3′-Deoxy-3′-[18F]-Fluorothymidine PET Imaging Reflects PI3K-mTOR-Mediated Pro-Survival Response to Targeted Therapy in Colorectal Cancer

Biomarkers that predict response to targeted therapy in oncology are an essential component of personalized medicine. In preclinical treatment response studies that featured models of wild-type KRAS or mutant BRAF colorectal cancer treated with either cetuximab or vemurafenib, respectively, we illustrate that [¹⁸F]-FLT PET, a non-invasive molecular imaging readout of thymidine salvage, closely reflects pro-survival responses to targeted therapy that are mediated by PI3K-mTOR activity. Activation of pro-survival mechanisms forms the basis of numerous modes of resistance. Therefore, we conclude that [¹⁸F]-FLT PET may serve a novel and potentially critical role to predict tumors that exhibit molecular features that tend to reflect recalcitrance to MAPK-targeted therapy. Though these studies focused on colorectal cancer, we envision that the results may be applicable to other solid tumors as well.     

Noninvasive Visualization of the Activated αvβ3 Integrin in Cancer Patients by Positron Emission Tomography and [18F]Galacto-RGD

BackgroundThe integrin αvβ3 plays an important role in angiogenesis and tumor cell metastasis, and is currently being evaluated as a target for new therapeutic approaches. Several techniques are being studied to enable noninvasive determination of αvβ3 expression. We developed [¹⁸F]Galacto-RGD, a ¹⁸F-labeled glycosylated αvβ3 antagonist, allowing monitoring of αvβ3 expression with positron emission tomography (PET).ConclusionsMolecular imaging with [¹⁸F]Galacto-RGD and PET can provide important information for planning and monitoring anti-angiogenic therapies targeting the αvβ3 integrins and can reveal the involvement and role of this integrin in metastatic and angiogenic processes in various diseases.     

Longitudinal Assessment of Tau Pathology in Patients with Alzheimer’s Disease Using [18F]THK-5117 Positron Emission Tomography

The formation of neurofibrillary tangles is believed to contribute to the neurodegeneration observed in Alzheimer’s disease (AD). Postmortem studies have shown strong associations between the neurofibrillary pathology and both neuronal loss and the severity of cognitive impairment. However, the temporal changes in the neurofibrillary pathology and its association with the progression of the disease are not well understood. Tau positron emission tomography (PET) imaging is expected to be useful for the longitudinal assessment of neurofibrillary pathology in the living brain. Here, we performed a longitudinal PET study using the tau-selective PET tracer [¹⁸F]THK-5117 in patients with AD and in healthy control subjects. Annual changes in [¹⁸F]THK-5117 binding were significantly elevated in the middle and inferior temporal gyri and in the fusiform gyrus of patients with AD. Compared to patients with mild AD, patients with moderate AD showed greater changes in the tau load that were more widely distributed across the cortical regions. Furthermore, a significant correlation was observed between the annual changes in cognitive decline and regional [¹⁸F]THK-5117 binding. These results suggest that the cognitive decline observed in patients with AD is attributable to the progression of neurofibrillary pathology. Longitudinal assessment of tau pathology will contribute to the assessment of disease progression and treatment efficacy.     

Use of 18F-Fluorodeoxyglucose Positron Emission Tomography–Computed Tomography to Aid in Diagnosing Intestinal Adenocarcinoma in 2 Rhesus Macaques (Macaca mulatta)

Two aged female rhesus macaques (Macaca mulatta) presented with weight loss and intermittent inappetence. The signalment and constellation of clinical signs led clinicians to suspect the presence of intestinal adenocarcinoma. Because of each animal''s advanced age and inconclusive radiographic findings, a noninvasive diagnostic tool was preferred over exploratory laparotomy to assist in determining a diagnosis. Consequently, 2-[¹⁸F]fluoro-2-deoxy-d-glucose (FDG) positron emission tomography–CT (FDG-PET–CT) was chosen to aid in confirming a suspicion of gastrointestinal adenocarcinoma in both animals. FDG is a glucose analogue labeled with fluorine-18 and is taken up by highly metabolically active cells, as observed in many cancers. Tomography revealed an annular constriction of the small intestine with focal FDG uptake in one animal, and an FDG avid transmural mass in the ascending colon of the second animal. Necropsy later confirmed both sites to be adenocarcinomas. This report supports the use of FDG-PET–CT as an adjunct to conventional radiography in the diagnosis of intestinal adenocarcinoma in nonhuman primates.Abbreviations: FDG, 2-[¹⁸F]fluoro-2-deoxy-d-glucose; PET, positron emission tomographyThe noninvasive imaging modality 2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography-computed tomography (FDG-PET–CT) is used primarily for the detection and staging of cancer and for the assessment of therapeutic response.²⁸ This modality also is useful for the identification of some infectious and inflammatory diseases, as demonstrated in the recent report of intense FDG uptake in a case of pneumonia in a miniature pig.¹⁴ Furthermore, FDG-PET–CT has been helpful in the detection and monitoring of inflammatory bowel disease and complicating infections of the gastrointestinal tract.²⁸PET detects the three-dimensional distribution of radioactivity based on the annihilation photons emitted by radiotracers labeled with positron-emitting radionuclides, such as ¹⁸F-labeled FDG. In this manner, PET enables noninvasive assessment of biochemical processes. In contrast, CT uses X-rays to generate high-resolution images, allowing clear visualization of anatomic structures. In PET–CT, both the multidetector CT apparatus and the PET detectors are mounted in the same scanner, one behind the other. The PET data are superimposed on the CT data (coregistration), enabling precise anatomic localization of FDG activity.²⁹ Combining PET imaging with CT allows the fusion of functional and anatomic information acquired almost simultaneously, facilitating the visualization and localization of metabolic information noninvasively.Intestinal adenocarcinoma is a substantial cause of morbidity and mortality in aged rhesus macaques.^25,26,30 Rhesus macaques often are maintained on long term-studies, resulting in a population of animals exhibiting morbidities associated with advanced age.^20,25,26 As the age of the animals in our care advances, so too must our diagnostic capabilities advance. Here we report the use of a noninvasive method, FDG-PET–CT, to support the diagnosis of intestinal adenocarcinoma in 2 aged rhesus macaques. We describe the physics of PET, biochemical rationale for the use of FDG, and pitfalls of interpretation.     

The Role of F-Fluorodeoxyglucose (FDG) Positron Emission Tomography–Computed Tomography (PET/CT) in the Screening of Cervical Cancer: A Literature Review

F-fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET/CT) has of late gained prominence in the investigation of cervical cancer since it gives a better clarity on imaging modalities for the status of the lymph node and distant metastasis. The current review is an appraisal of the recent updates on the role of FDG-PET/CT in the screening of cervical cancer as evidenced by publications till date. 985 studies were obtained in the initial search on cervical cancer and publications selected based on inclusion and exclusion criteria. In the final selection, 14 were selected and coded as the most appropriate for the present review. Valuable studies on (FDG) PET/CT have been identified. These studies point to the fact that recent advanced protocols like PET/CT supported by therapeutic innovations ensure better cancer care and survival chances in cervical cancer patients.     

Combined Injection of 18F-Fluorodeoxyglucose and 3′-Deoxy-3′-[18F]fluorothymidine PET Achieves More Complete Identification of Viable Lung Cancer Cells in Mice and Patients than Individual Radiopharmaceutical: A Proof-of-Concept Study

PURPOSE: The objective is to validate the combination of 3′-deoxy-3′-[¹⁸F]fluorothymidine (¹⁸F-FLT) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) as a “novel” positron emission tomography (PET) tracer for better visualization of cancer cell components in solid cancers than individual radiopharmaceutical. METHODS: Nude mice with subcutaneous xenografts of human non-small cell lung cancer A549 and HTB177 cells and patients with lung cancer were included. In ex vivo study, intratumoral radioactivity of ¹⁸F-FDG, ¹⁸F-FLT, and the cocktail of ¹⁸F-FDG and ¹⁸F-FLT detected by autoradiography was compared with hypoxia (by pimonidazole) and proliferation (by bromodeoxyuridine) in tumor section. In in vivo study, first, ¹⁸F-FDG PET and ¹⁸F-FLT PET were conducted in the same subjects (mice and patients) 10 to 14 hours apart. Second, PET scan was also performed 1 hour after one tracer injection; subsequently, the other was administered and followed the second PET scan in the mouse. Finally, ¹⁸F-FDG and ¹⁸F-FLT cocktail PET scan was also performed in the mouse. RESULTS: When injected individually, ¹⁸F-FDG highly accumulated in hypoxic zones and high ¹⁸F-FLT in proliferative cancer cells. In case of cocktail injection, high radioactivity correlated with hypoxic regions and highly proliferative and normoxic regions. PET detected that intratumoral distribution of ¹⁸F-FDG and ¹⁸F-FLT was generally mismatched in both rodents and patients. Combination of ¹⁸F-FLT and ¹⁸F-FDG appeared to map more cancer tissue than single-tracer PET. CONCLUSIONS: Combination of ¹⁸F-FDG and ¹⁸F-FLT PET imaging would give a more accurate representation of total viable tumor tissue than either tracer alone and would be a powerful imaging strategy for cancer management.     

No-carrier-added (NCA) (±)-N-(3-[18F]fluoropropyl)-N-normetazocine-Synthesis and PET studies in a baboon

No-carrier-added (NCA) (±)-N-(3-[¹⁸F]Fluoropropyl)-N-normetazocine (2) was synthesized by N-alkylation of (±)-N-normetazocine (1) with NCA 1-[¹⁸F]fluoro-3-iodopropane in an overall radiochemical yield of 10% (EOB) with a mass of 3.5 nmol in a synthesis time of 90 min from end of bombardment (EOB). PET studies of 2 in a baboon did not indicate specificity for opiate receptor sites alone: The activity declined rapidly in the striatum the frontal cortex and the cerebellum. The baboon total arterial plasma radioactivity clearance was very rapid and the metabolism of compound 2 in plasma was also very rapid. These results suggest that compound 2 is not a suitable radioligand for imaging opiate receptors in the human brain by positron tomography.     

Synthesis of 3′-Deoxy-3′-[4-(pyrimidin-1-yl)methyl-1,2,3-triazol-1-yl]thymidine via 1,3-Dipolar Cycloaddition

Abstract

The synthesis of new 3′-deoxy-3′-[4-(pyrimidin-1-yl)methyl-1,2,3-triazol-1-yl]thymidine 6a–f, from 3′-azido-3′-deoxy-5′-O-monomethoxytrityl-thymidine is described. The key step is the 1,3-dipolar cycloaddition between the azido group of the protected AZT 3 and N-1-propargylpyrimidine derivatives 2a–f. All new derivatives 6a–f were evaluated for their inhibitory effects against the replication of HIV-1 (IIIB), HIV-2 (ROD). No marked activity was found.     

The Preliminary Study of 16α-[18F]fluoroestradiol PET/CT in Assisting the Individualized Treatment Decisions of Breast Cancer Patients

Objective

To evaluate the clinical value of 16α-[18F]fluoroestradiol (18F-FES) PET/CT in assisting the individualized treatment decisions of breast cancer patients.

Methods

Thirty-three breast cancer patients, who underwent both 18F-FES and 18F-FDG PET/CT from July 2010 to March 2013 in our center, were enrolled in this preliminary study. All the patients used 18F-FES PET/CT as a diagnostic tool with a clinical dilemma. We used the maximum Standardized Uptake Value (SUVmax) to quantify ER expression and a cutoff value of 1.5 to dichotomize results into ER positive and negative lesions. All patients were clinically followed up at least 6 months.

Results

In evaluating equivocal lesions on conventional work-up group (n = 4), three lung lesions and another iliac lesion were enrolled. As for three lung lesions, 18F-FES PET/CT showed one lesion with high uptake, which suggested it was an ER positive metastasis. The other two lesions were 18F-FES negative, which meant an ER negative metastasis or secondary primary tumor. Additionally, one iliac lesion was detected by MRI. 18F-FDG uptake was high at the suspected lesion, whereas 18F-FES uptake was absent; In predicting origin of metastasis group (n = 2), two breast cancer patients had secondary primary tumors were collected. They were 18F-FES negative, which showed low possibility of metastasis from breast cancer and they were all confirmed by biopsy. In detecting ER status in metastasis group (n = 27), 18F-FES PET/CT showed increased 18F-FES uptake in all metastatic lesions in 11 patients; absent in all lesions in 13 patients; and the remaining 3 patients had both 18F-FES positive and negative lesions. Totally, on the basis of the 18F-FES PET/CT results, we found changes in the treatment plans in 16 patients (48.5%, 16/33).

Conclusions

18F-FES PET/CT could assess the entire tumor volume receptor status; therefore, it may be used to assist the individualized treatment decisions of breast cancer patients.     

Resistance Profiles of (+) 2′-Deoxy-3′-oxa-4′-thiocytidine and (-) 2′-Deoxy-3′-oxa-4′-thio-5-fluorocytidine

Abstract

Resistant variants were selected in vitro against two novel nucleoside analogues, (+) dOTC and (-) dOTFC using the HIV-1 molecular clone HXB2D. The variants obtained displayed 6.5-fold and 10-fold resistance to these compounds, respectively. Cloning and sequencing of the RT genes of the selected viruses identified two mutations, M184I for (+) dOTC and M184V for (-) dOTFC. Results with mutated recombinant clones of HXB2D confirmed the importance of these mutations in MT-4 cells. The resistance profiles of clinical samples with wild-type or 3TC-resistant phenotypes were also studied; low to moderate levels of cross-resistance were observed against the novel compounds.     

Evaluation of the Kinetics of Hydrolysis of Monoamino Analogues of 2′- or 3′-Deoxyadenosine and of 9-(2-Deoxy-β-D-Threo-pentofuranosyl)Adenine or 9-(3-Deoxy-β-D-threo-pentofuranosyl)Adenine by Liquid Chromatography

Abstract

Liquid chromatography was used to follow the degradation of monoamino analogues of 2′- or 3′-deoxyadenosine and of 9-(2-deoxy-β-D-threo-pentofuranosyl) adenine or 9-(3-deoxy-β-D-threo-pentofuranosyl) adenine in buffers of different pH and constant ionic strength (μ). Comparison of stabilities of some of the compounds under study with those of corresponding hydroxyl analogues showed that at acid pH the aminated compounds are more stable than the corresponding hydroxyl compounds. The higher stability associated with the presence of an amino group in the sugar is explained in function of pK_a values, which were determined by ¹³C NMR.     

Inhibition of 5-α-Reductase (TYPE-II) Expression by Antisense 3′-Deoxy-(2′-5′) Oligonucleotide Chimeras

Abstract

ABSTRACT: 3′-Deoxy-(2′-5′) oligonucleotides bind selectively to complementary RNA but not to DNA. 3′-Deoxy-(2′-5′) phosphorothioate ODN chimeras embedded with a short stretch of 3′-5′ phosphorothioate cassette are potent inhibitors of steroid 5-α-reductasc expression with significantly less non-specific interactions in cell culture.     

Synthesis and radiopharmacological investigation of 3-[4′-[18F]fluorobenzylidene]indolin-2-one as possible tyrosine kinase inhibitor

The radiosynthesis and radiopharmacological evaluation of 3-[4′-[¹⁸F]fluorobenzylidene]indolin-2-one, a derivative of tyrosine kinase inhibitor SU5416, is described. The radiosynthesis was accomplished by Knoevenagel condensation of 4-[¹⁸F]fluorobenzaldehyde with oxindole in a remotely controlled synthesis module. The reaction conditions were optimized through screening the influence of different bases on the radiochemical yield. The radiotracer was obtained after a two-step labelling procedure in 4% decay-corrected radiochemical yield at a specific activity of 48–61 GBq/μmol within 90 min. The radiochemical purity after semi-preparative HPLC purification exceeded 98%.The biodistribution was studied in Wistar rats. After distribution the radiotracer was rapidly accumulated in the adrenals, liver and kidneys, however, it was cleared from these and the most other organs. Only the adipose tissue remained the activity over 60 min. Unexpected high transient uptake was observed in the brain, pancreas, heart and lung. The fast clearance of 3-[4′-[¹⁸F]fluorobenzylidene]indolin-2-one was caused by excretion, approximately one half each was renal and biliary excreted and the other part cleared by metabolic processes. In arterial blood plasma two more polar metabolites were found by radio-HPLC. After 20 min post-injection, only 12% of intact radiotracer has been detected. Consequently, in small animal PET studies with FaDu tumour bearing mice no specific uptake in the tumours could be observed.     

Synthesis of 3′-Deoxy-3′ and 5′-Deoxy-5′-[4-(Purin-9-yl/Pyrimidin-1-yl) methyl-1,2,3-Triazol-1-yl]thymidine via 1,3-Dipolar Cycloaddition

Abstract

Synthesis of new 3′-deoxy-3′ and 5′-deoxy-5′-[(4-(purin-9-yl/pyrimidin-1-yl)methyl-1,2,3-Triazol-1-yl]thymidine 8a-g 10a-g from 3′-azido-3′-deoxy-5′-O-monomethoxytrityl-thymidine and 5′-azido-5′deoxythymidine respectively are described. The key step is the 1,3-dipolar cycloaddition between the azido group and N-9/N-1-propargylpurine/pyrimidine derivatives.     

Synthesis of 2-(3-Deoxy-β-D-erythropentofuranosyl)-thiazole-4-carboxamide (3′-Deoxytiazofurin)

Abstract

2-(3-Deoxy-β-D-erythropentofuranosyl)-thiazole-4-carboxamide was synthesized in four steps from its β-D-ribofuranosyl nucleoside precursor.     

Metabolic fates of 2′-deoxy-5-[18F]fluorouridine in tumor-bearing mice and human plasma

The metabolic fate of 2′-deoxy-5-[¹⁸F]fluorouridine ([¹⁸F]FdUrd), a useful positron emission tomography (PET) tracer of nucleic acid metabolism in tumors, was investigated in mice and humans. A rapid increase in labeled catabolites was found in mouse and human plasma. In mouse FM3A mammary carcinoma, the corresponding catabolites were also detected in addition to metabolites which were activated by the nucleic acid metabolism. From a biodistribution study of β-[³H]alanine, α-[¹⁸F]fluoro-β-alanine, a major catabolite, was assumed to be taken up twice as much by tumor than by the brain. Nucleic acid metabolism in brain tumors by [¹⁸F]FdUrd-PET may be assessed using normal brain regions as a reference.     

Synthesis of Two 3-(7′-Theophyllyl)glycals, 3-Deoxy-3-(7′-theophyllyl)-d-xylo-hex-1-enopyranose and Methyl 3-Deoxy-3-(7′-theophyllyl)-d-xylo-hex-1-enopyranuronate,and their Derivatives

Two 3-(7′-theophyllyl)glycals, (IV) and (V), were synthesized by fusion of theophylline and the appropriate glycals in the presence of p-toluenesulfonic acid. The structure and stereochemistry of the glycals were determined mainly from NMR analysis of their dihydro and 1,6-anhydro derivatives.     

Synthesis and preclinical characterization of 1-(6′-deoxy-6′-[18F]fluoro-β-d-allofuranosyl)-2-nitroimidazole (β-6′-[18F]FAZAL) as a positron emission tomography radiotracer to assess tumor hypoxia

Positron emission tomography (PET) using fluorine-18 (¹⁸F)-labeled 2-nitroimidazole radiotracers has proven useful for assessment of tumor oxygenation. However, the passive diffusion-driven cellular uptake of currently available radiotracers results in slow kinetics and low tumor-to-background ratios. With the aim to develop a compound that is actively transported into cells, 1-(6′-deoxy-6′-[¹⁸F]fluoro-β-d-allofuranosyl)-2-nitroimidazole (β-[¹⁸F]1), a putative nucleoside transporter substrate, was synthetized by nucleophilic [¹⁸F]fluoride substitution of an acetyl protected labeling precursor with a tosylate leaving group (β-6) in a final radiochemical yield of 12 ± 8% (n = 10, based on [¹⁸F]fluoride starting activity) in a total synthesis time of 60 min with a specific activity at end of synthesis of 218 ± 58 GBq/μmol (n = 10). Both radiolabeling precursor β-6 and unlabeled reference compound β-1 were prepared in multistep syntheses starting from 1,2:5,6-di-O-isopropylidene-α-d-allofuranose. In vitro experiments demonstrated an interaction of β-1 with SLC29A1 and SLC28A1/2/3 nucleoside transporter as well as hypoxia specific retention of β-[¹⁸F]1 in tumor cell lines. In biodistribution studies in healthy mice β-[¹⁸F]1 showed homogenous tissue distribution and excellent metabolic stability, which was unaffected by tissue oxygenation. PET studies in tumor bearing mice showed tumor-to-muscle ratios of 2.13 ± 0.22 (n = 4) at 2 h after administration of β-[¹⁸F]1. In ex vivo autoradiography experiments β-[¹⁸F]1 distribution closely matched staining with the hypoxia marker pimonidazole. In conclusion, β-[¹⁸F]1 shows potential as PET hypoxia radiotracer which merits further investigation.