Effect of alkyl groups on the cellular hydrolysis of stavudine phosphoramidates

We examined the effect of cellular metabolism of three alkyl-substituted amino acid ester phosphoramidate derivatives of stavudine in different cell lines. Marked cell-to-cell differences were found in both the rate of hydrolysis and chiral selectivity. This selectivity implies that different enzymes may be involved in the metabolism of these compounds depending on the cell type involved. Notably, both the methyl and ethyl substituted derivatives underwent hydrolysis in presence of various cell lines, whereas the tert-butyl substituted compound was resistant to hydrolysis implying that steric hindrance associated with this group along with electron density may play a key role in the hydrolysis profile of these compounds. Additionally we found this mimicked the hydrolysis profiles obtained for bacterial enzymes. Furthermore, our results suggest that the site of attack of the cellular enzymes is confined to the ester side chain of the molecule. This result is also consistent with our earlier observation using bacterial enzymes as well as using 'd' isomers.

Chemosensitivity of TEL-AML1 fusion transcript positive acute lymphoblastic leukemia cells

The TEL-AML1 fusion which results from a cryptic t(12;21) translocation is the most frequently occurring genetic abnormality in childhood acute lymphoblastic leukemia (ALL) and has been associated with an excellent treatment outcome. In the present study, we examined the FAS/BCL-2 expression profiles and chemosensitivity of primary leukemic cells from children with newly diagnosed t(12;21)TEL-AML1 fusion transcript-positive versus t(12;21)TEL-AML1 fusion transcript-negative standard risk ALL. TEL-AML1(+) ALL cells expressed higher levels of the pro-apoptotic protein Fas and lower levels of the anti-apoptotic protein Bcl2 than TEL-AML1(-) ALL cells, as determined by confocal laser scanning microscopy. TEL-AML1(+) ALL cells were more sensitive to the apoptosis-inducing effects of serum deprivation, dexamethasone and vincristine than TEL-AML1(-) ALL cells. This study provides novel mechanistic insights regarding the chemosensitivity of TEL-AML1(+) ALL cells and provides a cogent explanation for the excellent leukemia-free survival outcome of children with TEL-AML1(+) ALL treated on contemporary chemotherapy programs.

Residual bone marrow leukemic progenitor cell burden after induction chemotherapy in pediatric patients with acute lymphoblastic leukemia

We used highly sensitive multiparameter flow cytometry and blast colony assays to quantify the leukemic progenitor cell (LPC) burden of postinduction chemotherapy bone marrows from newly diagnosed and relapsed pediatric patients with acute lymphoblastic leukemia (ALL). Of 890 newly diagnosed patients, 243 (27%) had detectable LPC in the postinduction bone marrow samples with an average (mean +/- SE) LPC content of 22+/-9 LPC/10(6) mononuclear cell (MNC; range, 0-7199/10(6) MNC; median, 0/10(6) MNC). By comparison, 24 of 50 (48%) patients with relapsed ALL had detectable LPC in their postinduction bone marrow specimens (P = 0.003), and their average LPC content was 202+/-139 LPC/10(6) MNC. Fewer patients with B-lineage ALL (170 of 786; 22%) than patients with T-lineage ALL (73 of 104; 70%) harbored residual LPC in their postinduction bone marrow specimens (P < 0.0001). This correlation with immunophenotype was independent of the National Cancer Institute risk classification. Similarly, 19 of 44 (43%) patients with relapsed B-lineage ALL versus 5 of 6 (83%) patients with relapsed T-lineage ALL harbored residual LPC in their postinduction bone marrow specimens (P = 0.09). Among newly diagnosed patients, those with high-risk ALL seemed to have larger numbers of residual LPC in their bone marrow after induction chemotherapy than those with standard risk ALL (53+/-26, n = 286 versus 7+/-1, n = 604, P = 0.04). LPC of patients with standard risk ALL who had a slow early marrow response at day 7 seemed to be more resistant to the three-drug induction chemotherapy than patients who had a rapid early marrow response. Overall, the order of chemosensitivity of LPC was: newly diagnosed standard risk B-lineage > newly diagnosed higher risk B-lineage > newly diagnosed standard risk T-lineage > newly diagnosed higher risk T-lineage > relapsed B-lineage > relapsed T-lineage. Notably, LPC- patients whose end-of-induction remission bone marrow specimens had zero LPC had an excellent early event-free survival outcome. Within the standard and high-risk subsets, LPC- patients had a 2.6-fold lower and 2.4-fold lower incidence of events, respectively, than LPC+ patients. At 6 months, 12 months, as well as 24 months, the ranking order for better event-free survival was: standard risk, LPC- > high risk, LPC- > standard risk, LPC+ > high risk, and LPC+.

Microsatellite instability in sporadic parathyroid adenoma

Parathyroid adenomas are usually benign uniglandular tumors, and inactivation of several tumor suppressor genes, notably the MEN 1 gene, or activation of oncogenes have been implicated in the tumorigenesis. Genomic instability, indicative of the involvement of DNA mismatch repair genes, has not been previously described in parathyroid adenomas. A single large parathyroid adenoma was resected from an 8.5-yr-old Brazilian patient with no personal or family history of other endocrinopathies. Analysis of paired tumor-nontumor DNA using 23 microsatellite markers, located on chromosomes 1, 10, and 11 was carried out. Microsatellite instability was detected in nine markers (D1S191, D1S212, D1S413, D1S2848, RET, D11S901, D11S903, INSR, and INT2), whereas no allelic loss was detected with any of the analyzed markers. Immunohistochemical analysis of retinoblastoma protein expression revealed low levels of expression, but no histopathological signs of malignancy. We conclude that in this single, apparently sporadic parathyroid adenoma, DNA mismatch repair genes might be involved in parathyroid tumorigenesis.

Prognostic significance of T-lineage leukemic cell growth in SCID mice: a Children's Cancer Group study

Contemporary intensive therapies are effective for the majority of pediatric T-lineage acute lymphoblastic leukemia (ALL) patients, thus current challenge is to identify patients who may benefit from alternative treatment modalities. Previously, we demonstrated that human leukemic cell growth in the severe combined immunodeficiency (SCID) mouse was a significant prognostic factor for very high risk B-lineage ALL patients. In the current report we show that primary leukemic cells from 24 of 88 (27%) T-lineage ALL patients (SCID+) caused histopathologically detectable leukemia in SCID mice. These SCID+ patients were similar to SCID- (n = 64) patients with respect to virtually all presenting features, including age, sex, race, and leukocyte count. Growth of primary leukemic cells in SCID mice was not a significant predictor of outcome for the aggregate population of T-lineage ALL patients. Two-year event-free survival (EFS) outcomes for SCID+ patient and SCID- patients were 76.2% (SD = 5.6%) and a 64.0% (SD = 10.4%; p = 0.20). Overall survival also was similar between the two groups (p = 0.36). Among the subset of patients with M1 or M2 marrow status by day 7 of induction chemotherapy (rapid early responders), those who were SCID+ had poorer outcomes than those who were SCID-, with a 2-year EFS of 68.4% (SD = 11.9%) vs. 85.7% (SD = 6.0%) and relative hazard rate of 3.06 (p = 0.06). These data suggest that leukemic cell growth in SCID mice may identify a subset of T-lineage ALL patients who are at higher risk for relapse despite achieving a rapid early response to induction chemotherapy.

Large scale manufacturing of TXU(anti-CD7)-pokeweed antiviral protein (PAP) immunoconjugate for clinical trials

We have conjugated the murine monoclonal anti-CD7 antibody TXU to the plant hemitoxin pokeweed antiviral protein (PAP) to construct an effective immunotoxin against CD7 antigen positive hematologic malignancies. The scaled-up production and purification of TXU antibody, PAP toxin, and TXU-PAP immunotoxin permitted the manufacturing of a highly purified clinical-grade TXU-PAP preparation. In clonogenic assays, TXU-PAP elicited selective and potent cytotoxicity against CD7 antigen positive human leukemia cells and killed primary clonogenic leukemic cells from T-lineage acute lymphoblastic leukemia (ALL) patients. To our knowledge, this pre-IND work represents the first effort of producing a clinical-grade PAP immunotoxin for treatment of T-lineage ALL. Since the CD7 antigen is also expressed on AML cells, TXU-PAP could also be useful for the treatment of CD7 positive acute myeloid leukemia (AML) patients.

Expression of BCR-ABL, E2A-PBX1, and MLL-AF4 fusion transcripts in newly diagnosed children with acute lymphoblastic leukemia: a Children's Cancer Group initiative

We used reverse transcriptase polymerase chain reaction (RT-PCR) assays to examine primary leukemic cells in on-study diagnostic bone marrow specimens from 642 children with newly diagnosed acute lymphoblastic leukemia (ALL) for the expression of MLL-AF4, E2A-PBX1, and BCR-ABL fusion transcripts. All PCR assays were performed centrally in the Children's Cancer Group ALL Biology Reference Laboratory. MLL-AF4 transcript was found in only 0.7% of the study population which excluded infants. E2A-PBX1 transcript was found in 2.5% of the study population and 3.3% of B-precursor cases. Expression was associated with massive hepatomegaly. BCR-ABL transcript was found in 2.3% of cases and correlated with older age, induction failure, and inferior event-free survival (EFS). RT-PCR assays allow rapid identification of patients with MLL-AF4 and BCR-ABL positive ALL. These patients have a poor outcome with contemporary therapy and rapid identification facilitates timely allocation to innovative treatment programs.

Cellular expression of antiapoptotic BCL-2 oncoprotein in newly diagnosed childhood acute lymphoblastic leukemia: a Children's Cancer Group Study

We found a marked variation in BCL-2 oncoprotein expression levels of primary leukemic cells from 338 children with newly diagnosed acute lymphoblastic leukemia (ALL). None of the high-risk features predictive of poor treatment outcome in childhood ALL, such as older age, high white blood cell (WBC) count, organomegaly, T-lineage immunophenotype, ability of leukemic cells to cause overt leukemia in severe combined immunodeficient (SCID) mice, presence of MLL-AF4, and BCR-ABL fusion transcripts were associated with high levels of BCL-2 expression. Overall, high BCL-2 levels were not associated with slow early response, failure to achieve complete remission, or poor event-free survival. High BCL-2 levels in primary leukemic cells predicted slow early response only in T-lineage ALL patients, which comprised approximately 15% of the total patient population. Even for this small subset of patients, the level of BCL-2 expression did not have a significant impact on the short-term event-free survival.