Metal-Chelating Polymers (MCPs) with Zwitterionic Pendant Groups Complexed to Trastuzumab Exhibit Decreased Liver Accumulation Compared to Polyanionic MCP Immunoconjugates

Abstract

Metal-chelating polymers (MCPs) can amplify the radioactivity delivered to cancer cells by monoclonal antibodies or their Fab fragments. We focus on trastuzumab (tmAb), which is used to target cancer cells that overexpress human epidermal growth factor receptor 2 (HER2). We report the synthesis and characterization of a biotin (Bi) end-capped MCP, Bi-PAm(DET-DTPA)36, a polyacrylamide with diethylenetriaminepentaacetic acid (DTPA) groups attached as monoamides to the polymer backbone by diethylenetriamine (DET) pendant groups. We compared its behavior in vivo and in vitro to a similar MCP with ethylenediamine (EDA) pendant groups (Bi-PAm(EDA-DTPA)40). These polymers were complexed to a streptavidin-modified Fab fragment of tmAb, then labeled with (111)In to specifically deliver multiple copies of (111)In to HER2+ cancer cells. Upon decay, (111)In emits γ-rays that can be used in single-photon emission computed tomography radioimaging, as well as Auger electrons that cause lethal double strand breakage of DNA. Our previous studies in Balb/c mice showed that radioimmunoconjugates (RICs) containing the Bi-PAm(EDA-DTPA)40 polymer had extremely short blood circulation time and high liver uptake and were, thus, unsuitable for in vivo studies. The polymer Bi-PAm(EDA-DTPA)40 carries negative charges on each pendant group at neutral pH and a net charge of (-1) on each pendant group when saturated with stable In(3+). To test our hypothesis that charge associated with the polymer repeat unit is a key factor affecting its biodistribution profile, we examined the biodistribution of RICs containing Bi-PAm(DET-DTPA)36. While this polymer is also negatively charged at neutral pH, it becomes a zwitterionic MCP upon saturation of the DTPA groups with stable In(3+) ions. In both nontumor bearing Balb/c mice and athymic mice implanted with HER2+ SKOV-3 human ovarian cancer tumors, we show that the zwitterionic MCP has improved biodistribution, higher blood levels of radioactivity, lower levels of normal tissue uptake, and higher tumor uptake. Surface plasmon resonance experiments employing the extracellular domain of HER2 show that the MCP immunoconjugates retain high affinity antigen recognition, with dissociation constants in the low nM range. In vitro studies with SKOV-3 cells for both MCP immunoconjugates show a combination of specific binding that can be completed in the presence of excess tmAb IgG and nonspecific binding (NSB) that persists in the presence of tmAb IgG. We conclude that zwitterionic MCPs represent a much better choice than polymers with charges along the backbone for in vivo delivery of RICs to HER2+ cancer cells.

Functionalization of Cellulose Nanocrystals with PEG-Metal-Chelating Block Copolymers via Controlled Conjugation in Aqueous Media

“…The BCP employed in this study consists of an outer PEG block that provides “stealth” properties for in vivo applications 32 and an inner poly(glutamic acid) (PGlu) block that introduces functional groups for the conjugation of metal-chelating diethylenetriaminepentaacetic acid (DTPA) for future applications in radiotherapy ( Scheme 1 ). 33 As a proof-of-concept evaluation of their potential as imaging agents, the penetration properties of these BCP–CNCs were investigated in a 3D multicellular tumor spheroid (MCTS) model of ovarian cancer. Overall, the findings of this study demonstrate that the “grafting-to” method of CNC modification offers a robust platform for the preparation and characterization of BCP–CNC conjugates.…”

Recent Advances and Perspective of Nanotechnology-Based Implants for Orthopedic Applications

“…The zwitterionic metal-chelating polymers exhibit enhanced biodistribution, increased blood levels of radioactivity, decreased absorption by normal tissue, and increased tumour uptake. Using the extracellular domain of HER2, surface plasmon resonance investigations examined that the MCP immune conjugates retain excellent antigen binding, with dissociation constants in the low nM range ( Liu et al, 2015 ). Using a fluorescein isothiocyanate/neutravidin receptor as an intermediate, a biotin end group enabled conjugation to biotinylated beads.…”

Nanostructures as Radionuclide Carriers in Auger Electron Therapy

“…It was shown that the attachment of the MCP to the trastuzumab-streptavidin conjugates had no significant effect on the rate of binding to the extracellular domain of HER2 or the dissociation rate (the interaction was characterized by a low nanomolar binding constant). The biodistribution and micro SPECT/CT (single-photon emission computed tomography/computed tomography) imaging studies on Balb/C mice showed that the tissue distribution of the trastuzumab Fab-streptavidin-MCP conjugates was dependent on both the chemical structure of the polymer backbone and the nature of the pendant group to which the DTPA units were attached [43]. Rapid elimination from the blood and high liver uptake have been found to be related to the polyanionic character of the MCP.…”