Pediatric Efficacy Extrapolation in Drug Development Submitted to the US Food and Drug Administration 2015-2020.

Pediatric extrapolation plays a key role in the availability of reliable pediatric use information in approved drug labeling. This review examined the use of pediatric extrapolation in studies submitted to the US Food and Drug Administration and assessed changes in extrapolation approaches over time. Pediatric studies of 125 drugs submitted to the US Food and Drug Administration that led to subsequent pediatric information in drug labeling between 2015 and 2020 were reviewed. The use of pediatric extrapolation for each drug was identified and categorized as "complete," "partial," or "no" extrapolation. Approaches to pediatric extrapolation of efficacy changed over time. Complete extrapolation of efficacy was the predominantly used approach. "Complete," "partial," or "no" extrapolation was used for 51%, 23%, and 26% of the drugs, respectively. This represents a shift in extrapolation approaches when compared to a previous study that evaluated pediatrics drug applications between 2009 and 2014, which found complete, partial, or no extrapolation was used for 34%, 29%, and 37% of the drugs, respectively. Pediatric extrapolation approaches may continue to shift as emerging science fills gap in knowledge of the fundamental assumptions underlying this scientific tool. The international community continues to collaborate on discussions of pediatric extrapolation of efficacy from adults and other pediatric subpopulations to optimize its use for pediatric drug development.

Using Historical Data to Support Approval of Drug Products for Ophthalmia Neonatorum: Innovative Approach Toward Evidence-Based Medicine.

Importance: Off-label treatment was common for ophthalmia neonatorum because only erythromycin ointment had been approved by the US Food and Drug Administration (FDA) for this indication. Ophthalmia neonatorum was previously considered a different indication from bacterial conjunctivitis in older children and adults because of uncertain similarities in the cause of disease and the treatment course between the 2 populations. Prospective therapeutic clinical studies were required to demonstrate the effectiveness of treatment for ophthalmia neonatorum. Objective: To review the therapeutic clinical trials for patients with bacterial conjunctivitis to evaluate the similarity in the cause of disease and the treatment response between neonates and older children and adults. Design, Setting, and Participants: In this comparative effectiveness research review of pooled data from the most recent 30 bacterial conjunctivitis trials (N = 2018) submitted to the FDA to support the approval of topical ophthalmic solutions for older children and adults, 95% CIs were constructed from clinical cure rates. Cure rates in 3 neonatal randomized clinical trials (N = 392) of patients treated with ophthalmic anti-infective solutions of ciprofloxacin, gatifloxacin, and moxifloxacin were constructed and compared. The baseline ocular swab cultures were analyzed. Main Outcomes and Measures: Cure rates of neonatal trials were compared with the 95% CIs among older children and adults. The bacterial organisms isolated from these 2 populations were compared. Results: The 3 neonatal trials enrolled a total of 392 patients, and the 30 trials of older children and adults enrolled a total of 2018 patients. Neonatal clinical cure rates for moxifloxacin (day 4, 48%), ciprofloxacin (day 4, 49%; day 5, 61%), and gatifloxacin (day 7, 79%) were within the 95% CI for products approved to treat older children and adults with bacterial conjunctivitis. Bacterial organisms were consistent between these 2 populations. Conclusions and Relevance: Comparison of the pooled analysis of these historical trial data suggests similarity in the cause of disease and the treatment response between neonates and older children and adults with bacterial conjunctivitis. Therefore, it was appropriate to extrapolate the effectiveness from older children and adults to neonates to support the approval of therapies for ophthalmia neonatorum. Based on this analysis, ophthalmic solutions of ciprofloxacin, gatifloxacin, and moxifloxacin are now approved for all age groups. This analysis presents an approach of using pooled data from previously underpowered individual trials to establish the similarities in the cause of disease and in treatment response between children and adults, which are the fundamental elements used to evaluate whether extrapolation of effectiveness can be used to support drug approval.

Surrogate Endpoints in Pediatric Studies Submitted to the US FDA.

The 21st Century Cures Act was passed in December, 2016, and included a number of provisions to facilitate drug approval. Considerable discussion was generated related to some aspects of the Act, especially to the use of surrogate endpoints (SEs) as a means to shorten the time required prior to receiving US Food and Drug Administration (FDA) approval.1 The objective of this analysis was to identify the use and outcomes of SEs and clinical endpoints in pediatric drug development trials.

Extrapolation of Efficacy in Pediatric Drug Development and Evidence-based Medicine: Progress and Lessons Learned.

BACKGROUND: "Complete Extrapolation" of efficacy from adult or other pediatric data, to the pediatric population, is an important scientific tool that reduces the need for pediatric efficacy trials. Dose finding and safety studies in pediatrics are still needed. "No Extrapolation" requires 2 pediatric efficacy trials. "Partial Extrapolation" eliminates the need to conduct 2 pediatric efficacy trials; 1 efficacy or exposure/response study may be sufficient. We examined pediatric extrapolation from 2009 to 2014 evaluating any changes in extrapolation assumptions and the causes for these changes since a prior analysis published in 2011. METHODS: We reviewed all 157 products with 388 pediatric studies submitted to the FDA from 2009 through 2014. We assessed whether efficacy was extrapolated from adult or other pediatric data and categorized extrapolation as Complete, Partial, or No, and identified the reasons for the changes. RESULTS: Partial extrapolation decreased, whereas use of No and Complete extrapolation noticeably increased. Complete, Partial, or No extrapolations changed from 14%, 68%, and 18% in the 2011 study to 34%, 29%, and 37% respectively in the current study. The changes were mostly due to a better understanding of pediatric pathophysiology, why trials have failed, and improved endpoints. CONCLUSIONS: Evolving science and data obtained from clinical trials increases the certainty of extrapolation assumptions and drives decisions to utilize extrapolation. Lessons learned from the conduct of these trials are critical to improving evidence-based medicine. Extrapolation of Efficacy is a powerful scientific tool that streamlines pediatric product development. Increased knowledge and evolving science inform utilization of this tool.

Pediatric Crohn Disease Clinical Outcome Assessments and Biomarkers: Current State and Path Forward for Global Collaboration.

OBJECTIVE: There is a pressing need for drug development in pediatric Crohn disease (CD). Our aim was to provide strategic approaches toward harmonization of current thinking about clinical outcome assessments (COAs) and biomarkers to facilitate drug development in pediatric CD. METHODS: Scientists from the United States Food and Drug Administration, European Medicines Agency, Health Canada, and the Pharmaceuticals and Medical Devices Agency of Japan had monthly teleconferences from January 2014 through May 2015. A literature review was conducted to assess the measurement properties of all existing COA tools and to evaluate the current landscape of biomarkers used in pediatric CD. Based on the findings of literature review, we reached the consensus on the strategic approaches for evaluating outcomes in pediatric CD trials. RESULTS: The pediatric Crohn's Disease Activity Index, Crohn's Disease Activity Index, and Harvey-Bradshaw's index were used in pediatric CD clinical studies. But they lack adequate measurement properties (validity, reliability, and ability to detect change of the treatment) that are required to support approval of products intended to treat pediatric CD. Biomarkers (ie, fecal lactoferrin, osteoprotegerin, and calprotectin) have shown some promise for their potential as noninvasive surrogate endpoints in CD. CONCLUSIONS: Lack of well-defined and reliable COAs presents a hurdle for global drug development in pediatric CD. It is essential to develop well-defined and reliable COAs that can measure meaningful clinical benefit for patients in terms of how they feel, function, and survive. Development of noninvasive biomarkers as reliable surrogate endpoints needs to be further explored.

The Role of Biomarkers and Surrogate End Points in Drug Development for Neonatal Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a rare disease in newborns, infants, and children. It is associated with significant morbidity and mortality, but has limited treatment options. Except for inhaled nitric oxide, which is approved for persistent pulmonary hypertension of the newborn (PPHN), no drug is approved for the treatment of newborns, infants, and children with PAH. The lack of developmentally appropriate pediatric efficacy end points and pediatric clinical trials contribute to this unmet medical need. The noninvasive biomarkers reported in the literature that can be used as potential surrogate end points to assess disease severity and treatment response in neonates, infants, and children with PAH are reviewed herein. In addition, the role of the US Food and Drug Administration in developing potential biomarkers as surrogate end points to facilitate drug development for the treatment of children with PPHN and PAH in children is reviewed herein.

Well-defined and reliable clinical outcome assessments for pediatric Crohn disease: a critical need for drug development.

OBJECTIVES: The aim of the present study was to identify areas for further development of clinical outcome assessment (COA) in pediatric Crohn disease (CD). METHODS: The study analyzed the measurement properties of all existing COA tools for pediatric CD in literature and published registration trials of approved drugs for pediatric CD based on criteria described in Food and Drug Administration guidance for patient-reported outcome (PRO) development. RESULTS: The Pediatric Crohn's Disease Activity Index (PCDAI) and its derivatives (abbreviated, short, modified, and weighted PCDAIs) were reviewed. The Crohn's Disease Activity Index (CDAI) and Harvey-Bradshaw index (HBI), designed for adult patients, have been adapted for use in a few pediatric CD studies. The use of PCDAI as an endpoint in Remicade and Humira trials led to the Food and Drug Administration-approved indication in pediatric CD. Common issues in measurement properties of COA tools included the absence of direct patient or caregivers' input to generate the items measuring signs and symptoms; absence of evidence demonstrating correlation with clinically relevant inflammation observed with endoscopic measures; lack of standardization in measurement, age-appropriate interviewer script, and response rating criteria for the physician interviewer. CONCLUSIONS: Available evidence indicates that CDAI, HBI, and 5 versions of the PCDAI lack adequate measurement properties for use as a primary endpoint for phase 3 trials intended to support approval of products intended to treat pediatric CD. In order to facilitate pediatric drug development, a well-defined, reliable, sensitive, and globally recognized PRO that measures signs and symptoms in children with CD and that can be used in conjunction with endoscopy-based endpoints and/or biomarkers is sorely needed.

Steps toward harmonization for clinical development of medicines in pediatric ulcerative colitis-a global scientific discussion, part 1: efficacy endpoints and disease outcome assessments.

OBJECTIVES: There is a pressing need for drug development in pediatric ulcerative colitis (UC). Lack of scientific consensus on efficacy endpoints and disease outcome assessments presents a hurdle for global drug development in pediatric UC. Scientists from 4 regulatory agencies convened an International Inflammatory Bowel Disease Working Group (i-IBD Working Group) to harmonize present thinking about various aspects of drug development in pediatric UC globally. METHODS: The i-IBD Working Group was convened in 2012 by scientists from the US Food and Drug Administration, European Medicines Agency, Health Canada, and the Pharmaceuticals and Medical Devices Agency of Japan. The members of this group considered reasons for differences in their acceptance of efficacy endpoints and disease activity indices used in pediatric UC, reviewed the available literature, and developed consensus opinions regarding approaches for evaluating outcomes in pediatric UC trials. RESULTS: There is lack of harmonization in using efficacy endpoint and outcome assessments including disease activity indices to assess clinical benefit in pediatric UC trials. Many disease activity indices have been developed, but their biometric properties, such as responsiveness, reliability, and validity, have not been properly validated. Biomarkers, such as fecal calprotectin and lactoferrin, are being investigated for their potential as noninvasive surrogate endpoints in UC. CONCLUSIONS: Consensus on the efficacy endpoints, disease activity indices, and outcome assessments is needed for globalization of pediatric UC trials. The i-IBD Working Group offers several perspectives to facilitate harmonization across regions. The development of noninvasive biomarkers as reliable surrogate endpoints needs to be explored further.

Steps toward harmonization for clinical development of medicines in pediatric ulcerative colitis-a global scientific discussion, part 2: data extrapolation, trial design, and pharmacokinetics.

OBJECTIVES: To facilitate global drug development, the International Pediatric Inflammatory Bowel Disease Working Group (i-IBD Working Group) discussed data extrapolation, trial design, and pharmacokinetic (PK) considerations for drugs intended to treat pediatric ulcerative colitis (UC), and considered possible approaches toward harmonized drug development. METHODS: Representatives from the US Food and Drug Administration, European Medicines Agency, Health Canada, and the Pharmaceuticals and Medical Devices Agency of Japan convened monthly to explore existing regulatory approaches, reviewed the results of a literature search, and provided perspectives on pediatric UC drug development based on the available medical literature. RESULTS: Although pediatric UC, when compared with UC in adults, has a similar disease progression and response to intervention, the similarity of the exposure-response relation has not been adequately established. Consequently, clinical endpoints should be selected to optimally assess efficacy in children. The inclusion of a placebo control in pediatric trials to assure assay sensitivity may be appropriate under limited circumstances. In clinical studies, although the drug under investigation could provide possible direct benefit, placebo treatment should present no more than a minor increase over minimal risk to children with UC. CONCLUSIONS: Partial extrapolation of efficacy from informative adult studies may be appropriate. Placebo-controlled efficacy trials are scientifically and ethically appropriate for pediatric UC given appropriate patient selection and the use of early escape. Clinical studies in pediatric UC may include initial dose-finding studies and exposure-response modeling followed by an efficacy and safety study to further explore the exposure-response relation.

Alternate endpoints and clinical outcome assessments in pediatric ulcerative colitis registration trials.

OBJECTIVES: Presently, there is no consensus on endpoint measures to assess clinical outcomes for pediatric ulcerative colitis (UC). This study reviewed the endpoints used in the registration trials of approved drugs for pediatric UC. METHODS: The primary efficacy endpoints of all registration trials completed from 1950 to 2008 that led to Food and Drug Administration approval for indications in pediatric and adult UC were reviewed. RESULTS: Colazal and Remicade have been approved for pediatric UC indication, and clinical response was used as a primary endpoint in these registration trials. The clinical response in the adult Colazal trials was defined as a reduction of rectal bleeding and improvement in at least one of the other assessed symptoms (stool frequency, patient functional assessment, abdominal pain, sigmoidoscopic grade, and physician's global assessment) assessed by the Sutherland UC Activity Index. The pediatric Colazal trial defined clinical response using the Modified Sutherland UC Activity Index, which excluded abdominal pain and functional assessment. Both adult and pediatric Remicade trials used clinical response defined by the Mayo score as the primary endpoint. The Pediatric Ulcerative Colitis Activity Index was used to measure various secondary endpoints in the pediatric Remicade trial. CONCLUSIONS: Pediatric-specific endpoints were used, but outcome measures and definition of clinical response were not consistent in pediatric UC trials. Consensus on the definition of successful treatment outcome (clinical response and/or remission) and collaboration in the development of well-defined and reliable measures of signs and symptoms for use in conjunction with endoscopic parameters of mucosal healing will facilitate pediatric drug development.

Migraine therapeutics in adolescents: a systematic analysis and historic perspectives of triptan trials in adolescents.

OBJECTIVES To conduct a systematic review and analysis of trial data submitted to the US Food and Drug Administration (FDA) to identify possible causes for the failure of pediatric trials of triptans for treatment of migraines. DATA SOURCE The FDA website for drug information and published literature. STUDY SELECTION All pediatric efficacy and pharmacokinetics trial data of drugs used for abortive treatment of migraine submitted to the FDA from January 1, 1999, through December 31, 2011. MAIN OUTCOME MEASURES Patient demographic baseline characteristics, inclusion and exclusion criteria, trial designs, efficacy end points, and pharmacokinetic profiles were analyzed and compared across drug products. RESULTS We analyzed data for sumatriptan succinate nasal spray and zolmitriptan, eletriptan hydrobromide, almotriptan malate, and rizatriptan benzoate tablets. Seven efficacy trials had a randomized, double-blinded, placebo-controlled, parallel-group trial design. In 4 trials, patients were required to have a history of migraine attacks lasting at least 4 hours. High response rates for placebo were observed in all trials, with pain relief at 2 hours ranging from 53% to 57.5%. Nonrandomization of patients with an early placebo response design was used in the rizatriptan trial in 2011. Compared with the rizatriptan trial conducted in 1999, the 2011 rizatriptan trial reduced the placebo response rate by 6% for headache freedom at the 2-hour posttreatment end point owing to study design. The pharmacokinetic profiles between adolescents and adults were statistically similar. CONCLUSIONS High placebo response rates are consistent across all trials and may represent the principal challenge in pediatric trials of drugs for abortive treatment of migraine. Enrichment with selection of subjects with long-lasting migraine attacks is not sufficient to overcome high placebo response rates. Another enrichment strategy, the nonrandomization of patients with an early placebo response, successfully reduces the high placebo response rate for rizatriptan and is a trial design that should be considered for future pediatric trials of abortive migraine therapeutics.

Bioluminescent imaging study: FAK inhibitor, PF-562,271, preclinical study in PC3M-luc-C6 local implant and metastasis xenograft models.

Focal adhesion kinase (FAK) is essential in regulating integrin signaling pathways responsible for cell survival and proliferation, as well as motility, making FAK a distinctive target in the field of anticancer drug development, especially with regards to metastatic disease.(1) Our objective was to demonstrate tumor growth inhibition by PF-562,271, a selective inhibitor of FAK and FAK2, or Pyk2,(2) in mouse xenograft models, both subcutaneous and metastatic, employing the human prostate cancer cell line PC3M-luc-C6, a modified PC3M cell line that expresses luciferase. After 2 weeks of treatment with PF-562,271, 25 mg/kg PO BID 5x/wk, the subcutaneous model showed a 62% tumor growth inhibition compared to control based on tumor measurements (p < 0.05), with a 88% vs. a 490% increase in bioluminescent signal for treatment and control respectively (p < 0.05). In the metastasis model, the percent change from baseline, after 18 days of treatment, of the treatment group was 2,854 vs. 14,190% for the vehicle (p < 0.01). These results show that PF-562,271 has a potent effect on metastatic prostate cancer growth in vivo.

Phase II trial of bevacizumab, thalidomide, docetaxel, and prednisone in patients with metastatic castration-resistant prostate cancer.

PURPOSE We previously demonstrated that thalidomide appears to add to the activity of docetaxel in metastatic castration-resistant prostate cancer (CRPC). Phase II studies combining docetaxel with bevacizumab have had substantial antitumor activity. We hypothesized that the combination of docetaxel plus these antiangiogenic drugs with different targets would have substantial clinical activity. To explore safety and efficacy, this was tested in mice and in human patients. PATIENTS AND METHODS Preclinical efficacy of the combination therapy was evaluated in PC3 xenograft mice. Sixty patients with progressive metastatic CRPC received intravenous docetaxel and bevacizumab plus oral thalidomide and prednisone. The primary end point was a prostate-specific antigen (PSA) decline of > or = 50%. Secondary end points included time to progression, overall survival, and safety. Results In the mouse model, combination therapy of docetaxel, bevacizumab, and thalidomide inhibited tumor growth most effectively. In the clinical trial, 90% of patients receiving the combination therapy had PSA declines of > or = 50%, and 88% achieved a PSA decline of > or = 30% within the first 3 months of treatment. The median time to progression was 18.3 months, and the median overall survival was 28.2 months in this group with a Halabi-predicted survival of 14 months. While toxicities were manageable, all patients developed grade 3/4 neutropenia. CONCLUSION The addition of bevacizumab and thalidomide to docetaxel is a highly active combination with manageable toxicities. The estimated median survival is encouraging, given the generally poor prognosis of this patient population. These results suggest that definitive clinical trials combining antiangiogenic agent combinations with docetaxel are warranted to improve treatment outcomes for patients with metastatic CRPC.

Pulsed high-intensity focused ultrasound enhances uptake of radiolabeled monoclonal antibody to human epidermoid tumor in nude mice.

UNLABELLED: The aim of this study was to determine if pulsed high-intensity focused ultrasound (HIFU) exposures could enhance tumor uptake of (111)In-MX-B3, a murine IgG1kappa monoclonal antibody directed against the Le(y) antigen. METHODS: MX-B3 was labeled with (111)In, purified, and confirmed for its binding to the antigen-positive A431 cell line. Groups of nude mice were inoculated subcutaneously with A431 tumor cells on both hind flanks. A tumor on one flank was treated with pulsed-HIFU; the other tumor was used as an untreated control. Within 10 min after the HIFU exposure, the mice received intravenous (111)In-MX-B3 for imaging and biodistribution studies. Mice were euthanized at 1, 24, 48, and 120 h after injection for biodistribution studies. RESULTS: The HIFU exposure shortened the peak tumor uptake time (24 vs. 48 h for the control) and increased the peak tumor uptake value (38 vs. 25 %ID/g [percentage injected dose per gram] for the control). The HIFU effect on enhancing tumor uptake was greater at earlier times up to 24 h, but the effect was gradually diminished thereafter. The HIFU effect on enhancing tumor uptake was substantiated by nuclear imaging studies. HIFU also increased the uptake of the antibody in surrounding tissues, but the net increase was marginal compared with the increase in tumor uptake. CONCLUSION: This study demonstrates that pulsed-HIFU significantly enhances the delivery of (111)In-MX-B3 in human epidermoid tumors xenografted in nude mice. The results of this pilot study warrant further evaluation of other treatment regimens, such as repeated HIFU exposures for greater delivery enhancement of antibodies labeled with cytotoxic radioisotopes or pulsed-HIFU exposure in addition to a combined therapy of (90)Y-B3 and taxol to enhance the synergistic effect.

Tumor imaging using 1-(2'-deoxy-2'-18F-fluoro-beta-D-arabinofuranosyl)thymine and PET.

UNLABELLED: The kinetics of 1-(2'-deoxy-2'-fluoro-beta-d-arabinofuranosyl)thymine (FMAU) were studied using PET to determine the most appropriate and simplest approach to image acquisition and analysis. The concept of tumor retention ratio (TRR) is introduced and validated. METHODS: Ten patients with brain (n = 4) or prostate (n = 6) tumors were imaged using (18)F-FMAU PET (mean dose, 369 MBq). Sixty-minute dynamic images were obtained; this was followed by whole-body images. Mean and maximum standardized uptake values (SUVmean and SUVmax, respectively) of each tumor were determined as the mean over 3 planes of each time interval. For kinetic analyses, blood activity was measured in 18 samples over 60 min. Samples were analyzed by high-performance liquid chromatography at 3 selected times to determine tracer metabolites. FMAU kinetics were measured using a 3-compartment model yielding the flux (K1 x k3/(k2 + k3)) (K1, k2, and k3 are rate constants) and compared with TRR measurements. TRR was calculated as the tumor (18)F-FMAU uptake area under the curve divided by the product of blood (18)F-FMAU AUC and time. A similar analysis was performed using muscle to estimate (18)F-FMAU delivery. RESULTS: SUVmean measurements obtained from 5 to 11 min correlated with those obtained from 30 to 60 min (r(2) = 0.92, P < 0.0001) and 50 to 60 min (r(2) = 0.92, P < 0.0001) due to the rapid clearance of (18)F-FMAU. Similar results were obtained using SUVmax measurements (r(2) = 0.93, P < 0.0001; r(2) = 0.88, P < 0.0001, respectively). The measurement of TRR using either blood or muscle activity over 11 min provided results comparable to those of 60-min dynamic imaging and a 3-compartment model. This analysis required only 5 blood samples drawn at 1, 2, 3, 5, and 11 min without metabolite correction to produce comparable results. CONCLUSION: Tissue retention ratio measurements obtained over 11 min can replace flux measurements in (18)F-FMAU imaging. The SUVmean and the SUVmax in 5-11 min images correlated well with those of images obtained at 50-60 min. The quality of the images and tissue kinetics in 11 min of imaging makes it a desirable and shorter tumor imaging option.

Imaging the pharmacokinetics of [F-18]FAU in patients with tumors: PET studies.

PURPOSE: FAU (1-(2'-deoxy-2'-fluoro-beta-D: -arabinofuranosyl) uracil) can be phosphorylated by thymidine kinase, methylated by thymidylate synthase, followed by DNA incorporation and thus functions as a DNA synthesis inhibitor. This first-in-human study of [F-18]FAU was conducted in cancer patients to determine its suitability for imaging and also to understand its pharmacokinetics as a potential antineoplastic agent. METHODS: Six patients with colorectal (n = 3) or breast cancer (n = 3) were imaged with [F-18]FAU. Serial blood and urine samples were analyzed using HPLC to determine the clearance and metabolites. RESULTS: Imaging showed that [F-18]FAU was concentrated in breast tumors and a lymph node metastasis (tumor-to-normal-breast-tissue-ratio 3.7-4.7). FAU retention in breast tumors was significantly higher than in normal breast tissues at 60 min and retained in tumor over 2.5 h post-injection. FAU was not retained above background in colorectal tumors. Increased activity was seen in the kidney and urinary bladder due to excretion. Decreased activity was seen in the bone marrow with a mean SUV 0.6. Over 95% of activity in the blood and urine was present as intact [F-18]FAU at the end of the study. CONCLUSIONS: Increased [F-18]FAU retention was shown in the breast tumors but not in colorectal tumors. The increased retention of FAU in the breast compared to bone marrow indicates that FAU may be useful as an unlabeled antineoplastic agent. The low retention in the marrow indicates that unlabeled FAU might lead to little marrow toxicity; however, the images were not of high contrast to consider FAU for diagnostic clinical imaging.

Biodistribution and radiation dosimetry estimates of 1-(2'-deoxy-2'-(18)F-Fluoro-1-beta-D-arabinofuranosyl)-5-bromouracil: PET imaging studies in dogs.

UNLABELLED: This study reports on the biodistribution and radiation estimates of 1-(2'-deoxy-2'-(18)F-fluoro-1-beta-d-arabinofuranosyl)-5-bromouracil ((18)F-FBAU), a potential tracer for imaging DNA synthesis. METHODS: Three normal dogs were intravenously administered (18)F-FBAU and a dynamic PET scan was performed for 60 min over the upper abdomen followed by a whole-body scan for a total of 150 min. Blood samples were collected at stipulated time intervals to evaluate tracer clearance and metabolism. Tissue samples of various organs were analyzed for tracer uptake and DNA incorporation. Dynamic accumulation of the tracer in different organs was derived from reconstructed PET images. The radiation dosimetry of (18)F-FBAU was evaluated using the MIRD method. RESULTS: At 60 min after injection, blood analysis found >90% of the activity in unmetabolized form. At 2 h after injection, (18)F-FBAU uptake was highest in proliferating tissues (mean SUVs: marrow, 2.6; small intestine, 4.0), whereas nonproliferative tissues showed little uptake (mean SUVs: muscle, 0.75; lung, 0.70; heart, 0.85; liver, 1.28). Dynamic image analysis over 60 min showed progressive uptake of the tracer in marrow. Extraction studies demonstrated that most of the activity in proliferative tissues was in the acid-insoluble fraction (marrow, 83%; small intestine, 73%), consistent with incorporation into DNA. In nonproliferative tissue, most of the activity was not found in the acid-insoluble fraction (>84% for heart, muscle, and liver). CONCLUSION: These results demonstrate that (18)F-FBAU was resistant to metabolism, readily incorporated into DNA in proliferating tissues, and showed good contrast between organs of variable DNA synthesis. These findings indicate that (18)F-FBAU may find use in measuring DNA synthesis with PET.

Imaging DNA synthesis in vivo with 18F-FMAU and PET.

UNLABELLED: We imaged DNA synthesis in vivo with PET and (18)F-1-(2'-deoxy-2'-fluoro-beta-d-arabinofuranosyl)thymine (FMAU), which is phosphorylated by thymidine kinases and incorporated into DNA. METHODS: We produced (18)F-FMAU and injected the tracer into 5 normal dogs and studied them by imaging or biodistribution for up to 2.5 h. The pharmacokinetics of FMAU in blood and urine were determined using high-performance liquid chromatography analysis. At the end of each study, selected tissues were removed to measure the total activity retained in these tissues. In addition, the selected tissues were extracted by acid precipitation, by which the macromolecules can be precipitated to determine the radioactivity of (18)F-FMAU incorporated into DNA. RESULTS: Imaging and tissue analysis showed increased activity in the lymph nodes, stomach, small intestine, and bone marrow, with mean standardized uptake values of 1.4, 1.6, 2.3, and 3.9, respectively, because of varying degrees of increased cell proliferation. In contrast, (18)F-FMAU was distributed with tissue-to-muscle ratios of approximately 1.0 in nonproliferative organs such as lung, liver, and kidneys. Analysis of the tissue extracts using acid precipitation demonstrated that 88% of activity in marrow and 65% of activity in small intestine was acid precipitated. However, more than 90% of activity in the nonproliferating tissues such as heart and lungs was in the supernatant. Increased activity was seen in the heart because of a high level of thymidine kinase 2 and in the gallbladder because of excretion. Analysis of blood and urine demonstrated that more than 95% of activity was present as intact (18)F-FMAU at the end of the studies. CONCLUSION: The results showed that (18)F-FMAU was selectively retained in DNA of the proliferating tissues and was resistant to degradation. These features indicate that (18)F-FMAU might be an alternative to (11)C-thymidine for imaging DNA synthesis in normal tissues and tumors.

Imaging DNA synthesis with [18F]FMAU and positron emission tomography in patients with cancer.

PURPOSE: FMAU (1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)thymine) is a thymidine analog that can be phosphorylated by thymidine kinase and incorporated into DNA. This first-in-human study of [18F]FMAU was conducted as a pilot in patients to determine its biodistribution and suitability for imaging DNA synthesis in tumors using positron emission tomography (PET). METHODS: Fourteen patients with diverse cancers (brain, prostate, colorectal, lung, and breast) were imaged with [18F]FMAU. We obtained dynamic PET images for 60 min and a whole-body image. Blood and urine samples were analyzed by high-performance liquid chromatography to measure metabolites and clearance. RESULTS: Active tumors in the breast, brain, lung and prostate were clearly visualized with standardized uptake values (SUVs) of 2.19, 1.28, 2.21, and 2.27-4.42, respectively. Unlike with other tracers of proliferation, low uptake of [18F]FMAU was seen in the normal bone marrow (SUV(mean) 0.7), allowing visualization of metastatic prostate cancer (SUV 3.07). Low background was also observed in the brain, pelvis, and thorax, aside from heart uptake (SUV 3.36-8.78). In the abdomen, increased physiological uptake was seen in the liver (SUV 10.07-20.88) and kidneys (SUV 7.18-15.66) due to metabolism and/or excretion, but the urinary bladder was barely visible (SUV(mean) 2.03). On average, 95% of the activity in the blood was cleared within 10 min post injection and an average of 70% of the activity in the urine was intact FMAU at 60 min post injection. CONCLUSION: Tumors in the brain, prostate, thorax, and bone can be clearly visualized with FMAU. In the upper abdomen, visualization is limited by the physiological uptake by the liver and kidneys.