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Published on: January 29, 2019
Enhanced Retention of NTSR1-Targeted Radionuclide Therapeutics via Covalent Inhibitors in Pancreatic, Colorectal, and
Wenting Zhang1,2, Wei Fan1,2, Katie Brake3
1Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, 985830 Nebraska Medical Center, Omaha, Nebraska 68198, United States.
Abstract:
Neurotensin receptor subtype 1 (NTSR1) is overexpressed in numerous cancers. Our laboratory is exploring the utilization of covalent cysteine protease inhibitors (e.g., E-64) to increase tumor retention of targeted radionuclide therapeutics (TRTs) through protein adduct formation. Using this approach, we reported [177Lu]Lu-NA-ET1, an NTSR1-targeted construct. In this work, we continue the exploration of [177Lu]Lu-NA-ET1 in three different NTSR1-positive cancer models. [177Lu]Lu-3BP-227, a clinically investigated NTSR1-targeted construct, was utilized as a comparative benchmark. Both [177Lu]Lu-NA-ET1 and [177Lu]Lu-3BP-227 underwent in vitro investigation, including internalization and autoradiographic sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) studies, in NTSR1-positive AsPC-1, HT-29, and PC-3 cell lines. Biodistribution, human radiation dosimetry, and in vivo autoradiographic SDS-PAGE studies were performed by using the same models. A dose escalation study using 585 MBq (15.8 mCi) of [177Lu]Lu-NA-ET1 was implemented in immunocompetent CF-1 mice. In all three cell lines, [177Lu]Lu-NA-ET1 demonstrated similar cellular uptake profiles relative to those of [177Lu]Lu-3BP-227. Biodistribution studies of [177Lu]Lu-NA-ET1 revealed increased (1.9-4.4-fold) tumor retention and radiation dose delivery relative to the control. Analysis of the in vitro and in vivo cellular and tissue lysates showed protein adducts that ranged from approximately 25-35 kDa, consistent with cysteine cathepsins, the speculative protein binding partner. A total of 585 MBq (15.8 mCi) of [177Lu]Lu-NA-ET1 was administered and found to be well-tolerated. Incorporating the covalent inhibitor in [177Lu]Lu-NA-ET1 resulted in an improved retention and radiation dose delivery profile compared to [177Lu]Lu-3BP-227. Examination of the therapeutic potential of [177Lu]Lu-NA-ET1 and further exploration of the chemical biology of this approach is underway.
Insights
This study shows that [177Lu]Lu-NA-ET1, a targeted radionuclide therapeutic, improves tumor retention and radiation dose delivery in cancer models. This novel approach enhances therapeutic efficacy by forming protein adducts with cysteine cathepsins.
Area of Science:
- Nuclear medicine
- Oncology
- Radiopharmaceutical chemistry
Background:
- Neurotensin receptor subtype 1 (NTSR1) is overexpressed in various cancers.
- Targeted radionuclide therapeutics (TRTs) offer potential for cancer treatment.
- Covalent cysteine protease inhibitors can enhance TRT tumor retention via protein adduct formation.
Purpose of the Study:
- To evaluate the efficacy of [177Lu]Lu-NA-ET1, an NTSR1-targeted construct with a covalent inhibitor, in preclinical cancer models.
- To compare [177Lu]Lu-NA-ET1 with a clinically investigated NTSR1-targeted construct, [177Lu]Lu-3BP-227.
- To investigate the mechanism of enhanced tumor retention and identify potential protein binding partners.
Main Methods:
- In vitro studies: cellular uptake and autoradiographic SDS-PAGE in NTSR1-positive AsPC-1, HT-29, and PC-3 cell lines.
- In vivo studies: biodistribution, human radiation dosimetry, and in vivo autoradiographic SDS-PAGE in the same cancer models.
- Dose escalation study in immunocompetent CF-1 mice.
Main Results:
- [177Lu]Lu-NA-ET1 showed similar cellular uptake to [177Lu]Lu-3BP-227 across all tested cell lines.
- [177Lu]Lu-NA-ET1 demonstrated significantly increased tumor retention (1.9-4.4-fold) and radiation dose delivery compared to controls.
- Protein adducts of approximately 25-35 kDa were observed in vitro and in vivo, suggesting binding to cysteine cathepsins.
- [177Lu]Lu-NA-ET1 was well-tolerated in a dose escalation study.
Conclusions:
- Incorporating a covalent inhibitor into [177Lu]Lu-NA-ET1 improves tumor retention and radiation dose delivery compared to [177Lu]Lu-3BP-227.
- The formation of protein adducts with cysteine cathepsins is a key mechanism for enhanced therapeutic retention.
- [177Lu]Lu-NA-ET1 shows promise as a targeted radionuclide therapeutic for NTSR1-positive cancers.
