1. PK11007, a 2-sulfonylpyrimidine molecule, was able to inhibit cell division in cancer cell lines both with and without p53 mutations.
2. PK11007 was able to induce cell death in cancer cell lines through various mechanisms.
Evidence Rating Level: 2 (Good)
Study Rundown: Thiol alkylators are compounds that stabilize p53, a tumor suppressor protein typically mutated in cancer cells. 2-sulfonylpyrimidines are a class of thiol alkylators that were discovered in this study. One compound in particular, PK11007, was extensively tested to determine its effect on various cancer cell lines.
Initially, it was confirmed that PK11007 was able to increase the thermal stability of p53. This compound was then tested on p53 wild type, mutant, and knockout cancer cell lines to determine its effect both dependent and independent of a functional p53 protein. PK11007 reduced the viability of each of these cell lines, with those containing a mutant p53 protein demonstrating the largest reduction in viability. This data demonstrated that although this compound is able to work through p53, this was not the sole mechanism involved. Because of this, various other mechanisms of action involved in cell death were tested. First, p53 target genes were assessed and found to be upregulated upon drug exposure, demonstrating partial restoration in the function of mutant p53 proteins. In addition, PK11007 upregulated proteins involved in the unfolded protein response (UPR) pathway, a cell stress response that inhibits the production of misfolded proteins. PK11007 also increased the levels of reactive oxygen species (ROS), compounds known to kill cancer cells and directly increase p53 levels.
PK11007 was found to be an efficacious drug on cancer cells both with and without p53 mutations, showing its broad potential efficacy for various cancers. Although animal studies will need to be performed before clinical trials can be implemented, these new compounds have the potential to become therapeutic agents for a variety of cancers.
In-Depth [in vitro study]: Differential scanning fluorimetry was used to measure the thermal stability of p53. The maximum melting temperature of p53 following the introduction of PK11007 was maintained at around 3 Kelvins, whereas the melting temperatures in response to other agents were between 0.3 and 3 K. This demonstrated the increased stability of p53 in the presence of PK11007.
PK11007 was then tested on 4 wild type, 4 mutant, and 1 p53 knockout cancer cell line. After incubating these cell lines for 24 hours with increasing amounts of PK11007, mutant p53 cell lines showed the greatest decrease in survival. The wild type and knockout cell lines demonstrated reduced cell viability, but only at higher concentrations of 60 and 120 µM of the drug. Due to the response of all cell lines to PK11007, this drug is able to function both dependently and independently of a functionally stable p53 protein.
The effect of PK11007 on protein expression was assessed to determine specific mechanisms through which this drug is able to reduce cell viability. Using Western blotting, it was found that PK11007 upregulated protein levels of a variety of p53 target genes (p21, MDM2, and PUMA). Additionally, levels of XBP-1 and CHOP, proteins involved in the UPR pathway, were upregulated. Finally, the generation of ROS was tested. After incubating the cells with PK11007 for 2 hours, ROS levels were significantly increased in all cell lines (p<0.05).
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