Optimizing pyrazine-2-carboxamide derivatives as dual FLT3/HDAC inhibitors with enhanced pharmacokinetics and immunotherapeutic potential.

Dual FLT3/HDAC inhibition represents a promising synergistic strategy to address tumor heterogeneity. Building upon our prior lead 25h, we developed novel 6-ethylpyrazine-2-carboxamide derivatives via systematic structural optimization to enhance pharmacokinetic properties and target selectivity. The optimized compound, CF-2-17, demonstrated potent dual inhibition of FLT3 (IC50 = 1.1 nmol/L) and HDACs (IC50 = 9.6 nmol/L), and exhibited a 27-fold selectivity for HDAC1 over HDAC6. Its improved physicochemical properties, including enhanced solubility and metabolic stability, translated into favorable plasma exposure in vivo. In the MOLM-13 (FLT3-ITD) xenograft model, oral administration of CF-2-17 showed antitumor efficacy comparable to combination therapy, without observable toxicity. CF-2-17 also exhibited antiproliferative activity against non-FLT3-ITD hematological malignancies and solid tumors, outperforming single-target agents. Furthermore, CF-2-17 effectively remodeled the tumor immune microenvironment through CD4+ T cell activation and IFN-γ elevation, achieving 87% tumor growth inhibition in LLC syngeneic models. Mechanistically, CF-2-17 reversed FLT3 blockade-induced DC dysfunction via activation of the NF-κB pathway, thereby reinstating DC-mediated antitumor immunity. This dual FLT3/HDAC inhibitor demonstrates synergistic epigenetic-immune modulation, offering a promising approach for heterogeneous malignancies.