Curaxins: Anticancer Compounds That Simultaneously Suppress NF-κB and Activate p53 by Targeting FACT

Abstract

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.

Complex mutual regulation of facilitates chromatin transcription (FACT) subunits on both mRNA and protein levels in human cells

“…13 The importance of FACT for tumor cells was confirmed by experiments showing that reduced expression of either SSRP1 or SPT16 (via RNAi) led to tumor cell death 13 and by our finding that both SSRP1 and SPT16 are expressed at higher levels in tumor cells than in corresponding normal cells and that FACT is expressed more frequently in aggressive poorly differentiated tumors with low overall survival. 14 Importantly, while FACT expression is critical in tumor cells, it is not ubiquitously expressed in normal adult tissues of higher organisms.…”

“…13 During the course of those studies, we noticed that RNAi-mediated KD of SSRP1 or SPT16 led to reduction of not only the subunit targeted by the si/shRNA but also the other FACT complex subunit (Fig. 2).…”

“…The previously described tissue-, differentiation state-, and tumor-related differences in FACT subunit (SSRP1 and SPT16) levels 13,14,16 suggest that tight regulation of the complex is likely important for development and health of multicellular organisms. Indeed, FACT has been identified as a prospective target for anticancer treatment 13 and prognostic marker of aggressive cancers. 14 An improved understanding of endogenous mechanisms controlling FACT levels may enable rational design of strategies for inhibition of FACT as a cancer therapy.…”

“…N-GFP-SSRP1 construct was previously described. 13 C-GFP-SSRP1 was generated through subcloning of fulllength human SSRP1 lacking stop codon in frame with EGFP into the same pLM-CMV lentiviral vector (kind gift of Peter Chumakov, Cleveland Clinic). Non-translatable SSRP1 was generated from the pReceiver-Lv105-SSRP1 construct (Genecopeia; http://www.genecopoeia.com/product/search/ detail.php?prt=1&cid=&key=B0096) by introducing a mutation encoding a stop codon after the start codon of SSRP1 using Quick Change Lightning Site-Directed Mutagenesis kit (Agilent Technologies; http://www.genomics.agilent.com/en/ Site-Directed-Mutagenesis/QuikChange-Lightning/?cid=AG-PT-175&tabId=AG-PR-1162).…”

Butein impairs the protumorigenic activity of malignant pleural mesothelioma cells

“…This is relevant, in light of the potential efficacy of multitargeting molecules for cancer therapy, like curaxins and R-roscovitine (which simultaneously target NFκB and activate p53). 59,60 Second, butein has already been shown to suppress the proliferation of a variety of human tumor cells. 61 In some cases, the anticancer effect of butein has been directly correlated with its ability to inhibit NFκB or STAT3, such as in the case of osteosarcoma, breast and hepatocellular carcinoma cells.…”