Oncogenic and Circadian Effects of Small Molecules Directly and Indirectly Targeting the Core Circadian Clock

Circadian rhythms are essential for controlling the cell cycle, cellular proliferation, and apoptosis, and hence, are tightly linked to cell fate. Disruption of circadian rhythms has been shown to trigger various pathological developments, including cancer. Several recent studies have used a variety of small molecules to affect circadian oscillations, however, their concomitant cellular effects were not assessed. Here, we use five molecules, grouped into direct versus indirect effectors of the circadian clock, to modulate periods in a human osteosarcoma cell line (U2OS), and determined their influences on cellular behaviors, including motility and colony formation. Luciferase reporters, whose expression were driven via Bmal1- and Per2-promoters (positive and negative protein components of the core clock), were used to facilitate the visualization and quantitative analysis of circadian oscillations. We show that all molecules significantly increase or decrease the circadian periods of Bmal1 and Per2 in a dose-dependent manner, but period length does not correlate with the extent of cell migration or proliferation. We observed that only molecules that affected circadian oscillations to a greater extent showed significant influence on cell functions (e.g. motility and colony formation). Because it is important to consider the likelihood of biological effects resulting from non-circadian targets, we also provide a thorough discussion of potential modes of action. Future studies should employ additional compounds that directly target circadian proteins and/or have different circadian effects, and evaluation in other cancer models to determine whether results obtained here remain consistent.\n\nFor Table of Contents Only\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=100 SRC=\"FIGDIR/small/645861v1_fig1u.gif\" ALT=\"Figure 1U\">\nView larger version (25K):\norg.highwire.dtl.DTLVardef@ec8881org.highwire.dtl.DTLVardef@f601f1org.highwire.dtl.DTLVardef@f98f5aorg.highwire.dtl.DTLVardef@3278e1_HPS_FORMAT_FIGEXP M_FIG C_FIG