Advances in Targeted Therapy Against Driver Mutations and Epigenetic Alterations in Non-Small Cell Lung Cancer

The incidence and mortality of lung cancer rank top three of all cancers worldwide. Accounting for 85% of the total number of lung cancer, non-small cell lung cancer (NSCLC) is an important factor endangering human health. Recently, targeted therapies against driver mutations and epigenetic alterations have made encouraging advances that benefit NSCLC patients. Druggable driver mutations, which mainly occur in EGFR, KRAS, MET, HER2, ALK, ROS1, RET and BRAF, have been identified in more than a quarter of NSCLC patients. A series of highly selective mutant targeting inhibitors, such as EGFR tyrosine kinase inhibitors and KRAS inhibitors, have been well studied and applied in clinical treatments, which greatly promote the overall survival of NSCLC patients. However, drug resistance has become a major challenge for targeted treatment, and a variety of methods to overcome drug resistance are constantly being developed, including inhibitors against new mutants, combination therapy with other pathway inhibitors, etc. In addition, epigenetics-based therapy is emerging. Epigenetic regulators such as histone deacetylases and non-coding RNA play a crucial role in the development of cancer and drug resistance by affecting multiple signaling pathways. Epigenetics-based therapeutic strategies combined with targeted drugs show great clinical potential. Many agents targeting epigenetic changes are being investigated in preclinical studies, with some already under clinical trials. This article focuses on driver mutations and epigenetic alterations in association with relevant epidemiological data. We introduce the current status of targeted inhibitors and known drug resistance, review advances in major targeted therapies with recent data from preclinical and clinical trials, and discuss the possibility of combination therapy against driver mutations and epigenetic alterations in overcoming drug resistance.     

Dual HER2 blockade: preclinical and clinical data

DNA methylation and histone modifications are important epigenetic modifications associated with gene (dys)regulation. The epigenetic modifications are balanced by epigenetic enzymes, so-called writers and erasers, such as DNA (de)methylases and histone (de)acetylases. Aberrant epigenetic alterations have been associated with various diseases, including breast cancer. Since aberrant epigenetic modifications are potentially reversible, they might represent targets for breast cancer therapy. Indeed, several drugs have been designed to inhibit epigenetic enzymes (epi-drugs), thereby reversing epigenetic modifications. US Food and Drug Administration approval has been obtained for some epi-drugs for hematological malignancies. However, these drugs have had very modest anti-tumor efficacy in phase I and II clinical trials in breast cancer patients as monotherapy. Therefore, current clinical trials focus on the combination of epi-drugs with other therapies to enhance or restore the sensitivity to such therapies. This approach has yielded some promising results in early phase II trials. The disadvantage of epi-drugs, however, is genome-wide effects, which may cause unwanted upregulation of, for example, pro-metastatic genes. Development of gene-targeted epigenetic modifications (epigenetic editing) in breast cancer can provide a novel approach to prevent such unwanted events. In this context, identification of crucial epigenetic modifications regulating key genes in breast cancer is of critical importance. In this review, we first describe aberrant DNA methylation and histone modifications as two important classes of epigenetic mutations in breast cancer. Then we focus on the preclinical and clinical epigenetic-based therapies currently being explored for breast cancer. Finally, we describe epigenetic editing as a promising new approach for possible applications towards more targeted breast cancer treatment.     

Emerging epigenetic targets and therapies in cancer medicine

Abnormalities in the epigenetic regulation of chromatin structure and function can lead to aberrant gene expression and cancer development. Consequently, epigenetic therapies aim to restore normal chromatin modification patterns through the inhibition of various components of the epigenetic machinery. Histone deacetylase and DNA methyltransferase inhibitors represent the first putative epigenetic therapies; however, these agents have pleiotropic effects and it remains unclear how they lead to therapeutic responses. More recently, drugs that inhibit histone methyltransferases were developed, perhaps representing more specific agents. We review emerging epigenetic targets in cancer and present recent models of promising epigenetic therapies. SIGNIFICANCE: The use of DNA methyltransferase and histone deacetylase inhibitors in patients has validated the use of drugs targeted to epigenetic enzymes and strengthened the need for development of additional therapies. In this review, we summarize recently discovered epigenetic abnormalities, their implications for cancer, and the approaches taken for discovering small-molecule inhibitors targeting various properties of the epigenetic machinery.     

Epigenetic modifiers as new immunomodulatory therapies in solid tumours

BackgroundImmune therapies have revolutionized cancer treatment over the last few years by allowing improvements in overall survival. However, the majority of patients is still primary or secondary resistant to such therapies, and enhancing sensitivity to immune therapies is therefore crucial to improve patient outcome. Several recent lines of evidence suggest that epigenetic modifiers have intrinsic immunomodulatory properties, which could be of therapeutic interest.Material and methodsWe reviewed preclinical evidence and clinical studies which describe or exploit immunomodulatory properties of epigenetic agents. Experimental approaches, clinical applicability and corresponding ongoing clinical trials are described.ResultsSeveral epigenetic modifiers, such as histone deacetylase inhibitors, DNA methyl transferase inhibitors, bromodomain inhibitors, lysine-specific histone demethylase 1 inhibitors and enhancer of zeste homolog 2 inhibitors, display intrinsic immunomodulatory properties. The latter can be achieved through the action of these drugs either on cancer cells (e.g. presentation and generation of neoantigens, induction of immunogenic cell death, modulation of cytokine secretion), on immune cells (e.g. linage, differentiation, activation status and antitumor capability), or on components of the microenvironment (e.g. regulatory T cells and macrophages). Several promising combinations, notably with immune checkpoint blockers or adoptive T-cell therapy, can be envisioned. Dedicated clinically relevant approaches for patient selection and trial design will be required to optimally develop such combinations.ConclusionIn an era where immune therapies are becoming a treatment backbone in many tumour types, epigenetic modifiers could play a crucial role in modulating tumours’ immunogenicity and sensitivity to immune agents. Optimal trial design, including window of opportunity trials, will be key in the success of this approach, and clinical evaluation is ongoing.     

DNA methyltransferase inhibitors for cancer therapy

Aberrant DNA methylation patterns, including hypermethylation of tumor suppressor genes, have been described in many human cancers. These epigenetic mutations can be reversed by DNA methyltransferase inhibitors, which provide novel opportunities for cancer therapy. Clinical concepts for epigenetic therapies are currently being developed by using azanucleosides for the treatment of leukemias and other tumors. These trials will greatly benefit from the inclusion of molecular markers for monitoring epigenetic changes in patients and for maximizing biologic responses. In addition, novel inhibitors need to be developed that result in a direct and specific inhibition of DNA methyltransferase activity. Several recent developments indicate that rational design of small molecule DNA methyltransferase inhibitors is feasible and that this approach can result in the establishment of novel drug candidates. The use of novel DNA methyltransferase inhibitors in clinical trials that allow monitoring of drug-induced DNA methylation changes should provide the foundation for improved epigenetic cancer therapies.     

Epigenetic Therapy in Breast Cancer

Breast carcinogenesis is a multistep process involving both genetic and epigenetic changes. Epigenetics is defined as reversible changes in gene expression, not accompanied by alteration in gene sequence. DNA methylation, histone modification, and nucleosome remodeling are the major epigenetic changes that are dysregulated in breast cancer. Several genes involved in proliferation, anti-apoptosis, invasion, and metastasis have been shown to undergo epigenetic changes in breast cancer. Because epigenetic changes are potentially reversible processes, much effort has been directed toward understanding this mechanism with the goal of finding effective therapies that target these changes. Both demethylating agents and the histone deacetylase inhibitors (HDACi) are under investigation as single agents or in combination with other systemic therapies in the treatment of breast cancer. In this review, we discuss the role of epigenetic regulation in breast cancer, in particular focusing on the clinical trials using therapies that modulate epigenetic mechanisms.     

表观遗传学在结直肠癌中的应用进展

结直肠癌（CRC）的发生、发展伴随着许多基因的表达变化,但其具体调控机制至今仍未完全阐明。近年来对CRC表观遗传学尤其是微小RNA（miRNA）、异常DNA甲基化及组蛋白修饰状态等方面的研究受到广泛关注。研究证实,CRC进展过程中均存在异常的甲基化基因和miRNA的表达变化。与癌症基因组的基因突变一样,这类遗传学的分子改变在CRC中扮演着重要角色。表观遗传学的特异性改变可作为CRC诊断、治疗和预后的临床生物学标记物,对表观遗传学进行深入研究对CRC的防治具有重要指导意义。     

Targeting Epigenetic Modifications for the Treatment and Prevention of Breast Cancer

DNA methylation, histone modification, and nucleosome remodeling are the three intercalated events that result in epigenetic modification, which in turn alters gene expression. Aberrant epigenetic regulation resulting in altered gene expression has been clearly implicated in the initiation and progression of breast cancer. Our understanding of the landscape of these changes in breast cancer has increased tremendously over the past decade. Significant advancement has been made in the preclinical arena to identify targets that are epigenetically altered in breast cancer and to modulate these targets with epigenetic therapies to improve tumor response. Clinical translation of these concepts is currently ongoing and shows promise in improving outcomes in breast cancer. This article provides a comprehensive review of the completed and ongoing clinical trials of epigenetic therapy in the management and prevention of breast cancer and the rationale leading to the design of these trials.     

Acquired resistance to EGFR inhibitors: mechanisms and prevention strategies

Potent and specific, or relatively specific, inhibitors of epidermal growth factor receptor (EGFR) signaling, including monoclonal antibodies and small molecular weight compounds, have been successfully developed. Both types of agent have been found to have significant antitumor activity, especially when used in combination with radio- hormone- and chemotherapy in preclinical studies. Because of the potentiation of the conventional drug activity in these combination settings, inhibitors of EGFR signaling have often been referred to as sensitizers for chemotherapy or radiation, as well as drug resistance reversal agents. Phase II clinical trials in head-and-neck as well as lung cancer suggested this concept of chemosensitization might translate into the clinic, but this remains to be definitively proven in randomized, double-blind Phase III trials. Given the extensive preclinical literature on EGFR blocking drugs and the advanced clinical development of such agents, it is surprising that the possibility of development of acquired resistance to the EGFR inhibitors themselves, a common clinical problem with virtually all other currently used anticancer drugs, remains a largely unexplored subject of investigation. Here we summarize some of the possible mechanisms that can result in acquired resistance to EGFR-targeting drugs. Alternative combination therapies to circumvent and delay this problem are suggested.     

Combination epigenetic therapy has efficacy in patients with refractory advanced non-small cell lung cancer

Epigenetic alterations are strongly associated with the development of cancer. We conducted a phase I/II trial of combined epigenetic therapy with azacitidine and entinostat, inhibitors of DNA methylation and histone deacetylation, respectively, in extensively pretreated patients with recurrent metastatic non-small cell lung cancer. This therapy is well tolerated, and objective responses were observed, including a complete response and a partial response in a patient who remains alive and without disease progression approximately 2 years after completing protocol therapy. Median survival in the entire cohort was 6.4 months (95% CI 3.8-9.2), comparing favorably with existing therapeutic options. Demethylation of a set of 4 epigenetically silenced genes known to be associated with lung cancer was detectable in serial blood samples in these patients and was associated with improved progression-free (P = 0.034) and overall survival (P = 0.035). Four of 19 patients had major objective responses to subsequent anticancer therapies given immediately after epigenetic therapy. Significance: This study demonstrates that combined epigenetic therapy with low-dose azacitidine and entinostat results in objective, durable responses in patients with solid tumors and defines a blood-based biomarker that correlates with clinical benefit.     

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10–12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.     

骨髓增生异常综合征表观遗传学治疗进展

 表观遗传改变与基因改变有一个重要的区别就是表观遗传改变是可逆的,通过使用相应的表观遗传药物可使沉默的抑癌基因重新表达。骨髓增生异常综合征（MDS）的表观遗传治疗已经取得了很大的发展,当前应用于临床的表观遗传药物主要包括DNA去甲基化药物和去乙酰化酶抑制剂。得到FDA批准上市的DNA去甲基化药物5-氮杂胞苷和地西他滨均为MDS治疗药物,可作为中高危患者尤其是不能耐受化疗的老年患者重要的治疗选择;去乙酰化酶抑制剂如丙戊酸等目前在治疗MDS中大多处于I期临床试验阶段,可能在治疗低危MDS中有一定价值,但其剂量和治疗效果尚需进一步评估;去甲基化药物和去乙酰化抑制剂二者联用治疗MDS可能具有协同作用,但目前的临床试验尚不能证实其优于去甲基化药物的单用,仍需大样本的临床病例和合理的治疗方案来验证其安全有效性。     

Altered epigenetic signals in human disease

The genetic information of almost all eukaryotic cells is stored in chromatin. In cancer cells, alterations in chromatin organization or in its epigenetic marks occur frequently. Among these are changes in the patterns of DNA and histone methylation. Using Acute Promyelocytic Leukemia as model system we could demonstrate a direct correlation of epigenetic events induced by the driving oncogene product PML-RARalpha and cancer progression. Several of the enzymes ultimately responsible for these events can be inhibited by small compound inhibitors and thus can serve as targets in cancer therapy. In this article, we review the role of DNA methylation, histone methylation and chromatin alterations in human diseases. A picture is emerging in which these epigenetic signals "cross-talk" and are implicated in the physiological and pathological spreading of gene silencing.     

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10-12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.