Heather E. Tibbles

Role of a JAK3-dependent Biochemical Signaling Pathway in Platelet Activation and Aggregation

Here we provide experimental evidence that identifies JAK3 as one of the regulators of platelet function. Treatment of platelets with thrombin induced tyrosine phosphorylation of the JAK3 target substrates STAT1 and STAT3. Platelets from JAK3-deficient mice displayed a decrease in tyrosine phosphorylation of STAT1 and STAT3. In accordance with these data, pretreatment of human platelets with the JAK3 inhibitor WHI-P131 markedly decreased the base-line enzymatic activity of constitutively active JAK3 and abolished the thrombin-induced tyrosine phosphorylation of STAT1 and STAT3. Following thrombin stimulation, WHI-P131-treated platelets did not undergo shape changes indicative of activation such as pseudopod formation. WHI-P131 inhibited thrombin-induced degranulation/serotonin release as well as platelet aggregation. Highly effective platelet inhibitory plasma concentrations of WHI-P131 were achieved in mice without toxicity. WHI-P131 prolonged the bleeding time of mice in a dose-dependent manner and improved event-free survival in a mouse model of thromboplastin-induced generalized and invariably fatal thromboembolism. To our knowledge, WHI-P131 is the first anti-thrombotic agent that prevents platelet aggregation by inhibiting JAK3.

The Anti-leukemic Bruton's Tyrosine Kinase Inhibitor α-cyano-β-hydroxy-β-methyl-N-(2,5-dibromophenyl) Propenamide (LFM-A13) Prevents Fatal Thromboembolism

Abstract The leflunomide metabolite analog α-cyano-β-hydroxy-β-methyl-N-(2,5-dibromophenyl)-propenamide (LFM-A13) is a rationally-designed specific inhibitor of the TEC family protein tyrosine kinase, Bruto ns tyrosine kinase (BTK) which plays an important role in platelet physiology by regulating the glycoprotein GPVI-FcRγ-coupled collagen receptor signaling pathway. At low micromolar concentrations, LFM-A13 inhibited collagen-induced ultrastructural changes indicative of activation. LFM-A13 inhibited collagen (but not thrombin, TRAP-6, or ADP)-induced platelet aggregation in a concentration-dependent fashion with an IC50 value of 2.8 μM. LFM-A13 was not toxic to mice when administered systemically at dose levels ranging from 1 to 100mg/kg. At nontoxic dose levels, LFM-A13 prolonged the tail bleeding times of mice and improved event-free survival in two mouse models of agonist-induced invariably fatal pulmonary thromboembolism. To our knowledge, LFM-A13 is the first anti-thrombotic agent which prevents platelet aggregation by inhibiting BTK.

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.

Brutons Tyrosine Kinase as a New Therapeutic Target

Targeting Brutons tyrosine kinase (BTK) with a small molecule inhibitor may be useful in treatment of BTK-expressing malignancies because of the anti-apoptotic function of BTK in cancer cells. Furthermore, BTK inhibitors also exhibit anti-thrombotic properties that may be desirable in the context of the increased risk of thromboembolic complications in cancer patients. This review will focus on the role of BTK in drug resistance in cancer, thromboembolism, and various pathologic immune responses, such as graft versus host disease. The therapeutic potential of targeting BTK is illustrated by discussion of the biologic activity profile of the rationally designed BTK inhibitor LFM-A13.

CNS activity of Pokeweed Anti-viral Protein (PAP) in mice infected with Lymphocytic Choriomeningitis Virus (LCMV)

BackgroundOthers and we have previously described the potent in vivo and in vitro activity of the broad-spectrum antiviral agent PAP (Pokeweed antiviral protein) against a wide range of viruses. The purpose of the present study was to further elucidate the anti-viral spectrum of PAP by examining its effects on the survival of mice challenged with lymphocytic choriomeningitis virus (LCMV).MethodsWe examined the therapeutic effect of PAP in CBA mice inoculated with intracerebral injections of the WE54 strain of LCMV at a 1000 PFU dose level that is lethal to 100% of mice within 7–9 days. Mice were treated either with vehicle or PAP administered intraperitoneally 24 hours prior to, 1 hour prior to and 24 hours, 48 hours 72 hours and 96 hours after virus inoculation.ResultsPAP exhibits significant in vivo anti- LCMV activity in mice challenged intracerebrally with an otherwise invariably fatal dose of LCMV. At non-toxic dose levels, PAP significantly prolonged survival in the absence of the majority of disease-associated symptoms. The median survival time of PAP-treated mice was >21 days as opposed to 7 days median survival for the control (p = 0.0069).ConclusionOur results presented herein provide unprecedented experimental evidence that PAP exhibits antiviral activity in the CNS of LCMV-infected mice.

Role of the Leukemia-associated Transcription Factor STAT3 in Platelet Physiology

Actinomycin D, a transcriptional inhibitor, was found to inhibit platelet potentiation by thrombopoietin (TPO), suggesting that TPO stimulation of platelets involves mitochondrial transcription. We sought to determine a possible role for leukemia-associated signal transducers and activators of transcription (STAT) proteins as mitochondrial transcription factors, focusing specifically on STAT3 in human platelets. We found TPO stimulation of platelets activated STAT3 in vitro, that STAT3 was present in platelet mitochondrial-rich fractions as determined by Western Blot analysis and was capable of binding to the regulatory D-loop region of human mitochondrial DNA upon activation. These results suggest that platelet signaling pathways activated by TPO may affect mitochondrial transcription via activation of STAT3.

SYK and LYN mediate B-cell receptor-independent calcium-induced apoptosis in DT-40 lymphoma B-cells.

Here, we report that the calcium ionophore ionomycin induces a massive Ca 2+ -dependent apoptosis in wildtype DT-40 chicken B lymphoma cells, as well as in BTK-deficient, PLC γ 2-deficient and IP3 receptor-deficient DT-40 cells, but not in LYN- or SYK-deficient DT-40 cells. Notably, the deficiency of CSK, a negative regulator of Src-family PTK, promoted ionomycin-induced apoptosis of DT-40 cells. Reconstitution of SYK-deficient cells with wild-type SYK restored the apoptotic response of the cells to ionomycin, but the expression of FYN or LCK in LYN-deficient cells did not restore the apoptotic response of LYN-deficient cells. Taken together, our data suggests that both LYN and SYK, but not BTK, FYN or LCK, are crucial mediators of BCR-independent Ca 2+ -induced apoptosis in DT-40 lymphoma B cells.

Stampidine prevents mortality in an experimental mouse model of viral hemorrhagic fever caused by lassa virus

BACKGROUND The potential use of microorganisms as agents of biological warfare (BW) is a growing concern. Lassa virus, a member of the Arenavirus class of Hemorrhagic fever (HF) viruses has emerged as a worldwide concern among public health officials. The purpose of the present study was to further elucidate the antiviral activity spectrum of stampidine, a novel nucleoside analog with potent anti-viral activity against the immunodeficiency viruses HIV-1, HIV-2, and FIV, by examining its effects on survival of mice challenged with Lassa virus. METHODS We examined the therapeutic effect of Stampidine in CBA mice inoculated with intracerebral injections of the Josiah strain of Lassa virus. Mice were treated either with vehicle or nontoxic doses of stampidine administered intraperitoneally 24 hours prior to, 1 hour prior to, and 24 hours, 48 hours, 72 hours, and 96 hours after virus inoculation. RESULTS The probability of survival following the Lassa challenge was significantly improved for stampidine treated mice (Kaplan Meier, Chi-squared = 11.7, df = 2, Log-Rank p-value = 0.003). CONCLUSION Therefore, stampidine shows clinical potential as a new agent for treatment of viral hemorrhagic fevers caused by Lassa virus.

Targeting JAK3 and BTK tyrosine kinases with rationally-designed inhibitors.

Multifunctional rational drug design of protein tyrosine kinases inhibitors allows a potent drug to be utilized to treat more than one disease for greater patient benefits. Many protein tyrosine kinases (PTK), including Janus kinase 3 (JAK3) and Brutons tyrosine kinase (BTK), have been identified as potential drug targets to treat diverse diseases including cancer and disorders of the immune system. Here we review advances in JAK3 and BTK inhibitors and describe the therapeutic potential of these potent agents in the clinical setting.

A dual function anti-leukemic agent with anti-thrombotic activity.

Here we report that treatment with the anti-leukemic compound, LFM-A13 resulted in SYK kinase activation and caused distinct shape changes in platelets. Also provided is electron microscopic evidence that similar shape changes are observed in platelets from XID mice. We propose that LFM-A13 induces a conformational change in the PH domain of BTK and causes BTK to associate with PIP2 which effects actin bundling and shape change.