Local Radiation Treatment of HER2-Positive Breast Cancer Using Trastuzumab-Modified Gold Nanoparticles Labeled with 177Lu.

Abstract

To compare the effectiveness of trastuzumab-modified gold nanoparticles (AuNP) labeled with 177Lu (trastuzumab-AuNP-177Lu) targeted to HER2 with non-targeted AuNP-177Lu for killing HER2-overexpressing breast cancer (BC) cells in vitro and inhibiting tumor growth in vivo following intratumoral (i.t.) injection. AuNP (30nm) were modified with polyethylene glycol (PEG) polymers linked to trastuzumab or to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelators to complex 177Lu. The binding and internalization of trastuzumab-AuNP-177Lu in HER2-positive SK-BR-3, BT-474 and MDA-MB-361 human BC cells were studied. Clonogenic survival and DNA double-strand breaks (DSBs) were measured after exposure of SK-BR-3 or MDA-MB-361 cells to trastuzumab-AuNP-177Lu or AuNP-177Lu. NOD/SCID mice with s.c. MDA-MB-361 tumor xenografts were treated by i.t. injection of 3MBq (0.15mg) of trastuzumab-AuNP-177Lu, AuNP-177Lu or normal saline. Tumor growth was measured over 16days and normal tissue toxicity evaluated. Trastuzumab-AuNP-177Lu was bound and internalized by HER2 positive BC cells (KD = 7.6 ± 2.0 nM). Trastuzumab-AuNP-177Lu was 42.9 and 2.6-fold more effective than AuNP-177Lu at decreasing the clonogenic survival of SK-BR-3 (1.3 × 106 HER2/cell) and MDA-MB-361 (5.1 × 105 HER2/cell) cells, respectively, exposed overnight to these agents (1.5 nM; 20MBq/mg Au). Under the same treatment conditions, 10-fold and 2.8-fold more DNA DSBs were observed in SK-BR-3 and MDA-MB-361 cells, respectively, exposed to trastuzumab-AuNP-177Lu than AuNP-177Lu. Trastuzumab-AuNP-177Lu was 1.8-fold more effective at inhibiting tumor growth than AuNP-177Lu. No or minimal normal tissue toxicity was observed for trastuzumab-AuNP-177Lu or AuNP-177Lu treatments. Trastuzumab-AuNP-177Lu enables an efficient local radiation treatment of HER2-positive BC.