CF102 an A3 Adenosine Receptor Agonist Mediates Anti-Tumor and Anti-Inflammatory Effects in the Liver

The Gi protein-associated A3 adenosine receptor (A3AR) is a member of the adenosine receptor family. The A3AR was found to be highly expressed in a broad spectrum of cancerous and inflammatory tissues, as a result of over-expression of NF-κB and additional-related transcription factors, known to be up-regulated in these pathological conditions (Poulsen and Quinn, 1998; Ochaion et al., 2009). The natural ligand adenosine induces a direct anti-proliferative effect on various tumor cell types at micromolar (μM) concentrations. Indirectly, it affects tumor development via its capability to modulate cytokine release, cell migration, angiogenesis, and chemotaxis (Woodhouse et al., 1998; Barcz et al., 2000; Madi et al., 2004). Moreover, adenosine induces activation or suppression of T killer or natural killer cells, which affects tumor cell development (Harish et al., 2003). The anti-cancer effect of adenosine is partially mediated via the A3AR and is manifested by inhibition of some inflammatory cytokines such as TNF-α, interleukin-6, and interlukin-1 (Fishman et al., 2001, 2002a,b; Cronstein, 1994; Eigler et al., 1997; Mabley et al., 2003). Selective agonists at the A3AR such as CF101 (also referred to as IB-MECA) and CF102 (also referred to as Cl-IB-MECA) inhibit the development of a variety of tumors such as melanoma, lymphoma, prostate, and colon carcinoma (Kohno et al., 1996; Fishman et al., 2003, 2004; Lu et al., 2003; Madi et al., 2003; Bar-Yehuda et al., 2005, 2007, 2008). Recently, we demonstrated that CF102 has a robust anti-cancer effect towards hepatocellular carcinoma (HCC) in an orthotopic rat model. CF102 markedly inhibited HCC growth via a molecular mechanism that entailed up-regulation of Bax, Bad, and caspase-3, resulting in tumor cell apoptosis (Bar-Yehuda et al., 2008). CF102 was also found to induce apoptosis in lung cancer cells via down-regulation of cyclin D1, c-Myc, and CDK4 and up-regulation of caspase-3 (Kim et al., 2008). The anti-inflammatory effects mediated via the A3AR were extensively reported and include the utilization of CF101, CF102, and CF502 (also referred to as MRS3558) in experimental animal models of arthritis, osteoarthritis, inflammatory bowel disease, and septic peritonitis (Mabley et al., 2003; Lee et al., 2006; Ochaion et al., 2008). The anti-inflammatory mechanism of action mediated via the A3AR involves de-regulation of the NF-κB signaling pathway and induction of apoptosis of inflammatory cells (Ochaion et al., 2008). Interestingly, the effect of A3AR agonists on normal cells is different and includes stimulation of cell proliferation, for example, murine or human bone marrow cells and fibroblasts (Fishman et al., 2000; Ohana et al., 2001). This differential effect may be explained by the high versus low A3AR expression levels in the tumor and normal cells, respectively. Furthermore, A3AR agonists are known to induce protective effects in normal body tissues and cells. These include cardio-, neuro-, and chemo-protective effects both in vitro and in vivo (Fishman et al., 2001; Black et al., 2002; Shneyvays et al., 2005; Chen et al., 2006; Ge et al., 2006; Matot et al., 2006; Xu et al., 2006). Cross et al. showed that A3AR over-expression leads to cardio-protection against ischemia/reperfusion injury preserving energy during ischemia. Moreover, transgenic mice that over-express the A3AR in cardiomyocytes demonstrate increased tolerance to ischemia/reperfusion injury (Black et al., 2002; Cross et al., 2002). This protective effect was further investigated in ischemic brain injuries in which systemic administration of CF102-reduced cerebral infarction and improved locomotor activity in a rat model of stroke (Chen et al., 2006). CF102 also induced proliferation of murine bone marrow cells via the stimulation of granulocyte colony-stimulating factor production, thus counteracting chemotherapy-induced myelotoxicity via an increase of white blood cell and neutrophil counts (Fishman et al., 2001). The aim of the present study was to examine the ability of CF102 to induce a differential effect namely, anti-cancer and protection, in two pathological conditions originating in the liver. The anti-cancer effect of CF102 was demonstrated in in vitro and in vivo HCC models and the protective effect was exhibited in a liver inflammation model induced by Con. A. Interestingly, induction of apoptosis contributed to the anti-tumor effect, whereas prevention of apoptosis conferred the protective effect of CF102. The dual and differential effects of CF102 render it as an attractive drug candidate to be developed to combat liver pathological conditions.