Is There a Role of Artificial Intelligence in Preclinical Imaging?

This review provides an overview of the current opportunities for integrating artificial intelligence methods into the field of preclinical imaging research in nuclear medicine. The growing demand for imaging agents and therapeutics that are adapted to specific tumor phenotypes can be excellently served by the evolving multiple capabilities of molecular imaging and theranostics. However, the increasing demand for rapid development of novel, specific radioligands with minimal side effects that excel in diagnostic imaging and achieve significant therapeutic effects requires a challenging preclinical pipeline: from target identification through chemical, physical, and biological development to the conduct of clinical trials, coupled with dosimetry and various pre, interim, and post-treatment staging images to create a translational feedback loop for evaluating the efficacy of diagnostic or therapeutic ligands. In virtually all areas of this pipeline, the use of artificial intelligence and in particular deep-learning systems such as neural networks could not only address the above-mentioned challenges, but also provide insights that would not have been possible without their use. In the future, we expect that not only the clinical aspects of nuclear medicine will be supported by artificial intelligence, but that there will also be a general shift toward artificial intelligence-assisted in silico research that will address the increasingly complex nature of identifying targets for cancer patients and developing radioligands.

Fibroblast Activation Protein Inhibitor Theranostics: Preclinical Combination Treatment.

Fibroblast activation protein (FAP)-radioligand therapy might be effective in some patients without being curative. FAP-radioligands deliver ionizing radiation directly to FAP+ cancer-associated fibroblasts and, in some cancers, to FAP+ tumor cells; in addition, they indirectly irradiate FAP- cells in tumor tissue via cross-fire and bystander effects. Here, we discuss the potential to improve FAP-radioligand therapy through interfering with DNA damage repair, immunotherapy, and co-targeting cancer-associated fibroblasts. As the molecular and cellular effects of FAP-radioligands on the tumor and its microenvironment have not been investigated yet, we call for future research to close this gap in knowledge, which prevents the development of more effective FAP-radioligand therapies.

Quantitative In Vivo Imaging of the Androgen Receptor Axis Reveals Degree of Prostate Cancer Radiotherapy Response.

Noninvasive biomarkers for androgen receptor (AR) pathway activation are urgently needed to better monitor patient response to prostate cancer therapies. AR is a critical driver and mediator of resistance of prostate cancer but currently available noninvasive prostate cancer biomarkers to monitor AR activity are discordant with downstream AR pathway activity. External beam radiotherapy (EBRT) remains a common treatment for all stages of prostate cancer, and DNA damage induced by EBRT upregulates AR pathway activity to promote therapeutic resistance. [89Zr]11B6-PET is a novel modality targeting prostate-specific protein human kallikrein 2 (hK2), which is a surrogate biomarker for AR activity. Here, we studied whether [89Zr]11B6-PET can accurately assess EBRT-induced AR activity.Genetic and human prostate cancer mouse models received EBRT (2-50 Gy) and treatment response was monitored by [89Zr]11B6-PET/CT. Radiotracer uptake and expression of AR and AR target genes was quantified in resected tissue.EBRT increased AR pathway activity and [89Zr]11B6 uptake in LNCaP-AR and 22RV1 tumors. EBRT increased prostate-specific [89Zr]11B6 uptake in prostate cancer-bearing mice (Hi-Myc x Pb_KLK2) with no significant changes in uptake in healthy (Pb_KLK2) mice, and this correlated with hK2 protein levels. IMPLICATIONS: hK2 expression in prostate cancer tissue is a proxy of EBRT-induced AR activity that can noninvasively be detected using [89Zr]11B6-PET; further clinical evaluation of hK2-PET for monitoring response and development of resistance to EBRT in real time is warranted.

18F-PSMA Cerenkov Luminescence and Flexible Autoradiography Imaging in a Prostate Cancer Mouse Model and First Results of a Radical Prostatectomy Feasibility Study in Men.

Intraoperative identification of positive resection margins (PRMs) in high-risk prostate cancer (PC) needs improvement. Cerenkov luminescence imaging (CLI) with 68Ga-PSMA-11 is promising, although limited by low residual activity and artificial signals. Here, we aimed to assess the value of CLI and flexible autoradiography (FAR) with 18F-PSMA-1007. Methods: Mice bearing subcutaneous PSMA-avid RM1-PGLS tumors were administered 18F-PSMA-1007, and PET/CT was performed. After the animals had been killed, organs were excised and measured signals in CLI and FAR CLI were correlated with tracer activity concentrations (ACs) obtained from PET/CT. For clinical assessment, 7 high-risk PC patients underwent radical prostatectomy immediately after preoperative 18F-PSMA PET/CT. Contrast-to-noise ratios (CNRs) were calculated for both imaging modalities in intact specimens and after incision above the index lesion. Results: In the heterotopic in vivo mouse model (n = 5), CLI did not detect any lesion. FAR CLI detected a distinct signal in all mice, with a lowest AC of 7.25 kBq/mL (CNR, 5.48). After incision above the index lesion of the prostate specimen, no increased signal was observed at the cancer area in CLI. In contrast, using FAR CLI, a signal was detectable in 6 of 7 patients. The AC in the missed index lesion was 1.85 kBq/mL, resulting in a detection limit of at least 2.06 kBq/mL. Histopathology demonstrated 2 PRMs, neither of which was predicted by CLI or FAR CLI. Conclusion: 18F-PSMA FAR CLI was superior to CLI in tracer-related signal detectability. PC was could be visualized in radical prostatectomy down to 2.06 kBq/mL. However, the detection of PRMs was limited. Direct anatomic correlation of FAR CLI is challenging because of the scintillator overlay.

PSMA-Directed Imaging and Therapy of Salivary Gland Tumors: A Single-Center Retrospective Study.

We analyzed the diagnostic performance of prostate-specific membrane antigen (PSMA) PET/CT and the dosimetry, efficacy, and safety of 177Lu-PSMA-617 radioligand therapy (RLT) in salivary gland malignancies (SGMs). Methods: We identified 28 SGM patients with PSMA PET/CT from our database. CT and PSMA PET/CT images were evaluated separately by 3 masked readers in joint reading sessions. Pathologic findings were grouped into 6 TNM regions, and lesion-based disease extent was classified as no disease (n = 1, 4%), unifocal (n = 2, 7%), oligometastatic (n = 9, 32%), multifocal (n = 3, 11%), or disseminated (n = 13, 47%). For each region, the SUVmax of the lesion with the highest uptake was measured and the visual PSMA expression score was evaluated on a per-patient basis using PROMISE criteria. The association between PSMA expression and clinical and histopathologic markers was tested using the Student t test. Five patients underwent PSMA RLT with intratherapeutic dosimetry. Response was assessed using RECIST 1.1, and adverse events were graded according to version 5.0 of the Common Terminology Criteria for Adverse Events. Results: Compared with CT, PSMA PET/CT demonstrated additional metastatic lesions in 11 of 28 (39%) patients, leading to upstaging of TNM and lesion-based disease extent in 3 (11%) and 6 (21%) patients, respectively. PSMA PET/CT detected CT-occult local tumor, regional lymph nodes, nonregional lymph nodes, and bone metastases in 1 (4%), 4 (14%), 2 (7%), and 4 (14%) patients, respectively; no additional lesions were detected in the other predefined regions. PSMA expression level was higher than liver in 6 patients (25%). A significantly higher SUVmax was observed in male than female patients (15.8 vs. 8.5, P = 0.007) and in bone than lung lesions (14.2 vs. 6.4, P = 0.006). PSMA RLT was discontinued after 1 cycle in 3 of 5 patients because of insufficient tumor doses. No adverse events of grade 4 or higher occurred. Conclusion: In SGMs, PSMA PET/CT demonstrated a superior detection rate and led to upstaging in about one third of patients when compared with CT. The male sex and the presence of bone metastases were associated with significantly higher PSMA expression. PSMA RLT was well tolerated, but most patients did not have more than 1 cycle because of insufficient tumor doses.

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

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

Enzalutamide Enhances PSMA Expression of PSMA-Low Prostate Cancer.

Prostate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) prolongs overall survival in men with metastatic castration-resistant prostate cancer (mCRPC). However, men with low PSMA expression are excluded from RLT. We explored the effect of androgen receptor blockade with enzalutamide on PSMA expression. Assessment of PSMA and androgen receptor (AR) expression on the human PC cell lines 22Rv1, C4-2, and LNCaP by immunohistochemistry and flow cytometry revealed low (22Rv1) and high (C4-2 and LNCaP) PSMA expression, and high, comparable AR positivity. Treatment with enzalutamide increased PSMA levels in 22Rv1, C4-2, and LNCaP (2.2/2.3/2.6-fold, p = 0.0005/0.03/0.046) after one week compared to DMSO-treated controls as assessed by flow cytometry. NOD/Scid mice bearing 22Rv1 tumors were treated with enzalutamide for two weeks. Positron emission tomography/computed tomography (PET/CT) demonstrated higher tumor uptake of 68Ga-PSMA after enzalutamide treatment (p = 0.004). Similarly, a clinical case with low baseline PSMA avidity demonstrated increased uptake of 68Ga-PSMA after enzalutamide on PET/CT and post-therapeutic 177Lu-PSMA scintigraphy in a patient with mCRPC. Enzalutamide induced PSMA expression in the 22Rv1 xenograft model and in an mCRPC patient, both with low baseline tumoral PSMA levels. Therefore, enzalutamide pre-treatment might render patients with low PSMA expression eligible for 177Lu-PSMA RLT.

Drug and molecular radiotherapy combinations for metastatic castration resistant prostate cancer.

Metastatic castration resistant prostate cancer (mCRPC) is a highly lethal disease. Several novel therapies have been assessed in the past years. Targeting DNA damage response (DDR) pathways in prostate cancer became a promising treatment strategy and olaparib and rucaparib, Poly(ADP-ribose) polymerase (PARP) inhibitors, have been approved for patients carrying mutations in homologous recombination (HR) repair pathways. Other DDR inhibitor targets, such as ATM, ATR, CHK1, CHK2, and WEE1 are under extensive investigation. Additionally, molecular radiotherapy (MRT) including [177Lu]Lu-PSMA, [225Ac]Ac-PSMA, [223Ra]Ra-dichloride, [153Sm]-EDTMP, [188Re]Re-HDMP and GRPR-targeted MRT treat cancer through internal ionizing radiation causing DNA damage and demonstrate promising efficacy in clinical trials. In the field of immunotherapy, checkpoint inhibition as well as sipuleucel-T and PROSTVAC demonstrated only limited efficacy in mCRPC when used as monotherapy. This review discusses recent therapeutic strategies for mCRPC highlighting the need for rational combination of treatment options.

Imaging Inflammation with Positron Emission Tomography.

The impact of inflammation on the outcome of many medical conditions such as cardiovascular diseases, neurological disorders, infections, cancer, and autoimmune diseases has been widely acknowledged. However, in contrast to neurological, oncologic, and cardiovascular disorders, imaging plays a minor role in research and management of inflammation. Imaging can provide insights into individual and temporospatial biology and grade of inflammation which can be of diagnostic, therapeutic, and prognostic value. There is therefore an urgent need to evaluate and understand current approaches and potential applications for imaging of inflammation. This review discusses radiotracers for positron emission tomography (PET) that have been used to image inflammation in cardiovascular diseases and other inflammatory conditions with a special emphasis on radiotracers that have already been successfully applied in clinical settings.

PSA-Targeted Alpha-, Beta-, and Positron-Emitting Immunotheranostics in Murine Prostate Cancer Models and Nonhuman Primates.

PURPOSE: Most patients with prostate cancer treated with androgen receptor (AR) signaling inhibitors develop therapeutic resistance due to restoration of AR functionality. Thus, there is a critical need for novel treatment approaches. Here we investigate the theranostic potential of hu5A10, a humanized mAb specifically targeting free PSA (KLK3). EXPERIMENTAL DESIGN: LNCaP-AR (LNCaP with overexpression of wildtype AR) xenografts (NSG mice) and KLK3_Hi-Myc transgenic mice were imaged with 89Zr- or treated with 90Y- or 225Ac-labeled hu5A10; biodistribution and subcellular localization were analyzed by gamma counting, PET, autoradiography, and microscopy. Therapeutic efficacy of [225Ac]hu5A10 and [90Y]hu5A10 in LNCaP-AR tumors was assessed by tumor volume measurements, time to nadir (TTN), time to progression (TTP), and survival. Pharmacokinetics of [89Zr]hu5A10 in nonhuman primates (NHP) were determined using PET. RESULTS: Biodistribution of radiolabeled hu5A10 constructs was comparable in different mouse models. Specific tumor uptake increased over time and correlated with PSA expression. Treatment with [90Y]/[225Ac]hu5A10 effectively reduced tumor burden and prolonged survival (P ≤ 0.0054). Effects of [90Y]hu5A10 were more immediate than [225Ac]hu5A10 (TTN, P < 0.0001) but less sustained (TTP, P < 0.0001). Complete responses were observed in 7 of 18 [225Ac]hu5A10 and 1 of 9 mice [90Y]hu5A10. Pharmacokinetics of [89Zr]hu5A10 were consistent between NHPs and comparable with those in mice. [89Zr]hu5A10-PET visualized the NHP-prostate over the 2-week observation period. CONCLUSIONS: We present a complete preclinical evaluation of radiolabeled hu5A10 in mouse prostate cancer models and NHPs, and establish hu5A10 as a new theranostic agent that allows highly specific and effective downstream targeting of AR in PSA-expressing tissue. Our data support the clinical translation of radiolabeled hu5A10 for treating prostate cancer.

Immune-Checkpoint Blockade Enhances 225Ac-PSMA617 Efficacy in a Mouse Model of Prostate Cancer.

Prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (RNT) may increase tumor immunogenicity. We aimed at exploiting this effect by combining RNT with immunotherapy in a mouse model of prostate cancer (PC). Methods: C57BL/6-mice bearing syngeneic RM1-PGLS tumors were treated with 225Ac-PSMA617, an anti-PD-1 antibody, or both. Therapeutic efficacy was assessed by tumor volume measurements (CT), time to progression (TTP), and survival. Results: PSMA RNT or anti-PD-1 alone tended to prolong TTP (isotype control, 25 d; anti-PD-1, 33.5 d [P = 0.0153]; RNT, 30 d [P = 0.1038]) and survival (control, 28 d; anti-PD-1, 37 d [P = 0.0098]; RNT, 32 d [P = 0.1018]). Combining PSMA RNT and anti-PD-1 significantly improved disease control compared with either monotherapy. TTP was extended to 47.5 d (P ≤ 0.0199 vs. monotherapies), and survival to 51.5 d (P ≤ 0.0251 vs. monotherapies). Conclusion: PSMA RNT and PD-1 blockade synergistically improve therapeutic outcomes in our PC model, supporting the evaluation of RNT and immunotherapy combinations for PC patients.

Mechanisms of Resistance to Prostate-Specific Membrane Antigen-Targeted Radioligand Therapy in a Mouse Model of Prostate Cancer.

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is effective against prostate cancer (PCa), but all patients relapse eventually. Poor understanding of the underlying resistance mechanisms represents a key barrier to development of more effective RLT. We investigate the proteome and phosphoproteome in a mouse model of PCa to identify signaling adaptations triggered by PSMA RLT. Methods: Therapeutic efficacy of PSMA RLT was assessed by tumor volume measurements, time to progression, and survival in C4-2 or C4-2 TP53-/- tumor-bearing nonobese diabetic scid γ-mice. Two days after RLT, the proteome and phosphoproteome were analyzed by mass spectrometry. Results: PSMA RLT significantly improved disease control in a dose-dependent manner. Proteome and phosphoproteome datasets revealed activation of genotoxic stress response pathways, including deregulation of DNA damage/replication stress response, TP53, androgen receptor, phosphatidylinositol-3-kinase/AKT, and MYC signaling. C4-2 TP53-/- tumors were less sensitive to PSMA RLT than were parental counterparts, supporting a role for TP53 in mediating RLT responsiveness. Conclusion: We identified signaling alterations that may mediate resistance to PSMA RLT in a PCa mouse model. Our data enable the development of rational synergistic RLT-combination therapies to improve outcomes for PCa patients.

Genetic signature of prostate cancer mouse models resistant to optimized hK2 targeted α-particle therapy.

Hu11B6 is a monoclonal antibody that internalizes in cells expressing androgen receptor (AR)-regulated prostate-specific enzyme human kallikrein-related peptidase 2 (hK2; KLK2). In multiple rodent models, Actinium-225-labeled hu11B6-IgG1 ([225Ac]hu11B6-IgG1) has shown promising treatment efficacy. In the present study, we investigated options to enhance and optimize [225Ac]hu11B6 treatment. First, we evaluated the possibility of exploiting IgG3, the IgG subclass with superior activation of complement and ability to mediate FC-γ-receptor binding, for immunotherapeutically enhanced hK2 targeted α-radioimmunotherapy. Second, we compared the therapeutic efficacy of a single high activity vs. fractionated activity. Finally, we used RNA sequencing to analyze the genomic signatures of prostate cancer that progressed after targeted α-therapy. [225Ac]hu11B6-IgG3 was a functionally enhanced alternative to [225Ac]hu11B6-IgG1 but offered no improvement of therapeutic efficacy. Progression-free survival was slightly increased with a single high activity compared to fractionated activity. Tumor-free animals succumbing after treatment revealed no evidence of treatment-associated toxicity. In addition to up-regulation of canonical aggressive prostate cancer genes, such as MMP7, ETV1, NTS, and SCHLAP1, we also noted a significant decrease in both KLK3 (prostate-specific antigen ) and FOLH1 (prostate-specific membrane antigen) but not in AR and KLK2, demonstrating efficacy of sequential [225Ac]hu11B6 in a mouse model.

Targeted alpha therapy in a systemic mouse model of prostate cancer - a feasibility study.

225Ac-PSMA-617 targeted-therapy has demonstrated efficacy in 75-85% of patients; however, responses are not durable. We aimed to establish translatable mouse models of disseminated prostate cancer (PCa) to evaluate effectiveness of 225Ac-PSMA-617 at various disease stages. Methods: C4-2, C4-2B, or 22Rv1 cells were injected into the left ventricle of male NSG mice. Disease progression was monitored using bioluminescence imaging (BLI). For treatment, mice were injected with 40 kBq 225Ac-PSMA-617 at one (early treatment cohort) or three weeks (late treatment cohort) post-inoculation. Treatment efficacy was monitored by BLI of whole-body tumor burden. Mice were sacrificed based on body conditioning score. Results: C4-2 cells yielded metastases in liver, lungs, spleen, stomach, bones, and brain - achieving a clinically relevant model of widespread metastatic disease. The disease burden in the early treatment cohort was stable over 27 weeks in 5/9 mice and progressive in 4/9 mice. These mice were sacrificed due to brain metastases. Median survival of the late treatment cohort was superior to controls (13 vs. 7 weeks; p<0.0001) but inferior to that in the early treatment cohort (13 vs. 27 weeks; p<0.001). Late cohort mice succumbed to extensive liver involvement. The 22Rv1 and C4-2B systemic models were not used for treatment due to high kidney metastatic burden or low take rate, respectively. Conclusion: C4-2 cells reproduced metastatic cancer spread most relevantly. Early treatment with 225Ac-PSMA-617 prevented liver metastases and led to significant survival benefit. Late treatment improved survival without reducing tumor burden in the liver, the main site of metastasis. The current findings suggest that early 225Ac-PSMA-617 intervention is more efficacious in the setting of widespread metastatic PCa.

Preclinical evaluation of PSMA expression in response to androgen receptor blockade for theranostics in prostate cancer.

BACKGROUND: Prostate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) is a promising yet not curative approach in castration-resistant (CR) prostate cancer (PC). Rational combination therapies may improve treatment efficacy. Here, we explored the effect of androgen receptor blockade (ARB) on PSMA expression visualized by PET and its potential additive effect when combined with 177Lu-PSMA RLT in a mouse model of prostate cancer. METHODS: Mice bearing human CRPC (C4-2 cells) xenografts were treated with 10 mg/kg enzalutamide (ENZ), with 50 mg/kg bicalutamide (BIC), or vehicle (control) for 21 days. PSMA expression was evaluated by 68Ga-PSMA11 PET/CT and quantified by flow cytometry of tumor fine needle aspirations before treatment and on days 23, 29, 34, and 39 post-therapy induction. For the RLT combination approach, mice bearing C4-2 tumors were treated with 10 mg/kg ENZ or vehicle for 21 days before receiving either 15 MBq (84 GBq/µmol) 177Lu-PSMA617 or vehicle. DNA damage was assessed as phospho-γH2A.X foci in tumor biopsies. Reduction of tumor volume on CT and survival were used as study endpoints. RESULTS: Tumor growth was delayed by ARB while 68Ga-PSMA11 uptake increased up to 2.3-fold over time when compared to controls. ABR-induced upregulation of PSMA expression was confirmed by flow cytometry. Phospho-γH2A.X levels increased 1.8- and 3.4-fold at 48 h in response to single treatment ENZ or RLT and ENZ+RLT, respectively. Despite significantly greater DNA damage and persistent increase of PSMA expression at the time of RLT, no additional tumor growth retardation was observed in the ENZ+RLT group (vs. RLT only, p = 0.372 at day 81). Median survival did not improve significantly when ENZ was combined with RLT. CONCLUSION: ARB-mediated increases in PSMA expression in PC xenografts were evident by 68Ga-PSMA11 PET imaging and flow cytometry. 177Lu-PSMA617 effectively decreased C4-2 tumor size. However, while pre-treatment with ARB increased DNA damage significantly, it did not result in synergistic effects when combined with RLT.

Detection Threshold and Reproducibility of 68Ga-PSMA11 PET/CT in a Mouse Model of Prostate Cancer.

To improve prostate-specific membrane antigen (PSMA)-targeted theranostic approaches, robust murine models of prostate cancer are needed. However, important characteristics of preclinical PSMA imaging-that is, the reproducibility of the imaging signal and the relationship between quantitative cell surface PSMA expression and lesion detectability with small-animal PET/CT-have not been defined yet. Methods: Murine prostate cancer RM1 sublines (ras myc transformed cells of C57BL/6 prostate origin) expressing varying levels of human PSMA were injected into the shoulder of C57BL/6 mice on day 0. 68Ga-PSMA11 PET/CT was performed on days 7 and 8 and interpreted by 2 masked readers to determine interday and interreader reproducibility. PSMA expression was quantified on days 7 and 8 by flow cytometry of fine-needle aspiration tumor biopsy samples. Cell surface PSMA expression was correlated with PET signal. The threshold for PET positivity was based on the clinical Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria. Results: The maximum and average percentages of injected 68Ga-PSMA11 activity per gram of tissue (%IA/g) correlated nearly perfectly as determined by 2 independent readers and on 2 separate days (intraclass correlation coefficient, 1.00/0.89 and 0.95/0.88, respectively). The number of PSMA molecules per cell increased from the RM1-yellow fluorescent protein subline (PSMA-; 2,000/cell) to the RM1-low subline (PSMA+; 17,000/cell), the RM1-medium subline (PSMA++; 22,000/cell), and the RM1-PGLS subline (PSMA-positive, green fluorescent protein-positive, and luciferase-positive; PSMA+++; 45,000/cell). Expression levels correlated with the visual positivity rate on 68Ga-PSMA11 PET and with the PSMA PET %IA/g. The PSMA threshold for PET positivity was approximately 20,000 per cell. Signal correlation was close at lower PSMA levels (RM1-low to RM1-medium; 10-23 %IA/g) but was lost at higher PSMA levels (RM1-medium to RM1-PGLS; 23-27 %IA/g). Conclusion: The in vivo relationship between 68Ga-PSMA11 PET/CT and PSMA expression level in a murine model of prostate cancer was robust for lower cell surface PSMA expression levels (≤22,000/cell). Thus, preclinical 68Ga-PSMA11 PET/CT can be used as an imaging biomarker to test PSMA-targeted interventions in murine models.

Prognostic value of [18F]FDG-PET/CT in multiple myeloma patients before and after allogeneic hematopoietic cell transplantation.

PURPOSE: Despite improved treatment options, multiple myeloma (MM) remains an incurable disease. The aim of this study was to investigate the prognostic value of positron emission tomography/computed tomography (PET/CT) using 18F-2'-deoxy-2'-fluorodeoxyglucose ([18F]FDG) in MM patients shortly before and ~100 days after allogeneic hematopoietic cell transplantation (allo-HCT). METHODS: In this retrospective analysis, we evaluated [18F]FDG-PET/CT-scans of 45 heavily pre-treated MM patients before and 27 patients after scheduled allo-HCT. All scans were qualitatively and semi-quantitatively assessed for the presence of active disease. Serological response was recorded according to International Myeloma Working Group (IMWG) criteria. Progression-free (PFS) and overall survival (OS) were correlated with different PET/CT-derived parameters, such as presence, number and maximum standardized uptake value (SUVmax) of focal myeloma lesions. The impact of extramedullary disease on patient outcome was also assessed. RESULTS: PET/CT negativity -prior to or following allo-HCT- was a favorable prognostic factor for progression-free and overall survival (both, PFS and OS: pre-HSCT p < 0.001, post-HCT p < 0.005). High FDG-uptake (SUVmax > 6.5) revealed a significantly shortened survival compared to patients with a lower SUVmax (<6.5) (OS, 5.0 ± 1.1 m vs. not reached - longest 122.0 m; p < 0.001). Moreover, our data prove that a higher number (>3) of focal lesions (pre-HCT: both PFS and OS: p < 0.001; post-HCT PFS: p < 0.001, OS: p = 0.139) as well as the presence of extramedullary disease serve as adverse prognostic factors prior to and after allo-HCT. At response assessment after allo-HCT, [18F]FDG-PET/CT had a complementary value in prognostication in addition to IMWG criteria alone. CONCLUSION: [18F]FDG-PET/CT before and shortly after allogeneic HCT is a powerful predictor for progression-free and overall survival in MM patients.