Nanoparticles of a New Small-Molecule P-Selectin Inhibitor Attenuate Thrombosis, Inflammation, and Tumor Growth in Two Animal Models

Purpose

To assess whether the newly designed small-molecule oral P-selectin inhibitor 3S-1,2,3,4-tetrahydro-β-carboline-3-methyl aspartyl ester (THCMA) as a nanomedicine enhances antithrombosis, anti-inflammation, and antitumor activity more than the clinical trial drug PSI-697.

Methods

THCMA was designed as an amphiphile containing pharmacophores of PSI-697. Its nanofeatures were explored with TEM, SEM, Tyndall effect, ζ-potential, FT-ICR-MS, and NOESY 2D ¹H NMR. The P-selectin inhibitory effect of THCMA was demonstrated with molecular docking, ultraviolet (UV) spectra, and competitive ELISA. In vivo and in vitro assays — anti-arterial thrombosis, anti–venous thrombosis, anti-inflammation, antitumor growth, anti–platelet aggregation, rat-tail bleeding time, anticoagulation index, soluble P-selectin (sP-selectin) expression, and serum TNFα expression — were performed to explore bioactivity and potential mechanisms. Water solubility of THCMA was measured using UV-absorption spectra.

Results

THCMA self-assembled into nanorings of approximately 100 nm in diameter. Its water solubility was about 1,030-fold that of PSI-697. THCMA exhibited more potent P-selectin inhibitory effect than PSI-697. The oral efficacy of THCMA was 100-fold that of PSI-697 in inhibiting arterial and venous thrombosis and tenfold in inhibiting inflammation. THCMA inhibited thrombosis at a dose that produces no coagulation disorders and no bleeding risk. THCMA exhibited enhanced antitumor activity over PSI-697 without systemic chemotherapy toxicity. THCMA significantly inhibited platelet aggregation in vitro and downregulated the expression levels of serum sP-selectin and TNFα in vivo.

Conclusion

A new small-molecule P-selectin inhibitor, THCMA, has been successfully designed as a nanomedicine with largely enhanced oral efficacy compared to the clinical trial drug PSI-697, and thus might be developed for the oral treatment of arterial thrombosis, venous thrombosis, inflammation, and cancer-associated thrombosis.

Docking of THPDTPI: to explore P-selectin as a common target of anti-tumor, anti-thrombotic and anti-inflammatory agent

The impact of soluble P-selectin on tumor growth, thrombosis and inflammation has been individually documented. Whether the down-regulation of P-selectin expression can simultaneously slow the tumor growth, inhibit the thrombosis and attenuate the inflammatory response remains unknown. In this context, (2'S,5'S)- tetrahydropyrazino[1',2':1,6]-di{2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole}-1',4'-dione (THPDTPI) was designed as an inhibitor of P-selectin. The suitable docking of THPDTPI towards the active site of P-selectin, the significant down-regulation of THPDTPI to P-selectin expression, and the direct action of THPDTPI on P-selectin suggest that P-selectin could be a target of THPDTPI. In vivo THPDTPI possesses the anti-tumor activity, the anti-thrombotic activity and the anti-inflammatory activity. This implies that targeting P-selectin is of essential importance for this triple activity. The minimal effective doses of THPDTPI inhibiting the tumor growth, the rat arterial thrombosis and the mouse ear edema are 0.01 μmol/kg, 0.1 μmol/kg and 0.001 μmol/kg, respectively. Atomic force microscopy images and FT-MS spectra showed that the adhesion of THPDTPI onto the surfaces of the platelets may be the first step of P-selectin targeting. Besides, the dependence of the triple action of THPDTPI inhibiting the tumor growth, the thrombosis and the inflammation on the decrease of the soluble P-selectin led to the correlation of the soluble P-selectin with the serum TNF-α and serum IL-8.