Abstract LB066: Targeting low density lipoprotein receptors in the pancreatic adenocarcinoma

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a poor 5-year overall survival rate at all stages of disease (7-10%). The immunohistochemistry of pancreatic cancer tissue has shown a significantly higher level of positive LDLR (low-density lipoprotein receptor) staining in primary tumors compared to the normal adjacent pancreas. LDLR is overexpressed in the epithelial pancreatic adenocarcinoma, irrespectively of tumor size, stage, and aggressiveness. The objective of this study was to determine the LDLR-targeting properties of 68Ga-labeled peptide conjugate, 68Ga-RMX-VH, in pancreatic adenocarcinoma cell lines.

Methods: RMX-VH peptide conjugate (25-50μg) was labeled with 68Ga (50-100mCi, ITM Germany) in mild conditions in the presence of scavenger, sodium ascorbate (8mg/ml). The cellular uptake and competition studies of the radiotracer (15μCi/well) were completed in multiple pancreatic adenocarcinoma cell lines and in vivo in PDAC xenografts generated in athymic nude mice. The PET/CT images were acquired using a G4 PET/X-ray camera (Sofie Biosciences; 10min/scan) at 1h, 2h post-injection. This study determined in vivo and in vitro time-dependent accumulation of this agent in LDLR-overexpressing pancreatic adenocarcinoma cells.

Results: 68Ga-RMX-VH was synthesized with higher than 95% radiochemical purity. The radiotracer was incubated in pancreatic adenocarcinoma cell lines for 1h and has shown the highest uptake in HPAF-II (6.7%ID/mg) and BxPC-3 (5.3 %ID/mg) and MiaPaCa2 (4.75 %ID/mg), respectively. Western blot showed a variable level of LDLR overexpression in human pancreatic cancer cells. The microPET imaging studies confirmed rapid accumulation and retention of radiotracer in the tumor (1.18 %ID/g) and elimination through kidneys (4.5 %ID/g) and bladder (SUV ratio of tumor to kidneys: 0.21). These results correlate with previously reported retention of the agent in Pk4a pancreatic adenocarcinoma.

Conclusions: RMX-VH has the potential to evaluate the role of LDL receptors in pancreatic adenocarcinoma. We have initiated the exploratory clinical study of this agent in LDLR-overexpressing solid tumors, including pancreatic adenocarcinoma.

Citation Format: Leo Flores, Xuewei Qu, Cedric Malicet, Pascaline Lecorche, Ebrahim Delpassand, Jamal Temsamani, Izabela Tworowska. Targeting low density lipoprotein receptors in the pancreatic adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB066.

Abstract P099: Radionuclide imaging of low-density-lipoprotein receptor (LDLR)-overexpressing glioblastoma: A preclinical study of Gallium-68 RMX-VH

Introduction: One of the factors that limit the efficacy of the drugs, especially in primary brain tumors, is the permeability of the blood-brain barrier (BBB). The low-density lipoprotein receptor (LDL-R) expressed at the BBB mediates the transport of endogenous ligands through the BBB. We developed a new radiolabeled peptide 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, the pharmacokinetics of 68Ga radiolabeled RMX-VH in a glioblastoma model that expresses the human LDLR (hLDLR). Methods: The nonclinical studies of 68Ga-RMX-VH were completed in U87MG, A172, U373 glioblastoma cancer cell lines and xenografts mice models. The studies determined in vivo time-dependent accumulation of this agent, in vitro dose-depended cellular uptake, and cellular competition studies. We compared the tumor-specific accumulation of 68Ga-RMX-VH and normal organ distribution in female and male athymic nude mice. Radiotracer, RMX-VH (10-30ug) was labeled with isotope-Ga68 (10-25mCi, ITM GmBH). U87MG and A172- derived xenografts were generated in athymic nude mice (10 weeks) and PET/CT images were acquired using G4 PET/Xray camera (Sofie Biosciences) at 1h, 2h, 3h, and 4h post-injection. The followed up biodistribution studies were done at 30 min, 1h, 2h, and 3 hrs. post-injection. The organs and tumor were collected, weighed, and the tissue radioactivity was measured with Wizard2 Gamma Counter (Perkin-Elmer, Waltham, MA). The percentage of injected dose per gram of tissue (%ID/g) was calculated and decay-corrected. Results: Our studies confirmed the in vitro and in vivo selectivity and specificity of 68Ga-RMX-VH toward LDLR-positive tumors. 68Ga-RMX-VH is a small peptide (MW: 1432.7 g/mol) and renal excretion was expected as a route of agent elimination. The tumor-specific uptake of radiotracer in U87MG xenografts was 1.8%ID/g at 1h and remained unchanged at 3h post-injection. The kidney retention of the agent reached 12.2%ID/g and decreased to 10.2%ID/g. The accumulation of radiotracer in the liver, ovaries, and intestine correlated well with the known normal expression of LDLR. The tumor-to-muscle ratio was 5.97 at 1h; increased to 26.1 and 22.39 at 2h and 3h. The elimination t1/2 of radiotracer was only 18.6 min, with a clearance CL of 502 ml/min. Adsorption from the site of administration is rapid as the Cmax was 5 min. The tumor-specific uptake and normal organ distribution of 68Ga-RMX-VH were lower in male mice than in females. This correlated with differences in lipid and lipoproteins metabolism in males and females. Conclusions: RMX-VH showed favorable hLDLR targeting properties in vitro and in vivo in glioblastoma mice models. Our results suggest that hLDLR may serve as a target for imaging for glioblastoma. The first-in-human exploratory IND study of Ga68-RMX-VH will be initiated in Q2 of 2021.

Citation Format: Izabela Tworowska, Leo Garcia Flores II, Xuewei Qu, Cédric Malicet, Nilesh Wagh, David Ranganathan, Jonathan Nowak, Pascaline Lecorche, Jamal Temsamani, Ebrahim S. Delpassand. Radionuclide imaging of low-density-lipoprotein receptor (LDLR)-overexpressing glioblastoma: A preclinical study of Gallium-68 RMX-VH [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P099.

Abstract LB-A16: Imaging of glioblastoma using LDLR-based targeted delivery system

Introduction: Glioblastoma is the most agressive brain tumor with average life expectancy of 12-15 months from diagnosis. One of the factors that limit efficacy of drug, 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 by 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 (100mCi, ITG GmBH, Germany) or with 177Lu n.c.a (1mCi, ITG GmBH, Germany). The U87MG cell line has been 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 xenograft 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 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 and tumor-targeting properties both in in vitro as well as in vivo in U87MG xenografts. These results can postulate that hLDLR may serve as a target for the development of theranostic probes for the diagnosis and radiotherapy of glioblastoma.

Citation Format: Izabela Tworowska, Leo G Flores II, Rafal Zielinski, Jonathan Nowak, Pascaline Lecorche, Cedric Malicet, Michel Khrestchatisky, Jamal Temsamani, Ebrahim Delpassand. Imaging of glioblastoma using LDLR-based targeted delivery system [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A16. doi:10.1158/1535-7163.TARG-19-LB-A16