Impact of COX-2 inhibition by DuP-697 on cyclin B1/Cdc2 dynamics in human medullary thyroid carcinoma cells.

BACKGROUND: Cyclooxygenase-2 (COX-2) and its product prostaglandin E₂ (PGE₂) are key mediators of parafollicular cell proliferation and calcitonin secretion in medullary thyroid carcinoma (MTC). Although COX-2 inhibitors exhibit anti-proliferative effects, the molecular mechanisms underlying their influence on cell-cycle regulation remain unclear.

OBJECTIVE: This study explored the effects of the selective COX-2 inhibitor DuP-697 on proteins associated with G₂/M regulatory signaling in human medullary thyroid carcinoma TT cells.

METHODS: TT cells were treated with DuP-697 (40-160 nM) for 3-72 h. Immunofluorescence analyses were performed to quantify cyclin B1, phosphorylated Cdc2 (Tyr15), Myt1, phosphorylated Wee1, p21, and phosphorylated histone H3.

RESULTS: DuP-697 induced time-dependent alterations in multiple proteins associated with G₂/M regulation. Early exposure (3-24 h) was associated with increased cyclin B1 and phosphorylated Cdc2, accompanied by transient elevation of phosphorylated histone H3. With prolonged treatment (48-72 h), phosphorylated histone H3 levels declined, while Myt1 expression remained persistently elevated and phosphorylation of Wee1 displayed dynamic modulation. In parallel, p21 expression was selectively reduced at intermediate and late time points. These coordinated changes suggest a shift in the balance of G₂/M-associated regulatory signals over time.

CONCLUSION: Taken together, these findings indicate that DuP-697 is associated with time-dependent modulation of proteins involved in G₂/M regulatory signaling in TT cells. Rather than providing direct evidence of cell-cycle arrest, the results support an exploratory model in which COX-2 inhibitor exposure is accompanied by dynamic reorganization of mitotic and checkpoint-related regulatory components. Further functional studies, including direct assessment of cell-cycle distribution and mitotic progression, are required to clarify the biological consequences of these regulatory changes.