A novel dimeric FAP-targeting small molecule-radio conjugate with high and prolonged tumour uptake

Abstract

Imaging procedures based on small molecule-radio conjugates (SMRCs) targeting fibroblast activation protein (FAP) have recently emerged as a powerful tool for the diagnosis of a wide variety of tumours. However, the therapeutic potential of radiolabeled FAP-targeting agents is limited by their short residence time in neoplastic lesions. In this work, we present the development and in vivo characterization of BiOncoFAP, a new dimeric FAP-binding motif with extended tumour residence time and favorable tumour-to-organ ratio. Methods: The binding properties of BiOncoFAP and its monovalent OncoFAP analogue were assayed against recombinant hFAP. Preclinical experiments with [177Lu]Lu-OncoFAP-DOTAGA (177Lu-OncoFAP) and [177Lu]Lu-BiOncoFAP-DOTAGA (177Lu-BiOncoFAP) were performed in mice bearing FAP-positive HT-1080 tumours. OncoFAP and BiOncoFAP displayed comparable sub-nanomolar dissociation constants towards hFAP in solution, but the bivalent BiOncoFAP bound more avidly to the target immobilized on solid supports. In a comparative biodistribution study, 177Lu-BiOncoFAP exhibited a more stable and prolonged tumour uptake than 177Lu-OncoFAP (~20% ID/g vs ~4% ID/g, at 24h p.i., respectively). Notably, 177Lu-BiOncoFAP showed favorable tumour-to-organ ratios with low kidney uptake. Both 177Lu-OncoFAP and 177Lu-BiOncoFAP displayed potent anti-tumour efficacy when administered at therapeutic doses in tumour bearing mice. 177Lu-BiOncoFAP is a promising candidate for radioligand therapy of cancer, with favorable in vivo tumour-to-organ ratio, long tumour residence time and potent anti-cancer efficacy.

A mass spectrometry-based method for the determination ofin vivobiodistribution of tumor targeting small molecule-metal conjugates

“…tumor uptake as compared to its monovalent counterpart (Figures 3, TableS3). Uptake values in tumor and healthy organs (in %ID/g) measured by the LC-MS methodology were comparable to values obtained with radioactivity-based quantification11 . No significant differences were observed between the two analytical techniques (p>0.05 multiple t test,Table S4) (Figures 3).Orthogonal validation further confirms the accuracy of the newly developed MS quantification method, thereby opening new opportunities for non-radioactive LC-MS analysis of SMMCs.…”

“…Comparison of MS and γ Counter 11 biodistribution data for A) Lu-OncoFAP-DOTAGA and B) Lu-BiOncoFAP-DOTAGA. Mice bearing HT-1080.hFAP tumors were sacrificed 1 h after intravenous administration (250 nmol/kg).…”

“…OncoFAP and BiOncoFAP, as well as their metal chelator conjugates and "cold"-labeled derivatives were synthesized through established protocols 6,10,11 .…”

“…This compound represents an ideal candidate for imaging applications. More recently, we developed a dimeric derivative owing two targeting moieties (i.e., BiOncoFAP), showing higher tumor uptake and residence time than OncoFAP in preclinical models of cancer 11 .…”

“…The biodistribution properties of novel tumor targeting SMRCs are of key importance for the success of the diagnosis and therapeutic outcome. Preclinical biodistribution of radiopharmaceuticals in tumor-bearing animals is typically evaluated by direct measurement of the radioactivity present in each organ after sacrifice of experimental animals 10,11 . To date, these radioactivity-based analyses are still crucial to evaluate the tumor accumulation and to obtain spatial biodistribution data of the compounds in the animal/human body.…”