TY - JOUR T1 - Selective detection of GD2-positive pediatric solid tumors using<sup> 89</sup>Zr-Dinutuximab PET to facilitate anti-GD2 immunotherapy JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 170 LP - 170 VL - 59 IS - supplement 1 AU - Elizabeth Butch AU - Jitendra Mishra AU - Victor Amador-Diaz AU - Amy Vavere AU - Scott Snyder Y1 - 2018/05/01 UR - http://jnm.snmjournals.org/content/59/supplement_1/170.abstract N2 - 170Objectives: This project seeks to develop PET probes to facilitate anti-GD2 immunotherapy for pediatric solid tumor patients. GD2 is a disialoganglioside expressed in &gt;98% of neuroblastoma (NB) and minimally expressed in most other tissues, making it an excellent target for both therapy and imaging. Based on a recent successful Children’s Oncology Group study, the anti-GD2 antibody ch14.18 (dinutuximab, Unituxin®) was approved for immunotherapy in recurrent and refractory NB and is now the standard of care in metastatic NB. However, anti-GD2 immunotherapy has not yet been investigated in front-line scenarios or in other pediatric malignancies such as osteosarcoma (OS) where the frequency and extent of GD2 expression is less well characterized. Clinical trials with anti-GD2 immunotherapy are suboptimal without a method to evaluate GD2 expression and thus potential therapeutic efficacy prior to treatment. We present here initial evaluation of a novel GD2-targeted imaging agent based on dinutuximab that will identify those patients with GD2-expressing tumors most likely to benefit from anti-GD2 immunotherapy. Methods: Dinutuximab-DFO conjugates were prepared and radiolabeled with Zr-89 by standard methods (Vosjan, Nat Prot. 2010 5:739-43). Briefly, a 5-fold molar excess of p-SCN-Bn-DFO in DMSO was reacted with dinutuximab (United Therapeutics Corp) in 0.1M sodium carbonate (pH 9.0) for 40 min at 37°C and 550 rpm mixing. Conjugates were purified on a Centricon 30K (Millipore) centrifugal filter using 6 x 4 mL of 1 M HEPES (pH 7.1) with centrifugation for 25 min at 3000 rpm. Radiolabeling was performed using 2.32 mCi of [89Zr]Zr-oxalic acid solution, adjusted to pH 7.5 and added to 464 μg dinutuximab-DFO in 1 M HEPES (pH 7.1). After 1 h at 37°C, 5 μL of 50 mM DTPA was added to scavenge any free Zr-89. Sample was loaded onto a PD-10 column (Millipore) and eluted in 3.5 mL saline. The collected solution was centrifuged to concentrate (Centricon 30K). Nude mice were injected s.c. in the rear flank with 5 x 106 either CHLA-20 (&gt;99% GD2+ cells by flow cytometry,) or SK-N-SH (&lt;2% GD2+) cells in a 1:1 ratio with Matrigel® (BD Biosciences). CHLA-20 tumors were allowed to grow for 2-3 weeks and SK-N-SH tumors for 3-4 weeks to obtain tumors of comparable size. Tumor-bearing mice were then injected r.o. with 25 μCi of 89Zr-DFO-dinutuximab. Static 30 min PET images were obtained at 2, 5 and 7 days post-injection of radiotracer on an Inveon D-PET system, and co-registered with CT images obtained using an Inveon microCT (Siemens Medical Solutions, USA Inc.). Following imaging, animals were sacrificed, dissected and tissues weighed and counted for radioactivity. Results: The final 89Zr-DFO-dinutuximab was prepared at 100% radiochemical purity and 5 μCi/μg specific activity. Images at 48 h post-injection showed ~11% injected dose/gram radioactivity retention in the GD2- tumor (due to EPR effect) but 4-fold higher accumulation in the GD2+ tumor. At 5 days, the GD2- tumor is no longer visible and most other off-target activity has cleared. All non-target organs show &lt;5% i.d./g radioactivity retention at 120 h except bone (6.5%). Tumor:background ratios &gt;7:1 were observed vs. blood (7.3:1), muscle (45:1) and liver (7:1). Selectivity for GD2 binding was also observed for GD2+ vs GD2- tumors at a 6:1 ratio. Tumor radioactivity concentration was unchanged over 2-7 days post-injection. Conclusions: The high specificity of 89Zr-DFO-dinutuximab for binding GD2 vs non-target tissues and selectivity for GD2-expressing tumors vs. GD2- tumor demonstrated here lends strong support to the utility of this radiotracer for investigating GD2 expression and detecting GD2+ tumors to identify patients most likely to benefit from anti-GD2 immunotherapy. Such image-guided therapy could be of particular importance for investigation of diseases such as OS, and adult cancers such as small cell lung cancer, where GD2 expression is more variable and less well characterized than NB. ER -