Bhaskar C. Das

Mechanism of action of lenalidomide in hematological malignancies

Immunomodulatory drugs lenalidomide and pomalidomide are synthetic compounds derived by modifying the chemical structure of thalidomide to improve its potency and reduce its side effects. Lenalidomide is a 4-amino-glutamyl analogue of thalidomide that lacks the neurologic side effects of sedation and neuropathy and has emerged as a drug with activity against various hematological and solid malignancies. It is approved by FDA for clinical use in myelodysplastic syndromes with deletion of chromosome 5q and multiple myeloma. Lenalidomide has been shown to be an immunomodulator, affecting both cellular and humoral limbs of the immune system. It has also been shown to have anti-angiogenic properties. Newer studies demonstrate its effects on signal transduction that can partly explain its selective efficacy in subsets of MDS. Even though the exact molecular targets of lenalidomide are not well known, its activity across a spectrum of neoplastic conditions highlights the possibility of multiple target sites of action.

Retinoic acid signaling pathways in development and diseases.

Retinoids comprise a group of compounds each composed of three basic parts: a trimethylated cyclohexene ring that is a bulky hydrophobic group, a conjugated tetraene side chain that functions as a linker unit, and a polar carbon-oxygen functional group. Biochemical conversion of carotenoid or other retinoids to retinoic acid (RA) is essential for normal regulation of a wide range of biological processes including development, differentiation, proliferation, and apoptosis. Retinoids regulate various physiological outputs by binding to nuclear receptors called retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which themselves are DNA-binding transcriptional regulators. The functional response of RA and their receptors are modulated by a host of coactivators and corepressors. Retinoids are essential in the development and function of several organ systems; however, deregulated retinoid signaling can contribute to serious diseases. Several natural and synthetic retinoids are in clinical use or undergoing trials for treating specific diseases including cancer. In this review, we provide a broad overview on the importance of retinoids in development and various diseases, highlighting various retinoids in the drug discovery process, ranging all the way from retinoid chemistry to clinical uses and imaging.

Boron chemicals in diagnosis and therapeutics

Advances in the field of boron chemistry have expanded the application of boron from material use to medicine. Boron-based drugs represent a new class of molecules that possess several biomedical applications including use as imaging agents for both optical and nuclear imaging as well as therapeutic agents with anticancer, antiviral, antibacterial, antifungal and other disease-specific activities. For example, bortezomib (Velcade(®)), the only drug in clinical use with boron as an active element, was approved in 2003 as a proteasome inhibitor for the treatment of multiple myeloma and non-Hodgkins lymphoma. Several other boron-based compounds are in various phases of clinical trials, which illustrates the promise of this approach for medicinal chemists working in the area of boron chemistry. It is expected that in the near future, several boron-containing drugs should become available in the market with better efficacy and potency than existing drugs. This article discusses the current status of the development of boron-based compounds as diagnostic and therapeutic agents in humans.

Curcumin Inhibits Rift Valley Fever Virus Replication in Human Cells

Background: Rift Valley fever virus is a single-stranded RNA virus that causes disease in humans and livestock. Results: Rift Valley fever virus infection activates the host NFκB signaling cascade. Conclusion: NFκB inhibitors, particularly curcumin, down-regulate virus in both in vitro and in vivo models. Significance: Novel versions of host components resulting from an infection make them ideal therapeutic targets. Rift Valley fever virus (RVFV) is an arbovirus that is classified as a select agent, an emerging infectious virus, and an agricultural pathogen. Understanding RVFV-host interactions is imperative to the design of novel therapeutics. Here, we report that an infection by the MP-12 strain of RVFV induces phosphorylation of the p65 component of the NFκB cascade. We demonstrate that phosphorylation of p65 (serine 536) involves phosphorylation of IκBα and occurs through the classical NFκB cascade. A unique, low molecular weight complex of the IKK-β subunit can be observed in MP-12-infected cells, which we have labeled IKK-β2. The IKK-β2 complex retains kinase activity and phosphorylates an IκBα substrate. Inhibition of the IKK complex using inhibitors impairs viral replication, thus alluding to the requirement of an active IKK complex to the viral life cycle. Curcumin strongly down-regulates levels of extracellular infectious virus. Our data demonstrated that curcumin binds to and inhibits kinase activity of the IKK-β2 complex in infected cells. Curcumin partially exerts its inhibitory influence on RVFV replication by interfering with IKK-β2-mediated phosphorylation of the viral protein NSs and by altering the cell cycle of treated cells. Curcumin also demonstrated efficacy against ZH501, the fully virulent version of RVFV. Curcumin treatment down-regulated viral replication in the liver of infected animals. Our data point to the possibility that RVFV infection may result in the generation of novel versions of host components (such as IKK-β2) that, by virtue of altered protein interaction and function, qualify as unique therapeutic targets.

A Forward Chemical Screen Using Zebrafish Embryos with Novel 2-Substituted 2H-Chromene Derivatives

We synthesized 2‐substituted 2H‐chromene derivatives from salicylaldehyde using potassium vinylic borates in the presence of secondary amines. Our goal was to generate novel compounds that might modulate transforming growth factor‐β signaling, based on limited rational design. Potassium vinyl trifluoroborates react with salicylaldehydes at 80 °C in the presence of a secondary amine and produce 2‐substituted 2H‐chromene derivatives with a 70–90% yield. A small library of these compounds, predicted to potentially interact with transforming growth factor‐β receptors, was screened for bioactivity in living zebrafish embryos. We found that the related compounds differentially affect development, and demonstrate one compound that produces severe body axis alterations in early embryogenesis and at lower doses affects specifically cardiovascular development. This compound modulates specifically a Smad‐independent transforming growth factor‐β‐regulated mitogen‐activated protein kinase pathway, namely p‐SAPK/JNK. These compounds, as suggested by our biological assays, may prove useful to manipulate developmental programs and develop therapeutic tools.

Novel retinoic acid receptor alpha agonists for treatment of kidney disease.

Development of pharmacologic agents that protect podocytes from injury is a critical strategy for the treatment of kidney glomerular diseases. Retinoic acid reduces proteinuria and glomerulosclerosis in multiple animal models of kidney diseases. However, clinical studies are limited because of significant side effects of retinoic acid. Animal studies suggest that all trans retinoic acid (ATRA) attenuates proteinuria by protecting podocytes from injury. The physiological actions of ATRA are mediated by binding to all three isoforms of the nuclear retinoic acid receptors (RARs): RARα, RARβ, and RARγ. We have previously shown that ATRA exerts its renal protective effects mainly through the agonism of RARα. Here, we designed and synthesized a novel boron-containing derivative of the RARα-specific agonist Am580. This new derivative, BD4, binds to RARα receptor specifically and is predicted to have less toxicity based on its structure. We confirmed experimentally that BD4 binds to RARα with a higher affinity and exhibits less cellular toxicity than Am580 and ATRA. BD4 induces the expression of podocyte differentiation markers (synaptopodin, nephrin, and WT-1) in cultured podocytes. Finally, we confirmed that BD4 reduces proteinuria and improves kidney injury in HIV-1 transgenic mice, a model for HIV-associated nephropathy (HIVAN). Mice treated with BD4 did not develop any obvious toxicity or side effect. Our data suggest that BD4 is a novel RARα agonist, which could be used as a potential therapy for patients with kidney disease such as HIVAN.

A forward chemical screen in zebrafish identifies a retinoic acid derivative with receptor specificity.

Background Retinoids regulate key developmental pathways throughout life, and have potential uses for differentiation therapy. It should be possible to identify novel retinoids by coupling new chemical reactions with screens using the zebrafish embryonic model. Principal Findings We synthesized novel retinoid analogues and derivatives by amide coupling, obtaining 80–92% yields. A small library of these compounds was screened for bioactivity in living zebrafish embryos. We found that several structurally related compounds significantly affect development. Distinct phenotypes are generated depending on time of exposure, and we characterize one compound (BT10) that produces specific cardiovascular defects when added 1 day post fertilization. When compared to retinoic acid (ATRA), BT10 shows similar but not identical changes in the expression pattern of embryonic genes that are known targets of the retinoid pathway. Reporter assays determined that BT10 interacts with all three RAR receptor sub-types, but has no activity for RXR receptors, at all concentrations tested. Conclusions Our screen has identified a novel retinoid with specificity for retinoid receptors. This lead compound may be useful for manipulating components of retinoid signaling networks, and may be further derivatized for enhanced activity.

Use of zebrafish in chemical biology and drug discovery

The zebrafish (Danio rerio) is a small, tropical, freshwater fish that has emerged as a powerful vertebrate model organism for studying genetics and development. Its small size, transparency, cost-effectiveness, close genome homology to humans compared with invertebrates, and capacity for genetic manipulation are all valuable attributes for an excellent animal model. There are additional advantages for using zebrafish specifically in drug discovery, including ease of exposure to chemicals in water. In effect, zebrafish can bridge a gap between in vitro and mammalian work, reducing the use of larger animals and attrition rates. In the drug-discovery process, zebrafish can be used at many stages, including target identification and validation, identification of lead compounds, studying structure-activity relationships and drug safety profiling. In this review, we highlight the potential for the zebrafish model to make the drug-discovery process simpler, more effective and cost-efficient.

Design and synthesis of 4-HPR derivatives for rhabdoid tumors

Rhabdoid tumors (RTs) are aggressive pediatric malignancies with poor prognosis that arise due to loss of the hSNF5/INI1 tumor suppressor. Molecular studies indicate that cyclin D1, a downstream effector of INI1 is up regulated in RT, and is essential for this tumor formation. Previously we demonstrated that 4-HPR, a synthetic retinoid that targets Cyclin D1, is a potential chemotherapeutic agent for RT. To facilitate further chemical development of this retinoid, and to determine its active moiety, we synthesized small chemical libraries of 4-HPR and tested their cytotoxic effect on RT cells. We synthesized 4-HPR (1) and the derivatives (5a-5n) starting from retinoic acid. First, retinoic acid was converted to acid chloride derivatives, then in the presence of DMF, base, and aniline derivatives, we synthesized the corresponding 4-hydroxy phenyl amine derivatives (5a-5n). This procedure gave 70-90% yield. Then, the 4-HPR derivatives were tested for their ability to inhibit RT cells using an in vitro cell survival assay. We found that the 4-hydroxy group at para-position is essential for cytotoxic activity against RT cells. Furthermore, we identified a few derivatives of 4-HPR with higher cytotoxic potencies than 4-HPR. In addition, we demonstrate that either chloro, fluoro or iodo derivatives at meta-position of phenyl ring retain the cytotoxic activity. Interestingly, substitution of iodo-moiety at meta-position (5j) substantially increased the efficacy (IC(50) approximately 3muM, Fig. 1D). These results indicate that chemical modification of 4-HPR may result in derivatives with increased therapeutic potential for RTs and that halogen substituted 4-HPR that retain the activity can be synthesized for further therapeutic and diagnostic use.

Design, synthesis of novel peptidomimetic derivatives of 4-HPR for rhabdoid tumors.

Rhabdoid tumors (RTs) are an extremely aggressive pediatric malignancy that results from loss of the INI1/hSNF5 tumor suppressor gene. Loss of INI1 results in aberrant expression of Cyclin D1, which supports rhabdoid tumorigenesis and survival. 4-HPR, a synthetic retinoid that down-modulates Cyclin D1, has shown promise in treating various tumors including RTs. In this study, we have generated a chemical library of peptidomimetic derivatives of 4-HPR in an attempt to create a more biologically active compound for use as a therapeutic agent against RTs and other tumors. We have synthesized novel peptidomimetic compound by substituting alkene backbone with a ring structure that retains the biological activity in cell culture models of rhabdoid tumors. We further identified derivative of peptidomimetic compound (11d, IC(50) approximately 3 microM) with approximately five times higher potency than 4-HPR (1, IC(50) approximately 15 microM) based on a survival assay against rhabdoid tumor cells. These studies indicate that peptidomimetic derivatives that retain the cytotoxic activity are promising novel chemotherapeutic agents against RTs and other tumors.