Cationic eluate pretreatment for automated synthesis of [68Ga]CPCR4.2

CXCR4: From Signaling to Clinical Applications in Neuroendocrine Neoplasms

There are several well-described molecular mechanisms that influence cell growth and are related to the development of cancer. Chemokines constitute a fundamental element that is not only involved in local growth but also affects angiogenesis, tumor spread, and metastatic disease. Among them, the C-X-C motif chemokine ligand 12 (CXCL12) and its specific receptor the chemokine C-X-C motif receptor 4 (CXCR4) have been widely studied. The overexpression in cell membranes of CXCR4 has been shown to be associated with the development of different kinds of histological malignancies, such as adenocarcinomas, epidermoid carcinomas, mesenchymal tumors, or neuroendocrine neoplasms (NENs). The molecular synapsis between CXCL12 and CXCR4 leads to the interaction of G proteins and the activation of different intracellular signaling pathways in both gastroenteropancreatic (GEP) and bronchopulmonary (BP) NENs, conferring greater capacity for locoregional aggressiveness, the epithelial-mesenchymal transition (EMT), and the appearance of metastases. Therefore, it has been hypothesized as to how to design tools that target this receptor. The aim of this review is to focus on current knowledge of the relationship between CXCR4 and NENs, with a special emphasis on diagnostic and therapeutic molecular targets.

Second generation Al18F-labeled D-amino acid peptide for CXCR4 targeted molecular imaging

BACKGROUND

The C-X-C chemokine receptor type 4 (CXCR4) is overexpressed in many cancers, e.g. multiple myeloma and acute leukemia, yet solely [68Ga]PentixaFor is used for clinical PET imaging. The aim of this study was to develop and assess a second generation Al18F-labeled D-amino acid peptide based on the viral macrophage inflammatory protein II for CXCR4 targeted molecular imaging.

METHODS

We designed a library of monomer and multimer constructs and evaluated their binding affinity for human and mouse CXCR4. Based on these results, we selected the best vector molecule for development of an Al18F-labeled ligand, [18F]AlF-NOTA-2xDV1(c11sc12s), which was further evaluated in a cell-based binding assay to assess its binding properties and specificity for CXCR4. Next, pharmacokinetics and tumor uptake of [18F]AlF-NOTA-2xDV1(c11sc12s) were evaluated in naïve mice and mice with xenografts derived from U87.CXCR4 cells. Finally, we performed an imaging study in a non-human primate to assess the in vivo distribution of this novel radioligand in a species closely related to humans.

RESULTS

The lead ligand AlF-NOTA-2xDV1(c11sc12s) showed six-fold higher affinity for human CXCR4 compared to Ga-Pentixafor. The corresponding radiotracer was obtained in a good radiochemical yield of 40.1 ± 13.5 % (n = 4) and apparent molar activity of 20.4 ± 3.3 MBq/nmol (n = 4) after optimization. In U87.CD4.CXCR4 cell binding assays, the total bound fraction of [18F]AlF-NOTA-(2×)DV1(c11sc12s) was 32.4 ± 1.8 %. This fraction could be reduced by 82.5 % in the presence of 75 μM AMD3100. In naïve mice, [18F]AlF-NOTA-2xDV1(c11sc12s) accumulated in organs expressing mouse CXCR4, e.g. the liver (SUVmean (mean standardized uptake value) 75 min p.i. 11.7 ± 0.6), which was blockable by co-injecting AMD3100 (5 mg/kg). In U87.CXCR4 xenografted tumor mice, the tumor uptake of [18F]AlF-NOTA-2xDV1(c11sc12s) remained low (SUVmean 0.5 ± 0.1), but was reduced by co-administration of AMD3100. Surprisingly, [18F]AlF-NOTA-2xDV1(c11sc12s) exhibited a similar biodistribution in a non-human primate as in mice indicating off-target binding of [18F]AlF-NOTA-2xDV1(c11sc12s) in liver tissue. We confirmed that [18F]AlF-NOTA-2xDV1(c11sc12s) is taken up by hepatocytes using in vitro studies and that the uptake can be blocked with AMD3100 and rifampicin, a potent organic anion-transporting-polypeptide (OATP)1B1 and OATP1B3 inhibitor.

CONCLUSION

The second generation D-peptide AlF-NOTA-2xDV1(c11sc12s) showed high affinity for human CXCR4 and the corresponding radiotracer was produced in good radiochemical yields. However, [18F]AlF-NOTA-2xDV1(c11sc12s) is not specific for CXCR4 and is also a substrate for OATP1B1 and/or OATP1B3, known to mediate hepatic uptake. Therefore, D-amino acid peptides, based on the viral macrophage inflammatory protein II, are not the prefered vector molecule for the development of CXCR4 targeting molecular imaging tools.

The PRIMARY Score: Diagnostic Performance and Added Value Compared With MRI in Detecting Clinically Significant Prostate Cancer

PURPOSE

Multiparametric MRI is the current standard for detecting clinically significant prostate cancer (csPCa). However, men with negative or equivocal MRI often undergo unnecessary biopsies due to concerns about false-negative results. The recently proposed 68 Ga-PSMA PET/CT-based PRIMARY score exhibited good diagnostic performance for csPCa. This study aimed to externally validate the performance of the PRIMARY score and evaluate its added diagnostic value to MRI triage in detecting csPCa.

PATIENTS AND METHODS

This retrospective cohort study included 431 men who underwent both 68 Ga-PSMA PET/CT and MRI before biopsy. Performance was assessed using the area under the receiver operating characteristic curve and the decision curve analysis. The PRIMARY score + MRI was considered positive for either PRIMARY score 3-5 or Prostate Imaging Reporting and Data System (PI-RADS) 4/5.

RESULTS

The prevalence of csPCa was 51.7% (223/431). The area under the receiver operating characteristic curve of the 5-level PRIMARY score for csPCa was significantly higher than that of MRI (0.873 vs 0.786, P < 0.001). For the entire group, sensitivity, specificity, positive predictive value, and negative predictive value of the PRIMARY score were 90.6%, 61.1%, 71.4%, and 85.8%, respectively, which outperformed 87.9%, 49.0%, 64.9%, and 79.1% of PI-RADS on MRI. The PRIAMRY score + MRI improved sensitivity (96.0% vs 87.9%, P < 0.001) and negative predictive value (91.5% vs 79.1%, P < 0.001) without compromising specificity and positive predictive value compared with MRI alone. This combined approach avoided 24.6% (106/431) of unnecessary biopsies, while missing 4.0% (9/223) of csPCa cases. The addition of the PRIMARY score in men with PI-RADS 1-3 showed a net benefit, but not in men with PI-RADS 4/5.

CONCLUSIONS

The PRIMARY score was superior to MRI in detecting csPCa, and its added diagnostic value was in men with negative or equivocal MRI results. The PRIMARY score + MRI improved negative predictive value and sensitivity for csPCa compared with MRI alone. Further prospective trials will validate whether men with clinical suspicion of csPCa but negative PRIMARY score + MRI can safely avoid unnecessary biopsies.

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.

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 (SUV_peak) 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 (SUV_peakSpleen 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 SUV_peakSpleen (<3.35) experienced a significantly shorter overall survival of 5 months as compared to 62 months in patients with a high SUV_peakSpleen >5.79 (P < 0.001). Multivariate Cox analysis confirmed SUV_peakSpleen 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.

Synthesis of 68Ga-radiopharmaceuticals using both generator-derived and cyclotron-produced 68Ga as exemplified by [68Ga]Ga-PSMA-11 for prostate cancer PET imaging

[⁶⁸Ga]Ga-PSMA-11, a urea-based peptidomimetic, is a diagnostic radiopharmaceutical for positron emission tomography (PET) imaging that targets the prostate-specific membrane antigen (PSMA). The recent Food and Drug Administration approval of [⁶⁸Ga]Ga-PSMA-11 for PET imaging of patients with prostate cancer, expected follow-up approval of companion radiotherapeutics (e.g., [¹⁷⁷Lu]Lu-PSMA-617, [²²⁵Ac]Ac-PSMA-617) and large prostate cancer patient volumes requiring access are poised to create an unprecedented demand for [⁶⁸Ga]Ga-PSMA-11 in nuclear medicine clinics around the world. Meeting this global demand is going to require a variety of synthesis methods compatible with ⁶⁸Ga eluted from a generator or produced on a cyclotron. To address this urgent need in the PET radiochemistry community, herein we report detailed protocols for the synthesis of [⁶⁸Ga]Ga-PSMA-11, (also known as HBED-CC, Glu-urea-Lys(Ahx)-HBED-CC and PSMA-HBED-CC) using both generator-eluted and cyclotron-produced ⁶⁸Ga and contrast the pros and cons of each method. The radiosyntheses are automated and have been validated for human use at two sites (University of Michigan (UM), United States; Royal Prince Alfred Hospital (RPA), Australia) and used to produce [⁶⁸Ga]Ga-PSMA-11 for patient use in good activity yields (single generator, 0.52 GBq (14 mCi); dual generators, 1.04-1.57 GBq (28-42 mCi); cyclotron method (single target), 1.47-1.89 GBq (40-51 mCi); cyclotron method (dual target), 3.63 GBq (98 mCi)) and high radiochemical purity (99%) (UM, n = 645; RPA, n > 600). Both methods are appropriate for clinical production but, in the long term, the method employing cyclotron-produced ⁶⁸Ga is the most promising for meeting high patient volumes. Quality control testing (visual inspection, pH, radiochemical purity and identity, radionuclidic purity and identity, sterile filter integrity, bacterial endotoxin content, sterility, stability) confirmed doses are suitable for clinical use, and there is no difference in clinical prostate cancer PET imaging using [⁶⁸Ga]Ga-PSMA-11 prepared using the two production methods.

[68 Ga]Ga-FAPI uptake correlates with the state of chronic kidney disease

Purpose

Kidney fibrosis leads to a progressive reduction in kidney function ultimately resulting in kidney failure. Diagnostic tools to detect kidney fibrosis are all invasive in nature requiring kidney biopsies with subsequent histological validation. In this retrospective study, the diagnostic value of three different radiotracers for the noninvasive prediction of kidney fibrosis was analyzed, taking into account the glomerular filtration rate (GFR) and the intra-renal parenchymal radiotracer uptake.

Methods

In 81 patients receiving either one of the following molecular imaging probes, [⁶⁸ Ga]Ga-FAPI, [⁶⁸ Ga]Ga-PSMA, or [⁶⁸ Ga]Ga-DOTATOC, kidney function parameters were correlated with SUVmax and SUVmean of the renal parenchyma and background activity measured in lung parenchyma, myocardium, gluteal muscle, and the abdominal aorta. Patients were clustered according to their grade of chronic kidney disease (CKD), and a regression analysis and one-way ANOVA were conducted in this retrospective analysis.

Results

We found a negative correlation between GFR and [⁶⁸ Ga]Ga-FAPI uptake for both SUVmax and SUVmean values, whereas background activity showed no correlation with GFR. [⁶⁸ Ga]Ga-DOTATOC and [⁶⁸ Ga]Ga-PSMA did not correlate between CKD stage and intra-renal parenchymal radiotracer uptake. Only [⁶⁸ Ga]Ga-PSMA background activity exhibited a positive correlation with GFR suggesting an unspecific binding/retention potentially due to longer circulation times.

Conclusion

There is a significant negative correlation between renal parenchymal [⁶⁸ Ga]Ga-FAPI uptake and GFR, which was not the case for [⁶⁸ Ga]Ga-DOTATOC and [⁶⁸ Ga]Ga-PSMA. This correlation suggests a specific binding of FAPI rather than a potential unspecific retention in the renal parenchyma, underlining the potential value of [⁶⁸ Ga]Ga-FAPI for the noninvasive quantitative evaluation of kidney fibrosis.

The added value of PSMA PET/MR radiomics for prostate cancer staging

PURPOSE

To evaluate the performance of combined PET and multiparametric MRI (mpMRI) radiomics for the group-wise prediction of postsurgical Gleason scores (psGSs) in primary prostate cancer (PCa) patients.

METHODS

Patients with PCa, who underwent [68 Ga]Ga-PSMA-11 PET/MRI followed by radical prostatectomy, were included in this retrospective analysis (n = 101). Patients were grouped by psGS in three categories: ISUP grades 1-3, ISUP grade 4, and ISUP grade 5. mpMRI images included T1-weighted, T2-weighted, and apparent diffusion coefficient (ADC) map. Whole-prostate segmentations were performed on each modality, and image biomarker standardization initiative (IBSI)-compliant radiomic features were extracted. Nine support vector machine (SVM) models were trained: four single-modality radiomic models (PET, T1w, T2w, ADC); three PET + MRI double-modality models (PET + T1w, PET + T2w, PET + ADC), and two baseline models (one with patient data, one image-based) for comparison. A sixfold stratified cross-validation was performed, and balanced accuracies (bAcc) of the predictions of the best-performing models were reported and compared through Student's t-tests. The predictions of the best-performing model were compared against biopsy GS (bGS).

RESULTS

All radiomic models outperformed the baseline models. The best-performing (mean ± stdv [%]) single-modality model was the ADC model (76 ± 6%), although not significantly better (p > 0.05) than other single-modality models (T1w: 72 ± 3%, T2w: 73 ± 2%; PET: 75 ± 5%). The overall best-performing model combined PET + ADC radiomics (82 ± 5%). It significantly outperformed most other double-modality (PET + T1w: 74 ± 5%, p = 0.026; PET + T2w: 71 ± 4%, p = 0.003) and single-modality models (PET: p = 0.042; T1w: p = 0.002; T2w: p = 0.003), except the ADC-only model (p = 0.138). In this initial cohort, the PET + ADC model outperformed bGS overall (82.5% vs 72.4%) in the prediction of psGS.

CONCLUSION

All single- and double-modality models outperformed the baseline models, showing their potential in the prediction of GS, even with an unbalanced cohort. The best-performing model included PET + ADC radiomics, suggesting a complementary value of PSMA-PET and ADC radiomics.

Automated Radiosynthesis, Quality Control, and Biodistribution of Ga-68 Pentixafor: First Indian Experience

Background

Chemokine receptor CXCR4 is overexpressed in more than 27 different human tumors that make it a promising target in oncology. Ga-68 Pentixafor is the most promising positron emission tomography tracer for imaging CXCR4 receptors; hence, the present study was carried out to optimize the radiosynthesis of Ga-68-Pentixafor using fully automated method and the quality control (QC) checks were performed before being used as a clinical product. We also studied the normal biodistribution pattern of Ga-68-pentixafor intended for the use in variety of malignancies.

Materials and Methods

We optimized the automated radio-synthesis of Ga-68 Pentixafor under good manufacturing practice conditions. A total of 62 productions were carried out in a span of 4 years. Extensive QC tests were performed to check for potency, identity, efficacy, and stability of the tracer. Biodistribution of Ga-68 Pentixafor was investigated in a healthy volunteer to determine normal range of standardized uptake value_maximum (SUV_max) values in various organs.

Results

The radiotracer was prepared successfully in 57/62 productions with radiochemical purity of >99%. Mean radiolabelling efficiency of 73.1% ± 7.7% (n = 57) was obtained with synthesis time approximatively of 34 min. The radiolabeled complex showed no signs of dissociation up to 4 h at the room temperature. Ga-68 Pentixafor upon incubation with human serum was found to be stable at 37°C for 4 h. The highest normal organ uptake was seen in urinary bladder (SUV_mean = 146.0), spleen (SUV_mean = 6.80) followed by kidneys (SUV_mean = 4.99).

Conclusion

Using the automated radiosynthesis, Ga-68 Pentixafor exhibited good radiolabelling efficiency with excellent in vitro and in vivo stability and favorable biodistribution showing clinical applicability of the tracer.

PSMA-ligand uptake can serve as a novel biomarker in primary prostate cancer to predict outcome after radical prostatectomy

Background

The prostate-specific membrane antigen (PSMA) is a relevant target in prostate cancer, and immunohistochemistry studies showed associations with outcome. PSMA-ligand positron emission tomography (PET) is increasingly used for primary prostate cancer staging, and the molecular imaging TNM classification (miTNM) standardizes its reporting. We aimed to investigate the potential of PET-imaging to serve as a noninvasive imaging biomarker to predict disease outcome in primary prostate cancer after radical prostatectomy (RP).

Methods

In this retrospective analysis, 186 primary prostate cancer patients treated with RP who had undergone a ⁶⁸Ga-PSMA-11 PET up to three months prior to the surgery were included. Maximum standardized uptake value (SUV_max), SUV_mean, tumor volume (TV) and total lesion (TL) were collected from PET-imaging. Moreover, clinicopathological information, including age, serum prostate-specific antigen (PSA) level, and pathological characteristics, was assessed for disease outcome prediction. A stage group system for PET-imaging findings based on the miTNM framework was developed.

Results

At a median follow-up after RP of 38 months (interquartile range (IQR) 22–53), biochemical recurrence (BCR) was observed in 58 patients during the follow-up period. A significant association between a positive surgical margin and miN status (miN1 vs. miN0, odds ratio (OR): 5.428, p = 0.004) was detected. miT status (miT ≥ 3a vs. miT < 3, OR: 2.696, p = 0.003) was identified as an independent predictor for Gleason score (GS) ≥ 8. Multivariate Cox regression analysis indicated that PSA level (hazard ratio (HR): 1.024, p = 0.014), advanced GS (GS ≥ 8 vs. GS < 8, HR: 3.253, p < 0.001) and miT status (miT ≥ 3a vs. miT < 3, HR: 1.941, p = 0.035) were independent predictors for BCR. For stage I disease as determined by PET-imaging, a shorter BCR-free survival was observed in the patients with higher SUV_max (IA vs. IB stage, log-rank, p = 0.022).

Conclusion

Preoperative miTNM classification from ⁶⁸Ga-PSMA-11 PET correlates with postoperative GS, surgical margin status and time to BCR. The association between miTNM staging and outcome proposes ⁶⁸Ga-PSMA-11 PET as a novel non-invasive imaging biomarker and potentially serves for ancillary pre-treatment stratification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00818-2.

68Ga-Pentixafor-PET/CT imaging represents a novel approach to detect chemokine receptor CXCR4 expression in myeloproliferative neoplasms

C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for cancer diagnosis and treatment, as it is overexpressed in many solid and hematological malignancies. This study investigated the feasibility of CXCR4-directed imaging with positron emission tomography/computed tomography (PET/CT) using ⁶⁸Ga-Pentixafor to visualize and quantify disease involvement in myeloproliferative neoplasms (MPNs). Methods: 12 patients with MPNs (n = 4 primary myelofibrosis, n = 6 essential thrombocythemia, n = 2 polycythemia vera) and 5 controls underwent ⁶⁸Ga-Pentixafor-PET/CT. Imaging findings were compared with immunohistochemical stainings, laboratory data and splenic volume. Results: ⁶⁸Ga-Pentixafor-PET/CT was visually positive in 12/12 patients and CXCR4 target specificity could be confirmed by immunohistochemical staining. A significantly higher tracer uptake could be detected in the bone marrow of MPN patients (SUVmean 6.45±2.34 vs. 4.44±1.24). Dynamic changes of CXCR4 expression determined by ⁶⁸Ga-Pentixafor-PET/CT corresponded with treatment response. Conclusion: ⁶⁸Ga-Pentixafor-PET/CT represents a novel diagnostic tool to non-invasively detect and quantify the extent of disease involvement in MPNs.

CXCR4-Directed PET/CT in Patients with Newly Diagnosed Neuroendocrine Carcinomas

We aimed to elucidate the diagnostic potential of the C-X-C motif chemokine receptor 4 (CXCR4)-directed positron emission tomography (PET) tracer ⁶⁸Ga-Pentixafor in patients with poorly differentiated neuroendocrine carcinomas (NEC), relative to the established reference standard ¹⁸F-FDG PET/computed tomography (CT). In our database, we retrospectively identified 11 treatment-naïve patients with histologically proven NEC, who underwent ¹⁸F-FDG and CXCR4-directed PET/CT for staging and therapy planning. The images were analyzed on a per-patient and per-lesion basis and compared to immunohistochemical staining (IHC) of CXCR4 from PET-guided biopsies. ⁶⁸Ga-Pentixafor visualized tumor lesions in 10/11 subjects, while¹⁸F-FDG revealed sites of disease in all 11 patients. Although weak to moderate CXCR4 expression could be corroborated by IHC in 10/11 cases, ¹⁸F-FDG PET/CT detected significantly more tumor lesions (102 vs. 42; total lesions, n = 107; p < 0.001). Semi-quantitative analysis revealed markedly higher ¹⁸F-FDG uptake as compared to ⁶⁸Ga-Pentixafor (maximum and mean standardized uptake values (SUV) and tumor-to-background ratios (TBR) of cancerous lesions, SUV_max: 12.8 ± 9.8 vs. 5.2 ± 3.7; SUV_mean: 7.4 ± 5.4 vs. 3.1 ± 3.2, p < 0.001; and, TBR 7.2 ± 7.9 vs. 3.4 ± 3.0, p < 0.001). Non-invasive imaging of CXCR4 expression in NEC is inferior to the reference standard ¹⁸F-FDG PET/CT.

Improved Primary Staging of Marginal-Zone Lymphoma by Addition of CXCR4-Directed PET/CT

PET/CT with ¹⁸F-FDG is an integral component in the primary staging of most lymphomas. However, its utility is limited in marginal-zone lymphoma (MZL) because of inconsistent ¹⁸F-FDG avidity. One diagnostic alternative could be the targeting of C-X-C motif chemokine receptor 4 (CXCR4), shown to be expressed by MZL cells. This study investigated the value of adding CXCR4-directed ⁶⁸Ga-pentixafor PET/CT to conventional staging. Methods: Twenty-two newly diagnosed MZL patients were staged conventionally and with CXCR4 PET/CT. Lesions identified exclusively by CXCR4 PET/CT were biopsied as the standard of reference and compared with imaging results. The impact of CXCR4-directed imaging on staging results and treatment protocol was assessed. Results: CXCR4 PET/CT correctly identified all patients with viable MZL and was superior to conventional staging (P < 0.001). CXCR4-directed imaging results were validated by confirmation of MZL in 16 of 18 PET-guided biopsy samples. Inclusion of CXCR4 PET/CT in primary staging significantly impacted staging results in almost half of patients and treatment protocols in a third (upstaging, n = 7; downstaging, n = 3; treatment change, n = 8; P < 0.03). Conclusion: CXCR4 PET/CT is a suitable tool in primary staging of MZL and holds the potential to improve existing diagnostic algorithms.

A Rapid and Specific HPLC Method to Determine Chemical and Radiochemical Purity of [68Ga]Ga-DOTA-Pentixafor (PET) Tracer: Development and Validation

BACKGROUND

Due to its overexpression in a variety of tumor types, the chemokine receptor 4 (CXCR4) represents a highly relevant diagnostic and therapeutic target in nuclear oncology. Recently, [⁶⁸Ga]Ga-DOTA-Pentixafor has emerged as an excellent imaging agent for positron emission tomography (PET) of CXCR4 expression in vivo. Preparation conditions may influence the quality and in vivo behaviour of this tracer and no standard procedure for the quality controls (QCs) is available.

OBJECTIVE

The developed analytical test method was validated because a specific monograph in the Pharmacopoeia is not available for [68Ga]Ga-DOTA-Pentixafor.

METHOD

A stepwise approach was used based on the quality by design (QbD) concept of the ICH Q2 (R1) and Q8 (Pharmaceutical Development) guidelines in accordance with the regulations and requirements of EANM, SNM, IAEA and WHO.

RESULTS

The purity and quality of the radiopharmaceutical obtained according to the proposed method were found to be high enough to safely administrate it to patients. Excellent linearity was found between 0.5 and 4 μg/mL, with a correlation coefficient (r²) for calibration curves being equal to 0.999, the average coefficient of variation (CV%) < 2% and average bias% that did not deviate more than 5% for all concentrations.

CONCLUSION

This study developed a new rapid and simple HPLC method of analysis for the routine QCs of [⁶⁸Ga]Ga-DOTA-Pentixafor to guarantee the high quality of the finished product before release.

Clinical Molecular Imaging of Pulmonary CXCR4 Expression to Predict Outcome of Pirfenidone Treatment in Idiopathic Pulmonary Fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive disease for which two antifibrotic drugs recently were approved. However, an unmet need exists to predict responses to antifibrotic treatment, such as pirfenidone. Recent data suggest that upregulated expression of CXCR4 is indicative of outcomes in IPF.

RESEARCH QUESTION

Can quantitative, molecular imaging of pulmonary CXCR4 expression as a biomarker for disease activity predict response to the targeted treatment pirfenidone and prognosis in patients with IPF?

STUDY DESIGN AND METHODS

CXCR4 expression was analyzed by immunohistochemistry examination of lung tissues and reverse-transcriptase polymerase chain reaction analysis of BAL. PET-CT scanning with the specific CXCR4 ligand ⁶⁸Ga-pentixafor was performed in 28 IPF patients and compared with baseline clinical characteristics. In 16 patients, a follow-up scan was obtained 6 to 12 weeks after initiation of treatment with pirfenidone. Patients were followed up in our outpatient clinic for ≥ 12 months.

RESULTS

Immunohistochemistry analysis showed high CXCR4 staining of epithelial cells and macrophages in areas with vast fibrotic remodeling. Targeted PET scanning revealed CXCR4 upregulation in fibrotic areas of the lungs, particularly in zones with subpleural honeycombing. Baseline CXCR4 signal demonstrated a significant correlation with Gender Age Physiology stage (r = 0.44; P = .02) and with high-resolution CT scan score (r = 0.38; P = .04). Early changes in CXCR4 signal after initiation of pirfenidone treatment correlated with the long-term course of FVC after 12 months (r = -0.75; P = .0008). Moreover, patients with a high pulmonary CXCR4 signal on follow-up PET scan after 6 weeks into treatment demonstrated a statistically significant worse outcome at 12 months (P = .002). In multiple regression analysis, pulmonary CXCR4 signal on follow-up PET scan emerged as the only independent predictor of long-term outcome (P = .0226).

INTERPRETATION

CXCR4-targeted PET imaging identified disease activity and predicted outcome of IPF patients treated with pirfenidone. It may serve as a future biomarker for personalized guidance of antifibrotic treatment.

Comparison of 68Ga-PSMA-617 PET/CT with mpMRI for the detection of PCa in patients with a PSA level of 4-20 ng/ml before the initial biopsy

The study was aimed at assessing the diagnostic performance of ⁶⁸Ga-PSMA-617 PET/CT in the detection of prostate cancer (PCa) in patients with a prostate-specific antigen (PSA) level of 4–20 ng/ml and to compare its efficacy with that of multiparametric MRI (mpMRI). We analyzed the data of 67 consecutive patients with PSA levels of 4–20 ng/ml who almost simultaneously underwent ⁶⁸Ga-PSMA-617 PET/CT and mpMRI. ⁶⁸Ga-PSMA-617 PET/CT and mpMRI diagnostic performances were compared via receiver operating characteristic (ROC) curve analysis. Of the 67 suspected PCa cases, 33 had pathologically confirmed PCa. ⁶⁸Ga-PSMA-617 PET/CT showed a patient-based sensitivity, specificity, and positive and negative predictive values (PPVs and NPVs) of 87.88%, 88.24%, 87.88%, and 88.24%, respectively. The corresponding values for mpMRI were 84.85%, 52.94%, 63.64%, and 78.26%. The area under the curve values for ⁶⁸Ga-PSMA-617 PET/CT and mpMRI were 0.881 and 0.689, respectively. ⁶⁸Ga-PSMA-617 PET/CT showed a better diagnostic performance than mpMRI in the detection of PCa in patients with PSA levels of 4–20 ng/ml.

In Human Visualization of Ibrutinib-Induced CLL Compartment Shift

Bruton tyrosine kinase inhibitor ibrutinib is effective in treating chronic lymphocytic leukemia (CLL). However, after ibrutinib treatment initiation, patients frequently experience an increase of CLL blood cell count. This phenomenon in clinical practice is thought to reflect a "compartment shift" of CLL cells from lymph nodes to the peripheral blood, but the actual shifting has not yet been demonstrated. Using [⁶⁸Ga]Pentixafor-PET/MRI for in vivo CXCR4 visualization, we here provide images of topical changes of CLL cells upon ibrutinib treatment. Within the first month of ibrutinib treatment, mean standardized [⁶⁸Ga]Pentixafor uptake decreased in the bone marrow and lymph nodes, whereas [⁶⁸Ga]Pentixafor uptake increased in the spleen. Leukocytosis rose, as did numbers of CXCR4^high (tissue-resident) CLL cells. Volumes of lymph nodes and spleen decreased. Upon longer ibrutinib treatment, leukocytosis decreased, followed by a decrease of [⁶⁸Ga]Pentixafor uptake in the spleen. These results support the preexisting clinical hypothesis of a "compartment shift" of CLL cells from the lymph nodes to the peripheral blood, but also refine the mechanistic model by describing early clearing of the bone marrow and redistribution of CLL cells to the orthotopic splenic cavernous system in response to ibrutinib treatment.

CXCR4-Targeted PET Imaging of Central Nervous System B-Cell Lymphoma

C-X-C chemokine receptor 4 (CXCR4) is a transmembrane chemokine receptor involved in growth, survival, and dissemination of cancer, including aggressive B-cell lymphoma. MRI is the standard imaging technology for central nervous system (CNS) involvement of B-cell lymphoma and provides high sensitivity but moderate specificity. Therefore, novel molecular and functional imaging strategies are urgently required. Methods: In this proof-of-concept study, 11 patients with lymphoma of the CNS (8 primary and 3 secondary involvement) were imaged with the CXCR4-directed PET tracer ⁶⁸Ga-pentixafor. To evaluate the predictive value of this imaging modality, treatment response, as determined by MRI, was correlated with quantification of CXCR4 expression by ⁶⁸Ga-pentixafor PET in vivo before initiation of treatment in 7 of 11 patients. Results: ⁶⁸Ga-pentixafor PET showed excellent contrast with the surrounding brain parenchyma in all patients with active disease. Furthermore, initial CXCR4 uptake determined by PET correlated with subsequent treatment response as assessed by MRI. Conclusion: ⁶⁸Ga-pentixafor PET represents a novel diagnostic tool for CNS lymphoma with potential implications for theranostic approaches as well as response and risk assessment.

Pre-test 68Ga-PSMA-ligand PET/CT positivity in early biochemical recurrent prostate cancer after radical prostatectomy-validation of a prediction model

Objectives

The aim of this study was the validation of a recently established comprehensive and compact prediction model for ⁶⁸Ga-PSMA-11-ligand positron-emission tomography (PET) positivity with an independent subsequent patient series.

Methods

A total of 292 consecutive patients with early biochemical recurrence after radical prostatectomy and PSA values between 0.2 and 1 ng/ml who underwent ⁶⁸Ga-PSMA-11-ligand PET/computed tomography (CT) between January 2016 and June 2017 were retrospectively included. The cohort was divided into a very low PSA value (0.2–0.5 ng/ml, n = 151) and a low PSA value (> 0.5–1 ng/ml, n = 141) subgroup. First, pre-test positivity probabilities for each patient were calculated according to the previously published comprehensive prediction model using all clinical variables (PSA value, ISUP grade group, T- and N-stage, patient under androgen deprivation therapy (ADT), previous radiation therapy) and the compact model using just the most predictive factors PSA value, ADT, and grade group. Then, all ⁶⁸Ga-PSMA-11-ligand PET/CTs were analysed by one experienced nuclear medicine physician, and the results were correlated to the calculated pre-test probabilities.

Results

In the very low PSA value subgroup, mean pre-test probability for positive findings in ⁶⁸Ga-PSMA-11-ligand PET/CT was 57% (95% CI 55–60%) according to the compact model and 59% (95% CI 56–61%) according to the comprehensive model. In the low PSA value subgroup, mean pre-test probability was 72% (95% CI 70–74%) in the compact model and 74% (95% CI 72–76%) in the comprehensive model. After image analysis, 59% (89/151) of the patients in the very low PSA value subgroup revealed positive imaging findings. Seventy-nine percent (112/141) of the patients in the low PSA value subgroup presented with positive findings in the ⁶⁸Ga-PSMA-11-ligand PET/CT. The accuracy (AUC) of the prediction models was 0.71 (95% CI 0.65–0.78) for the compact model and 0.74 (95% CI 0.68–0.80) for the comprehensive model.

Conclusion

External validation of the recently proposed prediction models showed a high concordance of the calculated pre-test probabilities and actual ⁶⁸Ga-PSMA-11-ligand PET/CT findings in the validation cohort confirming the prediction models’ ability to determine the presence of a positive lesion at ⁶⁸Ga-PSMA-11-ligand PET. However, the predictive accuracy of the nomogram itself is suboptimal and should be used with caution. Furthermore, the model’s generalizability may be hampered due to the study design (in-house validation). Nevertheless, given the limited health resources and the costs of hybrid imaging techniques, prediction models might be a benefit in patient selection.

CXCR4-Directed Imaging in Solid Tumors

Despite histological evidence in various solid tumor entities, available experience with CXCR4-directed diagnostics and endoradiotherapy mainly focuses on hematologic diseases. With the goal of expanding the application of CXCR4 theranostics to solid tumors, we aimed to elucidate the feasibility of CXCR4-targeted imaging in a variety of such neoplasms. Methods: Nineteen patients with newly diagnosed, treatment-naïve solid tumors including pancreatic adenocarcinoma or neuroendocrine tumor, cholangiocarcinoma, hepatocellular carcinoma, renal cell carcinoma, ovarian cancer, and prostate cancer underwent [⁶⁸Ga]Pentixafor PET/CT. CXCR4-mediated uptake was assessed both visually and semi-quantitatively by evaluation of maximum standardized uptake values (SUV_max) of both primary tumors and metastases. With physiologic liver uptake as reference, tumor-to-background ratios (TBR) were calculated. [⁶⁸Ga]Pentixafor findings were further compared to immunohistochemistry and [¹⁸F]FDG PET/CT. Results: On [⁶⁸Ga]Pentixafor PET/CT, 10/19 (52.6%) primary tumors were visually detectable with a median SUV_max of 5.4 (range, 1.7-16.0) and a median TBR of 2.6 (range, 0.8-7.4), respectively. The highest level of radiotracer uptake was identified in a patient with cholangiocarcinoma (SUV_max, 16.0; TBR, 7.4). The relatively low uptake on [⁶⁸Ga]Pentixafor was also noted in metastases, exhibiting a median SUV_max of 4.5 (range, 2.3-8.8; TBR, 1.7; range, 1.0-4.1). A good correlation between uptake on [⁶⁸Ga]Pentixafor and histological derived CXCR4 expression was noted (R = 0.62, P < 0.05). In the 3 patients in whom [¹⁸F]FDG PET/CT was available, [⁶⁸Ga]Pentixafor exhibited lower uptake in all lesions. Conclusions: In this cohort of newly diagnosed, treatment-naïve patients with solid malignancies, CXCR4 expression as detected by [⁶⁸Ga]Pentixafor-PET/CT and immunohistochemistry was rather moderate. Thus, CXCR4-directed imaging may not play a major role in the management of solid tumors in the majority of patients.

Does lymph node localization affect prostate-specific membrane antigen uptake?

OBJECTIVE

To investigate the relationship between lymph node (LN) size and localization and prostate-specific membrane antigen (PSMA) uptake in patients with prostate cancer.

PATIENTS AND METHODS

Between February 2015 and February 2017, a total of 178 patients diagnosed with prostate adenocarcinoma by gallium-68 PSMA PET/computed tomography were evaluated. Seventy-eight patients with LN PSMA uptake were included in the study.The short-axis diameter and maximum and mean standardized uptake values (SUV) were measured from axial images of LNs with PSMA uptake. LN conglomerates were considered a single lesion. Patients were divided into two groups according to the presence (group 1) or absence (group 2) of bone uptake in addition to the LN uptake; subgroups were constituted according to the short-axis diameter and PSMA-positive LN region for each group. LNs were classified according to their localization as pelvic, abdominal, or cervical/thoracic.

RESULTS

In both groups, the SUV were significantly higher in LNs with short-axis diameters more than 8 mm than those with diameters up to 8 mm (P < 0.001 and < 0.001, respectively). Also, both groups showed a moderate correlation between the LN size and SUV.When the analysis was carried out according to the localization, but after excluding the LN conglomerates, the correlation between the pelvic and abdominal LNs was higher in the second group.

CONCLUSION

The highest significant positive correlation between LN size and SUV was in patients with pelvic and abdominal LN metastases without bone involvement according to the gallium-68 PSMA PET/computed tomography images in our study.

Imaging Characteristics and First Experience of [68Ga]THP-PSMA, a Novel Probe for Rapid Kit-Based Ga-68 Labeling and PET Imaging: Comparative Analysis with [68Ga]PSMA I&T

PURPOSE

[⁶⁸Ga]Trishydroxypyridinone (THP)-prostate-specific membrane antigen (PSMA) is a novel tracer that can be labeled in one step by cold reconstitution of a kit with unprocessed generator eluate, targeting PSMA via the lysine-urea-glutamate (KuE) motif. The aim of this study was to evaluate the human imaging characteristics of [⁶⁸Ga]THP-PSMA.

PROCEDURES

[⁶⁸Ga]THP-PSMA positron emission tomography (PET)/x-ray computed tomography (CT) was performed in 25 patients with biochemical recurrence after radical prostatectomy for prostate cancer. Urinary and biliary excretion and tumor lesion uptake were quantified using standardized uptake values (SUVs). Imaging characteristics were assessed in terms of non-target organ uptake, background activity, target-to-background ratios (TBRs) of tumor lesions, and frequency of bladder halo artifacts. Findings were compared to a matched cohort of 25 patients undergoing PET/CT with the established agent [⁶⁸Ga]PSMA I&T.

RESULTS

Physiologic uptake of [⁶⁸Ga]THP-PSMA was significantly lower in salivary glands (P < 0.0001), liver (P < 0.0001), spleen (P < 0.0001), and kidneys (P < 0.0001) than with [⁶⁸Ga]PSMA I&T. While biliary tracer excretion of [⁶⁸Ga]THP-PSMA was negligible, urinary tracer excretion of [⁶⁸Ga]THP-PSMA was fast, and significantly higher than for [⁶⁸Ga]PSMA I&T, contributing to a higher frequency of bladder artifacts. Malignant lesion uptake of [⁶⁸Ga]THP-PSMA assessed as either SUV or TBR was significantly lower than with [⁶⁸Ga]PSMA I&T.

CONCLUSION

[⁶⁸Ga]THP-PSMA yields suitable in vivo uptake characteristics. The simplified synthesis method for [⁶⁸Ga]THP-PSMA may facilitate wider application and higher patient throughput with PSMA imaging. However, direct intraindividual comparison studies are needed to assess the relative performance of [⁶⁸Ga]THP-PSMA vs other PSMA ligands in terms of clinical detection rate and image quality.

Automated production of [68 Ga]Ga-DOTANOC and [68 Ga]Ga-PSMA-11 using a TRACERlab FXFN synthesis module

The interest in gallium-68 labelled positron-emission tomography probes continues to increase around the world. However, one of the barriers for routine clinical use is the cost of the automated synthesis units for relatively simple labelling procedures. Herein, we describe the adaptation of a TRACERlab FX_FN synthesis module for the automated production of gallium-68 radiopharmaceuticals using a cation-exchange cartridge for postprocessing of the ⁶⁸ Ge/⁶⁸ Ga generator eluate. The recovery of activity from the cartridge was 95.6% to 98.9% using solutions of acidified sodium chloride (5 M with pH = 1-3). The radiosyntheses of [⁶⁸ Ga]Ga-DOTANOC and [⁶⁸ Ga]Ga-PSMA-11 were performed using acetate sodium buffer or 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid, with a total duration of 21 and 23 minutes, respectively, including generator elution and radiopharmaceutical dispensing. Activity yields were 77% ± 2% for [⁶⁸ Ga]Ga-PSMA-11 and 68% ± 3% for [⁶⁸ Ga]Ga-DOTANOC (n > 100). The labelled peptides had a radiochemical purity exceeding 97%, and all quality control parameters were in conformity with the limits prescribed by the European Pharmacopoeia.

Diagnostic performance of 68Ga-PSMA PET/CT in the detection of prostate cancer prior to initial biopsy: comparison with cancer-predicting nomograms

PURPOSE

To assess the diagnostic performance of ⁶⁸Ga-PSMA PET/CT for detecting suspected prostate cancer (PCa) and to compare it with that of two cancer-predicting nomograms.

METHODS

We performed a retrospective analysis of 146 consecutive patients with suspected PCa based on symptoms or elevated total prostate-specific antigen (tPSA) levels who underwent ⁶⁸Ga-PSMA PET/CT and histopathologic examinations from April 2017 to April 2018 in a large tertiary care hospital in China. The ⁶⁸Ga-PSMA PET/CT results (PCa or benignancy) were evaluated by two experienced nuclear medicine specialists. The risk of positive PCa was evaluated using ERSPC and PCPT nomograms. The diagnostic performances of ⁶⁸Ga-PSMA PET/CT and that of the two nomograms were compared via receiver operating characteristic (ROC) curve analysis, decision curve analysis, and logistic regression.

RESULTS

A total of 58 patients with tPSA of 0.4-50 ng/ml were included in the final analysis; PCa diagnosis was confirmed in 37 patients and excluded in 21 patients. ROC analysis showed that the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ⁶⁸Ga-PSMA PET/CT were 91.67, 81.82, 89.19, and 85.71%, respectively, in per-patient analyses. ⁶⁸Ga-PSMA PET/CT exhibited a higher AUC (0.867) than those of ERSPC-RC3 (0.855) and PCPT-RC (0.770). The net benefit of ⁶⁸Ga-PSMA PET/CT was greatest for patients within threshold probabilities of 15-90%. Among the 58 patients, 11 (19%) biopsies suggested by ERSPC-RC3 were unnecessary and could have been avoided if judged by the ⁶⁸Ga-PSMA PET/CT results. Multivariate analysis revealed that the maximum standardised uptake value (SUV_max) and prostate volume were significant predictive factors for positive PCa results.

CONCLUSION

In suspected PCa patients with tPSA of 0.4-50 ng/ml, ⁶⁸Ga-PSMA PET/CT outperformed the nomograms in predicting cancer and reducing unnecessary biopsies. In addition, the risk of PCa was positively correlated with a higher SUV_max and lower prostate volume, which could help clinicians in making preliminary estimates of individual cancer risk, monitoring ⁶⁸Ga-PSMA PET/CT false-positive results and making biopsy decisions in daily medical practice.

Comparison of 68 Ga-PSMA ligand PET/CT versus conventional cross-sectional imaging for target volume delineation for metastasis-directed radiotherapy for metachronous lymph node metastases from prostate cancer

PURPOSE

To assess the differences in the target volume (TV) delineation of metachronous lymph node metastases between ⁶⁸ Ga-PSMA ligand PET/CT and conventional imaging in a comparative retrospective contouring study.

PATIENTS AND METHODS

Twenty-five patients with biochemical prostate cancer recurrence after primary prostatectomy underwent ⁶⁸ Ga-PSMA ligand PET/CT in addition to conventional imaging techniques such as CT and/or MR imaging for restaging. All patients were diagnosed with at least one lymph node metastasis. TVs were manually delineated in two different ways: (a) based on conventional imaging (CT/MRI) and (b) based on conventional imaging (CT/MRI) plus ⁶⁸ Ga-PSMA ligand PET/CT. The size of TVs, overlap rates, and subjective assessment of the difficulty of TV delineation reported by the radiation oncologist (easy/moderate/difficult) were compared.

RESULTS

With the additional information from PSMA ligand PET, 47 lymph node metastases were identified and included in the gross tumor volume (GTV). The median clinical target volume (CTV) of non-PET-based TV delineation was statistically larger than the CTV based on PET imaging (134.8 ml [range 6.9-565.2] versus 44.9 ml [range 4.9-481.3; p = 0.001]). The CTV based on CT/MRI enclosed only 81.3% (39/48) of PET-positive lymph nodes. The CT/MRI-based CTV did not enclose all PET-positive lymph nodes in 24% (6/25) of patients. In 12% (3/25) of patients, all PET-positive lymph nodes were outside of the CT/MRI-based CTV. The median overlap rates (TV_PET/TV_CT/MRI × 100) were 45.7% (range 0-96.9) for the GTV and 71.7% (range 9.8-98.2) for the CTV. The assessment of difficulty of contouring revealed that contouring with the additional imaging information of the PET was categorized as easy/moderate in 92% (23/25) and as difficult in 8% (2/25) of the cases, whereas contouring based on CT/MRI without PET was categorized as difficult in 56% (14/25) and as easy/moderate in 44% of the cases (11/25; p = 0.003).

CONCLUSION

⁶⁸ Ga-PSMA ligand PET/CT is superior to conventional cross-sectional imaging for the delineation of lymph node metastases from prostate cancer. PET-based TV delineation allows for smaller target volumes and should be considered the standard for irradiation of metachronous lymph node metastases in recurrent prostate cancer. Conventional imaging is not sufficiently sensitive for radio-oncological treatment concepts in oligometastatic prostate cancer.

Development and evaluation of a rapid analysis for HEPES determination in 68Ga-radiotracers

BACKGROUND

HEPES is a favorable buffer for ⁶⁸Ga-complexations in radiochemical laboratories. The drawback of this buffer is its prescribed limit of 200 μg per recommended application volume in the final formulation. Currently, a TLC test according to the European Pharmacopoeia (Ph. Eur.) has to be performed for quantification, but this analysis suffers from low reliability and reproducibility and is based on a subjective, semi-quantitative visual evaluation. In this study, the TLC method according to the Ph. Eur. and two literature-known HPLC assays for HEPES quantification were evaluated. Additionally, the development of an improved TLC method was performed.

RESULTS

The assay according to Antunes et al. provided a reasonable quantification of HEPES using HPLC. Additionally, a reliable and conclusive TLC method was developed, which facilitates quantitative analysis by means of a pixel-based evaluation. A comparison of those two methods with the Ph. Eur. TLC assay pinpoints the superiority of the HPLC as well as the new TLC assay. Furthermore, evaluation of HEPES contents using both TLC assays by 28 subjects supported the conclusion that the newly developed TLC method is clearly favorable.

CONCLUSION

The TLC method according to the Ph. Eur. provides unsatisfactory results in terms of conclusiveness and reproducibility. In contrast, a reported HPLC assay showed valid results, with the drawback of high technical effort. An optimized alternative is provided by the improved TLC method described in this work that results in reliable outcomes and additionally offers quantitative analysis.

Imaging of chemokine receptor CXCR4 expression in culprit and nonculprit coronary atherosclerotic plaque using motion-corrected [68Ga]pentixafor PET/CT

Purpose

The chemokine receptor CXCR4 is a promising target for molecular imaging of CXCR4⁺ cell types, e.g. inflammatory cells, in cardiovascular diseases. We speculated that a specific CXCR4 ligand, [⁶⁸Ga]pentixafor, along with novel techniques for motion correction, would facilitate the in vivo characterization of CXCR4 expression in small culprit and nonculprit coronary atherosclerotic lesions after acute myocardial infarction by motion-corrected targeted PET/CT.

Methods

CXCR4 expression was analysed ex vivo in separately obtained arterial wall specimens. [⁶⁸Ga]Pentixafor PET/CT was performed in 37 patients after stent-based reperfusion for a first acute ST-segment elevation myocardial infarction. List-mode PET data were reconstructed to five different datasets using cardiac and/or respiratory gating. Guided by CT for localization, the PET signals of culprit and various groups of nonculprit coronary lesions were analysed and compared.

Results

Ex vivo, CXCR4 was upregulated in atherosclerotic lesions, and mainly colocalized with CD68⁺ inflammatory cells. In vivo, elevated CXCR4 expression was detected in culprit and nonculprit lesions, and the strongest CXCR4 PET signal (median SUV_max 1.96; interquartile range, IQR, 1.55–2.31) was observed in culprit coronary artery lesions. Stented nonculprit lesions (median SUV_max 1.45, IQR 1.23–1.88; P = 0.048) and hot spots in naive remote coronary segments (median SUV_max 1.34, IQR 1.23–1.74; P = 0.0005) showed significantly lower levels of CXCR4 expression. Dual cardiac/respiratory gating provided the strongest CXCR4 PET signal and the highest lesion detectability.

Conclusion

We demonstrated the basic feasibility of motion-corrected targeted PET/CT imaging of CXCR4 expression in coronary artery lesions, which was triggered by vessel wall inflammation but also by stent-induced injury. This novel methodology may serve as a platform for future diagnostic and therapeutic clinical studies targeting the biology of coronary atherosclerotic plaque.

Electronic supplementary material

The online version of this article (10.1007/s00259-018-4076-2) contains supplementary material, which is available to authorized users.

Isolated metastasis of an EGFR-L858R-mutated NSCLC of the meninges: the potential impact of CXCL12/CXCR4 axis in EGFRmut NSCLC in diagnosis, follow-up and treatment

Brain and leptomeningeal metastasis (LMM) of non-small cell lung cancer is still associated with poor prognosis. Moreover, the current diagnostic standard for LMM often yields false negative results and the scientific progress in this field is still unsatisfying. We present a case of a 71-year old patient with an isolated LMM. While standard diagnostics could only diagnose a cancer of unknown primary, the use of [⁶⁸Ga]-Pentixafor-PET/CT (CXCR4-PET/CT, a radiotracer targeting CXCR4) and a liquid biopsy of the cerebrospinal fluid revealed the primary NSCLC. The detection of L858R-EGFR, a common driver mutation in NSCLC, enabled us to treat the patient with Afatinib and monitor treatment using [⁶⁸Ga]-Pentixafor PET/CT. To estimate the impact of CXCR4 signaling and its ligands in NSCLC brain metastasis we looked at their expression and correlation with EGFR mutations in a primary and brain metastasis data set and investigated the previously described binding of extracellular ubiquitin to CXCR4. In conclusion, we describe a novel approach to improve diagnostics towards LMM and underline the impact of the CXCL12/CXCR4 axis in brain metastasis in a subset of NSCLC patients. We cannot confirm a correlation of CXCR4 expression with EGFR mutations or the binding of extracellular ubiquitin as previously reported.

The impact of [68Ga]PSMA I&T PET/CT on radiotherapy planning in patients with prostate cancer

PURPOSE

To determine the impact of Gallium-68-labled prostate-specific membrane antigen positron-emission tomography/computed tomography ([⁶⁸Ga]PSMA PET/CT) on radiotherapy planning for primary disease, biochemical cancer relapse, and advanced disease of prostate cancer.

METHODS

A total of 106 patients with prostate cancer scheduled for radiation therapy underwent 120 [⁶⁸Ga]PSMA PET/CT scans prior to radiotherapy treatment. In 20 cases, patients underwent [⁶⁸Ga]PSMA PET/CT for primary therapy (PT), 75 cases were referred for biochemical relapse after surgery (RL), and 25 cases were intended for palliative treatment of localized metastases (MD). We retrospectively compared the impact of [⁶⁸Ga]PSMA PET/CT on lesion detection and treatment decision to CT alone.

RESULTS

[⁶⁸Ga]PSMA PET/CT revealed a total of 271 positive lesions, whereas CT detected 86 lesions (32%). Overall, the radiotherapy regime was changed in 55 of 120 cases (46%) based on the higher detection rate of [⁶⁸Ga]PSMA PET/CT: in 15% of cases with PT, in 43% of cases with RL, and in 44% of cases with MD.

CONCLUSION

[⁶⁸Ga]PSMA PET/CT is superior to CT alone for lesion detection in prostate cancer, thereby significantly impacting on radiotherapy planning for primary disease, biochemical cancer relapse, and advanced disease of prostate cancer.

Dual Targeting of Acute Leukemia and Supporting Niche by CXCR4-Directed Theranostics

C-X-C chemokine receptor 4 (CXCR4) is a transmembrane receptor with pivotal roles in cell homing and hematopoiesis. CXCR4 is also involved in survival, proliferation and dissemination of cancer, including acute lymphoblastic and myeloid leukemia (ALL, AML). Relapsed/refractory ALL and AML are frequently resistant to conventional therapy and novel highly active strategies are urgently needed to overcome resistance. Methods: We used patient-derived (PDX) and cell line-based xenograft mouse models of ALL and AML to evaluate the efficacy and toxicity of a CXCR4-targeted endoradiotherapy (ERT) theranostic approach. Results: The positron emission tomography (PET) tracer 68Ga-Pentixafor enabled visualization of CXCR4 positive leukemic burden. In xenografts, CXCR4-directed ERT with 177Lu-Pentixather distributed to leukemia harboring organs and resulted in efficient reduction of leukemia. Despite a substantial in vivo cross-fire effect to the leukemia microenvironment, mesenchymal stem cells (MSCs) subjected to ERT were viable and capable of supporting the growth and differentiation of non-targeted normal hematopoietic cells ex vivo. Finally, three patients with refractory AML after first allogeneic hematopoietic stem cell transplantation (alloSCT) underwent CXCR4-directed ERT resulting in leukemia clearance, second alloSCT, and successful hematopoietic engraftment. Conclusion: Targeting CXCR4 with ERT is feasible and provides a highly efficient means to reduce refractory acute leukemia for subsequent cellular therapies. Prospective clinical trials testing the incorporation of CXCR4 targeting into conditioning regimens for alloSCT are highly warranted.

Targeting CXCR4 (CXC Chemokine Receptor Type 4) for Molecular Imaging of Aldosterone-Producing Adenoma

Primary aldosteronism is the most frequent cause of secondary hypertension and is associated with increased morbidity and mortality compared with hypertensive controls. The central diagnostic challenge is the differentiation between bilateral and unilateral disease, which determines treatment options. Bilateral adrenal venous sampling, currently recommended for differential diagnosis, is an invasive procedure with several drawbacks, making it desirable to develop novel noninvasive diagnostic tools. When investigating the expression pattern of chemokine receptors by quantitative real-time polymerase chain reaction and immunohistochemistry, we observed high expression of CXCR4 (CXC chemokine receptor type 4) in aldosterone-producing tissue in normal adrenals, adjacent adrenal cortex from adrenocortical adenomas, and in aldosterone-producing adenomas (APA), correlating strongly with the expression of CYP11B2 (aldosterone synthase). In contrast, CXCR4 was not detected in the majority of nonfunctioning adenomas that are frequently found coincidently. The specific CXCR4 ligand 68Ga-pentixafor has recently been established as radiotracer for molecular imaging of CXCR4 expression and showed strong and specific binding to cryosections of APAs in our study. We further investigated 9 patients with primary aldosteronism because of APA by 68Ga-pentixafor-positron emission tomography. The tracer uptake was significantly higher on the side of increased adrenocortical aldosterone secretion in patients with APAs compared with patients investigated by 68Ga-pentixafor-positron emission tomography for other causes. Molecular imaging of aldosterone-producing tissue by a CXCR4-specific ligand may, therefore, be a highly promising tool for noninvasive characterization of patients with APAs.

Preliminary results on response assessment using 68Ga-HBED-CC-PSMA PET/CT in patients with metastatic prostate cancer undergoing docetaxel chemotherapy

PURPOSE

To investigate the value of ⁶⁸Ga-HBED-CC PSMA (⁶⁸Ga-PSMA) PET/CT for response assessment in metastatic castration-sensitive and castration-resistant prostate cancer (mCSPC and mCRPC) during docetaxel chemotherapy.

METHODS

⁶⁸Ga-PSMA PET/CT was performed in seven mCSPC patients before and after six cycles of upfront docetaxel chemotherapy and in 16 mCRPC patients before and after three cycles of palliative docetaxel chemotherapy. Radiographic treatment response was evaluated separately on the ⁶⁸Ga-PSMA PET and CT datasets. Changes in ⁶⁸Ga-PSMA uptake (SUVmean) were assessed on a per-patient and a per-lesion basis using the PERCIST scoring system with slight modification. Treatment response was defined as absence of any PSMA uptake in all target lesions on posttreatment PET (complete response, CR) or a decrease in summed SUVmean of ≥30% (partial response, PR). The appearance of a new PET-positive lesion or an increase in summed SUVmean of ≥30% (progressive disease, PD) indicated nonresponse. A moderate change in summed SUVmean (between -30% and +30%) without a change in the number of target lesions was defined as stable disease (SD). For treatment response assessment on CT, RECIST1.1 criteria were used. Radiographic responses on ⁶⁸Ga-PSMA PET [RR(PET)] and on CT [RR(CT)] were compared and correlated with biochemical response (BR). A decrease in serum PSA level of ≥50% was defined as biochemical PR.

RESULTS

Biochemical PR was found in six of seven patients with mCSPC (86%, 95% confidence interval 42% to 99.6%). The concordance rate was higher between BR and RR(PET) than between BR and RR(CT) (6/7 vs. 3/6 patients. ⁶⁸Ga-PSMA PET and CT were concordant in only three patients (50%, 12% to 88%). In mCRPC patients, biochemical PR was found in six of 16 patients (38%, 15% to 65%). Outcome prediction was concordant between BR and RR(PET) in nine of 16 patients (56%), and between BR and RR(CT) in only four of 12 patients (33%) with target lesions on CT. ⁶⁸Ga-PSMA PET and CT results corresponded in seven of 12 patients (58%, 28% to 85%).

CONCLUSION

Our preliminary results suggest that ⁶⁸Ga-PSMA PET might be a promising method for treatment response assessment in mCSPC and mCRPC. The data indicate that for different metastatic sites, the performance of ⁶⁸Ga-PSMA PET in response assessment might be superior to that of the conventional CT approach and could help differentiate between progressive disease and treatment response. Because of the limited number of patients, the differences revealed in our study were not statistically significant. Thus larger and prospective studies are clearly needed and warranted to confirm the value of ⁶⁸Ga-PSMA PET as an imaging biomarker for response assessment.

Prostate-specific membrane antigen cleavage of vitamin B9 stimulates oncogenic signaling through metabotropic glutamate receptors

Kaittanis et al. show that the processing of glutamated folates by prostate-specific membrane antigen induces the activation of metabotropic glutamate receptors and initiation of PI3K–Akt signaling in prostate cancer.

Prostate-specific membrane antigen (PSMA) or folate hydrolase 1 (FOLH1) is highly expressed on prostate cancer. Its expression correlates inversely with survival and increases with tumor grade. However, the biological role of PSMA has not been explored, and its role in prostate cancer remained elusive. Filling this gap, we demonstrate that in prostate cancer, PSMA initiates signaling upstream of PI3K through G protein–coupled receptors, specifically via the metabotropic glutamate receptor (mGluR). PSMA’s carboxypeptidase activity releases glutamate from vitamin B9 and other glutamated substrates, which activate mGluR I. Activated mGluR I subsequently induces activation of phosphoinositide 3-kinase (PI3K) through phosphorylation of p110β independent of PTEN loss. The p110β isoform of PI3K plays a particularly important role in the pathogenesis of prostate cancer, but the origin of its activation was so far unknown. PSMA expression correlated with PI3K–Akt signaling in cells, animal models, and patients. We interrogated the activity of the PSMA–PI3K axis through positron emission tomography and magnetic resonance imaging. Inhibition of PSMA in preclinical models inhibited PI3K signaling and promoted tumor regression. Our data present a novel oncogenic signaling role of PSMA that can be exploited for therapy and interrogated with imaging.

68Ga-Pentixafor PET/CT Imaging of Chemokine Receptor CXCR4 in Chronic Infection of the Bone: First Insights

Because of its role in infection and inflammatory processes, the chemokine receptor CXCR4 might be a potent target in imaging of infectious and inflammatory diseases. The aim of this pilot study was to determine whether the CXCR4 ligand ⁶⁸Ga-pentixafor is suitable for imaging chronic infection of the bone. Methods: The study comprised 14 patients with suspected infection of the skeleton who underwent ⁶⁸Ga-pentixafor PET/CT between April 2015 and February 2017 in our facility. ⁶⁸Ga-pentixafor PET/CT results were retrospectively evaluated against a histologic, bacteriologic, and clinical standard. The results were also compared with available bone scintigraphy, white blood cell scintigraphy, and ¹⁸F-FDG PET/CT results. Results:⁶⁸Ga-pentixafor PET/CT was positive in 9 of 14 patients. Diagnoses included osteitis or osteomyelitis of peripheral bone, osteomyelitis of the maxilla, and infected endoprostheses. Target-to-background ratios were 5.1-15 (mean, 8.7). Eight of 9 cases were true-positive as confirmed by pathology, bacteriology, or clinical observation. All negative cases were confirmed as true-negative by other imaging modalities and follow-up. Conclusion: Imaging of CXCR4 expression with ⁶⁸Ga-pentixafor PET/CT appears suitable for diagnosing chronic infection of the skeleton. The findings of this study reveal a possible diagnostic gain in suspected chronic infections that are difficult to diagnose by other imaging modalities.

Targeting CXCR4 with [68Ga]Pentixafor: a suitable theranostic approach in pleural mesothelioma?

C-X-C motif chemokine receptor 4 (CXCR4) is a key factor for tumor growth and metastasis in several types of human cancer. This study investigated the feasibility of CXCR4-directed imaging with positron emission tomography/computed tomography (PET/CT) using [⁶⁸Ga]Pentixafor in malignant pleural mesothelioma.

Six patients with pleural mesothelioma underwent [⁶⁸Ga]Pentixafor-PET/CT. 2′-[¹⁸F]fluoro-2′-deoxy-D-glucose ([¹⁸F]FDG)-PET/CT (4/6 patients) and immunohistochemistry obtained from biopsy or surgery (all) served as standards of reference. Additionally, 9 surgical mesothelioma samples were available for histological work-up.

Whereas [¹⁸F]FDG-PET depicted active lesions in all patients, [⁶⁸Ga]Pentixafor-PET/CT recorded physiologic tracer distribution and none of the 6 patients presented [⁶⁸Ga]Pentixafor-positive lesions. This finding paralleled results of immunohistochemistry which also could not identify relevant CXCR4 surface expression in the samples analyzed.

In contrast to past reports, our data suggest widely absence of CXCR4 expression in pleural mesothelioma. Hence, robust cell surface expression should be confirmed prior to targeting this chemokine receptor for diagnosis and/or therapy.

Integrating MRI and Chemokine Receptor CXCR4-Targeted PET for Detection of Leukocyte Infiltration in Complicated Urinary Tract Infections After Kidney Transplantation

Complicated urinary tract infections (UTIs) are frequent in immunosuppressed patients after kidney transplantation and may lead to allograft failure or urosepsis. Noninvasive detection of allograft involvement as well as localization of the primary site of infection are challenging. Therefore, we sought to determine whether molecularly targeted PET, combined with diffusion-weighted MRI, enables detection of leukocytes in renal allografts. Methods: Thirteen kidney transplant recipients with complicated UTIs underwent both PET with a specific CXCR4 ligand, ⁶⁸Ga-pentixafor, and diffusion-weighted MRI. The spatial distribution and intensity of CXCR4 upregulation in renal allografts as determined by SUVs on PET and diffusion restriction as determined by apparent diffusion coefficients (ADCs) on MRI were analyzed and compared with urinalysis, clinical chemistry and bacteriology, and biopsy, if available. Results: Combined PET/MRI detected acute allograft infection in 9 patients and lower UTI/nonurologic infections in the remaining 4 patients. Leukocyte infiltration was identified by areas of CXCR4 upregulation compared with unaffected parenchyma in PET (SUV_mean, 4.6 vs. 3.7; P < 0.01), corresponding to areas with increased cell density in MRI (ADC_min, 0.89 vs. 1.59 × 10^-3 mm²/s, P < 0.01). Allograft CXCR4 signal was paralleled by CXCR4 upregulation in lymphoid organs. Histopathologic evaluation supported a correlation between CXCR4 signal and presence of leukocytes. Conclusion: Combined CXCR4-targeted PET/MRI with ⁶⁸Ga-pentixafor may enable the noninvasive detection of leukocytes in renal allografts. This novel methodology may refine the characterization of infectious and inflammatory kidney diseases and may serve as a platform for future clinical studies targeting allograft infection.

CXCR4-directed endoradiotherapy induces high response rates in extramedullary relapsed Multiple Myeloma

C-X-C-motif chemokine receptor 4 (CXCR4) is a key factor for tumor growth and metastasis in several types of human cancer. We have recently reported promising first-in-man experience with CXCR4-directed endoradiotherapy (ERT) in multiple myeloma (MM). Eight heavily pretreated MM patients underwent a total of 10 ERT cycles (7 patients with 1 cycle and a single patient with 3 cycles). ERT was administered in combination with chemotherapy and autologous stem cell support. End points were occurrence and timing of adverse events, progression-free and overall survival. ERT was overall well tolerated without any unexpected acute adverse events or changes in vital signs. With absorbed tumor doses >30-70 Gy in intra- or extramedullary lesions, significant anti-myeloma activity was observed with 1 patient achieving complete remission and 5/8 partial remission. Directly after ERT major infectious complications were seen in one patient who died from sepsis 22 days after ERT, another patient with high tumor burden experienced lethal tumor lysis syndrome. Median progression-free survival was 54 days (range, 13-175), median overall survival was 223 days (range, 13-313). During follow-up (6 patients available), one patient died from infectious complications, 2/8 from disease progression, the remaining 3/8 patients are still alive. CXCR4-directed ERT was well-tolerated and exerted anti-myeloma activity even at very advanced stage MM with presence of extramedullary disease. Further assessment of this novel treatment option is highly warranted.

Imaging of Chemokine Receptor 4 Expression in Neuroendocrine Tumors - a Triple Tracer Comparative Approach

C-X-C motif chemokine receptor 4 (CXCR4) and somatostatin receptors (SSTR) are overexpressed in gastro-entero-pancreatic neuroendocrine tumors (GEP-NET). In this study, we aimed to elucidate the feasibility of non-invasive CXCR4 positron emission tomography/computed tomography (PET/CT) imaging in GEP-NET patients using [⁶⁸Ga]Pentixafor in comparison to ⁶⁸Ga-DOTA-D-Phe-Tyr3-octreotide ([⁶⁸Ga]DOTATOC) and ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG). Twelve patients with histologically proven GEP-NET (3xG1, 4xG2, 5xG3) underwent [⁶⁸Ga]DOTATOC, [¹⁸F]FDG, and [⁶⁸Ga]Pentixafor PET/CT for staging and planning of the therapeutic management. Scans were analyzed on a patient as well as on a lesion basis and compared to immunohistochemical staining patterns of CXCR4 and somatostatin receptors SSTR2a and SSTR5. [⁶⁸Ga]Pentixafor visualized tumor lesions in 6/12 subjects, whereas [¹⁸F]FDG revealed sites of disease in 10/12 and [⁶⁸Ga]DOTATOC in 11/12 patients, respectively. Regarding sensitivity, SSTR-directed PET was the superior imaging modality in all G1 and G2 NET. CXCR4-directed PET was negative in all G1 NET. In contrast, 50% of G2 and 80% of G3 patients exhibited [⁶⁸Ga]Pentixafor-positive tumor lesions. Whereas CXCR4 seems to play only a limited role in detecting well-differentiated NET, increasing receptor expression could be non-invasively observed with increasing tumor grade. Thus, [⁶⁸Ga]Pentixafor PET/CT might serve as non-invasive read-out for evaluating the possibility of CXCR4-directed endoradiotherapy in advanced dedifferentiated SSTR-negative tumors.