Drug Conjugates for Targeting Eph Receptors in Glioblastoma

Abstract

Glioblastoma (GBM) is a complex and heterogeneous tumor that warrants a comprehensive therapeutic approach for treatment. Tumor-associated antigens offer an opportunity to selectively target various components of the GBM microenvironment while sparing the normal cells within the central nervous system. In this study, we conjugated a multivalent vector protein, QUAD 3.0, that can target four receptors: EphA3, EphA2, EphB2, and also IL-13RA2, spanning virtually 100% of the GBM microenvironment, to doxorubicin derivatives. The conjugates effectively bound to all four receptors, although to varying degrees, and delivered cytotoxic loads to both established and patient-derived GBM cell lines, with IC 50 values in the low nM range. The conjugates were also non-toxic to animals. We anticipate that the QUAD 3.0 Dox conjugates will be further used in preclinical models and possibly clinics in the foreseeable future.Pharmaceuticals 2020, 13, 77 2 of 17 in tumor cells and its microenvironment but not in their normal counterparts. The targeting of such receptors has been achieved in different ways. These include the use of ligand- [11-13], antibody-[14,15], and liposome/nanoparticles-based therapeutic agents [16,17]. Additionally, immunotherapy has utilized antigen-pulsed dendritic cells [18], chimeric antigen receptor T-cells (CAR T-cells) [19][20][21][22], and vaccines [23-25] to selectively target TAA in tumors. While immunotherapy has yet to show clinical benefit in GBM, it is considered a fourth pillar of cancer treatment and holds much promise [26].The Eph receptors represent the largest family of receptor tyrosine kinases. It comprises nine EphA receptors that bind to five ephrinA ligands, and five EphB receptors that bind to three ephrinB ligands. Receptors EphB2 and EphA4 can bind to ephrin ligands of different classes [27]. Their implications have been discovered in various developmental [28,29], physiological [30][31][32], and pathological phenomena [33][34][35]. Moreover, increasing indications of their involvement in tumor invasion, initiation [36], tumor immunity [37], and tumor angiogenesis [12,35] have been observed. Specifically, EphA2 and EphA3 have been shown to be expressed individually in 60% of GBM patients, including in regions of tumor neovasculature, tumor-associated immune cells, and tumor-infiltrating cells [12,35,38]. The increased expression of EphA2 and EphA3 in GBM patients is associated with poor patient prognosis and survival [39,40]. Similarly, the expression of EphB2 has been coupled with increased migration and invasion of GBM cells [41,42].The Eph receptors have been targeted using antibodies, kinase inhibitors, radionucides, and peptides that mimic the receptor ligand and carry a cytotoxic load [10]. The Eph receptors internalize once bound to their ligands and resurface later [12,13]. This allows ligand-based or ligand-mimicking peptide-based therapeutics to be administered in multiple doses given the re-expression of the receptors over time. Recently, an ephrinA5-based cytotoxin that c...

Updated Insights on EGFR Signaling Pathways in Glioma

“…Therapies may become more efficient by combining EGFR inhibitors with other downstream blocking agents. Several glioma specific epitopes such as IL13RA2 and EphA2 are under investigation for poly-target therapy with antibody drug conjugates (ADCs) and CAR-T cells [ 148 , 149 , 150 , 151 ].…”

Phase I trial of convection-enhanced delivery of IL13RA2 and EPHA2 receptor targeted cytotoxins in dogs with spontaneous intracranial gliomas

“… 4 We have shown in translational models that tumoricidal concentrations of IL13RA2/EPHA2-targeted cytotoxins are likely orders of magnitude less than MTD defined by neurotoxicity. 6 , 26 Non–dose limiting intraoperative systemic hypertension was the only adverse event possibly attributed to the cytotoxin infusion. Transient systemic hypertension was reported in dogs with gliomas treated using CED with an agent targeted at epidermal growth factor receptor, suggesting that this may be a nonspecific response to brain infusions in dogs.…”

“… 16 We envision an approach in which a targeted cytotoxin is administered to cause tumor death and release a spectrum of tumor-associated antigens that induce an adaptive immune response coupled with an immune checkpoint inhibitor. 26 …”

“…This trial serves as a template supporting our parallel development of cytotoxins simultaneously targeting 4 tumor-associated receptors—IL13RA2, EPHA2, EPHA3, and EPHB2—and our own arborizing, multiport CED catheter intended to facilitate locoregional CED infusions. 26 , 30 Expanding targeting to include EPHA3 and EPHB2 receptors will further address intra- and intertumoral heterogeneity and allow treatment of differentiated tumor cells, glioma stemlike cells, infiltrative tumor cells, neovasculature, and tumor-infiltrating cells. 26 …”

“… 26 , 30 Expanding targeting to include EPHA3 and EPHB2 receptors will further address intra- and intertumoral heterogeneity and allow treatment of differentiated tumor cells, glioma stemlike cells, infiltrative tumor cells, neovasculature, and tumor-infiltrating cells. 26 …”