Germline mutations of the CBL gene define a new genetic syndrome with predisposition to juvenile myelomonocytic leukaemia.

BACKGROUND: CBL missense mutations have recently been associated with juvenile myelomonocytic leukaemia (JMML), an aggressive myeloproliferative and myelodysplastic neoplasm of early childhood characterised by excessive macrophage/monocyte proliferation. CBL, an E3 ubiquitin ligase and a multi-adaptor protein, controls proliferative signalling networks by downregulating the growth factor receptor signalling cascades in various cell types. METHODS AND RESULTS: CBL mutations were screened in 65 patients with JMML. A homozygous mutation of CBL was found in leukaemic cells of 4/65 (6%) patients. In all cases, copy neutral loss of heterozygosity of the 11q23 chromosomal region, encompassing the CBL locus, was demonstrated. Three of these four patients displayed additional features suggestive of an underlying developmental condition. A heterozygous germline CBL p.Y371H substitution was found in each of them and was inherited from the father in one patient. The germline mutation represents the first hit, with somatic loss of heterozygosity being the second hit positively selected in JMML cells. The three patients display a variable combination of dysmorphic features, hyperpigmented skin lesions and microcephaly that enable a 'CBL syndrome' to be tentatively delineated. Learning difficulties and postnatal growth retardation may be part of the phenotype. CONCLUSION: A report of germline mutations of CBL in three patients with JMML is presented here, confirming the existence of an unreported inheritable condition associated with a predisposition to JMML.

In vitro all-trans retinoic acid sensitivity of acute promyelocytic leukemia blasts: a novel indicator of poor patient outcome.

Acute promyelocytic leukemia (APL) blasts possess a unique sensitivity to the differentiating effects of all-trans retinoic acid (ATRA). Multicenter trials confirm that the combination of differentiation and cytotoxic therapy prolongs survival in APL patients. However relapses still occur, and exquisite adaptation of therapy to prognostic factors is essential to aim at a possible cure of the disease. A heterogeneity was previously reported in the differentiation rate of patients' APL blasts, and it was postulated that this may reflect the in vivo heterogeneous outcome. In this study, it is demonstrated that patients of the APL93 trial whose leukemic cells achieved optimal differentiation with ATRA in vitro at diagnosis had a significantly improved event-free survival (P =.01) and lower relapse rate (P =.04). This analysis highlights the importance of the differentiation step in APL therapy and justifies ongoing studies aimed at identifying novel RA-differentiation enhancers.

All trans retinoic acid abrogates spontaneous monocytic growth in juvenile chronic myelomonocytic leukaemia.

INTRODUCTION: All trans retinoic acid, the active metabolite of vitamin A, exerts profound effects on cell differentiation. On normal myeloid progenitors, retinoids switch the differentiation program of granulo-macrophagic progenitors towards the granulocytic lineage and consequently reduce CFU-M colony formation. Bone marrow and peripheral blood mononuclear cells from children with Juvenile Chronic Myelomonocytic Leukaemia show typical spontaneous monocytic growth. We questioned whether in this disease, retinoids could switch myelomonocytic growth and inhibit the abnormal CFU-M colony proliferation. METHODS: Ten JCML samples were studied in the presence of ATRA in methyl cellulose colony assay, before (CFU-C) or after (pre-CFU) liquid suspension culture. RESULTS: In vitro characteristics of JCML such as spontaneous monocytic growth in the absence of growth factor was noted in all patients. In the presence of leucocyte-conditioned medium, nine samples showed only CFU-M growth and one sample CFU-GM growth. Incubation with ATRA inhibited CFU-M colony formation in nine cases. Enhancement of granulocytic differentiation (CFU-G) was noted in nine cases. ATRA also inhibited CD34+ JCML monocytic growth and GM-CSF hypersensitivity. CONCLUSION: These data suggest that, in JCML progenitors, retinoid pathways are functional and inhibition of immature monocytic progenitors cells may be achieved with retinoids, without impeding granulocytic cell growth.

Functional G-CSF pathways in t(8;21) leukemic cells allow for differentiation induction and degradation of AML1-ETO.

INTRODUCTION: Efficacy of differentiating agents requires that their specific cellular targets are still expressed and functional in the leukemic cells. One hypothesis to target sensitive cells is to select leukemic clones which harbor disrupted transcription factors. CBFalpha and CBFbeta are core-binding proteins which have been identified as transcription regulators of hematopoietic genes and shown to be altered in numerous leukemias. In M2 AML, the t(8;21) translocation, CBFalpha (AML1) is altered and produced as the AML1-ETO fusion protein. The fusion protein blocks transcription and differentiation mediated by G-CSF. Interestingly, AML1-ETO leukemic cell lines are sensitive to numerous cytokines in vitro and can be induced to differentiate in the presence of G-CSF and PMA. MATERIALS AND METHODS: As in the APL differentiation model, primary culture provides a useful tool for therapeutic screening of differentiation inducers, we analysed the in vitro sensitivity of 10 fresh M2 AML t(8;21) leukemic samples to G-CSF and the functionality of G-CSF intracellular pathways. In vitro data were compared with in vivo data from four patients treated with rhG-CSF at the dosage of 5 microg/kg/day i.v. for two to three weeks before the initiation of AML induction chemotherapy and immunophenotypic analysis performed weekly to monitor in vivo differentiation. RESULTS: In vitro, an increase in CD34+ cells expressing differentiation antigens (CD11b, CD13 or CD15) was noted along with a decrease of immature CD34+/differentiation antigen negative cells. After two weeks of a daily rhG-CSF administration in vivo, a significant, albeit transient, decrease of blast count was achieved, concomitant with an increase in differentiated leukemic cells suggesting that in vivo differentiation occurs. Fresh t(8;21) leukemic cells possess functional G-CSF signaling pathways as normal activity and kinetics of STAT1 and STAT3 binding was observed. Furthermore, differentiation induction leads to a subsequent degradation of the AML1-ETO oncoprotein. CONCLUSION: The data presented here supports the claim that G-CSF can induce in vitro and in vivo differentiation of M2 AML t(8;21) cells.

G-CSF activates STAT pathways in Kasumi-1 myeloid leukemic cells with the t(8; 21) translocation: basis for potential therapeutic efficacy.

In an attempt to find new agents that promote differentiation and have therapeutic potential in acute myeloid leukemias, we have studied the effect of recombinant human granulocyte colony stimulating factor (rhG-CSF) on the Kasumi-1 AML2 t(8; 21) cell line. Upon incubation with rhG-CSF (0.2-2000 ng/ml), Kasumi-1 cells showed a peak of cell growth, with a subsequent decrease of cell survival after 4 days of culture. At that time, more than 80% of the cell population expressed myeloid differentiation antigens (CD11b, CD13, CD15 and CDw85), and increased G-CSF receptors. Gel shift assays were performed with nuclear extracts of Kasumi-1 cells after 1, 5, 10, 15, 30 and 60 min incubations with G-CSF and oligonucleotides containing the high-affinity SIF-binding site. At least three specific complexes were obtained, and shown by supershift assays to be STAT3/STAT3, STAT1/STAT3 and STAT1/STAT1 dimers. These results suggest that in G-CSF-sensitive Kasumi-1 cells, normal JAK-STAT pathways are activated, providing a further molecular basis for the effect of G-CSF in these cells.

Chronic myelomonocytic leukemia: from biology to therapy.

Chronic myelomonocytic leukemia represents a distinct myelodysplastic syndrome in which an excess of monocytes is observed both in the blood and bone marrow of the patients. Whereas diagnosis is relatively easy, therapeutic design and efficacy is difficult and no treatment has to date provided complete or significant partial response. In vitro data suggest that the growth and differentiation of myelomonocytic progenitors may be altered inasmuch as monocytic or granulo-macrophagic colonies show spontaneous growth. Different entities may be observed: the childhood form, Juvenile Chronic Myelomonocytic Leukemia (JCML) shows in vitro a typical pattern with constitutive growth of only macrophagic colonies and hypersensitivity to GM-CSF; in the adult form at least two patterns may be observed one close to the JCML form and one more heterogeneous with absence of GM-CSF sensitivity and spontaneous growth of both CFU-GM and CFU-M colonies. Chemotherapy reduces all myeloid colonies in vitro whereas retinoic acid has a selective effect on monocytic colonies with a concomitant increase of CFU-G colonies forwarding an explanation for the correction of pancytopenia observed in some patients. Recent analysis of altered molecular pathways in this disease suggest a common disruption of intracellular signalling pathways namely the Ras pathway and targetting for drugs with may selectively control or inhibit a constitutive activation may forward novel therapeutic perspectives.

All-trans retinoic acid in adult chronic myelomonocytic leukemia: results of a pilot study.

Retinoids can inhibit the spontaneous in vitro growth of CFU-GM observed in juvenile chronic myeloid leukemia (JCML) and, when administered in vivo, have shown some clinical benefit in this disease. Because adult chronic myelomonocytic leukemia (CMML) has many features in common with JCML, we treated 10 cases of advanced adult CMML with ATRA (45 mg/m2/day). Five of them were also tested in vitro. After two patients had a rapid increase in WBC counts and clinical signs reminiscent of the 'ATRA syndrome' seen in acute promyelocytic leukemia, with fatal outcome in one of them, it was decided to add hydroxyurea (HY) to ATRA to patients with high WBC at inclusion or during ATRA treatment, and no more cases of ATRA syndrome were seen. Overall, six patients received ATRA + HY and four ATRA alone. Four patients had a minor but significant response with reduction of transfusion requirement (two cases) or increase in platelet counts (two cases). Apart from the ATRA syndrome, no other side-effect of ATRA was seen. Bone marrow mononuclear cells showed spontaneous growth of CFU-C in methylcellulose in the five patients tested in vitro, with a predominance of CFU-M. ATRA (10(-7) M) inhibited CFU-M growth in all cases, but increased CFU-G growth in one patient who developed the ATRA syndrome. No differentiation of bone marrow myeloid cells after short-term liquid culture with ATRA was observed. A decrease of CFU-C growth was observed in the four patients reevaluated during follow-up. In some cases of CMML, ATRA can improve anemia or thrombocytopenia but not other parameters. Furthermore, it can also induce hyperleukocytosis and ATRA syndrome in some patients, requiring the rapid addition of cytoreductive agents such as HY.

Characterization of nuclear retinoic acid binding activity in sensitive leukemic cell lines: cell specific uptake of ATRA and RAR alpha protein modulation.

The diverse effects of all-trans retinoic acid (ATRA) on growth, differentiation and homeostasis of vertebrate organisms are mediated by three distinct isoforms of retinoic acid receptors (RARs). Although it is not known to what extent each RAR contributes to the different effects of ATRA, several studies have demonstrated that ATRA induced granulocytic differentiation in human myeloid leukemic cell lines is mediated by RAR alpha. In this study, we investigated ATRA binding affinity of the endogenous nuclear receptors of HL-60 and NB4 leukemic cells. Scatchard plot analysis yielded an apparent dissociation constant of 5 +/- 0.3 nM and 1400 +/- 80 receptor sites per cell in HL-60 cells, whereas the NB4 promyelocytic leukemic cell line showed a lower affinity (8.5 +/- 0.5 nM and 900 +/- 30 receptor sites per cell). Modulation of RAR alpha protein (5 fold excess) was found in NB4 cells after 24 hours ATRA exposure, whereas HL-60 cells required a 72-hour culture period to weakly increase the RAR alpha protein level. These data were closely related to the ATRA intracellular concentration and kinetics of terminal differentiation of the cells.

Retinoid acid supports granulocytic but not erythroid differentiation of myeloid progenitors in normal bone marrow cells.

In the new context of the use of retinoic acid (RA) therapy as an inducer of leukemic differentiation and a selective inhibitor of human myeloid leukemia cell growth, we undertook to explore the potential physiological role of retinoids on the proliferation and differentiation of normal bone marrow myeloid progenitors. The effects of continuous exposure of all-trans-RA, its naturally occurring isomer, 13-cis-RA, and its metabolite 4-oxo-all-trans-RA were studied on the growth of normal human bone marrow cells in soft agar, directly and after liquid culture. Retinoids enhanced the total number of granulocytic colony and macrocluster formation in the presence of exogenous colony-stimulating factor (n = 9). Dose-response curve were bell-shaped, with a maximal increment between concentration of 0.5 and 0.05 nM. In all cases, a concomitant decrease of macrophagic colonies was noted. The positive effect on granulocytic colony formation was observed with each of the retinoids tested (all-trans, 13-cis and 4-oxo-all-trans) (n = 5). On erythroid colony formation, all-trans-RA had the opposite effect. Constant suppression of CFU-E and BFU-E colony formation and coloring was observed in a dose-related fashion from 0.1 to 10 microM (n = 5). Thus, in granulocytic, as in erythroid colony formation, retinoids affected both proliferation and differentiation parameters. However, after short-term suspension culture in the presence of all-trans-RA, an increase of both CFU-GM and BFU-E colonies, was observed. These results suggest a specific effect of retinoids on late myeloid precursors and places retinoids as possible candidates for enhancement of normal granulocytic differentiation.