Dualistic role of autophagy in cancer progression

Cytotoxic properties of unfractionated and fractionated bromelain alone or in combination with chemotherapeutic agents in colorectal cancer cells

BACKGROUND

Colorectal cancer (CRC) is one of the most lethal cancers worldwide. Long-term survival is not achieved in metastatic CRC despite the current multidisciplinary therapies. Bromelain, a compound extracted from the pineapple plant, has multiple functions and anticancer properties. Previously, bromelain has been chromatographically separated into four fractions. Fraction 3 (F3) exhibits the highest proteolytic activity. The anticancer effects of F3 bromelain in CRC cells is unknown.

METHODS

In vitro cytotoxicity was verified through a sulforhodamine B assay. Apoptosis in CRC cells induced by unfractionated or F3 bromelain was examined using Annexin V-FITC/PI staining and Western blot analysis. ROS status, autophagy and lysosome formation were determined by specific detection kit.

RESULTS

The cytotoxicity of F3 bromelain in CRC cells was found to be comparable to that of unfractionated bromelain. F3 bromelain induces caspase-dependent apoptosis in CRC cells. Treatment with unfractionated or F3 bromelain increased superoxide and oxidative stress levels and autophagy and lysosome formation. ATG5/12 and beclin-1 were upregulated, and the conversion of LC3B-I to LC3B-II was increased significantly by treatment with F3 bromelain. Treated CQ, autophagy inhibitor, with unfractionated or F3 bromelain enhances the cytotoxic effects. Finally, the combination of unfractionated and F3 bromelain with a routine chemotherapeutic agent (5-fluourouracil, irinotecan, or oxaliplatin) resulted in synergistically higher cytotoxic potency in CRC cells.

CONCLUSION

Unfractionated and F3 bromelain inhibits CRC cell proliferation in vitro, and the cytotoxic effects of unfractionated bromelain are equivalent to F3 bromelain. F3 bromelain may be a potential and potent drug for clinical use due to its anticancer efficacy and high synergistic cytotoxicity when combined with a routine chemotherapeutic agent for CRC.

Autophagy/Mitophagy Regulated by Ubiquitination: A Promising Pathway in Cancer Therapeutics

Autophagy is essential for organismal development, maintenance of energy homeostasis, and quality control of organelles and proteins. As a selective form of autophagy, mitophagy is necessary for effectively eliminating dysfunctional mitochondria. Both autophagy and mitophagy are linked with tumor progression and inhibition. The regulation of mitophagy and autophagy depend upon tumor type and stage. In tumors, mitophagy has dual roles: it removes damaged mitochondria to maintain healthy mitochondria and energy production, which are necessary for tumor growth. In contrast, mitophagy has been shown to inhibit tumor growth by mitigating excessive ROS production, thus preventing mutation and chromosomal instability. Ubiquitination and deubiquitination are important modifications that regulate autophagy. Multiple E3 ubiquitin ligases and DUBs modulate the activity of the autophagy and mitophagy machinery, thereby influencing cancer progression. In this review, we summarize the mechanistic association between cancer development and autophagy/mitophagy activities regulated by the ubiquitin modification of autophagic proteins. In addition, we discuss the function of multiple proteins involved in autophagy/mitophagy in tumors that may represent potential therapeutic targets.

6-(Methylsulfonyl) Hexyl Isothiocyanate: A Chemopreventive Agent Inducing Autophagy in Leukemia Cell Lines

Autophagy is a fundamental catabolic process of cellular survival. The role of autophagy in cancer is highly complex: in the early stages of neoplastic transformation, it can act as a tumor suppressor avoiding the accumulation of proteins, damaged organelles, and reactive oxygen species (ROS), while during the advanced stages of cancer, autophagy is exploited by cancer cells to survive under starvation. 6-(Methylsulfonyl) hexyl isothiocyanate (6-MITC) is the most interesting compound in the Wasabia Japonica rizhome. Recently, we proved its ability to induce cytotoxic, cytostatic, and cell differentiation effects on leukemic cell lines and its antimutagenic activity on TK6 cells. In the current study, to further define its chemopreventive profile, Jurkat and HL-60 cells were treated with 6-MITC for 24 h. The modulation of the autophagic process and the involvement of ROS levels as a possible trigger mechanisms were analyzed by flow cytometry. We found that 6-MITC induced autophagy in Jurkat and HL-60 cells at the highest concentration tested and increased ROS intracellular levels in a dose-dependent manner. Our results implement available data to support 6-MITC as an attractive potential chemopreventive agent.

Cancer cell's internal and external warriors: Autophagosomes and exosomes

"That survival instinct, that will to live, that need to get back to life again, is more powerful than any consideration of taste, decency, politeness, manners, civility, anything. It's such a powerful force." This quote by famous director Danny Boyle is a perfect analogy to describe the cancer cell's inexhaustible drive to persist against all odds. In order to adapt to a hostile environment, the cancer cells rely on multiple mechanisms including immune escape, epithelial to mesenchymal transition, angiogenesis, extravasation, autophagy, exosome release among others. Cancer cells depute their internal and external warriors, autophagosomes and exosomes, to dwell in the belligerent tumor microenvironment. It is quite reasonable for a cancer cell, striving to survive, to invest in pathways that will provide the maximum advantage. Autophagy is an important cellular degradation pathway, while the exosome pathway provides an alternative cargo disposal mechanism to maintain the homeostasis and cell survival. While autophagic degradation provides the essential nutrients to rapidly dividing cells, exosomal secretion ensures that the tumor microenvironment is attuned to accommodate the swiftly expanding tumor mass. Studies have revealed that exosomes secreted by cancer cells can modulate autophagy in recipient cells, while autophagy can influence the biogenesis of exosomes. Autophagy and exosome crosstalk is extremely complex and it is only beginning to be recognized and documented. This review is focused on discussing the roles of autophagy and exosomes in the cancer cell's adaptation to the tumor microenvironment and how the two pathways are coordinately regulated to facilitate cancer cell survival.

The Role of Chloride Channels in the Multidrug Resistance

Nowadays, one of medicine's main and most challenging aims is finding effective ways to treat cancer. Unfortunately, although there are numerous anti-cancerous drugs, such as cisplatin, more and more cancerous cells create drug resistance. Thus, it is equally important to find new medicines and research the drug resistance phenomenon and possibilities to avoid this mechanism. Ion channels, including chloride channels, play an important role in the drug resistance phenomenon. Our article focuses on the chloride channels, especially the volume-regulated channels (VRAC) and CLC chloride channels family. VRAC induces multidrug resistance (MDR) by causing apoptosis connected with apoptotic volume decrease (AVD) and VRAC are responsible for the transport of anti-cancerous drugs such as cisplatin. VRACs are a group of heterogenic complexes made from leucine-rich repetition with 8A (LRRC8A) and a subunit LRRC8B-E responsible for the properties. There are probably other subunits, which can create those channels, for example, TTYH1 and TTYH2. It is also known that the ClC family is involved in creating MDR in mainly two mechanisms-by changing the cell metabolism or acidification of the cell. The most researched chloride channel from this family is the CLC-3 channel. However, other channels are playing an important role in inducing MDR as well. In this paper, we review the role of chloride channels in MDR and establish the role of the channels in the MDR phenomenon.

Oxidative Stress and Autophagy as Key Targets in Melanoma Cell Fate

Melanoma originates from the malignant transformation of melanocytes and is one of the most aggressive forms of cancer. The recent approval of several drugs has increased the chance of survival although a significant subset of patients with metastatic melanoma do not show a long-lasting response to these treatments. The complex cross-talk between oxidative stress and the catabolic process autophagy seems to play a central role in all aspects of melanoma pathophysiology, from initiation to progression and metastasis, including drug resistance. However, determining the fine role of autophagy in cancer death and in response to redox disruption is still a fundamental challenge in order to advance both basic and translational aspects of this field. In order to summarize the interactions among reactive oxygen and nitrogen species, autophagy machinery and proliferation/growth/death/apoptosis/survival, we provide here a narrative review of the preclinical evidence for drugs/treatments that modulate oxidative stress and autophagy in melanoma cells. The significance and the potential for pharmacological targeting (also through multiple and combination approaches) of these two different events, which can contribute independently or simultaneously to the fate of melanoma, may help to define new processes and their interconnections underlying skin cancer biology and unravel new reliable approaches.