21 research outputs found
Development of Small Molecules that Specifically Inhibit the D‑loop Activity of RAD51
RAD51 is the central
protein in homologous recombination (HR) DNA
repair and represents a therapeutic target in oncology. Herein we
report a novel class of RAD51 inhibitors that were identified by high
throughput screening. In contrast to many previously reported RAD51
inhibitors, our lead compound <b>1</b> is capable of blocking
RAD51-mediated D-loop formation (IC<sub>50</sub> 21.3 ± 7.8 μM)
at concentrations that do not influence RAD51 binding to ssDNA. In
human cells, <b>1</b> inhibits HR (IC<sub>50</sub> 13.1 ±
1.6 μM) without blocking RAD51’s ability to assemble
into subnuclear foci at sites of DNA damage. We determined that the
active constituent of <b>1</b> is actually an oxidized derivative
(termed <b>RI(dl)-1</b> or <b>8</b>) of the original screening
compound. Our SAR campaign also yielded <b>RI(dl)-2</b> (hereafter
termed <b>9h</b>), which effectively blocks RAD51’s D-loop
activity in biochemical systems (IC<sub>50</sub> 11.1 ± 1.3 μM)
and inhibits HR activity in human cells (IC<sub>50</sub> 3.0 ±
1.8 μM)
Design and Synthesis of Mercaptoacetamides as Potent, Selective, and Brain Permeable Histone Deacetylase 6 Inhibitors
A series
of nonhydroxamate
HDAC6 inhibitors were prepared in our
effort to develop potent and selective compounds for possible use
in central nervous system (CNS) disorders, thus obviating the genotoxicity
often associated with the hydroxamates. Halogens are incorporated
in the cap groups of the designed mercaptoacetamides in order to increase
brain accessibility. The indole analogue <b>7e</b> and quinoline
analogue <b>13a</b> displayed potent HDAC6 inhibitory activity
(IC<sub>50</sub>, 11 and 2.8 nM) and excellent selectivity against
HDAC1. Both <b>7e</b> and <b>13a</b> together with their
ester prodrug <b>14</b> and disulfide prodrugs <b>15</b> and <b>16</b> were found to be effective in promoting tubulin
acetylation in HEK cells. The disulfide prodrugs <b>15</b> and <b>16</b> also released a stable concentration of <b>7e</b> and <b>13a</b> upon microsomal incubation. Administration
of <b>15</b> and <b>16</b> <i>in vivo</i> was
found to trigger an increase of tubulin acetylation in mouse cortex.
These results suggest that further exploration of these compounds
for the treatment of CNS disorders is warranted
Discovery of <i>N</i>‑Substituted (2-Phenylcyclopropyl)methylamines as Functionally Selective Serotonin 2C Receptor Agonists for Potential Use as Antipsychotic Medications
A series
of <i>N</i>-substituted (2-phenylcyclopropyl)methylamines
were designed and synthesized, with the aim of finding serotonin 2C
(5-HT<sub>2C</sub>)-selective agonists with a preference for G<sub>q</sub> signaling. A number of these compounds exhibit 5-HT<sub>2C</sub> selectivity with a preference for G<sub>q</sub>-mediated signaling
compared with β-arrestin recruitment. Furthermore, the <i>N-</i>methyl compound (+)-<b>15a</b>, which displayed
an EC<sub>50</sub> of 23 nM in the calcium flux assay while showing
no β-arrestin recruitment activity, is the most functionally
selective 5-HT<sub>2C</sub> agonist reported to date. The <i>N</i>-benzyl compound (+)-<b>19</b>, which showed an EC<sub>50</sub> of 24 nM at the 5-HT<sub>2C</sub> receptor, is fully selective
over the 5-HT<sub>2B</sub> receptor. In an amphetamine-induced hyperactivity
model, compound (+)-<b>19</b> showed significant antipsychotic-drug-like
activity. These novel compounds shed light on the role of functional
selectivity at the 5-HT<sub>2C</sub> receptor with respect to antipsychotic
activity
Thiol-Based Potent and Selective HDAC6 Inhibitors Promote Tubulin Acetylation and T‑Regulatory Cell Suppressive Function
Several
new mercaptoacetamides were synthesized and studied as HDAC6 inhibitors.
One compound, <b>2b</b>, bearing an aminoquinoline cap group,
was found to show 1.3 nM potency at HDAC6, with >3000-fold selectivity
over HDAC1. <b>2b</b> also showed excellent efficacy at increasing
tubulin acetylation in rat primary cortical cultures, inducing a 10-fold
increase in acetylated tubulin at 1 μM. To assess possible therapeutic
effects, compounds were assayed for their ability to increase T-regulatory
(Treg) suppressive function. Some but not all of the compounds increased
Treg function, and thereby decreased conventional T cell activation
and proliferation <i>in vitro</i>
An Optimized RAD51 Inhibitor That Disrupts Homologous Recombination without Requiring Michael Acceptor Reactivity
Homologous recombination (HR) is an essential process
in cells
that provides repair of DNA double-strand breaks and lesions that
block DNA replication. RAD51 is an evolutionarily conserved protein
that is central to HR. Overexpression of RAD51 protein is common in
cancer cells and represents a potential therapeutic target in oncology.
We previously described a chemical inhibitor of RAD51, called RI-1
(referred to as compound <b>1</b> in this report). The chloromaleimide
group of this compound is thought to act as a Michael acceptor and
react with the thiol group on C319 of RAD51, using a conjugate addition–elimination
mechanism. In order to reduce the likelihood of off-target effects
and to improve compound stability in biological systems, we developed
an analogue of compound <b>1</b> that lacks maleimide-based
reactivity but retains RAD51 inhibitory activity. This compound, 1-(3,4-dichlorophenyl)-3-(4-methoxyphenyl)-4-morpholino-1<i>H</i>-pyrrole-2,5-dione, named RI-2 (referred to as compound <b>7a</b> in this report), appears to bind reversibly to the same
site on the RAD51 protein as does compound <b>1</b>. Like compound <b>1</b>, compound <b>7a</b> specifically inhibits HR repair
in human cells
Synthesis and Pharmacological Evaluation of Selective Histone Deacetylase 6 Inhibitors in Melanoma Models
Only a handful of
therapies offer significant improvement in the
overall survival in cases of melanoma, a cancer whose incidence has
continued to rise in the past 30 years. In our effort to identify
potent and isoform-selective histone deacetylase (HDAC) inhibitors
as a therapeutic approach to melanoma, a series of new HDAC6 inhibitors
based on the nexturastat A scaffold were prepared. The new analogues <b>4d</b>, <b>4e</b>, and <b>7b</b> bearing added hydrophilic
substituents, so as to establish additional hydrogen bonding on the
rim of the HDAC6 catalytic pocket, exhibit improved potency against
HDAC6 and retain selectivity over HDAC1. Compound <b>4d</b> exhibits
antiproliferative effects on several types of melanoma and lymphoma
cells. Further studies indicates that <b>4d</b> selectively
increases acetylated tubulin levels <i>in vitro</i> and
elicits an immune response through down-regulating cytokine IL-10.
A preliminary <i>in vivo</i> efficacy study indicates that <b>4d</b> possesses improved capability to inhibit melanoma tumor
growth and that this effect is based on the regulation of inflammatory
and immune responses
Design and Discovery of Functionally Selective Serotonin 2C (5-HT<sub>2C</sub>) Receptor Agonists
On
the basis of the structural similarity of our previous 5-HT<sub>2C</sub> agonists with the melatonin receptor agonist tasimelteon
and the putative biological cross-talk between serotonergic and melatonergic
systems, a series of new (2,3-dihydro)benzofuran-based compounds were
designed and synthesized. The compounds were evaluated for their selectivity
toward 5-HT<sub>2A</sub>, 5-HT<sub>2B</sub>, and 5-HT<sub>2C</sub> receptors in the calcium flux assay with the ultimate goal to generate
selective 5-HT<sub>2C</sub> agonists. Selected compounds were studied
for their functional selectivity by comparing their transduction efficiency
at the G protein signaling pathway versus β-arrestin recruitment.
The most functionally selective compound (+)-<b>7e</b> produced
weak β-arrestin recruitment and also demonstrated less receptor
desensitization compared to serotonin in both calcium flux and phosphoinositide
(PI) hydrolysis assays. We report for the first time that selective
5-HT<sub>2C</sub> agonists possessing weak β-arrestin recruitment
can produce distinct receptor desensitization properties
Indole-2-carboxamide-based MmpL3 Inhibitors Show Exceptional Antitubercular Activity in an Animal Model of Tuberculosis Infection
Our
team had previously identified certain indolecarboxamides that
represented a new chemical scaffold that showed promising anti-TB
activity at both an <i>in vitro</i> and <i>in vivo</i> level. Based on mutational analysis using bacteria found resistant
to one of these indolecarboxamides, we identified the trehalose monomycolate
transporter MmpL3 as the likely target of these compounds. In the
present work, we now further elaborate on the SAR of these compounds,
which has led in turn to the identification of a new analog, 4,6-difluoro-<i>N</i>-((1<i>R</i>,2<i>R</i>,3<i>R</i>,5<i>S</i>)-2,6,6-trimethylbicyclo[3.1.1]heptan-3-yl)-1<i>H</i>-indole-2-carboxamide (<b>26</b>), that shows excellent
activity against drug-sensitive (MIC = 0.012 μM; SI ≥
16000), multidrug-resistant (MDR), and extensively drug-resistant
(XDR) <i>Mycobacterium tuberculosis</i> strains, has superior
ADMET properties, and shows excellent activity in the TB aerosol lung
infection model. Compound <b>26</b> is also shown to work in
synergy with rifampin. Because of these properties, we believe that
indolecarboxamide <b>26</b> is a possible candidate for advancement
to human clinical trials
Identification of a Maleimide-Based Glycogen Synthase Kinase-3 (GSK-3) Inhibitor, BIP-135, That Prolongs the Median Survival Time of Δ7 SMA KO Mouse Model of Spinal Muscular Atrophy
The discovery of upregulated glycogen synthase kinase-3
(GSK-3)
in various pathological conditions has led to the development of a
host of chemically diverse small molecule GSK-3 inhibitors, such as
BIP-135. GSK-3 inhibition emerged as an alternative therapeutic target
for treating spinal muscular atrophy (SMA) when a number of GSK-3
inhibitors were shown to elevate survival motor neuron (SMN) levels
in vitro and to rescue motor neurons when their intrinsic SMN level
was diminished by SMN-specific short hairpin RNA (shRNA). Despite
their cellular potency, the in vivo efficacy of GSK-3 inhibitors has
yet to be evaluated in an animal model of SMA. Herein, we disclose
that a potent and reasonably selective GSK-3 inhibitor, namely BIP-135,
was tested in a transgenic Δ7 SMA KO mouse model of SMA and
found to prolong the median survival of these animals. In addition,
this compound was shown to elevate the SMN protein level in SMA patient-derived
fibroblast cells as determined by Western blot, and was neuroprotective
in a cell-based, SMA-related model of oxidative stress-induced neurodegeneration
Indole-2-carboxamide-based MmpL3 Inhibitors Show Exceptional Antitubercular Activity in an Animal Model of Tuberculosis Infection
Our
team had previously identified certain indolecarboxamides that
represented a new chemical scaffold that showed promising anti-TB
activity at both an <i>in vitro</i> and <i>in vivo</i> level. Based on mutational analysis using bacteria found resistant
to one of these indolecarboxamides, we identified the trehalose monomycolate
transporter MmpL3 as the likely target of these compounds. In the
present work, we now further elaborate on the SAR of these compounds,
which has led in turn to the identification of a new analog, 4,6-difluoro-<i>N</i>-((1<i>R</i>,2<i>R</i>,3<i>R</i>,5<i>S</i>)-2,6,6-trimethylbicyclo[3.1.1]heptan-3-yl)-1<i>H</i>-indole-2-carboxamide (<b>26</b>), that shows excellent
activity against drug-sensitive (MIC = 0.012 μM; SI ≥
16000), multidrug-resistant (MDR), and extensively drug-resistant
(XDR) <i>Mycobacterium tuberculosis</i> strains, has superior
ADMET properties, and shows excellent activity in the TB aerosol lung
infection model. Compound <b>26</b> is also shown to work in
synergy with rifampin. Because of these properties, we believe that
indolecarboxamide <b>26</b> is a possible candidate for advancement
to human clinical trials