Nano-Delivery of a Novel Inhibitor of Polynucleotide Kinase/Phosphatase (PNKP) for Targeted Sensitization of Colorectal Cancer to Radiation-Induced DNA Damage

Inhibition of the DNA repair enzyme polynucleotide kinase/phosphatase (PNKP) increases the sensitivity of cancer cells to DNA damage by ionizing radiation (IR). We have developed a novel inhibitor of PNKP, i.e., A83B4C63, as a potential radio-sensitizer for the treatment of solid tumors. Systemic delivery of A83B4C63, however, may sensitize both cancer and normal cells to DNA damaging therapeutics. Preferential delivery of A83B4C63 to solid tumors by nanoparticles (NP) was proposed to reduce potential side effects of this PNKP inhibitor to normal tissue, particularly when combined with DNA damaging therapies. Here, we investigated the radio-sensitizing activity of A83B4C63 encapsulated in NPs (NP/A83) based on methoxy poly(ethylene oxide)-b-poly(α-benzyl carboxylate-ε-caprolactone) (mPEO-b-PBCL) or solubilized with the aid of Cremophor EL: Ethanol (CE/A83) in human HCT116 colorectal cancer (CRC) models. Levels of γ-H2AX were measured and the biodistribution of CE/A83 and NP/A83 administered intravenously was determined in subcutaneous HCT116 CRC xenografts. The radio-sensitization effect of A83B4C63 was measured following fractionated tumor irradiation using an image-guided Small Animal Radiation Research Platform (SARRP), with 24 h pre-administration of CE/A83 and NP/A83 to Luc+/HCT116 bearing mice. Therapeutic effects were analyzed by monitoring tumor growth and functional imaging using Positron Emission Tomography (PET) and [18F]-fluoro-3’-deoxy-3’-L:-fluorothymidine ([18F]FLT) as a radiotracer for cell proliferation. The results showed an increased persistence of DNA damage in cells treated with a combination of CE/A83 or NP/A83 and IR compared to those only exposed to IR. Significantly higher tumor growth delay in mice treated with a combination of IR and NP/A83 than those treated with IR plus CE/A83 was observed. [18F]FLT PET displayed significant functional changes for tumor proliferation for the drug-loaded NP. This observation was attributed to the higher A83B4C63 levels in the tumors for NP/A83-treated mice compared to those treated with CE/A83. Overall, the results demonstrated a potential for A83B4C63-loaded NP as a novel radio-sensitizer for the treatment of CRC.

Nghiên cứu điều chế dược chất phóng xạ 18F-FLT cho ghi hình PET/CT

Mục tiêu: Đánh giá khả năng sản xuất 18F-FLT và ghi hình 18F-FLT PET/CT tại Việt Nam. Đối tượng và phương pháp: Dược chất phóng xạ 18F-FLT được điều chế trên module tự phát triển của nhóm nghiên cứu Bệnh viện Trung ương Quân đội 108, chất lượng theo Ph.Eur. 14 và định tính ghi hình 18F-FLT PET so sánh với 18F-FDG PET trên chuột nhắt BALB/c gây u phổi thứ phát dòng LLC. Kết quả: Khi thay đổi thời gian bắn bia từ 10 phút đến 120 phút sản lượng 18F-FLT dao động từ 57 ± 4 đến 184 ± 14mCi/mẻ, hiệu suất tổng hợp (EOS) dao động từ 9,6 ± 1,3 đến 27,6 ± 2,1%, tuy nhiên với thời gian bắn bia là 20 phút cho sản lượng và hiệu suất tổng hợp là cao nhất. Thuốc đạt yêu cầu theo EurPh 14. Chụp 18F-FLT PET/ CT và 18F-FDG PET/CT cho thấy cả 2 DCPX đều tăng hấp thu vào khối u. Sự khác biệt là 18F-FDG tăng hấp thu ở não còn 18F-FLT không hấp thu vào não do 18F-FLT hầu như không đi qua hang rào máu não. Kết luận: Điều chế dược chất phóng xạ 18F-FLT cho ghi hình PET/CT hoàn toàn có thể thực hiện được ở Việt Nam.

Voxel-Based Analysis of the Relation of 3′-Deoxy-3′-[18F]fluorothymidine ([18F]FLT) PET and Diffusion-Weighted (DW) MR Signals in Subcutaneous Tumor Xenografts Does Not Reveal a Direct Spatial Relation of These Two Parameters

Purpose Multimodal molecular imaging allows a direct coregistration of different images, facilitating analysis of the spatial relation of various imaging parameters. Here, we further explored the relation of proliferation, as measured by [18F]FLT PET, and water diffusion, as an indicator of cellular density and cell death, as measured by diffusion-weighted (DW) MRI, in preclinical tumor models. We expected these parameters to be negatively related, as highly proliferative tissue should have a higher density of cells, hampering free water diffusion. Procedures Nude mice subcutaneously inoculated with either lung cancer cells (n = 11 A549 tumors, n = 20 H1975 tumors) or colorectal cancer cells (n = 13 Colo205 tumors) were imaged with [18F]FLT PET and DW-MRI using a multimodal bed, which was transferred from one instrument to the other within the same imaging session. Fiducial markers allowed coregistration of the images. An automatic post-processing was developed in MATLAB handling the spatial registration of DW-MRI (measured as apparent diffusion coefficient, ADC) and [18F]FLT image data and subsequent voxel-wise analysis of regions of interest (ROIs) in the tumor. Results Analyses were conducted on a total of 76 datasets, comprising a median of 2890 data points (ranging from 81 to 13,597). Scatterplots showing [18F]FLT vs. ADC values displayed various grades of relations (Pearson correlation coefficient (PCC) varied from − 0.58 to 0.49, median: -0.07). When relating PCC to tumor volume (median: 46 mm3, range: 3 mm3 to 584 mm3), lung tumors tended to have a more pronounced negative spatial relation of [18F]FLT and ADC with increasing tumor size. However, due to the low number of large tumors (> ~ 200 mm3), this conclusion has to be treated with caution. Conclusions A spatial relation of water diffusion, as measured by DW-MRI, and cellular proliferation, as measured by [18F]FLT PET, cannot be detected in the experimental datasets investigated in this study.

Assessing Bone Marrow Activity in Patients with Essential Thrombocythemia and Prefibrotic Myelofibrosis: Results of a Pilot Study of [18F]FLT PET

Background Among several groups of clinicians and hematopathologists a conflict of opinion has been repeatedly expressed concerning the validity of bone marrow (BM) features characterizing myeloproliferative neoplasms (MPNs). In this regard, controversy is mainly focused on the distinction between essential thrombocythemia (ET) and pre-fibrotic/early primary myelofibrosis (pre-PMF) Although other groups confirmed the characteristic BM features and emphasized the clinical impact to discriminate both MPN subtypes the existence of pre-PMF has been questioned, including clinical usefulness and particularly reproducibility of the corresponding diagnostic guidelines. In this context, it has been criticized that the MPN classification proposed by the World Health Organization (WHO), updated in 2008 and revised in 2016,was focused on BM morphology as the gold standard of diagnosis. The current standard for follow-up of these patients is based on pathological markers (peripheral blood counts and/ bone marrow histomorphology) and molecular markers. Bone marrow examination is the gold standard method to assess the disease's extent; it offers detailed information about cellularity, the morphology of each lineage, the degree of fibrosis, and the transformation and dysplastic features. However, many patients are reluctant to go for this invasive technique which precludes precise disease activity assessment at the desirable frequencies. A non-invasive technique that can offer reliable prognostic and predictive information about the disease is lacking. The objective of this study is to explore the diagnostic value of FLT-PET in malignant hematopoiesis of Pre-PMF and ET. The potential to use FLT-PET metrics to differentiate between Pre-PMF and ET is assessed Methods A total of 13 patients (mean age of 43.23 ± 14.42 years, 7 males and 6 females) with Essential Thrombocythemia (ET) and/or Prefibrotic myelofibrosis were included in this study. One male subject was excluded due to an inconclusive diagnosis. The study was approved by the institutional review board. Written informed consents were obtained from all subjects. Each subject underwent FLT PET imaging as well as bone marrow examination (gold standard) and all were tested for JAK2v617F , CALR and MPL . Semi-quantitative (SUVmax and SUVmean) measurements of FLT uptake in the liver, spleen and Lumbar spine, SUVmean, as well as the Total Lesion Glycolysis (TLG) of the Lspine were performed. Results from the two patient cohorts were compared using = Kruskal-Wallis statistical test. A P-value of <0.05 is considered to be statistically significant. Discussion: Pre-PMF and ET exhibited different features of bone marrow; however, this is not always easy to judge objectively, making pathologists' distinction often suboptimal. And in another scenario, bone marrow which is mandated for diagnosis, cannot be obtained due to technical issues or patient-related factors. In the 2016 revised classification,pre-PMF was recognized as a separate entity, distinct from ET. Thrombosis and hemorrhage represent two of the main causes of morbidity and mortality in patients with ET. Incidence of arterial and venous thrombosis prior to diagnosis revealed no significant differences (23% /20 and 9/8%) in WHO-defined ET compared with pre-PMF; thrombotic complications were also similar during the follow-thrombosis is not significantly different, whereas bleeding is more frequent in pre-PMF.From clinical prespective it is important to differentiate between the two categories. Results The differences in FLT SUVmax and SUVmean measurements in the three organs (liver, spleen, and LSpine) between the ET and Pre-PMF patients were not statistically significant (P>0.05). In contrast, TLG measurements in the LSpine were statistically different (P=0.013), and therefore, compared to gold standard bone marrow results, TLG can separate ET and Pre-PMF patients. Conclusion TLG of the Lumbar Spine in FLT PET images is a potential quantitative parameter to discriminate between ET and PRE-PMF patients Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

[[18F]Fluorothymidine Positron Emission Tomography Imaging in Primary Brain Tumours: A Systematic Review

Purpose : This review aimed to summarize the available literature on the clinical application of [18F]FLT PET imaging in primary brain tumours. Methods : A comprehensive search strategy based on Pubmed/Medline, Scopus, Web of Science, Cochrane Library, Google Scholar, and the Embase databases was carried on using the following search string: ('3` Fluorothymidine'/exp OR 'FLT' OR '[18F]-FLT' OR '[18F]Fluorothymidine') AND ('pet'/exp OR 'pet' OR 'positron emission tomography') AND ('glioma'/exp OR 'glioma' OR 'brain tumour'/exp OR 'brain tumour’). The search was updated till March 2021 and only articles in English and studies investigating the clinical applications of [18F]FLT PET and PET/CT in primary brain tumours were considered eligible for inclusion. Results: The literature search ultimately yielded 52 studies to be included in the systematic review, with main results as follows: a) the uptake of [18F]FLT may guide stereotactic biopsy but does not discriminate between grade II and III glioma. b) [18F]FLT uptake and texture parameters correlate with overall survival (OS) in newly diagnosed gliomas. c) In patients with recurrent glioma, proliferative volume (PV) and tumour-to-normal brain (T/N) uptake ratio are independent predictors of survival. d) Patients demonstrating response to therapy at [18F]FLT PET scan show longer OS compared to non-responders. e) [18F]FLT PET demonstrated good performance in discriminating tumour recurrence from radionecrosis. However, controversial results exist in comparative literature examining the performance of [18F]FLT vs. other radiotracers in the assessment of recurrence. Conclusion : [18F]FLT PET imaging has demonstrated potential benefits for grading, diagnostic and prognostic purposes, despite the small sample size studies due to the relatively low availability of the radiotracer.

STING-driven interferon signaling triggers metabolic alterations in pancreas cancer cells visualized by [18F]FLT PET imaging

Type I interferons (IFNs) are critical effectors of emerging cancer immunotherapies designed to activate pattern recognition receptors (PRRs). A challenge in the clinical translation of these agents is the lack of noninvasive pharmacodynamic biomarkers that indicate increased intratumoral IFN signaling following PRR activation. Positron emission tomography (PET) imaging enables the visualization of tissue metabolic activity, but whether IFN signaling–induced alterations in tumor cell metabolism can be detected using PET has not been investigated. We found that IFN signaling augments pancreatic ductal adenocarcinoma (PDAC) cell nucleotide metabolism via transcriptional induction of metabolism-associated genes including thymidine phosphorylase (TYMP). TYMP catalyzes the first step in the catabolism of thymidine, which competitively inhibits intratumoral accumulation of the nucleoside analog PET probe 3′-deoxy-3′-[18F]fluorothymidine ([18F]FLT). Accordingly, IFN treatment up-regulates cancer cell [18F]FLT uptake in the presence of thymidine, and this effect is dependent upon TYMP expression. In vivo, genetic activation of stimulator of interferon genes (STING), a PRR highly expressed in PDAC, enhances the [18F]FLT avidity of xenograft tumors. Additionally, small molecule STING agonists trigger IFN signaling–dependent TYMP expression in PDAC cells and increase tumor [18F]FLT uptake in vivo following systemic treatment. These findings indicate that [18F]FLT accumulation in tumors is sensitive to IFN signaling and that [18F]FLT PET may serve as a pharmacodynamic biomarker for STING agonist–based therapies in PDAC and possibly other malignancies characterized by elevated STING expression.

18F-fluorodeoxyglucose (FDG) PET or 18F-fluorothymidine (FLT) PET to assess early response to aromatase inhibitors (AI) in women with ER+ operable breast cancer in a window-of-opportunity study

Purpose This study evaluated the ability of 18F-Fluorodeoxyglucose (FDG) and 18F-Fluorothymidine (FLT) imaging with positron emission tomography (PET) to measure early response to endocrine therapy from baseline to just prior to surgical resection in estrogen receptor positive (ER+) breast tumors. Methods In two separate studies, women with early stage ER+ breast cancer underwent either paired FDG-PET (n = 22) or FLT-PET (n = 27) scans prior to endocrine therapy and again in the pre-operative setting. Tissue samples for Ki-67 were taken for all patients both prior to treatment and at the time of surgery. Results FDG maximum standardized uptake value (SUVmax) declined in 19 of 22 lesions (mean 17% (range −45 to 28%)). FLT SUVmax declined in 24 of 27 lesions (mean 26% (range −77 to 7%)). The Ki-67 index declined in both studies, from pre-therapy (mean 23% (range 1 to 73%)) to surgery [mean 8% (range < 1 to 41%)]. Pre- and post-therapy PET measures showed strong rank-order agreement with Ki-67 percentages for both tracers; however, the percent change in FDG or FLT SUVmax did not demonstrate a strong correlation with Ki-67 index change or Ki-67 at time of surgery. Conclusions A window-of-opportunity approach using PET imaging to assess early response of breast cancer therapy is feasible. FDG and FLT-PET imaging following a short course of neoadjuvant endocrine therapy demonstrated measurable changes in SUVmax in early stage ER+ positive breast cancers. The percentage change in FDG and FLT-PET uptake did not correlate with changes in Ki-67; post-therapy SUVmax for both tracers was significantly associated with post-therapy Ki-67, an established predictor of endocrine therapy response.