Human GPR84 Stable Cell Line - HEK293

Chronic innate immune activation is a key feature of many neurological disorders and is known to induce the upregulation of GPR84 in myeloid cells (macrophages, microglia, and monocytes). Consequently, GPR84 holds promise as a sensor for pro-inflammatory innate immune responses. To evaluate the potential of GPR84 as an imaging biomarker, researchers synthesized ¹¹C-MGX-10S and ¹¹C-MGX-11S via carbon-11 alkylation for use as positron emission tomography (PET) tracers targeting this receptor. In vitro experiments demonstrated that both radiotracers exhibited significantly higher binding to hGPR84-HEK293 cells compared to parental control HEK293 cells. Co-incubation with the GPR84 antagonist GLPG1205 reduced the binding of both tracers by more than 90%, confirming their high specificity for GPR84 in vitro. PET imaging evaluations in healthy mice revealed that ¹¹C-MGX-10S possessed superior brain uptake and pharmacokinetic profiles compared to ¹¹C-MGX-11S. Subsequent imaging of a well-established mouse model of systemic and neuro-inflammation using ¹¹C-MGX-10S showed high PET signals in affected tissues, including the brain, liver, lung, and spleen. Compared to ¹¹C-DPA-713-an existing radiotracer used clinically to image innate immune activation-¹¹C-MGX-10S offers several advantages, including higher binding signals in the central nervous system and inflamed peripheral tissues, as well as lower background signals in healthy, saline-treated subjects.

After obtaining two new candidate GPR84 radiotracers, researchers evaluated their binding to cells expressing human GPR84 versus cells lacking the receptor. Cell binding studies showed that, after a 40-minute incubation, the binding of ¹¹C-MGX-10S to hGPR84-HEK293 cells (Creative Biogene Biotechnology) was 14.5-fold higher than to parental HEK293 cells; a similar binding pattern was observed after 20 minutes (Figure 3). Co-incubation of ¹¹C-MGX-10S with the GPR84 antagonist GLPG1205 (35 μM) for 40 minutes significantly reduced binding to hGPR84-HEK293 cells by 91.7%, demonstrating high specificity. In contrast, after 40 minutes of incubation, the binding of ¹¹C-MGX-11S to hGPR84-HEK293 cells was only 3.25-fold higher than to parental cells. ¹¹C-MGX-10S exhibited a higher target-to-background binding ratio than ¹¹C-MGX-11S; this may be attributed to the higher lipophilicity of ¹¹C-MGX-11S (potentially leading to some non-specific binding) or the higher affinity of ¹¹C-MGX-10S (resulting in greater overall binding to hGPR84-expressing cells). Co-incubation with GLPG1205 (35 μM) reduced ¹¹C-MGX-11S binding by 91.5%, indicating that, despite lower overall binding compared to ¹¹C-MGX-10S, it remains specific for GPR84.

Figure 1. In vitro radiotracer binding specificity. (Kalita M, et al., 2023)