Octreotide Conjugates for Tumor Targeting and Imaging
Eduard Figueras1, Ana Martins2,3, Adina Borbély4
1Department of Chemistry, Organic and Bioorganic Chemistry, Bielefeld University, Universitätsstraße 25, DE-33615 Bielefeld, Germany. eduard.figueras@uni-bielefeld.de.
Abstract:
Tumor targeting has emerged as an advantageous approach to improving the efficacy and safety of cytotoxic agents or radiolabeled ligands that do not preferentially accumulate in the tumor tissue. The somatostatin receptors (SSTRs) belong to the G-protein-coupled receptor superfamily and they are overexpressed in many neuroendocrine tumors (NETs). SSTRs can be efficiently targeted with octreotide, a cyclic octapeptide that is derived from native somatostatin. The conjugation of cargoes to octreotide represents an attractive approach for effective tumor targeting. In this study, we conjugated octreotide to cryptophycin, which is a highly cytotoxic depsipeptide, through the protease cleavable Val-Cit dipeptide linker using two different self-immolative moieties. The biological activity was investigated in vitro and the self-immolative part largely influenced the stability of the conjugates. Replacement of cryptophycin by the infrared cyanine dye Cy5.5 was exploited to elucidate the tumor targeting properties of the conjugates in vitro and in vivo. The compound efficiently and selectively internalized in cells overexpressing SSTR2 and accumulated in xenografts for a prolonged time. Our results on the in vivo properties indicate that octreotide may serve as an efficient delivery vehicle for tumor targeting.
Insights
Octreotide effectively targets neuroendocrine tumors by delivering cytotoxic agents. This study demonstrates octreotide
Area of Science:
- Oncology
- Pharmacology
- Bioconjugation
Background:
- Tumor targeting enhances the efficacy and safety of therapeutic agents.
- Somatostatin receptors (SSTRs) are overexpressed in neuroendocrine tumors (NETs).
- Octreotide, a somatostatin analog, is a known SSTR-targeting agent.
Purpose of the Study:
- To develop and evaluate octreotide-conjugated agents for targeted delivery to SSTR-expressing tumors.
- To investigate the role of linker chemistry in the stability and efficacy of these conjugates.
- To assess the in vitro and in vivo tumor-targeting capabilities of novel octreotide conjugates.
Main Methods:
- Conjugation of the cytotoxic agent cryptophycin to octreotide via a protease-cleavable Val-Cit linker and self-immolative moieties.
- In vitro assessment of conjugate stability and biological activity.
- In vivo evaluation of tumor targeting using an infrared dye (Cy5.5) conjugate in xenograft models.
Main Results:
- The self-immolative moiety significantly influenced the stability of the octreotide conjugates.
- Octreotide-Cy5.5 conjugates demonstrated efficient and selective internalization in SSTR2-overexpressing cells.
- Conjugates showed prolonged accumulation in tumor xenografts in vivo.
Conclusions:
- Octreotide serves as an effective delivery vehicle for targeted cancer therapy.
- The linker and self-immolative group are critical for optimizing conjugate performance.
- This approach holds promise for improving the therapeutic index of cytotoxic agents in NETs.
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