Evaluation of targeted therapies in advanced breast cancer: the need for large-scale molecular screening and transformative clinical trial designs

Prognostic value and clinicopathological significance of serum- and tissue-based cytokeratin 18 express level in breast cancer: a meta-analysis

Cytokeratin 18 (CK18), a type I cytokeratin of the intermediate filament family, has been associated with the prognosis of cancer patients for decades. However, its exact role in predicting the clinical outcome of breast cancer remains controversial. To comprehensively investigated the prognostic value of CK18 in breast cancer, a systematically meta-analysis was conducted to explore the association between CK18 expression and overall survival. Literature collection was conducted by retrieving electronic databases Pubmed, Cochrane Library, Web of Science, EMBASE, and OVID completely (up to January 1, 2017). Nine relevant studies with 4857 cases assessing the relationship between CK18 high expression and the outcome of breast cancer patients were enrolled in our analysis. The results indicated that the high level of CK18 expression was significantly associated with overall survival of breast cancer patients via a specimen-depended manner. Reports which used serum to detect the expression of CK18 predicted a poor outcome of breast cancer (HR = 1.24, 95%CI: 1.11–1.38, P<0.0001), while studies which used tissue as specimen indicated a reverse result (HR = 0.71, 95%CI: 0.60–0.84, P<0.00001). Moreover, overexpression of CK18 was highly relevant to advanced clinicopathological parameters of breast cancer, such as progesterone receptor, human epidermal growth factor receptor-2, tumor size, tumor stage, nodal status, and tumor grade. Taken together, the present study demonstrated that CK18 might be served as a novel biomarker to predict clinicopathological features and the outcome of breast cancer.

Packaging and transfer of mitochondrial DNA via exosomes regulate escape from dormancy in hormonal therapy-resistant breast cancer

Increasing evidence suggests that extracellular vesicles (EVs) can transfer genetic material to recipient cells. However, the mechanism and role of this phenomenon are largely unknown. Here we have made a remarkable discovery: EVs can harbor the full mitochondrial genome. These extracellular vesicles can in turn transfer their mtDNA to cells with impaired metabolism, leading to restoration of metabolic activity. We determined that hormonal therapy induces oxidative phosphorylation-deficient breast cancer cells, which can be rescued via the transfer of mtDNA-laden extracellular vesicles. Horizontal transfer of mtDNA occurred in cancer stem-like cells and was associated with increased self-renewal potential of these cells, leading to resistance to hormonal therapy. We propose that mtDNA transfer occurs in human cancer via EVs.

The horizontal transfer of mtDNA and its role in mediating resistance to therapy and an exit from dormancy have never been investigated. Here we identified the full mitochondrial genome in circulating extracellular vesicles (EVs) from patients with hormonal therapy-resistant (HTR) metastatic breast cancer. We generated xenograft models of HTR metastatic disease characterized by EVs in the peripheral circulation containing mtDNA. Moreover, these human HTR cells had acquired host-derived (murine) mtDNA promoting estrogen receptor-independent oxidative phosphorylation (OXPHOS). Functional studies identified cancer-associated fibroblast (CAF)-derived EVs (from patients and xenograft models) laden with whole genomic mtDNA as a mediator of this phenotype. Specifically, the treatment of hormone therapy (HT)-naive cells or HT-treated metabolically dormant populations with CAF-derived mtDNA^hi EVs promoted an escape from metabolic quiescence and HTR disease both in vitro and in vivo. Moreover, this phenotype was associated with the acquisition of EV mtDNA, especially in cancer stem-like cells, expression of EV mtRNA, and restoration of OXPHOS. In summary, we have demonstrated that the horizontal transfer of mtDNA from EVs acts as an oncogenic signal promoting an exit from dormancy of therapy-induced cancer stem-like cells and leading to endocrine therapy resistance in OXPHOS-dependent breast cancer.

Transposon insertional mutagenesis in mice identifies human breast cancer susceptibility genes and signatures for stratification

Despite concerted efforts to identify causal genes that drive breast cancer (BC) initiation and progression, we have yet to establish robust signatures to stratify patient risk. Here we used in vivo transposon-based forward genetic screening to identify potentially relevant BC driver genes. Integrating this approach with survival prediction analysis, we identified six gene pairs that could prognose human BC subtypes into high-, intermediate-, and low-risk groups with high confidence and reproducibility. Furthermore, we identified susceptibility gene sets for basal and claudin-low subtypes (21 and 16 genes, respectively) that stratify patients into three relative risk subgroups. These signatures offer valuable prognostic insight into the genetic basis of BC and allow further exploration of the interconnectedness of BC driver genes during disease progression.

Robust prognostic gene signatures and therapeutic targets are difficult to derive from expression profiling because of the significant heterogeneity within breast cancer (BC) subtypes. Here, we performed forward genetic screening in mice using Sleeping Beauty transposon mutagenesis to identify candidate BC driver genes in an unbiased manner, using a stabilized N-terminal truncated β-catenin gene as a sensitizer. We identified 134 mouse susceptibility genes from 129 common insertion sites within 34 mammary tumors. Of these, 126 genes were orthologous to protein-coding genes in the human genome (hereafter, human BC susceptibility genes, hBCSGs), 70% of which are previously reported cancer-associated genes, and ∼16% are known BC suppressor genes. Network analysis revealed a gene hub consisting of E1A binding protein P300 (EP300), CD44 molecule (CD44), neurofibromin (NF1) and phosphatase and tensin homolog (PTEN), which are linked to a significant number of mutated hBCSGs. From our survival prediction analysis of the expression of human BC genes in 2,333 BC cases, we isolated a six-gene-pair classifier that stratifies BC patients with high confidence into prognostically distinct low-, moderate-, and high-risk subgroups. Furthermore, we proposed prognostic classifiers identifying three basal and three claudin-low tumor subgroups. Intriguingly, our hBCSGs are mostly unrelated to cell cycle/mitosis genes and are distinct from the prognostic signatures currently used for stratifying BC patients. Our findings illustrate the strength and validity of integrating functional mutagenesis screens in mice with human cancer transcriptomic data to identify highly prognostic BC subtyping biomarkers.

Targeted therapy for breast cancer and molecular mechanisms of resistance to treatment

In recent years, clinical trials investigating new drugs and therapeutic combinations have led to promising advances in breast cancer therapy. Subtyping breast cancers into hormone receptor (HR) positive, epidermal growth factor receptor (HER2) positive, and triple negative breast cancer (TNBC) is currently the basis of diagnosing and treating this disease. In addition to endocrine and HER2-targeted therapies in their respective subtypes, evidence from recent preclinical studies have shown several targetable pathways that overcome resistance in the clinical setting. The mTOR inhibitor everolimus and the CDK4/6 inhibitor palbociclib have been approved in HR-positive metastatic breast cancer (MBC) due to improved disease-free survival (DFS). Adding pertuzumab to trastuzumab in combination with taxanes further improves DFS in HER2-positive breast cancer. Targeted therapy to the heterogeneous group of TNBC is needed in combination with chemotherapy. However, patient selection and predictive biomarker development remains a big challenge for targeted therapy development in TNBC.

Deciphering and Targeting Oncogenic Mutations and Pathways in Breast Cancer

: Advances in DNA and RNA sequencing revealed substantially greater genomic complexity in breast cancer than simple models of a few driver mutations would suggest. Only very few, recurrent mutations or copy-number variations in cancer-causing genes have been identified. The two most common alterations in breast cancer are TP53 (affecting the majority of triple-negative breast cancers) and PIK3CA (affecting almost half of estrogen receptor-positive cancers) mutations, followed by a long tail of individually rare mutations affecting <1%-20% of cases. Each cancer harbors from a few dozen to a few hundred potentially high-functional impact somatic variants, along with a much larger number of potentially high-functional impact germline variants. It is likely that it is the combined effect of all genomic variations that drives the clinical behavior of a given cancer. Furthermore, entirely new classes of oncogenic events are being discovered in the noncoding areas of the genome and in noncoding RNA species driven by errors in RNA editing. In light of this complexity, it is not unexpected that, with the exception of HER2 amplification, no robust molecular predictors of benefit from targeted therapies have been identified. In this review, we summarize the current genomic portrait of breast cancer, focusing on genetic aberrations that are actively being targeted with investigational drugs.

IMPLICATIONS FOR PRACTICE

Next-generation sequencing is now widely available in the clinic, but interpretation of the results is challenging, and its impact on treatment selection is often limited. This work provides an overview of frequently encountered molecular abnormalities in breast cancer and discusses their potential therapeutic implications. This review emphasizes the importance of administering investigational targeted therapies, or off-label use of approved targeted drugs, in the context of a formal clinical trial or registry programs to facilitate learning about the clinical utility of tumor target profiling.

Manganese Superoxide Dismutase Acetylation and Dysregulation, Due to Loss of SIRT3 Activity, Promote a Luminal B-Like Breast Carcinogenic-Permissive Phenotype

SIGNIFICANCE

Breast cancer is the most common nondermatologic malignancy among women in the United States, among which endocrine receptor-positive breast cancer accounts for up to 80%. Endocrine receptor-positive breast cancers can be categorized molecularly into luminal A and B subtypes, of which the latter is an aggressive form that is less responsive to endocrine therapy with inferior prognosis.

RECENT ADVANCES

Sirtuin, an aging-related gene involved in mitochondrial metabolism, is associated with life span, and more importantly, murine models lacking Sirt3 spontaneously develop tumors that resemble human luminal B breast cancer. Furthermore, these tumors exhibit aberrant manganese superoxide dismutase (MnSOD) acetylation at lysine 68 and lysine 122 and have abnormally high reactive oxygen species (ROS) levels, which have been observed in many types of breast cancer.

CRITICAL ISSUES

The mechanism of how luminal B breast cancer develops resistance to endocrine therapy remains unclear. MnSOD, a primary mitochondrial detoxification enzyme, functions by scavenging excessive ROS from the mitochondria and maintaining mitochondrial and cellular homeostasis. Sirt3, a mitochondrial fidelity protein, can regulate the activity of MnSOD through deacetylation. In this study, we discuss a possible mechanism of how loss of SIRT3-guided MnSOD acetylation results in endocrine therapy resistance of human luminal B breast cancer.

FUTURE DIRECTIONS

Acetylation of MnSOD and other mitochondrial proteins, due to loss of SIRT3, may explain the connection between ROS and development of luminal B breast cancer and how luminal B breast cancer becomes resistant to endocrine therapy. Antioxid. Redox Signal. 25, 326-336.

New generation of breast cancer clinical trials implementing molecular profiling

The implementation of molecular profiling technologies in oncology deepens our knowledge for the molecular landscapes of cancer diagnoses, identifying aberrations that could be linked with specific therapeutic vulnerabilities. In particular, there is an increasing list of molecularly targeted anticancer agents undergoing clinical development that aim to block specific molecular aberrations. This leads to a paradigm shift, with an increasing list of specific aberrations dictating the treatment of patients with cancer. This paradigm shift impacts the field of clinical trials, since the classical approach of having clinico-pathological disease characteristics dictating the patients' enrolment in oncology trials shifts towards the implementation of molecular profiling as pre-screening step. In order to facilitate the successful clinical development of these new anticancer drugs within specific molecular niches of cancer diagnoses, there have been developed new, innovative trial designs that could be classified as follows: i) longitudinal cohort studies that implement (or not) "nested" downstream trials, 2) studies that assess the clinical utility of molecular profiling, 3) "master" protocol trials, iv) "basket" trials, v) trials following an adaptive design. In the present article, we review these innovative study designs, providing representative examples from each category and we discuss the challenges that still need to be addressed in this era of new generation oncology trials implementing molecular profiling. Emphasis is put on the field of breast cancer clinical trials.

BAG-1/SODD, HSP70, and HSP90 are potential prognostic markers of poor survival in node-negative breast carcinoma

The objective of this study was to analyze the expression and clinical role of 13 signaling molecules in a large cohort of breast carcinoma patients with long follow-up period. Breast carcinomas (n=410) were analyzed for protein expression of phosphorylated mitogen-activated protein kinases (p-ERK, p-JNK, p-p38) and phosphoinositide 3-kinase signaling pathway proteins (p-AKT, p-mTOR, p-p70S6K); the BAG family proteins BAG-1 and BAG-4/SODD; the antiapoptotic protein Bcl-2; the inhibitor of apoptosis family member Survivin; and the heat shock protein family members HSP27, HSP70, and HSP90. Protein expression was studied for association with clinicopathological parameters and survival. Significantly higher expression of p-AKT (P<.001), p-mTOR (P<.001), p-p70S6K (P<.001), Bcl-2 (P<.001), BAG-4/SODD (P<.001), HSP27 (P<.001), HSP70 (P=.012), HSP90 (P<.001), and Survivin (P=.004) was found in infiltrating ductal and lobular carcinomas compared to mucinous carcinomas. Bcl-2 expression was significantly higher in grades 1 and 2 compared to grade 3 carcinomas (P<.001). p-AKT expression was higher in tumors more than 2cm (P=.027), whereas p-mTOR expression was lowest in tumors more than 5cm (P=.019). Higher BAG-4/SODD, HSP70, and HSP90 expression was associated with poor overall survival (P=.016, P=.039, and P=.023, respectively) in univariate analysis, whereas the only independent prognosticator in Cox multivariate survival analysis was tumor diameter (P=.003). In conclusion, BAG-4/SODD, HSP70, and HSP90 are potential prognostic markers in node-negative breast carcinoma that merit further research.

Bridging academic science and clinical research in the search for novel targeted anti-cancer agents

This review starts with a brief history of drug discovery & development, and the place of Asia in this worldwide effort discussed. The conditions and constraints of a successful translational R&D involving academic basic research and clinical research are discussed and the Singapore model for pursuit of open R&D described. The importance of well-characterized, validated drug targets for the search for novel targeted anti-cancer agents is emphasized, as well as a structured, high quality translational R&D. Furthermore, the characteristics of an attractive preclinical development drug candidate are discussed laying the foundation of a successful preclinical development. The most frequent sources of failures are described and risk management at every stage is highly recommended. Organizational factors are also considered to play an important role. The factors to consider before starting a new drug discovery & development project are described, and an example is given of a successful clinical project that has had its roots in local universities and was carried through preclinical development into phase I clinical trials.