Novel drug-drug cocrystal form of Luteolin with Metformin: Improved solubility, bioavailability, and in vitro anticancer activity.

Due to the extremely low water solubility, poor oral bioavailability, and limited monotherapeutic efficacy of Luteolin (Lut), its clinical application is severely restricted. To overcome these limitations, this study successfully synthesized and characterized the pharmaceutical cocrystal (Lut-Met) with a 1:1 M ratio of Luteolin and Metformin (Met) using the ethanol slow cooling recrystallization method. Single-crystal X-ray diffraction confirmed that cocrystal Lut-Met belongs to the monoclinic crystal system (space group P21/n), in which Lut and Met are stable through intramolecular hydrogen bonds, intermolecular hydrogen bonds (e.g., Met-N4-H4B…O2-Lut), and π-π stacking interactions. Physicochemical characterization demonstrated a reduced melting point and increased hygroscopicity for the Lut-Met compared to pure Lut. Its dissolution performance in 0.2% SDS and 3% ethanol solution increased by 7.6 times and 4.8 times, respectively. The pharmacokinetic evaluation in mice revealed a 3.13-fold improvement in the relative oral bioavailability of Lut (based on AUC0-24h, p < 0.0001) after administration of the cocrystal. In vitro CCK-8 assays demonstrated that the Lut-Met cocrystal exhibits enhanced anti-tumor activity against HeLa, A549, and HepG2 cancer cell lines, as evidenced by its significantly lower IC50 values compared to both individual drugs and their physical mixture. Furthermore, in vivo distribution studies showed enhanced accumulation of Lut in tumor-related organs, including the heart, liver, spleen, and kidney, following cocrystal treatment. This study confirms that cocrystallization with Met can simultaneously enhance the solubility, bioavailability, and anticancer efficacy of Lut, offering a promising strategy for its pharmaceutical development.