In vivo evaluation of a novel 18F-labeled PET radioligand for translocator protein 18 kDa (TSPO) in monkey brain.

PURPOSE: [18F]SF51 was previously found to have high binding affinity and selectivity for 18 kDa translocator protein (TSPO) in mouse brain. This study sought to assess the ability of [18F]SF51 to quantify TSPO in rhesus monkey brain. METHODS: Positron emission tomography (PET) imaging was performed in monkey brain (n = 3) at baseline and after pre-blockade with the TSPO ligands PK11195 and PBR28. TSPO binding was calculated as total distribution volume corrected for free parent fraction in plasma (VT/fP) using a two-tissue compartment model. Receptor occupancy and nondisplaceable uptake were determined via Lassen plot. Binding potential (BPND) was calculated as the ratio of specific binding to nondisplaceable uptake. Time stability of VT was used as an indirect probe to detect radiometabolite accumulation in the brain. In vivo and ex vivo experiments were performed in mice to determine the distribution of the radioligand. RESULTS: After [18F]SF51 injection, the concentration of brain radioactivity peaked at 2.0 standardized uptake value (SUV) at ~ 10 min and declined to 30% of the peak at 180 min. VT/fP at baseline was generally high (203 ± 15 mL· cm-3) and decreased by ~ 90% after blockade with PK11195. BPND of the whole brain was 7.6 ± 4.3. VT values reached levels similar to terminal 180-min values by 100 min and remained relatively stable thereafter with excellent identifiability (standard errors < 5%), suggesting that no significant radiometabolites accumulated in the brain. Ex vivo experiments in mouse brain showed that 96% of radioactivity was parent. No significant uptake was observed in the skull, suggesting a lack of defluorination in vivo. CONCLUSION: The results demonstrate that [18F]SF51 is an excellent radioligand that can quantify TSPO with a good ratio of specific to nondisplaceable uptake and has minimal radiometabolite accumulation in brain. Collectively, the results suggest that [18F]SF51 warrants further evaluation in humans.

Discovery of a High-Affinity Fluoromethyl Analog of [11C]5-Cyano-N-(4-(4-methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide ([11C]CPPC) and Their Comparison in Mouse and Monkey as Colony-Stimulating Factor 1 Receptor Positron Emission Tomography Radioligands.

[11C]CPPC has been advocated as a radioligand for colony-stimulating factor 1 receptor (CSF1R) with the potential for imaging neuroinflammation in human subjects with positron emission tomography (PET). This study sought to prepare fluoro analogs of CPPC with higher affinity to provide the potential for labeling with longer-lived fluorine-18 (t 1/2 = 109.8 min) and for delivery of higher CSF1R-specific PET signal in vivo. Seven fluorine-containing analogs of CPPC were prepared and four were found to have high inhibitory potency (IC50 in low to sub-nM range) and selectivity at CSF1R comparable with CPPC itself. One of these, a 4-fluoromethyl analog (Psa374), was investigated more deeply by labeling with carbon-11 (t 1/2 = 20.4 min) for PET studies in mouse and monkey. [11C]Psa374 showed high peak uptake in monkey brain but not in mouse brain. Pharmacological challenges revealed no CSF1R-specific binding in either species at baseline. [11C]CPPC also failed to show specific binding at baseline. Moreover, both [11C]Psa374 and [11C]CPPC showed brain efflux transporter substrate behavior in both species in vivo, although Psa374 did not show liability toward human efflux transporters in vitro. Further development of [11C]Psa374 in non-human primate models of neuroinflammation with demonstration of CSF1R-specific binding would be required to warrant the fluorine-18 labeling of Psa374 with a view to possible application in human subjects.

First-in-Human Evaluation of 18F-PF-06445974, a PET Radioligand That Preferentially Labels Phosphodiesterase-4B.

Phosphodiesterase-4 (PDE4), which metabolizes the second messenger cyclic adenosine monophosphate (cAMP), has 4 isozymes: PDE4A, PDE4B, PDE4C, and PDE4D. PDE4B and PDE4D have the highest expression in the brain and may play a role in the pathophysiology and treatment of depression and dementia. This study evaluated the properties of the newly developed PDE4B-selective radioligand 18F-PF-06445974 in the brains of rodents, monkeys, and humans. Methods: Three monkeys and 5 healthy human volunteers underwent PET scans after intravenous injection of 18F-PF-06445974. Brain uptake was quantified as total distribution volume (V T) using the standard 2-tissue-compartment model and serial concentrations of parent radioligand in arterial plasma. Results: 18F-PF-06445974 readily distributed throughout monkey and human brain and had the highest binding in the thalamus. The value of V T was well identified by a 2-tissue-compartment model but increased by 10% during the terminal portions (40 and 60 min) of the monkey and human scans, respectively, consistent with radiometabolite accumulation in the brain. The average human V T values for the whole brain were 9.5 ± 2.4 mL ⋅ cm-3 Radiochromatographic analyses in knockout mice showed that 2 efflux transporters-permeability glycoprotein (P-gp) and breast cancer resistance protein (BCRP)-completely cleared the problematic radiometabolite but also partially cleared the parent radioligand from the brain. In vitro studies with the human transporters suggest that the parent radioligand was a partial substrate for BCRP and, to a lesser extent, for P-gp. Conclusion: 18F-PF-06445974 quantified PDE4B in the human brain with reasonable, but not complete, success. The gold standard compartmental method of analyzing brain and plasma data successfully identified the regional densities of PDE4B, which were widespread and highest in the thalamus, as expected. Because the radiometabolite-induced error was only about 10%, the radioligand is, in the opinion of the authors, suitable to extend to clinical studies.

An Economic Evaluation of Pembrolizumab Versus Other Adjuvant Treatment Strategies for Resected High-Risk Stage III Melanoma in the USA.

BACKGROUND AND OBJECTIVE: Over the past 5 years, adjuvant treatment options for surgically resected stage III melanoma have expanded with the introduction of several novel immune checkpoint inhibitors and targeted therapies. Pembrolizumab, a programmed cell death protein 1 inhibitor, received US Food and Drug Administration approval in 2019 for resected high-risk stage III melanoma based on significantly longer recurrence-free survival versus placebo. This study evaluated the cost-effectiveness of pembrolizumab versus other adjuvant treatment strategies for resected high-risk stage III melanoma from a US health system perspective. METHODS: A Markov cohort-level model with four states (recurrence-free, locoregional recurrence, distant metastases, death) estimated costs and quality-adjusted life-years (QALYs) for pembrolizumab versus routine observation and other adjuvant comparators: ipilimumab in the overall population; and dabrafenib + trametinib in the BRAF-mutation positive (BRAF+) subgroup. Transition probabilities starting from recurrence-free were estimated through parametric multi-state modeling based on phase 3 KEYNOTE-054 (NCT02362594) trial data for pembrolizumab and observation, and network meta-analyses for other comparators. Post-recurrence transitions were modeled based on electronic medical records data and trials in advanced/metastatic melanoma. Utilities were derived using quality-of-life data from KEYNOTE-054 and literature. Costs of treatment, adverse events, disease management, and terminal care were included. RESULTS: Over a lifetime, pembrolizumab, ipilimumab, and observation were associated with QALYs of 9.24, 7.09, and 5.95 and total costs of $511,290, $992,721, and $461,422, respectively (2019 US dollars). Pembrolizumab was thus dominant (less costly, more effective) versus ipilimumab, with an incremental cost-effectiveness ratio of $15,155/QALY versus observation. In the BRAF+ subgroup, pembrolizumab dominated dabrafenib + trametinib and observation, decreasing costs by $62,776 and $11,250 and increasing QALYs by 0.93 and 3.10 versus these comparators, respectively. Results were robust in deterministic and probabilistic sensitivity analyses. CONCLUSIONS: As adjuvant treatment for resected stage III melanoma, pembrolizumab was found to be dominant and therefore cost-effective compared with the active comparators ipilimumab and dabrafenib + trametinib. Pembrolizumab increased costs relative to observation in the overall population, with sufficient incremental benefit to be considered cost-effective based on typical willingness-to-pay thresholds.

Real-World Effectiveness and Tolerability of Pazopanib as First Targeted Therapy in Metastatic Renal Cell Carcinoma: A Retrospective Chart Review in Latin America.

INTRODUCTION: Pazopanib is approved in Latin America as first targeted therapy for patients with metastatic renal cell carcinoma (mRCC). METHODS: A retrospective chart review of adult patients with mRCC who initiated pazopanib as first targeted therapy between January 2011 and March 2016 was conducted among oncology care centers in Argentina, Brazil, Chile, Colombia, and Mexico. Patient characteristics, treatment patterns, overall survival (OS), progression-free survival (PFS), and adverse events were summarized. RESULTS: A total of 156 charts of patients with mRCC receiving first-line pazopanib were reviewed (29, 54, 27, 28, and 18 patients from Argentina, Brazil, Chile, Colombia, and Mexico, respectively). The mean age at initial mRCC diagnosis was 61.6 years, 73.7% were male, and 51.3% were Hispanic. The median dose of pazopanib was 800 mg and the median time from initial mRCC diagnosis to pazopanib start was 2.2 months. The median time on treatment was 10.0 months. At the time of data extraction, 16.7% of patients remained on pazopanib, with clinical progression listed as the main reason for discontinuation. Subsequent therapy was received by 25.6% of patients; the most common were everolimus (9.6%) and axitinib (5.8%). Overall, median PFS and OS were 10.8 and 16.9 months, respectively, and varied across countries. The most common all-grade adverse events were diarrhea (44.9%), asthenia/fatigue (43.6%), and nausea (28.8%). CONCLUSIONS: Pazopanib was used for first-line mRCC treatment in a clinically diverse patient population across Latin America. Real-world PFS and tolerability were similar to clinical studies of pazopanib. FUNDING: Novartis Pharmaceuticals Corporation, Inc.

Cost-effectiveness of pembrolizumab for the adjuvant treatment of resected high-risk stage III melanoma in the United States.

Aims: To evaluate the cost-effectiveness of adjuvant pembrolizumab relative to observation alone following complete resection of high-risk stage III melanoma with lymph node involvement, from a US health system perspective. Materials and methods: A Markov cohort model with four health states (recurrence-free, locoregional recurrence, distant metastases, and death) was developed to estimate costs, life-years, and quality-adjusted life-years (QALYs) associated with pembrolizumab vs observation over a lifetime (46-year) horizon. Using a parametric multi-state modeling approach, transition probabilities starting from recurrence-free were estimated based on patient-level data from KEYNOTE-054 (NCT02362594), a direct head-to-head phase 3 trial. Post-recurrence transition probabilities were informed by real-world retrospective data and clinical trials in advanced melanoma. Health state utilities and adverse event-related disutility were derived from KEYNOTE-054 trial data and published literature. Costs of drug acquisition and administration, adverse events, disease management, and terminal care were estimated in 2018 US dollars. Deterministic and probabilistic sensitivity analyses were conducted to assess robustness. Results: Over a lifetime horizon, adjuvant pembrolizumab and observation were associated with total QALYs of 9.24 and 5.95, total life-years of 10.54 and 7.15, and total costs of $489,820 and $440,431, respectively. The resulting incremental cost-effectiveness ratios (ICERs) for pembrolizumab vs observation were $15,009/QALY and $14,550/life-year. Across the range of input values and assumptions tested in deterministic sensitivity analyses, pembrolizumab ranged from being a dominant strategy to having an ICER of $57,449/QALY vs observation. The ICER was below a willingness-to-pay threshold of $100,000/QALY in 90.2% of probabilistic simulations. Limitations: Long-term extrapolation of outcomes was based on interim results from KEYNOTE-054, with a median follow-up of 15 months. Conclusions: Based on common willingness-to-pay benchmarks, pembrolizumab is highly cost-effective compared with observation alone for the adjuvant treatment of completely resected stage III melanoma in the US.