18F-BMS986192 PET imaging of PD-L1 in metastatic melanoma patients with brain metastases treated with immune checkpoint inhibitors. A pilot study

Immune checkpoint inhibitors (ICI) targeting PD-1/PD-L1 frequently induces tumor response in metastatic melanoma patients. However, tumor response often takes months and may be heterogeneous. Consequently, additional local treatment for non-responsive metastases may be needed, especially in the case of brain metastases. Non-invasive imaging may allow the characterization of (brain) metastases to predict response. This pilot study uses ¹⁸F-BMS986192 PET for PD-L1 expression to explore the variability in metastatic tracer uptake and its relation to tumor response, with a special focus on brain metastases. Methods: Metastatic melanoma patients underwent whole-body ¹⁸F-BMS986192 PET/CT scanning before and 6 weeks after starting ICI therapy. ¹⁸F-BMS986192 uptake was measured in healthy tissues, organs, and tumor lesions. Tumor response was evaluated at 12 weeks using CT thorax/abdomen and MRI brain. RECIST v 1.1 was used to define therapy response per patient. Response per lesion was measured by the percentage change in lesion diameter. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 4.0. Results: Baseline ¹⁸F-BMS986192 PET/CT was performed in 8 patients, with follow-up scans in 4 patients. The highest tracer uptake was observed in the spleen, bone marrow, kidneys, and liver. Tracer uptake in tumor lesions was heterogeneous. In total, 42 tumor lesions were identified at baseline with most lesions in the lungs (n = 21) and brain (n = 14). Tracer uptake was similar between tumor locations. ¹⁸F-BMS986192 uptake in lesions at baseline, corrected for blood pool activity, was negatively correlated with the change lesion diameter at response evaluation (r=-0.49, P = 0.005), both in intra- and extracerebral lesions. Receiver operating characteristic (ROC) analysis demonstrated that ¹⁸F-BMS986192 uptake can discriminate between responding and nonresponding lesions with an area under the curve of 0.82. At the follow-up scan an increased ¹⁸F-BMS986192 uptake compared to baseline scan was correlated with an increased lesion diameter at response evaluation. In the follow-up ¹⁸F-BMS986192-PET scan of two patients, ICI-related toxicity (thyroiditis and colitis) was detected. Conclusion: In this pilot study, ¹⁸F-BMS986192 PET showed heterogeneous uptake in intra and extracerebral metastatic lesions in melanoma patients. Baseline ¹⁸F-BMS986192 uptake was able to predict an ICI treatment-induced reduction in lesion volume, whereas the follow-up PET scan allowed the detection of treatment-induced toxicity.

Relationships between Serotonin Transporter Binding in the Raphe Nuclei, Basal Ganglia, and Hippocampus with Clinical Symptoms in Cervical Dystonia: A [11C]DASB Positron Emission Tomography Study

Purpose

Alterations of the central serotonergic system have been implicated in the pathophysiology of dystonia. In this molecular imaging study, we assessed whether altered presynaptic serotonin transporter (SERT) binding contributes to the pathophysiology of cervical dystonia (CD), concerning both motor and non-motor symptoms (NMS).

Methods

We assessed the non-displaceable binding potential (BP_ND) using the selective SERT tracer [¹¹C]DASB and positron emission tomography (PET) in 14 CD patients and 12 age- and gender-matched controls. Severity of motor symptoms was scored using the Toronto Western Spasmodic Torticollis Rating Scale and Clinical Global Impression jerks/tremor scale. NMS for depressive symptoms, anxiety, fatigue, and sleep disturbances were assessed with quantitative rating scales. The relationship between SERT binding and clinical patient characteristics was analyzed with the Spearman’s rho test and multiple regression.

Results

When comparing the CD patients with controls, no significant differences in BP_ND were found. Higher BP_ND in the dorsal raphe nucleus was statistically significantly correlated (p < 0.001) with motor symptom severity (r_s = 0.65), pain (r_s = 0.73), and sleep disturbances (r_s = 0.73), with motor symptom severity being the most important predictor of SERT binding. Furthermore, fatigue was negatively associated with the BP_ND in the medial raphe nucleus (r_s = −0.61, p = 0.045), and sleep disorders were positively associated with the BP_ND in the caudate nucleus (r_s = 0.58, p = 0.03) and the hippocampus (r_s = 0.56, p = 0.02).

Conclusion

Motor symptoms, as well as pain, sleep disturbances, and fatigue in CD showed a significant relationship with SERT binding in the raphe nuclei. Moreover, fatigue showed a significant relationship with the medial raphe nucleus and sleep disorders with the caudate nucleus and hippocampus. These findings suggest that an altered serotonergic signaling in different brain areas in CD is related to different motor as well as NMS, which will further stimulate research on the role of serotonin in the pathogenesis of dystonia.

Steroid hormones affect binding of the sigma ligand 11C-SA4503 in tumour cells and tumour-bearing rats

Purpose

Sigma receptors are implicated in memory and cognitive functions, drug addiction, depression and schizophrenia. In addition, sigma receptors are strongly overexpressed in many tumours. Although the natural ligands are still unknown, steroid hormones are potential candidates. Here, we examined changes in binding of the sigma-1 agonist ¹¹C-SA4503 in C6 glioma cells and in living rats after modification of endogenous steroid levels.

Methods

¹¹C-SA4503 binding was assessed in C6 monolayers by gamma counting and in anaesthetized rats by microPET scanning. C6 cells were either repeatedly washed and incubated in steroid-free medium or exposed to five kinds of exogenous steroids (1 h or 5 min before tracer addition, respectively). Tumour-bearing male rats were repeatedly treated with pentobarbital (a condition known to result in reduction of endogenous steroid levels) or injected with progesterone.

Results

Binding of ¹¹C-SA4503 to C6 cells was increased (~50%) upon removal and decreased (~60%) upon addition of steroid hormones (rank order of potency: progesterone > allopregnanolone = testosterone = androstanolone > dehydroepiandrosterone-3-sulphate, IC₅₀ progesterone 33 nM). Intraperitoneally administered progesterone reduced tumour uptake and tumour-to-muscle contrast (36%). Repeated treatment of animals with pentobarbital increased the PET standardized uptake value of ¹¹C-SA4503 in tumour (16%) and brain (27%), whereas the kinetics of blood pool radioactivity was unaffected.

Conclusions

The binding of ¹¹C-SA4503 is sensitive to steroid competition. Since not only increases but also decreases of steroid levels affect ligand binding, a considerable fraction of the sigma-1 receptor population in cultured tumour cells or tumour-bearing animals is normally occupied by endogenous steroids.