High precision in vivo PET/CT imaging of solid tumors improves diagnostic credibility and clinical outcome of patients. An epitope of the oligomerization domain of Hsp70 is exclusively exposed on the membrane of a large variety of tumor types, but not on normal cells, and thus provides a universal tumor-specific target. Here we developed a novel PET tracer TPP-PEG24-DFO[89Zr] based on the tumor cell–penetrating peptide probe TPP, which specifically recognizes membrane Hsp70 (mHsp70) on tumor cells. The implemented PEG24 moiety supported tracer stability and improved biodistribution characteristics in vivo. The Kd of the tracer ranged in the low nanomolar range (18.9 ± 11.3 nmol/L). Fluorescein isothiocyanate (FITC)-labeled derivatives TPP-[FITC] and TPP-PEG24-[FITC] revealed comparable and specific binding to mHsp70-positive 4T1, 4T1+, a derivative of the 4T1 cell line sorted for high Hsp70 expression, and CT26 tumor cells, but not to mHsp70-negative normal fibroblasts. The rapid internalization kinetics of mHsp70 into the cytosol and the favorable biodistribution of the peptide-based tracer TPP-PEG24-DFO[89Zr] in vivo enabled a tumor-specific accumulation with a high tumor-to-background contrast and renal body clearance. The tumor-specific enrichment of the tracer in 4T1+ (6.2 ± 1.1%ID/g), 4T1 (4.3 ± 0.7%ID/g), and CT26 (2.6 ± 0.6%ID/g) mouse tumors with very high, high, and intermediate mHsp70 densities, respectively, reflected mHsp70 expression profiles of the different tumor types, whereas benign mHsp70-negative fibroblastic hyperplasia showed no tracer accumulation (0.2 ± 0.03%ID/g). The ability of our chemically optimized peptide-based tracer TPP-PEG24-DFO[89Zr] to detect mHsp70 in vivo suggests its broad applicability in targeting and imaging with high specificity for any tumor type that exhibits surface expression of Hsp70. Significance: A novel peptide-based PET tracer against the oligomerization domain of Hsp70 has potential for universal tumor-specific imaging in vivo across many tumor type. Cancer Res; 78(21); 6268–81. ©2018 AACR.

Introduction: Radiohybrid prostate-specific membrane antigen (rhPSMA)-ligands allow for labelling with ¹⁸F and radiometals for endoradiotherapy. rhPSMA-7.3 is designated as lead compound with promising preclinical data for ¹⁷⁷Lu-rhPSMA-7.3 indicating higher tumor uptake compared with ¹⁷⁷Lu-PSMA-I&T. In this retrospective analysis we compared pre-therapeutic clinical dosimetry of both PSMA-ligands. Methods: Six mCRPC patients underwent both ¹⁷⁷Lu-rhPSMA-7.3 and ¹⁷⁷Lu-PSMA-I&T pre-therapeutic dosimetry. Whole-body scintigraphy was performed at 1h, 4h, 24h, 48h and 7d post injection. Regions of interest (ROI) covering the whole body, organs, bone marrow and tumor lesions per patient were drawn. Absorbed doses for individual patients and pre-therapeutic applications were calculated using OLINDA/EXM. To facilitate comparison of both ligands we introduced the therapeutic index (TI) defined as ratio of mean pre-therapeutic doses to tumor lesions over relevant organs-at-risk. Results: Mean whole-body pre-therapeutic effective doses were 0.12±0.07 vs. 0.05±0.03 Sv/GBq and mean absorbed organ doses were e.g. 1.65±0.28 vs. 0.73±0.18 Gy/GBq for the kidneys; 0.19±0.09 vs. 0.07±0.03 Gy/GBq for the liver and 2.35±0.78 vs. 0.80±0.41 Gy/GBq for the parotid, for the bone marrow 0.67±0.62 vs. 0.30±0.27 Gy/GBq for ¹⁷⁷Lu-rhPSMA-7.3 vs. ¹⁷⁷Lu-PSMA-I&T, respectively. Tumor lesions received a mean absorbed doses of 6.44±6.44 vs. 2.64±2.24 Gy/GBq for ¹⁷⁷Lu-rhPSMA-7.3 vs. ¹⁷⁷Lu-PSMA-I&T, respectively. The mean TI(kidney) and TI(bone_marrow) were 3.7±2.2 vs. 3.6±2.2 and 15.2±10.2 vs. 15.1±10.2, for ¹⁷⁷Lu-rhPSMA-7.3 vs. ¹⁷⁷Lu-PSMA-I&T, respectively. Conclusion: Pre-therapeutic clinical dosimetry confirmed preclinical results with 2-3 times higher mean absorbed doses for tumors of ¹⁷⁷Lu-rhPSMA-7.3 compared to ¹⁷⁷Lu-PSMA-I&T. Absorbed doses to normal organs also tended to be higher for ¹⁷⁷Lu-rhPSMA-7.3 resulting overall in a similar average TI for both radiopharmaceuticals with considerable inter-patient variability. ¹⁷⁷Lu-rhPSMA-7.3 holds promise for similar therapeutic efficacy as ¹⁷⁷Lu-PSMA-I&T at lower amounts of injected activity simplifying radiation safety measurements (especially for large patient numbers and/or dose escalation regimes).

A number of different technologies have been developed to monitor in vivo the distribution of gene-modified T cells used in immunotherapy. Nevertheless, in-depth characterization of novel approaches with respect to sensitivity and clinical applicability are so far missing. We have previously described a novel method to track engineered human T cells in tumors using ⁸⁹Zr-Df-aTCRmu-F(ab')₂ targeting the murinized part of the TCR beta domain (TCRmu) of a transgenic TCR. Here, we performed an in-depth in vitro characterization of the tracer in terms of antigen affinity, immunoreactivity, influence on T-cell functionality and stability in vitro and in vivo. Of particular interest, we have developed diverse experimental settings to quantify TCR-transgenic T cells in vivo. Local application of ⁸⁹Zr-Df-aTCRmu-F(ab')₂-labeled T cells in a spot-assay revealed signal detection down to approximately 1.8x10⁴ cells. In a more clinically relevant model, NSG mice were intravenously injected with different numbers of transgenic T cells, followed by injection of the ⁸⁹Zr-Df-aTCRmu-F(ab')₂ tracer, PET/CT imaging and subsequent ex vivo T-cell quantification in the tumor. Using this setting, we defined a comparable detection limit of 1.0x10⁴ T cells. PET signals correlated well to total numbers of transgenic T cells detected ex vivo independently of the engraftment rates observed in different individual experiments. Thus, these findings confirm the high sensitivity of our novel PET/CT T-cell tracking method and provide critical information about the quantity of transgenic T cells in the tumor environment suggesting our technology being highly suitable for further clinical translation.

Rationale: The high expression of Galectin-3 (Gal3) in macrophages of atherosclerotic plaques suggests its participation in atherosclerosis pathogenesis, and raises the possibility to use it as a target to image disease severity in vivo. Here, we explored the feasibility of tracking atherosclerosis by targeting Gal3 expression in plaques of apolipoprotein E knockout (ApoE-KO) mice via PET imaging.

Galectins (S-type lectins) are an evolutionarily-conserved family of lectin molecules, which can be expressed intracellularly and in the extracellular matrix, as well. Galectins bind β-galactose-containing glycoconjugates and are functionally active in converting glycan-related information into cell biological programs. Altered glycosylation notably occurring in cancer cells and expression of specific galectins provide, indeed, a fashionable mechanism of molecular interactions able to regulate several tumor relevant functions, among which are cell adhesion and migration, cell differentiation, gene transcription and RNA splicing, cell cycle and apoptosis. Furthermore, several galectin molecules also play a role in regulating the immune response. These functions are strongly dependent on the cell context, in which specific galectins and related glyco-ligands are expressed. Thyroid cancer likely represents the paradigmatic tumor model in which experimental studies on galectins’ glycobiology, in particular on galectin-3 expression and function, contributed greatly to the improvement of cancer diagnosis. The discovery of a restricted expression of galectin-3 in well-differentiated thyroid carcinomas (WDTC), compared to normal and benign thyroid conditions, contributed also to promoting preclinical studies aimed at exploring new strategies for imaging thyroid cancer in vivo based on galectin-3 immuno-targeting. Results derived from these recent experimental studies promise a further improvement of both thyroid cancer diagnosis and therapy in the near future. In this review, the biological role of galectin-3 expression in thyroid cancer, the validation and translation to a clinical setting of a galectin-3 test method for the preoperative characterization of thyroid nodules and a galectin-3-based immuno-positron emission tomography (immuno-PET) imaging of thyroid cancer in vivo are presented and discussed.

The high prevalence of thyroid nodules in the adult population and the relatively low incidence of thyroid cancer make the preoperative identification of malignant lesions challenging. The β-galactoside–binding protein galectin-3 is widely expressed in well-differentiated thyroid carcinomas, but not in normal thyrocytes and benign thyroid nodules. This molecule offers a candidate biomarker to improve thyroid cancer diagnosis. Here we report the development of an immunoPET approach for noninvasive imaging of thyroid cancer. The method employs a ⁸⁹Zr-labeled mAb to galectin-3, which shows high specificity and binding affinity in vitro. Reliable and specific immunoPET imaging was obtained of thyroid cancer in vivo in murine xenograft models of human thyroid cancer. Our findings provide a method to improve the clinical management of patients with thyroid nodules while reducing unnecessary surgery and social costs. Cancer Res; 76(12); 3583–92. ©2016 AACR.