Summary 5'-nucleotidase activity, arachidonate metabolism and adenosine uptake were measured in P388 murine leukaemia cells and in a subline resistant to doxorubicin. These membranes related activities were found to be increased in the doxorubicin resistant cell line, compared to the drug sensitive cells. It is suggested that these differences do not play a role in the mechanism of resistance to doxorubicin. Rather they reflect alterations in plasma membrane composition and structure between these cell lines.This study also suggests that the use of decreased 5'-nucleotidase activity as a marker of certain leukaemias should be reviewed with caution. An increase in cell enzyme activity in treated patients may not necessarly indicate a shift toward normal behaviour of these cells, but rather a selection of certain cell subpopulations.

The activities of three purine pathway enzymes--adenosine deaminase (ADA), 5'-nucleotidase (5'N) and purine nucleoside phosphorylase (PNP)--were examined in the circulating malignant cells (Sezary cells) of eight patients with cutaneous T-cell lymphoma (CTCL). Cell lines derived from two other patients with CTCL were also studied. These were compared with enzyme activities in peripheral blood T-lymphocytes from 11 normal donors and six samples of human thymocytes. ADA activities were similar in the Sezary cells and peripheral blood T-cells (medians 7 U and 15 U, P = 0.14), and both of these groups demonstrated significantly lower activity than did the thymocytes (median 100 U, P = 0.002). 5'N activity in the Sezary cells was also similar to that of the T-lymphocytes (median 0.022 U and 0.030 U, P greater than 0.05) and both of these groups had significantly greater activity than did the thymocytes (median 0.002 U, P = 0.001). Median PNP activity in the Sezary cell population was also comparable to that measured in normal T-cells. These findings suggest there is a characteristic purine pathway enzyme pattern in Sezary cells that is similar to that seen in normal T-lymphocytes. This pattern is clearly distinguishable from that of thymocytes and from that previously described in lymphoblasts from patients with T-cell acute lymphoblastic leukaemia. These results support the concept that Sezary cells are well-differentiated with respect to the T-cell axis. Quantitation of purine pathway enzymes may be useful in defining subsets of T-cell malignancy.