P53-null Colon Cancer Cells Research Articles

Anticancer effect of AZD2461 PARP inhibitor against colon cancer cells carrying wt or dysfunctional p53

Colon cancer is one of the most common cancers, currently treated with traditional chemotherapies or alternative therapies. However, these treatments are still not enough effective and induce several side effects, so that the search of new therapeutic strategies is needed. The use of Poly-(ADP-ribose)-polymerase (PARP) inhibitors, although originally approved against BRCA-1 or BRCA-2 mutated cancers, has been extended, particularly in combination with other treatments, to cure cancers that do not display defects in DNA repair signaling pathways. The role of p53 oncosuppressor in the regulating the outcome of PARP inhibitor treatment remains an open issue. In this study, we addressed this topic by using a well-tolerated PARP 1/2/3 inhibitor, namely AZD2461, against colon cancer cell lines with different p53 status. We found that AZD2461 reduced cell proliferation in wtp53 and p53−/− cancer cells by increasing ROS and DNA damage, while R273H mutant (mut) p53 counteracted these effects. Moreover, AZD2461 improved the reduction of cell proliferation by low dose radiation (IR) in wtp53 cancer cells, in which a down-regulation of BRCA-1 occurred. AZD2461 did not affect cell proliferation of mutp53 colon cancer cells also in combination with low dose radiation, suggesting that only wt p53 or p53 null colon cancer cells could benefit AZD2461 treatment.

Cytotoxicity of Frutalin on Distinct Cancer Cells Is Independent of Its Glycosylation.

Frutalin is a plant lectin with beneficial immunobiological action, although the access to its active form is still restricted. Moreover, there is a knowledge gap on isoform activity and glycosylation impact on its bioactivity, and recombinant production protocols were seen as ineffective. Here, a simpler and faster production and purification protocol was developed, attaining a yield of purified frutalin 3.3-fold higher than that obtained previously. Hemagglutination assays confirmed that this frutalin isoform could not agglutinate rabbit erythrocytes, while maintaining the native tetrameric structure, as indicated by DLS analysis, and strong interaction with methyl-alpha-galactose, in fluorescence spectroscopy studies. The cytotoxicity of the recombinant frutalin isoform was shown in a broad panel of human cancer cells: colon (HCT116), melanoma (A375), triple-negative breast cancer (MDA-MB-231), and ovarian (IGROV-1). Treatment with 8.5–11.8 μM TrxFTL reduced proliferation of all cancer cells to half in 48 h. This anti-proliferative effect encompasses the p53 pathway since it was significantly reduced in p53-null colon cancer cells (HCT116 p53−/−; GI50 of 25.0 ± 3.0 μM), when compared to the isogenic p53-positive cells (HCT116 p53+/+; GI50 of 8.7 ± 1.8 μM; p < 0.002). This recombinantly produced frutalin isoform has relevant cytotoxic effect and its biological activity is not dependent on glycosylation. The developed E. coli production and purification protocol generates high yield of non-glycosylated frutalin isoform with potent cytotoxic activity, enabling the development of novel anticancer p53-targeting therapies.

P53-dependent autophagic degradation of TET2 modulates cancer therapeutic resistance.

Tumor cells with p53 inactivation frequently exhibit chemotherapy resistance, which poses a longstanding challenge to cancer treatment. Here we unveiled a previously unrecognized role of TET2 in mediating p53-loss induced chemotherapy resistance in colon cancer. Deletion of TET2 in p53KO colon cancer cells enhanced DNA damage and restored chemotherapy sensitivity. By taking a two-pronged approach that combined pharmacological inhibition with genetic depletion, we discovered that p53 destabilized TET2 at protein level by promoting its autophagic degradation. At the molecular level, we further revealed a physical association between TET2 and p53 that facilitated the nucleoplasmic shuttling of TET2, as well as its recruitment to the autophagosome for degradation. Our study has unveiled a functional interplay between TET2 and p53 during anti-cancer therapy. Our findings establish the rationale for targeting TET2 to overcome chemotherapy resistance associated with mutant p53 tumors.

Enhancement of 5-FU sensitivity by the proapoptotic rpL3 gene in p53 null colon cancer cells through combined polymer nanoparticles.

Colon cancer is one of the leading causes of cancer-related death worldwide and the therapy with 5-fluorouracil (5-FU) is mainly limited due to resistance. Recently, we have demonstrated that nucleolar stress upon 5-FU treatment leads to the activation of ribosome-free rpL3 (L3) as proapoptotic factor. In this study, we analyzed L3 expression profile in colon cancer tissues and demonstrated that L3 mRNA amount decreased with malignant progression and the intensity of its expression was inversely related to tumor grade and Bcl-2/Bax ratio. With the aim to develop a combined therapy of 5-FU plus plasmid encoding L3 (pL3), we firstly assessed the potentiation of the cytotoxic effect of 5-FU on colon cancer cells by L3. Next, 10 μM 5-FU and 2 μg of pL3 were encapsulated in biocompatible nanoparticles (NPs) chemically conjugated with HA to achieve active tumor-targeting ability in CD44 overexpressing cancer cells. We showed the specific intracellular accumulation of NPs in cells and a sustained release for 5-FU and L3. Analysis of cytotoxicity and apoptotic induction potential of combined NPs clearly showed that the 5-FU plus L3 were more effective in inducing apoptosis than 5-FU or L3 alone. Furthermore, we show that the cancer-specific chemosensitizer effect of combined NPs may be dependent on L3 ability to affect 5-FU efflux by controlling P-gp (P-glycoprotein) expression. These results led us to propose a novel combined therapy with the use of 5-FU plus L3 in order to establish individualized therapy by examining L3 profiles in tumors to yield a better clinical outcomes.

The Role of Autophagic Cell Death and Apoptosis in Irinotecan-treated p53 Null Colon Cancer Cells

The roles of autophagic cell death and apoptosis induced by topoisomerase inhibitor irinotecan in colon cancer cells with deleted p53 were investigated during 48 h. We report that irinotecan-dependent cytotoxicity and proapoptotic activity were reduced in the present model while autophagy levels significantly increased. Upon p53 transfection, cell demise rates increased, with cells bearing the features of apoptosis and autophagic cell death. The subsequent studies into mechanisms of cell death process revealed the important role of Bax in mediating mitochondrial and lysosomal leakage which might serve as leading signals for both apoptosis and autophagic cell death. These results suggest that different modes of cell death in p53 null colon cancer cells treated with cytostatics (irinotecan) may be activated simultaneously. Moreover, their interactions possibly occur at several stages and aren't mutually exclusive. This might thus lead to a potential synergism with interesting therapeutic ramifications.

A kinase-directed RNAi screen identifies GSK-3b/a as a target to overcome drug resistance of p53-null colon cancer cells

Abstract Evasion from chemotherapy-induced apoptosis strongly contributes to drug resistance and tumor relapse. In particular, p53 loss renders colon carcinoma cells resistant to 5-fluorouracil-induced apoptosis. We have used the 5-fluorouracil-resistant HCT116p53KO colon carcinoma cell line and a kinase-directed retroviral shRNA library to identify kinases whose inactivation reverts resistance to drug-induced apoptosis. In this way we have identified 29 kinases whose downregulation abolished colony growth after 5-fluorouracil treatment. Silencing of these kinases in other drug-resistant p53-null colon cell lines also abolished cellular growth, suggesting that the effect is independent of the genetic background. We focused on GSK-3 since by tissue microarray we found that GSK-3 is overexpressed/activated in tumoral biopsies of infiltrating and invasive colon carcinomas. We demonstrated that GSK-3 silencing in different colon carcinoma cell lines reverts resistance not only to 5-fluorouracil, but also to oxaliplatin and the 2 drugs used in combination. Interestingly, we found that 5-fluorouracil-treated p53-null GSK-3-depleted colon carcinoma cells undergo caspase-independent but PARP-dependent and tBid- and AIF-mediated cell death. Therefore, we propose that GSK-3 is an excellent potential target for the development of anti-cancer therapy. Our results suggest that inhibitors of GSK-3 can be used in combination with chemotherapy to kill cancer cells unable to trigger caspase-dependent apoptosis.

An ARF/CtBP2 complex regulates BH3-only gene expression and p53-independent apoptosis

The alternative reading frame (ARF) tumor suppressor exerts both p53-dependent and p53-independent functions. The corepressor C-terminal binding protein (CtBP) interacts with ARF, resulting in proteasome-mediated degradation of CtBP. ARF can induce apoptosis in p53-null colon cancer cells, in a manner dependent on ARF interaction with CtBP. Bik was uniquely identified in an apoptotic gene array as coordinately upregulated in colon cancer cells after either CtBP2 knockdown or ARF overexpression. Validating the array findings, ARF induced Bik mRNA and protein expression, and this activity required an intact CtBP binding domain. Apoptosis induced by CtBP deficiency was substantially impaired when Bik expression was simultaneously silenced. An analysis of the Bik promoter revealed binding sites for the CtBP-interacting basic Kruppel-like factor (BKLF). A Bik promoter luciferase reporter was repressed by BKLF and CtBP2, and ARF reversed CtBP-associated repression. Chromatin immunoprecipitation analyses showed that CtBP was recruited to the Bik promoter largely by BKLF. Expression profiling of BH3-only gene expression in ARF-expressing or CtBP-deficient cells revealed that Bik was uniquely regulated by ARF/CtBP in colon cancer cells, whereas additional BH3-only proteins (Bim, Bmf) showed CtBP-dependent repression in osteosarcoma cells. ARF antagonism of CtBP repression of Bik and other BH3-only genes may have a critical role in ARF-induced p53-independent apoptosis and tumor suppression.