Antiproliferative effects of selective adenosine receptor agonists and antagonists on human lymphocytes: evidence for receptor-independent mechanisms

Abstract

The effects of standard adenosine receptor (AR) agonists and antagonists on the proliferation of human T lymphocytes, unstimulated and phytohemagglutininstimulated human peripheral blood lymphocytes (PBL), and Jurkat T cells were investigated. Real-time PCR measurements confirmed the presence of all four AR subtypes on the investigated cells, although at different expression levels. A 2A ARs were predominantly expressed in PBL and further upregulated upon stimulation, while malignant Jurkat T cells showed high expression levels of A 1 , A 2A , and A 2B ARs. Cell proliferation was measured by [ 3 H]-thymidine incorporation assays. Several ligands, including the subtype-selective agonists CPA (A 1 ), BAY60-6583 (A 2B ), and IB-MECA (A 3 ), and the antagonists PSB-36 (A 1 ), MSX-2 (A 2A ), and PSB-10 (A 3 ) significantly inhibited cell proliferation at micromolar concentrations, which were about three orders of magnitude higher than their AR affinities. In contrast, further investigated AR ligands, including the agonists NECA (nonselective) and CGS21680 (A 2A ), and the antagonists preladenant (SCH-420814, A 2A ), PSB-1115 (A 2B ), and PSB-603 (A 2B ) showed no or only minor effects on lymphocyte proliferation. The anti-proliferative effects of the AR agonists could not be blocked by the corresponding antagonists. The non-selective AR antagonist caffeine stimulated phytohemagglutinin-activated PBL with an EC 50 value of 104 μM. This is the first study to compare a complete set of commonly used AR ligands for all subtypes on lymphocyte proliferation. Our results strongly suggest that these compounds induce an inhibition of lymphocyte proliferation and cell death through AR-independent mechanisms.

Adenosine Inhibits Tumor Cell Invasion via Receptor-Independent Mechanisms

“…On the other hand, the overall pattern of purine homeostasis is markedly deregulated in the tumor environment by hypoxia and metabolic stress, as ascertained by data on constitutively elevated levels of intratumoral ATP (7,34), the accelerated rate of nucleotide turnover (4,9,33), and the ability of solid tumors to maintain adenosine gradient, with the highest nucleoside concentrations being reported in the center (14). Therefore, it may be speculated that besides dampening antitumor immunity, the sustained exposure of tumor cells to the elevated adenosine concurrently impairs their invasiveness (present study) and at higher micromolar concentrations also retards tumor growth and proliferation (15,21). This scenario might provide a partial explanation for the well-known phenomena of the high proliferative and invasive capacities of peripheral tumor cells located in the parenchyma and stroma, whereas the core environment of the tumor is maintained in a relatively stable, "semiquiescent," state (2).…”

“…1A, treatment of PC-3 cells with increasing concentrations of adenosine, but not inosine, guanosine, and uridine, progressively diminished their invasion through Matrigel-coated inserts with IC 50 of 0.19 AE 0.04 mmol/L. Pretreatment of PC-3 cells with a nonselective agonist of adenosine receptors NECA (21,26) diminished their invasion by approximately 40%, whereas a general A 2 receptor agonist CPCA (capable of stimulating both A 2A and A 2B adenosine receptors; ref. 27) did not affect the numbers of invaded cells (Fig.…”

“…18) activities, translocation of apoptosis-inducing factor AMID from the cytosol into the nucleus (19), and other mitochondrial apoptotic pathways (15). Likewise, high concentrations of adenosine receptor agonists, antagonists, and other nucleoside analogues also trigger antiproliferative and cytotoxic effects on normal and leukemic cells via receptor-independent mechanisms (3,20,21), presumably acting as antimetabolites competing with natural nucleosides and inhibiting key enzymes of purine homeostasis.…”

Upregulation of P2Y2 nucleotide receptor in human hepatocellular carcinoma cells

“…Therefore, therapeutic agents targeting P2Y2 levels or its enzymatic activity may be effective for treating HCC. 47 – 49 Furthermore, these current results showed that knockdown of P2Y2 using siRNA decreased the viability of HepG2 cells when cultured under hypoxic conditions. Immunohistochemical analysis showed that P2Y2 was overexpressed in 43 out of 68 patients (63.2%) with HCC, suggesting that P2Y2 plays an important role in the tumorigenesis of HCC and its resistance to anticancer therapies.…”

Nigella Sativa’nın Biyoaktif Komponenti Olan Timokinon Ovalbuminle Uyarılmış Ginedomuzlarında Adenozin A2 Reseptörlerini Etkileyebilir

“…Although the administration of this antagonist suppresses the anti-inflammatory effect of A 2A receptors on the cell surface, but results of A 2A receptor mRNA expression were controversial. Nowadays it is accepted that the level of mRNA expression does not correlate exactly with proteins expressed on the cell surface because of some epigenetic factors [36] .…”