Revealing the mechanism of action of a first-in-class covalent inhibitor of KRASG12C (ON) and other functional properties of oncogenic KRAS by 31P NMR

Individual oncogenic KRAS mutants confer distinct differences in biochemical properties and signaling for reasons that are not well understood. KRAS activity is closely coupled to protein dynamics and is regulated through two interconverting conformations: state 1 (inactive, effector binding deficient) and state 2 (active, effector binding enabled). Here, we use 31P NMR to delineate the differences in state 1 and state 2 populations present in WT and common KRAS oncogenic mutants (G12C, G12D, G12V, G13D, and Q61L) bound to its natural substrate GTP or a commonly used nonhydrolyzable analog GppNHp (guanosine-5'-[(β,γ)-imido] triphosphate). Our results show that GppNHp-bound proteins exhibit significant state 1 population, whereas GTP-bound KRAS is primarily (90% or more) in state 2 conformation. This observation suggests that the predominance of state 1 shown here and in other studies is related to GppNHp and is most likely nonexistent in cells. We characterize the impact of this differential conformational equilibrium of oncogenic KRAS on RAF1 kinase effector RAS-binding domain and intrinsic hydrolysis. Through a KRAS G12C drug discovery, we have identified a novel small-molecule inhibitor, BBO-8956, which is effective against both GDP- and GTP-bound KRAS G12C. We show that binding of this inhibitor significantly perturbs state 1-state 2 equilibrium and induces an inactive state 1 conformation in GTP-bound KRAS G12C. In the presence of BBO-8956, RAF1-RAS-binding domain is unable to induce a signaling competent state 2 conformation within the ternary complex, demonstrating the mechanism of action for this novel and active-conformation inhibitor.

MALDI-TOF Mass Spectrometry-Based Assay for Measuring Covalent Target Engagement of KRAS G12C Inhibitors

MALDI-TOF mass spectrometry enables high-throughput screening of covalent fragment libraries and SAR compound progressions of selective KRAS G12C inhibitors. Using the MALDI-TOF platform instead of the more traditional ESI-MS TOF/orbitrap instrumentation can radically shorten sample acquisition time, allowing up to 384 samples to be screened in 30 min. The typical throughput for a covalent library screen is 1152 samples per 8 h, including processing, calculation, and reporting steps. The throughput can be doubled without any significant assay modification.

NMR 1H, 13C, 15N backbone resonance assignments of the T35S and oncogenic T35S/Q61L mutants of human KRAS4b in the active, GppNHp-bound conformation

RAS proteins cycling between the active-form (GTP-bound) and inactive-form (GDP-bound) play a key role in cell signaling pathways that control cell survival, proliferation, and differentiation. Mutations at codon 12, 13, and 61 in RAS are known to attenuate its GTPase activity favoring the RAS active state and constitutively active downstream signaling. This hyperactivation accounts for various malignancies including pancreatic, lung, and colorectal cancers. Active KRAS is found to exist in equilibrium between two rapidly interconverting conformational states (State1-State2) in solution. Due to this dynamic feature of the protein, the ¹H-¹⁵N correlation cross-peak signals of several amino acid (AA) residues of KRAS belonging to the flexible loop regions are absent from its 2D ¹H-¹⁵N HSQC spectrum within and near physiological solution pH. A threonine to serine mutation at position 35 (T35S) shifts the interconverting equilibrium to State1 conformation and enables the emergence of such residues in the 2D ¹H-¹⁵N HSQC spectrum due to gained conformational rigidity. We report here the ¹H^N, ¹⁵N, and ¹³C backbone resonance assignments for the 19.2 kDa (AA 1-169) protein constructs of KRAS-GppNHp harboring T35S mutation (KRAS^T35S/C118S-GppNHp) and of its oncogenic counterpart harboring the Q61L mutation (KRAS^{T35S/Q61L/C118S}-GppNHp) using heteronuclear, multidimensional NMR spectroscopy at 298 K. High resolution NMR data allowed the unambiguous assignments of ¹H-¹⁵N correlation cross-peaks for all the residues except for Met1. Furthermore, 2D ¹H-¹⁵N HSQC overlay of two proteins assisted in determination of Q61L mutation-induced chemical shift perturbations for select residues in the regions of P-loop, Switch-II, and helix α3.

Abstract IA21: Preventing KRAS processing

Tipifarnib, a drug that targets HRAS through inhibiting farnesyl transferase, is in phase II clinical trials and appears to show activity in tumors harboring oncogenic HRAS mutations (https://kuraoncology.com/pipeline/#tipifarnib). Unfortunately, these drugs are not expected to be effective on KRAS cancers because KRAS, unlike HRAS, can be prenylated by geranylgeranyl transferase following farnesyl transferase inhibition. To address this, we have developed compounds that prevent farnesylation of KRAS 4B by covalent reaction with C185, the site of prenylation. These compounds bind to a pocket in the G-domain that is formed by interaction with the hypervariable region, an interaction that does not seem to occur in other RAS proteins. This existence of this pocket has been demonstrated through biochemical and biophysical analysis, including NMR and small-angle X-ray scattering. The compounds we have developed are active in cells: they prevent proliferation of MEFs driven by oncogenic KRAS proteins but do not affect MEFs supported by myristoylated KRAS G12D C185S at equivalent concentrations. We are currently optimizing these compounds for further preclinical development.

Citation Format: Anna Maciag, Yue Yang, David Turner, Marcin Dyba, Vandana Kumari, Brian Smith, Lixin Fan, Stephan Gysin, Andrew Wolfe, Hazem Abdelkarim, Vadim Gaponenko, Felice Lightstone, Dwight Nissley, Frank McCormick. Preventing KRAS processing [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr IA21.

Monoclonal Antibodies for the Detection of a Specific Cyclic DNA Adduct Derived from ω-6 Polyunsaturated Fatty Acids

Lipid peroxidation of polyunsaturated fatty acids (PUFAs) is an endogenous source of α,β-unsaturated aldehydes that react with DNA producing a variety of cyclic adducts. The mutagenic cyclic adducts, specifically those derived from oxidation of ω-6 PUFAs, may contribute to the cancer promoting activities associated with ω-6 PUFAs. ( E)-4-Hydroxy-2-nonenal (HNE) is a unique product of ω-6 PUFAs oxidation. HNE reacts with deoxyguanosine (dG) yielding mutagenic 1, N²-propanodeoxyguanosine adducts (HNE-dG). Earlier studies showed HNE can also be oxidized to its epoxide (EH), and EH can react with deoxyadenosine (dA) forming the well-studied εdA and the substituted etheno adducts. Using a liquid chromatography-based tandem mass spectroscopic (LC-MS/MS) method, we previously reported the detection of EH-derived 7-(1',2'-dihydroxyheptyl)-1, N⁶-ethenodeoxyadenosine (DHHεdA) as a novel endogenous background adduct in DNA from rodent and human tissues. The formation, repair, and mutagenicity of DHHεdA and its biological consequences in cells have not been investigated. To understand the roles of DHHεdA in carcinogenesis, it is important to develop an immuno-based assay to detect DHHεdA in cells and tissues. In this study we describe the development of monoclonal antibodies specifically against DHHεdA and its application to detect DHHεdA in human cells.

An endogenous DNA adduct as a prognostic biomarker for hepatocarcinogenesis and its prevention by Theaphenon E in mice

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide, mainly because of its poor prognosis. A valid mechanism-based prognostic biomarker is urgently needed. γ-hydroxy-1,N² -propanodeoxyguanosine (γ-OHPdG) is an endogenously formed mutagenic DNA adduct derived from lipid peroxidation. We examined the relationship of γ-OHPdG with hepatocarcinogenesis in two animal models and its potential role as a prognostic biomarker for recurrence in HCC patients. Bioassays were conducted in xeroderma pigmentosum group A knockout mice and diethylnitrosamine-injected mice, both prone to HCC development. γ-OHPdG levels in the livers of these animals were determined. The effects of antioxidant treatments on γ-OHPdG and hepatocarcinogenesis were examined. Using two independent sets of HCC specimens from patients, we examined the relationship between γ-OHPdG and survival or recurrence-free survival. γ-OHPdG levels in liver DNA showed an age-dependent increase and consistently correlated with HCC development in all three animal models. Theaphenon E treatment significantly decreased γ-OHPdG levels in the liver DNA of xeroderma pigmentosum group A knockout mice and remarkably reduced HCC incidence in these mice to 14% from 100% in the controls. It also effectively inhibited HCC development in the diethylnitrosamine-injected mice. Using clinical samples from two groups of patients, our study revealed that higher levels of γ-OHPdG are strongly associated with low survival (P < 0.0001) and low recurrence-free survival (P = 0.007).

CONCLUSION

These results support γ-OHPdG as a mechanism-based, biologically relevant biomarker for predicting the risk of HCC and its recurrence. (Hepatology 2018;67:159-170).

Abstract 4051: Lipid peroxidation-derived DNA adduct formation in obesity-related hepatocarcinogenesis

In this study we are investigating the role and mechanism of formation of Lipid-peroxidation (LPO)-derived DNA adduct formation in obesity-related hepatocarcinogenesis. Obesity has been implicated as a risk factor for many types of cancer, particularly hepatocellular carcinoma (HCC). HCC incidence correlates with the increasing prevalence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) in the US. The mechanisms underlying this increased risk of liver cancer in the obese population are still unclear. Liver tissue damage from fat accumulation in NAFLD and NASH produce inflammation and increased levels of reactive oxygen species (ROS). ROS induce LPO of polyunsaturated fatty acids (PUFAs) in cell membranes leading to the formation of reactive aldehydes, such as acrolein and 4-hydroxy-2-nonenal (HNE), which react with DNA forming the DNA adducts γ-OHPdG and DHH-ϵdA, respectively. γ-OHPdG is derived from ω-6 and ω-3 PUFAs, while DHH-ϵdA is specifically from ω-6 fatty acids. Previous data has indicated that mutational hotspots targeted by γ-OHPdG and DHH-ϵdA may be within key cancer driver genes, such as p53. Research has shown that B-6 mice fed a high fat diet (HFD) develop fatty liver disease and eventually HCC. The livers of B-6 mice fed a HFD showed an increased ω-6/ω-3 PUFAs ratio. We have detected and quantified γ-OHPdG and DHH-ϵdA by LC-MS/MS in livers from six healthy individuals and six NAFLD patients and found that levels of DHH-ϵdA in the DNA of the fatty liver samples were nearly three-fold higher than that in normal liver samples. Preliminary in vitro data using primary human hepatocytes has indicated that treatment with oleic and palmitic acid promote the formation of γ-OHPdG. Similarly, treatment of these cells with the epoxide of HNE, 2,3-epoxy-4-hydroxynonanal (EH), and the omega-6 fatty acid, arachidonic acid, induce the formation of DHH-ϵdA, supporting the proposed mechanism of adduct formation. In an 80-week tumor bioassay using C57Bl/6J mice on a HFD, we have observed through live-animal MRI imaging and immunohistochemistry, an increase in pro-inflammatory white adipose tissue accumulation, infiltration of fat into the liver and an increase in overall body weight compared to a low fat diet control. In addition, in mice fed a HFD combined with the green-tea derived antioxidant Theaphenon E, we observed through MRI, reduction in body weight gain, white adipose tissue, and lipid accumulation in liver. Theaphenon E has the potential to decrease fat accumulation and inflammation within the liver that lead to decreases in LPO-derived adduct formation and consequently, the mutations critical for HCC development.

Citation Format: Heidi Coia, Hongyi Guan, Ying Fu, Marcin Dyba, Fung-Lung Chung. Lipid peroxidation-derived DNA adduct formation in obesity-related hepatocarcinogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4051.

Abstract 4314: Using antioxidant to enhance liver cancer preventive effect of n-3 PUFAs

In various animal models, n-3 polyunsaturated fatty acids (PUFAs) have demonstrated cancer preventive effects. This protective effect is associated with reduced levels of inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), cyclooxygenase 2 (COX-2) and prostaglandin E2 (PGE2). On the other hand, an endogenous DNA adduct formed from the peroxidation of ω-3 PUFAs, γ-hydroxy-1, N2-propanodeoxyguanosine (γ-OHPdG), is known to be mutagenic. In light of these observations, we hypothesized that the combination of n-3 PUFAs with an antioxidant to inhibit lipid peroxidation (e.g. α-lipoic acid) will result in an enhanced cancer preventive effect than n-3 PUFAs alone. The chemical carcinogen diethylnitrosamine (DEN) induced HCC model is employed in this study. The DEN-induced HCC model has a histology and genetic signature similar to that of human HCCs, such that it has poor prognosis and recapitulates a dependence on inflammatory signaling. It also reflects the same gender disparity seen in human HCCs. Fat-1 transgenic mice were used because they express a Caenorhabditis elegans desaturase converting n-6 to n-3 PUFAs endogenously without using dietary supplementation. This model underlies the importance of dietary control of PUFAs intake and ratios due to the inability of mammalian cells to generate anti-inflammatory n-3 PUFAs from pro-inflammatory n-6 PUFAs, which are a major component of the standard Western diets. The results showed that antioxidant can efficiently suppress the elevated level of γ-OHPdG in fat-1 mice. The tumor incidence, multiplicity, and size are monitored continuously. This work was supported by the NCI grant: RO1-CA-134892. Y.F. thanks the Prevent Cancer Foundation for his fellowship (Marcia and Frank Carlucci Charitable Foundation Award in Cancer Prevention and Early Detection)

Citation Format: Ying Fu, Angela Y. Bai, Marcin Dyba, Jing X. Kang, Fung-Lung Chung. Using antioxidant to enhance liver cancer preventive effect of n-3 PUFAs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4314.

Abstract 2622: A LC-MS/MS method to quantify specific dietary isothiocyanates in human urine for epidemiological studies

Epidemiological studies have demonstrated an inverse relationship between the intake of cruciferous vegetables and risk of cancers. The protective effects may be attributed to glucosinolates and glucobrassicins in these vegetables. While glucosinolates and glucobrassicins are not chemopreventive, their metabolites, isothiocyanates (ITCs), indole-3-carbinol (I3C), and 3,3′-diindolylmethane (DIM), have been shown to inhibit tumorigenesis in rodent models. In the past studies the total ITCs intake was estimated through food frequency questionnaires and/or urinary total ITC by a HPLC-based method. Self-reported intake of cruciferous vegetables has inherent limitations in estimating the intake of ITCs because of differences in the contents of their precursors present in different kinds of cruciferous vegetables, different locations and methods of cultivation, or different methods of food preparation. Animal and cell culture studies have shown that different types of ITCs have different anticancer properties and potency, suggesting that they are not equal in protecting against the development of cancers. The lack of a reliable method to quantify specific ITCs derived from dietary intake of cruciferous vegetables hinders the investigation of the role of specific ITCs against the development of cancer in human populations. To address this deficiency, we developed a flexible, highly sensitive, fast and reliable quantitative liquid chromatography mass spectrometry method (LC-MS/MS) for detecting and quantifying common dietary ITCs plus DIM in human urine. Urinary ITCs are measured as mercapturic acid conjugates (ITCs-NAC), predominant metabolite of ITCs, using multiple reaction monitoring (MRM) technique and deuterated [2H3]-ITCs-NAC as internal standards. DIM is quantified in separate experiment using [2H2]-DIM internal standard. The method was validated by a small set of previously analyzed samples from Singapore Chinese Health Study. We found an excellent correlation between previously reported total ITCs levels and sum of ITCs detected by newly developed method. The combination of minimal sample preparation, ultra-performance liquid chromatography, and highly sensitive mass spectrometer resulted in a method that is fast (below 10 min for ITCs and 12 min for DIM) and sensitive (low femtomolar LOQ) amenable to population studies.

Citation Format: Marcin Dyba, Jian-Min Yuan, Jennifer Adams-Haduch, Fung-Lung Chung. A LC-MS/MS method to quantify specific dietary isothiocyanates in human urine for epidemiological studies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2622.

Reactivation of mutant p53 by a dietary-related compound phenethyl isothiocyanate inhibits tumor growth

Mutations in the p53 tumor-suppressor gene are prevalent in human cancers. The majority of p53 mutations are missense, which can be classified into contact mutations (that directly disrupts the DNA-binding activity of p53) and structural mutations (that disrupts the conformation of p53). Both of the mutations can disable the normal wild-type (WT) p53 activities. Nevertheless, it has been amply documented that small molecules can rescue activity from mutant p53 by restoring WT tumor-suppressive functions. These compounds hold promise for cancer therapy and have now entered clinical trials. In this study, we show that cruciferous-vegetable-derived phenethyl isothiocyanate (PEITC) can reactivate p53 mutant under in vitro and in vivo conditions, revealing a new mechanism of action for a dietary-related compound. PEITC exhibits growth-inhibitory activity in cells expressing p53 mutants with preferential activity toward p53^R175, one of the most frequent ‘hotspot' mutations within the p53 sequence. Mechanistic studies revealed that PEITC induces apoptosis in a p53^R175 mutant-dependent manner by restoring p53 WT conformation and transactivation functions. Accordingly, in PEITC-treated cells the reactivated p53^R175 mutant induces apoptosis by activating canonical WT p53 targets, inducing a delay in S and G2/M phase, and by phosphorylating ATM/CHK2. Interestingly, the growth-inhibitory effects of PEITC depend on the redox state of the cell. Further, PEITC treatments render the p53^R175 mutant sensitive to degradation by the proteasome and autophagy in a concentration-dependent manner. PEITC-induced reactivation of p53^R175 and its subsequent sensitivity to the degradation pathways likely contribute to its anticancer activities. We further show that dietary supplementation of PEITC is able to reactivate WT activity in vivo as well, inhibiting tumor growth in xenograft mouse model. These findings provide the first example of mutant p53 reactivation by a dietary compound and have important implications for cancer prevention and therapy.

Nucleotide excision repair deficiency increases levels of acrolein-derived cyclic DNA adduct and sensitizes cells to apoptosis induced by docosahexaenoic acid and acrolein

The acrolein derived cyclic 1,N(2)-propanodeoxyguanosine adduct (Acr-dG), formed primarily from ω-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) under oxidative conditions, while proven to be mutagenic, is potentially involved in DHA-induced apoptosis. The latter may contribute to the chemopreventive effects of DHA. Previous studies have shown that the levels of Acr-dG are correlated with apoptosis induction in HT29 cells treated with DHA. Because Acr-dG is shown to be repaired by the nucleotide excision repair (NER) pathway, to further investigate the role of Acr-dG in apoptosis, in this study, NER-deficient XPA and its isogenic NER-proficient XAN1 cells were treated with DHA. The Acr-dG levels and apoptosis were sharply increased in XPA cells, but not in XAN1 cells when treated with 125μM of DHA. Because DHA can induce formation of various DNA damage, to specifically investigate the role of Acr-dG in apoptosis induction, we treated XPA knockdown HCT116+ch3 cells with acrolein. The levels of both Acr-dG and apoptosis induction increased significantly in the XPA knockdown cells. These results clearly demonstrate that NER deficiency induces higher levels of Acr-dG in cells treated with DHA or acrolein and sensitizes cells to undergo apoptosis in a correlative manner. Collectively, these results support that Acr-dG, a ubiquitously formed mutagenic oxidative DNA adduct, plays a role in DHA-induced apoptosis and suggest that it could serve as a biomarker for the cancer preventive effects of DHA.

Abstract 1910: Reactivation of p53R175 mutant by dietary phenethyl isothiocyanate (PEITC) impairs tumor growth in vivo

Mutations in the p53 gene occur in a variety of human cancers with remarkably high frequencies (as high as 80%), depending on the type and stage of the tumors (www-p53.iarc.fr). The majority of mutations are missense that are localized to six “hotspot” residues, which play a role either in the structural integrity (structural mutants, e.g., R175H) or in the DNA binding domain (contact mutants, e.g., R273H). Previously, we showed that phenethyl isothiocyanate (PEITC), a naturally occurring dietary constituent present abundantly in watercress, selectively depletes p53 mutant protein, but not the WT p53, and induces apoptosis in tumor cells expressing p53 mutants. In this study we demonstrated that PEITC can reactivate p53R175 mutant protein and inhibit tumor growth in a mutant p53R175H -dependent manner.

PEITC displayed a 175 allele preference of inhibition of cell proliferation as compared to other hotspot mutants as detected by WST-1 assay and induced apoptosis in a p53R175 mutant -dependent manner. Immunofluorescence and co-immunoprecipitation assay on PEITC treated p53R175 cells using conformation-specific antibodies (PAB1620 and PAB240) showed restoration of the “WT-like” conformation to p53 mutant. Reactivation of the WT like functions to the p53R175 mutant was established by its ability to bind DNA, transactivate p53 regulated downstream target genes (p21, PUMA, MDM2, NOXA, BAX and BCL2), and overexpression of p21 protein. PEITC treatment induced DNA damage response as detected by pATM-S1981 and pCHK2-Thr68, G2/M and S-phase cell-cycle arrest and oxidative stress as measured by decrease in the GSH levels in the cells. In contrast, co-treatment of cells with PEITC and reducing agents alleviated the inhibitory effects of PEITC on cell proliferation. Elevated oxidative stress due to the combined effect of PEITC and elevated ROS levels in p53 mutant cells might be responsible for the activation of restored “WT-like” p53R175 mutant protein and induction of apoptosis. PEITC induced proteasomal degradation and autophagy of the p53R175 mutant. Animals fed with PEITC diet showed a statistically significant reduction in xenograft tumor volumes, proliferation marker Ki67, and mutant p53 stained cells. Elevated mRNA levels of p53 regulated genes from animals fed PEITC diet provide in vivo evidence for the p53R175H mutant reactivation and inhibition of xenograft growth in a mutant p53-dependent manner. These are important findings because they demonstrated that a dietary compound can inhibit the growth of tumor cells in vivo by restoring the tumor suppressor functions to mutant p53, and thus provide a target for the development of novel chemopreventive strategies through dietary interventions.

Citation Format: Monika Aggarwal, Elizabeth Sinclair, Anna Jacobs, Ying Fu, Marcin Dyba, Xiantao Wang, Idalia M. Cruz, Deborah Berry, Kallakury Bhaskar, Susette C. Mueller, Maria Laura Avantaggiati, Fung-Lung Chung. Reactivation of p53R175 mutant by dietary phenethyl isothiocyanate (PEITC) impairs tumor growth in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1910. doi:10.1158/1538-7445.AM2015-1910

Abstract 2733: Development of novel monoclonal antibodies for a cyclic DNA adduct derived from oxidation of ω-6 polyunsaturated fatty acids

Dietary polyunsaturated fatty acids (ω-3 and ω-6 PUFAs) play a role in certain human cancers. The oxidation of PUFAs produces reactive α,β-unsaturated aldehydes (enals) that can modify DNA producing mutagenic lesions. Of particular interest, 7-(1′,2′-dihydroxyheptyl)-1,N6- ethenodeoxyadenosine (DHHϵdA) is a novel DNA adduct in vitro and in vivo derived from lipid peroxidation of ω-6 PUFAs. Despite its recent identification in vivo, the role of DHHϵdA in tumorigenesis is not yet known. Previously, the endogenously formed DHHϵdA was detected by liquid chromatography tandem mass spectrometry (LC-MS/MS). Due to its low levels in vivo (1-30 adducts/109 DNA bases), a relatively high quantity of DNA is needed for its detection and quantification. In this study we developed a monoclonal antibody against DHHϵdA in order to detect and quantify this adduct in cells and tissues. Two antigens were synthesized by conjugating activated hapten: 5′-carboxy-7-(1′,2′-dihydroxyheptyl) adenosine (5′-carboxy DHHϵA) to BSA and KLH carrier proteins. KLH-conjugated hapten was used for mice immunization, whereas BSA-based hapten was used to test for an immune response. After immunization and several screenings, 6 monoclonal cell lines were chosen for further tests. Normal and competitive ELISA was performed to characterize the antibodies from all cell lines. Competitive ELISA revealed no cross-reactivity towards normal nucleosides and α- and γ-OHPdG, the cyclic 1,N2-propano adduct derived from acrolein, and 8-oxo-dG for all of the tested antibodies. However, we observed a weak (&lt; 1:100) specificity for HNE-dG, an adduct derived from (E)-4-hydroxy-2-nonenal produced from oxidized ω-6 PUFAs. Because of the relatively low level of endogenous HNE-dG compared to DHHϵdA, this weak cross-reactivity should not affect the specificity of the developed antibody to detect DHHϵdA. Two cell lines were discarded after antibodies from them showed moderate competitive effects against 1,N6-etheno-2′-deoxyadenosine (ϵdA). From the remaining 4 cell lines the best one was chosen to produce purified antibody. We believe that this antibody will be a useful tool in the studies of the role of DHHϵdA as an endogenous DNA lesion in cancer development associated with ω-6 PUFAs. This work was supported by the NCI grant CA134892.

Citation Format: Marcin Dyba, Brandon Da Silva, Jishen Pan, Fung-Lung Chung. Development of novel monoclonal antibodies for a cyclic DNA adduct derived from oxidation of ω-6 polyunsaturated fatty acids. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2733. doi:10.1158/1538-7445.AM2015-2733

Abstract 4561: Cancer preventive effect of antioxidants for spontaneous liver cancer in XPA(-/-) mice

γ-Hydroxy-1, N2-propanodeoxyguanosine (γ-OHPdG), a widely studied acrolein-derived cyclic adduct arisen from oxidized ω-3 and ω-6 polyunsaturated fatty acids (PUFAs), is a mutagenic lesion that is repaired by nucleotide excision repair (NER) pathway. C3H/HeN xeroderma pigmentosum group A (XPA) knockout mice which are deficient on NER pathway showed a significant elevation in liver tumors. We hypothesized that accumulation of γ-OHPdG is playing a role in liver tumorigenesis of XPA(-/-) mice; suppressing the formation of γ-OHPdG by dietary antioxidants should result in the prevention of liver cancer in this model. In this work, we investigated the chemoprotective efficacy of three antioxidants: α-lipoic acid, polyphenon E and vitamin E against liver tumorigenesis in XPA(-/-) mice. Autopsy at 19 months of age revealed that all the antioxidants exhibited significant inhibition effects on the development of liver tumors. Polyphenon E showed the most potent effects with 80% of the mice showing complete protection. The formation γ-OHPdG was measured in the livers of XPA(-/-) mice. An age-dependent increase of γ-OHPdG was found in the liver DNA of XPA(-/-) mice, but not in lungs (a non-target tissue). All the antioxidants decreased the formation of γ-OHPdG. Immunohistochemistry (IHC) for Ki-67 (proliferation index marker) was performed on all the liver samples, and the results showed that dietary antioxidants significantly decrease the proliferation in the liver tumors. α-Lipoic acid and vitamin E showed significant inhibitory effect, although to a lesser extent than Polyphenon E, against the spontaneous liver carcinogenesis in XPA gene-deficient mice model. A correlation between the cancer preventive efficacy and suppression of γ-OHPdG adduct level is observed, indicating a possible role of γ-OHPdG in the liver cancer development in this model. We also explored the feasibility of next-generation sequencing (NGS) to validate the mutation frequency changes as a result of feeding the antioxidant diets. This work was supported by the NCI grant: RO1-CA-134892. Y.F. thanks the Prevent Cancer Foundation for his fellowship (Marcia and Frank Carlucci Charitable Foundation Award in Cancer Prevention and Early Detection)

Note: This abstract was not presented at the meeting.

Citation Format: Ying Fu, Shana Silverstein, Marcin Dyba, Heidi Coia, Elizabeth Sinclair, Jishen Pan, Bhaskar Kallakury, Michael D. Johnson, Fung-Lung Chung. Cancer preventive effect of antioxidants for spontaneous liver cancer in XPA(-/-) mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4561. doi:10.1158/1538-7445.AM2015-4561

Abstract 5362: Deficiencies in mismatch repair proteins induce elevated levels of acrolein-derived 1,N2-propanodeoxyguanosine and apoptosis in human colon cancer cells treated with acrolein

Acrolein-derived 1,N2-propanodeoxyguanosine (Acr-dG) is a ubiquitous DNA modification in vivo that may play a role in carcinogenesis. It can be formed when DNA reacts with acrolein in environmental pollutants, such as cigarette smoking and oil combustion, and from endogenous source through oxidation of polyunsaturated fatty acids (PUFAs). We have previously demonstrated that the formation of Acr-dG at a threshold level is linked to apoptosis in cells treated with PUFAs under oxidative condition, suggesting a potential role of Acr-dG in the apoptosis induced by PUFAs, especially ω-3 PUFAs. Acr-dG can be repaired by the nucleotide excision repair (NER) pathway. To examine whether mismatch repair (MMR) pathway is also involved in the repair of Acr-dG, we treated MLH1-deficient HCT116 cell and its isogenic MLH1-proficient HCT116+ch3 cell with acrolein. The Acr-dG levels and apoptosis both were higher in HCT116 cells compared to HCT116+ch3 cells. To further study the role of MMR proteins in the repair of Acr-dG, either MLH1 or MSH2 was knocked down in HCT116+ch3 cells. The results showed that the levels of Acr-dG and apoptosis induction were both significantly higher in the knockdown cells than the cells transfected with control siRNA. The levels of p-ATM and γ-H2AX were also increased to a greater extent in HCT116 cells than HCT116+ch3 cells, and in the MLH1 and MSH2 knockdown cells than the control cells when treated with acrolein at the doses that induce higher levels of Acr-dG. This study shows that MMR proteins, MLH1 and MSH2, are involved in the repair of Acr-dG. The results also suggest that Acr-dG may cause double-strand breaks which lead to apoptosis. Whether MMR acts as an independent repair pathway for Acr-dG or MMR proteins cross-talk and interact with other DNA repair pathways, such as NER, is under investigation. (Supported by NCI grant CA43159)

Citation Format: Jishen Pan, Zhuoli Xuan, Marcin Dyba, Yongwei Zhang, Ying Fu, Rabindra Roy, Louis M. Weiner, Fung-Lung Chung. Deficiencies in mismatch repair proteins induce elevated levels of acrolein-derived 1,N2-propanodeoxyguanosine and apoptosis in human colon cancer cells treated with acrolein. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5362. doi:10.1158/1538-7445.AM2014-5362

Abstract 1588: Detection in vivo of a novel endogenous etheno DNA adduct derived from arachidonic acid and the effects of antioxidants on its formation

Previous studies showed that the 7-(1′,2′-dihydroxyheptyl) substituted etheno DNA adducts are products from reactions with epoxide of (E)-4-hydroxy-2-nonenal (HNE), an oxidation product of n-6 polyunsaturated fatty acids (PUFAs). In this work, we report the detection of 7-(1′,2′-dihydroxyheptyl)-1,N6-ethenodeoxyadenosine (DHHedA) in rodent and human tissues by two independent methods: a 32P-postlabeling/HPLC method and an isotope dilution liquid chromatography electrospray ionization tandem mass spectrometry method (ID-LC-ESI-MS/MS). This study demonstrated for the first time that DHHedA is a background DNA lesion in vivo. We showed that DHHedA can be formed upon incubation of arachidonic acid (AA) with deoxyadenosine (dA), supporting the notion that n-6 PUFAs are the endogenous source of DHHedA formation. Because the cyclic adducts are derived from the oxidation of PUFAs, we subsequently examined the effects of antioxidants, α-lipoic acid, polyphenon E and vitamin E on the formation of DHHedA and γ-hydroxy-1,N2-propanodeoxyguanosine (γ-OHPdG), a widely studied acrolein-derived cyclic adduct arisen from oxidized n-3 and n-6 PUFAs, in the livers of Long Evans Cinnamon (LEC) rats. LEC rats are inflicted with elevated lipid peroxidation and prone to the development of hepatocellular carcinomas. The results showed that while the survival of LEC rats was increased significantly by dietary α-lipoic acid, none of the antioxidants inhibited the formation of DHHedA and only polyphenon E treatment decreased the formation of γ-OHPdG. In contrast, vitamin E caused an increase in the formation of both γ-OHPdG and DHHedA in the livers of LEC rats. This work was supported by the NCI grant: RO1-CA-134892.

Citation Format: Ying Fu, Marcin Dyba, Jishen Pan, Casey Schultz, Peiying Yang, Dhimant Desai, Shantu Amin, Fung-Lung Chung. Detection in vivo of a novel endogenous etheno DNA adduct derived from arachidonic acid and the effects of antioxidants on its formation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1588. doi:10.1158/1538-7445.AM2014-1588

In vivo detection of a novel endogenous etheno-DNA adduct derived from arachidonic acid and the effects of antioxidants on its formation

Previous studies showed that 7-(1',2'-dihydroxyheptyl)-substituted etheno DNA adducts are products of reactions with the epoxide of (E)-4-hydroxy-2-nonenal, an oxidation product of ω-6 polyunsaturated fatty acids (PUFAs). In this work, we report the detection of 7-(1',2'-dihydroxyheptyl)-1,N(6)-ethenodeoxyadenosine (DHHedA) in rodent and human tissues by two independent methods: a (32)P-postlabeling/HPLC method and an isotope dilution liquid chromatography-electrospray ionization-tandem mass spectrometry method, demonstrating for the first time that DHHedA is a background DNA lesion in vivo. We showed that DHHedA can be formed upon incubation of arachidonic acid with deoxyadenosine, supporting the notion that ω-6 PUFAs are the endogenous source of DHHedA formation. Because cyclic adducts are derived from the oxidation of PUFAs, we subsequently examined the effects of antioxidants, α-lipoic acid, Polyphenon E, and vitamin E, on the formation of DHHedA and γ-hydroxy-1,N(2)-propanodeoxyguanosine (γ-OHPdG), a widely studied acrolein-derived adduct arising from oxidized PUFAs, in the livers of Long Evans Cinnamon (LEC) rats. LEC rats are afflicted with elevated lipid peroxidation and prone to the development of hepatocellular carcinomas. The results showed that although the survival of LEC rats was increased significantly by α-lipoic acid, none of the antioxidants inhibited the formation of DHHedA, and only Polyphenon E decreased the formation of γ-OHPdG. In contrast, vitamin E caused a significant increase in the formation of both γ-OHPdG and DHHedA in the livers of LEC rats.

Repair kinetics of acrolein- and (E)-4-hydroxy-2-nonenal-derived DNA adducts in human colon cell extracts

ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) play a role in the pathogenesis of colon cancer. Upon oxidation, PUFAs generate α,β-unsaturated aldehydes or enals, such as acrolein (Acr) and (E)-4-hydroxy-2-nonenal (HNE), which can form cyclic adducts of deoxyguanosine (Acr-dG and HNE-dG, respectively) in DNA. Both Acr-dG and HNE-dG adducts have been detected in human and animal tissues and are potentially mutagenic and carcinogenic. In vivo levels of Acr-dG in DNA are at least two orders of magnitude higher than those of HNE-dG. In addition to the facile reaction with Acr, the higher levels of Acr-dG than HNE-dG in vivo may be due to a lower rate of repair. Previous studies have shown that HNE-dG adducts are repaired by the NER pathway (Choudhury et al. [42]). We hypothesize that Acr-dG adducts are repaired at a slower rate than HNE-dG and that HNE-dG in DNA may influence the repair of Acr-dG. In this study, using a DNA repair synthesis assay and a LC-MS/MS method, we showed that Acr-dG in a plasmid DNA is repaired by NER proteins, but it is repaired at a much slower rate than HNE-dG in human colon cell extracts, and the slow repair of Acr-dG is likely due to poor recognition/excision of the lesions in DNA. Furthermore, using a plasmid DNA containing both adducts we found the repair of Acr-dG is significantly inhibited by HNE-dG, however, the repair of HNE-dG is not much affected by Acr-dG. This study demonstrates that the NER repair efficiencies of the two major structurally-related in vivo cyclic DNA adducts from lipid oxidation vary greatly. More importantly, the repair of Acr-dG can be significantly retarded by the presence of HNE-dG in DNA. Therefore, this study provides a mechanistic explanation for the higher levels of Acr-dG than HNE-dG observed in tissue DNA.

Abstract 120: Detection of acrolein-derived cyclic DNA adducts in human cells by monoclonal antibodies

Acrolein (Acr) is a ubiquitous environmental pollutant found in cigarette smoke and automobile exhaust. It can also be produced endogenously by oxidation of polyunsaturated fatty acids. The Acr-derived 1,N2-propanodeoxyguanosine (Acr-dG) adducts in DNA are mutagenic lesions that are potentially involved in human cancers. In this study, monoclonal antibodies were raised against Acr-dG adducts and characterized using ELISA. They showed strong reactivity and specificity towards Acr-dG, weaker reactivity towards crotonaldehyde- and trans-4-hydroxy-2-nonenal-derived 1,N2-propanodeoxyguanosines, and weak or no reactivity towards 1,N6-ethenodeoxyadenosine, 8-oxo-deoxyguanosine, and benzo(a)pyrene- and malondialdehdye-derived adducts. Using these novel antibodies, we developed assays to detect Acr-dG in vivo: First, a simple and quick FACS-based assay for detecting these adducts directly in cells; Second, a highly sensitive direct ELISA assay for measuring Acr-dG in cells and tissues using only one μg DNA; And third, a competitive ELISA for better quantitative measurement of Acr-dG levels in DNA. The assays were validated using Acr-treated HT29 cell DNA samples or calf thymus DNA and the results were confirmed by LC-MS/MS-MRM. An immunohistochemical assay was also developed to detect and visualize Acr-dG in HT29 cells as well as in human oral cells. These antibody-based methods provide useful tools for the studies of Acr-dG as a cancer biomarker and of the molecular mechanisms by which cells respond to Acr-dG as a ubiquitous DNA lesion. (This work was supported by NCI grant CA134892)

Citation Format: Jishen Pan, Bisola Awoyemi, Zhuoli Xuan, Priya Vohra, Hsiang-Tsui Wang, Marcin Dyba, Emily Greenspan, Ying Fu, Karen Creswell, Lihua Zhang, Deborah Berry, Moon-Shong Tang, Fung-Lung Chung. Detection of acrolein-derived cyclic DNA adducts in human cells by monoclonal antibodies. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 120. doi:10.1158/1538-7445.AM2013-120

Detection of acrolein-derived cyclic DNA adducts in human cells by monoclonal antibodies

Acrolein (Acr) is a ubiquitous environmental pollutant found in cigarette smoke and automobile exhaust. It can also be produced endogenously by oxidation of polyunsaturated fatty acids. The Acr-derived 1,N(2)-propanodeoxyguanosine (Acr-dG) adducts in DNA are mutagenic lesions that are potentially involved in human cancers. In this study, monoclonal antibodies were raised against Acr-dG adducts and characterized using ELISA. They showed strong reactivity and specificity toward Acr-dG, weaker reactivity toward crotonaldehyde- and trans-4-hydroxy-2-nonenal-derived 1,N(2)-propanodeoxyguanosines, and weak or no reactivity toward 1,N(6)-ethenodeoxyadenosine and 8-oxo-deoxyguanosine. Using these antibodies, we developed assays to detect Acr-dG in vivo: first, a simple and quick FACS-based assay for detecting these adducts directly in cells; second, a highly sensitive direct ELISA assay for measuring Acr-dG in cells and tissues using only 1 μg of DNA without DNA digestion and sample enrichment; and third, a competitive ELISA for better quantitative measurement of Acr-dG levels in DNA samples. The assays were validated using Acr-treated HT29 cell DNA samples or calf thymus DNA, and the results were confirmed by LC-MS/MS-MRM. An immunohistochemical assay was also developed to detect and visualize Acr-dG in HT29 cells as well as in human oral cells. These antibody-based methods provide useful tools for the studies of Acr-dG as a cancer biomarker and of the molecular mechanisms by which cells respond to Acr-dG as a ubiquitous DNA lesion.

High-throughput, quantitative analysis of acrolein-derived DNA adducts in human oral cells by immunohistochemistry

Acrolein (Acr) is a ubiquitous environmental pollutant as well as an endogenous compound. Acrolein-derived 1,N(2)-propanodeoxyguanosines (Acr-dG) are exocyclic DNA adducts formed following exposure to cigarette smoke or from lipid peroxidation. Acr-dG is mutagenic and potentially carcinogenic and may represent a useful biomarker for the early detection of cancers related to smoking or other oxidative conditions, such as chronic inflammation. In this study, we have developed a high-throughput, automated method using a HistoRx PM-2000 imaging system combined with MetaMorph software for quantifying Acr-dG adducts in human oral cells by immunohistochemical detection using a monoclonal antibody recently developed by our laboratory. This method was validated in a cell culture system using BEAS-2B human bronchial epithelial cells treated with known concentrations of Acr. The results were further verified by quantitative analysis of Acr-dG in DNA of BEAS-2B cells using a liquid chromatography/tandem mass spectrometry/multiple-reaction monitoring method. The automated method is a quicker, more accurate method than manual evaluation of counting cells expressing Acr-dG and quantifying fluorescence intensity. It may be applied to other antibodies that are used for immunohistochemical detection in tissues as well as cell lines, primary cultures, and other cell types.

Regioselective formation of acrolein-derived cyclic 1,N(2)-propanodeoxyguanosine adducts mediated by amino acids, proteins, and cell lysates

Acrolein (Acr) is a major component in cigarette smoke and a ubiquitous environmental pollutant. It is also formed as a product of lipid peroxidation. Following ring closure via the Michael addition, Acr modifies deoxyguanosine (dG) in DNA by forming cyclic 1,N(2)-propanodeoxyguanosine adducts (OHPdG). The reactions of Acr with dG yield, depending on the direction of ring closure, two regioisomers, α- and γ-OHPdG, in approximately equal amounts. However, previous (32)P-postlabeling studies showed that the γ isomers were detected predominantly in the DNA of rodent and human tissues. Because of the potential differential biological activity of the isomeric OHPdG adducts, it is important to confirm and study the chemical basis of the regioselective formation of γ isomers in vivo. In this study, it is confirmed that γ-OHPdG adducts are indeed the major isomers formed in vivo as evidenced by a LC-MS/MS method specifically developed for Acr-derived dG adducts. Furthermore, we have shown that the formation of γ-isomers is increased in the presence of amino-containing compounds, including amino acids, proteins, and cell lysates. A product of Acr and arginine that appears to mediate the regioselective formation of γ isomers was identified, but its structure was not fully characterized due to its instability. This study demonstrates that intracellular amino-containing compounds may influence the regiochemistry of the formation of OHPdG adducts and reveals a mechanism for the preferential formation of γ-OHPdG by Acr in vivo.

Metabolism of isothiocyanates in individuals with positive and null GSTT1 and M1 genotypes after drinking watercress juice

BACKGROUND & AIMS

Isothiocyanates (ITCs) derived from cruciferous vegetables have been shown to be promising agents against cancer in human cell culture, animal models, and in epidemiological studies. Several epidemiological studies have demonstrated an inverse relationship between intake of dietary isothiocyanates and the risk of cancers, particularly lung, colon, and breast. More importantly, the protective effects of dietary ITCs appear to be influenced by glutathione S-transferase (GST) genotype; specifically, individuals with glutathione S-transferase theta 1 (GSTT1) and glutathione S-transferase Mu 1 (GSTM1) null are better protected than those with GSTT1 and M1 positive. Although the majority of studies, especially those conducted in populations exposed to ITC rich diets, demonstrated such effects, there are a few studies that showed opposite or no association. While evidence for the interactions of dietary ITCs with GST genes is relatively strong, the reasons for the differential effects remain unclear. In this study, we examined one possible mechanism: whether subjects with null genotypes excrete ITCs at a slower rate than those with positive genotypes after drinking watercress juice, a rich source of ITCs.

METHODS

A total of 48 subjects, 28 GSTT1 and M1 positive and 20 null genotypes were enrolled in the study. The rates of excretion were determined using five urine samples collected over a period of 24 h after drinking watercress juice.

RESULTS

No statistically significant differences in the rates of isothiocyanate excretion and the time of peak excretion were observed between the two tested groups having positive and null genotypes.

CONCLUSIONS

GSTT1 and M1 genotypes are not likely to be involved in the rate of excretion of ITCs in watercress. The demonstrated differences in protection among subjects with the two genotypes are not likely due to differences in overall ITC excretion rates, however, excretion rates of ITCs other than PEITC need to be investigated. Other yet to be identified mechanism(s) may underlie the diet and gene interactions between dietary ITCs and GST genotypes in human cancer prevention. Further research is needed to evaluate the protective mechanisms of isothiocyanates against cancer.

Isothiocyanate exposure, glutathione S-transferase polymorphisms, and colorectal cancer risk

BACKGROUND

Isothiocyanates, compounds found primarily in cruciferous vegetables, have been shown in laboratory studies to possess anticarcinogenic activity. Glutathione S-transferases (GSTs) are involved in the metabolism and elimination of isothiocyanates; thus, genetic variations in these enzymes may affect in vivo bioavailability and the activity of isothiocyanates.

OBJECTIVE

The objective was to prospectively evaluate the association between urinary isothiocyanate concentrations and colorectal cancer risk as well as the potential modifying effect of GST genotypes on the association.

DESIGN

A nested case-control study of 322 cases and 1251 controls identified from the Shanghai Women's Health Study was conducted.

RESULTS

Urinary isothiocyanate concentrations were inversely associated with colorectal cancer risk; the inverse association was statistically significant or nearly significant in the GSTM1-null (P for trend = 0.04) and the GSTT1-null (P for trend = 0.07) genotype groups. The strongest inverse association was found among individuals with both the GSTM1-null and the GSTT1-null genotypes, with an adjusted odds ratio of 0.51 (95% CI: 0.27, 0.95), in a comparison of the highest with the lowest tertile of urinary isothiocyanates. No apparent associations between isothiocyanate concentration and colorectal cancer risk were found among individuals who carried either the GSTM1 or GSTT1 gene (P for interaction < 0.05).

CONCLUSION

This study suggests that isothiocyanate exposure may reduce the risk of colorectal cancer, and this protective effect may be modified by the GSTM1 and GSTT1 genes.

Urinary isothiocyanates; glutathione S-transferase M1, T1, and P1 polymorphisms; and risk of colorectal cancer: the Multiethnic Cohort Study

Although an association between diet, especially cruciferous vegetables, and colorectal cancer has been hypothesized, recent studies have been inconsistent with their findings. One possibility for the discrepant results is that the interaction with related genes has not generally been considered. The present study examined the associations among urinary isothiocyanates, glutathione S-transferase (GST) polymorphisms, and colorectal cancer risk in a case-control study nested within the Multiethnic Cohort Study, based in Hawaii and Los Angeles, California. We measured prediagnositic urinary isothiocyanate levels adjusted for creatinine and analyzed GSTM1, GSTT1, and GSTP1 polymorphisms in 173 cases and 313 matched controls, with biospecimens collected between 2001 and 2006. Conditional logistic regression was used to compute odds ratios and 95% confidence intervals (95% CI). A detectable amount of urinary isothiocyanates was associated with a 41% decrease in colorectal cancer risk (95% CI, 0.36-0.98). No significant, main-effect associations were seen with a homozygous deletion of the GSTM1 or GSTT1 polymorphism, or with the AG or GG genotypes for GSTP1 rs1695. There was a weak suggestion that for individuals with the GSTP1 AG or GG genotype, a detectable amount of isothiocyanates further decreases one's risk of colorectal cancer compared with those with the GSTP1 AA genotype, but the interaction term was not statistically significant (P = 0.09). This is only the second study published on the association between urinary isothiocyanates and colorectal cancer risk. The results suggest that further studies, with larger numbers, examining a possible interaction with the GSTP1 polymorphisms are warranted.

Detection of the acrolein-derived cyclic DNA adduct by a quantitative 32P-postlabeling/solid-phase extraction/HPLC method: blocking its artifact formation with glutathione

Acrolein (Acr), a hazardous air pollutant, reacts readily with deoxyguanosine (dG) in DNA to produce cyclic 1, N2-propanodeoxyguanosine adducts (Acr-dG). Studies demonstrate that these adducts are detected in vivo and may play a role in mutagenesis and carcinogenesis. In the study described here, a quantitative 32P-postlabeling/solid-phase extraction/HPLC method was developed by optimizing the solid-phase extraction and the 32P-postlabeling conditions for analysis of Acr-dG in DNA samples with a detection limit of 0.1 fmol. It was found that Acr-dG can form as an artifact during the assay. Evidence obtained from mass spectrometry indicates that the Acr in water used in the assay is a likely source of artifact formation of Acr-dG. The formation of Acr-dG as an artifact can be effectively blocked by adding glutathione (GSH) to the DNA sample to be analyzed. In addition, Acr-dG was detected as a contaminant in the commercial dG and dT 3'-monophosphate samples. Finally, this method was used to detect Acr-dG in calf thymus and human colon HT29 cell DNA with an excellent linear quantitative relationship.

Bombesin marine toxin conjugates inhibit the growth of lung cancer cells

Hemiasterlin (Hem) and dolastatin (Dol) are marine natural products which are cytotoxic for cancer cells. Hem, a tripeptide, and Dol, a hexapeptide, were conjugated with linkers (L) to the universal BB agonist DPhe-Gln-Trp-Ala-Val-betaAla-His-Phe-Nle-NH2(BA1) and the effects of the Hem-BB and Dol-BB conjugates investigated on NCI-H1299 lung cancer cells. Hem-LA-BA1 and Hem-LB-BA1 inhibited specific (125I-Tyr4)BB binding to NCI-H1299 cells, which have BB2 receptors (R), with IC50 values of 15 and 25 nM, respectively. Addition of Hem-LA-BA1 and Hem-LB-BA1 to Fura-2 AM loaded cells containing BB2R, caused elevated cytosolic Ca2+. In a growth assay, Hem-LA-BA1 and Hem-LB-BA1 inhibited the proliferation of NCI-H1299 cells. Dol-succinamide (Dols)-LD-BA1 and Dols-LE-BA1 bound with high affinity to NCI-H1299 cells and elevated cytosolic Ca2+, but did not inhibit the proliferation of NCI-H1299 cells. Also, Hem-LA-BA1 inhibited 125I-DTyr-Gln-Trp-Ala-Val-betaAla-His-Phe-Nle-NH2 (BA2) binding to Balb/3T3 cells transfected with BB1R or BB2R as well as with BRS-3 with IC50 values of 130, 8, and 540 nM, respectively. These results show that Hem-BB conjugates are cytotoxic for cancer cells containing BB2R.

Synthesis and biological activity of 5-aza-ellipticine derivatives

Novel 5-aza-ellipticine derivatives were synthesized and tested as antitumor agents. The new compounds were prepared more readily than the analogous ellipticine derivatives, which are known to be potent anti-tumor agents Although the novel 5-aza-ellipticine derivatives are not as biologically active as their corresponding ellipticine analogues, the new compounds represent a new, readily accessible class of heteroaromatic catalytic inhibitors of topoisomerase II and possible anti-tumor agents.

Products of Cu(II)-catalyzed oxidation in the presence of hydrogen peroxide of the 1-10, 1-16 fragments of human and mouse beta-amyloid peptide

The interactions of proteins with reactive oxygen species (ROS) may result in covalent modifications of amino acid residues in proteins, formation of protein-protein cross-linkages, and oxidation of the protein backbone resulting in protein fragmentation. In an attempt to elucidate the products of the metal-catalyzed oxidation of the human (H) and mouse (M) (1-10H), (1-10M), (1-16H) and (1-16M) fragments of beta-amyloid peptide, the high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) methods and Cu(II)/H(2)O(2) as a model oxidizing system were employed. Peptide solution (0.50 mM) was incubated at 37 degrees C for 24 h with metal:peptide:H(2)O(2) molar ratio 1:1:1 for the (1-16H), (1-16M) fragments, and 1:1:2 for the (1-10H), (1-10M) peptides in phosphate buffer, pH 7.4. Oxidation targets for all peptide studied are the histidine residues coordinated to the metal ions. For the (1-16H) peptide are likely His(13) and/or His(14), and for the (1-16M) fragment His(6) and/or His(14), which are converted to 2-oxo-His. Metal-binding residue, the aspartic acid (D(1)) undergoes the oxidative decarboxylation and deamination to pyruvate. The cleavages of the peptide bonds by either the diamide or alpha-amidation pathways were also observed.

Small Molecule Toxins Targeting Tumor Receptors

Targeting toxic therapeutics to tumors through receptors over expressed on the surface of cancer cells can reduce systemic toxicity and increase the effectiveness of the targeted compounds. Small molecule targeted therapeutics have a number of advantages over toxic immunoconjugates including better tumor penetration, lack of neutralizing host immune response and superior flexibility in selection of drug components with optimal specificity, potency and stability in circulation. Three major components of the targeted drug, the toxic warhead, tumor-specific ligand and the linker can influence the properties of each other and thus have to be optimized for each system. All receptor-targeted drugs are delivered inside the cells through endocytosis and undergo processing liberating the toxins in endosomes and lysosomes. Common delivery route defines a number of general requirements for each drug component. The review addresses currently known possible receptor targets and their ligands along with toxins that have been used and that have a potential to be successfully applied in tumor targeting. Linkers that are stable in circulation, but efficiently cleaved in lysosomes constitute an essential component of receptor-targeted drugs and are evaluated in greater detail.

Dimerization of the immunosuppressive peptide fragment of HLA-DR molecule enhances its potency

Our previous studies revealed that the nonapeptide fragment of HLA-DR molecule, located in the beta chain 164-172 with the VPRSGEVYT sequence, suppresses the immune responses. The sequence is located on the exposed molecule loop, therefore it may be involved in the interactions with other proteins. We suggested that the loop may serve as a functional epitope on the HLA class II surface for intermolecular binding, and that possible mechanism of biological action of the synthesized peptides is associated with interfering of adhesion of HLA class II molecules to their coreceptors. It has been postulated that oligomerization of the coreceptors is required for stable binding to class II HLA. Based on the crystal dimeric structure of HLA-DR molecules, we designed, and synthesized molecules able to induce the putative coreceptors dimerization. The synthesized series of compounds consisted of two VPRSGEVYT sequences linked through their C-termini by spacers of different length: (VPRSGEVYTGn)2K-NH2 ( n = 4-6). The results demonstrate that the dimerization of the nonapeptide fragment of HLA-DR results in enhanced immunosuppressory properties.

Short peptides are not reliable models of thermodynamic and kinetic properties of the N-terminal metal binding site in serum albumin

A comparative study of thermodynamic and kinetic aspects of Cu(II) and Ni(II) binding at the N-terminal binding site of human and bovine serum albumins (HSA and BSA, respectively) and short peptide analogues was performed using potentiometry and spectroscopic techniques. It was found that while qualitative aspects of interaction (spectra and structures of complexes, order of reactions) could be reproduced, the quantitative parameters (stability and rate constants) could not. The N-terminal site in HSA is much more similar to BSA than to short peptides reproducing the HSA sequence. A very strong influence of phosphate ions on the kinetics of Ni(II) interaction was found. This study demonstrates the limitations of short peptide modelling of Cu(II) and Ni(II) transport by albumins.

Differential zinc and DNA binding by partial peptides of human protamine HP2

The Zn(II) binding by partial peptides of human protamine HP2: HP2(1-15); HP2(1-25), HP2(26-40), HP2(37-47), and HP2(43-57) was studied by circular dichroism (CD). Precipitation of a 20-mer DNA by these partial peptides and the effects of Zn(II) thereon were investigated using polyacrylamide gel electrophoresis (GE). The results of this study suggest that reduced HP2 (thiol groups intact) can bind Zn(II) at various parts of the molecule. In the absence of DNA, the primary Zn(II) binding site in reduced HP2 is located in the 37-47 sequence (involving Cys-37, His-39, His-43, and Cys-47), while in the presence of DNA, the strongest Zn(II) binding is provided by sequences 12-22 (by His-12, Cys-13, His-19, and His-22) and 43-57 (His-43, Cys-47, Cys-53, and His-57). In its oxidized form, HP2 can bind zinc through His residues of the 7-22 sequence. Zn(II) markedly enhances DNA binding by all partial peptides. These findings suggest that Zn(II) ions may be a regulatory factor for sperm chromatin condensation processes.

New conformationally restricted analog of the immunosuppressory mini-domain of HLA-DQ and its biological properties

Our previous studies revealed that the nonapeptide fragment of HLA-DQ located in the beta 164-172 loop of the Thr-Pro-Gln-Arg-Gly-Asp-Val-Tyr-Thr sequence suppresses the immune humoral and cellular responses [30]. Based on the crystal structure of HLA-class II molecules we designed and synthesized a cyclic analog with restricted conformation, cyclo(Suc-Thr-Pro-Gln-Arg-Gly-Asp-Val-Lys)-Thr-OH (Suc = succinyl) by reacting a Lys side chain with a succinylated N-terminus. The cyclization product more potently suppresses the cellular immune response than its linear counterparts and is efficiently cleaved by trypsin. The results indicate that the beta 164-172 loop may serve as a functional epitope on the HLA class II surface for intermolecular binding.

Fluorescence microscopy with diffraction resolution barrier broken by stimulated emission

The diffraction barrier responsible for a finite focal spot size and limited resolution in far-field fluorescence microscopy has been fundamentally broken. This is accomplished by quenching excited organic molecules at the rim of the focal spot through stimulated emission. Along the optic axis, the spot size was reduced by up to 6 times beyond the diffraction barrier. The simultaneous 2-fold improvement in the radial direction rendered a nearly spherical fluorescence spot with a diameter of 90-110 nm. The spot volume of down to 0.67 attoliters is 18 times smaller than that of confocal microscopy, thus making our results also relevant to three-dimensional photochemistry and single molecule spectroscopy. Images of live cells reveal greater details.

The impact of the amino-acid sequence on the specificity of copper(II) interactions with peptides having nonco-ordinating side-chains

The review presents specific interactions that occur in complexes of Cu(II) ions with peptides composed only of amino acids with nonco-ordinating side chains. Three classes of such peptides are discussed. The first type (NSFRY analogues) is characterised by the presence of a specific combination of bulky and aromatic residues, leading to a formation of multiple weak interactions around Cu(II) that result in an extremely high stability of complexes. The second class is composed of complexes of vasopressins and oxytocins, achieving superstability through a pre-conformation in the peptide molecule. The third group are oligopeptides containing one or two proline residues. These peptides form exotic macrochelate loops with Cu(II) in a result of the break-point effect of Pro residues. Particular emphasis in the review was given to stability constants of complexes, compared to oligoglycine or oligoalanine peptides.

Specific interactions of bovine and human beta-casomorphin-7 with Cu(II) ions

Complex formation between Cu(II) and human and bovine beta-casomorphin heptapeptides, Tyr-Pro-Phe-Val-Glu-Pro-Ile and Tyr-Pro-Phe-Pro-Gly-Pro-Ile, respectively, was investigated by pH potentiometry and spectroscopic (CD, EPR and electronic absorption) techniques. The results showed the critical impact of Pro residues on the complex equilibria formed. The presence of the Pro residue at the second position leads to formation of very stable dimeric species in which two metal ions co-ordinate to N-terminal ¿NH2, C=O¿ binding sites of one peptide molecule and the deprotonated phenolic oxygen of the second ligand molecule. The presence of two additional hydrophobic residues on the C-terminal makes heptapeptide molecule much more effective ligand than its pentapeptide N-terminal fragment.

The impact of the amino-acid sequence on the specificity of copper(II) interactions with peptides having nonco-ordinating side-chains

The review presents specific interactions that occur in complexes of Cu(II) ions with peptides composed only of amino acids with nonco-ordinating side chains. Three classes of such peptides are discussed. The first type (NSFRY analogues) is characterised by the presence of a specific combination of bulky and aromatic residues, leading to a formation of multiple weak interactions around Cu(II) that result in an extremely high stability of complexes. The second class is composed of complexes of vasopressins and oxytocins, achieving superstability through a pre-conformation in the peptide molecule. The third group are oligopeptides containing one or two proline residues. These peptides form exotic macrochelate loops with Cu(II) in a result of the break-point effect of Pro residues. Particular emphasis in the review was given to stability constants of complexes, compared to oligoglycine or oligoalanine peptides.

Binding ability of Cu2+ ions by opiate-like fragments of bovine casein

The coordination modes of Cu(II) to alpha-casein (90-95) and alpha-casein (90-96) peptides with opioid activity isolated from pepsin hydrolisates of alpha-casein were investigated by means of electron paramagnetic resonance, absorption, and circular dichroism spectroscopy and potentiometry. The results allow the identification of the complex species involved and the attribution of the spectral data set to the various complex structures. According to the spectroscopic data, a phenolate side-chain of Tyr residue belonging to the Gly-Tyr-Leu or Gly-Tyr-Leu-Gln fragment of the peptides is involved in the metal coordination in a complex which is a minor species at neutral pH range.

Specific interactions of Cu2+ ions with fragments of envelope protein of hepatitis B virus

Potentionmetric and spectroscopic (EPR, CD and absorption spectra) data have shown that a fragment of envelope proteins of the hepatitis B virus could be very specific bind molecules for Cu2+ ions using arginine lateral NH2 donor sites. The presence of Pro and Asp residues makes Arg binding not only very specific, but also very efficient.