Genetic modification of hypoxia signaling in animal models and its effect on cancer

Role of Mitochondria in Cancer Stem Cell Resistance

Cancer stem cells (CSC) are associated with the mechanisms of chemoresistance to different cytotoxic drugs or radiotherapy, as well as with tumor relapse and a poor prognosis. Various studies have shown that mitochondria play a central role in these processes because of the ability of this organelle to modify cell metabolism, allowing survival and avoiding apoptosis clearance of cancer cells. Thus, the whole mitochondrial cycle, from its biogenesis to its death, either by mitophagy or by apoptosis, can be targeted by different drugs to reduce mitochondrial fitness, allowing for a restored or increased sensitivity to chemotherapeutic drugs. Once mitochondrial misbalance is induced by a specific drug in any of the processes of mitochondrial metabolism, two elements are commonly boosted: an increment in reactive nitrogen/oxygen species and, subsequently, activation of the intrinsic apoptotic pathway.

Molecular principles of metastasis: a hallmark of cancer revisited

Metastasis is the hallmark of cancer that is responsible for the greatest number of cancer-related deaths. Yet, it remains poorly understood. The continuous evolution of cancer biology research and the emergence of new paradigms in the study of metastasis have revealed some of the molecular underpinnings of this dissemination process. The invading tumor cell, on its way to the target site, interacts with other proteins and cells. Recognition of these interactions improved the understanding of some of the biological principles of the metastatic cell that govern its mobility and plasticity. Communication with the tumor microenvironment allows invading cancer cells to overcome stromal challenges, settle, and colonize. These characteristics of cancer cells are driven by genetic and epigenetic modifications within the tumor cell itself and its microenvironment. Establishing the biological mechanisms of the metastatic process is crucial in finding open therapeutic windows for successful interventions. In this review, the authors explore the recent advancements in the field of metastasis and highlight the latest insights that contribute to shaping this hallmark of cancer.

Tumor Dormancy and Interplay with Hypoxic Tumor Microenvironment

The tumor microenvironment is a key factor in disease progression, local resistance, immune-escaping, and metastasis. The rapid proliferation of tumor cells and the aberrant structure of the blood vessels within tumors result in a marked heterogeneity in the perfusion of the tumor tissue with regions of hypoxia. Although most of the tumor cells die in these hypoxic conditions, a part of them can adapt and survive for many days or months in a dormant state. Dormant tumor cells are characterized by cell cycle arrest in G0/G1 phase as well as a low metabolism, and are refractive to common chemotherapy, giving rise to metastasis. Despite these features, the cells retain their ability to proliferate when conditions improve. An understanding of the regulatory machinery of tumor dormancy is essential for identifying early cancer biomarkers and could provide a rationale for the development of novel agents to target dormant tumor cell populations. In this review, we examine the current knowledge of the mechanisms allowing tumor dormancy and discuss the crucial role of the hypoxic microenvironment in this process.

Prolyl hydroxylase domain 3 influences the radiotherapy efficacy of pancreatic cancer cells by targeting hypoxia-inducible factor-1α

Purpose

Pancreatic cancer is characterized by a hypoxic microenvironment and resistance to most currently available treatment modalities. Prolyl hydroxylase domain 3 (PHD3) is a rate-limiting enzyme that regulates the degradation of hypoxia-inducible factors (HIFs) and is deregulated in pancreatic cancer cells. Whether such alteration of PHD3 expression contributes to the sustained growth and radioresistance of pancreatic cancer cells remains largely unknown.

Materials and methods

PHD3 was overexpressed in pancreatic cancer Mia-paca2 cells via lentiviral expression. Cell cycle progression and apoptosis were assayed by flow cytometry. HIF-1α, EGFR, and PHD3 protein expression was assessed by Western blotting. Cell survival was determined in a colony formation assay.

Results

PHD3 overexpression suppressed HIF-1α protein expression and EGFR phosphorylation and enhanced the 2 Gy irradiation-mediated reductions in HIF-1α and phosphorylated (p)-EGFR under either normoxic or hypoxic conditions. PHD3 overexpression inhibited the growth and colony formation of Mia-paca2 cells in response to irradiation under either normoxic or hypoxic conditions. PHD3 overexpression exacerbated irradiation-induced apoptosis, with a greater effect under hypoxia than normoxia. Cell cycle distribution analysis demonstrated that PHD3 overexpression resulted in further shortened S phase and lengthened G2/M phase in response to irradiation.

Conclusion

PHD3 expression may contribute to the radiotherapy efficacy of pancreatic cancer cells and serve as a novel biomarker for improving radiotherapy efficacy in pancreatic cancer.

Decoding Warburg's hypothesis: tumor-related mutations in the mitochondrial respiratory chain

Otto Warburg observed that cancer cells derived their energy from aerobic glycolysis by converting glucose to lactate. This mechanism is in opposition to the higher energy requirements of cancer cells because oxidative phosphorylation (OxPhos) produces more ATP from glucose. Warburg hypothesized that this phenomenon occurs due to the malfunction of mitochondria in cancer cells. The rediscovery of Warburg's hypothesis coincided with the discovery of mitochondrial tumor suppressor genes that may conform to Warburg's hypothesis along with the demonstrated negative impact of HIF-1 on PDH activity and the activation of HIF-1 by oncogenic signals such as activated AKT. This work summarizes the alterations in mitochondrial respiratory chain proteins that have been identified and their involvement in cancer. Also discussed is the fact that most of the mitochondrial mutations have been found in homoplasmy, indicating a positive selection during tumor evolution, thereby supporting their causal role.