Structure of a novel thrombin inhibitor with an uncharged D-amino acid as P1 residue

Design, synthesis and antithrombotic evaluation of novel dabigatran etexilate analogs, a new series of non-peptides thrombin inhibitors

Thrombin is a serine protease that plays a key role in blood clotting, which makes it a promising target for the treatment of thrombotic diseases. Dabigatran is direct potent thrombin inhibitor. Based on bioisosteric and scaffold hopping principle, two dabigatran mimics (I-1 and II-1) in which the benzamidine moiety of dabigatran was replaced by a tricyclic fused scaffold were designed, synthesized and evaluated for their in vitro activities for inhibiting thrombin. The results reveal that compounds I-1 (IC50=9.20nM) and II-1 (IC50=7.48nM) are potent direct thrombin inhibitors and the activity is in the range of reference drug. On this basis, twenty-two ester and carbamate derivatives of I-1 or II-1 were prepared and evaluated for their anticoagulant activity. Prodrugs I-4a (IC50=0.73μM), I-4b (IC50=0.75μM), II-2a (IC50=1.44μM) and II-2b (IC50=0.91μM) display excellent effects of inhibiting thrombin induced-platelet aggregation. Moreover, compounds I-9 and II-4, which contain a cleavable moiety with anti-platelet activity, show the best anticoagulant efficacy among the tested compounds in the rat venous thrombosis model. The compounds which have better in vitro and in vivo activity were subjected to rat tail bleeding test, and the result demonstrates that compound I-9 is less likely to have bleeding risk than dabigatran etexilate.

A D-amino acid containing peptide as a potent, noncovalent inhibitor of α5β1 integrin in human prostate cancer invasion and lung colonization

Primary tumors often give rise to disseminated tumor cells (DTC's), which acquire full malignancy after invading distant site(s). Thus, DTC's may be a productive target for preventing prostate cancer metastasis progression. Our prior research showed that PHSCN peptide (Ac-PHSCN-NH2) targets activated α5β1 integrin to prevent invasion and metastasis in preclinical adenocarcinoma models, and disease progression in Phase I clinical trial. Here, we report that D-stereoisomer replacement of histidine and cysteine in PHSCN produces a highly potent derivative, Ac-PhScN-NH2 (PhScN). PhScN was 27,000- to 150,000-fold more potent as an inhibitor of basement membrane invasion by DU 145 and PC-3 prostate cancer cells. A large increase in invasion-inhibitory potency occurred after covalent modification of the sulfhydryl group in PHSCN to prevent disulfide bond formation; while the potency of covalently modified PhScN was not significantly increased. Thus PhScN and PHSCN invasion inhibition occurs by a noncovalent mechanism. These peptides also displayed similar cell surface binding dissociation constants (Kd), and competed for the same site. Consistent with its increased invasion-inhibitory potency, PhScN was also a highly potent inhibitor of lung extravasation and colonization in athymic nude mice: it was several hundred- or several thousand-fold more potent than PHSCN at blocking extravasation by PC-3 or DU 145 cells, and 111,000- or 379,000-fold more potent at inhibiting lung colonization, respectively. Furthermore, systemic 5 mg/kg PhScN monotherapy was sufficient to cause complete regression of established, intramuscular DU 145 tumors. PhScN thus represents a potent new family of therapeutic agents targeting metastasis by DTC's to prevent parallel progression in prostate cancer.