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Oxidative stress as an iceberg in carcinogenesis and cancer biology

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Shinya Toyokuni at Nagoya University
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After the conquest of numerous infectious diseases, the average life span for humans has been enormously prolonged, reaching more than 80 years in many developed countries. However, cancer is one of the top causes of death, and its incidence continues to increase in many countries, including Japan. I was deeply influenced during my career as a cancer researcher by the concept of oxidative stress, which was established by Helmut Sies in 1985. I have no doubt that oxidative stress is a major cause of carcinogenesis in humans but that other factors and chemicals modify it. Notably, established cancer cells are more oxidatively stressed than their non-tumorous counterparts are, and this stress may be associated with selection under oxidative stress and, thus, faster proliferation compared with non-tumorous cells. For cancer prevention, both avoidance of specific risks that are associated with genetic susceptibility and decreasing oxidative stress in general should delay carcinogenesis. For cancer therapy, individualization and precision medicine require further research in the future. In addition to the currently burgeoning array of humanized antibodies and protein kinase inhibitors, novel methods to increase oxidative stress only in cancer cells would be helpful.
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Oxidative stress as an iceberg in carcinogenesis and cancer biology
Shinya Toyokuni
Department of Pathology and Biological Responses, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi, 466-8550,
Japan
article info
Article history:
Received 5 June 2015
Received in revised form
6 June 2015
Accepted 14 September 2015
Keywords:
Iron
Carcinogenesis
Renal cell carcinoma
Mesothelioma
abstract
After the conquest of numerous infectious diseases, the average life span for humans has been enor-
mously prolonged, reaching more than 80 years in many developed countries. However, cancer is one of
the top causes of death, and its incidence continues to increase in many countries, including Japan. I was
deeply influenced during my career as a cancer researcher by the concept of oxidative stress, which was
established by Helmut Sies in 1985. I have no doubt that oxidative stress is a major cause of carcino-
genesis in humans but that other factors and chemicals modify it. Notably, established cancer cells are
more oxidatively stressed than their non-tumorous counterparts are, and this stress may be associated
with selection under oxidative stress and, thus, faster proliferation compared with non-tumorous cells.
For cancer prevention, both avoidance of specific risks that are associated with genetic susceptibility and
decreasing oxidative stress in general should delay carcinogenesis. For cancer therapy, individualization
and precision medicine require further research in the future. In addition to the currently burgeoning
array of humanized antibodies and protein kinase inhibitors, novel methods to increase oxidative stress
only in cancer cells would be helpful.
©2015 Elsevier Inc. All rights reserved.
1. Introduction
The concept of oxidative stress was established by Helmut Sies
in 1985 [1], which is when I graduated from the medical school of
Kyoto University. When I reflect on all of my present publications, I
recognize how deeply I have been influenced by the concept of
oxidative stress, and I am satisfied that what we have been heading
is still true (Fig. 1).
When I was a medical student, I belonged to the Department of
Pathology, under the guidance of Shigeru Okada (assistant profes-
sor) and Osamu Midorikawa (professor) as my mentors. At that
time, they were very excited to find that an iron chelate, ferric
nitrilotriacetate (Fe-NTA), could induce renal carcinogenesis in rats
[2,3] and mice [4]. Basically, iron is insoluble in water at neutral pH.
However, Fe-NTA as a chelated iron is soluble at neutral pH [5,6]
and is present in this form at least for a few hours in vivo [7]. Fe-
NTA has been used to load iron to transferrin [8]. Michiyasu Awai
of Okayama University noticed that intraperitoneal injections of Fe-
NTA into rats loaded iron in various parenchymal cells, which was
not possible by other means. He proposed this as a model of he-
mochromatosis and revealed the iron deposition in hepatocytes
and
b
-cells in pancreatic islets [7]. The point is that Shigeru Okada's
finding of renal cell carcinoma after repeated Fe-NTA administra-
tion was serendipitous because he did not euthanize the rats after
the subchrionic repeated treatment of Fe-NTA for a few months.
Then, Okada and Midorikawa found a high incidence of renal cell
carcinoma, and this model was first reported in Japan in 1982 [2].At
that time, the exact molecular mechanisms of renal cell carcino-
genesis were not known.
2. Role of iron in oxidative stress
Helmut Sies edited and published a book on the concept of
oxidative stress in 1985, which was fortunately translated into the
Japanese language by Masayasu Inoue [1]. Then, after reading the
book and the many subsequent discussions, Prof. Okada's research
team members and I became interested in oxidative stress associ-
ated with the Fe-NTA model.
Iron is a catalyst for the famous Fenton reaction:
Fe(II) þH
2
O
2
->Fe(III) þOH$þOH
[9]. However, this is a
chemical reaction in the tubes. Few people at that time believed
that this reaction could occur in vivo. Indeed, hydroxyl radical is
the most reactive chemical species in the biological system
[10,11]. In 1979, Prof. Kunio Yagi established a method to measure
lipid peroxidation using thiobartiburic acid [12]. Shuji Hamazaki
E-mail address: toyokuni@med.nagoya-u.ac.jp.
Contents lists available at ScienceDirect
Archives of Biochemistry and Biophysics
journal homepage: www.elsevier.com/locate/yabbi
http://dx.doi.org/10.1016/j.abb.2015.11.025
0003-9861/©2015 Elsevier Inc. All rights reserved.
Archives of Biochemistry and Biophysics 595 (2016) 46e49
in Okada's laboratory used this method and showed a renal in-
crease in lipid peroxidation in an acute phase of Fe-NTA treat-
ment [13].
In 1987, I officially entered the project as a graduate student
under Shigeru Okada. Thereafter, morphological methods became
available through the use of frozen sections [14], and we could
show the localization of lipid peroxidation catalyzed by iron in the
renal proximal tubules [15], which are the target cells for carcino-
genesis in this model. Then, we developed monoclonal antibodies
to detect oxidative stress using 8-hydroxy-2
0
-deoxyguanosine (8-
OHdG) [16]- and 4-hydroxy-2-nonenal (HNE) [17]-modified
keyhole limpet hemocyanin as antigens. This was based on the fact
that hydroxyl radicals could produce such products with a most
prominent increase [18,19] and that the levels of 8-OHdG and HNE-
modified proteins are the sum of production and the repair [20].
Using these monoclonal antibodies, it became possible for the first
time to localize oxidative stress in paraffin-embedded sections; this
is a routine method for pathologic diagnosis in medicine, and the
paraffin blocks for sections can be stored at room temperature for
decades. Currently, these antibodies are commercially available and
popular among researchers [11].
3. Role of iron in carcinogenesis and cancer as evolution
Then, we realized that the iron-induced oxidative stress of
chronic nature is indeed able to cause cancer in mammals. In 1996, I
summarized the strong association between iron overload and
carcinogenesis with a great deal of evidence [10]. The rodent renal
carcinogenesis model by Fe-NTA was the first to demonstrate iron
carcinogenicity, with an anatomical location other than the iron
injection site as the target. Thereafter, the evidence based on hu-
man epidemiology and animal experiments greatly increased to
support the role of iron-induced oxidative stress [21,22]. The paper
that appealed most strongly to me was one demonstrating that
phlebotomy twice a year for 5 years (500 ml each) significantly
reduced both cancer risk and cancer occurrence in the US [23].Itis
known that there is no active pathway to excrete iron to outside the
body once it is absorbed into the blood. Only hemorrhage/phle-
botomy or iron chelation therapy can decrease the total body iron
stores.
With the development of next-generation sequencing, it is now
established that the genomic alterations in cancer cells are similar
to the evolution from apes to Homo Sapiens, as suggested by
Charles Darwin [24]. Specifically, advanced or metastasized cancer
cells have obtained new mutations in addition to the original
genomic alterations found in the primary tumor [25]. I have been
long interested in the issue of whether there are any target genes in
oxidative stress-induced carcinogenesis. In the 1990s, we used F1
rats from two genetically distant inbred strains and microsatellite
analysis in Fe-NTA-induced renal carcinogenesis to determine that
p16/p15 tumor suppressor genes are the major targets for deletion
[26]. In 2012, we used a more sophisticated method (array-based
comparative genomic hybridization) to confirm the p16/p15 results
and, further, to find c-Met amplification in a large proportion of
tumors [27]. Thus, there are definitely target genes in iron-
mediated oxidative stress-induced carcinogenesis. Of note, these
genomic alterations at the chromosomal level were similar in
pattern to those of human cancers, which have not been observed
in other rodent models. Therefore, we hypothesized that iron-
induced oxidative stress is a major cause, i.e., an iceberg, of hu-
man cancer (Fig. 2). A recent finding that cell-of-origin chromatin
organization shapes the mutational landscape of cancer [28]
strongly supports our hypothesis by suggesting the presence of a
common endogenous mechanism to induce mutation in all types of
cells.
Asbestos is a natural fibrous mineral that has been commonly
used over the last century worldwide because of its resistance to
heat, acid and friction with economical merits. However, it now
presents a burden to society because of the unexpected occurrence
of malignant mesothelioma (MM), which has an extremely long
incubation period of 30e40 years after exposure. The expected
peak year for asbestos-induced MM is 2025 in Japan [29,30]. Given
this situation, my laboratory is focused on elucidating the molec-
ular carcinogenic mechanisms of asbestos-induced mesothelial
carcinogenesis using rodents. During this process, we found that
iron overload in the nearby mesothelium is an important pathology
in a rat model. Notably, asbestos-induced rat MM showed similar
genetic alterations to Fe-NTA-induced rat renal carcinogenesis,
including the homozygous deletion of p16/p15 tumor suppressor
genes, which is also a frequent observation in human MM [31,32].
Based on these observations, we tested iron chelation therapy with
deferasirox as a preventive strategy after asbestos exposure in the
rat model. We observed a fractional change in histology from highly
aggressive sarcomatoid subtype to epithelioid subtype that shows a
more favorable prognosis [33].
Fig. 1. Helmut Sies, Yuji Naito (left) and myself (right) at the 17th Biennial Meeting of
the Society for Free Radical Research International held in Kyoto on March 24e27,
2014. Yuji Naito and I were co-chairmen of the meeting, and Helmut Sies gave a Trevor
Slater award lecture.
Fig. 2. Oxidative stress as an iceberg in carcinogenesis.
S. Toyokuni / Archives of Biochemistry and Biophysics 595 (2016) 46e49 47
Recently, we extended these observations to the risk assessment
of a synthetic fibrous nanomaterial called carbon nanotubes [34].
These products are already in use in our lives and are included in
various common products, such as liquid crystal sheets and batte-
ries for cell phones [35,36]. Multi-wall carbon nanotubes
(MWCNT), particularly those with a diameter of 50 nm, showed a
similar carcinogenicity for mesothelial cells as asbestos did [37].
The genetic alterations observed in MWCNT-induced MM were
similar to those of asbestos and were thus similar to those of Fe-
NTA-induced renal carcinogenesis [38]. Other findings also sug-
gested the involvement of local iron overload in pathogenesis. In
2014, the International Agency for Research on Cancer reported the
classification of cancer risk on MWCNT (diameter ~50 nm; range
40e170 nm) as possibly carcinogenic to humans (Group 2B) based
on rodent studies, including ours [39]. Thus, these observations
suggest that fibrous foreign material-induced carcinogenesis is
induced by the oxidative stress associated with local iron overload.
The innate ability of mesothelial cells to engulf anything to clear the
somatic cavity [40,41] appears to be another reason why meso-
thelial cells are the target cells in fiber-induced carcinogenesis.
4. Persistent oxidative stress in cancer and antioxidant
enzymes
Here, I change the topic from carcinogenesis to tumor biology.
Carcinogenesis is a process in which a single cell commences pro-
liferation without regulation, occupies a certain anatomic location
and further invades/metastasizes based on both genetic and non-
genetic alterations. The process usually takes years to decades.
Alternatively, established cancer cells, which are basically mono-
clonal in nature, are in a steady state metabolically. In the 1990s, we
found that cancer cells are more oxidatively stressed than their
non-tumorous counterparts are, based on the measurement of 8-
OHdG [20,42]. This was accompanied by the overexpression of
repair enzymes for 8-OHdG, including MutT [43]. The steady level
of oxidative stress in cancer was set at a relatively low level, which
primarily allows for reversible conversion between eSH and eS-S-
[44]. Thus, cancer cells are resistant to oxidative stress (resistance
to chemotherapy and radiotherapy) and are prone to genetic
instability a priori [42] (Fig. 3).
Helmut Sies contributed tremendously to selenoproteins [45].A
variety of antioxidative enzymes, including thioredoxin reductase
and glutathione peroxidase, contain selenocysteine, which is
encoded by a termination codon TGA. Selenoprotein P was purified
from rat and human plasma [46]. Notably, selenoprotein P is
depleted in rat renal cell carcinoma induced by Fe-NTA [47]. The
depleted expression of selenoprotein P in Fe-NTA-induced renal
cell carcinoma may be responsible, at least partially, for the greater
amount of oxidative stress occurring in the neoplastic tissue
compared with the non-tumorous counterparts. There is much
discussion concerning whether supplementary selenium works for
cancer prevention in humans [48].
5. Conclusion: Toward ultimate cancer prevention
Helmut Sies established the concept of oxidative stress in 1985.
In my career as a cancer researcher, I have been deeply influenced
by this concept. Recently, with the help of new technology,
particularly next-generation sequencing, many targetable mole-
cules have been discovered as novel cancer therapies. Humanized
monoclonal antibodies [49] and small molecule tyrosine kinase
inhibitors [50] are the drugs that are currently in fashion as indi-
vidualized therapy, and these are designed to block the critical
signaling pathways in cancer that support its persistent prolifera-
tion. These molecules are either increased products by genome
amplification or novel products by gene fusion. A variety of DNA
modifications/damage can occur with the free radical reactions,
including base modifications [51], strand breaks and cross-links
[52] with other molecules [53]. It is highly possible that these re-
actions are responsible for the above-mentioned genomic
alterations.
As long as we live, we use oxygen, which causes oxidative stress.
The levels of oxidative stress are much increased in pathologic
conditions such as inflammation, radiation- and ultraviolet-
exposure, iron overload and intake of a variety of carcinogenic
chemicals [54]. Thus, oxidative stress can be the iceberg of carci-
nogenesis. Cancer cells are in general under more oxidative stress
compared with their non-tumorous counterparts. Accordingly,
cancer cells are accustomed to higher oxidative stress [42].
The most important triad of our life is oxygen, iron and food.
These three are interacting, and we cannot live without any of
them. Calorie restriction is a popular topic studied for its impact on
longevity [55]. It is usually difficult to change one's oxygen con-
centration unless you can live in a high altitude. I personally believe
that modulating iron stores to avoid its overload could be the ul-
timate cancer prevention (Fig. 4). Phlebotomy or a 400-ml blood
donation results in a ~4% decrease in the iron stores of our body.
Because an iron secretory pathway out of our body does not nor-
mally exist and because iron excess occurs in men and in women
after menopause [54], iron removal could work to melt the iceberg.
Blood donation in the Japanese system [56] thus has three merits
Fig. 3. Persistent oxidative stress in tumor biology. Fig. 4. Oxygen, iron and food as triad of our life.
S. Toyokuni / Archives of Biochemistry and Biophysics 595 (2016) 46e4948
for the donors: it is good for other people, it can serve as a health
check and it may possibly prevent cancer.
Competing interests
The authors declare that they have no competing interests.
Acknowledgments
This work was supported in part by the National Cancer Center
Research and Development Fund (25-A-5), a grant-in-aid for
research from the sMinistry of Education, Culture, Sports, Science
and Technology (MEXT) of Japan (24390094; 221S0001-04;
24108001) and the Yasuda Medical Foundation.
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... Research has confirmed that oxidative stress and the absorption of UV light by nucleic acids play a role in oxidative DNA damage, which may increase the risk of cancer development (Toyokuni 2016). Advances in the field Page 13 of 19 Bhoyar et al. ...
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Plasma is the 4th physical state of matter, characterized by ionized gaseous mixture, after solid, liquid and gas phases, and contains a wide array of components such as ions, electrons, radicals and ultraviolet ray. Whereas the sun and thunder are typical natural plasma, recent progress in the electronics enabled the generation of body-temperature plasma, designated as low-temperature plasma (LTP) or non-thermal plasma since the 1990's. LTP has attracted the attention of researchers for possible biological and medical applications. All the living species on earth utilize water as essential media for solvents and molecular transport. Thus, biological application of LTP naturally intervenes water whether LTP is exposed directly or indirectly, where plasma-activated lactate (PAL) is a standard, containing H2O2, NO2- and other identified molecules. Electron spin resonance and immunohistochemical studies demonstrated that LTP exposure is a handy method to load local oxidative stress. Cancer cells are characterized by persistent self-replication and high cytosolic catalytic Fe(II). Therefore, both direct exposure of LTP and PAL can provide higher damage to cancer cells in comparison to non-tumorous cells, which has been demonstrated in a variety of cancer types. The cell death mode is either apoptosis or ferroptosis, depending on the cancer-type. Thus, LTP and PAL are expected to work as an additional cancer therapy to the established guideline protocols, especially for use in somatic cavities or surgical margins.
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... In aerobic organisms, small amounts of ROS and nitrogen free radicals under physiological conditions are constantly generated under the influence of external and internal stimuli [2,3]. Oxygen homeostasis is, therefore, one of the critical conditions that must be maintained for aerobic organisms to properly function [1,4]. ...
The Influence of Winter Swimming on Oxidative Stress Indicators in the Blood of Healthy Males
Article
Full-text available
  • Jan 2023
Baths in cold water are a popular physical activity performed to improve health. This study aimed to determine whether repeated cold-water exposure leads to the up-regulation of antioxidant defenses and whether or not this leads to a reduction in basal and/or acute pulses of oxidative distress in humans. The study group consisted of 28 healthy male members of the WS club (average age 39.3 ± 6.1 years). The study sessions occurred at the beginning and the end of the WS season. During the WS season, the participants took 3-min cold-water baths in a cold lake once a week. Blood samples were collected three times during each session: before the bath, 30 min after the bath, and 24 h after the bath. The activity of selected antioxidant enzymes, including superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), as well as the concentration of lipid peroxidation (LPO) products, including thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (CD), were determined in erythrocytes. The concentration of TBARS, CD, retinol, and α-tocopherol were determined in the blood plasma, whereas the level of other LPO products, including 4-hydroxynonenal and 8-iso-prostaglandin F2α, were determined in the blood serum. The repeated cold exposure up-regulated most antioxidant defenses, and this led to an attenuation of most indicators of oxidative stress at the baseline and acute pulses in response to cold exposure. In conclusion, due to regular cold exposure, the antioxidant barrier of winter swimmers was stimulated. Thus, short cold-bath sessions seem to be an effective intervention, inducing promoting positive adaptive changes such as the increased antioxidant capacity of the organism.
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... Current understanding is that cancer is a disease of the genome [63]. Thus far, we suggested that iron and oxygen can be the major mutagens in the long human lifetime of more than 80 years [3,64]. Other than iron and oxygen, there are a plethora of mutagenic agents exposed to humans via skin, respiratory tract or gastrointestinal tract, which are both natural and industrial (https:// monog raphs. ...
Environmental impact on carcinogenesis under BRCA1 haploinsufficiency
Article
Full-text available
  • Jan 2023
  • Gene Environ
Cancer is the primary cause of human mortality in Japan since 1981. Although numerous novel therapies have been developed and applied in clinics, the number of deaths from cancer is still increasing worldwide. It is time to consider the strategy of cancer prevention more seriously. Here we propose a hypothesis that cancer can be side effects of long time-use of iron and oxygen and that carcinogenesis is an evolution-like cellular events to obtain “iron addiction with ferroptosis-resistance” where genes and environment interact each other. Among the recognized genetic risk factors for carcinogenesis, we here focus on BRCA1 tumor suppressor gene and how environmental factors, including daily life exposure and diets, may impact toward carcinogenesis under BRCA1 haploinsufficiency. Although mice models of BRCA1 mutants have not been successful for decades in generating phenotype mimicking the human counterparts, a rat model of BRCA1 mutant was recently established that reasonably mimics the human phenotype. Two distinct categories of oxidative stress, one by radiation and one by iron-catalyzed Fenton reaction, promoted carcinogenesis in Brca1 rat mutants. Furthermore, mitochondrial damage followed by alteration of iron metabolism finally resulted in ferroptosis-resistance of target cells in carcinogenesis. These suggest a possibility that cancer prevention by active pharmacological intervention may be possible for BRCA1 mutants to increase the quality of their life rather than preventive mastectomy and/or oophorectomy.
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Review on Phytochemicals, Ethnobotanical and Pharmacological Activities of Psidium Guajava
Article
  • May 2023
Ethnoveterinary medicine include people's indigenous knowledge, skills, methods, practises, and beliefs about caring for themselves. The use of medicinal plants to cure illnesses is an established practise in underdeveloped nations where traditional medicine is used to preserve human health. Guava (Psidium guajava Linn.) is well-known for its culinary and dietary benefits all over the world. Traditional systems of medicine are also aware of the therapeutic benefits of guava fruit, leaf, and other plant components. A range of plant-derived compounds, including quercetin, guaijaverin, isoflavonoids, gallic acid, catechin, epicathechin, rutin, naringenin, kaempferol flavonoids, and galactose-specific lecithins, have demonstrated potential action. Since the guava tree has economic value in every area, it is cultivated on a large scale. Guava fruit is referred to as the "poor man's apple of the tropics" because of the biological activity and therapeutic applications of the guava plant. Parts of the guava plant are utilised to create a range of commercial and medicinal goods. The nutritional value of guava fruit and the therapeutic characteristics of its many components have been examined in this study to give a comprehensive overview of its diverse commercial values.
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Iron Metabolism and Ferroptosis
Chapter
  • Oct 2023
No life on earth can stay alive without iron. Iron acquisition, transfer, storage, and its retrieval are explicitly regulated by various interacting mechanisms, including peptide hormones and transcriptional/posttranscriptional regulation. Mammals possess no physiological pathway to excrete iron outside of the body except for hemorrhage. Iron deficiency may cause anemia and muscle weakness. However, excess iron is a risk for cancer due to resultant oxidative stress. The word “ferroptosis” consists of Fe(II) and “falling down,” respecting the Fenton reaction. Cancer cells accommodate higher catalytic Fe(II) in general but with more resistance to oxidative stress in comparison to the non-tumorous counterpart cells. Therefore, carcinogenesis can be a genetic evolutionary process to obtain ferroptosis-resistance, in which small molecules, such as erastin, can demolish. Recently, low-temperature plasma has become available with the development of engineering, which can precisely load oxidative stress to the preferred surface locations. This novel strategy may specifically kill certain cancer cells or even germs by targeting higher catalytic Fe(II) to result in ferroptosis and is expected to work as an additional medical intervention.
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Transepithelial transport and cellular mechanisms of food-derived antioxidant peptides
Article
Full-text available
  • Oct 2022
Considering the involvement of oxidative stress in the etiology of many non-communicable diseases, food-derived antioxidant peptides (FDAPs) are strong candidates for nutraceutical development for disease prevention and management. This paper reviews current evidence on the transepithelial transport and cellular mechanisms of antioxidant activities of FDAPs. Several FDAPs have multiple health benefits such as anti-inflammatory and anti-photoaging activities, in addition to antioxidant properties through which they protect cellular components from oxidative damage. Some FDAPs have been shown to permeate the intestinal epithelium, which could facilitate their bioavailability and physiological bioactivities. Molecular mechanisms of FDAPs include suppression of oxidative stress as evidenced by reduction in intracellular reactive oxygen species production, lipid peroxidation and apoptotic protein activation as well as increase in antioxidant defense mechanisms (enzymatic and non-enzymatic). Since many FDAPs have demonstrated promising antioxidant activity, future investigation should focus on further elucidation of molecular mechanisms and human studies to explore their practical application for the prevention and management of oxidative stress-related diseases.
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Ferroptosis As Ultimate Target of Cancer Therapy
Article
  • Aug 2022
Ferroptosis is a new form of regulated non-apoptotic cell death, which is characterized by iron-dependent lipid peroxidation, leading eventually to plasma membrane rupture. Its core mechanisms have been elucidated consisting of a driving force as catalytic Fe(II)-dependent Fenton reaction and an incorporation of polyunsaturated fatty acids to membrane phospholipids via peroxisome-dependent and -independent pathways, whereas suppressing factors are the prevention of lipid peroxidation by glutathione peroxidase 4 to protect lipid peroxidation and direct membrane repair via coenzyme Q10 and ESCRT-III pathways. The significance of ferroptosis in cancer therapeutics has now been unveiled. Specific ferroptosis inducers are expected as a promising strategy for cancer treatment, especially in cancers with epithelial mesenchymal transition and possibly in cancers with activated Hippo signaling pathways, both of which cause resistance to traditional chemotherapy but tend to show ferroptosis susceptibility. Developments of ferroptosis inducers are in progress by nanotechnology-based drugs or by innovative engineering devices. Especially, low-temperature (non-thermal) plasma is a novel technology at the preclinical stage. The exposure can induce ferroptosis selectively in cancer cells which are generally rich in catalytic Fe(II). Here we summarize and discuss the recently uncovered responsible molecular mechanisms in association with iron metabolism, ferroptosis and cancer therapeutics. Finally, we also highlight the current classification of ferroptosis inducers.
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Cell-of-origin chromatin organization shapes the mutational landscape of cancer
Article
Full-text available
  • Feb 2015
  • NATURE
Cancer is a disease potentiated by mutations in somatic cells. Cancer mutations are not distributed uniformly along the human genome. Instead, different human genomic regions vary by up to fivefold in the local density of cancer somatic mutations, posing a fundamental problem for statistical methods used in cancer genomics. Epigenomic organization has been proposed as a major determinant of the cancer mutational landscape. However, both somatic mutagenesis and epigenomic features are highly cell-type-specific. We investigated the distribution of mutations in multiple independent samples of diverse cancer types and compared them to cell-type-specific epigenomic features. Here we show that chromatin accessibility and modification, together with replication timing, explain up to 86% of the variance in mutation rates along cancer genomes. The best predictors of local somatic mutation density are epigenomic features derived from the most likely cell type of origin of the corresponding malignancy. Moreover, we find that cell-of-origin chromatin features are much stronger determinants of cancer mutation profiles than chromatin features of matched cancer cell lines. Furthermore, we show that the cell type of origin of a cancer can be accurately determined based on the distribution of mutations along its genome. Thus, the DNA sequence of a cancer genome encompasses a wealth of information about the identity and epigenomic features of its cell of origin.
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Metamorphosis of mesothelial cells with active horizontal motility in tissue culture
Article
Full-text available
  • Jan 2013
Mesothelial cells, which have diverse roles in physiology and pathology, constitute the mesothelium along with connective tissue and the basement membrane; the mesothelium serves to shield the somatic cavities. After mesothelial injury, mesothelial cells undergo tissue recovery. However, the mechanism of mesothelial regeneration remains poorly understood. In this study, we used confocal time-lapse microscopy to demonstrate that transformed mesothelial cells (MeT5A) and mouse peritoneal mesothelial cells can randomly migrate between cells in cell culture and in ex vivo tissue culture, respectively. Moreover, peritoneal mesothelial cells changed their morphology from a flattened shape to a cuboidal one prior to the migration. Conversely, MDCKII epithelial cells forming tight cell-cell contacts with one another do not alter the arrangement of adjacent cells during movement. Our evidence complements the current hypotheses of mesothelial regeneration and suggests that certain types of differentiated mesothelial cells undergo morphological changes before initiating migration to repair injured sites.
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Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study
Article
Full-text available
  • Aug 2012
  • NATURE
Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14 years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.
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Fenton Reaction Induced Cancer in Wild Type Rats Recapitulates Genomic Alterations Observed in Human Cancer
Article
Full-text available
Iron overload has been associated with carcinogenesis in humans. Intraperitoneal administration of ferric nitrilotriacetate initiates a Fenton reaction in renal proximal tubules of rodents that ultimately leads to a high incidence of renal cell carcinoma (RCC) after repeated treatments. We performed high-resolution microarray comparative genomic hybridization to identify characteristics in the genomic profiles of this oxidative stress-induced rat RCCs. The results revealed extensive large-scale genomic alterations with a preference for deletions. Deletions and amplifications were numerous and sometimes fragmented, demonstrating that a Fenton reaction is a cause of such genomic alterations in vivo. Frequency plotting indicated that two of the most commonly altered loci corresponded to a Cdkn2a/2b deletion and a Met amplification. Tumor sizes were proportionally associated with Met expression and/or amplification, and clustering analysis confirmed our results. Furthermore, we developed a procedure to compare whole genomic patterns of the copy number alterations among different species based on chromosomal syntenic relationship. Patterns of the rat RCCs showed the strongest similarity to the human RCCs among five types of human cancers, followed by human malignant mesothelioma, an iron overload-associated cancer. Therefore, an iron-dependent Fenton chemical reaction causes large-scale genomic alterations during carcinogenesis, which may result in distinct genomic profiles. Based on the characteristics of extensive genome alterations in human cancer, our results suggest that this chemical reaction may play a major role during human carcinogenesis.
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Induction of rat renal adenocarcinoma by Fe-nitrilotriacetate (Fe-NTA)
Article
  • Jan 1982
Ferric nitrilotriacetate (Fe-NTA) has often been used in the laboratory as the specific iron donor to the apotransferrin. In 1977, Awai et al succeeded in the induction of diabetes in rats by intraperitoneal administration of Fe-NTA. This was the first demonstration of chronic iron poisoning in the experimental animals. During the course of our investigation, we find that Fe-NTA shows serious effect on kidneys. Eighty Wistar male rats were divided into 32 rats with Fe-NTA treatment, 16 with NTA, 16 with Fe-chondroitin sulfate (Fe-CS), 8 with saline treatment and 8 without any treatment. In the Fe-NTA solution, the molar ratio of Fe to NTA was 1:4. Many of the rats were serially sacrificed for the microscopical observations. Remaining rats (Fe-NTA treated 24, NTA 13, Fe-CS 15, saline 7, and no treatment 8) were kept for 240-260 days after Fe-NTA treated rats had been given a total of 100-150 mg iron. Fe-CS rats were also given a total of 150 mg iron. Twenty two of 24 rats given Fe-NTA developed renal adenocarcinoma at the end of the study. None of the control rats were found to have the neoplasm. Serially observed renal changes and the renal adenocarcinoma as observed histologically by the light microscopy are presented. The possible mechanism of the cancerous induction of Fe-NTA is discussed.
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Iron overload as a major targetable pathogenesis of asbestos-induced mesothelial carcinogenesis
Article
Few people expected that asbestos, a fibrous mineral, would be carcinogenic to humans. In fact, asbestos is a definite carcinogen in humans, causing a rare but aggressive cancer called malignant mesothelioma (MM). Mesothelial cells line the three somatic cavities and thus do not face the outer surface, but reduce the friction among numerous moving organs. MM has several characteristics: extremely long incubation period of 30-40 years after asbestos exposure, difficulty in clinical diagnosis at an early stage, and poor prognosis even under the current multimodal therapies. In Japan, 'Kubota shock' attracted considerable social attention in 2005 for asbestos-induced mesothelioma and, thereafter, the government enacted a law to provide the people suffering from MM a financial allowance. Several lines of recent evidence suggest that the major pathology associated with asbestos-induced MM is local iron overload, associated with asbestos exposure. Preclinical studies to prevent MM after asbestos exposure with iron reduction are in progress. In addition, novel target genes in mesothelial carcinogenesis have been discovered with recently recognized mesothelioma-prone families. Development of an effective preventive strategy is eagerly anticipated because of the long incubation period for MM.
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Deferasirox Induces Mesenchymal-Epithelial Transition in Crocidolite-Induced Mesothelial Carcinogenesis in Rats
Article
  • Sep 2013
  • CANCER PREV RES
Asbestos was used worldwide in huge quantities in the past century. However, because of the unexpected carcinogenicity to mesothelial cells with an extremely long incubation period, many countries face this long-lasting social problem. Mesothelioma is often diagnosed in an advanced stage, for which no effective therapeutic protocols are yet established. We previously reported based on animal experiments that the major pathology in asbestos-induced mesothelial carcinogenesis is local iron overload. Here we undertook to find an effective strategy to prevent, delay or lower the malignant potential of mesothelioma during asbestos-induced carcinogenesis. We used intraperitoneal injections of crocidolite to rats. We performed a 16-week study to seek the maximal tolerated intervention for iron reduction via oral deferasirox administration or intensive phlebotomy. Splenic iron deposition was significantly decreased with either method, and we found that Perls' iron staining in spleen is a good indicator for iron reduction. We injected a total of 10 mg crocidolite at the age of 6 weeks, and the preventive measures were via repeated oral administration of 25-50 mg/kg/day deferasirox or weekly to bimonthly phlebotomy of 4-10 ml/kg/day. The animals were observed till 110 weeks. Deferasirox administration significantly increased the fraction of less malignant epithelioid subtype. Although we found a slightly prolonged survival in deferasirox-treated female rats, larger sample size and refinement of the current protocol are necessary to deduce the cancer-preventive effects of deferasirox. Still, our results suggest deferasirox serves as a potential preventive strategy in people already exposed to asbestos via iron reduction.
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Toward Understanding Success and Failures in the Use of Selenium for Cancer Prevention
Article
  • Feb 2013
  • ANTIOXID REDOX SIGN
Significance: Adequate and supranutritional selenium (Se) intake, maintaining full expression of selenoproteins, has been assumed to be beneficial for human health with respect to prevention of cancer. Strikingly, the effectiveness of dietary Se supplementation depends on many factors: baseline Se status, age, gender, and genetic background of an individual; type of cancer; and time point of intervention in addition to metabolic conversion and dose of applied Se compounds. Recent advances: Se intake levels for optimization of plasma selenoproteins in humans have been delineated. Regulation, function, and genetic variants of several selenoproteins have been characterized in the intestine, where Se-mediated prevention of colorectal cancer appears to be particularly promising. Critical issues: Numerous cell culture and animal studies indicate anticarcinogenic capacity of various Se compounds but, at present, the outcome of human studies is inconsistent and, in large part, disappointing. Moreover, supranutritional Se intake may even trigger adverse health effects, possibly increasing the risk for Type 2 diabetes in Se-replete populations. Future directions: To improve protocols for the use of Se in cancer prevention, knowledge on cellular and systemic actions of Se compounds needs to be broadened and linked to individual-related determinants such as the occurrence of variants in selenoprotein genes and the Se status. Based on better mechanistic insight, populations and individuals that may benefit most from dietary Se supplementation need to be defined and studied in suitably planned intervention trials.
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Iron overload signature in chrysotile-induced malignant mesothelioma
Article
  • Nov 2012
  • J PATHOL
Exposure to asbestos is a risk for malignant mesothelioma (MM) in humans. Among the commercially used types of asbestos (chrysotile, crocidolite, and amosite), the carcinogenicity of chrysotile is not fully appreciated. Here, we show that all three asbestos types similarly induced MM in the rat peritoneal cavity and that chrysotile caused the earliest mesothelioma development with a high fraction of sarcomatoid histology. The pathogenesis of chrysotile-induced mesothelial carcinogenesis was closely associated with iron overload: repeated administration of an iron chelator, nitrilotriacetic acid, which promotes the Fenton reaction, significantly reduced the period required for carcinogenesis; massive iron deposition was found in the peritoneal organs with high serum ferritin; and homozygous deletion of the CDKN2A/2B/ARF tumour suppressor genes, the most frequent genomic alteration in human MM and in iron-induced rodent carcinogenesis, was observed in 92.6% of the cases studied with array-based comparative genomic hybridization. The induced rat MM cells revealed high expression of mesoderm-specific transcription factors, Dlx5 and Hand1, and showed an iron regulatory profile of active iron uptake and utilization. These data indicate that chrysotile is a strong carcinogen when exposed to mesothelia, acting through the induction of local iron overload. Therefore, an intervention to remove local excess iron might be a strategy to prevent MM after asbestos exposure. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
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