The farnesyltransferase inhibitor R115777 (tipifarnib) in combination with tamoxifen acts synergistically to inhibit MCF-7 breast cancer cell proliferation and cell cycle progression in vitro and in vivo

The Interplay between Heat Shock Proteins and Cancer Pathogenesis: A Novel Strategy for Cancer Therapeutics

Heat shock proteins (HSPs) are developmentally conserved families of protein found in both prokaryotic and eukaryotic organisms. HSPs are engaged in a diverse range of physiological processes, including molecular chaperone activity to assist the initial protein folding or promote the unfolding and refolding of misfolded intermediates to acquire the normal or native conformation and its translocation and prevent protein aggregation as well as in immunity, apoptosis, and autophagy. These molecular chaperonins are classified into various families according to their molecular size or weight, encompassing small HSPs (e.g., HSP10 and HSP27), HSP40, HSP60, HSP70, HSP90, and the category of large HSPs that include HSP100 and ClpB proteins. The overexpression of HSPs is induced to counteract cell stress at elevated levels in a variety of solid tumors, including anticancer chemotherapy, and is closely related to a worse prognosis and therapeutic resistance to cancer cells. HSPs are also involved in anti-apoptotic properties and are associated with processes of cancer progression and development, such as metastasis, invasion, and cell proliferation. This review outlines the previously mentioned HSPs and their significant involvement in diverse mechanisms of tumor advancement and metastasis, as well as their contribution to identifying potential targets for therapeutic interventions.

Progress in cancer neuroscience

Cancer of the central nervous system (CNS) can crosstalk systemically and locally in the tumor microenvironment and has become a topic of attention for tumor initiation and advancement. Recently studied neuronal and cancer interaction fundamentally altered the knowledge about glioma and metastases, indicating how cancers invade complex neuronal networks. This review systematically discussed the interactions between neurons and cancers and elucidates new therapeutic avenues. We have overviewed the current understanding of direct or indirect communications of neuronal cells with cancer and the mechanisms associated with cancer invasion. Besides, tumor-associated neuronal dysfunction and the influence of cancer therapies on the CNS are highlighted. Furthermore, interactions between peripheral nervous system and various cancers have also been discussed separately. Intriguingly and importantly, it cannot be ignored that exosomes could mediate the "wireless communications" between nervous system and cancer. Finally, promising future strategies targeting neuronal-brain tumor interactions were reviewed. A great deal of work remains to be done to elucidate the neuroscience of cancer, and future more research should be directed toward clarifying the precise mechanisms of cancer neuroscience, which hold enormous promise to improve outcomes for a wide range of malignancies.

Cancer-associated fibroblasts and its derived exosomes: a new perspective for reshaping the tumor microenvironment

Cancer-associated fibroblasts (CAFs) are the most abundant stromal cells within the tumor microenvironment (TME). They extensively communicate with the other cells. Exosome-packed bioactive molecules derived from CAFs can reshape the TME by interacting with other cells and the extracellular matrix, which adds a new perspective for their clinical application in tumor targeted therapy. An in-depth understanding of the biological characteristics of CAF-derived exosomes (CDEs) is critical for depicting the detailed landscape of the TME and developing tailored therapeutic strategies for cancer treatment. In this review, we have summarized the functional roles of CAFs in the TME, particularly focusing on the extensive communication mediated by CDEs that contain biological molecules such as miRNAs, proteins, metabolites, and other components. In addition, we have also highlighted the prospects for diagnostic and therapeutic applications based on CDEs, which could guide the future development of exosome-targeted anti-tumor drugs.

Dissecting exosome inhibitors: therapeutic insights into small-molecule chemicals against cancer

Intensive research in the field of cancer biology has revealed unique methods of communication between cells through extracellular vesicles called exosomes. Exosomes are released from a broad spectrum of cell types and serve as functional mediators under physiological or pathological conditions. Hence, blocking the release of exosome bio carriers may prove useful for slowing the progression of certain types of cancers. Therefore, efforts are being made to develop exosome inhibitors to be used both as research tools and as therapies in clinical trials. Thus, studies on exosomes may lead to a breakthrough in cancer research, for which new clinical targets for different types of cancers are urgently needed. In this review, we briefly outline exosome inhibitors and discuss their modes of action and potential for use as therapeutic tools for cancer.

Pharmacological Inhibition of Exosome Machinery: An Emerging Prospect in Cancer Therapeutics

Abstract:

Exosomes are nanocarriers that mediate intercellular communication, crucial for normal physiological functions. However, exponentially emerging reports have correlated their dysregulated release with various pathologies, including cancer. In cancer, from stromal remodeling to metastasis, where tumor cells bypass the immune surveillance and show drug resistivity, it has been established to be mediated via tumor-derived exosomes. Owing to their role in cancer pathogenicity, exosome-based strategies offer enormous potential in treatment regimens. These strategies include the use of exosomes as a drug carrier or as an immunotherapeutic agent, which requires advanced nanotechnologies for exosome isolation and characterization. In contrast, pharmacological inhibition of exosome machinery surpasses the requisites of nanotechnology and thus emerges as an essential prospect in cancer therapeutics. In this line, researchers are currently trying to dissect the molecular pathways to reveal the involvement of key regulatory proteins that facilitate the release of tumor-derived exosomes. Subsequently, screening of various molecules in targeting these proteins, with eventual abatement of exosome-induced cancer pathogenicity, is being done. However, their clinical translation requires more extensive studies. Here we comprehensively review the molecular mechanisms regulating exosome release in cancer. Moreover, we give insight into the key findings that highlight the effect of various drugs as exosome blockers, which will add to the route of drug development in cancer management.

Exosomes: Small vesicles with big roles in cancer, vaccine development, and therapeutics

Cancer is a deadly disease that is globally and consistently one of the leading causes of mortality every year. Despite the availability of chemotherapy, radiotherapy, immunotherapy, and surgery, a cure for cancer has not been attained. Recently, exosomes have gained significant attention due to the therapeutic potential of their various components including proteins, lipids, nucleic acids, miRNAs, and lncRNAs. Exosomes constitute a set of tiny extracellular vesicles with an approximate diameter of 30-100 nm. They are released from different cells and are present in biofluids including blood, cerebrospinal fluid (CSF), and urine. They perform crucial multifaceted functions in the malignant progression of cancer via autocrine, paracrine, and endocrine communications. The ability of exosomes to carry different cargoes including drug and molecular information to recipient cells make them a novel tool for cancer therapeutics. In this review, we discuss the major components of exosomes and their role in cancer progression. We also review important literature about the potential role of exosomes as vaccines and delivery carriers in the context of cancer therapeutics.

Ras Signaling in Breast Cancer

Ras proteins mediate extracellular and cytoplasmic signaling networks via receptor tyrosine kinase. The Ras pathway induces activation of signaling molecules involved in cell proliferation and growth, cell survival and apoptosis, metabolism, and motility. Although Ras mutations in breast cancer are not frequently reported, hyperactivation of Ras signaling plays an important role in breast cancer growth and progression. Oncogenic Ras activation occurs via loss of Ras GTPase-activating proteins, overexpression of growth factor receptor, and stimulation by various cytokines. Effective control of oncogenic Ras is one of the therapeutic strategies in breast cancer. The mechanisms of intracellular localization, activation, and signaling pathway of Ras in cancer have been used to develop therapeutic candidates. Recent studies have reported an effective therapy for breast cancer by inhibition of enzymes involved in the posttranslational modification of Ras, such as farnesyltransferase and geranylgeranyltransferase 1, and anti-cancer therapies targeting the epidermal growth factor receptor (EGFR). Emerging targets involved in EGF-mediated Ras activity in breast cancer have shed new insight into Ras activation in breast cancer progression. These alternative mechanisms for Ras signaling pathway may suggest novel therapeutic approaches for targeting Ras in breast cancer. In spite of the difficulties in targeting Ras protein, important discoveries highlight the direct inhibition of Ras activity. Further studies may elucidate the effects of targeting Ras protein and the clinical relevance thereof.

Advances in the discovery of exosome inhibitors in cancer

Exosomes are small membrane vesicles released by most eukaryotic cells. They are considered to play an essential role in cell-to-cell communication, and It is also found that they serve as functional mediators in many severe diseases, including progression of various types of cancers. Inhibition of exosome release may slow the progression of some cancers; thus, exosome has been an attractive target for cancer treatment. Over the years, considerable efforts have been made to discover novel, highly potent and excellently selective exosome inhibitors. Most of these inhibitors are derived from synthetic compounds, some of which are currently existed drugs and found to have the potential to inhibit exosome release. In this review, we briefly discussed the development of exosome inhibitors that are currently discovered and provided guidance for the future development of inhibitors.

Azaphenantherene derivatives as inhibitor of SARS CoV-2 Mpro: Synthesis, physicochemical, quantum chemical and molecular docking analysis

The crystal structure of 2-(1H-indol-3-yl)-4-phenyl-5,6-dihydrobenzo[h]quinoline-3-carbonitrile (Ia) and 2-(5-bromo-1H-indol-3-yl)-4-(4-methoxyphenyl)-5,6-dihydrobenzo[h]quinoline-3-carbonitrile (Ib) were elucidated using single crystal X-ray diffraction. The cyclohexadiene ring adopts screw boat conformation in compound (Ia) and distorted screw boat in compound (Ib). The pyridine ring is effectively planar. The qualitative and quantitative analyses of hydrogen bonding interactions in the compounds were done using Hirshfeld surface analysis, QTAIM and NCI. DFT/B3LYP level of theory was used to optimize both the compounds. These compounds drug-like behaviors were studied using HOMO-LUMO analysis. The molecular docking analysis against M^pro was carried out for the synthesized compounds and some suggested drugs for COVID-19. The docking results were then analyzed.

Cholesterol and beyond - The role of the mevalonate pathway in cancer biology

Cancer is a multifaceted global disease. Transformation of a normal to a malignant cell takes several steps, including somatic mutations, epigenetic alterations, metabolic reprogramming and loss of cell growth control. Recently, the mevalonate pathway has emerged as a crucial regulator of tumor biology and a potential therapeutic target. This pathway controls cholesterol production and posttranslational modifications of Rho-GTPases, both of which are linked to several key steps of tumor progression. Inhibitors of the mevalonate pathway induce pleiotropic antitumor-effects in several human malignancies, identifying the pathway as an attractive candidate for novel therapies. In this review, we will provide an overview about the role and regulation of the mevalonate pathway in certain aspects of cancer initiation and progression and its potential for therapeutic intervention in oncology.

Therapeutic potential of RAS prenylation pharmacological inhibitors in the treatment of breast cancer, recent progress, and prospective

Breast cancer is one of the most prevalent malignancies among women around the world. RAS proteins require posttranslational modifications, including protein prenylation for proper membrane localization and signaling. Regulation of RAS signaling via specific and novel pharmacological inhibitors is a potentially novel therapeutic approach in breast cancer therapy. This review summarizes the recent knowledge about the clinical value of RAS prenylation pharmacological inhibitors in breast cancer treatment.

High-throughput screening identified selective inhibitors of exosome biogenesis and secretion: A drug repurposing strategy for advanced cancer

Targeting exosome biogenesis and release may have potential clinical implications for cancer therapy. Herein, we have optimized a quantitative high throughput screen (qHTS) assay to identify compounds that modulate exosome biogenesis and/or release by aggressive prostate cancer (PCa) CD63-GFP-expressing C4-2B cells. A total of 4,580 compounds were screened from the LOPAC library (a collection of 1,280 pharmacologically active compounds) and the NPC library (NCGC collection of 3,300 compounds approved for clinical use). Twenty-two compounds were found to be either potent activators or inhibitors of intracellular GFP signal in the CD63-GFP-expressing C4-2B cells. The activity of lead compounds in modulating the secretion of exosomes was validated by a tunable resistive pulse sensing (TRPS) system (qNano-IZON) and flow cytometry. The mechanism of action of the lead compounds in modulating exosome biogenesis and/or secretion were delineated by immunoblot analysis of protein markers of the endosomal sorting complex required for transport (ESCRT)-dependent and ESCRT-independent pathways. The lead compounds tipifarnib, neticonazole, climbazole, ketoconazole, and triademenol were validated as potent inhibitors and sitafloxacin, forskolin, SB218795, fenoterol, nitrefazole and pentetrazol as activators of exosome biogenesis and/or secretion in PC cells. Our findings implicate the potential utility of drug-repurposing as novel adjunct therapeutic strategies in advanced cancer.

A phase II study of tipifarnib and gemcitabine in metastatic breast cancer

Background Tipifarnib is an orally active, competitive inhibitor of farnesyltransferase which has shown encouraging signs of activity either alone or when combined with other agents. Clinical studies of tipifarnib in combination with anti-estrogen therapy have yielded disappointing results. In contrast, tipifarnib appears to be synergistic in combination with anthracycline based chemotherapy. Here we report the results of the first prospective phase II trial evaluating the efficacy of the novel combination of tipifarnib and gemcitabine in the treatment of metastatic breast cancer. Patients and Methods 30 postmenopausal women with metastatic breast cancer were treated on a 21-day cycle with tipifarnib 300 mg PO twice daily from days 1 through 14. Gemcitabine was administered intravenously at a dose of 1000 mg/m² on days 1 and 8. Patients were treated until disease progression or unacceptable toxicity. Results There was one complete response and four partial responses yielding an objective response rate of 16.7%. Median progression-free survival and overall survival was 2.5 months (95% confidence interval: 1.6-5.7 months) and 13.1 months (95% confidence interval: 9.1-20.6 months), respectively. 40% of patients experienced grade 4 neutropenia in this study. Conclusion The combination of tipifarnib and gemcitabine is not well tolerated with high rates of myelosuppression and is not more effective than gemcitabine monotherapy in the treatment of metastatic breast cancer.

Treatment strategies for advanced hormone receptor-positive and human epidermal growth factor 2-negative breast cancer: the role of treatment order

Although survival rates among patients with breast cancer have improved in recent years, those diagnosed with advanced disease with distant metastasis face a 5-year survival rate of less than 25%, making the management of these patients an area still in significant need of continued research. Selecting the optimal treatment order from among the variety of currently available therapy options presents a relevant challenge for medical oncologists. With the understanding that the majority of patients with breast cancer and those who succumb to this disease have HR-positive disease, this review will focus on treatment options and treatment order in patients with HR-positive advanced breast cancer. While endocrine therapy is considered the preferred treatment for first-line therapy in HR-positive/HER2-negative breast cancer, selection of the specific agent depends on the menopausal status of the patient. Palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor, is also recommended as first-line treatment in patients with ER-positive/HER2-negative disease. In patients with endocrine therapy-resistant disease, specific strategies include sequencing of other antiestrogen receptor agents, or agents that target other molecular pathways. Future treatment strategies for patients with primary or secondary resistance to endocrine therapy for advanced disease are discussed. These strategies include first-line therapy with high-dose fulvestrant or everolimus (in combination with exemestane or letrozole or with other endocrine therapies), use of the PI3K inhibitors (e.g., buparlisib, alpelisib, pictilisib, taselisib), entinostat, CDK 4/6 inhibitors (e.g., palbociclib, ribociclib, abemaciclib), and novel selective estrogen receptor degradation agents that may enhance the targeting of acquired mutations in the ESR1 gene.

Effectiveness and molecular interactions of the clinically active mTORC1 inhibitor everolimus in combination with tamoxifen or letrozole in vitro and in vivo

INTRODUCTION

Strategies to improve the efficacy of endocrine agents in breast cancer (BC) therapy and to delay the onset of resistance include concomitant targeting of the estrogen receptor alpha (ER) and the mammalian target of rapamycin complex 1 (mTORC1), which regulate cell-cycle progression and are supported by recent clinical results.

METHODS

BC cell lines expressing aromatase (AROM) and modeling endocrine-sensitive (MCF7-AROM1) and human epidermal growth factor receptor 2 (HER2)-dependent de novo resistant disease (BT474-AROM3) and long-term estrogen-deprived (LTED) MCF7 cells that had acquired resistance associated with HER2 overexpression were treated in vitro and as subcutaneous xenografts with everolimus (RAD001-mTORC1 inhibitor), in combination with tamoxifen or letrozole. End points included proliferation, cell-cycle arrest, cell signaling, and effects on ER-mediated transactivation.

RESULTS

Everolimus caused a concentration-dependent decrease in proliferation in all cell lines, which was associated with reductions in S6 phosphorylation. Everolimus plus letrozole or tamoxifen enhanced the antiproliferative effect and G1-accumulation compared with monotherapy, as well as increased phosphorylation (Ser10) and nuclear accumulation of p27 and pronounced dephosphorylation of Rb. Sensitivity was greatest to everolimus in the LTED cells but was reduced by added estrogen. Increased pAKT occurred in all circumstances with everolimus and, in the BT474 and LTED cells, was associated with increased pHER3. Decreased ER transactivation suggested that the effectiveness of everolimus might be partly related to interrupting cross-talk between growth-factor signaling and ER. In MCF7-AROM1 xenografts, letrozole plus everolimus showed a trend toward enhanced tumor regression, versus the single agents. In BT474-AROM3 xenografts, everolimus alone was equally effective at reducing tumor volume as were the combination therapies.

CONCLUSIONS

The results provide mechanistic support for recent positive clinical data on the combination of everolimus and endocrine therapy, as well as data on potential routes of escape via enhanced HER2/3 signaling. This merits investigation for further improvements in treatment efficacy.

Curcumin enhanced antiproliferative effect of mitomycin C in human breast cancer MCF-7 cells in vitro and in vivo

AIM

To investigate the efficacy of mitomycin C (MMC) in combination with curcumin in suppressing human breast cancer in vitro and in vivo.

METHODS

Human breast cancer MCF-7 cells were used. Cell viability was measured using MTT assay. The cell cycle phase was detected with flow cytometric analysis. Cell cycle-associated proteins were examined using Western blot analysis. MCF-7 breast cancer xenografts were established to monitor tumor growth and cell cycle-associated protein expression.

RESULTS

Curcumin inhibited MCF-7 breast cancer cell viability in a concentration-dependent manner (IC(50) value=40 μmol/L). Similarly, MMC inhibited the cell viability with an IC(50) value of 5 μmol/L. Combined treatment of MMC and curcumin showed a synergistic antiproliferative effect. In the presence of curcumin (40 μmol/L), the IC(50) value of MMC was reduced to 5 μmol/L. In MCF-7 xenografts, combined administration of curcumin (100 mg/kg) and MMC (1-2 mg/kg) for 4 weeks produced significantly greater inhibition on tumor growth than either treatment alone. The combined treatment resulted in significantly greater G(1) arrest than MMC or curcumin alone. Moreover, the cell cycle arrest was associated with inhibition of cyclin D1, cyclin E, cyclin A, cyclin-dependent kinase 2 (CDK2) and CDK4, along with the induction of the cell cycle inhibitor p21 and p27 both in MCF-7 cells and in MCF-7 xenografts. These proteins were regulated through p38 MAPK pathway.

CONCLUSION

The results suggest that the combination of MMC and curcumin inhibits MCF-7 cell proliferation and cell cycle progression in vitro and in vivo via the p38 MAPK pathway.

Targeting the phosphatidylinositol 3-kinase signaling pathway in breast cancer

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) network plays a key regulatory function in cell survival, proliferation, migration, metabolism, angiogenesis, and apoptosis. Genetic aberrations found at different levels, either with activation of oncogenes or inactivation of tumor suppressors, make this pathway one of the most commonly disrupted in human breast cancer. The PI3K-dependent phosphorylation and activation of the serine/threonine kinase AKT is a key activator of cell survival mechanisms. The activation of the oncogene PIK3CA and the loss of regulators of AKT including the tumor suppressor gene PTEN are mutations commonly found in breast tumors. AKT relieves the negative regulation of mTOR to activate protein synthesis and cell proliferation through S6K and 4EBP1. The common activation of the PI3K pathway in breast cancer has led to the development of compounds targeting the effector mechanisms of the pathway including selective and pan-PI3K/pan-AKT inhibitors, rapamycin analogs for mTOR inhibition, and TOR-catalytic subunit inhibitors. The influences of other oncogenic pathways such as Ras-Raf-Mek on the PI3K pathway and the known feedback mechanisms of activation have prompted the use of compounds with broader effect at multiple levels and rational combination strategies to obtain a more potent antitumor activity and possibly a meaningful clinical effect. Here, we review the biology of the network, its role in the development and progression of breast cancer, and the evaluation of targeted therapies in clinical trials.

Biological evidence for dual antiangiogenic-antiaromatase activity of the VEGFR inhibitor PTK787/ZK222584 in vivo

PURPOSE

Targeting vascular endothelial growth factor (VEGF) and estrogen receptor signaling pathways concomitantly may enhance benefit in estrogen receptor-positive breast cancer. We had shown previously that the VEGF receptor tyrosine kinase inhibitor PTK787/ZK222584 (PTK/ZK) is a competitive aromatase inhibitor in vitro. Here we investigated (a) whether PTK/ZK shows both antiangiogenic and antiaromatase inhibitory properties in vivo, and (b) whether the combination of PTK/ZK and letrozole is superior to letrozole alone.

EXPERIMENTAL DESIGN

Estrogen-dependent human breast cancer cells engineered to express aromatase (MCF7 AROM 1 and BT474 AROM) were used. Mice were treated with vehicle, PTK/ZK (25, 50, or 100 mg/kg), letrozole, or PTK/ZK in combination with letrozole.

RESULTS

In MCF7 AROM 1 tumors, all treatments induced growth suppression and were associated with a reduction in cell turnover index, a composite measurement of both proliferation and apoptosis. PTK/ZK significantly reduced vessel density. Whereas letrozole caused tumor regression, PTK/ZK stabilized tumor volumes. The growth suppressive and antiangiogenic effects of PTK/ZK were confirmed in BT474 AROM xenografts. The addition of PTK/ZK did not enhance the growth-suppressive effects of letrozole. However, PTK/ZK decreased progesterone receptor (PgR) and TFF1 expression and uterine weight, indicating that PTK/ZK decreases 17beta-estradiol (E2) signaling in vivo.

CONCLUSION

The VEGF receptor inhibitor PTK/ZK showed effects on E2-dependent gene expression consistent with aromatase inhibition as well as antiangiogenesis in xenograft models of breast cancer. The combination with letrozole was not superior to letrozole alone. Overall, these results provide further support for a potential therapeutic approach of dual inhibition of VEGF and E2 signaling using a single agent.

A yeast-based genomic strategy highlights the cell protein networks altered by FTase inhibitor peptidomimetics

Background

Farnesyltransferase inhibitors (FTIs) are anticancer agents developed to inhibit Ras oncoprotein activities. FTIs of different chemical structure act via a conserved mechanism in eukaryotic cells. They have low toxicity and are active on a wide range of tumors in cellular and animal models, independently of the Ras activation state. Their ultimate mechanism of action, however, remains undetermined. FTase has hundred of substrates in human cells, many of which play a pivotal role in either tumorigenesis or in pro-survival pathways. This lack of knowledge probably accounts for the failure of FTIs at clinical stage III for most of the malignancies treated, with the notable exception of haematological malignancies. Understanding which cellular pathways are the ultimate targets of FTIs in different tumor types and the basis of FTI resistance is required to improve the efficacy of FTIs in cancer treatment.

Results

Here we used a yeast-based cellular assay to define the transcriptional changes consequent to FTI peptidomimetic administration in conditions that do not substantially change Ras membrane/cytosol distribution. Yeast and cancer cell lines were used to validate the results of the network analysis. The transcriptome of yeast cells treated with FTase inhibitor I was compared with that of untreated cells and with an isogenic strain genetically inhibited for FTase activity (Δram1). Cells treated with GGTI-298 were analyzed in a parallel study to validate the specificity of the FTI response. Network analysis, based on gene ontology criteria, identified a cell cycle gene cluster up-regulated by FTI treatment that has the Aurora A kinase IPL1 and the checkpoint protein MAD2 as hubs. Moreover, TORC1-S6K-downstream effectors were found to be down-regulated in yeast and mammalian FTI-treated cells. Notably only FTIs, but not genetic inhibition of FTase, elicited up-regulation of ABC/transporters.

Conclusions

This work provides a view of how FTIs globally affect cell activity. It suggests that the chromosome segregation machinery and Aurora A association with the kinetochore as well as TORC1-S6K downstream effectors are among the ultimate targets affected by the transcriptional deregulation caused by FTI peptidomimetics. Moreover, it stresses the importance of monitoring the MDR response in patients treated with FTIs.

EGFR/HER2 inhibitor AEE788 increases ER-mediated transcription in HER2/ER-positive breast cancer cells but functions synergistically with endocrine therapy

Background:

Cross-talk between receptor tyrosine kinases and the oestrogen receptor (ER) is implicated in resistance to endocrine therapy. We investigated whether AEE788 (a combined inhibitor of EGFR, HER2 and VEGFR) plus tamoxifen or letrozole enhanced the individual anti-tumour effects of these agents.

Methods:

Breast cancer cell lines modelling endocrine-resistant and -sensitive disease were engineered to express aromatase (A) and examined using proliferation, western blotting and ER-α transcription assays.

Results:

AEE788 enhanced the anti-proliferative effect of tamoxifen and letrozole in ER⁺ cell lines (MCF-7 2A, ZR75.1 A3 and BT474 A3). This associated with an elevated G1 arrest and nuclear accumulation of p27. It is noteworthy that AEE788 alone or in combination with endocrine therapy increased the expression of progesterone receptor (PGR) and TFF1 in BT474 A3 cells. This may indicate a mechanism of resistance to AEE788 in ER⁺/HER2⁺ breast cancers. In a ZR75.1 A3 xenograft, AEE788 alone or in combination with tamoxifen provided no further benefit compared with letrozole. However, letrozole plus AEE788 produced a significantly greater inhibition of tumour growth compared with letrozole alone.

Conclusion:

These data suggest that AEE788 plus letrozole in breast cancer overexpressing HER2 may provide superior anti-tumour activity, compared with single agents.

New strategies in estrogen receptor-positive breast cancer

Endocrine therapy has led to a significant improvement in outcomes for women with estrogen receptor-positive (ER+) breast cancer. Current questions in the adjuvant setting include the optimal duration of endocrine therapy, and the accurate molecular prediction of endocrine responsiveness using gene array-based assays compared with ER expression itself. In advanced disease, novel selective estrogen receptor antagonists (SERM) have failed to make an impact, although the pure ER antagonist fulvestrant may have a role, albeit optimal dose and sequence remain unclear. Overcoming de novo or acquired endocrine resistance remains critical to enhancing further the benefit of existing endocrine therapies. Recent progress has been made in understanding the molecular biology associated with acquired endocrine resistance, including adaptive "cross-talk" between ER and peptide growth factor receptor pathways such as epidermal growth factor receptor (EGFR)/human epidermal growth factor receptor 2 (HER2). Future strategies that are being evaluated include combining endocrine therapy with inhibitors of growth factor receptors or downstream signaling pathways, to treat or prevent critical resistance pathways that become operative in ER+ tumors. Preclinical experiments have provided great promise for this approach, although clinical data remain mixed. Enriching trial recruitment by molecular profiling of different ER+ subtypes will become increasingly important to maximize additional benefit that new agents may bring to current endocrine therapies for breast cancer.

Synergistic combinations of signaling pathway inhibitors: mechanisms for improved cancer therapy

Cancer cells contain multiple signal transduction pathways whose activities are frequently elevated due to their transformation, and that are often activated following exposure to established cytotoxic therapies including ionizing radiation and chemical DNA damaging agents. Many pathways activated in response to transformation or toxic stresses promote cell growth and invasion and counteract the processes of cell death. As a result of these findings many drugs, predominantly protein and lipid kinase inhibitors, of varying specificities, have been developed to block signaling by cell survival pathways in the hope of killing tumor cells and sensitizing them to toxic therapies. Unfortunately, due to the plasticity of signaling processes within a tumor cell, inhibition of any one growth factor receptor or signaling pathway frequently has only modest long-term effects on cancer cell viability, tumor growth, and patient survival. As a result of this realization, a greater emphasis has begun to be placed on rational combinations of drugs that simultaneously inhibit multiple inter-linked signal transduction/survival pathways. This, it is hoped, will limit the ability of tumor cells to adapt and survive because the activity within multiple parallel survival signaling pathways has been reduced. This review will discuss some of the approaches that have been taken to combine signal transduction modulatory agents to achieve enhanced tumor cell killing.

Phase II trial of the farnesyltransferase inhibitor tipifarnib plus fulvestrant in hormone receptor-positive metastatic breast cancer: New York Cancer Consortium Trial P6205

BACKGROUND

Fulvestrant produces a clinical benefit rate (CBR) of approximately 45% in tamoxifen-resistant, hormone receptor (HR)-positive metastatic breast cancer (MBC) and 32% in aromatase inhibitor (AI)-resistant disease. The farnesyltransferase inhibitor tipifarnib inhibits Ras signaling and has preclinical and clinical activity in endocrine therapy-resistant disease. The objective of this study was to determine the efficacy and safety of tipifarnib-fulvestrant combination in HR-positive MBC.

PATIENTS AND METHODS

Postmenopausal women with no prior chemotherapy for metastatic disease received i.m. fulvestrant 250 mg on day 1 plus oral tipifarnib 300 mg twice daily on days 1-21 every 28 days. The primary end point was CBR.

RESULTS

The CBR was 51.6% [95% confidence interval (CI) 34.0% to 69.2%] in 31 eligible patients and 47.6% (95% CI 26.3% to 69.0%) in 21 patients with AI-resistant disease. A futility analysis indicated that it was unlikely to achieve the prespecified 70% CBR. Tipifarnib dose modification was required in 8 of 33 treated patients (24%).

CONCLUSIONS

The target CBR of 70% for the tipifarnib-fulvestrant combination in HR-positive MBC was set too high and was not achieved. The 48% CBR in AI-resistant disease compares favorably with the 32% CBR observed with fulvestrant alone in prior studies and merit further clinical and translational evaluation.

Crosstalk between the estrogen receptor and the HER tyrosine kinase receptor family: molecular mechanism and clinical implications for endocrine therapy resistance

Breast cancer evolution and tumor progression are governed by the complex interactions between steroid receptor [estrogen receptor (ER) and progesterone receptor] and growth factor receptor signaling. In recent years, the field of cancer therapy has witnessed the emergence of multiple strategies targeting these specific cancer pathways and key molecules (ER and growth factor receptors) to arrest tumor growth and achieve tumor eradication; treatment success, however, has varied and both de novo (up front) and acquired resistance have proven a challenge. Recent studies of ER biology have revealed new insights into ER action in breast cancer and have highlighted the role of an intimate crosstalk between the ER and HER family signaling pathways as a fundamental contributor to the development of resistance to endocrine therapies against the ER pathway. The aim of this review article is to summarize the current knowledge on mechanisms of resistance of breast cancer cells to endocrine therapies due to the crosstalk between the ER and the HER growth factor receptor signaling pathways and to explore new available therapeutic strategies that could prolong duration of response and circumvent endocrine resistant tumor growth.

Clinical trials update: endocrine and biological therapy combinations in the treatment of breast cancer

A greater understanding of the biological mechanisms responsible for de novo and acquired endocrine resistance has led to the rational design of clinical trials exploring the benefit of combining hormonal therapies with novel biological agents in an effort to enhance the efficacy of ER+ breast cancer treatment. These studies are increasingly including parallel biological analyses to elucidate the molecular characteristics of those tumors that are most likely to respond to specific targeted/endocrine combinations in an effort to develop a tailored approach to the management of individual patients. Unfortunately despite encouraging preclinical data, some of these combinations have yielded disappointing results in the clinical setting. This article will review the results of clinical trials of endocrine/biological combinations conducted in early and advanced breast cancer as well as provide an update on ongoing studies.

A phase II, randomized, blinded study of the farnesyltransferase inhibitor tipifarnib combined with letrozole in the treatment of advanced breast cancer after antiestrogen therapy

BACKGROUND

This study assessed the clinical efficacy of the farnesyltransferase inhibitor, tipifarnib, combined with letrozole in patients with advanced breast cancer and disease progression following antiestrogen therapy.

PATIENTS AND METHODS

Postmenopausal women with estrogen-receptor-positive advanced breast cancer that had progressed after tamoxifen were given 2.5 mg letrozole once daily and were randomly assigned (2:1) to tipifarnib 300 mg (TL) or placebo (L) twice daily for 21 consecutive days in 28-day cycles. The primary endpoint was objective response rate.

RESULTS

Of 120 patients treated with TL (n = 80) or L (n = 40), 113 were evaluable for response. Objective response rate was 30% (95% CI; 20-41%) for TL and 38% (95% CI; 23-55%) for L. There was no significant difference in response duration, time to disease progression or survival. Clinical benefit rates were 49% (TL) and 62% (L). Tipifarnib was generally well tolerated; a higher incidence of drug-related asymptomatic grade 3/4 neutropenia was observed for TL (18%) than for L (0%). Tipifarnib population pharmacokinetics were similar to previous studies, with no significant difference in trough letrozole concentrations between the TL and L groups.

CONCLUSIONS

Adding tipifarnib to letrozole did not improve objective response rate in this population of patients with advanced breast cancer.