Recent advances in peptidomics have enabled the identification of previously uncharacterized peptides. However, sequence information alone does not allow us to identify candidates for bioactive peptides. To increase an opportunity to discover bioactive peptides, we have focused on C-terminal amidation, a post-translational modification shared by many bioactive peptides. We analyzed peptides secreted from human medullary thyroid carcinoma TT cells that produce amidated peptides, and we identified two novel amidated peptides, designated neuroendocrine regulatory peptide (NERP)-1 and NERP-2. NERPs are derived from distinct regions of the neurosecretory protein that was originally identified as a product of a nerve growth factorresponsive gene in PC12 cells. Mass spectrometric analysis of the immunoprecipitate using specific antibodies as well as reversed phase-high performance liquid chromatography coupled with radioimmunoassay analysis of brain extract demonstrated the endogenous presence of NERP-1 and NERP-2 in the rat. NERPs are abundant in the paraventricular and supraoptic nuclei of the rat hypothalamus and colocalized frequently with vasopressin but rarely with oxytocin. NERPs dose-dependently suppressed vasopressin release induced by intracerebroventricular injection of hypertonic NaCl or angiotensin II in vivo. NERPs also suppressed basal and angiotensin II-induced vasopressin secretion from hypothalamic explants in vitro. Bioactivity of NERPs required C-terminal amidation. Anti-NERP IgGs canceled plasma vasopressin reduction in response to water loading, indicating that NERPs could be potent endogenous suppressors of vasopressin release. These findings suggest that NERPs are novel modulators in body fluid homeostasis.

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Protein Kinase CK2 is a serine-threonine kinase frequently deregulated in many human tumors. Here, we hypothesized that a peptide binder to the CK2 phosphoacceptor site could exhibit anticancer properties in vitro, in tumor animal models, and in cancer patients. By screening a random cyclic peptide phage display library, we identified the CIGB-300 (formerly P15-Tat), a cyclic peptide which abrogates the CK2 phosphorylation by blocking recombinant substrates in vitro. Interestingly, synthetic CIGB-300 led to a dose-dependent antiproliferative effect in a variety of tumor cell lines and induced apoptosis as evidenced by rapid caspase activation. Importantly, CIGB-300 elicited significant antitumor effect both by local and systemic administration in murine syngenic tumors and human tumors xenografted in nude mice. Finally, we performed a First-in-Man trial with CIGB 300 in patients with cervical malignancies. The peptide was found to be safe and well tolerated in the dose range studied. Likewise, signs of clinical benefit were clearly identified after the CIGB-300 treatment as evidenced by significant decrease of the tumor lesion area and histological examination. Our results provide an early proof-of-principle of clinical benefit by using an anti-CK2 approach in cancer. Furthermore, this is the first clinical trial where an investigational drug has been used to target the CK2 phosphorylation domain.

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