Irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation.

Cells can irreversibly exit the cell cycle and become senescent to safeguard against uncontrolled proliferation. While the p53-p21 and p16-Rb pathways are thought to mediate senescence, they also mediate reversible cell cycle arrest (quiescence), raising the question of whether senescence is actually reversible or whether alternative mechanisms underly the irreversibility associated with senescence. Here, we show that senescence is irreversible and that commitment to and maintenance of senescence are mediated by irreversible MYC degradation. Senescent cells start dividing when a non-degradable MYC mutant is expressed, and quiescent cells convert to senescence when MYC is knocked down. In early oral carcinogenesis, epithelial cells exhibit MYC loss and become senescent as a safeguard against malignant transformation. Later stages of oral premalignant lesions exhibit elevated MYC levels and cellular dysplasia. Thus, irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation, but bypassing this degradation may allow tumor cells to escape during cancer initiation.

Loss of CDK4/6 activity in S/G2 phase leads to cell cycle reversal.

In mammalian cells, the decision to proliferate is thought to be irreversibly made at the restriction point of the cell cycle1,2, when mitogen signalling engages a positive feedback loop between cyclin A2/cyclin-dependent kinase 2 (CDK2) and the retinoblastoma protein3-5. Contrary to this textbook model, here we show that the decision to proliferate is actually fully reversible. Instead, we find that all cycling cells will exit the cell cycle in the absence of mitogens unless they make it to mitosis and divide first. This temporal competition between two fates, mitosis and cell cycle exit, arises because cyclin A2/CDK2 activity depends upon CDK4/6 activity throughout the cell cycle, not just in G1 phase. Without mitogens, mitosis is only observed when the half-life of cyclin A2 protein is long enough to sustain CDK2 activity throughout G2/M. Thus, cells are dependent on mitogens and CDK4/6 activity to maintain CDK2 activity and retinoblastoma protein phosphorylation throughout interphase. Consequently, even a 2-h delay in a cell's progression towards mitosis can induce cell cycle exit if mitogen signalling is lost. Our results uncover the molecular mechanism underlying the restriction point phenomenon, reveal an unexpected role for CDK4/6 activity in S and G2 phases and explain the behaviour of all cells following loss of mitogen signalling.

Efficacy of iron-silver bimetallic nanoparticles to enhance radiotherapy.

Radiotherapy (RT) is one of the primary cancer treatment methods. Radiosensitizers are used to enhance RT and protect healthy tissue. Heavy metals have been studied as radiosensitizers. Thus, iron oxide and iron oxide/silver nanoparticles have been the main subjects of this investigation. A simple honey-based synthesis of iron (IONPs) and iron-silver bimetallic nanoparticles (IO@AgNPs) were prepared followed by characterization with transmission electron microscope (TEM), absorption spectra, vibrating sample magnetometer (VSM), and X-ray diffraction (XRD). Additionally, Ehrlich carcinoma was induced in 30 adult BALB/c mice and divided into 6 groups. Mice of group G1 were not treated with nanoparticles or exposed to irradiation (control group), and group G2 and G3 were treated with IONPs and IO@AgNPs respectively. Mice of group G4 were exposed to a high dose of gamma radiation (HRD) (12 Gy). Groups G5 and G6 were treated with IONPs and IO@AgNPs followed by exposure to a low dose of gamma radiation (LRD) (6 Gy) respectively. The impact of NP on the treatment protocol was evaluated by checking tumor growth, DNA damage, and level of oxidative stress in addition to investigating tumor histopathology. Additional research on the toxicity of this protocol was also evaluated by looking at the liver's cytotoxicity. When compared to HRD therapy, combination therapy (bimetallic NPs and LRD) significantly increased DNA damage by about 75% while having a stronger efficacy in slowing Ehrlich tumor growth (at the end of treatment protocol) by about 45%. Regarding the biosafety concern, mice treated with combination therapy showed lower alanine aminotransferase (ALT) levels in their liver tissues by about half the value of HRD. IO@AgNPs enhanced the therapeutic effect of low-dose radiation and increased the efficacy of treating Ehrlich tumors with the least amount of harm to normal tissues as compared to high radiation dosage therapy.

Revealing ß-TrCP activity dynamics in live cells with a genetically encoded biosensor.

The F-box protein beta-transducin repeat containing protein (ß-TrCP) acts as a substrate adapter for the SCF E3 ubiquitin ligase complex, plays a crucial role in cell physiology, and is often deregulated in many types of cancers. Here, we develop a fluorescent biosensor to quantitatively measure ß-TrCP activity in live, single cells in real-time. We find ß-TrCP remains constitutively active throughout the cell cycle and functions to maintain discreet steady-state levels of its substrates. We find no correlation between expression levels of ß-TrCP and ß-TrCP activity, indicating post-transcriptional regulation. A high throughput screen of small-molecules using our reporter identifies receptor-tyrosine kinase signaling as a key axis for regulating ß-TrCP activity by inhibiting binding between ß-TrCP and the core SCF complex. Our study introduces a method to monitor ß-TrCP activity in live cells and identifies a key signaling network that regulates ß-TrCP activity throughout the cell cycle.

Assessment of risk factors and molecular biomarkers in children with supernumerary teeth: a single-center study.

BACKGROUND: Supernumerary teeth are considered one of the commonly observed dental anomalies in children. Several theories have been proposed to explain the presence of supernumerary teeth, including environmental and genetic factors. This study aimed to identify the different risk factors and molecular biomarkers in patients presented with supernumerary teeth. METHODS: This case-control study included 240 children, 6 to 12-year-old. They were divided into a test group (n = 120 children presented with supernumerary teeth) and a control group (n = 120 children with no supernumerary teeth). Questionnaires were distributed to assess demographics and exposure to several environmental factors. Ten extracted supernumerary teeth from the test group were processed for histopathological analysis. RESULTS: Male gender, dental history of severe oral infection or medical history of chemotherapy treatment, previous history of taking medication or illness during pregnancy, family history of neoplastic disorders, use of electronic devices, and living beside agricultural fields or industrial areas were found to be statistically significant associated with the risk of supernumerary teeth development. Immunohistochemistry panel revealed that supernumerary teeth showed enhanced expression of wingless (Wnt) and sonic hedgehog (SHH) proteins as well as a reduced expression of adenomatous polyposis coli (APC) protein, denoting molecular derangement in a group of pathways classically believed to be involved in its pathogenesis. CONCLUSIONS: Males were more frequently affected by supernumerary teeth than females. Several risk factors were notably correlated with the existence of supernumerary teeth. Additionally, molecular biomarkers assessment demonstrated a high expression level of pro-tumorigenic proteins such as Wnt and SHH in patients with supernumerary teeth.

Cell cycle inertia underlies a bifurcation in cell fates after DNA damage.

The G1-S checkpoint is thought to prevent cells with damaged DNA from entering S phase and replicating their DNA and efficiently arrests cells at the G1-S transition. Here, using time-lapse imaging and single-cell tracking, we instead find that DNA damage leads to highly variable and divergent fate outcomes. Contrary to the textbook model that cells arrest at the G1-S transition, cells triggering the DNA damage checkpoint in G1 phase route back to quiescence, and this cellular rerouting can be initiated at any point in G1 phase. Furthermore, we find that most of the cells receiving damage in G1 phase actually fail to arrest and proceed through the G1-S transition due to persistent cyclin-dependent kinase (CDK) activity in the interval between DNA damage and induction of the CDK inhibitor p21. These observations necessitate a revised model of DNA damage response in G1 phase and indicate that cells have a G1 checkpoint.

Following cytotoxic nanoconjugates from injection to halting the cell cycle machinery and its therapeutic implications in oral cancer.

BACKGROUND: The concept of personalized therapy has been proven to be a promising approach. A popular technique is to utilize gold nanoparticles (AuNPs) as drug delivery vectors for cytotoxic drugs and small molecule inhibitors to target and eradicate oral cancer cells in vitro and in vivo. Both drug and nanocarrier designs play important roles in the treatment efficacy. In our study, we standardized the nanosystem regarding NPs type, size, surface ligands and coverage percentage leaving only the drugs mode of action as the confounding variable. We propose that similarly constructed nanoparticles (NPs) can selectively leverage different conjugated drugs irrelevant to their original mode of action. If proven, AuNPs may have a secondary role beyond bypassing cancer cell membrane and delivering their loaded drugs. METHODS: We conjugated 5- fluorouracil (5Fu), camptothecin (CPT), and a fibroblast growth factor receptor1-inhibitor (FGFR1i) to gold nanospheres (AuNSs). We followed their trajectories in Syrian hamsters with chemically induced buccal carcinomas. RESULTS: Flow cytometry and cell cycle data shows that 5Fu- and CPT- induced a similar ratio of S-phase cell cycle arrest as nanoconjugates and in their free forms. On the other hand, FGFR1i-AuNSs induced significant sub-G1 cell population compared with its free form. Despite cell cycle dynamics variability, there was no significant difference in tumor cells' proliferation rate between CPT-, 5Fu- and FGFR1i- AuNSs treated groups. In our in vivo model, FGFR1i-AuNSs induced the highest tumor reduction rates followed by 5Fu- AuNSs. CPT-AuNSs induced significantly lower tumor reduction rates compared with the 5Fu- and FGFR1i- AuNSs despite showing similar proliferative rates in tumor cells. CONCLUSIONS: Our data indicates that the cellular biological events do not predict the outcome seen in our in vivo model. Furthermore, our results suggest that AuNSs selectively enhance the therapeutic effect of small molecule inhibitors such as FGFR1i than potent anticancer drugs. Future studies are required to better understand the underlying mechanism.

Function of gold nanoparticles in oral cancer beyond drug delivery: Implications in cell apoptosis.

OBJECTIVES: Gold nanoparticles (AuNPs) are used to deliver drugs and therapeutic small molecule inhibitors to cancer cells. Evidence shows that AuNPs coated with nuclear localization sequence can cross the nuclear membrane and induce cellular apoptosis. To determine the therapeutic role of AuNPs, we compared two nanoconstructs conjugated to doxorubicin (DOX) through pH-sensitive and pH-resistant linkers. MATERIALS AND METHODS: We tested DOX nanoconjugates' cytotoxicity, cellular and nuclear uptake in oral squamous cell carcinoma cell line. Furthermore, we evaluated the therapeutic effect of pH-sensitive and pH-resistant DOX bioconjugates in hamster buccal pouch carcinoma model. RESULTS: Our data indicate that pH-resistant and pH-sensitive DOX-nanoconjugates were equally localized in cancer cells, but the pH-resistant DOX nanoparticles were more localized in the nuclei inducing a 2-fold increase in the apoptotic effect compared with the pH-sensitive DOX nanoparticles. Our in vivo results show significantly higher tumor shrinkage and survival rates in animals treated with DOX pH-resistant AuNPs compared with pH-sensitive ones. CONCLUSION: Our findings suggest that AuNPs enhance the cytotoxic effect against cancer cells in addition to acting as drug carriers. DOX pH-resistant AuNPs enhanced accumulation of AuNPs in cancer cells' nuclei inducing a significant cellular apoptosis which was confirmed using in vitro and in vivo experiments without deleterious effects on blood cell count.

Oral and Extraoral Intermediate Tumors: Are MMP-9 and Ki-67 Biomarkers Correlated to Their High Recurrence Rates?

Intermediate tumors of the head and neck fall in the borderline category. They are clinically aggressive tumors with no malignant phenotyping. They are locally infiltrative and have high recurrence rate with less chances to metastasize. The standard care is surgical excision with wide margins. However, surgeons are challenged with the anatomic complexity of the head and neck, increasing the susceptibly of satellite cells being left behind. Ki-67 and MMP-9 are proliferative index and extracellular matrix degradation biomarkers, respectively. They are directly correlated to malignant tumors, whereas less associated with the benign ones. Our main objective was to correlate between Ki-67 and MMP-9 expressions and the recurrence rates in these borderline tumors. We performed a retrospective immunohistochemical study comparing the immunoexpression of Ki-67 and MMP-9. Tumors of interest were aggressive fibromatosis (AF, n=70), epithelioid hemangioendothelioma (EHE, n=25), hemangiopericytoma (HP, n=25), benign fibrous histiocytoma (BFH, n=80) and juvenile ossifying fibroma (JOF, n= 40). Our results revealed that AF followed by HP showed significant high levels of MMP-9 expression, with an average positive area percentage of 40% and 37.4% respectively, compared with other tumors (P<0.05). Ki-67 immunoreaction was significantly the lowest in AF (2.3%, P<0.05) and the highest in JOF (24.7%). To conclude, MMP-9 can be used as a possible target in these tumors as an adjuvant therapy to minimize recurrence rates.

Antitumor activity of silver nanoparticles in Ehrlich carcinoma-bearing mice.

Silver nanoparticles (AgNPs) have a wide range of industrial and biomedical applications. The aim of the present study was to determine the cytotoxic and genotoxic effects of AgNPs on Ehrlich carcinoma-bearing mice. AgNPs were characterized by ultraviolet-visible absorption spectroscopy, dynamic light scattering, and transmission electron microscopy (TEM). Furthermore, the cytotoxicity and genotoxicity of AgNPs were evaluated using a series of assays: superoxide dismutase (SOD) enzyme activity, malondialdehyde (MDA) levels, DNA damage (comet assay), and histopathological examination of tissues and tumor size in Ehrlich carcinoma-bearing mice. Treatment of Ehrlich carcinoma-bearing mice with various concentrations of AgNPs (6, 24, and 48 mg/kg) injected intra peritoneal (IP) and intra tumor (IT) revealed that AgNPs significantly elevated the levels (0.5- to 5-fold) of MDA and reduced the activity (32-64%) of SOD. Furthermore, AgNPs caused a 2- to 3-fold increase in comet parameters such as percent tail DNA. Additionally, AgNPs inhibit the promotion of Ehrlich carcinoma by masses of necrotic and fragmented tumor cells. Consequently, the volume of tumor reduced by about 31-95% compared to control one. The results indicate that AgNPs possess cytotoxic and genotoxic effects against Ehrlich tumor and confirm the antitumor properties of AgNPs.

Immunohistopathologic evaluation of Drynaria fortunei rhizome extract in the management of Class II furcation defects in a canine model.

BACKGROUND: Management of furcation defects is still a challenging subject in periodontal therapy. Drynaria fortunei (Df) is a common type of traditional Chinese herb in the area of orthopedics and traumatology. In vitro and tissue engineering studies have shown that Df induces osteoblastic proliferation and promotes the differentiation of human periodontal ligament cells. This study investigated the management of Class II furcation defects in dogs using guided tissue regeneration (GTR) and Df granules mixed with ß-tricalcium phosphate (ß- TCP) alloplast. METHODS: Sixteen Class II critical-sized furcation defects were surgically created in four mongrel dogs: Eight defects were treated with GTR and Df granules mixed with (ß-TCP) alloplast served as the experimental group, while the other eight were managed with GTR and alloplast, served as control. Dogs were sacrificed at 4 and 8 weeks and the premolars were processed for the evaluation of treatment outcome including; osteoblastic count (OC), cementum layer thickness (CLT), percentage of collagen in bone matrix (CBM), and alkaline phosphatase (ALP) immunoreaction. RESULTS: Experimental group treated with Df showed a significant increase (P < 0.001) in the values of OC, CLT, CBM, and ALP immunoreactivity when compared with control at 4 and 8 weeks after treatment. CONCLUSION: Drynaria fortunei demonstrated increased regeneration and bone formation when used in the treatment of furcation defects in a canine model.

Anti-angiogenic therapy (bevacizumab) in the management of oral lichen planus.

Oral lichen planus (OLP), a mucocutaneous chronic inflammatory disease, is conventionally managed using topical corticosteroid therapy. Given the fact that OLP is strongly linked to angiogenesis, anti-angiogenic drugs, such as bevacizumab, might be introduced as an alternative treatment for contraindicated, non-responsive patients. The aim of the present study was to report the short-term effectiveness and safety of intralesional bevacizumab injection in the management of atrophic/erosive OLP. A case series study was conducted in patients with atrophic/erosive OLP in the buccal mucosa, assigned to receive either 2.5 mg of bevacizumab, by intralesional injection (n = 20, test), or topical 0.1% triamcinolone acetonide ointment (n = 20, control). The size, score, and pain intensity of the lesions were assessed pre- and post-treatment. Tissue biopsies were collected for histopathologic, immunohistochemical, and ultrastructural examination. After 1 wk, the test group had significant reductions both in lesion seize and in pain scores compared with controls. A marked decrease in vascular endothelial growth factor (VEGF) and interleukin-8 immunoexpression was noted in tissue biopsies from bevacizumab-treated lesions compared with control lesions. Furthermore, ultrastructural examination of OLP tissue specimens revealed significant healing signs associated with bevacizumab treatment. Short-term data suggest that intralesional bevacizumab injection effectively and safely achieved resolution of atrophic/erosive OLP lesions without disease exacerbations during a 3-month follow-up period.

XAV939: from a small inhibitor to a potent drug bioconjugate when delivered by gold nanoparticles.

Nanoparticles as potential drug delivery vectors are drawing more attention every day. Here, we used gold nanopspheres (AuNSs) to selectively target the Wnt signaling pathway in human oral squamous cell carcinoma (HSC-3) cells. In a previously conducted study, XAV939, a small inhibiter, was found to strongly regulate the Wnt pathway by inhibiting the tankyrase enzyme and subsequent stabilization of cytoplasmic axin levels. In the present study, conjugating XAV939 molecules to AuNSs is found to enhance its potency by at least 100 times over its free form in killing HSC-3 cancer cells. Additionally, XAV 939 uptake studies have demonstrated an enhanced XAV939 bioconjugate delivery to the targeted cells compared to the passive cellular diffusion of the free drug at the same concentration. Furthermore, our study revealed that drug delivery and cytotoxicity are directly related to the size of the functionalized nanoparticles.

Exploiting the nanoparticle plasmon effect: observing drug delivery dynamics in single cells via Raman/fluorescence imaging spectroscopy.

Drug delivery systems (DDSs) offer efficient and localized drug transportation as well as reduce associated side effects. In order to better understand DDSs, precise observation of drug release and delivery is required. Here, we present a strategy, plasmonic-tunable Raman/fluorescence imaging spectroscopy, to track the release and delivery of an anticancer drug (doxorubicin) from gold nanoparticle carriers in real time at a single living cell level. A pH-responsive drug release profile was attained through the conjugation of doxorubicin (DOX) to the nanoparticle surface via a pH-sensitive hydrazone linkage. When DOX is bound to the surface of the gold nanoparticle, its surface-enhanced Raman spectrum can be seen, but its fluorescence is quenched. When released, due to the lysosomes' acidic pH, its Raman enhancement is greatly reduced, changing the acquired Raman spectrum and in turn allowing for the visualization of its fluorescence signal. The plasmonic-tunable Raman/fluorescence properties enabled the tracking of the DOX release and delivery process from the gold nanoparticle surface to the lysosomes of single living cells under the acidic pH change of their microenvironments. This technique offers great potential to follow the molecular mechanisms of drug delivery and release in living cells, as well as the cellular response to drug action.