BCR-ABL regulates death receptor expression for TNF-related apoptosis-inducing ligand (TRAIL) in Philadelphia chromosome-positive leukemia

Targeting of BCR-ABL1 and IRE1α induces synthetic lethality in Philadelphia-positive acute lymphoblastic leukemia

BCR-ABL1-positive acute lymphoblastic leukemia (ALL) cell survival is dependent on the inositol-requiring enzyme 1 alpha (IRE1α) branch of the unfolded protein response. In the current study, we have focused on exploring the efficacy of a simultaneous pharmacological inhibition of BCR-ABL1 and IRE1α in Philadelphia-positive (Ph+) ALL using tyrosine kinase inhibitor (TKI) nilotinib and the IRE1α inhibitor MKC-8866. The combination of 0.5 µM nilotinib and 30 µM MKC-8866 in Ph+ ALL cell lines led to a synergistic effect on cell viability. To mimic this dual inhibition on a genetic level, pre-B-cells from conditional Xbp1+/fl mice were transduced with a BCR-ABL1 construct and with either tamoxifen-inducible cre or empty vector. Cells showed a significant sensitization to the effect of TKIs after the induction of the heterozygous deletion. Finally, we performed a phosphoproteomic analysis on Ph+ ALL cell lines treated with the combination of nilotinib and MKC-8866 to identify potential targets involved in their synergistic effect. An enhanced activation of p38 mitogen-activated protein kinase α (p38α MAPK) was identified. In line with this findings, p38 MAPK and, another important endoplasmic reticulum-stress-related kinase, c-Jun N-terminal kinase (JNK) were found to mediate the potentiated cytotoxic effect induced by the combination of MKC-8866 and nilotinib since the targeting of p38 MAPK with its specific inhibitor BIRB-796 or JNK with JNK-in-8 hindered the synergistic effect observed upon treatment with nilotinib and MKC-8866. In conclusion, the identified combined action of nilotinib and MKC-8866 might represent a successful therapeutic strategy in high-risk Ph+ ALL.

AMP-activated protein kinase activation primes cytoplasmic translocation and autophagic degradation of the BCR-ABL protein in CML cells

Chronic myeloid leukemia is driven by the BCR‐ABL oncoprotein, a constitutively active protein tyrosine kinase. Although tyrosine kinase inhibitors (TKIs) have greatly improved the prognosis of CML patients, the emergence of TKI resistance is an important clinical problem, which deserves additional treatment options based on unique biological properties to CML cells. In this study, we show that metabolic homeostasis is critical for survival of CML cells, especially when the disease is in advanced stages. The BCR‐ABL protein activates AMP‐activated protein kinase (AMPK) for ATP production and the mTOR pathway to suppress autophagy. BCR‐ABL is detected in the nuclei of advanced‐stage CML cells, in which ATP is sufficiently supplied by enhanced glucose metabolism. AMP‐activated protein kinase is further activated under energy‐deprived conditions and triggers autophagy through ULK1 phosphorylation and mTOR inhibition. In addition, AMPK phosphorylates 14‐3‐3 and Beclin 1 to facilitate cytoplasmic translocation of nuclear BCR‐ABL in a BCR‐ABL/14‐3‐3τ/Beclin1/XPO1 complex. Cytoplasmic BCR‐ABL protein undergoes autophagic degradation when intracellular ATP is exhausted by disruption of the energy balance or forced autophagy flux with AMP mimetics, mTOR inhibitors, or arsenic trioxide, leading to apoptotic cell death. This pathway represents a novel therapeutic vulnerability that could be useful for treating TKI‐resistant CML.

The Philadelphia chromosome in leukemogenesis

The truncated chromosome 22 that results from the reciprocal translocation t(9;22)(q34;q11) is known as the Philadelphia chromosome (Ph) and is a hallmark of chronic myeloid leukemia (CML). In leukemia cells, Ph not only impairs the physiological signaling pathways but also disrupts genomic stability. This aberrant fusion gene encodes the breakpoint cluster region-proto-oncogene tyrosine-protein kinase (BCR-ABL1) oncogenic protein with persistently enhanced tyrosine kinase activity. The kinase activity is responsible for maintaining proliferation, inhibiting differentiation, and conferring resistance to cell death. During the progression of CML from the chronic phase to the accelerated phase and then to the blast phase, the expression patterns of different BCR-ABL1 transcripts vary. Each BCR-ABL1 transcript is present in a distinct leukemia phenotype, which predicts both response to therapy and clinical outcome. Besides CML, the Ph is found in acute lymphoblastic leukemia, acute myeloid leukemia, and mixed-phenotype acute leukemia. Here, we provide an overview of the clinical presentation and cellular biology of different phenotypes of Ph-positive leukemia and highlight key findings regarding leukemogenesis.

Specific Antileukemic Activity of PD0332991, a CDK4/6 Inhibitor, against Philadelphia Chromosome-Positive Lymphoid Leukemia

S-phase progression of the cell cycle is accelerated in tumors through various genetic abnormalities, and, thus, pharmacologic inhibition of altered cell-cycle progression would be an effective strategy to control tumors. In the current study, we analyzed the antileukemic activity of three available small molecules targeting CDK4/CDK6 against lymphoid crisis of chronic myeloid leukemia (CML-LC) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL), and found that all three molecules showed specific activities against leukemic cell lines derived from CML-LC and Ph(+) ALL. In particular, PD0332991 exhibited extremely high antileukemic activity against CML-LC and Ph(+) ALL cell lines in the nanomolar range by the induction of G0-G1 arrest and partially cell death through dephosphorylation of pRb and downregulation of the genes that are involved in S-phase transition. As an underlying mechanism for favorable sensitivity to the small molecules targeting CDK4/CDK6, cell-cycle progression of Ph(+) lymphoid leukemia cells was regulated by transcriptional and posttranscriptional modulation of CDK4 as well as Cyclin D2 gene expression under the control of BCR-ABL probably through the PI3K pathway. Consistently, the gene expression level of Cyclin D2 in Ph(+) lymphoid leukemia cells was significantly higher than that in Ph(-) lymphoid leukemia cells. Of note, three Ph(+) ALL cell lines having the T315I mutation also showed sensitivity to PD0332991. In a xenograft model, PD0332991, but not imatinib, suppressed dissemination of Ph(+) ALL having the T315I mutation and prolonged survival, demonstrating that this reagent would be a new therapeutic modality for relapsed CML-LC and Ph(+) ALL patients after treatment with tyrosine kinase inhibitors.

Anti-leukemic potency of piggyBac-mediated CD19-specific T cells against refractory Philadelphia chromosome-positive acute lymphoblastic leukemia

BACKGROUND AIMS

To develop a treatment option for Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+)ALL) resistant to tyrosine kinase inhibitors (TKIs), we evaluated the anti-leukemic activity of T cells non-virally engineered to express a CD19-specific chimeric antigen receptor (CAR).

METHODS

A CD19.CAR gene was delivered into mononuclear cells from 10 mL of blood of healthy donors through the use of piggyBac-transposons and the 4-D Nucleofector System. Nucleofected cells were stimulated with CD3/CD28 antibodies, magnetically selected for the CD19.CAR, and cultured in interleukin-15-containing serum-free medium with autologous feeder cells for 21 days. To evaluate their cytotoxic potency, we co-cultured CAR T cells with seven Ph(+)ALL cell lines including three TKI-resistant (T315I-mutated) lines at an effector-to-target ratio of 1:5 or lower without cytokines.

RESULTS

We obtained ∼1.3 × 10(8) CAR T cells (CD4(+), 25.4%; CD8(+), 71.3%), co-expressing CD45RA and CCR7 up to ∼80%. After 7-day co-culture, CAR T cells eradicated all tumor cells at the 1:5 and 1:10 ratios and substantially reduced tumor cell numbers at the 1:50 ratio. Kinetic analysis revealed up to 37-fold proliferation of CAR T cells during a 20-day culture period in the presence of tumor cells. On exposure to tumor cells, CAR T cells transiently and reproducibly upregulated the expression of transgene as well as tumor necrosis factor-related apoptosis-inducing ligand and interleukin-2.

CONCLUSIONS

We generated a clinically relevant number of CAR T cells from 10 mL of blood through the use of piggyBac-transposons, a 4D-Nulcleofector, and serum/xeno/tumor cell/virus-free culture system. CAR T cells exhibited marked cytotoxicity against Ph(+)ALL regardless of T315I mutation. PiggyBac-mediated CD19-specific T-cell therapy may provide an effective, inexpensive and safe option for drug-resistant Ph(+)ALL.

Genomic quantitative real-time PCR proves residual disease positivity in more than 30% samples with negative mRNA-based qRT-PCR in Chronic Myeloid Leukemia

Imatinib mesylate (IM) is the first line therapy against Chronic Myeloid Leukemia, effectively prolonging overall survival. Because discontinuation of treatment is associated with relapse, IM is required indefinitely to maintain operational cure. To assess minimal residual disease, cytogenetic analysis is insensitive in a high background of normal lymphocytes. The qRT-PCR provides highly sensitive detection of BCR-ABL1 transcripts, but mRNA levels are not directly related to the number of leukemic cells, and undetectable results are difficult to interpret. We developed a sensitive approach to detect the number of leukemic cells by a genomic DNA (gDNA) Q-PCR assay based on the break-point sequence, with a formula to calculate the number of Ph-positive cells. We monitored 8 CML patients treated with IM for more than 8 years. We tested each samples by patient specific gDNA Q-PCR in parallel by the conventional techniques. In all samples positive for chimeric transcripts we showed corresponding chimeric gDNA by Q-PCR, and in 32.8% (42/128) of samples with undetectable levels of mRNA we detected the persistence of leukemic cells. The gDNA Q-PCR assay could be a new diagnostic tool used in parallel to conventional techniques to support the clinician's decision to vary or to STOP IM therapy.

While at Rome miRNA and TRAIL do whatever BCR-ABL commands to do

It is a well-acclaimed fact that proteins expressed as a consequence of oncogenic fusions, mutations or amplifications can facilitate ectopic protein-protein interactions that re-wire signal dissemination pathways, in a manner that escalates malignancy. BCR-ABL-mediated signal transduction cascades in leukemic cells are assembled and modulated by a finely controlled network of protein-protein interactions, mediated by characteristic signaling domains and their respective binding motifs. BCR-ABL functions in a cell context-specific and cell type-specific manner to integrate signals that affect uncontrolled cellular proliferation. In this review, we draw attention to the recent progress made in outlining resistance against TRAIL-mediated apoptosis and diametrically opposed roles of miRNAs in BCR-ABL-positive leukemic cells. BCR-ABL governs carcinogenesis through well-organized web of antiapoptotic proteins and over-expressed oncomirs which target death receptors and pro-apoptotic genes. Set of oncomirs which inversely correlate with expression of TRAIL via suppression of SMAD is an important dimension which is gradually gaining attention of the researchers. Contrary to this, some current findings show a new role of BCR-ABL in nucleus with spotlight on apoptosis. It seems obvious that genetic heterogeneity of leukemias poses therapeutic challenges, and pharmacological agents that target components of the cancer promoting nano-machinery still need broad experimental validation to be considered competent as a component of the therapeutic arsenal for this group of diseases. Rapidly developing technologies are empowering us to explain the molecular "nature" of a patient and/or tumor and with this integration of personalized medicine, with maximized efficacy, cost effectiveness will hopefully improve survival chances of the patient.