CT20p as a therapeutic for lung cancer with elevated chaperonin containing TCP1 (CCT) expression levels.

Abstract

e23163 Background: We previously reported, in breast cancer, the effectiveness of a novel therapeutic peptide called CT20p that displays cancer-selective cytotoxicity. CT20p targets for inhibition a macromolecular complex called Chaperonin-Containing TCP-1 (CCT) that is responsible for folding actin and tubulin and other proteins, like STAT3, into their active forms. CCT is composed of 8 subunits (CCT1-8) that are highly conserved among species. In breast cancer cases, we found that the genes for CCT were frequently amplified (CCT2), upregulating the chaperonin’s activity, which correlated with decreased patient survival. Methods: To determine whether CCT is active in other cancers and thereby a broad therapeutic target, we examined the protein levels of CCT2 in colon, liver, prostate and lung cancer by immunohistochemistry (IHC), using human tissue microarrays (TMAs). Genomic data from The Cancer Genome Atlas (TCGA) was used to support IHC findings. Immunoblot probing of three CCT subunits (CCT2, CCT4, CCT5) was performed to determine their relative expression level in five small cell lung cancer (SCLC) cell lines compared to normal lung cells and these cells tested for susceptibility to killing by CT20p. Results: Results of IHC staining for CCT2 were interpreted on a scale of 1 to 4 (with 4 being the strongest staining). We found that with the exception of colon cancer, all cancers expressed high levels of CCT2 with advancing stage. We identified a significant correlation with cancer progression in both small cell lung carcinoma (SCLC) and squamous cell lung carcinoma (SqCLC). While individual levels of the three probed CCT subunits varied amongst the SCLC cell lines, overall CCT expression was higher in the SCLC cells when compared to normal lung cells and correlated with susceptibility to killing by CT20p. Using the TCGA database, CCT gene alterations were detected in clinical lung cancer cases, with amplification of CCT4 gene in SqCLC cases linked to decreased survival. Conclusions: These results indicate that targeted inhibition of CCT through CT20p treatment is a promising treatment approach for those cancers like SCLC that currently lack effective therapeutics to sustain progression-free survival.