Design and In vitro Evaluation of Branched Peptide Conjugates: Turning Nonspecific Cytotoxic Drugs into Tumor‐Selective Agents

Abstract

The use of peptide receptors as targets for tumor-selective therapies was envisaged years ago with the findings that receptors for different endogenous regulatory peptides are overexpressed in several primary and metastatic human tumors, and can be used as tumor antigens. Branched peptides can retain or even increase, through multivalent binding, the biological activity of a peptide and are very resistant to proteolysis, thus having a markedly higher in vivo activity compared with the corresponding monomeric peptides. Oligo-branched peptides, containing the human regulatory peptide neurotensin (NT) sequence, have been used as tumor-specific targeting agents. These peptides are able to selectively and specifically deliver effector units, for cell imaging or killing, to tumor cells that overexpress NT receptors. Results obtained with branched NT conjugated to different functional units for tumor imaging and therapy indicate that branched peptides are promising novel multifunctional targeting molecules. This study is focused on the role of the releasing pattern of drug-conjugated branched NT peptides. We present results obtained with oligo-branched neurotensin peptides conjugated to 6-mercaptopurin (6-MP), combretastain A-4 (CA4) and monastrol (MON). Drugs were conjugated to oligo-branched neurotensin through different linkers, and the mode-of-release, together with cytotoxicity, was studied in different human cancer cell lines. The results show that branched peptides are very promising pharmacodelivery options. Among our drug-armed branched peptides, NT4-CA4 was identified as a candidate for further development and evaluation in preclinical pharmacokinetic and pharmacodynamic studies. This peptide-drug exhibits significant activity against pancreas and prostate human cancer cells. Consequently, this derivative is of considerable interest due to the high mortality rates of pancreas neuroendocrine tumors and the high incidence of prostate cancer.

Target‐Selective Drug Delivery through Liposomes Labeled with Oligobranched Neurotensin Peptides

“…[21] It is well known that peptides synthesized in a branched form not only become resistant to proteases but also increase linear peptide biological activity through multivalent binding. Using branched NT 4 fragment 8-13, conjugated to various functional units for tumor imaging and therapy, [22] we found that NT 4 conjugated to methotrexate or 5-fluoro-deoxyuridine resulted in 60 % and 50 % reduction, respectively, [22][23][24] of tumor growth in xenografted mice. Additionally, branched NT peptides have been proven to discriminate between binding of tumor versus healthy tissue in human surgical samples, validating neurotensin receptors as highly promising tumor biomarkers.…”

The role of neurotensin in physiologic and pathologic processes

“…Our experiments suggested that HDACi suppression of NTS1 is dependent on GSK3b inhibition of ERK1/2 [88]. Perhaps most exciting is the successful coupling of chemotherapeutic drugs to modular branched neurotensin peptides by Falciani et al [89]. The oligo-branched peptide constructs are more resistant to serum proteases than monomeric peptides, and the addition of the neurotensin sequence allowed selective targeting of cells expressing neurotensin receptors.…”

Multifunctional dendrimer/combretastatin A4 inclusion complexes enable in vitro targeted cancer therapy

“…9 To decrease the toxicity of CA4, it is necessary to develop a carrier system to improve the water solubility and bioavailability of the drug and maintain the tumor inhibition effect. Commonly used drug delivery systems include liposomes, 10,11 polymeric nanoparticles, [12][13][14] and peptide conjugates, 15 which have been demonstrated to be able to load or conjugate CA4 to enhance its water solubility and improve its therapeutic efficacy. [16][17][18][19][20] For instance, in a recent study, Ho et al used methoxyl poly(ethylene glycol)-poly(lactic acid) copolymers to conjugate paclitaxel, followed by encapsulation of CA4 to form self-assembled polymeric nanoparticles with both anticancer and antivasculature activity.…”