Synthesis, Flow Cytometric Evaluation, and Identification of Highly Potent Dipyridamole Analogues as Equilibrative Nucleoside Transporter 1 Inhibitors

Abstract

Dipyridamole (Persantine) is a clinically used vasodilator with equilibrative nucleoside transporters 1, and 2 (ENT1 and ENT2) inhibitory activity albeit less potent than the prototype ENT1 inhibitor nitrobenzylmercaptopurine riboside (NBMPR). Dipyridamole is a good candidate for further exploration because it is a non-nucleoside and has a proven record of safe use in humans. A series of dipyridamole analogs were synthesized with systematic modification, and evaluated as ENT1 inhibitors by flow cytometry. Compounds with much higher potency were identified, the best being 2,6-bis(diethanolamino)-4,8-diheptamethyleneimino-pyrimido[5,4-d]pyrimidine (13), with a K i of 0.49 nM, compared to a K i of 308 nM for dipyridamole. Compound 13 is similar in potency to the prototype potent ENT1 inhibitor NBMPR (0.43 nM). For the first time, a dipyridamole analog has been identified that is equipotent with NBMPR. The SAR indicated that diethanolamine substituted analogs were more active than monoethanolamine compounds. Also, free hydroxyl groups are not essential for activity.

Coping with Unbalanced Class Data Sets in Oral Absorption Models

“…These compounds may be absorbed by carrier systems due to resemblance to natural metabolites. Examples of these are oxytetracycline, which contains an aromatic system with many oxygen and nitrogen functional groups and is a known substrate of human organic anion transporters 32 or dipyridamole transported via nucleoside transporters in the small intestine 33 .…”

Nucleoside and nucleobase transporters of primary human cardiac microvascular endothelial cells: characterization of a novel nucleobase transporter

“…In fact, cardiovascular drugs like dipyridamole inhibit NTs, thereby extending the lifespan of adenosine in the vasculature (25). Analogs of NBMPR (29) and dipyridamole (18) are now being designed and tested for the potential to act as cardioprotective agents, thus highlighting the importance of vascular NTs as potential therapeutic targets.…”

Structure-Activity Relationship and Mechanistic Studies on the Chemopreventive Activity of Dipyridamole and Its Analogues

“…The JB6 P + mouse epidermal cell line, C141, was purchased from American Type Culture Collection (ATCC). DPM analogues (101-164) were prepared previously (198) and 10 mM stock solutions in DMSO were used for all studies.…”

“…DPM inhibits [ 3 H] uridine uptake in PK15 hENT1 and hENT2 cells with an IC 50 of 5 nM and 356 nM, respectively (164). Its NT inhibitory activity has been exploited in clinical trials in efforts to increase cytotoxicity of the antimetabolite 5-fluorouracil (5-FU).…”

“…Of the nucleoside transport inhibitors studied, dipyridamole appeared to have the best antitumor promotion activity at the concentrations tested. In an independent study, with the aim to identify more potent nucleoside transport inhibitors, an extensive and structurally diverse series of dipyridamole analogues was synthesized and tested for NTI activity (164).…”