Ilker Dibirdik

Targeting Janus kinase 3 in mast cells prevents immediate hypersensitivity reactions and anaphylaxis.

Janus kinase 3 (JAK3), a member of the Janus family protein-tyrosine kinases, is expressed in mast cells, and its enzymatic activity is enhanced by IgE receptor/FcεRI cross-linking. Selective inhibition of JAK3 in mast cells with 4-(4′-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline) (WHI-P131) blocked the phospholipase C activation, calcium mobilization, and activation of microtubule-associated protein kinase after lgE receptor/FcεRI cross-linking. Treatment of IgE-sensitized rodent as well as human mast cells with WHI-P131 effectively inhibited the activation-associated morphological changes, degranulation, and proinflammatory mediator release after specific antigen challenge without affecting the functional integrity of the distal secretory machinery. In vivo administration of the JAK3 inhibitor WHI-P131 prevented mast cell degranulation and development of cutaneous as well as systemic fatal anaphylaxis in mice at nontoxic dose levels. Thus, JAK3 plays a pivotal role in IgE receptor/FcεRI-mediated mast cell responses, and targeting JAK3 with a specific inhibitor, such as WHI-P131, may provide the basis for new and effective treatment as well as prevention programs for mast cell-mediated allergic reactions.

Engagement of the CD19 receptor on human B-lineage leukemia cells activates LCK tyrosine kinase and facilitates radiation-induced apoptosis.

As presently reported, both ionizing radiation and engagement of the CD19 receptor are capable of inducing apoptosis in B-lineage acute lymphoblastic leukemia (ALL) cells. In both instances, activation of tyrosine kinases appears to be a proximal and mandatory step, since it can be prevented by the tyrosine kinase inhibitor genistein. This common biochemical signaling pathway involves the rapid activation of the Src family tyrosine kinase LCK (p56lck), which is physically associated with the CD19 receptor, and enhanced tyrosine phosphorylation of multiple substrates leading to stimulation of phosphoinositide turnover, and activation of protein kinase C. Importantly, engagement of the CD19 receptor promoted radiation-induced apoptosis in radiation-resistant B-lineage ALL cells in a cell type-specific fashion. Our results prompt the hypothesis that clonogenic B-lineage ALL blasts with an inherent or acquired resistance to radiation could be radiosensitized in clinical settings using anti-CD19 MoAb B43 or its homoconjugate as adjuncts.

ELECTROMAGNETIC FIELD-INDUCED STIMULATION OF BRUTON'S TYROSINE KINASE

Here we present evidence that exposure of DT40 lymphoma B-cells to low energy electromagnetic fields (EMF) results in activation of phospholipase C-γ 2 (PLC-γ2), leading to increased inositol phospholipid turnover. PLC-γ2 activation in EMF-stimulated cells is mediated by stimulation of the Bruton’s tyrosine kinase (BTK), a member of the Src-related TEC family of protein tyrosine kinases, which acts downstream of LYN kinase and upstream of PLC-γ2. B-cells rendered BTK-deficient by targeted disruption of thebtk gene did not show enhanced PLC-γ2 activation in response to EMF exposure. Introduction of the wild-type (but not a kinase domain mutant) human btk gene into BTK-deficient B-cells restored their EMF responsiveness. Thus, BTK exerts a pivotal and mandatory function in initiation of EMF-induced signaling cascades in B-cells.

CD22 EXON 12 deletion as a pathogenic mechanism of human B-precursor leukemia

Here, we report that primary leukemic cells from infants with newly diagnosed B-precursor leukemia express a truncated and functionally defective CD22 coreceptor protein that is unable to transmit apoptotic signals because it lacks most of the intracellular domain, including the key regulatory signal transduction elements and all of the cytoplasmic tyrosine residues. Expression of this structurally and functionally abnormal CD22 protein is associated with a very aggressive in vivo growth of patients’ primary leukemia cells causing disseminated overt leukemia in SCID mice. The abnormal CD22 coreceptor is encoded by a profoundly aberrant mRNA arising from a splicing defect that causes the deletion of exon 12 (c.2208-c.2327) (CD22ΔE12) and results in a truncating frameshift mutation. The splicing defect is associated with multiple homozygous mutations within a 132-bp segment of the intronic sequence between exons 12 and 13. These mutations cause marked changes in the predicted secondary structures of the mutant CD22 pre-mRNA sequences that affect the target motifs for the splicing factors hnRNP-L, PTB, and PCBP that are up-regulated in infant leukemia cells. Forced expression of the mutant CD22ΔE12 protein in transgenic mice perturbs B-cell development, as evidenced by B-precursor/B-cell hyperplasia, and corrupts the regulation of gene expression, causing reduced expression levels of several genes with a tumor suppressor function. We further show that CD22ΔE12-associated unique gene expression signature is a discriminating feature of newly diagnosed infant leukemia patients. These striking findings implicate CD22ΔE12 as a previously undescribed pathogenic mechanism in human B-precursor leukemia.

Targeting JAK3 Tyrosine Kinase-Linked Signal Transduction Pathways with Rationally-Designed Inhibitors

Inhibitors of Janus Kinase 3 (JAK3) show potential as a new class of apoptosis-inducing anti-cancer drugs. In addition, JAK3 inhibitors may also be useful as immunosuppressive agents. Rationally designed selective inhibitors of JAK3 such as JANEX-1, that do not inhibit other Janus kinases have recently undergone extensive preclinical testing that revealed a favorable pharmacodynamic profile. Here we discuss the clinical potential of targeting JAK3-linked signal transduction pathways with small molecule inhibitors such as JANEX-1.

In vivo Anti-Cancer Activity of a Liposomal Nanoparticle Construct of Multifunctional Tyrosine Kinase Inhibitor 4-(4'-Hydroxyphenyl)-Amino-6,7-Dimethoxyquinazoline

The quinazoline derivative 4-(4’-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P131/JANEX-1; CAS 202475-60-3) is a dual-function inhibitor of Janus kinase 3 (JAK3) and Epidermal Growth Factor (EGF) receptor kinase. A PEGylated liposomal nanoparticle formulation of GMP-grade WHI-P131 exhibited potent in vivo activity against breast cancer cells. Notably, this therapeutic nanoparticle formulation of GMP-grade WHI-P131 was substantially more effective than the standard chemotherapy drugs paclitaxel, gemcitabine, and ge fi tinib against chemotherapy-resistant breast cancer in the MMTV/ Neu transgenic mouse model. These experimental results demonstrate that the nanotechnology- enabled delivery of WHI-P131 shows therapeutic potential against breast cancer.

In vitro and in vivo chemosensitizing activity of LFM-A13, a dual-function inhibitor of Bruton's tyrosine kinase and polo-like kinases, against human leukemic B-cell precursors.

The present study documents the chemosensitizing anti-leukemic activity of the leflunomide metabolite (LFM) analog, LFM-A13, a dual-function inhibitor of Brutons tyrosine kinase (BTK) and Polo-like kinases (PLK), against human leukemic B-cell precursors. The results in 135 xenografted NOD/SCID mice regarding the anti-leukemic activity of GMP-grade LFM-A13, obtained with only 4-days of LFM-A13 therapy at nontoxic dose levels corresponding to 1-20% of its NOAEL (no observable advserse effect level), alone or in combination with the standard chemotherapy drug vincristine, demonstrate the potential of LFM-A13 as a new anti-leukemic drug candidate. All 82 LFM-A13-treated mice, including those receiving a combination of vincristine + LFM-A13 at the highest dose level of LFM-A13, tolerated their treatments well without weight loss, diarrhea, lethargy/ paralysis, other signs of morbidity, or mortality. The present study provides preclinical proof-of-principle for the development of LFM-A13 as a new chemosensitizing and apoptosis-promoting anti-leukemic agent and lends support to the hypothesis that the chemoresistance of relapsed B-cell precursor acute lymphoblastic leukemia (BCP-ALL) can be overcome by using LFM-A13 in combination with chemotherapy. Also presented are the results of a comprehensive meta-analysis of the overexpression of genes for LFM-A13 targeted kinases and their downstream effector molecules in B-lineage lymphoid malignancies utilizing the Oncomine database.

Augmentation of the Antileukemia Potency of Total-Body Irradiation (TBI) by a Novel P-site Inhibitor of Spleen Tyrosine Kinase (SYK)

Abstract A novel spleen tyrosine kinase (SYK) P-site inhibitor, 1,4-Bis (9-O dihydroquinidinyl) phthalazine/hydroquinidine 1,4-phathalazinediyl diether (C-61), (but not vehicle) markedly enhanced H2O2-induced apoptosis of primary leukemia cells from each of five relapsed B-lineage acute lymphoblastic leukemia (ALL) patients, as measured by in vitro TUNEL assays. A highly radiation-resistant subclone of the murine B-lineage leukemia cell line BCL-1 was next used to investigate the in vivo radiosensitizing effects of C-61. C-61 enhanced the antileukemia potency of 7 Gy total-body irradiation (TBI) in the context of syngeneic bone marrow transplantation (BMT) at 20% of its nonobservable adverse effect level (NOAEL) that does not exhibit detectable single-agent activity against BCL-1 leukemia in vivo. Based on this preclinical proof-of-principle study, we hypothesize that the incorporation of C-61 into the pretransplant TBI regimens of patients with recurrent or high-risk B-lineage acute lymphoblastic leukemia (ALL) will help overcome the radiochemotherapy resistance of their leukemia cells and thereby improve their treatment response and survival outcome after BMT.

Therapeutic nanoparticle constructs of a JAK3 tyrosine kinase inhibitor against human B-lineage ALL cells

WHI-P131 (CAS 202475-60-3) is a dual-function inhibitor of JAK3 tyrosine kinase that demonstrated potent in vivo anti-inflammatory and anti-leukemic activity in several preclinical animal models. This is the first report of the development of nanoparticle (NP) constructs ofWHI-P131. Fourty-eight distinct NP formulations were prepared and WHI-P131 encapsulation efficiencies > 95% and intraliposomal WHI-P131 concentrations >10 mg/mL were achieved in lead NP formulations. The anti-cancer activity of WHI-P131-NP, a PEGylated lead formulation was tested in vitro and in vivo. Notably, WHI-P131-NP was capable of causing apoptotic death in primary leukemia cells from chemotherapy-resistant acute lymphoblastic leukemia (ALL) as well as chronic lymphocytic leukemia (CLL) patients. WHI-P131-NP was also active in the RS4;11 SCID mouse xenograft model of chemotherapy-resistant B-lineage ALL. The life table analysis showed that WHI-P131-NP was more effective than WHI-P131 (P = 0.01), vincristine (P < 0.0001), or vehicle (P < 0.0001). These experimental results demonstrate that the nanotechnology-enabled delivery of WHI-P131 shows therapeutic potential against leukemias with constitutive activation of the JAK3-STAT3/STAT5 molecular target.

Stimulation of Bruton's tyrosine kinase (BTK) and inositol 1,4,5-trisphosphate production in leukemia and lymphoma cells exposed to low energy electromagnetic fields.

We examined the effects of low energy electromagnetic field (EMF) exposure on the BTK kinase activity in B18-2 ([Btk-, rBTK(wt)] DT40) chicken lymphoma B cells and NALM-6 leukemic pre-B cells. Exposure of B18-2 cells to EMF resulted in activation of BTK within 1 to 15 minutes in 8 of 8 independent experiments with stimulation indexes ranging from 1.2 to 13.3. While in some experiments the BTK stimulation was transient, in others the BTK activity continued to be significantly elevated for up to 4 hours. Similarly, exposure of NALM-6 cells to EMF resulted in activation of BTK within 30 minutes in 7 of 7 experiments with stimulation indexes ranging from 1.2 to 7.4. Stimulation of BTK activity in EMF exposed cells was associated with enhanced phosphoinositide turnover and increased inositol- 1,4,5-tri-sphosphate (IP3) production in 7 of 13 experiments with DT40 cells and 7 of 13 experiments with NALM-6 cells. The likelihood and magnitude of an IP3 response after EMF exposure were similar to those after BCR ligation on DT40 cells and CD 19 ligation on NALM-6 cells. These results confirm and extend our previous studies regarding EMF-induced biochemical signaling events in B-lineage lymphoid cells.