**7. References**

492 Selected Topics in DNA Repair

(Maurya et al. 2004). Intraperitoneal administration of troxerutin (175 mg/kg body weight) to mice before and after whole body radiation exposure inhibited micronuclei formation in blood reticulocytes significantly. The administration of different doses (75, 125 and 175 mg/kg body weight) of troxerutin 1 h prior to 4 Gy gamma*-*radiation exposure showed dose-dependent decrease in the yield of DNA strand breaks in murine blood leucocytes and bone marrow cells. The dose-dependent protection was more pronounced in bone marrow cells than in blood leucocytes. Administration of 175 mg/kg body weight of the drug (i.p.) 1 h prior or immediately after whole body irradiation of mice showed that the decrease in strand breaks depended on the post-irradiation interval at which the analysis was done. Measurement of DNA repair potential of the troxerutin shows that it enhances the DNA repair (Maurya et al. 2005a). So the observed time-dependent decrease in the DNA strand breaks could be attributed to enhanced DNA repair in troxerutin administered animals.

Vanillin (4-hydroxy-3-methoxybenzaldehyde), scheme 2E, is a compound used as a flavoring agent and as a dietary component. It is the major component of natural vanilla, which is one of the most widely used and important flavoring materials throughout the world. The source of vanilla is the bean, or pod, of the tropical Vanilla orchid (principally *Vanilla planifolia* Andrews, syn. *V. fragrans* (Salisb. Ames)). Vanillin is an antioxidant capable of protecting membrane against lipid peroxidation and DNA against strand breaks induced by reactive oxygen species like singlet oxygen. Vanillin and its analogs were strongly antimutagenic or anti-genotoxic in most studies. Vanillin also suppresses the chromosomal aberrations induced by X-rays in V79 cells *in vitro* (Keshava et al. 1998*)* and in mice *in vivo*  (Sasaki et al. 1990). Imanishi et al. have shown anti-mutagenic effect of vanillin against UV and X-rays in Chinese hamster V79 cells (Imanishi et al. 1990). We have explored the effect of vanillin on radiation-induced DNA damage in plasmid pBR322 (*in vitro*), human peripheral blood leucocytes and mouse splenic lymphocytes (*ex vivo*) and in mouse (*in vivo*), besides the possible mechanisms involved in terms of scavenging radiation related free radicals by pulse radiolysis. Our finding shows that presence of 0.5mM vanillin has a dosemodifying factor (DMF) of 6.75 for 50% inactivation of ccc form. Exposure of human peripheral blood leucocytes (*ex vivo*) to radiation causes strand breaks in the cellular DNA, as assessed by comet assay. When leucocytes were exposed to 2 Gy of -radiation there was an increase in parameters of comet assay such as %DNA in tail, tail length, 'tail moment' and 'Olive tail moment'. The presence of 0.5 mM vanillin during irradiation significantly reduced these parameters. Damage to DNA in mouse peripheral blood leucocytes after whole-body exposure of mice (*in vivo*) to radiation was studied at 1 and 2 h post-irradiation. There was recovery of DNA damage in terms of the above-mentioned parameters at 2h post-irradiation. This was more than that observed at 1 h (Maurya et al. 2007). The recovery was more in vanillin treated mice. Hence our studies showed that vanillin offers protection to DNA against radiation-induced damage possibly imparting a role other than modulation

**6. Future prospects for radioprotectors in mitigation of radiation damage** 

Research in the development of radioprotectors worldwide has focused on screening a variety of chemical and biological compounds (Maurya et al. 2006; Nair et al. 2001; Weiss and Landauer 2009). Various natural or synthetic compounds having either antioxidant or

**5.7 Vanillin** 

of DNA repair (Maurya et al. 2007).


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**22** 

*1Australia 2USA* 

**DNA-Binding Radioprotectors** 

*Center for Cancer Research, National Cancer Institute* 

For decades the world of radioprotectors has been dominated by the aminothiols, in particular WR1065 and its prodrug amifostine. These drugs emerged from an extensive programme of synthesis and evaluation under the auspices of the Walter Reed Army Institute of Research starting in the early 1950s (Sweeny, 1979). As discussed in detail in section 4 below, structure-activity studies on a series of aminothiols in John Ward's lab at the University of San Diego established a relationship between net charge and radioprotective activity. Positive charge conferred a DNA binding capability, by ionic interaction, and improved radioprotective activity. This was consistent with the fact that an important aspect of the mechanism of radioprotection by WR1065 is its radical scavenging activity. Given the limited range of diffusion of hydroxyl radicals generated from ionisation of water molecules, it makes sense that the radical scavengers will be most effective when located in the close vicinity of DNA. This basic rationale prompted the synthesis and evaluation of an aminothiol tethered to a DNA intercalating agent (Laayoun et al., 1994), but

Also, the new DNA binding radioprotector methylproamine emerged not from a rational design premise, but rather, from the serendipitous discovery of radioprotective activity of a minor groove binder Hoechst 33342 synthesized by the Hoechst company as part of a program aimed at developing antihelminthics. From that starting point, a modest lead optimisation program guided by a mechanistic hypothesis showed that radioprotective activity was enhanced by the introduction of more electron-rich substituents into the phenyl

Thus, this article links two groups of radioprotectors with the common feature of DNAbinding, albeit with quite different affinities. The dissociation constant for the WR1065-DNA interaction is in the mM range (Smoluk et al., 1986), whereas that for methylproamine is a few hundred nM (Martin et al., 2004). Accordingly, the relative radioprotective potency of WR1065 and methylproamine differs by more than 2-orders of magnitude. In contrast to this focus, other publications review a much wider range of radioprotectors (Hosseinimehr,

there is no evidence in the literature of a systematic follow-up.

**1. Introduction** 

ring of the molecule.

2007; Weiss & Landauer, 2009; Citrin, 2010).

Pavel Lobachevsky1, Alesia Ivashkevich1, Olga A. Martin1,2 and Roger F. Martin1 *1Laboratory of Molecular Radiation Biology,* 

*Peter MacCallum Cancer Centre* 

*2Laboratory of Molecular Pharmacology,* 

soluble derivative of vitamin E. *Journal of Radiation Research* (Tokyo), Vol. 43, No.2, pp.153-159

