(C) VEGF release into the culture medium of A375 cells transfected for 48 hours with scramble ribonucleotides or with siRNAA2B or siRNAA3 and then cultured for 24 hours in hypoxia in the absence (Control) and in the presence of VP-16 5 = 3). production and to improve the ability of chemotherapeutic drugs to block angiogenesis. Consequently, we conclude that adenosine receptor modulation may be useful for refining the use of chemotherapeutic drugs to treat human cancer more effectively. Introduction The incidence and mortality of cutaneous melanoma are still on the rise . Overall, melanoma accounts for 1% to 3% of all malignant tumors and is increasing in incidence by 6% to 7% each year. The prognosis of metastatic melanoma remains poor. Once the metastatic phase develops, it is almost always fatal . Different therapeutic approaches for metastatic melanoma have been evaluated, including chemotherapy and LY2811376 biologic therapies, both as single treatments and in combination . To date, however, none have had a significant impact on survival. Systemic chemotherapy is still considered the mainstay of treatment of stage IV melanoma and is used largely with palliative intent . Numerous chemotherapeutic agents have shown some activity in the treatment of malignant melanoma with dacarbazine (DTIC) being the most widely used . DTIC is a nonclassical alkylating agent, generally considered the most active agent for treating malignant melanoma . However, response rates for single-agent DTIC are disappointing [5,6]. A major obstacle to a successful treatment of metastatic melanoma is its notorious resistance to chemotherapy . Chemoresistance is widely explored in cancer research, and many mechanisms have been described by which a tumor can evade cell killing in a variety of malignancies . However, the mechanisms of chemoresistance of malignant melanoma are not established. The aggressive GPX1 nature of human melanomas is related to several abnormalities in growth factors, cytokines, and their receptor expression. For example, metastatic melanoma cells constitutively secrete the cytokine interleukin-8 (IL-8), whereas nonmetastatic cells produce low to negligible levels of IL-8 [9C11]. In fact, IL-8, originally discovered as a chemotactic factor for leukocytes, may play an important role in the progression of human melanomas . Serum levels of IL-8 are elevated in patients with malignant melanoma , and several studies have demonstrated that the expression levels of this interleukin correlate with disease progression in human melanomas [12C16]. In addition to IL-8, aggressive melanoma cells secrete vascular endothelial growth factor (VEGF), which promotes angiogenesis and metastasis of human cancerous cells . Cytotoxic therapy, including radiotherapy, and other stress conditions such as hypoxia are known to induce IL-8 and VEGF release by tumor cells [18,19]. In particular, hypoxic induction of VEGF is mediated by the transcription factor hypoxia-inducible factor 1 (HIF-1), which plays a key role in regulating the adaptation of tumors to hypoxia . HIF-1 is definitely a heterodimer composed of an inducibly indicated HIF-1 subunit and a constitutively indicated HIF-1 subunit. A growing body of evidence shows that HIF-1 contributes to tumor progression and metastasis [20,21]. HIF-1 is definitely a potent activator LY2811376 of angiogenesis and invasion through its up-regulation of target genes critical for these functions . Therefore, because HIF-1 manifestation and activity seem central to tumor growth and progression, HIF-1 inhibition becomes an appropriate anticancer target . Adenosine is definitely a ubiquitous mediator implicated in numerous inflammatory processes . Accumulating evidence LY2811376 suggests that adenosine-mediated pathways are involved in cutaneous swelling and epithelial cell stress reactions. Most adenosine effects are mediated by its connection with four seven-transmembrane G protein-coupled receptor, namely, A1, A2A, A2B, and A3 LY2811376 . Recently, it has been reported that epithelial cells launch adenosine in response to numerous stimuli, including adenosine receptor agonists . Moreover, we have shown that, in addition to generating adenosine, melanoma cell lines also communicate practical adenosine receptors [25,26]. In particular, activation of A2B receptor prospects to the production and launch of calcium, VEGF, and IL-8 [27C29], whereas A3 receptor prospects to the production and launch of calcium, VEGF, and angiopoietin-2 [30C35]. Recently, we have shown that A3 receptor induces a prosurvival transmission in tumor cells . Furthermore, A3 receptor activation.