Tumor-Penetrating Nanosystem Strongly Suppresses Breast Tumor Growth

Abstract

Antiangiogenic and vascular disrupting compounds have shown promise in cancer therapy, but tend to be only partially effective. We previously reported a potent theranostic nanosystem that was highly effective in glioblastoma and breast cancer mouse models, retarding tumor growth and producing some cures [Agemy et al. 2011,2013]. The nanosystem consists of iron oxide NPs (“nanoworms”) coated with a composite peptide with tumor-homing and pro-apoptotic domains. The homing component targets tumor vessels by binding to p32/gC1qR at the surface or tumor endothelial cells. We sought to further improve the efficacy nanosystem by searching for an optimally effective homing peptide that would also incorporate a tumor-penetrating function. To this effect, we tested a panel of candidate p32 binding peptides with a sequence motif that conveys tumor-penetrating activity (CendR motif). We identified a peptide designated as Linear TT1 (Lin TT1) (sequence: AKRGARSTA) as most effective in causing tumor homing and penetration of the nanosystem. This peptide had the lowest affinity for p32 among the peptides tested. The low affinity may have moderated the avidity effect from the multivalent presentation on nanoparticles (NPs), such that the NPs avoid getting trapped by the so called “binding-site barrier”, which can hinder tissue penetration of compounds with a high affinity for their receptors. Treatment of breast cancer mice with the LinTT1 nanosystem showed greatly improved efficacy compared to the original system. These results identify a promising treatment modality and underscore the value of tumor penetration effect in improving the efficacy tumor treatment.

Targeting of p32 in peritoneal carcinomatosis with intraperitoneal linTT1 peptide-guided pro-apoptotic nanoparticles

“…Significantly, the affinity of linTT1 for its target receptor, p32 (aka gC1qR), is lower than that of similar peptides, but it is particularly effective in causing tumor penetration of NPs [18,19]. The reason may be that the avidity effect of the multivalent presentation on NPs does not become so high that it would elicit the so-called “binding- site barrier”, which can hinder tissue penetration of compounds with a high affinity for their receptors [49,50].…”

“…The p32 protein has been used as a target molecule in systemic treatment of tumors [19,31,51,52], but this is the first study on PC. We show that a number of cell lines representing tumors that commonly present as PC express p32 at levels suitable for peptide-based tumor targeting.…”

“…A recently identified tumor penetrating peptide TT1 (active both as a disulfide-bridged CKRGARSTC and as linTT1, AKRGARSTA) homes robustly to breast cancer in mouse models and enhances the antitumor potency of therapeutic payloads [18,19]. The primary homing receptor for TT1 family of peptides is p32 (also known as gC1qR), a mitochondrial protein aberrantly expressed on the cell surface of activated malignant and stromal cells in solid tumors, often in hypoxic areas deep in the tumor tissue [20].…”

“…TT1 belongs to a novel class of tumor targeting peptides, tumor penetrating C-end Rule (CendR) peptides characterized by a multistep homing and tumor penetration pathway. After binding to p32 TT1 peptide is proteolytically cleaved by a urokinase type plasminogen activator at the second arginine residue (AKRGA R STA) and the processed peptide acquires affinity towards tissue penetration receptor NRP-1 via its C-terminal RGAR CendR motif [19] to trigger vascular exit and tumor penetration [21,22]. …”

“…Finally, linearly aggregated 10 cores in IONWs generate improved T2- relaxivity for improved MR imaging [29]. We used intraperitoneal linTTl-functionalized NWs carrying pro-apoptotic D [KLAKLAK] 2 effector module [19,31] for experimental therapy on a panel of peritoneal tumors in mice. Our data indicate that linTT1 peptide functionalization greatly improves tumor selectivity of NWs and increases therapeutic efficacy of a pro-apoptotic nanosystem based on the NWs.…”