JAK2 tyrosine kinase inhibitor AG490 suppresses cell growth and invasion of gallbladder cancer cells via inhibition of JAK2/STAT3 signaling

The Janus kinase-signal transducers and activators of transcription signaling pathway (JAK/STAT pathway) have displayed a critical role in tumor development and progression in multiple malignancies. Previous studies showed that inhibition of JAK/STAT signaling blocked cell growth and metastasis in cancer cells, however, the antitumor effects of JAK inhibitor AG490 on gallbladder cancer (GBC) have not been reported. Our present study aimed to investigate the effects and associated mechanisms of JAK inhibitor AG490 on cell growth, invasive potential and apoptosis in GBC cells (GBC-SD and SGC-996) indicated by MTT, cell colony formation, Transwell and flow cytometry. As a consequence, we found that JAK2 inhibitor AG490 inhibited cell growth and invasion, and induced cell apoptosis and cycle arrest in GBC-SD and SGC-996 cells. Furthermore, the expression levels of p-JAK2, p-STAT3, VEGFC-/-D and cyclinD1 were downregulated, while p53 expression was upregulated in AG490-treated GBC cells indicated by Western blot assay. Therefore, our findings demonstrate that JAK inhibitor AG490 inhibits growth and invasion of GBC cells via blockade of JAK2/STAT3 signaling and provides the potential therapeutic strategy for the treatment of GBC patients.

Liposomal honokiol inhibits VEGF-D-induced lymphangiogenesis and metastasis in xenograft tumor model

Lymph nodes metastasis of tumor could be a crucial early step in the metastatic process. Induction of tumor lymphangiogenesis by vascular endothelial growth factor-D may play an important role in promoting tumor metastasis to regional lymph nodes and these processes can be inhibited by inactivation of the VEGFR-3 signaling pathway. Honokiol has been reported to possess potent antiangiogenesis and antitumor properties in several cell lines and xenograft tumor models. However, its role in tumor-associated lymphangiogenesis and lymphatic metastasis remains unclear. Here, we established lymph node metastasis models by injecting overexpressing VEGF-D Lewis lung carcinoma cells into C57BL/6 mice to explore the effect of honokiol on tumor-associated lymphangiogenesis and related lymph node metastasis. The underlying mechanisms were systematically investigated in vitro and in vivo. In in vivo study, liposomal honokiol significantly inhibited the tumor-associated lymphangiogenesis and metastasis in Lewis lung carcinoma model. A remarkable delay of tumor growth and prolonged life span were also observed. In in vitro study, honokiol inhibited VEGF-D-induced survival, proliferation and tube-formation of both human umbilical vein endothelial cells (HUVECs) and lymphatic vascular endothelial cells (HLECs). Western blotting analysis showed that liposomal honokiol-inhibited Akt and MAPK phosphorylation in 2 endothelial cells, and downregulated expressions of VEGFR-2 of human vascular endothelial cells and VEGFR-3 of lymphatic endothelial cells. Thus, we identified for the first time that honokiol provided therapeutic benefit not only by direct effects on tumor cells and antiangiogenesis but also by inhibiting lymphangiogenesis and metastasis via the VEGFR-3 pathway. The present findings may be of importance to investigate the molecular mechanisms underlying the spread of cancer via the lymphatics and explore the therapeutical strategy of honokiol on antilymphangiogenesis and antimetastasis.

[Lymphangiogenesis and tumor progression]

Numerous data show a functional link between lymphangiogenesis, lymph node invasion by tumoral cells and metastasis. During the last decade, the identification of lymphatic endothelial cell-specific markers has allowed the investigation of lymphangiogenesis regulatory mechanisms and the analysis of its involvement in tumoral progression. Among regulatory systems, the growth factors VEGF-C and D, that bind and activate their common receptor VEGFR3, appear to play an important role in this process. Therapeutic strategies targeting this pathway or, in a general manner, aiming at inhibiting tumoral lymphangiogenesis are now considered to block the development of tumoral metastasis. Further fundamental and clinical studies are clearly needed to establish the pronostic value of lymphangiogenesis and to validate anti-lymphangiogenic therapies in the treatment of metastatic cancers.

Lymphangiogenic growth factor responsiveness is modulated by postnatal lymphatic vessel maturation

Lymphatic vessel plasticity and stability are of considerable importance when attempting to treat diseases associated with the lymphatic vasculature. Development of lymphatic vessels during embryogenesis is dependent on vascular endothelial growth factor (VEGF)-C but not VEGF-D. Using a recombinant adenovirus encoding a soluble form of their receptor VEGFR-3 (AdVEGFR-3-Ig), we studied lymphatic vessel dependency on VEGF-C and VEGF-D induced VEGFR-3 signaling in postnatal and adult mice. Transduction with AdVEGFR-3-Ig led to regression of lymphatic capillaries and medium-sized lymphatic vessels in mice under 2 weeks of age without affecting collecting lymphatic vessels or the blood vasculature. No effect was observed after this period. The lymphatic capillaries of neonatal mice also regressed partially in response to recombinant VEGFR-3-Ig or blocking antibodies against VEGFR-3, but not to adenovirus-encoded VEGFR-2-Ig. Despite sustained inhibitory VEGFR-3-Ig levels, lymphatic vessel regrowth was observed at 4 weeks of age. Interestingly, whereas transgenic expression of VEGF-C in the skin induced lymphatic hyperplasia even during embryogenesis, similar expression of VEGF-D resulted in lymphangiogenesis predominantly after birth. These results indicate considerable plasticity of lymphatic vessels during the early postnatal period but not thereafter, suggesting that anti-lymphangiogenic therapy can be safely applied in adults.

The lymphatic vasculature: recent progress and paradigms

The field of lymphatic research has been recently invigorated by the identification of genes and mechanisms that control various aspects of lymphatic development. We are beginning to understand how, starting from a subgroup of embryonic venous endothelial cells, the whole lymphatic system forms in a stepwise manner. The generation of genetically engineered mice with defects in different steps of the lymphangiogenic program has provided models that are increasing our understanding of the lymphatic system in health and disease. This knowledge, in turn, should lead to the development of better diagnostic methods and treatments of lymphatic disorders and tumor metastasis.

Lymphangiogenic growth factors as markers of tumor metastasis

Understanding the complex process of tumor metastasis is a problem which has challenged both clinician and scientist for well over 100 years. Defining molecular markers which reflect the metastatic potential of a tumor has also proved elusive. Recently, members of the vascular endothelial growth factor (VEGF) family of glycoproteins have been demonstrated to be potent mediators of both blood vessel and lymphatic vessel formation in the context of tumor biology. Experimental studies in animal models combined with extensive clinicopathological data provide a compelling case indicating that members of the VEGF family play a key role in the formation of metastases in a broad range of solid tumors. The question of whether VEGF signaling pathways can now serve as therapeutic targets alone, or in combination with other forms of anti-cancer agents, needs to be addressed.