The Use of Tyrosine Kinase Inhibitors in Modifying the Response of Tumor Microvasculature to Radiotherapy

Current research progress in targeted anti-angiogenesis therapy for osteosarcoma

Osteosarcoma (OS) is the most common primary malignant bone tumour with a peak in incidence during adolescence. Delayed patient presentation and diagnosis is common with approximately 15% of OS patients presenting with metastatic disease at initial diagnosis. With the introduction of neoadjuvant chemotherapy in the 1970s, disease prognosis improved from 17% to 60%-70% 5-year survival, but outcomes have not significantly improved since then. Novel and innovative therapeutic strategies are urgently needed as an adjunct to conventional treatment modalities to improve outcomes for OS patients. Angiogenesis is crucial for tumour growth, metastasis and invasion, and its prevention will ultimately inhibit tumour growth and metastasis. Dysregulation of angiogenesis in bone microenvironment involving osteoblasts and osteoclasts might contribute to OS development. This review summarizes existing knowledge regarding pre-clinical and developmental research of targeted anti-angiogenic therapy for OS with the aim of highlighting the limitations associated with this application. Targeted anti-angiogenic therapies include monoclonal antibody to VEGF (bevacizumab), tyrosine kinase inhibitors (Sorafenib, Apatinib, Pazopanib and Regorafenib) and human recombinant endostatin (Endostar). However, considering the safety and efficacy of these targeted anti-angiogenesis therapies in clinical trials cannot be guaranteed at this point, further research is needed to completely understand and characterize targeted anti-angiogenesis therapy in OS.

Famitinib enhances nasopharyngeal cancer cell radiosensitivity by attenuating radiation-induced phosphorylation of platelet-derived growth factor receptor and c-kit and inhibiting microvessel formation

PURPOSE

Famitinib is a novel tyrosine kinase inhibitor. We investigated the effects of famitinib on the radiosensitivity of human nasopharyngeal carcinoma (NPC) cell radiosensitivity in vitro and in vivo, and explored its possible mechanisms.

MATERIALS AND METHODS

Human nasopharyngeal carcinoma cell line (CNE-2) were treated with famitinib and radiation, and analyzed by3-(4,5-dimethylthaizol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), clonogenic survival assay, and Western blot. A xenograft model using CNE-2 cells was established to analyze the effects of famitinib and radiation on tumor volume and microvessel density (MVD).

RESULTS

Famitinib dose-dependently inhibited CNE-2 cells growth and significantly reduced clonogenic survival (p < 0.05), with a sensitivity enhancement ratio (SER) of 1.45. The tumor inhibition rate of the combined treatment group was 91%, which was significantly higher than the radiation group (35%, p < 0.05) and famitinib group (46%, p < 0.05). Famitinib attenuated radiation-induced phosphorylation of the platelet-derived growth factor receptor (PDGFR) and stem cell factor (c-kit) at 0, 30, 60 min after radiation treatment. Furthermore, radiation combined with famitinib decreased tumor MVD (p < 0.05).

CONCLUSIONS

Famitinib significantly increased CNE-2 cell radiosensitivity in vitro and in vivo by attenuating radiation-induced PDGFR and c-kit phosphorylation and by inhibiting microvessel formation.

Anti-angiogenic activity of Herba Epimedii on zebrafish embryos in vivo and HUVECs in vitro

Herba Epimedii, an herb commonly used in East Asian medicine, is commonly used for treatment of impotence, osteoporosis and many inflammatory conditions in traditional Chinese medicine. Recent studies revealed that Herba Epimedii also has anti-tumor or anti-cancer activities, which may possibly be mediated through anti-angiogenesis. This study aims to examine and confirm the anti-angiogenic activity in the herb using both in vivo and in vitro approaches. The 95% ethanol extract and four subsequent fractions (n-hexane, ethyl acetate (EA), n-butanol and aqueous fractions) of Herba Epimedii were tested on the zebrafish model by the quantitative assay for endogenous alkaline phosphatase; then, the active fraction was further tested on Tg(fli1a:EGFP)y1 zebrafish embryos and human umbilical vein endothelial cells (HUVECs) for the anti-angiogenic effects. In addition, the action mechanism of Herba Epimedii was further investigated on wild-type zebrafish embryos and HUVECs. The EA fraction showed anti-angiogenic effects in both in vivo and in vitro models. Further experiments demonstrated that it might affect angiogenesis by acting on multiple molecular targets in zebrafish embryos and ERK signaling pathway in HUVECs. In conclusion, Herba Epimedii can inhibit angiogenesis, which may be the mechanism for its anti-inflammatory, anti-tumor and anti-cancer actions.

5-Formylhonokiol exerts anti-angiogenesis activity via inactivating the ERK signaling pathway

Our previous report has demonstrated that 5-formylhonokiol (FH), a derivative of honokiol (HK), exerts more potent anti-proliferative activities than honokiol in several tumor cell lines. In present study, we first explored the antiangiogenic activities of 5-formylhonokiol on proliferation, migration and tube formation of human umbilical vein endothelial cells (HUVECs) for the first time in vitro. Then we investigated the in vivo antiangiogenic effect of 5-formylhonokiol on zebrafish angiogenesis model. In order to clarify the underlying molecular mechanism of 5-formylhonokiol, we investigated the signaling pathway involved in controlling the angiogenesis process by western blotting assay. Wound-healing results showed that 5-formylhonokiol significantly and dose-dependently inhibited migration of cultured human umbilical vein enthothelial cells. The invasiveness of HUVEC cells was also effectively suppressed at a low concentration of 5-formylhonokiol in the transwell assay. Further F-actin imaging revealed that inhibitory effect of 5-formylhonokiol on invasion may partly contribute to the disruption of assembling stress fiber. Tube formation assay, which is associated with endothelial cells migration, further confirmed the anti-angiogenesis effect of 5-formylhonokiol. In in vivo zebrafish angiogenesis model, we found that 5-formylhonokiol dose-dependently inhibited angiogenesis. Furthermore, western blotting showed that 5-formylhonokiol significantly down-regulated extracellular signal-regulated kinase (ERK) expression and inhibited the phosphorylation of ERK but not affecting the total protein kinase B (Akt) expression and related phosphorylation, suggesting that 5-formylhonokiol might exert anti-angiogenesis capacity via down-regulation of the ERK signal pathway. Taken together, these data suggested that 5-formylhonokiol might be a viable drug candidate in antiangiogenesis and anticancer therapies.

Thymoquinone inhibits tumor angiogenesis and tumor growth through suppressing AKT and extracellular signal-regulated kinase signaling pathways

Thymoquinone, a component derived from the medial plant Nigella sativa, has been used for medical purposes for more than 2,000 years. Recent studies reported that thymoquinone exhibited inhibitory effects on cell proliferation of many cancer cell lines and hormone-refractory prostate cancer by suppressing androgen receptor and E2F-1. Whether thymoquinone inhibits tumor angiogenesis, the critical step of tumor growth and metastasis, is still unknown. In this study, we found that thymoquinone effectively inhibited human umbilical vein endothelial cell migration, invasion, and tube formation. Thymoquinone inhibited cell proliferation and suppressed the activation of AKT and extracellular signal-regulated kinase. Thymoquinone blocked angiogenesis in vitro and in vivo, prevented tumor angiogenesis in a xenograft human prostate cancer (PC3) model in mouse, and inhibited human prostate tumor growth at low dosage with almost no chemotoxic side effects. Furthermore, we observed that endothelial cells were more sensitive to thymoquinone-induced cell apoptosis, cell proliferation, and migration inhibition compared with PC3 cancer cells. Thymoquinone inhibited vascular endothelial growth factor-induced extracellular signal-regulated kinase activation but showed no inhibitory effects on vascular endothelial growth factor receptor 2 activation. Overall, our results indicate that thymoquinone inhibits tumor angiogenesis and tumor growth and could be used as a potential drug candidate for cancer therapy.

Bone marrow X kinase-mediated signal transduction in irradiated vascular endothelium

Radiation-induced activation of the phosphatidyl inositol-3 kinase/Akt signal transduction pathway requires Akt binding to phosphatidyl-inositol phosphates (PIP) on the cell membrane. The tyrosine kinase bone marrow X kinase (Bmx) binds to membrane-associated PIPs in a manner similar to Akt. Because Bmx is involved in cell growth and survival pathways, it could contribute to the radiation response within the vascular endothelium. We therefore studied Bmx signaling within the vascular endothelium. Bmx was activated rapidly in response to clinically relevant doses of ionizing radiation. Bmx inhibition enhanced the efficacy of radiotherapy in endothelial cells as well as tumor vascular endothelium in lung cancer tumors in mice. Retroviral shRNA knockdown of Bmx protein enhanced human umbilical vascular endothelial cell (HUVEC) radiosensitization. Furthermore, pretreatment of HUVEC with a pharmacologic inhibitor of Bmx, LFM-A13, produced significant radiosensitization of endothelial cells as measured by clonogenic survival analysis and apoptosis as well as functional assays including cell migration and tubule formation. In vivo, LFM-A13, when combined with radiation, resulted in significant tumor microvascular destruction as well as enhanced tumor growth delay. Bmx therefore represents a molecular target for the development of novel radiosensitizing agents.

Autophagy upregulation by inhibitors of caspase-3 and mTOR enhances radiotherapy in a mouse model of lung cancer

Autophagy has been reported to be increased in irradiated cancer cells resistant to various apoptotic stimuli. We therefore hypothesized that induction of autophagy via mTOR inhibition could enhance radiosensitization in apoptosis-inhibited H460 lung cancer cells in vitro and in a lung cancer xenograft model. To test this hypothesis, combinations of Z-DEVD (caspase-3 inhibitor), RAD001 (mTOR inhibitor) and irradiation were tested in cell and mouse models. The combination of Z-DEVD and RAD001 more potently radiosensitized H460 cells than individual treatment alone. The enhancement in radiation response was not only evident in clonogenic survival assays, but also was demonstrated through markedly reduced tumor growth, cellular proliferation (Ki67 staining), apoptosis (TUNEL staining) and angiogenesis (vWF staining) in vivo. Additionally, upregulation of autophagy as measured by increased GFP-LC3-tagged autophagosome formation accompanied the noted radiosensitization in vitro and in vivo. The greatest induction of autophagy and associated radiation toxicity was exhibited in the tri-modality treatment group. Autophagy marker, LC-3-II, was reduced by 3-methyladenine (3-MA), a known inhibitor of autophagy, but further increased by the addition of lysosomal protease inhibitors (pepstatin A and E64d), demonstrating that there is autophagic induction through type III PI3 kinase during the combined therapy. Knocking down of ATG5 and beclin-1, two essential autophagic molecules, resulted in radiation resistance of lung cancer cells. Our report suggests that combined inhibition of apoptosis and mTOR during radiotherapy is a potential therapeutic strategy to enhance radiation therapy in patients with non-small cell lung cancer.

HIV protease inhibitors enhance the efficacy of irradiation

Tumor vascular endothelium is rather resistant to the cytotoxic effects of radiation. The HIV protease inhibitors (HPI) amprenavir, nelfinavir, and saquinavir have previously been shown to sensitize tumor cells to the cytotoxic effects of radiation. Additionally, this class of drug has been shown to inhibit angiogenesis and tumor cell migration. Therefore, in the current study, we wanted to determine whether HPIs could enhance the effect of radiation on endothelial function. Our study shows that HPIs, particularly nelfinavir, significantly enhance radiations effect on human umbilical vein endothelial cells (HUVEC) and tumor vascular endothelium. We show that pretreatment of HUVEC with nelfinavir results in enhanced cytotoxicity, including increased apoptosis, when combined with radiation. Moreover, using several functional assays, we show that combination treatment effectively blocks endothelial cell migration and organization. These findings were accompanied by attenuation of Akt phosphorylation, a known pathway for radioresistance. Last, in vivo analysis of tumor microvasculature destruction showed a more than additive effect for nelfinavir and radiation. This study shows that HPIs can enhance the effect of ionizing radiation on vascular endothelium. Therefore, the Food and Drug Administration-approved drug, nelfinavir, may be an effective radiosensitizer in the clinic.

Angiogenesis in colorectal cancer: prognostic and therapeutic implications

Angiogenesis is important for tumor growth and metastasis. This account reviews the clinicopathological studies conducted in the field of angiogenesis in colorectal cancer, the methods of assessing vascular-related characteristics in tissue sections and provides a background for the usefulness of antiangiogenic policies along with chemotherapy and radiotherapy. Highly angiogenic colorectal tumors are associated with aggressive histopathological features and poor patients' survival. Similarly, factors stimulating angiogenesis, such as vascular endothelial growth factor (VEGF), thymidine phosphorylase (TP), and others, are commonly related to increased vascular density (VD) and, therefore, to an unfavorable clinical course. Anti-VEGF agents have improved prognosis in patients with metastatic colorectal cancer, when added to standard chemotherapy. It is expected that, in addition to adjuvant chemotherapy and radiotherapy, agents blocking the stimulatory effect of VEGF on endothelial cells would prove beneficial to the patient.