"BIOLOGICAL CHARACTERIZATION OF ADENOSINE RECEPTOR LIGANDS AND THEIR POTENTIAL AS ANTITUMOR AGENTS"

Adenosine receptors (ARs) regulate tumors and their microenvironment in a context-dependent manner. The thesis evaluated novel subtype-selective AR ligands in brain, colorectal, and prostate tumor models using receptor assays, 2D/3D cultures, and an orthotopic glioma model. All numbered compounds were new: 4-phenylpyridine-3,5-dicarbonitriles were studied as A1AR agonists, adenine derivatives as A2AAR antagonists, nucleoside derivatives as A2AAR partial agonists, and adenosine derivatives as A3AR ligands. A1AR agonists inhibited LN229 and SNB19 glioblastoma cells at high micromolar concentrations, induced apoptosis in LN229 and delayed wound closure, whereas antagonists were inactive. A2AAR antagonist Compound 5 was broadly active in LN229, SNB19 and 1321N1 cells, retained activity in brain-tumor and colorectal spheroids, and caused stronger apoptosis than ZM241385 in HCT116 and Caco-2 models. A2AAR partial agonist Compound 6 (intrinsic activity 0.75) produced modest sustained effects on GL261 viability, cell-specific ERK/AKT responses in GL261 glioma and BV2 microglia, and altered extracellular-vesicle release. GL261 cultures accumulated approximately threefold more extracellular adenosine than BV2, supporting the conclusion that endogenous purinergic tone contributed to their divergent responses in vitro. Despite limited direct cytotoxicity, local administration reduced orthotopic GL261 tumor volume from about 4.0 to 3.1 mm3; lower-efficacy Compound 7 was inactive. In prostate spheroids, A3AR full agonist Compound 11 was most active in DU-145 and LNCaP, while antagonist Compound 10 was best in resistant PC3. Three- dimensional models revealed resistance shifts and phenotype-specific ligand rankings, identifying tumor architecture as a key selection factor. Overall, the results support phenotype/receptor/modality matching: each AR modulation strategy may be advantageous in a specific tumor context, while receptor affinity or expression alone cannot predict response.