Significance of Wild-Type p53 Signaling in Suppressing Apoptosis in Response to Chemical Genotoxic Agents: Impact on Chemotherapy Outcome

Changing the Landscape of Solid Tumor Therapy from Apoptosis-Promoting to Apoptosis-Inhibiting Strategies

The many limitations of implementing anticancer strategies under the term "precision oncology" have been extensively discussed. While some authors propose promising future directions, others are less optimistic and use phrases such as illusion, hype, and false hypotheses. The reality is revealed by practicing clinicians and cancer patients in various online publications, one of which has stated that "in the quest for the next cancer cure, few researchers bother to look back at the graveyard of failed medicines to figure out what went wrong". The message is clear: Novel therapeutic strategies with catchy names (e.g., synthetic "lethality") have not fulfilled their promises despite decades of extensive research and clinical trials. The main purpose of this review is to discuss key challenges in solid tumor therapy that surprisingly continue to be overlooked by the Nomenclature Committee on Cell Death (NCCD) and numerous other authors. These challenges include: The impact of chemotherapy-induced genome chaos (e.g., multinucleation) on resistance and relapse, oncogenic function of caspase 3, cancer cell anastasis (recovery from late stages of apoptosis), and pitfalls of ubiquitously used preclinical chemosensitivity assays (e.g., cell "viability" and tumor growth delay studies in live animals) that score such pro-survival responses as "lethal" events. The studies outlined herein underscore the need for new directions in the management of solid tumors.

Are hydroxyapatite-based biomaterials free of genotoxicity? A systematic review

Hydroxyapatite (HA) is a biomaterial widely used in clinical applications and pharmaceuticals. The literature on HA-based materials studies is focused on chemical characterization and biocompatibility. Generally, biocompatibility is analyzed through adhesion, proliferation, and differentiation assays. Fewer studies are looking for genotoxic events. Thus, although HA-based biomaterials are widely used as biomedical devices, there is a lack of literature regarding their genotoxicity. This systematic review was carried out following the PRISMA statement. Specific search strategies were developed and performed in four electronic databases (PubMed, Science Direct, Scopus, and Web of Science). The search used "Hydroxyapatite OR Calcium Hydroxyapatite OR durapatite AND genotoxicity OR genotoxic OR DNA damage" and "Hydroxyapatite OR Calcium Hydroxyapatite OR durapatite AND mutagenicity OR mutagenic OR DNA damage" as keywords and articles published from 2000 to 2022, after removing duplicate studies and apply include and exclusion criteria, 53 articles were identified and submitted to a qualitative descriptive analysis. Most of the assays were in vitro and most of the studies did not show genotoxicity. In fact, a protective effect was observed for hydroxyapatites. Only 20 out of 71 tests performed were positive for genotoxicity. However, no point mutation-related mutagenicity was observed. As the genotoxicity of HA-based biomaterials observed was correlated with its nanostructured forms as needles or rods, it is important to follow their effect in chronic exposure to guarantee safe usage in humans.

Interplay of p53 and XIAP protein dynamics orchestrates cell fate in response to chemotherapy

Chemotherapeutic drugs are used to treat almost all types of cancer, but the intended response, i.e., elimination, is often incomplete, with a subset of cancer cells resisting treatment. Two critical factors play a role in chemoresistance: the p53 tumour suppressor gene and the X-linked inhibitor of apoptosis (XIAP). These proteins have been shown to act synergistically to elicit cellular responses upon DNA damage induced by chemotherapy, yet, the mechanism is poorly understood. This study introduces a mathematical model characterising the apoptosis pathway activation by p53 before and after mitochondrial outer membrane permeabilisation upon treatment with the chemotherapy Doxorubicin (Dox). "In-silico" simulations show that the p53 dynamics change dose-dependently. Under medium to high doses of Dox, p53 concentration ultimately stabilises to a high level regardless of XIAP concentrations. However, caspase-3 activation may be triggered or not depending on the XIAP induction rate, ultimately determining whether the cell will perish or resist. Consequently, the model predicts that failure to activate apoptosis in some cancer cells expressing wild-type p53 might be due to heterogeneity between cells in upregulating the XIAP protein, rather than due to the p53 protein concentration. Our model suggests that the interplay of the p53 dynamics and the XIAP induction rate is critical to determine the cancer cells' therapeutic response.

Intratumor Heterogeneity and Treatment Resistance of Solid Tumors with a Focus on Polyploid/Senescent Giant Cancer Cells (PGCCs)

Single cell biology has revealed that solid tumors and tumor-derived cell lines typically contain subpopulations of cancer cells that are readily distinguishable from the bulk of cancer cells by virtue of their enormous size. Such cells with a highly enlarged nucleus, multiple nuclei, and/or multiple micronuclei are often referred to as polyploid giant cancer cells (PGCCs), and may exhibit features of senescence. PGCCs may enter a dormant phase (active sleep) after they are formed, but a subset remain viable, secrete growth promoting factors, and can give rise to therapy resistant and tumor repopulating progeny. Here we will briefly discuss the prevalence and prognostic value of PGCCs across different cancer types, the current understanding of the mechanisms of their formation and fate, and possible reasons why these tumor repopulating "monsters" continue to be ignored in most cancer therapy-related preclinical studies. In addition to PGCCs, other subpopulations of cancer cells within a solid tumor (such as oncogenic caspase 3-activated cancer cells and drug-tolerant persister cancer cells) can also contribute to therapy resistance and pose major challenges to the delivery of cancer therapy.

SNORD6 promotes cervical cancer progression by accelerating E6-mediated p53 degradation

Small nucleolar RNAs (snoRNAs) are a class of non-coding RNAs widely distributed in eukaryotic nucleoli. In recent years, studies have revealed that snoRNAs can also participate in the occurrence and development of malignant tumors through different pathways. Cervical cancer is one of the most common malignant tumors of the female reproductive system, and the high-risk HPV virus infection is its main pathogenic mechanism. However, the outcomes in different patients with malignant tumors vary, indicating that other factors might affect the pathogenic process of cervical cancer. In this study, we screened the poor prognosis indicator SNORD6 from the TCGA database to find the snoRNA that affects the disease outcome during the pathogenesis of cervical cancer. We discovered that SNORD6 expression in cervical cancer tissues was higher than that in normal cervical tissues. Cell phenotype experiments revealed that the knockdown of SNORD6 retarded cell proliferation and plate clone formation. Furthermore, G1-S phase cell cycle arrest was induced, DNA synthesis was decreased, cell migration and invasion were reduced, while the level of apoptosis increased, whereas the opposite results were obtained after SNORD6 overexpression. Moreover, after intratumoral injection of ASO-SNORD6, the tumor growth rate slowed down, and the tumor volume decreased compared with the control group. In the mechanism study, we found that SNORD6 concurrently acted as a binding "hub" to promote the formation of the tumor suppressor protein p53 degradation complex E6-E6AP-p53. This reaction enhanced the ubiquitination and degradation of p53, thus influenced the regulation of p53 activities in the cell cycle and apoptosis. This study preliminarily clarified the biological role and specific mechanism of SNORD6 in the occurrence of cervical cancer, broadening the basic theoretical research of ovarian cancer and may provide a new perspective on the diagnosis and treatment of cervical cancer.

Unraveling the Role of Scutellaria baicalensis for the Treatment of Breast Cancer Using Network Pharmacology, Molecular Docking, and Molecular Dynamics Simulation

Scutellaria baicalensis is often used to treat breast cancer, but the molecular mechanism behind the action is unclear. In this study, network pharmacology, molecular docking, and molecular dynamics simulation are combined to reveal the most active compound in Scutellaria baicalensis and to explore the interaction between the compound molecule and the target protein in the treatment of breast cancer. In total, 25 active compounds and 91 targets were screened out, mainly enriched in lipids in atherosclerosis, the AGE-RAGE signal pathway of diabetes complications, human cytomegalovirus infection, Kaposi-sarcoma-associated herpesvirus infection, the IL-17 signaling pathway, small-cell lung cancer, measles, proteoglycans in cancer, human immunodeficiency virus 1 infection, and hepatitis B. Molecular docking shows that the two most active compounds, i.e., stigmasterol and coptisine, could bind well to the target AKT1. According to the MD simulations, the coptisine-AKT1 complex shows higher conformational stability and lower interaction energy than the stigmasterol-AKT1 complex. On the one hand, our study demonstrates that Scutellaria baicalensis has the characteristics of multicomponent and multitarget synergistic effects in the treatment of breast cancer. On the other hand, we suggest that the best effective compound is coptisine targeting AKT1, which can provide a theoretical basis for the further study of the drug-like active compounds and offer molecular mechanisms behind their roles in the treatment of breast cancer.

MiR-290 family maintains developmental potential by targeting p21 in mouse pre-implantation embryos

The miR-290 family is a mouse-specific microRNA cluster, which maintains mouse embryonic stem cells (ESCs) pluripotency by increasing OCT3/4 and C-MYC expression. However, its functions in mouse pre-implantation embryos remain unclear, especially during zygotic genome activation (ZGA). In this study, miR-290 family expression increased from the two-cell embryo stage through the blastocyst stage. Inhibition of miR-294-3p/5p did not affect ZGA initiation or embryo development, whereas pri-miR-290 knockdown decreased ZGA gene expression and slowed embryonic development. In addition, pluripotency decreased in ESCs derived from pri-miR-290 knockdown blastocysts. To clarify the mechanism of action, 33 candidate miR-294-3p target genes were screened from three databases, and miR-294-3p directly targeted the 3'-untranslated region of Cdkn1a (p21) mRNA. Similar to pri-miR-290 knockdown, P21 overexpression impeded embryonic development, whereas simultaneous overexpression of P21 and pri-miR-290 partially rescued embryonic development. The results indicate that the miR-290 family participates in promoting ZGA process and maintaining developmental potency in embryos by targeting p21.

Cellular Senescence: Mechanisms and Therapeutic Potential

Cellular senescence is a complex and multistep biological process which cells can undergo in response to different stresses. Referring to a highly stable cell cycle arrest, cellular senescence can influence a multitude of biological processes-both physiologically and pathologically. While phenotypically diverse, characteristics of senescence include the expression of the senescence-associated secretory phenotype, cell cycle arrest factors, senescence-associated β-galactosidase, morphogenesis, and chromatin remodelling. Persistent senescence is associated with pathologies such as aging, while transient senescence is associated with beneficial programmes, such as limb patterning. With these implications, senescence-based translational studies, namely senotherapy and pro-senescence therapy, are well underway to find the cure to complicated diseases such as cancer and atherosclerosis. Being a subject of major interest only in the recent decades, much remains to be studied, such as regarding the identification of unique biomarkers of senescent cells. This review attempts to provide a comprehensive understanding of the diverse literature on senescence, and discuss the knowledge we have on senescence thus far.

The Role of Indoleamine 2,3-Dioxygenase in Renal Tubular Epithelial Cells Senescence under Anoxia or Reoxygenation

Ischemia-reperfusion injury is the commonest form of acute kidney injury (AKI). Tubular epithelial cell senescence contributes to incomplete recovery from AKI and predisposes to subsequent chronic kidney disease. In cultures of primary proximal renal tubular epithelial cells (RPTECs) subjected to anoxia or reoxygenation, we evaluated the role of indoleamine 2,3-dioxygenase 1 (IDO) in cellular senescence. Proteins of interest were assessed with Western blotting or enzyme-linked immunosorbent assay or histochemically. Under anoxia or reoxygenation, IDO expression and activity were increased. Moreover, the two IDO-derived pathways, the general control nonderepressible 2 kinase (GCN2K) pathway and the aryl-hydrocarbon receptor (AhR) pathway, were also activated. A DNA damage response (DDR) took place and led to increased levels of the cell-cycle inhibitors p21 and p16, and senescence-associated β-galactosidase (SA-β-Gal) activity. Cell proliferation was inhibited, and more IL-6 was produced. The IDO inhibitor 1-DL-methyl-tryptophan ameliorated the DDR; decreased p21, p16, and SA-β-Gal activity; restored cell proliferation; and decreased IL-6 production. The AhR inhibitor CH223191 did not affect the above parameters. In conclusion, anoxia and the subsequent reoxygenation upregulate IDO. IDO depletes tryptophan and activates GCN2K. The latter enhances the anoxia- or reoxygenation-induced DDR, resulting in increased p21 and p16 expression and eventually leading to RPTEC senescence. Since cellular senescence affects AKI outcome, the role of IDO in cellular senescence and the possible therapeutic role of IDO inhibitors deserve further investigation.

IL-6 promotes drug resistance through formation of polyploid giant cancer cells and stromal fibroblast reprogramming

To understand the role of polyploid giant cancer cells (PGCCs) in drug resistance and disease relapse, we examined the mRNA expression profile of PGCCs following treatment with paclitaxel in ovarian cancer cells. An acute activation of IL-6 dominated senescence-associated secretory phenotype lasted 2–3 weeks and declined during the termination phase of polyploidy. IL-6 activates embryonic stemness during the initiation of PGCCs and can reprogram normal fibroblasts into cancer-associated fibroblasts (CAFs) via increased collagen synthesis, activation of VEGF expression, and enrichment of CAFs and the GPR77 + /CD10 + fibroblast subpopulation. Blocking the IL-6 feedback loop with tocilizumab or apigenin prevented PGCC formation, attenuated embryonic stemness and the CAF phenotype, and inhibited tumor growth in a patient-derived xenograft high-grade serous ovarian carcinoma model. Thus, IL-6 derived by PGCCs is capable of reprogramming both cancer and stromal cells and contributes to the evolution and remodeling of cancer. Targeting IL-6 in PGCCs may represent a novel approach to combating drug resistance.

Metabolic Reprogramming: A Friend or Foe to Cancer Therapy?

Drug resistance is a major cause of cancer treatment failure, effectively driven by processes that promote escape from therapy-induced cell death. The mechanisms driving evasion of apoptosis have been widely studied across multiple cancer types, and have facilitated new and exciting therapeutic discoveries with the potential to improve cancer patient care. However, an increasing understanding of the crosstalk between cancer hallmarks has highlighted the complexity of the mechanisms of drug resistance, co-opting pathways outside of the canonical "cell death" machinery to facilitate cell survival in the face of cytotoxic stress. Rewiring of cellular metabolism is vital to drive and support increased proliferative demands in cancer cells, and recent discoveries in the field of cancer metabolism have uncovered a novel role for these programs in facilitating drug resistance. As a key organelle in both metabolic and apoptotic homeostasis, the mitochondria are at the forefront of these mechanisms of resistance, coordinating crosstalk in the event of cellular stress, and promoting cellular survival. Importantly, the appreciation of this role metabolism plays in the cytotoxic response to therapy, and the ability to profile metabolic adaptions in response to treatment, has encouraged new avenues of investigation into the potential of exploiting metabolic addictions to improve therapeutic efficacy and overcome drug resistance in cancer. Here, we review the role cancer metabolism can play in mediating drug resistance, and the exciting opportunities presented by imposed metabolic vulnerabilities.

Possibility of inducing tumor cell senescence during therapy

The treatment options for cancer include surgery, radiotherapy and chemotherapy. However, the traditional approach of high-dose chemotherapy brings tremendous toxic side effects to patients, as well as potentially causing drug resistance. Drug resistance affects cell proliferation, cell senescence and apoptosis. Cellular senescence refers to the process in which cells change from an active proliferative status to a growth-arrested status. There are multiple factors that regulate this process and cellular senescence is activated by various pathways. Senescent cells present specific characteristics, such as an increased cell volume, flattened cell body morphology, ceased cell division and the expression of β-galactosidase. Tumor senescence can be categorized into replicative senescence and premature senescence. Cellular senescence may inhibit the occurrence and development of tumors, serving as an innovative strategy for the treatment of cancer. The present review mainly focuses on senescent biomarkers, methods for the induction of cellular senescence and its possible application in the treatment of cancer.

Role of indoleamine 2,3-dioxygenase in ischemia-reperfusion injury of renal tubular epithelial cells

The present study evaluated indoleamine 2,3-dioxygenase 1 (IDO) kinetics and how it affects cell survival during the two distinct phases of ischemia-reperfusion (I-R) injury. Primary renal proximal tubular epithelial cells (RPTECs) were cultured under anoxia or reoxygenation with or without the IDO inhibitor 1-DL-methyltryptophan, the aryl-hydrocarbon receptor (AhR) inhibitor CH223191 or the ferroptosis inhibitor α-tocopherol. Using cell imaging, colorimetric assays, PCR and western blotting, it was demonstrated that IDO was upregulated and induced apoptosis during anoxia. The related molecular pathway entails tryptophan degradation, general control non-derepressible-2 kinase (GCN2K) activation, increased level of phosphorylated eukaryotic translation initiation factor 2α, activating transcription factor (ATF)4, ATF3, C/EBP homologous protein, phosphorylated p53, p53, Bax, death receptor-5 and eventually activated cleaved caspase-3. Reoxygenation also upregulated IDO, which, in this case, induced ferroptosis. The related molecular pathway encompasses kynurenine production, AhR activation, cytochrome p450 enzymes increase, reactive oxygen species generation and eventually ferroptosis. In conclusion, in RPTECs, both anoxia and reoxygenation upregulated IDO, which in turn induced GCN2K-mediated apoptosis and AhR-mediated ferroptosis. Since both phases of I-R injury share IDO upregulation as a common point, its inhibition may prove a useful therapeutic strategy for preventing or attenuating I-R injury.

Developmentally regulated GTP-binding protein 2 levels in prostate cancer cell lines impact docetaxel-induced apoptosis

Purpose

This study aimed to confirm the association between developmentally regulated GTP-binding protein 2 (DRG2) expression and docetaxel-induced apoptosis and to determine whether prostate cancer responses to docetaxel treatment differ with DRG2 expression.

Materials and Methods

PC3, DU145, and LNCaP prostate cancer cell lines were used. The MTT assay was used to determine cell viability. Western blotting analysis was performed using anti-DRG2 antibodies. Cells were transfected with 50 nmol DRG2 siRNA using an siRNA transfection reagent for DRG2 knockdown. The cell cycle was analyzed by using flow cytometry, and apoptosis was detected by using the Annexin V cell death assay.

Results

DRG2 expression differed in each prostate cancer cell line. Docetaxel reduced DRG2 expression in a dose-dependent manner. Upon DRG2 knockdown in prostate cancer cells, an increase in the sub-G1 phase was observed without a change in the G1 or G2/M phases. When 4 nM docetaxel was administered to DRG2 knockdown prostate cancer cell lines, an increase in the sub-G1 phase was observed without increasing the G2/M phase, which was similar to that in DU145 cells before DRG2 knockdown. In PC3 and DU145 cell lines, DRG2 knockdown increased docetaxel-induced Annexin V (+) apoptosis by 8.7 and 2.7 times, respectively.

Conclusions

In prostate cancer cells, DRG2 regulates G2/M arrest after docetaxel treatment. In prostate cancer cells with DRG2 knockdown, apoptosis increases without G2/M arrest in response to docetaxel treatment. These results show that inhibition of DRG2 expression can be useful to enhance docetaxel-induced apoptosis despite low-dose administration in castration-resistant prostate cancer.

p53 Enhances Artemisia annua L. Polyphenols-Induced Cell Death Through Upregulation of p53-Dependent Targets and Cleavage of PARP1 and Lamin A/C in HCT116 Colorectal Cancer Cells

Plant-derived natural polyphenols exhibit anticancer activity without showing any noticeable toxicities to normal cells. The aim of this study was to investigate the role of p53 on the anticancer effect of polyphenols isolated from Korean Artemisia annua L. (pKAL) in HCT116 human colorectal cancer cells. We confirmed that pKAL induced reactive oxygen species (ROS) production, propidium iodide (PI) uptake, nuclear structure change, and acidic vesicles in a p53-independent manner in p53-null HCT116 cells through fluorescence microscopy analysis of DCF/PI-, DAPI-, and AO-stained cells. The pKAL-induced anticancer effects were found to be significantly higher in p53-wild HCT116 cells than in p53-null by hematoxylin staining, CCK-8 assay, Western blot, and flow cytometric analysis of annexin V/PI-stained cells. In addition, expression of ectopic p53 in p53-null cells was upregulated by pKAL in both the nucleus and cytoplasm, increasing pKAL-induced cell death. Moreover, Western bot analysis revealed that pKAL-induced cell death was associated with upregulation of p53-dependent targets such as p21, Bax and DR5 and cleavage of PARP1 and lamin A/C in p53-wild HCT116 cells, but not in p53-null. Taken together, these results indicate that p53 plays an important role in enhancing the anticancer effects of pKAL by upregulating p53 downstream targets and inducing intracellular cell death processes.

The inhibition of tumor protein p53 by microRNA-151a-3p induced cell proliferation, migration and invasion in nasopharyngeal carcinoma

A close relation between microRNA-151a-3p (miR-151a-3p) and nasopharyngeal carcinoma (NPC) has been reported, however, the molecular mechanism is still unclear. The aim of the present study was to explore the mechanism in the promotion of miR-151a-3p to NPC progression. The levels of miR-151-3p in several NPC cell lines were detected in order to screen an experimental cell line. MiR-151a-3p mimic and inhibitor were constructed and transfected into 5-8F cells and cell proliferation were detected by Cell Counting Kit-8 (CCK-8). The apoptosis rate, cell migration and invasion were determined by flow cytometry, wound healing and Transwell assays. The predicted target was further verified by luciferase reporter assay. Real-time quantification-PCR and Western blot were carried out for mRNA and protein level analysis. Tumor protein p53 was co-transfected to verify the functions of miR-151a-3p. The miR-151a-3p level in NPC tissues was much higher than that in adjacent tissues. After transfecting cells with miR-151a-3p mimic, the cell proliferation and patients' survival rate were much increased, and this was accompanied by the increase in B-cell lymphoma 2 (Bcl-2) and decreases in Bax and cleaved caspase-3 (P<0.01). Moreover, the migration rate and number of invaded cells were also remarkably increased, however, the miR-151a-3p inhibitor had opposite effects on the 5-8F cells. Noticeably, p53 was revealed as a potential target of miR-151a-3p. Co-transfection of P53 could partially reverse the promotive effects of miR-151a-3p on NPC cell progression. Our data indicated that blocking p53 expression and mediated signal pathways contribute to the positive effects of miR-151a-3p on NPC cell proliferation, migration and invasion.

Cellular Responses to Platinum-Based Anticancer Drugs and UVC: Role of p53 and Implications for Cancer Therapy

Chemotherapy is intended to induce cancer cell death through apoptosis and other avenues. Unfortunately, as discussed in this article, moderate doses of genotoxic drugs such as cisplatin typical of those achieved in the clinic often invoke a cytostatic/dormancy rather than cytotoxic/apoptosis response in solid tumour-derived cell lines. This is commonly manifested by an extended apoptotic threshold, with extensive apoptosis only being seen after very high/supralethal doses of such agents. The dormancy response can be associated with senescence-like features, polyploidy and/or multinucleation, depending in part on the p53 status of the cells. In most solid tumour-derived cells, dormancy represents a long-term survival mechanism, ultimately contributing to disease recurrence. This review highlights the nonlinearity of key aspects of the molecular and cellular responses to bulky DNA lesions in human cells treated with chemotherapeutic drugs (e.g., cisplatin) or ultraviolet light-C (a widely used tool for unraveling details of the DNA damage-response) as a function of the level of genotoxic stress. Such data highlight the growing realization that targeting dormant cancer cells, which frequently emerge following conventional anticancer treatments, may represent a novel strategy to prevent or, at least, significantly suppress cancer recurrence.

Giants and monsters: Unexpected characters in the story of cancer recurrence

Polyploid giant cancer cells (PGCC) constitute a dangerous subpopulation of cancer cells and are a driving force in cancer recurrence. These unique cells arise from diploid tumor cells in response to stress encountered in the tumor microenvironment or during cancer therapy. PGCC are greatly dedifferentiated, acquire pluripotency, and are able to replicate through a form of asymmetric division called neosis, which results in new populations that are themselves able to differentiate into new cell types or to re-establish tumors. Progeny tend to be more genetically unstable than the founding population due to the dysregulation required to transition through a PGCC state. Therefore, cancers that escape stressors through this mechanism tend to re-emerge with a more aggressive phenotype that is therapy resistant. This review focuses on the clinical significance of PGCC, the need for standardized nomenclature and molecular markers, as well as possible avenues to develop therapies aimed at PGCC and the process of neosis. The biology underlying the development of PGCC including cell cycle checkpoint dysregulation, stress responses, dedifferentiation, stemness and epithelial-mesenchymal transition is discussed.

Radiosensitization of Hepatocellular Carcinoma through Targeting Radio-Associated MicroRNA

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related deaths worldwide. For patients who are resistant to monotherapy, multimodal therapy is a basic oncologic principle that incorporates surgery, radiotherapy (RT), and chemotherapy providing survival benefits for patients with most types of cancer. Although liver has low tolerance for radiation, high-precision RT for local HCC minimizes the likelihood of radiation-induced liver disease (RILD) in noncancerous liver tissue. RT have several therapeutic benefits, including the down-staging of tumors to make them resectable and repression of metastasis. The DNA damage response (DDR) is a cellular response to irradiation (IR), including DNA repair of injured cells and induction of programmed cell death, thereby resulting in maintenance of cell homeostasis. Molecules that block the activity of proteins in DDR pathways have been found to enhance radiotherapeutic effects. These molecules include antibodies, kinase inhibitors, siRNAs and miRNAs. MicroRNAs (miRNAs) are short non-coding regulatory RNAs binding to the 3'-untranslated regions (3'-UTR) of the messenger RNAs (mRNAs) of target genes, regulating their translation and expression of proteins. Thus, miRNAs and their target genes constitute complicated interactive networks, which interact with other molecules during carcinogenesis. Due to their promising roles in carcinogenesis, miRNAs were shown to be the potential factors that mediated radiosensitivity and optimized outcomes of the combination of systemic therapy and radiotherapy.

Intratumor Heterogeneity and Therapy Resistance: Contributions of Dormancy, Apoptosis Reversal (Anastasis) and Cell Fusion to Disease Recurrence

A major challenge in treating cancer is posed by intratumor heterogeneity, with different sub-populations of cancer cells within the same tumor exhibiting therapy resistance through different biological processes. These include therapy-induced dormancy (durable proliferation arrest through, e.g., polyploidy, multinucleation, or senescence), apoptosis reversal (anastasis), and cell fusion. Unfortunately, such responses are often overlooked or misinterpreted as “death” in commonly used preclinical assays, including the in vitro colony-forming assay and multiwell plate “viability” or “cytotoxicity” assays. Although these assays predominantly determine the ability of a test agent to convert dangerous (proliferating) cancer cells to potentially even more dangerous (dormant) cancer cells, the results are often assumed to reflect loss of cancer cell viability (death). In this article we briefly discuss the dark sides of dormancy, apoptosis, and cell fusion in cancer therapy, and underscore the danger of relying on short-term preclinical assays that generate population-based data averaged over a large number of cells. Unveiling the molecular events that underlie intratumor heterogeneity together with more appropriate experimental design and data interpretation will hopefully lead to clinically relevant strategies for treating recurrent/metastatic disease, which remains a major global health issue despite extensive research over the past half century.

Downregulation of SNRPG induces cell cycle arrest and sensitizes human glioblastoma cells to temozolomide by targeting Myc through a p53-dependent signaling pathway

Objective: Temozolomide (TMZ) is commonly used for glioblastoma multiforme (GBM) chemotherapy. However, drug resistance limits its therapeutic effect in GBM treatment. RNA-binding proteins (RBPs) have vital roles in posttranscriptional events. While disturbance of RBP-RNA network activity is potentially associated with cancer development, the precise mechanisms are not fully known. The SNRPG gene, encoding small nuclear ribonucleoprotein polypeptide G, was recently found to be related to cancer incidence, but its exact function has yet to be elucidated. Methods:SNRPG knockdown was achieved via short hairpin RNAs. Gene expression profiling and Western blot analyses were used to identify potential glioma cell growth signaling pathways affected by SNRPG. Xenograft tumors were examined to determine the carcinogenic effects of SNRPG on glioma tissues. Results: The SNRPG-mediated inhibitory effect on glioma cells might be due to the targeted prevention of Myc and p53. In addition, the effects of SNRPG loss on p53 levels and cell cycle progression were found to be Myc-dependent. Furthermore, SNRPG was increased in TMZ-resistant GBM cells, and downregulation of SNRPG potentially sensitized resistant cells to TMZ, suggesting that SNRPG deficiency decreases the chemoresistance of GBM cells to TMZ via the p53 signaling pathway. Our data confirmed that SNRPG suppression sensitizes GBM cells to TMZ by targeting Myc via the p53 signaling cascade. Conclusions: These results indicated that SNRPG is a probable molecular target of GBM and suggested that suppressing SNRPG in resistant GBM cells might be a substantially beneficial method for overcoming essential drug resistance.

Nonlinearities in the cellular response to ionizing radiation and the role of p53 therein

Many aspects of the cellular response to agents such as ionizing radiation that cause genotoxic and/or oxidative stress exhibit a nonlinear relationship to the applied stress level. These include elements of the antioxidant response and of the damage-signaling pathways that determine cell fate decisions. The wild-type p53 protein, which is mutated in many cancers, coordinates these responses and is a key determinant of this nonlinearity. Indeed, p53 has been referred to as a 'cellular rheostat' that favors antioxidant/cytoprotective functions at low stress levels while switching to a pro-oxidant/cytotoxic role under high-stress conditions. For solid tumor-derived cell lines, moderate doses of radiation, typical of those used to generate clonogenic survival curves (i.e. ≤10 Gy), predominantly invoke a dose-dependent cytostatic response. For cancer cell lines with wild-type p53, cytostasis is primarily associated with features of senescence, whereas cancer cells with aberrant p53 primarily undergo endopolyploidization and enlargement. In line with a commentary by Meyn et al. [Int J Radiat Biol. 2009, 85:107-115] concluding that apoptosis is not the primary cause of radiation-induced loss of clonogenicity in solid tumor-derived cell lines, significant levels of apoptosis are typically seen only after higher doses (≥5 Gy) and this is almost all of the delayed (rather than primary) type. Nonlinearity of the oxidative/genotoxic stress response is already apparent in the early antioxidant events activated by transcription factors such as p53 and Nrf2 and the Ref1 transcription coactivator. These cytoprotective pathways serve to minimize damage to important cellular targets caused by reactive oxygen species (ROS) and other electrophiles. After high/supra-lethal levels of stress these inducible antioxidant pathways can be deactivated in a manner that would reinforce the establishment of the pro-oxidant state, resulting in elevated ROS levels and to cytostasis or apoptosis. Understanding the complex regulation of these damage-signaling pathways in relation to the stress levels is important for the optimal utilization of radiation therapy for cancer.

Loss of p53 Sensitizes Cells to Palmitic Acid-Induced Apoptosis by Reactive Oxygen Species Accumulation

Palmitic acid, the most common saturated free fatty acid, can lead to lipotoxicity and apoptosis when overloaded in non-fat cells. Palmitic acid accumulation can induce pancreatic β-cell dysfunction and cardiac myocyte apoptosis. Under various cellular stresses, the activation of p53 signaling can lead to cell cycle arrest, DNA repair, senescence, or apoptosis, depending on the severity/type of stress. Nonetheless, the precise role of p53 in lipotoxicity induced by palmitic acid is not clear. Here, our results show that palmitic acid induces p53 activation in a dose- and time-dependent manner. Furthermore, loss of p53 makes cells sensitive to palmitic acid-induced apoptosis. These results were demonstrated in human colon carcinoma cells (HCT116) and primary mouse embryo fibroblasts (MEF) through analysis of DNA fragmentation, flow cytometry, colony formation, and Western blots. In the HCT116 p53^−/− cell line, palmitic acid induced greater reactive oxygen species formation compared to the p53^+/+ cell line. The reactive oxygen species (ROS) scavengers N-acetyl cysteine (NAC) and reduced glutathione (GSH) partially attenuated apoptosis in the HCT116 p53^−/− cell line but had no obvious effect on the p53^+/+ cell line. Furthermore, p53 induced the expression of its downstream target genes, p21 and Sesn2, in response to ROS induced by palmitic acid. Loss of p21 also leads to more palmitic acid-induced cell apoptosis in the HCT116 cell line compared with HCT116 p53^+/+ and HCT116 p53^−/−. In a mouse model of obesity, glucose tolerance test assays showed higher glucose levels in p53^−/− mice that received a high fat diet compared to wild type mice that received the same diet. There were no obvious differences between p53^−/− and p53^+/+ mice that received a regular diet. We conclude that p53 may provide some protection against palmitic acid- induced apoptosis in cells by targeting its downstream genes in response to this stress.

Mutant p53 induces SIRT3/MnSOD axis to moderate ROS production in melanoma cells

The TP53 tumor suppressor gene is the most frequently altered gene in tumors and mutant p53 isoforms can acquire oncogenic properties referred to as gain-of-function (GOF). In this study, we used wild-type (A375) and mutant p53 (MeWo) melanoma cell lines to assess the regulation of the mitochondrial antioxidant manganese superoxide dismutase (MnSOD) by mutant p53. The effects of mutant p53 were evaluated by qPCR, immunoblotting, enzyme activity assay, cell proliferation assay, reactive oxygen species (ROS) assay after cellular transfection. We demonstrate that mutant p53 induces MnSOD expression, which is recovered by the ROS scavenger N-acetyl-l-cysteine. This suggests MnSOD induction as a defense mechanism of melanoma cells to counterbalance the pro-oxidant conditions induced by mutant p53. We also demonstrate that mutant p53 induces the expression of Sirtuin3 (SIRT3), a major mitochondrial NAD⁺-dependent deacetylase, stimulating MnSOD deacetylation and enzymatic activity. Indeed, the restoration of SIRT3 reverses MnSOD activity decrease by mutant p53 knock-down. Finally, MnSOD knock-down further enhances mutant p53-mediated ROS increase, counteracting mutp53-dependent cell hyperproliferation. This indicates that SIRT3 and MnSOD act to maintain ROS levels controlled to promote cell proliferation and survival, providing new therapeutic opportunities to be further considered for clinical studies in cancer patients bearing mutant TP53 gene.

Diversity of the Senescence Phenotype of Cancer Cells Treated with Chemotherapeutic Agents

It is acknowledged that cancer cells are able to undergo senescence in response to clinically used chemotherapeutics. Moreover, recent years have provided evidence that some drugs can selectively remove senescent cells. Therefore, it is essential to properly identify and characterize senescent cells, especially when it comes to cancer. Senescence was induced in various cancer cell lines (A549, SH-SY-5Y, HCT116, MDA-MB-231, and MCF-7) following treatment with doxorubicin, irinotecan, methotrexate, 5-fluorouracil, oxaliplatin, or paclitaxel. Treatment with tested chemotherapeutics resulted in upregulation of p21 and proliferation arrest without cytotoxicity. A comparative analysis with the use of common senescence markers (i.e., morphology, SA-β-galactosidase, granularity, secretory phenotype, and the level of double-stranded DNA damage) revealed a large diversity in response to the chemotherapeutics used. The strongest senescence inducers were doxorubicin, irinotecan, and methotrexate; paclitaxel had an intermediate effect and oxaliplatin and 5-fluorouracil did not induce senescence. In addition, different susceptibility of cancer cells to senescence was observed. A statistical analysis aimed at finding any relationship between the senescence markers applied did not show clear correlations. Moreover, increased SA-β-gal activity coupled with p21 expression proved not to be an unequivocal senescence marker. This points to a need to simultaneously analyze multiple markers, given their individual limitations.

Immunohistochemical expression of P53, Ki-67, and CD34 in psoriasis and psoriasiform dermatitis

BACKGROUND

Psoriasis is the prime example of psoriasiform tissue pattern and should be differentiated from other psoriasiform dermatoses both clinically and histopathologically.

AIM

To evaluate immunohistochemical expression of P53, Ki-67, and CD34 in psoriasis and psoriasiform dermatitis for diagnostic purposes.

METHODS

An analytical cross-sectional study was performed on the paraffin blocks of 60 psoriasis and 31 psoriasiform dermatitis patients between 2014 and 2017. The selected formalin-fixed paraffin-embedded tissues from each biopsy specimen were cut into 4-micron sections. Initial sections were stained by hematoxylin and eosin staining. Primary antihuman antibodies against P53, Ki-67, and CD34 were applied. Positive control samples for biomarkers were received from former strongly positive samples of papillary endothelial hyperplasia, high grade lymphoma, and breast ductal carcinoma for CD34, Ki-67, and P53, respectively.

RESULTS

Out of 60 psoriasis patients, 56.7% were men, with the mean age of 36.8 years. From 31 psoriasiform patients, 45.2% were men, with the mean age of 37.5 years. Both groups were matched in terms of sex and age. The mean staining of three markers was more significant in psoriasiform dermatitis than psoriasis.

CONCLUSION

In spite of some other researches, the present study showed expression of P53, Ki-67, and CD34 biomarkers were significantly higher in psoriasiform dermatitis than psoriasis.

The androgen receptor antagonist enzalutamide induces apoptosis, dysregulates the heat shock protein system, and diminishes the androgen receptor and estrogen receptor β1 expression in prostate cancer cells

Enzalutamide's accepted mode of action is by targeting the androgen receptor's (AR) activity. In clinical practice, enzalutamide demonstrates a good benefit-risk profile for the treatment of advanced prostate cancer (PC), even after poor response to standard antihormonal treatment. However, since both, well-established antiandrogens and enzalutamide, target AR functionality, we hypothesized that additional unknown mechanisms might be responsible for enzalutamide's superior anticancer activity. In the current study, PC cells were incubated with enzalutamide and enzalutamide-dependent modulation of apoptotic mechanisms were assessed via Western blot analysis, TDT-mediated dUTP-biotin nick end-labeling assay, and nuclear morphology assay. Alterations of heat shock protein (HSP), AR, and estrogen receptor (ER) expression were examined by Western blot analysis. Enzalutamide attenuated the proliferation of PC cells in a time- and dose-dependent manner. In the presence of enzalutamide, apoptosis occurred which was shown by increased BAX expression, decreased Bcl-2 expression, nuclear pyknosis, and genomic DNA fragmentation. Moreover, enzalutamide inhibited the expression of HSPs primarily involved in steroid receptor stabilization and suppressed AR and ERβ1 expression. This study demonstrates for the first time that enzalutamide treatment of PC cells triggers varying molecular mechanisms resulting in antiproliferative effects of the drug. In addition to the well-characterized antagonistic inhibition of AR functionality, we have shown that enzalutamide also affects the intracellular synthesis of steroid receptor-associated HSPs, thereby diminishing the expression of AR and ERβ1 proteins and inducing apoptotic pathways. According to an indirect attenuation of HSP-associated factors such as steroid receptors, endometrial carcinoma, uterine leiomyosarcoma, and mamma carcinoma cells also demonstrated inhibited cell growth in the presence of enzalutamide. Our data, therefore, suggest that enzalutamide's high efficacy is at least partially independent of AR and p53 protein expression, which are frequently lost in advanced PC.

Methylation-regulated ZNF545 inhibits growth of the p53-mutant KYSE150 cell line by inducing p21 and Bax

The Krüppel-associated box zinc-finger protein 545 (ZNF545) was recently identified as a tumor suppressor in esophageal squamous cell carcinoma (ESCC). However, the role of ZNF545 in the tumorigenesis of esophageal cancer cells expressing loss-of-function mutant p53 has not been elucidated. In the present study, the role of ZNF545 in esophageal tumors and the p53-mutant ESCC cell line, KYSE150, was investigated. ZNF545 mRNA was significantly downregulated in tumors when compared with adjacent normal tissues. Methylated ZNF545 was detected in 76.6% of tumor tissues compared with 28.1% of adjacent normal tissues. Combined pharmacological treatment of KYSE150 cells with a demethylating reagent and deacetylase inhibitor restored the expression of ZNF545. Ectopic expression of ZNF545 activated p53 transcription and upregulated the protein expression levels of pivotal effectors p21 and Bax, which are associated with cell proliferation and apoptosis, respectively, in p53-mutant KYSE150 cells; while suppressing colony formation and inducing apoptosis. ZNF545 was therefore proposed as a potential tumor suppressor responsible for inhibiting the growth of p53-mutant ESCC cell lines. In addition, tumor-specific methylation of ZNF545 may represent an epigenetic diagnostic biomarker and a therapeutic target in patients with esophageal cancer.

Short-term detection of gastric genotoxicity using the DNA double-strand break marker γ-H2AX

DNA damage caused by Helicobacter pylori infection and chronic inflammation or exposure to genotoxic agents is considered an important risk factor of gastric carcinogenesis. In this study, we have evaluated a short-term technique to detect DNA damage response to various chemical carcinogens; it involves visualization of Ser 139-phosphorylated histone H2AX (γ-H2AX) foci by immunohistochemistry and expression analysis of other genes by quantitative RT-PCR. Six-week-old male rats were intragastrically administered N-methyl-N-nitrosourea (MNU), 3,2'-dimethyl-4-aminobiphenyl (DMAB), dimethylnitrosamine (DMN), and 1,2- dimethylhydrazine (DMH) for 5 days/week for 4 weeks, using corn oil as a vehicle. Animals were sacrificed at day 28, and their stomachs were excised. γ-H2AX foci formation, indicating DNA double-strand breaks, was observed in the proliferative zone of both fundic and pyloric glands. The number of positive cells per gland was significantly high in pyloric glands in the MNU group and in fundic glands in the MNU and DMAB groups. A significant increase in p21waf1 mRNA level was observed in the DMN group compared with the control, which was in contrast to the decreasing tendency of the h2afx mRNA level in the MNU and DMN groups. Apoptotic cells positive for γ-H2AX pan or peripheral nuclear staining were observed on the surface layer of the fundic mucosa in the MNU group. The fundic pepsinogen a5 (pga5) mRNA level showed a significant decrease, indicating gland damage. The pyloric pepsinogen c mRNA level showed no change. In conclusion, γ-H2AX in combination with other gene expression analyses could be a useful biomarker in a short-term experiment on gastric chemical genotoxicity.

Uniform Widespread Nuclear Phosphorylation of Histone H2AX Is an Indicator of Lethal DNA Replication Stress

Phosphorylated histone H2AX (γ-H2AX), a central player in the DNA damage response (DDR), serves as a biomarker of DNA double-strand break repair. Although DNA damage is generally visualized by the formation of γ-H2AX foci in injured nuclei, it is unclear whether the widespread uniform nuclear γ-H2AX (called pan-nuclear) pattern occurring upon intense replication stress (RS) is linked to DDR. Using a novel monoclonal antibody that binds exclusively to the phosphorylated C-terminus of H2AX, we demonstrate that H2AX phosphorylation is systematically pan-nuclear in cancer cells stressed with RS-inducing drugs just before they die. The pan-nuclear γ-H2AX pattern is abolished by inhibition of the DNA-PK kinase. Cell death induction of cancer cells treated with increasing combinations of replication and kinase (ATR and Chk1) inhibitory drugs was proportional to the appearance of pan-nuclear γ-H2AX pattern. Delivery of labeled anti-γ-H2AX Fabs in stressed cells demonstrated at a single cell level that pan-nuclear γ-H2AX formation precedes irreversible cell death. Moreover, we show that H2AX is not required for RS-induced cell death in HeLa cells. Thus, the nuclear-wide formation of γ-H2AX is an incident of RS-induced cell death and, thus, the pan nuclear H2AX pattern should be regarded as an indicator of lethal RS-inducing drug efficacy.

Transcriptional response of murine bone marrow cells to total-body carbon-ion irradiation

The need to understand the health effects of heavy ion irradiation is motivated by the use of this modality in radiotherapy and by the potential for exposure during space missions. We have studied the effects of carbon-ion total-body irradiation on the hematopoietic system of the mouse and, in particular, the transcriptional response of bone marrow (BM) cells. Carbon-ion irradiation caused BM cell DNA damage, apoptosis, elevated ROS, and myelosuppression. Transcriptomic analysis showed that overall gene expression in irradiated BM cells differed significantly from the controls. Of 253 genes that were modulated, 192 were up-regulated and 61 down-regulated. Gene ontology analysis showed that the modulated genes are involved in DNA damage response signaling, DNA repair, apoptosis, and the immune response. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that these functions are regulated by the p38 MAPK, TNF, and apoptosis pathways. These findings indicate pathways that may be involved in protection against carbon ion radiation injury.

MicroRNA-504 modulates osteosarcoma cell chemoresistance to cisplatin by targeting p53

Chemoresistance implicates the therapeutic value of cisplatin and remains a primary obstacle to its clinical use. MicroRNAs (miRs) negatively modulate the expression of their target genes and are associated with the occurrence and progression of various types of tumor. The abnormal expression of miR-504 has been reported in certain types of human tumor and has been associated with tumor prognosis. However, the association between miR-504 and cisplatin in human osteosarcoma remains unclear. The present study therefore aimed to assess the in vitro effects and possible mechanism of miR-504 in cell proliferation, apoptosis and cisplatin resistance in MG63 osteosarcoma cells. The results demonstrated that miR-504 was overexpressed in osteosarcoma tissues and cells. This overexpression also induced cell proliferation, as determined by MTT and EdU staining assays. Furthermore, miR-504 suppressed cisplatin-induced apoptosis, which was demonstrated via MTT, cell morphology analysis and flow cytometry. Cisplatin-induced G₁ arrest was also suppressed, which was determined by flow cytometry. The potential target genes of miR-504 were predicted using bioinformatics. p53 was confirmed to be a direct target of miR-504 using a luciferase reporter assay and western blot analysis revealed that miR-504 negatively regulated p53 expression at a molecular level. These results indicate that miR-504 contributes to cisplatin resistance in MG63 osteosarcoma cells by suppressing p53. miR-504 may therefore be a potential biomarker for cisplatin resistance in patients with osteosarcoma.

Knockdown of Ubiquitin Associated Protein 2-Like (UBAP2L) Inhibits Growth and Metastasis of Hepatocellular Carcinoma

BACKGROUND The aim of this study was to explore the influence of ubiquitin associated protein 2-like (UBAP2L) on the growth and metastasis of hepatocellular carcinoma (HCC) and its potential underlying mechanism. MATERIAL AND METHODS UBAP2L gene was knocked down in SMMC-7721 by RNA interference and cell function experiments were performed. A subcutaneous xenograft tumor model was constructed to examine the effect of UBAP2L silence on HCC growth. Finally, the whole genomic microarrays were used to screen the potential mechanism of UBAP2L in regulating the biological function of HCC. RESULTS Compared with those in the control group, the cell proliferation and clone formation were significantly reduced, cell cycle was arrested in G2/M phase, the number of apoptotic cells was remarkably increased, and the abilities of vascular formation and cell migration and metastasis were dramatically weakened in the shUBAP2L group (All P<0.05). UBAP2L knockdown significantly suppressed the tumor growth of HCC in vivo. Moreover, a total of 320 genes changed significantly after UBAP2L knockdown, among which, 159 genes were upregulated and 161 genes were downregulated. Then, gene enrichment analysis revealed that PI3K/AKT and P53 signal pathway were the most significant in the top 10 enrichments. Finally, Western blot analysis verified that UBAP2L knockdown caused the increase of P21 and PTEN and decrease of CDK1, CCNB1, p-PI3K, and p-AKT. CONCLUSIONS UBAP2L plays an oncogenic role in HCC, and knockdown of its expression significantly inhibits HCC growth and metastasis, which may be related to the regulation of PI3K/AKT and P53 signaling pathways by UBAP2L.

The 19q13 KRAB Zinc-finger protein ZFP82 suppresses the growth and invasion of esophageal carcinoma cells through inhibiting NF-κB transcription and inducing apoptosis

AIM

To study the epigenetic alternations and biological functions of ZFP82 in esophageal squamous cell carcinoma.

MATERIALS & METHODS

Analysis of ZFP82 expression was carried out by quantitative real-time PCR. Cell function was tested by MTS cell proliferation assay, transwell assay and flow cytometry. Gene mechanisms were studied by reverse transcription-PCR (RT-PCR), quantitative real-time PCR, luciferase reporter assay and Western blot.

RESULTS

ZFP82 promoter methylation was downregulated in esophageal squamous cell carcinoma. ZFP82 ectopic expression suppressed cell function and regulated NF-κB phosphorylation and genes involved in cell cycle arrest and apoptosis. Moreover, ZFP82 methylation was correlated with age, tumor stage and outcome.

CONCLUSION

ZFP82 is a tumor suppressor and is disrupted by promoter CpG methylation during esophageal carcinogenesis.

Viability Assessment Following Anticancer Treatment Requires Single-Cell Visualization

A subset of cells within solid tumors become highly enlarged and enter a state of dormancy (sustained proliferation arrest) in response to anticancer treatment. Although dormant cancer cells might be scored as “dead” in conventional preclinical assays, they remain viable, secrete growth-promoting factors, and can give rise to progeny with stem cell-like properties. Furthermore, cancer cells exhibiting features of apoptosis (e.g., caspase-3 activation) following genotoxic stress can undergo a reversal process called anastasis and survive. Consistent with these observations, single-cell analysis of adherent cultures (solid tumor-derived cell lines with differing p53 status) has demonstrated that virtually all cells—irrespective of their size and morphology—that remain adherent to the culture dish for a long time (weeks) after treatment with anticancer agents exhibit the ability to metabolize 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl- tetrazolium bromide (MTT). The purpose of this commentary is to briefly review these findings and discuss the significance of single-cell (versus population averaged) observation methods for assessment of cancer cell viability and metabolic activity.

DNA Damage-Response Pathway Heterogeneity of Human Lung Cancer A549 and H1299 Cells Determines Sensitivity to 8-Chloro-Adenosine

Human lung cancer H1299 (p53-null) cells often display enhanced susceptibility to chemotherapeutics comparing to A549 (p53-wt) cells. However, little is known regarding to the association of DNA damage-response (DDR) pathway heterogeneity with drug sensitivity in these two cells. We investigated the DDR pathway differences between A549 and H1299 cells exposed to 8-chloro-adenosine (8-Cl-Ado), a potential anticancer drug that can induce DNA double-strand breaks (DSBs), and found that the hypersensitivity of H1299 cells to 8-Cl-Ado is associated with its DSB overaccumulation. The major causes of excessive DSBs in H1299 cells are as follows: First, defect of p53-p21 signal and phosphorylation of SMC1 increase S phase cells, where replication of DNA containing single-strand DNA break (SSB) produces more DSBs in H1299 cells. Second, p53 defect and no available induction of DNA repair protein p53R2 impair DNA repair activity in H1299 cells more severely than A549 cells. Third, cleavage of PARP-1 inhibits topoisomerase I and/or topoisomerase I-like activity of PARP-1, aggravates DNA DSBs and DNA repair mechanism impairment in H1299 cells. Together, DDR pathway heterogeneity of cancer cells is linked to cancer susceptibility to DNA damage-based chemotherapeutics, which may provide aid in design of chemotherapy strategy to improve treatment outcomes.

Roles of Polyploid/Multinucleated Giant Cancer Cells in Metastasis and Disease Relapse Following Anticancer Treatment

Tumors and tumor-derived cell lines contain polyploid giant cells with significantly elevated genomic content, often with multiple nuclei. The frequency of giant cells can increase markedly following anticancer treatment. Although giant cells enter a dormant phase and therefore do not form macroscopic colonies (aggregates of ≥50 cells) in the conventional in vitro colony formation assay, they remain viable and metabolically active. The purpose of this commentary is to underscore the potential importance of polyploid/multinucleated giant cells in metastasis and cancer recurrence following exposure to anticancer agents. We also discuss the possibility that most preclinical (cell-based and animal model) drug discovery approaches might not account for delayed responses that are associated with dormant giant cells.

Temozolomide analog PMX 465 downregulates MGMT expression in HCT116 colorectal carcinoma cells

The efficacy of temozolomide (TMZ) treatment for cancers is currently limited by inherent or the development of resistance, particularly, but not exclusively, due to the expression of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) in a significant proportion of tumors. We have found that TMZ analog C8-methyl imidazole tetrazine (PMX 465) displayed good anticancer activity against the colorectal carcinoma HCT116 cells which are MGMT-overexpressing and mismatch repair (MMR)-deficient. In this study, we found that PMX 465 could downregulate the expression of MGMT in HCT116 cells at the protein and mRNA levels. We found that PMX 465 could reduce MGMT expression by increasing the binding of wild-type p53 to the MGMT promoter and reducing the binding of Sp1 to the MGMT promoter.

Emerging Roles of p53 Family Members in Glucose Metabolism

Glucose is the key source for most organisms to provide energy, as well as the key source for metabolites to generate building blocks in cells. The deregulation of glucose homeostasis occurs in various diseases, including the enhanced aerobic glycolysis that is observed in cancers, and insulin resistance in diabetes. Although p53 is thought to suppress tumorigenesis primarily by inducing cell cycle arrest, apoptosis, and senescence in response to stress, the non-canonical functions of p53 in cellular energy homeostasis and metabolism are also emerging as critical factors for tumor suppression. Increasing evidence suggests that p53 plays a significant role in regulating glucose homeostasis. Furthermore, the p53 family members p63 and p73, as well as gain-of-function p53 mutants, are also involved in glucose metabolism. Indeed, how this protein family regulates cellular energy levels is complicated and difficult to disentangle. This review discusses the roles of the p53 family in multiple metabolic processes, such as glycolysis, gluconeogenesis, aerobic respiration, and autophagy. We also discuss how the dysregulation of the p53 family in these processes leads to diseases such as cancer and diabetes. Elucidating the complexities of the p53 family members in glucose homeostasis will improve our understanding of these diseases.

Quercetrin from Toona sinensis leaves induces cell cycle arrest and apoptosis via enhancement of oxidative stress in human colorectal cancer SW620 cells

Finding effective strategies against colorectal cancer (CRC) is still an emergent health problem. In the present study, we investigated the anticancer activity of quercetrin from Toona sinensis leaves (QTL) and explored the underlying mechanism in human CRC cell line SW620. The cells were treated with various concentrations of QTL and the cytotoxic effects of QTL were determined using the MTT assay. Apoptosis and cell cycle status were detected by flow cytometry. Reactive oxygen species (ROS) levels and mitochondrial membrane potential (∆Ψm) were assessed using DCF-DA and JC-1 fluorescence spectrophotometry, respectively. Western blot analysis was used to quantify the expression of apoptosis-related proteins. RT-PCR was applied to determine the mRNA levels of glutathione peroxidase (GPx) and catalase (CAT). QTL exhibited growth inhibitory effects and caused cell cycle arrest in the G2/M phase, which was accompanied by increased expression of p53 and p21 proteins. QTL promoted apoptosis which was consistent with the upregulated expression of Bax, cytochrome c, caspase-9, Apaf-1 and caspase-3. In addition, QTL induced the loss of mitochondrial membrane potential and triggered ROS generation, as revealed by the downregulated mRNA expression and enzymatic activity of GPx and CAT. Furthermore, both N-acetyl cysteine (NAC) and GSH attenuated the QTL-induced growth inhibition observed in SW620 cells along with the increase of ROS levels. These findings revealed that QTL inhibited the growth of CRC cells and facilitated apoptosis by enhancing oxidative stress. QTL may therefore have potential for use in CRC chemotherapy.

Anticancer Activity of Ramalin, a Secondary Metabolite from the Antarctic Lichen Ramalina terebrata, against Colorectal Cancer Cells

Colorectal cancer is a leading cause of death worldwide and occurs through the highly complex coordination of multiple cellular pathways, resulting in carcinogenesis. Recent studies have increasingly revealed that constituents of lichen extracts exhibit potent pharmaceutical activities, including anticancer activity against various cancer cells, making them promising candidates for new anticancer therapeutic drugs. The main objective of this study was to evaluate the anticancer capacities of ramalin, a secondary metabolite from the Antarctic lichen Ramalina terebrata, in the human colorectal cancer cell line HCT116. In this study, ramalin displayed concentration-dependent anticancer activity against HCT116 cells, significantly suppressing proliferation and inducing apoptosis. Furthermore, ramalin induced cell cycle arrest in the gap 2/mitosis (G2/M) phase through the modulation of hallmark genes involved in the G2/M phase transition, such as tumour protein p53 (TP53), cyclin-dependent kinase inhibitor 1A (CDKN1A), cyclin-dependent kinase 1 (CDK1) and cyclin B1 (CCNB1). At both the transcriptional and translational level, ramalin caused a gradual increase in the expression of TP53 and its downstream gene CDKN1A, while decreasing the expression of CDK1 and CCNB1 in a concentration-dependent manner. In addition, ramalin significantly inhibited the migration and invasion of colorectal cancer cells in a concentration-dependent manner. Taken together, these data suggest that ramalin may be a therapeutic candidate for the targeted therapy of colorectal cancer.

Do Multiwell Plate High Throughput Assays Measure Loss of Cell Viability Following Exposure to Genotoxic Agents?

Cell-based assays in multiwell plates are widely used for radiosensitivity and chemosensitivity assessment with different mammalian cell types. Despite their relative ease of performance, such assays lack specificity as they do not distinguish between the cytostatic (reversible/sustained growth arrest) and cytotoxic (loss of viability) effects of genotoxic agents. We recently reported studies with solid tumor-derived cell lines demonstrating that radiosensitivity as measured by multiwell plate colorimetric (e.g., XTT) and fluorimetric (e.g., CellTiter-Blue) assays reflects growth arrest but not loss of viability. Herein we report similar observations with cancer cell lines expressing wild-type p53 (A549 lung carcinoma) or mutant p53 (MDA–MB-231 breast carcinoma) after treatment with the chemotherapeutic drug cisplatin. Importantly, we show that treatment of cancer cells with concentrations of cisplatin that result in 50% effect (i.e., IC₅₀) in multiwell plate assays trigger the emergence of growth-arrested cells that exhibit highly enlarged morphology, remain viable and adherent to the culture dish, and metabolize the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) to its formazan derivative. The emergence of markedly enlarged viable cells complicates the interpretation of chemosensitivity data obtained with multiwell plate high throughput assays. Relying solely on IC₅₀ values could be misleading.

Investigating the Influence of Magnesium Ions on p53-DNA Binding Using Atomic Force Microscopy

p53 is a tumor suppressor protein that plays a significant role in apoptosis and senescence, preserving genomic stability, and preventing oncogene expression. Metal ions, such as magnesium and zinc ions, have important influences on p53–DNA interactions for stabilizing the structure of the protein and enhancing its affinity to DNA. In the present study, we systematically investigated the interaction of full length human protein p53 with DNA in metal ion solution by atomic force microscopy (AFM). The p53–DNA complexes at various p53 concentrations were scanned by AFM and their images are used to measure the dissociation constant of p53–DNA binding by a statistical method. We found that the dissociation constant of p53 binding DNA is 328.02 nmol/L in physiological buffer conditions. The influence of magnesium ions on p53–DNA binding was studied by AFM at various ion strengths through visualization. We found that magnesium ions significantly stimulate the binding of the protein to DNA in a sequence-independent manner, different from that stimulated by zinc. Furthermore, the high concentrations of magnesium ions can promote p53 aggregation and even lead to the formation of self-assembly networks of DNA and p53 proteins. We propose an aggregation and self-assembly model based on the present observation and discuss its biological meaning.

Impact of Premature Senescence on Radiosensitivity Measured by High Throughput Cell-Based Assays

In most p53 wild-type human cell types, radiosensitivity evaluated by the colony formation assay predominantly reflects stress-induced premature senescence (SIPS) and not cell death (Int. J. Mol. Sci. 2017, 18, 928). SIPS is a growth-arrested state in which the cells acquire flattened and enlarged morphology, remain viable, secrete growth-promoting factors, and can give rise to tumor-repopulating progeny. The impact of SIPS on radiosensitivity measured by short-term assays remains largely unknown. We report that in four p53 wild-type human solid tumor-derived cell lines (HCT116, SKNSH, MCF7 and A172): (i) the conventional short-term growth inhibition assay (3 days post-irradiation) generates radiosensitivity data comparable to that measured by the laborious and time-consuming colony formation assay; (ii) radiation dose-response curves obtained by multiwell plate colorimetric/fluorimetric assays are markedly skewed towards radioresistance, presumably reflecting the emergence of highly enlarged, growth-arrested and viable cells; and (iii) radiation exposure (e.g., 8 Gy) does not trigger apoptosis or loss of viability over a period of 3 days post-irradiation. Irrespective of the cell-based assay employed, caution should be exercised to avoid misinterpreting radiosensitivity data in terms of loss of viability and, hence, cell death.