Secondary acute myeloid leukemia with inv(16): report of two cases following paclitaxel-containing chemotherapy and review of the role of intensified ara-C therapy.

Acute myeloid leukemia developing secondary to prior cytotoxic chemotherapy (s-AML) encompasses a range of distinct entities. We report two cases of s-AML with inv(16)(p13q22) who had prior exposure to paclitaxel. Additionally, two previously reported cases of s-AML with inv(16) had prior paclitaxel exposure raising the possibility that the taxanes may predispose to this specific syndrome of s-AML. One of our patients received escalated-dose ara-C chemotherapy, achieving a complete remission (12+ months). We therefore examined the prognosis of previously reported cases of s-AML with inv(16) and analyzed the influence of escalated-dose ara-C (>/=400 mg/m2/day). A total of 25 evaluable cases were identified, with 96% attaining CR independent of ara-C dose. The estimated median remission duration was 40 months and the median survival has not been reached (actuarial 5-year survival 52 +/- 18%). Although not achieving statistical significance, patients treated with escalated dose ara-C (n = 15) had longer remission duration and overall survival than those treated with standard dose ara-C (n = 10) (P = 0.063 and 0.20, respectively). In univariate analysis, younger age, male gender, and the presence of additional cytogenetic abnormalities were associated with a tendency towards adverse outcomes (P< 0.1). Age and gender were equally distributed between ara-C dose cohorts, but more patients treated with standard-dose ara-C had additional cytogenetic abnormalities (P = 0.048). Within the limitations of this retrospective study, this analysis suggests that, similar to de novo AML with inv(16), secondary cases may also potentially benefit from treatment with escalated-dose ara-C. This is consistent with the premise that the underlying molecular defect, rather than the presence of prior cytotoxic drug exposure, may be the most important determinant of disease behavior and chemotherapy responsiveness in AML.

Deoxycytidylate deaminase activity in lymphoproliferative disorders.

The activity of dCMPase has been measured in cell extracts from human lymphoproliferative disorders. The highest levels occurred in T helper-CLL and Thy-ALL, but high levels were also found in C-ALL, NPDLL transforming to DHL, DPDLL and DHL. A range of enzyme activities was found in the majority of types examined, with the widest range encountered in ALL, NPDLL and DHL. In DWDLL, a narrow range of dCMPase activities was found, with enzyme levels in the control range or moderately increased. Similarly, B-CLL exhibited a narrow range of enzyme activities, within that of the controls. The highest enzyme activity in HD was found in the highly malignant type - lymphocyte depleted HD. Statistically significant differences were found between the distribution of dCMPase activities in ALL and the chronic leukemias; and between favorable histologic types of non Hodgkin's lymphomas and the unfavorable DHL type. These data suggest that dCMPase activity is a marker of the clinical aggression of human lymphoid malignancies. Moreover, the marked variation in enzyme activity in each type of lymphoid malignancy suggests that this also applies to individual tumors as well. In view of the important role of dCMPase in pyrimidine metabolism and the profile of enzyme activities in leukemia and lymphoma, it is suggested that an inhibitor of dCMPase could be of clinical value in lymphoid malignancy.

Fetal thymidine kinase (TK1) in hairy cell leukaemia.

The thymidine kinase isoenzyme profile was determined in peripheral blood mononuclear cells and splenic tissue from 4 patients with hairy cell leukaemia, in order to assess the proliferative state of the hairy cell. The predominance of TK1 activity in all 4 spleens and in 2 out of 3 peripheral blood mononuclear cells examined, indicates that the hairy cell has significant proliferative capacity when compared to the neoplastic cell in other chronic lymphoproliferative disorders. It is suggested, in view of the heterogeneity in peripheral blood mononuclear TK isoenzyme types, that more extensive studies are warranted to examine the relationship between peripheral blood mononuclear TK1 activity and the occurrence of progressive disease in post-splenectomy patients.

Doxorubicin-associated delayed ventricular fibrillation in acute promyelocytic leukemia.

A 16-year-old schoolgirl presented with acute promyelocytic leukemia. 10 days after induction chemotherapy with doxorubicin and cytosine arabinoside together with heparinisation for the accompanying disseminated intravascular coagulopathy, she developed ventricular fibrillation. Following successful cardiac resuscitation a gated blood pool scan showed a left ventricular ejection fraction of 49%. Despite this event the patient was subsequently rechallenged with doxorubicin without any adverse cardiac effect. The exact mechanism for this delayed doxorubicin-associated cardiac arrhythmia is not clear, but electrolyte disturbance and heparin-doxorubicin interaction may have played a contributory role.

Kinetic behaviour and allosteric regulation of human deoxycytidylate deaminase derived from leukemic cells.

Deoxycytidylate deaminase has been highly purified (1232-fold) from human leukemia CCRF-CEM cells. The native molecular weight of the enzyme is 108 000 and subunit molecular weight 50 500, suggesting that the native enzyme exists as a dimer. The enzyme exhibits a sigmoidal initial velocity vs substrate concentration curve and is regulated by allosteric effectors, dCTP and TTP. The curve relating substrate concentration to initial velocity was changed from a sigmoidal shape to a hyperbolic one by the activator dCTP, while the inhibitor TTP increased the sigmoidicity of the curve. The molecular weight of deoxycytidylate deaminase was unchanged in the presence of allosteric effectors, indicating that aggregation-disaggregation is not the basis of regulation. Deoxycytidylate deaminase exhibited the greatest affinity for the substrate dCMP, with lesser affinity for ara-CMP, and least affinity for CMP. Ara-CMP was an effective substrate in the presence of dCTP concentrations exceeding 4 microM. These data indicate that human neoplastic cell deoxycytidylate deaminase is a highly regulated allosteric enzyme, which is likely to have a significant influence on cellular dUMP, dCTP and TTP pools. These findings further suggest, that the enzyme through its influence on dUMP levels is likely to modulate the biochemical effects of pyrimidine antimetabolites active against the thymidylate synthetase reaction and in the presence of elevated dCTP pools will promote deamination of ara-CMP to the inactive ara-UMP.

Clinical relevance of markers of cell proliferation in human lymphoid malignancies: a concise review.

The major advances being made in the understanding of the biology of human lymphoid malignancies have shown these to be a heterogenous group of tumours with respect to a variety of biological markers. The cell proliferative rate, an important determinant of tumor aggressiveness and response to therapy, is one of the biological phenomena currently being investigated in the lymphoid malignancies, particularly in the non-Hodgkin's lymphomas. In this paper we describe the techniques used in the analysis of cell proliferation in the lymphoid malignancies, and review the patterns of cell proliferation found in the various types of these tumours and the clinical relevance of these findings. We indicate that differences in cell proliferative rate are an important determinant of the response of non-Hodgkin's lymphomas to current therapeutic modalities and may explain the paradox that a significant number of reputed unfavorable tumors are now curable. Finally, we suggest that inherent differences in the proliferative rate of the neoplastic cell(s) of the so-called favorable histological types of non-Hodgkin's lymphomas may determine histologic progression as well as therapeutic responsiveness.

Thymidine as an anticancer agent, alone or in combination. A biochemical appraisal.

The value of thymidine as a cytotoxic drug alone or in combination with other pyrimidine antimetabolites has received considerable attention in recent years. In this paper, the biochemical basis for the cytotoxicity of thymidine and its interaction with other pyrimidine antimetabolites is described. It is indicated that early clinical trials have largely failed to substantiate data from experimental studies that have shown thymidine to be an effective antimetabolite and capable of potentiating the antineoplastic effect of several other agents. It is suggested that tumours likely to respond to thymidine alone or in combination may be identified by measuring in clinical tumour specimens known biochemical determinants of thymidine efficacy.

Human thymidine kinase: purification and some properties of the TK1 isoenzyme from placenta.

Human thymidine kinase TK1 isoenzyme has been purified 1800-fold from placenta to a specific activity of 2.9 nmoles/min/mg of protein. The rapid purification procedure includes affinity chromatography on a thymidine-Sepharose column. At all stages of purification, the enzyme showed irreversible lability. The native molecular weight was determined to be 45000. Human placental TK1 exhibited specificity for ATP and thymidine as substrates, and significant inhibition was found only with thymidine nucleotides. TTP was the most effective inhibitor.

Thymidine kinase isoenzymes in chronic lymphocytic leukaemia.

The profile of thymidine kinase isoenzymes was determined in peripheral blood lymphocytes from 14 patients with chronic lymphocytic leukaemia (CLL) and 31 controls. Twelve patients with indolent disease showed TK2 isoenzyme activity, while two patients in whom the disease evolved and two patients who presented with aggressive disease exhibited TK1 isoenzyme activity. The demonstration of TK1 activity in the peripheral blood lymphocytes of clinically aggressive CLL suggests that this isoenzyme may be a useful biochemical marker of such behaviour.

Prognostic relevance of thymidine kinase isozymes in adult non-Hodgkin's lymphoma.

To determine whether kinase (TK) isozyme status adds clinically useful information in adult non-Hodgkin's lymphoma (NHL), we have analyzed peripheral blood plasma and lymphocytes of 44 patients with NHL for either TK1 or TK2 isozyme activity. On the basis of isozyme status, patients could be divided into two groups that did not differ significantly with respect to known determinants for survival. The median survival of patients exhibiting peripheral blood TK1 thymidine kinase activity was 40 wk and that of individuals with TK2 activity was in excess of 200 wk. These data suggest that peripheral blood TK1 isozyme is a useful independent biochemical marker for a subgroup of NHL who respond poorly to current therapy and thus require new therapeutic approaches.

Kinetic mechanism and inhibition of human liver thymidine kinase.

Thymidine kinase (ATP : thymidine 5'-phosphotransferase, EC 2.7.1.21), purified to apparent homogeneity from human liver, was found to have Michaelis constants for thymidine and ATP of 5 and 90 microM, respectively. Based on studies of initial velocity and product inhibition, the enzyme kinetic mechanism is compatible with an ordered sequential reaction with thymidine binding first and thymidine monophosphate released last. The activity of various triphosphate nucleosides as phosphate donors for human liver thymidine kinase showed little specificity with ATP greater than CTP greater than UTP greater than GTP and the respective Michaelis constants ranged from 0.10 to 0.30 mM. Among various purine and pyrimidine compounds, only TTp and dCTP were effective inhibitors of the enzyme. Inhibition with TTP was competitive with respect to both thymidine and ATP with Ki values of 13.5 and 8.5 microM, respectively, while the inhibition produced by dCTP was complex. Deoxycytidine was found to be an effective nucleoside substrate for human liver thymidine kinase with a Michaelis constant of 6 microM. This finding suggests that human mitochondrial deoxycytidine and thymidine kinase activity is a single protein.

Thymidine kinase isoenzymes in human malignant lymphoma.

The activities of thymidine kinase (TK) isoenzyme 1 and 2 were examined in extracts of human benign or malignant lymphoid tissue and correlated with degrees of morphological differentiation. TK2 activity occurred in peripheral blood lymphocytes of normal individuals, patients with chronic lymphocytic leukemia, or solid lymphoid tissue, exhibiting either nonneoplastic histological findings or those of diffuse well-differentiated lymphocytic lymphoma. TK1 activity occurred in solid, non-Hodgkin's lymphoma tissue, exhibiting lesser degrees of cellular differentiation, or in peripheral blood lymphocytes of patients with clinical aggressive chronic lymphocytic leukemia or lymphosarcoma leukemia. In non-Hodgkin's lymphoma tissue, the range of TK1 activities correlated broadly with the Rappaport classification, with higher values occurring in tissue exhibiting changes of diffuse poorly differentiated lymphocytic lymphoma or diffuse histiocytic lymphoma.

Human liver thymidine kinase. Purification and some properties of the enzyme.

Thymidine kinase (EC 2.7.1.21) has been purified 5600-fold to apparent homogeneity from normal adult human liver. The purification included affinity chromatography on a thymidine column. The subunit molecular weight of the enzyme obtained from this purification was 48,000, and human liver thymidine kinase exhibited association and dissociation. The smallest native molecular form had a molecular weight as determined by gel filtration of 49,000 and the enzyme consistently associated into forms with a molecular weight of 98,000 and 340,000. With isoelectric focusing, the enzyme demonstrated a single form with an isoelectric point of 5.1.

Erythroleukemia following drug induced hypoplastic anemia.

Three patients with drug-induced hypoplastic anemia terminating 2 to 6 years after presentation with erythroleukemia are described. All were treated for prolonged periods with androgen and corticosteroid and two of the patients showed apparent dependence on this therapy for optimal hematologic status. The leukemic phase was heralded by loss of this dependence and development of sideroblastic dyserythropoiesis with progression to bizarre erythroid hyperplasia and fatal cytopenia. The exact relationship between androgen and corticosteroid therapy and the erythroleukemia remains speculative.