Cytoplasmatic compartmentalization by Bcr-Abl promotes TET2 loss-of-function in chronic myeloid leukemia.

The loss-of-function of ten-eleven-translocation (TET) 2, a Fe(2+) -oxoglutarate-dependent dioxygenase catalyzing 5 methyl cytosine (5mC) conversion into 5-hydroxymethylcytosine (5hmC), contributes to the hematopoietic transformation in vivo. The aim of our study was to elucidate its role in the phenotype of chronic myeloid leukemia (CML), a myeloproliferative disease caused by the Bcr-Abl rearranged gene. We first confirmed TET2 interaction with the Bcr-Abl protein predicted by a Fourier-based bioinformatic method. Such interaction led to TET2 cytoplasmatic compartmentalization in a complex tethered by the fusion protein tyrosine kinase (TK) and encompassing the Forkhead box O3a (FoxO3a) transcription factor. We then focused the impact of TET2 loss-of-function on epigenetic transcriptional regulation of Bcl2-interacting mediator (BIM), a pro-apoptotic protein transcriptionally regulated by FoxO3a. BIM downregulation is a critical component of CML progenitor extended survival and is also involved in the disease resistance to imatinib (IM). Here we reported that TET2 release from Bcr-Abl protein following TK inhibition in response to IM triggers a chain of events including TET2 nuclear translocation, re-activation of its enzymatic function at 5mC and recruitment at the BIM promoter followed by BIM transcriptional induction. 5hmC increment following TET2 re-activation was associated with the reduction of histone H3 tri-methylation at lysine 9 (H3K9me3), which may contribute with DNA de-methylation reported elsewhere to recast a permissive epigenetic "landscape" for FoxO3a transcriptional activity.

14-3-3 ligand prevents nuclear import of c-ABL protein in chronic myeloid leukemia.

Here we demonstrated that the 'loss of function' of not-rearranged c-ABL in chronic myeloid leukemia (CML) is promoted by its cytoplasmic compartmentalization bound to 14-3-3 sigma scaffolding protein. In particular, constitutive tyrosine kinase (TK) activity of p210 BCR-ABL blocks c-Jun N-terminal kinase (JNK) phosphorylation leading to 14-3-3 sigma phosphorylation at a critical residue (Ser(186)) for c-ABL binding in response to DNA damage. Moreover, it is associated with 14-3-3 sigma over-expression arising from epigenetic mechanisms (promoter hyper-acetylation). Accordingly, p210 BCR-ABL TK inhibition by the TK inhibitor Imatinib mesylate (IM) evokes multiple events, including JNK phosphorylation at Thr(183), p38 mitogen-activated protein kinase (MAPK) phosphorylation at Thr(180), c-ABL de-phosphorylation at Ser residues involved in 14-3-3 binding and reduction of 14-3-3 sigma expression, that let c-ABL release from 14-3-3 sigma and nuclear import, and address BCR-ABL-expressing cells towards apoptotic death. Informational spectrum method (ISM), a virtual spectroscopy method for analysis of protein interactions based on their structure, and mathematical filtering in cross spectrum (CS) analysis identified 14-3-3 sigma/c-ABL binding sites. Further investigation on CS profiles of c-ABL- and p210 BCR-ABL-containing complexes revealed the mechanism likely involved 14-3-3 precluded phosphorylation in CML cells.

A new nonpeptidic inhibitor of 14-3-3 induces apoptotic cell death in chronic myeloid leukemia sensitive or resistant to imatinib.

Resistance of chronic myeloid leukemia (CML) to tyrosine kinase inhibitor imatinib mesylate (IM) is most often due to point mutations in the Bcr-Abl fusion gene. T315I mutation (resulting in substitution of Ile for a Thr residue at the "gatekeeper" position 315) raises particular concern, because it also provides resistance to second-generation kinase inhibitors already approved for clinical use (nilotinib and dasatinib). Much effort is therefore focused on alternative molecular-based strategies. Previous studies proved that binding to 14-3-3 scaffolding proteins leads to cytoplasmic compartmentalization and suppression of proapoptotic and antiproliferative signals associated with Bcr-Abl protein kinase, hence contributing to leukemic clone expansion. Here we investigated the effect of 14-3-3 inhibition disruption on hematopoietic cells expressing the IM-sensitive wild type Bcr-Abl and the IM-resistant T315I mutation. Using a virtual screening protocol and docking simulations, we identified a nonpeptidic inhibitor of 14-3-3, named BV02, that exhibits a remarkable cytotoxicity against both cell types. c-Abl release from 14-3-3σ, promoting its relocation to nuclear compartment (where it triggers transcription of p73-dependent proapoptotic genes) and to mitochondrial membranes (where it induces the loss of mitochondrial transmembrane potential) combined with c-Abl enhanced association with caspase 9 (a critical step of sequential caspase activation further contributing to c-Abl pro-apoptotic function) has a prominent role in the effect of BV02 on Bcr-Abl-expressing cells. In conclusion, BV02 may be considered as a treatment option for CML and, in particular, for more advanced phases of the disease that developed IM resistance as a consequence of Bcr-Abl point mutations.

Interobserver variability of clinical target volume delineation in supra-diaphragmatic Hodgkin's disease: a multi-institutional experience.

BACKGROUND: To determine interobserver variability in clinical target volume (CTV) of supra-diaphragmatic Hodgkin's lymphoma. MATERIALS AND METHODS: At the 2008 AIRO (Italian Society of Radiation Oncology) Meeting, the Radiation Oncology Department of Chieti proposed a multi-institutional contouring dummy-run of two cases of early stage supra-diaphragmatic Hodgkin's lymphoma after chemotherapy. Clinical history, diagnostics, and planning CT imaging were available on Chieti's radiotherapy website (www.radioterapia.unich.it). Participating centers were requested to delineate the CTV and submit it to the coordinating center. To quantify interobserver variability of CTV delineations, the total volume, craniocaudal, laterolateral, and anteroposterior diameters were calculated. RESULTS: A total of 18 institutions for case A and 15 institutions for case B submitted the targets. Case A presented significant variability in total volume (range: 74.1-1,157.1 cc), craniocaudal (range: 6.5-22.5 cm; median: 16.25 cm), anteroposterior (range: 5.04-14.82 cm; median: 10.28 cm), and laterolateral diameters (range: 8.23-22.88 cm; median: 15.5 cm). Mean CTV was 464.8 cc (standard deviation: 280.5 cc). Case B presented significant variability in total volume (range: 341.8-1,662 cc), cranio-caudal (range: 8.0-28.5 cm; median: 23 cm), anteroposterior (range: 7.9-1.8 cm; median: 11.1 cm), and laterolateral diameters (range: 12.9-24.0 cm; median: 18.8 cm). Mean CTV was 926.0 cc (standard deviation: 445.7 cc). CONCLUSION: This significant variability confirms the need to apply specific guidelines to improve contouring uniformity in Hodgkin's lymphoma.

RAD 001 (everolimus) prevents mTOR and Akt late re-activation in response to imatinib in chronic myeloid leukemia.

The mammalian target of rapamycin (mTOR) is one target of BCR-ABL fusion gene of chronic myeloid leukemia (CML). Moreover, it drives a compensatory route to Imatinib mesylate (IM) possibly involved in the progression of leukemic progenitors towards a drug-resistant phenotype. Accordingly, mTOR inhibitors are proposed for combined therapeutic strategies in CML. The major caveat in the use of mTOR inhibitors for cancer therapy comes from the induction of an mTOR-phosphatidylinositol 3 kinase (PI3k) feedback loop driving the retrograde activation of Akt. Here we show that the rapamycin derivative RAD 001 (everolimus, Novartis Institutes for Biomedical Research) inhibits mTOR and, more importantly, revokes mTOR late re-activation in response to IM. RAD 001 interferes with the assembly of both mTOR complexes: mTORC1 and mTORC2. The inhibition of mTORC2 results in the de-phosphorylation of Akt at Ser(473) in the hydrophobic motif of C-terminal tail required for Akt full activation and precludes Akt re-phosphorylation in response to IM. Moreover, RAD 001-induced inhibition of Akt causes the de-phosphorylation of tuberous sclerosis tumor suppressor protein TSC2 at 14-3-3 binding sites, TSC2 release from 14-3-3 sigma (restoring its inhibitory function on mTORC1) and nuclear import (promoting the nuclear translocation of cyclin-dependent kinase [CDK] inhibitor p27(Kip1), the stabilization of p27(Kip1) ligand with CDK2, and the G(0)/G(1) arrest). RAD 001 cytotoxicity on cells not expressing the BCR-ABL fusion gene or its p210 protein tyrosine kinase (TK) activity suggests that the inhibition of normal hematopoiesis may represent a drug side effect.

Vincristine, doxorubicin, cyclophosfamide, actinomycin D, ifosfamide, and etoposide in adult and pediatric patients with nonmetastatic Ewing sarcoma. Final results of a monoinstitutional study.

AIMS AND BACKGROUND: To investigate a six-drug combination in patients with nonmetastatic Ewing sarcoma, focusing on chemotherapy-induced necrosis and chemotherapy toxicity in adult and pediatric patients. METHODS AND STUDY DESIGN: Alternating cycles of vincristine (1.5 mg/m2), doxorubicin (80 mg/m2) and cyclophosfamide (1200 mg/m2) (weeks 0, 6, 13, 22 and 31), ifosfamide (9 g/m2), vincristine (1.5 mg/m2), and actinomycin D (1.5 mg/m2) (weeks 3, 16, 25 and 34), and ifosfamide (9 g/m2) and etoposide (450 mg/m2) (weeks 9, 19, 28 and 37) were administered. Primary chemotherapy-induced necrosis was graded: G3 (complete necrosis), G2 (microfoci of tumor cells) and G1 (macrofoci of tumor cells). RESULTS: From 1996 to 1999, 50 patients with Ewing sarcoma were enrolled. The median age was 23.5 years (range, 4-56). Chemotherapy-induced necrosis (in 28 patients) was G3 in 36%, G2 in 21% and G1 in 43%. At a median follow-up of 110 months (range, 36-129), 5-year overall survival and event-free survival were 72% and 66%, respectively. According to histologic response, 5-year event-free survival was 90% in G3, 83% in G2, and 42% in G1 (P = 0.02). In adult and pediatric (<18 years) patients, the incidence of G4 leukopenia was 62% and 74%, respectively, with febrile neutropenia in 13% and 21%, respectively. G4 thrombocytopenia occurred in 3% of cycles in adults and in 7% in pediatric patients. Platelet and red blood cell transfusions were required respectively in 1% and 11% of cycles in adults and in 6% and 24% of cycles in pediatric patients. CONCLUSIONS: The six-drug combination can be administered safely in adult and pediatric populations. About 40% of patients have a poor chemotherapy-induced tumor necrosis, leading to poor probability of survival. New strategies are recommended to improve survival of poor responders to the six-drug combination.

Effects of probiotics for the prevention and treatment of radiation-induced diarrhea.

BACKGROUND AND AIMS: Probiotic supplementation seems to provide beneficial effects in the prevention and treatment of radiation-induced diarrhea. We performed a systematic review and meta-analysis to estimate the efficacy of probiotic supplementation for prevention and treatment of radiation-induced diarrhea. METHODS: Two reviewers independently searched PubMed, EMBASE, Cochrane Library, Google Scholar and on-line clinical trials registers (up to January 2009) for randomized controlled trials that evaluated the efficacy of probiotic supplementation for the prevention and treatment of radiation-induced diarrhea. Each clinical trial was separately evaluated for study characteristics, methodologic quality and outcomes. Results of the randomized controlled trials were pooled in a meta-analysis. RESULTS: Four randomized controlled trials were included. Three clinical trials, with a total of 632 subjects, evaluated the preventive effects of probiotic supplementation and 1 study evaluated the therapeutic role. Random effects meta-analysis of the preventive trials did not show significant differences between probiotic supplementation and control groups (odds ratio 0.47; 95% confidence interval: 0.13-1.67). However, the few available trials and the presence of significant clinical and statistical heterogeneity limited the analysis. Similarly, the therapeutic clinical trial did not show significant differences between active and placebo groups. No major adverse events owing to probiotic supplementation were reported in any study. CONCLUSIONS: Probiotic supplementation showed beneficial effect in the prevention and treatment of radiation-induced diarrhea in experimental animal studies. Encouraging results have been observed in humans; however, the few available clinical studies do not allow firm conclusions. More well-performed, randomized placebo-controlled studies are needed.

11C-methionine vs. 18F-FDG PET in soft tissue sarcoma patients treated with neoadjuvant therapy: preliminary results.

OBJECTIVE: In patients with soft tissue sarcoma (STS) the histological response (tumour grade regression: TGR) to neoadjuvant chemoradiotherapy (CRT) may influence the outcome. The main aim of the study was to evaluate the predictive value of 11C-methionine (MET) and 18F-FDG PET/CT in patients with STS treated with neoadjuvant CRT, correlating TGR with SUVmax (standardized uptake value) percentage variation before and after CRT. PATIENTS AND METHODS: Nine patients with STS already scheduled for a neoadjuvant CRT and surgery were enrolled. They underwent MET and FDG PET/CT in a one-day procedure before and after the CRT. Pre-therapy SUVmax and the percentage variation of SUVmax for MET and FDG were correlated with TGR according to the Huvos grade. Grades I-II were considered as partial responders (PR) and grades III-IV as complete responders (CR). RESULTS: FDG pre-treatment mean SUVmax in PR patients was 7.1, while in CR patients it was 13.2. Pre-treatment mean MET SUVmax in PR patients was 75, while in CR patients it was 4.9. The mean percentage variation in FDG SUVmax, was -21.2% in PR patients and -745% in CR patients while that for MET SUVmax was 48% in PR patients and -53.9% in CR patients. CONCLUSION: According to this preliminary study, the percentage variation in FDG before and after CRT seems to discriminate between PR and CR better than MET.

Treatment of nonmetastatic Ewing's sarcoma family tumors of the spine and sacrum: the experience from a single institution.

The objective of this study is to determine the best local treatment combined with neoadjuvant chemotherapy for ESFT of the spine and sacrum, for the best local treatment for Ewing sarcoma family tumors (ESFT) according to the primary site is still unclear. Nowadays surgery is used in local treatment of ESFT, but literature is scarce on the best local treatment in sites where surgery is problematic, such as the spine. This study evaluates the outcome and the rate of local recurrence of ESFT in the spine and sacrum when treated with neoadjuvant chemotherapy, and locally by radiotherapy alone or surgery, followed by reduced doses of radiotherapy. Forty-three patients with nonmetastatic ESFT located in the spine and sacrum were treated at our institution between 1983 and 2000 with neoadjuvant chemotherapy, and locally by radiotherapy alone in 26 cases, and surgery followed by radiotherapy at reduced doses in 17. The 5- and 10-year event-free survival (EFS) was 37 and 30%, and the 5- and 10-year overall survival was (OS) 42 and 32%. The prognosis was unrelated to gender and age, tumor volume, chemotherapy protocol, and local treatment. The outcome seemed worse for patients with primary tumors located in the sacrum than for patients with tumors located in the rest of the spine (5-year EFS = 23 vs. 46%). For these patients the results were significantly worse than for those we achieved with neoadjuvant treatment for ESFT located in other sites. However, no differences were observed between patients locally treated with radiotherapy alone and those treated by radiotherapy followed by surgery. We concluded that regardless of the type of local treatment even when associated with neoadjuvant therapy, ESFT in the spine and sacrum has a poor outcome and prognosis is significantly worse than that of primary ESFT in other sites.

P53 oncosuppressor influences selection of genomic imbalances in response to ionizing radiations in human osteosarcoma cell line SAOS-2.

PURPOSE: To investigate the impact of TP53 (tumor protein 53, p53) on genomic stability of osteosarcoma (OS). MATERIALS AND METHODS: In first instance, we expressed in OS cell line SAOS-2 (lacking p53) a wild type (wt) p53 construct, whose protein undergoes nuclear import and activation in response to ionizing radiations (IR). Thereafter, we investigated genomic imbalances (amplifications and deletions at genes or DNA regions most frequently altered in human cancers) associated with radio-resistance relative to p53 expression by mean of an array-based comparative genomic hybridization (aCGH) strategy. Finally we investigated a putative marker of radio-induced oxidative stress, a 4,977 bp deletion at mitochondrial (mt) DNA usually referred to as 'common' deletion, by mean of a polimerase chain reaction (PCR) strategy. RESULTS: In radio-resistant subclones generated from wt p53-transfected SAOS-2 cells DNA deletions were remarkably reduced and the accumulation of 'common' deletion at mtDNA (that may let the persistence of oxidative damage by precluding detoxification from reactive oxygen species [ROS]) completely abrogated. CONCLUSIONS: The results of our study confirm that wt p53 has a role in protection of OS cell DNA integrity. Multiple mechanisms involved in p53 safeguard of genomic integrity and prevention of deletion outcome are discussed.

Neoadjuvant chemotherapy for radioinduced osteosarcoma of the extremity: The Rizzoli experience in 20 cases.

PURPOSE: Evaluate treatment and outcome of 20 patients with radioinduced osteosarcoma (RIO). Because of previous primary tumor treatment, RIO protocols were different from others we used for non-RIO. PATIENTS AND METHODS: Between 1983 and 1998, we treated 20 RIO patients, ages 4-36 years (mean 16 years), with chemotherapy (two cycles before surgery, three postoperatively). The first preoperative cycle consisted of high-dose Methotrexate (HDMTX)/Cisplatinum (CDP)/Adriamycin (ADM) and the second of HDMTX/CDP/Ifosfamide (IFO). The three postoperative treatments were performed with cycles of MTX/CDP; IFO was used as single agent per cycle repeated three times. RESULTS: Two patients received palliative treatment because their osteosarcoma remained unresectable after preoperative chemotherapy. The remaining 18 patients had surgery (7 amputations, 11 resections); histologic response to preoperative chemotherapy was good in 8 patients, poor in 10. At a mean follow-up of 11 years (range, 7-22 years), 9 patients remained continuously disease-free, 10 died from osteosarcoma and 1 died from a third neoplasm (myeloid acute leukemia). These results are not significantly different from those achieved in 754 patients with conventional osteosarcoma treated in the same period with protocols used for conventional treatment. However, this later group had an 18% 3-year event-free survival after treatment of relapse vs. 0% in the RIO group. CONCLUSION: Treated with neoadjuvant chemotherapy RIO seem to have an outcome that is not significantly different from that of comparable patients with conventional primary high grade osteosarcoma (5-year event-free survival: 40% vs. 60%, p = NS; 5-year overall survival 40% vs. 67%, p < 0.01).

Persistent Cdk2 inactivation drives growth arrest of BCR-ABL-expressing cells in response to dual inhibitor of SRC and ABL kinases SKI606.

Complementary inhibition of tyrosine and SRC kinases implement dual SRC/ABL inhibitor effects in chronic myeloid leukemia (CML). Here, we show that one such inhibitor, SKI-606, induces persistent Cdk2 inactivation leading to growth arrest of BCR-ABL-expressing cells either IM-sensitive or driven to IM-resistance by other events than gene overexpression and point mutations. Inhibition of Akt serine/threonine kinase, a phosphatidylinositol 3 kinase (PI-3k) target that integrates p210 TK signaling with membrane-associated SRC kinases, is a central component of restored expression and subcellular redistribution of Cdk2 regulatory signals (p21 and p27 and Cdc25A phosphatase) in response to SKI-606. The putative roles of growth factor (namely IL-3) autocrine loop in BCR-ABL-expressing progenitor progression towards a drug-resistant phenotype are discussed.

Genomic imbalances associated with secondary acute leukemias in Hodgkin lymphoma.

Secondary tumors and leukemias are major complications in Hodgkin lymphoma (HL). They likely arise from clonal selection of cells that have accumulated genomic lesions induced by chemo- and radiotherapy and may be further promoted by the loss of DNA repair and/or other pathways ensuring the fidelity of replicated DNA. To distinguish genomic imbalances associated with the development of acute myeloid leukemia (AML) in HL we used an array-based comparative genomic hybridization (aCGH) strategy on whole lymph node biopsies of HL patient. Genomic imbalances (amplifications and deletions) associated with AML outcome in 3 classic HL patients, at clinical diagnosis they exhibited a discrete individual variability. Three amplifications and 5 deletions were shared by all 3 patients. They involved AFM137XA11, a 9p11.2 pericentric region; FGFR1, the FGF receptor most frequently translocated in AML; PPARBP, a co-activator of nuclear receptors RARalpha, RXR and TRbeta1; AFM217YD10, a 17q25 telomeric region; FGR, an SRC2 kinase involved in cytokine production by NK and CD4+ NKT cells; GATA3, a Th2-specific transcription factor; TOP1, involved in DNA recombination and repair; WT1, a transcription factor involved in CD8+ T cell response against leukaemic blasts. Immunohistochemistry confirmed aCGH results and distinguished the distribution of either amplified or deleted gene products in neoplastic Reed Sternberg (RS) cells and non-neoplastic lymph node components.

Adjuvant treatment of high-risk adult soft tissue sarcomas: a survey by the Italian Sarcoma Group.

AIMS AND BACKGROUND: After the first adjuvant study on adult soft tissue sarcomas was concluded, the participating institutions continued to select and treat patients according to that protocol. The aim of this study was to test the protocol reproducibility when applied as a standard practice. METHODS: A call for retrospective data was launched in June 1999 (self-referral of consecutive unregistered patients); thereafter, a prospective follow-up was performed. The treatment regimen consisted of epirubicin (60 mg/m2 days 1 and 2), ifosfamide (3 g/m2/die for 3 days) and equimolar doses of 6-mercapto-ethansulfonate (MESNA), with 300 microg G-CSF administered subcutaneously from day +8 until recovery, every 3 weeks for a total of 5 cycles. RESULTS: From November 1996 to June 1999, 55 high-risk, adult patients were treated. The average median dose intensity was 89% of the planned program. Grade 3-4 toxicities were leukopenia (49%), thrombocytopenia (14%), transfusion requiring anemia in 7 patients (16%), and alopecia in all patients (100%). After a median follow-up of 70 months, 23 patients (41.8%) relapsed and 19 died. Median disease-free, local disease-free and overall survival rates have not yet been reached. The disease-free survival rates at 2 and 4 years were 73% and 57%, respectively; the corresponding overall survival rates were 91% and 70%, respectively. CONCLUSIONS: The feasibility and reproducibility of the original protocol were confirmed, since disease-specific overall survival and disease-free survival rates at the same period of observation and with the same prolonged follow-up did not differ.

Primary non-Hodgkin's lymphoma of the bone: treatment and analysis of prognostic factors for Stage I and Stage II.

PURPOSE: Primary non-Hodgkin's lymphomas of the bone (PLB) are very rare diseases accounting for 3%-5% of primary bone tumors. The best treatment for PLB has not been found yet. We report on the experience of the Radiation Oncology Department of Bologna University, Italy, relative to the diagnosis and treatment of this disease. METHODS AND MATERIAL: Seventy-seven patients with newly diagnosed PLB were treated from June 1983 to October 2001. Fifty-six were male (72.7%) and 21 were female (27.3%); the median age was 41.8 years, with a range of 16-84 years. The majority of patients had B-cell high-grade histology. The median follow-up was 149 months. Forty-four patients had a solitary bone lesion (Stage I); and in 33 patients, the tumor was spread to locoregional lymphatic area (Stage II). All patients were treated with radiotherapy (RT) with a median dose of 40 Gy (range, 36-54 Gy), and 67 received an additional anthracycline-based regimen of chemotherapy (combined modality therapy [CMT]). RESULTS: After therapy 73 of 77 patients (94.8%) reached a complete remission. At a median time of 23 months, 14 of 77 patients (18.2%) had a disease relapse. Four of them were treated with RT alone (in these cases tumor lesions were <3 cm and located at sites different from mandible); 10 patients were treated with combined RT and CMT. Actuarial disease-free survival (DFS) and overall survival (OS) at 15 years were, respectively, 76.6% and 88.3%. No local failures were seen. Prognostic factors such as age, sex, stage, and bulky lesions were analyzed. Age (<40 vs. >40 years) was the only significant factor for DFS (85.3% vs. 66.6%, p = 0.03). Bulky lesions apparently did not affect OS (90.9% vs. 72.7%). However, the difference has no statistical significance (p = 0.05). Acute and late toxicity related to the treatment was moderate. CONCLUSIONS: In PLB the CMT seems to produce a better outcome than RT alone; that still remains the best treatment for local disease control. Radiation therapy alone should be reserved for mandibular tumors, which are usually very small and earlier diagnosed.

p53 loss of function enhances genomic instability and accelerates clonal evolution of murine myeloid progenitors expressing the p(210)BCR-ABL tyrosine kinase.

BACKGROUND AND OBJECTIVES: The p210 bcr-abl fusion protein has a key role in the pathogenesis of chronic myeloid leukemia (CML). However, its influence on disease progression to blast crisis is marginal and mostly due to its effect of impairing the genomic stability of clonal myeloid progenitors through pathways still largely unknown. DESIGN AND METHODS: To elucidate the role of p53 in CML progression we generated, from the 32D murine myeloid cell line, several clones co-expressing the E6 product gene of human papilloma virus (HPV) 16, which abrogates p53 function, and a temperature-sensitive bcr-abl construct encoding a fully active p210 protein only at the permissive temperature of 33 degrees C. RESULTS: Co-expression of the two proteins resulted in a significant enlargement of the G(2)/M phase of cell cycle and in the appearance of a poly-aneuploid cell population. Furthermore, with continuous in vitro passages the p210 tyrosine kinase became dispensable for growth. Increased levels of cyclin B(1) and enhanced activity of its associated cyclin-dependent kinase (cdc2) became apparent during the clonal evolution of p210 bcr-abl-transduced 32D cell clones lacking p53. INTERPRETATION AND CONCLUSIONS: The acceleration of clonal evolution of p210 bcr-abl-transduced 32D myeloid progenitors associated with p53 functional abrogation is consistent with oncosuppressor loss having a key role in CML progression. This would allow emergence of additional genomic aberrations which would lead to the fully transformed phenotype of blast crisis. Deregulated activity of the cyclin B1-cdc2 complex may be involved in the loss of temporal co-ordination of mitotic events and further free the barrier to genomic instability of CML clonal myeloid progenitors lacking p53.

Chk2 drives late G1/early S phase arrest of clonal myeloid progenitors expressing the p210 BCR-ABL tyrosine kinase in response to STI571.

STI571 is the most innovative drug for the cure of Chronic Myeloid Leukemia. It inhibits, in fact, the disease causative event, the p210 bcr-abl tyrosine kinase, and addresses clonal myeloid progenitors to apoptotic death. Here, we demonstrated that STI571 also induces growth arrest by activating the Chk2-Cdc25A-Cdk2 axis, a pathway complementary to p53 in the activation of G(1)/S cell cycle checkpoint. In vitro exposure to STI571 of 32D murine myeloid progenitor cell clones transducing a temperature-sensitive p210 bcr-abl construct was associated with Chk2 phosphorylation and activation, Cdc25A degradation and persistent Cdk2 inhibitory phosphorylation, preventing, in turn, cell transition to and progression throughout the S phase of cell cycle. Chk2 and Cdc25A are both components of a complex network that integrates signals involved in regulated cell cycle progression, DNA repair and cell decision between life or death. Chk2 gene mutations or decreased expression, leading to its protein loss of function on Cdc25A target, and Cdc25A overexpression have been linked to poor prognosis of human cancers. In CML, they might further enhance the proliferative advantage and genomic instability of clonal myeloid progenitors featuring a class of poor prognosis patients eventually resistant to STI571.

Cell-cycle deregulation in BALB/c 3T3 cells transformed by 1,2-dibromoethane and folpet pesticides.

The cell-transforming potential of 1,2-dibromoethane and folpet, two widely used agricultural pesticides that are potential sources of environmental pollution, has been previously ascribed to their promoting activity. In this study, we investigated whether BALB/c 3T3 transformation by these chemicals was associated with the deregulation of signals involved in cell-cycle progression and in cell-cycle checkpoint induction. We found that two BALB/c 3T3 cell clones transformed by in vitro medium-term (8-week) exposure to the carcinogens had a constitutive acceleration of cell transition from G(1) to S phase and an abrogation of the radiation-induced G(1)/S checkpoint. These events involved multiple signals; in particular, the inhibitors of cyclin/cyclin-dependent kinase complexes p21 and p27 were significantly down-modulated and the positive regulators of cell-cycle progression cyclin D(3) and E were up-modulated. As anticipated for cells where the G(1)/S checkpoint was abrogated, the transformed cells exhibited a significant reinforcement of the radiation-induced G(2)/M checkpoint, the only checkpoint remaining to protect genomic integrity. However, cyclin A(1) and B(1) coexpression and cyclin A(1) overexpression were found despite the G2 arrest in irradiated cells and these signals likely attenuate the G(2)/M checkpoint. These alterations to normal cell cycling may promote the emergence of both numerical and structural chromosomal abnormalities and their tolerance. Such a condition could play a key role in neoplastic transformation and be crucial in tumor progression. Furthermore, cyclin A(1) overexpression may play an autonomous role in the neoplastic transformation of BALB/c 3T3 cells, as it does in other cell types of mesenchymal origin.