Pharmacological inhibition of Mdm2 triggers growth arrest and promotes DNA breakage in mouse colon tumors and human colon cancer cells

Abstract

The p53 tumor suppressor protein performs a number of cellular functions, ranging from the induction of cell cycle arrest and apoptosis to effects on DNA repair. Modulating p53 activity with Mdm2 inhibitors is a promising approach for treating cancer; however, it is presently unclear how the in vivo application of Mdm2 inhibitors impact the myriad processes orchestrated by p53. Since approximately half of all colon cancers (predominately cancers with microsatellite instability) are p53-normal, we assessed the anticancer activity of the Mdm2 inhibitor Nutlin-3 in the mouse azoxymethane (AOM) colon cancer model, in which p53 remains wild type. Using a cell line derived from an AOM-induced tumor, we found that four daily exposures to Nutlin-3 induced persistent p53 stabilization and cell cycle arrest without significant apoptosis. A four day dosing schedule in vivo generated a similar response in colon tumors; growth arrest without significantly increased apoptosis. In adjacent normal colon tissue, Nutlin-3 treatment reduced both cell proliferation and apoptosis. Surprisingly, Nutlin-3 induced a transient DNA damage response in tumors but not in adjacent normal tissue. Nutlin-3 likewise induced a transient DNA damage response in human colon cancer cells in a p53-dependent manner, and enhanced DNA strand breakage and cell death induced by doxorubicin. Our findings indicate that Mdm2 inhibitors not only trigger growth arrest, but may also stimulate p53’s reported ability to slow homologous recombination repair. The potential impact of Nutlin-3 on DNA repair in tumors suggests that Mdm2 inhibitors may significantly accentuate the tumoricidal actions of certain therapeutic modalities.

Carnosol induces apoptosis through generation of ROS and inactivation of STAT3 signaling in human colon cancer HCT116 cells

“…Pharmacological inhibition of Mdm2 activates p53 and induces growth arrest in mouse colon tumor and human colon cancer cells (29). The inhibition of Mdm2 expression and concomitant increase in p53 expression by carnosol, thus, suggest that carnosol may induce apoptosis by inducing p53 expression.…”

Identification of novel compounds that enhance colon cancer cell sensitivity to inflammatory apoptotic ligands

“…67 The role of TNFR1 is colon cancer development is consistent with the finding that TNFR1 null mice are more sensitive to tumor formation than wild type animals (in the AOM/DSS model). 68 Although 71 Following background subtraction, both DAPI and immunofluorescent images were converted to binary using the convert to mask function. To remove any false positive signal, a binary image of the colocalized points was generated using the colocalization plugin of Bourdoncle (http://rsbweb.nih.gov/ij/ plugins/colocalization.html).…”

Novel Piperazine-based Compounds Inhibit Microtubule Dynamics and Sensitize Colon Cancer Cells to Tumor Necrosis Factor-induced Apoptosis

“…Images were acquired using a Nikon A1R confocal microscope (version 2.11; Nikon Instruments Inc.) and NISElements Advanced Research Software (version 4.13.01, build 916; Nikon Instruments Inc.). Quantification of immunostaining was performed using ImageJ image analysis software as described previously (20). Following background subtraction and image stacking, both DAPI and immunofluorescence images were merged.…”