Anti-tumor effects of retinoids combined with trastuzumab or tamoxifen in breast cancer cells: induction of apoptosis by retinoid/trastuzumab combinations

Overcoming retinoic acid resistance in HER2-enriched breast cancers: role of MYC

HER2-enriched (HER2+) breast cancers express high levels of the growth-promoting HER2 protein. Although these cancers are treated with the HER2-targeted drug, trastuzumab, resistance to treatment is common. Retinoic acid (RA) is an anti-cancer agent that has been successfully used for the treatment of leukemia and holds promise for the treatment of solid cancers, including breast cancer. The HER2 gene is frequently co-amplified with RARA, a key determinant of RA sensitivity in breast cancers. It seems surprising, therefore, that HER2+ breast cancers are refractory to RA treatment. Here, we show that MYC mediates RA resistance by suppressing the expression of cellular retinoic acid binding protein 2 (CRABP2), resulting in RARα inactivation. CRABP2 is an intracellular RA transporter that delivers RA to the nuclear receptor RARα for its activation. Our results indicate that response to RA is enhanced by MYC depletion in HER2+ breast cancer cells and that RA treatment enhances trastuzumab responsiveness. Our findings support the use of RA and trastuzumab for the treatment of subsets of patients with breast cancers that are HER2-RARα co-amplified and have low levels of MYC.

All-trans-retinoic acid modulates glycolysis via H19 and telomerase: the role of mir-let-7a in estrogen receptor-positive breast cancer cells

BACKGROUND

Breast cancer (BC) is the most commonly diagnosed cancer in women. Treatment approaches that differ between estrogen-positive (ER+) and triple-negative BC cells (TNBCs) and may subsequently affect cancer biomarkers, such as H19 and telomerase, are an emanating delight in BC research. For instance, all-trans-Retinoic acid (ATRA) could represent a potent regulator of these oncogenes, regulating microRNAs, mostly let-7a microRNA (miR-let-7a), which targets the glycolysis pathway, mainly pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) enzymes. Here, we investigated the potential role of ATRA in H19, telomerase, miR-let-7a, and glycolytic enzymes modulation in ER + and TNBC cells.

METHODS

MCF-7 and MDA-MB-231 cells were treated with 5 µM ATRA and/or 100 nM fulvestrant. Then, ATRA-treated or control MCF-7 cells were transfected with either H19 or hTERT siRNA. Afterward, ATRA-treated or untreated MDA-MB-231 cells were transfected with estrogen receptor alpha ER(α) or beta ER(β) expression plasmids. RNA expression was evaluated by RT‒qPCR, and proteins were assessed by Western blot. PKM2 activity was measured using an NADH/LDH coupled enzymatic assay, and telomerase activity was evaluated with a quantitative telomeric repeat amplification protocol assay. Student's t-test or one-way ANOVA was used to analyze data from replicates.

RESULTS

Our results showed that MCF-7 cells were more responsive to ATRA than MDA-MB-231 cells. In MCF-7 cells, ATRA and/or fulvestrant decreased ER(α), H19, telomerase, PKM2, and LDHA, whereas ER(β) and miR-let-7a increased. H19 or hTERT knockdown with or without ATRA treatment showed similar results to those obtained after ATRA treatment, and a potential interconnection between H19 and hTERT was found. However, in MDA-MB-231 cells, RNA expression of the aforementioned genes was modulated after ATRA and/or fulvestrant, with no significant effect on protein and activity levels. Overexpression of ER(α) or ER(β) in MDA-MB-231 cells induced telomerase activity, PKM2 and LDHA expression, in which ATRA treatment combined with plasmid transfection decreased glycolytic enzyme expression.

CONCLUSIONS

To the best of our knowledge, our study is the first to elucidate a new potential interaction between the estrogen receptor and glycolytic enzymes in ER + BC cells through miR-let-7a.

Cellular and micro-environmental responses influencing the antitumor activity of all-trans retinoic acid in breast cancer

All-trans retinoic acid (ATRA) is the most relevant and functionally active metabolite of Vitamin-A. From a therapeutic standpoint, ATRA is the first example of pharmacological agent exerting its anti-tumor activity via a cell differentiating action. In the clinics, ATRA is used in the treatment of Acute Promyelocytic Leukemia, a rare form of myeloid leukemia with unprecedented therapeutic results. The extraordinary effectiveness of ATRA in the treatment of Acute Promyelocytic Leukemia patients has raised interest in evaluating the potential of this natural retinoid in the treatment of other types of neoplasias, with particular reference to solid tumors.The present article provides an overview of the available pre-clinical and clinical studies focussing on ATRA as a therapeutic agent in the context of breast cancer from a holistic point of view. In detail, we focus on the direct effects of ATRA in breast cancer cells as well as the underlying molecular mechanisms of action. In addition, we summarize the available information on the action exerted by ATRA on the breast cancer micro-environment, an emerging determinant of the progression and invasive behaviour of solid tumors. In particular we discuss the recent evidences of ATRA activity on the immune system. Finally, we analyse and discuss the results obtained with the few ATRA-based clinical trials conducted in the context of breast cancer.

Fenretinide induces apoptosis and synergises the apoptosis inducing effect of gemcitabine through inhibition of key signalling molecules involved in A549 cell survival in in silico and in vitro analyses

Fenretinide is a synthetic retinoid compound, which induces apoptosis via generating reactive oxygen species (ROS) and modulating PI3K/Akt/mTOR signalling pathway. We hypothesise that fenretinide's mechanism of action in triggering apoptosis may involve other targets, beside mTOR signalling pathway and it may augment apoptosis inducing effects of chemotherapeutic drugs in lung cancer. Time-lapse microscopy and Western blotting were used to evaluate apoptosis and apoptotic marker cleaved-Caspase 3 in A549 cells. Relative levels of protein phosphorylation and ROS were quantified by Human Phospho-Kinase Array Kit and CellROX® Green Reagent, respectively. Docking and simulation analyses of proteins and fenretinide interactions were identified and visualised by Discovery Studio Visualizer and AutoDock Vina software. Our results showed that fenretinide induced apoptosis in a dose dependant manner and combinations of fenretinide (5 μg/mL) and gemcitabine (1, 2, 4, 8 and 16 μg/mL) synergistically enhanced apoptosis in A549 cells. Fenretinide caused significant increase of cleaved-Caspase 3, de-phosphorylated p-S473 of Akt and failed to inhibit mTORC1 downstream targets. In silico results revealed that Akt required the lowest energy (-10.2 kcal/mol) to interact with fenretinide in comparison with other proteins. In conclusion, Akt may be exploited as a good target for induction of apoptosis in A549 cells and fenretinide has great potentials to fulfil this task. The mechanism by which fenretinide boosts the apoptosis inducing effects of gemcitabine, which is likely expected to be via inhibiting mTORC2 downstream targets. However, docking investigation revealed that fenretinide lacks specificity as it may also interact with several secondary targets beside Akt.

Effects of Functional and Nutraceutical Foods in the Context of the Mediterranean Diet in Patients Diagnosed with Breast Cancer

Several studies report that breast cancer survivors (BCS) tend to have a poor diet, as fruit, vegetable, and legume consumption is often reduced, resulting in a decreased intake of nutraceuticals. Moreover, weight gain has been commonly described among BCS during treatment, increasing recurrence rate and mortality. Improving lifestyle and nutrition after the diagnosis of BC may have important benefits on patients' general health and on specific clinical outcomes. The Mediterranean diet (MD), known for its multiple beneficial effects on health, can be considered a nutritional pool comprising several nutraceuticals: bioactive compounds and foods with anti-inflammatory and antioxidant effects. Recent scientific advances have led to the identification of nutraceuticals that could amplify the benefits of the MD and favorably influence gene expression in these patients. Nutraceuticals could have beneficial effects in the postdiagnostic phase of BC, including helping to mitigate the adverse effects of chemotherapy and radiotherapy. Moreover, the MD could be a valid and easy-to-follow option for managing excess weight. The aim of this narrative review is to evaluate the recent scientific literature on the possible beneficial effects of consuming functional and nutraceutical foods in the framework of MD in BCS.

Blockade of exosome release alters HER2 trafficking to the plasma membrane and gives a boost to Trastuzumab

OBJECTIVE(S)

Exosomal HER2 has been evidenced to interfere with antibody-induced anti-tumor effects. However, whether the blockade of HER2+ exosomes release would affect antibody-mediated tumor inhibition has yet to be investigated.

METHODS

Exosomes derived from BT-474, SK-BR3 and SK-OV3 (HER2-overexpressing tumor cells) and MDA-MB-231 cells (HER2 negative) were purified and characterized by bicinchoninic acid (BCA) assay, western blotting and Transmission electron microscopy (TEM). Inhibition of exosome release was achieved by neutral sphingomyelinase-2 (nSMase-2) inhibitor, GW4869. The effects of exosome blockade on the anti-proliferative effects, apoptosis induction, and antibody-mediated cellular cytotoxicity (ADCC) activity of Trastuzumab were examined using MTT, flow cytometry, and LDH release assays. Also, the effects of exosome inhibition on the surface expression and endocytosis/internalization of HER2 were studied by flow cytometry.

RESULTS

Purified exosomes derived from HER2 overexpressing cancer cells were positive for HER2 protein. Blockade of exosome release was able to significantly improve apoptosis induction, anti-proliferative and ADCC responses of Trastuzumab dose dependently. The pretreatment of Trastuzumab/purified NK cells, but not PBMCs, with HER2+ exosomes could also decrease the ADCC effects of Trastuzumab. Exosome inhibition also remarkably downregulated surface HER2 levels in a time-dependent manner, but does not affect its endocytosis/internalization.

CONCLUSION

Based on our findings, HER2+ exosomes may benefit tumor progression by dually suppressing Trastuzumab-induced tumor growth inhibition and cytotoxicity of NK cells. It seems that concomitant blocking of exosome release might be an effective approach for improving the therapeutic effects of Trastuzumab, and potentially other HER2-directed mAbs. In addition, the exosome secretion pathway possibly contributes to the HER2 trafficking to plasma membrane, since the blockade of exosome secretion decreased surface HER2 levels.

Dietary Vitamin A Intake and Circulating Vitamin A Concentrations and the Risk of Three Common Cancers in Women: A Meta-Analysis

BACKGROUND

According to relevant clinical research, dietary and circulating antioxidants vitamin A are connected with the risk of breast, cervical, and ovarian cancer in women. However, there was inconsistency between the findings. We completed this meta-analysis at the right moment to address this contradiction of the problem.

METHODS

Web of Science, Embase, and PubMed databases were searched using the proposed search strategy and filtered using the inclusion and exclusion criteria as well as the NOS quality score. As of May 2022, low intake or low concentration was used as a control, and odds ratio (OR) or relative risk (RR) and ninety-five percent confidence intervals (95% CI) were extracted for high intake. Stata 12.0 was used to process the data.

RESULTS

Our meta-analysis included a total of 49 studies, 29 on breast cancer, 10 on ovarian cancer, and 10 on cervical cancer. There were 38 case-control studies included, with 25,363 cases and 42,281 controls; there were 11 cohort studies included, 1,334,176 individuals were followed up, and finally 9496 obtained cancer. The pooled OR value results were as follows: diet or supplements (OR = 0.83, 95% CI 0.76-0.90, I ² = 56.1%) and serum or plasma (OR = 0.96, 95% CI 0.86-1.09, I ² = 29.5%). Subgroup analyses were performed according to cancer type, diet or supplements, serum or plasma, study type, and geographic regions.

CONCLUSIONS

In North American and Asian populations, high dietary consumption of vitamin A or supplements decreases the incidence of three cancers in women, with breast and ovarian cancers being more significant. However, high circulating vitamin A concentrations were not significantly connected with the risk of the three malignancies.

Combination Treatment of Retinoic Acid Plus Focal Adhesion Kinase Inhibitor Prevents Tumor Growth and Breast Cancer Cell Metastasis

All-trans retinoic acid (RA), the primary metabolite of vitamin A, controls the development and homeostasis of organisms and tissues. RA and its natural and synthetic derivatives, both known as retinoids, are promising agents in treating and chemopreventing different neoplasias, including breast cancer (BC). Focal adhesion kinase (FAK) is a crucial regulator of cell migration, and its overexpression is associated with tumor metastatic behavior. Thus, pharmaceutical FAK inhibitors (FAKi) have been developed to counter its action. In this work, we hypothesize that the RA plus FAKi (RA + FAKi) approach could improve the inhibition of tumor progression. By in silico analysis and its subsequent validation by qPCR, we confirmed RARA, SRC, and PTK2 (encoding RARα, Src, and FAK, respectively) overexpression in all breast cells tested. We also showed a different pattern of genes up/down-regulated between RA-resistant and RA-sensitive BC cells. In addition, we demonstrated that both RA-resistant BC cells (MDA-MB-231 and MDA-MB-468) display the same behavior after RA treatment, modulating the expression of genes involved in Src-FAK signaling. Furthermore, we demonstrated that although RA and FAKi administered separately decrease viability, adhesion, and migration in mammary adenocarcinoma LM3 cells, their combination exerts a higher effect. Additionally, we show that both drugs individually, as well as in combination, induce the expression of apoptosis markers such as active-caspase-3 and cleaved-PARP1. We also provided evidence that RA effects are extrapolated to other cancer cells, including T-47D BC and the human cervical carcinoma HeLa cells. In an orthotopic assay of LM3 tumor growth, whereas RA and FAKi administered separately reduced tumor growth, the combined treatment induced a more potent inhibition increasing mice survival. Moreover, in an experimental metastatic assay, RA significantly reduced metastatic lung dissemination of LM3 cells. Overall, these results indicate that RA resistance could reflect deregulation of most RA-target genes, including genes encoding components of the Src-FAK pathway. Our study demonstrates that RA plays an essential role in disrupting BC tumor growth and metastatic dissemination in vitro and in vivo by controlling FAK expression and localization. RA plus FAKi exacerbate these effects, thus suggesting that the sensitivity to RA therapies could be increased with FAKi coadministration in BC tumors.

Augmented Therapeutic Potential of EC-Synthetic Retinoids in Caco-2 Cancer Cells Using an In Vitro Approach

Colorectal cancer therapies have produced promising clinical responses, but tumor cells rapidly develop resistance to these drugs. It has been previously shown that EC19 and EC23, two EC-synthetic retinoids, have single-agent preclinical anticancer activity in colorectal carcinoma. Here, isobologram analysis revealed that they have synergistic cytotoxicity with retinoic acid receptor (RAR) isoform-selective agonistic retinoids such as AC261066 (RARβ2-selective agonist) and CD437 (RARγ-selective agonist) in Caco-2 cells. This synergism was confirmed by calculating the combination index (lower than 1) and the dose reduction index (higher than 1). Flow cytometry of combinatorial IC₅₀ (the concentration causing 50% cell death) confirmed the cell cycle arrest at the SubG₀-G₁ phase with potentiated apoptotic and necrotic effects. The reported synergistic anticancer activity can be attributed to their ability to reduce the expression of ATP-binding cassette (ABC) transporters including P-glycoprotein (P-gp1), breast cancer resistance protein (BCRP) and multi-drug resistance-associated protein-1 (MRP1) and Heat Shock Protein 70 (Hsp70). This adds up to the apoptosis-promoting activity of EC19 and EC23, as shown by the increased Caspase-3/7 activities and DNA fragmentation leading to DNA double-strand breaks. This study sheds the light on the possible use of EC-synthetic retinoids in the rescue of multi-drug resistance in colorectal cancer using Caco-2 as a model and suggests new promising combinations between different synthetic retinoids. The current in vitro results pave the way for future studies on these compounds as possible cures for colorectal carcinoma.

An Updated Comprehensive Review on Vitamin A and Carotenoids in Breast Cancer: Mechanisms, Genetics, Assessment, Current Evidence, and Future Clinical Implications

Vitamin A and carotenoids are fat-soluble micronutrients that play important role as powerful antioxidants modulating oxidative stress and cancer development. Breast cancer is the most common malignancy in women. As the risk of breast cancer is dependent on various lifestyle factors such as dietary modifications, there is increasing interest surrounding the anti-cancerous properties of vitamin A and carotenoids. Despite the suggested protective roles of vitamin A and carotenoids in breast cancer development, their clinical application for the prevention and treatment of breast cancer is limited. In this narrative review, we discuss the roles of vitamin A and carotenoids along with the evaluation method of vitamin A status. We also exhibit the association of genetic variations involved in metabolism of vitamin A and carotenoids with cancers and other diseases. We demonstrate the epidemiological evidence for the relationship of vitamin A and carotenoids with breast cancer risk, their effects on cancer mechanism, and the recent updates in clinical practice of vitamin A or carotenoids as a potential therapeutic agent against breast cancer. This review provides insight into the preventive and therapeutic roles of vitamin A and carotenoids in breast cancer development and progression.

Nutraceuticals in the Mediterranean Diet: Potential Avenues for Breast Cancer Treatment

The traditional Mediterranean Diet constitutes a food model that refers to the dietary patterns of the population living in countries bordering the Mediterranean Sea in the early 1960s. A huge volume of literature data suggests that the Mediterranean-style diet provides several dietary compounds that have been reported to exert beneficial biological effects against a wide spectrum of chronic illnesses, such as cardiovascular and neurodegenerative diseases and cancer including breast carcinoma. Among bioactive nutrients identified as protective factors for breast cancer, natural polyphenols, retinoids, and polyunsaturated fatty acids (PUFAs) have been reported to possess antioxidant, anti-inflammatory, immunomodulatory and antitumoral properties. The multiple anticancer mechanisms involved include the modulation of molecular events and signaling pathways associated with cell survival, proliferation, differentiation, migration, angiogenesis, antioxidant enzymes and immune responses. This review summarizes the anticancer action of some polyphenols, like resveratrol and epigallocatechin 3-gallate, retinoids and omega-3 PUFAs by highlighting the important hallmarks of cancer in terms of (i) cell cycle growth arrest, (ii) apoptosis, (iii) inflammation and (iv) angiogenesis. The data collected from in vitro and in vivo studies strongly indicate that these natural compounds could be the prospective candidates for the future anticancer therapeutics in breast cancer disease.

Tamoxifen overcomes the trastuzumab-resistance of SK-BR-3 tumorspheres by targeting crosstalk between cytoplasmic estrogen receptor α and the EGFR/HER2 signaling pathway

Since trastuzumab-resistance remains a major obstacle to the successful treatment of HER2-positive breast cancer, a detailed understanding of the mechanisms responsible is required to direct future pharmacotherapeutic strategies. Recently, several studies have indicated that the quiescent natures of cancer stem cells contribute to treatment resistance and tumor recurrence. Thus, in this study, we investigated the mechanism underlying trastuzumab resistance in a quiescent cell population using tumorsphere cultures and explored better therapeutic strategies to overcome trastuzumab resistance in HER2-positive breast cancer patients. We observed that most cells in SK-BR-3 tumorspheres were quiescent, showing the accumulation of cells at the G0/G1 phase as compared to cells in monolayer culture. Furthermore, SK-BR-3 tumorspheres exhibited enhanced EGFR/HER2 signaling, which was incompletely inhibited by trastuzumab, and subsequently led to trastuzumab-resistance. Interestingly, cytoplasmic estrogen receptor α (ERα) expression was markedly elevated in tumorspheres and was associated with enhanced EGFR/HER2 signaling. Accordingly, inhibition of ERα with tamoxifen selectively targeted tumorspheres rather than cells in monolayer culture and overcame trastuzumab resistance in tumorspheres. Taken together, our findings indicate that crosstalk between cytoplasmic ERα and the HER2/EGFR signaling pathway can be considered a novel therapeutic target for quiescent cell populations within HER2-positive breast cancer and that simultaneous inhibition of ER and the EGFR/HER2 pathway may prevent trastuzumab resistance. We hope that these results provide a basis for the use of combinations of tamoxifen and trastuzumab in HER2-positive breast cancer patients.

The landscape of metabolic pathway dependencies in cancer cell lines

The metabolic reprogramming of cancer cells creates metabolic vulnerabilities that can be therapeutically targeted. However, our understanding of metabolic dependencies and the pathway crosstalk that creates these vulnerabilities in cancer cells remains incomplete. Here, by integrating gene expression data with genetic loss-of-function and pharmacological screening data from hundreds of cancer cell lines, we identified metabolic vulnerabilities at the level of pathways rather than individual genes. This approach revealed that metabolic pathway dependencies are highly context-specific such that cancer cells are vulnerable to inhibition of one metabolic pathway only when activity of another metabolic pathway is altered. Notably, we also found that the no single metabolic pathway was universally essential, suggesting that cancer cells are not invariably dependent on any metabolic pathway. In addition, we confirmed that cell culture medium is a major confounding factor for the analysis of metabolic pathway vulnerabilities. Nevertheless, we found robust associations between metabolic pathway activity and sensitivity to clinically approved drugs that were independent of cell culture medium. Lastly, we used parallel integration of pharmacological and genetic dependency data to confidently identify metabolic pathway vulnerabilities. Taken together, this study serves as a comprehensive characterization of the landscape of metabolic pathway vulnerabilities in cancer cell lines.

All-trans retinoic acid and protein kinase C α/β1 inhibitor combined treatment targets cancer stem cells and impairs breast tumor progression

Breast cancer is the leading cause of cancer death among women worldwide. Blocking a single signaling pathway is often an ineffective therapy, especially in the case of aggressive or drug-resistant tumors. Since we have previously described the mechanism involved in the crosstalk between Retinoic Acid system and protein kinase C (PKC) pathway, the rationale of our study was to evaluate the effect of combining all-trans-retinoic acid (ATRA) with a classical PCK inhibitor (Gö6976) in preclinical settings. Employing hormone-independent mammary cancer models, Gö6976 and ATRA combined treatment induced a synergistic reduction in proliferative potential that correlated with an increased apoptosis and RARs modulation towards an anti-oncogenic profile. Combined treatment also impairs growth, self-renewal and clonogenicity potential of cancer stem cells and reduced tumor growth, metastatic spread and cancer stem cells frequency in vivo. An in-silico analysis of “Kaplan–Meier plotter” database indicated that low PKCα together with high RARα mRNA expression is a favorable prognosis factor for hormone-independent breast cancer patients. Here we demonstrate that a classical PKC inhibitor potentiates ATRA antitumor effects also targeting cancer stem cells growth, self-renewal and frequency.

Desmoplasia and Biophysics in Pancreatic Ductal Adenocarcinoma: Can We Learn From Breast Cancer?

Pancreatic ductal adenocarcinoma (PDAC) treatments have historically focused on targeting tumor cells directly. However, in pancreatic masses, the stroma encasing the malignant epithelial cells constitutes up to 80% to 90% of the tumor bulk. This extracellular matrix, which was previously neglected when designing cancer therapies, is now considered fundamental for tumor progression and drug delivery. Desmoplastic tissue is extensively cross-linked, resulting in tremendous tensile strength. This key pathological feature is procarcinogenic, linking PDAC and breast cancer (BC). Physical forces exerted onto cellular surfaces are detected intracellularly and transduced via biochemical messengers in a process called mechanotransduction. Mechanotransduction and tensional homeostasis are linked, with an integral role in influencing tumor growth, metastasis, and interactions with the immune system. It is essential to enhance our knowledge of these integral elements of parenchymal tumors. We aim to review the topic, with a special emphasis on desmoplastic processes and their importance in pancreatic and BC development and treatments, mindful that innovative diagnostic and therapeutic strategies cannot focus on biochemical pathways alone. We then focus on common therapeutic targets identified in both PDAC and BC models and/or patients, aiming to understand these treatments and draw similarities between the two tumors.

Immune cells in the tumour: new routes of retinoids for chemoprevention and chemotherapeutics

Retinoids, vitamin A and its natural and synthetic analogues have various functions, including being involved in cell proliferation and differentiation and participating in the formation of vertebrate morphology. In addition, they may activate certain tumour suppressor genes that then act as tumour inhibitors. In the past decades, retinoids have been regarded as promising chemotherapeutic and chemopreventive agents; however, their mechanisms are still not fully understood. Immune cells that participate in or are associated with the immune response play vital roles in the initiation and development of many cancers. Interestingly, recent studies have demonstrated that retinoids can also exert various effects on immune cells including macrophages, T cells and dendritic cells in tumour tissues to execute anti-tumour actions, providing new insights into chemoprevention and chemotherapeutics. In this review, we focus on the effects of retinoids on immune cells in the tumour, which may provide new approaches for antineoplastic strategies.

Synergistic antitumor activity by combining trastuzumab with retinoic acid in HER2 positive human breast cancer cells

Breast cancer can be classified into molecular subtypes. Tumors overexpressing HER2 protein are more aggressive and metastatic; hence, patients have a poor prognosis. Anti-HER2 strategies, such as the monoclonal antibody Trastuzumab (Tz), have therefore been developed. Despite this progress, not all patients respond to the treatment. Retinoic acid (RA) has been proposed as an adjuvant treatment of breast carcinoma because of its ability to inhibit cell growth. We evaluated the effect of Tz in combination with RA on the viability, adhesion, migration, invasion and expression of migration-related proteins in SKBR3 and BT-474 human breast cancer cells. MTT, pharmacological interaction analysis, immunofluorescence, adhesion/migration/invasion and Western blot assays were performed. The coadministration of both drugs synergistically decreased cell survival. Tz+RA significantly decreased adhesion/migration/invasion in both cell types. Tz+RA strongly reduced FAK and HER2 expression and induced nuclear FAK translocation. In addition, a granular distribution of HER2 receptor was observed after the combined treatment. In conclusion, the coadministration of both drugs in patients with this type of cancer could contribute to the improvement of their prognosis and reduce the adverse effects of therapy because the applied Tz doses would be lower due to the adjuvant effect of RA.

Inactivation of nuclear factor κB by MIP-based drug combinations augments cell death of breast cancer cells

Background

Drug combination therapy to treat cancer is a strategic approach to increase successful treatment rate. Optimizing combination regimens is vital to increase therapeutic efficacy with minimal side effects.

Materials and methods

In the present study, we evaluated the in vitro cytotoxicity of double and triple combinations consisting of 1′S-1′-acetoxychavicol acetate (ACA), Mycobacterium indicus pranii (MIP) and cisplatin (CDDP) against 14 various human cancer cell lines to address the need for more effective therapy. Our data show synergistic effects in MCF-7 cells treated with MIP:ACA, MIP:CDDP and MIP:ACA:CDDP combinations. The type of interaction between MIP, ACA and CDDP was evaluated based on combination index being <0.8 for synergistic effect. Identifying the mechanism of cell death based on previous studies involved intrinsic apoptosis and nuclear factor kappa B (NF-κB) and tested in Western blot analysis. Inactivation of NF-κB was confirmed by p65 and IκBα, while intrinsic apoptosis pathway activation was confirmed by caspase-9 and Apaf-1 expression.

Results

All combinations confirmed intrinsic apoptosis activation and NF-κB inactivation.

Conclusion

Double and triple combination regimens that target induction of the same death mechanism with reduced dosage of each drug could potentially be clinically beneficial in reducing dose-related toxicities.

Cooperative antitumor activities of carnosic acid and Trastuzumab in ERBB2+ breast cancer cells

Background

ERBB2 is overexpressed in up to 20–30% of human breast cancers (BCs), and it is associated with aggressive disease. Trastuzumab (Tz), a humanized monoclonal antibody, improves the prognosis associated with ERBB2-amplified BCs. However, the development of resistance remains a significant challenge. Carnosic acid (CA) is a diterpene found in rosemary and sage, endowed with anticancer properties. In this in vitro study, we have investigated whether Tz and CA have cooperative effects on cell survival of ERBB2 overexpressing (ERBB2⁺) cells and whether CA might restore Tz sensitivity in Tz-resistant cells.

Methods

We have studied BC cell migration and survival upon CA and Tz treatment. In particular, migration ability was assessed by transwell assay while cell survival was assessed by MTT assay. In addition, we have performed cell cycle and apoptosis analysis by high-resolution DNA flow cytometry and annexin-V, resazurin and sytox blue staining by flow cytometry, respectively. The expression of proteins involved in cell cycle progression, ERBB2 signaling pathway, and autophagy was evaluated by immunoblot and immunofluorescence analysis. Cellular structures relevant to the endosome/lysosome and autophagy pathways have been studied by immunofluorescence and transmission electron microscopy.

Results

We report that, in ERBB2⁺ BC cells, CA reversibly enhances Tz inhibition of cell survival, cooperatively inhibits cell migration and induces cell cycle arrest in G0/G1. These events are accompanied by ERBB2 down-regulation, deregulation of the PI3K/AKT/mTOR signaling pathway and up-regulation of both CDKN1A/p21^WAF1 and CDKN1B/p27^KIP1. Furthermore, we have demonstrated that CA impairs late autophagy and causes derangement of the lysosomal compartment as shown by up-regulation of SQSTM1/p62 and ultrastructural analysis. Accordingly, we have found that CA restores, at least in part, sensitivity to Tz in SKBR-3 Tz-resistant cell line.

Conclusions

Our data demonstrate the cooperation between CA and Tz in inhibiting cell migration and survival of ERBB2⁺ BC cells that warrant further studies to establish if CA or CA derivatives may be useful in vivo in the treatment of ERBB2⁺ cancers.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0615-0) contains supplementary material, which is available to authorized users.

Fenretinide: A Potential Treatment for Endometriosis

OBJECTIVE

Fenretinide is a synthetic retinoid analogue that promotes apoptosis but has decreased toxicity when compared to other retinoids. We have previously shown that retinoic acid (RA) production in endometriotic tissue is decreased, resulting in reduced estrogen metabolism and apoptotic resistance. We hypothesize fenretinide may induce apoptosis in endometriotic cells and tissues, thereby reducing disease burden.

MATERIALS AND METHODS

Primary endometriotic stromal cells were collected, isolated, cultured, and treated with fenretinide in doses from 0 to 20 µmol/L. Cell count, viability, and immunoblots were performed to examine apoptosis. Quantitative reverse transcription-polymerase chain reaction from endometriotic cells treated with fenretinide was used to examine expression of genes involved in RA signaling including stimulated by RA 6 (STRA6), cellular RA binding protein 2 (CRABP2), and fatty acid binding protein 5 (FABP5). Endometriotic tissue was xenografted subcutaneously into the flanks of mice which were treated with fenretinide for 2 weeks, after which the mice were killed and lesion volumes calculated. Statistical analysis was performed using t test and analysis of variance.

RESULTS

Treatment with fenretinide significantly decreased total cell count (doses 5-20 µL) and viability (doses 10-20 µmol/L). Fenretinide increased protein levels of the apoptotic marker poly (ADP ribose) polymerase (starting at 10 µmol/L) and decreased proliferation marker proliferating cell nuclear antigen (10 µmol/L, starting at 8-day treatment). Examination of genes involved in retinoid uptake and action showed that treatment induced STRA6 expression while expression of CRABP2 and FABP5 remained unchanged. Fenretinide also significantly decreased the endometriotic lesion xenograft volume.

CONCLUSIONS

Fenretinide increases STRA6 expression thereby potentially reversing the pathological loss of retinoid availability. Treatment with this compound induces apoptosis. In vivo treatments decrease lesion volume. Targeting the RA signaling pathway may be a promising novel treatment for women with endometriosis.

Natural Products for Chemoprevention of Breast Cancer

Breast cancer is the primary cause of cancer death in women. Although current therapies have shown some promise against breast cancer, there is still no effective cure for the majority of patients in the advanced stages of breast cancer. Development of effective agents to slow, reduce, or reverse the incidence of breast cancer in high-risk women is necessary. Chemoprevention of breast cancer by natural products is advantageous, as these compounds have few side effects and low toxicity compared to synthetic compounds. In the present review, we summarize natural products which exert chemopreventive activities against breast cancer, such as curcumin, sauchinone, lycopene, denbinobin, genipin, capsaicin, and ursolic acid. This review examines the current knowledge about natural compounds and their mechanisms that underlie breast cancer chemopreventive activity both in vitro and in vivo. The present review may provide information on the use of these compounds for the prevention of breast cancer.

Mild hyperthermia influence on Herceptin(®) properties

Background

Mild hyperthermia (mHT) increases the tumor perfusion and vascular permeability, and reduces the interstitial fluid pressure, resulting in better intra-tumoral bioavailability of low molecular weight drugs. This approach is potentially also attractive for delivery of therapeutic macromolecules, such as antibodies. Here, we investigated the effects of mHT on the stability, immunological and pharmacological properties of Herceptin^®, a clinically approved antibody, targeting the human epidermal growth factor receptor 2 (HER-2) overexpressed in breast cancer.

Results

Herceptin^® was heated to 37°C (control) and 42°C (mHT) for 1 hour. Formation of Herceptin^® aggregates was measured using Nile Red assay. mHT did not result in additional Herceptin^® aggregates compared to 37°C, showing the Herceptin^® stability is unchanged. Immunological and pharmacological properties of Herceptin^® were evaluated following mHT using HER-2 positive breast cancer cells (BT-474). Exposure of Herceptin^® to mHT preserved recognition and binding affinity of Herceptin^® to HER-2. Western-blot and cell proliferation assays on BT-474 cells showed that mHT left the inhibitory activities of Herceptin^® unchanged.

Conclusions

The stability, and the immunological and pharmacological properties of Herceptin^® are not negatively affected by mHT. Further in-vivo studies are required to evaluate the influence of mHT on intra-tumoral bioavailability and therapeutic effectiveness of Herceptin^®.

SPLUNC1 is associated with nasopharyngeal carcinoma prognosis and plays an important role in all-trans-retinoic acid-induced growth inhibition and differentiation in nasopharyngeal cancer cells

Human SPLUNC1 can suppress nasopharyngeal carcinoma (NPC) tumor formation; however, the correlation between SPLUNC1expression and NPC patient prognosis has not been reported. In the present study, we used a large-scale sample of 1015 tissue cores to detect SPLUNC1 expression and its association with patient prognosis. SPLUNC1 expression was reduced in NPC samples compared to nontumor nasopharyngeal epithelium tissues. Positive expression of SPLUNC1 in NPC predicted a better prognosis (disease-free survival, P = 0.034; overall survival, P = 0.048). Cox's proportional hazards model revealed that SPLUNC1 could be a significant prognostic factor affecting disease-free survival (P = 0.027). A cDNA micro-array analyzed by significant analysis of micro-array (SAM) and ingenuity pathway analysis (IPA) revealed that an indirect interaction existed between SPLUNC1 and retinoic acid (RA) in the cancer regulatory network. To further investigate the molecular mechanisms involved, we utilized several bioinformatics tools and identified 12 retinoid X receptors heterodimer binding sites in the promoter region of the SPLUNC1 gene. The transcriptional activity of the SPLUNC1 promoter was up-regulated significantly by all-trans-retinoic acid (ATRA). SPLUNC1 and retinoic acid receptor expression were induced significantly by ATRA, and removal of ATRA led to a progressive loss of SPLUNC1 and retinoic acid receptor expression. ATRA inhibited proliferation and induced the differentiation of NPC cells. Interestingly, over-expression of SPLUNC1 sensitized NPC cells to ATRA, whereas knockdown of SPLUNC1 in HNE1 cells increased cell viability. Under SPLUNC1 knockdown conditions, differentiation was reversed by ATRA treatment. We concluded that SPLUNC1 could potentially predict prognosis for NPC patients and play an important role in ATRA-induced growth inhibition and differentiation in NPC cells.

Mitochondria: the gateway for tamoxifen-induced liver injury

Tamoxifen (TAM) is routinely used in the treatment of breast carcinoma. TAM-induced liver injury remains a major concern, as TAM causes hepatic steatosis in a significant number of patients, which can progress toward steatohepatitis. Liver toxicity is generally believed to involve mitochondrial dysfunction and TAM exerts multiple deleterious effects on mitochondria, which may account for the hepatotoxicity observed in patients treated with TAM. Endoxifen (EDX), a key active metabolite of TAM that is being investigated as an alternative to TAM in breast cancer therapy, slightly affects mitochondria in comparison with TAM and this demonstration well correlates with the absence of alterations in the clinical parameters of individuals taking EDX. The steady-state plasma concentrations of TAM and its active metabolites EDX and 4-hydroxytamoxifen (OHTAM) in patients taking TAM are highly variable, reflecting genetic variants of CYP2D6 involved in TAM metabolism. Besides de genetic polymorphisms, the intake of drugs that influence the enzymatic activity of CYP2D6 compromises the therapeutic efficiency of TAM. The knowledge of the impact of the variability of TAM metabolism in the breast cancer treatment explains the discrepant outcomes observed in patients taking TAM, as well as the individual variability of idiosyncratic liver injury and other sides effects observed. Therefore, and contrarily to the clinical use of EDX, the need of therapeutic drug monitoring and a regular assessment of liver function biomarkers should be considered in patients under therapies with TAM. In this review we focus on the mitochondrial effects of TAM and its metabolites and on the role played by mitochondria in the initiating events leading to TAM-induced hepatotoxicity, as well as the clinical implications.

Interplay between estrogen and retinoid signaling in breast cancer--current and future perspectives

All-trans-retinoic acid (RA) is a promising agent for breast cancer treatment, but it induces several adverse effects and the few clinical trials performed up to now in breast cancer patients have provided disappointing results. The combination of RA and antiestrogenic compounds, such as tamoxifen, synergistically decreases the proliferation of breast cancer cells and an interplay between retinoid and estrogen signaling has begun to be unraveled, turning these combinations into an appealing strategy for breast cancer treatment. This review focus on the current knowledge regarding the interplay between retinoid and estrogen signaling in breast cancer and the combinations of RA with antiestrogens, aiming their future utilization in cancer therapy.

Retinoids and their biological effects against cancer

There are more than 4000 natural and synthetic molecules structurally and/or functionally related to vitamin A. Retinoids are a class of these compounds that are structurally associated to vitamin A. The retinoids have a wide spectrum of functions. Retinoic acid, which is the active metabolite of retinol, regulates a wide range of biological processes including development, differentiation, proliferation and apoptosis. It suppresses carcinogenesis in tumorigenic animal models for the skin, oral, lung, breast, bladder, ovarian and prostate. It is important how major retinoids may act in cancer treatment or prevention. The reports have indicated that lower levels of vitamin A in humans may be associated with relative type 1 cytokine dominance and a higher proportion of NK cells. In addition, very low vitamin A levels would be undesirable explaining the essential role of vitamin A in epithelial and general cell maturation and function. However, the cytokine shifts associated with moderately low levels of vitamin A may be in some ways beneficial in an environment where HIV infection, M. tuberculosis infection, or other type 1 infections are highly prevalent and/or when acquired immunity is cooperated. In this review, we intend to describe the biochemical and immunological functions of retinoids against cancer.

Combination of fenretinide and selenite inhibits proliferation and induces apoptosis in ovarian cancer cells

The combination of fenretinide and selenite on ovarian cancer cells was investigated to assess its effects on proliferation and ability to induce apoptosis. Our results showed that fenretinide and selenite in combination significantly suppress the proliferation of ovarian cancer cells and induced apoptosis (including reactive oxygen species generation, and the loss of mitochondrial membrane potential) compared with either drug used alone. The caspase3/9-dependent pathway was triggered significantly in combination treatment, and moreover, the AMPK pathway also mediated the apoptosis induction in fenretinide and selenite combination. Fenretinide and selenite combination treatment was demonstrated to suppress tumor growth in vivo, this drug combination has been thus found to have an enhanced anti-tumor effect on ovarian cancers cells.

The combination of the antiestrogen endoxifen with all-trans-retinoic acid has anti-proliferative and anti-migration effects on melanoma cells without inducing significant toxicity in non-neoplasic cells

Melanoma incidence is dramatically increasing and the available treatments beyond partial efficacy have severe side effects. Retinoids are promising anticancer agents, but their clinical use has been limited by their toxicity, although a combination with other agents can possibly generate a therapeutic action at lower dosage. Thus, we investigated the effects of all-trans-retinoic acid combined with the antiestrogen endoxifen on melanoma cell proliferation and the effects were compared with its pro-drug tamoxifen. Moreover, we evaluated the effects of these combinations on non-neoplasic cells and assessed mitochondrial bioenergetic functions, to predict their potential toxicity. Individually, all-trans-retinoic acid and the antiestrogens endoxifen and tamoxifen decreased melanoma cell biomass, cell viability and DNA synthesis, without increased cell death, suggesting that the compounds inhibited cell proliferation. Noteworthy, endoxifen decreased cell proliferation more efficiently than tamoxifen. The combination of endoxifen with all-trans-retinoic acid enhanced the antiproliferative effects of the compounds individually more potently than tamoxifen, which did not enhance the effects induced by all-trans-retinoic acid alone, and blocked cell cycle progression in G1. Moreover, the combination of all-trans-retinoic acid with endoxifen significantly decreased melanoma cells migration, whereas the combination with tamoxifen did not present significant effects. At the concentrations used the compounds did not induce cytotoxicity in non-neoplasic cells and liver mitochondrial bioenergetic function was not affected. Altogether, our results show for the first time that a combined treatment of all-trans-retinoic acid with endoxifen may provide an anti-proliferative and anti-migration effect upon melanoma cells without major toxicity, offering a powerful therapeutic strategy for malignant melanoma.

Retinoids, carotenoids, and tocopherols in breast adipose tissue and serum of benign breast disease and breast cancer patients

Various retinoic acid (RA) isomers (all-trans, 13-cis, 11-cis, and 9-cis) as well as retinol, carotenoids, and tocopherol concentrations were determined in both serum and breast adipose tissue of 22 benign breast disease patients and 52 breast cancer patients categorized into 4 stages by malignancy. Serum RA isomers were analyzed by a newly developed sensitive method combining a high-performance liquid chromatography and a gas chromatography-mass spectrometry, and retinol, carotenoid, and tocopherol concentrations using a high-performance liquid chromatography system. The breast cancer patients showed significantly lower serum retinol, whereas significantly higher breast adipose tissue retinol concentration than those of benign breast disease patients. Although breast cancer patients showed significantly higher serum all-trans and 13-cis RA concentrations, 11-cis RA in breast adipose tissue was significantly lower in the breast cancer patients than those of benign breast disease patients and it was associated with the stage of malignancy. The current study indicates that the retinol and RA isomers in the target tissue of breast tumor patients are not reflecting their concentrations in circulation. The mechanisms of tissue specific uptake of RA isomers and their functions warrant further studies.

Progesterone-inducible cytokeratin 5-positive cells in luminal breast cancer exhibit progenitor properties

Progestins play a deleterious role in the onset of breast cancer, yet their influence on existing breast cancer and tumor progression is not well understood. In luminal estrogen receptor (ER)- and progesterone receptor (PR)-positive breast cancer, progestins induce a fraction of cells to express cytokeratin 5 (CK5), a marker of basal epithelial and progenitor cells in the normal breast. CK5(+) cells lose expression of ER and PR and are relatively quiescent, increasing their resistance to endocrine and chemotherapy compared to intratumoral CK5(-)ER(+)PR(+) cells. Characterization of live CK5(+) cells has been hampered by a lack of means for their direct isolation. Here, we describe optical (GFP) and bioluminescent (luciferase) reporter models to quantitate and isolate CK5(+) cells in luminal breast cancer cell lines utilizing the human KRT5 gene promoter and a viral vector approach. Using this system, we confirmed that the induction of GFP(+)/CK5(+) cells is specific to progestins, is dependent on PR, can be blocked by antiprogestins, and does not occur with other steroid hormones. Progestin-induced, fluorescence-activated cell sorting-isolated CK5(+) cells had lower ER and PR mRNA, were slower cycling, and were relatively more invasive and sphere forming than their CK5(-) counterparts in vitro. Repeated progestin treatment and selection of GFP(+) cells enriched for a persistent population of CK5(+) cells, suggesting that this transition can be semi-permanent. These data support that in PR(+) breast cancers, progestins induce a subpopulation of CK5(+)ER(-)PR(-) cells with enhanced progenitor properties and have implications for treatment resistance and recurrence in luminal breast cancer.

Retinoids regulate stem cell differentiation

Retinoids are ubiquitous signaling molecules that influence nearly every cell type, exert profound effects on development, and complement cancer chemotherapeutic regimens. All-trans retinoic acid (RA) and other active retinoids are generated from vitamin A (retinol), but key aspects of the signaling pathways required to produce active retinoids remain unclear. Retinoids generated by one cell type can affect nearby cells, so retinoids also function in intercellular communication. RA induces differentiation primarily by binding to RARs, transcription factors that associate with RXRs and bind RAREs in the nucleus. Binding of RA: (1) initiates changes in interactions of RAR/RXRs with co-repressor and co-activator proteins, activating transcription of primary target genes; (2) alters interactions with proteins that induce epigenetic changes; (3) induces transcription of genes encoding transcription factors and signaling proteins that further modify gene expression (e.g., FOX03A, Hoxa1, Sox9, TRAIL, UBE2D3); and (4) results in alterations in estrogen receptor α signaling. Proteins that bind at or near RAREs include Sin3a, N-CoR1, PRAME, Trim24, NRIP1, Ajuba, Zfp423, and MN1/TEL. Interactions among retinoids, RARs/RXRs, and these proteins explain in part the powerful effects of retinoids on stem cell differentiation. Studies of this retinol signaling cascade enhance our ability to understand and regulate stem cell differentiation for therapeutic and scientific purposes. In cancer chemotherapeutic regimens retinoids can promote tumor cell differentiation and/or induce proteins that sensitize tumors to drug combinations. Mechanistic studies of retinoid signaling continue to suggest novel drug targets and will improve therapeutic strategies for cancer and other diseases, such as immune-mediated inflammatory diseases.