5‑FU resistance abrogates the amplified cytotoxic effects induced by inhibiting checkpoint kinase 1 in p53‑mutated colon cancer cells

Thiolated pectin-chitosan composites: Potential mucoadhesive drug delivery system with selective cytotoxicity towards colorectal cancer

Mucoadhesive drug delivery systems (DDS) may promote safer chemotherapy for colorectal cancer (CRC) by maximizing local drug distribution and residence time. Carbohydrate polymers, e.g. pectin (P) and chitosan (CS), are potential biomaterials for CRC-targeted DDS due to their gelling ability, mucoadhesive property, colonic digestibility, and anticancer activity. Polymer mucoadhesion is augmentable by thiolation, e.g. pectin to thiolated pectin (TP). Meanwhile, P-CS polyelectrolyte complex has been shown to improve structural stability. Herein, we fabricated, characterized, and evaluated 5-fluorouracil-loaded primary DDS combining TP and CS as a composite (TPCF) through triple crosslinking actions (calcium pectinate, polyelectrolyte complex, disulfide). Combination of these crosslinking yields superior mucoadhesion property relative to single- or dual-crosslinked counterparts, with comparable drug release profile and drug compatibility. PCF and TPCF exhibited targeted cytotoxicity towards HT29 CRC cells with milder cytotoxicity towards HEK293 normal cells. In conclusion, TP-CS composites are promising next-generation mucoadhesive and selectively cytotoxic biomaterials for CRC-targeted DDS.

Alkaloids and Colon Cancer: Molecular Mechanisms and Therapeutic Implications for Cell Cycle Arrest

Cancer is the second most fatal disease worldwide, with colon cancer being the third most prevalent and fatal form of cancer in several Western countries. The risk of acquisition of resistance to chemotherapy remains a significant hurdle in the management of various types of cancer, especially colon cancer. Therefore, it is essential to develop alternative treatment modalities. Naturally occurring alkaloids have been shown to regulate various mechanistic pathways linked to cell proliferation, cell cycle, and metastasis. This review aims to shed light on the potential of alkaloids as anti-colon-cancer chemotherapy agents that can modulate or arrest the cell cycle. Preclinical investigated alkaloids have shown anti-colon cancer activities and inhibition of cancer cell proliferation via cell cycle arrest at different stages, suggesting that alkaloids may have the potential to act as anticancer molecules.

Recent Updates on Mechanisms of Resistance to 5-Fluorouracil and Reversal Strategies in Colon Cancer Treatment

5-Fluorouracil (5-FU) plus leucovorin (LV) remain as the mainstay standard adjuvant chemotherapy treatment for early stage colon cancer, and the preferred first-line option for metastatic colon cancer patients in combination with oxaliplatin in FOLFOX, or irinotecan in FOLFIRI regimens. Despite treatment success to a certain extent, the incidence of chemotherapy failure attributed to chemotherapy resistance is still reported in many patients. This resistance, which can be defined by tumor tolerance against chemotherapy, either intrinsic or acquired, is primarily driven by the dysregulation of various components in distinct pathways. In recent years, it has been established that the incidence of 5-FU resistance, akin to multidrug resistance, can be attributed to the alterations in drug transport, evasion of apoptosis, changes in the cell cycle and DNA-damage repair machinery, regulation of autophagy, epithelial-to-mesenchymal transition, cancer stem cell involvement, tumor microenvironment interactions, miRNA dysregulations, epigenetic alterations, as well as redox imbalances. Certain resistance mechanisms that are 5-FU-specific have also been ascertained to include the upregulation of thymidylate synthase, dihydropyrimidine dehydrogenase, methylenetetrahydrofolate reductase, and the downregulation of thymidine phosphorylase. Indeed, the successful modulation of these mechanisms have been the game plan of numerous studies that had employed small molecule inhibitors, plant-based small molecules, and non-coding RNA regulators to effectively reverse 5-FU resistance in colon cancer cells. It is hoped that these studies would provide fundamental knowledge to further our understanding prior developing novel drugs in the near future that would synergistically work with 5-FU to potentiate its antitumor effects and improve the patient's overall survival.

Structural insights into the distinctive RNA recognition and therapeutic potentials of RIG-I-like receptors

RNA viruses, including the coronavirus, develop a unique strategy to evade the host immune response by interrupting the normal function of cytosolic retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs). RLRs rapidly detect atypical nucleic acids, thereby triggering the antiviral innate immune signaling cascade and subsequently activates the interferons transcription and induction of other proinflammatory cytokines and chemokines. Nonetheless, these receptors are manipulated by viral proteins to subvert the host immune system and sustain the infectivity and replication potential of the virus. RIG-I senses the single-stranded, double-stranded, and short double-stranded RNAs and recognizes the key signature, a 5'-triphosphate moiety, at the blunt end of the viral RNA. Meanwhile, the melanoma differentiation-associated gene 5 (MDA5) is triggered by longer double stranded RNAs, messenger RNAs lacking 2'-O-methylation in their 5'-cap, and RNA aggregates. Therefore, structural insights into the nucleic-acid-sensing and downstream signaling mechanisms of these receptors hold great promise for developing effective antiviral therapeutic interventions. This review highlights the critical roles played by RLRs in viral infections as well as their ligand recognition mechanisms. In addition, we highlight the crosstalk between the toll-like receptors and RLRs and provide a comprehensive overview of RLR-associated diseases as well as the therapeutic potential of RLRs for the development of antiviral-drugs. Moreover, we believe that these RLR-based antivirals will serve as a step toward countering the recent coronavirus disease 2019 pandemic.

Ziyuglycoside II induces caspases-dependent and caspases-independent apoptosis in human colon cancer cells

The development of chemopreventive approaches using natural products including phytochemicals is a potentially useful cancer treatment. The aims of this study were to examine the apoptotic effects of ziyuglycoside II, a major bioactive compound isolated from Sanguisorba officinalis L., on human colon cancer cells. The anticancer effect of ziyuglycoside II was examined in HCT116 (as p53 normal cells) and SW480 (as p53 mutant cells) colon cancer cells. Ziyuglycoside II treatment decreased HCT116 and SW480 cell proliferation. Cell death following ziyuglycoside II treatment was predominantly apoptosis but not cell cycle arrest. Apoptosis caused by p53 phosphorylation following ziyuglycoside II treatment in HCT116 cells involved activation of caspases, increased expression of BAX, mitochondrial cytochrome c and apoptosis inducing factor (AIF) release, while BCL-2 became down-regulated. In contrast, ziyuglycoside II treated SW480 cells displayed no change in phosphorylated-p53 and activation of caspases. Overall, these results suggest that ziyuglycoside II induces apoptosis through caspase-dependent and caspases-independent apoptosis, which was characterized by decreased expression of BCL-2, mitochondrial targeting, and altered production of ROS and translocation of AIF to the nuclei.

DNA damage response and repair in colorectal cancer: Defects, regulation and therapeutic implications

DNA damage response, a key factor involved in maintaining genome integrity and stability, consists of several kinase-dependent signaling pathways, which sense and transduce DNA damage signal. The severity of damage appears to determine DNA damage responses, which can include cell cycle arrest, damage repair and apoptosis. A number of recent studies have demonstrated that defection in signaling through this network is thought to be an underlying mechanism behind the development and progression of various types of human malignancies, including colorectal cancer. In this review, colorectal cancer and its molecular pathology as well as DNA damage response is briefly introduced. Finally, the involvement of key components of this network in the initiation/progression, prognosis, response to treatment and development of drug resistance is comprehensively discussed.

Acriflavine enhances the antitumor activity of the chemotherapeutic drug 5-fluorouracil in colorectal cancer cells

5-Fluorouracil (5-FU)-based chemotherapy improves the overall survival rates of patients with colorectal cancer (CRC). However, only a small proportion of patients respond to 5-FU when used as a single agent. The aim of the present study was to investigate whether the anticancer property of 5-FU is potentiated by combination treatment with acriflavine (ACF) in CRC cells. Additionally, the potential underlying molecular mechanisms of the cytotoxic effect of ACF were determined. The cytotoxic effects of ACF, 5-FU and irinotecan on different CRC cell lines with different p53 status were investigated using an MTT assay. SW480 cells that express a mutated form of p53 and two other CRC cell lines were used, HCT116 and LS174T, with wild-type p53. To determine the effect of ACF on the sensitivity of cells to 5-FU, cells were co-treated with the 30% maximal inhibitory concentration (IC30) of ACF and various concentrations of 5-FU, or pretreated with the IC30 of ACF and various concentrations of 5-FU. To assess the mechanism of action of ACF, cells were treated with IC30 values of the compound and then the reverse transcription-quantitative polymerase chain reaction was used to evaluate mRNA levels of hypoxia-inducible factor-1α (HIF-1α) and topoisomerase 2. Results indicate that pretreatment with ACF markedly sensitized CRC cells to the cytotoxic effects of 5-FU, whereas simultaneous treatment with ACF and 5-FU were not able to alter the resistance of CRC cells to 5-FU. In comparison with irinotecan, ACF was a more potent agent for enhancing the antitumor activity of 5-FU. ACF did not alter the mRNA levels of either HIF-1α or topoisomerase 2. The results of the present study reveal for the first time that pretreatment of CRC cells with ACF markedly increases the cytotoxic effects of 5-FU, regardless of the p53 status of cells.

Targeting Cytosolic Nucleic Acid-Sensing Pathways for Cancer Immunotherapies

The innate immune system provides the first line of defense against pathogen infection though also influences pathways involved in cancer immunosurveillance. The innate immune system relies on a limited set of germ line-encoded sensors termed pattern recognition receptors (PRRs), signaling proteins and immune response factors. Cytosolic receptors mediate recognition of danger damage-associated molecular patterns (DAMPs) signals. Once activated, these sensors trigger multiple signaling cascades, converging on the production of type I interferons and proinflammatory cytokines. Recent studies revealed that PRRs respond to nucleic acids (NA) released by dying, damaged, cancer cells, as danger DAMPs signals, and presence of signaling proteins across cancer types suggests that these signaling mechanisms may be involved in cancer biology. DAMPs play important roles in shaping adaptive immune responses through the activation of innate immune cells and immunological response to danger DAMPs signals is crucial for the host response to cancer and tumor rejection. Furthermore, PRRs mediate the response to NA in several vaccination strategies, including DNA immunization. As route of double-strand DNA intracellular entry, DNA immunization leads to expression of key components of cytosolic NA-sensing pathways. The involvement of NA-sensing mechanisms in the antitumor response makes these pathways attractive drug targets. Natural and synthetic agonists of NA-sensing pathways can trigger cell death in malignant cells, recruit immune cells, such as DCs, CD8⁺ T cells, and NK cells, into the tumor microenvironment and are being explored as promising adjuvants in cancer immunotherapies. In this minireview, we discuss how cGAS–STING and RIG-I–MAVS pathways have been targeted for cancer treatment in preclinical translational researches. In addition, we present a targeted selection of recent clinical trials employing agonists of cytosolic NA-sensing pathways showing how these pathways are currently being targeted for clinical application in oncology.

NFYB-induced high expression of E2F1 contributes to oxaliplatin resistance in colorectal cancer via the enhancement of CHK1 signaling

As a third-generation platinum drug, oxaliplatin has been widely applied in colorectal cancer (CRC); however, acquired resistance to oxaliplatin has become a major obstacle. In the present study, we found that the nuclear transcription factor Y subunit beta (NFYB) and E2F transcription factor 1 (E2F1) expression levels were significantly higher in oxaliplatin-resistant DLD1 and RKO CRC (OR-CRC) cells than in non-resistant cells. Additionally, highly expressed NFYB transactivated the E2F1 gene, which is important to maintain oxaliplatin resistance in OR-CRC cells. And Sirt1-dependent deacetylation suppresses the proapoptotic activity of E2F1 in OR-CRC cells. Through profiling the transcriptome of OR-CRC cells following E2F1 knockdown, CHK1 was identified as a target of E2F1. Deprivation of CHK1 sensitized OR-CRC cells to oxaliplatin. In vitro and in vivo phenotype experiments confirmed that an intact NFYB-E2F1-CHK1 axis was required to suppress oxaliplatin-induced apoptosis and maintain the tumorigenicity in OR-CRC cells. Knockdown of E2F1 in OR-CRC cells also decreased the expression of Pol κ, which was essential for CHK1 activation. Consistently, a high level of NFYB, E2F1, or CHK1 predicted poor survival in CRC patients, especially with oxaliplatin treatment. Collectively, the NFYB-E2F1 pathway displays a crucial role in the chemoresistance of OR-CRC by inducing the expression and activation of CHK1, providing a possible therapeutic target for oxaliplatin resistance in CRC.

The anticancer functions of RIG-I-like receptors, RIG-I and MDA5, and their applications in cancer therapy

Cancer is a major cause of death worldwide, and its incidence and mortality continuously increase in China. Nowadays, cancer heavily influences our health and constitutes enormous burden on society and families. Although there are many tools for cancer treatment, but the overall therapeutic effect is poor. In addition, cancer cells often develop resistance to therapy due to defective cell death or immune escape mechanisms. Therefore, it is a promising way for cancer treatment to effectively activate apoptosis and conquer immunosuppression. RIG-I-like receptors (RLRs) belong to RNA-sensing pattern recognition receptors (PRRs), one of the major subsets of PRRs, and play a critical role in sensing RNA viruses and initiate host antiviral responses such as the production of type I interferons (IFNs), proinflammatory cytokines, and other immune response molecules. Recent studies have demonstrated that tumor cells could mimic viral infection to activate viral recognition of immune system and the activation of interferon response pathway. RIG-I and MDA5, two members of RLRs family, could induce growth inhibition or apoptosis of multiple types of cancer cells on the activation by RNA ligands in IFN-dependent or IFN-independent approach. Previous studies have reviewed PRRs as promising immunotherapy targets for colorectal cancer and pancreatic cancer. However, until now, a comprehensive review on the role of RLRs in the development and treatment of various cancers is still lacking. In this article, we reviewed the latest studies on the roles as well as the mechanisms of RIG-I and MDA5 in the development of various cancers and therapeutic potentials of targeting RIG-I and MDA5 for cancer treatment.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Gambogic acid inhibits growth, induces apoptosis, and overcomes drug resistance in human colorectal cancer cells

The emergence of chemoresistance is a major limitation of colorectal cancer (CRC) therapies and novel biologically based therapies are urgently needed. Natural products represent a novel potential anticancer therapy. Gambogic acid (GA), a small molecule derived from Garcinia hanburyi Hook. f., has been demonstrated to be highly cytotoxic to several types of cancer cells and have low toxicity to the hematopoietic system. However, the potential role of GA in colorectal cancer and its ability to overcome the chemotherapeutic resistance in CRC cells have not been well studied. In the present study, we showed that GA directly inhibited proliferation and induced apoptosis in both 5-fluorouracil (5-FU) sensitive and 5-FU resistant colorectal cancer cells; induced apoptosis via activating JNK signaling pathway. The data, therefore, suggested an alternative strategy to overcome 5-FU resistance in CRC and that GA could be a promising medicinal compound for colorectal cancer therapy.