br Materials and methods br Results br
Materials and methods
Discussion Cisplatin, as one member of a class of platinum-containing anti-cancer drugs, which displays a great deal of clinical activity on a wide variety of solid tumors. In addition, cisplatin often used in combination with other chemotherapy drugs to treat patients with advanced melanoma (9), (10). As we know, cisplatin exert their function mainly by inducing DNA damage, and then cell apoptosis. However, melanoma between are generally insensitive to chemotherapy or developing a resistance in a short time period (11), (12). The mechanisms for drug resistance in melanoma is most likely dysregulation of apoptosis, accumulation of agents caused by drug pumps, DNA repair up-regulation, cell signaling dysfunction (13), (14), (15), (16). Except for these pharmacologic based mechanisms, PI3K/AKT signaling activation, overexpression of HER2, p53 dysfunction could be the factors contribution to cisplatin resistance at the molecular level (17), (18), (19). In the current study, we developed a melanoma xenograft model, which resistant to cisplatin. The results of gene expression microarray showed that EphB4 overexpression but not amplification by comparing the genome-wide gene profile of the sensitive and resistant xenografts. The results of Western blot also indicated EphB4 was highly expressed in cisplatin-resistant A375 xenografts. This founding may help us to understand acquired resistance in melanoma from a new angle. The Eph (erythropoietin producing hepatocellular) family of receptors make up the largest subgroup of the receptor tyrosine kinase, which could be divided into the A- or B-type based on their interactions with Ephrin ligands (20), (21). Durg et al. reported that EphA2 is an important oncogene and potentially a common source of 'addiction' for many melanoma cells (22). Benchun et al. also mentioned that EphA2 was an important factor for vemurafenib resistance (23). However, we did not found high EphA2 gene expression in the current resistant model. Since EphA2 and EphB4 have no cross-binding to Ephrins of the opposing subclass and NVP-BHG712 was well designed and further optimization led to a potent and selective inhibitor of the EphB4 receptor tyrosine kinase, we proposed EphB4 overexpression contributed to the cisplatin resistance in the current model. Nevertheless, the relationship between EphB4 and apoptosis pathway is still unclear and needed further investigation.
Conflicts of interest
Introduction Angiogenesis plays a critical role in the pathogenesis of a variety of disorders including cancer, proliferative retinopathies, rheumatoid arthritis or psoriasis, and it has been identified as a crucial factor in metastasis, which is a major factor leading to cancer-related death . Thus, anti-angiogenesis has been considered as a valid strategy for tumor therapy, and many efforts have been focused on developing angiogenesis inhibitors. In the past decades, numbers of pro-angiogenic factors such as VEGFR-2, FGFR, PDGFR, Tie-2 and EphB4, also known as receptor tyrosine kinases (RTKs), have been identified as potential targets for angiogenesis inhibitors . However, it's a known fact that many anti-angiogenic agents have failed in clinic trails. Even though some angiogenesis inhibitors have been approved for clinical use, many problems have been occurred including resistance, enhancing hypoxia, and reducing delivery of drugs. The main reason is the compensatory activation of multiple RTKs . Meanwhile, cancer cells secrete various RTKs involved in the process of angiogenesis . Therefore, simultaneous inhibition and combinatorial targeting of multiple pro-angiogenic RTKs have been applied as valuable strategy to promote anti-angiogenesis therapy. VEGFR-2, Tie-2, EphB4, highly expressed in endothelial cells (ECs), have been indicated to play an essential role in both vasculogenesis and angiogenesis . VEGFR-2 mainly contributes to very early steps of angiogenesis including ECs survival, proliferation and migration, while TIE2 and EphB4 contribute to later step including vessel stabilization, maturation, remodeling of vasculature, and vascular development [, , , ]. Furthermore, these three RTKs have been confirmed to be significant in tumor development and prognosis . To the best of our knowledge, these three RTKs contain a high conserved catalytic site binding with ATP, and their catalytic domains and ATP-binding site are quite similar [11,12]. Overlay of crystal structures of the three RTKs is depicted in Fig. 1, which shows no significant difference among each other with RMSD value 0.849 Å, 0.725 Å and 0.706 Å respectively. Therefore, VEGFR-2, TIE-2 and EphB4 are chose as targets for developing multi-targeted anti-angiogenesis agents.