The differential role of the lipid raft-associated protein flotillin 2 for progression of myeloid leukemia.

Lipid raft-associated proteins play a vital role in membrane-mediated processes. The lipid microdomain-associated protein flotillin 2 (FLOT2), which has a scaffolding function, is involved in polarization, as well as in actin cytoskeletal organization of primitive and mature hematopoietic cells and has been associated with different malignancies. However, its involvement in myeloid leukemias is not well studied. Using murine transplantation models, we show here that the absence of FLOT2 from leukemia-initiating cells (LICs) altered the disease course of BCR-ABL1+ chronic myeloid leukemia (CML), but not of MLL-AF9-driven acute myeloid leukemia (AML). While FLOT2 was required for expression of the adhesion molecule CD44 on both CML- and AML-LIC, a defect in the cytoskeleton, cell polarity, and impaired homing ability of LIC was only observed in FLOT2-deficient BCR-ABL1+ compared with MLL-AF9+ cells. Downstream of CD44, BCR-ABL1 kinase-independent discrepancies were observed regarding expression, localization, and activity of cell division control protein 42 homolog (CDC42) between wild-type (WT) and FLOT2-deficient human CML and AML cells. Inhibition of CDC42 by ML141 impaired the homing of CML LIC and, thereby, CML progression. This suggested that alteration of both CD44 and CDC42 may be causative of impaired CML progression in the absence of FLOT2. In summary, our data suggest a FLOT2-CD44-CDC42 axis, which differentially regulates CML vs AML progression, with deficiency of FLOT2 impairing the development of CML.

Combined Treatment with a WNT Inhibitor and the NSAID Sulindac Reduces Colon Adenoma Burden in Mice with Truncated APC.

Adenomatous polyposis coli (APC) truncations occur in many colorectal cancers and are often associated with immune infiltration. The aim of this study was to determine whether a combination of Wnt inhibition with anti-inflammatory (sulindac) and/or proapototic (ABT263) drugs can reduce colon adenomas. Apc min/+ and doublecortin-like kinase 1 (Dclk1)Cre/+ ;Apc fl/fl mice were exposed to dextran sulphate sodium (DSS) in their drinking water to promote the formation of colon adenomas. Mice were then treated with either a Wnt-signaling antagonist pyrvinium pamoate (PP), an anti-inflammatory agent sulindac or proapoptotic compound ABT263 or a combination of PP+ABT263, or PP+sulindac. Colon adenoma frequency, size, and T-cell abundance were measured. DSS treatment resulted in significant increases in colon adenoma number (P < 0.001, n > 5) and burden in Apc min/+ (P < 0.01, n > 5) and Dclk1 Cre/+ ;Apc fl/fl (P < 0.02, n > 5) mice. There was no effect on adenomas following treatment with PP in combination with ABT263. Adenoma number and burden were reduced with PP+sulindac treatment in Dclk1 Cre/+;Apc fl/fl mice (P < 0.01, n > 17) and in Apc min/+ mice (P < 0.001, n > 7) treated with sulindac or PP+sulindac with no detectable toxicity. PP treatment of Apc min/+ mice increased the frequency of CD3+ cells in the adenomas. The combination of Wnt pathway inhibition with sulindac was more effective in Dclk1 Cre/+;Apc fl/fl mice and provides an opportunity for killing Apc-mutant colon adenoma cells, indicating a strategy for both colorectal cancer prevention and potential new treatments for patients with advanced colorectal cancer. Outcomes from the results of this study may be translatable to the clinic for management of FAP and other patients with a high risk of developing colorectal cancer. Significance: Colorectal cancer is one of the most common cancers worldwide with limited therapeutic options. APC and other Wnt signaling mutations occur in the majority of colorectal cancers but there are currently no Wnt inhibitors in the clinic. The combination of Wnt pathway inhibition with sulindac provides an opportunity for killing Apc-mutant colon adenoma cells and suggests a strategy for colorectal cancer prevention and new treatments for patients with advanced colorectal cancer.