Targeting bromodomain and extraterminal proteins in breast cancer

Targeting Bromodomain-Containing Protein 9 in Human Uterine Fibroid Cells

Bromodomain (BRD)-containing proteins are evolutionarily conserved protein-protein interaction modules involved in many biological processes. BRDs selectively recognize and bind to acetylated lysine residues, particularly in histones, and thereby have a crucial role in the regulation of gene expression. BRD protein dysfunction has been linked to many diseases, including tumorigenesis. Previously, we reported the critical role of BRD-containing protein 9 (BRD9) in the pathogenesis of UFs. The present study aimed to extend our previous finding and further understand the role of the BRD9 in UFs. Our studies demonstrated that targeted inhibition of BRD9 with its potent inhibitor TP-472 inhibited the pathogenesis of UF through increased apoptosis and proliferation arrest and decreased extracellular matrix deposition in UF cells. High-throughput transcriptomic analysis further and extensively demonstrated that targeted inhibition of BRD9 by TP-472 impacted the biological pathways, including cell cycle progression, inflammatory response, E2F targets, ECM deposition, and m6A reprogramming. Compared with the previous study, we identified common enriched pathways induced by two BRD9 inhibitors, I-BRD9 and TP-472. Taken together, our studies further revealed the critical role of BRD9 in UF cells. We characterized the link between BRD9 and other vital pathways, as well as the connection between epigenetic and epitranscriptome involved in UF progression. Targeted inhibition of BRD proteins might provide a non-hormonal treatment strategy for this most common benign tumor in women of reproductive age.

Peptide Inhibitor Targeting the Extraterminal Domain in BRD4 Potently Suppresses Breast Cancer Both In Vitro and In Vivo

BRD4 is associated with a variety of human diseases, including breast cancer. The crucial roles of amino-terminal bromodomains (BDs) of BRD4 in binding with acetylated histones to regulate oncogene expression make them promising drug targets. However, adverse events impede the development of the BD inhibitors. BRD4 adopts an extraterminal (ET) domain, which recruits proteins to drive oncogene expression. We discovered a peptide inhibitor PiET targeting the ET domain to disrupt BRD4/JMJD6 interaction, a protein complex critical in oncogene expression and breast cancer. The cell-permeable form of PiET, TAT-PiET, and PROTAC-modified TAT-PiET, TAT-PiET-PROTAC, potently inhibits the expression of BRD4/JMJD6 target genes and breast cancer cell growth. Combination therapy with TAT-PiET/TAT-PiET-PROTAC and JQ1, iJMJD6, or Fulvestrant exhibits synergistic effects. TAT-PiET or TAT-PiET-PROTAC treatment overcomes endocrine therapy resistance in ERα-positive breast cancer cells. Taken together, we demonstrated that targeting the ET domain is effective in suppressing breast cancer, providing a therapeutic avenue in the clinic.

Bromodomain-Containing Protein 9 Regulates Signaling Pathways and Reprograms the Epigenome in Immortalized Human Uterine Fibroid Cells

Bromodomain-containing proteins (BRDs) are involved in many biological processes, most notably epigenetic regulation of transcription, and BRD dysfunction has been linked to many diseases, including tumorigenesis. However, the role of BRDs in the pathogenesis of uterine fibroids (UFs) is entirely unknown. The present study aimed to determine the expression pattern of BRD9 in UFs and matched myometrium and further assess the impact of a BRD9 inhibitor on UF phenotype and epigenetic/epitranscriptomic changes. Our studies demonstrated that the levels of BRD9 were significantly upregulated in UFs compared to matched myometrium, suggesting that the aberrant BRD expression may contribute to the pathogenesis of UFs. We then evaluated the potential roles of BRD9 using its specific inhibitor, I-BRD9. Targeted inhibition of BRD9 suppressed UF tumorigenesis with increased apoptosis and cell cycle arrest, decreased cell proliferation, and extracellular matrix deposition in UF cells. The latter is the key hallmark of UFs. Unbiased transcriptomic profiling coupled with downstream bioinformatics analysis further and extensively demonstrated that targeted inhibition of BRD9 impacted the cell cycle- and ECM-related biological pathways and reprogrammed the UF cell epigenome and epitranscriptome in UFs. Taken together, our studies support the critical role of BRD9 in UF cells and the strong interconnection between BRD9 and other pathways controlling the UF progression. Targeted inhibition of BRDs might provide a non-hormonal treatment option for this most common benign tumor in women of reproductive age.

Design, synthesis, and evaluation of 4-(3-(3,5-dimethylisoxazol-4-yl)benzyl)phthalazin-1(2H)-one derivatives: potent BRD4 inhibitors with anti-breast cancer activity

BRD4 inhibitors have demonstrated promising potential in cancer therapy. However, their therapeutic efficacy in breast cancer varies depending on the breast cancer subtype, particularly in the treatment of TNBC. In this study, we designed and synthesized 94 derivatives of 4-(3-(3,5-dimethylisoxazol-4-yl)benzyl)phthalazin-1(2H)-one to evaluate their inhibitory activities against BRD4. Notably, compound DDT26 exhibited the most potent inhibitory effect on BRD4, with an IC50 value of 0.237 ± 0.093 μM. DDT26 demonstrated significant anti-proliferative activity against both TNBC cell lines and MCF-7 cells. Intriguingly, the phthalazinone moiety of DDT26 mimicked the PAPR1 substrate, resulting in DDT26 displaying a moderate inhibitory effect on PARP1 with an IC50 value of 4.289 ± 1.807 μM. Further, DDT26 was shown to modulate the expression of c-MYC and γ-H2AX, induce DNA damage, inhibit cell migration and colony formation, and arrest the cell cycle at the G1 phase in MCF-7 cells. Our findings present potential lead compounds for the development of potent anti-breast cancer agents targeting BRD4.

Targeting the epigenetic reader "BET" as a therapeutic strategy for cancer

Bromodomain and extraterminal (BET) proteins have the ability to bind to acetylated lysine residues present in both histones and non-histone proteins. This binding is facilitated by the presence of tandem bromodomains. The regulatory role of BET proteins extends to chromatin dynamics, cellular processes, and disease progression. The BET family comprises of BRD 2, 3, 4 and BRDT. The BET proteins are a class of epigenetic readers that regulate the transcriptional activity of a multitude of genes that are involved in the pathogenesis of cancer. Thus, targeting BET proteins has been identified as a potentially efficacious approach for the treatment of cancer. BET inhibitors (BETis) are known to interfere with the binding of BET proteins to acetylated lysine residues of chromatin, thereby leading to the suppression of transcription of several genes, including oncogenic transcription factors. Here in this review, we focus on role of Bromodomain and extra C-terminal (BET) proteins in cancer progression. Furthermore, numerous small-molecule inhibitors with pan-BET activity have been documented, with certain compounds currently undergoing clinical assessment. However, it is apparent that the clinical effectiveness of the present BET inhibitors is restricted, prompting the exploration of novel technologies to enhance their clinical outcomes and mitigate undesired adverse effects. Thus, strategies like development of selective BET-BD1, & BD2 inhibitors, dual and acting BET are also presented in this review and attempts to cover the chemistry needed for proper establishment of designed molecules into BRD have been made. Moreover, the review attempts to summarize the details of research till date and proposes a space for future development of BET inhibitor with diminished side effects. It can be concluded that discovery of isoform selective BET inhibitors can be a way forward in order to develop BET inhibitors with negligible side effects.

Disabled C3ar1/C5ar1 Signaling in Foxp3+ T Regulatory Cells Leads to TSDR Demethylation and Long-Term Stability

Demethylation of the T regulatory cell (Treg)-specific demethylation region (TSDR) of the Foxp3 gene is the hallmark of Foxp3+ Treg stability, but the cellular signaling that programs this epigenetic state remains undefined. In this article, we show that suppressed C3a and C5a receptor (C3ar1/C5ar1) signaling in murine Tregs plays an obligate role. Murine C3ar1-/-C5ar1-/- Foxp3+ cells showed increased suppressor of cytokine signaling 1/2/3 expression, vitamin C stabilization, and ten-eleven translocation (TET) 1, TET2, and TET3 expression, all of which are linked to Treg stability. C3ar1-/-C5ar1-/- Foxp3+ cells additionally were devoid of BRD4 signaling that primes Th17 cell lineage commitment. Orally induced OVA-specific C3ar1-/-C5ar1-/- Foxp3+ OT-II Tregs transferred to OVA-immunized wild-type recipients remained >90% Foxp3+ out to 4 mo, whereas identically generated CD55-/- (DAF-/-) Foxp3+ OT-II Tregs (in which C3ar1/C5ar1 signaling is potentiated) lost >75% of Foxp3 expression by 14 d. After 4 mo in vivo, the C3ar1-/-C5ar1-/- Foxp3+ OT-II Tregs fully retained Foxp3 expression even with OVA challenge and produced copious TGF-β and IL-10. Their TSDR was demethylated comparably with that of thymic Tregs. They exhibited nuclear translocation of NFAT and NF-κB reported to stabilize thymic Tregs by inducing hairpin looping of the TSDR to the Foxp3 promoter. Thus, disabled CD4+ cell C3ar1/C5ar1 signaling triggers the sequential cellular events that lead to demethylation of the Foxp3 TSDR.

Establishment of environment-sensitive probes targeting BRD3/BRD4 for imaging and therapy of tumor

The BET (bromo and extra-terminal) family proteins are epigenetic readers and master transcription coactivators, which have attracted great interests as cancer therapeutic targets. However, there are few developed labeling toolkits that can be applied for the dynamic studies of BET family proteins in living cells and tissue slices. In order to label and study the distribution of the BET family proteins in tumor cells and tumor tissues, a novel series of environment-sensitive fluorescent probes (6a-6c) were designed and evaluated for their labeling properties. Interestingly, 6a is capable of identifying tumor tissue slices and making a distinction between the tumor and normal tissues. Moreover, it can localize to the nuclear bodies in tumor slices just like BRD3 antibody. In addition, it also played an anti-tumor role through the induction of apoptosis. All these features render 6a may compatible for immunofluorescent studies and future cancer diagnosis, and guide for the discovery of new anticancer drugs.

BAP18 facilitates CTCF-mediated chromatin accessible to regulate enhancer activity in breast cancer

The estrogen receptor alpha (ERα) signaling pathway is a crucial target for ERα-positive breast cancer therapeutic strategies. Co-regulators and other transcription factors cooperate for effective ERα-related enhancer activation. Recent studies demonstrate that the transcription factor CTCF is essential to participate in ERα/E2-induced enhancer transactivation. However, the mechanism of how CTCF is achieved remains unknown. Here, we provided evidence that BAP18 is required for CTCF recruitment on ERα-enriched enhancers, facilitating CTCF-mediated chromatin accessibility to promote enhancer RNAs transcription. Consistently, GRO-seq demonstrates that the enhancer activity is positively correlated with BAP18 enrichment. Furthermore, BAP18 interacts with SMARCA1/BPTF to accelerate the recruitment of CTCF to ERα-related enhancers. Interestingly, BAP18 is involved in chromatin accessibility within enhancer regions, thereby increasing enhancer transactivation and enhancer-promoter looping. BAP18 depletion increases the sensitivity of anti-estrogen and anti-enhancer treatment in MCF7 cells. Collectively, our study indicates that BAP18 coordinates with CTCF to enlarge the transactivation of ERα-related enhancers, providing a better understanding of BAP18/CTCF coupling chromatin remodeling and E-P looping in the regulation of enhancer transcription.

Prodrug nanoparticles potentiate tumor chemo-immunometabolic therapy by disturbing oxidative stress

Constant oxidative stress and lactate accumulation are two main causes of tumor immunosuppression, their concurrent reduction plays a dominant role in effective antitumor immunity, but remains challenging. Herein, reactive oxygen species (ROS) responsive prodrug nanoparticles (designed as DHCRJ) are constructed for metabolic amplified chemo-immunotherapy against triple-negative breast cancer (TNBC) by modulating oxidative state and hyperglycolysis. Specifically, DHCRJ is prepared by the self-assembly of DOX prodrug-tethered ROS consuming bond-bridged copolymers with the loading of bromodomain-containing protein 4 inhibitor (BRD4i) JQ1. Interestingly, the nanoparticle polymer network could reduce ROS to relieve tumor hypoxia and realize the dense-to-loose structure inversion arising from ROS-triggered network collapse, which favors JQ1 release and hyaluronidase (Hyal)-activatable DOX prodrugs generation. More importantly, disruption of oxidative stress decreases glucose uptake and assists JQ1 to down-regulate oncogene c-Myc driven tumor glycolysis for blocking the source of lactate and reshaping immunosuppressive tumor microenvironment (ITME). Meanwhile, benefiting from the synergistic effect of DOX prodrugs and JQ1, DHCRJ is able to facilitate tumor immunogenicity and potentiate systemic immune responses through antigen processing and presentation pathway. In this manner, DHCRJ significantly suppresses tumor growth and metastasis with prolonged survival. Collectively, this study represents a proof of concept antioxidant-enhanced chemo-immunometabolic therapy strategy using ROS-reducing nanoparticles for efficient synergistic therapeutic modality of TNBC.

Epigenetic alterations in canine mammary cancer

In dogs, mammary cancer is the most common tumor type, especially in unspayed females. As in humans, this type of cancer has spontaneous development and is influenced by several risk factors, such as age and hormonal exposure in addition to genetic and epigenetic factors. Epigenetic mechanisms are responsible for gene expression modulation without alterations in the DNA sequence and include but are not limited to DNA methylation, histone modifications, and noncoding RNAs. Epigenetic patterns are known to influence a variety of biological mechanisms, such as cellular differentiation and development, and dysregulations of those patterns may result in several diseases, such as cancer. In this respect, this review summarizes the main findings concerning epigenetic alterations in canine mammary cancer, their relationship with the carcinogenic process, and their use as diagnostic and prognostic markers.

Co-Encapsulation of Paclitaxel and JQ1 in Zein Nanoparticles as Potential Innovative Nanomedicine

The manuscript describes the development of zein nanoparticles containing paclitaxel (PTX) and the bromo-and extra-terminal domain inhibitor (S)-tertbutyl2-(4-(4-chlorophenyl)-2,3,9-trimethyl-6H-thieno(3,2-f)(1,2,4)triazolo(4,3-a)(1,4)diazepin-6-yl)acetate (JQ1) together with their cytotoxicity on triple-negative breast cancer cells. The rationale of this association is that of exploiting different types of cancer cells as targets in order to obtain increased pharmacological activity with respect to that exerted by the single agents. Zein, a protein found in the endosperm of corn, was used as a biomaterial to obtain multidrug carriers characterized by mean sizes of ˂200 nm, a low polydispersity index (0.1-0.2) and a negative surface charge. An entrapment efficiency of ~35% of both the drugs was obtained when 0.3 mg/mL of the active compounds were used during the nanoprecipitation procedure. No adverse phenomena such as sedimentation, macro-aggregation or flocculation occurred when the nanosystems were heated to 37 °C. The multidrug nanoformulation demonstrated significant in vitro cytototoxic activity against MDA-MB-157 and MDA-MB-231 cancer cells by MTT-test and adhesion assay which was stronger than that of the compounds encapsulated as single agents. The results evidence the potential application of zein nanoparticles containing PTX and JQ1 as a novel nanomedicine.

Synergistic anti-proliferative activity of JQ1 and GSK2801 in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) constitutes 10-20% of breast cancers and is challenging to treat due to a lack of effective targeted therapies. Previous studies in TNBC cell lines showed in vitro growth inhibition when JQ1 or GSK2801 were administered alone, and enhanced activity when co-administered. Given their respective mechanisms of actions, we hypothesized the combinatorial effect could be due to the target genes affected. Hence the target genes were characterized for their expression in the TNBC cell lines to prove the combinatorial effect of JQ1 and GSK2801.

METHODS

RNASeq data sets of TNBC cell lines (MDA-MB-231, HCC-1806 and SUM-159) were analyzed to identify the differentially expressed genes in single and combined treatments. The topmost downregulated genes were characterized for their downregulated expression in the TNBC cell lines treated with JQ1 and GSK2801 under different dose concentrations and combinations. The optimal lethal doses were determined by cytotoxicity assays. The inhibitory activity of the drugs was further characterized by molecular modelling studies.

RESULTS

Global expression profiling of TNBC cell lines using RNASeq revealed different expression patterns when JQ1 and GSK2801 were co-administered. Functional enrichment analyses identified several metabolic pathways (i.e., systemic lupus erythematosus, PI3K-Akt, TNF, JAK-STAT, IL-17, MAPK, Rap1 and signaling pathways) enriched with upregulated and downregulated genes when combined JQ1 and GSK2801 treatment was administered. RNASeq identified downregulation of PTPRC, MUC19, RNA5-8S5, KCNB1, RMRP, KISS1 and TAGLN (validated by RT-qPCR) and upregulation of GPR146, SCARA5, HIST2H4A, CDRT4, AQP3, MSH5-SAPCD1, SENP3-EIF4A1, CTAGE4 and RNASEK-C17orf49 when cells received both drugs. In addition to differential gene regulation, molecular modelling predicted binding of JQ1 and GSK2801 with PTPRC, MUC19, KCNB1, TAGLN and KISS1 proteins, adding another mechanism by which JQ1 and GSK2801 could elicit changes in metabolism and proliferation.

CONCLUSION

JQ1-GSK2801 synergistically inhibits proliferation and results in selective gene regulation. Besides suggesting that combinatorial use could be useful therapeutics for the treatment of TNBC, the findings provide a glimpse into potential mechanisms of action for this combination therapy approach.

Mcl-1 inhibition overcomes BET inhibitor resistance induced by low FBW7 expression in breast cancer

While the promise of bromodomains and extraterminal (BET) protein inhibitors (BETis) is emerging in breast cancer (BC) therapy, resistance in these cells to BETis conspicuously curbs their therapeutic potential. FBW7 is an important tumour suppressor. However, the role of FBW7 in BC is not clear. In the current study, our data indicated that the low expression of FBW7 contributes to the drug resistance of BC cells upon JQ1 treatment. shRNA‐mediated FBW7 silencing in FBW7 WT BC cells suppressed JQ1‐induced apoptosis. Mechanistically, it was revealed that this diminished FBW7 level leads to Mcl‐1 stabilization, while Mcl‐1 upregulation abrogates the killing effect of JQ1. Mcl‐1 knockdown or inhibition resensitized the BC cells to JQ1‐induced apoptosis. Moreover, FBW7 knockdown in MCF7 xenografted tumours demonstrated resistance to JQ1 treatment. The combination of JQ1 with a Mcl‐1 inhibitor (S63845) resensitized the FBW7 knockdown tumours to JQ1 treatment in vivo. Our study paves the way for a novel therapeutic potential of BETis with Mcl‐1 inhibitors for BC patients with a low FBW7 expression.

Bidirectional Regulatory Cross-Talk between Cell Context and Genomic Aberrations Shapes Breast Tumorigenesis

Breast cancers are classified into five intrinsic subtypes and 10 integrative clusters based on gene expression patterns and genomic aberrations, respectively. Although the cell-of-origin, adaptive plasticity, and genomic aberrations shape dynamic transcriptomic landscape during cancer progression, how interplay between these three core elements governs obligatory steps for a productive cancer progression is unknown. Here, we used genetic ancestry-mapped immortalized breast epithelial cell lines generated from breast biopsies of healthy women that share gene expression profiles of luminal A, normal-like, and basal-like intrinsic subtypes of breast cancers and breast cancer relevant oncogenes to develop breast cancer progression model. Using flow cytometry, mammosphere growth, signaling pathway, DNA damage response, and in vivo tumorigenicity assays, we provide evidence that establishes cell context-dependent effects of oncogenes in conferring plasticity, self-renewal/differentiation, intratumor heterogeneity, and metastatic properties. In contrast, oncogenic aberrations, independent of cell context, shaped response to DNA damage-inducing agents. Collectively, this study reveals how the same set of genomic aberration can have distinct effects on tumor characteristics based on cell-of-origin of tumor and highlights the need to utilize multiple "normal" epithelial cell types to decipher oncogenic properties of a gene of interest. In addition, by creating multiple isogenic cell lines ranging from primary cells to metastatic variants, we provide resources to elucidate cell-intrinsic properties and cell-oncogene interactions at various stages of cancer progression. IMPLICATIONS: Our findings demonstrate that how an interplay between the normal cell type that encountered genomic aberrations and type of genomic aberration influences heterogeneity, self-renewal/differentiation, and tumor properties including propensity for metastasis.

BRD4 in physiology and pathology: ''BET'' on its partners

Bromodomain-containing 4 (BRD4), a member of Bromo and Extra-Terminal (BET) family, recognizes acetylated histones and is of importance in transcription, replication, and DNA repair. It also binds non-histone proteins, DNA and RNA, contributing to development, tissue growth, and various physiological processes. Additionally, BRD4 has been implicated in driving diverse diseases, ranging from cancer, viral infection, inflammation to neurological disorders. Inhibiting its functions with BET inhibitors (BETis) suppresses the progression of several types of cancer, creating an impetus for translating these chemicals to the clinic. The diverse roles of BRD4 are largely dependent on its interaction partners in different contexts. In this review we discuss the molecular mechanisms of BRD4 with its interacting partners in physiology and pathology. Current development of BETis is also summarized. Further understanding the functions of BRD4 and its partners will facilitate resolving the liabilities of present BETis and accelerate their clinical translation.

Co-targeting BET bromodomain BRD4 and RAC1 suppresses growth, stemness and tumorigenesis by disrupting the c-MYC-G9a-FTH1axis and downregulating HDAC1 in molecular subtypes of breast cancer

BET bromodomain BRD4 and RAC1 oncogenes are considered important therapeutic targets for cancer and play key roles in tumorigenesis, survival and metastasis. However, combined inhibition of BRD4-RAC1 signaling pathways in different molecular subtypes of breast cancer including luminal-A, HER-2 positive and triple-negative breast (TNBC) largely remains unknown. Here, we demonstrated a new co-targeting strategy by combined inhibition of BRD4-RAC1 oncogenic signaling in different molecular subtypes of breast cancer in a context-dependent manner. We show that combined treatment of JQ1 (inhibitor of BRD4) and NSC23766 (inhibitor of RAC1) suppresses cell growth, clonogenic potential, cell migration and mammary stem cells expansion and induces autophagy and cellular senescence in molecular subtypes of breast cancer cells. Mechanistically, JQ1/NSC23766 combined treatment disrupts MYC/G9a axis and subsequently enhances FTH1 to exert antitumor effects. Furthermore, combined treatment targets HDAC1/Ac-H3K9 axis, thus suggesting a role of this combination in histone modification and chromatin modeling. C-MYC depletion and co-treatment with vitamin-C sensitizes different molecular subtypes of breast cancer cells to JQ1/NSC23766 combination and further reduces cell growth, cell migration and mammosphere formation. Importantly, co-targeting RAC1-BRD4 suppresses breast tumor growth in vivo using xenograft mouse model. Clinically, RAC1 and BRD4 expression positively correlates in breast cancer patient's samples and show high expression patterns across different molecular subtypes of breast cancer. Both RAC1 and BRD4 proteins predict poor survival in breast cancer patients. Taken together, our results suggest that combined inhibition of BRD4-RAC1 pathways represents a novel and potential therapeutic approach in different molecular subtypes of breast cancer and highlights the importance of co-targeting RAC1-BRD4 signaling in breast tumorigenesis via disruption of C-MYC/G9a/FTH1 axis and down regulation of HDAC1.

PROTACs: A Hope for Breast Cancer Patients?

BACKGROUND

Breast Cancer (BC) is the most widely recognized disease in women. A massive number of women are diagnosed with breast cancer and many lost their lives every year. Cancer is the subsequent driving reason for dying, giving rise to it one of the current medication's most prominent difficulties.

OBJECTIVES

The main objective of the study is to examine and explore novel therapy (PROTAC) and its effectiveness against breast cancer.

METHODS

The literature search was done across Medline, Cochrane, ScienceDirect, Wiley Online, Google Scholar, PubMed, Bentham Sciences from 2001 to 2020. The articles were collected; screened, segregated, and selected papers were included for writing the review article.

RESULTS AND CONCLUSION

A novel innovation emerged around two decades ago that has great potential to not only overcome the limitations but also can provide future direction for the treatment of many diseases which has presently not many therapeutic options available and regarded as incurable with traditional techniques; that innovation is called PROTAC (Proteolysis Targeting Chimera) and able to efficaciously ubiquitinate and debase cancer encouraging proteins by noncovalent interaction. PROTACs are constituted of two active regions isolated by a linker and equipped for eliminating explicit undesirable protein. It is empowering greater sensitivity to "drug-resistant targets" as well as a more prominent opportunity to influence non-enzymatic function. PROTACs have been demonstrated to show better target selectivity contrasted with traditional small-molecule inhibitors. So far, the most investigation into PROTACs possesses particularly concentrated on applications to cancer treatment including breast cancer, the treatment of different ailments may profit from this blossoming innovation.

Degradation of BRD4 - a promising treatment approach not only for hematologic but also for solid cancer

Bromodomain (BRD) and extra-terminal (BET) proteins are epigenetic readers that regulate gene expression and promote cancer evolution. Pharmacological inactivation of BRD4 has recently been introduced as a promising anti-neoplastic approach that targets MYC oncogene expression. However, resistance against BRD4-targeting drugs has been described. We compared the efficacy of the small-molecule-type BET BRD inhibitor JQ1 with the recently developed BET protein degraders dBET1 and dBET6 in colon, breast, melanoma, ovarian, lung and prostate cancer cell lines. As determined by qPCR, all BRD4 targeting drugs dose-dependently decreased MYC expression, with dBET6 introducing the strongest downregulation of MYC. This correlated with the anti-proliferative activity of these drugs, which was at least one order of magnitude higher for dBET6 (IC₅₀ 0.001-0.5 µM) than for dBET1 or JQ1 (IC₅₀ 0.5-5 µM). Interestingly, when combined with commonly used cytotoxic therapeutics, dBET6 was found to promote anti-neoplastic effects and to counteract chemoresistance in most cancer cell lines. Moreover, JQ1 and both BET degraders strongly downregulated baseline and interferon-gamma induced expression of the immune checkpoint molecule PD-L1 in all cancer cell lines. Together, our data suggest that dBET6 outperforms first-generation BRD4 targeting drugs like dBET1 and JQ1, and decreases chemoresistance and immune resistance of cancer.

Protein kinase C inhibitor anchored BRD4 PROTAC PEGylated nanoliposomes for the treatment of vemurafenib-resistant melanoma

Limited treatment options and development of resistance to targeted therapy within few months pose significant challenges in the treatment of BRAF-mutated malignant melanoma. Moreover, extensive angiogenesis and vasculogenic mimicry promote the rapid progression of disease. The purpose of this study was to develop a protein kinase C inhibitor anchored BRD4 PROTAC (ARV) loaded PEGylated nanoliposomes (LARPC). Palmitoyl-dl-carnitine chloride (PC) was used as a protein kinase C inhibitor to provide a cationic surface charge to LARPC. The formulation was characterized for particle size, zeta potential, drug release and various cell culture assays using HUVEC and vemurafenib resistant melanoma cells. The particle size of LARPC was found to be 105.25 ± 2.76 nm with a zeta potential of +26.6 ± 6.25 mV. Inhibition of angiogenesis was demonstrated by ARV and LARPC using human umbilical vein endothelial cells (HUVEC)-based matrigel basement membrane model. Additionally, LARPC demonstrated very low IC50 with promising inhibition of vasculogenic mimicry channel formation, cell migration as well as colony formation in vemurafenib-resistant melanoma cell lines. Hence, the outcome of this combination therapy indicated the suitability of LARPC as a potential and novel approach for eradicating vemurafenib-resistant melanoma.

Improving TRAIL-induced apoptosis in cancers by interfering with histone modifications

Epigenetic regulation refers to alterations to the chromatin template that collectively establish differential patterns of gene transcription. Post-translational modifications of the histones play a key role in epigenetic regulation of gene transcription. In this review, we provide an overview of recent studies on the role of histone modifications in carcinogenesis. Since tumour-selective ligands such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) are well-considered as promising anti-tumour therapies, we summarise strategies for improving TRAIL sensitivity by inhibiting aberrant histone modifications in cancers. In this perspective we also discuss new epigenetic drug targets for enhancing TRAIL-mediated apoptosis.

Inhibitors of bromodomain and extra-terminal proteins for treating multiple human diseases

Clinical development of bromodomain and extra‐terminal (BET) protein inhibitors differs from the traditional course of drug development. These drugs are simultaneously being evaluated for treating a wide spectrum of human diseases due to their novel mechanism of action. BET proteins are epigenetic “readers,” which play a primary role in transcription. Here, we briefly describe the BET family of proteins, of which BRD4 has been studied most extensively. We discuss BRD4 activity at latent enhancers as an example of BET protein function. We examine BRD4 redistribution and enhancer reprogramming in embryonic development, cancer, cardiovascular, autoimmune, and metabolic diseases, presenting hallmark studies that highlight BET proteins as attractive targets for therapeutic intervention. We review the currently available approaches to targeting BET proteins, methods of selectively targeting individual bromodomains, and review studies that compare the effects of selective BET inhibition to those of pan‐BET inhibition. Lastly, we examine the current clinical landscape of BET inhibitor development.

Antibody-PROTAC Conjugates Enable HER2-Dependent Targeted Protein Degradation of BRD4

Targeting protein degradation with Proteolysis-Targeting Chimeras (PROTACs) is an area of great current interest in drug discovery. Nevertheless, although the high effectiveness of PROTACs against a wide variety of targets has been established, most degraders reported to date display limited intrinsic tissue selectivity and do not discriminate between cells of different types. Here, we describe a strategy for selective protein degradation in a specific cell type. We report the design and synthesis of a trastuzumab-PROTAC conjugate (Ab-PROTAC 3) in which E3 ligase-directed degrader activity is caged with an antibody linker which can be hydrolyzed following antibody-PROTAC internalization, releasing the active PROTAC and inducing catalytic protein degradation. We show that 3 selectively targets bromodomain-containing protein 4 (BRD4) for degradation only in HER2 positive breast cancer cell lines, while sparing HER2 negative cells. Using live cell confocal microscopy, we show internalization and lysosomal trafficking of the conjugate specifically in HER2 positive cells, leading to the release of active PROTAC in quantities sufficient to induce potent BRD4 degradation. These studies demonstrate proof-of-concept for tissue-specific BRD4 degradation, overcoming limitations of PROTAC selectivity, with significant potential for application to novel targets.

Differential impacts of charcoal-stripped fetal bovine serum on c-Myc among distinct subtypes of breast cancer cell lines

Charcoal-stripped fetal bovine serum (CS-FBS) is frequently used in studies on hormone-responsive cancers to provide hormone-free cell culture conditions. CS-FBS may influence the growth of cancer cells; however, the underlying mechanisms remain unclear. In this study, we aimed to clarify the effects of CS-FBS on distinct subtypes of breast cancer cells. We found that the crucial oncoprotein c-Myc was significantly inhibited in estrogen receptor alpha (ER-α)-positive breast cancer cells when cultured in CS-FBS-supplemented medium, but it was not suppressed in ER-α-negative cells. The addition of 17β-estradiol (E2) to CS-FBS-supplemented medium rescued the CS-FBS-induced inhibition of c-Myc, while treatment with 5α-dihydrotestosterone (DHT) suppressed c-Myc expression. Our data demonstrated that CS-FBS may impede the growth of ER-α-positive breast cancer cells via c-Myc inhibition, and this was possibly due to the removal of estrogen. These results highlighted that the core drivers of c-Myc expression were subtype-specific depending on the distinct cell context and special caution should be exercised when using CS-FBS in studies of hormone-responsive cancer cells.

Nanoparticles Loaded with the BET Inhibitor JQ1 Block the Growth of Triple Negative Breast Cancer Cells In Vitro and In Vivo

Inhibition of bromo-and extra-terminal domain (BET) proteins, epigenetic regulators of genes involved in cell viability, has been efficiently tested in preclinical models of triple negative breast cancer (TNBC). However, the use of the selective BET-inhibitor JQ1 on humans is limited by its very short half-life. Herein, we developed, characterized and tested a novel formulation of nanoparticles containing JQ1 (N-JQ1) against TNBC in vitro and in vivo. N-JQ1, prepared using the nanoprecipitation method of preformedpoly-lactid-co-glycolic acid in an aqueous solution containing JQ1 and poloxamer-188 as a stabilizer, presented a high physico-chemical stability. Treatment of MDA-MB 157 and MDA-MB 231 TNBC cells with N-JQ1 determined a significant decrease in cell viability, adhesion and migration. Intra-peritoneal administration (5 days/week for two weeks) of N-JQ1 in nude mice hosting a xenograft TNBC after flank injection of MDA-MB-231 cells determined a great reduction in the growth and vascularity of the neoplasm. Moreover, the treatment resulted in a minimal infiltration of nearby tissues. Finally, the encapsulation of JQ1 in nanoparticles improved the anticancer efficacy of this epigenetic compound against TNBC in vitro and in vivo, opening the way to test it in the treatment of TNBC.

Properties of FDA-approved small molecule protein kinase inhibitors: A 2020 update

Because genetic alterations including mutations, overexpression, translocations, and dysregulation of protein kinases are involved in the pathogenesis of many illnesses, this enzyme family is currently the subject of many drug discovery programs in the pharmaceutical industry. The US FDA approved four small molecule protein kinase antagonists in 2019; these include entrectinib, erdafitinib, pexidartinib, and fedratinib. Entrectinib binds to TRKA/B/C and ROS1 and is prescribed for the treatment of solid tumors with NTRK fusion proteins and for ROS1-postive non-small cell lung cancers. Erdafitinib inhibits fibroblast growth factor receptors 1-4 and is used in the treatment of urothelial bladder cancers. Pexidartinib is a CSF1R antagonist that is prescribed for the treatment of tenosynovial giant cell tumors. Fedratinib blocks JAK2 and is used in the treatment of myelofibrosis. Overall, the US FDA has approved 52 small molecule protein kinase inhibitors, nearly all of which are orally effective with the exceptions of temsirolimus (which is given intravenously) and netarsudil (an eye drop). Of the 52 approved drugs, eleven inhibit protein-serine/threonine protein kinases, two are directed against dual specificity protein kinases, eleven target non-receptor protein-tyrosine kinases, and 28 block receptor protein-tyrosine kinases. The data indicate that 46 of these drugs are used in the treatment of neoplastic diseases (eight against non-solid tumors such as leukemias and 41 against solid tumors including breast and lung cancers; some drugs are used against both tumor types). Eight drugs are employed in the treatment of non-malignancies: fedratinib, myelofibrosis; ruxolitinib, myelofibrosis and polycythemia vera; fostamatinib, chronic immune thrombocytopenia; baricitinib, rheumatoid arthritis; sirolimus, renal graft vs. host disease; nintedanib, idiopathic pulmonary fibrosis; netarsudil, glaucoma; and tofacitinib, rheumatoid arthritis, Crohn disease, and ulcerative colitis. Moreover, sirolimus and ibrutinib are used for the treatment of both neoplastic and non-neoplastic diseases. Entrectinib and larotrectinib are tissue-agnostic anti-cancer small molecule protein kinase inhibitors. These drugs are prescribed for the treatment of any solid cancer harboring NTRK1/2/3 fusion proteins regardless of the organ, tissue, anatomical location, or histology type. Of the 52 approved drugs, seventeen are used in the treatment of more than one disease. Imatinib, for example, is approved for the treatment of eight disparate disorders. The most common drug targets of the approved pharmaceuticals include BCR-Abl, B-Raf, vascular endothelial growth factor receptors (VEGFR), epidermal growth factor receptors (EGFR), and ALK. Most of the approved small molecule protein kinase antagonists (49) bind to the protein kinase domain and six of them bind covalently. In contrast, everolimus, temsirolimus, and sirolimus are larger molecules (MW ≈ 1000) that bind to FK506 binding protein-12 (FKBP-12) to generate a complex that inhibits the mammalian target of rapamycin (mTOR) protein kinase complex. This review presents the physicochemical properties of all of the FDA-approved small molecule protein kinase inhibitors. Twenty-two of the 52 drugs have molecular weights greater than 500, exceeding a Lipinski rule of five criterion. Excluding the macrolides (everolimus, sirolimus, temsirolimus), the average molecular weight of the approved drugs is 480 with a range of 306 (ruxolitinib) to 615 (trametinib). More than half of the antagonists (29) have lipophilic efficiency values of less than five while the recommended optima range from 5 to 10. One of the troublesome problems with both targeted and cytotoxic drugs in the treatment of malignant diseases is the near universal development of resistance to every therapeutic modality.

BET inhibitor bromosporine enhances 5-FU effect in colorectal cancer cells

Treatment of colorectal cancer (CRC) remains a challenge because of the lack of effective early treatment strategies and high incidence of relapse. 5-Fluorouracil (5-FU) is a typical CRC treatment. Bromosporine is an innovative bromodomain and extraterminal domain (BET) inhibitor. We investigated if CRC could be targeted by the combination of 5-FU and bromosporine in a synergistic manner in vivo and in vitro. Our findings shown that the combination treatment inhibits cell viability, formation of colonies, increased apoptosis and cell cycle arrest at G0-G1. In addition, the expression level of BRD4 was high in HCT116 cells exposed to 5-FU that showed lower apoptosis against the parental cells. Moreover, the 5-FU-resistance was reversed significantly by BRD4 knockdown or inhibition. The drug combination showed increased activity against tumor than individual drug exposure in the xenograft model. In conclusion, this work serves as a basic clinical evaluation of 5-FU and bromosporine as an effective therapeutic approach for CRC.

A novel benzoxazinone derivative YLT-LL-11 inhibits diffuse large B-cell lymphoma growth via inducing cell cycle arrest and apoptosis

Diffuse large B-cell lymphoma (DLBCL) is a clinically aggressive B-cell non-Hodgkin’s lymphoma (NHL) with high treatment difficulty and high relapse rate. The bromodomain and extra-terminal (BET) proteins play significant roles in supporting the transcription of known DLBCL oncogene MYC, which provides a way for the development of targeted therapeutic agents to address this kind of malignant tumor. Here, we reported a novel benzoxazinone derivative YLT-LL-11 as potential BRD4 inhibitor and further investigated the biological activities against DLBCL. The results suggested that YLT-LL-11 inhibited cell growth against a panel of human hematopoietic malignancies cell lines in a dose- and time-dependent manner. In addition, flow cytometry and Western blotting assays showed that YLT-LL-11 inhibited the proliferation of a DLBCL cell line OCI-LY10 via inducing G0/G1 cell cycle arrest with regulation of the cyclin-dependent kinases (CDKs) expression. Furthermore, YLT-LL-11 facilitated OCI-LY10 cell apoptosis by up-regulation of pro-apoptotic protein BAX and down-regulation of anti-apoptotic protein Bcl-2. Taken together, these results revealed that BRD4 inhibitor YLT-LL-11 can down-regulate growth-associated transcription factors MYC in DLBCL thus resulted in cell growth inhibition and apoptosis.

The Kindlin2-p53-SerpinB2 signaling axis is required for cellular senescence in breast cancer

In cancer, cellular senescence is a complex process that leads to inhibition of proliferation of cells that may develop a neoplastic phenotype. A plethora of signaling pathways, when dysregulated, have been shown to elicit a senescence response. Two well-known tumor suppressor pathways, controlled by the p53 and retinoblastoma proteins, have been implicated in maintaining the cellular senescence phenotype. Kindlin-2, a member of an actin cytoskeleton organizing and integrin activator proteins, has been shown to play a key role in the regulation of several hallmarks of several cancers, including breast cancer (BC). The molecular mechanisms whereby Kindlin-2 regulates cellular senescence in BC tumors remains largely unknown. Here we show that Kindlin-2 regulates cellular senescence in part through its interaction with p53, whereby it regulates the expression of the p53-responsive genes; i.e., SerpinB2 and p21, during the induction of senescence. Our data show that knockout of Kindlin-2 via CRISPR/Cas9 in several BC cell lines significantly increases expression levels of both SerpinB2 and p21 resulting in the activation of hallmarks of cellular senescence. Mechanistically, interaction between Kindlin-2 and p53 at the promotor level is critical for the regulated expression of SerpinB2 and p21. These findings identify a previously unknown Kindlin-2/p53/SerpinB2 signaling axis that regulates cellular senescence and intervention in this axis may serve as a new therapeutic window for BCs treatment.

VDAC1 is regulated by BRD4 and contributes to JQ1 resistance in breast cancer

Voltage-dependent anion channels (VDACs) are situated in the outer membrane of the mitochondria and serve as gatekeepers that control metabolite and ion exchange between the cytosol and mitochondria. VDAC1 is one of the most studied members of the VDAC protein family and is overexpressed in multiple types of cancer. However, the specific biological function and regulatory mechanism of VDAC1 in breast cancer remains unclear. The present study investigated the biological role of VDAC1 in breast cancer cells using an MTS assay. The association of clinicopathological features with VDAC1 in breast cancer was analyzed by Gene Expression Profiling Interactive Analysis. The regulatory mechanism of VDAC1 was determined by cell transfection, western blot analysis, reverse transcription-quantitative (q)PCR analysis, chromatin immunoprecipitation (ChIP) and ChIP-qPCR analysis. The results of the present study demonstrated that VDAC1 promoted breast cancer proliferation and was associated with a poor prognosis in patients with breast cancer. Additionally, it was observed that the expression of VDAC1 could be decreased by the bromodomain inhibitor (JQ1), and bromodomain-containing protein 4 (BRD4) was indicated to be a regulator of VDAC1. Furthermore, results suggested that VDAC1 may be involved in the resistance of breast cancer to JQ1. Collectively, the present findings uncovered important aspects of the function of VDAC1 in the tumor progression of breast cancer, and may provide a basis for potential therapeutic strategies for the treatment of breast cancer.

Anti-tumor Drug THZ1 Suppresses TGFβ2-mediated EMT in Lens Epithelial Cells via Notch and TGFβ/Smad Signaling Pathway

Selective covalent CDK7 inhibitor THZ1 is a promising potential anti-tumor drug in many kinds of cancers. Epithelial-mesenchymal Transition (EMT) is highly related to cancer initiation, development, invasion and metastasis and other pathogenesis processes. We treated cancer cell line Hela229 and three retinoblastoma cell lines so-RB50, WERI-Rb-1, Y79 with gradient concentration of THZ1, and found that THZ1 could inhibit cell viability and EMT, suggesting that THZ1 may be a promising drug for human cervical cancer and retinoblastoma treatment. Our results verified the role of THZ1 in EMT for the first time, however, the mechanism needs further study. Here we report that THZ1 suppresses the TGFβ2 induced EMT in human SRA01/04 lens epithelial cells (LECs), rabbit primary lens epithelial cells, and whole rat lens culture semi-in vivo model. RNA-sequencing and KEGG analysis revealed that the THZ1 inhibits EMT by down-regulating phosphorylate Smad2 and Notch signaling pathway. On the other hand, we found that THZ1 could strongly inhibit LECs proliferation through G2/M phase arrest as well as attenuating of MAPK, PI3K/AKT signaling pathway. Our results uncovered the function and underlying mechanism of THZ1 in regulation of EMT, which provides a new perspective of the anti-tumor effect by THZ1 and may offer a novel treatment for PCO.

I-BET151 suppresses osteoclast formation and inflammatory cytokines secretion by targetting BRD4 in multiple myeloma

Background: Multiple myeloma (MM) is an incurable hematologic cancer, accompanied by excessive osteoclast formation and inflammatory cytokine secretion. The mechanisms by which bromodomain and extra-terminal domain (BET) protein inhibitor I-BET151 regulates osteoclast differentiation and inflammatory cytokine secretion in MM are largely unknown. Methods: The isolated peripheral blood mononuclear cells from normal or patients with MM were treated with receptor activator of NF-κB ligand (RANKL) and M-CSF to induce osteoclast differentiation. RAW 264.7 cells were treated with RANKL. I-BET151 was applied to investigate the effects of BRD4 inhibition on osteoclast formation and inflammatory cytokine secretion. Osteoclast formation was determined by tartrate-resistant acid phosphatase (TRACP) staining. The expression of osteoclast-specific genes TRACP, matrix metalloproteinase-9 (MMP-9), cathepsin K (Ctsk), and c-Src was tested using quantitative real-time PCR. And the level of inflammatory cytokines TNF-α, IL-1β, and IL-6 was assessed by ELISA. Tumor necrosis factor receptor-associated factor 6 (TRAF6), BRD4, nuclear and cytoplasm p65, IκB-α, nuclear factor of activated T cells cytoplasmic (NFATc1), and osteoprotegerin (OPG) expression were measured by Western blotting. RNAi technology was applied to knock down BET family member BRD4. Results: I-BET151 dose-dependently suppressed osteoclast formation, inhibited the levels of osteoclast-specific genes TRACP, MMP-9, Ctsk, and c-Src and inflammatory cytokines TNF-α, IL-1β, and IL-6 secretion in peripheral blood mononuclear cells and RAW 264.7. I-BET151 inhibited the protein levels of BRD4 and NFATc1, increased OPG expression, and suppressed IκB-α degradation and p65 nuclear translocation. Further, the effects of I-BET151 on osteoclast formation, osteoclast-specific genes expression, inflammatory cytokine secretion, and NF-κB inhibition were promoted by BRD4 knockdown. Conclusion: I-BET151 inhibits osteoclast formation and inflammatory cytokine secretion by targetting BRD4-mediated RANKL-NF-κB signal pathway and BRD4 inhibition might be beneficial for MM treatment.

Epigenetic treatment combinations to effectively target cisplatin-resistant germ cell tumors: past, present, and future considerations

BACKGROUND

Type II germ cell tumors represent the most common solid malignancy in men aged 15-45 years. Despite high cure rates of >90% over all stages, 10-15% of advanced patients develop treatment resistance and potentially succumb to their disease. Treatment of refractory germ cell tumors remains unsatisfactory, and new approaches are needed to further improve outcomes.

OBJECTIVES

With this narrative review, we highlight epigenetic mechanisms related to resistance to standard systemic treatment, which may act as promising targets for novel combined epigenetic treatment approaches.

MATERIALS AND METHODS

A comprehensive literature search of PubMed and MEDLINE was conducted to identify original and review articles on resistance mechanisms and/or epigenetic treatment of germ cell tumors in vitro and in vivo. Review articles were hand-searched to identify additional articles.

RESULTS

Distinct epigenetic phenomena have been linked to chemotherapy resistance in germ cell tumors, among which DNA hypermethylation, histone acetylation, and bromodomain proteins appear as promising targets for therapeutic exploitation. Inhibitors of key regulators, for example DNA methyltransferases (e.g. decitabine, guadecitabine), histone deacetylases (e.g. romidepsin), and bromodomain proteins (e.g. JQ1) decreased cell viability, triggered apoptosis, and growth arrest. Additionally, these epigenetic drugs induced differentiation and led to loss of pluripotency and re-sensitization towards cisplatin in cell lines and animal models.

DISCUSSION

Epigenetic treatments hold promise to (i) reduce the treatment burden of and (ii) overcome resistance to standard cisplatin-based chemotherapy. Combined approaches may enhance activity, while the ideal target and treatment combination of epigenetic drugs, either with another epigenetic agent or conventional cytotoxic agents need to be defined.

CONCLUSION

Epigenetic (combination) treatment for germ cell tumors should be further explored in pre-clinical and clinical research for its potential to further improve germ cell tumor treatment.

Differential Methylation and Acetylation as the Epigenetic Basis of Resveratrol's Anticancer Activity

Numerous studies support the potent anticancer activity of resveratrol and its regulation of key oncogenic signaling pathways. Additionally, the activation of sirtuin 1, a deacetylase, by resveratrol has been known for many years, making resveratrol perhaps one of the earliest nutraceuticals with associated epigenetic activity. Such epigenetic regulation by resveratrol, and the mechanism thereof, has attracted much attention in the past decade. Focusing on methylation and acetylation, the two classical epigenetic regulations, we showcase the potential of resveratrol as an effective anticancer agent by virtue of its ability to induce differential epigenetic changes. We discuss the de-repression of tumor suppressors such as BRCA-1, nuclear factor erythroid 2-related factor 2 (NRF2) and Ras Associated Domain family-1α (RASSF-1α) by methylation, PAX1 by acetylation and the phosphatase and tensin homologue (PTEN) by both methylation and acetylation, in addition to the epigenetic regulation of oncogenic NF-κB and STAT3 signaling by resveratrol. Further, we evaluate the literature supporting the potentiation of HDAC inhibitors and the inhibition of DNMTs by resveratrol in different human cancers. This discussion underlines a robust epigenetic activity of resveratrol that warrants further evaluation, particularly in clinical settings.

Structural underpinnings of oestrogen receptor mutations in endocrine therapy resistance

Oestrogen receptor-α (ERα), a key driver of breast cancer, normally requires oestrogen for activation. Mutations that constitutively activate ERα without the need for hormone binding are frequently found in endocrine-therapy-resistant breast cancer metastases and are associated with poor patient outcomes. The location of these mutations in the ER ligand-binding domain and their impact on receptor conformation suggest that they subvert distinct mechanisms that normally maintain the low basal state of wild-type ERα in the absence of hormone. Such mutations provide opportunities to probe fundamental issues underlying ligand-mediated control of ERα activity. Instructive contrasts between these ERα mutations and those that arise in the androgen receptor (AR) during anti-androgen treatment of prostate cancer highlight differences in how activation functions in ERs and AR control receptor activity, how hormonal pressures (deprivation versus antagonism) drive the selection of phenotypically different mutants, how altered protein conformations can reduce antagonist potency and how altered ligand-receptor contacts can invert the response that a receptor has to an agonist ligand versus an antagonist ligand. A deeper understanding of how ligand regulation of receptor conformation is linked to receptor function offers a conceptual framework for developing new anti-oestrogens that might be more effective in preventing and treating breast cancer.