Selective Apoptotic Killing of Solid and Hematologic Tumor Cells by Bombesin-Targeted Delivery of Mitochondria-Disrupting Peptides

Biodistribution and evaluation of 131 I-labeled neuropilin-binding peptide for targeted tumor imaging

Neuropilin-1 (NRP-1) is overexpressed in several kinds of cancer cell and contributes to tumor aggressiveness. Recently, the arginine/lysine-rich peptide with C-terminal motifs (R/K)XX(R/K) indicated promising penetrating and transporting capability into NRP-1 positive cancer cells. In the present study, we describe a ¹³¹ I-labeled C-end rule motif peptide conjugate, Tyr-tLyp-1, for NRP-1 positive tumor targeting and imaging properties. Briefly, a truncated Lyp-1 peptide was designed to expose its C-end motif and conjugated to tyrosine for radiolabeling after structural modification. The peptide indicated specific binding to A549 cancer cells at 2 μM concentration, and its binding was dependent on NRP-1 expression and could be inhibited by other NRP-1-binding peptides. In vivo imaging of ¹³¹ I-labeled Tyr-tLyp-1peptide showed that a subcutaneous A549 xenograft tumor could be visualized using a SPECT/CT scanner. The tumor uptake of ¹³¹ I-Tyr-tLyp-1 was 4.77 times higher than the uptake in muscles by SPECT/CT software quantification at 6 h post injection. Together, this study indicated that truncated Lyp-1 peptide could specifically localize in NRP-1 positive tumors and successfully mediate the ¹³¹ I radionuclide diagnosis, indicating promising targeted imaging capability for NRP-1 positive tumors. Copyright © 2016 John Wiley & Sons, Ltd.

Recent Innovations in Peptide Based Targeted Drug Delivery to Cancer Cells

Targeted delivery of chemotherapeutics and diagnostic agents conjugated to carrier ligands has made significant progress in recent years, both in regards to the structural design of the conjugates and their biological effectiveness. The goal of targeting specific cell surface receptors through structural compatibility has encouraged the use of peptides as highly specific carriers as short peptides are usually non-antigenic, are structurally simple and synthetically diverse. Recent years have seen many developments in the field of peptide based drug conjugates (PDCs), particularly for cancer therapy, as their use aims to bypass off-target side-effects, reducing the morbidity common to conventional chemotherapy. However, no PDCs have as yet obtained regulatory approval. In this review, we describe the evolution of the peptide-based strategy for targeted delivery of chemotherapeutics and discuss recent innovations in the arena that should lead in the near future to their clinical application.

Enhancing the circulating half-life and the antitumor effects of a tumor-selective cytotoxic peptide by exploiting endogenous serum albumin as a drug carrier

The elevated expression of bombesin receptors in many of the deadliest cancers has attracted special interest in developing bombesin-directed agents for tumor imaging and therapy. Previously, we constructed the chimeric peptide BB28 by fusing bombesin to a mitochondria-disrupting peptide. BB28 selectively induced the apoptosis of various tumor cells in vitro and showed promising in vivo antitumor effects. In general, a short circulating half-life limits the in vivo effect of peptides. To prolong the half-life of BB28, here, we generated the novel peptide ABB28 by fusing an albumin-binding domain (ABD) to the N-terminus of BB28. ABB28 exhibited much higher binding affinity for albumin than BB28, and this modification extended the peptide half-life from several minutes to 2 h. Optical imaging revealed that ABB28 accumulated in xenografted tumors within 1h post-injection and persisted at an evident level for up to 24 h. ABB28 exerted stronger tumor-suppressive effects than BB28. Significant differences in the tumor volumes (P<0.001) and the tumor weights (P=0.002) were observed between ABB28- and BB28-treated mice. Moreover, ABB28 exhibited tumor suppression comparable to that of PEGylated 5K-BB28 in vivo. These results suggest that half-life extension via ABD fusion represents a useful strategy for optimizing bombesin-directed pharmaceuticals for cancer-targeted therapy.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Penetratin-mediated delivery enhances the antitumor activity of the cationic antimicrobial peptide Magainin II

Cationic antimicrobial peptides (CAPs) with antitumor activity have potential for use as novel antitumor agents because of their lower risk for induction of resistance. Of these peptides, magainin II (MG2) exhibited cytotoxicity in tumor cells only at high concentrations, likely due to the inefficiency of MG2 in cell membrane binding and cell entry. Conjugation to a cell-penetrating peptide (CPP) might enhance the cytotoxicity of MG2 in tumor cells. Here, we constructed a fusion peptide MG2A by conjugating MG2 to the N-terminus of the CPP penetratin (Antp). It was found that the fusion peptide MG2A is more potent than unconjugated MG2 at tumor cell killing. The IC50s of MG2A for the tumor cells tested were at least 30 times lower than the IC50s of unconjugated MG2. These data indicate that conjugation to Antp significantly enhanced the cytotoxicity of MG2 in tumor cells. Moreover, the IC50s of MG2A for tumor cells are within 2 to 3 μM, which are about three to five times lower than the IC50 for normal cells. Furthermore, chondroitin sulfate (CS) was found to be overexpressed on the surface of the tested tumor cells, and the cytotoxicity of MG2A could be inhibited by the addition of exogenous CS. These results suggest that binding of Antp to CS on tumor cells might be one important cause for the selective cytotoxicity of MG2A in tumor cells. Taken together, conjugation of MG2 to Antp can significantly enhance its antitumor activity, and the fusion of CAP to Antp might be an alternative for cancer-targeted therapy.

On the selectivity and efficacy of defense peptides with respect to cancer cells

Here, we review potential determinants of the anticancer efficacy of innate immune peptides (ACPs) for cancer cells. These determinants include membrane-based factors, such as receptors, phosphatidylserine, sialic acid residues, and sulfated glycans, and peptide-based factors, such as residue composition, sequence length, net charge, hydrophobic arc size, hydrophobicity, and amphiphilicity. Each of these factors may contribute to the anticancer action of ACPs, but no single factor(s) makes an overriding contribution to their overall selectivity and toxicity. Differences between the anticancer actions of ACPs seem to relate to different levels of interplay between these peptide and membrane-based factors.

Biology of mammalian bombesin-like peptides and their receptors

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of mammalian bombesin receptor-related pathophysiological roles in disease states and new insights into bombesin receptor pharmacology.

RECENT FINDINGS

Studies regarding bombesin-like peptides and mammalian bombesin receptor functions have demonstrated significant biological impact on a broad array of physiological and pathophysiological conditions. Pharmacological experiments in vitro and in vivo as well as utilization of genetic rodent models of the gastrin-releasing peptide receptor (GRP-R/BB2) and neuromedin B receptor (NMB-R/BB1) further delineated roles in memory and fear behavior, inhibition of tumor cell growth, mediating signals for pruritus and male reproductive behavior. All three mammalian bombesin receptors were shown to possess some role in the regulation of energy balance. Novel synthesis of selective high affinity agonists and antagonists of the orphan bombesin receptor subtype-3 (BRS-3/BB3) has been accomplished and will facilitate further studies using animal model systems.

SUMMARY

Mammalian bombesin receptors participate in the regulation of energy homeostasis and may represent an attractive target for pharmacological treatment of obesity and certain eating disorders. Novel pharmacological insights of bombesin-like peptides and the interaction with their respective receptors have been elucidated to aid future treatment and imaging of epithelial cell-derived tumors.

Approaches for targeting mitochondria in cancer therapy

The recognition of the role that mitochondria play in human health and disease is evidenced by the emergence in recent decades of a whole new field of "Mitochondrial Medicine". Molecules located on or inside mitochondria are considered prime pharmacological targets and a wide range of efforts are underway to exploit these targets to develop targeted therapies for various diseases including cancer. However the concept of targeting, while seemingly simple in theory, has multiple subtly different practical approaches. The focus of this article is to highlight these differences in the context of a discussion on the current status of various mitochondria-targeted approaches to cancer therapy.