Small Molecule Inhibitors of 8-Oxoguanine DNA Glycosylase-1 (OGG1)

Abstract

The DNA base excision repair (BER) pathway, which utilizes DNA glycosylases to initiate repair of specific DNA lesions, is the major pathway for the repair of DNA damage induced by oxidation, alkylation, and deamination. Early results from clinical trials suggest that inhibiting certain enzymes in the BER pathway can be a useful anticancer strategy when combined with certain DNA-damaging agents or tumor-specific genetic deficiencies. Despite this general validation of BER enzymes as drug targets, there are many enzymes that function in the BER pathway that have few, if any, specific inhibitors. There is a growing body of evidence that suggests inhibition of 8-oxoguanine DNA glycosylase-1 (OGG1) could be useful as a monotherapy or in combination therapy to treat certain types of cancer. To identify inhibitors of OGG1, a fluorescence-based screen was developed to analyze OGG1 activity in a high-throughput manner. From a primary screen of ~50 000 molecules, 13 inhibitors were identified, 12 of which were hydrazides or acyl hydrazones. Five inhibitors with an IC50 value of less than 1 μM were chosen for further experimentation and verified using two additional biochemical assays. None of the five OGG1 inhibitors reduced DNA binding of OGG1 to a 7,8-dihydro-8-oxoguanine (8-oxo-Gua)-containing substrate, but all five inhibited Schiff base formation during OGG1-mediated catalysis. All of these inhibitors displayed a >100-fold selectivity for OGG1 relative to several other DNA glycosylases involved in repair of oxidatively damaged bases. These inhibitors represent the most potent and selective OGG1 inhibitors identified to date.

Enzymatically inactive OGG1 binds to DNA and steers base excision repair toward gene transcription

“…TH5487, which blocks OGG1 substrate binding 48 prevented TNFα‐induced enrichment of OGG1 to the CXCL1 promoter (Figure 4C). Another potent OGG1 inhibitor O8, which inhibits catalytic imine formation in OGG1 without blocking its substrate binding, 49 allowed recruitment of wt OGG1 to the CXCL1 promoter (Figure 4C). As expected, TH5487 inhibited gene expression, while O8 slightly increased it (Figure 4D).…”

“…In order to further understand the importance of DNA binding for OGG1 in modulation of gene expression, the present study also examined the effects of OGG1 inhibitors TH5487 and O8 48,49 . The small‐molecule TH5487 binds OGG1’s active site and inhibits its searching for and binding to 8‐oxoG in the genome 48 .…”

Potent and Selective Inhibitors of 8-Oxoguanine DNA Glycosylase

“…The only previously known small molecule inhibitors of OGG1 were reported recently by Lloyd, who described simple hydrazine and hydrazone derivatives that inhibited the enzyme as measured by an assay that measures DNA strand cleavage subsequent to base excision. 35 Since hydrazones can spontaneously hydrolyze, 36 and hydrazines are known to react generally with abasic sites in DNA, 37,38 such classes of compounds may raise questions of stability and specificity. In general, the use of BER assays that measure DNA cleavage rather than the excision event may result in identification of hit compounds that do not act by inhibiting initial base excision.…”

Targeting BER enzymes in cancer therapy

“…To this date, targeting the initial repair steps performed by the DNA glycosylases has resulted in only moderate success of developing small molecules against UNG, NEIL1 and OGG1 [40][41][42][43][44][45][46]. The underlying reasons for this might be due to the challenging nature of drugging carbohydrate or DNA-binding proteins, often regarded as close to undruggable, and glycosylases in DNA-bound and apo-states in general [47][48][49].…”