Abstract 1621: The proprotein convertase PCSK1 is a novel drug target in alveolar soft part sarcoma (ASPS)

Abstract

Abstract Proprotein convertases (PCs) are a family of calcium-dependent serine endoproteases which mediate the proteolytic cleavage, at pairs of dibasic amino acids, of many precursor proteins, including growth factors and pro-hormones, into their functionally active forms. One family member, PCSK1, was identified as a potential therapeutic target in ASPS. This was based on gene expression profiling of 4 primary and 3 metastatic ASPS tumors (BMC Cancer 9:22, 2009). Affymetrix 133 Plus 2 arrays revealed that PCSK1, but not PCSK2 or furin, was significantly up-regulated (range 18.6 to 131 fold) relative to universal RNA, a multi-organ pool of non-tumor RNA's. PCSK1 expression was confirmed by immunohistochemistry and Western Blot analysis in patient tumors, in an ASPS xenograft model, and in a cell line developed from the xenograft tumor (ASPS-1; J Pediatr. Hematol. Oncol., in press 2010) as well as in tumors produced by ASPS-1 in immunocompromised mice. ASPS-1 was utilized, in-vitro, to evaluate a panel of PCSK1 siRNA's, the most potent of these produced a 75% reduction in the PCSK1 RNA transcript, reduced expression of PCSK1 protein and produced a 50% reduction in ASPS-1 growth. As part of an effort to develop new therapeutic approaches toward the treatment of ASPS we have implemented a high-throughput screening effort to identify small molecule inhibitors of PCSK1. Utilizing recombinant PCSK1 and the fluorescent substrate (Pyr-Arg-Thr-Lys-Arg-MCA) a high-throughput screen of a small molecule library (∼15 K compounds) was initiated. Results of a pilot screen of ∼2400 compounds at concentrations ranging from 0.1 to 100 uM yielded several inhibitors of PCSK1 which were retested in a 20 concentration assay to confirm activity. Preliminary analysis of structure-activity relationships identified several active inhibitor chemotypes, comparable in potency to the known peptide PCSK1 inhibitor, Ac-Leu-Leu-Arg-Val-Lys-Arg-NH2, containing aryl groups linked by aliphatic chains containing peptide bonds. Such compounds may act as substrate mimetic inhibitors and will be further evaluated for inhibition of growth of ASPS-1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1621. doi:10.1158/1538-7445.AM2011-1621