DNA Repair and Cancer Therapy: Targeting APE1/Ref-1 Using Dietary Agents.

Epidemiological studies have demonstrated the cancer protective effects of dietary agents and other natural compounds isolated from fruits, soybeans, and vegetables on neoplasia. Studies have also revealed the potential for these natural products to be combined with chemotherapy or radiotherapy for the more effective treatment of cancer. In this paper we discuss the potential for targeting the DNA base excision repair enzyme APE1/Ref-1 using dietary agents such as soy isoflavones, resveratrol, curcumin, and the vitamins ascorbate and α-tocopherol.

Potential anticancer properties of grape antioxidants.

Dietary intake of foods rich in antioxidant properties is suggested to be cancer protective. Foods rich in antioxidant properties include grape (Vitis vinifera), one of the world's largest fruit crops and most commonly consumed fruits in the world. The composition and cancer-protective effects of major phenolic antioxidants in grape skin and seed extracts are discussed in this review.

Oxidative stress alters base excision repair pathway and increases apoptotic response in apurinic/apyrimidinic endonuclease 1/redox factor-1 haploinsufficient mice.

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is the redox regulator of multiple stress-inducible transcription factors, such as NF-kappaB, and the major 5'-endonuclease in base excision repair (BER). We utilized mice containing a heterozygous gene-targeted deletion of APE1/Ref-1 (Apex(+/-)) to determine the impact of APE1/Ref-1 haploinsufficiency on the processing of oxidative DNA damage induced by 2-nitropropane (2-NP) in the liver tissue of mice. APE1/Ref-1 haploinsufficiency results in a significant decline in NF-kappaB DNA-binding activity in response to oxidative stress in liver.

Radiation-induced HIF-1alpha cell survival pathway is inhibited by soy isoflavones in prostate cancer cells.

We previously showed that treatment of prostate cancer cells with soy isoflavones and radiation resulted in greater cell killing in vitro, and caused downregulation of NF-kappaB and APE1/Ref-1. APE1/Ref-1 functions as a redox activator of transcription factors, including NF-kappaB and HIF-1alpha. These molecules are upregulated by radiation and implicated in radioresistance of cancer cells.

Radiosensitization of prostate cancer by soy isoflavones.

A trend in investigating the use of several nutritional compounds for cancer chemoprevention has revealed that phytochemicals demonstrated anti-cancer properties by inhibiting signal transduction pathways essential for cancer cell proliferation, tumor growth, invasion and metastasis. Emerging evidence suggests that the anti-proliferative and anti-oxidant effects of some of these dietary agents could be utilized to both potentiate the response of cancer cells to radiotherapy and reduce radiation-induced toxicity to normal surrounding tissues. Using pre-clinical orthotopic models of prostate cancer, studies on the combination of soy isoflavones with tumor irradiation demonstrate a synergistic anti-cancer effect between these two modalities and emphasize the potential and safety of dietary factors to improve conventional radiotherapy for a better control of tumor growth and metastasis.

Down-regulation of apurinic/apyrimidinic endonuclease 1/redox factor-1 expression by soy isoflavones enhances prostate cancer radiotherapy in vitro and in vivo.

We previously showed that genistein, the major bioactive component of soy isoflavones, acts as a radiosensitizer and potentiates prostate tumor cell killing by radiation in vitro and in animal tumor models in vivo. However, when given alone in vivo, pure genistein promoted increased lymph node metastasis, which was not observed with a soy isoflavone mixture consisting of genistein, daidzein, and glycitein. In this study, we show that soy inhibit tumor cell growth and potentiates radiation-induced cell killing in vitro like pure genistein.

Soy isoflavones enhance radiotherapy in a metastatic prostate cancer model.

We previously reported that genistein, the bioactive isoflavone of soybeans, acts as a radiosensitizer for prostate cancer. Pretreatment of tumor cells with genistein potentiated radiation-induced killing in vitro and in orthotopic models in vivo. However, pure genistein promoted increased lymph node metastasis, when administered alone in vivo.

Progression of renal cell carcinoma is inhibited by genistein and radiation in an orthotopic model.

Background: We have previously reported the potentiation of radiotherapy by the soy isoflavone genistein for prostate cancer using prostate tumor cells in vitro and orthotopic prostate tumor models in vivo. However, when genistein was used as single therapy in animal models, it promoted metastasis to regional para-aortic lymph nodes. To clarify whether these intriguing adverse effects of genistein are intrinsic to the orthotopic prostate tumor model, or these results could also be recapitulated in another model, we used the orthotopic metastatic KCI-18 renal cell carcinoma (RCC) model established in our laboratory.

Prostate cancer treatment is enhanced by genistein in vitro and in vivo in a syngeneic orthotopic tumor model.

Pretreatment with genistein, a bioactive component of soy isoflavones, potentiated cell killing induced by radiation in human PC-3 prostate cancer cells in vitro. Using an orthotopic xenograft in nude mice, we demonstrated that genistein combined with prostate tumor irradiation caused greater inhibition of primary tumor growth and increased control of spontaneous metastasis to para-aortic lymph nodes, increasing mouse survival. Paradoxically, treatment with genistein alone increased metastasis to lymph nodes.

Age-related loss of the DNA repair response following exposure to oxidative stress.

Young (4- to 6-month-old) and aged (24- to 28-month-old) mice were exposed to 2-nitropropane (2-NP), a DNA oxidizing agent, and the ability to induce DNA polymerase beta (beta-pol) and AP endonuclease (APE) was determined. In contrast to the inducibility of these gene products in response to oxidative damage in young mice, aged mice showed a lack of inducibility of beta-pol and APE. APE protein level and endonuclease activity were both reduced 40% (p<.

Genistein inhibits radiation-induced activation of NF-kappaB in prostate cancer cells promoting apoptosis and G2/M cell cycle arrest.

Background: New cancer therapeutic strategies must be investigated that enhance prostate cancer treatment while minimizing associated toxicities. We have previously shown that genistein, the major isoflavone found in soy, enhanced prostate cancer radiotherapy in vitro and in vivo. In this study, we investigated the cellular and molecular interaction between genistein and radiation using PC-3 human prostate cancer cells.

Imbalanced base excision repair in response to folate deficiency is accelerated by polymerase beta haploinsufficiency.

The mechanism by which folate deficiency influences carcinogenesis is not well established, but a phenotype of DNA strand breaks, mutations, and chromosomal instability suggests an inability to repair DNA damage. To elucidate the mechanism by which folate deficiency influences carcinogenicity, we have analyzed the effect of folate deficiency on base excision repair (BER), the pathway responsible for repairing uracil in DNA. We observe an up-regulation in initiation of BER in liver of the folate-deficient mice, as evidenced by an increase in uracil DNA glycosylase protein (30%, p < 0.

Apurinic/apyrimidinic endonuclease (APE/REF-1) haploinsufficient mice display tissue-specific differences in DNA polymerase beta-dependent base excision repair.

Apurinic/apyrimidinic (AP) endonuclease (APE) is a multifunctional protein possessing both DNA repair and redox regulatory activities. In base excision repair (BER), APE is responsible for processing spontaneous, chemical, or monofunctional DNA glycosylase-initiated AP sites via its 5'-endonuclease activity and 3'-"end-trimming" activity when processing residues produced as a consequence of bifunctional DNA glycosylases. In this study, we have fully characterized a mammalian model of APE haploinsufficiency by using a mouse containing a heterozygous gene-targeted deletion of the APE gene (Apex(+/-)).

Base excision repair deficiency caused by polymerase beta haploinsufficiency: accelerated DNA damage and increased mutational response to carcinogens.

The base excision repair pathway (BER) is believed to maintain genomic integrity by repairing DNA damage arising spontaneously or induced by oxidizing and alkylating agents. To establish the role of DNA polymerase beta (beta-pol) in BER and beta-pol-dependent BER in maintaining genomic stability, we have measured the impact of a gene-targeted disruption in the beta-pol gene on DNA repair capacity and on in vivo sensitivity to carcinogens. We have extensively phenotyped the DNA beta-pol heterozygous (beta-pol(+/-)) mouse as expressing approximately 50% less beta-pol mRNA and protein and as exhibiting an equivalent reduction in the specific activity of beta-pol.

Caloric restriction promotes genomic stability by induction of base excision repair and reversal of its age-related decline.

Caloric restriction is a potent experimental manipulation that extends mean and maximum life span and delays the onset and progression of tumors in laboratory rodents. While caloric restriction (CR) clearly protects the genome from deleterious damage, the mechanism by which genomic stability is achieved remains unclear. We provide evidence that CR promotes genomic stability by increasing DNA repair capacity, specifically base excision repair (BER).

Induction of DNA polymerase beta-dependent base excision repair in response to oxidative stress in vivo.

Base excision repair (BER) is the DNA repair pathway primarily responsible for repairing small base modifications and abasic sites caused by normal cellular metabolism or environmental insult. Strong evidence supports the requirement of DNA polymerase beta (beta-pol) in the BER pathway involving single nucleotide gap filling DNA synthesis in mammalian systems. In this study, we examine the relationship between oxidative stress, cellular levels of beta-pol and BER to determine whether oxidizing agents can upregulate BER capacity in vivo.

Attenuation of DNA polymerase beta-dependent base excision repair and increased DMS-induced mutagenicity in aged mice.

The biological mechanisms responsible for aging remain poorly understood. We propose that increases in DNA damage and mutations that occur with age result from a reduced ability to repair DNA damage. To test this hypothesis, we have measured the ability to repair DNA damage in vitro by the base excision repair (BER) pathway in tissues of young (4-month-old) and old (24-month-old) C57BL/6 mice.