Preventing invasive prostate cancer

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Abstract: Cell motility is required for in situ cancer to form invasive primary prostate cancer (PCa). Inhibiting motility would intercept formation of invasive cancer. Until now it has not been possible to selectively inhibit motility. We have discovered a precision acting first-in-class agent, KBU2046. It selectively inhibits motility, has a wide therapeutic window, has led us to uncover heretofore unknown regulatory pathways, targets those pathways, performs well in GLP grade IND enabling studies, and opens up new high value innovative concepts for cancer prevention-interception. Studies support the hypothesis that KBU2046 is an effective cancer interception agent that operates through a novel mechanism, and that it and the pathways it modulates will have high potential for inhibiting the development of invasive cancer, which in turn has lethal potential. Aim 1. Identify and validate KBU2046’s pharmacologic binding site. In silico, biophysical and biochemical studies suggest that KBU2046 binds at the protein-protein interface between HSP90β and CDC37 and selectively decreases binding to Raf1. Using KBU2046-based photo-crosslinkable probes and proteolysis targeting chimeras (PROTACs), coupled to chemo-proteomic approaches and bioinformatic analysis, studies will identify and validate KBU2046 binding sites in the cellular milieu. Aim 2. Characterize the signaling pathway by which Raf1 regulates the motility of human prostate cells. We show KBU2046 decreases phosphorylation of ser338 on Raf1’s activation motif, that downstream regulation of motility is mediated through a novel pathway wherein Raf1 forms a complex with the actin binding protein, L- plastin (LCP1), while mass spectrometer (MS) proteomic / bioinformatic analysis demonstrates primary effects on cell motility proteins. Studies will examine this pathway in at risk human prostate cells, will use Raf1 active/inactive constructs, similarly engineer LCP1 constructs, probe signaling through orthogonal analytics, profile effects on protein signature using MS, and will examine the role of individual pathway members on cell motility and KBU2046 efficacy. Aim 3. Evaluate targeting motiliy in clinically relevant models of human disease. In the RapidCaP transgenic model, codeletion of Pten and p53 induces in situ→invasive→metastatic PCa. It supports treatment before versus after development of in situ lesions, allowing us to examine prevention and interception efficacy, respectively, for inhibiting formation of invasive cancer. Using primary cells from our prostate rapid autopsy program (RAP), we show mechanistically relevant responsiveness to KBU2046. Primary cells and resultant organoids provide a unique opportunity to examine efficacy in clinically relevant models. RapidCaP and RAP tissues will be interrogated at molecular and functional levels to examine effects of KBU2046. Impact. Investigators seek to advance the innovative concept that cell motility is an important cancer prevention-interception target. It has applicability to many cancer types.