Abstract 2821: Mitigation of radiation-induced colon injuries in mice by oral sepiapterin (PTC923)

The rectum is the primary dose limiting structure for radiation therapy (RT) in treating prostate cancer. Two clinical forms of rectal injury have been described: early and late. Early injury typically develops during RT and occurs to some degree in most patients. The condition is usually self-limiting, but can predispose patients to the development of late injury. Late rectal injury occurs in up to 25% of patients months to years after pelvic RT and is more concerning, since it can be irreversible and can have a major impact on a patient’s lifestyle. Development of new pharmacologic approaches to eliminate the risk of RT-dependent rectal injury remains an important goal. Although detailed mechanisms underlying normal tissue toxicities vary from tissue to tissue, the central underlying mechanism is abnormal wound healing involving endothelial dysfunction (ED) and subsequently fibrosis. Regardless of its cause, ED is characterized by an “uncoupled” endothelial NOS (eNOS) activity that generates superoxide (O2 -) and peroxynitrite (ONOO-) rather than NO. One mechanism for uncoupling in inflammatory conditions is oxidation of the reduced cofactor tetrahydrobiopterin (BH4). The product of uncoupling, ONOO-, oxidizes BH4, initiating a feed forward mechanism to sustain uncoupling. Oral treatment with sepiapterin (PTC923), a tetrahydrobiopterin precursor, decreased infiltrating inflammatory cells and cytokine levels in mice with colitis. We therefore tested whether a synthetic PTC923 might mitigate radiation-induced colon injuries. C57L/J wild-type 6-8-week-old males mice received 13.5 Gy total-body irradiation (TBI). Starting from 24 h post-irradiation, mice were treated once daily with 1 mg/kg PTC923 for six days by oral gavage. Colon injuries were accessed on 6th day after IR by colonoscopy and scored by using distal-proximal endoscopic colitis scoring system (D-PECS). The system has a core inflammatory component of four non-co-linear parameters and decimal units to notable lesions or complications. Relative expression of cytokines IL-1β, IL-6, IL-17α, and TGF-β1 in colon endothelial cells were measured by RT-PCR 8 days after IR. According with D-PECS estimation, post-irradiation colon injury was significantly reduced by PTC923 treatment: on the 6th day after TBI mice demonstrated D-PECS score 5.8±1.48 vs 1.6±0.55 D-PECS score for animals received PTC923 treatment after TBI (p-value=0.00). Increase of cytokines IL-6 and TGF-β1 in the colon endothelium after TBI was effectively blocked by PTC923 treatment (IL-6: IR+Vehicle = 4.31±1.31 fold increase vs IR+PTC923 = 1.29±0.37 fold increase (p-value=0.0016); TGF-β1: IR+Vehicle = 5.18±0.66 fold increase vs IR+PTC923 = 2.01±0.75 fold increase (p-value=0.00029)). In conclusion, these findings support the proposal that oral treatment with sepiapterin is a potential mitigator of colon injury caused by RT.

Citation Format: Vasily A. Yakovlev, Christopher S. Rabender, Ross B. Mikkelsen. Mitigation of radiation-induced colon injuries in mice by oral sepiapterin (PTC923) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2821.

Uncoupled nitric oxide synthase activity promotes colorectal cancer progression

Increased levels of reactive oxygen/nitrogen species are one hallmark of chronic inflammation contributing to the activation of pro-inflammatory/proliferative pathways. In the cancers analyzed, the tetrahydrobiopterin:dihydrobiopterin ratio is lower than that of the corresponding normal tissue, leading to an uncoupled nitric oxide synthase activity and increased generation of reactive oxygen/nitrogen species. Previously, we demonstrated that prophylactic treatment with sepiapterin, a salvage pathway precursor of tetrahydrobiopterin, prevents dextran sodium sulfate-induced colitis in mice and associated azoxymethane-induced colorectal cancer. Herein, we report that increasing the tetrahydrobiopterin:dihydrobiopterin ratio and recoupling nitric oxide synthase with sepiapterin in the colon cancer cell lines, HCT116 and HT29, inhibit their proliferation and enhance cell death, in part, by Akt/GSK-3β-mediated downregulation of β-catenin. Therapeutic oral gavage with sepiapterin of mice bearing azoxymethane/dextran sodium sulfate-induced colorectal cancer decreased metabolic uptake of [18F]-fluorodeoxyglucose and enhanced apoptosis nine-fold in these tumors. Immunohistochemical analysis of both mouse and human tissues indicated downregulated expression of key enzymes in tetrahydrobiopterin biosynthesis in the colorectal cancer tumors. Human stage 1 colon tumors exhibited a significant decrease in the expression of quinoid dihydropteridine reductase, a key enzyme involved in recycling tetrahydrobiopterin suggesting a potential mechanism for the reduced tetrahydrobiopterin:dihydrobiopterin ratio in these tumors. In summary, sepiapterin treatment of colorectal cancer cells increases the tetrahydrobiopterin:dihydrobiopterin ratio, recouples nitric oxide synthase, and reduces tumor growth. We conclude that nitric oxide synthase coupling may provide a useful therapeutic target for treating patients with colorectal cancer.

Mitigation of Radiation-Induced Lung and Heart Injuries in Mice by Oral Sepiapterin after Irradiation

After radiation exposure, endothelium-dependent vasorelaxation is impaired due to impaired nitric oxide production. Endothelial dysfunction is characterized by uncoupled endothelial nitric oxide synthase activity, oxidation of the reduced cofactor tetrahydrobiopterin to dihydrobiopterin as one well recognized mechanism. Oral treatment with sepiapterin, a tetrahydrobiopterin precursor, decreased infiltrating inflammatory cells and cytokine levels in mice with colitis. We therefore tested whether a synthetic sepiapterin, PTC923, might mitigate radiation-induced cardiac and pulmonary injuries. C57L/J wild-type 6-8-week-old mice of both sexes received 5 Gy total-body irradiation (TBI), followed by a top-up dose of 6.5 Gy to the thorax (total thoracic dose of 11.5 Gy). Starting from 24 h postirradiation, mice were treated once daily with 1 mg/kg PTC923 for six days by oral gavage. Assessment of lung injury by breathing rate was measured every other week and echocardiography to assess heart function was performed at different time points (8, 30, 60, 90 and 180 days). Plasma proteins (fibrinogen, neutrophil elastase, C-reactive protein, and IL-6) were assessed as well. TBI induced a reduction in cardiac contractile reserve and an impairment in diastolic function restored by daily oral PTC923. Postirradiation lung injury was significantly delayed by PTC923. TBI mice treated with PTC923 experienced a longer survival compared to nonirradiated mice (71% vs. 40% of mice alive after 180 days). PTC923-treated mice showed a reduction in inflammatory mediators, especially IL-6 and IL-1b. In conclusion, these findings support the proposal that PTC923 is a potential mitigator of cardiac and lung injury caused by TBI.

Sepiapterin Enhances Tumor Radio- and Chemosensitivities by Promoting Vascular Normalization

Previously, we demonstrated that nitric oxide (NO) synthase (NOS) is uncoupled in a wide range of solid tumors and that restoring NOS coupling with the tetrahydrobiopterin precursor sepiapterin (SP) inhibits tumor progression. Endothelial dysfunction characterizes the poorly functional vasculature of solid tumors, and since NO is critical for regulation of endothelial function we asked whether SP, by recoupling NOS, improves tumor vasculature structure and function-enhancing chemotherapeutic delivery and response to radiotherapy. MMTV-neu mice with spontaneous breast tumors were treated with SP by oral gavage and evaluated by multispectral optoacoustic tomographic analysis of tumor HbO2 and by tissue staining for markers of hypoxia, blood perfusion, and markers of endothelial and smooth muscle proteins. Recoupling tumor NOS activity results in vascular normalization observed as reduced tumor hypoxia, improved tumor percentage of HbO2 and perfusion, as well as increased pericyte coverage of tumor blood vessels. The normalized vasculature and improved tumor oxygenation led to a greater than 2-fold increase in radiation-induced apoptosis compared with radiation or SP alone. High-performance liquid chromatography analysis of tumor doxorubicin levels showed a greater than 50% increase in doxorubicin uptake and a synergistic effect on tumor cell apoptosis. This study highlights for the first time the importance of NOS uncoupling and endothelial dysfunction in the development of tumor vasculature and presents a new approach for improving the tumoricidal efficacies of chemotherapy and radiotherapy.

Abstract 5196: Recoupling nitric oxide synthetase to normalize tumor vasculature and enhance tumor radiosensitivity and anti-tumor drug uptake

The aberrant nature of tumor vasculature results in uneven, heterogeneous blood flow and leaky, hemorrhagic blood vessels. Due to the unusual nature of tumor vessels, areas of hypoxia develop that contribute to radioresistance and inefficiency of therapeutic drug delivery. Our current studies examine the role of nitric oxide synthase (NOS) in tumor vasculature. NOS has been demonstrated to be “uncoupled” in tumors and isolated tumor cells due to reduced levels of tetrahydrobiopterin (BH4), a necessary cofactor, resulting in superoxide and peroxynitrite formation in lieu of NO (Rabender et al 2015 Molecular Cancer Research). NO signaling is critical for vascular function and thus uncoupling of eNOS in tumor endothelial cells may partly explain the poor vasculature found within solid tumors. Having previously demonstrated that NOS can be “recoupled” and NO production restored through treatment of tumor cells with Sepiapterin (SP), a BH4 precursor, we examined whether SP could normalize tumor vasculature, promoting radiosensitivity and improving drug uptake. Multispectral optoacoustic tomography analysis of both flank tumor xenografts and a spontaneous breast tumor model (MMTV) demonstrate that SP given by oral gavage once a day for 7 days significantly enhances tumor BH4 levels and the percent of oxyhemoglobin in the tumor. Immunohistochemical analysis of tumors from mice treated with SP showed a significant reduction in CD31 staining and a significant increase in smooth muscle actin (SMA), both hallmarks of vascular normalization. A significant decrease in pimonidazole staining and concomitant increase in Hoescht staining in MMTV mice treated with SP confirms the reduction in tumor hypoxia as well as increased tumor perfusion. Increased tumor perfusion was also demonstrated through enhanced doxorubicin uptake in tumors of mice treated with SP. Lastly, the enhanced tumor oxygenation correlated with more than a 2-fold increase in radiation induced cell killing measured by ex vivo clonogenic assay. These preliminary data demonstrate the need for continued study of NOS uncoupling in solid tumors, especially when we take into consideration that SP has been demonstrated to be cytotoxic to both breast and colon tumors. On-going studies are examining the consequences of enhanced drug uptake on both normal and tumor tissue as well as the mechanism behind the vascular normalization.

Note: This abstract was not presented at the meeting.

Citation Format: Christopher S. Rabender, Sundaresan Gobalakrishnan, Li Wang, Jamal Zweit, Ross B. Mikkelsen. Recoupling nitric oxide synthetase to normalize tumor vasculature and enhance tumor radiosensitivity and anti-tumor drug uptake [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5196. doi:10.1158/1538-7445.AM2017-5196

Abstract 3800: Analysis of circulating tumor exosomes: their ability to serve as a biomarker for recurrence in lung cancer

Objectives: Exosomes (Exos) are 30-150 nm wide nanovesicles originating from the endosomal network and are found in most body fluids. Production of Exos increases in cancer, making Exos potential biomarkers. Exos are a fundamental driver of intercellular communication by transferring proteins, lipids and miRNA. Analysis of Exos and their interaction with the microenvironment may uncover cellular pathways involved with disease progression. We hypothesized that Exos may serve as a liquid biopsy for tumor recurrence.

Materials and Methods: Six lung cancer patients (LCPs) were prospectively enrolled on an IRB approved study. Exos were precipitated and purified with a Norgen kit from 0.7 ml of blood samples collected prior to, during and 6 months after radiation therapy (RT). Exos numbers were quantified by Exocet Exosome Quantitation Kit (System Biosciences). Total exosomal RNA was isolated by the Norgen RNA/DNA/Protein Purification kit. For the miRNAs expression profiling we used the miRCURY LNA™ Universal RT microRNA PCR assay (Exiqon) and ExiLENT SYBR® Green Maser Mix (Exiqon). Expressions of 10 different miRNAs (let-7a-5p, miR-20a-5p, miR-21-5p, miR-30b-5p, miR-106a-5p, miR-146a-5p, miR-155-5p, miR-200b-5p, miR-203a, miR-208a) for all samples were determined. Human lung fibroblasts (MRC-5s) in serum-free medium for 24 hrs were treated with Exos, TGF-β (positive control) or PBS (negative control) to determine their relative effects on MRC-5 proliferation.

Results: Of the 6 LCPs, 2 had limited stage small cell and 4 had non-small cell at diagnosis. Three patients were diagnosed with recurrence at the time of their post-RT blood draw. Six miRNAs demonstrated significantly different expressions between recurrent and non-recurrent groups of LCPs: let-7a-5p, miR-20a-5p, miR-21-5p, miR-106a-5p, miR-155-5p, and miR-203a. MRC-5 proliferation increases 2-fold when treated with Exos from blood collected prior to RT compared to PBS (p = 0.01). There is <2-fold increase compared to TGF-β (p = 0.03). Plasma Exos levels decrease during RT as do their relative effects on MRC-5 proliferation when compared at equivalent numbers. Exos collected at 6 months from patients with recurrence significantly stimulated MRC-5 proliferation (p = 0.03), whereas Exos from patients without recurrence do not. Western blot analyses of MRC-5 cells stimulated with Exos revealed decreased PTEN but enhanced CDC25A expression and increased AKT and SMAD phosphorylation, regardless of when the Exos were collected.

Conclusions: Recurrent and non-recurrent groups of LCPs demonstrated significant differences in exosomal miR profile before and after RT. Exos from untreated LCPs, and recurrent LCPs after RT, stimulate MRC-5 proliferation and possible conversion to CAFs. Our results suggest that Exos could serve as a “liquid biopsy” to assess the potential for recurrence when imaging modalities are equivocal.

Citation Format: Nicholas Serrano, John Blue, Asim Alam, Christopher S. Rabender, Elisabeth Weiss, Mitchell S. Anscher, Ross B. Mikkelsen, Vasily A. Yakovlev. Analysis of circulating tumor exosomes: their ability to serve as a biomarker for recurrence in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3800. doi:10.1158/1538-7445.AM2017-3800

A Preliminary Study on Racial Differences in HMOX1, NFE2L2, and TGFβ1 Gene Polymorphisms and Radiation-Induced Late Normal Tissue Toxicity

PURPOSE

This study tested whether racial differences in genetic polymorphisms of 4 genes involved in wound repair and response to radiation can be used to predict the occurrence of normal tissue late effects of radiation therapy and indicate potential therapeutic targets.

METHODS AND MATERIALS

This prospective study examined genetic polymorphisms that modulate the expression of 4 genes involved in inflammation and fibrosis and response to radiation (HMOX1, NFE2L2, NOS3, and TGFβ1). DNA from blood samples of 179 patients (∼ 80% breast and head and neck) collected at the time of diagnosis by their radiation oncologist as exhibiting late normal tissue toxicity was used for the analysis. Patient demographics were as follows: 56% white, 43% African American, 1% other. Allelic frequencies of the different polymorphisms of the participants were compared with those of the general American population stratified by race. Twenty-six additional patients treated with radiation, but without toxicity at 3 months or later after therapy, were also analyzed.

RESULTS

Increased frequency of a long GT repeat in the HMOX1 promoter was associated with late effects in both African American and white populations. The single nucleotide polymorphisms (SNP) rs1800469 in the TGFβ1 promoter and the rs6721961 SNP in the NFE2L2 promoter were also found to significantly associate with late effects in African Americans but not whites. A combined analysis of these polymorphisms revealed that >90% of African American patients with late effects had at least 1 of these minor alleles, and 58% had 2 or more. No statistical significance was found relating the studied NOS3 polymorphisms and normal tissue toxicity.

CONCLUSIONS

These results support a strong association between wound repair and late toxicities of radiation. The presence of these genetic risk factors can vary significantly among different ethnic groups, as demonstrated for some of the SNPs. Future studies should account for the possibility of such ethnic heterogeneity in the late toxicities of radiation.

The Role of Nitric Oxide Synthase Uncoupling in Tumor Progression

Here, evidence suggests that nitric oxide synthases (NOS) of tumor cells, in contrast with normal tissues, synthesize predominantly superoxide and peroxynitrite. Based on high-performance liquid chromatography analysis, the underlying mechanism for this uncoupling is a reduced tetrahydrobiopterin:dihydrobiopterin ratio (BH4:BH2) found in breast, colorectal, epidermoid, and head and neck tumors compared with normal tissues. Increasing BH4:BH2 and reconstitution of coupled NOS activity in breast cancer cells with the BH4 salvage pathway precursor, sepiapterin, causes significant shifts in downstream signaling, including increased cGMP-dependent protein kinase (PKG) activity, decreased β-catenin expression, and TCF4 promoter activity, and reduced NF-κB promoter activity. Sepiapterin inhibited breast tumor cell growth in vitro and in vivo as measured by a clonogenic assay, Ki67 staining, and 2[18F]fluoro-2-deoxy-D-glucose-deoxyglucose positron emission tomography (FDG-PET). In summary, using diverse tumor types, it is demonstrated that the BH4:BH2 ratio is lower in tumor tissues and, as a consequence, NOS activity generates more peroxynitrite and superoxide anion than nitric oxide, resulting in important tumor growth-promoting and antiapoptotic signaling properties.

IMPLICATIONS

The synthetic BH4, Kuvan, is used to elevate BH4:BH2 in some phenylketonuria patients and to treat diseases associated with endothelial dysfunction, suggesting a novel, testable approach for correcting an abnormality of tumor metabolism to control tumor growth.

Sepiapterin ameliorates chemically induced murine colitis and azoxymethane-induced colon cancer

The effects of modulating tetrahydrobiopterin (BH4) levels with a metabolic precursor, sepiapterin (SP), on dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)-induced colorectal cancer were studied. SP in the drinking water blocks DSS-induced colitis measured as decreased disease activity index (DAI), morphologic criteria, and recovery of Ca(2+)-induced contractility responses lost as a consequence of DSS treatment. SP reduces inflammatory responses measured as the decreased number of infiltrating inflammatory macrophages and neutrophils and decreased expression of proinflammatory cytokines interleukin 1β (IL-1β), IL-6, and IL-17A. High-performance liquid chromatography analyses of colonic BH4 and its oxidized derivative 7,8-dihydrobiopterin (BH2) are inconclusive although there was a trend for lower BH4:BH2 with DSS treatment that was reversed with SP. Reduction of colonic cGMP levels by DSS was reversed with SP by a mechanism sensitive to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the NO-sensitive soluble guanylate cyclase (sGC). ODQ abrogates the protective effects of SP on colitis. This plus the finding that SP reduces DSS-enhanced protein Tyr nitration are consistent with DSS-induced uncoupling of NOS. The results agree with previous studies that demonstrated inactivation of sGC in DSS-treated animals as being important in recruitment of inflammatory cells and in altered cholinergic signaling and colon motility. SP also reduces the number of colon tumors in AOM/DSS-treated mice from 7 to 1 per unit colon length. Thus, pharmacologic modulation of BH4 with currently available drugs may provide a mechanism for alleviating some forms of colitis and potentially minimizing the potential for colorectal cancer in patients with colitis.

Proteomic analysis of radiation-induced changes in rat lung: Modulation by the superoxide dismutase mimetic MnTE-2-PyP(5+)

PURPOSE

To identify temporal changes in protein expression in the irradiated rat lung and generate putative mechanisms underlying the radioprotective effect of the manganese superoxide dismutase mimetic MnTE-2-PyP(5+).

METHODS AND MATERIALS

Female Fischer 344 rats were irradiated to the right hemithorax with a single dose of 28 Gy and killed from day 1 to 20 weeks after irradiation. Proteomic profiling was performed to identify proteins that underwent significant changes in abundance. Some irradiated rats were administered MnTE-2-PyP(5+) and changes in protein expression and phosphorylation determined at 6 weeks after irradiation.

RESULTS

Radiation induced a biphasic stress response in the lung, as shown by the induction of heme oxygenase 1 at 1-3 days and at 6-8 weeks after irradiation. At 6-8 weeks after irradiation, the down-regulation of proteins involved in cytoskeletal architecture (filamin A and talin), antioxidant defense (biliverdin reductase and peroxiredoxin II), and cell signaling (β-catenin, annexin II, and Rho-guanosine diphosphate dissociation inhibitor) was observed. Treatment with MnTE-2-PyP(5+) partially prevented the apparent degradation of filamin and talin, reduced the level of cleaved caspases 3 and 9, and promoted Akt phosphorylation as well as β-catenin expression.

CONCLUSION

A significant down-regulation of proteins and an increase in protein markers of apoptosis were observed at the onset of lung injury in the irradiated rat lung. Treatment with MnTE-2-PyP(5+), which has been demonstrated to reduce lung injury from radiation, reduced apparent protein degradation and apoptosis indicators, suggesting that preservation of lung structural integrity and prevention of cell loss may underlie the radioprotective effect of this compound.

Tyrosine nitration of IkappaBalpha: a novel mechanism for NF-kappaB activation

The NF-kappaB family of transcription factors is an important component of stress-activated cytoprotective signal transduction pathways. Previous studies demonstrated that some activation mechanisms require phosphorylation, ubiquitination, and degradation of the inhibitor protein, IkappaBalpha. Herein, it is demonstrated that ionizing radiation in the therapeutic dose range stimulates NF-kappaB activity by a mechanism in which IkappaBalpha tyrosine 181 is nitrated as a consequence of constitutive NO* synthase activation, leading to dissociation of intact IkappaBalpha from NF-kappaB. This mechanism does not appear to require IkappaBalpha kinase-dependent phosphorylation or proteolytic degradation of IkappaBalpha. Tyrosine 181 is involved in several noncovalent interactions with the p50 subunit of NF-kappaB stabilizing the IkappaBalpha-NF-kappaB complex. Evaluation of hydropathic interactions of the IkappaBalpha-p50 complex on the basis of the crystal structure of the complex is consistent with nitration disrupting these interactions and dissociating the IkappaBalpha-NF-kappaB complex. Tyrosine nitration is not commonly studied in the context of signal transduction. However, these results indicate that tyrosine nitration is an important post-translational regulatory modification for NF-kappaB activation and possibly for other signaling molecules modulated by mild and transient oxidative and nitrosative stresses.