[18F]-AZAFOL AS POSITRON EMISSION TOMOGRAPHY (PET) TRACER in FR Positive Cancer Imaging

Human research study using a radiopharmaceutical product to reveal folate receptor (FR) expression in tumors in patients. It is known that the FR is overexpressed on a variety of tumor types. FR-positive tumors can be treated with investigational drugs specifically targeting the FR. Although the FR-expression status may be determined by immunohistochemical staining of tumor biopsies there is a need for a non-invasive method to determine the presence of the FR on primary tumors and metastases in humans. For this purpose a radiopharmaceutical product will be used as a radiotracer. Positron Emission Tomography (PET) is an imaging method which allows assessing the distribution of radiotracers (called PET tracer). With this imaging method it is possible to obtain (semi)quantitative measures of FR-expression on tumors of at least 4-10 mm diameter in patients. Such a folate-based radiotracer would be a very helpful tool to non-invasively discriminate FR-positive (often found in ovarian and NSC-lung cancer) from FR-negative tumors in patients with cancer disease as this would allow selecting FR-positive patients amenable to FR-targeted therapies, e.g. folate-targeted antimitotic substances such as EC145 VintafolideTM (Endocyte Inc.) or anti-FR-antibodies such as FarletuzumabTM (Morphotek Inc). Moreover, \[18F\]-AzaFol PET could be used for tumor staging and monitoring therapy as well as for follow-up investigations of patients with FR-positive tumors. Currently there is a radiopharmaceutical product for research purposes available (99mTc-EC20, EtarfolatideTM, Endocyte Inc.) which can be used for Single Photon Emission Computed Tomography (SPECT) imaging. SPECT, however, has multiple limitations compared to PET, such as inferior spatial resolution, soft tissue attenuation, lack of dynamic acquisition etc. Therefore, a PET-compound for FR imaging has been shown to image FR-positive tumors in experimental animals . Calculations regarding the incidence and mortality of six frequent cancer types in Switzerland indicate that in over 53% of the new cases the FR is expressed (OncoSuisse, Cancer Statistics 2012). Investigators demonstrate impressively why FR-targeting emerged as an attractive strategy for tumor diagnosis and for the development of new targeted therapy strategies . The vitamin folic acid (pteroylglutamic acid) emerged as an almost ideal FR-targeting agent because of the high affine binding to the FR (KD \< 1 nM). Due to the small size and vitamin character of folic acid, it is non-immunogenic and non-toxic. In spite of a large number of folate-based nuclear imaging agents which have been developed in the last two decades only one SPECT radiotracer (99mTc-EC20, EtarfolatideTM) is currently being used in clinical trials in the U.S. for SPECT imaging. For over a decade investigators have been focusing research activities on the development of a 18F-based folate radiotracer for PET imaging (13-16). Recently, a novel folate radiotracer has been developed, 3'-aza-3-\[18F\]fluorofolic acid (herein referred to as \[18F\]-AzaFol), for PET imaging purposes. Compared to SPECT, PET is the more sensitive nuclear imaging method which provides images of an improved resolution and the possibility for accurate quantification of accumulated radioactivity in tumor lesions.