Evolution of Resistance in Cancer: A Cell Cycle Perspective

Cancer cell cycle heterogeneity as a critical determinant of therapeutic resistance

Intra-tumor heterogeneity is now arguably one of the most-studied topics in tumor biology, as it represents a major obstacle to effective cancer treatment. Since tumor cells are highly diverse at genetic, epigenetic, and phenotypic levels, intra-tumor heterogeneity can be assumed as an important contributing factor to the nullification of chemotherapeutic effects, and recurrence of the tumor. Based on the role of heterogeneous subpopulations of cancer cells with varying cell-cycle dynamics and behavior during cancer progression and treatment; herein, we aim to establish a comprehensive definition for adaptation of neoplastic cells against therapy. We discuss two parallel and yet distinct subpopulations of tumor cells that play pivotal roles in reducing the effects of chemotherapy: "resistant" and "tolerant" populations. Furthermore, this review also highlights the impact of the quiescent phase of the cell cycle as a survival mechanism for cancer cells. Beyond understanding the mechanisms underlying the quiescence, it provides an insightful perspective on cancer stem cells (CSCs) and their dual and intertwined functions based on their cell cycle state in response to treatment. Moreover, CSCs, epithelial-mesenchymal transformed cells, circulating tumor cells (CTCs), and disseminated tumor cells (DTCs), which are mostly in a quiescent state of the cell cycle are proved to have multiple biological links and can be implicated in our viewpoint of cell cycle heterogeneity in tumors. Overall, increasing our knowledge of cell cycle heterogeneity is a key to identifying new therapeutic solutions, and this emerging concept may provide us with new opportunities to prevent the dreadful cancer recurrence.

Glucose-dependent effect of insulin receptor isoforms on tamoxifen antitumor activity in estrogen receptor-positive breast cancer cells

Introduction

Breast cancer is the most common malignancy in women, and it is linked to several risk factors including genetic alterations, obesity, estrogen signaling, insulin levels, and glucose metabolism deregulation. Insulin and Insulin-like growth factor signaling exert a mitogenic and pro-survival effect. Indeed, epidemiological and pre-clinical studies have shown its involvement in the development, progression, and therapy resistance of several cancer types including breast cancer. Insulin/Insulin-like growth factor signaling is triggered by two insulin receptor isoforms identified as IRA and IRB and by Insulin-like growth factor receptor I. Both classes of receptors show high homology and can initiate the intracellular signaling cascade alone or by hybrids formation. While the role of Insulin-like growth factor receptor I in breast cancer progression and therapy resistance is well established, the effects of insulin receptors in this context are complex and not completely elucidated.

Methods

We used estrogen-dependent insulin-like growth factor receptor I deleted gene (MCF7^IGFIRKO) breast cancer cell models, lentivirally transduced to over-express empty-vector (MCF7^IGFIRKO/EV), IRA (MCF7^IGFIRKO/IRA) or IRB (MCF7^IGFIRKO/IRB), to investigate the role of insulin receptors on the antiproliferative activity of tamoxifen in presence of low and high glucose concentrations. The tamoxifen-dependent cytotoxic effects on cell proliferation were determined by MTT assay and clonogenic potential measurement. Cell cycle and apoptosis were assessed by FACS, while immunoblot was used for protein analysis. Gene expression profiling was investigated by a PCR array concerning genes involved in apoptotic process by RT-qPCR.

Results

We found that glucose levels played a crucial role in tamoxifen response mediated by IRA and IRB. High glucose increased the IC50 value of tamoxifen for both insulin receptors and IRA-promoted cell cycle progression more than IRB, independently of glucose levels and insulin stimulation. IRB, in turn, showed anti-apoptotic properties, preserving cells' survival after prolonged tamoxifen exposure, and negatively modulated pro-apoptotic genes when compared to IRA.

Discussion

Our findings suggest that glucose levels modify insulin receptors signaling and that this event can interfere with the tamoxifen therapeutic activity. The investigation of glucose metabolism and insulin receptor expression could have clinical implications in Estrogen Receptor positive breast cancer patients receiving endocrine treatments.

Proposal for a New Diagnostic Histopathological Approach in the Evaluation of Ki-67 in GEP-NETs

Introduction: Studies have shown that the Ki-67 index is a valuable biomarker for the diagnosis, and classification of gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs). We re-evaluated the expression of Ki-67 based on the intensity of the stain, basing our hypothesis on the fact that the Ki-67 protein is continuously degraded. Background: The aim was to evaluate whether a new scoring method would be more effective in classifying NETs by reducing staining heterogeneity. Methods: Patients with GEP-NET (n = 87) were analyzed. The classification difference between the two methods was determined. Results: The classification changed significantly when the Ki-67 semiquantal index was used. The percentage of G1 patients increased from 18.4% to 60.9%, while the G2 patients decreased from 66.7% to 29.9% and the G3 patients also decreased from 14.9% to 9.2%. Moreover, it was found that the traditional Ki-67 was not significantly related to the overall survival (OS), whereas the semiquantal Ki-67 was significantly related to the OS. Conclusions: The new quantification was a better predictor of OS and of tumor classification. Therefore, it could be used both as a marker of proliferation and as a tool to map tumor dynamics that can influence the diagnosis and guide the choice of therapy.

MEK1/2 regulates APOBEC3B and polymerase iota-induced mutagenesis in head and neck cancer cells

Resistance to chemotherapy provides a major challenge in treatment of metastatic cancer. Prolonged exposure to almost any drug regimen leads to the formation of resistant subclones in almost all advanced solid tumors. Tumor heterogeneity because of intrinsic genetic instability is seen as one of the major contributing factors. In this work, we present evidence that genetic instability measured by mutation frequency is induced by treatment with the EGFR inhibitor afatinib or cisplatin in head and neck squamous cancer cells. We find that APOBEC3B and polymerase iota are upregulated, and inhibition of MEK1/2 by U0126 leads to downregulation on the protein level. Costimulation of afatnib and cisplatin with U0126 leads to a significantly lower mutation frequency. These findings may represent a molecular mechanism for dynamically controlling genetic instability during chemotherapy in head and neck squamous cell carcinoma (HNSCC) cancer cells.

Molecular markers associated with the outcome of tamoxifen treatment in estrogen receptor-positive breast cancer patients: scoping review and in silico analysis

Tamoxifen (TMX) is used as adjuvant therapy for estrogen receptor-positive (ER+) breast cancer cases due to its affinity and inhibitory effects. However, about 30% of cases show drug resistance, resulting in recurrence and metastasis, the leading causes of death. A literature review can help to elucidate the main cellular processes involved in TMX resistance. A scoping review was performed to find clinical studies investigating the association of expression of molecular markers profiles with long-term outcomes in ER+ patients treated with TMX. In silico analysis was performed to assess the interrelationship among the selected markers, evaluating the joint involvement with the biological processes. Forty-five studies were selected according to the inclusion and exclusion criteria. After clustering and gene ontology analysis, 23 molecular markers were significantly associated, forming three clusters of strong correlation with cell cycle regulation, signal transduction of proliferative stimuli, and hormone response involved in morphogenesis and differentiation of mammary gland. Also, it was found that overexpression of markers in selected clusters is a significant indicator of poor overall survival. The proposed review offered a better understanding of independent data from the literature, revealing an integrative network of markers involved in cellular processes that could modulate the response of TMX. Analysis of these mechanisms and their molecular components could improve the effectiveness of TMX.

A machine learning approach for single cell interphase cell cycle staging

The cell nucleus is a tightly regulated organelle and its architectural structure is dynamically orchestrated to maintain normal cell function. Indeed, fluctuations in nuclear size and shape are known to occur during the cell cycle and alterations in nuclear morphology are also hallmarks of many diseases including cancer. Regrettably, automated reliable tools for cell cycle staging at single cell level using in situ images are still limited. It is therefore urgent to establish accurate strategies combining bioimaging with high-content image analysis for a bona fide classification. In this study we developed a supervised machine learning method for interphase cell cycle staging of individual adherent cells using in situ fluorescence images of nuclei stained with DAPI. A Support Vector Machine (SVM) classifier operated over normalized nuclear features using more than 3500 DAPI stained nuclei. Molecular ground truth labels were obtained by automatic image processing using fluorescent ubiquitination-based cell cycle indicator (Fucci) technology. An average F1-Score of 87.7% was achieved with this framework. Furthermore, the method was validated on distinct cell types reaching recall values higher than 89%. Our method is a robust approach to identify cells in G₁ or S/G₂ at the individual level, with implications in research and clinical applications.

Tumor-associated neutrophils: orchestrating cancer pathobiology and therapeutic resistance

Introduction: Neutrophils or polymorphonuclear cells (PMNs) account for a considerable portion of the tumor immune stroma. Emerging single-cell transcriptomic analyses have elucidated the striking cellular heterogeneity of PMNs during homeostasis and pathologic conditions and have established their diverse roles in cancer. PMNs have emerged as important players in cancer pathobiology and therapeutic resistance. Tumor-associated neutrophils (TANs) effector functions influence tumor development and resistance or response to therapy.Areas covered: This review focuses on PMN heterogeneity and functional diversity in the context of carcinogenesis. TANs, by activating diverse signaling pathways, contribute to cancer progression and resistance to therapies. Mechanisms by which TANs impact therapeutic resistance include alterations of the tumoral DNA damage response, angiogenesis, reactivation of cancer dormancy, enhancement of tumor cell proliferation/survival and immune evasion.Expert opinion: With the emerging phenotypic and function heterogeneity of TANs, targeting specific TAN functions in developing tumors can lead to translatable therapeutic approaches and limit drug resistance. We propose that combining specific targeting of TAN activity with standard cancer therapy can help patients achieving a complete response and prevent cancer relapse.

Deubiquitinating enzyme inhibitor alleviates cyclin A1-mediated proteasome inhibitor tolerance in mixed-lineage leukemia

Drug resistance is a significant obstacle to effective cancer treatment. Drug resistance develops from initially reversible drug-tolerant cancer cells, which offer therapeutic opportunities to impede cancer relapse. The mechanisms of resistance to proteasome inhibitor (PI) therapy have been investigated intensively, however the ways by which drug-tolerant cancer cells orchestrate their adaptive responses to drug challenges remain largely unknown. Here, we demonstrated that cyclin A1 suppression elicited the development of transient PI tolerance in mixed-lineage leukemia (MLL) cells. This adaptive process involved reversible downregulation of cyclin A1, which promoted PI resistance through cell-cycle arrest. PI-tolerant MLL cells acquired cyclin A1 dependency, regulated directly by MLL protein. Loss of cyclin A1 function resulted in the emergence of drug tolerance, which was associated with patient relapse and reduced survival. Combination treatment with PI and deubiquitinating enzyme (DUB) inhibitors overcame this drug resistance by restoring cyclin A1 expression through chromatin crosstalk between histone H2B monoubiquitination and MLL-mediated histone H3 lysine 4 methylation. These results reveal the importance of cyclin A1-engaged cell-cycle regulation in PI resistance in MLL cells, and suggest that cell-cycle re-entry by DUB inhibitors may represent a promising epigenetic therapeutic strategy to prevent acquired drug resistance.

Berberine-A potent chemosensitizer and chemoprotector to conventional cancer therapies

Chemotherapy and radiotherapy are mainstay treatments for cancer patients. However, their clinical outcomes are highly limited by the resistance of malignant tumors to these therapies and the incurrence of serious damages in vital organs. This in turn necessitates the development of adjunct drugs that overcomes chemo/radioresistance in refractory cancers and protects vital organs from the cytotoxic effects of cancer therapies. In recent years, Berberine (BBR), a natural isoquinoline alkaloid has garnered more attention due to its potent chemosensitizing and chemoprotective properties. BBR effectively sensitizes refractory cancers to chemotherapy and radiotherapy by ameliorating the diverse events underlying therapy resistance. Furthermore, it protects the heart, liver, lungs, and kidneys from severe damages caused by these therapies. In this review, we discuss the molecular mechanisms underlying the chemo/radiosensitizing and chemo/radioprotective potential of BBR during cancer treatment. Also, we highlight the limitations that hamper the clinical application of BBR as an adjunct drug and how novel innovations have been made in recent years to circumvent these challenges.

Uncovering the Pharmacological Mechanism of 2-Dodecyl-6-Methoxycyclohexa-2,5 -Diene-1,4-Dione Against Lung Cancer Based on Network Pharmacology and Experimental Evaluation

Background: 2-Dodecyl-6-Methoxycyclohexa-2, 5-Diene-1,4-Dione (DMDD) was purified from the roots of Averrhoa carambola L. Previous research demonstrated that DMDD is a small molecular compound with significant therapeutic potential for tumors. However, the potential targets and pharmacological mechanism of DMDD to treat lung cancer has not been reported.

Methods: We employed network pharmacology and experimental evaluation to reveal the pharmacological mechanism of DMDD against lung cancer. Potential therapeutic targets of DMDD were screened by PharmMapper. Differentially expressed genes (DEGs) in The Cancer Genome Atlas (TCGA) lung cancer data sets were extracted and analyzed by GEPIA2. The mechanism of DMDD against lung cancer was determined by PPI, gene ontology (GO) and KEGG pathway enrichment analysis. Survival analysis and molecular docking were employed to obtain the key targets of DMDD. Human lung cancer cell lines H1975 and PC9 were used to detect effects of DMDD treatment in vitro. The expression of key targets after DMDD treated was validated by Western Blot.

Results: A total of 60 Homo sapiens potential therapeutic targets of DMDD and 3,545 DEGs in TCGA lung cancer datasets were identified. Gene ontology and pathway analysis revealed characteristic of the potential targets of DMDD and DEGs in lung cancer respectively. Cell cycle and pathways in cancer were overlapping with DMDD potential targets and lung cancer DEGs. Eight overlapping genes were found between DMDD potential therapeutic targets and lung cancer related DEGs. Survival analysis showed that high expression of DMDD potential targets CCNE1 and E2F1 was significantly related to poor patient survival in lung cancer. Molecular docking found that DMDD exhibited significant binding affinities within the active site of CCNE1 and E2F1. Further tests showed that DMDD inhibited the proliferation, migration and clone formation in lung cancer cell lines (H1975 and PC9) in a dose and time dependent manner. Mechanistically, DMDD treatment decreased the expression of CDK2, CCNE1, E2F1 proteins and induced cell cycle arrest at the G1/S phase in H1975 and PC9 cells.

Conclusion: These results delineated that DMDD holds therapeutic potential that blocks tumorigenesis by cell cycle regulation in lung cancer, and may provide potential therapies for lung cancer.

A novel evaluation method for Ki-67 immunostaining in paraffin-embedded tissues

The Ki-67 labeling index is traditionally used to investigate tumor aggressiveness. However, no diagnostic or prognostic value has been associated to the heterogeneous pattern of nuclear positivity. The aims of this study were to develop a classification for the patterns of Ki-67-positive nuclei; to search scientific evidence for the Ki-67 expression and location throughout the cell cycle; and to develop a protocol to apply the classification of patterns of Ki-67-positive nuclei in squamous epithelium with different proliferative activities. Based on empirical observation of paraffin sections submitted to immunohistochemistry for the determination of Ki-67 labeling index and literature review about Ki-67 expression, we created a classification of the patterns of nuclear positivity (NP1, NP2, NP3, NP4, and mitosis). A semi-automatic protocol was developed to identify and quantify the Ki-67 immunostaining patterns in target tissues. Two observers evaluated 7000 nuclei twice to test the intraobserver reliability, and six evaluated 1000 nuclei to the interobserver evaluation. The results showed that the immunohistochemical patterns of Ki-67 are similar in the tumoral and non-tumoral epithelium and were classified without difficulty. There was a high intraobserver reliability (Spearman correlation coefficient > 0.9) and moderate interobserver agreement (k = 0.523). Statistical analysis showed that non-malignant epithelial specimens presented a higher number of NP1 (geographic tongue = 83.8 ± 21.8; no lesion = 107.6 ± 52.7; and mild dysplasia = 86.6 ± 25.8) when compared to carcinoma in Situ (46.8 ± 34.8) and invasive carcinoma (72.6 ± 37.9). The statistical evaluation showed significant difference (p < 0.05). Thus, we propose a new way to evaluate Ki-67, where the pattern of its expression may be associated with the dynamics of the cell cycle. Future proof of this association will validate the use of the classification for its possible impact on cancer prognosis and guidance on personalized therapy.

Protein phosphatase 1 in tumorigenesis: is it worth a closer look?

Cancer cells take advantage of signaling cascades to meet their requirements for sustained growth and survival. Cell signaling is tightly controlled by reversible protein phosphorylation mechanisms, which require the counterbalanced action of protein kinases and protein phosphatases. Imbalances on this system are associated with cancer development and progression. Protein phosphatase 1 (PP1) is one of the most relevant protein phosphatases in eukaryotic cells. Despite the widely recognized involvement of PP1 in key biological processes, both in health and disease, its relevance in cancer has been largely neglected. Here, we provide compelling evidence that support major roles for PP1 in tumorigenesis.

LINC00160 mediates sunitinib resistance in renal cell carcinoma via SAA1 that is implicated in STAT3 activation and compound transportation

Patients with advanced renal cell carcinoma who are resistant to sunitinib currently have limited clinical options for treatment. Therefore, it is necessary to explore the biological basis of sunitinib resistance and to uncover new targets for the intervention of sunitinib resistance. In this study, we identified that LINC00160 was associated with sunitinib resistance in renal cell carcinoma. Resistant tumor cells highly expressed LINC00160 to recruit transcriptional factor TFAP2A, which bound to SAA1 promoter regions and activated its expression. On one hand, SAA1 linked to ABCB1 protein, which facilitated sunitinib cellular efflux and diminished drug accumulation. On the other hand, SAA1 stimulated JAK-STAT signaling pathways, which countered cellular survival inhibition from drug. All these regulatory networks were well organized and collaborated, thus promoting sunitinib resistance in renal cell carcinoma. LINC00160 mediates sunitinib resistance in renal cell carcinoma via SAA1 that is implicated in STAT3 activation and compound transportation, which offers an opportunity for targeted intervention and molecular therapies in the future.