Effects of methyl derivatives of the rexinoid UAB30 on methylnitrosourea (MNU) induced mammary cancers and on various indicators of toxicity

Abstract #1108

UAB30 is a RXR selective retinoid that has shown excellent activity in preventing chemically-induced mammary cancers with minimal toxicity (specifically not increasing serum triglycerides), and is currently undergoing a Phase I clinical trial. Several methyl analogs were synthesized in an attempt to obtain a more active preventive agent and to better understand the mechanisms of activity/toxicity of this class of agents. The retinoids included 4-methyl-UAB30, 5-methyl-UAB30, 6-methyl-UAB30, 7-methyl-UAB30, and 8-methyl-UAB30. The compounds were evaluated in the MNU-induced mammary cancer model using female Sprague-Dawley rats. MNU (75 mg/kg BW) was administered at 50 days of age and the animals observed for 120 days afterward for the development of ER+ mammary cancers. The retinoids were given at a dose of 200 mg/kg diet, except 7-methyl-UAB30 (given at 100 mg/kg diet). 4-Methyl-UAB30 and 7-methyl-UAB30 were highly active; reducing mammary cancer multiplicity by 74 and 61%, respectively. The retinoids 5-methyl-UAB30, 6-methyl-UAB30, and 8-methyl-UAB30 did not have chemopreventive activity in this model. The 8-methyl-UAB30 derivative actually caused a 108% increase in growth of the mammary cancers. As we have previously shown (Carcinogenesis 27, 1232-1239, 2006), serum triglycerides correlated with cancer preventive activity; i.e., high levels were observed with active retinoids. 4-methyl-UAB30 caused an initial large increase in body weight gain of the rats. Of interest, serum levels of 6-methyl-UAB30 and 7-methyl-UAB30 were high, while the other agents were low or could not be detected. All methyl derivatives caused varying decreases in liver retinyl palmitate levels. Structure-activity relationships are also being evaluated using crystallography of RXR/UAB-rexinoid complexes as a guide. Structure-based and dynamic-based approaches are used to facilitate the design of new rexinoids that fit into the LBD of RXRs. For example, 4-methyl-UAB30 had a 5-fold greater binding affinity to hRXR alpha LBD than 9-cis-retinoic-acid. These studies emphasize that minor modifications of a retinoid molecule can drastically change its absorption, metabolism, toxicity, binding affinities to receptors, and activity in preventing mammary cancers. (Supported by NCI Breast SPORE CA089019 and contract HHSN261200433001C).

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1108.

Novel aromatic inhibitors of influenza virus neuraminidase make selective interactions with conserved residues and water molecules in the active site

The active site of type A or B influenza virus neuraminidase is composed of 11 conserved residues that directly interact with the substrate, sialic acid. An aromatic benzene ring has been used to replace the pyranose of sialic acid in our design of novel neuraminidase inhibitors. A bis(hydroxymethyl)pyrrolidinone ring was constructed in place of the N-acetyl group on the sialic acid. The hydroxymethyl groups replace two active site water molecules, which resulted in the high affinity of the nanomolar inhibitors. However, these inhibitors have greater potency for type A influenza virus than for type B influenza virus. To resolve the differences, we determined the X-ray crystal structure of three benzoic acid substituted inhibitors bound to the active site of B/Lee/40 neuraminidase. The investigation of a hydrophobic aliphatic group and a hydrophilic guanidino group on the aromatic inhibitors shows changes in the interaction with the active site residue Glu275. The results provide an explanation for the difference in efficacy of these inhibitors against types A and B viruses, even though the 11 active site residues of the neuraminidase are conserved.

Hydrophobic benzoic acids as inhibitors of influenza neuraminidase

Neuraminidase (NA) plays a critical role in the life cycle of influenza virus and is a target for new therapeutic agents. A new benzoic acid inhibitor (11) containing a lipophilic side chain at C-3 and a guanidine at C-5 was synthesized. The X-ray structure of 4-(N-acetylamino)-5-guanidino-3-(3-pentyloxy)benzoic acid in complex with NA revealed that the lipophilic side chain binds in a newly created hydrophobic pocket formed by the movement of Glu 278 to interact with Arg 226, whereas the guanidine of 11 interacts in a negatively charged pocket created by Asp 152, Glu 120 and Glu 229. Compound 11 was highly selective for type A (H2N2) influenza NA (IC50 1 microM) over type B (B/Lee/40) influenza NA (IC50 500 microM).

Design of benzoic acid inhibitors of influenza neuraminidase containing a cyclic substitution for the N-acetyl grouping

A 2-pyrrolidinone ring containing a single hydroxymethyl side chain effectively replaces the N-acetylamino group of 4-(N-acetylamino)-3-guanidinobenzoic acid, a low micromolar inhibitor of influenza neuraminidase. This novel structural template affords new opportunities to evolve more potent benzoic acid inhibitors.

Potent inhibition of influenza sialidase by a benzoic acid containing a 2-pyrrolidinone substituent

On the basis of the lead compound 4-(N-acetylamino)-3-guanidinobenzoic acid (BANA 113), which inhibits influenza A sialidase with a Ki of 2.5 microM, several novel aromatic inhibitors of influenza sialidases were designed. In this study the N-acetyl group of BANA 113 was replaced with a 2-pyrrolidinone ring, which was designed in part to offer opportunities for introduction of spatially directed side chains that could potentially interact with the 4-, 5-, and/or 6-subsites of sialidase. While the parent structure 1-(4-carboxy-2-guanidinophenyl)pyrrolidin-2-one (8) was only a modest inhibitor of sialidase, the introduction of a hydroxymethyl or bis(hydroxymethyl) substituent at the C5' position of the 2-pyrrolidinone ring resulted in inhibitors (9 and 12, respectively) with low micromolar activity. Crystal structures of these inhibitors in complex with sialidase demonstrated that the substituents at the 5'-position of the 2-pyrrolidinone ring interact in the 4- and/or 5-subsites of the enzyme. Replacement of the guanidine in 12 with a hydrophobic 3-pentylamino group resulted in a large enhancement in binding to produce an inhibitor (14) with an IC50 of about 50 nM against influenza A sialidase, although the inhibition of influenza B sialidase was 2000-fold less. This represents the first reported example of a simple, achiral benzoic acid with potent (low nanomolar) activity as an inhibitor of influenza sialidase.