Cyclophosphamide decreases O6-alkylguanine-DNA alkyltransferase activity in peripheral lymphocytes of patients undergoing bone marrow transplantation

Abstract

Summary 06-alkylguanine-DNA-alkyltransferase (ATase) levels were measured in extracts of peripheral blood lymphocytes taken at various times during chemotherapy from 19 patients with various haematological malignancies. Seven patients with advanced Hodgkin's disease received preparative treatment consisting of cyclophosphamide (1.5 g m-2, daily) administered on days 1 to 4 and BCNU (600 mg m-2) on day 5 prior to autologous bone marrow rescue (ABMR) delivered on day 7. Treatment in the remaining 12 patients consisted of cyclophosphamide (1.8 g m2, daily) given on days 1 and 2 followed at day 4 with total body irradiation (TBI) administered in six fractions over the subsequent 3 days to a total dose of 1200 cGy prior to bone marrow transplantation. In the Hodgkin's group, significant decreases in ATase activity were seen during the cyclophosphamide treatment, and the median ATase nadir was 32% (range 0% to 57%) of pretreatment levels following 4 days of cyclophosphamide. In one patient, no ATase activity was detectable following the 4th cyclophosphamide treatment. ATase activities decreased further after BCNU administration to a median of 19% (range 0% to 32%) of pretreatment levels. Extensive cyclophosphamide-induced reduction of lymphocyte ATase levels was also seen in the other group of 12 patients treated with cyclophosphamide/TBI: postcyclophosphamide median ATase nadir was 35% (range 12% to 78%) of the pretreatment levels. No ATase depletion was seen when cyclophosphamide (up to 1O mM) was incubated for 2 h with pure recombinant human ATase in vitro whereas ATase activity was reduced by 90% on preincubation with 100 tsm acrolein or with > 1 mM phosphoramide mustard. This suggests that a cyclophosphamide-induced decrease in ATase levels in human peripheral lymphocytes in vivo may be due to depletion mediated by the production of intracellular acrolein. Since ATase appears to be a principal mechanism in cellular resistance to the cytotoxic effects of BCNU and related alkylating agents, these observations suggest that a cyclophosphamide-induced reduction in ATase activity may be an additional factor in the effectiveness of the combined sequential therapy.

Role of MGMT in protecting against cyclophosphamide-induced toxicity in cells and animals

“…scavenging, is a reasonable possibility particularly since the Cys 145 acceptor site of MGMT has a very low pK a (4-5) and is very reactive [88]. MGMT activity levels are reduced in peripheral blood mononuclear cells from patients receiving cyclophosphamide treatment [89]. In addition, MGMT activity in cell lysates is reduced 60% following exposure to acrolein (although this was observed at concentrations greater than 3-fold above physiological concentrations of acrolein) [90].…”

“…In addition, MGMT activity in cell lysates is reduced 60% following exposure to acrolein (although this was observed at concentrations greater than 3-fold above physiological concentrations of acrolein) [90]. Furthermore, purified recombinant MGMT incubated with increasing concentrations of acrolein for 2 h results in a dose dependent decrease in residual MGMT activity [89]. Approximately 60% and 10% MGMT activity remained following incubation with physiological achievable concentrations of 10 and 100 μM acrolein, respectively [89].…”

O6-methylguanine-DNA methyltransferase activity and sensitivity to cyclophosphamide and cisplatin in human lung tumor xenografts

“…Therefore, modulation of MGMT expression in experimental cell systems by either depletion of MGMT with an inhibitor (Dolan et al, 1990) or transfection of MGMT cDNA (Preuss et al, 1996) did not clearly affect the sensitivity of cells to CTX-related drugs (e.g., mafosfamide). We should note, however, that the cellular toxicity of CTX is due in part to the degradation product acrolein, which can inactivate MGMT (Lee et al, 1992). As recently proposed in a preliminary report, acrolein may also react with DNA to form an adduct repaired by MGMT, which in this way may modulate CTX toxicity (Friedman et al, 1998).…”

Anticancer system created by acrolein and hydroxyl radical generated in enzymatic oxidation of spermine and other biochemical reactions

“…Studies followed with observations on its capability to lower cellular glutathione levels, resulting in secondary decreases of cellular defenses and corresponding increases in the effects of anticancer agents and endogenous toxic products. Also described by other researchers, acrolein involvement in the decrease of the enzyme O6-alkylguanine-DNA alkyl transferase, what appeared as an additional confirmation on the participation of acrolein in CPA cytotoxic and anti-tumor effects [63][64][65][66][67].…”