Selective inhibitor of Janus tyrosine kinase 3, PNU156804, prolongs allograft survival and acts synergistically with cyclosporine but additively with rapamycin

Janus tyrosine kinases and signal transducers and activators of transcription regulate critical functions of T cells in allograft rejection and transplantation tolerance

Full activation of T cells requires three sequential signals. Engagement by antigen presenting cells (APC) delivers signals 1/2, whereas signal 3 is delivered by multiple cytokines to regulate the immune homeostasis by influencing proliferation, differentiation, and survival/death. Signaling by cytokines acting through their receptors is delivered by two major molecular families, namely Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Findings obtained from mice genetically deficient in Jaks and Stats suggest that these molecules may serve as therapeutic targets to prevent allograft rejection, induce transplantation tolerance, and inhibit autoimmune disease and lymphoid-derived tumors. This review describes the role of Jak tyrosine kinases and Stat transcription factors and their putative function in regulating T and B cell activity.

Development of pyrimidine-based inhibitors of Janus tyrosine kinase 3

A new class of pyrimidine-based Janus tyrosine kinase 3 (JAK3) inhibitors are described. Many of these inhibitors showed low nanomolar activity against JAK3.

Activating alleles of JAK3 in acute megakaryoblastic leukemia

Tyrosine kinases are aberrantly activated in numerous malignancies, including acute myeloid leukemia (AML). To identify tyrosine kinases activated in AML, we developed a screening strategy that rapidly identifies tyrosine-phosphorylated proteins using mass spectrometry. This allowed the identification of an activating mutation (A572V) in the JAK3 pseudokinase domain in the acute megakaryoblastic leukemia (AMKL) cell line CMK. Subsequent analysis identified two additional JAK3 alleles, V722I and P132T, in AMKL patients. JAK3(A572V), JAK3(V722I), and JAK3(P132T) each transform Ba/F3 cells to factor-independent growth, and JAK3(A572V) confers features of megakaryoblastic leukemia in a murine model. These findings illustrate the biological importance of gain-of-function JAK3 mutations in leukemogenesis and demonstrate the utility of proteomic approaches to identifying clinically relevant mutations.

Indoloprodigiosins from the C-10 bipyrrolic precursor: New antiproliferative prodigiosin analogs

The condensation of the C-10 methoxybipyrrole precursor (3) of prodigiosin with indoles and a related pyrrole derivative yields novel analogs of prodigiosin. Biological evaluation of these products revealed compounds that inhibit cancer cell proliferation from 50 nM to 50 microM.

Immunotherapy for De Novo Renal Transplantation

Immunosuppressive drugs have been traditionally developed to prevent acute rejection and to improve short-term kidney transplant outcomes. There is still a medical need to improve outcomes among subgroups of patients at higher risk for graft loss and to reduce cardiovascular, infectious and malignancy-associated morbidity and mortality, and improve long-term adherence. Several new immunosuppressive agents and formulations are undergoing clinical investigation and are discussed in this review.A modified release tacrolimus formulation (MR4) for once-daily administration is undergoing phase III trials. It has been developed to be administered de novo or for maintenance using the same therapeutic target tacrolimus trough concentrations as for the original formulation. Belatacept (LEA29Y), a second generation cytotoxic-T-lymphocyte-associated antigen immunoglobulin (CTLA4-Ig), blocks the interaction between CD80/86 and CD28 costimulatory pathways. In phase II trials, belatacept was as effective as ciclosporin (cyclosporine) when administered in combination with basiliximab, mycophenolate mofetil (MMF) and corticosteroids. Currently, belatacept is undergoing phase III trials including one study in recipients of organs from expanded criteria donors. Inhibitors of the Janus protein tyrosine kinase (JAK)-3 show some selectivity for cells of the lymphoid lineage and have been shown to be effective in late preclinical transplant models. The most frequent adverse effects have been related to nonspecific binding to JAK2 kinases. CP-690550, a JAK3 inhibitor is currently in phase II clinical trials.FK778, is a synthetic malononitrilamide that targets the critical enzyme of the de novo pyrimidine synthesis, dihydroorotic acid dehydrogenase, and receptor-associated tyrosine kinases has completed phase II trials. FK778 also shows antiviral activities that have been tested in patients with polyomavirus nephropathy. Fingolimod (FTY720), a synthetic sphingosine phosphate receptor modulator that reduces the recirculation of lymphocytes to blood and peripheral tissues including inflammatory lesions and graft sites is undergoing phase III trials. Although the efficacy of fingolimod is similar to MMF in patients receiving full doses of ciclosporin, safety issues such as a negative chronotropic effect, macular oedema, pulmonary adverse reactions and graft function resulted in premature discontinuation of the development programme for kidney transplantation. Because there was no clear clinical benefit over treatment options, the clinical development programme of FK778 was discontinued.Finally, a new evolving strategy with powerful induction-induced prolonged T-cell depletion followed by low-dose immunosuppressive monotherapy is showing promising results.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Effective prevention of lethal acute graft-versus-host disease by combined immunosuppressive therapy with prodigiosin and cyclosporine A

Prodigiosin (PDG), a bacterial metabolite, is a known T cell-specific immunosuppressant. Here, we compared its inhibitory potency and mode of action with cyclosporine A (CsA) in a mouse model. PDG efficiently inhibited T cell proliferation with an IC(50) of 3.37 ng/ml, a similar dose to that of CsA (IC(50) of 2.71 ng/ml). PDG inhibited only IL-2Ralpha expression, but not IL-2 expression, whereas CsA inhibited both. Exogenously added IL-2 reversed the suppressive activity of CsA, but not that of PDG. Moreover, although both PDG and CsA markedly reduced mortality rates in lethal acute graft-versus-host disease (GVHD), the combined treatment was more effective than either drug alone. These results demonstrate that PDG and CsA have similar inhibitory potencies, but different modes of action, and suggest that PDG has potential use as a supplementary immunosuppressant in combination with CsA for the treatment of GVHD.

Janus kinase 3: a novel target for selective transplant immunosupression

Existing immunosuppressants inhibit lymphocyte activation and T cell cytokine signal transduction pathways, reducing the rate of acute rejection episodes to < 10%. However, the widespread tissue distribution of their molecular targets engenders pleiotropic toxicities. One strategy to address this problem seeks to identify compounds that selectively inhibit a target restricted in distribution to the lymphoid system. Janus kinase (Jak) 3 is such a molecule; it mediates signal transduction via the gamma common chain of lymphokine surface receptors. Disruption of this lymphoid-restricted enzyme would not be predicted to produce collateral damage in other organ systems. Development of selective Jak3 inhibitors has been difficult due to crossreactivity with its homologue, Jak2. In contrast to all other putative antagonists, which are discussed in detail herein, one Jak3 inhibitor, NC1153, shows at least 40-fold greater selective inhibition for Jak3 than for Jak2, is robustly synergistic with calcineurin antagonists, and, either alone or in combination with cyclosporin, produces no adverse effects in rodents preconditioned to be at heightened risk for nephrotoxicity, bone marrow suppression, or altered lipid metabolism.

Immunosuppression by the JAK3 Inhibitor CP-690,550 Delays Rejection and Significantly Prolongs Kidney Allograft Survival in Nonhuman Primates

BACKGROUND

Janus kinase 3 (JAK3) mediates signal transduction from cytokine receptors using the common chain (gammac). Because mutations in genes encoding gammac or JAK3 result in immunodeficiency, we investigated the potential of a rationally designed inhibitor of JAK3, CP-690,550, to prevent renal allograft rejection in nonhuman primates.

METHODS

Life-supporting kidney transplantations were performed between mixed leukocyte reaction-mismatched, ABO blood group-matched cynomolgus monkeys. Animals were treated with CP-690,550 (n = 18) or its vehicle (controls, n = 3) and were euthanized at day 90 or earlier if there was allograft rejection.

RESULTS

Mean survival time (+/- standard error of mean) in animals treated with CP-690,550 (53 +/- 7 days) was significantly longer than in control animals (7 +/- 1 days, P=0.0003) and was positively correlated with exposure to the drug (r = 0.79, P < 0.01). Four treated animals were euthanized at 90 days with a normal renal function and low-grade rejection at final pathology. Occurrence of rejection was significantly delayed in treated animals (46 +/- 7 days from transplantation vs. 7 +/- 1 days in controls, P = 0.0003). Persistent anemia, polyoma virus-like nephritis (n = 2), and urinary calcium carbonate accretions (n = 3) were seen in animals with high exposure. Natural killer cell and CD4 and CD8 T-cell numbers were significantly reduced in treated animals. Blood glucose, serum lipid levels, and arterial blood pressure were within normal range in treated animals, and no cancers were demonstrated.

CONCLUSIONS

CP-690,550 is the first reported JAK3 inhibitor combining efficacy and good tolerability in a preclinical model of allotransplantation in nonhuman primates and thus has interesting potential for immunosuppression in humans.

Janus kinase-3 (JAK3) inhibition: a novel immunosuppressive option for allogeneic transplantation

Current immunosuppressive therapy in clinical organ transplantation is based on drugs that suppress various functions of immunocompetent cells but still affect cells and organ compartments other than the immune system. Hence, these drugs have considerable side effects which lead to increased morbidity and reduced life-quality of transplant recipients. A major step forward in the rationale design of clinical immunosuppression resides in the elucidation of molecular targets that play a critical role specifically within the immune system. Recently, Janus kinase 3 (JAK3) has been identified as such a molecule. Genetic absence or ablation of this tyrosine kinase is associated with defective T-cell immunity that results in severe combined immunodeficiency (SCID) without apparent changes in other organ systems. Furthermore, pharmacological inhibition has significantly prolonged allograft survival in several experimental models of organ transplantation. The present review provides an overview of the emerging role of JAK3 in the immune system and the development of JAK3-inhibiting drugs. The potential clinical application of JAK3 inhibitors in organ transplantations is discussed in the light of a recent series of successful kidney transplantations in non-human primates immunosuppressed solely with a novel JAK3 inhibitor.

Inhibitors of JAKs/STATs and the kinases: a possible new cluster of drugs

JAK(s)/STAT(s) relay cytokine signals through tyrosine site-specific phosphorylation of the proteins involved in cellular responses for the activation and proliferation of bone marrow-derived cells. In recent years, the constitutive or elevated expression of JAK/STAT has been found in cancer cells and oncogene transfected cells, and has been shown to be involved in the immune rejection of allografts and the inflammatory processes of autoimmune diseases. This review discusses the strategies for screening and rational design of selective, potent JAK/STAT and kinase inhibitors that are either ATP-competitive or non-ATP competitive, naturally derived or synthetic, as well as other unique inhibitors and analogues for different therapeutic indications.

Specific inhibition of Stat5a/b promotes apoptosis of IL-2-responsive primary and tumor-derived lymphoid cells

Stat5a/b exhibits 96% homology and are required for normal immune function. The present studies examined Stat5a/b function in lymphoid cells by specific and simultaneous disruption of both proteins using novel phosphorothioate-2'-O-methoxyethyl antisense oligodeoxynucleotides (asODN). Efficient delivery was confirmed by the presence of fluorescent TAMRA-labeled ODN in >or=55 and 95% in human primary and tumor cell lines, respectively. Acute asODN administration reduced levels of Stat5a (90%) in 6 h, whereas Stat5b required nearly 48 h to attain the same inhibition, suggesting that the apparent turnover rate for Stat5a was 8-fold higher than that for Stat5b. Expression of the closely related Stat3 protein was unchanged after asODN treatment, however. Molecular ablation of Stat5a/b promoted apoptotic cell death in a significant population of primary PHA-activated T cells (72%) and lymphoid tumor cell line (e.g., YT; 74%) within 24 h, as assessed by 1) visualization of karyolytic nuclear degeneration and other generalized cytoarchitectural alterations, 2) enzymatic detection of TdT-positive DNA degradation, and 3) automated cytometric detection of annexin V translocation. Contrary to findings from Stat5a/b-null mice, cell cycle progression did not appear to be significantly affected. Interestingly, IL-2-insensitive and unprimed T cells and Jurkat cells remained mostly unaffected. Finally, evidence is provided that the cytotoxicity associated with Stat5a/b ablation may derive from activation of caspase-8, an initiator protease that contributes to apoptotic cell commitment. We propose that in lymphoid cells competent to activate Stat5a and Stat5b, both proteins preferentially mediate an antiapoptotic survival influence.

The novel JAK-3 inhibitor CP-690550 is a potent immunosuppressive agent in various murine models

JAK-3 has been shown to play a key role in cytokine signaling via gammac, e.g. IL-2, 4, 7, 9, 15, 21. The current study describes the immunosuppressive effects of CP-690550, a novel, small molecule inhibitor of JAK-3, in various murine models. In vitro, CP-690550 effectively inhibited a murine mixed lymphocyte reaction (MLR) (IC50= 91 nm). Mice chronically dosed with CP-690550 (1.5-15 mg/kg/day) demonstrated dose- and time-dependent alterations in lymphocyte subsets when examined by flow cytometry. The most dramatic change observed was a 96% reduction in splenic NK1.1 + TCRbeta- cell numbers following 21 days of treatment. Delayed-type hypersensitivity (DTH) responses in sensitized mice were reduced in a dose-dependent manner following treatment with the JAK-3 inhibitor (1.87-30 mg/kg, s.c.). Extended survival of neonatal Balb/c hearts implanted into the ear pinna of MHC mismatched C3H/HEN mice was observed with CP-690550 monotherapy (10-30 mg/kg/day), but improved upon combination with cyclosporin (10 mg/kg/day). These data support the participation of JAK-3 in various lymphocyte homeostatic functions in mature mice. Furthermore, the ability of CP-690550 to extend cardiac allograft survival in murine models suggests it may afford a new treatment for prevention of transplant rejection.

Prevention of CD40-triggered dendritic cell maturation and induction of T-cell hyporeactivity by targeting of Janus kinase 3

Pharmacological targeting of Janus kinase 3 (JAK3) has been employed successfully to control allograft rejection and graft-vs.-host disease (GVHD). Recent evidence suggests that in addition to its involvement in common-gamma chain (cgamma) signaling of cytokine receptors, JAK3 is also engaged in the CD40 signaling pathway of peripheral blood monocytes. In this study, we assessed the consequences of JAK3 inhibition during CD40-induced maturation of myeloid dendritic cells (DCs), and tested the impact thereof on the induction of T-cell alloreactivity. Dendritic cells triggering through CD40 induced JAK3 activity, the expression of costimulatory molecules, production of IL-12, and potent allogeneic stimulatory capacity. In contrast, JAK3 inhibition with the rationally designed JAK3 inhibitor WHI-P-154 prevented these effects arresting the DCs at an immature level. Interestingly, DCs exposed to the JAK3-inhibitor during CD40-ligation induced a state of hyporeactivity in alloreactive T cells that was reversible upon exogenous IL-2 supplementation to secondary cultures. These results suggest that immunosuppressive therapies targeting the tyrosine kinase JAK3 may also affect the function of myeloid cells. This property of JAK3 inhibitors therefore represents a further level of interference, which together with the well-established suppression of cgamma signaling could be responsible for their clinical efficacy.

The prodigiosins, proapoptotic drugs with anticancer properties

The family of natural red pigments, called prodigiosins (PGs), characterised by a common pyrrolylpyrromethene skeleton, are produced by various bacteria. Some members have immunosuppressive properties and apoptotic effects in vitro and they have also displayed antitumour activity in vivo. Understanding the mechanism of action of PGs is essential for drug development and will require the identification and characterisation of their still unidentified cell target. Four possible mechanisms of action have been suggested for these molecules: (i) PGs as pH modulators; (ii) PGs as cell cycle inhibitors; (iii) PGs as DNA cleavage agents; (iv) PGs as mitogen-activated protein kinase regulators. Here, we review the pharmacological activity of PG and related compounds, including novel synthetic PG derivatives with lower toxicity and discuss the mechanisms of action and the molecular targets of those molecules. The results reported in this review suggest that PGs are a new class of anticancer drugs, which hold out considerable promise for the Pharmacological Industry.

Recent developments in the biology and therapy of T-cell and natural killer-cell lymphomas

PURPOSE OF REVIEW

T-cell/natural killer (T/NK)-cell lymphomas represent a group of poor-risk lymphoproliferative disorders that have only recently been recognized as distinct clinicopathologic entities. The average outcome with currently available therapy is substantially inferior to that of aggressive B-cell lymphomas. Significant gaps remain in our knowledge of their origin, diagnosis, and clinical spectrum. This review outlines recent developments in the biology and molecular genetics of these disorders, current diagnostic challenges, and future avenues for therapy.

RECENT FINDINGS

Several cancer-prone transgenic mouse models that develop predominantly T/NK-cell lymphomas have been produced in the past 2 to 3 years. These models point to an important role for chronic cytokine stimulation and for disruption of genes involved in the control of chromatin remodeling and maintenance of genome integrity in the pathogenesis of T-cell lymphomas. The recognition of T/NK-cell lymphomas has been greatly facilitated by the broad acceptance of standard diagnostic criteria and by the increasing availability of assays for the analysis of T-cell receptor rearrangement and a more precise definition of functional T/NK-cell subsets. New drugs with potential for use in T/NK-cell lymphomas, including monoclonal antibodies, tyrosine kinase inhibitors, synthetic retinoids, immunoconjugates, and immunosuppressive molecules with novel mechanisms of action are in the early phase of clinical investigation.

SUMMARY

Much remains to be learned in the pathogenesis, clinical spectrum, and optimal therapy of T/NK-cell lymphomas. The availability of animal models of disease, new diagnostic tools, and targeted drugs with novel mechanisms of action should lead to rapid progress in this group of malignancies in the near future.

Synergistic immunosuppressive effects of rosmarinic acid and rapamycin in vitro and in vivo

BACKGROUND

We previously demonstrated that rosmarinic acid (RosA) inhibits T-cell antigen receptor-induced T-cell activation and proliferation. In this study, we evaluated the ability of RosA alone and in conjunction with currently used immunosuppressive drugs to inhibit in vitro splenic T-cell proliferation and prolong skin graft survival in vivo.

METHODS

Mouse splenic T-cell proliferation assays were performed in the presence of RosA alone or in combination with cyclosporine, rapamycin (Rapa), or prednisone (Pred). The in vivo synergistic efficacy of RosA and Rapa was evaluated in the mouse skin allograft model.

RESULTS

RosA combined with Rapa or prednisone synergistically inhibited splenic T-cell proliferation, whereas the combination of RosA and cyclosporine additively inhibited T-cell proliferation. The combination of RosA and Rapa synergistically prolonged allograft survival.

CONCLUSIONS

We conclude that the combination of RosA and Rapa promotes immunosuppressive effects.

Molecular actions of sirolimus: sirolimus and mTor

Recent therapeutic strategies to combat organ allograft rejection have focused on T-cell signaling pathways and the molecules that comprise them. The macrolide antibiotic produced by the bacterium Streptomyces hygroscopicus, known as sirolimus or rapamycin, has shown great therapeutic potential in the transplant setting. Sirolimus alone or in combination with other immunosuppressive agents can block acute rejection, chronic graft destruction, and promote permanent allograft acceptance. Sirolimus targets a unique serine-threonine kinase, mammalian target of rapamycin (mTor), which plays a key role in mitogenic and nutritional cells signals. Within T cells, mTor regulates a number of proteins likely dependent on T cell growth factors such as interleukin 2. This review is focused on the molecular mechanisms by which mTor may regulate T-cell signaling cascades and affect T-cell responsiveness, and how sirolimus likely uncouples this activity.

Prodigiosin induces apoptosis of B and T cells from B-cell chronic lymphocytic leukemia

We have previously reported that prodigiosin (2-methyl-3-pentyl-6-methoxyprodigiosene) induces apoptosis in human hematopoietic cancer cell lines with no marked toxicity in nonmalignant cell lines. In this study, we demonstrate that prodigiosin induces apoptosis of B-cell chronic lymphocytic leukemia (B-CLL) cells (n=32 patients). The dose-response for the cytotoxic effect of prodigiosin was analyzed in cells from 12 patients showing an IC(50) of 116+/-25 nM. Prodigiosin induced apoptosis of B-CLL cells through caspase activation. We also analyzed the cytotoxic effect of prodigiosin in T cells from B-CLL samples and no differences were observed with respect to leukemia cells. This is the first report showing that prodigiosin induces apoptosis in human primary cancer cells.

Zinc and copper complexes of prodigiosin: implications for copper-mediated double-strand DNA cleavage

[reaction: see text] Zinc(II) and copper(II) complexes of prodigiosin (1) have been characterized. All N-atoms of 1 bind Cu(II) to generate 5: the complex exhibits regiospecific oxidation of the C-pyrrole. In contrast, coordination by Zn(II) to 1 produces Zn(1)(2) (8), a 4-coordinate tetrahedral complex. The influence of these binding geometries on Cu-mediated double-strand (ds) DNA cleavage by 1 is discussed.

BE-18591 as a new H(+)/Cl(-) symport ionophore that inhibits immunoproliferation and gastritis

In our previous papers [e.g. Sato et al., J. Biol. Chem. 273 (1998) 21455-21462], we have shown that prodigiosins can uncouple various H(+)-ATPases through their H(+)/Cl(-) symport activity. BE-18591 is an enamine of 4-methoxy-2,2'-bipyrrole-5-carboxyaldehyde (tambjamine group antibiotics) which resembles the prodigiosins. We found that BE-18591 was a new group of antibiotics that uncouples various H(+)-ATPases: it inhibited proton pump activities with IC(50)s of about 1-2 nM (about 20 pmol/mg protein) for submitochondrial particles as well as gastric vesicles and of 230 nM (about 230 pmol/mg protein) for lysosomes, but it had little effect on their ATP hydrolyses (up to 10 microM), a property of H(+)/Cl(-) symport activity. At low concentrations (<1 microM), BE-18591 inhibited immunoproliferation, the IC(50) of lipopolysaccharide-stimulated mouse splenocytes was 38 nM, that of Concanavalin A-stimulated cells was 230 nM. Gastritis of rabbits was also inhibited. At higher concentrations (>1 microM), BE-18591 induced neurite outgrowth (15% induction in 48 h at 4 microM), inhibited bone resorption (approximately 35% in 48 h at 10 microM) and caused cell death (approximately 30% in 48 h at 4 microM) but with little apoptosis.