New imaging methods are important for the early detection and clinical therapy of breast cancer (BrCa). Optical molecular imaging (OMI) and MRI can reveal morphology, structure and function while not requiring radiation or breast compression. A versatile synthesis of targeted molecular imaging agents (TMIAs) for OMI and MRI of breast cancer (BrCa) has been developed. The strategy is based on a targeting deca-peptide, 18-4, reported by Kaur to be an effective targeting agent for keratin receptor KRT1, a biomarker that is independent of hormone expression in BrCa cells. This can target the virulent strains including triple negative (TN) cell lines such as MDA-MB-231 that are so lethal. Kaur’s solid phase peptide synthesis (SPPS) was modified to enable the use of Sieber resin, which is cleaved in mild acid to enable use of near infrared (NIR) dyes and Gd based agents for MRI that are unstable in strong acid. We have merged the synthesis of 18-4 on Sieber resin with a modular method we developed for single and multi-modal TMIAs. In the modular approach, NIR dyes or DOTA-chelated metals are placed on the side chains of Fmoc-lysines which allow their conjugation onto targeting peptides using coupling methods. It is also applicable to the synthesis of dual modal agents. NIR dye Cy5.5 was placed on two viable positions of peptide 18-4: on the third lysine residue and next, onto the N-terminal. The method was utilized to conjugate a lysine module with a Gd-DOTA onto the N-terminal of 18-4. In confocal fluorescence microscopy (CFM), the molecularly targeted agents displayed a high affinity to MDA-MB-231 cells, and endocytosis was observed. Our focus then turned to a comparison of a lipophilic Cy5.5 dye (no sulfonates) to a water soluble (tri-sulfonated) analog of Cy5.5. This paved the way for the use of water soluble dyes for fluorescent imaging at higher wavelengths, and the synthesis of dual modal agents for OMI and MRI to provide new imaging methods for early detection of BrCa, and to plan cancer therapy.

Solid phase synthesis of molecularly targeted agents for breast cancer imaging

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.