Differential Modulation of JAK/STAT3 Signaling and BCL-2 Family Proteins by Tetracycline Analogues in Leukemia Models

Background/Objectives: Drug repurposing offers a time- and cost-efficient strategy for accelerating the development of anticancer therapies by leveraging the established safety profiles of existing pharmaceuticals. This study aimed to investigate the anticancer potential of three tetracycline analogues chemically modified tetracycline-3 (COL-3), doxycycline (DOX), and minocycline (MIN) in leukemia models, with a particular focus on their cytotoxic effects and modulation of the JAK2/STAT3 signaling pathway. Methods: Cytotoxicity was evaluated in K562, KG-1a and Jurkat cell lines using luminescence-based viability assays, whereas the mechanisms of cell death were analyzed by Annexin-V/7-AAD staining and Western blotting. Results: COL-3 displayed the highest cytotoxic potency across all cell lines, with Jurkat cells showing the greatest overall sensitivity. Flow cytometry revealed that tetracycline analogues primarily induced apoptosis, although the molecular mechanisms differed between cell lines. In K562 and KG-1a cells, apoptosis occurred largely through JAK2/STAT3-independent mechanisms, involving differential regulation of BCL-2 family proteins: COL-3 reduced BCL-2 expression, whereas DOX and MIN increased BAX expression. In contrast, Jurkat cell apoptosis correlated with suppression of phosphorylated JAK2 and STAT3 and downregulation of BCL-2, implicating a JAK2/STAT3-dependent mechanism. Conclusions: Taken together, these findings demonstrate that tetracycline analogues exert cell line-specific anticancer activities through distinct molecular pathways. Among them, COL-3 emerges as the most potent analogue and acts through both JAK/STAT-dependent and -independent mechanisms. This work supports further investigation of COL-3 as a candidate for drug repurposing strategies in hematological malignancies.