Ramachandra S. Hosmane

Identification of Small Molecules That Suppress MicroRNA Function and Reverse Tumorigenesis

MicroRNAs (miRNAs) act in post-transcriptional gene silencing and are proposed to function in a wide spectrum of pathologies, including cancers and viral diseases. Currently, to our knowledge, no detailed mechanistic characterization of small molecules that interrupt miRNA pathways have been reported. In screening a small chemical library, we identified compounds that suppress RNA interference activity in cultured cells. Two compounds were characterized; one impaired Dicer activity while the other blocked small RNA-loading into an Argonaute 2 (AGO2) complex. We developed a cell-based model of miRNA-dependent tumorigenesis, and using this model, we observed that treatment of cells with either of the two compounds effectively neutralized tumor growth. These findings indicate that miRNA pathway-suppressing small molecules could potentially reverse tumorigenesis.

Ring Expanded Nucleoside Analogues Inhibit RNA Helicase and Intracellular Human Immunodeficiency virus type 1 Replication

A series of ring expanded nucleoside (REN) analogues were synthesized and screened for inhibition of cellular RNA helicase activity and human immunodeficiency virus type 1 (HIV-1) replication. We identified two compounds, 1 and 2, that inhibited the ATP dependent activity of human RNA helicase DDX3. Compounds 1 and 2 also suppressed HIV-1 replication in T cells and monocyte-derived macrophages. Neither compound at therapeutic doses was significantly toxic in ex vivo cell culture or in vivo in mice. Our findings provide proof-of-concept that a cellular factor, an RNA helicase, could be targeted for inhibiting HIV-1 replication.

Characterization of Imidazo[4,5-d]Pyridazine Nucleosides as Modulators of Unwinding Reaction Mediated by West Nile Virus Nucleoside Triphosphatase/Helicase: Evidence for Activity on the Level of Substrate and/or Enzyme

ABSTRACT Compounds that interact with DNA or RNA generally act as inhibitors of enzymes that unwind DNA or RNA. In the present study we describe the synthesis and properties of some nucleoside analogues that interact with double-stranded DNA but that, in contrast, facilitate the unwinding reaction mediated by West Nile (WN) virus nucleoside triphosphatase (NTPase)/helicase. The nucleoside analogues described, 1-(2′-O-methyl-β-d-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)-dione (HMC-HO4), 1-(β-d-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)-dione, and 1-(2′-deoxy-α-d-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)dione, all contain the imidazo[4,5-d]pyridazine ring system. The extent of the enhancing effect on helicase activity was found to be dependent on the time of exposure of the DNA substrate to the compounds and their concentrations. The nucleoside analogues were nevertheless found to be capable of uncoupling the ATPase and helicase activities of the enzyme by a mechanism operating on the level of the enzyme. Thus, in the case of HMC-HO4, the direct interaction with the enzyme caused inhibition of its helicase activity, with a half-maximal inhibitory concentration of 30 μM. The similar potency of the compound against replication of WN virus in cell culture suggests that inhibition of the helicase activity of the viral enzyme is responsible for the observed antiviral activity of HMC-HO4 and may indeed represent an important mode of action of antiviral drugs in general. Comparative studies performed with the related NTPase/helicase from hepatitis C virus revealed that the extent of the effects mediated by imidazo[4,5-d]pyridazine nucleosides is enzyme specific. The substances described may represent a starting point for the development of a new class of helicase-specific antivirals.

Tri-s-triazine: synthesis, chemical behavior, and spectroscopic and theoretical probes of valence orbital structure

Synthese du tri-s-triazine, et determination de sa structure par diffraction RX; etude de ses proprietes chimiques, spectroscopiques et physiques. On utilise la spectrometrie photoelectronique ainsi que des calculs ab initio et HAM3

Targeting DDX3 with a small molecule inhibitor for lung cancer therapy

Lung cancer is the most common malignancy worldwide and is a focus for developing targeted therapies due to its refractory nature to current treatment. We identified a RNA helicase, DDX3, which is overexpressed in many cancer types including lung cancer and is associated with lower survival in lung cancer patients. We designed a first‐in‐class small molecule inhibitor, RK‐33, which binds to DDX3 and abrogates its activity. Inhibition of DDX3 by RK‐33 caused G1 cell cycle arrest, induced apoptosis, and promoted radiation sensitization in DDX3‐overexpressing cells. Importantly, RK‐33 in combination with radiation induced tumor regression in multiple mouse models of lung cancer. Mechanistically, loss of DDX3 function either by shRNA or by RK‐33 impaired Wnt signaling through disruption of the DDX3–β‐catenin axis and inhibited non‐homologous end joining—the major DNA repair pathway in mammalian somatic cells. Overall, inhibition of DDX3 by RK‐33 promotes tumor regression, thus providing a compelling argument to develop DDX3 inhibitors for lung cancer therapy.

Application of real-time PCR for testing antiviral compounds against Lassa virus, SARS coronavirus and Ebola virus in vitro

Abstract This report describes the application of real-time PCR for testing antivirals against highly pathogenic viruses such as Lassa virus, SARS coronavirus and Ebola virus. The test combines classical cell culture with a quantitative real-time PCR read-out. The assay for Lassa virus was validated with ribavirin, which showed an IC50 of 9μg/ml. Small-scale screening identified a class of imidazole nucleoside/nucleotide analogues with antiviral activity against Lassa virus. The analogues contained either dinitrile or diester groups at the imidazole 4,5-positions, and many of which possessed an acyclic sugar or sugar phosphonate moiety at the imidazole 1-position. The IC50 values of the most active compounds ranged from 5 to 21μg/ml. The compounds also inhibited replication of SARS coronavirus and Ebola virus in analogous assays, although to a lesser extent than Lassa virus.

Inhibitors of glycogen phosphorylase b: synthesis, biochemical screening, and molecular modeling studies of novel analogues of hydantocidin

The synthesis and biochemical screening of four novel spironucleosides 1-4 against rabbit liver glycogen phosphorylase b (Gpb), along with molecular modeling studies on compound 2 and its 4-hydroxy analogue VII, have been presented. Gpb is a key enzyme of glycogen metabolism, and is known to be involved in the control of diabetes mellitus. The general strategy for synthesis involved base-catalyzed condensation of diethyl 2,4-dioxoimidazolidine-5-phosphonate (5) with either 2-deoxy-D-ribose or D-ribose, followed by sequential reactions involving ring-closure with phenylselenenyl chloride and reduction with tri-n-butyltin hydride catalyzed by azobisisobutyronitrile. Compounds 2 and 4 were found to be weak competitive inhibitors of Gpb, whereas 1 and 3 were inactive.

A Unique Ring-Expanded Acyclic Nucleoside Analogue that Inhibits Both Adenosine Deaminase (ADA) and Guanine Deaminase (GDA; Guanase): Synthesis and Enzyme Inhibition Studies of 4,6-Diamino-8H-1-hydroxyethoxymethyl-8-iminoimidazo[4,5-e][1,3]diazepine

The synthesis and enzyme inhibition studies of a novel ring-expanded acyclic nucleoside analogue are reported. Compound has been found to be a competitive inhibitor of both adenosine deaminase (ADA) and guanine deaminase (GDA; guanase) with K(i)s equal to 1.52+/-0.34 x 10(-4) M and 2.97+/-0.25 x 10(-5) M, respectively. Inhibition of two enzymes of purine metabolism may bear beneficial implications in antiviral therapy.

The First Synthesis of a Novel 5:7:5-Fused Diimidazodiazepine Ring System and Some of Its Chemical Properties

The first synthesis of a novel 5:7:5-fused heterocyclic ring system, a diimidazodiazepine, is reported. The propensity of the ring system to undergo facile, acid-catalyzed nucleophilic addition reactions by neutral carbon and nitrogen nucleophiles has been explored. The ring system has potential future applications in mechanistic studies of formation and repair of DNA interstrand cross-links.

NZ51, a ring-expanded nucleoside analog, inhibits motility and viability of breast cancer cells by targeting the RNA helicase DDX3.

DDX3X (DDX3), a human RNA helicase, is over expressed in multiple breast cancer cell lines and its expression levels are directly correlated to cellular aggressiveness. NZ51, a ring-expanded nucleoside analogue (REN) has been reported to inhibit the ATP dependent helicase activity of DDX3. Molecular modeling of NZ51 binding to DDX3 indicated that the 5:7-fused imidazodiazepine ring of NZ51 was incorporated into the ATP binding pocket of DDX3. In this study, we investigated the anticancer properties of NZ51 in MCF-7 and MDA-MB-231 breast cancer cell lines. NZ51 treatment decreased cellular motility and cell viability of MCF-7 and MDA-MB-231 cells with IC50 values in the low micromolar range. Biological knockdown of DDX3 in MCF-7 and MDA-MB-231 cells resulted in decreased proliferation rates and reduced clonogenicity. In addition, NZ51 was effective in killing breast cancer cells under hypoxic conditions with the same potency as observed during normoxia. Mechanistic studies indicated that NZ51 did not cause DDX3 degradation, but greatly diminished its functionality. Moreover, in vivo experiments demonstrated that DDX3 knockdown by shRNA resulted in reduced tumor volume and metastasis without altering tumor vascular volume or permeability-surface area. In initial in vivo experiments, NZ51 treatment did not significantly reduce tumor volume. Further studies are needed to optimize drug formulation, dose and delivery. Continuing work will determine the in vitro-in vivo correlation of NZ51 activity and its utility in a clinical setting.