Novel therapeutic strategies combining antihormonal and biological targeted therapies in breast cancer: focus on clinical trials and perspectives

S P, Wei WC, Lin HT, Yin SY, Yang NS. Rapamycin Promotes Mouse 4T1 Tumor Metastasis that Can Be Reversed by a Dendritic Cell-Based Vaccine

Suppression of tumor metastasis is a key strategy for successful cancer interventions. Previous studies indicated that rapamycin (sirolimus) may promote tumor regression activity or enhance immune response against tumor targets. However, rapamycin also exhibits immunosuppressant effects and is hence used clinically as an organ transplantation drug. We hypothesized that the immunosuppressive activities of rapamycin might also negatively mediate host immunity, resulting in promotion of tumor metastasis. In this study, the effects of rapamycin and phytochemical shikonin were investigated in vitro and in vivo in a 4T1 mouse mammary tumor model through quantitative assessment of immunogenic cell death (ICD), autophagy, tumor growth and metastasis. Tumor-bearing mice were immunized with test vaccines to monitor their effect on tumor metastasis. We found that intraperitoneal (ip) administration of rapamycin after a tumor-resection surgery drastically increased the metastatic activity of 4T1 tumors. Possible correlation of this finding to human cancers was suggested by epidemiological analysis of data from Taiwan’s National Health Insurance Research Database (NHIRD). Since our previous studies showed that modified tumor cell lysate (TCL)-pulsed, dendritic cell (DC)-based cancer vaccines can effectively suppress metastasis in mouse tumor models, we assessed whether such vaccines may help offset this rapamycin-promoted metastasis. We observed that shikonin efficiently induced ICD of 4T1 cells in culture, and DC vaccines pulsed with shikonin-treated TCL (SK-TCL-DC) significantly suppressed rapamycin-enhanced metastasis and Treg cell expansion in test mice. In conclusion, rapamycin treatment in mice (and perhaps in humans) promotes metastasis and the effect may be offset by treatment with a DC-based cancer vaccine.

Combination of letrozole, metronomic cyclophosphamide and sorafenib is well-tolerated and shows activity in patients with primary breast cancer

PURPOSE

To assess whether the combination of letrozole, metronomic cyclophosphamide and sorafenib (LCS) is well tolerated and shows activity in primary breast cancer (BC).

METHODS

Thirteen oestrogen receptor-positive, postmenopausal, T2-4, N0-1 BC patients received the LCS combination for 6 months. In these patients we examined the pharmacokinetics of sorafenib and cyclophosphamide, toxicity of the regimen, the clinical response to therapy and changes in the levels of biologically relevant biomarkers.

RESULTS

Adequate plasma concentrations of sorafenib were achieved in patients when it was dosed in combination with L+C. The mean plasma concentrations of C were consistently lower following administration of LCS, compared with administration of L+C only. The most common drug-related grade 3/4 adverse events were skin rash (69.3%), hand-foot skin reaction (69.3%) and diarrhoea (46.1%). According to RECIST Criteria, a clinical complete response was observed in 6 of 13 patients. A significant reduction in tumour size, evaluated with MRI, was also observed between baseline and 14 days of treatment in all 13 patients (P=0.005). A significant reduction in SUV uptake, measured by (18)FDG-PET/CT, was observed in all patients between baseline and 30 days of treatment (P=0.015) and between baseline and definitive surgery (P=0.0002). Using modified CT Criteria, a response was demonstrated in 8 out of 10 evaluable patients at 30 days and in 11 out of 13 evaluable patients at the definitive surgery. A significant reduction in Ki67 expression was observed in all patients at day 14 compared with baseline (P<0.00001) and in 9 out of 13 patients at the definitive surgery compared with baseline (P<0.03). There was also a significant suppression of CD31 and VEGF-A expression in response to treatment (P=0.01 and P=0.007, respectively).

CONCLUSIONS

The LCS combination is feasible and tolerable. The tumour response and target biomarker modulation indicate that the combination is clinically and biologically active.

[Targeted based therapies in metastatic breast cancer: future evolution]

Research on molecular alteration process mechanisms leading to cancerogenesis permitted the elaboration of many targeted therapies. Some therapeutic classes appeared recently and are currently being tested, including HER-2 dimerization inhibitors. However, most of these therapies are mostly ineffective with monotherapy. Clinical trials are ongoing, testing their efficiency in association with other molecules of the therapeutic arsenal which is available in oncology. Nevertheless, breast cancer remains a pathology life-threatening, most of the time. Within this review will be introduced the most efficient of these targeted therapies, including their eventual association with other cytotoxic molecules.

Rapamycin and mTOR: a serendipitous discovery and implications for breast cancer

Rapamycin was discovered more than thirty years ago from a soil sample from the island of Rapa Nui. It was isolated from Streptomyces hygroscopicus and initial characterization focused on its antifungal activities. Subsequent characterization showed that it has immunosuppressive properties and has been used successfully to reduce organ rejection with kidney transplantation. Rapamycin has proven to be a versatile compound with several seemingly unrelated properties, including antifungal, immunosuppressive, and anticancer. The National Cancer Institute (NCI) Developmental Therapeutics Program demonstrated that rapamycin inhibited cell growth in tumor cell lines. These observations stimulated research to explore the underlying mechanism of anti-tumor activities. Cell growth inhibition involves binding to the mammalian Target of Rapamycin (mTOR). The mTOR signaling pathway is critical to cell growth, proliferation, and survival and rapamycin inhibits these hallmark processes of cancer. Binding of growth factors activates mTOR signaling, which in turn leads to downstream phosphorylation of protein kinases, e.g., p70S6 kinase and lipid kinases in the phosphorylation of phosphoinositides. Understanding of mTOR signaling provided the biological basis for targeted chemotherapeutics development, including several rapamycin analogues for treating breast and other cancers.

Presurgical (neoadjuvant) endocrine therapy is a useful model to predict response and outcome to endocrine treatment in breast cancer patients

Endocrine therapy of breast cancer has been improved continuously during the last decades. Currently, aromatase inhibitors are dominating treatment algorithms for postmenopausal women with hormone-receptor positive breast cancer while tamoxifen still is the most widely used drug for premenopausal women. Several research tools and study designs have been used to challenge established drugs and develop the field of antihormonal therapy. One pivotal study option has been the observation of clinical responses during presurgical/neoadjuvant endocrine therapy (PSET/NET). This strategy has several major advantages. First, the breast tumor, still present in the patient's breast during therapy, can be followed by clinical observations and radiological measurements and any treatment effect will be immediately registered. Second, tumor biopsies may be obtained before initiation and following therapy allowing intra-patient comparisons. These tumor-biopsies may be used for the evaluation of intra-tumor changes associated with drug treatment. As examples, presurgical breast cancer trials have been used to evaluate intra-tumor estrogen levels during therapy with aromatase inhibitors and also to study mechanisms involved in the adaptation processes to estrogen suppression. Biomarker studies have provided information that may be used for patient selection in the future. Finally, recently published results from presurgical trials testing combinations of classical endocrine drugs and novel targeted therapies have produced promising results.

Translational advances regarding hereditary breast cancer syndromes

Approximately 5-10% of breast cancers may be inheritable, up to 90% of which are due to mutations in BRCA1 and BRCA2. A substantial minority are caused by non-BRCA mutations, such as TP53, PTEN, STK11, CHEK2, ATM, BRIP1, and PALB2 mutations. This review highlights translational research advances with regard to the development of probabilistic models for hereditary breast cancer syndromes, the identification of specific genetic mutations responsible for these syndromes, as well as their testing and interpretations.

Emerging roles for mammalian target of rapamycin inhibitors in the treatment of solid tumors and hematological malignancies

PURPOSE OF REVIEW

The mammalian target of rapamycin (mTOR) is a key regulator of cell growth and survival in mammalian cells. mTOR pathways are frequently dysregulated in various malignancies, providing targets for new anticancer drugs and therapeutic strategies. Here, we summarize the clinical experience of trials using the first generation of mTOR inhibitors, the rapalogs, and highlight the development of the next generation of catalytic inhibitors of the pathway.

RECENT FINDINGS

mTOR inhibitors have shown major clinical activity in the treatment of renal cell carcinoma and two rapalogs have been approved for treatment of this malignancy. Recently, clinically significant trials with these agents were conducted in mantle cell lymphoma, pancreatic neuroendocrine tumors and astrocytomas. There are also promising results emerging in sarcomas, breast cancer and lung carcinoma. Multiple agents targeting mTOR, belonging to the new class of catalytic inhibitors with activity against both mTORC1 and mTORC2, are currently in various stages of preclinical and clinical development.

SUMMARY

The rapalogs are the first mTOR inhibitors to show promising, yet modest, antitumor effects. To fully exploit the potential of targeting this pathway, it will be important to better understand the mechanisms of action and precise targets of the various inhibitors. Moreover, definition of biomarkers of susceptibility and identification of predictors and/or correlates to drug resistance will substantially advance this area.

Inhibitors of mTOR

Inhibitors of mammalian target of rapamycin (mTOR) have been approved for the treatment of renal cell carcinoma and appear to have a role in the treatment of other malignancies. The primary objective of this drug review is to provide pharmacokinetic and dynamic properties of the commonly used drugs everolimus and temsirolimus. Additionally, information on clinical use, mechanism of action, bioanalysis, drug-drug interactions, alterations with disease or age, pharmacogenetics, and drug resistance is given. This overview should assist the treating medical oncologist in adjusting treatment with mTOR inhibitors to individual patient circumstances.

[Management of metastatic HER2-positive breast cancer: present and future]

HER2-positive breast cancer accounts for 20 to 25% of breast cancers. The surexpression of this tyrosine-kinase receptor is often associated with a poor prognosis. However, the management and the outcome of these patients have changed these last ten years with trastuzumab. Despite the encouraging results obtained with this humanized monoclonal antibody directed against the HER2-receptor, used alone or in association with chemotherapy in metastatic patients, progression under trastuzumab are usually observed and resistances to this treatment are described. Thus, many other monoclonal antibodies and tyrosine-kinase inhibitors emerged. These therapeutics, used alone or in association with chemotherapy or trastuzumab have variable properties: anti-HER2 and anti-EGFR such as lapatinib, pertuzumab and neratinib; anti-EGFR such as erlotinib and gefitinib; antiangiogenesis (bevacizumab, pazopanib); anti-mTOR pathway (temsirolimus, everolimus) or inhibitor of HSP90 (tanespimycine). In this paper, we present an overview on validated targeted therapies and those which are currently under investigation and seem promising in first line or after progression under trastuzumab. Data regarding cardiotoxicity and the use of trastuzumab under particular clinical circumstances (brain metastases, pregnancy) are also reviewed.

Synergistic activity of letrozole and sorafenib on breast cancer cells

Estrogens induce breast tumor cell proliferation by directly regulating gene expression via the estrogen receptor (ER) transcriptional activity and by affecting growth factor signaling pathways such as mitogen-activated protein kinase (MAPK) and AKT/mammalian target of rapamycin Complex1 (mTORC1) cascades. In this study we demonstrated the preclinical therapeutic efficacy of combining the aromatase inhibitor letrozole with the multi-kinase inhibitor sorafenib in aromatase-expressing breast cancer cell lines. Treatment with letrozole reduced testosterone-driven cell proliferation, by inhibiting the synthesis of estrogens. Sorafenib inhibited cell proliferation in a concentration-dependent manner; this effect was not dependent on sorafenib-mediated inhibition of Raf1, but involved the down-regulation of mTORC1 and its targets p70S6K and 4E-binding protein 1 (4E-BP1). At concentrations of 5-10 μM the growth-inhibitory effect of sorafenib was associated with the induction of apoptosis, as indicated by release of cytochrome c and Apoptosis-Inducing Factor into the cytosol, activation of caspase-9 and caspase-7, and PARP-1 cleavage. Combination of letrozole and sorafenib produced a synergistic inhibition of cell proliferation associated with an enhanced accumulation of cells in the G(0)/G(1) phase of the cell cycle and with a down-regulation of the cell cycle regulatory proteins c-myc, cyclin D1, and phospho-Rb. In addition, longer experiments (12 weeks) demonstrated that sorafenib may be effective in preventing the acquisition of resistance towards letrozole. Together, these results indicate that combination of letrozole and sorafenib might constitute a promising approach to the treatment of hormone-dependent breast cancer.

Novel therapeutic approaches to the treatment of metastatic breast cancer

Metastatic breast cancer is ultimately an incurable disease, although recent data have shown that its incidence is decreasing and that patients with metastatic breast cancer live longer. This improvement in survival seems to be linked with the introduction of new therapeutic agents, novel combinations of existing therapies and targeted therapies. Our increasing understanding of the molecular biology of metastatic disease has allowed the development of therapies aimed at specific molecular targets. Some of these have already been approved for the treatment of metastatic breast cancer in combination with cytotoxics, and others have shown promising results regarding disease-free survival, overall response rates and time to disease progression. Given the enormous amount of information about drug discovery in cancer, it is important to be familiar with the present state of the treatment of metastatic breast cancer. The purpose of this review is to provide an update on the development of some of the most promising novel agents and treatment strategies in metastatic breast cancer.

Targeting tumorigenesis: development and use of mTOR inhibitors in cancer therapy

The mammalian target of rapamycin (mTOR) is an intracellular serine/threonine protein kinase positioned at a central point in a variety of cellular signaling cascades. The established involvement of mTOR activity in the cellular processes that contribute to the development and progression of cancer has identified mTOR as a major link in tumorigenesis. Consequently, inhibitors of mTOR, including temsirolimus, everolimus, and ridaforolimus (formerly deforolimus) have been developed and assessed for their safety and efficacy in patients with cancer. Temsirolimus is an intravenously administered agent approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) for the treatment of advanced renal cell carcinoma (RCC). Everolimus is an oral agent that has recently obtained US FDA and EMEA approval for the treatment of advanced RCC after failure of treatment with sunitinib or sorafenib. Ridaforolimus is not yet approved for any indication. The use of mTOR inhibitors, either alone or in combination with other anticancer agents, has the potential to provide anticancer activity in numerous tumor types. Cancer types in which these agents are under evaluation include neuroendocrine tumors, breast cancer, leukemia, lymphoma, hepatocellular carcinoma, gastric cancer, pancreatic cancer, sarcoma, endometrial cancer, and non-small-cell lung cancer. The results of ongoing clinical trials with mTOR inhibitors, as single agents and in combination regimens, will better define their activity in cancer.

Novel therapeutic strategy for breast cancer: mammalian target of rapamycin inhibition

BACKGROUND

Mammalian target of rapamycin (mTOR) plays a central role in regulating cellular protein synthesis. Dysregulation of mTOR signaling pathway is strongly associated with tumorigenesis, angiogenesis, tumor progression and drug resistance. Inhibition of mTOR might not only promote cell cycle arrest, but also sensitize resistant cancer cells to chemotherapeutic and other targeted agents.

OBJECTIVE

To review and summarize the mechanism of mTOR on regulation of protein synthesis and latest clinical data, and to discuss the novel therapeutic strategy for the use of mTOR inhibitors in the treatment of breast cancer.

METHODS

A review of published literatures and conference abstracts obtained from MEDLINE, American Society of Clinical Oncology Meeting and San Antonio Breast Cancer Symposia proceedings for results of previous preclinical and latest clinical studies of mTOR inhibition in breast cancer was performed.

CONCLUSIONS

mTOR inhibitors seemed to be potentially useful for the treatment of breast cancer with acceptable safety profile. The challenge remains the identification of suitable candidates with different phenotypes. More structured studies incorporating molecular, clinical and translational research need to be initiated. Future research on mTOR inhibitors for breast cancer should focus on the evaluation of optimal schedule, patient selection and combination strategies to maximize the use of this new class of targeted agents.

Optimal treatment strategies in postmenopausal women with hormone-receptor-positive and HER2-negative metastatic breast cancer

Metastatic breast cancer (MBC) is unfortunately still considered incurable; treatment aims to prolong progression-free and overall survival, relieve disease symptoms, and maintain quality of life. Treatment can include endocrine therapy, radiotherapy, chemotherapy, bisphosphonates, and/or targeted therapy; which is used depends on the characteristics of the disease [e.g., hormone receptor status, disease site(s), and response to previous treatment] and the patient (age, comorbidity, and personal preferences). For most patients with hormone-receptor-positive tumors, the first choice of treatment is further endocrine therapy, but endocrine resistance is a common problem in advanced disease. Several novel anticancer agents have been developed with the aim of overcoming endocrine resistance, many of which target intracellular signaling pathways implicated in disease progression or resistance. Among these, inhibitors of growth factor receptor tyrosine kinases and of mammalian target of rapamycin have shown the most promise in clinical trials. Chemotherapy is the cornerstone of MBC treatment in most women. Important considerations when choosing chemotherapy include the choice of agents, and whether to use single-agent or combination therapy. Anthracyclines are one of the most active cytotoxic agents currently used for the treatment of breast cancer, and for many women, further anthracycline therapy at progression or relapse would be the preferred option. However, lifetime exposure to anthracyclines is limited by cumulative cardiotoxicity, which often prevents rechallenge in later lines of therapy. Newer anthracycline formulations have been developed with lower cardiotoxicity than the conventional anthracycline doxorubicin, but these agents still impair cardiac function, and have maximum recommended lifetime doses. Recently, the concomitant use of cardioprotective agents, such as dexrazoxane, has emerged as an effective approach to reducing the cardiotoxic effects of anthracyclines, thus permitting retreatment. Bisphosphonates, which are not associated with the acute toxicities of cytotoxic chemotherapy drugs, are the established standard of care for patients with metastatic bone disease, and have greatly improved outcomes over the last decade. The search is ongoing for novel agents that will, hopefully, bring a cure closer to reality.

The antitumor activity of an anti-CD54 antibody in SCID mice xenografted with human breast, prostate, non-small cell lung, and pancreatic tumor cell lines

We have previously described the development and testing of a monoclonal anti-human CD54 antibody (UV3) in SCID mice xenografted with human multiple myeloma, lymphoma, and melanoma cell lines. In all 3 cases, UV3 was highly effective at slowing the growth of tumors and/or prolonging survival. Since CD54 (ICAM-1) is up-regulated on many different types of cancer cells, we have now investigated the anti-tumor activity of UV3 in several other CD54(+) epithelial tumors. A panel of 16 human breast, prostate, non-small cell (NSC) lung, and pancreatic tumor cell lines was examined for reactivity with UV3, and 13 were positive. A representative CD54(+) cell line from each cancer was grown subcutaneously in SCID mice. Once the tumors were established, UV3 was administered using different dose regimens. UV3 slowed the growth of all 4 tumors, although it was not curative. When UV3 or gemcitabine were administered to SCID mice xenografted with a NSC lung tumor cell line or a pancreatic tumor cell line, UV3 was as effective as the chemotherapy alone. When gemcitabine and UV3 were administered together, the best anti-tumor responses were observed. UV3 has been chimerized (cUV3) and both toxicology studies and clinical trials are planned to assess the safety and activity of cUV3 in patients with one or more of these tumors.

Hereditary breast cancer: new genetic developments, new therapeutic avenues

Six genes confer a high risk for developing breast cancer (BRCA1/2, TP53, PTEN, STK11, CDH1). Both BRCA1 and BRCA2 have DNA repair functions, and BRCA1/2 deficient tumors are now being targeted by poly(ADP-ribose) polymerase inhibitors. Other genes conferring an increased risk for breast cancer include ATM, CHEK2, PALB2, BRIP1 and genome-wide association studies have identified lower penetrance alleles including FGFR2, a minor allele of which is associated with breast cancer. We review recent findings related to the function of some of these genes, and discuss how they can be targeted by various drugs. Gaining deeper insights in breast cancer susceptibility will improve our ability to identify those families at increased risk and permit the development of new and more specific therapeutic approaches.

Molecular targeted therapies for breast cancer treatment

Targeting the oestrogen receptor, HER2 (human epidermal growth factor receptor 2) and vascular endothelial growth factor has markedly improved breast cancer therapy. New targeted therapeutic approaches to induction of apoptosis or inhibition of anti-apoptosis, cell cycle progression, signal transduction and angiogenesis are described. The molecular pathways and their inhibitory or repair mechanisms are discussed in the preclinical and clinical settings.

Molecular targets of breast cancer: AKTing in concert

Despite significant advancement in the diagnosis and treatment of breast cancer, many patients succumb to this disease. The elucidation of aberrant signaling pathways that lead to breast cancer should help develop more effective therapeutic strategies. The Akt signaling pathway plays an important role in the development and progression of breast cancer. Overexpression/activation of Akt has been associated with poor prognosis and resistance to hormonal and chemotherapy. Although mutations in Akt are rare in breast cancer, the activity of Akt is regulated by hormones, growth factors, growth factor receptors, oncogenes and tumor suppressor genes that are often deregulated in breast cancer. The objective of this commentary is to discuss recent literature on how activation of Akt by various signaling pathways contributes to breast cancer and confers resistance to current therapy.