Imaging calreticulin for early detection of immunogenic cell death during anticancer treatment

Abstract

Surface-exposed calreticulin (ecto-CRT) is a well-known ‘eat-me’ signal exhibited by dying cells that contributes to their recognition and destruction by the immune system. We assessed the use of a CRT-specific binding peptide for imaging ecto-CRT during immunogenic cell death and its utility for the early prediction of treatment response. Methods: A synthetic CRT-specific peptide KLGFFKR (CRTpep) was labeled with fluorescein isothiocyanate or ¹⁸F and characteristics of ecto-CRT was evaluated in colon cancer cell line in vitro and in vivo. Results: In vitro flow cytometry, immunofluorescence staining, and in vivo micro positron emission tomography imaging results showed that CRTpep detected pre-apoptotic cells treated with immunogenic drugs or radiation, but not those treated with the non-immunogenic drug or a non-therapeutic dose of immunogenic drug. Conclusion: The present results indicate that the CRT-specific peptide would enable the prediction of therapeutic response, thereby facilitating early decisions regarding the continuation or discontinuation of immunogenic treatment.