Mammary carcinomas induced in human c-Ha-ras proto-oncogene transgenic rats are estrogen-independent, but responsive to d-limonene treatment

Proximal discrepancy in intrinsic atomic interaction arrests G2/M phase by inhibiting Cyclin B1/CDK1 to infer molecular and cellular biocompatibility of D-limonene

The quest for different natural compounds for different biomedical applications especially in the treatment of cancer is at a high pace with increasing incidence of severity. D-limonene has been portrayed as one of the effective potential candidate centered to the context of breast cancer. The anticipation of its count as an effective biomedical agent required a detailed understanding of their molecular mechanism of biocompatibility. This study elucidates the mechanistic action of D-limonene channelized by the induction of apoptosis for controlling proliferation in breast cancer cells. The possible mechanism was explored through an experimental and computational approach to estimate cell proliferation inhibition, cell cycle phase distribution, apoptosis analysis using a flow cytometry, western blotting and molecular docking. The results showed reduced dose and time-dependent viability of MCF7 cells. The study suggested the arrest of the cell cycle at G2/M phase leading to apoptosis and other discrepancies of molecular activity mediated via significant alteration in protein expression pattern of anti-apoptotic proteins like Cyclin B1 and CDK1. Computational analysis showed firm interaction of D-limonene with Cyclin B1 and CDK1 proteins influencing their structural and functional integrity indicating the mediation of mechanism. This study concluded that D-limonene suppresses the proliferation of breast cancer cells by inducing G2/M phase arrest via deregulation of Cyclin B1/CDK1.

Effect of Limonene on Cancer Development in Rodent Models: A Systematic Review

Cancer is a major health issue and one of the leading causes of death worldwide. Many natural compounds, e.g., lycopene, curcumin, resveratrol, etc., have been shown to inhibit the growth of cancer cells. Similarly, limonene, a major active component in citrus essential oils and widely used flavoring additive, has demonstrated anticarcinogenic effects in both cell and animal studies. This systematic review aimed to evaluate the anticarcinogenic effects of limonene and its potential underlying mechanisms. Eight peer-reviewed articles published in English between 2000 and 2020 were identified after screening using MEDLINE, Academic Search Premier, and CINAHL plus. All 8 studies showed an effect of limonene on reducing tumor burden, resulting in either decreased size, number, weight, or multiplicities of tumors. Limonene treatment extended the latency and survival periods in 2 studies yet did not reduce tumor incidence rate in another study. Limonene was shown to promote cell apoptosis in 4 studies that examined either the apoptosis index or apoptosis related gene/protein expressions. Two studies tried to explain the cancer preventive mechanisms of limonene and found limonene could restore the antioxidant capacity or immune functions that were impaired by cancer. These results supported the potential applicability of limonene on inhibiting cancer development, yet the real-world applicability on human requires more research and evaluation through clinical studies.

Systematic Review Registration: PROSPERO, identifier: CRD42020168387.

Effect of d-limonene and its derivatives on breast cancer in human trials: a scoping review and narrative synthesis

BACKGROUND

D-limonene and its derivatives have demonstrated potential chemopreventive and anticancer activity in preclinical and clinical studies. The aim of this scoping review was to assess and critically appraise current literature on the effect of these bioactive citrus peel compounds on breast cancer in human trials and to identify knowledge gaps for exploration in future studies.

METHODS

This study followed a scoping review framework. Peer-reviewed journal articles were included if they reported the effect of d-limonene or its derivatives on breast cancer in human subjects. Articles were retrieved from academic databases - PubMed, EMBASE, CINAHL, Web of Science, and Cochrane reviews - and iteratively through review of bibliographies of relevant manuscripts. Titles and abstracts were appraised against the aforementioned inclusion criteria in a first round of screening. Through consensus meetings and full article review by authors, a final set of studies were selected. Results were reported according to the PRISMA extension for scoping reviews.

RESULTS

Our search strategy yielded 367 records. Following screening and adjudication, five articles reporting on phase 1(n = 2), phase 2 (n = 2) and both trial phases (n = 1) were included as the final dataset for this review. Trials evaluating the effect of d-limonene (n = 2) showed it was well tolerated in subjects. One study (n = 43 participants) showed d-limonene concentrated in breast tissue (mean 41.3 μg/g tissue) and reduction in tumor cyclin D1 expression, which is associated with tumor proliferation arrest. This study did not show meaningful change in serum biomarkers associated with breast cancer, except for a statistically significant increase in insulin-like growth factor-1 (IGF-I) levels. While elevation of IGF-I is associated with increased cancer risk, the clinical implication of this study remains uncertain given its short duration. Trials with perillyl alcohol (n = 3) showed low tolerance and no effect on breast cancer.

CONCLUSION

This review demonstrated a dearth of clinical studies exploring the effect of d-limonene and its derivatives on breast cancer. Limited literature suggests d-limonene is safe and tolerable in human subjects compared to its derivative, perillyl alcohol. Our review demonstrates the need for additional well-powered placebo-controlled trials that assess d-limonene's efficacy on breast cancer compared to other therapies.

The interaction of a thiosemicarbazone derived from R - (+) - limonene with lipid membranes

As a potential drug, 2-nitrobenzaldehyde-thiosemicarbazone (2-TSC), a thiosemicarbazone derived from the terpene R-(+)-limonene, was studied through calorimetric and spectroscopic techniques. Differential Scanning Calorimetry (DSC) data showed that 2-TSC causes structural changes in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DMPC) membrane, strongly decreasing the cooperativity of the bilayer gel-fluid thermal transition. Optical absorption spectroscopy showed that 2-TSC is more soluble in ethanol and lipids than in water medium, and that the drug displays different structures in the different environments. Though 2-TSC displays no fluorescence, time resolved fluorescence showed that the drug is an effective quencher of the fluorescent probe 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan). As it is well accepted that Laurdan is positioned into the bilayer close to the membrane surface, that is possibly the localization of 2-TSC in a bilayer. Electron spin resonance (ESR) of the probe 1-palmitoyl-2-stearoyl-(14-doxyl)-sn-glycero-3-phosphocholine (14-PCSL) revealed that 2-TSC is inserted into the hydrocarbon part of the bilayer, fluidizing the lipid bilayer gel phase and rigidifying or organizing the bilayer fluid phase. Similar effects are found for other lipophilic molecules, including cholesterol. These results are useful to improve the understanding of the processes that govern the interaction of thiosemicarbazones with cell membranes, related to the activity of the drugs and their cytotoxicity.

Evaluation of chemical components in Citri Reticulatae Pericarpium of different cultivars collected from different regions by GC-MS and HPLC

To discriminate the feasible differences and find potential similarities and relationships of Citri Reticulatae Pericarpium (CRP), this work was accomplished by a comprehensive and reliable method using gas chromatography–mass spectrometer (GC–MS) to analyze the volatile oils and high‐performance liquid chromatography (HPLC) simultaneously to determine the contents of five bioactive flavonoids, namely hesperidin, nobiletin, 3,5,6,7,8,3′,4′‐heptamethoxyflavone, tangeretin, and 5‐hydroxy‐6,7,8,3′,4′‐pentamethoxyflavone in 25 batches of CRP samples of 10 cultivars collected from different regions in China. The GC–MS analyses indicated that 98 compounds were successfully identified from the volatile oils obtained and the major constituents of volatile oil are d‐limonene, γ‐terpinene, α‐pinene, linalool, and myrcene. Even 2‐(methylamino) benzoate was found in all cultivar samples harvested at maturation stage. Under the optimal condition, the quantitative analyses of five bioactive flavonoids were successfully performed by HPLC and hierarchical cluster analysis (HCA). Results showed significant differences among cultivars in the contents of five bioactive flavonoids mentioned earlier. The HCA and GC–MS results provided a convenient approach which might be applied for rapid similarity evaluation and also holds the potential for analysis of compounds present in other plants. Therefore, this work obtained offers scientific basis to control quality and develop medicinal value of the medicinal materials in CRP.

Transgenic rat models for mutagenesis and carcinogenesis

Rats are a standard experimental animal for cancer bioassay and toxicological research for chemicals. Although the genetic analyses were behind mice, rats have been more frequently used for toxicological research than mice. This is partly because they live longer than mice and induce a wider variety of tumors, which are morphologically similar to those in humans. The body mass is larger than mice, which enables to take samples from organs for studies on pharmacokinetics or toxicokinetics. In addition, there are a number of chemicals that exhibit marked species differences in the carcinogenicity. These compounds are carcinogenic in rats but not in mice. Such examples are aflatoxin B1 and tamoxifen, both are carcinogenic to humans. Therefore, negative mutagenic/carcinogenic responses in mice do not guarantee that the chemical is not mutagenic/carcinogenic to rats or perhaps to humans. To facilitate research on in vivo mutagenesis and carcinogenesis, several transgenic rat models have been established. In general, the transgenic rats for mutagenesis are treated with chemicals longer than transgenic mice for more exact examination of the relationship between mutagenesis and carcinogenesis. Transgenic rat models for carcinogenesis are engineered mostly to understand mechanisms underlying chemical carcinogenesis. Here, we review papers dealing with the transgenic rat models for mutagenesis and carcinogenesis, and discuss the future perspective.

Transcriptome profiling of Elettaria cardamomum (L.) Maton (small cardamom)

Elettaria cardamomum (L.) Maton, known as 'queen of spices, is a perennial herbaceous monocot of the family Zingiberaceae, native to southern India. Cardamom is an economically valuable spice crop and used widely in culinary and medicinal purposes. In the present study, using Ion Proton RNA sequencing technology, we performed transcriptome sequencing and de novo transcriptome assembly of a wild and five cultivar genotypes of cardamom. RNA-seq generated a total of 22,811,983 (92 base) and 24,889,197 (75 base) raw reads accounting for approximately 8.21GB and 7.65GB of sequence data for wild and cultivar genotypes of cardamom respectively. The raw data were submitted to SRA database of NCBI under the accession numbers SRX1141272 (wild) and SRX1141276 (cultivars). The raw reads were quality filtered and assembled using MIRA assembler resulted with 112,208 and 264,161contigs having N50 value 616 and 664 for wild and cultivar cardamom respectively. The assembled unigenes were functionally annotated using several databases including PlantCyc for pathway annotation. This work represents the first report on cardamom transcriptome sequencing. In order to generate a comprehensive reference transcriptome, we further assembled the raw reads of wild and cultivar genotypes which might enrich the plant transcriptome database and trigger advanced research in cardamom genomics.

Purple corn color suppresses Ras protein level and inhibits 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis in the rat

Anthocyanins belong to the class of phenolic compounds collectively named flavonoids. Many anthocyanins are reported to have inhibitory effects on carcinogenesis. Purple corn color (PCC), an anthocyanin containing extract of purple corn seeds, is used as a food colorant. The major anthocyanin in PCC is cyanidin 3-O-beta-D-glucoside (C3-G). The present study was conducted to assess the influence of dietary PCC on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in rats. PCC significantly inhibited DMBA-induced mammary carcinogenesis in human c-Ha-ras proto-oncogene transgenic (Hras128) rats and in their non-transgenic counterparts. PCC and C3-G also inhibited cell viability and induced apoptosis in mammary tumor cells derived from Hras128 rat mammary carcinomas. At the molecular level, PCC and C3-G treatment resulted in a preferential activation of caspase-3 and reduction of Ras protein levels in tumor cells. It is proposed that C3-G could act as a chemopreventive and possibly chemotherapeutic agent for cancers with mutations in ras. Secondly, the in vitro-in vivo system used in this study can be utilized for screening for cancer preventive compounds that act via Ras down-regulation.

High susceptibility of human c-Ha-ras proto-oncogene transgenic rats to carcinogenesis: a cancer-prone animal model

Transgenic animals carrying human c-Ha-ras proto-oncogene, v-Ha-ras transgenic mice, pim-1 transgenic mice and several knockout mice deficient of tumor suppressor genes, such as p53, have been shown to exhibit increased carcinogen susceptibility. As a result, studies into practical application and medium-term screening of environmental carcinogens are under way. Given the advantages of rat models characterized by larger organ size, abundant information regarding preneoplasias and virus-free constitution, we have concentrated on the generation of transgenic rats bearing copies of the human c-Ha-ras proto-oncogene and shown the Hras128 strain to be extremely sensitive to the induction of mammary carcinomas, and to a lesser extent, lesions in the urinary bladder, esophagus and skin. In most, if not all, the mammary cancers mutations of the transgene but not the endogenous H-ras gene are present, appearing to occur early in the process of tumorigenesis, which involves proliferation of cells in TEB and intraductal hyperplasia before carcinomas arise. Preliminary findings suggest that this is independent of endogenous ovarian hormones, although inhibited by soy isoflavones and promoted by atrazine and nonylphenols. Although further studies of the mechanisms are clearly necessary, the model appears to have great potential for screening purposes, not only for modifiers active in the breast, but also other organs where tumors characterized by ras gene mutations develop.

Preferential mammary carcinogenic effects of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human c-Ha-ras proto-oncogene transgenic rats

In order to clarify the susceptibility of the Hras128 rat harboring copies of the human c-Ha-ras proto-oncogene to 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), Hras128 rats were intragastically treated with 100 mg/kg PhIP 8 times (females) or 80 mg/kg PhIP 10 times (males) over a 9-week period, then sacrificed at weeks 12 and 30. Multiple mammary tumors of adenocarcinoma type were induced in all females, while 83% of treated males developed adenocarcinomas, sarcomas and transitional carcinosarcomas, as evidenced by casein and vimentin immunoreactivity. All tumors examined had mutations in the c-Ha-ras transgene, while the endogenous rat c-Ha-ras gene was intact. Our results indicate that 1) Hras128 rats of both sexes are preferentially susceptible to mammary carcinogenesis with PhIP; 2) activation of the transgene, but not the endogenous c-Ha-ras gene, may be important in this regard; 3) the variety of tumor types evident in male rats indicates that immature mammary gland cells of the terminal end buds may be a target of PhIP; 4) although the transgene is expressed in all organs, susceptibility to PhIP is limited to mammary glands.

Possible enhancing effects of atrazine and nonylphenol on 7,12-dimethylbenz[a]anthracene-induced mammary tumor development in human c-Ha-ras proto-oncogene transgenic rats

Our transgenic (Tg) strain carrying copies of the human c-Ha-ras proto-oncogene is highly susceptible to 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis, possibly due to activation of the transgene, and can be used in medium-term bioassay models to test for modifying effects of estrogenic environmental compounds on tumor development. The present study was conducted to assess the influence of dietary feeding of the endocrine disruptors atrazine and nonylphenol on DMBA-induced carcinogenesis in c-Ha-ras Tg rats. Animals of both sexes were given a single oral dose of DMBA (25 mg/kg body weight) at 50 days of age and thereafter received soybean-free diet containing 5, 50 or 500 ppm atrazine, or 10, 25, 100 or 250 ppm nonylphenol. In female Tg rats, atrazine at a dose of 5 ppm increased the incidences of mammary adenomas and adenocarcinomas (P < 0.01 and P < 0.05), while 50 ppm increased the adenocarcinoma incidence (P < 0.05). In males, skin tumor development, in contrast, was significantly decreased at the highest dose. Nonylphenol at 10 ppm increased adenocarcinoma and total mammary tumor multiplicity in female Tg rats (P < 0.05), but there was no dose dependence, a significant quadratic dose-response trend rather being observed (P < 0.05). In vitro, atrazine did not cause proliferation of MCF-7 cells at any of a range of doses tested. These results suggest that endocrine disruptors may enhance mammary carcinogenesis, but only in a certain limited dose range under the present experimental conditions. The doses applied, moreover, were all extremely high compared to the possible environmental human exposure levels.

Rapid induction of skin and mammary tumors in human c-Ha-ras proto-oncogene transgenic rats by treatment with 7,12-dimethylbenz[a]anthracene followed by 12-O-tetradecanoylphorbol 13-acetate

We have established a transgenic rat line carrying 3 copies of the human c-Ha-ras proto-oncogene with its own promoter region (Jcl/SD-TgN(HrasGen)128Ncc) (Hras128 rat), expression being detectable in almost all organs. We have already demonstrated that the rat is highly sensitive to mammary, esophagus and bladder carcinogenesis. In the present study, male and female transgenic and wild-type littermates were topically treated with 2.5 mg of 7,12-dimethylbenz[a]anthracene (DMBA) dissolved in 1.0 ml of acetone on the back skin at 50 days after birth. Starting 1 week thereafter, they were again topically treated with 100 nmol of 12-O-tetradecanoylphorbol 13-acetate (TPA) dissolved in 0.5 ml of acetone 3 times weekly for the following 31 weeks. In males treated with DMBA and/or TPA, skin tumors, including both squamous cell papillomas (SCP) and carcinomas (SCC), were preferentially induced at the DMBA-TPA painting sites: DMBA-TPA, 15/15 (100%); DMBA, 6/8 (75%); TPA, 1/6 (16.7%). They were also, unexpectedly, induced on remote scrotal skin: DMBA-TPA, 13/15 (86.7%); DMBA, 5/8 (62.5%); TPA, 0/6 (0%). Lesions were thus more frequent in the DMBA-TPA group than with DMBA or TPA alone. In females, adenomas and adenocarcinomas of the mammary glands were preferentially induced: DMBA-TPA, 12/14 (85.7%); DMBA, 6/8 (75%); TPA, 3/6 (50%), with only a few small skin papillomas at painting sites. Incidences and numbers of the mammary and skin tumors were much greater in Hras128 rats than in their wild-type counterparts. PCR-RFLP analysis of the transgene indicated that the percentage of the cell populations harboring a mutation in codons 12 and/or 61 ranged from 2% to 60% in individual tumors; skin tumors showed more mutations in codon 61 in the DMBA-treated groups. In contrast, no mutations were detected in the endogenous rat c-Ha-ras gene. These results indicate that the Hras128 rat is highly susceptible to DMBA-TPA skin and mammary carcinogenesis, thus providing a unique painting model for skin as well as mammary gland carcinogenesis, that would be suitable for investigating the role of transgene mutations.

Lack of effect of human c-Ha-ras proto-oncogene overexpression on prostate carcinogenesis in probasin/SV40 T antigen transgenic rats

We have previously reported that transgenic (Tg) rats bearing the SV40 T antigen under probasin promoter control (PB/SV40T) develop prostate carcinomas at 100% incidence, showing their prostate carcinoma growth to be completely androgen-dependent. Transgenic rats carrying three copies of the human c-Ha-ras proto-oncogene (Hras128) are also highly susceptible to carcinogen induction of multiple mammary carcinomas, in this case estrogen-independent, since ovariectomy does not affect mammary tumor formation. A relationship between ras/mitogen-activated protein kinase signaling and androgen responsiveness of prostate cancer cells has been reported. Therefore it is of interest to investigate whether expression of human c-Ha-ras affects the androgen-dependence of prostate carcinomas developing in the PB/SV40T Tg rat. For this purpose, we established double transgenic (rasTag) rats bearing both PB/SV40T and Hras128. In prostate tissues of the rasTag rats, expression of both human c-Ha-ras and SV40T was confirmed, but the prostate tumor incidence and growth were not significantly affected. Castration at 15 weeks of age induced complete tumor involution in the rasTag rats. These results indicate that the human c-Ha-ras proto-oncogene product does not influence the androgen-dependence of prostate carcinogenesis due to the probasin-mediated SV40 T antigen, despite the estrogen-independence of mammary carcinogenesis in Hras128 rats.

Novel agents for the prevention of breast cancer: targeting transcription factors and signal transduction pathways

Transformation of breast cells occurs through loss or mutation of tumor suppressor genes, or activation or amplification of oncogenes, leading to deregulation of signal transduction pathways, abnormal amplification of growth signals, and aberrant expression of genes that ultimately transform the cells into invasive cancer. The goal of cancer preventive therapy, or "chemoprevention," is to eliminate premalignant cells or to block the progression of normal cells into cancer. Multiple alterations in signal pathways and transcription factors are observed in mammary gland tumorigenesis. In particular, estrogen receptor (ER) deregulation plays a critical role in breast cancer development and progress, and targeting ER with selective ER modulators (SERMs) has achieved significant reduction of breast cancer incidence in women at high risk for breast cancer. However, not all breast cancer is prevented by SERMs, because 30-40% of the tumors are ER-negative. Other receptors for retinoids, vitamin D analogs and peroxisome proliferator-activiator, along with transcription factors such as AP-1, NF-kappaB, and STATs (signal transducers and activators of transcription) affect breast tumorigenesis. This is also true for the signal transduction pathways, for example cyclooxygenase 2 (Cox-2), HER2/neu, mitogen-activated protein kinase (MAPK), and PI3K/Akt. Therefore, proteins in pathways that are altered during the process of mammary tumorigenesis may be promising targets of future chemopreventive drugs. Many newly-developed synthetic or natural compounds/agents are now under testing in preclinical studies and clinical trials. Receptor selective retinoids, receptor tyrosine kinase inhibitors (TKIs), SERMs, Cox-2 inhibitors, and others are some of the promising novel agents for the prevention of breast cancer. The chemopreventive activity of these agents and other novel signal transduction inhibitors are discussed in this chapter.