[Recent advances in mutant p53 and novel personalized strategies for cancer therapy]

Identification of a new member of Mortaparib class of inhibitors that target mortalin and PARP1

Mortalin, a heat shock family protein enriched in cancer cells, is known to inactivate tumor suppressor protein p53. Abrogation of mortalin-p53 interaction and reactivation of p53 has been shown to trigger growth arrest/apoptosis in cancer cells and hence, suggested to be useful in cancer therapy. In this premise, we earlier screened a chemical library to identify potential disruptors of mortalin-p53 interaction, and reported two novel synthetic small molecules (5-[1-(4-methoxyphenyl) (1,2,3,4-tetraazol-5-yl)]-4-phenylpyrimidine-2-ylamine) and (4-[(1E)-2-(2-phenylindol-3-yl)-1-azavinyl]-1,2,4-triazole) called Mortaparib and Mortaparib^Plus, respectively. These compounds were shown to possess anticancer activity that was mediated through targeting mortalin and PARP1 proteins, essential for cancer cell survival and proliferation. Here, we report characterization of the third compound, {4-[(4-amino-5-thiophen-2-yl-1,2,4-triazol-3-yl)sulfanylmethyl]-N-(4-methoxyphenyl)-1,3-thiazol-2-amine}, isolated in the same screening. Extensive computational and molecular analyses suggested that the new compound has the capability to interact with mortalin, p53, and PARP1. We provide evidence that this new compound, although required in high concentration as compared to the earlier two compounds (Mortaparib and Mortaparib^Plus) and hence called Mortaparib^Mild, also downregulates mortalin and PARP1 expression and functions in multiple ways impeding cancer cell proliferation and migration characteristics. Mortaparib^Mild is a novel candidate anticancer compound that warrants further experimental and clinical attention.

Comparative computational and experimental analyses of some natural small molecules to restore transcriptional activation function of p53 in cancer cells harbouring wild type and p53Ser46 mutant

Genetic mutations in p53 are frequently associated with many types of cancers that affect its stability and activity through multiple ways. The Ser46 residue present in the transactivation domain2 (TAD2) domain of p53 undergoes phosphorylation that blocks its degradation by MDM2 and leads to cell cycle arrest/apoptosis/necrosis upon intrinsic or extrinsic stresses. On the other hand, unphosphorylated p53 mutants escape cell arrest or death triggered by these molecular signaling axes and lead to carcinogenesis. Phosphorylation of Ser in the TAD2 domain of p53 mediates its interactions with transcription factor p62, yielding transcriptional activation of downstream pro-apoptotic genes. The p53 phosphorylation causes string-like elongated conformation that increases its binding affinity with the PH domain of p62. On the other hand, lack of phosphorylation causes helix-like motifs and low binding affinity to p62. We undertook molecular simulation analyses to investigate the potential of some natural small molecules (Withanone (Wi-N) & Withaferin-A (Wi-A) from Ashwagandha; Cucurbitacin-B (Cuc-B) from bitter Cucumber; and Caffeic acid phenethyl ester (CAPE) and Artepillin C (ARC) from honeybee propolis) to interact with p62-binding region of p53 and restore its wild-type activity. We found that Wi-N, Wi-A, and Cuc-B have the potential to restore p53-p62 interaction for phosphorylation-deficient p53 mutants. Wi-N, in particular, caused a reversal of the α-helical structure into an elongated string-like conformation similar to the wild-type p53. These data suggested the use of these natural compounds for the treatment of p53^Ser46 mutant harbouring cancers. We also compared the efficiency of Wi-N, Wi-A, Cuc-B, CAPE, and ARC to abrogate Mortalin-p53 binding resulting in nuclear translocation and reactivation of p53 function and provide experimental evidence to the computational analysis. Taken together, the use of these small molecules for reactivation of p53 in cancer cells is suggested.

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Wild type p53 (p53^WT) and its mutant form (p53^S46PΔ) are associated with multiple cancers.

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Natural compounds serve as a potential mediator to restore the function of p53 in wild type and Ser46 phosphor mutant.

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In-silico analysis suggested that Wi-A, Wi-N, and Cuc-B are stronger inhibitors of p53 -mortalin interaction.

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These entities could also bind to p53^S46PΔ and mimic the phosphorylated conformation, suggesting reactivation of p53^WT.

[Role of ovarian tumor stem-like cells sorted from human epithelial ovarian cancer SKOV3 cells in vasculogenic mimicry formation]

OBJECTIVE

To isolate tumor stem-like cells from human epithelial ovarian cancer SKOV3 cells and explore their role in the formation of vascularization mimicry (VM).

METHODS

SKOV3 cells were passaged to the 7th generation by suspension culture in serum-free medium, and the percentages of CD133- and CD117-positive cells in the 1st, 3rd, 5th and 7th generations were analyzed using flow cytometry. The proliferative activity of the cells sorted from the 7th generation SKOV3 cells was assessed with colony formation assay. A three-dimensional cell culture model was established to compare the ability of VM formation between the sorted cells and the parental SKOV3 cells. The expression levels of matrix metalloproteinases-2 (MMP-2) and MMP-9 in the two groups were detected using real-time PCR and Western blotting.

RESULTS

Some SKOV3 cells formed typical cell spheres with suspension growth in serum-free medium and were passaged to the 7th generation. Flow cytometry revealed that the percentage of CD133-positive cells increased with cell passaging. The cloning efficiency of the sorted cells was significantly higher than that of the parental SKOV3 cells (50.33% vs 5.33%, P < 0.001). The VM formation ability of the sorted cells was stronger than that of the parental SKOV3 cells in the three-dimensional cell culture system. RT-PCR and Western blotting showed that the expression levels of MMP-2 and MMP-9 were significantly higher in the 7th passage cells than in the parental cells (P < 0.05).

CONCLUSIONS

The sorted cells from SKOV3 cells cultured in serum-free medium exhibit biological properties of tumor stem cells with strong VM formation ability, suggesting their role in VM formation.

Association of p53 codon 72 polymorphism with susceptibility to hepatocellular carcinoma in a Chinese population from northeast Sichuan

The p53 tumor suppressor gene is key in tumor development and progression, and the single nucleotide polymorphism (SNP) of the p53 gene codon 72 (p53Arg/Pro) changes the structure of the protein. In addition, it affects its activity, which may affect cancer risk. The aim of the present study was to investigate the association between p53 codon 72 polymorphism and susceptibility to hepatocellular carcinoma (HCC) in a Chinese population from northeast Sichuan. A total of 342 HCC patients and 347 non-cancer control subjects were recruited, and the polymorphism of p53 codon 72 was measured by TaqMan^® minor groove binder fluorescent quantitative polymerase chain reaction assay. The distribution frequency of p53 sites of arginine (Arg)/Arg, Arg/proline (Pro), Pro/Pro were 18.4, 48.8 and 32.8% in the control group, as compared with 18.7, 49.9 and 31.4% in the case group, which indicated that there was no difference between two groups (χ²=0.14; P=0.93). Upon further stratification with smoking, alcohol consumption, gender and hepatitis B virus (HBV) infection, no risk increasing genotype was identified. However, interactions between p53 codon 72 SNP and smoking, alcohol consumption and HBV infection may increase the risk of HCC [smoking odds ratio (OR), 2.00; 95% confidence interval (CI), 1.21-3.29; alcohol consumption OR, 1.87; 95% CI, 1.08-3.26; HBV infection OR, 1.84; 95% CI, 1.10-3.08]. No significant association was identified between p53 codon 72 polymorphism and HCC, and it may not have an independent effect on the susceptibility to HCC in a Chinese population from northeast Sichuan. However, interaction between genetic factors and environment exposure significantly increased the risk of HCC.