Genistein enhances the radiosensitivity of breast cancer cells via G₂/M cell cycle arrest and apoptosis

Cancer prevention and therapy through the modulation of the tumor microenvironment

Cancer arises in the context of an in vivo tumor microenvironment. This microenvironment is both a cause and consequence of tumorigenesis. Tumor and host cells co-evolve dynamically through indirect and direct cellular interactions, eliciting multiscale effects on many biological programs, including cellular proliferation, growth, and metabolism, as well as angiogenesis and hypoxia and innate and adaptive immunity. Here we highlight specific biological processes that could be exploited as targets for the prevention and therapy of cancer. Specifically, we describe how inhibition of targets such as cholesterol synthesis and metabolites, reactive oxygen species and hypoxia, macrophage activation and conversion, indoleamine 2,3-dioxygenase regulation of dendritic cells, vascular endothelial growth factor regulation of angiogenesis, fibrosis inhibition, endoglin, and Janus kinase signaling emerge as examples of important potential nexuses in the regulation of tumorigenesis and the tumor microenvironment that can be targeted. We have also identified therapeutic agents as approaches, in particular natural products such as berberine, resveratrol, onionin A, epigallocatechin gallate, genistein, curcumin, naringenin, desoxyrhapontigenin, piperine, and zerumbone, that may warrant further investigation to target the tumor microenvironment for the treatment and/or prevention of cancer.

Activation and Inhibition of ATM by Phytochemicals: Awakening and Sleeping the Guardian Angel Naturally

Double-stranded breaks (DSBs) are cytotoxic DNA lesions caused by oxygen radicals, ionizing radiation, and radiomimetic chemicals. Increasing understanding of DNA damage signaling has provided an ever-expanding list of modulators reported to orchestrate DNA damage repair and ataxia telangiectasia mutated (ATM) is the master regulator and main transducer of the DSB response. Increasingly, it is being realized that DNA damage response is a synchronized and branched network that functionalizes different molecular cascades to activate special checkpoints, thus temporarily arresting progression of the cell cycle while damage is being assessed and processed. It is noteworthy that both nutrigenetics and nutrigenomics have revolutionized the field of molecular biology and rapidly accumulating experimental evidence has started to shed light on biological activities of a wide range of phytochemicals reported to modulate cell cycle, DNA repair, cell growth, differentiation and apoptosis as evidenced by cell-based studies. In this review, we have attempted to provide an overview of DNA damage signaling, how ATM signaling regulates tumor necrosis factors-related apoptosis inducing ligand (TRAIL)-induced intracellular network. We also illuminate on how resveratrol, epigallocatechin gallate, curcumin, jaceosidin, cucurbitacin, apigenin, genistein, and others trigger activation of ATM in different cancer cells as well as agents for ATM inactivation. Understanding the interplay of TRAIL-induced intracellular signaling and ATM modulation of downstream effectors is very important. This holds particularly for a reconceptualization of the apparently paradoxical roles and therapeutically targetable for enhancing the response to DNA damage-inducing therapy.

Radioprotective effects of genistein on HL-7702 cells via the inhibition of apoptosis and DNA damage

Radiation induced normal tissue damage is the most important limitation for the delivery of a high potentially curative radiation dose. Genistein (GEN), one of the main soy isoflavone components, has drawn wide attention for its bioactivity in alleviating radiation damage. However, the effects and molecular mechanisms underlying the radioprotective effects of GEN remain unclear. In the present study, we showed that low concentration of GEN (1.5 µM) protected L-02 cells against radiation damage via inhibition of apoptosis, alleviation of DNA damage and chromosome aberration, down-regulation of GRP78 and up-regulation of HERP, HUS1 and hHR23A. In contrast, high concentration of GEN (20 µM) demonstrated radiosensitizing characteristics through the promotion of apoptosis and chromosome aberration, impairment of DNA repair, up-regulation of GRP78, and down-regulation of HUS1, SIRT1, RAD17, RAD51 and RNF8. These findings shed light on using low, but not high-concentration GEN, as a potential candidate for adjuvant therapy to alleviate radiation-induced injuries to human recipients of ionizing radiation.

Disturbance of redox status enhances radiosensitivity of hepatocellular carcinoma

AIMS

High constitutive expression of Nrf2 has been found in many types of cancers, and this high level of Nrf2 also favors resistance to drugs and radiation. Here we investigate how isoliquiritigenin (ISL), a natural antioxidant, inhibits the Nrf2-dependent antioxidant pathway and enhances the radiosensitivity of HepG2 cells and HepG2 xenografts.

RESULTS

Treatment of HepG2 cells with ISL for 6 h selectively enhanced transcription and expression of Keap1. Keap1 effectively induced ubiquitination and degradation of Nrf2, and inhibited translocation of Nrf2 to the nucleus. Consequently, expression of Nrf2 downstream genes was reduced, and the Nrf2-dependent antioxidant system was suppressed. Endogenous ROS was higher than before ISL treatment, causing redox imbalance and oxidative stress in HepG2 cells. Moreover, pretreatment with ISL for 6 h followed by X-ray irradiation significantly increased γ-H2AX foci and cell apoptosis, and reduced clonogenic potential compared with cells irradiated with X-rays alone. In addition, HepG2 xenografts, ISL, and X-ray co-treatments induced greater apoptosis and tumor growth inhibition, when compared with X-ray treatments alone. Additionally, HepG2 xenografts, in which Nrf2 was expressed at very low levels due to ectopic expression of Keap1, showed that ISL-mediated radiosensitization was Keap1 dependent.

INNOVATION AND CONCLUSIONS

ISL inhibited the Nrf2-antioxidant pathway by increasing the levels of Keap1 and ultimately inducing oxidative stress via disturbance of the redox status. The antioxidant ISL possessed pro-oxidative properties, and enhanced the radiosensitivity of liver cancer cells, both in vivo and in vitro. Taken together, these results demonstrated the effectiveness of using ISL to decrease radioresistance, suggesting that ISL could be developed as an adjuvant radiosensitization drug. Disturbance of redox status could be a potential target for radiosensitization.