Background: Despite extensive research in systemic treatments for HER2 positive breast cancer brain metastases (BCBM), only limited benefits have been observed often at the cost of significant toxicities. Treatment failure is attributed to the limited capacity of drugs to cross the blood-tumor-barrier (BTB) or to resistance mechanisms in the brain lesion microenvironment. In this study we evaluate the radiolabeled drug CAM-H2 as a new systemic treatment for the irradiation of HER2 positive BCBM. Single domain antibody fragments (sdAbs) are small (15 kDa) heavy-chain-only antibody fragments. Due to their favorable pharmacokinetics, sdAbs are tested as targeting vehicles for the delivery of cytotoxic irradiation to cancer lesions inside and outside the brain. Here we measure the potential of CAM-H2 (131-Iodine conjugated anti-HER2 sdAb 2Rs15d) for targeting brain lesions with imaging and compare its therapeutic efficacy with Trastuzumab in a preclinical model. Methods: Tumors were inoculated through intracranial injection of HER2+SKOV3.ip1 or MDA-MB-231Br (MDA) cancer cells. Biodistribution of radiolabeled 2Rs15d and Trastuzumab was evaluated through in vivoSPECT/CT imaging at 1h and 72h post injection followed by ex vivotissue radioactivity counting. Five groups of MDA-tumor-bearing mice were treated with either CAM-H2, Trastuzumab plus CAM-H2, unlabeled 2Rs15d, Trastuzumab, or PBS. Results: Mice treated with CAM-H2 and the combination of CAM-H2 plus Trastuzumab showed a significant increase (p < 0.05) in median survival compared to the Trastuzumab only, unlabeled 2Rs15d or PBS. The addition of Trastuzumab did not significantly prolong survival, compared to cold 2Rs15d or PBS. SPECT/CT imaging of CAM-H2 treated animals showed specific uptake in the brain lesions up to 2 days after administration. Conclusions: CAM-H2 crosses the BTB and binds HER2 positive brain lesions. Treatment with therapeutic doses of CAM-H2 significantly increased survival compared to Trastuzumab. Systemically delivered cytotoxic irradiation conjugated to sdAbs has the potential to effectively treat cancer lesions inside the brain, with limited exposure to healthy brain. Clinical translation of CAM-H2 for treatment of BCBM is currently ongoing. Legal entity responsible for the study: Vrije Universiteit Brussel. Funding: Camel-IDS NV/SA. Disclosure: M. D'Huyvetter: Ownership interest, employee: Camel-IDS NV/SA. B. Windhorst: Editor in chief: Nuclear Medicine & Biology; Editor: Journal of Radiolabelled Compounds & Radiopharmaceuticals T. Lahoutte: Holds ownership interest, consultant: Camel-IDS NV/SA; Member of the scientific advisory board: Ion Beam Applications; Member of the strategic committee: IRE; Preclinical contract research: Roche, Telix Pharmaceuticals. N. Devoogdt: Ownership interest, consultant for Camel-IDS NV/SA; Preclinical contract research: Roche, Telix Pharmaceuticals. All other authors have declared no conflicts of interest.

Tau pathology is related to clinical progression in Alzheimer's disease (AD). Longitudinal tau PET imaging in preclinical stages of AD may help to identify individuals at risk of progression. Individuals with subjective cognitive decline (SCD) may suffer from preclinical AD. As dynamic scanning protocols allow for accurate quantitative measures of tracer retention over time, the aim of this study was to investigate whether there is a change in tau pathology, as measured with dynamic [18F]Flortaucipir (FTP) PET, in subjects with SCD over a time period of two years. In an ongoing sub-study of the SCIENCe project, we included 20 SCD subjects (age 66±8, 45% female, MMSE 29±1, 25% [18F]Florbetapir PET positive based on visual read)[Table1]. All subjects underwent a 90 minute dynamic [18F]Florbetapir PET scan at baseline and a 130 minutes dynamic [18F]FTP PET scan at baseline and 2±.06 (1.9-2.1) year follow-up. Parametric images were generated using receptor parametric mapping (RPM; reference region cerebellar grey matter) to extract non-displaceable binding potential (BPND). For [18F]FTP three non-overlapping regions-of-interest reflecting early (medial temporal), intermediate (limbic) and late stage (neocortical) tau pathology were selected. Analyses were performed using ANOVA for repeated measures, adjusting for age and sex. To examine the interaction effect of amyloid pathology, global [18F]Florbetapir BPND was added in additional analyses. We found a significant increase in [18F]FTP BPND in the medial temporal region, F(1,17)=5.205, p=0.036, reflecting an average increase in tau pathology from 0.01 to 0.02 BPND over the two year period[Figure1]. No significant [18F]FTP BPND changes were found for the limbic and neocortical regions, F(1,17)=1.654 and 1.660, p>0.05. Addition of global [18F]Florbetapir BPND to the model revealed an interaction effect in the limbic and neocortical regions (both p<0.05), attributable to a larger increase in [18F]FTP BPND in amyloid positive individuals[Figure2]. Data collection is still ongoing.

Background: Tumor PD-L1 IHC relates moderately with treatment outcome following anti-PD1 therapy in pts with NSCLC and single biopsies do not account for tumor heterogeneity. Aim: 1. Assess safety of the PET procedures. 2. Quantify 89Zirconium-labeled nivolumab (89Zr-nivo) and 18F-labeled BMS-986192 (18F-PD-L1) uptake. 3. Assess tracer uptake heterogeneity. 4. Correlate tracer uptake with PD-1/PD-L1 IHC in tumor, stroma and with treatment outcome. Methods: NSCLC pts eligible for treatment with nivolumab were included. Pts received whole body 18F-PD-L1 and 89Zr-nivo PET scans. Baseline tumor biopsy was required to assess PD-(L)1 IHC status (28.8 assay). SUVpeak was calculated for delineable lesions and correlated to PD-(L)1 IHC and response after 12 wks of nivolumab treatment. Results: 10 pts (3 ≥50%, 5 ≥1%, 5 negative by PD-L1 IHC) were enrolled and 37 lesions analysed. No toxicity related to radiotracer was observed. Tumor uptake of both tracers was visualized in all pts, but not in all lesions. Tracer uptake varied among pts with mean 18F-PD-L1 SUVpeak 4.6, range 0.5 - 14.4 and mean 89Zr-nivo SUVpeak 5.0, range 1.6 – 11 (p = 0.03) and within pts with mean SUVpeak difference 3.6-fold (±2.1) and 2.4-fold (±0.77) between lesions for 18F-PD-L1 and 89Zr-nivo, respectively. For lesions with ≥50% PD-L1 IHC, mean 18F-PD-L1 SUVpeak was 8.0 (±4.7) as compared to 3.5 (±1.6) for lesions with <50% PD-L1 IHC (p = 0.03). For tumors with high TIL/stromal PD-1 expression, mean 89Zr-nivo SUVpeak was 8.6 (±2.4) as compared to 6.1 (±2.1) for lesions with low PD-1 expression (p = 0.1). Mean SUVpeak for 18F-PD-L1 was 8.4 (±5.4) for pts with PR and 4.5 (±2.9) for pts with PD/SD (p = 0.3). Mean SUVpeak for 89Zr-nivo was 7.8 (±1.8) for pts with PR and 5.4 (±2.2) for pts with PD/SD (p = 0.2). Conclusions: 1. PET-imaging with both tracers is safe and feasible, with good tumor-to-normal tissue contrast. 2. Tumor uptake showed heterogeneity among pts and among tumors within pts. 3. Pts with ≥50% tumor PD-L1 expression showed higher 18F-PD-L1 uptake. 4. Pts with high PD-1 expression showed higher 89Zr-nivo uptake, and pts with PR demonstrated higher 18F-PD-L1 and 89Zr-nivo tracer uptake than pts with PD/SD, although these are without statistical significance which may be due to the small dataset. Clinical trial identification: EUDRA-CT-number: 2015‐004760‐11 Legal entity responsible for the study: Joop de Langen Funding: Bristol-Myers Squibb Disclosure: E. Smit: Has an advisory role at Lilly. Received research funding from Company: Boehringer Ingelheim, Bayer, Roche/Genentech and AstraZeneca (paid to institution). D.K. Leung, R.A. Smith, L.M. Wilson, W. Hayes: Is employed at BMS and owns stock and/or other ownership interests in BMS. All other authors have declared no conflicts of interest.

Background Activated macrophages play a key role in the pathophysiology of rheumatoid arthritis (RA). Earlier, we reported that folate receptor β (FR-β) expression on activated macrophages in synovial tissue of RA patients [1] could be harnessed for disease monitoring with [18F]-PEG-folate positron emission tomography (PET) in arthritic rats [2]. We explored whether [18F]-PEG-folate PET can also guide therapy monitoring with the antifolate Methotrexate (MTX) and whether glucocorticoids can be utilized as potential modulators of FR expression. Objectives To study in arthritic rats: (1) The feasibility of [18F]-PEG-folate PET for Methotrexate (MTX) therapy efficacy and (2) The impact of dexamethasone (DEX) on in vivo modulation of FR expression on macrophages. Methods Wistar rats (3-6 per group) were immunized twice with methylated bovine serum albumin (mBSA) in complete Freund9s adjuvant and Bordetella pertussis antigen followed by local arthritis induction (intra-articular mBSA injection with 3 repeated injections in the right knee (RA) with the contralateral left knee serving as internal control [3]. Therapeutic interventions were performed with MTX (1mg/kg; 1/week x4, i.p.). For FR modulation studies, DEX (0.25 mg/kg, i.p.) was dosed 5x during mBSA injections. [18F]-PEG-folate PET was analyzed in manually drawn regions of interest (ROI) to determine the semi-quantitative radioactivity concentration, expressed as standardized uptake values (SUV). Following PET, ex vivo tissue distribution was performed and the amount of tissue radioactivity was expressed as percentage of the injected dose/gram tissue (%ID/g). Results All rats showed macroscopic thickening of the right, arthritic knee compared to the contralateral knee, impaired movement and synovial inflammation in the affected joint. Arthritic joints were clearly depicted on [18F]-PEG-folate PET scans, while only background activity of the folate tracer was noticed in the contralateral, non-inflamed knee joints. After MTX therapy, [18F]-PEG-folate uptake in arthritic knees was markedly reduced (up to 11-fold) compared to rats receiving no treatment. This was corroborated by ex vivo tissue distribution studies demonstrating a 6-fold decrease of [18F]-PEG-folate uptake in affected knees after MTX therapy (0.032%ID/g) compared to saline-treated arthritic knees (0.2%ID/g). Furthermore, DEX modulation studies revealed a 1.5-fold increase (0.30%ID/g) in the arthritic knees compared to the saline-treated arthritic knee. Conclusions This study emphasizes the feasibility of exploiting [18F]-PEG-folate for PET-guided imaging of MTX-based therapy monitoring in arthritis. Beyond this, FR modulation by DEX may warrant further exploration to enhance FR-targeted macrophage therapies with MTX/antifolates in rheumatoid arthritis. References Van der Heijden et al, Arthr & Rheum (2009); 60:12-21. Gent et al, Arthr Res & Ther (2013); 15:R37. Chandrupatla et al, BioMed Res Int (2015), in press. Disclosure of Interest None declared