Abstract
Peripheral T-cell lymphoma (PTCL) is a heterogeneous group of non-Hodgkin lymphomas with poor prognosis. Up to 30% of PTCL lack distinctive features and are classified as PTCL, not otherwise ...specified (PTCL-NOS). To further improve our understanding of the genetic landscape and biology of PTCL-NOS, we perform RNA-sequencing of 18 cases and validate results in an independent cohort of 37 PTCL cases. We identify
FYN-TRAF3IP2
,
KHDRBS1-LCK
and
SIN3A-FOXO1
as new in-frame fusion transcripts, with
FYN-TRAF3IP2
as a recurrent fusion detected in 8 of 55 cases. Using ex vivo and in vivo experiments, we demonstrate that
FYN-TRAF3IP2
and
KHDRBS1-LCK
activate signaling pathways downstream of the T cell receptor (TCR) complex and confer therapeutic vulnerability to clinically available drugs.
TAL1 is ectopically expressed in about 30% of T-cell acute lymphoblastic leukemia (T-ALL) due to chromosomal rearrangements leading to the STIL-TAL1 fusion genes or due to noncoding mutations leading ...to a de novo enhancer driving TAL1 expression. Analysis of sequence data from T-ALL cases demonstrates a significant association between TAL1 expression and activating mutations of the PI3K-AKT pathway. We investigated the oncogenic function of TAL1 and the possible cooperation with PI3K-AKT pathway activation using isogenic pro-T cell cultures ex vivo and in vivo leukemia models. We find that TAL1 on its own is suppressing T-cell growth, in part by affecting apoptosis genes, while the combination with AKT pathway activation reduced apoptosis and was strongly driving cell proliferation ex vivo and leukemia development in vivo. As a consequence, we find that TAL1+AKTE17K transformed cells are more sensitive to PI3K-AKT pathway inhibition compared to AKTE17K transformed cells, related to the negative effect of TAL1 in the absence of activated PI3K-AKT signaling. We also find that both TAL1 and PI3K-AKT signaling increase the DNA-repair signature in T cells resulting in synergy between PARP and PI3KAKT pathway inhibition. In conclusion, we have developed a novel mouse model for TAL1+AKTE17K driven T-ALL development and identify a vulnerability of these leukemia cells to PI3K-AKT and PARP inhibitors.
RNA-seq is a promising technology to re-sequence protein coding genes for the identification of single nucleotide variants (SNV), while simultaneously obtaining information on structural variations ...and gene expression perturbations. We asked whether RNA-seq is suitable for the detection of driver mutations in T-cell acute lymphoblastic leukemia (T-ALL). These leukemias are caused by a combination of gene fusions, over-expression of transcription factors and cooperative point mutations in oncogenes and tumor suppressor genes. We analyzed 31 T-ALL patient samples and 18 T-ALL cell lines by high-coverage paired-end RNA-seq. First, we optimized the detection of SNVs in RNA-seq data by comparing the results with exome re-sequencing data. We identified known driver genes with recurrent protein altering variations, as well as several new candidates including H3F3A, PTK2B, and STAT5B. Next, we determined accurate gene expression levels from the RNA-seq data through normalizations and batch effect removal, and used these to classify patients into T-ALL subtypes. Finally, we detected gene fusions, of which several can explain the over-expression of key driver genes such as TLX1, PLAG1, LMO1, or NKX2-1; and others result in novel fusion transcripts encoding activated kinases (SSBP2-FER and TPM3-JAK2) or involving MLLT10. In conclusion, we present novel analysis pipelines for variant calling, variant filtering, and expression normalization on RNA-seq data, and successfully applied these for the detection of translocations, point mutations, INDELs, exon-skipping events, and expression perturbations in T-ALL.
The majority of gastrointestinal stromal tumors harbor mutations in the receptor tyrosine kinases KIT or platelet-derived growth factor receptor A (PDGFRA), and respond to treatment with the tyrosine ...kinase inhibitor imatinib. Some tumors, however, show primary resistance to imatinib treatment, and most others become resistant during treatment. The most common mechanism of imatinib resistance involves specific mutations in the kinase domains of KIT or PDGFRA. We tested the activity of SU11248, an orally active small-molecule tyrosine kinase inhibitor, to inhibit important imatinib-resistant KIT and PDGFRA mutants.
Primary imatinib-resistant tumor cells and cell lines expressing clinically identified imatinib-resistant KIT-V654A, KIT-T670I, or PDGFRA-D842V mutant isoforms were evaluated for sensitivity to SU11248 by Western immunoblotting and proliferation assays. Three patients with the KIT-V654A mutation were treated with SU11248.
Based on ex vivo assays, SU11248 potently inhibits KIT kinase activity of V654A and T670I mutants and suppresses proliferation of the cells expressing these mutations. Sensitivity of KIT-V654A and KIT-T670I mutants to SU11248 was confirmed using cell lines expressing these mutants. In contrast, SU11248 did not potently inhibit the PDGFRA-D842V mutant. In agreement with these results, two of the three imatinib-resistant patients with the KIT-V654A mutation responded to SU11248 treatment.
These studies suggest that SU11248 may be a useful therapeutic agent to treat gastrointestinal stromal tumors harboring the imatinib-resistant KIT-V654A or KIT-T670I mutations, but it has no effect on the activity of the PDGFRA-D842V mutant. Specific kinase inhibitors should be designed to inhibit the constitutive activating PDGFRA mutation at codon 842.
Background & Aims:
Resistance is a major challenge in the treatment of patients with gastrointestinal stromal tumors (GISTs). We investigated the mechanisms of resistance in patients with progressive ...GISTs with primary
KIT mutations and the efficacy of the kinase inhibitor PKC412 for the inhibition of imatinib-resistant mutants.
Methods:
We performed a cytogenetic analysis and screened for mutations of the KIT and PDGFRA kinase domains in 26 resistant GISTs. KIT autophosphorylation status was assessed by Western immunoblotting. Imatinib-resistant GIST cells and Ba/F3 cells expressing these mutant proteins were tested for sensitivity to imatinib and PKC412.
Results:
Six distinct secondary mutations in
KIT were detected in 12 progressive tumors, with V654A and T670I found to be recurrent. One progressive tumor showed acquired
PDGFRA-D842V mutation. Amplification of
KIT or
KIT/
PDGFRA was found in 2 patients. Eight of 10 progressive tumors available for analysis showed phosphorylated KIT. Two remaining progressive tumors lost KIT protein expression. GIST cells carrying
KIT-del557-558/T670I or
KIT-InsAY502-503/V654A mutations were resistant to imatinib, while PKC412 significantly inhibited autophosporylation of these mutants. Resistance to imatinib and sensitivity to PKC412 of
KIT-T670I and
PDGFRA-D842V mutants was confirmed using Ba/F3 cells.
Conclusions:
This study shows the high frequency of KIT/PDGFRA kinase domain mutations in patients with secondary resistance and defines genomic amplification of
KIT/
PDGFRA as an alternative cause of resistance to the drug. In a subset of patients, cancer cells lost their dependence on the targeted tyrosine kinase. Our findings show the sensitivity of the imatinib-resistant
KIT-T670I and
KIT-V654A and of
PDGFRA-D842V mutants to PKC412.
Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma is characterized by 2p23/
aberrations, including the classic t(2;5)(p23;q35)/
rearrangement present in ~80% of cases and ...several variant t(2p23/ALK) occurring in the remaining cases. The
fusion partners play a key role in the constitutive activation of the chimeric protein and its subcellular localization. Using various molecular technologies, we have characterized ALK fusions in eight recently diagnosed anaplastic large cell lymphoma cases with cytoplasmic-only ALK expression. The identified partner genes included
(one case),
(one case),
(four cases) and
(two cases). Notably, all cases showed copy number gain of the rearranged
gene, which is never observed in
-positive lymphomas. We hypothesized that this could be due to lower expression levels and/or lower oncogenic potential of the variant
fusions. Indeed, all partner genes, except
, showed lower expression in normal and malignant T cells, in comparison with
In addition, we investigated the transformation potential of endogenous Npm1-Alk and Atic-Alk fusions generated by clustered regularly interspaced short palindromic repeats/Cas9 genome editing in Ba/F3 cells. We found that Npm1-Alk has a stronger transformation potential than Atic-Alk, and we observed a subclonal gain of
after a longer culture period, which was not observed for
Taken together, our data illustrate that lymphomas driven by the variant ATIC-ALK fusion (and likely by RNF213-ALK and TPM3-ALK), but not the classic NPM1-ALK, require an increased dosage of the
hybrid gene to compensate for the relatively low and insufficient expression and signaling properties of the chimeric gene.
The NUP214-ABL1 fusion protein is a constitutively active protein tyrosine kinase that is found in 6% of patients with T-cell acute lymphoblastic leukemia and that promotes proliferation and survival ...of T-lymphoblasts. Although NUP214-ABL1 is sensitive to ABL1 kinase inhibitors, development of resistance to these compounds is a major clinical problem, underlining the need for additional drug targets in the sparsely studied NUP214-ABL1 signaling network. In this work, we identify and validate the SRC family kinase LCK as a protein whose activity is absolutely required for the proliferation and survival of T-cell acute lymphoblastic leukemia cells that depend on NUP214-ABL1 activity. These findings underscore the potential of SRC kinase inhibitors and of the dual ABL1/SRC kinase inhibitors dasatinib and bosutinib for the treatment of NUP214-ABL1-positive T-cell acute lymphoblastic leukemia. In addition, we used mass spectrometry to identify protein interaction partners of NUP214-ABL1. Our results strongly support that the signaling network of NUP214-ABL1 is distinct from that previously reported for BCR-ABL1. Moreover, we found that three NUP214-ABL1-interacting proteins, MAD2L1, NUP155, and SMC4, are strictly required for the proliferation and survival of NUP214-ABL1-positive T-cell acute lymphoblastic leukemia cells. In conclusion, this work identifies LCK, MAD2L1, NUP155 and SMC4 as four new potential drug targets in NUP214-ABL1-positive T-cell acute lymphoblastic leukemia.
Genetic abnormalities that result in expression of chimeric tyrosine kinase proteins such as BCR-ABL1 and ETV6-PDGFRβ are common causes of hematopoietic malignancies. The paradigm for constitutive ...activation of these fusion tyrosine kinases is enforced homodimerization by self-association domains present in the fusion partner proteins. The unique interstitial deletion on chromosome 4q12 that leads to expression of the FIP1L1-PDGFRα fusion tyrosine kinase was recently identified as a cause of chronic eosinophilic leukemia. In this report, we demonstrate that FIP1L1 is completely dispensable for PDGFRα activation
in vitro
and
in vivo
. Instead, truncation of PDGFRα between two conserved tryptophan residues in the juxtamembrane (JM) domain is required for kinase activation and transforming potential of FIP1L1-PDGFRα. The presence of a complete JM domain in FIP1L1-PDGFRα is inhibitory, but this autoinhibition can be overcome by enforced homodimerization. Similar effects of the JM domain in the context of PDGFRβ were observed. These results suggest that disruption of the autoinhibitory JM domain is an alternative, dimerization-independent mechanism by which chimeric tyrosine kinases are constitutively activated and induce leukemogenesis.
Activating NOTCH1 mutations are common in T-cell acute lymphoblastic leukemia. Inhibition of NOTCH1 signaling with gamma-secretase inhibitors causes cell cycle block, but only after treatment for ...several days. We further documented the effects of gamma-secretase inhibitor treatment on T-cell acute lymphoblastic leukemia cell lines and tested whether combining gamma-secretase inhibitors with other anti-cancer drugs offers a therapeutic advantage.
The effect of gamma-secretase inhibitor treatment and combinations of gamma-secretase inhibitors with chemotherapy or glucocorticoids was assessed on T-cell acute lymphoblastic leukemia cell lines. We sequenced NOTCH1 in T-cell acute lymphoblastic leukemia cases with ABL1 fusions and tested combinations of gamma-secretase inhibitors and the ABL1 inhibitor imatinib in a T-cell acute lymphoblastic leukemia cell line.
gamma-secretase inhibitor treatment for 5-7 days reversibly inhibited cell proliferation, caused cell cycle block in sensitive T-cell acute lymphoblastic leukemia cell lines, and caused differentiation of some T-cell acute lymphoblastic leukemia cell lines. Treatment for 14 days or longer was required to induce significant apoptosis. The cytotoxic effects of the chemotherapeutic agent vincristine were not significantly enhanced by addition of gamma-secretase inhibitors to T-cell acute lymphoblastic leukemia cell lines, but gamma-secretase inhibitor treatment sensitized cells to the effect of dexamethasone. NOTCH1 mutations were identified in all T-cell acute lymphoblastic leukemia patients with ABL1 fusions and in a T-cell acute lymphoblastic leukemia cell line expressing NUP214-ABL1. In this cell line, the anti-proliferative effect of imatinib was increased by pre-treatment with gamma-secretase inhibitors.
Short-term treatment of T-cell acute lymphoblastic leukemia cell lines with gamma-secretase inhibitors had limited effects on cell proliferation and survival. Combinations of gamma-secretase inhibitors with other drugs may be required to obtain efficient therapeutic effects in T-cell acute lymphoblastic leukemia, and not all combinations may be useful.
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