Biological assay for activity and molecular mechanism of retinoids in cervical tumor cells

SHetA2 Attack on Mortalin and Colleagues in Cancer Therapy and Prevention

Heat Shock Proteins of the 70-kDa family (HSP70s) do not cause cancer by themselves, but instead protect cells as they transform into cancer. These molecular chaperones bind numerous client proteins and utilize ATP hydrolysis to facilitate proper protein folding, formation of functional complexes and cellular localizations, or degradation of irreparably damaged proteins. Their transient upregulation by stressful situations avoids induction of programmed cell death. Continued upregulation of the mortalin, heat shock cognate (hsc70) and glucose regulated protein 78 (Grp78) support cancer development and progression by supporting pro-proliferative and metabolic functions and repressing pro-death functions of oncoproteins and tumor suppressor proteins. This review describes the discovery and development of a lead anti-cancer compound, sulfur heteroarotinoid A2 (SHetA2, NSC726189), which was originally developed to bind retinoic acid receptors, but was subsequently found to work independently of these receptors. The discovery and validation of mortalin, hsc70 and Grp78 as SHetA2 target proteins is summarized. The documented and hypothesized roles of these HSP70 proteins and their clients in the mechanism of SHetA2 inhibition of cancer without toxicity are discussed. Use of this mechanistic data to evaluate drug action in a cancer clinical trial and develop synergistic drug combinations is explained. Knowledge needed to optimize SHetA2 analogs for use in cancer therapy and prevention is proposed as future directions.

Efficacy of commercially available biological agents for the topical treatment of cervical intraepithelial neoplasia: a systematic review

BACKGROUND

Cervical cancer is a major public health issue in the world, especially in developing countries. It can be prevented through vaccination against HPV (primary prevention) and through screening and treatment of cervical intraepithelial neoplasia (CIN) (secondary prevention). Surgical methods for treatment of CIN are linked to complications such as bleeding and adverse pregnancy outcomes. Furthermore, these methods are not generally available in resource-poor settings. Therefore, topical agents for local application on the cervix have been used since decades to overpass complications and limitations of the surgical methods.

AIMS

Review of the literature on the efficacy of commercially available biological agents used for topical treatment of cervical intraepithelial neoplasia (CIN).

METHODS

A systematic search through PubMed and the Cochrane database was performed up to December 2017, using the medical subheadings (MesH) for topical agent, treatment, and cervical intraepithelial neoplasia. Appropriate inclusion/exclusion criteria have been used for the selection of eligible clinical studies. Clinical studies containing a minimum of 20 women, aged 18-50 with a diagnosis of CIN 1-3, and at least a 4 weeks follow-up after the end of the topical treatment were included.

RESULTS

The initial electronic database search resulted in a total of 849 articles. After screening titles and abstracts, 62 articles were selected as potential studies. Of these, six articles were included in the review after reading the full text: two were on 5-FluoroUracil, two on trans retinoic acid, one on Imiquimod, and one on Cidofovir. The reported regression/remission rates for CIN differed among studies. In CIN2 patients, the overall remission rate ranged between 43 and 93% for the active agents.

CONCLUSION

Among the topical agents studied, 5-FluoroUracil showed good remission rates above 80%. Varying results seen in this review is due to the differences in quality of the design between studies. Large-scale and less biaised studies are needed to elucidate the true efficacy and safety of topical agents in the treatment of CIN.

Decreased RARβ expression induces abundant inflammation and cervical precancerous lesions

It is well known that vitamin A and its receptors protect against cancer development and that Retinoid Acid Receptor β (RARβ) is epigenetically silenced during tumoral progression. Cervical Cancer (CC) has been causally linked to high risk human papillomavirus (HR-HPV) infection. However, host factors are important in determining the outcome of persistent HR-HPV infection as most cervical precancerous lesions containing HR-HPVs do not progress to invasive carcinomas. Increasing evidence suggests that low diet in vitamin A and their receptors participate in the development of CC. The aim of this study has been to investigate the effects of abated RARβ expression in the development of cervical premalignant lesions in 4 month-old conditional mice (RARβ(L-/L-)). Results demonstrated the development of spontaneous squamous metaplasia, inflammatory infiltrate, enhanced mitotic activity, loss of cell differentiation, as well as decreased apoptosis and p16(INK4a) protein levels in RARβ(L-/L-) mice cervix. All these changes are hallmarks of moderate dysplasia. Importantly, our results suggest that the low expression of RARβ, may induce the down regulation of p16(INK4a), chronic inflammation and decreased apoptosis and may be involved in vulnerability to HR-HPV and early stage cervical carcinogenesis.

Quantitative DNA methylation analysis of candidate genes in cervical cancer

Aberrant DNA methylation has been observed in cervical cancer; however, most studies have used non-quantitative approaches to measure DNA methylation. The objective of this study was to quantify methylation within a select panel of genes previously identified as targets for epigenetic silencing in cervical cancer and to identify genes with elevated methylation that can distinguish cancer from normal cervical tissues. We identified 49 women with invasive squamous cell cancer of the cervix and 22 women with normal cytology specimens. Bisulfite-modified genomic DNA was amplified and quantitative pyrosequencing completed for 10 genes (APC, CCNA, CDH1, CDH13, WIF1, TIMP3, DAPK1, RARB, FHIT, and SLIT2). A Methylation Index was calculated as the mean percent methylation across all CpG sites analyzed per gene (~4-9 CpG site) per sequence. A binary cut-point was defined at >15% methylation. Sensitivity, specificity and area under ROC curve (AUC) of methylation in individual genes or a panel was examined. The median methylation index was significantly higher in cases compared to controls in 8 genes, whereas there was no difference in median methylation for 2 genes. Compared to HPV and age, the combination of DNA methylation level of DAPK1, SLIT2, WIF1 and RARB with HPV and age significantly improved the AUC from 0.79 to 0.99 (95% CI: 0.97–1.00, p-value = 0.003). Pyrosequencing analysis confirmed that several genes are common targets for aberrant methylation in cervical cancer and DNA methylation level of four genes appears to increase specificity to identify cancer compared to HPV detection alone. Alterations in DNA methylation of specific genes in cervical cancers, such as DAPK1, RARB, WIF1, and SLIT2, may also occur early in cervical carcinogenesis and should be evaluated.

The Ki67+ proliferation index correlates with increased cellular retinol-binding protein-1 and the coordinated loss of plakophilin-1 and desmoplakin during progression of cervical squamous lesions

AIMS

To investigate the modulation of cellular retinol-binding protein (CRBP)-1 and the desmosomal plaque proteins plakophilin (PKP)-1 and desmoplakin (DP) in correlation with the Ki67+ proliferation index (PI) during the progression of cervical squamous intraepithelial lesions (SIL) to squamous cell carcinoma (SCC).

METHODS

Using in situ imaging by brightfield and confocal laser scanning microscopy, the expression of CRBP-1 protein and transcripts, PKP-1, DP and the Ki67 PI were analysed in 38 low-grade (L) SIL, 56 high-grade (H) SIL, 49 SCC, 30 control cervices and 10 human papillomavirus-positive condylomatous lesions.

RESULTS

CRBP-1+ cells increased from 11.4% in the normal cervix to 80.3% in LSILs, 92.3% in HSILs and slightly decreased to 78.3% in invasive SCCs (P = 0.0001) in close association with the Ki67 PI (r =0.41; P < 0.0001). PKP-1+ and DP+ cells were correlated (0.32; P < 0.0001) and decreased from normal (81% versus 92.3%) to LSIL (53.1% versus 85.3%), to HSIL (46.4% versus 67.5%) and SCC (35.1% versus 35.9%). The Ki67+ PI was inversely correlated with DP (-0.20, P = 0.0014) and PKP-1 (-0.19, P = 0.015). Condylomata retained low CRBP-1 and high expression of PKP-1 and DP.

CONCLUSIONS

The gain of CRBP-1 and the loss of desmosomal proteins occur early in cervical carcinogenesis.

Flexible heteroarotinoids (Flex-Hets) exhibit improved therapeutic ratios as anti-cancer agents over retinoic acid receptor agonists

The anti-cancer activities and toxicities of retinoic acid (RA) and synthetic retinoids are mediated through nuclear RA receptors (RARs) and retinoid X receptors (RXRs) that act as transcription factors. Heteroarotinoids (Hets), which contain a heteroatom in the cyclic ring of an arotinoid structure, exhibit similar anti-cancer activities, but reduced toxicity in vivo, in comparison to parent retinoids and RA. A new class of Flexible Hets (Flex-Hets), which contain 3-atom urea or thiourea linkers, regulate growth and differentiation similar to RA, but do not activate RARs or RXRs. In addition, Flex-Hets induce potent apoptosis in ovarian cancer and in head and neck cancer cell lines through the intrinsic mitochondrial pathway. In this study, 4 cervical cancer cell lines were growth inhibited by micromolar concentrations of Flex-Hets to greater extents than RAR/RXR active retinoids. The most potent Flex-Het (SHetA2) inhibited each cell line of the National Cancer Institute's human tumor cell line panel at micromolar concentrations. Oral administration of Flex-Hets (SHetA2 and SHetA4) inhibited growth of OVCAR-3 ovarian cancer xenografts to similar extents as administration of a RAR/RXR-panagonist (SHet50) and Fenretinide (4-HPR) in vivo. None of these compounds induced evidence of skin, bone or liver toxicity, or increased levels of serum alanine aminotransferase (ALT) in the treated mice. Topical application of Flex-Hets did not induce skin irritation in vivo, whereas a RAR/RXR-panagonist (NHet17) and a RARgamma-selective agonist (SHet65) induced similar irritancy as RA. In conclusion, Flex-Hets exhibit improved therapeutic ratios for multiple cancer types over RAR and/or RXR agonists.

Interaction between the Aryl Hydrocarbon Receptor and Retinoic Acid Pathways Increases Matrix Metalloproteinase-1 Expression in Keratinocytes

Exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) results in a variety of pathological lesions in humans via activation of the aryl hydrocarbon receptor (AhR) pathway. It has become apparent that this pathway interacts with a variety of signaling pathways that are believed to be involved in mediating TCDD/AhR biological effects. Our hypothesis is that TCDD mediates these pathological lesions by directly altering the expression of genes involved in matrix deposition and remodeling and that the retinoic acid signaling pathway is involved in modulating TCDD-induced effects. Therefore, we examined the effect of TCDD and all-trans retinoic acid (atRA) on the expression of matrix metalloproteinase-1 (MMP-1, interstitial collagenase), one of the proteolytic enzymes that degrade type I collagen, in normal human keratinocytes. The data show that TCDD exposure results in increased MMP-1 expression in keratinocytes that is further enhanced by co-treatment with all-trans retinoic acid. TCDD-induced expression of MMP-1 appears to be mediated through two AP-1 elements in the proximal promoter of the MMP-1 gene. However, retinoic acid-mediated induction of keratinocyte MMP-1 is a result of both promoter activation and increased mRNA stability. These findings are the first to demonstrate TCDD-induced expression of MMP-1 and to demonstrate interactions between the TCDD/AhR and retinoic acid pathways on MMP-1 expression.

Synthesis of flexible sulfur-containing heteroarotinoids that induce apoptosis and reactive oxygen species with discrimination between malignant and benign cells

Regulation of growth, differentiation, and apoptosis by synthetic retinoids can occur through mechanisms that are dependent and independent of their ability to bind and activate nuclear retinoic acid receptors. The objective of this study was to determine if increasing flexibility of the heteroarotinoid structure would affect the specificity of the synthetic retinoids for the receptors and for their regulation of cancerous and nonmalignant cells. Methods were developed to produce the first examples of heteroarotinoids 15a-15h, which contain urea and/or thiourea linking groups between two aryl rings. Substituents at the para position of the single phenyl ring were either an ester, a nitro group, or a sulfonamide group. Ovarian cancer cell lines Caov-3, OVCAR-3, SK-OV-3, UCI-101, and 222 were utilized, and the inhibitory prowess of the heteroarotinoids was referenced to that of 4-HPR (25). Similar to 4-HPR (25), the heteroarotinoids inhibited growth of all cell lines at micromolar concentrations. Although the heteroarotinoids did not activate retinoic acid receptors, the agents induced potent growth inhibition against the cancer cells with weak activity against normal and benign cells. The growth inhibition was associated with cell loss and induction of reactive oxygen species.

Expression patterns of retinoid X receptors, retinaldehyde dehydrogenase, and peroxisome proliferator activated receptor gamma in bovine preattachment embryos

In cattle, administration of retinol at the time of superovulation has been indirectly associated with enhanced developmental potential of the embryo. Vitamin A and its metabolites influence several developmental processes by interacting with 2 different types of nuclear receptors, retinoic acid receptors and retinoid X receptors (RXRs). Given the limited information available concerning the RXR-mediated retinoid signaling system, particularly in species other than rodents, this study was performed to gain insight into the potential role of retinoid signaling during preattachment embryo development in the cow. Bovine embryos were produced in vitro from oocytes harvested from abattoir ovaries and frozen in liquid nitrogen at the oocyte, 2-, 4-, 8-, and 16- to 20-cell, morula, blastocyst, and hatched blastocyst stages. Reverse transcription polymerase chain reaction (PCR) and whole mount in situ hybridization were utilized to investigate mRNA expression for RXR alpha, RXR beta, RXR gamma, alcohol dehydrogenase I (ADH-I), retinaldehyde dehydrogenase 2 (RALDH2), peroxisome proliferator activated receptor gamma (PPAR gamma), and glyceraldehyde-3-phosphate dehydrogenase. Transcripts for RXR alpha, RXR beta, RALDH2, and PPAR gamma were detected in all stages beginning from the oocyte through to the hatched blastocyst. Whole mount in situ hybridization performed using digoxigenin-labeled antisense probes detected all 4 transcripts in both the inner cell mass and the trophectoderm of hatched blastocysts. PCR products obtained for ADH-I exhibited very low homology to known human and mouse sequences. Immunohistochemistry was performed using polyclonal anti-rabbit antibodies against RXR beta and PPAR gamma to investigate whether these embryonic mRNAs were translated to the mature protein. Strong immunostaining was observed for both RXR beta and PPAR gamma in the trophectoderm and inner cell mass cells of intact and hatched blastocysts. Messenger RNA was not detected at any stage for RXR gamma. Expression of mRNA for RXR alpha, RXR beta, RALDH2, and PPAR gamma suggests that the early embryo may be competent to synthesize retinoic acid and regulate gene expression during preattachment development in vitro.

Mechanisms of induction of human tissue inhibitor of metalloproteinases-1 (TIMP-1) gene expression by all-trans retinoic acid in combination with basic fibroblast growth factor

The addition of all-trans retinoic acid (ATRA) in combination with basic fibroblast growth factor (bFGF) to human fibroblasts results in a synergistic induction of tissue inhibitor of metalloproteinases-1 (TIMP-1) protein production. The synergistic stimulation of TIMP-1 protein by ATRA and bFGF increased across 72 h. An incubation of 10 min to 12 h with bFGF alone followed by ATRA gave a similar synergistic induction of TIMP-1 protein to that seen with both agents together. Treatment of cells with ATRA first followed by bFGF was ineffective. Expression of RARbeta mRNA was induced by ATRA alone, but not further induced by ATRA and bFGF; expression of RARgamma mRNA was induced by both ATRA or bFGF alone, and further induced by both reagents together; expression of RXRgamma was repressed by ATRA alone, but not by ATRA in combination with bFGF. Steady-state levels of TIMP-1 mRNA were induced 14 to 40-fold above control by ATRA and bFGF. Treatment with ATRA and bFGF did not alter the stability of TIMP-1 mRNA. The induction of TIMP-1 mRNA by ATRA and bFGF was greatly diminished by cycloheximide and therefore required new protein synthesis. The tyrosine kinase inhibitor genistein caused a dose-dependent inhibition of TIMP-1 protein induction by ATRA and bFGF. A MEK1 inhibitor (PD98059) inhibited both basal and induced levels of TIMP-1. At high concentrations, p38 MAP kinase inhibitors further enhanced the synergistic stimulation of TIMP-1 protein by ATRA and bFGF, but at these concentrations, p42/44 MAP kinase was strongly activated. These data begin to elucidate the mechanisms by which TIMP-1 gene expression can be upregulated.

Heteroarotinoids inhibit head and neck cancer cell lines in vitro and in vivo through both RAR and RXR retinoic acid receptors

A class of less toxic retinoids, called heteroarotinoids, was evaluated for their molecular mechanism of growth inhibition of two head and neck squamous cell carcinoma (HNSCC) cell lines SCC-2 and SCC-38. A series of 14 heteroarotinoids were screened for growth inhibition activity in vitro. The two most active compounds, one that contained an oxygen heteroatom (6) and the other a sulfur heteroatom (16), were evaluated in a xenograph model of tumor establishment in nude mice. Five days after subcutaneous injection of 10(7) SCC-38 cells, groups of 5 nu/nu mice were gavaged daily (5 days/week for 4 weeks) with 20 mg/kg/day of all-trans-retinoic acid (t-RA, 1), 10 mg/kg/day of 6, 10 mg/kg/day of 16, or sesame oil. After a few days, the dose of t-RA (1) was decreased to 10 mg/kg/day to alleviate the side effects of eczema and bone fracture. No significant toxic effects were observed in the heteroarotinoid groups. All three retinoids caused a statistically significant reduction in tumor size as determined by the Student t-test (P < 0. 05). Complete tumor regression was noted in 3 of 5 mice treated with t-RA (1), 4 of 5 mice treated with 16, 1 of 5 mice treated with 6, and 1 of 5 mice treated with sesame oil. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine that the expression levels of RARalpha, RXRalpha, and RXRbeta were similar in the two cell lines, while RARbeta expression was higher in SCC-2 over SCC-38, and RARgamma expression was higher in SCC-38 over SCC-2. Receptor cotransfection assays in CV-1 cells demonstrated that 16 was a potent activator of both RAR and RXR receptors, while 6 was selective for the RXR receptors. Transient cotransfection assays in CV-1 cells using an AP-1 responsive reporter plasmid demonstrated that t-RA (1), 6, and 16 each inhibited AP-1-driven transcription in this cell line. In conclusion, the growth inhibition activity of the RXR-selective 6 and the more potent growth inhibition activity of the RAR/RXR pan-agonist 16 implicate both RARs and RXRs in the molecular mechanism of retinoid growth inhibition. Moreover, the chemoprevention activity and the lack of toxicity of heteroarotinoids demonstrate their clinical potential in head and neck cancer chemoprevention.

Ki-67 Expression in a Cervical Cancer Organotypic Model Correlates with Growth and EGF-R Expression

OBJECTIVE

The study objective was to measure the effects of retinoid treatment on Ki-67 expression in a cervical carcinoma organotypic culture model and to determine whether a correlation exists between retinoid effects on Ki-67 expression and effects on growth and epidermal growth factor receptor (EGF-R) expression.

METHODS

Organotypic cultures of the cervical carcinoma cell line were treated for 7 days with all-trans retinoic acid, 9-cis retinoic acid, or control solvent. Cultures were fixed and embedded in paraffin, and sections were stained with Ki-67 antibodies. Ki-67 expression was determined by light microscopy.

RESULTS

Ki-67 expression was inhibited 25% in the organotypic culture treated with 9-cis retinoic acid and 32% in the culture treated with all-frans retinoic acid. Previous data demonstrated a 45% and 44% inhibition of EGF-R expression and a 49% and 63% inhibition of growth, respectively.

DISCUSSION

The inhibition of Ki-67 expression by retinoids correlates with inhibition of EGF-R expression and growth as determined by a Pearson correlation (R = 0.88). Inhibition of Ki-67 and EGF-R demonstrates quantifiable effects of retinoids at both the membrane receptor and nuclear protein levels in our organotypic culture model.

Synthesis and characterization of heteroarotinoids demonstrate structure specificity relationships

Heteroarotinoids are synthetic retinoids derived from trans-retinoic acid and the arotinoid structures and include a heteroatom in a five- or six-membered cyclic ring. This is the first systematic study of influences of the heteroatom, ring size, number of aryl groups, and terminal side chain on retinoid receptor specificity. Two new heteroarotinoids were synthesized and characterized. Although all heteroarotinoids activated RAR receptors, two dominant associations between structure and specificity were identified across all compounds. The six-membered ring conferred increased RARbeta specificity over the five-membered ring. The sulfur atom conferred greater specificity for RARgamma than the oxygen atom. RARalpha specificity was attenuated by a combination of influences from the heteroatom and aryl groups. In summary, the heteroatom and cyclic ring size exerted dominant effects, while the number of aryl rings and terminal side chain had attenuating effects on retinoid receptor specificity of heteroarotinoids.

Biologically active heteroarotinoids exhibiting anticancer activity and decreased toxicity

A series of retinoids, containing heteroatoms in a cyclic ring and called heteroarotinoids, were synthesized, and their biological activity was evaluated using tissue culture lines that have measurable responses to trans-retinoic acid (t-RA). Transglutaminase (TGase) was assessed in the human erythroleukemia cell line (GMO6141A) as an indicator of differentiation and apoptosis. Proliferation was evaluated in a human cervical cell line, CC-1, which exhibits dose-dependent alterations in growth rate in response to treatment with trans-retinoic acid. Activation of nuclear retinoic acid receptors was determined in a reporter cell line established from CC-1. The reporter line, called CC-B, contains a reporter gene controlled by a retinoic acid responsive element (RARE) and a thymidine kinase (tk) promoter. Treatment of the CC-B line with the heteroarotinoids resulted in a dose-responsive and retinoid-dependent regulation of reporter gene expression. The heteroarotinoids exhibited activity in all assays and correlated in a statistically significant manner between assays. RARE transactivation activity in CC-B cells correlated with induction of TGase in GMO6141A (R = 0.96) and with a decrease in the growth rate of CC-1 cells (R = -0.90). The ability of the selected heteroarotinoids to induce differentiation, inhibit proliferation, and activate nuclear receptors demonstrates the chemotherapeutic potential of these agents. In view of the biological activity cited, an in vivo toxicity study was conducted on male B6D2F1 mice with three heteroarotinoids, namely 8 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylthiochroman-6-yl)-2,4,6-heptatrienoic acid], 10 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylchroman-6-yl)-2, 4,6-heptatrienoic acid], and 13 [(E)-p-[2-(4,4-dimethylchroman-6-yl)propenyl]benzoic acid]. The mice were used with gavage of heteroarotinoids in corn oil [0.1, 0.2, 0.4, or 0.8 mg/kg] and with 0.01 or 0.05 mg/kg of TTNPB (5) [(E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1- propenyl]benzoic acid] as reference controls. The target organs affected in the mice by the three heteroarotinoids were those typically associated with t-RA (1) toxicity. The maximum tolerated dose (MTD) of 13 was 9.4 mg/kg/day, which was equal in toxicity to that of t-RA (1) and 1000-fold less toxic than TTNPB (5). The MTDs of 8 and 10 were 34 and 32 mg/kg/day, respectively, which is 3-fold less toxic than t-RA (1) and 3000-fold less toxic than TTNPB (5). The 3000-fold reduced toxicity, compared with only a 27% reduction biological activity of 8 and 10 with respect to that of TTNPB, observed in our assays indicates a good therapeutic ratio of these heteroarotinoids over the parent compound. The biological activity and reduced toxicity of these heteroartinoids demonstrate the potential efficacy as anticancer agents.