Pladienolide is a naturally occurring antitumor macrolide that was discovered by using a cell-based reporter gene expression assay controlled by the human vascular endothelial growth factor promoter. Despite the unique mechanisms of action and prominent antitumor activities of pladienolides B and D in diverse in vitro and in vivo systems, their target protein has remained unclear. We used 3H-labeled, fluorescence-tagged and photoaffinity/biotin (PB)-tagged 'chemical probes' to identify a 140-kDa protein in splicing factor SF3b as the binding target of pladienolide. Immunoblotting of an enhanced green fluorescent protein fusion protein of SF3b subunit 3 (SAP130) revealed direct interaction between the PB probe and SAP130. The binding affinities of pladienolide derivatives to the SF3b complex were highly correlated with their inhibitory activities against reporter gene expression and cell proliferation. Furthermore, pladienolide B impaired in vivo splicing in a dose-dependent manner. Our results demonstrate that the SF3b complex is a pharmacologically relevant protein target of pladienolide and suggest that this splicing factor is a potential antitumor drug target.

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The sulfonamides constitute an important class of drugs, with several types of pharmacological agents possessing antibacterial, anti- carbonic anhydrase, diuretic, hypoglycemic and antithyroid activity among others. A large number of structurally novel sulfonamide derivatives have ultimately been reported to show substantial antitumor activity in vitro and in vivo. Although they have a common chemical motif of aromatic/heterocyclic or amino acid sulfonamide, there are a variety of mechanisms of their antitumor action, such as carbonic anhydrase inhibition, cell cycle perturbation in the G1 phase, disruption of microtubule assembly, functional suppression of the transcriptional activator NF-Y, and angiogenesis (matrix metalloproteinase, MMP) inhibition among others. Some of these compounds selected via elaborate preclinical screenings or obtained through computer-based drug design, are currently being evaluated in clinical trials. The review summarizes recent classes of sulfonamides and related sulfonyl derivatives disclosed as effective tumor cell growth inhibitors, or for the treatment of different types of cancer. Another research line that progressed much in the last time regards different sulfonamides with remarkable antiviral activity. Thus, at least two clinically used HIV protease inhibitors possess sulfonamide moieties in their molecules, whereas a very large number of other derivatives are constantly being synthesized and evaluated in order to obtain compounds with less toxicity or activity against drug-resistant viruses. Several non nucleoside HIV reverse transcriptase or HIV integrase inhibitors containing sulfonamido groups were also reported. Another approach to inhibit the growth of retroviruses, including HIV, targets the ejection of zinc ions from critical zinc finger viral proteins, which has as a consequence the inhibition of viral replication in the absence of mutations leading to drug resistance phenotypes. Most compounds with antiviral activity possessing this mechanism of action incorporate in their molecules primary sulfonamide groups. Some small molecule chemokine antagonists acting as HIV entry inhibitors also possess sulfonamide functionalities in their scaffold.

Treatment of mammalian cells with small molecule histone deacetylase (HDAC) inhibitors induces changes in the transcription of specific genes. These changes correlate directly with an increase in the acetylation levels of all four core histones in vivo. Antibodies directed against endogenous HDAC1, HDAC2, or HDAC3 immunoprecipitate histone deacetylase activity that is inhibited in vitro by the small molecule trapoxin (TPX), and all three HDACs are retained by a TPX-affinity matrix. HDAC1 and HDAC2 are associated in HeLa cells in a complex that is predominantly separate from an HDAC3 immune complex. Both Jurkat HDAC1 and HeLa HDAC1͞2 immune complexes deacetylate all four core histones and recombinant HDAC1 deacetylates free and nucleosomal histones in vitro. Purified recombinant HDAC1 deacetylates core histones in the absence of protein cofactors. Site-directed mutagenesis was used to identify residues required for the enzymatic and structural integrity of HDAC1. Mutation of any one of four conserved residues causes deleterious effects on deacetylase activity and a reduced ability to bind a TPX-affinity matrix. A subset of these mutations also cause a decreased interaction with the HDAC1-associated proteins RbAp48 and mSin3A. Disruption of histone deacetylase activity either by TPX or by direct mutation of a histidine presumed to be in the active site abrogates HDAC1-mediated transcriptional repression of a targeted reporter gene in vivo.The genetic information of eukaryotes is packaged into chromatin, a highly organized and dynamic protein-DNA complex. The fundamental subunit of chromatin, the nucleosome, is composed of an octamer of four core histones; an H3͞H4 tetramer and two H2A͞H2B dimers, surrounded by 146 bp of DNA. The N-terminal tail domains of the core histones contain highly conserved lysines that are sites for posttranslational acetylation. Acetylation and deacetylation are catalyzed by histone acetyltransferases and histone deacetylases (HDACs), respectively. Converting the -amino groups of lysines into neutral -acetamido groups results in changes in chromatin structure and gene transcription (1-4). The precise mechanism(s) by which histone acetylation alters transcription is poorly understood, although naturally occurring HDAC inhibitors are beginning to provide useful insights into this cellular phenomenon.The small molecule HDAC inhibitor trapoxin (TPX) induces cell cycle arrest and differentiation of many cell types in culture (5). These effects correlate with TPX-induced histone hyperacetylation in vivo and inhibition of HDAC activity in vitro (5). A modified synthetic version of TPX, K-trap, was used as an affinity ligand to purify and characterize the first identified HDAC-HDAC1 (6). HDAC1 is highly related to the yeast transcriptional regulator Rpd3p, thus providing a molecular link between histone deacetylation and transcription. The yeast RPD3 and related HDA1 genes encode proteins with HDAC enzymatic activity and disruption of either of these genes causes histone hyperacetylation ...

Target-protein degradation is an emerging field in drug discovery and development. In particular, the substrate-receptor proteins of the cullin-ubiquitin ligase system play a key role in selective protein degradation, which is an essential component of the anti-myeloma activity of immunomodulatory drugs (IMiDs), such as lenalidomide. Here, we demonstrate that a series of anticancer sulfonamides NSC 719239 (E7820), indisulam, and NSC 339004 (chloroquinoxaline sulfonamide, CQS) induce proteasomal degradation of the U2AF-related splicing factor coactivator of activating protein-1 and estrogen receptors (CAPERα) via CRL4 mediated ubiquitination in human cancer cell lines. Both CRISPR-Cas9-based knockout of DCAF15 and a single amino acid substitution of CAPERα conferred resistance against sulfonamide-induced CAPERα degradation and cell-growth inhibition. Thus, these sulfonamides represent selective chemical probes for disrupting CAPERα function and designate DCAFs as promising drug targets for promoting selective protein degradation in cancer therapy.