Abstract
1024
Introduction: The prognosis of patients with glioblastoma is poor with an average life expectancy of 12-15 months from diagnosis. One of the factors that limit efficacy of the drugs, especially in primary brain tumor, is permeability of the blood-brain barrier (BBB). The low-density lipoprotein receptor (LDLR) expressed at the BBB mediates the transport of endogenous ligands through the BBB, a process referred to as receptor-mediated transcytosis. VECT-HORUS (VH) has identified and chemically optimized a family of peptide-vectors targeting both the human and murine LDLR and able i) to cross the BBB and ii) to target tumors such as glioblastoma that express high levels of the LDLR. The objective of this study was to determine the LDLR targeting properties of 68Ga/177Lu- radiolabeled peptide vectors (developed based on the VH proprietary platform) using a glioblastoma model that expresses the human LDLR (hLDLR) at high levels.
Methods: The LDLR targeted DOTA-conjugates (VH-DO31, VH-DO33) and NODAGA conjugate (VH-NO31), (10-30ug, VECT-HORUS SAS, France) were labeled with 68Ga (1.5mCi) eluted from 68Ge/68Ga generator (ITG GmBH, Germany) or with 177Lu n.c.a (1mCi, ITG GmBH, Germany). The U87MG cell line was shown to express high levels of the hLDLR. The LDLR targeting properties of these conjugates were thus determined in vitro in U87MG cellular uptake studies, as well as, in vivo in U87MG xenografted mice. The PET/CT images of U87MG xenografts generated in athymic nude mice (10 weeks, n=3) were acquired using G4 PET/Xray camera (Sofie Biosciences; 10min/scan) at 1h, 2h, 3h, and 4h post-injection.
Results: All 68Ga/177Lu-labeled conjugates were synthesized with radiochemical purity higher than 91 % as determined by radio-HPLC. Radiolytic stability of agents was increased using C18 ethanol purification of the final products. 177Lu-VH-DO33 showed the highest retention of the agent in U87MG cell line at 1h (13.88± 1.6 %ID/mg) and 21h incubation time (8.7± 4 %ID/mg) compared to 177Lu-VH-DO31 (8.28 ±6.2 %ID/mg). The microPET imaging studies showed rapid accumulation and retention of all VH derivatives in the tumor as monitored up to 4h post-injection. All agents were eliminated through bladder and kidneys. There was no accumulation of agents in the bone marrow. The image-based biodistribution studies of 68Ga-VH-DO31, 68Ga-VH-DO33 and 68Ga-VH-NO31 showed that the tumor to muscle ratios (SUV ratio) after 30 min post-injection were 4.12, 5.07 and 3.88, respectively and remained at the same levels up to 3h post-injection. The SUV ratios of tumor to kidneys were as follows: 68Ga-VH-DO31 (0.46), 68Ga-VH-DO33 (0.84) and 68Ga-VH-NO31 (0.46) confirming renal elimination of the agents.
Conclusions: VH derivatives showed favorable hLDLR targeting properties in vitro and in vivo in U87MG models. These preliminary results suggest that hLDLR may serve as a target for the development of radiotheranostic drugs for glioblastoma.