Structure-function correlation of G6, a novel small molecule inhibitor of Jak2: indispensability of the stilbenoid core

Dietary Pterostilbene and Resveratrol Modulate the Gut Microbiota Influenced by Circadian Rhythm Dysregulation

SCOPE

A causal relationship between circadian misalignment and microbiota dysbiosis has been discussed recently, due to their association to pathogenesis. Herein, the possible impact of pterostilbene (PSB) and resveratrol (RES) on the gut microbiota brought by chronic jet-lag in mice is investigated.

METHODS AND RESULTS

Dietary supplement of RES and PSB (0.25%) are given to 16 week-jetlagged mice to examine the effects on microbiota and physiological functions. Jetlag significantly induces weight gained that could be effectively prevented by PSB. Both supplements also retain oscillation patterns that found to be lost in jetlag induced (JLG) group, including serum biochemical parameters and gut microbiota. The results of beta diversity suggest the supplementations efficiently lead to distinct gut microbial composition as compared to JLG group. Besides, the supplementation forestalls some microbial elevation, such as Eubacterium ventriosum and Acetitomaculum. Growth of health beneficial bacteria like Blautia and Lachnospiraceae UCG-001 is facilitated and abundance of these bacteria could be correlated to oscillation of biochemical parameters. Result of KEGG indicates distinct effect brought by microbial re-shaping.

CONCLUSION

The result suggests that supplementation of RES and PSB could potentially dampen some adverse effects of gut microbiota dysbiosis, and at the same time, re-composite and facilitate the growth of health beneficial microbiota.

The Jak2 small molecule inhibitor, G6, reduces the tumorigenic potential of T98G glioblastoma cells in vitro and in vivo

Glioblastoma multiforme (GBM) is the most common and the most aggressive form of primary brain tumor. Jak2 is a non-receptor tyrosine kinase that is involved in proliferative signaling through its association with various cell surface receptors. Hyperactive Jak2 signaling has been implicated in numerous hematological disorders as well as in various solid tumors including GBM. Our lab has developed a Jak2 small molecule inhibitor known as G6. It exhibits potent efficacy in vitro and in several in vivo models of Jak2-mediated hematological disease. Here, we hypothesized that G6 would inhibit the pathogenic growth of GBM cells expressing hyperactive Jak2. To test this, we screened several GBM cell lines and found that T98G cells express readily detectable levels of active Jak2. We found that G6 treatment of these cells reduced the phosphorylation of Jak2 and STAT3, in a dose-dependent manner. In addition, G6 treatment reduced the migratory potential, invasive potential, clonogenic growth potential, and overall viability of these cells. The effect of G6 was due to its direct suppression of Jak2 function and not via off-target kinases, as these effects were recapitulated in T98G cells that received Jak2 specific shRNA. G6 also significantly increased the levels of caspase-dependent apoptosis in T98G cells, when compared to cells that were treated with vehicle control. Lastly, when T98G cells were injected into nude mice, G6 treatment significantly reduced tumor volume and this was concomitant with significantly decreased levels of phospho-Jak2 and phospho-STAT3 within the tumors themselves. Furthermore, tumors harvested from mice that received G6 had significantly less vimentin protein levels when compared to tumors from mice that received vehicle control solution. Overall, these combined in vitro and in vivo results indicate that G6 may be a viable therapeutic option against GBM exhibiting hyperactivation of Jak2.

Elevated levels of mast cells are involved in pruritus associated with polycythemia vera in JAK2V617F transgenic mice

Pruritus occurs frequently in patients with polycythemia vera (PV), and the pathophysiology of PV-associated pruritus is unclear. We have previously demonstrated that transgenic mice expressing JAK2V617F displayed clear PV-like phenotypes. In the current study, we found frequent occurrence of pruritus with aged JAK2V617F transgenic mice and further investigated the underlying mechanisms by studying mast cells, key players in allergic reactions and anaphylaxis. Massive accumulations of mast cells were observed in the skin of pruritic JAK2V617F transgenic mice. In vitro culture yielded much higher mast cell counts from the bone marrow, spleen, peripheral blood, and peritoneal cavity of JAK2V617F transgenic mice than from controls. Cultured mast cells from JAK2V617F transgenic mice exhibited enhanced proliferative signals, relative resistance to cell death upon growth factor deprivation, and a growth advantage over control cells under suboptimal growth conditions. However, these mast cells displayed normal morphology and contained normal levels of mast cell proteases before and after degranulation. Finally, the JAK2 inhibitor G6 effectively reduced mast cell numbers and alleviated pruritus in JAK2V617F transgenic mice. Collectively, these data demonstrate that mast cells are involved in PV-associated pruritogenesis and that JAK2 inhibitors are potential antipruritus drugs.

The small molecule inhibitor G6 significantly reduces bone marrow fibrosis and the mutant burden in a mouse model of Jak2-mediated myelofibrosis

Philadelphia chromosome-negative myeloproliferative neoplasms, including polycythemia vera, essential thrombocytosis, and myelofibrosis, are disorders characterized by abnormal hematopoiesis. Among these myeloproliferative neoplasms, myelofibrosis has the most unfavorable prognosis. Furthermore, currently available therapies for myelofibrosis have little to no efficacy in the bone marrow and hence, are palliative. We recently developed a Janus kinase 2 (Jak2) small molecule inhibitor called G6 and found that it exhibits marked efficacy in a xenograft model of Jak2-V617F-mediated hyperplasia and a transgenic mouse model of Jak2-V617F-mediated polycythemia vera/essential thrombocytosis. However, its efficacy in Jak2-mediated myelofibrosis has not previously been examined. Here, we hypothesized that G6 would be efficacious in Jak2-V617F-mediated myelofibrosis. To test this, mice expressing the human Jak2-V617F cDNA under the control of the vav promoter were administered G6 or vehicle control solution, and efficacy was determined by measuring parameters within the peripheral blood, liver, spleen, and bone marrow. We found that G6 significantly reduced extramedullary hematopoiesis in the liver and splenomegaly. In the bone marrow, G6 significantly reduced pathogenic Jak/STAT signaling by 53%, megakaryocytic hyperplasia by 70%, and the Jak2 mutant burden by 68%. Furthermore, G6 significantly improved the myeloid to erythroid ratio and significantly reversed the myelofibrosis. Collectively, these results indicate that G6 is efficacious in Jak2-V617F-mediated myelofibrosis, and given its bone marrow efficacy, it may alter the natural history of this disease.

The Jak2 inhibitor, G6, alleviates Jak2-V617F-mediated myeloproliferative neoplasia by providing significant therapeutic efficacy to the bone marrow

We recently developed a Janus kinase 2 (Jak2) small-molecule inhibitor called G6 and found that it inhibits Jak2-V617F-mediated pathologic cell growth in vitro, ex vivo, and in vivo. However, its ability to inhibit Jak2-V617F-mediated myeloproliferative neoplasia, with particular emphasis in the bone marrow, has not previously been examined. Here, we investigated the efficacy of G6 in a transgenic mouse model of Jak2-V617F-mediated myeloproliferative neoplasia. We found that G6 provided therapeutic benefit to the peripheral blood as determined by elimination of leukocytosis, thrombocytosis, and erythrocytosis. G6 normalized the pathologically high plasma concentrations of interleukin 6 (IL-6). In the liver, G6 eliminated Jak2-V617F-driven extramedullary hematopoiesis. With respect to the spleen, G6 significantly reduced both the splenomegaly and megakaryocytic hyperplasia. In the critically important bone marrow, G6 normalized the pathologically high levels of phospho-Jak2 and phospho-signal transducer and activator of transcription 5 (STAT5). It significantly reduced the megakaryocytic hyperplasia in the marrow and completely normalized the M/E ratio. Most importantly, G6 selectively reduced the mutant Jak2 burden by 67%on average, with virtual elimination of mutant Jak2 cells in one third of all treated mice. Lastly, clonogenic assays using marrow stem cells from the myeloproliferative neoplasm mice revealed a time-dependent elimination of the clonogenic growth potential of these cells by G6. Collectively, these data indicate that G6 exhibits exceptional efficacy in the peripheral blood, liver, spleen, and, most importantly, in the bone marrow, thereby raising the possibility that this compound may alter the natural history of Jak2-V617F-mediated myeloproliferative neoplasia.

Identification of novel SAR properties of the Jak2 small molecule inhibitor G6: significance of the para-hydroxyl orientation

In this study, we analyzed the structure-activity relationship properties of the small molecule Jak2 inhibitor G6. We synthesized a set of derivatives containing the native para-hydroxyl structure or an alternative meta-hydroxyl structure and examined their Jak2 inhibitory properties. We found that the para-hydroxyl derivative known as NB15 had excellent Jak2 inhibitory properties in silico, in vitro, and ex vivo when compared with meta-hydroxyl derivatives. These results indicate that NB15 is a potent derivative of the Jak2 inhibitor G6, and that maintaining the para-hydroxyl orientation of G6 is critical for its Jak2 inhibitory potential.

A46, a benzothiophene-derived compound, suppresses Jak2-mediated pathologic cell growth

Hyperkinetic Jak2 tyrosine kinase signaling has been implicated in several hematological disorders, including myeloproliferative neoplasms. Effective Jak2 inhibitors can have significant therapeutic potential. Here, using structure-based virtual screening, we identified a benzothiophene-derived Jak2 inhibitor named A46. We hypothesized that this compound would inhibit Jak2-V617F-mediated pathologic cell growth. To test this, A46 was analyzed for its ability to inhibit recombinant Jak2 protein catalysis; suppress Jak2-mediated pathogenic cell growth in vitro; inhibit the aberrant ex vivo growth of Jak2-V617F-expressing primary human bone marrow cells; and inhibit Jak2-mediated pathogenesis in vivo. To this end, we found that A46 selectively inhibited Jak2-V617F protein when compared to wild-type Jak2 protein. The drug also selectively inhibited the proliferation of Jak2-V617F-expressing cells in both a time- and dose-dependent manner, and this correlated with decreased Jak2 and signal transducers and activators of transcription 5 phosphorylation within treated cells. The Jak2-V617F cell growth inhibition correlated with an induction of cell cycle arrest and promotion of apoptosis. A46 also inhibited the pathologic growth of primary Jak2-V617F-expressing bone marrow cells ex vivo. Lastly, using a mouse model of Jak2-V617F-mediated myeloproliferative neoplasia. A46 significantly reduced the splenomegaly and megakaryocytic hyperplasia in the spleens of treated mice and the levels of interleukin-6 in the plasma. Collectively, our data demonstrate that the benzothiophene-based compound, A46, suppresses Jak2-mediated pathogenesis, thereby making it a potential candidate drug against Jak2-mediated disorders.

Cell death induced by the Jak2 inhibitor, G6, correlates with cleavage of vimentin filaments

Hyperkinetic Jak2 tyrosine kinase signaling has been implicated in several human diseases including leukemia, lymphoma, myeloma, and the myeloproliferative neoplasms. Using structure-based virtual screening, we previously identified a novel Jak2 inhibitor named G6. We showed that G6 specifically inhibits Jak2 kinase activity and suppresses Jak2-mediated cellular proliferation. To elucidate the molecular and biochemical mechanisms by which G6 inhibits Jak2-mediated cellular proliferation, we treated Jak2-V617F expressing human erythroleukemia (HEL) cells for 12 h with either vehicle control or 25 μM of the drug and compared protein expression profiles using two-dimensional gel electrophoresis. One differentially expressed protein identified by electrospray mass spectroscopy was the intermediate filament protein, vimentin. It was present in DMSO treated cells but absent in G6 treated cells. HEL cells treated with G6 showed both time- and dose-dependent cleavage of vimentin as well as a marked reorganization of vimentin intermediate filaments within intact cells. In a mouse model of Jak2-V617F mediated human erythroleukemia, G6 also decreased the levels of vimentin protein, in vivo. The G6-induced cleavage of vimentin was found to be Jak2-dependent and calpain-mediated. Furthermore, we found that intracellular calcium mobilization is essential and sufficient for the cleavage of vimentin. Finally, we show that the cleavage of vimentin intermediate filaments, per se, is sufficient to reduce HEL cell viability. Collectively, these results suggest that G6-induced inhibition of Jak2-mediated pathogenic cell growth is concomitant with the disruption of intracellular vimentin filaments. As such, this work describes a novel pathway for the targeting of Jak2-mediated pathological cell growth.

The stilbenoid tyrosine kinase inhibitor, G6, suppresses Jak2-V617F-mediated human pathological cell growth in vitro and in vivo

Using structure-based virtual screening, we previously identified a novel stilbenoid inhibitor of Jak2 tyrosine kinase named G6. Here, we hypothesized that G6 suppresses Jak2-V617F-mediated human pathological cell growth in vitro and in vivo. We found that G6 inhibited proliferation of the Jak2-V617F expressing human erythroleukemia (HEL) cell line by promoting marked cell cycle arrest and inducing apoptosis. The G6-dependent increase in apoptosis levels was concomitant with increased caspase 3/7 activity and cleavage of PARP. G6 also selectively inhibited phosphorylation of STAT5, a downstream signaling target of Jak2. Using a mouse model of Jak2-V617F-mediated hyperplasia, we found that G6 significantly decreased the percentage of blast cells in the peripheral blood, reduced splenomegaly, and corrected a pathologically low myeloid to erythroid ratio in the bone marrow by eliminating HEL cell engraftment in this tissue. In addition, drug efficacy correlated with the presence of G6 in the plasma, marrow, and spleen. Collectively, these data demonstrate that the stilbenoid compound, G6, suppresses Jak2-V617F-mediated aberrant cell growth. As such, G6 may be a potential therapeutic lead candidate against Jak2-mediated, human disease.