ITIH5-Derived Polypeptides Covering the VIT Domain Suppress the Growth of Human Cancer Cells In Vitro

Simple Summary ITIH5 has been shown to be an effective tumor and metastasis suppressor which is being lost in various tumor entities including breast, bladder and lung cancer. In the present study a translational approach was pursued to develop truncated polypeptides derived from the full-length ITIH5 protein that are able to mimic its tumor suppressive functions. In fact, it was found that ITIH5 ' s vault protein inter-alpha- trypsin (VIT) domain (approximately 125 amino acids long) can specifically impair the growth of human cancer cells. Thus, our findings highlight polypeptides covering the VIT domain as a basis for the development of novel biological drugs potentially able to reactivate ITIH5 specific tumor-suppressive pathways in human cancers. Oncogenic drivers such as mutated EGFR are the preferred targets in modern drug development. However, restoring the lost function of tumor suppressor proteins could also be a valid approach to combatting cancer. ITIH5 has been revealed as a potent metastasis suppressor in both breast and pancreatic cancer. Here, we show that ITIH5 overexpression in MDA-MB-231 breast cancer cells can also locally suppress tumor growth by 85%, when transplanted into the mammary fat pad of nude mice. For a potential drug development approach, we further aimed to define downsized ITIH5 polypeptides that still are capable of mediating growth inhibitory effects. By cloning truncated and His-tagged ITIH5 fragments, we synthesized two recombinant N-terminal polypeptides (ITIH5(681aa) and ITIH5(161aa)), both covering the ITI heavy chain specific "vault protein inter-alpha-trypsin" (VIT) domain. Truncated ITIH5 variants caused dose-dependent cell growth inhibition by up to 50% when applied to various cancer cell lines (e.g., MDA-MB-231, SCaBER, A549) reflecting breast, bladder and lung cancer in vitro. Thus, our data suggest the substantial role of the ITIH5-specific VIT domain in ITIH5-mediated suppression of tumor cell proliferation. As extracellularly administered ITIH5 peptides mimic the growth-inhibitory effects of the full-length ITIH5 tumor suppressor protein, they may constitute the basis for developing anticancer drugs in the future.