Noninvasive Quantification of Radiation-Induced Lung Injury Using a Targeted Molecular Imaging Probe

PURPOSE

Radiation-induced lung injury (RILI) is a progressive inflammatory process seen after irradiation for lung cancer. The disease can be insidious, often characterized by acute pneumonitis followed by chronic fibrosis with significant associated morbidity. No therapies are approved for RILI, and accurate disease quantification is a major barrier to improved management. Here, we sought to noninvasively quantify RILI using a molecular imaging probe that specifically targets type 1 collagen in mouse models and patients with confirmed RILI.

METHODS AND MATERIALS

Using a murine model of lung radiation, mice were imaged with EP-3533, a type 1 collagen probe, to characterize the development of RILI and to assess disease mitigation after losartan treatment. The human analog probe 68Ga-CBP8, targeting type 1 collagen, was tested on excised human lung tissue containing RILI and was quantified via autoradiography. 68Ga-CBP8 positron emission tomography was used to assess RILI in vivo in 6 human subjects.

RESULTS

Murine models demonstrated that probe signal correlated with progressive RILI severity over 6 months. The probe was sensitive to mitigation of RILI by losartan. Excised human lung tissue with RILI had increased binding versus unirradiated control tissue, and 68Ga-CBP8 uptake correlated with collagen proportional area. Human imaging revealed significant 68Ga-CBP8 uptake in areas of RILI and minimal background uptake.

CONCLUSIONS

These findings support the ability of a molecular imaging probe targeted at type 1 collagen to detect RILI in preclinical models and human disease, suggesting a role for targeted molecular imaging of collagen in the assessment of RILI.

Improved purification of cyclotron [68Ga]GaCl3 for the production of 68Ga radiopharmaceuticals

INTRODUCTION

Increased demand for NetSpot and Illuccix as requirement to receive the respective Lutathera and Pluvicto radiotherapies, and monitor subsequent response to treatment, have reinforced the need to develop alternative ways of producing gallium-68 (68Ga). Building on our efforts to produce 68Ga in a liquid target on a GE PETtrace, the goal of this work is to modify the current GE Gallium Chloride cassette using the FASTLab 2 synthesis module to produce [68Ga]GaCl3 equivalent to a 1.85 GBq generator and demonstrate compatibility with FDA-approved kits for production of 68Ga-labeled radiopharmaceuticals.

METHODS

68Ga was produced in a liquid target via the 68Zn(p,n)68Ga reaction. 68Ga was loaded onto various sizes of ZR resins (ZR Load, 0.3 mL, 1 mL, or 2 mL). The loading efficiency was determined using a dose calibrator. After washing with HNO3, 1.75 M HCl was used to elute the ZR Load resin through various sizes of a second ZR resin (ZR CG, 0 mL, 2 mL, 4 mL). Using 0.5 mL fractions, the elution profile was determined. Compatibility of the [68Ga]GaCl3 with NetSpot and Illuccix kits was investigated. Radiochemical purity (RCP) and 4 h stability were determined using radioTLC and radioHPLC. Using a modified [68Ga]GaCl3 cassette and new FASTLab program, 6 validation preparations were conducted using NetSpot and Illuccix kits for which RCP, stability, sterility and suitability were determined. Dual irradiation of 2 liquid targets was also performed, which was used to simultaneously prepare 1 NetSpot and 2 Illuccix kits by diluting the required activity with 0.1 M HCl.

RESULTS

The commercially available GE Cassette gave low RCP using commercial FDA kits. To optimize this, the loading efficiency onto ZR Load and the ratio of ZR resin used to load the initial activity and subsequent elution were explored. When using a 2:4 ratio of ZR Load to ZR CG, 97.89 % RCP was observed when a 3.8 mL [68Ga]GaCl3 solution was used. For Dotatate validation, 0.55 mL of buffer was added to 4.2 mL of [68Ga]GaCl3 which gave 1.35 GBq of formulated product. For Illuccix validation, [68Ga]GaCl3 was added to 2.5 mL of buffer which gave 1.52 GBq of [68Ga]Ga-PSMA-11. Formulated products passed package insert quality control (QC) requirements. When dual target irradiations were performed, 2.84 GBq was delivered to an external vial and used to label 1 NetSpot and 2 Illuccix kits simultaneously, and each kit also met or exceeded established QC criteria.

CONCLUSION

Methods are reported for using cyclotron-produced 68Ga from a liquid target in conjunction with FDA-approved NetSpot and Illucix kits. By employing a 2 mL ZR Load resin with a 4 mL ZR CG resin, adequate resolution between residual 68Zn and desired 68Ga was achieved. By modifying the FASTLab procedure to retain the final 2.5 mL of eluate from the ZR CG resin, [68Ga]GaCl3 equivalent to a new 1.85 GBq generator was obtained. This was suitable for labeling NetSpot and Illucix kits, resulting in high incorporation of 68Ga (RCP >95 %), which has not previously been demonstrated. Delivering [68Ga]GaCl3 into an external vial and diluting with 0.1 M HCl makes it possible to prepare multiple kits simultaneously. These new procedures should facilitate use of cyclotron-produced [68Ga]GaCl3 for clinical production going.

A comparison of the performance of 68Ga-Pentixafor PET/CT versus adrenal vein sampling for subtype diagnosis in primary aldosteronism

Objective

To investigate the diagnostic efficiency and prognostic value of 68Ga-Pentixafor PET/CT in comparison with adrenal vein sampling (AVS) for functional lateralization in primary aldosteronism (PA). Histology and long-term clinical follow-up normally serve as the gold standard for such diagnosis.

Methods

We prospectively recruited 26 patients diagnosed with PA. All patients underwent 68Ga-Pentixafor PET/CT and AVS. Postsurgical biochemical and clinical outcomes of patients with unilateral primary aldosteronism (UPA), as diagnosed by PET/CT or AVS, were assessed by applying standardized Primary Aldosteronism Surgical Outcome (PASO) criteria. Immunohistochemistry (IHC) was performed to detect the expression of aldosterone synthase (CYP11B2) and CXCR4.

Results

On total, 19 patients were diagnosed with UPA; of these, 13 patients were lateralized by both PET/CT and AVS, four patients were lateralized by PET-only, and two by AVS-only. Seven subjects with no lateralization on AVS and PET received medical therapy. All patients achieved complete biochemical success except one with nodular hyperplasia lateralized by AVS alone. The consistency between PET/CT and AVS outcomes was 77% (20/26). Moreover, CYP11B2-positive nodules were all CXCR4-positive and showed positive findings on PET. Patients who achieved complete biochemical and clinical success had a higher uptake on PET as well as stronger expression levels of CXCR4 and CYP11B2.

Conclusion

Our analysis showed that 68Ga-Pentixafor PET/CT could enable non-invasive diagnosis in most patients with PA and identify additional cases of unilateral and surgically curable PA which could not be classified by AVS. 68Ga-Pentixafor PET/CT should be considered as a first-line test for the future classification of PA.

n Vivo

Noninvasive imaging of amyloid-β (Aβ) species in vivo is important for the early diagnosis of Alzheimer's disease (AD). In this paper, we report a near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe (NIR-[68Ga]) for in vivo imaging of both soluble and insoluble Aβ species. NIR-[68Ga] holds a high binding affinity, high selectivity and high sensitivity toward Aβ42 monomers, oligomers, and aggregates in vitro. In vivo imaging results show that NIR-[68Ga] can cross the blood-brain-barrier (BBB), and produce significantly higher PET and NIR FL bimodal signals in the brains of APP/PS1 transgenic AD mice relative to that of age-matched wild-type mice, which are also validated by the ex vivo autoradiography and histological staining images. Our results demonstrate that NIR-[68Ga] is an efficient NIR FL and PET bimodal probe for the sensitive imaging of soluble and insoluble Aβ species in AD mice.

68 Ga-PSMA-11 PET/CT Imaging in Brain Gliomas and Its Correlation With Clinicopathological Prognostic Parameters

BACKGROUND

Gliomas are the most common primary central nervous system tumors, of which the malignant gliomas account for 60%-75%. The primary and secondary brain malignancies are highly treatment resistant, and their marked angiogenesis attracts interest as a potential therapeutic target. The grade of gliomas, Ki-67 index, and IDH mutation status are among the major prognostic markers in gliomas. Prostate-specific membrane antigen (PSMA) is a zinc-dependent peptidase that is not only expressed in prostate cancer cells but also in the tumor neovasculature. The initial PSMA PET studies in central nervous system tumors using 68 Ga-HBED-CC-PSMA ( 68 Ga-PSMA-11) PET tracer confirmed selective target expression in gliomas of different grades, with higher expression in high-grade glioma compared with low-grade glioma.

AIMS AND OBJECTIVES

The aim of the present study was to correlate and compare the 68 Ga-PSMA-11 and 18 F-FDG uptake in brain tumors with their clinicopathological prognostic parameters, so as to study their prognostic implications. In addition, the study also aimed to identify patients who are likely to benefit from potential PSMA-targeted therapies.

PATIENTS AND METHODS

This ongoing prospective study was approved by the institutional scientific and medical ethics committee. The patients with primary or recurrent glioma lesions on MRI underwent regional brain PET/CT scanning with 68 Ga-PSMA-11 and 18 F-FDG. The final histopathology of the brain lesions (glioma grade), Ki-67 index, and IDH mutation status were compared with SUV max values of the 68 Ga-PSMA-11 and 18 F-FDG PET/CT.

RESULTS

A total of 15 patients (13 males and 2 females; age range, 21-73 years; median age, 58 years) were included in this study analysis. Among the 15 patients, 10 were treatment naive and 2 were patients with recurrent glioma. Three patients turned out to be WHO grade I-II, 6 belonged to grade III, and 6 grade IV (glioblastoma multiforme) on final histopathology. The 68 Ga-PSMA-11 PET/CT showed tracer uptake in all high-grade gliomas with good tumor-to-background ratio. It was PSMA nonavid in 2/3 low-grade gliomas, and it showed low-grade uptake in 1/3 patients. PSMA expression (as evaluated by SUV max values) was significantly higher in higher-grade tumors, those with IDH mutation wildtype status, and higher Ki-67 indices. FDG PET SUV max also showed significant correlation with these prognostic parameters.

CONCLUSIONS

In these preliminary results, PSMA PET appears to be an important tool in the evaluation and prognosis of gliomas. PSMA-directed theranostics can be explored as a personalized approach in gliomas with high PSMA uptake. However, with the limitation of small sample size, larger clinical trials are warranted to draw conclusive evidence regarding the same.

Improving Theranostic Gallium-68/Lutetium-177-Labeled PSMA Inhibitors with an Albumin Binder for Prostate Cancer

We developed a novel therapeutic radioligand, [177Lu]1h, with an albumin binding motif and evaluated it in a prostate-specific membrane antigen (PSMA)-expressing tumor xenograft mouse model. Fourteen PSMA target candidates were synthesized, and binding affinity was evaluated with an in vitro competitive binding assay. First, four compound candidates were selected depending on binding affinity results. Next, we selected four compounds ([68Ga]1e, [68Ga]1g, [68Ga]1h, and [68Ga]1k) were screened for tumor targeting efficiency by micro-positron emission tomography/computed tomography (micro-PET/CT) imaging. Finally, [177Lu]1h compound was evaluated the tumor targeting efficiency and therapeutic efficiency by micro-single-photon emission computed tomography/computed tomography (micro-SPECT/CT), biodistribution, and radiotherapy studies. Estimated human effective dose was calculated by biodistribution data. Compound 1h showed a high binding affinity (Ki value = 4.08 ± 0.08 nmol/L), and [177Lu]1h showed extended blood circulation (1 hour = 10.32 ± 0.31, 6 hours = 2.68 ± 1.07%ID/g) compared to [177Lu]PSMA-617 (1 h = 0.17 ± 0.10%ID/g). [177Lu]1h was excreted via the renal pathway and showed high tumor uptake (24.43 ± 3.36%ID/g) after 1 hour, which increased over 72 hours (72 hours = 51.39 ± 9.26%ID/g). Mice treated with 4 and 6 MBq of [177Lu]1h showed a median survival rate of >61 days. In particular, all mice treated with 6 MBq of [177Lu]1h survived for the entire monitoring period. The estimated human effective dose of [177Lu]1h was 0.07 ± 0.01 and 0.03 ± 0.00 mSv/MBq in total body and kidney, respectively. The current study indicates that [177Lu]1h has the potential for further investigation of metastatic castration-resistant prostate cancer (mCRPC) therapy in clinical trials.

Comparison of a New 68Ga-Radiolabelled PET Imaging Agent sCD146 and RGD Peptide for In Vivo Evaluation of Angiogenesis in Mouse Model of Myocardial Infarction

Ischemic vascular diseases are associated with elevated tissue expression of angiomotin (AMOT), a promising molecular target for PET imaging. On that basis, we developed an AMOT-targeting radiotracer, ⁶⁸Ga-sCD146 and performed the first in vivo evaluation on a myocardial infarction mice model and then, compared AMOT expression and α_vβ₃-integrin expression with ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ imaging. After myocardial infarction (MI) induced by permanent ligation of the left anterior descending coronary artery, myocardial perfusion was evaluated by Doppler ultrasound and by ¹⁸F-FDG PET imaging. ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ PET imaging were performed. In myocardial infarction model, heart-to-muscle ratio of ⁶⁸Ga-sCD146 imaging showed a significantly higher radiotracer uptake in the infarcted area of MI animals than in sham (* p = 0.04). Interestingly, we also observed significant correlations between ⁶⁸Ga-sCD146 imaging and delayed residual perfusion assessed by ¹⁸F-FDG (* p = 0.04), with lowest tissue fibrosis assessed by histological staining (* p = 0.04) and with functional recovery assessed by ultrasound imaging (** p = 0.01). ⁶⁸Ga-sCD146 demonstrated an increase in AMOT expression after MI. Altogether, significant correlations of early post-ischemic ⁶⁸Ga-sCD146 uptake with late heart perfusion, lower tissue fibrosis and better functional recovery, make ⁶⁸Ga-sCD146 a promising radiotracer for tissue angiogenesis assessment after MI.

Clinical parameters and nomograms for predicting lymph node metastasis detected with 68 Ga-PSMA-PET/CT in prostate cancer patients candidate to definitive radiotherapy

BACKGROUND

Defining the extent of disease spread with imaging modalities is crucial for therapeutic decision-making and definition of treatment. This study aimed to investigate whether clinical parameters and nomograms predict prostate-specific membrane antigen (PSMA)-positive lymph nodes in treatment-naïve nonmetastatic prostate cancer (PC) patients.

MATERIALS AND METHODS

The clinical data of 443 PC patients (83.3% high-risk and 16.7% intermediate-risk) were retrospectively analyzed. Receiver operating characteristic (ROC) curves with areas under the curve (AUC) were generated to evaluate the accuracy of clinical parameters (prostate-specific antigen [PSA], T stage, Gleason score [GS], International Society of Urological Pathology [ISUP] grade) and nomograms (Roach formula [RF], Yale formula [YF], and a new formula [NF]) in predicting lymph node metastasis. The AUCs of the various parameters and clinical nomograms were compared using ROC and precision-recall (PR) curves.

RESULTS

A total of 288 lymph node metastases were identified in 121 patients (27.3%) using ⁶⁸ Ga-PSMA-11-positron emission tomography (PET)/computed tomography (CT). Most PSMA-avid lymph node metastases occurred in external or internal iliac lymph nodes (142; 49.3%). Clinical T stage, PSA, GS, and ISUP grade were significantly associated with PSMA-positive lymph nodes according to univariate logistic regression analysis. The PSMA-positive lymph nodes were more frequently detected in patients with PSA >20 ng/ml, GS ≥7 or high risk disease compared to their counterparts. The clinical T stage, serum PSA level, GS, and ISUP grade showed similar accuracy in predicting PSMA-positive metastasis, with AUC values ranging from 0.675 to 0.704. The median risks for PSMA-positive lymph nodes according to the RF, YF, and NF were 31.3% (range: 12.3%-100%), 22.3% (range: 4.7%-100%), and 40.5% (range: 12.3%-100%), respectively. The AUC values generated from ROC and PR curve analyses were similar for all clinical nomograms, although the RF and YF had higher accuracy compared to NF.

CONCLUSION

The clinical T stage, PSA, GS, and ISUP grade are independent predictors of PSMA-positive lymph nodes. The RF and YF can be used to identify patients who can benefit from ⁶⁸ Ga-PSMA-11 PET/CT for the detection of lymph node metastasis. Together with nomograms, ⁶⁸ Ga-PSMA-11 PET/CT images help to localize PSMA-positive lymph node metastases and can thus assist in surgery and radiotherapy planning.

Immuno-PET imaging of 68Ga-labeled nanobody Nb109 for dynamic monitoring the PD-L1 expression in cancers

The checkpoint blockade immunotherapy has become a potent treatment strategy for cancers, and programmed death ligand-1 (PD-L1) is a prominent checkpoint ligand that is highly expressed in some cancers. The identification of immune checkpoint marker PD-L1 is critical for improving the success of immunotherapy. Accordingly, the binding specificity and dynamic monitoring property of a non-blocking nanobody tracer ⁶⁸Ga-NOTA-Nb109 to PD-L1 were assessed in this study. The endogenous expression level of PD-L1 in several cancer cells was measured by flow cytometry, Western blot, and cellular uptake assay. Sensitivity and specificity of ⁶⁸Ga-NOTA-Nb109 in monitoring the expression of PD-L1 in vivo were evaluated by PET imaging of different tumor-bearing models (U87, high PD-L1 expression; HCT 116, medium PD-L1 expression; and NCI-H1299, low PD-L1 expression). In vivo PET imaging results agreed well with those detected in vitro. In addition, PET imaging of PD-L1 expression in U87 and NCI-H1299 xenografts using ¹⁸F-FDG was also performed for comparison. The maximum tumor-to-muscle uptake ratio of ⁶⁸Ga-NOTA-Nb109 was more than twofold that of ¹⁸F-FDG in U87 xenograft. The change of PD-L1 expression in NCI-H1299 cells and xenografts induced by cisplatin (CDDP) was sensitively monitored by ⁶⁸Ga-NOTA-Nb109. This study demonstrated the feasibility of tracer ⁶⁸Ga-NOTA-Nb109 for specifically targeting endogenous PD-L1 and dynamic monitoring the change of PD-L1 expression, and could guide the immunotherapy and immunochemotherapy for refractory cancers.

The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides

PURPOSE

The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range.

PROCEDURES

To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects.

RESULTS

Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV.

CONCLUSION

Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.

Head-to-Head Comparison of 68Ga-PSMA-11 and 131I in the Follow-Up of Well-Differentiated Metastatic Thyroid Cancer: A New Potential Theragnostic Agent

INTRODUCTION

Thyroid cancer is the main endocrine neoplasia worldwide, for which ¹³¹I therapy is the cornerstone treatment. One of the main problems of follow up in patients with this type of cancer, is the need for thyroglobulin stimulation, not to mention the poor availability of ¹²³I or ¹²⁴I, to perform studies with a higher degree of sensitivity. Prostatic Specific Membrane Antigen (PSMA) PET/CT has demonstrated to be quite useful in a diversified number of neoplasms, on behalf of its capacity of evaluating the extent of type II carboxypeptidase expression in vascular endothelium. The end point of this article is to assess whether this novel image method possesses applicability in thyroid neoplasms follow up, for diagnostic and potentially therapeutic purposes.

METHODS

We retrospectively evaluated well differentiated metastatic thyroid cancer patients, who underwent a post therapeutic ¹³¹I dose whole body scan (WBS) and complementary SPECT/CT, as well as ⁶⁸Ga-PSMA-11 PET/CT.

RESULTS

Ten patients with differentiated thyroid cancer were included, of whom 80% were women and 20% men, mean age was 58 years old (± 11.6). Sixty-four metastatic lesions were analyzed, 67.19% had papillary histology and 32.81% were follicular type, the most affected site of metastases was bone in 57.81%, followed by lung 17.19%, lymph nodes 7.81%, postoperative thyroid bed 4.69%, brain 4.69% and others 7.81%. ⁶⁸Ga PSMA-11 PET/CT detected 64/64 lesions, all of them also identified by computed tomography (CT), whereas ¹³¹I SPECT/CT detected 55/64 lesions. Discrepant lesions were localized in lung 44.4%, brain 22.2%, postoperative thyroid bed 11.1%, lymph nodes 11.1% and bone 11.1%. The degree of correspondence among observers was outstanding for both radiotracers, but close upon perfect for PSMA-11 (κ = 0.98; 95% CI, 0.80 - 0.91), as opposed to ¹³¹ I (κ = 0.86; 95% CI, 0.71 - 0.76).

CONCLUSIONS

⁶⁸Ga-PSMA PET/CT showed an utterly superior capability for metastatic lesion detection when compared to ¹³¹I SPECT/CT. These findings suggest that PSMA PET/CT could possibly and precociously identify radioiodine refractoriness. PSMA uptake values not only expedite diagnosis, but also award it the ability to be used for therapeutic intents.

The Impact of 68Gallium DOTA PET/CT in Managing Patients With Sporadic and Familial Pancreatic Neuroendocrine Tumours

OBJECTIVE

Pancreatic neuroendocrine tumours (panNETs) arise sporadically or as part of a genetic predisposition syndrome. CT/MRI, endoscopic ultrasonography and functional imaging using Octreoscan localise and stage disease. This study aimed to evaluate the complementary role of ⁶⁸Gallium (⁶⁸Ga)-DOTA PET/CT in managing patients with panNETs.

DESIGN

A retrospective study conducted across three tertiary UK NET referral centres.

METHODS

Demographic, clinical, biochemical, cross-sectional and functional imaging data were collected from patients who had undergone a ⁶⁸Ga-DOTA PET/CT scan for a suspected panNET.

RESULTS

We collected data for 183 patients (97 male): median (SD) age 63 (14.9) years, 89.1 vs. 9.3% (n=163 vs. 17) alive vs. dead (3 data missing), 141 sporadic vs. 42 familial (MEN1, n=36; 85.7%) panNETs. Non-functional vs. functional tumours comprised 73.2 vs. 21.3% (n=134 vs. 39) (10 missing). Histological confirmation was available in 89% of individuals (n=163) but tumour grading (Ki67 classiifcation) was technically possible only in a smaller cohort (n=143): grade 1, 50.3% (n=72); grade 2, 46.2% (n=66) and grade 3, 3.5% (n=5) (40 histopathological classification either not technically feasible or biopsy not perfomed). 60.1% (n=110) were localised, 14.2% (n=26) locally advanced and 23.5% (n=43) metastatic (4 missing). 224 ⁶⁸Ga-DOTA PET/CT scans were performed in total for: diagnosis/staging 40% (n=88), post-operative assessment/clinical surveillance 53% (n=117) and consideration of peptide receptor radionuclide therapy (PRRT) 8% (n=17) (2 missing). PET/CT results confirmed other imaging findings (53%), identified new disease sites (28.5%) and excluded suspected disease (5%). Overall, ⁶⁸Ga-DOTA PET/CT imaging findings provided additional information in 119 (54%) patients and influenced management in 85 (39%) cases.

CONCLUSION

⁶⁸Ga-DOTA PET/CT imaging more accurately stages and guides treatment in patients with sporadic/familial panNETs with newly diagnosed/recurrent disease.

GMP production of [68Ga]Ga-BOT5035 for imaging of liver fibrosis in microdosing phase 0 study

INTRODUCTION

Early detection of liver fibrosis and monitoring response to treatment crucial for the management of patients are currently not feasible in clinical practice. Platelet derived growth factor receptor β (PDGFR-β) expression is regarded as a potential biomarker to determine the stages of fibrotic diseases including liver fibrosis. [⁶⁸Ga]Ga-BOT5035 comprising a bicyclic peptide was developed for specific targeting of PDGFR-β overexpressed in pathological fibrosis. The realization of microdosing phase 0 study using [⁶⁸Ga]Ga-BOT5035 positron emission tomography required automated good manufacturing practice (GMP) compliant production of [⁶⁸Ga]Ga-BOT5035 presented herein. Moreover, the investigation of radiation dosimetry was conducted to ensure possibility of multiple annual examinations for disease monitoring in clinical setup.

METHODS

The active pharmaceutical ingredient starting material BOT5035 (GMP grade) was provided by BiOrion Technologies BV. The ⁶⁸Ga-labelling process was developed and automated using synthesis platform (Modular-Lab PharmTrace, Eckert & Ziegler), disposable cassettes for ⁶⁸Ga-labelling, and pharmaceutical grade ⁶⁸Ge/⁶⁸Ga generator (GalliaPharm®) purchased from Eckert & Ziegler. Radiolysis sensitive BOT5035 required development and systematic optimization of the labelling synthesis parameters such as time, temperature, precursor concentration, radical scavenger, buffer concentration and pH. The validation process was conducted with regard to the product quality and quantity, as well as production reproducibility. Human organ equivalent doses and total body effective doses were calculated using Organ Level Internal Dose Assessment Code software (OLINDA/EXM 1.1), based on ex vivo organ distribution in Sprague-Dawley rats.

RESULTS

The GMP compliant automated production of [⁶⁸Ga]Ga-BOT5035 with on-line documentation demonstrated high reproducibility. The time for the labelling synthesis and quality control was approximately 60 min. The non-decay corrected radiochemical yield and radiochemical purity of the radiopharmaceutical were 43.7 ± 7.6% (n = 3, process validation) and 97.7 ± 0.4% (n = 3, process validation), respectively. Predefined acceptance criteria were met for the sterility, endotoxins level, radionuclidic purity and residual solvent content. The stability at ambient temperature was controlled for 120 min with approved results. Ex vivo organ distribution data revealed fast blood clearance and washout from most of the organs. The dose-limiting organs were kidney and bone marrow. The total effective dose as limiting parameter would allow for up to 3-4 PET scans per annum.

CONCLUSION

The fully automated and GMP compliant production of [⁶⁸Ga]Ga-BOT5035 was developed and thoroughly validated. The radiopharmaceutical was approved by Swedish Medicinal Products Agency and the Ethical Review Authority for the Phase 0 clinical study of the quantitative imaging of liver fibrosis. Human dosimetry calculations extrapolated from animal experiment indicated possibility of 3-4 PET examinations per year.

Manipulating the In Vivo Behaviour of 68Ga with Tris(Hydroxypyridinone) Chelators: Pretargeting and Blood Clearance

Pretargeting is widely explored in immunoPET as a strategy to reduce radiation exposure of non-target organs and allow the use of short-lived radionuclides that would not otherwise be compatible with the slow pharmacokinetic profiles of antibodies. Here we investigate a pretargeting strategy based on gallium-68 and the chelator THPMe as a high-affinity pair capable of combining in vivo. After confirming the ability of THPMe to bind 68Ga in vivo at low concentrations, the bifunctional THPMe-NCS was conjugated to a humanised huA33 antibody targeting the A33 glycoprotein. Imaging experiments performed in nude mice bearing A33-positive SW1222 colorectal cancer xenografts compared pretargeting (100 μg of THPMe-NCS-huA33, followed after 24 h by 8-10 MBq of 68Ga3+) with both a directly labelled radioimmunoconjugate (89Zr-DFO-NCS-huA33, 88 μg, 7 MBq) and a 68Ga-only negative control (8-10 MBq of 68Ga3+). Imaging was performed 25 h after antibody administration (1 h after 68Ga3+ administration for negative control). No difference between pretargeting and the negative control was observed, suggesting that pretargeting via metal chelation is not feasible using this model. However, significant accumulation of "unchelated" 68Ga3+ in the tumour was found (12.9 %ID/g) even without prior administration of THPMe-NCS-huA33, though tumour-to-background contrast was impaired by residual activity in the blood. Therefore, the 68Ga-only experiment was repeated using THPMe (20 μg, 1 h after 68Ga3+ administration) to clear circulating 68Ga3+, producing a three-fold improvement of the tumour-to-blood activity concentration ratio. Although preliminary, these results highlight the potential of THPMe as a 68Ga clearing agent in imaging applications with gallium citrate.

In vivo preclinical evaluation of the new 68Ga-labeled beta-cyclodextrin in prostaglandin E2 (PGE2) positive tumor model using positron emission tomography

The cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) pathway plays an important role in tumor development and formation of metastases. It was earlier reported that cyclodextrin derivatives have a high affinity to form complexes with PGE2. Based on these results radiolabeled cyclodextrins - as new radiopharmaceuticals - may open a new pathway in the in vivo imaging and diagnosis of PGE2 positive tumors. The aims of this study were to synthetize the PGE2 specific ⁶⁸Ga-labeled NODAGA-randomly methylated beta-cyclodextrin (⁶⁸Ga-NODAGA-RAMEB) and investigate its tumor-targeting properties. NODAGA-RAMEB was labeled with Gallium-68 (⁶⁸Ga), and the radiochemical purity (RCP%), partition coefficient (logP values), and in vitro-in vivo stability of ⁶⁸Ga-NODAGA-RAMEB were determined. After intravenous injection of ⁶⁸Ga-NODAGA-RAMEB the accumulation in organs and tissues was monitored in vivo by positron emission tomography (PET) and ex vivo by gamma counter in BxPC-3 and PancTu-1 tumor-bearing CB17 SCID mice. The RCP% of the newly synthesized ⁶⁸Ga-NODAGA-RAMEB was higher than 98%. The molar activity was 15.34 ± 1.93 GBq/μmol. The logP of ⁶⁸Ga labeled NODAGA-RAMEB was - 3.63 ± 0.04. Biodistribution studies showed high accumulation of ⁶⁸Ga-NODAGA-RAMEB in PGE2 positive BxPC-3 tumors; approximately 15-20-fold higher radiotracer uptake was observed, than that of the background. ⁶⁸Ga-labeled RAMEB is a promising radiotracer in PET diagnostics of PGE2 positive tumors.

The Clinical Impact of [68 Ga]-DOTATATE PET/CT for the Diagnosis and Management of Ectopic Adrenocorticotropic Hormone - Secreting Tumours

OBJECTIVES

Localization of ectopic ACTH-secreting tumours causing Cushing syndrome (ECS) is essential for clinical management, yet often difficult. [⁶⁸ Ga]-DOTATATE PET/CT ([⁶⁸ Ga]-DOTA-(Tyr³ )-octreotate)] is an FDA-approved high-resolution diagnostic tool for imaging neuroendocrine tumours. Data on the clinical utility of [⁶⁸ Ga]-DOTATATE in patients with ECS, however, are scarce. The objectives of this study were to determine the efficacy for ECS localization and the clinical benefit of [⁶⁸ Ga]-DOTATATE imaging.

METHOD

We conducted a retrospective review of all cases with ECS evaluated with [⁶⁸ Ga]-DOTATATE from November 2016 through October 2018 at three referral centres. The clinical benefit of [⁶⁸ Ga]-DOTATATE was based on detection of new tumours and resultant changes in management.

RESULTS

Over the study period, 28 patients with ECS underwent [⁶⁸ Ga]-DOTATATE: 17 for identification of the primary tumour and 11 during follow-up. [⁶⁸ Ga]-DOTATATE identified the suspected primary ECS in 11/17 patients (65%). Of these, nine patients underwent surgery: eight with confirmed ECS (5 bronchial, 1 thymic, 1 pancreatic and 1 metastatic neuroendocrine tumour of unknown primary origin) and one patient with a false-positive scan (adrenal gland). Of the 11 patients with ECS who underwent [⁶⁸ Ga]-DOTATATE evaluation during follow-up, the study led to changes in clinical management in 7/11 (64%) patients.

CONCLUSIONS

[⁶⁸ Ga]-DOTATATE is sensitive in detecting primary and metastatic ECS, often identifies occult tumours after conventional imaging, and impacts clinical care in the majority of patients.

On-cartridge preparation and evaluation of 68Ga-, 89Zr- and 64Cu-precursors for cell radiolabelling

INTRODUCTION

Indium-111 when formulated as indium-111 oxine remains the gold standard for long term cell tracking, whereas radiometals for improved PET applications still have to be established. We here describe the on-cartridge formation of gallium-68, zirconium-89 and copper-64 complexes in small volumes suitable for cell labelling, including labelling of red blood cells (RBC) and white blood cells (WBC) and their biological evaluation in vivo.

METHODS

Small volumes (1-2 mL) of tracers (oxine, tropolone) were directly prepared on an anion exchange cartridge (Sep-Pak QMA). Cells were radiolabelled and the labelling efficiency and efflux were evaluated. The in vivo biodistribution of copper-64-labelled WBC using [⁶⁴Cu][Cu(oxinate)₂] and [⁶⁴Cu][Cu(tropolonate)₂] was monitored in an infection and inflammation animal model using BALB/c mice.

RESULTS

On-cartridge concentration of gallium-68, zirconium-89 and copper-64 enabled formation of oxine and tropolone tracers in small volumes with good yields (≥50%) and quality (extraction ≥90%). Prepared tracers radiolabelled the RBC comparable to indium-111 tracers and in vivo biodistribution of copper-64 labelled WBC showed clear accumulation of cells at the site of infection and inflammation.

CONCLUSIONS

This on-cartridge preparation method enables simple formation of various PET tracers for cell radiolabelling. Zirconium-89 and copper-64 tracers radiolabelled cells with sufficient stability. Due to their longer half-life this approach could be promising for routine applications where longer evaluation periods for cell tracking are needed.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This novel approach for on-cartridge concentration and preparation of oxine and tropolone precursors with different positron emitters, in small volume and suitable pH, offers a versatile tool towards cell labelling for preclinical and clinical PET applications.

Development of a Potential Gallium-68-Labelled Radiotracer Based on DOTA-Curcumin for Colon-Rectal Carcinoma: From Synthesis to In Vivo Studies

Colorectal cancer is the third most commonly occurring cancer in men and the second most commonly occurring cancer in women worldwide. We have recently reported that curcuminoid complexes labelled with gallium-68 have demonstrated preferential uptake in HT29 colorectal cancer and K562 lymphoma cell lines compared to normal human lymphocytes. In the present study, we report a new gallium-68-labelled curcumin derivative (⁶⁸Ga-DOTA-C21) and its initial validation as marker for early detection of colorectal cancer. The precursor and non-radioactive complexes were synthesized and deeply characterized by analytical methods then the curcuminoid was radiolabelled with gallium-68. The in vitro stability, cell uptake, internalization and efflux properties of the probe were studied in HT29 cells, and the in vivo targeting ability and biodistribution were investigated in mice bearing HT29 subcutaneous tumour model. ⁶⁸Ga-DOTA-C21 exhibits decent stability (57 ± 3% after 120 min of incubation) in physiological media and a curcumin-mediated cellular accumulation in colorectal cancer cell line (121 ± 4 KBq of radiotracer per mg of protein within 60 min of incubation). In HT29 tumour-bearing mice, the tumour uptake of ⁶⁸Ga-DOTA-C21 is 3.57 ± 0.3% of the injected dose per gram of tissue after 90 min post injection with a tumour to muscle ratio of 2.2 ± 0.2. High amount of activity (12.73 ± 1.9% ID/g) is recorded in blood and significant uptake of the radiotracer occurs in the intestine (13.56 ± 3.3% ID/g), lungs (8.42 ± 0.8% ID/g), liver (5.81 ± 0.5% ID/g) and heart (4.70 ± 0.4% ID/g). Further studies are needed to understand the mechanism of accumulation and clearance; however, ⁶⁸Ga-DOTA-C21 provides a productive base-structure to develop further radiotracers for imaging of colorectal cancer.

Evidence of 68Ga-DOTA-NT-20.3 Uptake in Pancreatic Adenocarcinoma AsPC-1 Cell Line - in vitro Study

BACKGROUND

Neurotensin receptors are overexpressed in several cancer types including pancreatic ductal adenocarcinoma. Three NTR subtypes have been cloned: NTR-1, NTR-2 and NTR-3. The most expressed NTR-1 is not present in normal pancreatic tissue and has a low expression in chronic pancreatitis.

OBJECTIVE

Objective of this study was to test in vitro affinity of the new 68Ga labelled neurotensin analogue DOTA-NT-20.3 (fragment 6-13, Ac-Lys(DOTA)-Pro-Arg(N-CH3)-Arg-Pro-Tyr-Tle-Leu) on the human pancreatic ductal adenocarcinoma cell line AsPC-1.

METHOD

For the preparation of 68Ga-DOTA-NT-20.3, 68GaCl3 solution (eluted from 68Ge/68Ga generator) and 50 μg of precursor (Iason, Graz, Austria) water dissolved were used in an automatic synthesis module. The labeled compound was added to cell culture flask and incubated at 37°C. At various time points after tracer addition up to 80min, cells were recovered, rinsed and counted for radioactivity. Results were expressed as percent binding normalized to 200000 cells and affinity parameters were calculated.

RESULTS

Labeling yield was ≥98 %. The molar ratio between labelled and total peptide was about 1/400. AsPC-1 cell line showed rapid uptake of the tracer including surface and internalized binding, tending to a plateau phase 80 min after tracer addition (11%/200.000 cells). The Kd (7.335 pmol) and Bmax (90.52 kBq) value indicated high tracer affinity for AsPC-1cell line especially if compared with the literature data regarding other malignancies (e.g. colonic cancer cell line). Binding sites were 1.09x106 sites per cell.

CONCLUSION

New tracer 68Ga-DOTA-NT-20.3 can be a suitable candidate for the clinical use in patients with pancreatic ductal adenocarcinoma.

67Ga as a biosensor of iron needs in different organs: Study performed on male and female rats subjected to iron deficiency and exercise

The aim of the present study was to determine the iron needs in different organs and tissues using ⁶⁷Ga as a biosensor in males and females rats subjected to iron deficiency (ID) and voluntary exercise (EX). ⁶⁷Ga citrate was injected i.p. to female and male Wistar rats (n=5/sex/group). Groups: Control (sedentary conditions), Control+EX, ID and ID+EX. To determine the ⁶⁷Ga uptake, samples from the following regions of interest (ROIs) were extracted 12h post-injection: blood, liver, gonads, bone marrow, heart, adrenal glands, skeletal muscle, stomach, kidney, eyeball, sciatic nerve, small intestine and peritoneum. The total ⁶⁷Ga uptake was 412% higher in ID subjects than in control subjects, being 1011% higher in ID-males than ID-females. In ID-females, the ROIs with the greater ⁶⁷Ga uptake were blood, kidney and bone marrow, while in ID-males they were sciatic nerve, eyeball and adrenals, which demonstrates that the biodistribution differed between sexes in sedentary conditions but when subjected to EX, the biodistribution was similar in each sex group although females had a greater ⁶⁷Ga uptake. In ID+EX subjects, the ROIs that showed the highest uptake were sciatic nerve, eyeball and adrenal glands. Using ⁶⁷Ga as a biosensor, it is possible to identify the needs of iron that each organ requires to perform their functions in normal physiological conditions. In addition, a higher or lower ⁶⁷Ga uptake in a specific organ may indicate its malfunction or show damage.

Complexes of gastrin with In3+, Ru3+ or Ga3+ ions are not recognised by the cholecystokinin 2 receptor

The peptide hormone gastrin (Gamide) binds trivalent metal ions, including indium (In), ruthenium (Ru) and gallium (Ga), with high affinity. Complexes of gastrin with chelated isotopes of In and Ga have previously been used for the location of tumours expressing the cholecystokinin 2 receptor (CCK2R). The aim of the present study was to purify the complexes of Gamide with radioactive isotopes of In, Ru or Ga and to investigate their ability to bind to the CCK2R. The radioactive Gamide complexes were purified on Sep-Pak C18 cartridges or by anion exchange HPLC. Binding to the CCK2R was assessed with a stably transfected clone of the gastric carcinoma cell line AGS. The ¹⁰⁶Ru-Gamide complex could be eluted from the C18 cartridge; the ¹¹¹In-Gamide and ⁶⁸Ga-Gamide complexes bound irreversibly. All three complexes were successfully purified by anion exchange HPLC. The failure to detect binding of the ¹¹¹In-Gamide, ¹⁰⁶Ru-Gamide and ⁶⁸Ga-Gamide complexes to the CCK2R suggests that formation of these complexes will not be useful for the detection of tumours expressing this receptor, but may instead provide alternative ways to block the actions of Gamide as a growth factor or a stimulant of gastric acid secretion. The complexes between the hormone gastrin and radioactive ¹¹¹In, ¹⁰⁶Ru or ⁶⁸Ga ions were purified by anion exchange HPLC using a NaCl gradient. The failure to detect binding of the complexes to the cholecystokinin 2 receptor suggests that metal ion treatment may provide novel approaches to block the biological actions of gastrin.

PSMA ligands in prostate cancer - Probe optimization and theranostic applications

Due to its selective overexpression in prostate cancer (PCa), the prostate-specific membrane antigen (PSMA) has been recognized as a highly promising target for diagnostic and therapeutic applications. So far, various PSMA ligands have been developed for radiolabeling with radioisotopes such as ⁶⁸Ga or ¹⁸F which can be used for specific visualization and diagnosis of PSMA-expressing PCa. In addition, PSMA ligands suitable for radiolabeling with ¹³¹I or ¹⁷⁷Lu have become available to the clinics, allowing PSMA-based radioligand therapies. Here, we provide a comprehensive review of the most frequently used PSMA ligands, their structural modifications, and the impact of those on clinical applications.

Preparation and 68Ga-radiolabeling of porous zirconia nanoparticle platform for PET/CT-imaging guided drug delivery

This paper describes the preparation of gallium-68 (⁶⁸Ga) isotope labeled porous zirconia (ZrO₂) nanoparticle (NP) platform of nearly 100nm diameter and its first pharmacokinetic and biodistribution evaluation accomplished with a microPET/CT (μPet/CT) imaging system. Objectives of the investigations were to provide a nanoparticle platform which can be suitable for specific delivery of various therapeutic drugs using surface attached specific molecules as triggering agents, and at the same time, suitable for positron emission tomography (PET) tracing of the prospective drug delivery process. Radiolabeling was accomplished using DOTA bifunctional chelator. DOTA was successfully adsorbed onto the surface of nanoparticles, while the ⁶⁸Ga-radiolabeling method proved to be simple and effective. In the course of biodistribution studies, the ⁶⁸Ga-labeled DOTA-ZrNPs showed proper radiolabeling stability in their original suspension and in blood serum. μPet/CT imaging studies confirmed a RES-biodistribution profile indicating stable nano-sized labeled particles in vivo. Results proved that the new method offers the opportunity to examine further specifically targeted and drug payload carrier variants of zirconia NP systems using PET/CT imaging.

New Tris(hydroxypyridinone) Bifunctional Chelators Containing Isothiocyanate Groups Provide a Versatile Platform for Rapid One-Step Labeling and PET Imaging with (68)Ga(3.)

Two new bifunctional tris(hydroxypyridinone) (THP) chelators designed specifically for rapid labeling with (68)Ga have been synthesized, each with pendant isothiocyanate groups and three 1,6-dimethyl-3-hydroxypyridin-4-one groups. Both compounds have been conjugated with the primary amine group of a cyclic integrin targeting peptide, RGD. Each conjugate can be radiolabeled and formulated by treatment with generator-produced (68)Ga(3+) in over 95% radiochemical yield under ambient conditions in less than 5 min, with specific activities of 60-80 MBq nmol(-1). Competitive binding assays and in vivo biodistribution in mice bearing U87MG tumors demonstrate that the new (68)Ga(3+)-labeled THP peptide conjugates retain affinity for the αvβ3 integrin receptor, clear within 1-2 h from circulation, and undergo receptor-mediated tumor uptake in vivo. We conclude that bifunctional THP chelators can be used for simple, efficient labeling of (68)Ga biomolecules under mild conditions suitable for peptides and proteins.

Temporal changes in phosphatidylserine expression and glucose metabolism after myocardial infarction: an in vivo imaging study in mice

Positron emission tomography (PET) for in vivo monitoring of phosphatidylserine externalization and glucose metabolism can potentially provide early predictors of outcome of cardioprotective therapies after myocardial infarction. We performed serial [⁶⁸Ga]annexin A5 PET (annexin-PET) and [¹⁸F]fluorodeoxyglucose PET (FDG-PET) after myocardial infarction to determine the time of peak phosphatidylserine externalization in relation to impaired glucose metabolism in infracted tissue. Annexin- and FDG-PET recordings were obtained in female (C57BL6/N) mice on days 1 to 4 after ligation of the left anterior descending (LAD) artery. [⁶⁸Ga]annexin A5 uptake (%ID/g) in the LAD artery territory increased from 1.7 ± 1.1 on day 1 to 5.0 ± 3.3 on day 2 and then declined to 2.0 ± 1.4 on day 3 (p  =  .047 vs day 2) and 1.6 ± 1.4 on day 4 (p  =  .014 vs day 2). These results matched apoptosis rates as estimated by autoradiography and fluorescein staining. FDG uptake (%ID/g) declined from 28 ± 14 on day 1 to 14 ± 3.5 on day 4 (p < .0001 vs day 1). Whereas FDG-PET revealed continuous loss of cell viability after permanent LAD artery occlusion, annexin-PET indicated peak phosphatidylserine expression at day 2, which might be the optimal time point for therapy monitoring.

Quantitative analysis and comparison study of [18F]AlF-NOTA-PRGD2, [18F]FPPRGD2 and [68Ga]Ga-NOTA-PRGD2 using a reference tissue model

With favorable pharmacokinetics and binding affinity for α_vβ₃ integrin, ¹⁸F-labeled dimeric cyclic RGD peptide ([¹⁸F]FPPRGD2) has been intensively used as a PET imaging probe for lesion detection and therapy response monitoring. A recently introduced kit formulation method, which uses an ¹⁸F-fluoride-aluminum complex labeled RGD tracer ([¹⁸F]AlF-NOTA-PRGD2), provides a strategy for simplifying the labeling procedure to facilitate clinical translation. Meanwhile, an easy-to-prepare ⁶⁸Ga-labeled NOTA-PRGD2 has also been reported to have promising properties for imaging integrin α_vβ₃. The purpose of this study is to quantitatively compare the pharmacokinetic parameters of [¹⁸F]FPPRGD2, [¹⁸F]AlF-NOTA-PRGD2, and [⁶⁸Ga]Ga-NOTA-PRGD2. U87MG tumor-bearing mice underwent 60-min dynamic PET scans following the injection of three tracers. Kinetic parameters were calculated using Logan graphical analysis with reference tissue. Parametric maps were generated using voxel-level modeling. All three compounds showed high binding potential (Bp_ND = k₃/k₄) in tumor voxels. [¹⁸F]AlF-NOTA-PRGD2 showed comparable Bp_ND value (3.75±0.65) with those of [¹⁸F]FPPRGD2 (3.39±0.84) and [⁶⁸Ga]Ga-NOTA-PRGD2 (3.09±0.21) (p>0.05). Little difference was found in volume of distribution (V_T) among these three RGD tracers in tumor, liver and muscle. Parametric maps showed similar kinetic parameters for all three tracers. We also demonstrated that the impact of non-specific binding could be eliminated in the kinetic analysis. Consequently, kinetic parameter estimation showed more comparable results among groups than static image analysis. In conclusion, [¹⁸F]AlF-NOTA-PRGD2 and [⁶⁸Ga]Ga-NOTA-PRGD2 have comparable pharmacokinetics and quantitative parameters compared to those of [¹⁸F]FPPRGD2. Despite the apparent difference in tumor uptake (%ID/g determined from static images) and clearance pattern, the actual specific binding component extrapolated from kinetic modeling appears to be comparable for all three dimeric RGD tracers.

One case of Candidemia developed after surgery for tongue cancer in a young adult

Candidemia is an opportunistic infection caused primarily by Candida albicans. We experienced a case of severe Candidemia that developed after surgical treatment for tongue cancer and required considerable labor to diagnose and to treat, though no particular immunodeficiency was seen before. The case was resistant to an antifungal agent, fluconazole, but was successfully treated with amphotericin B. Positive blood cultures, local wound culture, and increased β;-D-glucan were useful to diagnose the infection. In particular, gallium-67 scintigraphy was remarkably useful for the diagnosis and the evaluation of therapeutic effects in this case. Development of Candidemia following an oral and maxillofacial surgery is extremely rare among young adults, thus this case report serves to draw attention to the risk in oral and maxillofacial surgery.

The Effect of Blood Decrease on 67Ga Uptake by the Liver in Partially Hepatectomized Rats

As (67)Ga is injected into the blood, (67)Ga is immediately bound to transferrin (Tf) and transported to various tissues and the Tf-(67)Ga complex binds to Tf receptor on various tissues. In partial hepatectomy (PH) a part of blood in circulation is lost together with removed liver tissues, consequently the amounts of blood cells and Tf in circulation decrease. In order to investigate the effect of those decreases on (67)Ga uptake by the liver, we compared the uptake in partially hepatectomized rats with that in venesectioned rats in which only a part of blood in circulation decreased. A two-thirds PH was performed. Two milliliters of blood was venesectioned. Each treated rat was intraveneously injected with (67)Ga. The changes of erythrocyte and reticulocyte contents after PH did not differ from those after venesection (VS) at all. But (67)Ga uptake by reticulocytes significantly increased after VS but did not after PH. On the other hand, (67)Ga uptake by the liver significantly increased after PH but did not after VS. These differences must be related to the different expression of Tf receptors on the liver after PH and VS.

The Uptake Mechanism of Gallium-67 into Hepatocytes Treated with Carbon Tetrachloride

We have recently reported that transferrin (Tf)-unbound gallium-67 (67Ga) may be taken up into the liver of carbon tetrachloride (CCl4)-treated rats. In the present study, we attempted to clarify detailed mechanism of Tf-unbound 67Ga uptake by hepatocytes treated with CCl4 using in vitro experimental system. Hepatotoxic damages by CCl4 are mostly attributed to radical formed by an action of cytochrome P450. P450 isozymes have a higher expression in the perivenous hepatocytes (PVH) more than periportal hepatocytes (PPH). Therefore, we thought that the uptake of 67Ga which had been used for the detection of liver damage might have a zonal difference. The results of ALT activities showed that the CCl4 exposure for 4 h strongly impaired PVH more than PPH. The uptake of 67Ga by PVH treated with CCl4 was also higher than that by PPH. Moreover, the uptake of 45Ca by PVH was higher than that by PPH. In order to investigate whether 67Ga passed through calcium channel of hepatocytes, we made use of calcium channel blocker and activator. The Ca2+-channel blocker, verapamil, significantly decreased the uptakes of 45Ca and 67Ga by PPH and PVH pretreated with CCl4. The addition of the Ca2+-channel activator, Bay K8644, significantly increased the uptake both of 45Ca and 67Ga by PPH pretreated with CCl4. In the present study, it was demonstrated that the uptake of Tf-unbound 67Ga preferentially occurred in CCl4-damaged PVH and 67Ga was taken up into the hepatocytes in part through calcium channel.

Myeloperoxidase activity imaging using (67)Ga labeled substrate

PURPOSE

The aim of the study is to assess the feasibility of imaging specific activity of myeloperoxidase (MPO), a leukocyte enzyme with important roles in inflammation and atherosclerosis, by single photon emission computed tomography (SPECT) using a novel (67)Ga-labeled radiotracer obtained by conjugating desferrioxamine (DF) and hydroxyindolyl acetic acid in vivo.

MATERIALS AND METHODS

A reducing substrate of MPO (I) was synthesized by reacting commercially available DF with 2-(5-hydroxy-1H-indol-3-yl) acetic acid in the presence of a coupling agent [dicyclohexyl carbodiimide (DCC)]. The chelating unit was labeled with (67)Ga, and its interaction with MPO was characterized using MALDI-TOF and UV-vis. Mice with Matrigel implants containing human MPO were used to model diseased tissues rich in MPO. Three hours after the injection of (67)Ga-I, SPECT/computed tomography (CT) imaging was performed on a high-resolution Gamma Medica X-SPECT system. Biodistribution studies were performed six hours after the injection of the radiotracer.

RESULTS

The feasibility of compound I oligomerization in the presence of MPO and MPO-mediated cross-linking with proteins was initially confirmed in vitro. In vivo, a 2.7-fold increase in target-to-muscle ratio could be measured in MPO-containing Matrigel implants in mice. Biodistribution experiments demonstrated a 60% increase of radioactivity in MPO-containing vs. control (contralateral) Matrigel implants.

CONCLUSION

(67)Ga-I can be used to image MPO activity in a model system. The accumulation mechanism is based on a differential pharmacokinetics because of the size increase resulting from (67)Ga-I interaction with the target enzyme.

Neurosarcoidosis: clinical experience and diagnostic pitfalls

OBJECTIVE

To describe a group of patients with neurosarcoidosis and to highlight diagnostic difficulties based on current diagnostic criteria.

METHODS

The patient database of a general neurological department was searched for patients with established or suspected diagnosis of neurosarcoidosis. Twenty-four patients were identified with definite (n = 3), probable (n = 10) and possible neurosarcoidosis (n = 10). History and clinical, laboratory and imaging data of patients with definite and probable neurosarcoidosis were analyzed.

RESULTS

Cranial nerve symptoms were a dominant clinical feature, with the optic nerve being affected most frequently. Cerebrospinal fluid pleocytosis was found in more than half of the patients. Intrathecal IgG synthesis and oligoclonal bands were less frequent. There was a wide array of MRI lesions in both groups. Chest X-ray was false negative in 2 of 5 patients who also underwent a thoracic CT. Therapy with prednisolone was initiated in all patients. After a median of 36 months, 6 of 8 patients with follow-up data of >24 months were still in remission. Aggravation of symptoms required therapy escalation in 2 patients.

CONCLUSION

There is a wide range of clinical symptoms and test results in patients with "definite" or "probable" neurosarcoidosis. Because systemic involvement is a crucial diagnostic criterion, extensive medical work-up may be necessary. Prognosis under corticosteroid treatment may be better than previously thought.

Uptake of Gallium-67 by the Hepatocytes during Liver Regeneration in Carbon Tetrachloride-Treated Mice

Gallium-67 (67Ga) has been used as a tumor or inflammation-imaging agent in nuclear medicine. We recently reported that the peak of serum alanine aminotransferase (ALT) level was 1 d after carbon tetrachloride (CCl4) treatment in rats. However, the peak of 67Ga uptake by the liver tissue and hepatocytes was 2 d after the treatment. If 67Ga is taken in the hepatic disorder phase, the pattern of 67Ga uptake by the hepatocytes should be consistent with that of the ALT level. In order to answer why it was not, we carried out a detailed examination. The lipid peroxidation of hepatocytes from CCl4-treated mice was greatly increased 1 d after CCl4 treatment; serum ALT was also increased 1 d after the treatment. The uptake of 67Ga by the liver tissue reached a maximum 1 and 2 d after the treatment, while maximum by the hepatocytes was achieved after 2 d. The incorporation of bromodeoxyuridine into the hepatocytes also reached maximum 2 d after the treatment. These results suggest that the uptake of 67Ga by the hepatocytes is carried out during liver regeneration rather than during hepatic disorder by CCl4 treatment.

A possible mechanism for the exchange of transferrin-67Ga complex to heparan sulfate-67Ga complex

We attempted to identify the exchange mechanism of transferrin-67Ga complex to heparan sulfate-67Ga complex. The effect of phosphate on the binding ability of 67Ga to transferrin and heparan sulfate was studied by the dialysis method. The phosphate inhibited the binding ability of 67Ga to transferrin, while the phosphate enhanced the 67Ga binding ability to heparan sulfate. The results suggest that the phosphate is involved in the translocation of 67Ga from the transferrin to the heparan sulfate.

Transferrin is not involved in the entry of 67Ga into hepatocytes from regenerating liver of partially hepatectomized rats

Ever since the first observation of 67Ga accumulation in tumors and inflammatory lesions, 67Ga has been used to detect various tumors and inflammations. The aims of this study were to clarify whether or not transferrin is involved in the uptake of 67Ga by the regenerating liver after partial hepatectomy. The uptake of 67Ga by the liver of rats reached a maximum 2 d after partial hepatectomy. In order to inhibit the binding of 67Ga to transferrin in the blood, FeCl3 was administered 5 min before the injection of 67Ga. The administration of FeCl3 decreased the uptake of 67Ga by the liver of the partially hepatectomized rats, suggesting that transferrin is involved in the uptake by the liver. However, 67Ga was taken up only slightly by hepatocytes obtained from the liver of these rats. We conclude that transferrin is involved in the uptake of 67Ga by the liver tissue of partially hepatectomized rats but is not involved in its entry into the hepatocytes. Only a slight amount of gallium-67 enters the hepatocytes, and may accumulate primarily in the extracellular matrix of the liver tissue of these rats.

Advantages of short-lived positron-emitting radioisotopes for intracoronary radiation therapy with liquid-filled balloons to prevent restenosis

Balloon catheters filled with liquid radioisotopes provide excellent dose homogeneity for intracoronary radiation therapy but are associated with risk for rupture or leakage. We hypothesized that the safety of liquid-filled balloons may be improved once positron emitters with half-lives below 2 h are used instead of the high-energy beta-emitters 166Ho, 186Re, or 188Re, all of which have a longer half-life of at least 17 h.

METHODS

To support this concept, the suitability of 18F (half-life, 109.8 min), 68Ga (half-life, 67.6 min), 11C (half-life, 20.4 min), 13N (half-life, 9.97 min), and 15O (half-life, 2.04 min) for intracoronary radiation therapy was evaluated. Potential tissue penetration of positron radiation was assessed in a series of phantom experiments using Gafchromic film. Antiproliferative efficacy of positrons emitted by 68Ga was investigated in vitro using cultured bovine aortic smooth muscle cells (BASMCs), and was compared with gamma-radiation emitted by 137Cs. To characterize the remaining risk, we estimated radiotoxicity after accidental intravascular balloon rupture on the basis of tabulated isotope-specific doses (ICRP 53) and compared these values with 188Re.

RESULTS

Half-dose depth of tissue penetration measured in phantom experiments was 0.29 mm for 18F, 0.42 mm for 11C, 0.54 mm for 13N, 0.79 mm for 15O, and 0.9 mm for 68Ga. Irradiation of cultured BASMCs with positron radiation (68Ga) induced dose-dependent inhibition of proliferation with complete proliferative arrest at doses exceeding 6 Gy. ED(50) and ED(80) were 2.5 +/- 0.4 Gy (mean +/- SD) and 4.4 +/- 0.8 Gy, respectively. Antiproliferative efficacy was equal to that of the 662-keV gamma-radiation emitted by 137Cs (ED(50), 3.8 +/- 0.2 Gy; ED(80), 8.0 +/- 0.3 Gy). Estimates made for patient whole-body and organ doses were generally below 50 mSv/1.85 GBq for all investigated positron emitters. The same dose estimates for 188Re were 6-20 fold higher.

CONCLUSION

Among the studied radioisotopes, 68Ga is the most attractive source for liquid-filled balloons because of its convenient half-life, sufficient positron energy (2.92 MeV), documented antiproliferative efficacy, and uncomplicated availability from a radioisotope generator. The safety profile for 68Ga is significantly better than that of 188Re, which suggests this radioisotope should be evaluated further in preclinical studies.

Therapy of disseminated B-cell lymphoma xenografts in severe combined immunodeficient mice with an anti-CD74 antibody conjugated with (111)indium, (67)gallium, or (90)yttrium

A radiolabeled antibody (Ab) to CD74 (the MHC class II invariant chain, Ii) was shown previously to effectively kill human B-lymphoma cells in vitro. Conjugates with both Auger electron and beta-particle emitters were able to kill cells, but the former displayed less nonspecific toxicity in the in vitro assay used. In this report, we have extended the studies to an in vivo model of tumor growth. The human B-cell lymphoma Raji was injected i.v. into severe combined immunodeficient mice, and radiolabeled Abs were injected at various times after tumor inoculation. The maximum tolerated dose (MTD), as well as lower doses, was tested. Tumor growth was monitored by hind-leg paralysis. With a 3-5-day interval before Ab injection, anti-CD74 conjugated to either (111)In or (67)Ga, at a dose of 240-350 microCi/mouse, produced a strong therapeutic effect, with greatly delayed tumor growth, and many of the treated mice were tumor free for >6 months. Control mice became paralyzed in 16-24 days, uniformly. Treatment at later time points (9-day interval) had little therapeutic effect. The MTD was required for optimal therapy. With the beta-particle emitter (90)Y, the MTD was much less, 25 microCi/mouse, and at this dose there was only a weak therapeutic effect. In conclusion, the data suggest that low-energy electrons are more effective than beta-particles in this model system. These results may be applicable to humans, particularly in the case of micrometastatic disease. This approach may also be effective with other Abs that accrete in large amounts.

Liquid-filled balloon brachytherapy using (68)Ga is effective and safe because of the short 68-minute half-life: results of a feasibility study in the porcine coronary overstretch model

BACKGROUND

Liquid-filled balloons for coronary brachytherapy provide significant advantages over solid sources in dose homogeneity but carry the risk of life-threatening radiointoxication after balloon rupture and laboratory contamination in case of a spill. We hypothesized that the positron emitter (68)Ga, with a half-life of only 68 minutes, was well suited to overcome these safety obstacles while providing full therapeutic efficacy.

METHODS AND RESULTS

The feasibility, efficacy, and safety of (68)Ga liquid-filled balloon brachytherapy were investigated in the porcine coronary overstretch model. Four groups of 5 balloon-induced coronary lesions were irradiated with 8, 12, 16, and 24 Gy targeted to the adventitia. Ten unirradiated lesions served as controls. Segments treated with 16 or 24 Gy exhibited marked suppression of neointimal proliferation at 28-day follow-up, with quantitative parameters of intraluminal proliferation reduced to <20%. This beneficial effect was not compromised by untoward edge effects. Uninjured but irradiated vessels did not show histological signs of radiation damage. The (68)Ga whole-body dose due to balloon rupture was estimated to be 5 rem/50 mCi treatment activity and compared favorably with that of (188)Re (78 rem/50 mCi).

CONCLUSIONS

(68)Ga positron radiation suppresses neointimal proliferation at doses of 16 and 24 Gy. This biological efficacy, coupled with the attractive safety profile, suggests the selection of (68)Ga as an attractive isotope for liquid-filled balloon brachytherapy.

Cell cycle dependency of 67gallium uptake and cytotoxicity in human cell lines of hematological malignancies

67Gallium (67Ga) is a radionuclide which accumulates in hematological malignancies and is used for diagnostic imaging. We investigated in this in vitro study the cell cycle dependency of cellular uptake and cytotoxicity of 67Ga. Cell cycle synchronization of cells was achieved by counterflow centrifugal elutriation and the use of cytostatic drugs. The human lymphoma cell lines U-937 and U-715 were used and in elutriation experiments we also used the leukemic cell line HL-60. The transferrin receptor (CD71) expression, 67Ga uptake and cell proliferation inhibition were the parameters measured. We also studied cytotoxicity in various schedules for combination of 67Ga and drugs and the residual proliferative capacity was measured. The CD71 expression in the three cell lines increased from 106-177% on S phase cells and from 118-233% on G2M cells, as compared to the G0/G1 cell fraction. The 67Ga uptake varied from 108-127% for S cells and 128-139% for G2M cells. The drugs chosen induced cell cycle phase accumulation in S and/or G2M phase during preincubation. 67Ga preincubation induced accumulation in the G2M phase. Almost all combinations of 67Ga and drugs resulted in a non-interactive effect, except for methotrexate which resulted in an antagonistic effect. No preferential effect of any of the incubation schemes was seen. CD71 expression and 67Ga uptake were increased in S and G2M cells. Combination of 67Ga with drugs which arrest cells in these cell cycle phases did not result in a change in cytotoxicity. However, these results implicate that 67Ga and the cytostatic drugs tested except for methotrexate might be used together or sequentially in therapy.

Comparison of tissue retention of aluminum and Ga-67: effects of iron status in rats

The purposes of this study were to separate the effect of iron status from the effect of acute iron intake on tissue retention of aluminum and Ga-67 and to evaluate Ga-67 as a marker for aluminum. Anemic and control rats were dosed by gavage with a citrate solution containing 20 microCi Ga-67 with no added aluminum and iron (Gavage Ga-67), with 0.8 mmol aluminum (Gavage Al), with 0.8 mmol iron (Gavage Fe), or with both 0.8 mmol aluminum and 0.8 mmol iron (Gavage Fe and Al). After 24 h, anemic rats in the Gavage Al treatment had lower concentrations of aluminum in their tibias, kidneys, and spleens than control rats in that treatment. In contrast, anemic rats dosed with only Ga-67 (Gavage Ga-67 treatment) had lower concentrations of Ga-67 in their tibias and kidneys, but greater concentrations of Ga-67 in their livers and spleens than control rats in that treatment. The single dose of iron had no effect on tissue aluminum concentrations but depressed tissue Ga-67 concentrations. All rats accumulated aluminum predominantly in bone and control rats accumulated Ga-67 predominantly in bone, but anemic rats accumulated Ga-67 predominantly in liver. A major limitation of Ga-67 as a marker for aluminum is its greater sensitivity than aluminum to iron intake and status.

Radiotoxicity of 67-gallium on myeloid leukemic blasts

Promising clinical results are obtained with radiolabeled antibodies in leukemia patients. 67Gallium (67Ga) is a radionuclide that accumulates in many malignant tissues without need for a monoclonal antibody. For this reason, the use of 67Ga as a therapeutic agent is appealing. In the present we study, we report data about the radiotoxicity of 67Ga on peripheral blast cells of 23 patients with acute myelogenous leukemia (AML) in vitro. Isolated blast cells were incubated for 4 days with 0.74 MBq/ml (20 microCi/ml), 1.48 MBq/ml (40 microCi/ml) or 2.96 MBq/ml (80 microCi/ml) 67Ga. Compared with non-irradiated control cells proliferation during incubation was almost abolished. Clonogenic survival was measured by a colony forming unit assay (CFU-assay). In 13 of the 23 patients (56%) sufficient colony growth was observed for evaluation. The mean clonogenic survival of blasts after incubation with 0.74 MBq/ml and 2.96 MBq/ml 67Ga was 22.5, 11.3 and 3.5%, respectively. In some cases colony growth was completely abolished after incubation with only 0.74 MBq/ml 67Ga. No correlation was found between cellular 67Ga-uptake, (micro)dosimetry and transferrin receptor density (CD-71) via which 67Ga enters the cell. In vitro the blasts received a dose of > 10 Gy in 9 of the 2.96 MBq/ml, in 3 of the 1.48 MBq/ml and in 2 of the 0.74 MBq/ml incubations. In one patient, even a radiation dose > 40 Gy was reached. Low dose rate irradiation is known to arrest cells in G2/M-phase of the cell cycle, but no such arrest was observed during incubation with 67Ga. Thus, 67Ga induces clonogenic cell death in leukemic blasts. Cellular uptake of 67Ga in vitro varies between patients and can be very high in some patients. The easy availability, low costs and absence of immunological problems warrant further investigation of the therapeutic potential of 67Ga in refractory or relapsed AML patients.

Human metabolism of aluminium-26 and gallium-67 injected as citrates

1. 26Al and 67Ga were given as citrates to a healthy male volunteer by intravenous injection. The retention of both tracers was studied by body radioactivity measurement. Levels in blood and excreta were determined by gamma-ray spectrometry and/or accelerator mass spectrometry. 2. More than half of the 26Al had left the blood after 15 min and the decline continued, leaving < 1% in blood after 2 d; the losses occurred both to renal excretion and through uptake by other compartments. Estimated excretion up to 13 d was 83% (urine) and 1.8% (faeces). Whole-body retention of 15% at 13 d declined to approximately 4% at 1178 d, when the daily reduction corresponded to a biological half-life of 7 y, suggesting that sustained intake of dietary aluminium may lead to a progressively increasing internal deposit. 3. The metabolism of 67Ga differed markedly from that of 26Al in all aspects studied.

Multistep tumor targeting in nude mice using bispecific antibodies and a gallium chelate suitable for immunoscintigraphy with positron emission tomography

To improve tumor:tissue ratios in immunoscintigraphy, a three-step targeting method has been developed. The reagents used were (a) a radioactive, low molecular weight chelate prepared from ionic gallium and a phenolic polyaminocarboxylic acid, which can be labeled either with the single-photon emitter 67Ga or with the short-lived positron emitter 68Ga (t1/2 = 68 min); (b) a bispecific monoclonal antibody (bs-mAb) synthesized from the F(ab)2 fragment of the 1.1ASML antibody specific for the glycoprotein CD44v associated with a rat pancreas carcinoma cell line and the F(ab') fragment of an antibody specific for the gallium chelate; and (c) the nonradioactive gallium chelate covalently coupled to transferrin, which served as a high molecular weight blocker to prevent binding of the radioactive gallium chelate to bs-mAbs in the circulation. Targeting experiments in tumor-bearing nude mice with different doses of bs-mAbs, blocker, and 67Ga chelate were adjusted to maximize tumor to tissue contrasts and tumor uptake. Compared with the biodistribution of the 131I-labeled, native 1.1ASML antibody 24 h postinjection, a schedule using 100 pmol bs-mab 24 h later 100 pmol blocker, 15 min later 16 pmol 67Ga chelate, 1 h later examination, increased tumor:blood and tumor: liver ratios by a factor of 5 while keeping the localization of radioactivity in the tumor constant (10.1% injected dose/g). High-contrast images using either 67Ga or 68Ga were obtained within 1 h. The targeting method described enables the use of the short-lived positron emitter 68Ga and thus allows the combination of an improved immunoscintigraphy and positron emission tomography.

Tissue turnover of aluminum and Ga-67: effect of iron status

The purposes of this study were to evaluate the effect of nutritional status in regard to iron on aluminum distribution and turnover and to evaluate Ga-67 as a marker for aluminum. Anemic (n = 27) and normal (n = 30) rats were dosed by gavage with 0.8 mmoles of aluminum and 20 microCi Ga-67 in a 0.75 mol/l citrate solution and sacrificed 1, 3, 6, 9, 15, and 21 days later. Anemic rats generally retained more aluminum in their livers but less in tibias and spleens than normal rats. The half-lives of aluminum in liver (56 vs 17 days), muscle (33 vs 16 days), and serum (12 vs 8 days) were significantly greater in anemic than normal rats, respectively. Total body retention of Ga-67 could be described on the basis of a two-compartment model. The turnover of Ga-67 from the first compartment was rapid (half-life = 0.8 and 0.6 days) in anemic and normal rats, respectively, and was similar to the turnover of Ga-67 from the Gl tract (half-life = 0.7 and 0.6 days in anemic and normal rats, respectively). The turnover of Ga-67 from the second compartment was also rapid (2.8 vs 4.0 days in anemic and normal rats, respectively). Anemia affected the retention of Ga-67 more than the retention of aluminum; anemic rats retained more Ga-67 in their livers, spleens, kidneys, hearts, and muscles but less in their tibias than normal rats. In general, Ga-67 was not a satisfactory marker for aluminum distribution and turnover in normal and anemic rats.

Technetium-99m-DTPA aerosol and gallium-67 scanning in pulmonary complications of human immunodeficiency virus infection

We retrospectively compared the results of 67Ga chest scans and 99mTc-DTPA aerosol clearance measurements with those of fiberoptic bronchoscopy in 88 patients infected with the human immunodeficiency virus. Of 100 investigations, a pulmonary infection was diagnosed in 39, mainly Pneumocystis carinii pneumonia and a noninfectious disorder was found in 42, mainly Kaposi's sarcoma and lymphocytic alveolitis. Gallium scans and DTPA clearance were abnormal respectively in 74% and 92% of infectious complications, and in 12% and 60% of noninfectious disorders. In 10 cases, DTPA clearance was accelerated, while chest x-ray, arterial blood gases and even gallium scanning were normal. A value of DTPA clearance greater than 4.5%.min-1 was both sensitive and specific for the diagnosis of Pneumocystis carinii pneumonia. The gallium scan was always normal in bronchopulmonary Kaposi's sarcoma. We conclude that in symptomatic patients: (1) DTPA clearance measurements are useful for detecting lung disease when chest x-ray and/or PaO2 are normal and (2) a gallium scan is indicated to distinguish progressive Kaposi's sarcoma from a superimposed second process when radiological abnormalities of pulmonary Kaposi's sarcoma are present.

The role of the interaction between Fe(III) and cell surface in the accumulation of 67Ga by tumor cells

The study of the interaction between complexed iron and tumor cells in the presence of 67Ga-citrate indicates that a phenomenon of iron-binding related to the thermodynamic constant of stability of the iron complex, and a hydrolysis (or anion penetration) of the interaction product determine the uptake of 67Ga. The effects of various parameters such as ionic composition of the medium, nature of the iron complex, time of incubation and number of cells are discussed.

Defective gallium-transferrin binding in Alzheimer disease and Down syndrome: possible mechanism for accumulation of aluminium in brain

The plasma distribution of gallium (as an analogue of aluminium) was investigated in patients with Alzheimer disease, Down syndrome, or stroke dementia, in subjects on haemodialysis for chronic renal failure, and in healthy controls. Gallium-transferrin binding was significantly lower in the Alzheimer (mean [SEM] 7.9 [1.1]%) and Down syndrome groups (6.9 [0.7]%) than in the controls (17.1 [1.6]%), whereas stroke dementia and haemodialysis patients had normal binding. There were no differences among the groups in plasma citrate concentration. The plasma transferrin concentration was slightly lower in the Alzheimer and Down syndrome groups than in the controls, but even lower in stroke dementia patients (1.74 [0.14] g/l vs 2.98 [0.18] g/l in controls). Transferrin iron saturation was higher in the Alzheimer (58.9%) and Down syndrome groups (81.6%) than in the controls (39.0%) or stroke dementia patients (33.4%). This deficiency of gallium/aluminium binding would leave more unbound aluminium which could move readily into the brain, where it has neurotoxic effects.