandiyl) bis (2,6-piperazinedione) (trans-5), and cis-4,41-(1,2-cyclopropandiyl) bis (2,6-piperazinedione) (cis-7) independently accelerated primary tumour growth. Pretreatment of B16 melanoma cultures either with ICRF-159 or the analogue cis-7 decreased the yield of lung-colonies following i.v. injection of tumour cells. In contrast, pretreatment of tumour cells with the trans-5 analogue led to an increase in lung colonies. The effect on colony formation in vitro of these analogues correlated with increased growth in vivo, and not with lung colony formation.PREVIOUS REPORTS from these laboratories have shown that ICRF-159 and analogue trans-5 stimulated the growth of a hamster adenocarcinoma of the lung, whereas ICRF-159 and Analogue cis-7 had no effect on primary tumour growth. The results also suggested that Analogue cis-7 reduced metastasis of this tumour model whilst trans-5 stimulated it (Witiak et al., 1978). Since ICRF-159 is active against a variety of tumours (Adamson, 1975;Atherton, 1975), and has been reported to inhibit metastasis to the lung of subcutaneously growing Lewis lung carcinoma (LeServe & Hellmann, 1972;Salsbury et al., 1970), this stereochemical effect on tumour growth and metastasis is particularly significant. As a prerequisite to mechanism studies we have re-examined the activity of these compounds, using the syngeneic B 16-Fl and F 10 melanoma in C57BL/6 mice (Fidler & Nicholson, 1976 Fig. 1) were studied to throw light on the specificity of the apparent stereoselective effect. The results described in this article are compared to those previously reported by Lazo et al. (1978), who observed that ICRF-159 treatment of B16 melanoma cells in culture significantly increased their lung-colony formation in vivo.
MATERIALS AND METHODSAnimals.-Male, C57BL/6J mice were obtained from the Jackson Laboratory, Bar Harbor, Maine, when 5 weeks old. The animals were housed 20 per cage and given food and water ad libitum. Mice were used when 8-12 weeks of age.Tumours. The B16-Fl and B16-FIO melanoma tumour cells were kindly provided by Dr Isiah J. Fidler. The B16-F1 cell line forms few lung colonies when injected i.v., whereas (orre.;Pondence to: Bruce S. Zvilling, The