MET signaling in colon cancer stem-like cells blunts the therapeutic response to EGFR inhibitors

The Roles of RAC1 and RAC1B in Colorectal Cancer and Their Potential Contribution to Cetuximab Resistance

Colorectal cancer (CRC) is one of the most diagnosed cancers and a leading contributor to cancer-related deaths in the United States. Clinically, standard treatment regimens include surgery, radiation, and chemotherapy; however, there has been increasing development and clinical use of targeted therapies for CRC. Unfortunately, many patients develop resistance to these treatments. Cetuximab, the first targeted therapy approved to treat advanced CRC, is a monoclonal antibody that targets the epidermal growth factor receptor and inhibits downstream pathway activation to restrict tumor cell growth and proliferation. CRC resistance to cetuximab has been well studied, and common resistance mechanisms include constitutive signal transduction through downstream protein mutations and promotion of the epithelial-to-mesenchymal transition. While the most common resistance mechanisms are known, a proportion of patients develop resistance through unknown mechanisms. One protein predicted to contribute to therapy resistance is RAC1, a small GTPase that is involved in cytoskeleton rearrangement, cell migration, motility, and proliferation. RAC1 has also been shown to be overexpressed in CRC. Despite evidence that RAC1 and its alternative splice isoform RAC1B play important roles in CRC and the pathways known to contribute to cetuximab resistance, there is a need to directly study the relationship between RAC1 and RAC1B and cetuximab resistance. This review highlights the recent studies investigating RAC1 and RAC1B in the context of CRC and suggests that these proteins could play a role in resistance to cetuximab.

Tumor cell stemness in gastrointestinal cancer: regulation and targeted therapy

The cancer stem cells are a rare group of self-renewable cancer cells capable of the initiation, progression, metastasis and recurrence of tumors, and also a key contributor to the therapeutic resistance. Thus, understanding the molecular mechanism of tumor stemness regulation, especially in the gastrointestinal (GI) cancers, is of great importance for targeting CSC and designing novel therapeutic strategies. This review aims to elucidate current advancements in the understanding of CSC regulation, including CSC biomarkers, signaling pathways, and non-coding RNAs. We will also provide a comprehensive view on how the tumor microenvironment (TME) display an overall tumor-promoting effect, including the recruitment and impact of cancer-associated fibroblasts (CAFs), the establishment of an immunosuppressive milieu, and the induction of angiogenesis and hypoxia. Lastly, this review consolidates mainstream novel therapeutic interventions targeting CSC stemness regulation.

Unveiling the mechanisms and challenges of cancer drug resistance

Cancer treatment faces many hurdles and resistance is one among them. Anti-cancer treatment strategies are evolving due to innate and acquired resistance capacity, governed by genetic, epigenetic, proteomic, metabolic, or microenvironmental cues that ultimately enable selected cancer cells to survive and progress under unfavorable conditions. Although the mechanism of drug resistance is being widely studied to generate new target-based drugs with better potency than existing ones. However, due to the broader flexibility in acquired drug resistance, advanced therapeutic options with better efficacy need to be explored. Combination therapy is an alternative with a better success rate though the risk of amplified side effects is commonplace. Moreover, recent groundbreaking precision immune therapy is one of the ways to overcome drug resistance and has revolutionized anticancer therapy to a greater extent with the only limitation of being individual-specific and needs further attention. This review will focus on the challenges and strategies opted by cancer cells to withstand the current therapies at the molecular level and also highlights the emerging therapeutic options -like immunological, and stem cell-based options that may prove to have better potential to challenge the existing problem of therapy resistance. Video Abstract.

Potential mechanisms of cancer-associated fibroblasts in therapeutic resistance

Despite continuous improvements in research and new cancer therapeutics, the goal of eradicating cancer remains elusive because of drug resistance. For a long time, drug resistance research has been focused on tumor cells themselves; however, recent studies have found that the tumor microenvironment also plays an important role in inducing drug resistance. Cancer-associated fibroblasts (CAFs) are a main component of the tumor microenvironment. They cross-talk with cancer cells to support their survival in the presence of anticancer drugs. This review summarizes the current knowledge of the role of CAFs in tumor drug resistance. An in-depth understanding of the mechanisms underlying the cross-talk between CAFs and cancer cells and insight into the importance of CAFs in drug resistance can guide the development of new anticancer strategies.

The differential cancer growth associated with anaesthetics in a cancer xenograft model of mice: mechanisms and implications of postoperative cancer recurrence

Anaesthetics may modify colorectal cancer cell biology which potentially affects long-term survival. This study aims to compare propofol and sevoflurane regarding with the direct anaesthetic effects on cancer malignancy and the indirect effects on host immunity in a cancer xenograft mode of mice. Cultured colon cancer cell (Caco-2) was injected subcutaneously to nude mice (day 1). Mice were exposed to either 1.5% sevoflurane for 1.5 h or propofol (20 μg g-1; ip injection) with or without 4 μg g-1 lipopolysaccharide (LPS; ip) from days 15 to 17, compared with those without anaesthetic exposure as controls. The clinical endpoints including tumour volumes over 70 mm3 were closely monitored up to day 28. Tumour samples from the other cohorts were collected on day 18 for PCR array, qRT-PCR, western blotting and immunofluorescent assessment. Propofol treatment reduced tumour size (mean ± SD; 23.0 ± 6.2mm3) when compared to sevoflurane (36.0 ± 0.3mm3) (p = 0.008) or control (23.6 ± 4.7mm3). Propofol decreased hypoxia inducible factor 1α (HIF1α), interleukin 1β (IL1β), and hepatocyte growth factor (HGF) gene expressions and increased tissue inhibitor of metalloproteinases 2 (TIMP-2) gene and protein expression in comparison to sevoflurane in the tumour tissue. LPS suppressed tumour growth in any conditions whilst increased TIMP-2 and anti-cancer neutrophil marker expressions and decreased macrophage marker expressions compared to those in the LPS-untreated groups. Our data indicated that sevoflurane increased cancer development when compared with propofol in vivo under non-surgical condition. Anaesthetics tested in this study did not alter the effects of LPS as an immune modulator in changing immunocyte phenotype and suppressing cancer development.

Progress and prospects of targeted therapy and immunotherapy for urachal carcinoma

Introduction: Urachal carcinoma (UrC) is a rare and aggressive disease. Systematic chemotherapy shows limited efficacy in patients with advanced disease, while targeted therapy and immunotherapy may provide a reasonable alternative for specific populations. The molecular pattern of colorectal cancer (CRC) have recently been identified; this understanding has significantly influenced the clinical management of CRC in terms of molecular-targeted therapy. Although some genetic alterations have been associated with UrC, there is still no systematic overview of the molecular profile of this rare malignancy. Methods: In this review, we comprehensively discuss the molecular profile of UrC and further identify potential targets for the personalized treatment of UrC as well as immune checkpoint inhibitors that represent underlying biomarkers. A systematic literature search was carried out by searching the PubMed, EMBASE, and Web of Science databases to identify all literature related to targeted therapy and immunotherapy in urachal carcinoma from inception to February 2023. Results: A total of 28 articles were eligible, and most studies included were case report sand retrospective case series. Furthermore, 420 cases of UrC were identified to analyze the association between mutations and UrC. The most commonly mutated gene in UrC was TP53 with the prevalence of 70%, followed by KRAS mutations in 28.3%, MYC mutations in 20.3%, SMAD4 mutations in 18.2% and GNAS mutations in 18%, amongst other genes. Discussion: The molecular patterns of UrC and CRC are similar yet distinct. Notably, targeted therapy, especially EGFR-targeting therapy, might provide curative efficacy for patients with UrC by applying specific molecular markers. Additional potential biomarkers for the immunotherapy of UrC are mismatch repair (MMR) status and PD-L1 expression profile. In addition, combined regimens featuring targeted agents and immune checkpoint blockers might increase antitumor activity and exert better efficacy in UrC patients with specific mutational burden.

Application of nanotechnology in reversing therapeutic resistance and controlling metastasis of colorectal cancer

Colorectal cancer (CRC) is the most common digestive malignancy across the world. Its first-line treatments applied in the routine clinical setting include surgery, chemotherapy, radiotherapy, targeted therapy, and immunotherapy. However, resistance to therapy has been identified as the major clinical challenge that fails the treatment method, leading to recurrence and distant metastasis. An increasing number of studies have been attempting to explore the underlying mechanisms of the resistance of CRC cells to different therapies, which can be summarized into two aspects: (1) The intrinsic characters and adapted alterations of CRC cells before and during treatment that regulate the drug metabolism, drug transport, drug target, and the activation of signaling pathways; and (2) the suppressive features of the tumor microenvironment (TME). To combat the issue of therapeutic resistance, effective strategies are warranted with a focus on the restoration of CRC cells’ sensitivity to specific treatments as well as reprogramming impressive TME into stimulatory conditions. To date, nanotechnology seems promising with scope for improvement of drug mobility, treatment efficacy, and reduction of systemic toxicity. The instinctive advantages offered by nanomaterials enable the diversity of loading cargoes to increase drug concentration and targeting specificity, as well as offer a platform for trying the combination of different treatments to eventually prevent tumor recurrence, metastasis, and reversion of therapy resistance. The present review intends to summarize the known mechanisms of CRC resistance to chemotherapy, radiotherapy, immunotherapy, and targeted therapy, as well as the process of metastasis. We have also emphasized the recent application of nanomaterials in combating therapeutic resistance and preventing metastasis either by combining with other treatment approaches or alone. In summary, nanomedicine is an emerging technology with potential for CRC treatment; hence, efforts should be devoted to targeting cancer cells for the restoration of therapeutic sensitivity as well as reprogramming the TME. It is believed that the combined strategy will be beneficial to achieve synergistic outcomes contributing to control and management of CRC in the future.

MicroRNA 483-3p overexpression unleashes invasive growth of metastatic colorectal cancer via NDRG1 downregulation and ensuing activation of the ERBB3/AKT axis

In colorectal cancer, the mechanisms underlying tumor aggressiveness require further elucidation. Taking advantage of a large panel of human metastatic colorectal cancer xenografts and matched stem-like cell cultures (m-colospheres), here we show that the overexpression of microRNA 483-3p (miRNA-483-3p; also known as MIR-483-3p), encoded by a frequently amplified gene locus, confers an aggressive phenotype. In m-colospheres, endogenous or ectopic miRNA-483-3p overexpression increased proliferative response, invasiveness, stem cell frequency, and resistance to differentiation. Transcriptomic analyses and functional validation found that miRNA-483-3p directly targets NDRG1, known as a metastasis suppressor involved in EGFR family downregulation. Mechanistically, miRNA-483-3p overexpression induced the signaling pathway triggered by ERBB3, including AKT and GSK3β, and led to the activation of transcription factors regulating epithelial-mesenchymal transition (EMT). Consistently, treatment with selective anti-ERBB3 antibodies counteracted the invasive growth of miRNA-483-3p-overexpressing m-colospheres. In human colorectal tumors, miRNA-483-3p expression inversely correlated with NDRG1 and directly correlated with EMT transcription factor expression and poor prognosis. These results unveil a previously unrecognized link between miRNA-483-3p, NDRG1, and ERBB3-AKT signaling that can directly support colorectal cancer invasion and is amenable to therapeutic targeting.

Resistance to targeted therapy in metastatic colorectal cancer: Current status and new developments

Colorectal cancer (CRC) is one of the most lethal and common malignancies in the world. Chemotherapy has been the conventional treatment for metastatic CRC (mCRC) patients. However, the effects of chemotherapy have been unsatisfactory. With the advent of targeted therapy, the survival of patients with CRC have been prolonged. Over the past 20 years, targeted therapy for CRC has achieved substantial progress. However, targeted therapy has the same challenge of drug resistance as chemotherapy. Consequently, exploring the resistance mechanism and finding strategies to address the resistance to targeted therapy, along with searching for novel effective regimens, is a constant challenge in the mCRC treatment, and it is also a hot research topic. In this review, we focus on the current status on resistance to existing targeted therapies in mCRC and discuss future developments.

Cancer-associated fibroblasts: The chief architect in the tumor microenvironment

Stromal heterogeneity of tumor microenvironment (TME) plays a crucial role in malignancy and therapeutic resistance. Cancer-associated fibroblasts (CAFs) are one of the major players in tumor stroma. The heterogeneous sources of origin and subsequent impacts of crosstalk with breast cancer cells flaunt serious challenges before current therapies to cure triple-negative breast cancer (TNBC) and other cancers. The positive and reciprocal feedback of CAFs to induce cancer cells dictates their mutual synergy in establishing malignancy. Their substantial role in creating a tumor-promoting niche has reduced the efficacy of several anti-cancer treatments, including radiation, chemotherapy, immunotherapy, and endocrine therapy. Over the years, there has been an emphasis on understanding CAF-induced therapeutic resistance in order to enhance cancer therapy results. CAFs, in the majority of cases, employ crosstalk, stromal management, and other strategies to generate resilience in surrounding tumor cells. This emphasizes the significance of developing novel strategies that target particular tumor-promoting CAF subpopulations, which will improve treatment sensitivity and impede tumor growth. In this review, we discuss the current understanding of the origin and heterogeneity of CAFs, their role in tumor progression, and altering the tumor response to therapeutic agents in breast cancer. In addition, we also discuss the potential and possible approaches for CAF-mediated therapies.

The importance of being CAFs (in cancer resistance to targeted therapies)

In the last two decades, clinical oncology has been revolutionized by the advent of targeted drugs. However, the efficacy of these therapies is significantly limited by primary and acquired resistance, that relies not only on cell-autonomous mechanisms but also on tumor microenvironment cues. Cancer-associated fibroblasts (CAFs) are extremely plastic cells of the tumor microenvironment. They not only produce extracellular matrix components that build up the structure of tumor stroma, but they also release growth factors, chemokines, exosomes, and metabolites that affect all tumor properties, including response to drug treatment. The contribution of CAFs to tumor progression has been deeply investigated and reviewed in several works. However, their role in resistance to anticancer therapies, and in particular to molecular therapies, has been largely overlooked. This review specifically dissects the role of CAFs in driving resistance to targeted therapies and discusses novel CAF targeted therapeutic strategies to improve patient survival.

Interplay Between Chemotherapy-Activated Cancer Associated Fibroblasts and Cancer Initiating Cells Expressing CD44v6 Promotes Colon Cancer Resistance

Cancer-initiating cells (CICs) drive colorectal tumor growth by their supportive niches where CICs interact with multiple cell types within the microenvironment, including cancer-associated fibroblasts (CAFs). We investigated the interplay between the CICs and the clinically relevant chemotherapeutic FOLFOX that creates the persistent tumorigenic properties of colorectal CICs, and stimulates the microenvironmental factors derived from the CAFs. We found that the CICs expressing an immunophenotype (CD44v6[+]) promote FOLFOX-resistance and that the CIC-immunophenotype was enhanced by factors secreted by CAFs after FOLFOX treatment These secreted factors included periostin, IL17A and WNT3A, which induced CD44v6 expression by activating WNT3A/β-catenin signaling. Blocking the interaction between CICs with any of these CAF-derived factors through tissue-specific conditional silencing of CD44v6 significantly reduced colorectal tumorigenic potential. To achieve this, we generated two unique vectors (floxed-pSico-CD44v6 shRNA plus Fabpl-Cre) that were encapsulated into transferrin coated PEG-PEI/(nanoparticles), which when introduced in vivo reduced tumor growth more effectively than using CD44v6-blocking antibodies. Notably, this tissue-specific conditional silencing of CD44v6 resulted in long lasting effects on self-renewal and tumor growth associated with a positive feedback loop linking WNT3A signaling and alternative-splicing of CD44. These findings have crucial clinical implications suggesting that therapeutic approaches for modulating tumor growth that currently focus on cell-autonomous mechanisms may be too limited and need to be broadened to include mechanisms that recognize the interplay between the stromal factors and the subsequent CIC-immunophenotype enrichment. Thus, more specific therapeutic approaches may be required to block a chemotherapy induced remodeling of a microenvironment that acts as a paracrine regulator to enrich CD44v6 (+) in colorectal CICs.

Drug Resistance in Colorectal Cancer: From Mechanism to Clinic

Colorectal cancer (CRC) is one of the leading causes of death worldwide. The 5-year survival rate is 90% for patients with early CRC, 70% for patients with locally advanced CRC, and 15% for patients with metastatic CRC (mCRC). In fact, most CRC patients are at an advanced stage at the time of diagnosis. Although chemotherapy, molecularly targeted therapy and immunotherapy have significantly improved patient survival, some patients are initially insensitive to these drugs or initially sensitive but quickly become insensitive, and the emergence of such primary and secondary drug resistance is a significant clinical challenge. The most direct cause of resistance is the aberrant anti-tumor drug metabolism, transportation or target. With more in-depth research, it is found that cell death pathways, carcinogenic signals, compensation feedback loop signal pathways and tumor immune microenvironment also play essential roles in the drug resistance mechanism. Here, we assess the current major mechanisms of CRC resistance and describe potential therapeutic interventions.

Drug resistance in cancer therapy: the Pandora's Box of cancer stem cells

Drug resistance is the main culprit of failure in cancer therapy that may lead to cancer relapse. This resistance mostly originates from rare, but impactful presence of cancer stem cells (CSCs). Ability to self-renewal and differentiation into heterogeneous cancer cells, and harboring morphologically and phenotypically distinct cells are prominent features of CSCs. Also, CSCs substantially contribute to metastatic dissemination. They possess several mechanisms that help them to survive even after exposure to chemotherapy drugs. Although chemotherapy is able to destroy the bulk of tumor cells, CSCs are left almost intact, and make tumor entity resistant to treatment. Eradication of a tumor mass needs complete removal of tumor cells as well as CSCs. Therefore, it is important to elucidate key features underlying drug resistance raised by CSCs in order to apply effective treatment strategies. However, the challenging point that threatens safety and specificity of chemotherapy is the common characteristics between CSCs and normal peers such as signaling pathways and markers. In the present study, we tried to present a comprehensive appraisal on CSCs, mechanisms of their drug resistance, and recent therapeutic methods targeting this type of noxious cells.

The HER family as therapeutic targets in colorectal cancer

The human epidermal growth factor receptor (HER, ErbB) family has four members, epidermal growth factor receptor (EGFR), HER2, HER3, and HER4. Although distinct in ligands and functions, all of the HER family members are receptor tyrosine kinases playing important roles in the pathogenesis of cancers. In the era of precision medicine, the HER family is one of the most important and successful cancer therapeutic targets, hallmarked by the approval of anti-EGFR therapies for the treatment of colorectal cancer and non-small cell lung cancer, and anti-HER2 therapies for the treatment of breast cancer and gastric cancer. This review briefly discusses how HER family members were discovered, their functions and roles in cancer, and most importantly, the developmental history and recent updates of therapies targeting HER family members, with colorectal cancer as a focus. We also discussed the patient selection and drug resistance to anti-EGFR therapies in the treatment of colorectal cancer.

Cabozantinib with or without Panitumumab for RAS wild-type metastatic colorectal cancer: impact of MET amplification on clinical outcomes and circulating biomarkers

PURPOSE

Acquired resistance to EGFR inhibitors in metastatic colorectal cancer (mCRC) remains a hurdle for effective treatment. MET amplification has been indicated as a driver of acquired resistance. Clinical activity has been demonstrated for the combination of EGFR and MET inhibitors in mCRC. But the impact of this regimen on angiogenesis and inflammation remains largely unknown.

METHODS

In this non-randomized, open-label phase Ib/II study, four patients were treated with cabozantinib alone and 25 patients received the combination of cabozantinib and panitumumab. MET amplification was detected in blood in all four patients treated with cabozantinib monotherapy and 5/25 patients treated with cabozantinib and panitumumab combination therapy. Plasma samples from 28 patients were available for biomarker analysis.

RESULTS

A panel of circulating protein biomarkers was assessed in patient plasma at baseline and on-treatment. Baseline marker levels were analyzed for prognostic value for clinical outcomes, including MET amplification as a covariate. HGF and OPN were prognostic for both progression-free survival (PFS) and overall survival (OS), while six markers (IL-6, VCAM-1, VEGF-R1, TSP-2, TIMP-1, ICAM-1) were prognostic only for OS. In patients with MET amplification, baseline PDGF-AA, PDGF-BB, TGF-β1, and VEGF-C levels were significantly higher, whereas baseline TGFβ-R3 levels were significantly lower than MET non-amplified patients. On-treatment change of four markers (CD73, PlGF, PDGF-BB, VEGF) were significantly different between MET amplified and non-amplified subpopulations.

CONCLUSION

This study identified circulating HGF and several inflammatory and angiogenic proteins as prognostic biomarkers. Furthermore, MET amplification status is associated with both baseline expression and on-treatment modulation of members of angiogenesis and TGF-β pathway proteins.

CLINICAL TRIALS REGISTRATION NUMBER

ClinicalTrials.gov identifier: NCT02008383.

Improving therapeutic resistance: beginning with targeting the tumor microenvironment

Cancer is a serious threat to human health and life. The tumor microenvironment (TME) not only plays a key role in the occurrence, development and metastasis of cancer, but also has a profound impact on treatment resistance. To improve and solve this problem, an increasing number of strategies targeting the TME have been proposed, and great progress has been made in recent years. This article reviews the characteristics and functions of the main matrix components of the TME and the mechanisms by which each component affects drug resistance. Furthermore, this article elaborates on targeting the TME as a strategy to treat acquired drug resistance, reduce tumor metastasis, recurrence, and improve efficacy.

FACT-seq: profiling histone modifications in formalin-fixed paraffin-embedded samples with low cell numbers

The majority of biopsies in both basic research and translational cancer studies are preserved in the format of archived formalin-fixed paraffin-embedded (FFPE) samples. Profiling histone modifications in archived FFPE tissues is critically important to understand gene regulation in human disease. The required input for current genome-wide histone modification profiling studies from FFPE samples is either 10-20 tissue sections or whole tissue blocks, which prevents better resolved analyses. But it is desirable to consume a minimal amount of FFPE tissue sections in the analysis as clinical tissues of interest are limited. Here, we present FFPE tissue with antibody-guided chromatin tagmentation with sequencing (FACT-seq), the first highly sensitive method to efficiently profile histone modifications in FFPE tissues by combining a novel fusion protein of hyperactive Tn5 transposase and protein A (T7-pA-Tn5) transposition and T7 in vitro transcription. FACT-seq generates high-quality chromatin profiles from different histone modifications with low number of FFPE nuclei. We proved a very small piece of FFPE tissue section containing ∼4000 nuclei is sufficient to decode H3K27ac modifications with FACT-seq. H3K27ac FACT-seq revealed disease-specific super enhancers in the archived FFPE human colorectal and human glioblastoma cancer tissue. In summary, FACT-seq allows decoding the histone modifications in archival FFPE tissues with high sensitivity and help researchers to better understand epigenetic regulation in cancer and human disease.

Cetuximab resistance induced by hepatocyte growth factor is overcome by MET inhibition in KRAS, NRAS, and BRAF wild-type colorectal cancers

PURPOSE

Recent evidence has highlighted the role of hepatocyte growth factor (HGF) as a putative biomarker to predict EGFR inhibitor resistance. This study investigated the impact of plasma HGF levels on EGFR inhibition and the counter effect of MET inhibition in KRAS, NRAS, and BRAF (RAS/RAF) wild-type colorectal cancers (CRCs).

METHODS

Plasma HGF levels were analyzed with clinical outcomes of patients with metastatic CRC (mCRC) receiving palliative first-line chemotherapy. Then, in vitro experiments were conducted to validate the clinical findings and to establish pre-clinical evidence of MET inhibition by capmatinib.

RESULTS

A total of 80 patients were included: cetuximab + FOLFIRI (n = 35) and bevacizumab + FOLFIRI (n = 45). Both progression-free survival (PFS) and overall survival (OS) were significantly lesser in the high vs low HGF group: median 11.8 vs. 24.7 months, respectively, for PFS (p = 0.009), and median 21.1 months vs. not reached, respectively, for OS (p = 0.018). The difference was significantly evident in the cetuximab group. In five RAS/RAF wild-type CRC cells, the addition of HGF activated ERK1/2 and AKT via MET phosphorylation, resulting in cetuximab resistance in vitro. In cetuximab-sensitive Caco-2 and SNU-C4 cells, capmatinib overcame cetuximab resistance in the presence of HGF by attenuating HGF-induced MET signaling activation.

CONCLUSION

Patients with mCRC receiving cetuximab + FOLFIRI who presented with high plasma HGF levels had significantly worse PFS and OS. Cetuximab resistance induced by HGF was mediated by AKT and ERK activation and overcome by MET inhibition in vitro.

Resistance to anti-EGFR therapies in metastatic colorectal cancer: underlying mechanisms and reversal strategies

Cetuximab and panitumumab are monoclonal antibodies (mAbs) against epidermal growth factor receptor (EGFR) that are effective agents for metastatic colorectal cancer (mCRC). Cetuximab can prolong survival by 8.2 months in RAS wild-type (WT) mCRC patients. Unfortunately, resistance to targeted therapy impairs clinical use and efficiency. The mechanisms of resistance refer to intrinsic and extrinsic alterations of tumours. Multiple therapeutic strategies have been investigated extensively to overcome resistance to anti-EGFR mAbs. The intrinsic mechanisms include EGFR ligand overexpression, EGFR alteration, RAS/RAF/PI3K gene mutations, ERBB2/MET/IGF-1R activation, metabolic remodelling, microsatellite instability and autophagy. For intrinsic mechanisms, therapies mainly cover the following: new EGFR-targeted inhibitors, a combination of multitargeted inhibitors, and metabolic regulators. In addition, new cytotoxic drugs and small molecule compounds increase the efficiency of cetuximab. Extrinsic alterations mainly disrupt the tumour microenvironment, specifically immune cells, cancer-associated fibroblasts (CAFs) and angiogenesis. The directions include the modification or activation of immune cells and suppression of CAFs and anti-VEGFR agents. In this review, we focus on the mechanisms of resistance to anti-EGFR monoclonal antibodies (anti-EGFR mAbs) and discuss diverse approaches to reverse resistance to this therapy in hopes of identifying more mCRC treatment possibilities.

Comprehensive analysis of partial methylation domains in colorectal cancer based on single-cell methylation profiles

Epigenetic aberrations have played a significant role in affecting the pathophysiological state of colorectal cancer, and global DNA hypomethylation mainly occurs in partial methylation domains (PMDs). However, the distribution of PMDs in individual cells and the heterogeneity between cells are still unclear. In this study, the DNA methylation profiles of colorectal cancer detected by WGBS and scBS-seq were used to depict PMDs in individual cells for the first time. We found that more than half of the entire genome is covered by PMDs. Three subclasses of PMDS have distinct characteristics, and Gain-PMDs cover a higher proportion of protein coding genes. Gain-PMDs have extensive epigenetic heterogeneity between different cells of the same tumor, and the DNA methylation in cells is affected by the tumor microenvironment. In addition, abnormally elevated promoter methylation in Gain-PMDs may further promote the growth, proliferation and metastasis of tumor cells through silent transcription. The PMDs detected in this study have the potential as epigenetic biomarkers and provide a new insight for colorectal cancer research based on single-cell methylation data.

Insulin-Like Growth Factor 2 mRNA-Binding Protein 1 (IGF2BP1) Is a Prognostic Biomarker and Associated with Chemotherapy Responsiveness in Colorectal Cancer

Insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) is an RNA-binding protein and serves as a post-transcriptional fine-tuner regulating the expression of mRNA targets. However, the clinicopathological roles of IGF2BP1 in colorectal cancer (CRC) remains limited. Thus, we aimed to elucidate the clinical significance and biomarker potentials of IGF2BP1 in CRC. A total of 266 specimens from two sets of CRC patients were collected. IGF2BP1 expression was studied by immunohistochemical (IHC) staining. The Kaplan-Meier survival plot and a log-rank test were used for survival analysis. The Cox proportional hazards model was applied to determine the survival impact of IGF2BP1. Public datasets sets from The Cancer Genome Atlas (TCGA) and Human Cancer Metastasis Database (HCMDB), receiver operating characteristic (ROC) plotter, and two CRC cell lines, HCT-116 and DLD-1, were used for validating our findings. We showed that IGF2BP1 was overexpressed in tumor specimens compared to 13 paired normal parts by examining the immunoreactivity of IGF2BP1 (p = 0.045). The increased expression of IGF2BP1 in primary tumor parts was observed regardless of metastatic status (p < 0.001) in HCMDB analysis. IGF2BP1 expression was significantly associated with young age (59.6% vs. 46.7%, p-value = 0.043) and advanced stage (61.3% vs. 40.0%, p-value = 0.001). After controlling for confounding factors, IGF2BP1 remained an independent prognostic factor (HR = 1.705, p-value = 0.005). TCGA datasets analysis indicated that high IGF2BP1 expression showed a lower 5-year survival rate (58% vs. 65%) in CRC patients. The increased expression of IGF2BP1 in chemotherapy non-responder rectal cancer patients was observed using a ROC plotter. Overexpression of IGF2BP1 promoted the colony-forming capacity and 5-fluorouracil and etoposide resistance in CRC cells. Here, IGF2BP1 was an independent poor prognostic marker in CRC patients and contributed to aggressive phenotypes in CRC cell lines.

Long noncoding RNA SH3PXD2A-AS1 promotes colorectal cancer progression by regulating p53-mediated gene transcription

Long non-coding RNAs (lncRNAs) play key roles in various human cancers. We aimed to determine the key lncRNAs mediating colorectal cancer (CRC) progression. We identified some lncRNAs aberrantly expressed in CRC tissues by using lncRNA microarrays and demonstrated that SH3PXD2A-AS1 was one of the most highly overexpressed lncRNAs in CRC. We further aimed to explore the roles and possible molecular mechanisms of SH3PXD2A-AS1 in CRC. RNA ISH revealed that SH3PXD2A-AS1 was overexpressed in CRC compared with adjacent normal colon tissues and indicated poor prognosis in CRC. Functional analyses showed that SH3PXD2A-AS1 enhanced cell proliferation, angiogenesis, and metastasis. Mechanistically, SH3PXD2A-AS1 can directly interact with p53 protein and regulate p53-mediated gene transcription in CRC. We provided mechanistic insights into the regulation of SH3PXD2A-AS1 on p53-mediated gene transcription and suggested its potential as a new prognostic biomarker and target for the clinical management of CRC.

Cancer of unknown primary stem-like cells model multi-organ metastasis and unveil liability to MEK inhibition

Cancers of unknown primary (CUPs), featuring metastatic dissemination in the absence of a primary tumor, are a biological enigma and a fatal disease. We propose that CUPs are a distinct, yet unrecognized, pathological entity originating from stem-like cells endowed with peculiar and shared properties. These cells can be isolated in vitro (agnospheres) and propagated in vivo by serial transplantation, displaying high tumorigenicity. After subcutaneous engraftment, agnospheres recapitulate the CUP phenotype, by spontaneously and quickly disseminating, and forming widespread established metastases. Regardless of different genetic backgrounds, agnospheres invariably display cell-autonomous proliferation and self-renewal, mostly relying on unrestrained activation of the MAP kinase/MYC axis, which confers sensitivity to MEK inhibitors in vitro and in vivo. Such sensitivity is associated with a transcriptomic signature predicting that more than 70% of CUP patients could be eligible to MEK inhibition. These data shed light on CUP biology and unveil an opportunity for therapeutic intervention.

Cancer of unknown primary (CUP) is a mysterious malignancy featuring metastatic dissemination in the absence of a recognizable primary tumor. By characterizing CUP cancer stem cells we show that self-sustained long-term propagation and sensitivity to MEK inhibition are CUP common features.

Clinical Implications of Colorectal Cancer Stem Cells in the Age of Single-Cell Omics and Targeted Therapies

The cancer stem cell (CSC) concept emerged from the recognition of inherent tumor heterogeneity and suggests that within a given tumor, in analogy to normal tissues, there exists a cellular hierarchy composed of a minority of more primitive cells with enhanced longevity (ie, CSCs) that give rise to shorter-lived, more differentiated cells (ie, cancer bulk populations), which on their own are not capable of tumor perpetuation. CSCs can be responsible for cancer therapeutic resistance to conventional, targeted, and immunotherapeutic treatment modalities, and for cancer progression through CSC-intrinsic molecular mechanisms. The existence of CSCs in colorectal cancer (CRC) was first established through demonstration of enhanced clonogenicity and tumor-forming capacity of this cell subset in human-to-mouse tumor xenotransplantation experiments and subsequently confirmed through lineage-tracing studies in mice. Surface markers for CRC CSC identification and their prospective isolation are now established. Therefore, the application of single-cell omics technologies to CSC characterization, including whole-genome sequencing, RNA sequencing, and epigenetic analyses, opens unprecedented opportunities to discover novel targetable molecular pathways and hence to develop novel strategies for CRC eradication. We review recent advances in this field and discuss the potential implications of next-generation CSC analyses for currently approved and experimental targeted CRC therapies.

Germ line polymorphisms of genes involved in pluripotency transcription factors predict efficacy of cetuximab in metastatic colorectal cancer

BACKGROUND

Cancer stem cells (CSCs) are primarily maintained by a network of pluripotency transcription factors (PTFs). Given a close relationship of CSC regulation with epidermal growth factor receptor and vascular endothelial growth factor signalling, we investigated whether single-nucleotide polymorphisms (SNPs) in PTF genes are related to the efficacy of cetuximab and/or bevacizumab in patients with metastatic colorectal cancer (mCRC).

PATIENTS AND METHODS

Genomic and clinical data from three independent clinical trial cohorts were tested: cetuximab cohort (FOLFIRI/cetuximab arm in FIRE-3, n = 129), bevacizumab cohort 1 (FOLFIRI/bevacizumab arm in FIRE-3, n = 107) and bevacizumab cohort 2 (FOLFIRI/bevacizumab arm in TRIBE, n = 215). Genomic DNA extracted from blood samples was genotyped, and ten SNPs were tested for association with clinical outcomes.

RESULTS

In the cetuximab cohort, four SNPs were significantly associated with progression-free survival in univariate analysis: NANOG rs11055767 (any A allele vs C/C, hazard ratio [HR] = 0.62, 95% confidence interval [CI] = 0.42-0.94, p = 0.02), NANOG rs10744044 (any A allele vs G/G, HR = 0.59, 95% CI = 0.39-0.90, p = 0.01), NANOGP8 rs2168958 (any C allele vs A/A, HR = 2.12, 95% CI = 1.36-3.29, p < 0.001) and NANOGP8 rs2279066 (any C allele vs T/T, HR = 1.80, 95% CI = 1.06-1.68, p = 0.03). Multivariate analysis confirmed the significant associations for NANOGP8 rs2168958 and NANOGP8 rs2279066. In either bevacizumab cohort, no significant associations were observed in univariate analysis.

CONCLUSIONS

Germ line polymorphisms in the PTF genes could be predictive markers for cetuximab in mCRC.

Cancer-Associated Fibroblast-Induced Resistance to Chemotherapy and Radiotherapy in Gastrointestinal Cancers

In the past few decades, the role of cancer-associated fibroblasts (CAFs) in resistance to therapies for gastrointestinal (GI) cancers has emerged. Clinical studies focusing on GI cancers have revealed that the high expression of CAF-related molecules within tumors is significantly correlated with unfavorable therapeutic outcomes; however, the exact mechanisms whereby CAFs enhance resistance to chemotherapy and radiotherapy in GI cancers remain unclear. The cells of origin of CAFs in GI cancers include normal resident fibroblasts, mesenchymal stem cells, endothelial cells, pericytes, and even epithelial cells. CAFs accumulated within GI cancers produce cytokines, chemokines, and growth factors involved in resistance to therapies. CAF-derived exosomes can be engaged in stroma-related resistance to treatments, and several non-coding RNAs, such as miR-92a, miR-106b, CCAL, and H19, are present in CAF-derived exosomes and transferred to GI cancer cells. The CAF-induced desmoplastic reaction interferes with drug delivery to GI cancer cells, evoking resistance to chemotherapy. However, due to the heterogeneity of CAFs in GI cancers, identifying the exact mechanism underlying CAF-induced resistance may be difficult. Recent advancements in single-cell "omics" technologies could offer clues for revealing the specific subtypes and biomarkers related to resistance.

Adaptive Mechanisms of Tumor Therapy Resistance Driven by Tumor Microenvironment

Cancer is a disease which frequently has a poor prognosis. Although multiple therapeutic strategies have been developed for various cancers, including chemotherapy, radiotherapy, and immunotherapy, resistance to these treatments frequently impedes the clinical outcomes. Besides the active resistance driven by genetic and epigenetic alterations in tumor cells, the tumor microenvironment (TME) has also been reported to be a crucial regulator in tumorigenesis, progression, and resistance. Here, we propose that the adaptive mechanisms of tumor resistance are closely connected with the TME rather than depending on non-cell-autonomous changes in response to clinical treatment. Although the comprehensive understanding of adaptive mechanisms driven by the TME need further investigation to fully elucidate the mechanisms of tumor therapeutic resistance, many clinical treatments targeting the TME have been successful. In this review, we report on recent advances concerning the molecular events and important factors involved in the TME, particularly focusing on the contributions of the TME to adaptive resistance, and provide insights into potential therapeutic methods or translational medicine targeting the TME to overcome resistance to therapy in clinical treatment.

Research advances of secretory proteins in malignant tumors

Secretory proteins in tumor tissues are important components of the tumor microenvironment. Secretory proteins act on tumor cells or stromal cells or mediate interactions between tumor cells and stromal cells, thereby affecting tumor progression and clinical treatment efficacy. In this paper, recent research advances in secretory proteins in malignant tumors are reviewed.

A receptor-antibody hybrid hampering MET-driven metastatic spread

Background

The receptor encoded by the MET oncogene and its ligand Hepatocyte Growth Factor (HGF) are at the core of the invasive-metastatic behavior. In a number of instances genetic alterations result in ligand-independent onset of malignancy (MET addiction). More frequently, ligand stimulation of wild-type MET contributes to progression toward metastasis (MET expedience). Thus, while MET inhibitors alone are effective in the first case, combination therapy with ligand inhibitors is required in the second condition.

Methods

In this paper, we generated hybrid molecules gathering HGF and MET inhibitory properties. This has been achieved by ‘head-to-tail’ or ‘tail-to-head’ fusion of a single chain Fab derived from the DN30 MET antibody with a recombinant ‘ad-hoc’ engineered MET extracellular domain (decoyMET), encompassing the HGF binding site but lacking the DN30 epitope.

Results

The hybrid molecules correctly bind MET and HGF, inhibit HGF-induced MET downstream signaling, and quench HGF-driven biological responses, such as growth, motility and invasion, in cancer cells of different origin. Two metastatic models were generated in mice knocked-in by the human HGF gene: (i) orthotopic transplantation of pancreatic cancer cells; (ii) subcutaneous injection of primary cells derived from a cancer of unknown primary. Treatment with hybrid molecules strongly affects time of onset, number, and size of metastatic lesions.

Conclusion

These results provide a strategy to treat metastatic dissemination driven by the HGF/MET axis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01822-5.

Mapping a Circular RNA-microRNA-mRNA-Signaling Regulatory Axis That Modulates Stemness Properties of Cancer Stem Cell Populations in Colorectal Cancer Spheroid Cells

Spheroidal cancer cell cultures have been used to enrich cancer stem cells (CSC), which are thought to contribute to important clinical features of tumors. This study aimed to map the regulatory networks driven by circular RNAs (circRNAs) in CSC-enriched colorectal cancer (CRC) spheroid cells. The spheroid cells established from two CRC cell lines acquired stemness properties in pluripotency gene expression and multi-lineage differentiation capacity. Genome-wide sequencing identified 1503 and 636 circRNAs specific to the CRC parental and spheroid cells, respectively. In the CRC spheroids, algorithmic analyses unveiled a core network of mRNAs involved in modulating stemness-associated signaling pathways, driven by a circRNA–microRNA (miRNA)–mRNA axis. The two major circRNAs, hsa_circ_0066631 and hsa_circ_0082096, in this network were significantly up-regulated in expression levels in the spheroid cells. The two circRNAs were predicted to target and were experimentally shown to down-regulate miR-140-3p, miR-224, miR-382, miR-548c-3p and miR-579, confirming circRNA sponging of the targeted miRNAs. Furthermore, the affected miRNAs were demonstrated to inhibit degradation of six mRNA targets, viz. ACVR1C/ALK7, FZD3, IL6ST/GP130, SKIL/SNON, SMAD2 and WNT5, in the CRC spheroid cells. These mRNAs encode proteins that are reported to variously regulate the GP130/Stat, Activin/Nodal, TGF-β/SMAD or Wnt/β-catenin signaling pathways in controlling various aspects of CSC stemness. Using the CRC spheroid cell model, the novel circRNA–miRNA–mRNA axis mapped in this work forms the foundation for the elucidation of the molecular mechanisms of the complex cellular and biochemical processes that determine CSC stemness properties of cancer cells, and possibly for designing therapeutic strategies for CRC treatment by targeting CSC.

cIRCR201-dPBD, a Novel Pyrrolobenzodiazepine Dimer-Containing Site-Specific Antibody-Drug Conjugate Targeting c-Met Overexpression Tumors

c-Met, as a receptor expressed on the cell membrane, contributes to the growth and metastasis of tumors, as well as angiogenesis, mainly through the hepatocyte growth factor (HGF)/c-Met axis during tumor progression. Although several c-Met inhibitors, including small molecules and monoclonal antibody inhibitors, are currently being investigated, their clinical outcomes have not been promising. Development of an antibody-drug conjugate (ADC) against c-Met could be an attractive therapeutic strategy that would provide superior antitumor efficacy with broad-spectrum c-Met expression levels. In the present study, site-specific drug-conjugate technology was applied to develop an ADC using the human-mouse cross-reactive c-Met antibody and a prodrug pyrrolobenzodiazepine (PBD). The toxin payload was uniformly conjugated to the light-chain C-terminus of the native cIRCR201 antibody (drug-to-antibody ratio = 2), as confirmed using LC-MS. Using a high-throughput screening system, we found that cIRCR201-dPBD exhibited varying sensitivities depending on the expression levels of c-Met, and it induced receptor-mediated endocytosis and toxin-mediated apoptosis in 47 different cancer cell lines. cIRCR201-dPBD also showed significant antitumor activity on the MET-amplified cancer cells using in vivo xenograft models. Therefore, cIRCR201-dPBD could be a promising therapeutic strategy for tumors with c-Met expression.

Hepatocyte growth factor/MET and CD44 in colorectal cancer: partners in tumorigenesis and therapy resistance

Intestinal epithelial self-renewal is a tightly controlled process, which is critically dependent on WNT signalling. Aberrant activation of the WNT pathway in intestinal stem cells (ISCs) results in constitutive transcription of target genes, which collectively drive malignant transformation in colorectal cancer (CRC). However, the contribution of individual genes to intestinal homeostasis and tumorigenesis often is incompletely defined. Here, we discuss converging evidence indicating that the receptor tyrosine kinase (RTK) MET and its ligand hepatocyte growth factor (HGF) play a major role in the intestinal damage response, as well as in intestinal tumorigenesis, by controlling the proliferation, survival, motility, and stemness of normal and neoplastic intestinal epithelial cells. These activities of MET are promoted by specific CD44 isoforms expressed by ISCs. The accrued data indicate that MET and the EGFR have overlapping roles in the biology of intestinal epithelium and that metastatic CRCs can exploit this redundancy to escape from EGFR-targeted treatments, co-opting HGF/MET/CD44v signalling. Hence, targeting both pathways may be required for effective treatment of (a subset of) CRCs. The RTK identity of MET, the distinctive 'plasminogen-like' structure and activation mode of its ligand HGF, and the specific collaboration of MET with CD44, provide several unique targeting options, which merit further exploration.

Cancer associated fibroblast mediated chemoresistance: A paradigm shift in understanding the mechanism of tumor progression

One of the undeniable issues with cancer eradication is the evolution of chemoresistance in due course of treatment, and the mechanisms of chemoresistance have been the subject of extensive research for several years. The efficacy of chemotherapy is hindered by cancer epithelium, mostly in a cell-autonomous mechanism. However, recently the valid experimental evidence showed that the surrounding tumor microenvironment (TME) is equivalently responsible for the induction of chemoresistance. Of the verities of cells in the tumor microenvironment, cancer-associated fibroblasts (CAFs) are the major cellular component of TME and act as a key regulator in the acquisition of cancer chemoresistance by providing a protective niche to the cancer cells against the anti-cancer drugs. Moreover, the symbiotic relationship between the tumor and CAFs to obtain key resources such as growth factors and nutrients for optimal tumor growth and proliferation favors the chemoresistance phenotype. Here, in this review, we provide an up-to-date overview of our knowledge of the role of the CAFs in inducing chemoresistance and tumor progression. We also further delineated the emerging events leading to the CAF origins and activation of normal fibroblasts to CAFs. Along with this, we also discuss the novel area of research confined to the CAF targeted therapies of cancer. The identification of CAF-specific markers may allow unveiling new targets and avenues for blunting or reverting the detrimental pro-tumorigenic potential of CAFs in the foreseeable future.

Colorectal cancer residual disease at maximal response to EGFR blockade displays a druggable Paneth cell-like phenotype

Blockade of epidermal growth factor receptor (EGFR) causes tumor regression in some patients with metastatic colorectal cancer (mCRC). However, residual disease reservoirs typically remain even after maximal response to therapy, leading to relapse. Using patient-derived xenografts (PDXs), we observed that mCRC cells surviving EGFR inhibition exhibited gene expression patterns similar to those of a quiescent subpopulation of normal intestinal secretory precursors with Paneth cell characteristics. Compared with untreated tumors, these pseudodifferentiated tumor remnants had reduced expression of genes encoding EGFR-activating ligands, enhanced activity of human epidermal growth factor receptor 2 (HER2) and HER3, and persistent signaling along the phosphatidylinositol 3-kinase (PI3K) pathway. Clinically, properties of residual disease cells from the PDX models were detected in lingering tumors of responsive patients and in tumors of individuals who had experienced early recurrence. Mechanistically, residual tumor reprogramming after EGFR neutralization was mediated by inactivation of Yes-associated protein (YAP), a master regulator of intestinal epithelium recovery from injury. In preclinical trials, Pan-HER antibodies minimized residual disease, blunted PI3K signaling, and induced long-term tumor control after treatment discontinuation. We found that tolerance to EGFR inhibition is characterized by inactivation of an intrinsic lineage program that drives both regenerative signaling during intestinal repair and EGFR-dependent tumorigenesis. Thus, our results shed light on CRC lineage plasticity as an adaptive escape mechanism from EGFR-targeted therapy and suggest opportunities to preemptively target residual disease.

Anti-EGFR therapy in metastatic colorectal cancer: mechanisms and potential regimens of drug resistance

Cetuximab and panitumumab, as the highly effective antibodies targeting epidermal growth factor receptor (EGFR), have clinical activity in the patients with metastatic colorectal cancer (mCRC). These agents have good curative efficacy, but drug resistance also exists at the same time. The effects of KRAS, NRAS, and BRAF mutations and HER2 amplification on the treatment of refractory mCRC have been elucidated and the corresponding countermeasures have been put forward. However, the changes in EGFR and its ligands, the mutations or amplifications of PIK3CA, PTEN, TP53, MET, HER3, IRS2, FGFR1, and MAP2K1, the overexpression of insulin growth factor-1, the low expression of Bcl-2-interacting mediator of cell death, mismatch repair-deficient, and epigenetic instability may also lead to drug resistance in mCRC. Although the emergence of drug resistance has genetic or epigenetic heterogeneity, most of these molecular changes relating to it are focused on the key signaling pathways, such as the RAS/RAF/mitogen-activated protein kinase or phosphatidylinositol 3-kinase/Akt/mammalian target of the rapamycin pathway. Accordingly, numerous efforts to target these signaling pathways and develop the novel therapeutic regimens have been carried out. Herein, we have reviewed the underlying mechanisms of the resistance to anti-EGFR therapy and the possible implications in clinical practice.

Structural and Functional Insight Into the Glycosylation Impact Upon the HGF/c-Met Signaling Pathway

Upon interactions with its specific ligand hepatocyte growth factor (HGF), the c-Met signal is relayed to series of downstream pathways, exerting essential biological roles. Dysregulation of the HGF-c-Met signaling pathway has been implicated in the onset, progression and metastasis of various cancers, making the HGF-c-Met axis a promising therapeutic target. Both c-Met and HGF undergo glycosylation, which appears to be biologically relevant to their function and structural integrity. Different types of glycoconjugates in the local cellular environment can also regulate HGF/c-Met signaling by distinct mechanisms. However, detailed knowledge pertaining to the glycosylation machinery of the HGF-c-Met axis as well as its potential applications in oncology research is yet to be established. This mini review highlights the significance of the HGF-c-Met signaling pathway in physiological and pathological context, and discusses the molecular mechanisms by which affect the glycosylation of the HGF-c-Met axis. Owing to the crucial role played by glycosylation in the regulation of HGF/c-Met activity, better understanding of this less exploited field may contribute to the development of novel therapeutics targeting glycoepitopes.

BRAF and KRAS mutations in metastatic colorectal cancer: future perspectives for personalized therapy

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers worldwide and 30% of patients with CRC experience metastasis. Patients with metastatic colorectal cancer (mCRC) have a 5-year overall survival rate of <10%. V-raf murine sarcoma viral oncogene homolog B1 (BRAF) and V-Ki-ras2 Kirsten ratsarcoma viral oncogene homolog (KRAS) mutations are mostly studied in mCRC, as clinical trials found that first-line chemotherapy with anti-epidermal growth factor receptor agent confers limited efficacy for mCRC. Treatment decisions for early-stage mCRC do not consider BRAF or KRAS mutations, given the dramatically poor prognosis conferred by these mutations in clinical trials. Thus, it is necessary to identify patients with mCRC harboring BRAF or KRAS mutations to formulate rational therapeutic strategies to improve prognosis and survival. BRAF and KRAS mutations occur in ∼10% and ∼44% of patients with mCRC, respectively. Although the survival rate of patients with mCRC has improved in recent years, the response and prognosis of patients with the aforementioned mutations are still poor. There is a substantial unmet need for prospective personalized therapies for patients with BRAF- or KRAS-mutant mCRC. In this review, we focus on BRAF and KRAS mutations to understand the mechanisms underlying resistance and improving the response rate, outcomes, and prognosis of patients with mCRC bearing these mutations and to discuss prospective personalized therapies for BRAF- and KRAS-mutant mCRC.

The Roles of Cancer Stem Cells and Therapy Resistance in Colorectal Carcinoma

Cancer stem cells (CSCs) are the main culprits involved in therapy resistance and disease recurrence in colorectal carcinoma (CRC). Results using cell culture, animal models and tissues from patients with CRC suggest the indispensable roles of colorectal CSCs in therapeutic failure. Conventional therapies target proliferating and mature cancer cells, while CSCs are mostly quiescent and poorly differentiated, thereby they can easily survive chemotherapeutic insults. The aberrant activation of Wnt/β-catenin, Notch, Hedgehog, Hippo/YAP (Yes-associated protein) and phosphatidylinositol 3-kinase/protein kinase B facilitates CSCs with excessive self-renewal and therapy resistance property in CRC. CSCs survive the chemo-radiotherapies by escaping therapy mediated DNA damage via altering the cell cycle checkpoints, increasing DNA damage repair capacity and by an efficient scavenging of reactive oxygen species. Furthermore, dysregulations of miRNAs e.g., miR-21, miR-93, miR-203, miR-215, miR-497 etc., modulate the therapeutic sensitivity of colorectal CSCs by regulating growth and survival signalling. In addition, a reversible quiescent G₀ state and the re-entering cell cycle capacity of colorectal CSCs can accelerate tumour regeneration after treatment. Moreover, switching to favourable metabolic signatures during a therapeutic regimen will add more complexity in therapeutic outcomes against CSCs. Therapeutic strategies targeting these underlying mechanisms of CSCs’ therapy resistance could provide a promising outcome, however, deep understanding and concerted research are necessary to design novel therapies targeting CSCs. To conclude, the understanding of these mechanisms of CSC in CRC could lead to the improved management of patients with CRC.

A phase 1b study of the MET inhibitor capmatinib combined with cetuximab in patients with MET-positive colorectal cancer who had progressed following anti-EGFR monoclonal antibody treatment

Background Overcoming resistance to anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (mAbs) in patients with KRAS wildtype (WT) metastatic colorectal cancer (mCRC) could help meet the needs of patients with limited treatment options. Methods In this phase 1b study, patients with N/KRAS WT, MET-positive mCRC who had progressed following anti-EGFR mAb treatment received escalating oral doses of capmatinib (150, 300, and 400 mg) twice daily plus weekly intravenous cetuximab (at the approved dose). The primary objective was to establish a recommended dose for expansion (RDE) of capmatinib in combination with cetuximab. Safety, preliminary activity, pharmacokinetics, and pharmacodynamics were also explored. Results Thirteen patients were enrolled. No patients experienced a dose-limiting toxicity at investigated doses; the RDE was established as capmatinib 400 mg twice daily plus cetuximab. All patients experienced adverse events (AEs) suspected to be related to the study treatment. Five patients (38.5%) reported study-drug-related AEs of grade 3/4 in severity. No patients achieved a complete or partial response according to RECIST v1.1; however, tumor shrinkage of 29-44% was observed in 4 patients. Conclusions Capmatinib plus cetuximab was well tolerated. Preliminary signs of activity were observed. Further investigation is warranted to obtain efficacy data and refine predictive biomarkers of response. Clinical trial registration NCT02205398.

Comprehensive review of targeted therapy for colorectal cancer

Colorectal cancer (CRC) is among the most lethal and prevalent malignancies in the world and was responsible for nearly 881,000 cancer-related deaths in 2018. Surgery and chemotherapy have long been the first choices for cancer patients. However, the prognosis of CRC has never been satisfying, especially for patients with metastatic lesions. Targeted therapy is a new optional approach that has successfully prolonged overall survival for CRC patients. Following successes with the anti-EGFR (epidermal growth factor receptor) agent cetuximab and the anti-angiogenesis agent bevacizumab, new agents blocking different critical pathways as well as immune checkpoints are emerging at an unprecedented rate. Guidelines worldwide are currently updating the recommended targeted drugs on the basis of the increasing number of high-quality clinical trials. This review provides an overview of existing CRC-targeted agents and their underlying mechanisms, as well as a discussion of their limitations and future trends.

MET inhibitors in cancer: pitfalls and challenges

Introduction: The HGF/MET axis is a key therapeutic pathway in cancer; it is aberrantly activated because of mutations, fusions, amplification or aberrant ligand production. Extensive efforts have been made to discover predictive factors of anti-MET therapeutic efficacy, but they have mostly unsuccessful. An understanding of the intrinsic and acquired mechanism of MET resistance will be fundamental for the development of new therapeutic interventions.Areas covered: This article provides a systematic review of phase II randomized and phase III clinical trials investigating the use of MET inhibitors in the treatment of cancer. We discuss preliminary findings on efficacy and methodologic design flaws in these trials.Expert opinion: MET inhibitors showed poor activity in unselected patients or patients selected by MET expression, p-MET or high HGF basal levels. The efficacy in advanced solid tumors is very modest and in phase III clinical trials, survival differences did not fulfill the stringent requirements of ESMO-Magnitude Clinical Benefit Score (MCBS). Prospective novel liquid biomarker-driven studies and novel trial designs such as Umbrella and Basket trials are necessary to progress MET inhibitor development.

The notch target gene HEYL modulates metastasis forming capacity of colorectal cancer patient-derived spheroid cells in vivo

BACKGROUND

While colorectal cancer (CRC) patients with localized disease have a favorable prognosis, the five-year-survival rate in patients with distant spread is still below 15%. Hence, a detailed understanding of the mechanisms regulating metastasis formation is essential to develop therapeutic strategies targeting metastasized CRC. The notch pathway has been shown to be involved in the metastatic spread of various tumor entities; however, the impact of its target gene HEYL remains unclear so far.

METHODS

In this study, we functionally assessed the association between high HEYL expression and metastasis formation in human CRC. Therefore, we lentivirally overexpressed HEYL in two human patient-derived CRC cultures differing in their spontaneous metastasizing capacity and analyzed metastasis formation as well as tumor cell dissemination into the bone marrow after xenotransplantation into NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (NSG) mice.

RESULTS

HEYL overexpression decreased tumor cell dissemination and the absolute numbers of formed metastases in a sub-renal capsular spontaneous metastasis formation model, addressing all steps of the metastatic cascade. In contrast, metastatic capacity was not decreased following intrasplenic xenotransplantation where the cells are placed directly into the blood circulation.

CONCLUSION

These results suggest that HEYL negatively regulates metastasis formation in vivo presumably by inhibiting intravasation of metastasis-initiating cells.

Linking stemness with colorectal cancer initiation, progression, and therapy

The discovery of cancer stem cells caused a paradigm shift in the concepts of origin and development of colorectal cancer. Several unresolved questions remain in this field though. Are colorectal cancer stem cells the cause or an effect of the disease? How do cancer stem cells assist in colorectal tumor dissemination to distant organs? What are the molecular or environmental factors affecting the roles of these cells in colorectal cancer? Through this review, we investigate the key findings until now and attempt to elucidate the origins, physical properties, microenvironmental niches, as well as the molecular signaling network that support the existence, self-renewal, plasticity, quiescence, and the overall maintenance of cancer stem cells in colorectal cancer. Increasing data show that the cancer stem cells play a crucial role not only in the establishment of the primary colorectal tumor but also in the distant spread of the disease. Hence, we will also look at the mechanisms adopted by cancer stem cells to influence the development of metastasis and evade therapeutic targeting and its role in the overall disease prognosis. Finally, we will illustrate the importance of understanding the biology of these cells to develop improved clinical strategies to tackle colorectal cancer.

Mechanistically detailed systems biology modeling of the HGF/Met pathway in hepatocellular carcinoma

Hepatocyte growth factor (HGF) signaling through its receptor Met has been implicated in hepatocellular carcinoma tumorigenesis and progression. Met interaction with integrins is shown to modulate the downstream signaling to Akt and ERK (extracellular-regulated kinase). In this study, we developed a mechanistically detailed systems biology model of HGF/Met signaling pathway that incorporated specific interactions with integrins to investigate the efficacy of integrin-binding peptide, AXT050, as monotherapy and in combination with other therapeutics targeting this pathway. Here we report that the modeled dynamics of the response to AXT050 revealed that receptor trafficking is sufficient to explain the effect of Met-integrin interactions on HGF signaling. Furthermore, the model predicted patient-specific synergy and antagonism of efficacy and potency for combination of AXT050 with sorafenib, cabozantinib, and rilotumumab. Overall, the model provides a valuable framework for studying the efficacy of drugs targeting receptor tyrosine kinase interaction with integrins, and identification of synergistic drug combinations for the patients.

Genomic and Transcriptomic Determinants of Therapy Resistance and Immune Landscape Evolution during Anti-EGFR Treatment in Colorectal Cancer

Despite biomarker stratification, the anti-EGFR antibody cetuximab is only effective against a subgroup of colorectal cancers (CRCs). This genomic and transcriptomic analysis of the cetuximab resistance landscape in 35 RAS wild-type CRCs identified associations of NF1 and non-canonical RAS/RAF aberrations with primary resistance and validated transcriptomic CRC subtypes as non-genetic predictors of benefit. Sixty-four percent of biopsies with acquired resistance harbored no genetic resistance drivers. Most of these had switched from a cetuximab-sensitive transcriptomic subtype at baseline to a fibroblast- and growth factor-rich subtype at progression. Fibroblast-supernatant conferred cetuximab resistance in vitro, confirming a major role for non-genetic resistance through stromal remodeling. Cetuximab treatment increased cytotoxic immune infiltrates and PD-L1 and LAG3 immune checkpoint expression, potentially providing opportunities to treat cetuximab-resistant CRCs with immunotherapy.

Cancer-associated fibroblasts in gastrointestinal cancer

The tumour microenvironment, also termed the tumour stroma or tumour mesenchyme, includes fibroblasts, immune cells, blood vessels and the extracellular matrix and substantially influences the initiation, growth and dissemination of gastrointestinal cancer. Cancer-associated fibroblasts (CAFs) are one of the critical components of the tumour mesenchyme and not only provide physical support for epithelial cells but also are key functional regulators in cancer, promoting and retarding tumorigenesis in a context-dependent manner. In this Review, we outline the emerging understanding of gastrointestinal CAFs with a particular emphasis on their origin and heterogeneity, as well as their function in cancer cell proliferation, tumour immunity, angiogenesis, extracellular matrix remodelling and drug resistance. Moreover, we discuss the clinical implications of CAFs as biomarkers and potential targets for prevention and treatment of patients with gastrointestinal cancer.