Hak Sung Kim

Roles of heme oxygenase-1 in curcumin-induced growth inhibition in rat smooth muscle cells.

In vascular smooth muscle cells (VSMCs), induction of the heme oxygenase-1 (HO-1) confers vascular protection against cellular proliferation mainly via its up-regulation of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) that is involved in negative regulation of cellular proliferation. In the present study, we investigated whether the phytochemical curcumin and its metabolite tetrahydrocurcumin could induce HO-1 expression and growth inhibition in rat VSMCs and, if so, whether their antiproliferative effect could be mediated via HO-1 expression. At non-toxic concentrations, curcumin possessing two Michael-reaction acceptors induced HO-1 expression by activating antioxidant response element (ARE) through translocation of the nuclear transcription factor E2-related factor-2 (Nrf2) into the nucleus and also inhibited VSMC growth triggered by 5% FBS in a dose-dependent manner. In contrast, tetrahydrocurcumin lacking Michael-reaction acceptor showed no effect on HO-1 expression, ARE activation and VSMC growth inhibition. The antiproliferative effect of curcumin in VSMCs was accompanied by the increased expression of p21(WAF1/CIP1). Inhibition of VSMC growth and expression of p21(WAF1/CIP1) by curcumin were partially, but not completely, abolished when the cells were co- incubated with the HO inhibitor tin protoporphyrin. In human aortic smooth muscle cells (HASMCs), curcumin also inhibited growth triggered by TNF-α and increased p21(WAF1/CIP1) expression via HO-1-dependent manner. Our findings suggest that curcumin has an ability to induce HO-1 expression, presumably through Nrf2-dependent ARE activation, in rat VSMCs and HASMCs, and provide evidence that the antiproliferative effect of curcumin is considerably linked to its ability to induce HO-1 expression.

Pyran Template Approach to the Design of Novel A3 Adenosine Receptor Antagonists.

A3 adenosine receptor antagonists have potential as anti‐inflammatory, anti‐asthmatic, and anti‐ischemic agents. We previously reported the preparation of chemical libraries of 1,4‐dihydropyridine (DHP) and pyridine derivatives and identification of members having high affinity at A3 adenosine receptors. These derivatives were synthesized through standard three‐component condensation/oxidation reactions, which permitted versatile ring substitution at five positions, i.e., the central ring served as a molecular scaffold for structurally diverse substituents. We extended this template approach from the DHP series to chemically stable pyran derivatives, in which the ring NH is replaced by O and which is similarly derived from a stepwise reaction of three components. Since the orientation of substituent groups may be conformationally similar to the 1,4‐DHPs, a direct comparison between the structure activity relationships of key derivatives in binding to adenosine receptors was carried out. Affinity at human A3 receptors expressed in CHO cells was determined vs. binding of [125I]AB‐MECA (N6‐(4‐amino‐3‐iodobenzyl)‐5′‐N‐methylcarbamoyladenosine). There was no potency‐enhancing effect, as was observed for DHPs, of 4‐styryl, 4‐phenylethynyl, or 6‐phenyl substitutions. The most potent ligands in this group in binding to human A3 receptors were 6‐methyl and 6‐phenyl analogs, 3a (MRS 1704) and 4a (MRS 1705), respectively, of 3,5‐diethyl 2‐methyl‐4‐phenyl‐4H‐pyran‐3,5‐dicarboxylate, which had Ki values of 381 and 583 nM, respectively. These two derivatives were selective for human A3 receptors vs. rat brain A1 receptors by 57‐fold and 24‐fold, respectively. These derivatives were inactive in binding at rat brain A2A receptors, and at recombinant human A2B receptors displayed Ki values of 17.3 and 23.2 μM, respectively. The selectivity, but not affinity, of the pyran derivatives in binding to the A3 receptor subtype was generally enhanced vs. the corresponding DHP derivatives. Drug Dev. Res. 48:171–177, 1999. Published 1999 Wiley‐Liss, Inc.

Ribose modified nucleosides and nucleotides as ligands for purine receptors.

Molecular modeling of receptors for adenosine and nucleotide (P2) receptors with docked ligand, based on mutagenesis, was carried out. Adenosine 3′,5′-bisphosphate derivatives act as selective P2Y1 antagonists/partial agonists. The ribose moiety was replaced with carbocyclics, smaller and larger rings, conformationally constrained rings, and acyclics, producing compounds that retained receptor affinity. Conformational constraints were built into the ribose rings of nucleoside and nucleotide ligands using the methanocarba approach, i.e. fused cyclopropane and cyclopentane rings in place of ribose, suggesting a preference for the Northern (N) conformation among ligands for P2Y1 and A1 and A3ARs.