Effects of azacitidine in 93 patients with IDH1/2 mutated acute myeloid leukemia/myelodysplastic syndromes: a French retrospective multicenter study

Isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) mutations in Myeloid Neoplams (MNs) exhibit DNA hypermethylation via 2-hydroxyglutarate (2HG) over-production. Clinical impact of azacitidine (AZA) remains inconsistent in IDH1/2-mutated MNs and the potential of serum 2HG as a suitable marker of response to AZA is unknown. To address these questions, we retrospectively analyzed 93 MNs patients (78 AML, 11 MDS, 4 CMML) with IDH1/2 mutations treated with AZA. After a median of 5 cycles of AZA, overall response rate was 28% (including 15% complete remission) and median OS was 12.3 months (significantly shorter in AML compared to MDS/CMML patients). In multivariate analysis of AML patients, DNMT3A mutation was associated with shorter OS while IDH1/2 mutation subtypes had no independent impact. No difference was observed in serum 2HG levels upon AZA treatment between responding and refractory patients suggesting that serum 2HG cannot be used as a surrogate marker of AZA response.

Ivosidenib to treat adult patients with relapsed or refractory acute myeloid leukemia

Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key metabolic enzymes that convert isocitrate to alpha-ketoglutarate (alphaKG). Somatic point mutations in IDH1/2 that are found in rare distinct subsets of cancers confer a gain of function in cancer cells which results in the accumulation and secretion in vast excess of the oncometabolite D-2-hydroxyglutarate (D-2HG). Overproduction of D-2HG interferes with cellular metabolism and epigenetic regulation, contributing to oncogenesis. High levels of D-2HG inhibit alphaKG-dependent dioxygenases including histone, DNA and RNA demethylases, resulting in histone, DNA and RNA hypermethylation and cell differentiation blockade. In addition, D-2HG is a biomarker suitable for the detection of IDH1/2 mutations at diagnosis, and is also predictive of clinical response. The U.S. Food and Drug Administration (FDA) approved ivosidenib, a mutant-IDH1 enzyme inhibitor, for patients with relapsed or refractory IDH1-mutated acute myeloid leukemia (AML) in 2018, and also as front-line therapy for newly diagnosed elderly patients 75 years or older or who are ineligible to receive intensive chemotherapy in 2019. Ivosidenib represents a novel drug class for targeted therapy in AML.

Abstract PL02-04: IDH mutations and tumorigenicity

Mutations in the isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) genes are present in ∼20% of acute myeloid leukemia, and cause a neomorphic enzyme activity that results in the production of 2-hydroxyglutarate (2HG). Mutational and epigenetic profiling of a large patient cohort of acute myeloid leukemia (AML) has revealed that IDH1/2-mutant AMLs display global DNA hypermethylation and impaired hematopoietic differentiation.

To further investigate the intrinsic effect of 2HG on hematopoietic proliferation and differentiation, we transfected an erythroleukemia cell line (TF-1) with either IDH1 or IDH2 mutant alleles. These cells overexpress the mutant enzyme, have high levels of 2HG, and exhibit GM-CSF independent growth. Consistent with clinical observations, overexpression of the IDH mutant proteins led to hypermethylation of both histones and DNA. These results suggest that mutations in IDH1/2 could lead to epigenetic rewiring of cells that could facilitate the gain of function phenotype. We are currently studying the global and specific effects of IDH1/2 mutant overexpression to gain a broader understanding of the biological consequence of the IDH1/2 gain of function mutations.

We have also generated mutation selective molecules that are capable of inhibiting IDHm enzymes. Upon compound treatment in vitro, we are able to reverse hypermethylation of both histones and DNA and induce cellular differentiation in IDHm cell lines and primary human IDHm AML patient samples(1, 2). These data suggest that an inhibitor of IDH1/2 mutations could correct the altered gene expression patterns seen in IDH1/2 mutant AML tumors leading to a profound effect on hematopoietic differentiation, proliferation and tumor growth.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):PL02-04.

Citation Format: F. Wang, J. Travins, B. DeLaBarre, V. Penard-Lacronique, S. Schalm, E. Hansen, K. Straley, A. Kernytsky, W. Liu, C. Gliser, H. Yang, S. Gross, E. Artin, V Saada, E. Mylonas, C. Quivoron, J. Popovici-Muller, J. O. Saunders, F. G. Salituro, S. Yan, S. Murray, W. Wei, Y. Gao, L. Dang, M. Dorsch, S. Agresta, D. P. Schenkein, S. A. Biller, S. M. Su, S. de Botton, Katharine E. Yen. IDH mutations and tumorigenicity. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr PL02-04.

The Src tyrosine kinase Hck is required for Tel-Abl- but not for Tel-Jak2-induced cell transformation

Tel-Abl and Tel-Jak2 are fusion proteins associated with human haematologic neoplasms. They possess constitutive tyrosine kinase activity and activate common downstream signalling pathways like Stat-5, PI3-K/Akt, Ras/MapK and NF-kappaB. In this study, we showed the specific requirement of Src family members for the Tel-Abl-mediated cell growth, activation of Stat5, PI3-K/Akt and Ras/MapK while dispensable for Tel-Jak2. Hck was found strongly phosphorylated in Tel-Abl-expressing Ba/F3 cells and sensitive to imatinib mesylate treatment, providing evidence that Hck is a target of Tel-Abl tyrosine kinase activity. Overexpression of a kinase dead form of Hck inhibits the proliferation of Ba/F3 cells expressing Tel-Abl as the phosphorylation of Akt and Erk1/2. These results argue for an important role of Hck in Tel-Abl oncogenic signalling.

Activation of the NF-kappaB pathway by the leukemogenic TEL-Jak2 and TEL-Abl fusion proteins leads to the accumulation of antiapoptotic IAP proteins and involves IKKalpha

Abnormal activation of tyrosine kinases and of signaling pathways they control plays a critical role in the neoplastic process of human hematopoietic malignancy. The nuclear factor-kappaB (NF-kappaB) pathway is one of the signalings activated by the TEL-Jak2 and TEL-Abl oncoproteins and required for their antiapoptotic activity. To define the signal relay responsible for this activation, we used mouse embryonic fibroblast (MEF) cells and observed that TEL-Jak2- and TEL-Abl-mediated NF-kappaB induction was abolished in cells lacking the IkappaB kinase (IKK)alpha but not in IKKbeta(-/-) cells. Similar observations were performed with oncogenic forms of the FMS-like tyrosine kinase 3 (Flt-3) involved in the pathogenesis of one-third of acute myeloid leukemias. Rescue of TEL-Jak2-mediated NF-kappaB activation was obtained with a kinase-proficient form of IKKalpha in IKKalpha(-/-) MEF. Hematopoietic cells transformed by TEL-Jak2 and TEL-Abl showed sustained IKKalpha activity without promotion of NF-kappaB2/p100 processing, generally associated to IKKalpha functions. Furthermore, IAP1, IAP2 and XIAP, which are central regulators of the NF-kappaB-mediated survival pathway, were highly expressed in cells transformed by these oncoproteins. Our results indicate that these oncogenic tyrosine kinases preferentially use an IKKalpha-dependent mechanism to induce a persistent NF-kappaB activity and allow the production of antiapoptotic effectors that participate to their leukemogenic properties.

A new recurrent and specific cryptic translocation, t(5;14)(q35;q32), is associated with expression of the Hox11L2 gene in T acute lymphoblastic leukemia

FISH identified a cryptic t(5;14)(q35;q32) in T acute lymphoblastic leukemia (ALL), whereas it was not observed in B ALL samples. This translocation is present in five out of 23 (22%) children and adolescents with T ALL tested. RanBP17, a gene coding for a member of the importin beta protein family, and Hox11Like2, an orphan homeobox gene were mapped close to the chromosome 5 breakpoints and CTIP2, which is highly expressed during normal T cell differentiation, was localized in the vicinity of the chromosome 14 breakpoints. The Hox11L2 gene was found to be transcriptionally activated as a result of the translocation, probably under the influence of CTIP2 transcriptional regulation elements. These data establish the t(5;14)(q35;q32) as a major abnormality, and Hox11 family member activation as an important pathway in T ALL leukemogenesis.

Involvement of the NF-κB pathway in the transforming properties of the TEL-Jak2 leukemogenic fusion protein

Constitutively active tyrosine kinases are frequently expressed in various types of human leukemias as the result of chromosomal translocations. The TEL-Jak2 fusion oncoprotein possesses transforming properties in both animal and cellular models, that are tightly dependent on Stat5 activation. In the IL-3-independent TEL-Jak2-transformed Ba/F3 cells, activation of the PI-3K/Akt pathway appears essential to cell proliferation. Here we report a sustained activation of NF-kappaB factors in Ba/F3 cells, which inhibition dramatically impairs cell viability, indicating that NF-kappaB signaling exerts a major role in the anti-apoptotic activities of TEL-Jak2 oncoprotein.

The TEL-Jak2 oncoprotein induces Socs1 expression and altered cytokine response in Ba/F3 cells

The leukemia-associated TEL-Jak2 fusion protein possesses a constitutive tyrosine kinase activity and transforming properties in hematopoietic cell lines and animal models. In the murine pro-B Ba/F3 cell line, this fusion constitutively activates the Signal Transducer and Activator of Transcription 5 (Stat5) factors and, as a consequence, induces the sustained expression of various Stat5-target genes including the Cytokine Inducible SH2-containing protein (Cis) gene, which codes for a member of the Suppressor of Cytokine Signaling (Socs) protein family. In TEL-Jak2-transformed Ba/F3 cells, we also observed the upregulation of the Socs1 gene, whose product has been reported to negatively regulate the Jak kinase activity. In transient transfection experiments, Socs1 physically interacts with TEL-Jak2 and interferes with the TEL-Jak2-induced phosphorylation and activation of Stat5 factors, probably through the Socs1-induced proteasome-mediated degradation of the fusion protein. Interestingly, TEL-Jak2-expressing Ba/F3 cells were found to be resistant to the anti-proliferative activities of gamma interferon (IFN-gamma) seemingly as a consequence of Socs1 constitutive expression. These results indicate that the Socs1-dependent cytokine feedback loop, although active, is bypassed by the TEL-Jak2 fusion, but may play a role in the leukemogenic process by altering the cytokine responses of the leukemic cells. Our results also suggest that Socs1 plays a role in shutting down the signaling from the normally activated Jak2 kinase by inducing its proteasome-dependent degradation.