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Recombinant human erythropoietin (rhuEpo) is used clinically to treat anaemia. However, rhuEpo-treated cancer patients show decreased survival rates and erythropoietin receptor (EpoR) expression has been found in patient tumour tissue. Thus, rhuEpo application might promote EpoR(+) tumour progression. We therefore developed the positron emission tomography (PET)-probe (68)Ga-DOTA-rhuEpo and evaluated its performance in EpoR(+) A549 non-small-cell lung cancer (NSCLC) xenografts.(68)Ga-DOTA-rhuEpo was generated by coupling DOTA-hydrazide to carbohydrate side-chains of rhuEpo. Biodistribution was determined in tumour-bearing mice 0.5, 3, 6, and 9 h after probe injection. Competition experiments were performed by co-injecting (68)Ga-DOTA-rhuEpo and rhuEpo in five-fold excess. Probe specificity was further evaluated histologically using Epo-Cy5.5 stainings.The blood half-life of (68)Ga-DOTA-rhuEpo was 2.6 h and the unbound fraction was cleared by the liver and kidney. After 6 h, the highest tumour to muscle ratio was reached. The highest (68)Ga-DOTA-rhuEpo accumulation was found in liver (10.06 ± 6.26%ID/ml), followed by bone marrow (1.87 ± 0.53%ID/ml), kidney (1.58 ± 0.39%ID/ml), and tumour (0.99 ± 0.16%ID/ml). EpoR presence in these organs was histologically confirmed. Competition experiments showed significantly (p 0.05) lower PET-signals in tumour and bone marrow at 3 and 6 h.(68)Ga-DOTA-rhuEpo shows favourable pharmacokinetic properties and detects EpoR specifically. Therefore, it might become a valuable radiotracer to monitor EpoR status in tumours and support decision-making in anaemia therapy.• PET-probe (68) Ga-DOTA-rhuEpo was administered to assess the EpoR status in vivo • (68) Ga-DOTA-rhuEpo binds specifically to EpoR positive organs in vivo • Tumour EpoR status determination might enable decision-making in anaemia therapy with rhuEpo.

Molecular imaging of apoptosis is frequently discussed for monitoring cancer therapies. Here, we compare the low molecular weight phosphatidylserine-targeting ligand zinc2+-dipicolylamine (Zn2+-DPA) with the established but reasonably larger protein annexin V. Molecular apoptosis imaging with the fluorescently labelled probes annexin V (750 nm, 36 kDa) and Zn2+-DPA (794 nm, 1.84 kDa) was performed in tumour-bearing mice (A431). Three animal groups were investigated: untreated controls and treated tumours after 1 or 4 days of anti-angiogenic therapy (SU11248). Additionally, μPET with 18 F-FDG was performed. Imaging data were displayed as tumour-to-muscle ratio (TMR) and validated by quantitative immunohistochemistry. Compared with untreated control tumours, TUNEL staining indicated significant apoptosis after 1 day (P

Tumour xenografts of well-discernible sizes can be examined well by molecular ultrasound. Here, we investigated whether very early breast carcinomas express sufficient levels of VEGFR2 for reliable molecular ultrasound imaging with targeted microbubbles.MCF-7 breast cancer xenografts were orthotopically implanted in nude mice (n = 26). Tumours measuring from 4 mm(3) (2 mm diameter) up to 65 mm(3) (5 mm diameter) were examined with automated 3D molecular ultrasound using clinically translatable VEGFR2-targeted microbubbles (BR55). Additionally, the relative tumour blood volume was assessed with non-targeted microbubbles (BR38). In vivo ultrasound data were validated by quantitative immunohistochemistry.Very small lesions 2 mm in diameter showed the highest binding of VEGFR2-specific microbubbles. In larger tumours significantly less BR55 accumulated (p = 0.023). Nonetheless, binding of VEGFR2-targeted microbubbles was still high enough for imaging. The relative blood volume was comparable at all tumour sizes. Both findings were confirmed by immunohistochemistry. Additionally, a significantly enhanced number of large and mature vessels were detected with increasing tumour size (p 0.01), explaining the decrease in VEGFR2 expression during tumour growth.3D molecular ultrasound using BR55 is very well suited to depicting the angiogenic activity in very small breast lesions, suggesting its potential for detecting and characterising these lesions.

To characterise clinically translatable long-circulating (BR38) and VEGFR2-targeted (BR55) microbubbles (MB) and to assess their ability to discriminate breast cancer models with different aggressiveness.The circulation characteristics of BR38 and BR55 were investigated in healthy mice. The relative blood volume (rBV) of MDA-MB-231 (n = 5) or MCF-7 (n = 6) tumours was determined using BR38. In the same tumours in-vivo binding specificity of BR55 was tested and VEGFR2 expression assessed. Data validation included quantitative immunohistological analysis.BR38 had a longer blood half-life than BR55 (600 s vs. 218 s). BR38-enhanced ultrasound showed greater vascularisation in MDA-MB-231 tumours (p = 0.022), which was in line with immunohistology (p = 0.033). In-vivo competitive binding experiments proved the specificity of BR55 to VEGFR2 (p = 0.027). Binding of BR55 was significantly higher in MDA-MB-231 than in MCF-7 tumours (p = 0.049), which corresponded with the VEGFR2 levels found histologically (p = 0.015). However, differences became smaller when normalising the levels of BR55 to the rBV.BR38 and BR55 are well suited to characterising and distinguishing breast cancers with different angiogenesis and aggressiveness. Long-circulating BR38 MB allow extensive 3-dimensional examinations of larger or several organs. BR55 accumulation faithfully reflects the VEGFR2 status in tumours and depicts even small differences in angiogenesis.