Neuroendocrine lineage commitment of small cell lung cancers can be leveraged into p53-independent non-cytotoxic therapy.

Small cell lung cancers (SCLCs) rapidly resist cytotoxic chemotherapy and immune checkpoint inhibitor (ICI) treatments. New, non-cross-resistant therapies are thus needed. SCLC cells are committed into neuroendocrine lineage then maturation arrested. Implicating DNA methyltransferase 1 (DNMT1) in the maturation arrests, we find (1) the repression mark methylated CpG, written by DNMT1, is retained at suppressed neuroendocrine-lineage genes, even as other repression marks are erased; (2) DNMT1 is recurrently amplified, whereas Ten-Eleven-Translocation 2 (TET2), which functionally opposes DNMT1, is deleted; (3) DNMT1 is recruited into neuroendocrine-lineage master transcription factor (ASCL1, NEUROD1) hubs in SCLC cells; and (4) DNMT1 knockdown activated ASCL1-target genes and released SCLC cell-cycling exits by terminal lineage maturation, which are cycling exits that do not require the p53/apoptosis pathway used by cytotoxic chemotherapy. Inhibiting DNMT1/corepressors with clinical compounds accordingly extended survival of mice with chemorefractory and ICI-refractory, p53-null, disseminated SCLC. Lineage commitment of SCLC cells can hence be leveraged into non-cytotoxic therapy able to treat chemo/ICI-refractory SCLC.

Oral tetrahydrouridine and decitabine for non-cytotoxic epigenetic gene regulation in sickle cell disease: A randomized phase 1 study.

BACKGROUND: Sickle cell disease (SCD), a congenital hemolytic anemia that exacts terrible global morbidity and mortality, is driven by polymerization of mutated sickle hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) interferes with this polymerization, but HbF is epigenetically silenced from infancy onward by DNA methyltransferase 1 (DNMT1). METHODS AND FINDINGS: To pharmacologically re-induce HbF by DNMT1 inhibition, this first-in-human clinical trial (NCT01685515) combined 2 small molecules-decitabine to deplete DNMT1 and tetrahydrouridine (THU) to inhibit cytidine deaminase (CDA), the enzyme that otherwise rapidly deaminates/inactivates decitabine, severely limiting its half-life, tissue distribution, and oral bioavailability. Oral decitabine doses, administered after oral THU 10 mg/kg, were escalated from a very low starting level (0.01, 0.02, 0.04, 0.08, or 0.16 mg/kg) to identify minimal doses active in depleting DNMT1 without cytotoxicity. Patients were SCD adults at risk of early death despite standard-of-care, randomized 3:2 to THU-decitabine versus placebo in 5 cohorts of 5 patients treated 2X/week for 8 weeks, with 4 weeks of follow-up. The primary endpoint was ≥ grade 3 non-hematologic toxicity. This endpoint was not triggered, and adverse events (AEs) were not significantly different in THU-decitabine-versus placebo-treated patients. At the decitabine 0.16 mg/kg dose, plasma concentrations peaked at approximately 50 nM (Cmax) and remained elevated for several hours. This dose decreased DNMT1 protein in peripheral blood mononuclear cells by >75% and repetitive element CpG methylation by approximately 10%, and increased HbF by 4%-9% (P < 0.001), doubling fetal hemoglobin-enriched red blood cells (F-cells) up to approximately 80% of total RBCs. Total hemoglobin increased by 1.2-1.9 g/dL (P = 0.01) as reticulocytes simultaneously decreased; that is, better quality and efficiency of HbF-enriched erythropoiesis elevated hemoglobin using fewer reticulocytes. Also indicating better RBC quality, biomarkers of hemolysis, thrombophilia, and inflammation (LDH, bilirubin, D-dimer, C-reactive protein [CRP]) improved. As expected with non-cytotoxic DNMT1-depletion, platelets increased and neutrophils concurrently decreased, but not to an extent requiring treatment holds. As an early phase study, limitations include small patient numbers at each dose level and narrow capacity to evaluate clinical benefits. CONCLUSION: Administration of oral THU-decitabine to patients with SCD was safe in this study and, by targeting DNMT1, upregulated HbF in RBCs. Further studies should investigate clinical benefits and potential harms not identified to date. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01685515.

GATA4 loss of function in liver cancer impedes precursor to hepatocyte transition.

The most frequent chromosomal structural loss in hepatocellular carcinoma (HCC) is of the short arm of chromosome 8 (8p). Genes on the remaining homologous chromosome, however, are not recurrently mutated, and the identity of key 8p tumor-suppressor genes (TSG) is unknown. In this work, analysis of minimal commonly deleted 8p segments to identify candidate TSG implicated GATA4, a master transcription factor driver of hepatocyte epithelial lineage fate. In a murine model, liver-conditional deletion of 1 Gata4 allele to model the haploinsufficiency seen in HCC produced enlarged livers with a gene expression profile of persistent precursor proliferation and failed hepatocyte epithelial differentiation. HCC mimicked this gene expression profile, even in cases that were morphologically classified as well differentiated. HCC with intact chromosome 8p also featured GATA4 loss of function via GATA4 germline mutations that abrogated GATA4 interactions with a coactivator, MED12, or by inactivating mutations directly in GATA4 coactivators, including ARID1A. GATA4 reintroduction into GATA4-haploinsufficient HCC cells or ARID1A reintroduction into ARID1A-mutant/GATA4-intact HCC cells activated hundreds of hepatocyte genes and quenched the proliferative precursor program. Thus, disruption of GATA4-mediated transactivation in HCC suppresses hepatocyte epithelial differentiation to sustain replicative precursor phenotype.

Somatic SETBP1 mutations in myeloid malignancies.

Here we report whole-exome sequencing of individuals with various myeloid malignancies and identify recurrent somatic mutations in SETBP1, consistent with a recent report on atypical chronic myeloid leukemia (aCML). Closely positioned somatic SETBP1 mutations encoding changes in Asp868, Ser869, Gly870, Ile871 and Asp880, which match germline mutations in Schinzel-Giedion syndrome (SGS), were detected in 17% of secondary acute myeloid leukemias (sAML) and 15% of chronic myelomonocytic leukemia (CMML) cases. These results from deep sequencing demonstrate a higher mutational detection rate than reported with conventional sequencing methodology. Mutant cases were associated with advanced age and monosomy 7/deletion 7q (-7/del(7q)) constituting poor prognostic factors. Analysis of serially collected samples indicated that SETBP1 mutations were acquired during leukemic evolution. Transduction with mutant Setbp1 led to the immortalization of mouse myeloid progenitors that showed enhanced proliferative capacity compared to cells transduced with wild-type Setbp1. Somatic mutations of SETBP1 seem to cause gain of function, are associated with myeloid leukemic transformation and convey poor prognosis in myelodysplastic syndromes (MDS) and CMML.

High cytidine deaminase expression in the liver provides sanctuary for cancer cells from decitabine treatment effects.

We document for the first time that sanctuary in an organ which expresses high levels of the enzyme cytidine deaminase (CDA) is a mechanism of cancer cell resistance to cytidine analogues. This mechanism could explain why historically, cytidine analogues have not been successful chemotherapeutics against hepatotropic cancers, despite efficacy in vitro. Importantly, this mechanism of resistance can be readily reversed, without increasing toxicity to sensitive organs, by combining a cytidine analogue with an inhibitor of cytidine deaminase (tetrahydrouridine). Specifically, CDA rapidly metabolizes cytidine analogues into inactive uridine counterparts. Hence, to determine if sheltering/protection of cancer cells in organs which express high levels of CDA (e.g., liver) is a mechanism of resistance, we utilized a murine xenotransplant model of myeloid cancer that is sensitive to epigenetic therapeutic effects of the cytidine analogue decitabine in vitro and hepato-tropic in vivo. Treatment of tumor-bearing mice with decitabine (subcutaneous 0.2mg/kg 2X/week) doubled median survival and significantly decreased extra-hepatic tumor burden, but hepatic tumor burden remained substantial, to which the animals eventually succumbed. Combining a clinically-relevant inhibitor of CDA (tetrahydrouridine) with a lower dose of decitabine (subcutaneous 0.1mg/kg 2X/week) markedly decreased liver tumor burden without blood count or bone marrow evidence of myelotoxicity, and with further improvement in survival. In conclusion, sanctuary in a CDA-rich organ is a mechanism by which otherwise susceptible cancer cells can resist the effects of decitabine epigenetic therapy. This protection can be reversed without increasing myelotoxicity by combining tetrahydrouridine with a lower dose of decitabine.

Effects of tetrahydrouridine on pharmacokinetics and pharmacodynamics of oral decitabine.

The deoxycytidine analog decitabine (DAC) can deplete DNA methyl-transferase 1 (DNMT1) and thereby modify cellular epigenetics, gene expression, and differentiation. However, a barrier to efficacious and accessible DNMT1-targeted therapy is cytidine deaminase, an enzyme highly expressed in the intestine and liver that rapidly metabolizes DAC into inactive uridine counterparts, severely limiting exposure time and oral bioavailability. In the present study, the effects of tetrahydrouridine (THU), a competitive inhibitor of cytidine deaminase, on the pharmacokinetics and pharmacodynamics of oral DAC were evaluated in mice and nonhuman primates. Oral administration of THU before oral DAC extended DAC absorption time and widened the concentration-time profile, increasing the exposure time for S-phase-specific depletion of DNMT1 without the high peak DAC levels that can cause DNA damage and cytotoxicity. THU also decreased interindividual variability in pharmacokinetics seen with DAC alone. One potential clinical application of DNMT1-targeted therapy is to increase fetal hemoglobin and treat hemoglobinopathy. Oral THU-DAC at a dose that would produce peak DAC concentrations of less than 0.2µM administered 2×/wk for 8 weeks to nonhuman primates was not myelotoxic, hypomethylated DNA in the γ-globin gene promoter, and produced large cumulative increases in fetal hemoglobin. Combining oral THU with oral DAC changes DAC pharmacology in a manner that may facilitate accessible noncytotoxic DNMT1-targeted therapy.

Noncytotoxic differentiation treatment of renal cell cancer.

Current drug therapy for metastatic renal cell cancer (RCC) results in temporary disease control but not cure, necessitating continued investigation into alternative mechanistic approaches. Drugs that inhibit chromatin-modifying enzymes involved in transcription repression (chromatin-relaxing drugs) could have a role, by inducing apoptosis and/or through differentiation pathways. At low doses, the cytosine analogue decitabine (DAC) can be used to deplete DNA methyl-transferase 1 (DNMT1), modify chromatin, and alter differentiation without causing apoptosis (cytotoxicity). Noncytotoxic regimens of DAC were evaluated for in vitro and in vivo efficacy against RCC cell lines, including a p53-mutated RCC cell line developed from a patient with treatment-refractory metastatic RCC. The cell division-permissive mechanism of action-absence of early apoptosis or DNA damage, increase in expression of HNF4α (hepatocyte nuclear factor 4α), a key driver associated with the mesenchymal to epithelial transition, decrease in mesenchymal marker expression, increase in epithelial marker expression, and late increase in cyclin-dependent kinase inhibitor CDKN1B (p27) protein-was consistent with differentiation-mediated cell-cycle exit. In vivo blood counts and animal weights were consistent with minimal toxicity of therapy. The distinctive mechanism of action of a dose and schedule of DAC designed for noncytotoxic depletion of DNMT1 suggests a potential role in treating RCC.

Decitabine maintains hematopoietic precursor self-renewal by preventing repression of stem cell genes by a differentiation-inducing stimulus.

The cytosine analogue decitabine alters hematopoietic differentiation. For example, decitabine treatment increases self-renewal of normal hematopoietic stem cells. The mechanisms underlying decitabine-induced shifts in differentiation are poorly understood, but likely relate to the ability of decitabine to deplete the chromatin-modifying enzyme DNA methyltransferase 1 (DNMT1), which plays a central role in transcription repression. HOXB4 is a transcription factor that promotes hematopoietic stem cell self-renewal. In hematopoietic precursors induced to differentiate by the lineage-specifying transcription factor Pu.1 or by the cytokine granulocyte-colony stimulating factor, there is rapid repression of HOXB4 and other stem cell genes. Depletion of DNMT1 using shRNA or decitabine prevents HOXB4 repression by Pu.1 or granulocyte-colony stimulating factor and maintains hematopoietic precursor self-renewal. In contrast, depletion of DNMT1 by decitabine 6 hours after the differentiation stimulus, that is, after repression of HOXB4 has occurred, augments differentiation. Therefore, DNMT1 is required for the early repression of stem cell genes, which occurs in response to a differentiation stimulus, providing a mechanistic explanation for the observation that decitabine can maintain or increase hematopoietic stem cell self-renewal in the presence of a differentiation stimulus. Using decitabine to deplete DNMT1 after this early repression phase does not impair progressive differentiation.

Expression, purification, and characterization of the intra-cellular domain of the ANP receptor.

The membrane-bound atrial natriuretic peptide receptor (GCA) catalyzes the formation of cGMP from GTP in response to natriuretic peptide hormones. Previous structural studies have focused on the extra-cellular hormone binding domain of this receptor whereas its intra-cellular domain has not yet been amenable to such studies. We report here the baculovirus expression and purification of the GCA intra-cellular domain construct GCA(ID) comprising the complete intra-cellular region which includes the kinase-homology domain, coiled-coil region, and catalytic cyclase domain. The intra-cellular domain was enzymatically characterized in terms of guanylyl cyclase activity and the effects of ATP, manganese, and Triton X-100. Our results indicate that the activity of the intra-cellular domain of the ANP receptor is about 2 fold less active compared to a truncated cyclase domain construct lacking the kinase-like domain that was also expressed and purified. In addition, unlike the full length receptor, the intra-cellular domain could not be activated by Triton X-100/Mn(2+) or its activity stimulated by ATP. These data therefore indicate that the major part of the transition from the basal state to the fully, ANP/ATP-dependent, activated state as well its stimulation/enhancement by Triton X-100/Mn(2+) requires the full length receptor. These receptor insights could aid in the development of novel therapeutics as the GCA receptor is a key drug target for cardiovascular diseases.

Retinal pigment epithelium lipofuscin proteomics.

Lipofuscin accumulates with age in the retinal pigment epithelium (RPE) in discrete granular organelles and may contribute to age-related macular degeneration. Because previous studies suggest that lipofuscin contains protein that may impact pathogenic mechanisms, we pursued proteomics analysis of lipofuscin. The composition of RPE lipofuscin and its mechanisms of pathogenesis are poorly understood in part because of the heterogeneity of isolated preparations. We purified RPE lipofuscin granules by treatment with proteinase K or SDS and showed by light, confocal, and transmission electron microscopy that the purified granules are free of extragranular material and associated membranes. Crude and purified lipofuscin preparations were quantitatively compared by (i) LC MS/MS proteomics analyses, (ii) immunoanalyses of oxidative protein modifications, (iii) amino acid analysis, (iv) HPLC of bisretinoids, and (v) assaying phototoxicity to RPE cells. From crude lipofuscin preparations 186 proteins were identified, many of which appeared to be modified. In contrast, very little protein ( approximately 2% (w/w) by amino acid analysis) and no identifiable protein were found in the purified granules, which retained full phototoxicity to cultured RPE cells. Our analyses showed that granules in purified and crude lipofuscin preparations exhibit no statistically significant differences in diameter or circularity or in the content of the bisretinoids A2E, isoA2E, and all-trans-retinal dimer-phosphatidylethanolamine. The finding that the purified granules contain minimal protein yet retain phototoxic activity suggests that RPE lipofuscin pathogenesis is largely independent of associated protein. The purified granules also exhibited oxidative protein modifications, including nitrotyrosine generated from reactive nitrogen oxide species and carboxyethylpyrrole and iso[4]levuglandin E(2) adducts generated from reactive lipid fragments. This finding is consistent with previous studies demonstrating RPE lipofuscin to be a potent generator of reactive oxygen species and supports the hypothesis that such species, including reactive fragments from lipids and retinoids, contribute to the mechanisms of RPE lipofuscin pathogenesis.

Podocalyxin increases the aggressive phenotype of breast and prostate cancer cells in vitro through its interaction with ezrin.

Podocalyxin is an anti-adhesive transmembrane sialomucin that has been implicated in the development of more aggressive forms of breast and prostate cancer. The mechanism through which podocalyxin increases cancer aggressiveness remains poorly understood but may involve the interaction of podocalyxin with ezrin, an established mediator of metastasis. Here, we show that overexpression of podocalyxin in MCF7 breast cancer and PC3 prostate cancer cell lines increased their in vitro invasive and migratory potential and led to increased expression of matrix metalloproteases 1 and 9 (MMP1 and MMP9). Podocalyxin expression also led to an increase in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) activity. To determine the role of ezrin in these podocalyxin-dependent phenotypic events, we first confirmed that podocalyxin formed a complex with ezrin in MCF7 and PC3 cells. Furthermore, expression of podocalyxin was associated with a changed ezrin subcellular localization and increased ezrin phosphorylation. Transient knockdown of ezrin protein abrogated MAPK and PI3K signaling as well as MMP expression and invasiveness in cancer cells overexpressing podocalyxin. These findings suggest that podocalyxin leads to increased in vitro migration and invasion, increased MMP expression, and increased activation of MAPK and PI3K activity in MCF7 and PC3 cells through its ability to form a complex with ezrin.

Role of IKK and oscillatory NFkappaB kinetics in MMP-9 gene expression and chemoresistance to 5-fluorouracil in RKO colorectal cancer cells.

Nuclear factor kappa B (NFkappaB) is a central participant in the metastasis and chemoresistance of colorectal cancer (CRC). However, it is not fully understood to what extent NFkappaB contributes to induction of the metastasis-associated matrix metalloprotease-9 (MMP-9) gene and sensitivity to the commonly used chemotherapeutic 5-fluorouracil (5-Fu) in CRC. Using the RKO human CRC cell line and two NFkappaB signaling deficient RKO mutants, we investigated NFkappaB's role in the induction of MMP-9 and 5-Fu sensitivity in RKO CRC cells. NFkappaB plays a predominant role in MMP-9 gene induction in RKO cells, as evidenced by the failure of tumor necrosis factor alpha (TNFalpha) to induce MMP-9 in either of the NFkappaB signaling mutants. RKO cells exhibit a robust, oscillatory NFkappaB activity in response to TNFalpha not seen in either of the NFkappaB mutant cell lines, which instead demonstrate diminished, nonoscillatory NFkappaB activation. Analysis of TNFalpha-induced phosphorylation and MMP-9 promoter recruitment of the p65 NFkappaB subunit revealed a significant reduction in p65 phosphorylation as well as reduced and altered recruitment of p65 to the MMP-9 gene promoter in the mutants compared to the parental RKO cell line. 5-Fu only activated NFkappaB in the parental RKO cells through induction of IkappaB-kinase (IKK) activity and increased sensitivity to 5-Fu is observed in both NFkappaB mutant lines. Our results suggest that TNFalpha-dependent induction of MMP-9 gene expression is tightly regulated by oscillatory/cumulative activation of NFkappaB and that 5-Fu stimulates NFkappaB and RKO CRC cell survival through induction of IKK activity.

PTP alpha regulates integrin-stimulated FAK autophosphorylation and cytoskeletal rearrangement in cell spreading and migration.

We investigated the molecular and cellular actions of receptor protein tyrosine phosphatase (PTP) alpha in integrin signaling using immortalized fibroblasts derived from wild-type and PTP alpha-deficient mouse embryos. Defects in PTP alpha-/- migration in a wound healing assay were associated with altered cell shape and focal adhesion kinase (FAK) phosphorylation. The reduced haptotaxis to fibronectin (FN) of PTP alpha-/- cells was increased by expression of active (but not inactive) PTP alpha. Integrin-mediated formation of src-FAK and fyn-FAK complexes was reduced or abolished in PTP alpha-/- cells on FN, concomitant with markedly reduced phosphorylation of FAK at Tyr397. Reintroduction of active (but not inactive) PTP alpha restored FAK Tyr-397 phosphorylation. FN-induced cytoskeletal rearrangement was retarded in PTP alpha-/- cells, with delayed filamentous actin stress fiber assembly and focal adhesion formation. This mimicked the effects of treating wild-type fibroblasts with the src family protein tyrosine kinase (Src-PTK) inhibitor PP2. These results, together with the reduced src/fyn tyrosine kinase activity in PTP alpha-/- fibroblasts (Ponniah et al., 1999; Su et al., 1999), suggest that PTP alpha functions in integrin signaling and cell migration as an Src-PTK activator. Our paper establishes that PTP alpha is required for early integrin-proximal events, acting upstream of FAK to affect the timely and efficient phosphorylation of FAK Tyr-397.