MEDI0639: a novel therapeutic antibody targeting Dll4 modulates endothelial cell function and angiogenesis in vivo

Informed by Cancer Stem Cells of Solid Tumors: Advances in Treatments Targeting Tumor-Promoting Factors and Pathways

Cancer stem cells (CSCs) represent a subpopulation within tumors that promote cancer progression, metastasis, and recurrence due to their self-renewal capacity and resistance to conventional therapies. CSC-specific markers and signaling pathways highly active in CSCs have emerged as a promising strategy for improving patient outcomes. This review provides a comprehensive overview of the therapeutic targets associated with CSCs of solid tumors across various cancer types, including key molecular markers aldehyde dehydrogenases, CD44, epithelial cellular adhesion molecule, and CD133 and signaling pathways such as Wnt/β-catenin, Notch, and Sonic Hedgehog. We discuss a wide array of therapeutic modalities ranging from targeted antibodies, small molecule inhibitors, and near-infrared photoimmunotherapy to advanced genetic approaches like RNA interference, CRISPR/Cas9 technology, aptamers, antisense oligonucleotides, chimeric antigen receptor (CAR) T cells, CAR natural killer cells, bispecific T cell engagers, immunotoxins, drug-antibody conjugates, therapeutic peptides, and dendritic cell vaccines. This review spans developments from preclinical investigations to ongoing clinical trials, highlighting the innovative targeting strategies that have been informed by CSC-associated pathways and molecules to overcome therapeutic resistance. We aim to provide insights into the potential of these therapies to revolutionize cancer treatment, underscoring the critical need for a multi-faceted approach in the battle against cancer. This comprehensive analysis demonstrates how advances made in the CSC field have informed significant developments in novel targeted therapeutic approaches, with the ultimate goal of achieving more effective and durable responses in cancer patients.

The Prognostic Role and Significance of Dll4 and Toll-like Receptors in Cancer Development

Simple Summary

The aim of this review is to summarize the latest details considering the role of Dll4 in cancer, since recent data report that Dll4 has a major key role in tumor angiogenesis. Moreover, the authors try to seek any correlation between Dll4 and cancer stem cells in tumor development. Considering that cancer stem cells have proven to be implicated in the progression of many cancer types, any impact from Dll4 could lead to the alteration of cancer development. Additionally, the authors make a report on current advantages on immunotherapy and tumor-draining lymph nodes in cancer. Finally, this study analyzes toll like receptors, pattern recognition receptors that are capable of recognizing different molecules and activating different genes. These immunogenetic molecules have remarkable roles including angiogenesis promotion, while their activation can lead to either cancer progression or inhibition, representing a very promising therapeutic alliance for cancer treatment.

Abstract

The Notch signaling pathway regulates the development of embryonic and tissue homeostasis of various types of cells. It also controls cell proliferation, variation, fate and cell death because it emits short-range messages to nearby cells. The pathway plays an important role in the pathophysiology of various malignancies, controlling cancer creation. It also limits cancer development by adjusting preserved angiogenesis and cellular programs. One of the Notch signaling ligands (in mammals) is Delta-like ligand 4 (Dll4), which plays a significant role in the overall malignancies’ advancement. Particularly, sequencing Notch gene mutations, including those of Dll4, have been detected in many types of cancers portraying information on the growth of particular gynecological types of tumors. The current research article examines the background theory that implies the ability of Dll4 in the development of endometrial and other cancer types, and the probable therapeutic results of Dll4 inhibition.

Targeting Notch to Maximize Chemotherapeutic Benefits: Rationale, Advanced Strategies, and Future Perspectives

Simple Summary

The Notch signaling pathway regulates cell proliferation, apoptosis, stem cell self-renewal, and differentiation in a context-dependent fashion both during embryonic development and in adult tissue homeostasis. Consistent with its pleiotropic physiological role, unproper activation of the signaling promotes or counteracts tumor pathogenesis and therapy response in distinct tissues. In the last twenty years, a wide number of studies have highlighted the anti-cancer potential of Notch-modulating agents as single treatment and in combination with the existent therapies. However, most of these strategies have failed in the clinical exploration due to dose-limiting toxicity and low efficacy, encouraging the development of novel agents and the design of more appropriate combinations between Notch signaling inhibitors and chemotherapeutic drugs with improved safety and effectiveness for distinct types of cancer.

Abstract

Notch signaling guides cell fate decisions by affecting proliferation, apoptosis, stem cell self-renewal, and differentiation depending on cell and tissue context. Given its multifaceted function during tissue development, both overactivation and loss of Notch signaling have been linked to tumorigenesis in ways that are either oncogenic or oncosuppressive, but always context-dependent. Notch signaling is critical for several mechanisms of chemoresistance including cancer stem cell maintenance, epithelial-mesenchymal transition, tumor-stroma interaction, and malignant neovascularization that makes its targeting an appealing strategy against tumor growth and recurrence. During the last decades, numerous Notch-interfering agents have been developed, and the abundant preclinical evidence has been transformed in orphan drug approval for few rare diseases. However, the majority of Notch-dependent malignancies remain untargeted, even if the application of Notch inhibitors alone or in combination with common chemotherapeutic drugs is being evaluated in clinical trials. The modest clinical success of current Notch-targeting strategies is mostly due to their limited efficacy and severe on-target toxicity in Notch-controlled healthy tissues. Here, we review the available preclinical and clinical evidence on combinatorial treatment between different Notch signaling inhibitors and existent chemotherapeutic drugs, providing a comprehensive picture of molecular mechanisms explaining the potential or lacking success of these combinations.

Therapeutic Targeting of Notch Signaling: From Cancer to Inflammatory Disorders

Over the past two decades, the Notch signaling pathway has been investigated as a therapeutic target for the treatment of cancers, and more recently in the context of immune and inflammatory disorders. Notch is an evolutionary conserved pathway found in all metazoans that is critical for proper embryonic development and for the postnatal maintenance of selected tissues. Through cell-to-cell contacts, Notch orchestrates cell fate decisions and differentiation in non-hematopoietic and hematopoietic cell types, regulates immune cell development, and is integral to shaping the amplitude as well as the quality of different types of immune responses. Depriving some cancer types of Notch signals has been shown in preclinical studies to stunt tumor growth, consistent with an oncogenic function of Notch signaling. In addition, therapeutically antagonizing Notch signals showed preclinical potential to prevent or reverse inflammatory disorders, including autoimmune diseases, allergic inflammation and immune complications of life-saving procedures such allogeneic bone marrow and solid organ transplantation (graft-versus-host disease and graft rejection). In this review, we discuss some of these unique approaches, along with the successes and challenges encountered so far to target Notch signaling in preclinical and early clinical studies. Our goal is to emphasize lessons learned to provide guidance about emerging strategies of Notch-based therapeutics that could be deployed safely and efficiently in patients with immune and inflammatory disorders.

Targeting the Notch Signaling Pathway in Chronic Inflammatory Diseases

The Notch signaling pathway regulates developmental cell-fate decisions and has recently also been linked to inflammatory diseases. Although therapies targeting Notch signaling in inflammation in theory are attractive, their design and implementation have proven difficult, at least partly due to the broad involvement of Notch signaling in regenerative and homeostatic processes. In this review, we summarize the supporting role of Notch signaling in various inflammation-driven diseases, and highlight efforts to intervene with this pathway by targeting Notch ligands and/or receptors with distinct therapeutic strategies, including antibody designs. We discuss this in light of lessons learned from Notch targeting in cancer treatment. Finally, we elaborate on the impact of individual Notch members in inflammation, which may lay the foundation for development of therapeutic strategies in chronic inflammatory diseases.

ABL001, a Bispecific Antibody Targeting VEGF and DLL4, with Chemotherapy, Synergistically Inhibits Tumor Progression in Xenograft Models

Delta-like-ligand 4 (DLL4) is a promising target to augment the effects of VEGF inhibitors. A simultaneous blockade of VEGF/VEGFR and DLL4/Notch signaling pathways leads to more potent anti-cancer effects by synergistic anti-angiogenic mechanisms in xenograft models. A bispecific antibody targeting VEGF and DLL4 (ABL001/NOV1501/TR009) demonstrates more potent in vitro and in vivo biological activity compared to VEGF or DLL4 targeting monoclonal antibodies alone and is currently being evaluated in a phase 1 clinical study of heavy chemotherapy or targeted therapy pre-treated cancer patients (ClinicalTrials.gov Identifier: NCT03292783). However, the effects of a combination of ABL001 and chemotherapy on tumor vessels and tumors are not known. Hence, the effects of ABL001, with or without paclitaxel and irinotecan were evaluated in human gastric or colon cancer xenograft models. The combination treatment synergistically inhibited tumor progression compared to each monotherapy. More tumor vessel regression and apoptotic tumor cell induction were observed in tumors treated with the combination therapy, which might be due to tumor vessel normalization. Overall, these findings suggest that the combination therapy of ABL001 with paclitaxel or irinotecan would be a better clinical strategy for the treatment of cancer patients.

Cancer Stem Cells, Quo Vadis? The Notch Signaling Pathway in Tumor Initiation and Progression

The Notch signaling pathway regulates cell proliferation, cytodifferentiation and cell fate decisions in both embryonic and adult life. Several aspects of stem cell maintenance are dependent from the functionality and fine tuning of the Notch pathway. In cancer, Notch is specifically involved in preserving self-renewal and amplification of cancer stem cells, supporting the formation, spread and recurrence of the tumor. As the function of Notch signaling is context dependent, we here provide an overview of its activity in a variety of tumors, focusing mostly on its role in the maintenance of the undifferentiated subset of cancer cells. Finally, we analyze the potential of molecules of the Notch pathway as diagnostic and therapeutic tools against the various cancers.

The Role of DLLs in Cancer: A Novel Therapeutic Target

Delta-like ligands (DLLs) control Notch signaling. DLL1, DLL3 and DLL4 are frequently deregulated in cancer and influence tumor growth, the tumor vasculature and tumor immunity, which play different roles in cancer progression. DLLs have attracted intense research interest as anti-cancer therapeutics. In this review, we discuss the role of DLLs in cancer and summarize the emerging DLL-relevant targeting methods to aid future studies.

EGF-like and Other Disulfide-rich Microdomains as Therapeutic Scaffolds

Disulfide bonds typically introduce conformational constraints into peptides and proteins, conferring improved biopharmaceutical properties and greater therapeutic potential. In our opinion, disulfide-rich microdomains from proteins are potentially a rich and under-explored source of drug leads. A survey of the UniProt protein database shows that these domains are widely distributed throughout the plant and animal kingdoms, with the EGF-like domain being the most abundant of these domains. EGF-like domains exhibit large diversity in their disulfide bond topologies and calcium binding modes, which we classify in detail here. We found that many EGF-like domains are associated with disease phenotypes, and the interactions they mediate are potential therapeutic targets. Indeed, EGF-based therapeutic leads have been identified, and we further propose that these domains can be optimized to expand their therapeutic potential using chemical design strategies. This Review highlights the potential of disulfide-rich microdomains as future peptide therapeutics.

Overview of Crosstalk Between Multiple Factor of Transcytosis in Blood Brain Barrier

Blood brain barrier (BBB) conserves unique regulatory system to maintain barrier tightness while allowing adequate transport between neurovascular units. This mechanism possess a challenge for drug delivery, while abnormality may result in pathogenesis. Communication between vascular and neural system is mediated through paracellular and transcellular (transcytosis) pathway. Transcytosis itself showed dependency with various components, focusing on caveolae-mediated. Among several factors, intense communication between endothelial cells, pericytes, and astrocytes is the key for a normal development. Regulatory signaling pathway such as VEGF, Notch, S1P, PDGFβ, Ang/Tie, and TGF-β showed interaction with the transcytosis steps. Recent discoveries showed exploration of various factors which has been proven to interact with one of the process of transcytosis, either endocytosis, endosomal rearrangement, or exocytosis. As well as providing a hypothetical regulatory pathway between each factors, specifically miRNA, mechanical stress, various cytokines, physicochemical, basement membrane and junctions remodeling, and crosstalk between developmental regulatory pathways. Finally, various hypotheses and probable crosstalk between each factors will be expressed, to point out relevant research application (Drug therapy design and BBB-on-a-chip) and unexplored terrain.

Future Options of Molecular-Targeted Therapy in Small Cell Lung Cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. With a focus on histology, there are two major subtypes: Non-small cell lung cancer (NSCLC) (the more frequent subtype), and small cell lung cancer (SCLC) (the more aggressive one). Even though SCLC, in general, is a chemosensitive malignancy, relapses following induction therapy are frequent. The standard of care treatment of SCLC consists of platinum-based chemotherapy in combination with etoposide that is subsequently enhanced by PD-L1-inhibiting atezolizumab in the extensive-stage disease, as the addition of immune-checkpoint inhibition yielded improved overall survival. Although there are promising molecular pathways with potential therapeutic impacts, targeted therapies are still not an integral part of routine treatment. Against this background, we evaluated current literature for potential new molecular candidates such as surface markers (e.g., DLL3, TROP-2 or CD56), apoptotic factors (e.g., BCL-2, BET), genetic alterations (e.g., CREBBP, NOTCH or PTEN) or vascular markers (e.g., VEGF, FGFR1 or CD13). Apart from these factors, the application of so-called 'poly-(ADP)-ribose polymerases' (PARP) inhibitors can influence tumor repair mechanisms and thus offer new perspectives for future treatment. Another promising therapeutic concept is the inhibition of 'enhancer of zeste homolog 2' (EZH2) in the loss of function of tumor suppressors or amplification of (proto-) oncogenes. Considering the poor prognosis of SCLC patients, new molecular pathways require further investigation to augment our therapeutic armamentarium in the future.

A phase I, dose-escalation study of PF-06650808, an anti-Notch3 antibody-drug conjugate, in patients with breast cancer and other advanced solid tumors

Background PF-06650808 is a novel anti-Notch3 antibody-drug conjugate (ADC) able to deliver an auristatin-based cytotoxic payload to target cells. In this first-in-human, dose-finding, phase I study (NCT02129205), we investigated safety, pharmacokinetics, immunogenicity, and preliminary antitumor activity of single-agent PF-06650808 in 40 patients with advanced breast cancer (BC) and other solid tumors unselected for Notch3 expression. Primary endpoint was dose-limiting toxicity (DLT). PF-06650808 was administered intravenously every 3 weeks at a starting dose of 0.2 mg/kg, escalated up to 6.4 mg/kg following the modified continual reassessment method. An additional dose level, 2.0 mg/kg, was evaluated in patients with advanced, estrogen receptor-positive (ER⁺) BC. Results The majority of patients had advanced BC (60%) and almost all (90%) had received ≥3 prior lines of anticancer therapy. Treatment with PF-06650808 was generally well tolerated at dose levels ≤2.0 mg/kg with no DLTs. The maximum tolerated dose (MTD) was estimated to be 2.4 mg/kg. The most common treatment-related AEs in all patients were fatigue (40.0%), decreased appetite (37.5%), nausea (35.0%), alopecia (32.5%), abdominal pain (25.0%), pruritus (25.0%), and vomiting (25.0%). Five patients achieved a partial response (PR), including 2 unconfirmed PRs; 4 of the responders had ER⁺/PR⁺/HER2^- BC. Sixteen (51.6%) patients achieved stable disease, including 8 (57.1%) of 14 patients with ER⁺ BC. Tumor samples from all responders tested positive for NOTCH3 expression in a retrospective, exploratory analysis. Conclusions The anti-Notch3 ADC PF-06650808 has demonstrated a manageable safety profile and early signs of antitumor activity in patients with advanced BC.

Crosstalk between Notch, HIF-1α and GPER in Breast Cancer EMT

The Notch signaling pathway acts in both physiological and pathological conditions, including embryonic development and tumorigenesis. In cancer progression, diverse mechanisms are involved in Notch-mediated biological responses, including angiogenesis and epithelial-mesenchymal-transition (EMT). During EMT, the activation of cellular programs facilitated by transcriptional repressors results in epithelial cells losing their differentiated features, like cell–cell adhesion and apical–basal polarity, whereas they gain motility. As it concerns cancer epithelial cells, EMT may be consequent to the evolution of genetic/epigenetic instability, or triggered by factors that can act within the tumor microenvironment. Following a description of the Notch signaling pathway and its major regulatory nodes, we focus on studies that have given insights into the functional interaction between Notch signaling and either hypoxia or estrogen in breast cancer cells, with a particular focus on EMT. Furthermore, we describe the role of hypoxia signaling in breast cancer cells and discuss recent evidence regarding a functional interaction between HIF-1α and GPER in both breast cancer cells and cancer-associated fibroblasts (CAFs). On the basis of these studies, we propose that a functional network between HIF-1α, GPER and Notch may integrate tumor microenvironmental cues to induce robust EMT in cancer cells. Further investigations are required in order to better understand how hypoxia and estrogen signaling may converge on Notch-mediated EMT within the context of the stroma and tumor cells interaction. However, the data discussed here may anticipate the potential benefits of further pharmacological strategies targeting breast cancer progression.

Interrogation of transcriptomic changes associated with drug-induced hepatic sinusoidal dilatation in colorectal cancer

Drug-related sinusoidal dilatation (SD) is a common form of hepatotoxicity associated with oxaliplatin-based chemotherapy used prior to resection of colorectal liver metastases (CRLM). Recently, hepatic SD has also been associated with anti-delta like 4 (DLL4) cancer therapies targeting the NOTCH pathway. To investigate the hypothesis that NOTCH signaling plays an important role in drug-induced SD, gene expression changes were examined in livers from anti-DLL4 and oxaliplatin-induced SD in non-human primate (NHP) and patients, respectively. Putative mechanistic biomarkers of bevacizumab (bev)-mediated protection against oxaliplatin-induced SD were also investigated. RNA was extracted from whole liver sections or centrilobular regions by laser-capture microdissection (LCM) obtained from NHP administered anti-DLL4 fragment antigen-binding (F(ab’)₂ or patients with CRLM receiving oxaliplatin-based chemotherapy with or without bev. mRNA expression was quantified using high-throughput real-time quantitative PCR. Significance analysis was used to identify genes with differential expression patterns (false discovery rate (FDR) < 0.05). Eleven (CCL2, CCND1, EFNB2, ERG, ICAM1, IL16, LFNG, NOTCH1, NOTCH4, PRDX1, and TGFB1) and six (CDH5, EFNB2, HES1, IL16, MIK67, HES1 and VWF) candidate genes were differentially expressed in the liver of anti-DLL4- and oxaliplatin-induced SD, respectively. Addition of bev to oxaliplatin-based chemotherapy resulted in differential changes in hepatic CDH5, HEY1, IL16, JAG1, MMP9, NOTCH4 and TIMP1 expression. This work implicates NOTCH and IL16 pathways in the pathogenesis of drug-induced SD and further explains the hepato-protective effect of bev in oxaliplatin-induced SD observed in CRLM patients.

Emerging application of genomics-guided therapeutics in personalized lung cancer treatment

In lung cancer, genomics-driven comprehensive molecular profiling has identified novel chemically and immunologically addressable vulnerabilities, resulting in an increasing application of precision medicine by targeted inactivation of tumor oncogenes and immunogenic activation of host anti-tumor surveillance as modes of treatment. However, initially profound response of these targeted therapies is followed by relapse due to therapy-resistant residual disease states. Although distinct mechanisms and frameworks for therapy resistance have been proposed, accounting for and upfront prediction of resistance trajectories has been challenging. In this review, we discuss in both non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), the current standing, and challenges associated with genomics-guided strategies for personalized therapy against both oncogenic alterations as well as post-therapy resistance mechanisms. In NSCLC, we catalog the targeted therapy approaches against most notable oncogenic alterations such as epidermal growth factor receptor (EGFR), serine/threonine-protein kinase b-raf (BRAF), Kirsten rat sarcoma viral proto-oncogene (KRAS), anaplastic lymphoma kinase (ALK), ROS1 proto-oncogene receptor tyrosine kinase (ROS1). For SCLC, currently highly recalcitrant to targeted therapy, we enumerate a range of exciting and maturing precision medicine approaches. Furthermore, we discuss a number of immunotherapy approaches, in combination or alone, that are being actively pursued clinically in lung cancer. This review not only highlights common mechanistic themes underpinning different classes of resistance and discusses tumor heterogeneity as a source of residual disease, but also discusses potential ways to overcome these barriers. We emphasize how an extensive understanding of these themes can predict and improve therapeutic strategies, such as through poly-therapy approaches, to forestall tumor evolution upfront.

Concurrent Treatment with Anti-DLL4 Enhances Antitumor and Proapoptotic Efficacy of a γ-Secretase Inhibitor in Gastric Cancer

The Notch signaling pathway has been identified as a therapeutic target for cancers. γ-Secretase inhibitors (GSIs) have been progressively recognized as potential anticancer drugs. The present study aimed to investigate the effects of anti-delta like legend 4 (anti-DLL4) treatment on the anticancer efficacy of GSIs in gastric cancer. SGC-7901-GFP human gastric cancer cells were tested for DLL4 expression by rosette formation test and immunofluorescence, and then were treated with anti-DLL4 antibody N-[N-(3,5-difluorophenacetyl)-L-ananyl]-S-phenylglycine t-butyl ester (DAPT, a type of GSI), or a combination of anti-DLL4 antibody and DAPT. The effects of in vitro treatments on cell apoptosis, cell cycle, and cell invasion were analyzed. For in vivo study, an orthotopic mouse model of gastric cancer was established with green fluorescence expressing SGC-7901. Ultrasound targeted microbubble destruction was used to treat tumor-bearing mice with anti-DLL4 antibody conjugated microbubbles, DAPT, and a combination of the two. Real-time fluorescence imaging was performed to assess tumor cell inhibition in each group. Following in vivo treatments, apoptosis of tumor cells and the expression of apoptosis-related genes BAX, Bcl-2, and P53 were detected by TUNEL and immunohistochemical staining. In vivo combined treatment of anti-DLL4 and DAPT led to a higher rate of cell apoptosis and greater inhibition of cell invasion than that observed with DAPT treatment alone. DAPT and anti-DLL4 combination therapy resulted in decreased cell distribution at G1 phase and increased cell distribution at S phase, compared to the untreated control group (P < .01). In vivo combined therapy with anti-DLL4 and DAPT significantly increased tumor growth inhibition and tumor cell apoptosis when compared to DAPT therapy alone (P < .05). In addition, combined treatment significantly increased expression of BAX and P53 and reduced Bcl-2 expression (P < .05). Conversely, treatment with DAPT alone only increased expression of BAX and P53 (P < .05), suggesting that the reduction of Bcl-2 expression may play an important role in the synergetic antitumor and proapoptosis effects of the combined treatment. Concurrent treatment with anti-DLL4 enhances the antitumor and proapoptotic efficacy of the γ-secretase inhibitor in gastric cancer both in vitro and in vivo.

γ-Secretase inhibitors in cancer clinical trials are pharmacologically and functionally distinct

γ-Secretase inhibitors (GSIs) are being actively repurposed as cancer therapeutics based on the premise that inhibition of NOTCH1 signaling in select cancers is therapeutic. Using novel assays to probe effects of GSIs against a broader panel of substrates, we demonstrate that clinical GSIs are pharmacologically distinct. GSIs show differential profiles of inhibition of the various NOTCH substrates, with some enhancing cleavage of other NOTCH substrates at concentrations where NOTCH1 cleavage is inhibited. Several GSIs are also potent inhibitors of select signal peptide peptidase (SPP/SPPL) family members. Extending these findings to mammosphere inhibition assays in triple-negative breast cancer lines, we establish that these GSIs have different functional effects. We also demonstrate that the processive γ-secretase cleavage pattern established for amyloid precursor protein (APP) occurs in multiple substrates and that potentiation of γ-secretase cleavage is attributable to a direct action of low concentrations of GSIs on γ-secretase. Such data definitively demonstrate that the clinical GSIs are not biological equivalents, and provide an important framework to evaluate results from ongoing and completed human trials with these compounds.

Targeting the Wnt/beta-catenin pathway in cancer: Update on effectors and inhibitors

The Wnt/beta-catenin pathway is a family of proteins that is implicated in many vital cellular functions such as stem cell regeneration and organogenesis. Several intra-cellular signal transduction pathways are induced by Wnt, notably the Wnt/beta-catenin dependent pathway or canonical pathway and the non-canonical or beta-catenin-independent pathway; the latter includes the Wnt/Ca2+ and Planar Cell Polarity pathway (PCP). Wnt activation occurs at the intestinal crypt floor, and is critical to optimal maintenance of stem cells. Colorectal cancers show evidence of Wnt signaling pathway activation and this is associated with loss of function of the tumor regulator APC. Wnt activation has been observed in breast, lung, and hematopoietic malignancies and contributes to tumor recurrence. The Wnt pathway cross talks with the Notch and Sonic Hedgehog pathways, which has implications for therapeutic interventions in cancers. There are significant challenges in targeting the Wnt pathway, including finding agents that are efficacious without damaging the system of normal somatic stem cell function in cellular repair and tissue homeostasis. Here, we comprehensively review the Wnt pathway and its interactions with the Notch and Sonic Hedgehog pathways. We present the state of the field in effectors and inhibitors of Wnt signaling, including updates on clinical trials in various cancers with inhibitors of Wnt, Notch, and Sonic Hedgehog.

Relevance of genetic alterations in squamous and small cell lung cancer

The precision medicine revolution has led to the development and US FDA approval of multiple targeted therapies in non-squamous non-small cell lung cancers, including tyrosine kinase inhibitors targeting EGFR, ALK, and ROS1. However, the development of targeted therapies for squamous cell lung cancers (SQCLCs) and small cell lung cancers (SCLCs) has lagged behind and the mainstay of systemic therapy for most patients with metastatic disease remains chemotherapy; which has seen little meaningful progress over the past three decades. The ideal of precision medicine in these diseases may appear elusive; however, recent comprehensive genomic analysis of SQCLC and SCLC has led to multiple breakthroughs in our understanding of the biology of these diseases and has led to new therapeutic approaches currently under active clinical investigation. This review will focus on the therapeutic relevance of these alterations in their respective diseases and new insights into promising therapeutics currently under investigation.

Generation of a functional humanized Delta-like ligand 4 transgenic mouse model

Humanized mouse models are important tools in many areas of biological drug development including, within oncology research, the development of antagonistic antibodies that have the potential to block tumor growth by controlling vascularization and are key to the generation of in vivo proof-of-concept efficacy data. However, due to cross reactivity between human antibodies and mouse target such studies regularly require mouse models expressing only the human version of the target molecule. Such humanized knock-in/knock-out, KIKO, models are dependent upon the generation of homozygous mice expressing only the human molecule, compensating for loss of the mouse form. However, KIKO strategies can fail to generate homozygous mice, even though the human form is expressed and the endogenous mouse locus is correctly targeted. A typical strategy for generating KIKO mice is by ATG fusion where the human cDNA is inserted downstream of the endogenous mouse promoter elements. However, when adopting this strategy it is possible that the mouse promoter fails to express the human form in a manner compensating for loss of the mouse form or alternatively the human protein is incompatible in the context of the mouse pathway being investigated. So to understand more around the biology of KIKO models, and to overcome our failure with a number of ATG fusion strategies, we developed a range of humanized models focused on Delta-like 4 (Dll4), a target where we initially failed to generate a humanized model. By adopting a broader biologic strategy, we successfully generated a humanized DLL4 KIKO which led to a greater understanding of critical biological aspects for consideration when developing humanized models.

A humanized anti-DLL4 antibody promotes dysfunctional angiogenesis and inhibits breast tumor growth

Blockage of Delta-like 4 (DLL4)-directed Notch signaling induces excessive tip cell formation and endothelial proliferation resulting in dysfunctional angiogenesis in tumors. MMGZ01, as a murine anti-human DLL4 monoclonal antibody, specifically binds to human DLL4 and blocks Notch pathway. Here, the structure of MMGZ01 variable fragment (Fv) was established and framework region (FR) residues which supported complementarily determining region (CDR) loop conformation were identified. Important residues interactions were also identified through docking MMGZ01 Fv with antigen epitope in DLL4. To humanize the murine antibody, we modified MMGZ01 Fv through CDR grafting and the reconstructed antibody (H₃L₂) maintained similar structure and binding affinity to parental MMGZ01 after back mutation of 12 canonical murine residues in the FRs. Meanwhile, H₃L₂ promoted human umbilical vein endothelial cell (HUVEC) proliferation through inhibiting DLL4-directed Notch pathway. Moreover, in MDA-MB-231-bearing nude mice, H₃L₂ induced dysfunctional angiogenesis and tumor cell apoptosis and showed superior anti-tumor activity. In conclusion, H₃L₂ is an ideal humanized antibody that inhibits tumor growth through targeting DLL4-Notch pathway and has attracting potentials for clinical applications.

Simultaneous blockade of VEGF and Dll4 by HD105, a bispecific antibody, inhibits tumor progression and angiogenesis

Several angiogenesis inhibitors targeting the vascular endothelial growth factor (VEGF) signaling pathway have been approved for cancer treatment. However, VEGF inhibitors alone were shown to promote tumor invasion and metastasis by increasing intratumoral hypoxia in some preclinical and clinical studies. Emerging reports suggest that Delta-like ligand 4 (Dll4) is a promising target of angiogenesis inhibition to augment the effects of VEGF inhibitors. To evaluate the effects of simultaneous blockade against VEGF and Dll4, we developed a bispecific antibody, HD105, targeting VEGF and Dll4. The HD105 bispecific antibody, which is composed of an anti-VEGF antibody (bevacizumab-similar) backbone C-terminally linked with a Dll4-targeting single-chain variable fragment, showed potent binding affinities against VEGF (KD: 1.3 nM) and Dll4 (KD: 30 nM). In addition, the HD105 bispecific antibody competitively inhibited the binding of ligands to their receptors, i.e., VEGF to VEGFR2 (EC50: 2.84 ± 0.41 nM) and Dll4 to Notch1 (EC50: 1.14 ± 0.06 nM). Using in vitro cell-based assays, we found that HD105 effectively blocked both the VEGF/VEGFR2 and Dll4/Notch1 signaling pathways in endothelial cells, resulting in a conspicuous inhibition of endothelial cell proliferation and sprouting. HD105 also suppressed Dll4-induced Notch1-dependent activation of the luciferase gene. In vivo xenograft studies demonstrated that HD105 more efficiently inhibited the tumor progression of human A549 lung and SCH gastric cancers than an anti-VEGF antibody or anti-Dll4 antibody alone. In conclusion, HD105 may be a novel therapeutic bispecific antibody for cancer treatment.

Self-Renewal and High Proliferative Colony Forming Capacity of Late-Outgrowth Endothelial Progenitors Is Regulated by Cyclin-Dependent Kinase Inhibitors Driven by Notch Signaling

Since the discovery of endothelial colony forming cells (ECFC), there has been significant interest in their therapeutic potential to treat vascular injuries. ECFC cultures display significant heterogeneity and a hierarchy among cells able to give rise to high proliferative versus low proliferative colonies. Here we aimed to define molecularly this in vitro hierarchy. Based on flow cytometry, CD34 expression levels distinguished two populations. Only CD34 + ECFC had the capacity to reproduce high proliferative potential (HPP) colonies on replating, whereas CD34- ECFCs formed only small clusters. CD34 + ECFCs were the only ones to self-renew in stringent single-cell cultures and gave rise to both CD34 + and CD34- cells. Upon replating, CD34 + ECFCs were always found at the centre of HPP colonies and were more likely in G0/1 phase of cell cycling. Functionally, CD34 + ECFC were superior at restoring perfusion and better engrafted when injected into ischemic hind limbs. Transcriptomic analysis identified cyclin-dependent kinase (CDK) cell cycle inhibiting genes (p16, p21, and p57), the Notch signaling pathway (dll1, dll4, hes1, and hey1), and the endothelial cytokine il33 as highly expressed in CD34 + ECFC. Blocking the Notch pathway using a γ-secretase inhibitor (DAPT) led to reduced expression of cell cycle inhibitors, increased cell proliferation followed by a loss of self-renewal, and HPP colony formation capacity reflecting progenitor exhaustion. Similarly shRNA knockdown of p57 strongly affected self-renewal of ECFC colonies. ECFC hierarchy is defined by Notch signalling driving cell cycle regulators, progenitor quiescence and self-renewal potential.

MMGZ01, an anti-DLL4 monoclonal antibody, promotes nonfunctional vessels and inhibits breast tumor growth

Increasing evidence suggests that DLL4 (Delta-like 4)-Notch signaling plays a critical role in cell fate determination and differentiation in tissues. Blocking DLL4-Notch signaling results in inhibition of tumor growth, which is associated with increased nonfunctional vessels and poor perfusion in the tumor. We successfully generated a human DLL4 monoclonal antibody MMGZ01 that binds specifically to DLL4 to disrupt the interaction between DLL4 and Notch1. MMGZ01 showed high affinity to DLL4 to inhibit the DLL4-mediated human umbilical vein endothelial cell (HUVEC) phenotype. Furthermore, MMGZ01 stimulated HUVEC vessel sprouting and tubule formation in vitro. In addition, MMGZ01 had a pronounced effect in promoting immature vessels and reduced breast cancer cell growth in vivo. Finally, MMGZ01 treatment inhibited the proliferation of breast cancer cells, induced tumor cell apoptosis, suppressed mammosphere formation, decreased CD44(+)/CD24(-) cell population, and reduced epithelial mesenchymal transition (EMT). These findings suggest that antagonism of the DLL4-Notch signaling pathway might provide a potential therapeutic approach for breast cancer treatment.

Notch and Wnt signaling pathway in cancer: Crucial role and potential therapeutic targets (Review)

There is no radical cure for all cancer types. The most frequently used therapies are surgical treatment, radiotherapy and chemotherapy. However, recrudescence, radiation resistance and chemotherapy resistance are the most challenging issues in clinical practice. To address these issues, they should be further studied at the molecular level, and the signaling pathways involved represent a promising avenue for this research. In the present review, we mainly discuss the components and mechanisms of activation of the Notch and Wnt signaling pathways, and we summarize the recent research efforts on these two pathways in different cancers. We also evaluate the ideal drugs that could target these two signaling pathways for cancer therapy, summarize alterations in the Notch and Wnt signaling pathways in cancer, and discuss potential signaling inhibitors as effective drugs for cancer therapy.

Notch signaling: an emerging therapeutic target for cancer treatment

The Notch pathway is involved in cell proliferation, differentiation and survival. The Notch signaling pathway is one of the most commonly activated signaling pathways in cancer. Alterations include activating mutations and amplification of the Notch pathway, which play key roles in the progression of cancer. Accumulating evidence suggests that the pharmacological inhibition of this pathway can overcome chemoresistance. Efforts have been taken to develop Notch inhibitors as a single agent or in combination with clinically used chemotherapeutics to treat cancer. Some Notch inhibitors have been demonstrated to have therapeutic efficacy in preclinical studies. This review summarizes the recent studies and clinical evaluations of the Notch inhibitors in cancer.

PET Imaging of Dll4 Expression in Glioblastoma and Colorectal Cancer Xenografts Using (64)Cu-Labeled Monoclonal Antibody 61B

Delta-like ligand 4 (Dll4) expressed in tumor cells plays a key role to promote tumor growth of numerous cancer types. Based on a novel antihuman Dll4 monoclonal antibody (61B), we developed a (64)Cu-labeled probe for positron emission tomography (PET) imaging of tumor Dll4 expression. In this study, 61B was conjugated with the (64)Cu-chelator DOTA through lysine on the antibody. Human IgG (hIgG)-DOTA, which did not bind to Dll4, was also prepared as a control. The Dll4 binding activity of the probes was evaluated through the bead-based binding assay with Dll4-alkaline phosphatase. The resulting PET probes were evaluated in U87MG glioblastoma and HT29 colorectal cancer xenografts in athymic nude mice. Our results demonstrated that the 61B-DOTA retained (77.2 ± 3.7) % Dll4 binding activity of the unmodified 61B, which is significantly higher than that of hIgG-DOTA (0.06 ± 0.03) %. Confocal microscopy analysis confirmed that 61B-Cy5.5, but not IgG-Cy5.5, predominantly located within the U87MG and HT29 cells cytoplasm. U87MG cells showed higher 61B-Cy5.5 binding as compared to HT29 cells. In U87MG xenografts, 61B-DOTA-(64)Cu demonstrated remarkable tumor accumulation (10.5 ± 1.7 and 10.2 ± 1.2%ID/g at 24 and 48 h postinjection, respectively). In HT29 xenografts, tumor accumulation of 61B-DOTA-(64)Cu was significantly lower than that of U87MG (7.3 ± 1.3 and 6.6 ± 1.3%ID/g at 24 and 48 h postinjection, respectively). The tumor accumulation of 61B-DOTA-(64)Cu was significantly higher than that of hIgG-DOTA-(64)Cu in both xenografts models. Immunofluorescence staining of the tumor tissues further confirmed that tumor accumulation of 61B-Cy5.5 was correlated well with in vivo PET imaging data using 61B-DOTA-(64)Cu. In conclusion, 61B-DOTA-(64)Cu PET probe was successfully synthesized and demonstrated prominent tumor uptake by targeting Dll4. 61B-DOTA-(64)Cu has great potential to be used for noninvasive Dll4 imaging, which could be valuable for tumor detection, Dll4 expression level evaluation, and Dll4-based treatment monitoring.

Application of anti-ligand antibodies to inhibit Notch signaling

Emerging evidence suggests that Notch signaling not only regulates biological processes during development but also participates in the pathogenesis of various diseases in adults, including tumor angiogenesis, hematopoietic malignancies, and cardiometabolic syndromes. Notch signaling involves several ligands and receptors that have unique and overlapping functions. Therefore, blocking function of a ligand or receptor with a neutralizing antibody is a useful approach to examine the specific role of each Notch component. In addition, administration of Notch signaling blocking antibodies in experimental animals offers important insights into clinical translation of Notch biology. In this chapter, we describe examples of in vitro and in vivo loss-of-function experiments with blockade of Notch ligands, particularly Delta-like ligand 4 (Dll4).

Notching on Cancer's Door: Notch Signaling in Brain Tumors

Notch receptors play an essential role in the regulation of central cellular processes during embryonic and postnatal development. The mammalian genome encodes for four Notch paralogs (Notch 1–4), which are activated by three Delta-like (Dll1/3/4) and two Serrate-like (Jagged1/2) ligands. Further, non-canonical Notch ligands such as epidermal growth factor like protein 7 (EGFL7) have been identified and serve mostly as antagonists of Notch signaling. The Notch pathway prevents neuronal differentiation in the central nervous system by driving neural stem cell maintenance and commitment of neural progenitor cells into the glial lineage. Notch is therefore often implicated in the development of brain tumors, as tumor cells share various characteristics with neural stem and progenitor cells. Notch receptors are overexpressed in gliomas and their oncogenicity has been confirmed by gain- and loss-of-function studies in vitro and in vivo. To this end, special attention is paid to the impact of Notch signaling on stem-like brain tumor-propagating cells as these cells contribute to growth, survival, invasion, and recurrence of brain tumors. Based on the outcome of ongoing studies in vivo, Notch-directed therapies such as γ-secretase inhibitors and blocking antibodies have entered and completed various clinical trials. This review summarizes the current knowledge on Notch signaling in brain tumor formation and therapy.

Antagonism of Ang-Tie2 and Dll4-Notch signaling has opposing effects on tumor endothelial cell proliferation, evidenced by a new flow cytometry method

Sustained angiogenesis is essential for tumor growth as it provides the tumor with a network of blood vessels that supply both oxygen and essential nutrients. Limiting tumor-associated angiogenesis is a proven strategy for the treatment of human cancer. To date, the rapid detection and quantitation of tumor-associated endothelial cell (TAEC) proliferation has been challenging, largely due to the low frequency of endothelial cells (ECs) within the tumor microenvironment. In this report, we address this problem using a new multiparametric flow cytometry method capable of rapid and precise quantitation of proliferation by measuring bromodeoxyuridine (BrdUrd) uptake in mouse TAECs from established human tumor xenografts. We determined the basal proliferation labeling index of TAECs in two human tumor xenografts representing two distinct histologies, COLO 205 (colorectal cancer) and U-87 (glioblastoma). We then investigated the effects of two large-molecule antiangiogenic agents targeting different biochemical pathways. Blocking angiopoietin-Tie2 signaling with the peptide-Fc fusion protein, trebananib (AMG 386), inhibited proliferation of TAECs, whereas blocking Dll4-Notch signaling with an anti-Dll4-specific antibody induced hyperproliferation of TAECs. These pharmacodynamic studies highlight the sensitivity and utility of this flow cytometry-based method and demonstrate the value of this assay to rapidly assess the in vivo proliferative effects of angiogenesis-targeted agents on both the tumor and the associated vasculature.

Phase 2 study of RO4929097, a gamma-secretase inhibitor, in metastatic melanoma: SWOG 0933

BACKGROUND

Aberrant Notch activation confers a proliferative advantage to many human tumors, including melanoma. This phase 2 trial assessed the antitumor activity of RO4929097, a gamma-secretase inhibitor of Notch signaling, with respect to the progression-free and overall survival of patients with advanced melanoma.

METHODS

Chemotherapy-naive patients with metastatic melanoma of cutaneous or unknown origin were treated orally with RO4929097 at a dose of 20 mg daily 3 consecutive days per week. A 2-step accrual design was used with an interim analysis of the first 32 patients and with continuation of enrollment if 4 or more of the 32 patients responded.

RESULTS

Thirty-six patients from 23 institutions were enrolled; 32 patients were evaluable. RO4929097 was well tolerated, and most toxicities were grade 1 or 2. The most common toxicities were nausea (53%), fatigue (41%), and anemia (22%). There was 1 confirmed partial response lasting 7 months, and there were 8 patients with stable disease lasting at least through week 12, with 1 of these continuing for 31 months. The 6-month progression-free survival rate was 9% (95% confidence interval [CI], 2%-22%), and the 1-year overall survival rate was 50% (95% CI, 32%-66%). Peripheral blood T-cell assays showed no significant inhibition of the production of interleukin-2, a surrogate pharmacodynamic marker of Notch inhibition, and this suggested that the drug levels were insufficient to achieve Notch target inhibition.

CONCLUSIONS

RO4929097 showed minimal clinical activity against metastatic melanoma in this phase 2 trial, possibly because of inadequate exposure to therapeutic drug levels. Although Notch inhibition remains a compelling target in melanoma, the results do not support further investigation of RO4929097 with this dose and schedule.

Tackling the cancer stem cells - what challenges do they pose?

Since their identification in 1994, cancer stem cells (CSCs) have been objects of intensive study. Their properties and mechanisms of formation have become a major focus of current cancer research, in part because of their enhanced ability to initiate and drive tumour growth and their intrinsic resistance to conventional therapeutics. The discovery that activation of the epithelial-to-mesenchymal transition (EMT) programme in carcinoma cells can give rise to cells with stem-like properties has provided one possible mechanism explaining how CSCs arise and presents a possible avenue for their therapeutic manipulation. Here we address recent developments in CSC research, focusing on carcinomas that are able to undergo EMT. We discuss the signalling pathways that create these cells, cell-intrinsic mechanisms that could be exploited for selective elimination or induction of their differentiation, and the role of the tumour microenvironment in sustaining them. Finally, we propose ways to use our current knowledge of the complex biology of CSCs to design novel therapies to eliminate them.

Understanding the mechanisms of action of antiangiogenic agents in metastatic colorectal cancer: a clinician's perspective

Multiple clinical trials using bevacizumab, ziv-aflibercept, and regorafenib have recently demonstrated efficacy for patients with metastatic colorectal cancer. While the net clinical benefit of each of these therapies in the second-line and refractory disease setting appears to be similar, important distinctions exist between the agents at the pharmacodynamic, tumor microenvironment, and clinical levels. The purpose of this review is to survey the preclinical evidence regarding the mechanisms of action of these novel antiangiogenic agents and provide an overview of their respective clinical activity, while highlighting distinctions between therapies. Fundamental understanding of these distinctions may aid in clinical decisions and choice of antiangiogenic therapies.

Therapeutic modulation of Notch signalling--are we there yet?

The Notch signalling pathway is evolutionarily conserved and is crucial for the development and homeostasis of most tissues. Deregulated Notch signalling leads to various diseases, such as T cell leukaemia, Alagille syndrome and a stroke and dementia syndrome known as CADASIL, and so strategies to therapeutically modulate Notch signalling are of interest. Clinical trials of Notch pathway inhibitors in patients with solid tumours have been reported, and several approaches are under preclinical evaluation. In this Review, we focus on aspects of the pathway that are amenable to therapeutic intervention, diseases that could be targeted and the various Notch pathway modulation strategies that are currently being explored.

High-content analysis to leverage a robust phenotypic profiling approach to vascular modulation

Phenotypic screening seeks to identify substances that modulate phenotypes in a desired manner with the aim of progressing first-in-class agents. Successful campaigns require physiological relevance, robust screening, and an ability to deconvolute perturbed pathways. High-content analysis (HCA) is increasingly used in cell biology and offers one approach to prosecution of phenotypic screens, but challenges exist in exploitation where data generated are high volume and complex. We combine development of an organotypic model with novel HCA tools to map phenotypic responses to pharmacological perturbations. We describe implementation for angiogenesis, a process that has long been a focus for therapeutic intervention but has lacked robust models that recapitulate more completely mechanisms involved. The study used human primary endothelial cells in co-culture with stromal fibroblasts to model multiple aspects of angiogenic signaling: cell interactions, proliferation, migration, and differentiation. Multiple quantitative descriptors were derived from automated microscopy using custom-designed algorithms. Data were extracted using a bespoke informatics platform that integrates processing, statistics, and feature display into a streamlined workflow for building and interrogating fingerprints. Ninety compounds were characterized, defining mode of action by phenotype. Our approach for assessing phenotypic outcomes in complex assay models is robust and capable of supporting a range of phenotypic screens at scale.

Understanding and targeting resistance to anti-angiogenic therapies

Therapies targeting tumor angiogenesis are used in a variety of malignancies, however not all patients benefit from treatment and impact on tumor control may be transient and modest. Mechanisms of resistance to anti-angiogenic therapies can be broadly categorized into VEGF-axis dependent alterations, non-VEGF pathways, and stromal cell interactions. Complimentary combinations of agents that inhibit alternative mechanisms of blood vessel formation may optimize inhibition of angiogenesis and improve clinical benefit for patients. The purpose of this review is to detail the preclinical evidence for mechanisms of angiogenic resistance and provide an overview of novel therapeutic approaches exploiting these pathways.

Clinical implications of DLL4 expression in gastric cancer

BACKGROUND

Delta-like ligand 4 (DLL4)-Notch signaling plays a key role in tumor neovascular development and angiogenesis during tumor growth. The clinical significance of DLL4 expression in gastric cancer has not been clarified.

METHODS

Gastric cancer cell lines and 180 gastric cancer patients were enrolled. DLL4 expression in gastric cancer cells and stroma was identified and evaluated immunohistochemically. The association between DLL4 and clinicopathological factors was also assessed.

RESULTS

DLL4 expression was identified in the cellular membrane and cytoplasm of gastric cancer cells by immunoblotting and immunohistochemical staining. DLL4 positivity in cancer cells and stroma was found in 88 (48%) and 41 (22%) of the 180 gastric cancer patients respectively. Both cancer and stromal DLL4 expression significantly correlated with more advanced tumor depth, nodal involvement, and lymphatic and venous invasion. A strongly positive association between cancerous and stromal DLL4 expression was identified (p < 0.01). Both cancerous and stromal DLL4 expression were prognostic markers in gastric cancer as determined by univariate analysis.

CONCLUSIONS

Cancerous and stromal DLL4 expression was found in 48% and 22% in gastric cancer, and significantly affected postoperative clinical outcomes. Cancerous and stromal DLL4 expression may be an effective target of anti-DLL4 treatment in gastric cancer.

A phase Ib combination study of RO4929097, a gamma-secretase inhibitor, and temsirolimus in patients with advanced solid tumors

Background To determine the recommended phase II dose (RP2D) and assess the safety, pharmacokinetics (PKs) and pharmacodynamics of RO4929097in combination with temsirolimus. Methods Escalating doses of RO4929097 and temsirolimus were administered at three dose levels. Patients received once daily oral RO4929097 on a 3 days on/4 days off schedule every week, and weekly intravenous temsirolimus. Blood samples were collected for PK analysis. Archival tissue specimens were collected for Notch pathway biomarker analysis and genotyping of frequent oncogenic mutations. Results Seventeen patients with refractory advanced solid tumors were enrolled in three dose levels (DLs): DL1 (RO4929097 10 mg; Temsirolimus 25 mg), DL2 (RO4929097 20 mg; Temsirolimus 25 mg), and DL3 (RO4929097 20 mg; Temsirolimus 37.5 mg). The most common toxicities related to the study drug combination included: fatigue (82 %; grade 3 6 %), mucositis, (71 %; grade 3 6 %), neutropenia (59 %; grade 3 12 %), anemia (59 %; grade 3 0 %), and hypertriglyceridemia (59 %; grade 3 0 %). Two dose-limiting toxicities, grade 3 rash and grade 3 mucositis, were observed in the same patient in the first dose level prompting dose expansion. Eleven patients (73 %) had stable disease as their best response. Co-administration of RO4929097 was associated with increased clearance and reduced exposure to temsirolimus, suggestive of drug-drug interaction via CYP3A4 induction. No correlation between the expression of Notch pathway biomarkers or genotype and time to progression was noted. Conclusions RO4929097 can be safely combined with temsirolimus in patients with advanced solid tumors. The RP2D was established at 20 mg of RO4929097 combined with 37.5 mg of temsirolimus.

The Notch signaling pathway as a mediator of tumor survival

The Notch signaling pathway is evolutionarily conserved and responsible for cell fate determination in the developing embryo and mature tissue. At the molecular level, ligand binding activates Notch signaling by liberating the Notch intracellular domain, which then translocates into the nucleus and activates gene transcription. Despite the elegant simplicity of this pathway, which lacks secondary messengers or a signaling cascade, Notch regulates gene expression in a highly context- and cell-type-dependent manner. Notch signaling is frequently dysregulated, most commonly by overactivation, across many cancers and confers a survival advantage on tumors, leading to poorer outcomes for patients. Recent studies demonstrate how Notch signaling increases tumor cell proliferation and provide evidence that active Notch signaling maintains the cancer stem-cell pool, induces epithelial-mesenchymal transition and promotes chemoresistance. These studies imply that pharmacological inhibition of Notch signaling may refine control of cancer therapy and improve patient survival. Gamma secretase inhibitors (GSIs) are drugs that inhibit Notch signaling and may be successful in controlling cancer cell growth in conjunction with standard chemotherapy, but substantial side effects have hampered their widespread use. Recent efforts have been aimed at the development of antibodies against specific Notch receptors and ligands with the hope of limiting side effects while providing the same therapeutic benefit as GSIs. Together, studies characterizing Notch signaling and modulation have offered hope that refined methods targeting Notch may become powerful tools in anticancer therapeutics.