Effects of Bioactive Compounds on Odontogenic Differentiation and Mineralization

Direct pulp capping involves the placement of dental materials directly onto vital pulp tissues after deep caries removal to stimulate the regeneration of reparative dentin. This physical barrier will serve as a "biological seal" between these materials and the pulp tissue. Although numerous direct pulp capping materials are available, the use of small bioactive compounds that can potently stimulate and expedite reparative dentin formation is still underexplored. Here, the authors compared and evaluated the pro-osteogenic and pro-odontogenic effects of 4 small bioactive compounds- phenamil (Phen), purmorphamine (Pur), genistein (Gen), and metformin (Met). The authors found that these compounds at noncytotoxic concentrations induced differentiation and mineralization of preosteoblastic MC3T3-E1 cells and preodontoblastic dental pulp stem cells (DPSCs) in a dose-dependent manner. Among them, Phen consistently and potently induced differentiation and mineralization in vitro. A single treatment with Phen was sufficient to enhance the mineralization potential of DPSCs in vitro. More importantly, Phen-treated DPSCs showed enhanced odontogenic differentiation and mineralization in vivo. Our study suggests that these small bioactive compounds merit further study for their potential clinical use as pulp capping materials.

Regulation of p53 during senescence in normal human keratinocytes

p53, the guardian of the genome, is a tumor suppressor protein and critical for the genomic integrity of the cells. Many studies have shown that intracellular level of p53 is enhanced during replicative senescence in normal fibroblasts, and the enhanced level of p53 is viewed as the cause of senescence. Here, we report that, unlike in normal fibroblasts, the level of intracellular p53 reduces during replicative senescence and oncogene-induced senescence (OIS) in normal human keratinocytes (NHKs). We found that the intracellular p53 level was also decreased in age-dependent manner in normal human epithelial tissues. Senescent NHKs exhibited an enhanced level of p16^INK4A, induced G₂ cell cycle arrest, and lowered the p53 expression and transactivation activity. We found that low level of p53 in senescent NHKs was due to reduced transcription of p53. The methylation status at the p53 promoter was not altered during senescence, but senescent NHKs exhibited notably lower level of acetylated histone 3 (H3) at the p53 promoter in comparison with rapidly proliferating cells. Moreover, p53 knockdown in rapidly proliferating NHKs resulted in the disruption of fidelity in repaired DNA. Taken together, our study demonstrates that p53 level is diminished during replicative senescence and OIS and that such diminution is associated with H3 deacetylation at the p53 promoter. The reduced intracellular p53 level in keratinocytes of the elderly could be a contributing factor for more frequent development of epithelial cancer in the elderly because of the loss of genomic integrity of cells.

Abstract 605: Intermittent treatment of hormone-dependent breast cancer using exemestane: Translational research from lab bench to bedside

Although aromatase inhibitors (AIs) are useful in the treatment of hormone-responsive breast cancer, unfortunately, resistance to such therapy still develops. Based on our published preclinical results that ER, AREG and EGFR play important roles in the acquired resistance mechanism of exemestane (EXE), a steroidal AI, intermittent use of EXE was thought to delay the development of acquired resistance by preventing up-regulation of AREG and activation of EGFR-mediated pathways. This hypothesis was verified by preclinical cell culture and animal studies. Microarray analysis was performed using RNA isolated from week-14 (EXE-resistant) MCF7aro cells that were continuously treated with EXE, week-14 (EXE-responsive) cells that were intermittently treated with EXE (2 weeks on and 1 week off), and cells without EXE treatment. A selective number of estrogen-regulated genes, including AREG and SGK3 (serum/glucocorticoid regulated kinase family member 3), were differentially transcribed between the continuously treated samples and intermittently treated samples. Treatment of EXE resistant cells with siRNAs against AREG and SGK3 suppressed cell growth, supporting the roles of these two proteins in the development of resistance to EXE. Additional results from ChIP and gene expression analyses confirm that the expression of SGK3 can be up-regulated by E2 as well as EXE, and over-expression of SGK3 suppresses apoptosis and increases cell survival. Our animal experiments revealed that intermittent treatment of EXE (250 µg/day, 2 weeks on and 1 week off) was effective at suppressing androgen-induced MCF7aro tumor growth in nude mice, and that after 21 weeks of treatment, resistance resulted in continuous EXE treatment group, while the tumor volumes in the positive control group (androgen treated only) reached 10 cm3 at week 18. qPCR analysis indicated that SGK3 expression in tumors from continous EXE mice was two times that in tumors from the positive control mice, with lowest expression in tumors from the intermittent EXE group (30% of that of the positive control). An analysis on 11 pairs of malignant and adjacent normal tissue has revealed that SGK3 expression is significantly greater in breast tumor specimens than adjacent non-cancer specimens (P=0.006). Since results from these translational research studies provide an important mechanistic basis for intermittent EXE therapy, a clinical trial to evaluate the intermittent use of EXE on postmenopausal women with ER-positive metastatic breast cancer has been recently approved and initiated at the City of Hope NCI-designated Comprehensive Cancer Center.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 605.

Molecular Characterization of Endocrine Resistance

Background. Tamoxifen (TAM), anastrozole (ANA), letrozole (LET), and exemestane (EXE) are major drugs to treat estrogen (E)-dependent breast cancer. Although they are effective, disease recurrence often occurs as a result of acquired resistance to them. To unravel the mechanisms involved, MCF-7aro cell lines resistant to each of the 4 drugs or undergone long-term E deprivation (i.e., LTEDaro) were generated. LET-R, ANA-R, and LTEDaro cells contain a constitutively active ERa. TAM-R cells are thought to have hypersensitive ERa. Furthermore, EXE has weak E-like properties, leading to an ER-dependent crosstalk with EGFR signaling. Thus, our results indicate that resistance mechanisms of the 4 drugs are not identical, activation of ERa is critical for endocrine resistance, and our cell lines are valuable for studying the resistance mechanisms to these drugs. Results. Genome-wide gene expression microarray analysis of these lines was carried out. Hierarchical clustering identified many E-responsive genes with varied expression in our cell lines. At least 3 types of E-responsive genes were observed: up-regulated in all cell lines, up-regulated in all lines except LTEDaro, and up-regulated in all lines but LTEDaro and TAM-R. To better understand the roles of ERa, we initiated ChIP-sequencing experiments for a genome-wide analysis of ERa-binding sites in MCF-7aro and LTEDaro, and plan to correlate the ERa-binding data and the gene expression data. There was a significant overlap of ERa-binding sites identified in the two lines. Furthermore, a substantial number of ERa-binding sites were identified in LTEDaro without E. To study the post-transcriptional regulatory mechanisms, miRNA microarray profiling analysis of resistant lines was also initiated. Global miRNA expression was correlated with a similarity matrix analysis which revealed 4 miRNA clusters, with 2 having E-driven miRNAs. We identified expression of 9 miRNAs as down-regulated in AI resistant cells but up-regulated in TAM-R and LTEDaro, expression of 16 miRNAs as up-regulated in LET-R and ANA-R, and expression of 24 miRNAs as up-regulated in EXE-R. Functional analysis also revealed that miRNA-128a down-regulated the TGFb response in LET-R. Finally, to determine the ER-Signal Transduction cross-talk mechanisms, we initiated an unbiased screen of kinases that participate in the development of resistance to the 4 drugs. Our cell lines were screened against a focused dicer substrate siRNA library that targets 544 kinases. The kinomic approach revealed that hits from MCF-7aro and LTEDaro were different. Twenty hits were identified using LTEDaro, as indicated by more than 40% suppression of cell proliferation with 3 or 4 siRNAs/target. These hits included several kinases known for their roles in endocrine resistance as well as several novel kinases. Discussion. We anticipate that these bioinformatics studies will produce valuable molecular information regarding the mechanisms of endocrine resistance, and the information will help design approaches to reduce disease recurrence and improve the efficacy of endocrine treatments of breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 407.

Intermittent treatment of hormone-dependent breast cancer using exemestane: translational research from lab bench to bedside

Abstract #3040

Background and Rationale: Endocrine therapy agents such as aromatase inhibitors (AIs) have shown good clinical efficacy in the treatment of post-menopausal breast cancer patients. Currently, the major clinical hindrance with endocrine therapy is disease progression or acquired resistance. Intermittent treatment of endocrine therapy agents has been proposed in several clinical trials to address whether this treatment strategy can delay the onset of acquired resistance in hormone-dependent breast cancers. To support these clinical trials, we have performed a pre-clinical study using the steroidal AI exemestane (EXE) to understand potential molecular features that differentiate continuous treatment of EXE from intermittent administration.
 Methods: The ER+ and aromatase-overexpressing cell culture model system (MCF-7aro) was used in this pre-clinical study. The cells were treated either continuously (T+EXE Cont) or intermittently (T+EXE Interm) for 2 weeks with EXE and 1 week without EXE, in the presence of testosterone (T). In addition, a non-steroidal AI letrozole, was used in an identical intermittent manner.
 Results: Based on cell culture studies, acquired resistance was reached at 14 weeks in the T+EXE Cont treated cells, while T+EXE Interm cells were still responsive to EXE. At 34 weeks, acquired resistance developed in the T+EXE Interm cell lines, which demonstrates a delay in time to progression. The non-steroidal AI letrozole did not demonstrate a delay in acquired resistance using this intermittent model. Based on microarray analysis, we observed that gene expression of certain estrogen-responsive genes was elevated in the T+EXE Cont cells, while select genes showed lower levels of up-regulation in T+EXE Interm lines.
 Discussion: Based on our previous studies, up-regulation of a key estrogen-responsive gene, amphiregulin (AREG), is responsible for activating EGFR and mediating resistance to EXE. Expression of genes such as AREG are decreased in the T+EXE Interm cell lines, suggesting the suppression of growth factor signaling implicated in driving resistance. In addition, we have reported that EXE acts as an aromatase destabilizer at the protein level. Unlike letrozole or anastrozole, EXE-mediated protein degradation of aromatase may play a key role in reducing estrogen levels that are responsible for driving breast cancer survival and proliferation. Since these pre-clinical studies provide an important mechanistic basis for intermittent endocrine therapy, a clinical trial to evaluate the intermittent use of exemestane has been discussed and is planned to initiate in the near future.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3040.

Susceptibility to opportunistic infections in HIV-infected patients with increased CD4 T-cell counts on antiretroviral therapy may be predicted by markers of dysfunctional effector memory CD4 T cells and B cells

OBJECTIVES

HIV-infected patients responding to combination antiretroviral therapy (ART) after experiencing severe immunodeficiency may exhibit persistent immune defects and occasionally experience opportunistic infections (OIs) despite increased CD4 T-cell counts. The investigation of immune defects in such patients was examined in this study.

METHODS

CD4 effector memory T-cell (T(em)-cell) function [assessed by blood cytomegalovirus (CMV) interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) counts] and B-cell dysregulation [assessed by serum immunoglobulin A (IgA) and IgE levels] were examined in 27 patients with increased CD4 T-cell counts after receiving ART for over 2 years. Two of these patients and one other had developed OIs on ART and are described in detail.

RESULTS

Serum levels of IgA and IgE were higher than reference intervals (P<0.001) and CMV IFN-gamma ELISPOT counts were lower than those in non-HIV-infected controls (P<0.001) in the HIV-infected patients. Low CMV IFN-gamma ELISPOT counts were associated with high IgA levels (r=-0.5, P=0.01, Spearman's correlation test) and segregated with high IgE levels (P=0.06, Fisher's test). CMV IFN-gamma ELISPOT counts and serum IgA and IgE levels did not change significantly over a median time of 35 (range 8-60) months after the first measurement, whereas CD4 T-cell counts increased. All three patients who experienced OIs had repeatedly low CMV IFN-gamma ELISPOT counts and increased serum levels of IgA and/or IgE.

CONCLUSION

Low CD4 T(em)-cell function and B-cell dysregulation are immune defects that may persist independently of changes in the CD4 T-cell count in HIV-1-infected patients responding to ART and are associated with an increased risk of developing an OI.