Chaperonin Containing TCP-1 Protein Level in Breast Cancer Cells Predicts Therapeutic Application of a Cytotoxic Peptide

Abstract

Purpose: Metastatic disease is a leading cause of death for patients with breast cancer, driving the need for new therapies. CT20p is a peptide previously discovered by our group that displays cancer-specific cytotoxicity. To design the optimal therapeutic use of the peptide, we identified the intracellular target of CT20p in breast cancer cells, correlating expression patterns of the target with susceptibility to CT20p. Experimental Design: Using polymeric nanoparticles to deliver CT20p, we assessed cytoskeletal changes, cell migration, adhesion, and viability in cells treated with the peptide. Protein pull-down experiments, coupled to mass spectrometry, enabled identification of the peptide's intracellular target. Biochemical and histologic techniques validated target identity in human cell lines and breast cancer tissue microarrays and revealed susceptibility patterns to CT20p. Results: Chaperonin containing TCP-1 (CCT) was identified as the intracellular target of CT20p. Cancer cells susceptible to CT20p had increased CCT, and overexpression of CCTβ, a subunit of the CCT complex, enhanced susceptibility to CT20p. Susceptible cells displayed reduced tubulin, a substrate of CCT, and inhibition of migration upon CT20p treatment. CCTβ levels were higher in invasive ductal carcinomas than in cancer adjacent tissues and increased with breast cancer stage. Decreased breast cancer patient survival correlated with genomic alternations in CCTβ and higher levels of the chaperone. Conclusions: Increased CCT protein in breast cancer cells underlies the cytotoxicity of CT20p. CCT is thus a potential target for therapeutic intervention and serves as a companion diagnostic to personalize the therapeutic use of CT20p for breast cancer treatment. Clin Cancer Res; 22(17); 4366–79. ©2016 AACR.

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“…responsible for folding 5-10% of the cell proteome, and it is the essential chaperone for folding actin and tubulin into their native forms. CCT inhibition results in the changes in cytoskeletal dynamics and inhibition of actin and tubulin polymerization that we observed in CT20p-treated cells 21-22. Our studies and that of others have reported that CCT is overexpressed in cancer cells and could be an indicator of cancer progression and metastasis 23-26, which makes it a novel target for cancer therapeutics.…”

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“…Recent work has implicated disruption of the cytoskeleton in the efficacy of CT20, a peptide demonstrating selective cancer‐cell toxicity . Importantly, TRiC has been identified as the target of CT20; TRiC overexpression in breast cancer cell lines is required for increased susceptibility to CT20 …”

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“…another class of protein-folding complexes, called chaperonins, gained interest with the recognition that cancer cells highly express these mediators of protein-folding [14][15][16][17][18][19][20][21][22][23] . The cytosolic, eukaryotic chaperonin-containing TCP-1 (CCT) is an emerging player in neoplastic transformation with potential for development as a novel diagnostic marker and therapeutic target.…”

“…Our lab discovered a CCT inhibitor called CT20p that kills cancer cells in a CCT-dependent manner. Cancer cells in which CCT was inhibited were resistant to CT20p killing, while cells in which CCT was increased were susceptible 14,16 . However, the complexity of CCT, with its multiple subunits, and the lack of a full understanding of CCT substrate selectivity in vivo, are some of the challenge that hinder the development of promising therapeutics like CT20p.…”