Rongliang
Zheng
*a,
Zhongjian
Jia
b,
Ji
Li
a,
Shuangsheng
Huang
a,
Ping
Mu
a,
Fangxin
Zhang
b,
Chunming
Wang
a and
Chengshan
Yuan
b
aInstitute of Biophysics, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China. E-mail: zhengrl@lzu.edu.cn; Fax: +86-931-8912561; Tel: +86-931-8911136
bState Key Laboratory of Applied Organic Chemistry, School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, China
First published on 18th October 2011
Genomic instability is a characteristic of most cancers and could be directly caused by DNA damage. DNA repair maintains genomic integrity, reducing the onset of cancer. A distinct DNA fast repair process, synonymous fast repair, is initiated and finished in a microsecond time scale, enormously faster by approximately 9 orders than enzymatic repair, and thus eradicates the headstream of DNA damage, DNA radicals exclusively, in the earliest stage of carcinogenesis. The known enzymatic repair cannot repair DNA radicals and mutation, but fast repair can. Therefore, the fast repair mechanism is a defence in the front line in fighting carcinogenesis. If there was no fast repair, certainly much more DNA steady damage would accumulate and would lead to mutation and cancer with high risk. Almost all the tested phytophenols with fast repair activity, except one, are able to suppress the hallmarks of cancer, such as morphological normalization, redifferentiation, decrease of cancer growth and transplanting rate, inhibition of telomerase, metastasis and angiogenesisin vitro and in vivo, reducing cancer incidence and mortality rate in animals.
Rongliang Zheng | Rongliang Zheng, professor at the Institute of Biophysics, School of Life Sciences, Lanzhou University, China, won the 2009 National Prize for Natural Sciences of China and was selected for the National Outstanding Scientist for life honor in 2010. He graduated from the Graduate School of Peking University in 1956, and was a postdoctoral fellow and visiting professor at Johns Hopkins University, USA, and Brunel University, UK, and a co-supervisor of PhD students at 7 Paris University. His research focuses on the antitumor, antioxidant and fast repair of DNA radical damage activities of natural products from herbs, as well as the role of oxygen radicals in cell carcinogenesis. |
Zhongjian Jia | Zhongjian Jia is a professor at the College of Chemistry and Chemical Engineering, Lanzhou University, and graduated from the Department of Chemistry, Graduate School of Peking University in 1958. She won the 2009 National Prize for Natural Sciences, and the Gold Cattle Prize awarded jointly by the National Development Program Commission, Ministry of Education and Ministry of Sciences and Techniques of China. Her research field is natural organic chemistry, especially, the extraction, isolation, elucidation and bioactivities of natural products from folk herbs grown in the Northwest Plateau of China. |
Ji Li | Ji Li received his PhD degree in Prof. Rongliang Zheng's laboratory in 1998. He completed his molecular signaling postdoctoral training at Sichuan University and the National Institute on Aging/NIH during 1998–2002. He was appointed as a research faculty member at Yale University School of Medicine from 2003 to 2007. He then set up his laboratory in the University of Wyoming in 2007. He is currently assistant professor at the State University of New York (SUNY) at Buffalo; his group focuses on investigating the signaling mechanisms of aging-associated cardiovascular diseases. |
Shuangsheng Huang | Shuangsheng Huang received his PhD degree in cell biology in 2005 under the supervision of Prof. Rongliang Zheng. During his PhD studies, he studied the biphasic regulating effects of reactive oxygen species on angiogenesis. He is currently working at the Northwest University for Nationalities as an associate professor. His interests focus mainly on reactive oxygen species and tumor angiogenesis. |
Ping Mu | Ping Mu received her PhD degree from the Institute of Biophysics, School of Life Sciences, Lanzhou University in China in 2007, before working as a postdoctoral fellow in Washington State University, USA. During her PhD studies, she focused on the biphasic regulating effects of reactive oxygen species on angiogenesis as well as the anti-angiogenesis and anti-tumorigenesis of natural compounds. |
Fangxin Zhang | Fangxin Zhang is a chief professor of the Department of Gastroenterology in Lanzhou General Hospital, Gansu, China. He obtained his medical doctor's degree from Xijing Hospital, Fourth Military Medical University, Xi'an, China, in 1997. His research is in the field of digestive tract tumors, especially in early cancer diagnosis and treatment, and in the prevention of plateau gastrointestinal diseases. He won the prize of outstanding researcher in the medical and health sector of Gansu Province. |
Not only does DNA damage trigger the development of cancer, but may trigger cancer cell-cycle arrest and death.9 Correspondingly, there are two strategies for cancer prevention relating to DNA repair. One strategy is to inhibit cancer cells’ DNA repair activity, leading to accumulation of extensive and massive DNA steady damage and finally resulting in selective cancer cell death.10 Another potential strategy is oppositely to enhance the repair mechanism, especially the fast repair mechanism, leading to elimination or abolition of DNA damage and finally resulting in cancer prevention. Both strategies illustrate the essentiality of DNA repair mechanisms in cancer prevention and therapy. The results of some recent studies of the latter potential strategy that may shed light on this important area are summarized in this review.
Although DNA steady damage can be repaired by the enzymatic repair system, this takes place over a time scale of hours,13 while DNA transient damage, DNA radicals, are known to possess half-lives of only seconds,14 so the enzymatic repair mechanism cannot repair the transient damage.
Obviously, how to protect against DNA radicals is a serious problem in living things. Fortunately, there is another repair mechanism named “fast repair”, “non-enzymatic repair” or “chemical repair”, which operates by a quite different mechanism and has been recognized only in recent years.15 The fast repair process is initiated and finished within a microsecond time scale,16 and is enormously faster, by approximately 9 orders, than enzymatic repair, hence the term fast repair. Therefore, fast repair is able to eradicate the headstream of DNA damage, DNA radicals, exclusively.
Secondly, although DNA damage can be recognized by enzymes, and, thus, can be repaired by enzymatic repair, a mutation cannot be recognized by enzymes, and, thus, cannot be repaired by enzymes. However, both DNA transient damage and mutation can be prevented in their extremely early stages by fast repair.
1) DNA repair enzymes themselves can be easily damaged by various stresses and lose their function.17
2) During the processes of aging and disease, or metabolism of xenobiotics, most enzymatic repair activities decrease.18
3) Some repairing enzymes are error prone during DNA replication, and may lead to genomic instability, even tumorigenesis.10
Based on the experimental data, a mechanism involving electron transfer between phytophenols and damaged DNA has been proposed.15 For example, in the repair of the hydroxyl adducts of dGMP by verbascoside (VER), one kind of phytophenol. The primary transient absorption spectrum (λmax = 390 nm) of dGMP–OH˙ declined in a few microseconds, concurrently with the transient absorption spectrum (λmax = 310 nm) of the VER phenoxyl radical (VER–PhO˙) rising, indicating that the dGMO–OH˙ was repaired by VER, and that VER finally became VER–PhO˙. This also means that the fast repair was initiated as soon as the DNA radical was formed; that is the reason why it was called fast repair. The proposed mechanism shows dGMP being attacked by OH˙, becoming dGMP–OH˙, the latter accepting one electron from the phenolic group of verbascoside and then repaired to dGMP. The reactions are as follows:
dGMP |
–OH˙ + VER–PhOH → VER–PhO˙ + dGMP–OH |
− |
+ H |
+ |
(dGMP–OH) |
− |
→ dGMP or hydrated dGMP |
Fig. 1 Cistanoside C (left side in red) docks into the minor groove of DNA with telomere sequence (TTAGGG)3 (right side). |
Some phenylpropanoid glycosides, one kind of phytophenol, with different structures isolated from Tibetan folk herbs by us,29 and some other phytophenols (Fig. 2) are able to repair all 3 types of DNA radicals: DNA anions, DNA cations and DNA–OH˙ adducts (Table 1). Repair rate constants as high as 109 M−1s−1 were measured using the pulse radiolysis technique and transient absorption spectral method.15
Fig. 2 Structures of some phytophenols. |
Phytophenol | Type of DNA | Damaged DNA | Reference |
---|---|---|---|
Verbascoside | Base | T–OH˙ | 16a |
Base | T˙ − | 36a | |
Nucleotide | dAMP(–H)˙ | 34a | |
Nucleotide | dAMP˙ − | 36c | |
Nucleotide | dCMP(–H)˙ | 34a | |
Nucleotide | dGMP–OH˙ | 16b | |
Nucleotide | dGMP–OH˙ | 32c | |
Nucleotide | TMP˙ − | 36b | |
Poly-nucleotide | polyG–OH˙ | 32a | |
Pedicularioside A | Base | T–OH˙ | 32b |
Base | T˙ − | 36a | |
Nucleotide | dAMP–OH˙ | 16b | |
Nucleotide | dGMP–OH˙ | 16b | |
Nucleotide | TMP˙ − | 36b | |
Nucleotide | dAMP˙ − | 36c | |
Nucleotide | dAMP(–H)˙ | 34a | |
Nucleotide | dCMP(–H)˙ | 34a | |
Poly-nucleotide | polyC˙+ | 34b | |
Pedicularioside N | Base | T˙ − | 36a |
EGCG | Nucleotide | dGMP–OH˙ | 26 |
Cistanoside C | Nucleotide | dAMP–OH˙ | 16b,34a |
Nucleotide | dAMP(–H)˙ | 36c | |
Nucleotide | dAMP˙ − | ||
Nucleotide | dCMP(–H)˙ | 34a | |
Nucleotide | dGMP–OH˙ | 16b | |
Nucleotide | dGMP(–H)˙ | 34a | |
nucleotide | polyG–OH˙ | 32a | |
Nucleotide | TMP˙ − | 36b | |
Poly-nucleotide | polyC˙+ | 34b | |
Strand of DNA | dsDNA˙+ | 34b | |
Martynoside | Base | T˙ − | 36a |
Echinocoside | Base | T˙ − | 48b |
Leucosceptoside A | Base | T˙ − | 36a |
Quercetin | Nucleoside | dT˙ − | 36d |
Nucleotide | dAMP(–H)˙ | 34d | |
Nucleotide | dCMP(–H)˙ | 34c | |
Nucleotide | dGMP–OH˙ | 32d | |
Nucleotide | dGMP(–H)˙ | 34d | |
Poly-nucleotide | polyC+ | 34d | |
Rutin | Nucleoside | dT− | 36d |
Nucleotide | dCMP(–H) | 34d | |
Nucleotide | dCMP(–H) | 34c | |
Nucleotide | dGMP–OH˙ | 32d | |
Nucleotide | dGMP(–H) | 34d | |
Poly-nucleotide | polyC˙+ | 34d | |
Silybin | Nucleotide | dGMP–OH˙ | 28 |
Caffeic acid | Base | T˙ − | 25 |
Nucleoside | dT˙ − | 25 | |
Ferulic acid | Nucleotide | dGMP–OH˙ | 26 |
Fig. 3 The hydrogen bonds of a base pair are broken in a DNA–OH˙ adduct. |
The OH˙ adduction reaction is too fast to prevent, therefore, strategies for elimination of DNA damage induced by OH˙ should focus on the elimination of the secondary DNA radicals by reductant via fast repair. Different structures of phytophenols were proven to fast repair 7 types of DNA–OH˙ adducts, including T–OH˙, dT–OH˙, dAMP–OH˙, dGMP–OH˙, polyG–OH˙, ssDNA–OH˙ and dsDNA–OH˙.16,32
Moreover, phytophenols can fast repair not only damage to bases, deoxynucleosides and deoxynucleotides but also damage to integral DNA, such as poly C, poly G and dsDNA radicals, with the latter being closer to cellular conditions.16b,32a,34
All above 5 different structural levels of DNA radicals, such as base–, nucleosid–, nucleotid–, polynucleotid– or strand DNA–radicals are able to induce DNA strand breaks and form stable damage.37 This demonstrates that the fast repair machinery acts as a rescuer of the genome to maintain genomic integrity.
Fig. 4 Graphical illustration of the fast repair activity suppressing the hallmarks of cancer. |
Almost all of the above-mentioned phytophenols (except one unique case: angoroside C, for which no report of its antitumor activity has been found), with fast repair activity are able to suppress the hallmarks of cancer (Table 2), involving genomic instability, mutation, proliferative signaling, immortality, telomerase activity, telomere maintenance, angiogenesis, invasion and metastasis, which have been described in the above two papers.
Phytophenols | Suppressed hallmarks of cancer | Reference |
---|---|---|
a Note: although rosmarinic acid and pedicularioside G have not been measured for fast repair activity, their structures are very similar to that of verbascoside. | ||
Verbascoside | Inhibited the proliferation of human leukemia HL-60 cells | 39 |
Induced human leukemia HL-60 cell redifferentiation into monocytes | 39 | |
Inhibited lung metastasis of melanoma cells in mice and prolonged survival time significantly | 40 | |
Decreased human gastric adenocarcinoma cell growth curve, mitotic index and cell surface charge, reduced microvilli on the surface, delayed doubling time | 41 | |
Decrease tumorigencity (75%) when inoculated subcutaneously in nude mice | 41 | |
Induced gastric carcinoma cell apoptosis by telomerase inhibition and telomere shortening | 43 | |
Significantly inhibited tumor-induced angiogenesis and down-regulated MMPs expression, which are necessary for blood vessel invasion of the tumor tissue. | 44 | |
An antiestrogen in breast cancer cells | 46b | |
The antitumor activity of L-1210 cells may be due to inhibition of protein kinase C | 46a | |
Inhibited PMA-induced invasion and migration of human fibrosarcoma cellsviaCa2+-dependent CaMK/ERK and JNK/NF-κB-signaling pathways | 45 | |
Rosmarinic acid (analog of verbascoside)a | Inhibited human umbilical vein endothelial cell proliferation, migration, adhesion and tube formation | 49 |
Reduced murine tumorigenesis | 48c | |
Pedicularioside G (isomer of verbascoside)a | Inhibited hepatoma cell growth, cell migration, angiogenesis and tumorigenesis | 47 |
Pedicularioside A | Against the growth and viability of human hepatoma cells, human pulmonary adenocarcinoma cells and human gastric adenocarcinoma cells | 48d |
Pedicularioside N | Against the growth and viability of human hepatoma cells, human pulmonary adenocarcinoma cells and human gastric adenocarcinoma cells | 48d |
Tea phenols including EGCG | Inhibited human prostate carcinoma, chemoprevention of squamous cell carcinoma of the head and neck | 53,54b,55 |
Inhibited growth of peripheral blood T lymphocytes of adult T-cell leukemia patients | 54b | |
Suppressed cell proliferation and enhanced apoptosis, inhibited cell invasion, angiogenesis and metastasis | 54a,58 | |
Suppressed angiogenesis in lung tumorigenesis in mice | 57a | |
Reduced cell proliferation, surface charge and microvilli, and DNA damage in human hepatoma cells | 57b | |
Inhibited tumorigenesis in a variety of organs, including skin, lung, oral cavity, esophagus, stomach, small intestine, colon, liver, pancreas, ovary, and breast | 51 | |
Suppressed various tumor promotion and mitogenic signals, and blocked signal transduction | 52 | |
Inhibited telomerase activity and led to telomerase fragmentation | 56 | |
Cistanoside C | Inhibited growth of human hepatoma cells, human lung adenocarcinoma cells and human gastric adenocarcinoma cells | 48a |
Martynoside | Decreased the growth and viability of some cancer cells, but did not affect normal cells | 48c |
Echinocoside | An antiestrogen in breast cancer cells | 45,48c |
Leucosceptoside A | Against the growth and viability of human hepatoma cells, human pulmonary adenocarcinoma cells and human gastric adenocarcinoma cells | 48d |
Decreased the growth and viability of some cancer cells, but did not affect normal cells | 48c | |
Quercetin | Chemoprevention of human colorectal cancer | 60 |
Inhibited azoxymethane-induced colorectal carcinogenesis in rats | 62 | |
Decreased pancreatic cancer growth, increased apoptosis and prevented metastasis in nude mice | 63 | |
Inhibited proliferation and mutant p53 protein expression of human breast cancer cells | 64 | |
Induced human leukemia HL-60 cell apoptosis | 65 | |
Rutin | Chemoprevention of human colorectal cancer, increased apoptotic index of colonic crypts, reduced the number of focal areas of dysplasia in mice | 60–61 |
Reduced the formation of metastasis nodules of melanoma cells | 66 | |
Silybin | Inhibited invasiveness of human hepatoma cells. Silybin is now being tested in clinical trials to treat prostate cancer, ovarian cancer, and skin cancer | 67–68,73 |
Caffeic acid | Suppressed the growth and metastasis of human hepatoma cells in nude mice | 69 |
Ferulic acid | Antiproliferation and apoptosis of human breast cancer cells | 70 |
Induced apoptosis of human hepatoma cells | 71 | |
Preventing cancer induced by carcinogenic compounds in mice | 72a |
Results of our study showed that verbascoside decreased the cell growth curve, mitotic index and cell surface charge, and delayed the doubling time of human gastric adenocarcinoma cells. The microvilli on the surface of the treated cells were reduced significantly (Fig. 5). There was a 75% decrease of the tumorigenicity for the treated cells compared with the untreated cells inoculated subcutaneously in nude mice. It confirmed that verbascoside could reverse gastric adenocarcinoma cells' malignant phenotypic characteristics.41
Fig. 5 Reverse transformation of human gastric adenocarcinoma cell line MGc80-3 (upper) induced by 20 μmol l−1 verbascoside for 7 days, the abundant amounts of microvilli and microfilaments were reduced significantly (lower). Reproduced by permission of Georg Thieme Verlag KG Publishers. |
Suppression of telomerase activity leading to telomere shortening has been rationalized as a crucial anticancer defence.38 Although telomerase inhibiting activity is not a universal mechanism for all antitumor drugs, it is just one of the several possible mechanisms.42 We found that verbascoside inhibited the telomerase activity of human gastric carcinoma cells MKN45 with an IC50 of 17.8 μg ml−1, shortened the average telomere length and displayed a cell cycle sub-G0/G1 peak and G2/M arrest, implying that verbascoside may induce tumor cell apoptosis by telomerase inhibition and telomere shortening.43
Tumors cannot grow beyond a few millimetres without blood supply from the host tissue. Tumors require nutrients and oxygen as well as an ability to evacuate metabolic waste and carbon dioxide. The tumor-associated neovasculature, generated by the process of angiogenesis, addresses these needs. Inhibition of angiogenesis would deprive the growing tumor of nutrients and oxygen supplied by the host circulation and consequently would retard or even abolish tumor growth. Verbascoside significantly inhibited tumor-induced angiogenesis and down-regulated MMPs expression, which are necessary for blood vessel invasion of the tumor tissue.44 Verbascoside inhibited PMA-induced invasion and migration of human fibrosarcoma cellsviaCa2+-dependent CaMK/ERK and JNK/NF-κB-signaling pathways.45 There are 2 other references related to this topic.46
Pedicularioside G (Ped G, compound 9) is an isomer of verbascoside (compound 1), with only a conformational nuance between both: the link of the caffeyl-C4 of glucose (Fig. 2, red circle) in verbascoside is an axial bond, while in Ped G it is an equatorial bond.
Ped G inhibited tumor growth, cell migration, angiogenesis and tumorigenesis.47
Ped G inhibited vascular formation of solid tumors in vivo. A suspension of human hepatoma cells was inoculated onto a chicken embryo chorioallantoic membrane; after 3 days, grafted cells yielded solid tumors that were vascularized. The distribution of vessels radiated around the solid tumor. Ped G treatment for another 3 days evidently suppressed the tumor growth and vessel density, and the radiating vessels disappeared. After solid tumor formation, no chick embryos died, which means that Ped G is not toxic to the chicken embryo chorioallantoic membrane itself. Moreover, the malignant hepatoma cells could be reverse transformed by Ped G. Intact human hepatoma cells were inoculated onto the chorioallantoic membranes of chick embryos. They yielded a light colored disc of tumor lump, whereas in cells pre-incubated with Ped G for 24 h, the tumorigenic ability decreased remarkably in a concentration-dependent manner (Fig. 6).
Fig. 6 After pretreatment with pedicularioside G, low tumorigenicity and angiogenic activity of human hepatoma cells transplanted in chicken embryo chorioallantoic membranes is exhibited. + represents the centre of a tumor lump, which is a visible light colored disc, but the disc is very thin and small in the Ped G treated groups. Reproduced by permission of Wiley-Blackwell Publishing. |
Cistanoside C (compound 4) inhibited the growth of human hepatoma cells, human lung adenocarcinoma cells and human gastric adenocarcinoma cells.45
The effects of martynoside (compound 5), echinocoside (compound 6), and leucosceptoside A (compound 7)48 are listed in Table 2.
Silybin (compound 13) is now being tested in clinical trials to treat prostate cancer67, ovarian cancer,67a and skin cancer.67bSilybin inhibited MMP-2,-9 release as well as invasiveness of HepG2 cells.68 MMP-9 (matrix metalloproteinase 9) is the angiogenic enzyme, directly involved in human hepatic tumorigenesis, invasion and metastasis.
Ferulic acid (compound 15), a hydroxycinnamic acid, is biosynthesized from caffeic acid. Animal and in vitro studies suggest that ferulic acid may have direct antitumor activity against breast cancer70 and liver cancer,71 and may be effective at preventing cancer induced by exposure to carcinogenic compounds.72
It is worth noting that the correlation between fast repair and cancer prevention must be carefully interpreted, as correlation does not imply causation. If such causation exists, substantial studies would be needed in future.
Besides, the DNA radicals per se may induce mutation and cancer directly, but also may undergo intramolecular rearrangement or react with proteins and lipids, and in this case, DNA radicals are considered to play a causative role in aging and several degenerative diseases, such as Alzheimer's disease, Parkinson's disease, cognitive dysfunction, heart disease, cataracts, Xeroderma pigmentosum, ataxia telangiectasia, Bloom's syndrome, Cockayne syndrome and various types of inflammatory disease. There seems to be little doubt that the fast repair mechanism could be valuable to protect against these chronic and stubborn diseases, and to develop a broad pharmacological action potential. Unfortunately, knowledge of the fast repair of DNA radicals in many diseases is still in infancy. More in-depth understanding of its physiological and pathophysiological significance is awaited. Simpler and easier detection methods for DNA radicals in cells are anxiously expected, so that the fast repair mechanism may attract more scientists from many disciplines and develop at a faster pace.
We thank Professors Nianyun Lin, Side Yao and Wenfeng Wang (Laboratory of Radiation Chemistry, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China) for the valuable guide on experiments into fast repair activity. The late Professor Botao Fan (ITODYS, CNRS UMR7086, Université Paris 7, Paris, France) contributed to the guide on the theoretical studies of phytophenol docking into DNA. He regrettably died of liver cancer in 2007. We also thank Dr Changjun Lin for the excellent illustration of the graphical abstract.
The authors declare no potential conflict of interest relevant to this article.
This journal is © The Royal Society of Chemistry 2011 |