Selective inhibition of the BD2 bromodomain of BET proteins in prostate cancer.

Proteins of the bromodomain and extra-terminal (BET) domain family are epigenetic readers that bind acetylated histones through their bromodomains to regulate gene transcription. Dual-bromodomain BET inhibitors (DbBi) that bind with similar affinities to the first (BD1) and second (BD2) bromodomains of BRD2, BRD3, BRD4 and BRDt have displayed modest clinical activity in monotherapy cancer trials. A reduced number of thrombocytes in the blood (thrombocytopenia) as well as symptoms of gastrointestinal toxicity are dose-limiting adverse events for some types of DbBi1-5. Given that similar haematological and gastrointestinal defects were observed after genetic silencing of Brd4 in mice6, the platelet and gastrointestinal toxicities may represent on-target activities associated with BET inhibition. The two individual bromodomains in BET family proteins may have distinct functions7-9 and different cellular phenotypes after pharmacological inhibition of one or both bromodomains have been reported10,11, suggesting that selectively targeting one of the bromodomains may result in a different efficacy and tolerability profile compared with DbBi. Available compounds that are selective to individual domains lack sufficient potency and the pharmacokinetics properties that are required for in vivo efficacy and tolerability assessment10-13. Here we carried out a medicinal chemistry campaign that led to the discovery of ABBV-744, a highly potent and selective inhibitor of the BD2 domain of BET family proteins with drug-like properties. In contrast to the broad range of cell growth inhibition induced by DbBi, the antiproliferative activity of ABBV-744 was largely, but not exclusively, restricted to cell lines of acute myeloid leukaemia and prostate cancer that expressed the full-length androgen receptor (AR). ABBV-744 retained robust activity in prostate cancer xenografts, and showed fewer platelet and gastrointestinal toxicities than the DbBi ABBV-07514. Analyses of RNA expression and chromatin immunoprecipitation followed by sequencing revealed that ABBV-744 displaced BRD4 from AR-containing super-enhancers and inhibited AR-dependent transcription, with less impact on global transcription compared with ABBV-075. These results underscore the potential value of selectively targeting the BD2 domain of BET family proteins for cancer therapy.

Optimization of decalcification techniques for histologic examination of the rat maxillary and mandibular incisors for toxicity studies.

The objective of this study was to provide optimized processing for examination of rat incisors in nonclinical toxicity studies that enables analysis using immunohistochemistry (IHC). Rat maxillas and mandibles were decalcified in Immunocal, a formic acid decalcifier, and Decal Stat, a hydrochloric acid decalcifier, to evaluate tissue quality when with hematoxylin and eosin (H&E) stain and an IHC. Following necropsy of 10 to 13-week-old male Sprague Dawley rats, tissues were collected, trimmed, fixed in neutral buffered formalin (NBF), and placed into the corresponding decalcifying solution. After a pilot study with multiple timepoints for both decalcifying solutions, times were selected for the definitive study. Incisors in the definitive study were decalcified for 72, 96 or 120 hours in Immunocal and 24 hours in Decal Stat, trimmed, processed, embedded in paraffin, and sectioned. The microtomy process and sections were evaluated by histotechnologists. Sections were stained withH&E or an IHC to detect vimentin. Veterinary pathologists used blinded assessment to evaluate staining and tissue quality. The H&E sections from Immunocal timepoints scored higher based on criteria such as cellular morphology. However, tissue quality decreased at 120 hours with Immunocal but was adequate after 24 hours with Decal Stat. For IHC, moderate to excellent expression of vimentin was observed at timepoints for both decalcifiers. Optimal tissue sectioning and histological quality were achieved on incisor sections decalcified for 96 hours with Immunocal and 24 hours with Decal Stat.

Oncostatin M promotes STAT3 activation, VEGF production, and invasion in osteosarcoma cell lines.

BACKGROUND: We have previously demonstrated that both canine and human OSA cell lines, as well as 8 fresh canine OSA tumor samples, exhibit constitutive phosphorylation of STAT3, and that this correlates with enhanced expression of matrix metalloproteinase-2 (MMP2). While multiple signal transduction pathways can result in phosphorylation of STAT3, stimulation of the cytokine receptor gp130 through either IL-6 or Oncostatin M (OSM) is the most common mechanism through which STAT3 is activated. The purpose of this study was to evaluate the role of IL-6 and OSM stimulation on both canine and human OSA cell lines to begin to determine the role of these cytokines in the biology of OSA. METHODS: RT-PCR and Western blotting were used to interrogate the consequences of OSM and IL-6 stimulation of OSA cell lines. OSA cells were stimulated with OSM and/or hepatocyte growth factor (HGF) and the effects on MMP2 activity (gel zymography), proliferation (CyQUANT), invasion (Matrigel transwell assay), and VEGF production (Western blotting, ELISA) were assessed. The small molecule STAT3 inhibitor LLL3 was used to investigate the impact of STAT3 inhibition following OSM stimulation of OSA cells. RESULTS: Our data demonstrate that the OSM receptor (OSMR), but not IL-6 or its receptor, is expressed by all human and canine OSA cell lines and canine OSA tumor samples; additionally, OSM expression was noted in all tumor samples. Treatment of OSA cell lines with OSM induced phosphorylation of STAT3, Src, and JAK2. OSM stimulation also resulted in a dose dependent increase in MMP2 activity and VEGF expression that was markedly reduced following treatment with the small molecule STAT3 inhibitor LLL3. Lastly, OSM stimulation of OSA cell lines enhanced invasion through Matrigel, particularly in the presence of rhHGF. In contrast, both OSM and HGF stimulation of OSA cell lines did not alter their proliferative capacity. CONCLUSIONS: These data indicate OSM stimulation of human and canine OSA cells induces STAT3 activation, thereby enhancing the expression/activation of MMP2 and VEGF, ultimately promoting invasive behavior and tumor angiogenesis. As such, OSM and its receptor may represent a novel target for therapeutic intervention in OSA.

The novel curcumin analog FLLL32 decreases STAT3 DNA binding activity and expression, and induces apoptosis in osteosarcoma cell lines.

BACKGROUND: Curcumin is a naturally occurring phenolic compound shown to have a wide variety of antitumor activities; however, it does not attain sufficient blood levels to do so when ingested. Using structure-based design, a novel compound, FLLL32, was generated from curcumin. FLLL32 possesses superior biochemical properties and more specifically targets STAT3, a transcription factor important in tumor cell survival, proliferation, metastasis, and chemotherapy resistance. In our previous work, we found that several canine and human osteosarcoma (OSA) cell lines, but not normal osteoblasts, exhibit constitutive phosphorylation of STAT3. Compared to curcumin, we hypothesized that FLLL32 would be more efficient at inhibiting STAT3 function in OSA cells and that this would result in enhanced downregulation of STAT3 transcriptional targets and subsequent death of OSA cells. METHODS: Human and canine OSA cells were treated with vehicle, curcumin, or FLLL32 and the effects on proliferation (CyQUANT®), apoptosis (SensoLyte® Homogeneous AMC Caspase- 3/7 Assay kit, western blotting), STAT3 DNA binding (EMSA), and vascular endothelial growth factor (VEGF), survivin, and matrix metalloproteinase-2 (MMP2) expression (RT-PCR, western blotting) were measured. STAT3 expression was measured by RT-PCR, qRT- PCR, and western blotting. RESULTS: Our data showed that FLLL32 decreased STAT3 DNA binding by EMSA. FLLL32 promoted loss of cell proliferation at lower concentrations than curcumin leading to caspase-3- dependent apoptosis, as evidenced by PARP cleavage and increased caspase 3/7 activity; this could be inhibited by treatment with the pan-caspase inhibitor Z-VAD-FMK. Treatment of OSA cells with FLLL32 decreased expression of survivin, VEGF, and MMP2 at both mRNA and protein levels with concurrent decreases in phosphorylated and total STAT3; this loss of total STAT3 occurred, in part, via the ubiquitin-proteasome pathway. CONCLUSIONS: These data demonstrate that the novel curcumin analog FLLL32 has biologic activity against OSA cell lines through inhibition of STAT3 function and expression. Future work with FLLL32 will define the therapeutic potential of this compound in vivo.

The small molecule curcumin analog FLLL32 induces apoptosis in melanoma cells via STAT3 inhibition and retains the cellular response to cytokines with anti-tumor activity.

BACKGROUND: We characterized the biologic effects of a novel small molecule STAT3 pathway inhibitor that is derived from the natural product curcumin. We hypothesized this lead compound would specifically inhibit the STAT3 signaling pathway to induce apoptosis in melanoma cells. RESULTS: FLLL32 specifically reduced STAT3 phosphorylation at Tyr705 (pSTAT3) and induced apoptosis at micromolar amounts in human melanoma cell lines and primary melanoma cultures as determined by annexin V/propidium iodide staining and immunoblot analysis. FLLL32 treatment reduced expression of STAT3-target genes, induced caspase-dependent apoptosis, and reduced mitochondrial membrane potential. FLLL32 displayed specificity for STAT3 over other homologous STAT proteins. In contrast to other STAT3 pathway inhibitors (WP1066, JSI-124, Stattic), FLLL32 did not abrogate IFN-gamma-induced pSTAT1 or downstream STAT1-mediated gene expression as determined by Real Time PCR. In addition, FLLL32 did not adversely affect the function or viability of immune cells from normal donors. In peripheral blood mononuclear cells (PBMCs), FLLL32 inhibited IL-6-induced pSTAT3 but did not reduce signaling in response to immunostimulatory cytokines (IFN-gamma, IL 2). Treatment of PBMCs or natural killer (NK) cells with FLLL32 also did not decrease viability or granzyme b and IFN-gamma production when cultured with K562 targets as compared to vehicle (DMSO). CONCLUSIONS: These data suggest that FLLL32 represents a lead compound that could serve as a platform for further optimization to develop improved STAT3 specific inhibitors for melanoma therapy.

The novel HSP90 inhibitor STA-1474 exhibits biologic activity against osteosarcoma cell lines.

Osteosarcoma (OSA), the most common malignant bone tumor in dogs and children, exhibits a similar clinical presentation and molecular biology in both species. Unfortunately, 30-40% of children and 90% of dogs still die of disease despite aggressive therapy. The purpose of this study was to test the biologic activity of a novel heat shock protein 90 (HSP90) inhibitor, STA-1474, against OSA. Canine and human OSA cell lines and normal canine osteoblasts were treated with STA-1474 and evaluated for effects on proliferation (CyQuant), apoptosis (Annexin V, PARP cleavage, caspase 3/7 activation) and known HSP90 client proteins. HSP90 was immunoprecipitated from normal and malignant osteoblasts and Western blotting for co-chaperones was performed. Mice bearing canine OSA xenografts were treated with STA-1474, and tumors samples were evaluated for caspase-3 activation and loss of p-Akt/Akt. Treatment with STA-1474 promoted loss of cell viability, inhibition of cell proliferation and induction of apoptosis in OSA cell lines. STA-1474 and its active metabolite STA-9090 also demonstrated increased potency compared to 17-AAG. STA-1474 exhibited selectivity for OSA cells versus normal canine osteoblasts, and HSP90 co-precipitated with co-chaperones p23 and Hop in canine OSA cells but not in normal canine osteoblasts. Furthermore, STA-1474 downregulated the expression of p-Met/Met, p-Akt/Akt and p-STAT3. Finally, STA-1474 induced tumor regression, caspase-3 activation and downregulation of p-Met/Met and p-Akt/Akt in OSA xenografts. Together, these data suggest that HSP90 represents a relevant target for therapeutic intervention in OSA.

Characterization of STAT3 activation and expression in canine and human osteosarcoma.

BACKGROUND: Dysregulation of signal transducer and activator of transcription 3 (STAT3) has been implicated as a key participant in tumor cell survival, proliferation, and metastasis and is often correlated with a more malignant tumor phenotype. STAT3 phosphorylation has been demonstrated in a subset of human osteosarcoma (OSA) tissues and cell lines. OSA in the canine population is known to exhibit a similar clinical behavior and molecular biology when compared to its human counterpart, and is often used as a model for preclinical testing of novel therapeutics. The purpose of this study was to investigate the potential role of STAT3 in canine and human OSA, and to evaluate the biologic activity of a novel small molecule STAT3 inhibitor. METHODS: To examine STAT3 and Src expression in OSA, we performed Western blotting and RT-PCR. OSA cells were treated with either STAT3 siRNA or small molecule Src (SU6656) or STAT3 (LLL3) inhibitors and cell proliferation (CyQUANT), caspase 3/7 activity (ELISA), apoptosis (Western blotting for PARP cleavage) and/or viability (Wst-1) were determined. Additionally, STAT3 DNA binding after treatment was determined using EMSA. Expression of STAT3 targets after treatment was demonstrated with Western blotting, RT-PCR, or gel zymography. RESULTS: Our data demonstrate that constitutive activation of STAT3 is present in a subset of canine OSA tumors and human and canine cell lines, but not normal canine osteoblasts. In both canine and human OSA cell lines, downregulation of STAT3 activity through inhibition of upstream Src family kinases using SU6656, inhibition of STAT3 DNA binding and transcriptional activities using LLL3, or modulation of STAT3 expression using siRNA, all resulted in decreased cell proliferation and viability, ultimately inducing caspase-3/7 mediated apoptosis in treated cells. Furthermore, inhibition of either Src or STAT3 activity downregulated the expression of survivin, VEGF, and MMP2, all known transcriptional targets of STAT3. CONCLUSION: These data suggest that STAT3 activation contributes to the survival and proliferation of human and canine OSA cells, thereby providing a potentially promising target for therapeutic intervention. Future investigational trials of LLL3 in dogs with spontaneous OSA will help to more accurately define the role of STAT3 in the clinical setting.

Cutaneous wound reepithelialization is compromised in mice lacking functional Slug (Snai2).

BACKGROUND: Keratinocytes at wound margins undergo partial epithelial to mesenchymal transition (EMT). Based on previous in vitro and ex vivo findings, Slug (Snai2), a transcriptional regulator of EMT in development, may play an important role in this process. OBJECTIVES: This study was designed to validate an in vivo role for Slug in wound healing. METHODS: Excisional wounds in Slug null and wild type mice were examined histologically at 6, 24, 48, and 72h after wounding; reepithelialization was measured and immunohistochemistry for keratins 8, 10, 14, and 6 and E-cadherin was performed. In 20 Slug null and 20 wild type mice exposed three times weekly to two minimal erythemal doses of UVR, the development of non-healing cutaneous ulcers was documented. Ulcers were examined histologically and by immunohistochemistry. RESULTS: The reepithelialization component of excisional wound healing was reduced 1.7-fold and expression of the Slug target genes keratin 8 and E-cadherin was increased at wound margins in Slug null compared to wild type mice. In contrast, no differences in expression of keratins 10 or 14 or in markers of proliferation K6 and Ki-67 were observed. Forty per cent of Slug null mice but no wild type mice developed non-healing cutaneous ulcers in response to chronic UVR. Keratinocytes at ulcer margins expressed high levels of keratin 8 and retained E-cadherin expression, thus resembling excisional wounds. CONCLUSION: Slug is an important modulator of successful wound repair in adult tissue and may be critical for maintaining epidermal integrity in response to chronic injury.

Snai2 expression enhances ultraviolet radiation-induced skin carcinogenesis.

Snai2, encoded by the SNAI2 gene, has been shown to modulate epithelial-mesenchymal transformation (EMT), the conversion of sessile epithelial cells attached to adjacent cells and to the basement membrane into dissociated and motile fibroblastic cells. EMT occurs during development, wound healing, and carcinoma progression. Using Snai2-null mice (Snai2(lacZ)), we evaluated the role of Snai2 in UV radiation (UVR)-induced skin carcinogenesis. In chronically UVR-exposed nontumor-bearing skin from Snai2-null mice, inflammation and epidermal proliferation were decreased compared with wild-type (+/+) skin. Snai2-null mice had a consistently lower tumor burden than +/+ mice. In addition, null mice developed fewer aggressive spindle cell tumors, believed to arise from squamous cell carcinomas that have undergone EMT, than +/+ mice; however, the difference in tumor type distribution between the two genotypes was not statistically significant. No metastases were observed in either the +/+ or Snai2-null mice. Using quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry, we showed that the spindle cell tumors in the Snai2-null mice demonstrated impaired EMT, as shown by decreased vimentin and increased cadherin 1 expression. This study confirms a role for Snai2 in EMT, but demonstrates that Snai2 expression is not required for the development or progression of UVR-induced skin tumors.