Activated oncogenes in human skin tumors from a repair-deficient syndrome, xeroderma pigmentosum.

The recessive autosomal hereditary disease, xeroderma pigmentosum (XP), is characterized by a high incidence of tumors in sun-exposed skin. The defect in early steps of excision repair of XP cells leads to hypermutability towards UV-mimicking agents. DNA from eight XP tumors were screened for activated transforming genes using 3T3 transfection. In two skin tumors isolated from a XP child, an activated N-ras oncogene was detected. Synthetic oligonucleotide probes were used to characterize the mutation in the ras gene. Both tumors were found to be mutated in the 61st N-ras codon from gln to his. The mutation was accompanied by an increase in the level of N-ras specific mRNA and in one transformant, by the alteration of the p21 protein. In the same tumors, c-myc amplification and over transcription, and Ha-ras gene rearrangement and amplification were also detected. Analysis of other XP tumors with eleven different oncogene probes revealed an amplification of the Ha-ras gene in 6 out of 10 cases. The normal skin fibroblasts from XP patients show normal pattern levels of N-ras, c-myc and Ha-ras sequences. The hypothesis is proposed that the presence of several oncogene alterations in the same tumor could be due to the high amount of UV-induced DNA lesions found in the exposed skin cells, in the absence of efficient repair.

Plasma and cellular pharmacokinetics of mitoxantrone in high-dose chemotherapeutic regimen for refractory lymphomas.

We have studied the plasma and peripheral leukocyte pharmacokinetics of mitoxantrone associated, in a high-dose regimen, with cyclophosphamide, carmustine, and etoposide in patients with refractory lymphoma undergoing autologous bone marrow transplantation. Nineteen patients with refractory lymphoma were involved in a clinical trial with escalated doses (15-90 mg/m2) of mitoxantrone administered by 30-min i.v. infusion 8 days before an autologous bone marrow transfusion. Mitoxantrone was measured by high-performance liquid chromatography in plasma and peripheral lymphocytes. The plasma pharmacokinetics of mitoxantrone was linear between 15 and 90 mg/m2: total body clearance (19.3 +/- 6.2 liter/h/m2) and volume of distribution at steady state (486 +/- 254 liter/m2) were not altered by increasing the dose. The exposure of bone marrow transplant to the plasma residual concentration of mitoxantrone was correlated with the limiting hematological toxicity of the regimen (P < 0.001). At all times, the mitoxantrone concentration in peripheral cells was much higher than in plasma and was retained at a constantly high concentration level. Whereas cellular versus plasma maximum concentration ratio was near 1, the area under the concentration +/- time curve ratio reached 100, suggesting a long elimination half-life from cells. Plasma and cellular pharmacokinetics data of mitoxantrone reinforce the idea that this drug is a good candidate for high-dose chemotherapy regimen.

Escalating dose of mitoxantrone with high-dose cyclophosphamide, carmustine, and etoposide in patients with refractory lymphoma undergoing autologous bone marrow transplantation.

PURPOSE: We conducted a dose-finding study of mitoxantrone (MITO) in combination with high-dose cyclophosphamide, carmustine (BCNU), and etoposide (CBV) in refractory lymphoma undergoing autologous bone marrow transplantation (ABMT). The objective were to determine the following: (1) the maximum-tolerated dose of MITO, (2) the extramedullary toxicity of this regimen, (3) its antitumor activity, and (4) the pharmacokinetic characteristics of MITO at each dose level. PATIENTS AND METHODS: Escalating doses of MITO (15 to 90 mg/m2, single bolus infusion on day -8) followed by CBV were administered to 20 patients (mean age, 38.5 years) with refractory lymphoma. MITO concentrations were determined by high-performance liquid chromatography (HPLC). RESULTS: No toxic death occurred. The maximum-tolerated dose appears to be 75 mg/m2. Two of five patients treated with 90 mg/m2 developed severe organ toxicity, versus zero of 15 treated with doses up to 75 mg/m2. Duration of neutropenia was longer for patients treated with 90 mg/m2 (31.7 days) than for patients treated with doses up to 75 mg/m2 (22.1 days) (P < .05). A linear relationship was observed between administered dose of MITO and (1) plasma peak value, (2) area under the curve (AUC), and (3) plasma concentration on the day of marrow infusion (day 0). Hematologic toxicity was related to the terminal half-life (T1/2) of MITO, and day-0 plasma concentration. A high complete response (CR) rate was observed (60%), and eight of 11 (73%) patients treated with MITO > or = 60 mg/m2 achieved a CR. CONCLUSION: MITO (up to 75 mg/m2) and CBV can be administered with acceptable toxicity and a promising CR rate in this poor-risk population, justifying further phase II studies.

Prevention of gram-positive infections after bone marrow transplantation by systemic vancomycin: a prospective, randomized trial.

Gram-positive bacteria are the most commonly isolated organisms after bone marrow transplantation (BMT) and severe streptococcus septicemia has been reported. In order to evaluate the benefit of a gram-positive prophylaxis after BMT, we conducted a prospective, randomized trial of systemic vancomycin among 60 patients undergoing BMT for hematologic malignancies. Patients were randomized to receive (n = 30) or not receive (n = 30) prophylactic vancomycin 15 mg/kg every 12 hours from day -2 until resolution of neutropenia or until the first episode of fever. All patients were treated in laminar air-flow rooms, received sterile diet, total gut decontamination, and had central venous catheters placed surgically. Vancomycin was found to be highly effective in preventing gram-positive infections that occurred in 11 of 30 patients in the control group versus zero of 30 in the vancomycin group (P less than .002). All gram-positive infections occurring in the control group were symptomatic (nine septicemia and two local infections), and one patient with Streptococcus septicemia died with pneumonia. Thus, gram-positive prophylaxis was found to decrease infection morbidity after BMT. Moreover, the number of days with fever (P less than .001), and empiric antibiotic therapy (P less than .01) was reduced without added toxicity or cost. This study confirmed the high prevalence of gram-positive infections after BMT and emphasized the clinical benefits of an adapted prophylaxis.

Potential strategies for circumventing myeloperoxidase-catalyzed degradation of vinca alkaloids.

Myeloperoxidase (MPO) has recently been shown in an in vitro, cell-free system to catalyze the peroxidative degradation of vincristine (VCR). Oxidation of VCR involves a ring fission between positions 20' and 21', and is thought to be facilitated by the presence of an hydroxyl (-OH) group at position 20'. We report here two different approaches, both with potential clinical application, to decrease MPO-catalyzed vinca degradation. Firstly, we tested the hypothesis that -OH substitution at position 20' increases vinca susceptibility to peroxidation by comparing the relative extent of degradation of vinorelbine (Navelbine or NVB), which lacks a 20' hydroxyl substitution, with that of VCR. As anticipated, NVB was significantly less susceptible to MPO-catalyzed peroxidation than was VCR (p < 0.01). Secondly, we screened an array of compounds that are in current clinical use for their ability to inhibit MPO. Acetaminophen, N-acetylcysteine, propylthiouracil, D-penicillamine, mefenamic acid, dapsone, and methimazole all inhibited MPO at clinically achievable concentrations. Insofar as increased MPO activity has been observed in patients with acute myeloid leukemia, these findings suggest potential strategies for improving the activity of vinca alkaloids in this disease.

B-cell lymphoma following polycythemia vera: evidence for the involvement of two different clones.

We report here two patients with polycythemia vera (PV) who developed secondary non-Hodgkin's lymphoma (NHL). Both cases were high grade B-cell NHL. Cytogenetic analysis of bone marrow and lymph node was performed in each case and showed numerous chromosomal abnormalities. Of interest, chromosomal abnormalities of the PV and of the NHL clones were different, suggesting the possible involvement of two different clones. A 11q23 breakpoint was common between the two cases and the putative role of this breakpoint in the pathogenesis of the NHLs is discussed.

Antisense inhibition of myeloperoxidase increases the sensitivity of the HL-60 cell line to vincristine.

Myeloperoxidase (MPO), a heme-peroxidase found in the HL-60 myeloblastic cell line, is involved in vincristine (VCR) metabolism and the inactivation of this drug. We have examined whether decreased MPO activity correlated with increased sensitivity to VCR toxicity in myeloid leukemia cells. We have used MPO antisense RNA to reduce 60% of the MPO activity in the HL-60 cells. The MPO-deficient HL-60 cell line, C15, was significantly more sensitive to VCR than the parental MPO-positive cell line. Both cell lines were negative for P170-glycoprotein expression. Conversely, an MPO-positive C15 subclone was more resistant to VCR than the MPO-deficient C15 cell line. No significant differences in cytotoxic effects were observed between MPO-positive and MPO-deficient cells, following treatment with either daunorubicin or actinomycin D, two multidrug resistance-related drugs. These results strongly support an important role for MPO in VCR resistance in HL-60 cells. Antisense manipulation of the MPO content of myeloid cells could be of potential interest in leukemia treatment.

Epstein-Barr virus (EBV) replicative gene expression in tumour cells of AIDS-related non-Hodgkin's lymphoma in relation to CD4 cell number and antibody titres to EBV.

OBJECTIVE: To determine whether activation of Epstein-Barr virus (EBV) replication in tumour cells of AIDS-related non-Hodgkin's lymphoma (ARNHL) is correlated with CD4+ cell counts and influences antibody response to EBV [anti-Z Epstein-Barr replicative activator (ZEBRA), anti-early antigen (EA), anti-viral capsid antigen (VCA)]. DESIGN: Retrospective study based on immunohistochemistry and in situ hybridization to detect EBV replicative gene products in tissue samples from patients affected by ARNHL and correlation with CD4+ cell counts and results of EBV serology (including anti-ZEBRA activity) in sera from the same patients. METHODS: Seventeen out of 22 cases of ARNHL were selected for the presence of EBV [Epstein-Barr early region (EBER) RNA-positive]. Immunohistochemistry was performed with anti-ZEBRA, anti-EA-restricted, anti-VCA antibodies and in situ hybridization with BHLF1/NotI oligoprobes on tumour samples. Results were statistically correlated with those of CD4+ cell counts (17 out of 17) and with anti-EBV antibody titres (13 out of 17) assessed using standard immunofluorescence method and enzyme-linked immunosorbent assay procedure using recombinant ZEBRA protein and synthetic peptides as antigens. RESULTS: BZLF1 (ZEBRA) or early gene products (EA-R and EA-D/BHLF1/NotI) were detected in a small proportion (< 0.01-5%) of tumour cells in eight of these 17 cases by immunohistochemistry and in situ hybridization. Demonstration of replicative gene expression did not correlate with either low CD4+ cell counts (P > 0.05) or anti-EBV antibody titres (P > 0.05). Anti-ZEBRA activity was not significantly increased in patients affected with ARNHL, the cells of which expressed replicative gene products (P > 0.05). CONCLUSION: The degree of immunodeficiency does not clearly enhance replicative gene expression in tumour cells of ARNHL. EBV serology, including anti-ZEBRA activity, is not a reliable tool for predicting the occurrence of such proliferations.

Expression of the cell death-inducing gene bax in carcinomas developed from the follicular cells of the thyroid gland.

The expression of apoptosis-regulating proteins, Bcl-2, Bax, Mcl-1, and Bcl-X, was evaluated by immunohistochemical methods in 39 cases of thyroid carcinomas. Normal thyroid tissues showed a consistent expression of Bcl-2 and Mcl-1 whereas Bax and Bcl-X proteins were essentially absent from most follicular thyroid cells. Bax expression was observed in all papillary carcinomas (n = 23) and in 8 of 10 follicular carcinomas. The intensity of Bcl-2 immunostaining was generally higher in follicular tumors (n = 10) than in papillary carcinomas (n = 21 of 23). However, in undifferentiated tumors, both Bax and Bcl-2 were weakly expressed. Mcl-1 protein expression was similar to that of Bax in papillary and follicular tumors, but was also frequently detectable in undifferentiated tumors. Bcl-X immunostaining was seen in all undifferentiated tumors (n = 6), in 22 of 23 papillary tumors, and in 5 of 10 follicular tumors. Our findings show that the regulation of bcl-2 family gene expression is different in normal thyroid tissue compared to that of its neoplastic counterpart and varies with the tumor subtype. In particular, unlike normal thyroid epithelium, the apoptosis-blocking gene bcl-X and the apoptosis-inducing gene bax are frequently expressed in thyroid carcinomas derived from the follicular cells. Thus, alterations in the expression of these bcl-2 family genes may contribute to the pathogenesis of thyroid carcinomas.

The management of adult aggressive non-Hodgkin's lymphomas.

Aggressive non-Hodgkin's lymphona include diffuse large B-cell lymphoma, anaplastic large cell lymphona, and different peripheral T-cell lymphomas. An international prognostic index has been developed including age, serum LDH, performance status, and extranodal involvement. For localized aggressive lymphoma, the preferred treatment is 3-4 CHOP and radiation therapy, with a cure rate of 70-80%. For disseminated aggressive lymphoma, current regimens have a cure rate of less than 40%. Innovative strategies, including dose escalation, autologus stem cell support, new drugs, and immunotherapy are being explored to improve these results.

Human immunodeficiency virus-related lymphoma: relation between clinical features and histologic subtypes.

PURPOSE: Non-Hodgkin's lymphoma occurs frequently in patients with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS). We determined the association between the clinical and histologic features of HIV-related lymphoma. SUBJECTS AND METHODS: We reviewed the medical records of 291 patients with noncerebral HIV-related lymphoma who had been treated in multicenter trials coordinated by the Groupe d'Etude des Lymphomes de l'Adulte between 1988 and 1997. This study was performed mainly before the availability of combination antiretroviral therapy. RESULTS: The main histologic subtypes were centroblastic lymphoma in 131 patients (45%), immunoblastic lymphoma in 39 patients (13%), and Burkitt's lymphoma (including the classical form and the variant with plasmacytic differentiation) in 115 patients (40%). Burkitt's lymphoma was the most aggressive form, whereas immunoblastic lymphoma occurred in severely immunodeficient patients. Two-year survival after enrollment was 15% in immunoblastic lymphoma, 32% in Burkitt's lymphoma, and 31% in centroblastic lymphoma (P = 0.006), but multivariate analysis did not confirm the independent prognostic value of histologic subtype. Instead, five independent pretreatment factors increased the risk of mortality: age 40 years or older [relative risk (RR) = 1.5; 95% confidence interval (CI), 1.1 to 2.1; P = 0.005], elevated serum lactate dehydrogenase level (RR = 1.5; 95% CI, 1.1 to 2.1; P = 0.02), having a diagnosis of AIDS before lymphoma (RR = 1.8; 95% CI, 1.2 to 2.6; P = 0.006), CD4(+) cell count less than 100 x 10(6)/L (RR = 1.8; 95% CI, 1.3 to 2.6; P = 0.0004), and impaired performance status (RR = 2.4; 95% CI, 1.7 to 3.4; P <0.0001). CONCLUSION: Several pretreatment characteristics of HIV-related lymphoma were linked to the histologic form, but HIV disease parameters other than those of lymphoma were the main determinants of outcome, so the histologic features of the lymphoma were not associated with prognosis.

Primary mediastinal large B-cell lymphoma. A clinicopathologic study of 141 cases compared with 916 nonmediastinal large B-cell lymphomas, a GELA ("Groupe d'Etude des Lymphomes de l'Adulte") study.

Among non-Hodgkin's lymphomas, primary mediastinal large B-cell lymphoma (PMLCL) has been considered a separate entity that has specific clinical and histological aspects and a poor prognosis. In this study, we reexamined the clinicopathologic features and the response to current treatment of 141 PMLCL and compare them with 916 nonmediastinal large B-cell lymphomas (NMLCL) recorded in the same period and treated with similar combined chemotherapy. The clinical features of PMLCL at diagnosis were largely homogeneous and distinct from NMLCL, with a predilection for young women (59% with a mean age of 37 years versus 42% with a mean age of 54 years), bulky tumor (77% versus 7%, p < 10(4)), high serum lactic dehydrogenase (LDH) level 76% versus 51%, p < 10(4)), and frequent intrathoracic extension to adjacent organs such as pleura, pericardium, and lung. By contrast, extrathoracic or hematologic dissemination was uncommon (2% of bone marrow involvement versus 17%). All patients had diffuse large B-cell nonimmunoblastic, nonanaplastic lymphomas. Histological analysis of the 141 PMLCL evaluated two common patterns: the presence of large cells with clear cytoplasm (found in 38% of cases) and the presence of fibrosis (marked in 25% of cases). The presence of clear cells or intense fibrosis did not constitute prognostic indicators. Immunologic and molecular analysis assessed the profile of bcl-2 expression and the presence of Epstein-Barr virus (EBV) in PMLCL: 30% expressed a high level of bcl-2 protein; EBER RNAs were detected by in situ hybridization in only two of the 41 cases tested. Monotypic light chain restriction could be demonstrated in seven of the 41 PMLCL tested on fixed-section. Treated with polychemotherapy regimens without radiotherapy, 79% of PMLCL patients achieved a complete remission compared with 68% in the NMLCL patient group (p = 0.01). Overall, 3-year survival rates were estimated at 66 and 61%, respectively (p = 0.05), and disease-free survival rates were not significantly different (61 versus 64%). Stratified analysis on the International Prognostic Index (based on age, tumor stage, serum LDH level, and performance status) showed no difference in the overall and disease-free survivals between the two lymphoma groups. In conclusion, PMLCL can be combined with other diffuse large B-cell lymphomas on morphologic grounds; it is not associated with EBV. It responds favorably to treatment and should be managed like other high-grade lymphomas of equivalent histology. However, the uncommon clinical presentation makes it a distinct entity.

Characterization of Epstein-Barr virus-infected cells in benign lymphadenopathy of patients seropositive for human immunodeficiency virus.

The authors investigated 25 benign lymph nodes in patients infected with the human immunodeficiency virus (HIV) by in situ hybridization (ISH) and immunohistochemistry (IHC) to detect and characterize the Epstein-Barr virus (EBV)-infected cells. After ISH, 22 lymph nodes were found to contain various numbers of Epstein-Barr-encoded RNA (EBER)-positive cells. Most of these cells were B cells. In six lymph nodes with numerous EBV-infected cells, EBNA2-positive/LMP1-positive lymphoblastoid cells were detected by IHC. Exceptional cells (in two specimens) were positively labeled with antigen-Z Epstein-Barr replicative activator (ZEBRA) antibody or BamHI Left Frame 1/Not I (BHLF1/Not I) probes, indicating that EBV replication is not enhanced in the lymphocytes. In normal conditions (healthy individuals), small lymphocytes that express a restricted pattern of viral genes do escape immune response, whereas lymphoblastoid cells do not. Thus, impaired immune system may account for the late proliferation of lymphoblastoid cells (Epstein-Barr nuclear antigen [EBNA]2positive/latent membrane protein [LMP]1 positive) in HIV-infected patients, and could explain why EBV-driven, acquired immunodeficiency syndrome (AIDS)-related, non-Hodgkin's lymphoma occur more frequently in patients with low CD4-positive T cells.

Maintenance treatment with recombinant alpha interferon after autologous bone marrow transplantation for aggressive myeloma in first remission after conventional induction chemotherapy.

Twenty patients (median age 57 years) with high tumor mass myeloma in first remission after conventional chemotherapy received a two-phase treatment: autologous bone marrow transplantation (ABMT) using a preparative regimen of high dose melphalan plus total body irradiation followed by maintenance treatment with recombinant alpha interferon. Before ABMT all patients were in partial remission, while after ABMT 10 (50%) achieved complete remission, and 10 remained in partial remission (with a 90% decrease in measurable paraprotein in 7/10). With a median follow-up of 19.8 months (12.2-33.5) after diagnosis and 13 months (4-25) after ABMT, the Kaplan-Meier 2-year post-ABMT probability of progression-free survival was 85% (95% CI = 58.7-95.8%). None of the 10 patients in complete remission has relapsed. No toxic death occurred. Alpha interferon was introduced early after ABMT (2.7 months) and was well tolerated. This strategy may represent an advance in the management of aggressive myeloma.

Bone marrow involvement in anaplastic large cell lymphoma. Immunohistochemical detection of minimal disease and its prognostic significance.

Bone marrow involvement by anaplastic large cell anaplastic large cell (ALC) lymphoma can be difficult to detect on routine morphologic examination alone. In a series of 42 patients with ALC lymphoma, the authors analyzed: (1) the usefulness of a limited panel of monoclonal antibodies directed against CD30 (Ber-H2, HRS4) and epithelial marrow involvement on routinely processed biopsy specimens; and (2) the prognostic significance of bone marrow involvement as detected on both morphologic and immunohistochemical grounds. On conventional examination, 17% of the patients were found to have bone marrow involvement at diagnosis. However, after immunohistochemical analysis, occult malignant cells were detected in 23% of the patients with negative bone marrow biopsy on routine histology. The low percentage of positive cases on routine morphologic examination compared to immunohistochemical examination was related to: (1) the scarcity of neoplastic cells which were scattered among hematopoietic cells; (2) the difficulty of distinguishing malignant cells from immature hematopoietic elements; and (3) the absence of alteration of the reticulin network. The authors observed a significant association between marrow infiltration and the presence of hematologic abnormalities (mostly anemia or cytopenias) at diagnosis, both in children and adult patients. More importantly, a significant lower survival was seen in patients with bone marrow involvement compared to those without bone marrow involvement. Immunohistochemistry with anti-CD30 and anti-EMA antibodies should be performed systematically in bone marrow biopsies from patients with ALC lymphoma to reliably identify the presence of bone marrow involvement that appears to carry a poor prognosis.

Hodgkin's disease following mycosis fungoides: phenotypic and molecular evidence for different tumour cell clones.

AIMS: (1) To assess the clonality of tumour cells in two patients with mycosis fungoides who subsequently developed Hodgkin's disease; and (2) to determine whether there is a clonal relation between these two disorders. METHODS: Cutaneous tissue samples involved by mycosis fungoides and lymph nodes involved by Hodgkin's disease from both patients were investigated by immunohistochemistry and the polymerase chain reaction. RESULTS: Mycosis fungoides tumour cells in both patients expressed multiple T cell associated antigens; Reed-Sternberg (RS) cells had the null phenotype. T cell receptor gamma chain genes were clonally rearranged in mycosis fungoides cells but not in RS cells, including variants, in both patients. In the patient with intermediate transformation to large cell lymphoma, immunoglobulin heavy chain genes were rearranged in the cutaneous tumour, but not in the lymph node involved by Hodgkin's disease. CONCLUSION: The divergent antigen expression and gene rearrangements observed in these two patients strongly suggest that Hodgkin's disease and mycosis fungoides are not derived from a single tumour cell clone.

Detection of the cell death-inducing protein BAK in Reed-Sternberg cells of Hodgkin's disease.

The expression of the cell death-inducing protein, Bak, was investigated in 41 cases of Hodgkin's disease and was correlated with Epstein-Barr virus (EBV) status. Overall, Bak immunostaining was observed in 35/41 cases (85%). Among the 22 EBV-positive cases, 20 cases (91%) expressed Bak while 15/19 EBV-negative cases (79%) contained Bak-positive Reed-Sternberg cells. The expression of Bak, as assessed by the staining intensity and the numbers of positive tumor cells, varied greatly from case to case but was high in 6 cases (15%). Our findings show that, similar to Bax, a second apoptosis-inducing gene Bak is frequently expressed in Hodgkin's disease. Whilst Bak is suspected to protect cells immortalized by EBV from apoptosis, its expression in Hodgkin's disease appears to be unrelated to the EBV status of Reed-Sternberg cells. Moreover, the potential pro-apoptotic functions related to Bak and Bax in Hodgkin's disease might be surpassed by a stronger expression of anti-apoptotic molecules thus explaining tumor progression.

Bcl-x gene expression in Hodgkin's disease.

Bcl-x is a Bcl-2-family protein that has been previously detected in cortical thymocytes, plasma cells, and activated lymphocytes. We report here on the high detection rate of the Bcl-x protein found in 86% of Hodgkin's disease samples and on the significance regarding its complex role among the Bcl-2-family of proteins: Bcl-x is known to heterodimerize with Bcl-2 (an anti-apoptosis protein) and with Bax, a potent inducer of cell death. Moreover, recent evidences show that Bcl-x may induce multiple drug resistance in vitro, suggesting that chemical or biological interactions with this protein may have potential therapeutic value in Hodgkin's disease.

Vincristine degradation by serum from leukemic patients: role of myeloperoxidase.

Myeloperoxidase (MPO) has been shown to catalyze the in vitro degradation of vincristine (VCR). Given that MPO is a lysosomal enzyme that can be released into the circulation by both normal activated and leukemic myeloid cells, we investigated the possibility that sera from patients with acute myeloblastic leukemia (AML) might exhibit an increased capacity to degrade VCR. 31 serum samples (23 from patients with acute myeloblastic leukemia and 8 from patients with other conditions) were analyzed after incubation with ((3)H)VCR by using HPLC. Sera from patients with AML demonstrated an increased ability to breakdown VCR when compared to either normal sera or to sera from patients with lymphoid leukemias. VCR degradation was significantly increased by adding hydrogen peroxide, an electron donor for MPO, to the sera and was almost completely inhibited by adding 1 mM acetaminophen, an inhibitor of MPO. VCR peroxidation in the presence of hydrogen peroxide correlated both with the number of leukemic blasts in the circulation at the time the sera were obtained and with serum MPO concentrations determined by an immunoassay. These data suggest that the inactivity of VCR in AML may be due in part to its rapid peroxidation to inactive species by the MPO of leukemic myeloblasts.