Synthesis and exploration of novel radiolabeled bombesin peptides for targeting receptor positive tumor

Synthesis, Characterization, and Biological Evaluation of Radiolabeled Glutamine Conjugated Polymeric Nanoparticles: A Simple Approach for Tumor Imaging

Application of nanoradiopharmaceuticals for molecular imaging has gained worldwide importance for their multifaceted potentials focusing on providing a safe and cost-effective approach. Biodistribution studies on such species are capable of bringing nanomedicine to patients. Current therapeutically available labeling strategies suffer from different limitations, including off-target cytotoxicity and radiolabel release over time. Poly(lactic-co-glycolic acid)(PLGA) nanoparticles are biodegradable carriers for a variety of contrast agents that can be employed in medicine with high loading capacity for multimodal imaging agents. Here, glutamine-conjugated PLGA polymers were used to construct polymeric nanoparticles (G-PNP) similar to unconjugated PLGA nanoparticles (PNP)s formulated for ex vivo cell labeling and in vivo tumor scintigraphy studies. G-PNP/PNP, characterized by Fourier-transform infrared, atomic-force-microscopy, particle-size, and zeta-potential studies, were biocompatible as evaluated by MTT assay. G-PNPs were radiolabeled with ^99mtechnetium (^99mTc) by borohydrite reduction. G-PNPs demonstrated higher cellular uptake than PNPs, with no major cytotoxicity. Radiochemical purity indicated that ^99mTc labeled G-PNP (^99mTc-G-PNP) can form a stable complex with substantial stability in serum with respect to time. Imaging studies showed that ^99mTc-G-PNP significantly accumulated at the C6 glioma cell induced tumor-site in rats. Thus, ^99mTc-G-PNP demonstrated favorable characteristics and imaging potential which may make it a promising tumor imaging nanoprobe as a nanoradiopharmaceutical.

Targeting the Gastrin-Releasing Peptide Receptor (GRP-R) in Cancer Therapy: Development of Bombesin-Based Peptide-Drug Conjugates

Targeted tumour therapy has proved to be an efficient alternative to overcome the limitations of conventional chemotherapy. Among several receptors upregulated in cancer cells, the gastrin-releasing peptide receptor (GRP-R) has recently emerged as a promising target for cancer imaging, diagnosing and treatment due to its overexpression on cancerous tissues such as breast, prostate, pancreatic and small-cell lung cancer. Herein, we report on the in vitro and in vivo selective delivery of the cytotoxic drug daunorubicin to prostate and breast cancer, by targeting GRP-R. Exploiting many bombesin analogues as homing peptides, including a newly developed peptide, we produced eleven daunorubicin-containing peptide-drug conjugates (PDCs), acting as drug delivery systems to safely reach the tumour environment. Two of our bioconjugates revealed remarkable anti-proliferative activity, an efficient uptake by all three tested human breast and prostate cancer cell lines, high stability in plasma and a prompt release of the drug-containing metabolite by lysosomal enzymes. Moreover, they revealed a safe profile and a consistent reduction of the tumour volume in vivo. In conclusion, we highlight the importance of GRP-R binding PDCs in targeted cancer therapy, with the possibility of further tailoring and optimisation.

99mTc-labeled peptide targeting interleukin 13 receptor α 2 for tumor imaging in a cervical cancer mouse model

OBJECTIVE

Pep-1 (CGEMGWVRC) can potently bind to interleukin 13 receptor α 2 (IL-13Rα2), a tumor-restricted receptor found to be expressed in various malignancies. In this study, we intended to prepare a ^99mTc-labeled probe and evaluate its in vivo tumor accumulation properties in a cervical cancer xenograft model.

METHODS

The Pep-1 was designed and radiolabeled with ^99mTc by conjugation with mercaptoacetyl-triglycine (MAG₃). The labeling yield, radiochemical purity and stability were characterized in vitro. Cell uptake assays and fluorescence imaging were conducted for qualitative and quantitative evaluation of the specificity and affinity of Pep-1. Flow cytometry and tissue immunofluorescence were used to confirm the IL-13Rα2 expression in cervical cancer. Biodistribution and in vivo imaging were performed periodically to evaluate the imaging value of ^99mTc-MAG₃-Pep-1 in cervical cancer xenograft model.

RESULTS

^99mTc-MAG₃-Pep-1 was successfully prepared with a high labeling yield and radiochemical purity (> 95%). Specific cell uptake was demonstrated by scramble control and unlabeled MAG₃-Pep-1 blockade. Flow cytometry and tissue immunofluorescence also confirmed the mild IL-13Rα2 expression of HeLa. In the gamma imaging study and biodistribution, the tumors were imaged clearly at 2-6 h after injection of ^99mTc-MAG₃-Pep-1 and the accumulation of ^99mTc-MAG₃-Pep-1 in tumor was significantly higher than that in the blocking and scramble controls, demonstrating ligand-receptor binding specificity.

CONCLUSIONS

This work demonstrated that ^99mTc-MAG₃-Pep-1 can bind to cervical cancer with high affinity and specificity. MAG₃-Pep-1 may be a prospective precursor for IL-13Rα2-expressing cancer therapy.

Decapeptide Modified Doxorubicin Loaded Solid Lipid Nanoparticles as Targeted Drug Delivery System against Prostate Cancer

Growing instances of prostate cancer with poor prognosis have become a challenging task in cancer therapy. Luteinizing-hormone-releasing-hormone (LHRH) receptors are overexpressed in prostate cancer cells. Polyethylene glycol (PEG) conjugated lipids exhibit superiority in terms of retention/circulation in biological systems. PEGylated dipalmitoylphosphatedylethanolamine (DPPE-PEG), covalently linked with 6-hydrazinopyridine-3-carboxylic-acid, was conjugated with new LHRH-receptor positive peptide analog (DPPE-PEG-HYNIC-d-Glu-His-Trp-Ser-Tyr-d-Asn-Leu-d-Gln-Pro-Gly-NH₂). Surface modified doxorubicin (DOX) loaded solid lipid nanoparticle (SLN) was prepared using soylecithin, stearic acid and Poloxamer-188 by solvent emulsification/evaporation method for targeted delivery of DOX into prostate cancer cells. SLN, DOX loaded SLN (DSLN) and surface modified DSLN (M-DSLN) were characterized by means of their size, zeta potential, morphology, storage time, drug payload, and subsequent release kinetics studies. Homogeneity of surface morphology, upon modification of SLN, was revealed from the dynamic light scattering, atomic force microscopy, and scanning electron microscopic studies. Homogeneous adsolubilization of DOX throughout the hydrophobic moiety of SLN was established by the differential scanning calorimetric studies. Release of DOX were sustained in DSLN and M-DSLN. Cellular uptake and in vitro activities of formulations against LHRH positive PC3/SKBR3 cancer cell lines revealed higher cellular internalization, cytotoxicity that followed the sequence DOX < DSLN < M-DSLN. Dye staining and flow cytometry studies revealed higher apoptosis in cancer cells. Such receptor specific drug delivery systems are considered to have substantial potential in prostate cancer therapy.

Therapeutic peptides for chemotherapy: Trends and challenges for advanced delivery systems

The past decades witnessed an increasing interest in peptides as clinical therapeutics. Rightfully considered as a potential alternative for small molecule therapy, these remarkable pharmaceuticals can be structurally fine-tuned to impact properties such as high target affinity, selectivity, low immunogenicity along with satisfactory tissue penetration. Although physicochemical and pharmacokinetic challenges have mitigated, to some extent, the clinical applications of therapeutic peptides, their potential impact on modern healthcare remains encouraging. According to recent reports, there are more than 400 peptides under clinical trials and 60 were already approved for clinical use. As the demand for efficient and safer therapy became high, especially for cancers, peptides have shown some exciting developments not only due to their potent antiproliferative action but also when used as adjuvant therapies, either to decrease side effects with tumor-targeted therapy or to enhance the activity of anticancer drugs via transbarrier delivery. The first part of the present review gives an insight into challenges related to peptide product development. Both molecular and formulation approaches intended to optimize peptide's pharmaceutical properties are covered, and some of their current issues are highlighted. The second part offers a comprehensive overview of the emerging applications of therapeutic peptides in chemotherapy from bioconjugates to nanovectorized therapeutics.

Strategies for improving stability and pharmacokinetic characteristics of radiolabeled peptides for imaging and therapy

Tumor cells overexpress a variety of receptors that are emerging targets in cancer chemotherapy. Radiolabeled peptides with high affinity and selectivity for these overexpressed receptors have been designed for both imaging and therapy purposes. Such peptides display advantages such as high selectivity for tumor cells, rapid tumor tissue penetration, and rapid clearance from non-target tissues and the circulation. However, the very short in vivo half-life of radiolabeled peptides, arising from enzymatic degradation and/or efficient clearance by the kidney, limits their accumulation in tumors. This review presents various strategies that have been applied to extend the half-life extension and improve the pharmacokinetic characteristics of radiolabeled peptides. These include amino acid substitution, modification of the peptide termini, dimerization and multimerization of the peptide, cyclization, conjugation with polymers, sugars and albumin and use of peptidase inhibitors.

HYNIC and DOMA conjugated radiolabeled bombesin analogs as receptor-targeted probes for scintigraphic detection of breast tumor

Background

Among the many peptide receptor systems, gastrin-releasing-peptide (GRP) receptors, the mammalian equivalent of bombesin (BN) receptors, are potential targets for diagnosis and therapy of breast tumors due to their overexpression in various frequently occurring human cancers. The aim of this study was to synthesize and comparative evaluation of ^99mTc-labeled new BN peptide analogs. Four new BN analogs, HYNIC-Asp[PheNle]BN(7-14)NH₂, BN1; HYNIC-Pro-Asp[TyrMet]BN(7-14)NH₂, BN2; HYNIC-Asp-Asn[Lys-CHAla-Nle]BN(7-14)NH₂, BN3; and DOMA-GABA[Pro-Tyr-Nle]BN(7-14)NH₂, BN4 were synthesized and biologically evaluated for targeted imaging of GRP receptor-positive breast-tumors.

Methods

Solid-phase synthesis using Fmoc-chemistry was adopted for the synthesis of peptides. BN1–BN4 analogs were better over the standard Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH₂ (BNS). Lipophilicity, serum stability, internalization, and binding affinity studies were carried out using ^99mTc-labeled analogs. Biodistribution and imaging analyses were performed on MDA-MB-231 cell-induced tumor-bearing mice. BN-analogs induced angiogenesis; tumor formation and GRP-receptor-expression were confirmed by histology and immunohistochemistry analyses of tumor sections and important tissue sections.

Results

All the analogs displayed ≥ 97% purity after the HPLC purification. BN-peptide-conjugates exhibited high serum stability and significant binding affinity to GRP-positive tumor; rapid internalization/externalization in/from MDA-MB-231 cells were noticed for the BN analogs. BN4 and BN3 exhibited higher binding affinity, stability than BN1 and BN2. Highly specific in vivo uptakes to the tumor were clearly visualized by scintigraphy; rapid excretion from non-target tissues via kidneys suggests a higher tumor-to-background ratio. BN4, among all the analogs, stimulates the expression of angiogenic markers to a maximum.

Conclusion

Considering its most improved pharmacological characteristics, BN4 is thus considered as most promising probes for early non-invasive diagnosis of GRP receptor-positive breast tumors.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0493-x) contains supplementary material, which is available to authorized users.