Exploring Theranostic Avenues in Adrenocortical Carcinoma Using Chemokine Receptor and Prostate-Specific Membrane Antigen-Directed PET/CT.

ABSTRACT: We report on an adrenocortical carcinoma (ACC) patient, which has exhausted previous treatment options and was scheduled for prostate-specific membrane antigen (PSMA)- and C-X-C motif chemokine receptor 4 (CXCR4)-targeted PET/CT. We identified PSMA-avid pulmonary metastases exhibiting modest radiotracer accumulation, while chemokine receptor PET/CT provided intense uptake. This dual-tracer molecular imaging approach revealed that chemokine receptor PET appears to be more suitable in patients with advanced ACC, indicating that CXCR4-directed radioligand therapy may be considered in such patients suffering from end-stage disease. Given its dismal prognosis, chemokine receptor-directed theranostics may therefore extend the therapeutic armamentarium as last-line option in advanced ACC.

Prognostic role of quantitative [18F]FDG PET/CT parameters in adrenocortical carcinoma.

PURPOSE: We aimed to evaluate the prognostic potential of baseline [18F]FDG PET/CT for overall survival (OS) in patients with adrenocortical carcinoma (ACC). METHODS: We performed a retrospective analysis of 67 treatment-naïve ACC patients with available [18F]FDG PET/CT at time of initial diagnosis. Pretherapeutic PETs of primary tumors were manually segmented and quantitative parameters (maximum/mean/peak standardized uptake value (SUVmax/mean/peak), metabolic tumor volume (MTV) and tumor lesion glycolysis (TLG, defined as TV*SUVmean) were derived. Based on a visual read, absence (M0) or presence of metastatic disease (M1) were evaluated. Kaplan-Meier and Cox regression analyses were used to determine the prognostic value of the above mentioned markers on overall survival adjusted for established prognostic markers. RESULTS: 24/67 patients (36%) presented with M0 based on PET/CT, while the remaining 43/67 (64%) had M1-status. 32/67 patients died during follow-up and median OS was 48 months. In 12% of patients FDG-PET detected additional metastatic lesion not clearly visible by CT only. In univariable analysis, all quantitatively derived PET parameters failed to reach significance (P ≥ 0.1), and only PET/CT-based M1-status and Ki-67 were associated with increased mortality (M1: HR 13.89, 95% CI 4.15-86.32, P < 0.001; Ki-67 HR 1.29, 95% CI 1.16-1.42; P < 0.0001). Using multivariable Cox regression analyses, M1-status (HR 9.69, 95% CI 2.82-60.99) and Ki-67 index (HR 1.29, 95% CI 1.13-1.04; P < 0.05) remained significant associated with OS. CONCLUSION: In treatment-naïve ACC patients, the quantitative PET parameter failed to predict OS, but presence of metastases detected by [18F]FDG PET/CT and Ki-67 index were independently associated with shorter OS. Therefore, a simple visual PET-based read-out is of prognostic value at initial diagnosis, while time-consuming PET-based quantification can be omitted.

CXCR4-directed PET/CT with [68 Ga]Ga-pentixafor in solid tumors-a comprehensive analysis of imaging findings and comparison with histopathology.

BACKGROUND: C-X-C motif chemokine receptor 4 (CXCR4) is overexpressed in various solid cancers and can be targeted by CXCR4-directed molecular imaging. We aimed to characterize the in-vivo CXCR4 expression in patients affected with solid tumors, along with a comparison to ex-vivo findings. METHODS: A total 142 patients with 23 different histologically proven solid tumors were imaged with CXCR4-directed PET/CT using [68 Ga]Ga-pentixafor (total number of scans, 152). A semi-quantitative analysis of the CXCR4-positive tumor burden including maximum standardized uptake values (SUVmax) and target-to-background ratios (TBR) using blood pool was conducted. In addition, we performed histopathological staining to determine the immuno-reactive score (IRS) from patients' tumor tissue and investigated possible correlations with SUVmax (by providing Spearman's rho ρ). Based on imaging, we also assessed the eligibility for CXCR4-targeted radioligand therapy or non-radioactive CXCR4 inhibitory treatment (defined as more than five CXCR4-avid target lesions [TL] with SUVmax above 10). RESULTS: One hundred three of 152 (67.8%) scans showed discernible uptake above blood pool (TBR > 1) in 462 lesions (52 primary tumors and 410 metastases). Median TBR was 4.4 (1.05-24.98), thereby indicating high image contrast. The highest SUVmax was observed in ovarian cancer, followed by small cell lung cancer, desmoplastic small round cell tumor, and adrenocortical carcinoma. When comparing radiotracer accumulation between primary tumors and metastases for the entire cohort, comparable SUVmax was recorded (P > 0.999), except for pulmonal findings (P = 0.013), indicative for uniform CXCR4 expression among TL. For higher IRS, a weak, but statistically significant correlation with increased SUVmax was observed (ρ = 0.328; P = 0.018). In 42/103 (40.8%) scans, more than five TL were recorded, with 12/42 (28.6%) exhibiting SUVmax above 10, suggesting eligibility for CXCR4-targeted treatment in this subcohort. CONCLUSIONS: In a whole-body tumor read-out, a substantial portion of prevalent solid tumors demonstrated increased and uniform [68 Ga]Ga-pentixafor uptake, along with high image contrast. We also observed a respective link between in- and ex-vivo CXCR4 expression, suggesting high specificity of the PET agent. Last, a fraction of patients with [68 Ga]Ga-pentixafor-positive tumor burden were rendered potentially suitable for CXCR4-directed therapy.

Diagnostic efficacy of C-X-C motif chemokine receptor 4-directed PET/CT in newly diagnosed head and neck squamous cell carcinoma - a head-to-head comparison with [18F]FDG.

BACKGROUND: The aim of this study was to determine the read-out capabilities of the novel C-X-C motif chemokine receptor 4 (CXCR4)-targeting radiotracer [68Ga]Ga-PentixaFor compared to the reference radiotracer [18F]FDG in untreated individuals with head and neck squamous cell carcinoma (HNSCC). MATERIAL AND METHODS: 12 patients with histologically confirmed HNSCC were scheduled for [18F]FDG and [68Ga]Ga-PentixaFor PET/CT. Maximum standardized uptake values (SUVmax) and target-to-background ratios (TBR) were applied with vena cava superior serving as reference. In addition, we compared [68Ga]Ga-PentixaFor-PET findings with immunohistochemical (IHC) results of CXCR4 expression. RESULTS: On visual assessment, [18F]FDG identified more sites of disease, with increased detection rates for both the primary tumor ([18F]FDG, 12/12 [100%] vs. [68Ga]Ga-PentixaFor, 10/12 [83%]) and LN metastases ([18F]FDG, 9/12 [75%] vs. [68Ga]Ga-PentixaFor, 8/12 [67%]). Indicative for improved image contrast using [18F]FDG, quantification showed a higher TBR for the latter radiotracer, when compared to [68Ga]Ga-PentixaFor for all lesions ([18F]FDG, 11.7 ± 8.5 vs. [68Ga]Ga-PentixaFor, 4.3 ± 1.3; P=0.03), primary tumors ([18F]FDG, 13.6 ± 8.7 vs. [68Ga]Ga-PentixaFor, 4.4 ± 1.4; P<0.01), and LN lesions ([18F]FDG, 9.3 ± 10.6 vs. [68Ga]Ga-PentixaFor, 4.7 ± 1.5; P=0.3). IHC showed variable CXCR4 expression in the primary and LN, along with no associations between ex-vivo CXCR4 upregulation and [68Ga]Ga-PentixaFor-based TBR (R=0.33, P=0.39) or SUVmax (R=0.44, P=0.2). Of note, IHC also revealed heterogeneous expression of CXCR4 in immune cells in the tumor microenvironment and in germinal centers, indicative for inflammatory reactions. CONCLUSIONS: In HNSCC, [18F]FDG demonstrated superior diagnostic performance relative to [68Ga]Ga-PentixaFor, in particular for assessment of the primary. Based on the IHC analyses, these findings may be explained by CXCR4 upregulation not only by tumor but also by immune cells in the tumor microenvironment.

Fluorinated aldosterone synthase (CYP11B2)-inhibitors for differential diagnosis between bilateral and unilateral conditions of primary aldosteronism.

The enzyme aldosterone synthase (CYP11B2) is specifically expressed in aldosterone-producing tissue of the adrenal cortex and is overexpressed in aldosterone-producing adenomas (APA). It therefore represents an ideal target for molecular imaging, particularly for the differential diagnosis between bilateral hyperplasia and unilateral APA in primary aldosteronism. However, the presence of the cortisol-producing enzyme 11ß-hydroxylase (CYP11B1) in the adrenal cortex remains very challenging owing to its high homology to CYP11B2. Within this study, we efficiently synthesized a variety of disubstituted fluorinated pyridines and pyrazines by Suzuki coupling reactions. These compounds were evaluated for their ability to inhibit CYP11B1 and CYP11B2 in transfected Y1 cells and in NCI-h295 cells. Several compounds were found to exhibit excellent affinity (IC50 < 10 nM) to CYP11B2 as well as strong selectivity (up to 125-fold) over CYP11B1. These findings support the further development of an analogous 18F-labelled PET tracer.

Early biochemical and radiographic response after one cycle of [177Lu]Lu-PSMA I&T radioligand therapy in metastatic castration-resistant prostate cancer patients.

PURPOSE: The aim of this study was to investigate very early radiographic PSMA PET response after one cycle of [177Lu]Lu-PSMA I&T radioligand therapy (RLT) of metastatic castration-resistant prostate cancer (mCRPC) and to assess its role in predicting overall response and survival. METHODS: This retrospective study enrolled 40 mCRPC patients who were treated with a median of 3 (2-9) [177Lu]Lu-PSMA I&T RLT cycles. Biochemical response was based on the relative change of serum PSA according to PCWG3 criteria, while radiographic response referred to the relative change of PSMA-derived total viable tumor volumes expressed as total lesion PSMA (TLP). RESULTS: After one cycle of RLT, biochemical partial response (PR) was seen in 8/40 (20.0%), stable disease (SD) in 22/40 (55.0%), and progressive disease (PD) in 10/40 (25%) patients. In PSMA PET, very early molecular PR was observed in 12 (30.0%), SD in 19 (47.5%), and PD in 9 (22.5%) subjects. The PSA and TLP nadir were achieved after a median of 1 (1-5) and 2 (1-6) cycles, respectively. Nineteen (47.5%) patients showed overall biochemical PR, 11 (27.5%) had SD, and 10 (25%) experienced PD. In PSMA-directed PET, 4 patients experienced molecular complete response (CR), 24 (60.0%) had PR, 4 (10.0%) SD, and 8 (20.0%) PD. Early biochemical or radiographic response was not associated with longer overall survival (OS). Overall biochemical responders had a nearly significantly longer median OS (22.7 months) than non-responders (14.4 months, p = 0.08). Early PSA progression was associated with shorter OS (12.2 months), compared to biochemical SD/PR (18.7 months, p = 0.09). CONCLUSION: In this retrospective cohort, there was no association between early PSMA PET radiographic response and overall survival; hence, treatment should not be prematurely discontinued. In contrast, early PSA progression after one cycle of [177Lu]Lu-PSMA I&T RLT was an indicator of overall progression and poor clinical outcome.

CXCR4-Directed Imaging and Endoradiotherapy in Desmoplastic Small Round Cell Tumors.

Desmoplastic small round cell tumor (DSRCT) is a rare, radiosensitive, yet difficult-to-treat sarcoma subtype affecting predominantly male adolescents. Extensive intraperitoneal seeding is common and requires multimodal management. With no standard therapy established, the prognosis remains poor, and new treatment options are needed. We demonstrate the clinical potential of C-X-C motif chemokine receptor 4 (CXCR4)-directed imaging and endoradiotherapy in DSRCT. Methods: Eight male patients underwent dual-tracer imaging with [18F]FDG and CXCR4-directed [68Ga]pentixafor PET/CT. A visual comparison of both tracers, along with uptake quantification in active DSRCT lesions, was performed. [68Ga]pentixafor uptake was correlated with immunohistochemical CXCR4 expression on tumor cells. Four patients with end-stage progressive disease underwent CXCR4-based endoradiotherapy. We report the safety, response by RECIST 1.1, and survival after endoradiotherapy. Results: Uptake of [68Ga]pentixafor in tumor lesions was demonstrated in all patients with DSRCT, providing diagnostic power comparable to [18F]FDG PET. Corresponding CXCR4 expression was confirmed by immunohistochemistry in all DSRCT biopsies. Finally, 4 patients were treated with CXCR4-directed [90Y]endoradiotherapy, 3 in a myeloablative dose range with subsequent autologous stem cell transplantation. All 3 required transfusions, and febrile neutropenia occurred in 2 patients (resulting in 1 death). Notably, severe nonhematologic adverse events were absent. We observed signs of response in all 3 patients, translating into disease stabilization in 2 patients for 143 and 176 d, respectively. In the third patient, postmortem autopsy confirmed a partial pathologic response. Conclusion: We validated CXCR4 as a diagnostic biomarker and a promising target for endoradiotherapy in DSRCT, demonstrated its feasibility, and provided the first evidence of its clinical efficacy.

Impact of CXCR4-Directed PET/CT on Staging and Proposed Oncologic Management in Patients With Digestive System Tumors.

PURPOSE: To elucidate the influence of CXC motif chemokine receptor 4 (CXCR4)-directed imaging on staging and proposed oncologic management in patients with digestive system tumors compared with guideline-appropriate imaging (GAI). METHODS: From our PET/CT database, we retrospectively identified 37 patients with advanced digestive system tumors, which had been scheduled for CXCR4-targeted [ 68 Ga]Ga-pentixafor PET/CT for potential theranostic considerations. In all subjects, concurrent GAI was also available. Patients were afflicted with gastroenteropancreatic neuroendocrine neoplasms (21/37 [56.8%]), pancreatic duct adenocarcinoma (6/37 [16.2%]), cholangiocarcinoma (5/37 [13.5%]), hepatocellular carcinoma (4/37 [10.8%]), and colorectal carcinoma (1/37 [2.7%]). Staging results and impact on proposed oncologic management by a board-certified gastroenterologist were compared between GAI and [ 68 Ga]Ga-pentixafor PET/CT. RESULTS: Relative to GAI, CXCR4-directed PET/CT resulted in staging changes in 14 of 37 patients (37.8%). Upstaging was seen in 1 of 14 patients (7.1%), whereas downstaging was recorded in the remaining 13 of 14 patients (92.9%). Among those, staging changes would not have triggered any changes in oncological management in 4 of 14 (28.6%). For the remaining 10 of 14 patients (71.4%), however, findings on [ 68 Ga]Ga-pentixafor PET/CT would have impacted subsequent clinical algorithm, including the necessity for further diagnostic steps or failure to initiate antitumor therapy. CONCLUSION: [ 68 Ga]Ga-pentixafor PET/CT missed tumor lesions in 13 patients with digestive system tumors, which would have led to inappropriate downstaging and clinical treatment of 10 patients. As such, our results do not support a more widespread use of [ 68 Ga]Ga-pentixafor PET/CT for clinical staging in those tumor entities.

Molecular imaging of arterial fibroblast activation protein: association with calcified plaque burden and cardiovascular risk factors.

PURPOSE: We aimed to assess prevalence, distribution, and intensity of in-vivo arterial wall fibroblast activation protein (FAP) uptake, and its association with calcified plaque burden, cardiovascular risk factors (CVRFs), and FAP-avid tumor burden. METHODS: We analyzed 69 oncologic patients who underwent [68 Ga]Ga-FAPI-04 PET/CT. Arterial wall FAP inhibitor (FAPI) uptake in major vessel segments was evaluated. We then investigated the associations of arterial wall uptake with calcified plaque burden (including number of plaques, plaque thickness, and calcification circumference), CVRFs, FAP-positive total tumor burden, and image noise (coefficient of variation, from normal liver parenchyma). RESULTS: High focal arterial FAPI uptake (FAPI +) was recorded in 64/69 (92.8%) scans in 800 sites, of which 377 (47.1%) exhibited concordant vessel wall calcification. The number of FAPI + sites per patient and (FAPI +)-derived target-to-background ratio (TBR) correlated significantly with the number of calcified plaques (FAPI + number: r = 0.45, P < 0.01; TBR: r = - 0.26, P = 0.04), calcified plaque thickness (FAPI + number: r = 0.33, P < 0.01; TBR: r = - 0.29, P = 0.02), and calcification circumference (FAPI + number: r = 0.34, P < 0.01; TBR: r = - 0.26, P = 0.04). In univariate analysis, only body mass index was significantly associated with the number of FAPI + sites (OR 1.06; 95% CI, 1.02 - 1.12, P < 0.01). The numbers of FAPI + sites and FAPI + TBR, however, were not associated with other investigated CVRFs in univariate and multivariate regression analyses. Image noise, however, showed significant correlations with FAPI + TBR (r = 0.30) and the number of FAPI + sites (r = 0.28; P = 0.02, respectively). In addition, there was no significant interaction between FAP-positive tumor burden and arterial wall FAPI uptake (P ≥ 0.13). CONCLUSION: [68 Ga]Ga-FAPI-04 PET identifies arterial wall lesions and is linked to marked calcification and overall calcified plaque burden, but is not consistently associated with cardiovascular risk. Apparent wall uptake may be partially explained by image noise.

Somatostatin Receptor-Directed PET/CT for Therapeutic Decision-Making and Disease Control in Patients Affected With Small Cell Lung Cancer.

BACKGROUND: Somatostatin receptor (SSTR)-targeted PET/CT is used for patients affected with small cell lung cancer (SCLC), but the clinical impact has not been elucidated yet. We aimed to determine whether SSTR PET/CT can trigger relevant therapeutic management changes in patients with SCLC and whether those modifications achieve disease control and are associated with prolonged survival. METHODS: One hundred patients with SCLC received SSTR PET/CT. In a retrospective setting, we evaluated the diagnostic performance of PET versus CT and compared therapies before and after PET/CT to determine the impact of molecular imaging on treatment decision. We also determined the rate of disease control after therapeutic modifications and assessed survival in patients with and without changes in the therapeutic regimen. RESULTS: Relative to CT, SSTR PET alone was superior for assessing bone lesions in 19 of 39 instances (49%). Treatment was modified in 59 of 100 (59%) after SSTR PET/CT. Forty of 59 (74.6%) received systemic treatment after hybrid imaging, with the remaining 15 of 59 (25.4%) scheduled for nonsystemic therapy. In the latter group, 13 of 15 (86.7%) received local radiation therapy or active surveillance (2/15 [13.3%]). Individuals scheduled for systemic treatment after imaging received peptide receptor radionuclide therapy (PRRT) in 28 of 44 (63.6%), followed by chemotherapy in 10 of 44 (22.7%), change in chemotherapy regimen in 3 of 44 (6.8%), and initiation of tyrosine kinase inhibitor in the remaining 3 of 44 (6.8%). Among patients with modified treatment, follow-up was available in 53 subjects, and disease control was achieved in 14 of 53 (26.4%). However, neither change to systemic treatment (155 days; hazard ratio, 0.94; 95% confidence interval, 0.53-1.67) nor change to nonsystemic treatment (210 days; hazard ratio, 0.67; 95% confidence interval, 0.34-1.34) led to a prolonged survival when compared with subjects with no change (171 days, P ≥ 0.22, respectively). CONCLUSIONS: In patients with SCLC, SSTR-targeted hybrid imaging provides complementary information on the disease status. PET/CT led to management changes in 59% (mainly PRRT), achieving disease control in >26%. The high fraction of patients scheduled for PRRT may lay the foundation for combination strategies to achieve synergistic antitumor effects, for example, by combining PRRT plus recently introduced RNA polymerase II inhibitors.

C-X-C Motif Chemokine Receptor 4-Targeted Radioligand Therapy in Patients with Advanced T-Cell Lymphoma.

C-X-C motif chemokine receptor 4 (CXCR4)-targeted radioligand therapy (RLT) has already been applied to advanced blood cancers, such as multiple myeloma or diffuse large B-cell lymphoma. We present a series of patients with advanced T-cell lymphoma (TCL) who were scheduled for CXCR4-directed therapy as a conditioning regimen, followed by hematopoietic stem cell transplantation (HSCT). Methods: Four patients with advanced, heavily pretreated, and relapsed TCL (2 men, 2 women; median age, 50 y) without suitable alternative therapeutic options underwent CXCR4-directed PET and pretherapeutic dosimetry. We then conducted CXCR4-targeted RLT in combination with allogeneic (3/4, 75%) or autologous (1/4, 25%) HSCT. One patient also underwent radioimmunotherapy targeting CD66 to enhance therapeutic efficacy. We investigated safety, best response, progression-free survival, and overall survival. Results: Pretherapeutic dosimetry indicated lymphoma-absorbed doses of up to 33.2 Gy from CXCR4-targeted RLT. Except for 1 patient who developed tumor lysis syndrome along with transient grade 3 kidney failure, no acute toxicity, allergic reactions, or other adverse events were recorded during therapy. One patient developed septicemia and subsequently died 16 d after RLT, whereas engraftment was achieved in the remaining 3 patients (75%). During follow-up, a partial response was recorded in 1 of 3 patients (33.3%) and a complete metabolic response in the other two (66.7%, with 1 patient also receiving additional radioimmunotherapy). Median progression-free survival was 7 mo (range, 4-25 mo). After a median follow-up of 54 mo (range, 4-56 mo), 3 patients were still alive at the date of censoring. Conclusion: For advanced, heavily pretreated TCL, CXCR4-directed RLT may serve as an effective conditioning therapy before HSCT and can cause substantial antilymphoma activity, leading to a remarkable response in selected cases.

Impact of 68 Ga-FAPI-04 PET/CT on Staging and Therapeutic Management in Patients With Digestive System Tumors.

PURPOSE: We aimed to determine the impact of fibroblast activation protein inhibitor (FAPI)-directed molecular imaging on staging and therapeutic management in patients affected with digestive system tumors when compared with guideline-compatible imaging (GCI). PATIENTS AND METHODS: Thirty-two patients with tumors of the digestive system were included: colon adenocarcinoma, 2/32 (6.3%); hepatocellular carcinoma (HCC), 6/32 (18.8%); pancreatic duct adenocarcinoma (PDAC), 6/32 (18.8%), and gastroenteropancreatic neuroendocrine neoplasms, 18/32 (56.3%). All patients underwent GCI and 68 Ga-FAPI-04 PET/CT within median 4 days. Staging outcomes and subsequent treatment decisions were compared between GCI and 68 Ga-FAPI-04 PET/CT. RESULTS: Compared with GCI, 68 Ga-FAPI-04 PET/CT led to staging changes in 15/32 patients (46.9%). Among those, downstaging was recorded in 3/15 cases (20.0%) and upstaging in the remaining 12/15 patients (HCC, 4/12 [33.3%]; PDAC, 4/12 [33.3%]; neuroendocrine neoplasms, 3/12 [25%]; colon adenocarcinoma, 1/12 [8.3%]). Therapeutic management was impacted in 8/32 patients (25.0%), including 4 instances of major and 4 instances of minor therapeutic changes. The highest proportion of treatment modifications was observed in patients diagnosed with PDAC and HCC in 6/8 (75%). CONCLUSIONS: In patients affected with digestive system tumors, 68 Ga-FAPI-04 PET/CT resulted in staging changes in more than 46% and therapeutic modifications in 25% of the cases, in particular in patients with HCC and PDAC. In clinical routine, such findings may favor a more widespread adoption of FAP-directed imaging in those tumor types.

Radiopharmaceuticals for Treatment of Adrenocortical Carcinoma.

Adrenocortical carcinoma (ACC) represents a rare tumor entity with limited treatment options and usually rapid tumor progression in case of metastatic disease. As further treatment options are needed and ACC metastases are sensitive to external beam radiation, novel theranostic approaches could complement established therapeutic concepts. Recent developments focus on targeting adrenal cortex-specific enzymes like the theranostic twin [123/131I]IMAZA that shows a good image quality and a promising therapeutic effect in selected patients. But other established molecular targets in nuclear medicine such as the C-X-C motif chemokine receptor 4 (CXCR4) could possibly enhance the therapeutic regimen as well in a subgroup of patients. The aims of this review are to give an overview of innovative radiopharmaceuticals for the treatment of ACC and to present the different molecular targets, as well as to show future perspectives for further developments since a radiopharmaceutical with a broad application range is still warranted.

Adrenal functional imaging - which marker for which indication?

PURPOSE OF REVIEW: In recent years, a broad spectrum of molecular image biomarkers for assessment of adrenal functional imaging have penetrated the clinical arena. Those include positron emission tomography and single photon emission computed tomography radiotracers, which either target glucose transporter, CYP11B enzymes, C-X-C motif chemokine receptor 4, norepinephrine transporter or somatostatin receptors. We will provide an overview of key radiopharmaceuticals and determine their most relevant clinical applications, thereby providing a roadmap for the right image biomarker at the right time for the right patient. RECENT FINDINGS: Numerous radiotracers for assessment of adrenal incidentalomas ([ 18 F]FDG; [ 123 I]IMTO/IMAZA), ACC ([ 123 I]IMTO/IMAZA; [ 18 F]FDG; [ 68 Ga]PentixaFor), pheochromocytomas and paragangliomas ([ 123 I]mIBG; [ 18 F]flubrobenguane; [ 18 F]AF78; [ 68 Ga]DOTATOC/-TATE), or primary aldosteronism ([ 11 C]MTO, [ 68 Ga]PentixaFor) are currently available and have been extensively investigated in recent years. In addition, the field is currently evolving from adrenal functional imaging to a patient-centered adrenal theranostics approach, as some of those radiotracers can also be labeled with ß-emitters for therapeutic purposes. SUMMARY: The herein reviewed functional image biomarkers may not only allow to increase diagnostic accuracy for adrenal gland diseases but may also enable for achieving substantial antitumor effects in patients with adrenocortical carcinoma, pheochromocytoma or paraganglioma.

Reduced splenic uptake on 68Ga-Pentixafor-PET/CT imaging in multiple myeloma - a potential imaging biomarker for disease prognosis.

Beyond being a key factor for tumor growth and metastasis in human cancer, C-X-C motif chemokine receptor 4 (CXCR4) is also highly expressed by a number of immune cells, allowing for non-invasive read-out of inflammatory activity. With two recent studies reporting on prognostic implications of the spleen signal in diffusion-weighted magnetic resonance imaging in patients with plasma cell dyscrasias, the aim of this study was to correlate splenic 68Ga-Pentixafor uptake in multiple myeloma (MM) with clinical parameters and to evaluate its prognostic impact. Methods: Eighty-seven MM patients underwent molecular imaging with 68Ga-Pentixafor-PET/CT. Splenic CXCR4 expression was semi-quantitatively assessed by peak standardized uptake values (SUVpeak) and corresponding spleen-to-bloodpool ratios (TBR) and correlated with clinical and prognostic features as well as survival parameters. Results:68Ga-Pentixafor-PET/CT was visually positive in all MM patients with markedly heterogeneous tracer uptake in the spleen. CXCR4 expression determined by 68Ga-Pentixafor-PET/CT corresponded with advanced disease and was inversely associated with the number of previous treatment lines as compared to controls or untreated smouldering multiple myeloma patients (SUVpeakSpleen 4.06 ± 1.43 vs. 6.02 ± 1.16 vs. 7.33 ± 1.40; P < 0.001). Moreover, reduced splenic 68Ga-Pentixafor uptake was linked to unfavorable clinical outcome. Patients with a low SUVpeakSpleen (<3.35) experienced a significantly shorter overall survival of 5 months as compared to 62 months in patients with a high SUVpeakSpleen >5.79 (P < 0.001). Multivariate Cox analysis confirmed SUVpeakSpleen as an independent predictor of survival (HR 0.75; P = 0.009). Conclusion: These data suggest that splenic 68Ga-Pentixafor uptake might provide prognostic information in pre-treated MM patients similar to what was reported for diffusion-weighted magnetic resonance imaging. Further research to elucidate the underlying biologic implications is warranted.

CXCR4 expression of multiple myeloma as a dynamic process: influence of therapeutic agents.

Chemokine receptors represent novel targets for treatment of multiple myeloma (MM). However, CXCR4 expression appears to be highly dynamic. This in vitro study investigated the impact of commonly used anti-myeloma agents on CXCR4 expression. Established human myeloma cell lines as well as patient-derived CD138+ plasma cells were exposed to antineoplastic drugs. Cells were analyzed for CXCR4 expression by flow cytometry and direct stochastic optical reconstruction microscopy (dSTORM). In addition, cellular uptake of 68Ga-Pentixafor, a PET radiotracer for noninvasive assessment of CXCR4 expression in vivo, was assessed. CXCR4 expression was highly variable and turned out to be substance, dose and time dependent. Treatment with bortezomib was associated with reduced expression, while dexamethasone and doxorubicin significantly increased expression of CXCR4. Combination of these compounds further increased CXCR4 expression. In conclusion, drugs or combination of drugs can induce CXCR4 expression in myeloma cells. Hence, pretreatment may impact on response to CXCR4-based therapies.

Baseline clinical characteristics predict overall survival in patients undergoing radioligand therapy with [177Lu]Lu-PSMA I&T during long-term follow-up.

BACKGROUND: Radioligand therapy (RLT) with 177Lu-labeled prostate-specific membrane antigen (PSMA) ligands is associated with prolonged overall survival (OS) in patients with advanced, metastatic castration-resistant prostate cancer (mCRPC). A substantial number of patients, however, are prone to treatment failure. We aimed to determine clinical baseline characteristics to predict OS in patients receiving [177Lu]Lu-PSMA I&T RLT in a long-term follow-up. MATERIALS AND METHODS: Ninety-two mCRPC patients treated with [177Lu]Lu-PSMA I&T with a follow-up of at least 18 months were retrospectively identified. Multivariable Cox regression analyses were performed for various baseline characteristics, including laboratory values, Gleason score, age, prior therapies, and time interval between initial diagnosis and first treatment cycle (intervalDiagnosis-RLT, per 12 months). Cutoff values for significant predictors were determined using receiver operating characteristic (ROC) analysis. ROC-derived thresholds were then applied to Kaplan-Meier analyses. RESULTS: Baseline C-reactive protein (CRP; hazard ratio [HR], 1.10, 95% CI 1.02-1.18; P = 0.01), lactate dehydrogenase (LDH; HR, 1.07, 95% CI 1.01-1.11; P = 0.01), aspartate aminotransferase (AST; HR, 1.16, 95% CI 1.06-1.26; P = 0.001), and intervalDiagnosis-RLT (HR, 0.95, 95% CI 0.91-0.99; P = 0.02) were identified as independent prognostic factors for OS. The following respective ROC-based thresholds were determined: CRP, 0.98 mg/dl (area under the curve [AUC], 0.80); LDH, 276.5 U/l (AUC, 0.83); AST, 26.95 U/l (AUC, 0.73); and intervalDiagnosis-RLT, 43.5 months (AUC, 0.68; P < 0.01, respectively). Respective Kaplan-Meier analyses demonstrated a significantly longer median OS of patients with lower CRP, lower LDH, and lower AST, as well as prolonged intervalDiagnosis-RLT (P ≤ 0.01, respectively). CONCLUSION: In mCRPC patients treated with [177Lu]Lu-PSMA I&T, baseline CRP, LDH, AST, and time interval until RLT initiation (thereby reflecting a possible indicator for tumor aggressiveness) are independently associated with survival. Our findings are in line with previous findings on [177Lu]Lu-PSMA-617, and we believe that these clinical baseline characteristics may support the nuclear medicine specialist to identify long-term survivors.

Associations between Normal Organs and Tumor Burden in Patients Imaged with Fibroblast Activation Protein Inhibitor-Directed Positron Emission Tomography.

(1) Background: We aimed to quantitatively investigate [68Ga]Ga-FAPI-04 uptake in normal organs and to assess a relationship with the extent of FAPI-avid tumor burden. (2) Methods: In this single-center retrospective analysis, thirty-four patients with solid cancers underwent a total of 40 [68Ga]Ga-FAPI-04 PET/CT scans. Mean standardized uptake values (SUVmean) for normal organs were established by placing volumes of interest (VOIs) in the heart, liver, spleen, pancreas, kidneys, and bone marrow. Total tumor burden was determined by manual segmentation of tumor lesions with increased uptake. For tumor burden, quantitative assessment included maximum SUV (SUVmax), tumor volume (TV), and fractional tumor activity (FTA = TV × SUVmean). Associations between uptake in normal organs and tumor burden were investigated by applying Spearman's rank correlation coefficient. (3) Results: Median SUVmean values were 2.15 in the pancreas (range, 1.05-9.91), 1.42 in the right (range, 0.57-3.06) and 1.41 in the left kidney (range, 0.73-2.97), 1.2 in the heart (range, 0.46-2.59), 0.86 in the spleen (range, 0.55-1.58), 0.65 in the liver (range, 0.31-2.11), and 0.57 in the bone marrow (range, 0.26-0.94). We observed a trend towards significance for uptake in the myocardium and tumor-derived SUVmax (ρ = 0.29, p = 0.07) and TV (ρ = -0.30, p = 0.06). No significant correlation was achieved for any of the other organs: SUVmax (ρ ≤ 0.1, p ≥ 0.42), TV (ρ ≤ 0.11, p ≥ 0.43), and FTA (ρ ≤ 0.14, p ≥ 0.38). In a sub-analysis exclusively investigating patients with high tumor burden, significant correlations of myocardial uptake with tumor SUVmax (ρ = 0.44; p = 0.03) and tumor-derived FTA with liver uptake (ρ = 0.47; p = 0.02) were recorded. (4) Conclusions: In this proof-of-concept study, quantification of [68Ga]Ga-FAPI-04 PET showed no significant correlation between normal organs and tumor burden, except for a trend in the myocardium. Those preliminary findings may trigger future studies to determine possible implications for treatment with radioactive FAP-targeted drugs, as higher tumor load or uptake may not lead to decreased doses in the majority of normal organs.

CXCR4-targeted theranostics in oncology.

A growing body of literature reports on the upregulation of C-X-C motif chemokine receptor 4 (CXCR4) in a variety of cancer entities, rendering this receptor as suitable target for molecular imaging and endoradiotherapy in a theranostic setting. For instance, the CXCR4-targeting positron emission tomography (PET) agent [68 Ga]PentixaFor has been proven useful for a comprehensive assessment of the current status quo of solid tumors, including adrenocortical carcinoma or small-cell lung cancer. In addition, [68 Ga]PentixaFor has also provided an excellent readout for hematological malignancies, such as multiple myeloma, marginal zone lymphoma, or mantle cell lymphoma. PET-based quantification of the CXCR4 capacities in vivo allows for selecting candidates that would be suitable for treatment using the theranostic equivalent [177Lu]/[90Y]PentixaTher. This CXCR4-directed theranostic concept has been used as a conditioning regimen prior to hematopoietic stem cell transplantation and to achieve sufficient anti-lymphoma/-tumor activity in particular for malignant tissues that are highly sensitive to radiation, such as the hematological system. Increasing the safety margin, pretherapeutic dosimetry is routinely performed to determine the optimal activity to enhance therapeutic efficacy and to reduce off-target adverse events. The present review will provide an overview of current applications for CXCR4-directed molecular imaging and will introduce the CXCR4-targeted theranostic concept for advanced hematological malignancies.