IN-VITRO EVALUATION OF FOTEMUSTINE AS A POTENTIAL AGENT FOR LIMB PERFUSION IN MELANOMA

The mechanism of action of fotemustine, a relatively new chloroethylni trosourea, was evaluated in human melanoma cells in order to assess it s potential as an agent for hyperthermic limb perfusion. Fotemustine w as more toxic to O-6-alkylguanine methyl transferase (AGT) deficient ( Mer(-)) cells than Mer(+) cells, implicating AGT as a major determinan t of resistance. Mer(+) cells derived from Mer(-) cell lines following exposure to the monofunctional alkylating metabolite of dacarbazine ( DTIC) were also resistant to fotemustine. Mer status did not influence the replication of fotemustine-damaged adenovirus 5, whereas virus tr eated with the monofunctional alkylating agent N-methyl-N-1-nitro-N-ni trosoguanidine (MNNG) was replicated much more efficiently by Mer(+) c ells. This suggests that the initial O-6-alkylated product, if not imm ediately repaired, rearranges to form DNA crosslinks which cannot be r epaired by AGT. Replication of a control virus was not affected by tre ating the cells with fotemustine, indicating that the drug acted prima rily on DNA rather than at epigenetic levels. Fotemustine generally pr oduced a G(2)-M block in the cell cycle, most strikingly in Mer(-) cel ls at low, minimally toxic concentrations; MNNG and high doses of fote mustine induced S phase arrest. Concurrent hyperthermia (41.5 degrees C for 1 h) increased the toxicity of fotemustine in some cell lines. F otemustine decomposed in culture medium in two phases; the first was c omplete within 5 min and was most marked in Mer(+) cells. The results suggest that fotemustine may be suitable for isolated limb perfusion i n melanoma, with the potential for overcoming resistance by including inhibitors of AGT. (C) 1998 Rapid Science Ltd.