CPSF3 inhibition blocks pancreatic cancer cell proliferation through disruption of core histone mRNA processing

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited effective treatment options, potentiating the importance of uncovering novel drug targets. Here, we target cleavage and polyadenylation specificity factor 3 (CPSF3), the 3' endonuclease that catalyzes mRNA cleavage during polyadenylation and histone mRNA processing. We find that CPSF3 is highly expressed in PDAC and is associated with poor prognosis. CPSF3 knockdown blocks PDAC cell proliferation and colony formation in vitro and tumor growth in vivo. Chemical inhibition of CPSF3 by the small molecule JTE-607 also attenuates PDAC cell proliferation and colony formation, while it has no effect on cell proliferation of nontransformed immortalized control pancreatic cells. Mechanistically, JTE-607 induces transcriptional readthrough in replication-dependent histones, reduces core histone expression, destabilizes chromatin structure, and arrests cells in the S-phase of the cell cycle. Therefore, CPSF3 represents a potential therapeutic target for the treatment of PDAC.

The Combination of Curaxin CBL0137 and Histone Deacetylase Inhibitor Panobinostat Delays KMT2A-Rearranged Leukemia Progression

Rearrangements of the Mixed Lineage Leukemia (MLL/KMT2A) gene are present in approximately 10% of acute leukemias and characteristically define disease with poor outcome. Driven by the unmet need to develop better therapies for KMT2A-rearranged leukemia, we previously discovered that the novel anti-cancer agent, curaxin CBL0137, induces decondensation of chromatin in cancer cells, delays leukemia progression and potentiates standard of care chemotherapies in preclinical KMT2A-rearranged leukemia models. Based on the promising potential of histone deacetylase (HDAC) inhibitors as targeted anti-cancer agents for KMT2A-rearranged leukemia and the fact that HDAC inhibitors also decondense chromatin via an alternate mechanism, we investigated whether CBL0137 could potentiate the efficacy of the HDAC inhibitor panobinostat in KMT2A-rearranged leukemia models. The combination of CBL0137 and panobinostat rapidly killed KMT2A-rearranged leukemia cells by apoptosis and significantly delayed leukemia progression and extended survival in an aggressive model of MLL-AF9 (KMT2A:MLLT3) driven murine acute myeloid leukemia. The drug combination also exerted a strong anti-leukemia response in a rapidly progressing xenograft model derived from an infant with KMT2A-rearranged acute lymphoblastic leukemia, significantly extending survival compared to either monotherapy. The therapeutic enhancement between CBL0137 and panobinostat in KMT2A-r leukemia cells does not appear to be mediated through cooperative effects of the drugs on KMT2A rearrangement-associated histone modifications. Our data has identified the CBL0137/panobinostat combination as a potential novel targeted therapeutic approach to improve outcome for KMT2A-rearranged leukemia.

Alkaloid-rich fraction of Ervatamia coronaria sensitizes colorectal cancer through modulating AMPK and mTOR signalling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Ervatamia coronaria, a popular garden plant in India and some other parts of the world is known traditionally for its anti-inflammatory and anti-cancer properties. The molecular bases of these functions remain poorly understood.

AIM OF THE STUDY

Efficacies of the existing therapies for colorectal cancer (CRC) are limited by their life-threatening side effects and unaffordability. Therefore, identifying a safer, efficient, and affordable therapeutic is urgent. We studied the anti-CRC activity of an alkaloid-rich fraction of E. coronaria leaf extracts (AFE) and associated underlying mechanism.

MATERIALS AND METHODS

Activity guided solvant fractionation was adopted to identify the activity in AFE. Different cell lines, and tumor grown in syngeneic mice were used to understand the anti-CRC effect. Methodologies such as LCMS, MTT, RT-qPCR, immunoblot, immunohistochemistry were employed to understand the molecular basis of its activity.

RESULTS

We showed that AFE, which carries about six major compounds, is highly toxic to colorectal cancer (CRC) cells. AFE induced cell cycle arrest at G1 phase and p21 and p27 genes, while those of CDK2, CDK-4, cyclin-D, and cyclin-E genes were downregulated in HCT116 cells. It predominantly induced apoptosis in HCT116p53+/+ cells while the HCT116p53-/- cells under the same treatment condition died by autophagy. Notably, AFE induced upregulation of AMPK phosphorylation, and inhibition of both of the mTOR complexes as indicated by inhibition of phosphorylation of S6K1, 4EBP1, and AKT. Furthermore, AFE inhibited mTOR-driven conversion of cells from reversible cell cycle arrest to senescence (geroconversion) as well as ERK activity. AFE activity was independent of ROS produced, and did not primarily target the cellular DNA or cytoskeleton. AFE also efficiently regressed CT26-derived solid tumor in Balb/c mice acting alone or in synergy with 5FU through inducing autophagy as a major mechanism of action as indicated by upregulation of Beclin 1 and phospho-AMPK, and inhibition of phospho-S6K1 levels in the tumor tissue lysates.

CONCLUSION

AFE induced CRC death through activation of both apoptotic and autophagy pathways without affecting the normal cells. This study provided a logical basis for consideration of AFE in future therapy regimen to overcome the limitations associated with existing anti-CRC chemotherapy.

Stimulation of an anti-tumor immune response with "chromatin-damaging" therapy

Curaxins are small molecules that bind genomic DNA and interfere with DNA-histone interactions leading to the loss of histones and decondensation of chromatin. We named this phenomenon 'chromatin damage'. Curaxins demonstrated anti-cancer activity in multiple pre-clinical tumor models. Here, we present data which reveals, for the first time, a role for the immune system in the anti-cancer effects of curaxins. Using the lead curaxin, CBL0137, we observed elevated expression of several group of genes in CBL0137-treated tumor cells including interferon sensitive genes, MHC molecules, some embryo-specific antigens suggesting that CBL0137 increases tumor cell immunogenicity and improves recognition of tumor cells by the immune system. In support of this, we found that the anti-tumor activity of CBL0137 was reduced in immune deficient SCID mice when compared to immune competent mice. Anti-tumor activity of CBL0137 was abrogated in CD8+ T cell depleted mice but only partially lost when natural killer or CD4+ T cells were depleted. Further support for a key role for the immune system in the anti-tumor activity of CBL0137 is evidenced by an increased antigen-specific effector CD8+ T cell and NK cell response, and an increased ratio of effector T cells to Tregs in the tumor and spleen. CBL0137 also elevated the number of CXCR3-expressing CTLs in the tumor and the level of interferon-γ-inducible protein 10 (IP-10) in serum, suggesting IP-10/CXCR3 controls CBL0137-elicited recruitment of effector CTLs to tumors. Our collective data underscores a previously unrecognized role for both innate and adaptive immunity in the anti-tumor activity of curaxins.

Dual Targeting of Chromatin Stability By The Curaxin CBL0137 and Histone Deacetylase Inhibitor Panobinostat Shows Significant Preclinical Efficacy in Neuroblastoma

PURPOSE

We investigated whether targeting chromatin stability through a combination of the curaxin CBL0137 with the histone deacetylase (HDAC) inhibitor, panobinostat, constitutes an effective multimodal treatment for high-risk neuroblastoma.

EXPERIMENTAL DESIGN

The effects of the drug combination on cancer growth were examined in vitro and in animal models of MYCN-amplified neuroblastoma. The molecular mechanisms of action were analyzed by multiple techniques including whole transcriptome profiling, immune deconvolution analysis, immunofluorescence, flow cytometry, pulsed-field gel electrophoresis, assays to assess cell growth and apoptosis, and a range of cell-based reporter systems to examine histone eviction, heterochromatin transcription, and chromatin compaction.

RESULTS

The combination of CBL0137 and panobinostat enhanced nucleosome destabilization, induced an IFN response, inhibited DNA damage repair, and synergistically suppressed cancer cell growth. Similar synergistic effects were observed when combining CBL0137 with other HDAC inhibitors. The CBL0137/panobinostat combination significantly delayed cancer progression in xenograft models of poor outcome high-risk neuroblastoma. Complete tumor regression was achieved in the transgenic Th-MYCN neuroblastoma model which was accompanied by induction of a type I IFN and immune response. Tumor transplantation experiments further confirmed that the presence of a competent adaptive immune system component allowed the exploitation of the full potential of the drug combination.

CONCLUSIONS

The combination of CBL0137 and panobinostat is effective and well-tolerated in preclinical models of aggressive high-risk neuroblastoma, warranting further preclinical and clinical investigation in other pediatric cancers. On the basis of its potential to boost IFN and immune responses in cancer models, the drug combination holds promising potential for addition to immunotherapies.

Abstract 4496: Induction of immunogenicity in tumor cells by small molecule drugs that destabilize nucleosomes

Curaxins are DNA binding small molecules that bind genomic DNA with high affinity and disrupt DNA-histone interactions, leading to dose-dependent nucleosome disassembly and chromatin decondensation in cells. Curaxins have anti-cancer activity against multiple mouse cancer models, and lead curaxin CBL0137 is currently being tested in several clinical trials. During preclinical testing, we observed that CBL0137 caused complete regression of spontaneous tumors in many transgenic mice but only inhibited tumor growth in xenograft models. One of the hypotheses to explain this difference is that the immune system, which is intact in transgenic mice but compromised in mice with xenograft tumors, may play an important role in the anti-cancer activity of curaxins. To test this hypothesis, we compared the growth of the same tumor cells (mouse 4T1 breast cancer cells) in syngeneic, immunocompetent BALB/c mice and immunocompromised SCID mice. CBL0137 had a much stronger inhibitory effect on tumor growth in BALB/c compared to SCID mice. There were also fewer suppressor cells and more active lymphocytes in tumors from BALB/c mice treated with CBL0137 compared to those treated with vehicle. Furthermore, CBL0137 substantially increased the abscopal effect of ionizing radiation. To understand the relationship between the immune system and CBL0137, we measured changes in gene expression in normal mouse organs and tumors upon treatment with CBL0137. The most prominent effect of CBL0137 observed was the induction of the type I interferon response (IFN-I). The same effect was also detected in PBMC from the blood of healthy volunteers treated ex vivo with CBL0137 and clinical trial cancer patients after a single IV injection of CBL0137. In this study, we aimed to establish how chromatin decondensation leads to IFN-I and increased immunogenicity of tumor cells. We identified several complementary mechanisms: (i) bi-directional expression of constitutive heterochromatin, leading to the accumulation of double-stranded RNA, known trigger of IFN-I; (ii) reactivation of facultative heterochromatin and expression of embryo-specific antigens, such as NY-ESO-I, recognized as a foreign antigen by T cells; (iii) increased expression of epigenetically silenced MHC-I proteins in tumor cells; (iv) departure of architectural chromatin proteins, such as HMGB1, from chromatin, which normally serve as a ligand-damage associated molecular pattern (DAMP) receptor. Thus, chromatin decondensation serves as a potent inducer of tumor cell immunogenicity. An immune response may significantly improve the anti-cancer activity of CBL0137, and the presence of an intact IFN-I could serve as a potential predictive marker of patient response to curaxin treatment.

Citation Format: Katerina Leonova, Alfiya Safina, Andrei V. Gudkov, Katerina V. Gurova. Induction of immunogenicity in tumor cells by small molecule drugs that destabilize nucleosomes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4496.

Abstract 1747: Induction of nucleosome disassembly with small molecules as a novel anti-cancer approach

CBL0137 is a clinical-stage anti-cancer drug candidate that is active against multiple preclinical cancer models. It is a carbazole-based DNA intercalator, discovered by cell-based screening for p53 activation in cells lacking DNA damage. Binding of curaxin to DNA results in alterations in DNA length, charge, and flexibility, which together impair the ability of DNA to wrap around the histone core. Treatment of cells with CBL0137 leads to decondensation of chromatin accompanied by histone eviction. This causes the binding of histone chaperone FACT to epitopes normally hidden within nucleosomes and the activation of p53 by FACT-bound CK2. p53 activation occurs in the absence of detectable DNA damage. However, CBL0137 is also toxic to p53-deficient cells, suggesting that its toxicity is mediated by events upstream of p53 activation. Trying to understand the mechanisms of CBL0137 toxicity, we found that FACT is essential for the viability of tumor but not normal cells. FACT was discovered as a transcription elongation factor performing disassembly and reassembly of nucleosomes in cell-free conditions. However, no reduction of transcription is observed with FACT depletion in cells. Moreover, measurement of FACT chromatin binding and gene expression upon FACT loss suggest that FACT negatively regulates gene expression. mammalian FACT does not disassemble nucleosomes during transcription but binds “open” nucleosomes, with partially unwrapped DNA, appearing during transcription, and tethers nucleosome components together to prevent histone loss from chromatin. In cells treated with CBL0137 nucleosomes are mostly lost in regions enriched with tandem AC/TG dinucleotide repeats, known as microsatellites. These regions accumulate FACT in treated cells. To understand the effects of FACT loss from other chromatin regions, we measured nucleosome distribution in cells with genetically-depleted FACT. Regions normally enriched with FACT lose nucleosomes in a transcription-dependent manner. Thus, curaxin induces chromatin disassembly via a direct effect on nucleosomal DNA and inhibition of FACT-mediated nucleosome restoration at transcribed regions. To explain the reasons for the higher toxicity of curaxin in tumor versus normal cells, we hypothesized that chromatin is, in general, less stable in tumor than in normal cells. Thus, less drug is needed to cause unrepairable nucleosome disassembly in tumor cells. We compared chromatin organization in syngeneic normal, immortalized, and transformed cells and found that during tumor progression, there is loss of histones, reduction of condensed chromatin and increase of DNA accessibility to the transcriptional machinery. The same signs are observed in human tumors. In summary, curaxin kills cells via the destabilization of nucleosomes and disassembly of chromatin, a phenomenon that we have named “chromatin damage.” Tumor cells are more sensitive to chromatin damage due to their preexisting, less stable chromatin.

Citation Format: Alfiya Safina, Poorva Sandlesh, Jianmin Wang, Katerina V. Gurova. Induction of nucleosome disassembly with small molecules as a novel anti-cancer approach [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1747.

Prevention of Chromatin Destabilization by FACT Is Crucial for Malignant Transformation

Histone chaperone FACT is commonly expressed and essential for the viability of transformed but not normal cells, and its expression levels correlate with poor prognosis in patients with cancer. FACT binds several components of nucleosomes and has been viewed as a factor destabilizing nucleosomes to facilitate RNA polymerase passage. To connect FACT's role in transcription with the viability of tumor cells, we analyzed genome-wide FACT binding to chromatin in conjunction with transcription in mouse and human cells with different degrees of FACT dependence. Genomic distribution and density of FACT correlated with the intensity of transcription. However, FACT knockout or knockdown was unexpectedly accompanied by the elevation, rather than suppression, of transcription and with the destabilization of chromatin in transformed, but not normal cells. These data suggest that FACT stabilizes and reassembles nucleosomes disturbed by transcription. This function is vital for tumor cells because malignant transformation is accompanied by chromatin destabilization.

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FACT is essential for viability of the tumor, but not for normal cells

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FACT level depends on transcription, but transcription does not depend on FACT

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FACT preserves nucleosomes during transcription to maintain chromatin integrity

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FACT maintains chromatin in destabilized state during malignant transformation

A Translational Hepatic Artery Infusion (HAI) Model for Hepatocellular Carcinoma in Woodchucks

BACKGROUND

Woodchucks (Marmota monax) are a well-accepted animal model for the investigation of spontaneous hepatocellular carcinoma (HCC). As HCC tumors obtain nutrient blood supply exclusively from the hepatic artery, hepatic artery infusion (HAI) has been applied to HCC. However, there is a scarcity of experimental animal models to standardize drug regimens and examine novel agents. The purpose of this study was to establish an HAI model in woodchucks.

MATERIALS AND METHODS

HAI ports were placed in the gastroduodenal artery (GDA) of 11 woodchucks. The ports were infused with either a vehicle (dextrose 5% in water) or an experimental drug, CBL0137, once a week for 3 wk. Technical success rates, anatomical variation, morbidity and mortality, and tumor responses between groups were analyzed.

RESULTS

The GDA access was feasible and reproducible in all woodchucks (11/11). The average operation time was 95 ± 20 min with no increase in the levels of liver enzymes detected from either infusate. The most common morbidity of CBL0137 therapy was anorexia after surgery. One woodchuck died due to hemorrhage at the gallbladder removal site from hepatic coagulopathy. Significantly higher CBL0137 concentrations were measured in the liver compared with blood after each HAI. Tumor growth was suppressed after multiple CBL0137 HAI treatments which corresponded to greater T cell infiltration and increased tumor cell apoptosis.

CONCLUSIONS

HAI via GDA was a feasible and reproducible approach with low morbidity and mortality in woodchucks. The described techniques serve as a reliable platform for the identification and characterization of therapeutics for HCC.

Histone Chaperone FACT and Curaxins: Effects on Genome Structure and Function

The histone chaperone FACT plays important roles in essentially every chromatin-associated process and is an important indirect target of the curaxin class of anti-cancer drugs. Curaxins are aromatiс compounds that intercalate into DNA and can trap FACT in bulk chromatin, thus interfering with its distribution and its functions in cancer cells. Recent studies have provided mechanistic insight into how FACT and curaxins cooperate to promote unfolding of nucleosomes and chromatin fibers, resulting in genome-wide disruption of contact chromatin domain boundaries, perturbation of higher order chromatin organization, and global disregulation of gene expression. Here, we discuss the implications of these insights for cancer biology.

Prevention of Colorectal Carcinogenesis by DNA-Binding Small-Molecule Curaxin CBL0137 Involves Suppression of Wnt Signaling

Chemoprevention is considered a valid approach to reduce the incidence of colorectal cancer, one of the most common malignancies worldwide. Here, we investigated the tumor-preventive activity of curaxin CBL0137. This compound represents a new class of nonmutagenic DNA-binding small molecules that alter chromatin stability and inhibit the function of the histone chaperone FACT. Among downstream effects of CBL0137 treatment are activation of p53 and type I interferons and inhibition of NFκB, HSF1, and MYC. In addition, our data show that in both human and mouse colorectal cancer cells in vitro, CBL0137 inhibits the APC/WNT/β-catenin signaling pathway, which plays a key role in colon carcinogenesis. Using quantitative RT-PCR and microarray hybridization, we have demonstrated decreased expression of multiple components and downstream targets of the WNT pathway in colon cancer cells treated with CBL0137. At the same time, CBL0137 induced expression of WNT antagonists. Inhibition of WNT signaling activity by CBL0137 was also confirmed by luciferase reporter assay. Tumor-preventive activity of CBL0137 in vivo was tested in a murine model of colorectal carcinogenesis induced by 1,2-dimethylhydrazine (DMH), which is known to involve WNT pathway dysregulation. After DMH subcutaneous treatment, mice were administered CBL0137 in drinking water. Efficacy of CBL0137 in suppressing development of colorectal cancer in this model was evidenced by reduced incidence of adenocarcinomas and adenomas in both males and females and decrease in tumor multiplicity. These data support the prospective use of CBL0137 in chemoprevention of colorectal cancer as well as of other malignances associated with activated WNT signaling.

Chromatin Stability as a Target for Cancer Treatment

In this essay, I propose that DNA-binding anti-cancer drugs work more via chromatin disruption than DNA damage. Success of long-awaited drugs targeting cancer-specific drivers is limited by the heterogeneity of tumors. Therefore, chemotherapy acting via universal targets (e.g., DNA) is still the mainstream treatment for cancer. Nevertheless, the problem with targeting DNA is insufficient efficacy due to high toxicity. I propose that this problem stems from the presumption that DNA damage is critical for the anti-cancer activity of these drugs. DNA in cells exists as chromatin, and many DNA-targeting drugs alter chromatin structure by destabilizing nucleosomes and inducing histone eviction from chromatin. This effect has been largely ignored because DNA damage is seen as the major reason for anti-cancer activity. I discuss how DNA-binding molecules destabilize chromatin, why this effect is more toxic to tumoral than normal cells, and why cells die as a result of chromatin destabilization.

Mechanism of FACT removal from transcribed genes by anticancer drugs curaxins

Human FACT (facilitates chromatin transcription) is a multifunctional protein complex that has histone chaperone activity and facilitates nucleosome survival and transcription through chromatin. Anticancer drugs curaxins induce FACT trapping on chromatin of cancer cells (c-trapping), but the mechanism of c-trapping is not fully understood. Here, we show that in cancer cells, FACT is highly enriched within the bodies of actively transcribed genes. Curaxin-dependent c-trapping results in redistribution of FACT from the transcribed chromatin regions to other genomic loci. Using a combination of biochemical and biophysical approaches, we have demonstrated that FACT is bound to and unfolds nucleosomes in the presence of curaxins. This tight binding to the nucleosome results in inhibition of FACT-dependent transcription in vitro in the presence of both curaxins and competitor chromatin, suggesting a mechanism of FACT trapping on bulk nucleosomes (n-trapping).

Uncovering the fine print of the CreERT2-LoxP system while generating a conditional knockout mouse model of Ssrp1 gene

FAcilitates Chromatin Transcription (FACT) is a complex of SSRP1 and SPT16 that is involved in chromatin remodeling during transcription, replication, and DNA repair. FACT has been mostly studied in cell-free or single cell model systems because general FACT knockout (KO) is embryonically lethal (E3.5). FACT levels are limited to the early stages of development and stem cell niches of adult tissues. FACT is upregulated in poorly differentiated aggressive tumors. Importantly, FACT inhibition (RNAi) is lethal for tumors but not normal cells, making FACT a lucrative target for anticancer therapy. To develop a better understanding of FACT function in the context of the mammalian organism under normal physiological conditions and in disease, we aimed to generate a conditional FACT KO mouse model. Because SPT16 stability is dependent on the SSRP1-SPT16 association and the presence of SSRP1 mRNA, we targeted the Ssrp1 gene using a CreERT2- LoxP approach to generate the FACT KO model. Here, we highlight the limitations of the CreERT2-LoxP (Rosa26) system that we encountered during the generation of this model. In vitro studies showed an inefficient excision rate of ectopically expressed CreERT2 (retroviral CreERT2) in fibroblasts with homozygous floxed Ssrp1. In vitro and in vivo studies showed that the excision efficiency could only be increased with germline expression of two alleles of Rosa26CreERT2. The expression of one germline Rosa26CreERT2 allele led to the incomplete excision of Ssrp1. The limited efficiency of the CreERT2-LoxP system may be sufficient for studies involving the deletion of genes that interfere with cell growth or viability due to the positive selection of the phenotype. However, it may not be sufficient for studies that involve the deletion of genes supporting growth, or those crucial for development. Although CreERT2-LoxP is broadly used, it has limitations that have not been widely discussed. This paper aims to encourage such discussions.

Role of Chromatin Damage and Chromatin Trapping of FACT in Mediating the Anticancer Cytotoxicity of DNA-Binding Small-Molecule Drugs

Precisely how DNA-targeting chemotherapeutic drugs trigger cancer cell death remains unclear, as it is difficult to separate direct DNA damage from other effects in cells. Recent work on curaxins, a class of small-molecule drugs with broad anticancer activity, shows that they interfere with histone-DNA interactions and destabilize nucleosomes without causing detectable DNA damage. Chromatin damage caused by curaxins is sensed by the histone chaperone FACT, which binds unfolded nucleosomes becoming trapped in chromatin. In this study, we investigated whether classical DNA-targeting chemotherapeutic drugs also similarly disturbed chromatin to cause chromatin trapping of FACT (c-trapping). Drugs that directly bound DNA induced both chromatin damage and c-trapping. However, chromatin damage occurred irrespective of direct DNA damage and was dependent on how a drug bound DNA, specifically, in the way it bound chromatinized DNA in cells. FACT was sensitive to a plethora of nucleosome perturbations induced by DNA-binding small molecules, including displacement of the linker histone, eviction of core histones, and accumulation of negative supercoiling. Strikingly, we found that the cytotoxicity of DNA-binding small molecules correlated with their ability to cause chromatin damage, not DNA damage. Our results suggest implications for the development of chromatin-damaging agents as selective anticancer drugs.Significance: These provocative results suggest that the anticancer efficacy of traditional DNA-targeting chemotherapeutic drugs may be based in large part on chromatin damage rather than direct DNA damage. Cancer Res; 78(6); 1431-43. ©2018 AACR.

Anticancer drug candidate CBL0137, which inhibits histone chaperone FACT, is efficacious in preclinical orthotopic models of temozolomide-responsive and -resistant glioblastoma

Background

The survival rate for patients with glioblastoma (GBM) remains dismal. New therapies targeting molecular pathways dysregulated in GBM are needed. One such clinical-stage drug candidate, CBL0137, is a curaxin, small molecules which simultaneously downregulate nuclear factor-kappaB (NF-ĸB) and activate p53 by inactivating the chromatin remodeling complex, Facilitates Chromatin Transcription (FACT).

Methods

We used publicly available databases to establish levels of FACT subunit expression in GBM. In vitro, we evaluated the toxicity and effect of CBL0137 on FACT, p53, and NF-ĸB on U87MG and A1207 human GBM cells. In vivo, we implanted the cells orthotopically in nude mice and administered CBL0137 in various dosing regimens to assess brain and tumor accumulation of CBL0137, its effect on tumor cell proliferation and apoptosis, and on survival of mice with and without temozolomide (TMZ).

Results

FACT subunit expression was elevated in GBM compared with normal brain. CBL0137 induced loss of chromatin-unbound FACT, activated p53, inhibited NF-ĸB-dependent transcription, and was toxic to GBM cells. The drug penetrated the blood-brain barrier and accumulated in orthotopic tumors significantly more than normal brain tissue. It increased apoptosis and suppressed proliferation in both U87MG and A1207 tumors. Intravenous administration of CBL0137 significantly increased survival in models of early- through late-stage TMZ-responsive and -resistant GBM, with a trend toward significantly increasing the effect of TMZ in TMZ-responsive U87MG tumors.

Conclusion

CBL0137 targets GBM according to its proposed mechanism of action, crosses the blood-brain barrier, and is efficacious in both TMZ-responsive and -resistant orthotopic models, making it an attractive new therapy for GBM.

Abstract 809: A novel woodchuck model of hepatic artery infusion (HAI) with FACT complex targeted drug CBL0137

Background: The liver has unique anatomy in that most blood flow to normal hepatocytes is derived from the portal venous system, while liver tumors obtain their nutrient blood supply exclusively from the hepatic artery. Hepatic artery infusion (HAI) concentrates chemotherapy agents delivering them directly to the tumor bed with the first-pass effect. Although, HAI chemotherapy as a regional therapy has been used clinically for decades in the treatment of both primary and metastatic cancers of the liver, significant toxicity remains a concern, and clinical results have been mixed. The purpose of this study was to establish preclinical HAI model in a woodchuck and administer the FACT (facilitates chromatin transcription) complex targeted drug CBL0137.

Material and methods: Woodchuck hepatitis virus infected Eastern Woodchucks (Marmota monax) were used for the study. Hepatocellular carcinoma (HCC) developed spontaneously about 18 months after birth. The size of HCC was monitored with ultrasound every 2 weeks, and 4 woodchucks bearing over 2 cm tumors were used for the experimental group. Prophylactic cholecystectomy was performed first, and then a 2Fr. (ID=0.012”, OD=0.025”) vascular access port (VAP) was implanted in the gastroduodenal artery (GDA) after collateral vessel ligations. HAI was performed at room temperature via a VAP using 15mg/kg of CBL0137 at a volume of 3 mL/kg for 30 minutes, and tumor responses were investigated with MRI on day 0 (the surgery day of HAI port) and day 7 after HAI.

Results: Anatomy variations existed in the size and location of the supraduodenal artery or pancreatico-duodenal artery. 4/4 success rate of a port implantation was achieved without mortality, but 1/4 animals suffered post-operative bleeding at the port head site, attributed to coagulopathy secondary to hepatic dysfunction. And, 4/4 animals were partially anorexic for up to 7 days post-surgery. Decreased tumor volume and Ktrans (a measure of capillary permeability) were detected 7 days after single HAI with CBL0137.

Conclusion: Although the anticancer effect of CBL0137 on HCC was not clear because of a lack of the control group, we successfully implanted a VAP into the GDA of 4 woodchucks bearing unresectable HCC for HAI. The described woodchuck model may serve as a platform for identifying novel drugs and optimal conditions for the treatment of primary and metastatic liver tumors.

Citation Format: Minhyung Kim, Leslie I. Curtin, Colin A. Powers, Sandra Sexton, Katerina V. Gurova, Andrei V. Gudkov, Renuka V. Iyer. A novel woodchuck model of hepatic artery infusion (HAI) with FACT complex targeted drug CBL0137 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 809. doi:10.1158/1538-7445.AM2017-809

Abstract 13: Chromatin unfolding small molecules as a novel type of anticancer agents

Although targeted therapy was the major focus of anti-cancer drug development, recently revealed enormous heterogeneity of tumors planted a seed of doubt in it as a potential cure for cancer. Very few universal cancer targets are known and they lack cancer specificity. DNA is one of this sort, but activity of drugs targeting DNA was traditionally attributed to their ability to block DNA replication and cause DNA damage with a plethora of harmful long lasting effects in normal cells. We have found that reversible binding of DNA by non-DNA damaging small molecules, curaxins, has strong anticancer effect in different preclinical models without deleterious consequences associated with DNA damage (REF). In this study we explained the mechanism of activity of curaxin clinical lead, CBL0137, through alteration of chromatin organization in tumor cells. Intercalation of the curaxin carbazole moiety between base pairs and DNA major and minor groove binding with curaxin side chains cause an increase in inter base pair distance and untwisting of the double helix (~18o). Such alteration of DNA helical shape leads to decreased nucleosome stability and chromatin opening, creating sites for the high affinity binding of histone chaperone complex FACT. We named this phenomenon “chromatin trapping of FACT” or c-trapping. Consequences of C-trapping are much more deleterious for tumor, than for normal cells. First, c-trapping is an equivalent of functional inactivation of FACT. FACT is critical for oncogenic transformation and tumor, but not normal cell, viability and growth (REF). FACT is essential for the activity of several transcription factors, such as NF-kappaB, HSF1, MYC etc., with important roles in tumor cell proliferation and survival (REF). Further, deregulation of transcription caused by curaxin-dependent chromatin decondensation leads to upregulation of transcription from heterochromatin. This leads to the formation of double stranded RNAs from centromeric and pericentromeric repetitive elements, which mimics a viral infection and induces an IFN response, a powerful inhibitor of tumor cell growth. Additionally, c-trapping of FACT leads to casein kinase 2 mediated phosphorylation and activation of wild type p53 leading to p53-dependent death of cells. Thus non-DNA damaging DNA binding small molecules compromise cancer cell viability via alteration of nucleosome stability and chromatin organization. This is a novel mechanism of anti-cancer activity of small molecules with broad applicability to different types of cancer while lacking the harmful effects of DNA damaging chemotherapy.

Citation Format: Katerina V. Gurova. Chromatin unfolding small molecules as a novel type of anticancer agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 13. doi:10.1158/1538-7445.AM2017-13

Preclinical Validation of a Single-Treatment Infusion Modality That Can Eradicate Extremity Melanomas

Isolated limb perfusion (ILP) with the chemotherapeutic agent melphalan is an effective treatment option for extremity in-transit melanoma but is toxic and technically challenging to deliver locoregionally. CBL0137 is an experimental clinical drug with broad anticancer activity in animal models, owing to its ability to bind DNA in a nongenotoxic manner and inactivate the FACT chromatin modulator essential for tumor cell viability. Here, we report that CBL0137 delivered by ILP in a murine melanoma model is as efficacious as melphalan, displaying antitumor activity at doses corresponding to only a fraction of the systemic MTD of CBL0137. The ability to bind DNA quickly combined with a favorable safety profile made it possible to substitute CBL0137 in the ILP protocol, using an intra-arterial infusion method, to safely achieve effective tumor suppression. Our findings of a preclinical proof of concept for CBL0137 and its administration via intra-arterial infusion as a superior treatment compared with melphalan ILP allows for locoregional treatment anywhere a catheter can be placed. Cancer Res; 76(22); 6620-30. ©2016 AACR.

Therapeutic targeting of the MYC signal by inhibition of histone chaperone FACT in neuroblastoma

Amplification of the MYCN oncogene predicts treatment resistance in childhood neuroblastoma. We used a MYC target gene signature that predicts poor neuroblastoma prognosis to identify the histone chaperone FACT (facilitates chromatin transcription) as a crucial mediator of the MYC signal and a therapeutic target in the disease. FACT and MYCN expression created a forward feedback loop in neuroblastoma cells that was essential for maintaining mutual high expression. FACT inhibition by the small-molecule curaxin compound CBL0137 markedly reduced tumor initiation and progression in vivo. CBL0137 exhibited strong synergy with standard chemotherapy by blocking repair of DNA damage caused by genotoxic drugs, thus creating a synthetic lethal environment in MYCN-amplified neuroblastoma cells and suggesting a treatment strategy for MYCN-driven neuroblastoma.

Pharmacological Targeting of the Histone Chaperone Complex FACT Preferentially Eliminates Glioblastoma Stem Cells and Prolongs Survival in Preclinical Models

The nearly universal recurrence of glioblastoma (GBM) is driven in part by a treatment-resistant subpopulation of GBM stem cells (GSC). To identify improved therapeutic possibilities, we combined the EGFR/HER2 inhibitor lapatinib with a novel small molecule, CBL0137, which inhibits FACT (facilitates chromatin transcription), a histone chaperone complex predominantly expressed in undifferentiated cells. Lapatinib and CBL0137 synergistically inhibited the proliferation of patient-derived GBM cells. Compared with non-stem tumor cells (NSTC) enriched from the same specimens, the GSCs were extremely sensitive to CBL0137 monotherapy or FACT knockdown. FACT expression was elevated in GSCs compared with matched NSTCs and decreased in GSCs upon differentiation. Acute exposure of GSCs to CBL0137 increased asymmetric cell division, decreased GSC marker expression, and decreased the capacity of GSCs to form tumor spheres in vitro and to initiate tumors in vivo Oral administration of CBL0137 to mice bearing orthotopic GBM prolonged their survival. Knockdown of FACT reduced the expression of genes encoding several core stem cell transcription factors (SOX2, OCT4, NANOG, and OLIG2), and FACT occupied the promoters of these genes. FACT expression was elevated in GBM tumors compared with non-neoplastic brain tissues, portended a worse prognosis, and positively correlated with GSC markers and stem cell gene expression signatures. Preferential targeting of GSCs by CBL0137 and synergy with EGFR inhibitors support the development of clinical trials combining these two agents in GBM. Cancer Res; 76(8); 2432-42. ©2016 AACR.

Abstract PR09: MYCN and is a therapeutic target in neuroblastoma

Neuroblastoma is a childhood cancer of the sympathetic nervous system. Approximately 20% of patients present with an aggressive metastatic disease characterized by amplification of the MYCN locus. However, an additional 30% of patients suffer from an equally aggressive disease, yet there are no unified genetic markers available.

To identify potential biomarkers of poor prognosis in neuroblastoma, we conducted unsupervised hierarchical clustering on 649 primary neuroblastoma tumors based on a 51 gene MYC core target signature. This demonstrated strong activation within the MYCN amplified cohort as expected, but surprisingly there was a large subset of MYCN non-amplified patients that exhibited high MYC signaling. High expression of this MYC signature proved to be strongly predictive of poor overall survival, in both the full cohort (Hazard ratio (HR): 47.6, p= 2.7x10-35, n=649) and in MYCN non-amplified patients (HR=32.8, p=1.3x10-13, n=554), suggesting that neuroblastoma can be driven by MYC signaling in the absence of MYCN amplification. To evaluate potential therapeutic targets within this MYC signature, we conducted cox regression analysis on the 51 individual members and identified that SPT16 was a particularly potent predictor of poor outcome in these 649 neuroblastoma patients (HR: 7.2, p=2.7x10-17). SPT16 is a subunit of the FACT histone chaperone complex, which together with its heterodimer partner SSRP1, has previously been shown to function in dynamic regulation of chromatin to drive transcription, DNA replication and DNA repair. Similar to SPT16, high SSRP1 expression was a strong predictor of poor prognosis in 649 neuroblastoma patients (HR: 12.5, p=5.812x10-26) implicating FACT as a mediator of MYC driven neuroblastoma.

Next we investigated the biological relationship between FACT and MYCN in neuroblastoma. siRNA experiments showed that FACT and MYCN participate in a positive feedback transcriptional loop that is essential for maintaining mutual high expression. Immunohistochemistry in sympathetic ganglia of pre-tumor TH-MYCN mouse model of neuroblastoma identified that FACT was highly expressed at tumor initiation and chemical inhibition of FACT by CBL0137 markedly reduced tumor initiation and subsequent tumorigenesis in vivo. Next we tested CBL0137 against established neuroblastoma in TH-MYCN mice. CBL0137 was highly cytotoxic to tumors either as a single agent or by synergistically promoting clinically used chemotherapeutics. This was accompanied by marked MYCN depletion and prolonged tumor regression in a majority of recipient mice. Pulsed-field electrophoresis showed that CBL0137 impaired FACT dependent DNA damage repair in the presence of genotoxic chemotherapy, thus creating a synthetic lethal environment in MYCN-amplified neuroblastoma cells. Together our data define FACT as a mediator of neuroblastoma tumorigenesis and MYCN-related treatment target. Given the current poor survival rates of children with high-risk neuroblastoma, our findings provide support for the clinical development of CBL0137 as a novel treatment approach for this refractory malignancy.

Citation Format: Daniel R. Carter, Jayne Murray, Belamy B. Cheung, Heyam Kalla, Laura Gamble, Joanna Tsang, Selina Sutton, Jessica Koach, Sarah Syed, Andrew Gifford, Natalia Issaeva, Asel Biktasova, Bernard Atmadibrata, Yuting Sun, Nicolas Sokolowski, Dora Ling, Patrick Y. Kim, Hannah Webber, Ashleigh Clark, Michelle Ruhle, Bing Liu, André Oberthuer, Matthias Fischer, Jennifer Byrne, Federica Saletta, Andrei Purmal, David Ziegler, Tao Liu, Katerina V. Gurova, Andrei V. Gudkov, Murray D. Norris, Michelle Haber, Glenn M. Marshall. MYCN and is a therapeutic target in neuroblastoma. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr PR09.

Facilitates chromatin transcription complex is an "accelerator" of tumor transformation and potential marker and target of aggressive cancers

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 class of anticancer 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 low overall survival. In addition, FACT was found to be upregulated during in vitro transformation and to be necessary, but not sufficient, for driving 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 most likely involves selective chromatin remodeling of genes that stimulate proliferation, inhibit cell death and differentiation, and regulate cellular stress responses.

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

Facilitates chromatin transcription (FACT) is a chromatin remodeling complex with two subunits: SSRP1 and SPT16. Mechanisms controlling FACT levels are of interest, since the complex is not expressed in most differentiated cells, but is frequently upregulated in cancer, particularly in poorly differentiated, aggressive tumors. Moreover, inhibition of FACT expression or function in tumor cells interferes with their survival. Here we demonstrate that SSRP1 and SPT16 protein levels decline upon induction of cellular differentiation or senescence in vitro and that similar declines in protein levels for both SSRP1 and SPT16 occur upon RNAi-mediated knockdown of either SSRP1 or SPT16. The interdependence of SSRP1 and SPT16 protein levels was found to be due to their association with SSRP1 and SPT16 mRNAs, which stabilizes the proteins. In particular, presence of SSRP1 mRNA is critical for SPT16 protein stability. In addition, binding of SSRP1 and SPT16 mRNAs to the FACT complex increases the stability and efficiency of translation of the mRNAs. These data support a model in which the FACT complex is stable when SSRP1 mRNA is present, but quickly degrades when SSRP1 mRNA levels drop. In the absence of FACT complex, SSRP1 and SPT16 mRNAs are unstable and inefficiently translated, making reactivation of FACT function unlikely in normal cells. Thus, we have described a complex and unusual mode of regulation controlling cellular FACT levels that results in amplified and stringent control of FACT activity. The FACT dependence of tumor cells suggests that mechanisms controlling FACT levels could be targeted for anticancer therapy.

Abstract 2759: Anticancer compound curaxin CBL0137, that simultaneously suppresses NF-κB and activates p53, is highly effective in two independent mouse models of neuroblastoma

Background: We have reported that the anti-malarial drug, quinacrine (QC), has significant in vivo anti-tumor activity (Neznanov et al, Cell Cycle, 2009, 8: 1-11). We have since identified curaxins, a more potent class of compounds with similar mechanism of action, whose anti-cancer activity results from chromatin-trapping of the Facilitates Chromatin Transcription (FACT) complex (Gasparian et al, Science Transl. Med, 2011, 3, 95ra74). These novel nongenotoxic agents, like QC, cause simultaneous p53 activation and NF-kB inhibition and tumor cell death. We have now studied the effects of QC and one of the most active curaxins, CBL0137, in the TH-MYCN mouse model of neuroblastoma as well as a nude mouse xenograft model of the disease.

Methods: Cohorts of homozygous TH-MYCN mice with small palpable tumors or of human MYCN-amplified BE(2)-C neuroblastoma tumor-bearing nude mice (n=10) were treated with QC (TH-MYCN mice only) or CBL0137, alone or combined with chemotherapeutic drugs.

Results: QC alone had no significant effect on tumor progression and did not enhance cisplatin or VP16 activity. However, strong anti-tumor activity was observed when QC was combined with cyclophosphamide (CPM) (4/10 QC/CPM-treated vs 0/10 CPM-treated long-term survivors, P<0.001). The effect of CBL0137 alone, administered either orally or iv, on tumor progression was more dramatic. Oral CBL0137 significantly extended survival (median survival time from start of treatment = 31.0±9.9 days versus controls = 3.0±0.2 days; P<0.0001), and was as effective as cisplatin or CPM single-agent treatment. Remarkably, CBL0137 administered iv resulted in a significant number of long-term tumor free survivors (7/9 alive at Day 120). When oral CBL0137 treatment was combined with CPM, survival was substantially increased (7/10 long-term tumor-free TH-MYCN mice) compared to either CBL0137 (0/10 alive) or CPM (1/10 alive) alone (P<0.005 in each case). Most dramatic results were observed when CBL0137 was combined with the standard neuroblastoma relapse protocol of CPM plus topotecan (TOPO). CPM/TOPO treatment resulted in 0/10 long-term survivors, however when combined with either oral or iv CBL0137, this combination cured 5/8 or 11/12 TH-MYCN mice, respectively. Moreover, the combination of iv CBL0137/CPM/TOPO resulted in more than a doubling of lifespan in BE(2)-C tumor-bearing mice compared to those treated with CPM/TOPO or CBL0137 alone (P<0.0001).

Conclusions: These are the most impressive results that we have ever observed for any therapeutic protocol in either the TH-MYCN homozygous or BE(2)-C xenograft mouse models. The combination of CPM/TOPO with iv CBL0137 appears to be a highly promising new treatment approach for refractory neuroblastoma. Safety and efficacy of CBL0137 is currently being investigated in a Phase I clinical trial in advanced cancer patients.

Citation Format: Michelle Haber, Jayne Murray, Ashleigh Carnegie-Clark, Hannah Webber, Glenn M. Marshall, Katerina V. Gurova, Catherine A. Burkhart, Andrei Purmal, Andrei V. Gudkov, Murray D. Norris. Anticancer compound curaxin CBL0137, that simultaneously suppresses NF-κB and activates p53, is highly effective in two independent mouse models of neuroblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2759. doi:10.1158/1538-7445.AM2013-2759

Abstract 5043: The facilitates chromatin transcription (FACT) protein complex promotes neuroblastoma tumor initiation

Tumour initiation in the TH-MYCN transgenic mouse model of neuroblastoma is characterised by transient repression of p53 stress responses in embryonal ganglionic neuroblasts, causing them to persist postnatally as cancer-prone lesions 1, 2. p53 re-activation may be a potential therapeutic strategy for removal of these lesions before they later transform in response to oncogenic stimuli. One potential target for p53 activation is the FACT protein complex which is known to inhibit p53 signalling. Here we show that high mRNA expression levels of the two FACT subunits, SSRP1 and SPT16, in human primary neuroblastoma tissue were significantly associated with poor patient outcome (p<0.001) on Kaplan Meier analysis of 650 neuroblastoma patients. Both SSRP1 and SPT16 levels had a strong correlation with the level of MYCN expression, particularly in high risk MYCN-amplified neuroblastoma tissues (p<0.05). Inhibition of MYCN expression by a specific siRNA, lowered SSRP1 and SPT16 expression in two neuroblastoma tumor cell lines (BE(2)C and Kelly). Alamar blue assays revealed that a chemical inhibitor of FACT, Curaxin or CBL137, potently and selectively promoted cytotoxicity in neuroblastoma cell lines as compared to non-malignant MRC5 fibroblasts (p<0.001). To examine the role of FACT in MYCN-driven tumourigenesis we evaluated the effect of Curaxin on tumor initiation in TH-MYCN mice. Low micromolar Curaxin doses effectively restored normal in vitro, p53-dependent death responses to primary ganglion cells deprived of serum from neonatal TH-MYCN mice, while ganglion cultures from wild-type littermate mice were significantly more resistant to Curaxin treatment, with or without serum deprivation (p<0.001). Most importantly, prophylactic Curaxin treatment of 6 day old TH-MYCN mice had a marked inhibitory effect on postnatal ganglion neuroblast persistence in vivo for both hemizygote and homozygote TH-MYCN mice, as compared to vehicle-only treated animals (p=0.01, p=0.035, respectively). Taken together, our data for the first time identifies FACT as a novel effector of MYCN-driven neuroblastoma tumorigenesis. Inhibitors of the FACT complex may be a novel treatment for high risk MYCN-amplified neuroblastoma and a potential strategy for neuroblastoma prevention.

1. Hansford, L. et al. Mechanisms of embryonal tumor initiation: Distinct roles for MycN expression and MYCN amplification. Proceedings of the National Academy of Sciences of the United States of America 101, 12664-12669 (2004).

2. Calao, M. et al. Direct effects of Bmi1 on p53 protein stability inactivates oncoprotein stress responses in embryonal cancer precursor cells at tumor initiation. Oncogene [ahead of print]

Citation Format: Daniel R. Carter, Belamy B. Cheung, Tao Liu, Carol Au, Murray D. Norris, Michelle Haber, Jayne Murray, Katerina V. Gurova, Andrei V. Gudkov, Glenn M. Marshall. The facilitates chromatin transcription (FACT) protein complex promotes neuroblastoma tumor initiation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5043. doi:10.1158/1538-7445.AM2013-5043

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.

Abstract 3843: Targeting FACT complex suppresses mammary tumorigenesis in Her2/neu transgenic mice

We have recently found that expression of Facilitates Chromatin Transcription (FACT) complex consisting of SSRP1 and SPT16 protein subunits is elevated in many types of cancer comparing with normal tissues. Moreover, survival of tumor cell, but not normal cells is significantly compromised upon genetic knockdown of any of the FACT subunits. In our recent studies we have shown that FACT is essential for the transcriptional activity of NF-κB and Heat Shock Factor 1 and identified small molecules that inhibit activity of both transcription factors by causing functional inactivation of FACT. Since both NF-kB and HSF1 are activated in the process of transformation, we proposed that FACT may be involved in tumor transformation and that inhibition of FACT activity may prevent or reduce tumorigenesis. Objectives of our study were: (i) to check if FACT level is changed in the process of oncogene-induced transformation in vitro and in vivo; and (ii) to test safety and efficacy of anti-FACT therapy with Curaxin-137 in prevention of tumor formation in mice prone to cancer due to oncogene overexpression. We used in vitro (Ha-ras12V) and in vivo (MMTV-neu transgenic mouse model) models of transformation to monitor changes in FACT subunits. We treated the MMTV-neu transgenic mice, in which mammary carcinomas are spontaneously developed due to estrogen receptor-regulated expression of the Her2 proto-oncogene, with Curaxin-137 to determine whether the drug has any toxic effect on normal tissues and/or impact on mammary carcinogenesis. Expression of FACT was elevated in the process of transformation in all models tested. Chronic administration of Curaxin-137 to MMTV-neu mice at doses not having any toxic effect, inhibited tumor onset, delayed tumor progression, and prolonged survival of mice in a dose-dependent manner. Curaxin-137 induced much stronger changes in FACT in tumors than in normal organs, expressing FACT (spleen). Thus, Curaxin-137 may be considered as a potential preventive and/or early stage therapeutic agent for breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3843. doi:1538-7445.AM2012-3843

Curaxins: anticancer compounds that simultaneously suppress NF-κB and activate p53 by targeting FACT

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 Ser(392) 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.

Inflammation and p53: A Tale of Two Stresses

Numerous observations indicate a strong link between chronic inflammation and cancer. This link is supported by substantial experimental evidence indicating mutual negative regulation of NF-κB, the major regulator of inflammation, and p53, the major tumor suppressor. This antagonistic relationship reflects the opposite principles of the physiological responses driven by these transcription factors, which act as sensors and mediators of intrinsic and extrinsic cell stresses, respectively. Constitutive activation of NF-κB, the underlying cause of chronic inflammation, is a common acquired characteristic of tumors. A variety of experimental methods have been used to demonstrate that constitutive activation of NF-κB reduces the tumor suppressor activity of p53, thereby creating permissive conditions for dominant oncogene-mediated transformation. Loss of p53 activity is also a characteristic of the majority of tumors and results in unleashed inflammatory responses due to loss of p53-mediated NF-κB suppression. On the other hand, in natural or pharmacological situations of enforced p53 activation, NF-κB activity, inflammation, and immune responses are reduced, resulting in different pathologies. It is likely that the chronic inflammation that is commonly acquired in various tissues of older mammals leads to general suppression of p53 function, which would explain the increased risk of cancer observed in aging animals and humans. Although the molecular mechanisms underlying reciprocal negative regulation of p53 and NF-κB remain to be deciphered, this phenomenon has important implications for pharmacological prevention of cancer and aging and for new approaches to control inflammation.

Anti-malaria drug blocks proteotoxic stress response: anti-cancer implications

The number of physical conditions and chemical agents induce accumulation of misfolded proteins creating proteotoxic stress. This leads to activation of adaptive pro-survival pathway, known as heat shock response (HSR), resulting in expression of additional chaperones. Several cancer treatment approaches, such as proteasome inhibitor Bortezomib and hsp90 inhibitor geldanamycin, involve activation of proteotoxic stress. Low efficacy of these therapies is likely due to the protective effects of HSR induced in treated cells, making this pathway an attractive target for pharmacological suppression. We found that the anti-malaria drugs quinacrine (QC) and emetine prevented HSR in cancer cells, as judged by induction of hsp70 expression. As opposed to emetine, which inhibited general translation, QC did not affect protein synthesis, but rather suppressed inducible HSF1-dependent transcription of the hsp70 gene in a relatively selective manner. The treatment of tumor cells in vitro with a combination of non-toxic concentrations of QC and proteotoxic stress inducers resulted in rapid induction of apoptosis. The effect was similar if QC was substituted by siRNA against hsp70, suggesting that the HSR inhibitory activity of QC was responsible for cell sensitization to proteotoxic stress inducers. QC was also found to enhance the antitumor efficacy of proteotoxic stress inducers in vivo: combinatorial treatment with 17-DMAG + QC resulted in suppression of tumor growth in two mouse syngeneic models. These results reveal that QC is an inhibitor of HSF1-mediated HSR. As such, this compound has significant clinical potential as an adjuvant in therapeutic strategies aimed at exploiting the cytotoxic potential of proteotoxic stress.

Small molecule screening reveals a transcription-independent pro-survival function of androgen receptor in castration-resistant prostate cancer

In prostate cancer (PCa) patients, initial responsiveness to androgen deprivation therapy is frequently followed by relapse due to development of treatment-resistant androgen-independent PCa. This is typically associated with acquisition of mutations in AR that allow activity as a transcription factor in the absence of ligand, indicating that androgen-independent PCa remains dependent on AR function. Our strategy to effectively target AR in androgen-independent PCa involved using a cell-based readout to isolate small molecules that inhibit AR transactivation function through mechanisms other than modulation of ligand binding. A number of the identified inhibitors were toxic to AR-expressing PCa cells regardless of their androgen dependence. Among these, some only suppressed PCa cell growth (ARTIS), while others induced cell death (ARTIK). ARTIK, but not ARTIS, compounds caused disappearance of AR protein from treated cells. siRNA against AR behaved like ARTIK compounds, while a dominant negative AR mutant that prevents AR-mediated transactivation but does not eliminate the protein showed only a growth suppressive effect. These observations reveal a transcription-independent function of AR that is essential for PCa cell viability and, therefore, is an ideal target for anti-PCa treatment. Indeed, several of the identified AR inhibitors demonstrated in vivo efficacy in mouse models of PCa and are candidates for pharmacologic optimization.

Small-molecule multidrug resistance-associated protein 1 inhibitor reversan increases the therapeutic index of chemotherapy in mouse models of neuroblastoma

The multidrug resistance-associated protein 1 (MRP1) has been closely linked to poor treatment response in several cancers, most notably neuroblastoma. Homozygous deletion of the MRP1 gene in primary murine neuroblastoma tumors resulted in increased sensitivity to MRP1 substrate drugs (vincristine, etoposide, and doxorubicin) compared with tumors containing both copies of wild-type MRP1, indicating that MRP1 plays a significant role in the drug resistance in this tumor type and defining this multidrug transporter as a target for pharmacologic suppression. A cell-based readout system was created to functionally determine intracellular accumulation of MRP1 substrates using a p53-responsive reporter as an indicator of drug-induced DNA damage. Screening of small-molecule libraries in this readout system revealed pyrazolopyrimidines as a prominent structural class of potent MRP1 inhibitors. Reversan, the lead compound of this class, increased the efficacy of both vincristine and etoposide in murine models of neuroblastoma (syngeneic and human xenografts). As opposed to the majority of inhibitors of multidrug transporters, Reversan was not toxic by itself nor did it increase the toxicity of chemotherapeutic drug exposure in mice. Therefore, Reversan represents a new class of nontoxic MRP1 inhibitor, which may be clinically useful for the treatment of neuroblastoma and other MRP1-overexpressing drug-refractory tumors by increasing their sensitivity to conventional chemotherapy.

Mycoplasma infection suppresses p53, activates NF-kappaB and cooperates with oncogenic Ras in rodent fibroblast transformation

Prokaryotes of the genus Mycoplasma are the smallest cellular organisms that persist as obligate extracellular parasites. Although mycoplasma infection is known to be associated with chromosomal instability and can promote malignant transformation, the mechanisms underlying these phenomena remain unknown. Since persistence of many cellular parasites requires suppression of apoptosis in host cells, we tested the effect of mycoplasma infection on the activity of the p53 and nuclear factor (NF)-kappaB pathways, major mechanisms controlling programmed cell death. To monitor the activity of p53 and NF-kappaB in mycoplasma-infected cells, we used a panel of reporter cell lines expressing the bacterial beta-galactosidase gene under the control of p53- or NF-kappaB-responsive promoters. Cells incubated with media conditioned with different species of mycoplasma showed constitutive activation of NF-kappaB and reduced activation of p53, common characteristics of the majority of human tumor cells, with M. arginini having the strongest effect among the species tested. Moreover, mycoplasma infection reduced the expression level and inducibility of an endogenous p53-responsive gene, p21(waf1), and inhibited apoptosis induced by genotoxic stress. Infection with M. arginini made rat and mouse embryo fibroblasts susceptible to transformation with oncogenic H-Ras, whereas mycoplasma-free cells underwent irreversible p53-dependent growth arrest. Mycoplasma infection was as effective as shRNA-mediated knockdown of p53 expression in making rodent fibroblasts permissive to Ras-induced transformation. These observations indicate that mycoplasma infection plays the role of a p53-suppressing oncogene that cooperates with Ras in cell transformation and suggest that the carcinogenic and mutagenic effects of mycoplasma might be due to inhibition of p53 tumor suppressor function by this common human parasite.

Prostate cancer cells tolerate a narrow range of androgen receptor expression and activity

BACKGROUND

The precise role of androgen receptor (AR) in the normal development of prostate and the progression of prostate cancer (CaP) remains controversial. While AR expression and activity is associated with growth arrest and differentiation of normal prostate cells, it is maintained in CaP cells that are characterized by continued proliferation. Our objective was to determine the importance of AR signaling for survival and growth of CaP cells, particularly those with a hormone-refractory phenotype.

METHOD

AR expression was modulated in androgen-sensitive (AS) and androgen-insensitive (AI) CaP cells using RNAi and cDNA transduction. Resulting changes in AR transcriptional activity and cell growth were quantified.

RESULTS

Interference with AR expression in both AS and AI CaP cells by shRNA transduction demonstrated a direct correlation between residual AR expression and cell viability. CaP cells lacking AR expression undergo apoptosis several days after AR down-regulation. This delayed response suggests that AR regulates apoptosis likely through an indirect mechanism. Overexpression of AR or hyper-stimulation of AR with high levels of androgen was also poorly tolerated by CaP cells. Cells with elevated AR had a growth disadvantage due to G1 cell cycle arrest and induction of p21 and GADD45 expression.

CONCLUSIONS

CaP cells expressing endogenous AR are sensitive to both increases and decreases in AR expression levels and activity. AR in CaP cells is delicately regulated to provide a balance between cell death and continued proliferation. Thus, both approaches, inhibition and over-stimulation of AR activity, may have therapeutic value for treatment of prostate cancer.

p53 determines multidrug sensitivity of childhood neuroblastoma

For pediatric cancers like neuroblastoma, the most common extracranial solid tumor of infancy, p53 mutations are rare at diagnosis, but may be acquired after chemotherapy, suggesting a potential role in drug resistance. Heavy metal-selected neuroblastoma cells were found to acquire an unusually broad multidrug resistance (MDR) phenotype but displayed no alterations in genes associated with "classic" MDR. These cells had acquired a mutant p53 gene, linking p53 to drug sensitivity in neuroblastoma. We therefore generated p53-deficient variants in neuroblastoma cell lines with wild-type p53 by transduction of p53-suppressive constructs encoding either short hairpin RNA or a dominant-negative p53 mutant. Analysis of these cells indicated that (a) in contrast to previous reports, wild-type p53 was fully functional in all neuroblastoma lines tested; (b) inactivation of p53 in neuroblastoma cells resulted in establishment of a MDR phenotype; (c) p53-dependent senescence, the primary response of some neuroblastoma cells to DNA damage, is replaced after p53 inactivation by mitotic catastrophe and subsequent apoptosis; (d) knockdown of mutant p53 did not revert the MDR phenotype, suggesting it is determined by p53 inactivation rather than gain of mutant function. These results suggest the importance of p53 status as a prognostic marker of treatment response in neuroblastoma. p53 suppression may have opposite effects on drug sensitivity as determined by analysis of isogenic pairs of tumor cell lines of nonneuroblastoma origin, indicating the importance of tissue context for p53-mediated modulation of tumor cell sensitivity to treatment.

Quinacrine inhibits the epidermal dendritic cell migration initiating T cell-mediated skin inflammation

Quinacrine (QC) is an anti-inflammatory drug that has been used for the treatment of malaria and rheumatoid diseases. The mechanism(s) underlying the anti-inflammatory activity of QC remains poorly understood. We recently reported the QC-mediated inhibition of the NF-kappaB pathway using an in vitro model. To test this potential mechanism in vivo, we used the contact hypersensitivity response (CHS) to chemical allergen sensitization and challenge in mice as a model of skin inflammation. The results indicated that QC treatment inhibited NF-kappaB activation in the skin during allergen sensitization. This inhibition was reflected by decreased mRNA expression and protein production of the NF-kappaB-dependent cytokines TNF-alpha and IL-1beta and the chemokine CCL21 in the skin. The decreases in these cytokines resulted in reduced migration of allergen-presenting dendritic cells from the skin into skin-draining lymph nodes and markedly decreased activation of effector CD8+ T cells for the CHS response to allergen challenge (inhibitory concentration 50% or IC50 was 55 mg/kg). These findings reveal a previously unrecognized mechanism of QC-mediated inhibition of inflammation.

Targeted disruption of the mouse ing1 locus results in reduced body size, hypersensitivity to radiation and elevated incidence of lymphomas

Ing1 belongs to the family of evolutionary conserved genes encoding nuclear PHD finger-containing proteins implicated in a variety of processes, including tumorigenesis, replicative senescence, excision repair and response to genotoxic stress. We have generated mice deficient in all the isoforms of Ing1 by targeted disruption of the exon that is common for all ing1 transcripts. Embryonic fibroblasts from ing1-knockout mice were similar to the wild-type cells in their growth characteristics, replicative lifespan in culture, p53 induction and sensitivity to various cytotoxic treatments with minor alterations in cell cycle distribution in response to genotoxic stress. ing1-deficient animals are characterized by reduced size with no obvious morphological, physiological or behavioral abnormalities, indicating that ing1 function is dispensable for the viability of mice under normal physiological conditions. Loss of ing1 was associated with earlier onset and higher incidence of lymphomas. Consistent with the possible involvement of Ing1 in DNA repair, ing1-deficient mice were more sensitive to total body gamma radiation. Our observations are well in line with the suggested role of ing1 as a candidate tumor suppressor gene involved in control of DNA damage response.

Small molecules that reactivate p53 in renal cell carcinoma reveal a NF-kappaB-dependent mechanism of p53 suppression in tumors

Renal cell carcinomas (RCC) commonly retain wild-type but functionally inactive p53, which is repressed by an unknown dominant mechanism. To help reveal this mechanism, we screened a diverse chemical library for small molecules capable of restoring p53-dependent transactivation in RCC cells carrying a p53-responsive reporter. Among the compounds isolated were derivatives of 9-aminoacridine (9AA), including the antimalaria drug quinacrine, which strongly induced p53 function in RCC and other types of cancer cells. Induction of p53 by these compounds does not involve genotoxic stress and is mediated by suppression of NF-kappaB activity. In contrast to agents that target IkappaB kinase 2, 9AA and quinacrine can effectively suppress both basal and inducible activities of NF-kappaB, representing inhibitors of a previously undescribed type that convert NF-kappaB from a transactivator into a transrepressor, leading to accumulation of inactive nuclear complexes with unphosphorylated Ser-536 in the p65/RelA subunit. p53 function in RCC can be restored by ectopic expression of a superrepressor of IkappaB as effectively as by 9AA-derived compounds. These findings suggest that the complete or partial repression of p53 observed in many tumors can be the result of constitutive activation of NF-kappaB. The results demonstrate, in principle, the possibility to kill cancer cells selectively through simultaneous inhibition of NF-kappaB and activation of p53 by a single small molecule and suggest anticancer applications for the well known antimalaria drug quinacrine.

p53 pathway in renal cell carcinoma is repressed by a dominant mechanism

Renal cell carcinoma (RCC) rarely acquires mutations in p53 tumor suppressor gene, suggesting that p53 signaling in this tumor type might be repressed by some other mechanism. In fact, all four RCC-derived cell lines we tested maintained wild-type p53 but were not capable of transactivating p53-responsive reporters and endogenous p53-responsive genes. p53 protein in RCC showed normal response to genotoxic stress, including accumulation, nuclear translocation, and activation of specific DNA binding. Functional and expression analysis of Mdm2, MdmX, and Arf showed lack of involvement of these p53 regulators in the observed defect of p53 function in RCC. However, activation of p53-mediated transactivation could be achieved by extremely high levels of p53 attained by lentivirus vector-driven transduction, suggesting the involvement of a dominant inhibitor in repression of p53-dependent transactivation in RCC. Consistently, p53 inactivation prevailed in the hybrids of RCC cells with the cells possessing fully functional p53. Remarkably, cells of normal kidney epithelium also caused partial p53 repression in cell fusion experiments, suggesting that RCC-specific p53 repression may be based on an unknown dominant mechanism also acting in normal kidney tissue.

Cooperation of two mutant p53 alleles contributes to Fas resistance of prostate carcinoma cells

Both inactivation of p53 function and loss of sensitivity to Fas contribute to a malignant phenotype and frequently occur during tumor progression. Although in the majority of cases only one of the p53 alleles is mutated, some tumors acquire mutations in both alleles of the p53 gene. To determine the biological significance of this phenomenon, we analyzed p53 mutants, p53(223Leu) and p53(274Phe), from Fas-resistant prostate carcinoma cell line DU145. Both mutants differed from wild-type p53 in their conformation, transactivation ability, and effect on the growth of p53-deficient cells, with p53(223Leu) being more similar to wild-type p53 than was p53(274Phe). Interestingly, the biological effect of coexpression of the DU145-derived mutants was dramatically different from that of each mutant expressed alone. Whereas neither of the two mutants was found to be dominant-negative against wild-type p53, each neutralized the other's growth-suppressive effects and, in combination, were capable of down-regulating Fas expression and converting Fas-sensitive prostate carcinoma cells PC3 into Fas-resistant ones. These results indicate that two different p53 mutants that are separately rather weak can cooperate to generate p53 protein with anti-Fas function that is likely to provide additional selective advantages to the tumor.

Paradoxical role of apoptosis in tumor progression

Tumors frequently acquire resistance to apoptosis that is expected to contribute to malignant phenotype and reduce sensitivity to treatment. In fact, inactivation of p53 tumor suppressor gene resulting in suppression of apoptosis serves as a negative prognostic marker. Surprisingly, expression of a strong anti-apoptotic protein Bcl-2, another mechanism to avoid apoptosis, was found to be associated with a favorable prognosis. This paradoxical anti-progressor function of Bcl-2 has been explained in literature based on the negative effect of Bcl-2 on cell proliferation. Here, by analyzing accumulated experimental and clinical data, we provide evidence supporting another hypothesis that defines apoptosis as an accelerator of tumor progression. The mechanism of anti-progressor function of Bcl-2 is based on creation of tumors that maintain control of genomic stability by eliminating selective advantages for the cells that acquire resistance to apoptosis through loss of p53. Thus, inhibition of apoptosis does not lead to loss of genomic stability and creates tumor environment that no longer supports further tumor progression and inhibitors of apoptosis can be considered as factors suppressing tumor progression.

Expression of prostate specific antigen (PSA) is negatively regulated by p53

Although prostate-specific antigen (PSA) is considered a uniquely important tumor marker and is broadly used for early detection of prostate cancer, the molecular mechanisms underlying its elevated expression in tumors have been unknown. By using cDNA microarray gene expression profiling, we found a fourfold increase in the PSA mRNA level in prostatic carcinoma cell line LNCaP, in which the p53 pathway was suppressed by a dominant negative p53 mutant. Consistently, p53 suppression caused a 4-8-fold increase in secretion of PSA protein in culture medium, suggesting that PSA gene expression is under negative control of p53. While wild type p53 strongly repressed, dominant negative p53 mutants stimulated PSA promoter-driven transcription and secretion of PSA in transient transfection experiments. The inhibitory effect of wild type p53 was undetectable in the presence of trichostatin A, suggesting the involvement of histone deacetylation in negative regulation of PSA promoter activity. Thus, PSA is likely to be a tissue specific indicator of transformation-associated p53 suppression in prostate cells. This finding provides a plausible explanation for a frequent increase of PSA levels in advanced prostate cancer.

Apoptosis inhibitor as a suppressor of tumor progression: expression of Bcl-2 eliminates selective advantages for p53-deficient cells in the tumor

Inactivation of p53 and expression of Bcl-2, frequently occurring during tumor progression, have different prognostic value: while inactivation of p53 is generally associated with unfavorable prognosis, expression of Bcl-2 often correlates with better clinical outcome and delays selection of metastatic variants of experimental tumors. To analyze the mechanisms underlying the "anti-progression" function of Bcl-2, we engineered tumor cell variants differing in their p53 status and Bcl-2 expression and compared their expansion in experimental tumors. Although neither p53 suppression nor Bcl-2-expression altered cell growth properties in vitro, both variants showed rapid accumulation in growing tumors in vivo, presumably due to their resistance to hypoxia. However, no expansion of p53-deficient variants occurred in the tumors formed by Bcl-2-overexpressing cells, indicating that p53 deficiency has no selective advantages in the Bcl-2-expressing environment. Importantly, expression of Bcl-2, unlike p53 suppression, did not lead to genomic instability as judged by the frequencies of gene amplification. Thus, acquisition of Bcl-2 expression is as advantageous for tumor cell growth in vivo as is p53 inactivation but does not affect genomic stability and creates the environment restrictive for the expansion of genetically unstable and potentially malignant p53-deficient cells, causing a delay in tumor progression and explaining the different prognostic value of Bcl-2 and p53.

Structure and regulation of the mouse ing1 gene. Three alternative transcripts encode two phd finger proteins that have opposite effects on p53 function

The human ING1 gene encodes nuclear protein p33(ING1), previously shown to cooperate with p53 in cell growth control (Garkavtsev, I., Grigorian, I. A., Ossovskaya, V. S., Chernov, M. V., Chumakov, P. M., and Gudkov, A. V. (1998) Nature 391, 295-298). p33(ING1) belongs to a small family of proteins from human, mouse, and yeast of approximately the same size that show significant similarity to one another within the C-terminal PHD finger domain and also contain an additional N-terminal region with subtle but reliably detectable sequence conservation. Mouse ing1 is transcribed from three differently regulated promoters localized within a 4-kilobase pair region of genomic DNA. The resulting transcripts share a long common region encoded by a common exon and differ in their 5'-exon sequences. Two transcripts are translated into the same protein of 185 amino acids, the mouse equivalent of the human p33(ING1), while the third transcript encodes a longer protein that has 94 additional N-terminal amino acids. Overexpression of the longer protein interferes with the accumulation of p53 protein and activation of p53-responsive promoters after DNA damage. Between the two products of ing1, only the longer one forms a complex with p53 detectable by immunoprecipitation. These results indicate that a single gene, ing1, encodes both p53-suppressing and p53-activating proteins that are regulated by alternative promoters.

Accumulation in "normal" lungs of live tumorigenic cells during sub-cutaneous growth of weakly and highly metastasizing tumors and their in vitro sensitivity to growth regulation by normal fibroblasts

The main purposes of the study were: (1) in vivo comparison of accumulation of live tumorigenic cells (LTC) in macroscopically normal lungs of animals bearing 6 s.c. Syrian hamster sarcomas differing in spontaneous metastasizing activity (SMA); (2) in vitro examination of the sensitivity of these cell strains to the growth-regulating signals of normal fibroblasts. Cell strains used differed in SMA from very weak (WM) to extremely high (HM). The numbers of LTC doses in "normal" lung tissue of tumor-bearing animals were determined in s.c. transplantation tests by titrating single-cell suspensions prepared from the lung tissues of 5 tumor-bearing animals, for each cell strain, every 5 days during 30 days of s.c. tumor growth, until the appearance of the first spontaneous lung metastases. The sensitivity of WM and HM cells to growth-regulating signals of normal hamster embryo fibroblasts (HEFs) was examined by in vitro co-culturing during 6 days with daily determination of 3H-TdR incorporation in the WM and HM cells grown with or without contact with HEFs. The data presented demonstrate (1) the surprisingly similar efficiency in the occupation of macroscopically normal lung tissues by live tumorigenic cells of WM and HM strains, disseminating spontaneously from the s.c. tumors; (2) the significantly lower sensitivity of HM cells, in contrast to WM, to growth inhibition by contact with HEFs and especially their marked ability to usurp the growth-stimulating signals of normal HEFs.