IODODEOXYURIDINE CHEMOSENSITIZATION OF CIS-DIAMMINEDICHLOROPLATINUM(II) IN HUMAN BLADDER-CANCER CELLS

We investigated the effect of iododeoxyuridine (IdUrd) exposure on cis -diamminedichloroplatinum (CDDP) cytotoxicity in the human bladder can cer cell line 647V. Following a 48-h incubation with 2-20 mu M IdUrd, a 1-h exposure to 0-120 mu M CDDP produced a dose-dependent increase i n CDDP cytotoxicity as measured by clonogenic survival. IdUrd exposure of 2, 5, 10, and 20 mu M prior to CDDP resulted in dose modifying fac tors at 10% survival of 1.2, 1.6, 2.0, and 3.5, respectively. The incr ease in CDDP cytotoxicity appears to be associated with the level of D NA thymidine replacement in DNA by IdUrd over the range of 13-36%. Ato mic absorption spectrophotometric analysis of DNA extracted from 647V cells showed that IdUrd substitution did not affect the total amount o f platinum bound to the DNA or the persistence of the bound platinum o ver a 24-h period post-CDDP exposure versus control cells. IdUrd, unli ke thymidine, was found to form two monofunctional adducts with CDDP b oth in vitro and in vivo. IdUrd was also found to form a mixed bifunct ional adduct with deoxyguanosine (dGua) and CDDP in vitro. H-1 NMR ana lysis of purified IdUrd-Pt and IdUrd-Pt-dGua adducts confirmed the ide ntity of these adducts. High pressure liquid chromatography analysis o f [H-3]IdUrd-labeled 647V DNA digests exposed to CDDP showed the prese nce of two monofunctional adducts. Unlike the free solution production of adducts in vitro, the predominant adduct formed was not IdUrd-Pt. Results using (125)IdUrd-labeled 647V DNA suggests that this adduct is 5-Pt-deoxyuridine. We were not able, however, to detect the presence of the bifunctional adducts IdUrd-Pt-dGua or dUrd-Pt-dGua. This was mo st likely due to the extremely low proportion of mixed bifunctional ad ducts produced in vivo. Nonetheless, these results suggest that IdUrd DNA incorporation may enhance CDDP cytotoxicity through the increase o f available sites for Pt adduct formation. A Phase I clinical trial of this approach is planned.