TRANSIENT PERFUSION IN HUMAN-MELANOMA XENOGRAFTS

Studies of transplantable rodent tumours have suggested that malignant tissue might experience transient perfusion at the microvascular leve l. The purpose of the work reported here was to investigate whether tr ansient perfusion can be demonstrated in xenografted human tumours. Tu mours of four melanoma lines (A-07, D-12, R-18, U-25), grown orthotopi cally in Balb/c nu/nu mice, were included in the study. Transient perf usion was studied by using the double-fluorescent staining technique. Hoechst 33342 and DiOC(7)(3) were either administered simultaneously o r Hoechst 33342 was administered 20 min before DiOC(7)(3). Detection o f transient perfusion by this method requires that vessels are non-fun ctional for at least 5 min owing to the distribution half-lives of the dyes in the blood. Usable combinations of dye concentrations were fou nd by varying the concentrations of Hoechst 33342 and DiOC(7)(3) syste matically. The level of perfusion mismatch following simultaneous admi nistration of the dyes ranged from approximately 1.5% for U-25 tumours to approximately 3.0% for R-18 tumours at these combinations. Moreove r, the fraction of vessels stained only with Hoechst 33342 and the fra ction of vessels stained only with DiOC(7)(3) were not significantly d ifferent whether the dyes were administered simultaneously or sequenti ally. Transient perfusion could not be demonstrated in any of the tumo ur lines. Thus, the fraction of vessels stained only with Hoechst 3334 2 and the fraction of vessels stained only with DiOC(7)(3) were not si gnificantly higher after sequential than after simultaneous administra tion of the dyes. Moreover, the vessels stained only with Hoechst 3334 2 and the vessels stained only with DiOC(7)(3) were randomly distribut ed within the tumours whether the dyes were administered simultaneousl y or sequentially. Consequently, acute hypoxia caused by transient per fusion is probably a less pronounced phenomenon in malignant tissue th an previous studies of rodent tumours have suggested.