Risk factors of using late-autophagy inhibitors: Aspects to consider when combined with anticancer therapies.

Cancer resistance to therapy is still an unsolved scientific and clinical problem. In 2022, the hallmarks of cancer have been expanded to include four new features, including cellular senescence. Therapy-induced senescence (TIS) is a stressor-based response to conventional treatment methods, e.g. chemo- and radiotherapy, but also to non-conventional targeted therapies. Since TIS reinforces resistance in cancers, new strategies for sensitizing cancer cells to therapy are being adopted. These include macroautophagy as a potential target for inhibition due to its potential cytoprotective role in many cancers. The mechanism of late-stage autophagy inhibitors is based on blockage of autophagolysosome formation or an increase in lysosomal pH, resulting in disrupted cargo degradation. Such inhibitors are relevant candidates for increasing anticancer therapy effectiveness. In particular, 4-aminoquoline derivatives: chloroquine/hydroxychloroquine (CQ/HCQ) have been tested in multiple clinical trials in combination with senescence-inducing anti-cancer drugs. In this review, we summarize the properties of selected late-autophagy inhibitors and their role in the regulation of autophagy and senescent cell phenotype in vitro and in vivo models of cancer as well as treatment response in clinical trials on oncological patients. Additionally, we point out that, although these compounds increase the effectiveness of treatment in some cases, their practical usage might be hindered due to systemic toxicity, hypoxic environment, dose- ant time-dependent inhibitory effects, as well as a possible contribution to escaping from TIS.

Role of Oxygen Starvation in Right Ventricular Decompensation and Failure in Pulmonary Arterial Hypertension.

Right ventricular (RV) function and eventually failure determine outcome in patients with pulmonary arterial hypertension (PAH). Initially, RV responds to an increased load caused by PAH with adaptive hypertrophy; however, eventually RV failure ensues. Unfortunately, it is unclear what causes the transition from compensated RV hypertrophy to decompensated RV failure. Moreover, at present, there are no therapies for RV failure; those for left ventricular (LV) failure are ineffective, and no therapies specifically targeting RV are available. Thus there is a clear need for understanding the biology of RV failure and differences in physiology and pathophysiology between RV and LV that can ultimately lead to development of such therapies. In this paper, we discuss RV adaptation and maladaptation in PAH, with a particular focus of oxygen delivery and hypoxia as the principal drivers of RV hypertrophy and failure, and attempt to pinpoint potential sites for therapy.

Comparative analysis of the effect of hypoxia in two different tumor cell models shows the differential involvement of PTEN control of proangiogenic pathways.

Hypoxia, low, non-physiological oxygen tension is a key regulator of tumor microenvironment, determining the pathological tumor vascularization. Alleviation of hypoxia through vessel normalization may be a promising therapeutic approach. We aimed to assess the role of low oxygen tension in PTEN-related pathways and proangiogenic response, in vitro, in two different tumor cell lines, focusing on potential therapeutic targets for tumor vessel normalization. Downregulation of PTEN in hypoxia mediates the activation of distinct mechanisms: cytoplasmic pAKT activation in melanoma and pMDM2 modulation in kidney cancer. We show that hypoxia-induced proangiogenic potential was stronger in Renca cells than B16 F10-confirmed by a distinct secretory potential and different ability to affect endothelial cells functions. Therefore, the impact of hypoxia on PTEN-mediated regulation may determine the therapeutic targets and effectiveness of vessel normalization and intrinsic characteristics of cancer cell have to be taken into account when designing treatment.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy.

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Molecular tracking of interactions between progenitor and endothelial cells via Raman and FTIR spectroscopy imaging: a proof of concept of a new analytical strategy for in vitro research.

Circulating endothelial cell progenitors originating from the bone marrow are considered to be a powerful tool in the repair of endothelium damage. Due to their unique properties, endothelial progenitors are now broadly investigated to assess their clinical significance in diseases e.g., associated with brain endothelial dysfunction. However, their distinction in terms of the expression of specific markers remains ambiguous. Additionally, endothelial progenitor cells may change their repertoire of markers depending on the microenvironment of the tissue in which they are currently located. Here, we applied the label-free Raman and FTIR imaging to discriminate mice brain endothelium and endothelial progenitors. Cells cultured separately showed distinctly different spectral signatures extracted from the whole cellular interior as well as the detected intracellular compartments (nucleus, cytoplasm, perinuclear area, and lipid droplets). Then, we used these spectroscopic signals to examine the cells co-cultured for 24 h. Principal cluster analysis showed their grouping with the progenitor cells and segregation from brain endothelium at a level of the entire cell machinery (in FTIR images) which resulted from biochemical alternations in the cytoplasm and lipid droplets (in Raman images). The models included in partial least square regression indicated that lipid droplets are the key element for the classification of endothelial progenitor-brain endothelial cells interactions.

Pten knockout affects drug resistance differently in melanoma and kidney cancer.

BACKGROUND: PTEN is a tumor suppressor that is often mutated and nonfunctional in many types of cancer. The high heterogeneity of PTEN function between tumor types makes new Pten knockout models necessary to assess its impact on cancer progression and/or treatment outcomes. METHODS: We aimed to show the effect of CRISPR/Cas9-mediated Pten knockout on murine melanoma (B16 F10) and kidney cancer (Renca) cells. We evaluated the effect of PTEN deregulation on tumor progression in vivo and in vitro, as well as on the effectiveness of drug treatment in vitro. In addition, we studied the molecular changes induced by Pten knockout. RESULTS: In both models, Pten mutation did not cause significant changes in cell proliferation in vitro or in vivo. Cells with Pten knockout differed in sensitivity to cisplatin treatment: in B16 F10 cells, the lack of PTEN induced sensitivity and, in Renca cells, resistance to drug treatment. Accumulation of pAKT was observed in both cell lines, but only Renca cells showed upregulation of the p53 level after Pten knockout. PTEN deregulation also varied in the way that it altered PAI-1 secretion in the tested models, showing a decrease in PAI-1 in B16 F10 Pten/KO and an increase in Renca Pten/KO cells. In kidney cancer cells, Pten knockout caused changes in epithelial to mesenchymal transition marker expression, with downregulation of E-cadherin and upregulation of Snail, Mmp9, and Acta2 (α-SMA). CONCLUSIONS: The results confirmed heterogenous cell responses to PTEN loss, which may lead to a better understanding of the role of PTEN in particular types of tumors and points to PTEN as a therapeutic target for personalized medicine.

Microenvironment commits breast tumor ECs to dedifferentiation by micro-RNA-200-b-3p regulation and extracellular matrix remodeling.

Introduction: Hypoxia shapes the tumor microenvironment, modulates distinct cell population activities, and activates pathological angiogenesis in cancer, where endothelial cells (ECs) are the most important players. This study aimed to evidence the influences of the tumor microenvironment on the global gene expression pattern characteristic for ECs and the distinct responses displayed by tumor-derived ECs in comparison to the healthy endothelium during endothelial to mesenchymal transition (EndMT) and its regulation by miR-200-b-3p. Methodology: Immortalized lines of ECs from the same patient with breast cancer, healthy breast tissue (HBH.MEC), and primary tumor (HBCa.MEC) were used. The experiments were performed in normoxia and hypoxia for 48 h. By using the wound healing test, we investigated the migration abilities of ECs. Global gene expression analysis with NGS was carried out to detect new pathways altered in pathological ECs and find the most changed miRNAs. The validation of NGS data from RNA and miRNA was estimated by qPCRs. Mimic miR-200b-3p was used in HBH.MEC, and the targets VEGF, Bcl2, ROCK2, and SP1 were checked. Results: Hypoxia influences EC migration properties in wound healing assays. In hypoxia, healthy ECs migrate slower than they do in normoxia, as opposed to HBCa.MEC, where no decreased migration ability is induced by hypoxia due to EndMT features. NGS data identified this process to be altered in cancer ECs through extracellular matrix (ECM) organization. The deregulated genes, validated by qPCR, included SPP1, ITGB6, COL4A4, ADAMST2, LAMA1, GAS6, PECAM1, ELN, FBLN2, COL6A3, and COL9A3. NGS also identified collagens, laminins, fibronectins, and integrins, as being deregulated in tumor-derived ECs. Moreover, the analysis of the 10 most intensively modified miRNAs, when breast tumor-derived ECs were compared to healthy ECs, shed light on miR-200b-3p, which is strongly upregulated in HBCa.MECs when compared to HBH.MECs. Discussion and conclusion: The pathological ECs differed significantly, both phenotypically and functionally, from the normal corresponding tissue, thus influencing their microenvironment cross-talk. The gene expression profile confirms the EndMT phenotype of tumor-derived ECs and migratory properties acquisition. Moreover, it indicates the role of miR-200b-3p, that is, regulating EndMT in pathological ECs and silencing several angiogenic growth factors and their receptors by directly targeting their mRNA transcripts.

Oxygen therapeutic window induced by myo-inositol trispyrophosphate (ITPP)-Local pO2 study in murine tumors.

Hypoxia, an inevitable feature of locally advanced solid tumors, has been known as an adverse prognostic factor, a driver of an aggressive phenotype, and an unfavorable factor in therapies. Myo-inositol trispyrophosphate (ITPP) is a hemoglobin modifier known to both increase O2 release and normalize microvasculature. Our goal was to measure the tumor oxygen partial pressure dynamic changes and timing of the therapeutic window after ITPP systemic administration. Two syngeneic tumor models in mice, B16 melanoma and 4T1 breast carcinoma, were used, with varying ITPP dose schedules. Tissue oxygenation level was measured over several days in situ in live animals by Electron Paramagnetic Resonance oximetry with implanted OxyChip used as a constant sensor of the local pO2 value. Both B16 and 4T1 tumors became more normoxic after ITPP treatment, with pO2 levels elevated by 10-20 mm Hg compared to the control. The increase in pO2 was either transient or sustained, and the underlying mechanism relied on shifting hypoxic tumor areas to normoxia. The effect depended on ITPP delivery intervals regarding the tumor type and growth rate. Moreover, hypoxic tumors before treatment responded better than normoxic ones. In conclusion, the ITPP-generated oxygen therapeutic window may be valuable for anti-tumor therapies requiring oxygen, such as radio-, photo- or immunotherapy. Furthermore, such a combinatory treatment can be especially beneficial for hypoxic tumors.

Hypoxia, but Not Normoxia, Reduces Effects of Resveratrol on Cisplatin Treatment in A2780 Ovarian Cancer Cells: A Challenge for Resveratrol Use in Anticancer Adjuvant Cisplatin Therapy.

Natural compounds, such as resveratrol (Res), are currently used as adjuvants for anticancer therapies. To evaluate the effectiveness of Res for the treatment of ovarian cancer (OC), we screened the response of various OC cell lines to the combined treatment with cisplatin (CisPt) and Res. We identified A2780 cells as the most synergistically responding, thus optimal for further analysis. Because hypoxia is the hallmark of the solid tumor microenvironment, we compared the effects of Res alone and in combination with CisPt in hypoxia (pO2 = 1%) vs. normoxia (pO2 = 19%). Hypoxia caused an increase (43.2 vs. 5.0%) in apoptosis and necrosis (14.2 vs. 2.5%), reactive oxygen species production, pro-angiogenic HIF-1α (hypoxia-inducible factor-1α) and VEGF (vascular endothelial growth factor), cell migration, and downregulated the expression of ZO1 (zonula occludens-1) protein in comparison to normoxia. Res was not cytotoxic under hypoxia in contrast to normoxia. In normoxia, Res alone or CisPt+Res caused apoptosis via caspase-3 cleavage and BAX, while in hypoxia, it reduced the accumulation of A2780 cells in the G2/M phase. CisPt+Res increased levels of vimentin under normoxia and upregulated SNAI1 expression under hypoxia. Thus, various effects of Res or CisPt+Res on A2780 cells observed in normoxia are eliminated or diminished in hypoxia. These findings indicate the limitations in using Res as an adjuvant with CisPt therapy in OC.

Tumour suppressor PTEN activity is differentially inducible by myo-inositol phosphates.

Tumour evolution and efficacy of treatments are controlled by the microenvironment, the composition of which is primarily dependent on the angiogenic reaction to hypoxic stress. Tumour angiogenesis normalization is a challenge for adjuvant therapy strategies to chemo-, radio- and immunotherapeutics. Myo-inositol trispyrophosphate (ITPP) appears to provide the means to alleviate hypoxia in the tumour site by a double molecular mechanism. First, it modifies the properties of red blood cells (RBC) to release oxygen (O2 ) in the hypoxic sites more easily, leading to a rapid and stable increase in the partial pressure of oxygen (pO2 ). And second, it activates the endothelial phosphatase and tensin homologue deleted on Chromosome 10 (PTEN). The hypothesis that stable normalization of the vascular system is due to the PTEN, a tumour suppressor and phosphatase which controls the proper angiogenic reaction was ascertained. Here, by direct biochemical measurements of PTEN competitive activity in relation to PIP2 production, we show that the kinetics are complex in terms of the activation/inhibition effects of ITPP with an inverted consequence towards the kinase PI3K. The use of the surface plasmon resonance (SPR) technique allowed us to demonstrate that PTEN binds inositol derivatives differently but weakly. This method permitted us to reveal that PTEN is highly sensitive to the local concentration conditions, especially that ITPP increases the PTEN activity towards PIP3, and importantly, that PTEN affinity for ITPP is considerably increased by the presence of PIP3, as occurs in vivo. Our approach demonstrates the validity of using ITPP to activate PTEN for stable vessel normalization strategies.

High Hemin Concentration Induces Escape from Senescence of Normoxic and Hypoxic Colon Cancer Cells.

Hemoglobin from either red meat or bowel bleeding may promote oxidative stress and increase the risk of colorectal cancer (CRC). Additionally, solid cancers or their metastases may be present with localized bruising. Escape from therapy-induced senescence (TIS) might be one of the mechanisms of tumor re-growth. Therefore, we sought to study whether hemin can cause escape from TIS in CRC. To induce senescence, human colon cancer cells were exposed to a chemotherapeutic agent irinotecan (IRINO). Cells treated with IRINO exhibited common hallmarks of TIS. To mimic bleeding, colon cancer cells were additionally treated with hemin. High hemin concentration activated heme oxygenase-1 (HO-1), induced escape from TIS and epithelial-to-mesenchymal transition, and augmented progeny production. The effect was even stronger in hypoxic conditions. Similar results were obtained when TIS cells were treated with another prooxidant agent, H2O2. Silencing of antioxidative enzymes such as catalase (CAT) or glutathione peroxidase-1 (GPx-1) maintained colon cancer cells in a senescent state. Our study demonstrates that a high hemin concentration combined with an increased activity of antioxidative enzymes, especially HO-1, leads to escape from the senescence of colon cancer cells. Therefore, our observations could be used in targeted anti-cancer therapy.

New potential treatment for cardiovascular disease through modulation of hemoglobin oxygen binding curve: Myo-inositol trispyrophosphate (ITPP), from cancer to cardiovascular disease.

The human body is a highly aerobic organism, which needs large amount of oxygen, especially in tissues characterized by high metabolic demand, such as the heart. Inadequate oxygen delivery underlies cardiovascular diseases, such as coronary artery disease, heart failure and pulmonary hypertension. Hemoglobin, the oxygen-transport metalloprotein in the red blood cells, gives the blood enormous oxygen carrying capacity; thus oxygen binding to hemoglobin in the lungs and oxygen dissociation in the target tissues are crucial points for oxygen delivery as well as potential targets for intervention. Myo-inositol trispyrophosphate (ITPP) acts as an effector of hemoglobin, shifting the oxygen dissociation curve to the right and increasing oxygen release in the target tissues, especially under hypoxic conditions. ITPP has been successfully used in cancer studies, demonstrating anti-cancer properties due to prevention of tumor hypoxia. Currently it is being tested in phase 2 clinical trials in humans with various tumors. First preclinical evidence also indicates that it can successfully alleviate myocardial hypoxia and prevent adverse left ventricular and right ventricular remodeling in post-myocardial infarction heart failure and pulmonary hypertension. The aim of the article is to summarize the current knowledge on ITTP, as well as to determine the prospects for its potential use in the treatment of many cardiovascular disorders.

"Endothelial Antibody Factory" at the Blood Brain Barrier: Novel Approach to Therapy of Neurodegenerative Diseases.

The failures of anti-ß-amyloid immunotherapies suggested that the very low fraction of injected antibodies reaching the brain parenchyma due to the filtering effect of the BBB may be a reason for the lack of therapeutic effect. However, there is no treatment, as yet, for the amyotrophic lateral sclerosis (ALS) despite substantial evidence existing of the involvement of TDP-43 protein in the evolution of ALS. To circumvent this filtering effect, we have developed a novel approach to facilitate the penetration of antibody fragments (Fabs) into the brain parenchyma. Leveraging the homing properties of endothelial progenitor cells (EPCs), we transfected, ex vivo, such cells with vectors encoding anti-ß-amyloid and anti-TDP43 Fabs turning them into an "antibody fragment factory". When injected these cells integrate into the BBB, where they secrete anti-TDP43 Fabs. The results showed the formation of tight junctions between the injected engineered EPCs and the unlabeled resident endothelial cells. When the EPCs were further modified to express the anti-TDP43 Fab, we could observe integration of these cells into the vasculature and the secretion of Fabs. Results confirm that production and secretion of Fabs at the BBB level leads to their migration to the brain parenchyma where they might exert a therapeutic effect.

miRNA Pattern in Hypoxic Microenvironment of Kidney Cancer-Role of PTEN.

MicroRNAs are post-transcriptional regulators of gene expression, and disturbances of their expression are the basis of many pathological states, including cancers. The miRNA pattern in the context of tumor microenvironment explains mechanisms related to cancer progression and provides a potential target of modern therapies. Here we show the miRNA pattern in renal cancer focusing on hypoxia as a characteristic feature of the tumor microenvironment and dysregulation of PTEN, being a major tumor suppressor. Methods comprised the CRSPR/Cas9 mediated PTEN knockout in the Renca kidney cancer cell line and global miRNA expression analysis in both in vivo and in vitro (in normoxic and hypoxic conditions). The results were validated on human cancer models with distinct PTEN status. The increase in miR-210-3p in hypoxia was universal; however, the hypoxia-induced decrease in PTEN was associated with an increase in miR-221-3p, the loss of PTEN affected the response to hypoxia differently by decreasing miR-10b-5p and increasing miR-206-3p. In turn, the complete loss of PTEN induces miR-155-5p, miR-100-5p. Upregulation of miR-342-3p in knockout PTEN occurred in the context of the whole tumor microenvironment. Thus, effective identification of miRNA patterns in cancers must consider the specificity of the tumor microenvironment together with the mutations of key suppressors.

Spheroid culture models adequately imitate distinctive features of the renal cancer or melanoma microenvironment.

Tumor development studies should adapt to cancer cells' specific mechanisms in connection with their microenvironment. Standard two-dimensional cultures and gas composition are not relevant to the real cancer environment. Existing three-dimensional models are often requiring sophisticated conditions. Here, we propose and characterize, in two cancer models, melanoma (B16F10) and kidney cancer (RenCa), a three-dimensional culture method, reporting the presence of hypoxia-related genes/proteins and aggressiveness mechanisms (epithelial mesenchymal transition and cancer stem cells). We validate the designed three-dimensional method by comparing it with in vivo growing tumors. The developed method brings simplicity and data reproducibility. Melanoma spheroid-growing cells reached a cell cycle arrest at the G0/G1 phase and showed induction of hypoxia. Spheroid-recovered RenCa cells were enriched in proliferating cells and displayed delayed hypoxia. Moreover, the responses to hypoxia observed in spheroids were validated by in vivo tumor studies for both lines. Three-dimensional shapes induced cancer stem cells in renal cancer, whereas epithelial to mesenchymal transition occurred in the melanoma model. Such distinction in the use of different aggressiveness-leading pathways was observed in in vivo melanoma vs kidney tumors. Thus, this 3D culture model approach is adequate to uncover crucial molecular pathways using distinct mechanisms to reach aggressiveness; i.e., B16F10 cells perform epithelial to mesenchymal transition while RenCa cells dedifferentiate into cancer stem cells. Such three-dimensional models help mimic the in vivo tumor features, i.e., hypoxia and aggressiveness mechanisms as validated here by next-generation sequencing analysis, and are proposed for further alternative methods to in vivo studies.

Heme Oxygenase-1 Has a Greater Effect on Melanoma Stem Cell Properties Than the Expression of Melanoma-Initiating Cell Markers.

Melanoma-initiating cells (MICs) contribute to the tumorigenicity and heterogeneity of melanoma. MICs are identified by surface and functional markers and have been shown to display cancer stem cell (CSC) properties. However, the existence of MICs that follow the hierarchical CSC model has been questioned by studies showing that single unselected melanoma cells are highly tumorigenic in xenotransplantation assays. Herein, we characterize cells expressing MIC markers (CD20, CD24, CD133, Sca-1, ABCB1, ABCB5, ALDHhigh) in the B16-F10 murine melanoma cell line. We use flow cytometric phenotyping, single-cell sorting followed by in vitro clonogenic assays, and syngeneic in vivo serial transplantation assays to demonstrate that the expression of MIC markers does not select CSC-like cells in this cell line. Previously, our group showed that heme-degrading enzyme heme oxygenase-1 (HO-1) can be upregulated in melanoma and increase its aggressiveness. Here, we show that HO-1 activity is important for non-adherent growth of melanoma and HO-1 overexpression enhances the vasculogenic mimicry potential, which can be considered protumorigenic activity. However, HO-1 overexpression decreases clone formation in vitro and serial tumor initiation in vivo. Thus, HO-1 plays a dual role in melanoma, improving the progression of growing tumors but reducing the risk of melanoma initiation.

Spheroid Culture Differentially Affects Cancer Cell Sensitivity to Drugs in Melanoma and RCC Models.

2D culture as a model for drug testing often turns to be clinically futile. Therefore, 3D cultures (3Ds) show potential to better model responses to drugs observed in vivo. In preliminary studies, using melanoma (B16F10) and renal (RenCa) cancer, we confirmed that 3Ds better mimics the tumor microenvironment. Here, we evaluated how the proposed 3D mode of culture affects tumor cell susceptibility to anti-cancer drugs, which have distinct mechanisms of action (everolimus, doxorubicin, cisplatin). Melanoma spheroids showed higher resistance to all used drugs, as compared to 2D. In an RCC model, such modulation was only observed for doxorubicin treatment. As drug distribution was not affected by the 3D shape, we assessed the expression of MDR1 and mTor. Upregulation of MDR1 in RCC spheroids was observed, in contrast to melanoma. In both models, mTor expression was not affected by the 3D cultures. By NGS, 10 genes related with metabolism of xenobiotics by cytochrome p450 were deregulated in renal cancer spheroids; 9 of them were later confirmed in the melanoma model. The differences between 3D models and classical 2D cultures point to the potential to uncover new non-canonical mechanisms to explain drug resistance set by the tumor in its microenvironment.

Polyploidy formation in cancer cells: How a Trojan horse is born.

Ploidy increase has been shown to occur in different type of tumors and participate in tumor initiation and resistance to the treatment. Polyploid giant cancer cells (PGCCs) are cells with multiple nuclei or a single giant nucleus containing multiple complete sets of chromosomes. The mechanism leading to formation of PGCCs may depend on: endoreplication, mitotic slippage, cytokinesis failure, cell fusion or cell cannibalism. Polyploidy formation might be triggered in response to various genotoxic stresses including: chemotherapeutics, radiation, hypoxia, oxidative stress or environmental factors like: air pollution, UV light or hyperthermia. A fundamental feature of polyploid cancer cells is the generation of progeny during the reversal of the polyploid state (depolyploidization) that may show high aggressiveness resulting in the formation of resistant disease and tumor recurrence. Therefore, we propose that modern anti-cancer therapies should be designed taking under consideration polyploidization/ depolyploidization processes, which confer the polyploidization a hidden potential similar to a Trojan horse delayed aggressiveness. Various mechanisms and stress factors leading to polyploidy formation in cancer cells are discussed in this review.