Recent Advances in Imaging Agents Anchored with pH (Low) Insertion Peptides for Cancer Theranostics

Abstract

The acidic extracellular microenvironment has become an effective target for diagnosing and treating tumors. A pH (low) insertion peptide (pHLIP) is a kind of peptide that can spontaneously fold into a transmembrane helix in an acidic microenvironment, and then insert into and cross the cell membrane for material transfer. The characteristics of the acidic tumor microenvironment provide a new method for pH-targeted molecular imaging and tumor-targeted therapy. As research has increased, the role of pHLIP as an imaging agent carrier in the field of tumor theranostics has become increasingly prominent. In this paper, we describe the current applications of pHLIP-anchored imaging agents for tumor diagnosis and treatment in terms of different molecular imaging methods, including magnetic resonance T1 imaging, magnetic resonance T2 imaging, SPECT/PET, fluorescence imaging, and photoacoustic imaging. Additionally, we discuss relevant challenges and future development prospects.

Keywords: cancer theranostics; imaging agents; molecular imaging; pH (low) insertion peptide.

Figure 1

Interaction between pHLIP and cell membrane.

Figure 2

Preparation (A) and in vivo imaging (B) of pH-anchor gadolinium-based nanoparticles. Reprinted from [41] under the CC BY-NC-ND license.

Figure 3

The imaging route of pH-triggered delivery of magnetic nanoparticles conjugated with pH (low) insertion peptide. Reprinted from [47]. Copyright 2022 Elsevier.