Nanobody-shell functionalized thermosensitive core-crosslinked polymeric micelles for active drug targeting.

The aim of this study was to develop poly(ethylene glycol)-b-poly[N-(2-hydroxypropyl) methacrylamide-lactate] (mPEG-b-p(HPMAm-Lac(n))) core-crosslinked thermosensitive biodegradable polymeric micelles suitable for active tumor targeting, by coupling the anti-EGFR (epidermal growth factor receptor) EGa1 nanobody to their surface. To this end, PEG was functionalized with N-succinimidyl 3-(2-pyridyldithio)-propionate (SPDP) to yield a PDP-PEG-b-p(HPMAm-Lac(n)) block copolymer. Micelles composed of 80% mPEG-b-p(HPMAm-Lac(n)) and 20% PDP-PEG-b-p(HPMAm-Lac(n)) were prepared and lysozyme (as a model protein) was modified with N-succinimidyl-S-acetylthioacetate, deprotected with hydroxylamine hydrochloride and subsequently coupled to the micellar surface. The micellar conjugates were characterized using SDS-PAGE and gel permeation chromatography (GPC). Using the knowledge obtained with lysozyme conjugation, the EGa1 nanobody was coupled to mPEG/PDP-PEG micelles and the conjugation was successful as demonstrated by western blot and dot blot analysis. Rhodamine labeled EGa1-micelles showed substantially higher binding as well as uptake by EGFR over-expressing cancer cells (A431 and UM-SCC-14C) than untargeted rhodamine labeled micelles. Interestingly, no binding of the nanobody micelles was observed to EGFR negative cells (3T3) as well as to14C cells in the presence of an excess of free nanobody. This demonstrates that the binding of the nanobody micelles is indeed by interaction with the EGF receptor. In conclusion, EGa1 decorated (mPEG/PDP-PEG)-b-(pHPMAm-Lac(n)) polymeric micelles are highly promising systems for active drug targeting.