Effective eradication of cancer requires treatment directed against multiple targets. The p53 and nuclear factor κB (NF-κB) pathways are dysregulated in nearly all tumors, making them attractive targets for therapeutic activation and inhibition, respectively. We have isolated and structurally optimized small molecules, curaxins, that simultaneously activate p53 and inhibit NF-κB without causing detectable genotoxicity. Curaxins demonstrated anticancer activity against all tested human tumor xenografts grown in mice. We report here that the effects of curaxins on p53 and NF-κB, as well as their toxicity to cancer cells, result from “chromatin trapping” of the FACT (facilitates chromatin transcription) complex. This FACT inaccessibility leads to phosphorylation of the p53 Ser392 by casein kinase 2 and inhibition of NF-κB–dependent transcription, which requires FACT activity at the elongation stage. These results identify FACT as a prospective anticancer target enabling simultaneous modulation of several pathways frequently dysregulated in cancer without induction of DNA damage. Curaxins have the potential to be developed into effective and safe anticancer drugs.

Signal transducers and activators of transcription (STATs) enhance transcription of specific genes in response to cytokines and growth factors. STAT1 is also required for efficient constitutive expression of the caspases Ice, Cpp32, and Ich-1 in human fibroblasts. As a consequence, STAT1-null cells are resistant to apoptosis by tumor necrosis factor alpha (TNF-alpha). Reintroduction of STAT1alpha restored both TNF-alpha-induced apoptosis and the expression of Ice, Cpp32, and Ich-1. Variant STAT1 proteins carrying point mutations that inactivate domains required for STAT dimer formation nevertheless restored protease expression and sensitivity to apoptosis, indicating that the functions of STAT1 required for these activities are different from those that mediate induced gene expression.

Interleukin-1 (IL-1), a proinflammatory cytokine produced mainly by macrophages and monocytes in response to inflammation, infection, and other challenges, stimulates a wide spectrum of responses, including fever, lymphocyte activation, and leukocyte infusion to the site of injury or infection (16). IL-1 stimulates the expression of several genes by activating the transcription factors NF-B, ATF, and AP-1 (6, 51, 52).The activation of NF-B has been studied extensively (4, 6, 16). NF-B is kept in the cytoplasm through interaction with B inhibitory proteins. Following stimulation with cytokines (e.g., IL-1 and tumor necrosis factor alpha [TNF-␣]) or other agents (e.g., lipopolysaccharide, phorbol ester, and doublestranded RNA), IB undergoes phosphorylation on specific serine residues and is rapidly ubiquitinated and degraded. The liberated NF-B translocates to the nucleus, where it activates transcription (5,63,66,69). Recent studies have provided a model for how NF-B is activated in response to IL-1 (Fig. 1). First, a complex is formed between the type 1 receptor (IL-1R1) and the receptor accessory protein (IL-1RAcP) (21, 24, 29, 70). The cytosolic myeloid differentiation protein (MyD88) (36) is then recruited to the complex, where it functions as an adaptor, recruiting IL-1R-associated kinase (IRAK) in turn (10,48,71,75). IRAK is phosphorylated and then leaves the receptor complex to interact with TRAF6 (11). IRAK2, an IRAK homolog, was shown to interact with the IL-1R complex, MyD88, and TRAF6 in transfected cells, but how IRAK and IRAK2 function in IL-1 signaling is not understood (48). Six TRAFs (TNF receptor-associated factors) have been described so far (2,17,22,23,25,31,49,58). TRAF2 and TRAF5 have been implicated in activating NF-B in response to the activation of members of the TNF-␣ receptor superfamily (2,17,22,23,25,31,49,58). The TRAFs interact with NF-Binducing kinase (NIK), another serine-threonine kinase believed to be a common downstream component in activating NF-B in response to IL-1, TNF-␣, and other stimuli (41). TRAFs might also activate mitogen-activated protein kinase/ ERK kinase kinase 1 (MEKK1) (30,32,35,64,76). Recently, two IB kinases (IKK␣ and IKK␤) have been implicated in signal-induced phosphorylation of the IB proteins (15,44,57,73,78). Both NIK and MEKK1 activate the IKKs by serine phosphorylation (34, 50). The activated IKKs then phosphorylate IBs on specific serine residues, resulting in the degradation of IB and activation of NF-B. The IKKs are components of a large complex (15,44,78). Two additional components, NEMO (NF-B essential modulator or IKK␥) and IKAP are also part of the IKK complex and are required for its formation (12,59,74).Recent studies provide evidence for a second signaling pathway parallel to the cascade leading to IB degradation and specifically required for NF-B-dependent transcriptional competency (Fig.

Summary The Facilitates Chromatin Transcription (FACT) complex is involved in chromatin remodeling during transcription, replication, and DNA repair. FACT was previously considered to be ubiquitously expressed and not associated with any disease. However, we discovered that FACT is the target of a novel class of anti-cancer compounds and is not expressed in normal cells of adult mammalian tissues, except for undifferentiated and stem-like cells. Here, we show that FACT expression is strongly associated with poorly differentiated aggressive cancers with poor overall survival. In addition, FACT was found to be upregulated during in vitro transformation and to be necessary, but not fully sufficient, to drive transformation. FACT also promoted survival and growth of established tumor cells. Genome-wide mapping of chromatin-bound FACT indicated that FACT’s role in cancer likely involves selective chromatin remodeling of genes that stimulate proliferation, inhibit cell death and differentiation, and regulate cellular stress responses.

Use of an NF-B-dependent selectable marker facilitated the isolation of a cell line containing a cDNA encoding Act1, an NF-B activator. Act1 associates with and activates I B kinase (IKK), leading to the liberation of NF-B from its complex with I B. Many signaling pathways that liberate NF-B also activate activating transcription factor (ATF) and activator protein 1 (AP-1) through Jun kinase (JNK). Act1 also activates JNK, suggesting that it might be part of a multifunctional complex involved in the activation of both NF-B and JNK. Act1 fails to activate NF-B in an IL-1-unresponsive mutant cell line in which all known signaling components are present, suggesting that it interacts with an unknown component in IL-1 signaling.

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The Facilitates Chromatin Transcription (FACT) chromatin remodeling complex, comprised of two subunits, SSRP1 and SPT16, is involved in transcription, replication and DNA repair. We recently showed that curaxins, small molecules with anti-cancer activity, target FACT and kill tumor cells in a FACT-dependent manner. We also found that FACT is overexpressed in human and mouse tumors and that tumor cells are sensitive to FACT downregulation. To clarify the clinical potential of FACT inhibition, we were interested in physiological role(s) of FACT in multicellular organisms. We analyzed SSRP1 and SPT16 expression in different cells, tissues and conditions using Immunohistochemical (IHC) staining of mouse and human tissues and analysis of publically available high-content gene expression datasets. Both approaches demonstrated coordinated expression of the two FACT subunits, which was primarily associated with the stage of cellular differentiation. Most cells of adult tissues do not have detectable protein level of FACT. High FACT expression was associated with stem or less-differentiated cells, while low FACT levels were seen in more differentiated cells. Experimental manipulation of cell differentiation and proliferation in vitro, as well as tissue staining for the Ki67 proliferation marker, showed that FACT expression is related more to differentiation than to proliferation. Thus, FACT may be part of a stem cell-like gene expression signature and play a role in maintaining cells in an undifferentiated state, which is consistent with its potential role as an anti-cancer target.

The tyrosine kinase JAK1 and the transcription factors STAT1 and STAT3 are phosphorylated in response to epidermal growth factor (EGF) and other growth factors. We have used EGF receptor-transfected cell lines defective in individual JAKs to assess the roles of these kinases in STAT activation and signal transduction in response to EGF. Although JAK1 is phosphorylated in response to EGF, it is not required for STAT activation or for induction of the c-fos gene. STAT activation in JAK2- and TYK2-defective cells is also normal, and the tyrosine phosphorylation of these two kinases does not increase upon EGF stimulation in wild-type or JAK1-negative cells. In cells transfected with a kinase-negative mutant EGF receptor, there is no STAT activation in response to EGF and c-fos is not induced, showing that the kinase activity of the receptor is required, directly or indirectly, for these two responses. The data do not support a role for any of the three JAK family members tested in STAT activation and are consistent with a JAK-independent pathway in which the intrinsic kinase domain of the EGF receptor is crucial. Furthermore, data from transient transfection experiments in HeLa cells, using c-fos promoters lacking the STAT regulatory element c-sis-inducible element, indicate that this element may play only a minor role in the induction of c-fos by EGF in these cells.