Babu Joseph

Wnt Inhibitor Screen Reveals Iron Dependence of β-Catenin Signaling in Cancers

Excessive signaling from the Wnt pathway is associated with numerous human cancers. Using a high throughput screen designed to detect inhibitors of Wnt/β-catenin signaling, we identified a series of acyl hydrazones that act downstream of the β-catenin destruction complex to inhibit both Wnt-induced and cancer-associated constitutive Wnt signaling via destabilization of β-catenin. We found that these acyl hydrazones bind iron in vitro and in intact cells and that chelating activity is required to abrogate Wnt signaling and block the growth of colorectal cancer cell lines with constitutive Wnt signaling. In addition, we found that multiple iron chelators, desferrioxamine, deferasirox, and ciclopirox olamine similarly blocked Wnt signaling and cell growth. Moreover, in patients with AML administered ciclopirox olamine, we observed decreased expression of the Wnt target gene AXIN2 in leukemic cells. The novel class of acyl hydrazones would thus be prime candidates for further development as chemotherapeutic agents. Taken together, our results reveal a critical requirement for iron in Wnt signaling and they show that iron chelation serves as an effective mechanism to inhibit Wnt signaling in humans.

Abstract 156: Screening and characterization of inhibitors of G-protein coupled receptor kinase GRK6 as potential therapeutics for multiple myeloma

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Multiple myeloma (MM) is one of the most common hematological malignancies, but current therapy options are limited to high-dose chemotherapy or high-risk stem-cell transplantation. It is clear that the development of more selective and less toxic treatments for MM is greatly needed. In a recent kinome-wide RNAi study by Tiedemann and colleagues (2010), the G-protein coupled receptor kinase-6 (GRK6) was identified as a critical kinase required for survival of MM cells. This study also suggests that MM cells, but not other cell types, are dependent on GRK6; and that gene silencing by shRNA or siRNA of GRK6, but not other GRKs, results in decreased survival. At present, the G-protein coupled receptor (GPCR) signaling mediated by GRK6 in MM cells is not well understood. Our current research aims to identify the important GPCRs phosphorylated by GRK6 and the signaling proteins/pathways implicated in survival of multiple myeloma cells. Through gene silencing techniques and expression of either the wild-type or kinase-dead form of GRK6 protein, we have determined that a functional GRK6 kinase domain is required for survival of MM cells. We have also demonstrated that the signaling pathway downstream of CXCR4 phosphorylation by GRK6 is defective in cells expressing the kinase-dead GRK6-mutant protein. This loss of signaling by the GRK6-mutant protein was observed for other GPCRs found to be important for survival of MM cells. These findings helped to validate that the kinase domain of GRK6 is a potential target for MM, and spurred the identification of small molecule kinase inhibitors of GRK6. Compounds with high potency in preliminary biochemical assays were screened against MM and non-MM cell lines to evaluate their activity and specificity in vivo. Small molecule inhibition of GRK6 kinase activity is a novel approach to the treatment of MM, as it specifically targets a protein found to be critical for survival of these cells through an unbiased RNAi study. Treatment options for patients with MM are limited and based on our preliminary findings small molecule inhibitors of GRK6 offer an alternative therapeutic approach to the treatment of MM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 156. doi:1538-7445.AM2012-156