FACT maintains nucleosomes during transcription and stem cell viability in adult mice.

Preservation of nucleosomes during replication has been extensively studied, while the maintenance of nucleosomes during transcription has gotten less attention. The histone chaperone FACT has a role in transcription elongation, although whether it disassembles or assembles nucleosomes during this process is unclear. To elucidate the function of FACT in mammals, we deleted the Ssrp1 subunit of FACT in adult mice. FACT loss is lethal, possibly due to the loss of the earliest progenitors in bone marrow and intestine, while more differentiated cells are not affected. Using cells isolated from several tissues, we show that FACT loss reduces the viability of stem cells but not of cells differentiated in vitro. FACT depletion increases chromatin accessibility in a transcription-dependent manner in adipose mesenchymal stem cells, indicating that nucleosomes are lost in these cells during transcription in the absence of FACT. We also observe activation of interferon (IFN) signaling and the accumulation of immunocytes in organs sensitive to FACT loss. Our data indicate that FACT maintains chromatin integrity during transcription in mammalian adult stem cells, suggesting that chromatin transcription in stem cells and differentiated cells is different.

Curaxin CBL0137 eradicates drug resistant cancer stem cells and potentiates efficacy of gemcitabine in preclinical models of pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDA) continues to be one of the deadliest cancers due to the absence of effective treatment. Curaxins are a class of small molecules with anti-cancer activity demonstrated in different models of cancer in mice. The lead curaxin compound, CBL0137, recently entered Phase I clinical trials. Curaxins modulate several important signaling pathways involved in the pathogenesis of PDA through inhibition of chromatin remodeling complex FACT. FACT is overexpressed in multiple types of tumor, with one of the highest rate of overexpression in PDA (59%). In this study, the efficacy of CBL0137 alone or in combination with current standard of care, gemcitabine, was tested against different models of PDA in vitro and in mouse models. It was found that CBL0137 alone is a potent inducer of apoptosis in pancreatic cancer cell lines and is toxic not only for proliferating bulk tumor cells, but also for pancreatic cancer stem cells. In mice, CBL0137 was effective against several PDA models, including orthotopic gemcitabine resistant PANC-1 model and patient derived xenografts, in which CBL0137 anti-tumor effect correlated with overexpression of FACT. Moreover, we observed synergy of CBL0137 with gemcitabine which may be explained by the ability of CBL0137 to inhibit several transcriptional programs induced by gemcitabine, including NF-kappaB response and expression of ribonucleotide reductase, one of the targets of gemcitabine in cells. This data suggest testing of CBL0137 efficacy in Phase II trial in PDA patients alone and in combination with gemcitabine.

Targeting FACT complex suppresses mammary tumorigenesis in Her2/neu transgenic mice.

Development of safe and effective tumor-preventive treatments for high-risk patient populations and therapies for early-stage cancer remains a critical need in oncology. We have recently discovered compound with anticancer activity, Curaxin-137, which modulates several important signaling pathways involved in even the very early stages of cancer. In tumor cells, Curaxin-137 inhibits NF-κB- and HSF1-dependent transcription (prosurvival pathways) and activates p53 (a proapoptotic pathway) without inducing DNA damage. These effects result from chromatin trapping and inhibition of activity of the FACT (facilitates chromatin transcription) complex by Curaxin-137. FACT has not been previously implicated in cancer, but we found that its subunits are overexpressed in breast cancer. On the basis of this background, we tested whether Curaxin-137 could suppress tumorigenesis in MMTV-neu transgenic mice, which spontaneously develop mammary carcinoma due to steroid receptor-regulated expression of the Her2 proto-oncogene. We found that chronic administration of Curaxin-137 in a preventive regimen to MMTV-neu mice did not cause any detectable changes in normal organs and tissues, yet inhibited tumor onset, delayed tumor progression, and prolonged survival of mice in a dose-dependent manner. Curaxin-137 induced changes in FACT, altered NF-κB localization, and activated p53 in tumor cells as expected from its defined mechanism of action. These results support further investigation of Curaxin-137 as a potential preventive and/or early-stage therapeutic agent for breast cancer.