Klaus Schomäcker

Qualitative [18F]FDG positron emission tomography in primary breast cancer: clinical relevance and practicability

Positron emission tomography (PET) using fluorine-18 2-deoxy-2-fluoro-d-glucose (FDG) is of potential value for the diagnosis of malignant tumours. The aim of this study was to evaluate the use of FDG PET in patients with breast tumours, appraising its applicability in visualising primary carcinomas and regional metastases in a clinical setting. Results of FDG PET were compared with those of mammography, breast ultrasonography and histology in 30 patients with inconclusive breast findings. For PET, transmission and emission images were taken in one or two scan positions, depending on the available time and the clinical status of patients. PET showed focal FDG uptake with high contrast in 21 of 23 primary carcinomas. In one patient, only PET correctly visualized multifocal disease (three foci, Ø 0.4–1 cm). The accuracy of PET in the detection of primary breast cancer was 90%, and in the detection of involved axillary lymph nodes, 94%. All metastases (lymph nodes, lungs, bones, soft tissues) covered by the field of view and demonstrated by other methods (X-ray, computed tomography, magnetic resonance imaging, bone scan) showed FDG uptake. In three patients, only PET initiated further diagnostic procedures. The results indicate that FDG PET can provide a rapid diagnostic study (45–60 min) and allows accurate tumour staging of several organ systems for primary tumour and metastases with a single imaging study in a routine clinical setting.

Comparison of [18F]DCFPyL and [68Ga]Ga-PSMA-HBED-CC for PSMA-PET Imaging in Patients with Relapsed Prostate Cancer

PurposeGallium-68 (Ga-68)-labeled tracers for imaging expression of the prostate-specific membrane antigen (PSMA) such as the [68Ga]Ga-PSMA-HBED-CC have already demonstrated high potential for the detection of recurrent prostate cancer. However, compared to Ga-68, a labeling with fluorine-18 (F-18) would offer advantages with respect to availability, production amount, and image resolution. [18F]DCFPyL is a promising F-18-labeled candidate for PSMA-positron emission tomography (PET) imaging that has been recently introduced. In the current study, we aimed to compare [68Ga]Ga-PSMA-HBED-CC and [18F]DCFPyL for clinical use in biochemically relapsed prostate cancer.ProceduresIn 14 selected patients with PSA relapse of prostate cancer, [18F]DCFPyL PET/X-ray computed tomography (CT) was performed in addition to [68Ga]Ga-PSMA-HBED-CC PET/CT. A systematic comparison was carried out between results obtained with both tracers with regard to the number of detected PSMA-positive lesions, the standardized uptake value (SUV)max and the lesion to background ratios.ResultsAll suspicious lesions identified by [68Ga]Ga-PSMA-HBED-CC were also detected with [18F]DCFPyL. In three patients, additional lesions were observed using [18F]DCFPyL PET/CT. The mean SUVmax in the concordant [18F]DCFPyL PSMA-positive lesions was significantly higher as compared to [68Ga]Ga-PSMA-HBED-CC (14.5 vs. 12.2, p = 0.028, n = 15). The mean tumor to background ratios (n = 15) were significantly higher for [18F]DCFPyL compared to [68Ga]Ga-PSMA-HBED-CC using kidney, spleen, or parotid as reference organs (p = 0.006, p = 0.002, p = 0.008), but no significant differences were found using the liver (p = 0.167) or the mediastinum (p = 0.363) as reference organs.Conclusion[18F]DCFPyL PET/CT provided a high image quality and visualized small prostate lesions with excellent sensitivity. [18F]DCFPyL represents a highly promising alternative to [68Ga]Ga-PSMA-HBED-CC for PSMA-PET/CT imaging in relapsed prostate cancer.

Role of balloon occlusion for mononuclear bone marrow cell deposition after intracoronary injection in pigs with reperfused myocardial infarction

AIMS In clinical studies on cell therapy for acute myocardial infarction (MI), cells are usually applied by intracoronary infusion with balloon (IC/B). To test the utility of balloon occlusion, mononuclear bone marrow cell (MNC) retention after intracoronary infusion without balloon (IC/noB) was compared with IC/B and intramyocardial (IM) injection. METHODS AND RESULTS Four hours after LAD ligation in male pigs, reperfusion was allowed (confirmed by coronary angiography). Five days later, 1 x 10(8) autologous (111)Indium-labelled MNC were injected IC/noB (n = 4), IC/B (n = 4), or IM (n = 4). At 1 h the fraction of injected MNC that was detected in the heart was 4.1 +/- 1.1% after IC/noB injection, 6.1 +/- 2.5% after IC/B injection (P = 0.19), and 20.7 +/- 2.3% after IM injection (P < 0.001 vs. IC/noB and IC/B). At 24 h it was 3.0 +/- 0.6% (IC/noB), 3.3 +/- 0.5% (IC/B, P = 0.43), and 15.0 +/- 3.1% (IM, P < 0.001 vs. IC/noB and IC/B). Dynamic scintigrammes during each of four consecutive IC/B injections showed a rapid 19.6 +/- 8.0% cell loss during balloon inflation (no-flow period, phase 1) and a rapid 36.6 +/- 17.8% cell loss after balloon deflation (re-flow period, phase 2). After each of four consecutive IC/noB injections the peak cell deposit was lower, followed by one phase of rapid cell loss (30.9 +/- 11.0% after 6 min). After IM injection only a slow linear cell loss was observed (9.7% per h). In histology, PKH-67 labelled cells only rarely had passed the endothelial barrier after 24 h after IC injection, while they were exclusively found in the interstitium after IM injection. CONCLUSION The observation of a similar cell persistence after IC injections with and without balloon occlusion suggests that the balloon procedures currently applied in clinical studies are not necessary for cell deposit. If longer term persistence of cells plays a role for the clinical benefit of cardiac cell therapy, IM injection may be superior to IC applications.

Imaging of central nervous system lymphomas with iodine‐123 labeled rituximab

Most patients with primary central nervous system (CNS) lymphoma (PCNSL) relapse after initial response to chemotherapy or the combination of chemotherapy and irradiation. Thus, novel treatment regimens for relapsed PCNSL are needed. As the majority of PCNSL are B‐cell neoplasms expressing the CD20 antigen, treatment with the chimeric monoclonal antibody (MAb) rituximab might be reasonable. Nevertheless, the potential efficacy of intravenous rituximab in PCNSL seems to be limited as MAbs are high molecular weight proteins, which might be unable to pass the blood brain barrier. Thus, we performed dosimetric measurements with iodine‐123 (123I)‐rituximab to evaluate rituximab uptake in PCNSL after systemic intravenous administration. We analyzed four patients with PCNSL receiving a preinfusion of 250 mg/m2 rituximab followed by 200–500 MBq of the gamma‐emitter 123I‐rituximab. Single photon emission computed tomography (SPECT) was performed 1, 24 and 48 h after administration of the radio‐immunoconstruct. Only one patient showed a very weak or questionable uptake of 123I‐rituximab into tumor tissue which was ninefold lower compared with the blood‐pool accumulation. These data suggest that systemic MAb‐based radio‐immunotherapy is not feasible in patients with PCNSL because a sufficient activity in the tumor will be associated with severe hematotoxicity. If an uptake of therapeutic rituximab doses into PCNSL can be achieved remains questionable.

PSA-stratified performance of 18F- and 68Ga-labeled tracers in PSMA-PET imaging of patients with biochemical recurrence of prostate cancer.

Several studies outlined the sensitivity of 68Ga-labeled PET tracers against the prostate-specific membrane antigen (PSMA) for localization of relapsed prostate cancer in patients with renewed increase in the prostate-specific antigen (PSA), commonly referred to as biochemical recurrence. Labeling of PSMA tracers with 18F offers numerous advantages, including improved image resolution, longer half-life, and increased production yields. The aim of this study was to assess the PSA-stratified performance of the 18F-labeled PSMA tracer 18F-DCFPyL and the 68Ga-labeled reference 68Ga-PSMA-HBED-CC. Methods: We examined 191 consecutive patients with biochemical recurrence according to standard acquisition protocols using 18F-DCFPyL (n = 62, 269.8 MBq, PET scan at 120 min after injection) or 68Ga-PSMA-HBED-CC (n = 129, 158.9 MBq, 60 min after injection). We determined PSA-stratified sensitivity rates for both tracers and corrected our calculations for Gleason scores using iterative matched-pair analyses. As an orthogonal validation, we directly compared tracer distribution patterns in a separate cohort of 25 patients, sequentially examined with both tracers. Results: After prostatectomy (n = 106), the sensitivity of both tracers was significantly associated with absolute PSA levels (P = 4.3 × 10−3). Sensitivity increased abruptly, when PSA values exceeded 0.5 μg/L (P = 2.4 × 10−5). For a PSA less than 3.5 μg/L, most relapses were diagnosed at a still limited stage (P = 3.4 × 10−6). For a PSA of 0.5–3.5 μg/L, PSA-stratified sensitivity was 88% (15/17) for 18F-DCFPyL and 66% (23/35) for 68Ga-PSMA-HBED-CC. This significant difference was preserved in the Gleason-matched-pair analysis. Outside of this range, sensitivity was comparably low (PSA < 0.5 μg/L) or high (PSA > 3.5 μg/L). After radiotherapy (n = 85), tracer sensitivity was largely PSA-independent. In the 25 patients examined with both tracers, distribution patterns of 18F-DCFPyL and 68Ga-PSMA-HBED-CC were strongly comparable (P = 2.71 × 10−8). However, in 36% of the PSMA-positive patients we detected additional lesions on the 18F-DCFPyL scan (P = 3.7 × 10−2). Conclusion: Our data suggest that 18F-DCFPyL is noninferior to 68Ga-PSMA-HBED-CC, while offering the advantages of 18F labeling. Our results indicate that imaging with 18F-DCFPyL may even exhibit improved sensitivity in localizing relapsed tumors after prostatectomy for moderately increased PSA levels. Although the standard acquisition protocols, used for 18F-DCFPyL and 68Ga-PSMA-HBED-CC in this study, stipulate different activity doses and tracer uptake times after injection, our findings provide a promising rationale for validation of 18F-DCFPyL in future prospective trials.

Use of myocardial imaging agents for tumour diagnosis – a success story?

Abstract. The search for new radiopharmaceuticals for tumour diagnosis usually proceeds on the basis of rational concepts drawing on the latest advances in molecular biology. Using this approach, radioactive peptide hormones, antibodies and oligonucleotides have been developed that are used increasingly in nuclear medicine for diagnostic and therapeutic purposes. This article, however, focusses on a group of radiopharmaceuticals whose use in tumour diagnosis was not the outcome of a methodical development programme but rather the result of a chance discovery. These radiopharmaceuticals, thallium-201 and technetium-99m labelled 2-methoxyisobutylisonitrile (MIBI), tetrofosmin and furifosmin, were first developed through extensive research efforts for cardiac imaging, but during their worldwide application for myocardial scintigraphy they were accidentally found to accumulate in tumours. Intensive studies were then begun on cell cultures in an attempt to discover the cause of their uptake into tumours. The aim was to compare the effectiveness of the radiopharmaceuticals for tumour diagnosis in a range of indications and to investigate the various mechanisms by which they are taken up into tumours. While the more favourable radiophysical properties of 99mTc-MIBI render it superior to 201Tl for many diagnostic purposes, neither 99mTc-tetrofosmin nor 99mTc-furifosmin has yet proved suitable for clinical routine examinations, although the former has found limited application. In the case of 99mTc complexes, the breakthrough came with the experimental finding that these substances are substrates of P-glycoprotein, a product of the human multidrug resistance gene (MDR1). The concentration of 99mTc complexes in tumour cells is a function of a passive, membrane potential-dependent influx into and a P-glycoprotein-controlled efflux out of the tumour cell. Preliminary studies suggest that in vivo detection of MDR may even be possible. There is also evidence that the P-glycoprotein-mediated transport system can be blocked competitively. However, it will be some time before a system can be developed for detection of MDR on a routine basis.

Stabilities of lanthanide-protein complexes

After incubation of both serum and HSA solutions with radioactive lanthanide complexes the binding constants of the corresponding lanthanide-protein complexes formed in the protein solutions under physiologic conditions, pH: 7.4, temperature: 310 K, isotonic ionic strength: 0.15 mol/L, were determined. The association constants of the lanthanide-protein complexes formed both in serum and HSA-solutions are equal within the experimental error. In conclusion, serum albumin binding predominates for the radiolanthanides. With the decrease of the ionic radii from 1.034 A (Ce) to 0.858 (Yb) the association constants increased by five orders of magnitude from 1 g Kpr = 4.90 (Ce) to 1 g Kpr = 9.54 (Yb). Further, a serum fractionation with alcohol was carried out to prove that the albumin fraction of serum is responsible for the lanthanide binding in blood.

Diethylstilbestrol (DES) labeled with Auger emitters: Potential radiopharmaceutical for therapy of estrogen receptor-positive tumors and their metastases?

Purpose: Diethylstilbestrol (DES) is a well-known, non-steroidal estrogen with high affinity to the estrogen receptor (ER). Labeled DES would be a useful tool for therapy of ER-positive mammary carcinomas and their metastases. Particularly with Auger emitters, high cytotoxic potential combined with only slight side effects can be expected. Materials and methods: DES was labeled by a new method with higher yield and specific activity than former methods. Cytotoxic effects on MCF-7 (human, Caucasian, breast, adenocarcinoma) cells, were tested in relation to radioactivity concentration applied and location of decay. Different iodine isotopes (123I, 125I, 131I) bound to DES or in the form of iodide were compared with regard to induction of intracellular DNA (deoxyribonucleic acid) fragmentation, and decrease of viability. For this purpose the ‘Cell Death Detection Enzyme-Linked ImmunoSorbent Assay (ELISA)’ and the water soluble tetrazolium salt WST-1 were used. The radiation protective effects of the radical scavenger vitamin C were also tested. Results: The experiments showed a significantly lower viability of cells exposed to the Auger emitters than those with the β-emitter 131I. All nuclides induced intracellular DNA fragments. The maximum amount of intracellular DNA fragments was different for all nuclides: 131I-DES <125I-DES <123I-DES. With isotopes in the form of iodide, no increase of intracellular DNA fragmentation could be detected. Vitamin C reduced intracellular DNA fragmentation significantly, which points to an induction mechanism mainly via free radicals. Conclusions: Labeled DES is a promising compound with high cytotoxic potential for treatment of ER-positive mamma carcinomas and their metastases.

The influence of isotopic and nonisotopic carriers on the biodistribution and biokinetics of M3+-citrate complexes

The influence of carrier amounts of Fe, Ga, and Tm on the biodistribution of 67Ga-, 59Fe-, and 167Tm-citrate in mice was investigated. Our results suggest that 167Tm, unlike 67Ga and 59Fe, is not transported by transferrin in the blood. Of the three radioisotopes tested, 167Tm had the highest tumor/background ratio (10 h after the injection). The application of Fe carrier led to an enhancement of the elimination of 67Ga from the blood and muscles, resulting in a better tumor/background ratio.

One step generation of fully chimeric antibodies using Cgamma1- and Ckappa mutant mice.

Humanized antibodies (Abs) are effective drugs against a variety of diseases such as cancer, autoimmune diseases, transplant rejection and others. The most powerful technology to develop humanized Abs is the use of mice that produce humanized Abs. By modifying the genetic background of F004 mice a new mouse substrain was developed for optimized “one step” generation of chimeric humanized monoclonal Abs. The new mice (F004-Jen) demonstrated improved fertility still expressing the human locus at the same level as the parental F004 mouse. The value of these mice for the generation of chimeric Abs was exemplified for a panel of chimeric Abs against the human neural cell adhesion molecule (NCAM): The fully chimeric human IgG1/κ Ab Ch.MK1 bound to NCAM expressing cells with a KD=4.3-8.7×10−8 M and was functionally active as demonstrated by depleting NCAM expressing cells. We also demonstrated that chimeric IgG1/κ Abs can be induced by hybridoma class switching of IgM producing hybridoma cells, providing an alternative way to chimeric Abs. The present data highlight F004-Jen mice as an efficient tool for “one step” generation of chimeric Abs.