Assessment of PARP-1 Distribution in Tissues of Cynomolgus Monkeys

Stress-Induced Changes in Nucleocytoplasmic Localization of Crucial Factors in Gene Expression Regulation

This study investigates the toxic effect of harmful materials, unfiltered by the placenta, on neonatal umbilical cord (UC) vessels, focusing on stress-induced adaptations in transcriptional and translational processes. It aims to analyze changes in pathways related to mRNA condensate formation, transcriptional regulation, and DNA damage response under maternal smoking-induced stress. UC vessels from neonates born to smoking (Sm) and nonsmoking mothers (Ctr) were examined. Immunofluorescence staining and confocal microscopy assessed the localization of key markers, including Transcription Complex Subunit 1 (CNOT1) and the largest subunit of RNA polymerase II enzyme (RPB1). Additionally, markers of DNA damage response, such as Poly(ADP-ribose) polymerase-1, were evaluated. In Sm samples, dissolution of CNOT1 granules in UC vessels was observed, potentially aiding stalled translation and enhancing transcription via RPB1 assembly and translocation. Control vessels showed predominant cytoplasmic RPB1 localization. Despite adaptive responses, Sm endothelial cells exhibited significant damage, indicated by markers like Poly(ADP-ribose) polymerase-1. Ex vivo metal treatment on control vessels mirrored Sm sample alterations, emphasizing marker roles in cell survival under toxic exposure. Maternal smoking induces specific molecular adaptations in UC vessels, affecting mRNA condensate formation, transcriptional regulation, and DNA damage response pathways. Understanding these intricate molecular mechanisms could inform interventions to improve neonatal health outcomes and mitigate adverse effects of toxic exposure during pregnancy.

Preclinical evaluation of a brain penetrant PARP PET imaging probe in rat glioblastoma and nonhuman primates

PURPOSE

Currently, there are multiple active clinical trials involving poly(ADP-ribose) polymerase (PARP) inhibitors in the treatment of glioblastoma. The noninvasive quantification of baseline PARP expression using positron emission tomography (PET) may provide prognostic information and lead to more precise treatment. Due to the lack of brain-penetrant PARP imaging agents, the reliable and accurate in vivo quantification of PARP in the brain remains elusive. Herein, we report the synthesis of a brain-penetrant PARP PET tracer, (R)-2-(2-methyl-1-(methyl-11C)pyrrolidin-2-yl)-1H-benzo[d]imidazole-4-carboxamide ([11C]PyBic), and its preclinical evaluations in a syngeneic RG2 rat glioblastoma model and healthy nonhuman primates.

METHODS

We synthesized [11C]PyBic using veliparib as the labeling precursor, performed dynamic PET scans on RG2 tumor-bearing rats and calculated the distribution volume ratio (DVR) using simplified reference region method 2 (SRTM2) with the contralateral nontumor brain region as the reference region. We performed biodistribution studies, western blot, and immunostaining studies to validate the in vivo PET quantification results. We characterized the brain kinetics and binding specificity of [11C]PyBic in nonhuman primates on FOCUS220 scanner and calculated the volume of distribution (VT), nondisplaceable volume of distribution (VND), and nondisplaceable binding potential (BPND) in selected brain regions.

RESULTS

[11C]PyBic was synthesized efficiently in one step, with greater than 97% radiochemical and chemical purity and molar activity of 148 ± 85 MBq/nmol (n = 6). [11C]PyBic demonstrated PARP-specific binding in RG2 tumors, with 74% of tracer binding in tumors blocked by preinjected veliparib (i.v., 5 mg/kg). The in vivo PET imaging results were corroborated by ex vivo biodistribution, PARP1 immunohistochemistry and immunoblotting data. Furthermore, brain penetration of [11C]PyBic was confirmed by quantitative monkey brain PET, which showed high specific uptake (BPND > 3) and low nonspecific uptake (VND < 3 mL/cm3) in the monkey brain.

CONCLUSION

[11C]PyBic is the first brain-penetrant PARP PET tracer validated in a rat glioblastoma model and healthy nonhuman primates. The brain kinetics of [11C]PyBic are suitable for noninvasive quantification of available PARP binding in the brain, which posits [11C]PyBic to have broad applications in oncology and neuroimaging.

Pre-clinical investigation of astatine-211-parthanatine for high-risk neuroblastoma

Astatine-211-parthanatine ([211At]PTT) is an alpha-emitting radiopharmaceutical therapeutic that targets poly(adenosine-diphosphate-ribose) polymerase 1 (PARP1) in cancer cells. High-risk neuroblastomas exhibit among the highest PARP1 expression across solid tumors. In this study, we evaluated the efficacy of [211At]PTT using 11 patient-derived xenograft (PDX) mouse models of high-risk neuroblastoma, and assessed hematological and marrow toxicity in a CB57/BL6 healthy mouse model. We observed broad efficacy in PDX models treated with [211At]PTT at the maximum tolerated dose (MTD 36 MBq/kg/fraction x4) administered as a fractionated regimen. For the MTD, complete tumor response was observed in 81.8% (18 of 22) of tumors and the median event free survival was 72 days with 30% (6/20) of mice showing no measurable tumor >95 days. Reversible hematological and marrow toxicity was observed 72 hours post-treatment at the MTD, however full recovery was evident by 4 weeks post-therapy. These data support clinical development of [211At]PTT for high-risk neuroblastoma.

Modulation of PARP activity by Monomethylarsonous (MMA+3) acid and uranium in mouse thymus

Arsenic exposure is well established to impair the function of zinc finger proteins, including PARP-1. Previous studies from our lab show that early developing T cells in the thymus are very sensitive to arsenite (As+3)-induced genotoxicity mediated through PARP-1 inhibition. Additionally, it has been shown that uranium (in the form of uranyl acetate, UA) also suppresses PARP-1 activity in HEK cells. However, very little is known about whether the As+3 metabolite, monomethylarsonous acid (MMA+3), also inhibits PARP-1 activity and if this is modified by combined exposures with other metals, such as uranium. In the present study, we found that MMA+3 significantly suppressed PARP-1 function, whereas UA at high concentrations significantly increased PARP-1 activity. To evaluate whether the effects on PARP-1 activity were mediated through oxidative stress, we measured the induction of hemoxygenase-1 (Hmox-1) expression by qPCR. MMA+3, but not UA, significantly induced oxidative stress; however, the inhibition of PARP-1 produced by MMA+3 was not reversed by the addition of the antioxidant, Tempol. Further evaluation revealed minimal interactive effects of MMA+3 and UA on PARP-1 function. Collectively, our results show that contrary to As+3, the suppressive effects of MMA+3 on PARP-1 were not substantially driven by oxidative stress. in mouse thymus cells. Results for this study provide important insights into the effects of MMA+3 and uranium exposures on PARP-1 function, which is essential for future studies focused on understanding the effects of complex environmentally relevant metal mixtures.