The in vitro effects and cross-resistance patterns of some novel anthracyclines

A range of new anthracyclines, structurally related to adriamycin (ADM), has been synthesised and studied in vitro. Three compounds described in this paper (Ro 31-1215; Ro 31-1741; Ro 31-2035) are all 4-demethoxyanthracyclines. In the mouse mammary tumour cell line, EMT6/Ca/VJAC, using a 1 h drug exposure followed by colony formation as the response endpoint, we found Ro 31-1215 and Ro 31-1741 to be 2-3 x and 4-7 x more potent then ADM, whilst Ro 31-2035 was 3-4 x less potent. For continuous drug exposure and suppression of population growth as the endpoint, the potency of Ro 31-1741 was similar to that of ADM, whereas that of Ro 31-1215 was 1.5-2 x higher and that of Ro 31-2035 was 10-20 x lower. The potency ratios for continuous drug exposure of a human small cell lung cancer line were similar to those for continuous exposure of EMT6. Variants of the two cell lines selected for resistance to ADM were also studied. These variants also showed considerable resistance to Ro 31-1741 and Ro 31-2035 but much less resistance to Ro 31-1215 (a 9-methyl derivative). A variant of EMT6 made resistant to Ro 31-1215 by continuous growth in this drug was more resistant to ADM than it was to Ro 31-1215. Human cells resistant to ADM contained 6 x less ADM after 24 h exposure than did the parent line, whereas the ratio of drug content for Ro 31-1215 was only 2.