In Vivo Molecular Imaging of the Efficacy of Aminopeptidase N (APN/CD13) Receptor Inhibitor Treatment on Experimental Tumors Using Ga-68-NODAGA-c(NGR) Peptide

Abstract

<italic>Introduction</italic>. The aminopeptidase N (APN/CD13) receptor plays an important role in the neoangiogenic process and metastatic tumor cell invasion. Clinical and preclinical studies reported that bestatin and actinonin are cytotoxic to APN/CD13-positive tumors and metastases due to their APN/CD13-specific inhibitor properties. Our previous studies have already shown that 68Ga-labeled NGR peptides bind specifically to APN/CD13 expressing tumor cells. The APN/CD13 specificity of 68Ga-NGR radiopharmaceuticals enables the following of the efficacy of antiangiogenic therapy with APN/CD13-specific inhibitors using positron emission tomography (PET). The aim of this <italic>in vivo</italic> study was to assess the antitumor effect of bestatin and actinonin treatment in subcutaneous transplanted HT1080 and B16-F10 tumor-bearing animal models using 68Ga-NODAGA-c(NGR). <italic>Materials and Methods</italic>. Three days after the inoculation of HT1080 and B16-F10 cells, mice were treated with intraperitoneal injection of bestatin (15 mg/kg) or actinonin (5 mg/kg) for 7 days. On the 5th and 10th day, <italic>in vivo</italic> PET scans and <italic>ex vivo</italic> biodistribution studies were performed 90 min after intravenous injection of <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mn>5.5</mml:mn><mml:mo>±</mml:mo><mml:mn>0.2</mml:mn><mml:mtext> </mml:mtext><mml:mtext>MBq</mml:mtext></mml:math></inline-formula>68Ga-NODAGA-c(NGR). <italic>Results</italic>. Control-untreated HT1080 and B16-F10 tumors were clearly visualized by the APN/CD13-specific 68Ga-NODAGA-c(NGR) radiopharmaceutical. The western blot analysis also confirmed the strong APN/CD13 positivity in the investigated tumors. We found significantly (<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>p</mml:mi><mml:mo>≤</mml:mo><mml:mn>0.05</mml:mn></mml:math></inline-formula>) lower radiopharmaceutical uptake after bestatin treatment and higher radiotracer accumulation in the actinonin-treated HT1080 tumors. In contrast, significantly lower (<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mi>p</mml:mi><mml:mo>≤</mml:mo><mml:mn>0.01</mml:mn></mml:math></inline-formula>) 68Ga-NODAGA-c(NGR) accumulation was observed in both bestatin- and actinonin-treated B16-F10 melanoma tumors compared to the untreated-control tumors. Bestatin inhibited tumor growth and 68Ga-NODAGA-c(NGR) uptake in both tumor models. <italic>Conclusion</italic>. The bestatin treatment is suitable for suppressing the neoangiogenic process and APN/CD13 expression of experimental HT1080 and B16-F10 tumors; furthermore, 68Ga-NODAGA-c(NGR) is an applicable radiotracer for the <italic>in vivo</italic> monitoring of the efficacy of the APN/CD13 inhibition-based anticancer therapies.