Abstract
Adjusting the molecular size, the valency and the pharmacokinetics of drug conjugates are as many leverages to improve their therapeutic window, notably by affecting tumor penetration, renal clearance, and short systemic exposure. In that regard, small tumor-targeting ligands are gaining attention. In this study, we demonstrate the benefits of the small Nanofitin alternative scaffolds (7 kDa) as selective tumor-targeting modules for the generation of drug conjugates, focusing on Nanofitins B10 and D8 directed against the EGFR. Owing to their small size and monovalent format, the two Nanofitins displayed a fast and deep tumor penetration in EGFR-positive A431 xenografts in BALB/c nude mice after intravenous administration, yielding to a targeting of respectively 67.9% ± 14.1 and 98.9% ± 0.7 of the tumor cells as demonstrated by IHC. Conjugation with the monomethyl auristatin E toxin provided homogeneous Nanofitin-drug conjugates, with an overall yield of ≥97%, for in vivo assessment in a curative xenograft model using bioluminescent, EGFR-positive, A431 cells in BALB/c nude mice. Internalization was found critical for efficient release of the toxin. Hence, the intravenous administration of the D8-based construct showed significant antitumor effect in vivo as determined by monitoring tumor volumes and bioluminescence levels over 2 months.