Prediction of response to lomustine-based chemotherapy in glioma patients at recurrence using MRI and FET PET

BACKGROUND

We evaluated O-(2-[18F]fluoroethyl)-l-tyrosine (FET) PET and MRI for early response assessment in recurrent glioma patients treated with lomustine-based chemotherapy.

METHODS

Thirty-six adult patients with WHO CNS grade 3 or 4 gliomas (glioblastoma, 69%) at recurrence (median number of recurrences, 1; range, 1-3) were retrospectively identified. Besides MRI, serial FET PET scans were performed at baseline and early after chemotherapy initiation (not later than two cycles). Tumor-to-brain ratios (TBR), metabolic tumor volumes (MTV), the occurrence of new distant hotspots with a mean TBR >1.6 at follow-up, and the dynamic parameter time-to-peak were derived from all FET PET scans. PET parameter thresholds were defined using ROC analyses to predict PFS of ≥6 months and OS of ≥12 months. MRI response assessment was based on RANO criteria. The predictive values of FET PET parameters and RANO criteria were subsequently evaluated using univariate and multivariate survival estimates.

RESULTS

After treatment initiation, the median follow-up time was 11 months (range, 3-71 months). Relative changes of TBR, MTV, and RANO criteria predicted a significantly longer PFS (all P ≤ .002) and OS (all P ≤ .045). At follow-up, the occurrence of new distant hotspots (n ≥ 1) predicted a worse outcome, with significantly shorter PFS (P = .005) and OS (P < .001). Time-to-peak changes did not predict a significantly longer survival. Multivariate survival analyses revealed that new distant hotspots at follow-up FET PET were most potent in predicting non-response (P < .001; HR, 8.578).

CONCLUSIONS

Data suggest that FET PET provides complementary information to RANO criteria for response evaluation of lomustine-based chemotherapy early after treatment initiation.

Differentiation of a Falcine Meningioma From Cerebral Venous Sinus Thrombosis Using DOTATATE PET

ABSTRACT

Differentiating brain tumors from nonneoplastic lesions using conventional MRI may be challenging. Clinical symptoms often remain unspecific, and imaging findings from MRI may be inconclusive. We present the case of a 23-year-old woman in whom an MRI suggested a cerebral venous sinus thrombosis. On the other hand, additional atypical MRI findings raised doubts regarding the initial diagnosis. Given the need for a diagnostic procedure with higher sensitivity and specificity for neoplastic tissue, PET with the radiolabeled somatostatin receptor ligand DOTATATE ( 68 Ga-DOTA- d -Phe1-Tyr3-octreotate) was performed. DOTATATE PET facilitated the diagnosis of a falcine meningioma consistent with its value for the differential diagnosis of meningioma.

Advances in PET imaging for meningioma patients

In patients with meningioma, diagnosis and treatment planning are predominantly based on anatomical imaging using MRI or CT. Constraints of these imaging modalities include precise meningioma delineation-especially at the skull base, in the case of trans-osseus growth, and in tumors with complex geometry-and the differentiation of post-therapeutic reactive changes from meningioma relapse. Advanced metabolic imaging using PET may help to characterize specific metabolic and cellular features providing additional information beyond the information derived from anatomical imaging alone. Accordingly, the use of PET in meningioma patients is steadily increasing. This review summarizes recent advances in PET imaging helpful for improving the clinical management of patients with meningioma.

Endoscopic vacuum therapy significantly improves clinical outcomes of anastomotic leakages after 2-stage, 3-stage, and transhiatal esophagectomies

BACKGROUND

Anastomotic leakages after esophagectomies continue to constitute significant morbidity and mortality. Intrathoracic anastomoses pose a high risk for mediastinitis, sepsis, and death, if a leak is not addressed timely and appropriately. However, there are no standardized treatment recommendations or algorithms as for how to treat these leakages.

METHODS

The study included all patients at the University Hospital Regensburg, who developed an anastomotic leakage after esophagectomy with gastric pull-up reconstruction from 2007 to 2022. Patients receiving conventional treatment options for an anastomotic leakage (stents, drainage tubes, clips, etc.) were compared to patients receiving endoscopic vacuum-assisted closure (eVAC) therapy as their mainstay of treatment. Treatment failure was defined as cervical esophagostomy formation or death.

RESULTS

In total, 37 patients developed an anastomotic leakage after esophagectomy with a gastric pull-up reconstruction. Twenty patients were included into the non-eVAC cohort, whereas 17 patients were treated with eVAC. Treatment failure was observed in 50% of patients (n = 10) in the non-eVAC cohort and in 6% of patients (n = 1) in the eVAC cohort (p < 0.05). The 90-day mortality in the non-eVAC cohort was 15% (n = 3) compared to 6% (n = 1) in the eVAC cohort. Cervical esophagostomy formation was required in 40% of cases (n = 8) in the non-eVAC cohort, whereas no patient in the eVAC cohort underwent cervical esophagostomy formation.

CONCLUSION

eVAC therapy for leaking esophagogastric anastomoses appears to be superior to other treatment strategies as it significantly reduces morbidity and mortality. Therefore, we suggest eVAC as an essential component in the treatment algorithm for anastomotic leakages following esophagectomies, especially in patients with intrathoracic anastomoses.

Clinical applications and prospects of PET imaging in patients with IDH-mutant gliomas

PET imaging using radiolabeled amino acids in addition to MRI has become a valuable diagnostic tool in the clinical management of patients with brain tumors. This review provides a comprehensive overview of PET studies in glioma patients with a mutation in the isocitrate dehydrogenase gene (IDH). A considerable fraction of these tumors typically show no contrast enhancement on MRI, especially when classified as grade 2 according to the World Health Organization classification of Central Nervous System tumors. Major diagnostic challenges in this situation are differential diagnosis, target definition for diagnostic biopsies, delineation of glioma extent for treatment planning, differentiation of treatment-related changes from tumor progression, and the evaluation of response to alkylating agents. The main focus of this review is the role of amino acid PET in this setting. Furthermore, in light of clinical trials using IDH inhibitors targeting the mutated IDH enzyme for treating patients with IDH-mutant gliomas, we also aim to give an outlook on PET probes specifically targeting the IDH mutation, which appear potentially helpful for response assessment.

CTNI-07. LOMUSTINE/TEMOZOLOMIDE CHEMOTHERAPY FOR NEWLY DIAGNOSED MGMT-METHYLATED IDHWT GLIOBLASTOMA ACCORDING TO CETEG/NOA-09: REAL-WORLD EXPERIENCE IN A MULTICENTER COHORT

INTRODUCTION

The CeTeG/NOA-09 trial demonstrated superior median overall survival (mOS, 48.1 months) in MGMT-methylated glioblastoma treated with lomustine/temozolomide compared to temozolomide. We retrospectively analyzed an off-study cohort of patients treated with lomustine/temozolomide to gather real-world data on this new regimen.

METHODS

Adult patients from 20 centers in Germany, Austria and Switzerland were included. Inclusion criteria were MGMT-methylated IDHwt glioblastoma newly diagnosed prior to end of 2020, and lomustine/temozolomide treatment as part of first-line therapy.

RESULTS

321 patients with a median age of 57 years (range, 21-78) and a median follow-up of 19.9 months were included. In the whole cohort, mOS was 41.0 months (95%CI, 33.0 – not reached). In patients starting lomustine/temozolomide immediately upon initiation of radiotherapy strictly following the CeTeG protocol (88%), mOS was 52.8 months (35.8 – not reached) as compared to 24.6 months (17.6 – not reached) in patients starting lomustine/temozolomide after completion of radiotherapy/concomitant temozolomide (12%, logrank test: p = 0.06). Patients with a KPS &lt; 80 had a shorter mOS of 19.7 months (95%CI, 16.6 – not reached) compared to 41.0 months (33.0 – not reached, p = 0.009) in KPS 80-100. Gross total resection (GTR, 53.9%) was associated with longer mOS (52.8 months, 95%CI 24.1 – not reached) compared to partial resection/biopsy (30.5 months, 95%CI 36.8 – not reached, p=0.004). Multivariable Cox regression analysis confirmed GTR (HR 0.66, p = 0.033) and younger age ( ≤ 50 years: HR 0.42, p = 0.001), but not KPS (80-100 vs. lower: HR 0.66, p = 0.12) as independent prognostic factors.

DISCUSSION

In this real-world multicenter cohort, survival was similar to the promising results of CeTeG/NOA-09. Further analyses should investigate a potentially reduced benefit from lomustine/temozolomide in patients with low KPS/no GTR and a possible detrimental effect from deferred lomustine/temozolomide initiation. The median follow-up is admittedly short, updated data will be presented.

NIMG-27. THE PROGNOSTIC VALUE OF FET PET IN PATIENTS WITH RECURRENT GLIOMA TREATED WITH BEVACIZUMAB

BACKGROUND

After multiple recurrences in glioma patients, bevacizumab is frequently used as salvage therapy. In this group of patients, we evaluated the prognostic value of amino acid PET using O-(2-[18F]fluoroethyl)-L-tyrosine (FET) before initiation of bevacizumab.

METHODS

We retrospectively identified adult glioma patients at recurrence with (i) at least one or more previous recurrences, (ii) who were treated with bevacizumab, and (iii) who underwent FET PET imaging before bevacizumab initiation. Maximum and mean tumor-to-brain ratios (TBRmax, TBRmean), metabolic tumor volume (MTV), and dynamic parameters (i.e., time-to-peak, slope) were obtained from FET PET. Additionally, contrast-enhancing volumes on MRI were calculated. Threshold values of imaging parameters for evaluating the prognosis were established by ROC analyses using overall survival (OS) of ≥ 6 months as reference. The prognostic value of imaging parameters was subsequently evaluated using the log-rank test and multiple logistic regression analyses.

RESULTS

Twenty-eight patients (glioblastoma, 96%) with a median of 2 recurrences (range, 1-5) were eligible for data evaluation. The patients received a median number of 7 bevacizumab cycles (range, 1-27). The static FET PET parameter TBRmean was the best parameter (threshold, 2.1; AUC, 0.78; P=0.014) to identify patients with a significantly longer OS (8.2 vs. 4.9 months; P=0.044). In contrast, the MTV, contrast-enhancing volume, and dynamic FET PET parameters were not significant. TBRmean remained significant in multiple logistic regression analysis (P=0.031), indicating an independent predictor for OS.

CONCLUSION

Our data suggest that static FET PET allows identifying patients with longer OS before initiation of bevacizumab.

NIMG-83. MULTIMODAL PET/MRI RADIOMICS AND CLINICAL PARAMETERS FOR OVERALL SURVIVAL PREDICTION IN PATIENTS WITH IDH WILDTYPE GLIOBLASTOMA

BACKGROUND

Currently, most radiomics studies on survival prediction in brain tumor patients are based on MRI only. The goal of our study was to evaluate multimodal radiomics derived from amino acid PET/MRI and clinical parameters for survival prediction in patients with newly diagnosed IDH wildtype glioblastoma.

METHODS

Sixty-three patients with newly diagnosed IDH wildtype glioblastoma were evaluated retrospectively. At initial diagnosis, all patients underwent structural MRI and O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET. Tumor volumes were automatically segmented using a deep learning-based tool followed by visual inspection. Predefined and deep radiomics features were extracted from both imaging modalities. Feature repeatability analyses and feature selection were performed to avoid overfitting. Cox regression models for overall survival were built from clinical parameters such as age or the extent of resection, radiomics features, and combinations thereof, and finally validated using 5-fold cross-validation. Further evaluation of the model in an external test dataset is ongoing.

RESULTS

The median overall survival was 12 months (range, 0-64 months). Higher age and larger FET PET tumor volumes were significantly correlated with shorter overall survival (age, r=-0.39, p&lt; 0.001; volume, r=-0.31, p&lt; 0.05). Models solely based on predefined FET PET or MRI radiomics features showed a similar mean concordance index (C-index) as the model based on clinical parameters (C-indices, 0.68±0.04; 0.64±0.03; and 0.69±0.08, respectively). Multimodal radiomics based on predefined and deep features yielded improved C-indices of 0.75±0.06 and 0.72±0.09, respectively. A model based on multimodal radiomics and clinical parameters achieved the best prognostic performance (C-index, 0.80±0.04).

CONCLUSION

Our results suggest an added clinical value of multimodal FET PET/MRI radiomics with clinical parameters for the non-invasive survival prediction in patients with IDH wildtype glioblastoma.

NIMG-84. PREDICTION OF RESPONSE TO LOMUSTINE-BASED CHEMOTHERAPY IN GLIOMA PATIENTS AT RECURRENCE USING MRI AND FET PET

BACKGROUND

This study evaluates O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET and contrast-enhanced MRI for early response assessment in glioma patients at recurrence treated with lomustine-based chemotherapy.

METHODS

Thirty-six adult patients with WHO CNS Grade 3 or 4 gliomas (glioblastoma, 69%) at recurrence (median number of recurrences, 1; range, 1-3) were retrospectively identified. Besides MRI, serial FET PET scans were performed at baseline and early after chemotherapy initiation (median number of cycles, 2). Mean and maximum tumor-to-brain ratios (TBR), metabolic tumor volumes (MTV), the occurrence of new distant hotspots with a mean TBR &gt; 1.6 at follow-up, and the dynamic parameter time-to-peak were derived from all FET PET scans. Threshold values of PET parameters were defined using receiver operating characteristic analyses to predict progression-free survival (PFS) of ≥ 6 months and overall survival (OS) of ≥ 12 months. MRI response assessment was based on RANO criteria. Using univariate and multivariate survival estimates, the predictive value of FET PET parameters and RANO criteria were subsequently evaluated.

RESULTS

After treatment initiation, the median follow-up time was 11 months (range, 3-71 months). Relative changes of the mean and maximum TBR, MTV, and RANO criteria predicted a significantly longer PFS (all P&lt; 0.003) and OS (all P&lt; 0.05). At follow-up, the occurrence of new distant hotspots (n≥ 1) predicted a worse outcome, with significantly shorter PFS (P=0.001) and OS (P&lt; 0.001). Changes of the dynamic parameter time-to-peak did not predict a significantly longer PFS or OS (P &gt; 0.05). Multivariate survival analyses revealed that new distant hotspots at follow-up had the highest significance level to predict non-response (P&lt; 0.001; hazard ratio, 8.578), independent of RANO criteria, IDH mutation status, and O6-methylguanine-DNA-methyltransferase promoter methylation.

CONCLUSIONS

FET PET seems to be a powerful tool for identifying responders to lomustine-based chemotherapy early after treatment initiation.

An updated review on the diagnosis and assessment of post-treatment relapse in brain metastases using PET

INTRODUCTION

Brain metastases in patients with extracranial cancer are typically associated with increased morbidity and mortality. Stereotactic radiotherapy and immunotherapy using checkpoint inhibitors currently are essential in brain metastases treatment. Since conventional contrast-enhanced MRI alone cannot reliably differentiate between treatment-induced changes and brain metastasis relapse, several studies investigated the role of PET imaging and, more recently, radiomics, based on routinely acquired PET images, to overcome this clinically relevant challenge.

AREAS COVERED

The current literature on PET imaging, including radiomics, in patients with brain metastases, focusing on the diagnosis and assessment of post-treatment relapse, is summarized.

EXPERT OPINION

Available data suggest that imaging parameters, including radiomics features, mainly derived from amino acid PET, are helpful for diagnosis and assessment of post-treatment relapse in patients with brain metastases.

Efficacy and tolerability of regorafenib in pretreated patients with progressive CNS grade 3 or 4 gliomas

Background

The phase 2 REGOMA trial suggested an encouraging overall survival benefit in glioblastoma patients at first relapse treated with the multikinase inhibitor regorafenib. Here, we evaluated the efficacy and side effects of regorafenib in a real-life setting.

Methods

From 2018 to 2021, 30 patients with progressive WHO CNS grade 3 or 4 gliomas treated with regorafenib (160 mg/day; first 3 weeks of each 4-week cycle) with individual dose adjustment depending on toxicity were retrospectively identified. Side effects were evaluated according to the Common Terminology Criteria for Adverse Events (version 5.0). MRI was obtained at baseline and after every second cycle. Tumor progression was assessed according to RANO criteria. After regorafenib initiation, the median PFS and OS were calculated.

Results

The median number of treatment lines before regorafenib was 2 (range 1–4). Most patients (73%) had two or more pretreatment lines. At first relapse, 27% of patients received regorafenib. A total of 94 regorafenib cycles were administered (median 2 cycles; range 1–9 cycles). Grade 3 and 4 side effects were observed in 47% and 7% of patients, respectively, and were not significantly increased in patients with two or more pretreatments (P > 0.05). The most frequent grade 3 or 4 side effects were laboratory abnormalities (62%). PFS was 2.6 months (range 0.8–8.2 months), and the OS was 6.2 months (range 0.9–24 months).

Conclusions

In patients with progressive WHO grade 3 or 4 gliomas, predominantly with two pretreatment lines or more, regorafenib seems to be effective despite considerable grade 3 or 4 side effects.

Oncologic Outcome and Immune Responses of Radiotherapy with Anti-PD-1 Treatment for Brain Metastases Regarding Timing and Benefiting Subgroups

While immune checkpoint inhibitors (ICIs) in combination with radiotherapy (RT) are widely used for patients with brain metastasis (BM), markers that predict treatment response for combined RT and ICI (RT-ICI) and their optimal dosing and sequence for the best immunogenic effects are still under investigation. The aim of this study was to evaluate prognostic factors for therapeutic outcome and to compare effects of concurrent and non-concurrent RT-ICI. We retrospectively analyzed data of 93 patients with 319 BMs of different cancer types who received PD-1 inhibitors and RT at the University Hospital Cologne between September/2014 and November/2020. Primary study endpoints were overall survival (OS), progression-free survival (PFS), and local control (LC). We included 66.7% melanoma, 22.8% lung, and 5.5% other cancer types with a mean follow-up time of 23.8 months. Median OS time was 12.19 months. LC at 6 months was 95.3% (concurrent) vs. 69.2% (non-concurrent; p = 0.008). Univariate Cox regression analysis detected following prognostic factors for OS: neutrophil-to-lymphocyte ratio NLR favoring <3 (low; HR 2.037 (1.184−3.506), p = 0.010), lactate dehydrogenase (LDH) favoring ≤ULN (HR 1.853 (1.059−3.241), p = 0.031), absence of neurological symptoms (HR 2.114 (1.285−3.478), p = 0.003), RT concept favoring SRS (HR 1.985 (1.112−3.543), p = 0.019), RT dose favoring ≥60 Gy (HR 0.519 (0.309−0.871), p = 0.013), and prior anti-CTLA4 treatment (HR 0.498 (0.271−0.914), p = 0.024). Independent prognostic factors for OS were concurrent RT-ICI application (HR 0.539 (0.299−0.971), p = 0.024) with a median OS of 17.61 vs. 6.83 months (non-concurrent), ECOG performance status favoring 0 (HR 7.756 (1.253−6.061), p = 0.012), cancer type favoring melanoma (HR 0.516 (0.288−0.926), p = 0.026), BM volume (PTV) favoring ≤3 cm3 (HR 1.947 (1.007−3.763), p = 0.048). Subgroups with the following factors showed significantly longer OS when being treated concurrently: RT dose <60 Gy (p = 0.014), PTV > 3 cm3 (p = 0.007), other cancer types than melanoma (p = 0.006), anti-CTLA4-naïve patients (p < 0.001), low NLR (p = 0.039), steroid intake ≤4 mg (p = 0.042). Specific immune responses, such as abscopal effects (AbEs), pseudoprogression (PsP), or immune-related adverse events (IrAEs), occurred more frequently with concurrent RT-ICI and resulted in better OS. Other toxicities, including radionecrosis, were not statistically different in both groups. The concurrent application of RT and ICI, the ECOG-PS, cancer type, and PTV had an independently prognostic impact on OS. In concurrently treated patients, treatment response (LC) was delayed and specific immune responses (AbE, PsP, IrAE) occurred more frequently with longer OS rates. Our results suggest that concurrent RT-ICI application is more beneficial than sequential treatment in patients with low pretreatment inflammatory status, more and larger BMs, and with other cancer types than melanoma.

Use of advanced neuroimaging and artificial intelligence in meningiomas

Anatomical cross‐sectional imaging methods such as contrast‐enhanced MRI and CT are the standard for the delineation, treatment planning, and follow‐up of patients with meningioma. Besides, advanced neuroimaging is increasingly used to non‐invasively provide detailed insights into the molecular and metabolic features of meningiomas. These techniques are usually based on MRI, e.g., perfusion‐weighted imaging, diffusion‐weighted imaging, MR spectroscopy, and positron emission tomography. Furthermore, artificial intelligence methods such as radiomics offer the potential to extract quantitative imaging features from routinely acquired anatomical MRI and CT scans and advanced imaging techniques. This allows the linking of imaging phenotypes to meningioma characteristics, e.g., the molecular‐genetic profile. Here, we review several diagnostic applications and future directions of these advanced neuroimaging techniques, including radiomics in preclinical models and patients with meningioma.

Case Report: Detection of Symptomatic Treatment-Related Changes in a Patient With Anaplastic Oligodendroglioma Using FET PET

Following local and systemic treatment of gliomas, the differentiation between glioma relapse and treatment-related changes such as pseudoprogression or radiation necrosis using conventional MRI is limited. To overcome this limitation, various amino acid PET tracers such as O-[2-(¹⁸F)-fluoroethyl]-L-tyrosine (FET) are increasingly used and provide valuable additional clinical information. We here report neuroimaging findings in a clincally symptomatic 53-year-old woman with a recurrent anaplastic oligodendroglioma with MRI findings highly suspicious for tumor progression. In contrast, FET PET imaging suggested treatment-related changes considerably earlier than the regression of contrast enhancement on MRI. In patients with oligodendroglioma, the phenomenon of symptomatic treatment-related changes is not well described, making these imaging findings unique and important for clinical decision-making.

NIMG-27. REGORAFENIB RESPONSE ASSESSMENT USING FET PET IN PATIENTS WITH PROGRESSIVE GLIOMA

BACKGROUND

The REGOMA phase 2 trial showed an encouraging overall survival benefit of the multikinase inhibitor regorafenib in glioblastoma patients at first progression. We used O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET for the early assessment of response to regorafenib in patients with progressive glioma in an advanced disease stage.

METHODS

Thirty patients with progressive glioma were treated according to the REGOMA trial and prospectively followed. FET PET and MRI were performed at baseline and after the second cycle of regorafenib. Static PET parameters such as maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) and metabolic tumor volumes (MTV) were calculated. Threshold values of FET PET parameters to predict a response were established by ROC analyses using an overall survival of ≥ 6 months as reference. The predictive value of FET PET parameters and their changes concerning overall survival was subsequently evaluated using the Kaplan-Meier test. MRI changes were evaluated according to the RANO criteria.

RESULTS

Up to now, 18 of 30 patients (glioblastoma, 83%; age range, 24-71 years) were eligible for data evaluation. The median number of tumor relapses before regorafenib was 2 (range, 1-4). During regorafenib (median cycles, 4; range, 2-9 cycles), CTCAE grade 3 or 4 side effects occurred in 56% and 11%, respectively. The median overall survival was 6 months (range, 3-18 months). After two cycles of regorafenib, a TBRmean reduction of 13% predicted a significantly longer overall survival (12 vs. 6 months; P=0.034). In contrast, MRI changes evaluated according to RANO criteria (i.e., Stable Disease or Partial Response vs. Progressive Disease) were not predictive (11 vs. 8 months; P=0.644).

CONCLUSION

Data suggest that amino acid PET using the tracer FET may be clinically valuable for identifying responders to regorafenib early after treatment initiation.

Prognostic value of pre-irradiation FET PET in patients with not completely resectable IDH-wildtype glioma and minimal or absent contrast enhancement

In glioma patients, complete resection of the contrast-enhancing portion is associated with improved survival, which, however, cannot be achieved in a considerable number of patients. Here, we evaluated the prognostic value of O-(2-[¹⁸F]-fluoroethyl)-L-tyrosine (FET) PET in not completely resectable glioma patients with minimal or absent contrast enhancement before temozolomide chemoradiation. Dynamic FET PET scans were performed in 18 newly diagnosed patients with partially resected (n = 8) or biopsied (n = 10) IDH-wildtype astrocytic glioma before initiation of temozolomide chemoradiation. Static and dynamic FET PET parameters, as well as contrast-enhancing volumes on MRI, were calculated. Using receiver operating characteristic analyses, threshold values for which the product of paired values for sensitivity and specificity reached a maximum were obtained. Subsequently, the prognostic values of FET PET parameters and contrast-enhancing volumes on MRI were evaluated using univariate Kaplan–Meier and multivariate Cox regression (including the MTV, age, MGMT promoter methylation, and contrast-enhancing volume) survival analyses for progression-free and overall survival (PFS, OS). On MRI, eight patients had no contrast enhancement; the remaining patients had minimal contrast-enhancing volumes (range, 0.2–5.3 mL). Univariate analyses revealed that smaller pre-irradiation FET PET tumor volumes were significantly correlated with a more favorable PFS (7.9 vs. 4.2 months; threshold, 14.8 mL; P = 0.012) and OS (16.6 vs. 9.0 months; threshold, 23.8 mL; P = 0.002). In contrast, mean tumor-to-brain ratios and time-to-peak values were only associated with a longer PFS (P = 0.048 and P = 0.045, respectively). Furthermore, the pre-irradiation FET PET tumor volume remained significant in multivariate analyses (P = 0.043), indicating an independent predictor for OS. Our results suggest that pre-irradiation FET PET parameters have a prognostic impact in this subgroup of patients.

P14.41 Cost-effectiveness of FET PET for early treatment response assessment in glioma patients following adjuvant temozolomide chemotherapy

BACKGROUND

In light of increasing healthcare costs, higher medical expenses should be justified socio-economically. Therefore, we calculated the effectiveness and cost-effectiveness of PET using the radiolabeled amino acid O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) compared to conventional MRI for early identification of responders to adjuvant temozolomide chemotherapy. A recent study in IDH-wildtype glioma patients suggested that after two cycles, FET-PET parameter changes predicted a significantly longer survival while MRI changes were not significant.

MATERIALS AND METHODS

To determine the effectiveness and cost-effectiveness of serial FET-PET imaging, we analyzed published clinical data and calculated the associated costs in the context of the German healthcare system.Based on a decision-tree model, FET-PET and MRI’s effectiveness was calculated, i.e., the probability to correctly identify a responder as defined by an overall survival ≥15 months. To determine the cost-effectiveness, the incremental cost-effectiveness ratio (ICER) was calculated, i.e., the cost for each additionally identified responder by FET-PET who would have remained undetected by MRI. The robustness of the results was tested by deterministic and probabilistic (Monte Carlo simulation) sensitivity analyses.

RESULTS

Compared to MRI, FET-PET increases the rate of correctly identified responders to chemotherapy by 26%; thus, four patients need to be examined by FET-PET to identify one additional responder. Considering the respective cost for serial FET-PET and MRI, the ICER resulted in €4,396.83 for each additional correctly identified responder by FET-PET. The sensitivity analyses confirmed the robustness of the results.

CONCLUSION

In contrast to conventional MRI, the model suggests that FET PET is cost-effective in terms of ICER values. Concerning the high cost of temozolomide, the integration of FET-PET has the potential to avoid premature chemotherapy discontinuation at a reasonable cost.

Uncovering an Optic Nerve Sheath Meningioma Using 68Ga-DOTATATE PET/CT

ABSTRACT

A 56-year-old woman was initially diagnosed with optic neuritis. However, several "red flags" were present: older age at presentation, no multiple sclerosis suspicious findings on MRI, and negative oligoclonal bands. 68Ga-DOTATATE PET/CT confirmed the differential diagnosis of an optic sheath meningioma. Our case stresses the value of the somatostatin receptor ligand PET/CT in patients with suspected optic neuritis if the diagnostic workup does not support immune-mediated pathogenesis.

Diagnosis of Pseudoprogression Following Lomustine-Temozolomide Chemoradiation in Newly Diagnosed Glioblastoma Patients Using FET-PET

PURPOSE

The CeTeG/NOA-09 phase III trial demonstrated a significant survival benefit of lomustine-temozolomide chemoradiation in patients with newly diagnosed glioblastoma with methylated O⁶-methylguanine-DNA methyltransferase (MGMT) promoter. Following lomustine-temozolomide chemoradiation, late and prolonged pseudoprogression may occur. We here evaluated the value of amino acid PET using O-(2-[¹⁸F]fluoroethyl)-l-tyrosine (FET) for differentiating pseudoprogression from tumor progression.

EXPERIMENTAL DESIGN

We retrospectively identified patients (i) who were treated off-study according to the CeTeG/NOA-09 protocol, (ii) had equivocal MRI findings after radiotherapy, and (iii) underwent additional FET-PET imaging for diagnostic evaluation (number of scans, 1-3). Maximum and mean tumor-to-brain ratios (TBR_max, TBR_mean) and dynamic FET uptake parameters (e.g., time-to-peak) were calculated. In patients with more than one FET-PET scan, relative changes of TBR values were evaluated, that is, an increase or decrease of >10% compared with the reference scan was considered as tumor progression or pseudoprogression. Diagnostic performances were evaluated using ROC curve analyses and Fisher exact test. Diagnoses were confirmed histologically or clinicoradiologically.

RESULTS

We identified 23 patients with 32 FET-PET scans. Within 5-25 weeks after radiotherapy (median time, 9 weeks), pseudoprogression occurred in 11 patients (48%). The parameter TBR_mean calculated from the FET-PET performed 10 ± 7 days after the equivocal MRI showed the highest accuracy (87%) to identify pseudoprogression (threshold, <1.95; P = 0.029). The integration of relative changes of TBR_mean further improved the accuracy (91%; P < 0.001). Moreover, the combination of static and dynamic parameters increased the specificity to 100% (P = 0.005).

CONCLUSIONS

The data suggest that FET-PET parameters are of significant clinical value to diagnose pseudoprogression related to lomustine-temozolomide chemoradiation.

Imaging challenges of immunotherapy and targeted therapy in patients with brain metastases: response, progression, and pseudoprogression

The advent of immunotherapy using immune checkpoint inhibitors (ICIs) and targeted therapy (TT) has dramatically improved the prognosis of various cancer types. However, following ICI therapy or TT-either alone (especially ICI) or in combination with radiotherapy-imaging findings on anatomical contrast-enhanced MRI can be unpredictable and highly variable, and are often difficult to interpret regarding treatment response and outcome. This review aims at summarizing the imaging challenges related to TT and ICI monotherapy as well as combined with radiotherapy in patients with brain metastases, and to give an overview on advanced imaging techniques which potentially overcome some of these imaging challenges. Currently, major evidence suggests that imaging parameters especially derived from amino acid PET, perfusion-/diffusion-weighted MRI, or MR spectroscopy may provide valuable additional information for the differentiation of treatment-induced changes from brain metastases recurrence and the evaluation of treatment response.

Feature-based PET/MRI radiomics in patients with brain tumors

Radiomics allows the extraction of quantitative features from medical images such as CT, MRI, or PET, thereby providing additional, potentially relevant diagnostic information for clinical decision-making. Because the computation of these features is performed highly automated on medical images acquired during routine follow-up, radiomics offers this information at low cost. Further, the radiomics features can be used alone or combined with other clinical or histomolecular parameters to generate predictive or prognostic mathematical models. These models can then be applied for various important diagnostic indications in neuro-oncology, for example, to noninvasively predict relevant biomarkers in glioma patients, to differentiate between treatment-related changes and local brain tumor relapse, or to predict treatment response. In recent years, amino acid PET has become an important diagnostic tool in patients with brain tumors. Therefore, the number of studies in patients with brain tumors investigating the potential of PET radiomics or combined PET/MRI radiomics is steadily increasing. This review summarizes current research regarding feature-based PET as well as combined PET/MRI radiomics in neuro-oncology.

FET PET Radiomics for Differentiating Pseudoprogression from Early Tumor Progression in Glioma Patients Post-Chemoradiation

Simple Summary

Following chemoradiation with alkylating agents in glioma patients, structural magnetic resonance imaging (MRI) may suggest tumor progression which subsequently improves during the course of the disease without any treatment change. This phenomenon has been termed pseudoprogression. Despite advances in medical imaging, a reliable diagnosis of pseudoprogression remains a challenging task. Radiomics is a subdiscipline of artificial intelligence and allows the identification and extraction of imaging features from various routine imaging modalities. These features can be used for the generation of mathematical models to improve diagnostics in patients with brain tumors. The present study highlights the potential of radiomics obtained from amino acid positron emission tomography (PET) for the diagnosis of pseudoprogression. In 34 patients with suspicious MRI early after chemoradiation completion, our radiomics model correctly identified all patients with pseudoprogression.

Abstract

Currently, a reliable diagnostic test for differentiating pseudoprogression from early tumor progression is lacking. We explored the potential of O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) positron emission tomography (PET) radiomics for this clinically important task. Thirty-four patients (isocitrate dehydrogenase (IDH)-wildtype glioblastoma, 94%) with progressive magnetic resonance imaging (MRI) changes according to the Response Assessment in Neuro-Oncology (RANO) criteria within the first 12 weeks after completing temozolomide chemoradiation underwent a dynamic FET PET scan. Static and dynamic FET PET parameters were calculated. For radiomics analysis, the number of datasets was increased to 102 using data augmentation. After randomly assigning patients to a training and test dataset, 944 features were calculated on unfiltered and filtered images. The number of features for model generation was limited to four to avoid data overfitting. Eighteen patients were diagnosed with early tumor progression, and 16 patients had pseudoprogression. The FET PET radiomics model correctly diagnosed pseudoprogression in all test cohort patients (sensitivity, 100%; negative predictive value, 100%). In contrast, the diagnostic performance of the best FET PET parameter (TBR_max) was lower (sensitivity, 81%; negative predictive value, 80%). The results suggest that FET PET radiomics helps diagnose patients with pseudoprogression with a high diagnostic performance. Given the clinical significance, further studies are warranted.

NIMG-26. DIAGNOSIS OF PSEUDOPROGRESSION FOLLOWING RADIOTHERAPY PLUS LOMUSTINE-TEMOZOLOMIDE CHEMOTHERAPY IN NEWLY DIAGNOSED GLIOBLASTOMA PATIENTS USING FET PET

BACKGROUND

The CeTeG/NOA-09 trial demonstrated a significant survival benefit of radiotherapy plus lomustine-temozolomide chemotherapy in glioblastoma patients with methylated O6-methylguanine-DNA-methyltransferase (MGMT) promoter compared to standard temozolomide chemoradiation (1). However, data on pseudoprogression following treatment according to the CeTeG/NOA-09 trial is lacking. Due to the limited specificity of conventional MRI we evaluated the value of O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET for the differentiation of pseudoprogression from actual tumor progression.

METHODS

Twenty-one patients with newly diagnosed IDH-wildtype glioblastoma and methylated MGMT promoter with conventional MRI findings suspicious for tumor progression according to RANO criteria (2) after radiotherapy completion were investigated using FET PET. The maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) were calculated. Pseudoprogression was diagnosed neuropathologically or clinicoradiologically (i.e, if (i) a stable clinical course, (ii) stable or improved MRI findings, and (iii) no treatment change occurred within the next six months). Diagnostic performance of FET PET parameters was evaluated using receiver-operating-characteristic (ROC) analyses and Fisher’s exact test. Imaging results were also related to progression-free survival (PFS).

RESULTS

Pseudoprogression was identified in 9 of 21 patients (43%). In the majority of patients (n=8; 89%), pseudoprogression was diagnosed clinicoradiologically. The median time between radiotherapy completion and pseudoprogression was nine weeks (range, 5-25 weeks). ROC analysis yielded an optimal cutoff value of 1.95 for TBRmean to differentiate between pseudoprogression and tumor progression (sensitivity, 89%; specificity, 75%; accuracy, 81%; area under the curve, 0.72±0.13; P = 0.008).

CONCLUSIONS

In a considerable number of patients, pseudoprogression may occur following radiotherapy plus off-study lomustine-temozolomide chemotherapy according to the CeTeG/NOA-09 trial. FET PET appears of value for the differentiation of pseudoprogression from tumor progression in this group of patients. Literature: 1. Herrlinger et al., 2019 Lancet; 2. Wen et al., 2010 J Clin Oncol

NIMG-43. IMAGING FINDINGS FOLLOWING REGORAFENIB IN PATIENTS WITH MALIGNANT GLIOMA: FET PET ADDS VALUABLE INFORMATION TO ANATOMICAL MRI

BACKGROUND

Recent phase 2 data showed that the small molecule regorafenib with antiangiogenic properties has promising effectivity in glioblastoma patients at first progression. Following antiangiogenic therapy with bevacizumab, amino acid PET provides valuable additional diagnostic information regarding bevacizumab-related effects on MRI (e.g., pseudoresponse). In contrast, only a little is known about regorafenib. Thus, we evaluated prospectively the value of O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET for the assessment of regorafenib-related treatment effects.

METHODS

Twenty-two patients with progressive malignant glioma (median number of relapses, 2; range, 1-4) were included. Up to now, 10 of 22 patients were eligible for data evaluation and underwent regorafenib therapy (median number of cycles, 2; range, 1-5 cycles). FET PET and MRI were performed at baseline and after the second cycle. After the second cycle, MRI was performed every 8 weeks. In case of a suspicious MRI after the second cycle, a FET PET scan was added. MRI changes were evaluated according to the RANO criteria. Maximum tumor-to-brain ratios (TBRmax) were calculated. Pseudoresponse was considered if (i) the follow-up MRI showed an improvement (i.e., at least “partial response” according to RANO criteria) despite subsequent clinical progression, and (ii) an increase of TBRmax&gt;25% occurred. Pseudoresponse was confirmed if (i) the subsequent MRI follow-up showed progression, and/or (ii) the clinical status worsened, or the patient died.

RESULTS

In 4 of 10 patients, FET PET provided clinically relevant additional information. In two patients, pseudoresponse could be confirmed. Furthermore, in one patient with stable disease according to MRI, increasing TBRmax (+138%) enabled earlier diagnosis of tumor progression (time benefit, 5 weeks). In another patient without signs of MRI response after 2 cycles, decreasing TBRmax (-23%) indicated metabolic response and was associated with a significant clinical improvement.

CONCLUSIONS

FET PET seems to add valuable diagnostic information for regorafenib therapy monitoring.

NIMG-38. NON-INVASIVE PREDICTION OF MGMT PROMOTER METHYLATION USING COMBINED FET PET/MRI RADIOMICS

BACKGROUND

Recently, the Response Assessment in Neuro-Oncology (RANO) Working Group emphasized the additional diagnostic value of amino acid PET in addition to MRI. However, the number of studies using amino acid PET/MRI radiomics is still low. We investigated the potential of combined O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET/MRI radiomics for the non-invasive prediction of the O6-methylguanine-DNA methyl-transferase (MGMT) promoter methylation status in glioma patients.

METHODS

Seventy-one patients with newly diagnosed glioma (predominantly WHO grade III and IV glioma, 82%) underwent a hybrid FET PET/MRI scan. Forty-six patients (65%) had a methylated MGMT promoter. The tumor and tumor subregions were manually segmented on conventional MRI. In total, 199 standardized features were obtained from FET PET, contrast-enhanced T1-weighted, T2-weighted, and fluid attenuated inversion recovery (FLAIR) MRI. After feature extraction and data normalization, patients were randomly assigned to a training and a test dataset for final model evaluation in a ratio of 70/30, with a balanced distribution of the MGMT promoter methylation status. Feature selection was performed by recursive feature elimination using random forest regressors. For the final model generation, the number of features was limited to seven to avoid data overfitting. Different algorithms for model generation were compared, and the model performance in the training data was assessed by 5-fold cross-validation. Finally, the best performing models were applied to the test dataset to evaluate the robustness of the models.

RESULTS

In the test dataset, the best radiomics signatures obtained from MRI or FET PET alone achieved diagnostic accuracies for the prediction of the MGMT promoter methylation of 64% and 70%, respectively. In contrast, the highest diagnostic accuracy of 83% was obtained by combining FET PET and MRI features.

CONCLUSION

Combined FET PET/MRI radiomics allows the non-invasive prediction of the MGMT promoter methylation status in patients with gliomas, providing more diagnostic information than either modality alone.

Early Treatment Response Assessment Using 18F-FET PET Compared with Contrast-Enhanced MRI in Glioma Patients After Adjuvant Temozolomide Chemotherapy

The goal of this study was to compare the value of contrast-enhanced MRI and O-(2-[¹⁸F]fluoroethyl)-l-tyrosine (¹⁸F-FET) PET for response assessment in glioma patients after adjuvant temozolomide chemotherapy (TMZ). Methods: After biopsy or resection and completion of radiotherapy with concomitant TMZ, 41 newly diagnosed and histomolecularly characterized glioma patients (glioblastoma, 90%; age range, 20-79 y) were subsequently treated with adjuvant TMZ. MR and ¹⁸F-FET PET imaging were performed at baseline and after the second cycle of adjuvant TMZ. We obtained ¹⁸F-FET metabolic tumor volumes (MTVs) as well as mean and maximum tumor-to-brain ratios (TBR_mean and TBR_max, respectively). Threshold values of ¹⁸F-FET PET parameters to predict outcome were established by receiver-operating-characteristic analyses using a median progression-free survival (PFS) of ≥ 9 mo and overall survival (OS) of ≥ 15 mo as reference. MRI response assessment was based on the Response Assessment in Neuro-Oncology (RANO) working group criteria. The predictive value of changes of ¹⁸F-FET PET and MRI parameters on survival was evaluated subsequently using univariate and multivariate survival estimates. Results: After 2 cycles of adjuvant TMZ chemotherapy, a treatment-induced reduction of MTV and TBR_max predicted a significantly longer PFS and OS (both P ≤ 0.03; univariate survival analyses) whereas RANO criteria were not significant (P > 0.05). Multivariate survival analysis revealed that TBR_max changes predicted a prolonged PFS (P = 0.012) and changes of MTV a prolonged OS (P = 0.005) independent of O⁶-methylguanine-DNA-methyltransferase promoter methylation and other strong prognostic factors. Conclusion: Changes of ¹⁸F-FET PET parameters appear to be helpful for identifying responders to adjuvant TMZ early after treatment initiation.

Treatment Monitoring of Immunotherapy and Targeted Therapy Using 18F-FET PET in Patients with Melanoma and Lung Cancer Brain Metastases: Initial Experiences

We investigated the value of O-(2-¹⁸F-fluoroethyl)-l-tyrosine (¹⁸F-FET) PET for treatment monitoring of immune checkpoint inhibition (ICI) or targeted therapy (TT) alone or in combination with radiotherapy in patients with brain metastasis (BM) since contrast-enhanced MRI often remains inconclusive. Methods: We retrospectively identified 40 patients with 107 BMs secondary to melanoma (n = 29 with 75 BMs) or non-small cell lung cancer (n = 11 with 32 BMs) treated with ICI or TT who had ¹⁸F-FET PET (n = 60 scans) for treatment monitoring from 2015 to 2019. Most patients (n = 37; 92.5%) had radiotherapy during the course of the disease. In 27 patients, ¹⁸F-FET PET was used to differentiate treatment-related changes from BM relapse after ICI or TT. In 13 patients, ¹⁸F-FET PET was performed for response assessment to ICI or TT using baseline and follow-up scans (median time between scans, 4.2 mo). In all lesions, static and dynamic ¹⁸F-FET PET parameters were obtained (i.e., mean tumor-to-brain ratios [TBR], time-to-peak values). Diagnostic accuracies of PET parameters were evaluated by receiver-operating-characteristic analyses using the clinical follow-up or neuropathologic findings as a reference. Results: A TBR threshold of 1.95 differentiated BM relapse from treatment-related changes with an accuracy of 85% (P = 0.003). Metabolic responders to ICI or TT on ¹⁸F-FET PET had a significantly longer stable follow-up (threshold of TBR reduction relative to baseline, ≥10%; accuracy, 82%; P = 0.004). Furthermore, at follow-up, time to peak in metabolic responders increased significantly (P = 0.019). Conclusion: ¹⁸F-FET PET may add valuable information for treatment monitoring in BM patients treated with ICI or TT.

32. TREATMENT MONITORING OF IMMUNOTHERAPY AND TARGETED THERAPY USING AMINO ACID PET IN PATIENTS WITH BRAIN METASTASES

PURPOSE

Recently, the RANO group has analyzed the additional diagnostic value of amino acid PET in patients with primary and secondary brain tumors and recommended the use of this imaging technique in addition to conventional MRI. Here, we investigated the value of PET using the radiolabled amino acid O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) for treatment monitoring of immune checkpoint inhibition (ICI) or targeted therapy (TT) alone or in combination with radiotherapy in patients with brain metastases (BM) since contrast-enhanced MRI often remains inconclusive.

METHODS

We retrospectively identified 40 patients with 107 BM secondary to melanoma (n=29 with 75 BM) or non-small cell lung cancer (n=11 with 32 BM) treated with ICI or TT who had FET PET (n=60 scans) for treatment monitoring from 2015–2019. The majority of patients (n=37; 92.5%) had radiotherapy during the course of disease. In 27 patients, FET PET was used for the differentiation of treatment-related changes from BM relapse following ICI or TT. In 13 patients, FET PET was performed for response assessment to ICI or TT using baseline and follow-up scans (median time between scans, 4.2 months). In all lesions, static and dynamic FET PET parameters were obtained (i.e., mean tumour-to-brain ratios (TBR), time-to-peak values). Diagnostic accuracies of PET parameters were evaluated by receiver-operating-characteristic analyses using the clinical follow-up or neuropathological findings as reference.

RESULTS

A TBR threshold of 1.95 differentiated BM relapse from treatment-related changes with an accuracy of 85% (P=0.003). Metabolic Responders to ICI or TT on FET PET had a significantly longer stable follow-up (threshold of TBR reduction relative to baseline, ≥10%; accuracy, 82%; P=0.004). Furthermore, at follow-up, time-to-peak values in metabolic responders increased significantly (P=0.019).

CONCLUSIONS

FET PET may add valuable information for treatment monitoring in BM patients treated with ICI or TT.

Current Landscape and Emerging Fields of PET Imaging in Patients with Brain Tumors

The number of positron-emission tomography (PET) tracers used to evaluate patients with brain tumors has increased substantially over the last years. For the management of patients with brain tumors, the most important indications are the delineation of tumor extent (e.g., for planning of resection or radiotherapy), the assessment of treatment response to systemic treatment options such as alkylating chemotherapy, and the differentiation of treatment-related changes (e.g., pseudoprogression or radiation necrosis) from tumor progression. Furthermore, newer PET imaging approaches aim to address the need for noninvasive assessment of tumoral immune cell infiltration and response to immunotherapies (e.g., T-cell imaging). This review summarizes the clinical value of the landscape of tracers that have been used in recent years for the above-mentioned indications and also provides an overview of promising newer tracers for this group of patients.

Studies on acceptance, evaluation and impact of the Cologne program "Research and Medical Studies"

Introduction: The curricular implementation of events (or programs) for science-related training in human medicine has been on the agenda of the medical faculties since the publication of the Federal-State Working Group [1]. The Medical Faculty of the University of Cologne developed and established a systematic, longitudinal science curriculum together with the start of the model curriculum in human medicine in 2003. Here, we investigate the questions of whether the described (para-) curricular elements are accepted by students and lecturers and how they are evaluated, especially by students. In addition, we investigate whether selected parameters can be used to demonstrate changes in the students' scientific activities. Project description: The program "Research and Medical Studies" (RaMS) consists of several components: these elements of the mandatory curricular (Scientific Projects, SP) and optional components (Research in Medical Studies (RiMS), Research Track (RT), Research Fair Cologne (RFC)) are described here. Results were recorded at various levels: Likert Scale evaluation of the event's elements were collected as satisfaction parameters from the studentsProcess data on participation in the voluntary events were collected and evaluated as absolute and relational figures (WS 12/13-SS 17). Data on the outcome of the RaMS program were collected: Type of scientific projects in the academic years 2011/12-2014/15), number and type of available projects offered at the RFC (in the years 2011-18) and number of student research funding applications in a comparison of the periods 2010-13 vs. 2014-17). Results: The students' acceptance of mandatory and paracurricular courses of the RaMS program is pleasingly high, which is not surprising, at least in the case of the voluntary courses. The participation of students in RiMS, RT and RFC is satisfactory for voluntary courses. In the case of the RT, with certified participation of approximately 47% of all registrations (corresponding to 10% of the total cohort), this is comparable to similar programs. It can be shown that the number of experimental science projects has more than doubled over time in parallel with the development of RaMS. The average number of provided projects according to the RFC is 42 (which corresponds to a placement rate of approx. 1:4). The number of successful student applications for a research support grant during the period the measures were implemented has doubled. Discussion and conclusion: The RaMS program shows a route for the implementation of the SP required by the next licensing regulations in medical education, which was initially supported and expanded solitarily, later by further elements (RiMS), also in the sense of a science-based career development (RT, RFC). The student acceptance and the measured success, in the form of successful participation in the Research Track, increased choice of experimental projects, significant increase of submitted as well as approved research grants and the high project placement rate of the Research Fair, encourage the further development of the program, which is indicated in the conclusion.

Molecular imaging and advanced MRI findings following immunotherapy in patients with brain tumors

Introduction: Currently, immunotherapy using vaccination strategies or oncolytic virus approaches, cell-based immunotherapy, and the blockade of immune checkpoints are under evaluation in patients with brain cancer. Here we summarize clinically significant imaging findings such as treatment-related changes detected by advanced neuroimaging techniques following the most suitable immunotherapy options currently used in neuro-oncology. We, furthermore, provide an overview of how these advanced imaging techniques may help to overcome shortcomings of standard MRI in the assessment and follow-up of patients with brain cancer.Areas covered: The current literature on neuroimaging for immunotherapy in the field of brain tumors, with a focus on gliomas and brain metastases is summarized.Expert commentary: Data suggest that imaging parameters primarily derived from amino acid PET, diffusion- and perfusion-weighted MRI, or MR spectroscopy are particularly helpful for the evaluation of treatment response and provide valuable information for the differentiation of treatment-induced changes from actual brain tumor progression following various immunotherapy approaches.

NIMG-05. THE T2-FLAIR MISMATCH SIGN IN IDH-MUTANT ASTROCYTOMAS - IS THERE AN ASSOCIATION WITH FET PET UPTAKE?

BACKGROUND

The purpose of this study was (i) to assess the reproducibility of the previously described T2-FLAIR mismatch sign as a highly specific MR imaging marker in non-enhancing IDH-mutant, 1p/19q non-codeleted lower-grade gliomas (LGG) of the WHO grades II or III, and (ii) its association with the uptake of the radiolabeled amino acid O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) in PET to further metabolically characterize that sign, which is currently poorly understood.

METHODS

Consecutive MRI and dynamic FET PET scans (n=134) from newly diagnosed and neuropathologically confirmed IDH-mutant LGG (n=65) and IDH-wildtype gliomas as control group (n=69) were evaluated by two independent raters to assess presence/absence of the T2-FLAIR mismatch sign as well as FET uptake. Interrater agreement was assessed using Cohen’s kappa (κ), as well as diagnostic performance (i.e., positive/negative predictive value; PPV, NPV) of the T2-FLAIR mismatch sign to identify IDH-mutant astrocytomas.

RESULTS

In the LGG group, 13 patients (20%) had a T2-FLAIR mismatch sign, which could be identified with a substantial interrater agreement (κ=0.75). In contrast, that sign was absent in IDH-wildtype gliomas. All 13 cases that were positive for the T2/FLAIR mismatch sign were IDH-mutant, 1p/19q non-codeleted tumors (PPV=100%, NPV=57%). Interestingly, compared to IDH-mutant gliomas without the T2-FLAIR mismatch sign, the sign was significantly (P=0.027; 10 of 13 patients) associated with a negative FET PET scan (i.e., 5 tumors with indifferent FET uptake comparable to the background activity, or FET uptake below background activity (photopenic defect) in 5 tumors).

CONCLUSIONS

With a robust interrater agreement, our findings are in line with previously reported findings regarding the T2-FLAIR mismatch sign. Additionally, the T2-FLAIR mismatch sign seems to be significantly related with a lack of increased FET uptake in PET, which may help to further characterize patients with that sign. Notwithstanding, the clinical relevance of this imaging constellation warrants further investigation.

NIMG-46. IMPACT OF FET PET ON MULTIDISCIPLINARY NEUROONCOLOGICAL TUMOR BOARD DECISIONS IN PATIENTS WITH BRAIN TUMORS

BACKGROUND

Following neurooncological treatment of brain tumors, neurooncologists are frequently confronted with equivocal MRI findings (e.g., treatment-related changes, nonmeasurable (speckled) contrast-enhancing lesions, increase of T2/FLAIR signal alterations, pseudoresponse). Especially in Europe, amino acid PET is increasingly being integrated into multidisciplinary neurooncological tumor boards (MNTB) to overcome these diagnostic uncertainties as well as to improve patient management. We here evaluated the correctness of MNTB decisions, in which amino acid PET findings were taken into account.

METHODS

In a single university center, we retrospectively evaluated 114 MNTB decisions concerning 99 patients with malignant glioma (n=81) (glioblastoma, n=54; anaplastic glioma, n=26; gliosarcoma, n=1) or brain metastases (n=18) secondary to NSCLC, melanoma, breast cancer, or colorectral cancer, presenting with equivocal MRI findings following neurooncological treatment. All patients underwent amino acid PET imaging using O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) as an adjunct for decision-making. Additionally, the patients’ clinical status, pretreatment, and multimodal MRI findings were considered for decision-making. Presence of neoplastic tissue in PET was considered if the mean FET uptake as assessed by tumor-to-brain ratios was >2. The decisions’ diagnostic performance was evaluated by 2x2 contingency tables using the neuropathological results or clinicoradiological follow-up.

RESULTS

In the majority of MNTB decisions (n=102; 89%), FET PET results were integrated into the decision-making with considerable impact on the clinical management. In particular, 85% of MNTB decisions (n=87) prompted a treatment change (i.e., resection, radiotherapy, chemotherapy, or combinations thereof, as well as palliative therapy), or, in the case of suspected treatment-related changes, the continuation of the initial treatment regimen (15%; n=15). The MNTB decisions were validated using neuropathological data in 38% (n=39) or clinicoradiological information in 62% (n=63) and yielded a diagnostic accuracy of 88% (sensitivity, 89%; specificity, 75%; P=0.008).

CONCLUSIONS

Our results suggest that the integration of FET PET derived information significantly aids MNTB decisions.

P14.29 Prediction of overall survival in patients with malignant glioma using dynamic O-(2-[18F]-fluoroethyl)-L-tyrosine PET

BACKGROUND

Characterization of gliomas according to the revised World Health Organization (WHO) classification of 2016 has gained major importance regarding prognostication. The present study aimed at exploring the prognostic value of dynamic O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET in newly diagnosed and molecularly defined astrocytic high-grade glioma (HGG) of the WHO grades III or IV.

MATERIAL AND METHODS

Before initiation of treatment, dynamic FET PET imaging was performed in patients with newly diagnosed glioblastoma (GBM) and anaplastic astrocytoma (AA). Static FET PET parameters such as maximum and mean tumor/brain ratios (TBRmax/mean), as well as the dynamic FET PET parameters time-to-peak (TTP) and slope, were obtained. The predictive ability of FET PET parameters was evaluated with regard to the overall survival (OS). Using ROC analyses, threshold values for FET PET parameters were obtained. Subsequently, univariate Kaplan-Meier and multivariate Cox regression survival analyses were performed to assess their predictive power for OS.

RESULTS

Sixty patients (45 GBM, 15 AA) of two university centers were retrospectively identified. Patients with a methylated MGMT promoter as well as with an IDH mutation had a significantly longer OS (both P<0.001). Furthermore, ROC analysis revealed in IDH-wildtype HGG (n=45) that a TTP>25 minutes (AUC, 0.90; sensitivity, 90%; specificity, 87%; P<0.001) was highly prognostic for a longer OS (29 vs. 12 months; P<0.001). Besides a complete resection and a methylated MGMT promoter, TTP remained significant in the multivariate survival analysis (P=0.002, P=0.016, and P=0.003, respectively), indicating an independent predictor for OS. In contrast, both TBRmax and TBRmean were not prognostic (AUC, 0.37 and 0.32, respectively).

CONCLUSION

Data suggest that within the subgroup of patients with newly diagnosed and untreated IDH-wildtype GBM and AA, dynamic FET PET additionally allows the identification of patients with an improved OS.

OTHR-14. TREATMENT MONITORING OF IMMUNOTHERAPY AND TARGETED THERAPY USING FET PET IN PATIENTS WITH MELANOMA AND LUNG CANCER BRAIN METASTASES: INITIAL EXPERIENCES

BACKGROUND: Due to the lack of specificity of contrast-enhanced (CE) MRI, both the response assessment and differentiation of progression from pseudoprogression (PsP) following immunotherapy using checkpoint inhibitors (ICI) or targeted therapy (TT) may be challenging, especially when ICI or TT is applied in combination with radiotherapy (RT). Here, we evaluated the value of amino acid PET using O-(2-[18F]fluoroethyl)-L-tyrosine (FET) as a problem-solving tool in comparison to CE-MRI in patients with brain metastases (BM) secondary to malignant melanoma (MM) and NSCLC. METHODS: We retrospectively identified 31 patients with 74 BM secondary to MM (n=20 with 42 BM) and NSCLC (n=11 with 32 BM) who underwent 52 FET-PET scans during the course of disease. All patients had RT prior to ICI or TT initiation (61%) or RT concurrent to ICI or TT (39%). In 13 patients, FET-PET was performed for treatment response assessment of ICI or TT using baseline and follow-up scans (median time between scans, 4.2 months). In the remaining 18 patients, FET-PET was used for the differentiation of progression from PsP related to RT plus ICI or TT. In all BM, metabolic activity on FET-PET was evaluated by calculation of tumor/brain ratios. FET-PET imaging findings were compared to CE-MRI and correlated to the clinical follow-up or neuropathological findings after neuroimaging. RESULTS: In 4 of 13 patients (31%), FET-PET provided additional information for treatment response evaluation beyond the information provided by CE-MRI alone. Furthermore, responding patients on FET-PET had a median stable clinical follow-up of 10 months. In 10 of 18 patients (56%) with CE-MRI findings suggesting progression, FET-PET detected PsP. In 9 of these 10 patients, PsP was confirmed by a median stable clinical follow-up of 11 months. CONCLUSIONS: FET-PET may add valuable information for treatment monitoring in individual BM patients undergoing RT in combination with ICI or TT.

Differentiation of treatment-related changes from tumour progression: a direct comparison between dynamic FET PET and ADC values obtained from DWI MRI

BACKGROUND

Following brain cancer treatment, the capacity of anatomical MRI to differentiate neoplastic tissue from treatment-related changes (e.g., pseudoprogression) is limited. This study compared apparent diffusion coefficients (ADC) obtained by diffusion-weighted MRI (DWI) with static and dynamic parameters of O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) PET for the differentiation of treatment-related changes from tumour progression.

PATIENTS AND METHODS

Forty-eight pretreated high-grade glioma patients with anatomical MRI findings suspicious for progression (median time elapsed since last treatment was 16 weeks) were investigated using DWI and dynamic FET PET. Maximum and mean tumour-to-brain ratios (TBR_max, TBR_mean) as well as dynamic parameters (time-to-peak and slope values) of FET uptake were calculated. For mean ADC calculation, regions-of-interest analyses were performed on ADC maps calculated from DWI coregistered with the contrast-enhanced MR image. Diagnoses were confirmed neuropathologically (21%) or clinicoradiologically. Diagnostic performance was evaluated using receiver-operating-characteristic analyses or Fisher's exact test for a combinational approach.

RESULTS

Ten of 48 patients had treatment-related changes (21%). The diagnostic performance of FET PET was significantly higher (threshold for both TBR_max and TBR_mean, 1.95; accuracy, 83%; AUC, 0.89 ± 0.05; P < 0.001) than that of ADC values (threshold ADC, 1.09 × 10^-3 mm²/s; accuracy, 69%; AUC, 0.73 ± 0.09; P = 0.13). The addition of static FET PET parameters to ADC values increased the latter's accuracy to 89%. The highest accuracy was achieved by combining static and dynamic FET PET parameters (93%). Moreover, in contrast to ADC values, TBRs <1.95 at suspected progression predicted a significantly longer survival (P = 0.01).

CONCLUSIONS

Data suggest that static and dynamic FET PET provide valuable information concerning the differentiation of early treatment-related changes from tumour progression and outperform ADC measurement for this highly relevant clinical question.

Death Receptor 6 (DR6) Is Overexpressed in Astrocytomas

BACKGROUND/AIM

Death receptor 6 (DR6) is a member of the tumor necrosis factor receptor superfamily. The expression of DR6 is elevated in different kinds of tumors including ovarian, breast cancer and adult sarcoma. In these tumors, the receptor may be handled as a new diagnostic and prognostic marker. Thus, we investigated the expression of DR6 in gliomas.

MATERIALS AND METHODS

Tumor and control tissues were extracted during neurosurgery and grouped according to the WHO classification. DR6 expression was investigated in low- and high-grade gliomas PCR (n=70), immunofluorescence staining (n=33) and western blot (n=58). Additional analysis of TCGA-data was performed to assess the general alteration of DR6 in cancer and influence of IDH-mutation on DR6 expression in gliomas.

RESULTS

The expression of DR6 was significantly enhanced in gliomas (p<0.05). It showed a trend towards rising expression with increasing malignancy of the tumor. Chemotherapy treatment could have an influence on DR6 expression.

CONCLUSION

In our investigation, DR6 acts as a potential suitable diagnostic marker for gliomas.

Expression of CD40 Correlates Negatively with Overall and Progression-Free Survival of Low- and High-Grade Gliomas

BACKGROUND

Low-grade gliomas (LGGs) are known to progress to glioblastoma (GBM), decreasing the chances of survival. The tumor necrosis factor receptor CD40 and its ligand CD40L have shown value as biomarkers for GBM. The present study evaluated the role of CD40/CD40L in LGG and GBM in differentiating isocitrate dehydrogenase (IDH) wild-type and IDH-mutant GBM.

METHODS

The present study was based on patient-derived samples (74 grade II gliomas, 36 grade III gliomas, and 40 cases of GBM) and expression analysis using real-time polymerase chain reaction. Open-access data from The Cancer Genome Atlas (TCGA) and the strong cohorts of TCGA data sets "brain lower grade glioma" and "glioblastoma" were used to run the analysis on mRNA expression as a validation data set.

RESULTS

We found that patients with LGG and CD40 overexpression experienced shorter progression-free survival (43 vs. 29 months; hazard ratio, 0.5715; P = 0.0262) and overall survival (116 vs. 54 months; hazard ratio, 0.3431; P < 0.0001). Consistently, relapsed grade II glioma showed greater CD40 expression compared with primary grade II glioma (P = 0.0028). Just as with LGG, CD40 was a negative marker for overall survival in GBM (12 vs. 10 months; hazard ratio, 0.5178; P = 0.0491). In this context, we found greater CD40 expression in IDH wild-type GBM than in IDH-mutant GBM. The data obtained from TCGA supported our findings, with similar results for PFS and OS in LGG and GBM. CD40L expression showed no correlation with the survival data.

CONCLUSION

High CD40 expression showed a significant correlation with poor outcomes for both LGG and GBM and was overexpressed in IDH wild-type GBM.

Treatment monitoring of immunotherapy and targeted therapy using FET PET in patients with melanoma and lung cancer brain metastases: Initial experiences

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Background: Due to the lack of specificity of contrast-enhanced (CE) MRI, the differentiation of progression from pseudoprogression (PsP) following immunotherapy using checkpoint inhibitors (IT) or targeted therapy (TT) may be challenging, especially when IT or TT is applied in combination with radiotherapy (RT). Similarly, for response assessment of RT plus IT or targeted therapy (TT), the use of CE MRI alone may also be difficult. For problem solving, the integration of advanced imaging methods may add valuable information. Here, we evaluated the value of amino acid PET using O-(2-[18F]fluoroethyl)-L-tyrosine (FET) in comparison to CE MRI for these important clinical situations in patients with brain metastases (BM) secondary to malignant melanoma (MM) and non-small cell lung cancer (NSCLC). Methods: From 2015-2018, we retrospectively identified 31 patients with 74 BM secondary to MM (n = 20 with 42 BM) and NSCLC (n = 11 with 32 BM) who underwent 52 FET PET scans during the course of disease. All patients had RT prior to IT or TT initiation (61%) or RT concurrent to IT or TT (39%). In 13 patients, FET PET was performed for treatment response assessment of IT or TT using baseline and follow-up scans (median time between scans, 4.2 months). In the remaining 18 patients, FET PET was used for the differentiation of progression from PsP related to RT plus IT or TT. In all BM, metabolic activity on FET PET was evaluated by calculation of tumor/brain ratios. FET PET imaging findings were compared to CE MRI and correlated to the clinical follow-up or neuropathological findings after neuroimaging. Results: In 4 of 13 patients (31%), FET PET provided additional information for treatment response evaluation beyond the information provided by CE MRI alone. Furthermore, responding patients on FET PET had a median stable clinical follow-up of 10 months. In 10 of 18 patients (56%) with CE MRI findings suggesting progression, FET PET detected PsP. In 9 of these 10 patients, PsP was confirmed by a median stable clinical follow-up of 11 months. Conclusions: FET PET may add valuable information for treatment monitoring in individual BM patients undergoing RT in combination with IT or TT.

Magnetic Resonance Imaging Reveals a Pronounced Treatment Response of a Isocitrate Dehydrogenase- and B-Raf Proto-Oncogene-Wildtype Epithelioid Glioblastoma

We here report findings on magnetic resonance imaging from a 60-year-old patient with an epithelioid glioblastoma of the corpus callosum treated with radiotherapy in combination with concomitant and adjuvant temozolomide. Neuropathology revealed a highly aggressive molecular subtype of the epithelioid glioblastoma without an isocitrate dehydrogenase and B-Raf proto-oncogene mutation or a O6-methylguanine-DNA-methyltransferase promoter hypermethylation. This subtype is typically associated with an unfavorable clinical course and poor overall survival. Unexpectedly, the first follow-up magnetic resonance imaging 10 weeks after chemoradiation completion revealed an early and almost complete treatment response.

Successful Treatment of Myasthenia Gravis Following PD-1/CTLA-4 Combination Checkpoint Blockade in a Patient With Metastatic Melanoma

Currently, the blockade of certain immune checkpoints such as the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death-1 (PD-1) using checkpoint inhibitors is standard of care in patients with metastatic melanoma, especially with BRAF wild-type. However, several checkpoint inhibitor-related complications have been reported, including severe adverse events in the central and peripheral nervous system. In particular, in the recent past, the occurrence of myasthenia gravis following checkpoint inhibitor monotherapy, particularly nivolumab or ipilimumab, has been reported. In contrast, reports on PD-1/CTLA-4 combination blockade—usually with fatal clinical outcome—are scarce. We here report a case with combination immune checkpoint blockade-related myasthenia gravis with favorable clinical outcome.

Combined Amino Acid Positron Emission Tomography and Advanced Magnetic Resonance Imaging in Glioma Patients

Imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) provide valuable information about brain tumor patients. Particularly amino acid PET, advanced MRI techniques, and combinations thereof are of great interest for the non-invasive assessment of biological characteristics in patients with primary or secondary brain cancer. A methodological innovation that potentially advances research in patients with brain tumors is the increasing availability of hybrid PET/MRI systems, which enables the simultaneous acquisition of both imaging modalities. Furthermore, the advent of ultra-high field MRI scanners operating at magnetic field strengths of 7 T or more will allow further development of metabolic MR imaging at higher resolution. This review focuses on the combination of amino acid PET with MR spectroscopic imaging, perfusion- and diffusion-weighted imaging, as well as chemical exchange saturation transfer in patients with high-grade gliomas, especially glioblastomas.

FET PET reveals considerable spatial differences in tumour burden compared to conventional MRI in newly diagnosed glioblastoma

PURPOSE

Areas of contrast enhancement (CE) on MRI are usually the target for resection or radiotherapy target volume definition in glioblastomas. However, the solid tumour mass may extend beyond areas of CE. Amino acid PET can detect parts of the tumour that show no CE. We systematically investigated tumour volumes delineated by amino acid PET and MRI in patients with newly diagnosed, untreated glioblastoma.

METHODS

Preoperatively, 50 patients with neuropathologically confirmed glioblastoma underwent O-(2-[¹⁸F]-fluoroethyl)-L-tyrosine (FET) PET, and fluid-attenuated inversion recovery (FLAIR) and contrast-enhanced MRI. Areas of CE were manually segmented. FET PET tumour volumes were segmented using a tumour-to-brain ratio of ≥1.6. The percentage overlap volumes, and Dice and Jaccard spatial similarity coefficients (DSC, JSC) were calculated. FLAIR images were evaluated visually.

RESULTS

In 43 patients (86%), the FET tumour volume was significantly larger than the CE volume (21.5 ± 14.3 mL vs. 9.4 ± 11.3 mL; P < 0.001). Forty patients (80%) showed both increased uptake of FET and CE. In these 40 patients, the spatial similarity between FET uptake and CE was low (mean DSC 0.39 ± 0.21, mean JSC 0.26 ± 0.16). Ten patients (20%) showed no CE, and one of these patients showed no FET uptake. In five patients (10%), increased FET uptake was present outside areas of FLAIR hyperintensity.

CONCLUSION

Our results show that the metabolically active tumour volume delineated by FET PET is significantly larger than tumour volume delineated by CE. Furthermore, the results strongly suggest that the information derived from both imaging modalities should be integrated into the management of patients with newly diagnosed glioblastoma.

Expression of FAS-L Differs from Primary to Relapsed Low-grade Gliomas and Predicts Progression-free Survival

BACKGROUND/AIM

The tumor necrosis factor FAS is overexpressed in high-grade gliomas (HGG). Only little is known about FAS or FAS ligand (FAS-L) in low-grade gliomas (LGG). We explored FAS/FAS-L expression in LGG, focusing on differences in primary and relapsed LGG and on its prognostic value.

PATIENTS AND METHODS

A total of 133 glioma samples (73 LGG, 60 HGG) were collected. The LGG samples included 15 matched pairs of primary and relapsed tumors. RT-PCR was performed to measure FAS/FAS-L expression, using subunit A, flavoprotein variant (SDHA) as housekeeper. Clinical data included progression free- (PFS) and overall survival (OS).

RESULTS

LGG showed significantly lower FAS but higher FAS-L expression than HGG. The FAS-L expression was higher in primary compared to relapsed LGG and had a positive prognostic value concerning PFS (median 45.20 vs. 31.37 months).

CONCLUSION

FAS-L could act as a prognostic marker and potential target in primary LGG.

Discordance and Conversion Rates of Progesterone-, Estrogen-, and HER2/neu-Receptor Status in Primary Breast Cancer and Brain Metastasis Mainly Triggered by Hormone Therapy

BACKGROUND/AIM

Knowing the molecular footprint of tumors is a precondition for personalized medicine. For breast cancer, targeted therapies are frequently based on the molecular status of the tissue gained from the primary tumor operation. However, it is unclear whether metastases in different organs maintain the same status.

PATIENTS AND METHODS

We compared the estrogen- (ER), progesterone- (PgR) and HER2/neu receptor status of the primary tumor with brain metastases in a series of 24 consecutive breast cancer patients.

RESULTS

62.5-75% of patients exhibited a constant receptor status between the primary tumor and the brain metastasis, whereas discordance rates of 25-37.5% were found, depending on the receptor. The rate of ER and PgR expression was each 41.6% in the primary tumors and decreased to 12.5% and 16.6% in the brain metastases. In contrast, the rate for Her2+ tumors increased from 41.6% in primary breast cancer to 65.2% in the respective brain metastases. The Ki-67 proliferation index increased significantly from a mean of 21% at the primary tumor site to 60% in brain metastases (p<0.001). All anti-estrogen treated breast tumors lost the estrogen receptor expression in the brain metastases, whereas no Her2/neu conversions occurred after treatment with trastuzumab.

CONCLUSION

In summary, receptor conversion is frequent during disease progression. Therefore, the receptor status of the primary tumor is invalid for planning a therapy targeted against brain metastases, especially after hormone-therapy. In these cases, new tissue collection by biopsy or resection is mandatory for the selection of adequate therapeutic targets and accurate decision-making for systemic therapies.

X-ray, spectroscopic and normal-mode dynamics of calexcitin: structure-function studies of a neuronal calcium-signalling protein

The protein calexcitin was originally identified in molluscan photoreceptor neurons as a 20 kDa molecule which was up-regulated and phosphorylated following a Pavlovian conditioning protocol. Subsequent studies showed that calexcitin regulates the voltage-dependent potassium channel and the calcium-dependent potassium channel as well as causing the release of calcium ions from the endoplasmic reticulum (ER) by binding to the ryanodine receptor. A crystal structure of calexcitin from the squid Loligo pealei showed that the fold is similar to that of another signalling protein, calmodulin, the N- and C-terminal domains of which are known to separate upon calcium binding, allowing interactions with the target protein. Phosphorylation of calexcitin causes it to translocate to the cell membrane, where its effects on membrane excitability are exerted and, accordingly, L. pealei calexcitin contains two protein kinase C phosphorylation sites (Thr61 and Thr188). Thr-to-Asp mutations which mimic phosphorylation of the protein were introduced and crystal structures of the corresponding single and double mutants were determined, which suggest that the C-terminal phosphorylation site (Thr188) exerts the greatest effects on the protein structure. Extensive NMR studies were also conducted, which demonstrate that the wild-type protein predominantly adopts a more open conformation in solution than the crystallographic studies have indicated and, accordingly, normal-mode dynamic simulations suggest that it has considerably greater capacity for flexible motion than the X-ray studies had suggested. Like calmodulin, calexcitin consists of four EF-hand motifs, although only the first three EF-hands of calexcitin are involved in binding calcium ions; the C-terminal EF-hand lacks the appropriate amino acids. Hence, calexcitin possesses two functional EF-hands in close proximity in its N-terminal domain and one functional calcium site in its C-terminal domain. There is evidence that the protein has two markedly different affinities for calcium ions, the weaker of which is most likely to be associated with binding of calcium ions to the protein during neuronal excitation. In the current study, site-directed mutagenesis has been used to abolish each of the three calcium-binding sites of calexcitin, and these experiments suggest that it is the single calcium-binding site in the C-terminal domain of the protein which is likely to have a sensory role in the neuron.

Structure of the Neuronal Protein Calexcitin Suggests a Mode of Interaction in Signalling Pathways of Learning and Memory

The three-dimensional structure of the neuronal calcium-sensor protein calexcitin from Loligo pealei has been determined by X-ray analysis at a resolution of 1.8A. Calexcitin is up-regulated following Pavlovian conditioning and has been shown to regulate potassium channels and the ryanodine receptor. Thus, calexcitin is implicated in neuronal excitation and plasticity. The overall structure is predominantly helical and compact with a pronounced hydrophobic core between the N and C-terminal domains of the molecule. The structure consists of four EF-hand motifs although only the first three EF hands are involved in binding calcium ions; the C-terminal EF-hand lacks the amino acids required for calcium binding. The overall structure is quite similar to that of the sarcoplasmic calcium-binding protein from Amphioxus although the sequence identity is very low at 31%. The structure shows that the two amino acids of calexcitin phosphorylated by protein kinase C are close to the domain interface in three dimensions and thus phosphorylation is likely to regulate the opening of the domains that is probably required for binding to target proteins. There is evidence that calexcitin is a GTPase and the residues, which have been implicated by mutagenesis in its GTPase activity, are in a short but highly conserved region of 3(10) helix close to the C terminus. This helix resides in a large loop that is partly sandwiched between the N and C-terminal domains suggesting that GTP binding may also require or may cause domain opening. The structure possesses a pronounced electropositive crevice in the vicinity of the 3(10) helix, that might provide an initial docking site for the triphosphate group of GTP. These findings elucidate a number of the reported functions of calexcitin with implications for neuronal signalling.