Aminoimidazolylmethyluracil Analogues as Potent Inhibitors of Thymidine Phosphorylase and Their Bioreductive Nitroimidazolyl Prodrugs

Abstract

Thymidine phosphorylase (TP) is an important target enzyme for cancer chemotherapy because it is expressed at high levels in the hypoxic regions of many tumors and inhibitors of TP have been shown in animal model studies to inhibit angiogenesis and metastasis, and to promote tumor cell apoptosis. The 5-halo-6-[(2'-aminoimidazol-1'-yl)methyl]uracils (3, X = Cl, Br) are very potent inhibitors of E. coli and human TP with IC(50) values of approximately 20 nM when the enzyme concentration is approximately 40 nM. Their 4'-aminoimidazol-1'-yl analogues (4, X = Cl, Br) are >350-fold less active with IC(50) values of approximately 7 microM. The 5-unsubstituted analogues (3 and 4, X = H) were both less active than their 5-halo derivatives. Determination of pK(a) values and molecular modeling studies of these compounds in the active site of human TP was used to rationalize their activities. The finding that 3, X = Br has a poor pharmacokinetic (PK) profile in mice, coupled with the desire for tumor selectivity, led us to design prodrugs. The corresponding 2'-nitroimidazol-1'-ylmethyluracils (5, X = Cl, Br) are >1000-fold less active (IC(50) 22-24 microM) than their 2'-amino analogues and are reduced to the 2'-amino inhibitors (3, X = Cl, Br) by xanthine oxidase (XO). As XO is also highly expressed in many tumors, the 2'-nitro prodrugs have the potential to selectively deliver the potent 2'-aminoimidazol-1'-yl TP inhibitors into hypoxic solid tumors.

Synthesis and Biological Evaluation of Some Novel Polysubstituted Pyrimidine Derivatives as Potential Antimicrobial and Anticancer Agents

“…Thioethers were found to show enhanced antimicrobial and antitumor activities [35 -37], beside being analogs of SDABOs (dihydro-alkylthio-benzyl-oxopyrimidines) which possess antiproliferative as well as antiviral activities [38,39]. Moreover, at a certain stage of this investigation, the synthesis of chloropyrimidines was planned owing to their reported potential antimicrobial and antitumor activities [40,41]. The fact that hydrazino derivatives are capable of exerting anticancer activity by alkylating DNA through a free radical intermediate [42], prompted the synthesis of some substituted amino-and hydrazinopyrimidines in order to study the influence of such structure variation on the anticipated biological activities.…”

Recent advances in thymidine phosphorylase inhibitors: syntheses and prospective medicinal applications

“…7,8 This enzyme is usually expressed in blood platelets and human placenta and it has been produced by different cell types in culture, such as human foreskin fibroblasts and vascular smooth muscle cells. TPase is overexpressed in several solid tumors, including carcinomas of the stomach, colon, ovary, and bladder.…”

Assessment of 4-nitro-1,8-naphthalic anhydride reductase activity in homogenates of bakers’ yeast by reversed-phase high-performance liquid chromatography

“…However, there are examples in the literature that nitroarylreductases (NTR) from other sources also possess this ability [32][33][34][35][36][37][38][39][40]. In addition, several enzymes including cytosolic nitroreductase [41][42][43], xanthine oxidase [44][45][46], aldehyde oxidase [47,48], cytochrome NAD(P)H:P450 reductase [49,50], and DT-diaphorase (NAD(P)H:quinone oxidoreductases) [51][52][53] were proposed to participate in the reduction of a variety of nitroaromatic substrates to the corresponding hydroxylamines. Based on the known metabolism of nitroarene compounds by nitroreductase [2,4,39], a plausible description of the reaction is as follows: The nitroarene compound is first reduced via two electrons to form an intermediate which accepts another two electrons to form an arenehydroxylamine.…”