Practical applications of the SCE studies for guiding and improving chemotherapy.

The effect of diphylline (DP) or (1,2-dihydroxy-3-propyl)-theophylline and theobromine (TB) on sister chromatid exchange (SCE) rates induced in vitro by cytosine arabinoside (AraC) was studied in normal human lymphocytes. The combined treatments with AraC plus DP or TB showed the potentiating ability of the latter drugs. In a combined in vivo and in vitro study, lymphocytes taken from 14 patients suffering from various types of cancer who had been given Cytoxan (5 patients) or AraC (9 patients) by injection 3 hr before and then treated with DP or TB in vitro were found to have synergistically increased exchange rates. This has implications for interpreting the repair processes involved and for monitoring drug combinations that synergistically damage DNA in vivo and in vitro.