P53 Mutant Colon Cancer Cells Research Articles

TRIM29 Reverses Oxaliplatin Resistance of P53 Mutant Colon Cancer Cell.

Background Oxaliplatin is the first-choice chemotherapy method for patients with advanced colon cancer. However, its resistance leads to treatment failure for many patients. In our experiments, we aim to elucidate the associations among TRIM29 protein, mutant P53, and the resistance of colon cancer cells to oxaliplatin. Methods HCT116 and HT-29 cells were cultured and transfected with plasmids pIRES2-ZsGreen1-TRIM29-flag. Western blot and real-time qRT-PCR were utilized to examine the protein and mRNA expressions of TRIM29 and other related markers, respectively. MTT assay was utilized to determine the cell growth rate and generate the inhibition curve. Continuous culture in low-concentration oxaliplatin was conducted to construct oxaliplatin-resistant cell lines. The coimmunoprecipitation method and immunofluorescence detection were used to examine the interaction between TRIM29 and mutant P53 protein in HT29 cells. Results We successfully transfected pIRES2-ZsGreen1-TRIM29-flag into HCT116 and HT29 cells, which were utilized in the whole experiments. TRIM29 significantly increased the sensitivity of P53 mutant colon cancer cell HT29 to oxaliplatin. The oxaliplatin-resistant model of P53 mutant colon cancer cell HT29 was successfully constructed. TRIM29 physically bound with mutant P53 and retained it in the cytoplasm from the nucleus, which inhibited its transcription function of downstream genes such as MDR1. In addition, TRIM29 successfully reversed the resistance of HT29-OX resistant cell model to oxaliplatin. Conclusion In mutant P53 colon cancer cell HT29, TRIM29 greatly increased the sensitivity of HT29 to oxaliplatin and reverse oxaliplatin resistance. The underlying mechanism is TRIM29 may increase the sensitivity of HT29 to oxaliplatin by blocking the transcriptional function of mutant P53, which inhibits the transcription function of its downstream gene such as MDR1.

Phase II study of lamivudine in p53 mutant metastatic colorectal cancer (mCRC).

149 Background: Non-coding repeat RNAs in cancers are pervasive and “mimic” viruses with activation of pattern recognition receptors and the innate immune response. Many repeat RNAs replicate in cancer genomes through a reverse transcriptional intermediate analogous to retroviruses. Nucleoside reverse transcriptase inhibitors (NRTIs) block this retroviral life cycle to increases repeat RNAs in p53 mutant colon cancer cell cancer lines. We initiated a Phase 2 study of lamivudine (3TC) in TP53 mutant mCRC. Methods: Two-stage design with target accrual of 20 patients (pts) in stage 1 and total of 32. Eligibility: pts with p53 mutant refractory mCRC with progression on or intolerance to 5FU, oxaliplatin and irinotecan and anti-EGFR if RAS WT. RNA sequencing was performed on pre-treatment (tx) and on tx biopsy to evaluate for repeat RNA expression and expression of other genes linked to 3TC response/resistance. Radiation was allowed. 9 pts were treated with 3TC 150 mg po bid for 28-day cycles, the maximum FDA approved dose of 3TC in HIV. Subsequent pts were treated at 600 mg po bid, previously tested in P1 trials. Tumor assessments were performed every 8 weeks until documented disease progression by RECIST 1.1 criteria or drug intolerance. Results: 29/32 pts have been treated. Median age: 60 yrs. (27-82) 18 males, 11 females. 2/ 9 (22%) pts on standard 3TC dosing had stable disease (SD) on single agent 3TC with a duration of tx of 169 and 167 days, respectively. Both pts had an initial drop in CEA upon initiation of 3TC. Of the next 20 pts on high dose 3TC, 19 were evaluable. 4 had SD, for 110, 159, 130 and 228+ days. 14 pts had tx-related adverse events (TRAE). 1 pt with a definite Grade 1 TRAE (fatigue). No pts with Grade ≥3 TRAEs. We obtained pre-tx fresh frozen biopsies on 24/29 pts. Of those with SD, 4 had biopsies and differential expression identified significantly higher HSATII repeat RNA in pts with SD compared to PD. There was an association of decreased epigenetic gene expression in HSATII repeat RNA high tumors. Conclusions: This proof-of-concept study demonstrates the safety and activity of single-agent 3TC. Repeat RNA levels appear to correlate with clinical benefit and can be measured in biopsies. Further combination studies and correlatives are planned. Clinical trial information: NCT03144804.

Radiosensitization of Irinotecan is Attributed to G2/M Phase Arrest, Followed by Enhanced Apoptosis Probably Through the ATM/Chk/Cdc25C/Cdc2 Pathway in P53-mutant Colon Cancer Cells

Irinotecan, an analog of camptothecin, the inhibitor of Topoisomerase I, is currently used to treat metastatic colorectal cancer. Camptothecin derivatives were demonstrated to have radiosensitization effects on several kinds of cancer cells. However, few studies have been published in terms of colorectal cancer cell lines. In this study, we try to examine the radiosentization effects of irinotecan on p53 mutant colon cancer lines HT29, SW620 and explore the potential mechanisms. HT29 (radiation-resistant) cells and SW620 (radiation-sensitive) cells were chosen for the following experiments. First, 24h IC50s of irinotecan as a single agent were obtained through drug cytotoxicity tests. Concentrations below 10% IC50 were considered to be combined with radiation. Second, cells were treated with irinotecan (24h) followed by radiation at a dosage gradient, and radiosentization effects of irinotecan were examined through clonogenic assays. Next, cells were divided into four arms: control arm, irinotecan arm, radiation arm and the combined arm. Cell growth curves were obtained through CCK-8 assays. Foci of γH2AX were illustrated through immunofluorescence straining. Cell cycle and apoptosis were examined using Flow Cytometry. Expression of proteins related to DNA damage and repair system and cell cycle were examined through Western Blot. The 24h IC50s of irinotecan were 39.84μg/ml (HT29 95% CI 38.27-41.48) and 96.86μg/ml (SW620 95%CI 89.04-105.4), thus concentrations below 4μg/ml were chosen for the experiments. Clonogenic assays showed that irinotecan had radiosentization effects on HT29 and SW620 cells, and the SERs increased with the increase of concentration (SER= 1.41 for HT29 cells, SER=1.87 for SW620 cells, with irinotecan at 2μg/ml). Compared with the control arm, irinotecan arm and radiation arm, the combined arm had the slowest cell growing rate and the most obvious foci of γH2AX. The combined treatment could result in the most significant G2/M phase arrest and last for more than 24h, followed by the most significant increase of apoptosis. And results of western blot indicated that the expression of proteins related to DNA damage and repair system (Ser1981p-ATM, Ser345p-Chk1, Thr68p-Chk2, γ-H2AX)，cell cycle (Tyr15p-Cdc2, Cyclin B1) increased the most in the combined arm. In addition, we found that the expression of Ser216p-Cdc25C also increased the most in the combined arm, which indicating that irinotecan radiosentized the p53-mutant HT29 and SW620 cells probably through ATM/Chk/Cdc25C/Cdc2 pathway. Irinotecan has radiosensitization effects on HT29 and SW620 cells and the SER increases with the increase of concentration. It attributes to the activation of DNA damage and repair system, leading to significant G2/M phase arrest followed by enhanced apoptosis. And the process is probably through ATM/Chk/Cdc25C/Cdc2 pathway in p53-mutant colon cancer cells.

EP-2309: Irinotecan radiosensitizes p53-mutant colon cancer cells through G2/M arrest followed by apoptosis

EP-2309: Irinotecan radiosensitizes p53-mutant colon cancer cells through G2/M arrest followed by apoptosis

MiR-338-3p confers 5-fluorouracil resistance in p53 mutant colon cancer cells by targeting the mammalian target of rapamycin

Evidence demonstrate that p53 mutations and microRNAs (miRs) are important components of 5-FU resistance in colorectal cancer (CRC). miR-338-3p has been reported associated with cancer prognosis. However whether or not it influences chemotherapy sensitivity and the underlying mechanisms have not been elucidated. Here, three types of human colon cancer cell lines, HT29 (mutant p53), HCT116 (wild-type p53), and HCT116 p53-/- (deficient p53), were treated with 5-FU. We showed that expression of miR-338-3p was correlated with apoptosis and 5-FU resistance in colon cancer cells. Ectopic expression of miR-338-3p conferred resistance to 5-FU in HCT116 cells. Further experiments indicated that miR-338-3p mediated 5-FU resistance through down-regulation of mTOR expression. Moreover, inhibition of miR-338-3p in HT29 and HCT116 p53-/- cells increased their sensitivity to 5-FU treatment. Furthermore, we detected autophagy changes in our experiment because mTOR was known prominently regulating autophagy and the competition between autophagy and apoptosis in response to 5-FU was a mechanism influencing 5-FU sensitivity. Our results reveal a critical and novel role of miR-338-3p in the correlation of 5-FU resistance with p53 status. Moreover, the miR-338-3p inhibitor has the potential to overcome 5-FU resistance in p53 mutant colon cancer cells.

HDAC inhibitors show differential epigenetic regulation and cell survival strategies on p53 mutant colon cancer cells

Besides inactivating tumour suppressor activity in cells, mutations in p53 confer significant oncogenic functions and promote metastasis and resistance to anticancer therapy. A variety of therapies involving genetic and epigenetic signalling events regulate tumorogenesis and progression in such cases. Pharmacological interventions with HDAC inhibitors have shown promise in therapy. This work explores the changes in efficacy of the four HDAC inhibitors SAHA, MS-275, valproic acid and sodium butyrate on a panel of colon cancer cell lines – HCT116 (p53 wt), HCT116 p53-/-, HT29 and SW480 (with mutations in p53). Clonogenic assays, gene profiling and epigenetic expression done on these cells point to p53 dependent differential activity of the 4 HDAC inhibitors which also elevate methylation levels in p53 mutant cell lines. In silico modelling establishes the alterations in interactions that lead to such differential activity of valproic acid, one of the inhibitors considered for the work. Molecular Dynamic simulations carried out on the valproic acid complex ensure stability of the complex. This work establishes a p53 dependent epigenetic signalling mechanism triggered by HDAC inhibition expanding the scope of HDAC inhibitors in adjuvant therapy for p53 mutant tumours.

Efficient Activation of Apoptotic Signaling during Mitotic Arrest with AK301.

Mitotic inhibitors are widely utilized chemotherapeutic agents that take advantage of mitotic defects in cancer cells. We have identified a novel class of piperazine-based mitotic inhibitors, of which AK301 is the most potent derivative identified to date (EC50 < 200 nM). Colon cancer cells arrested in mitosis with AK301 readily underwent a p53-dependent apoptosis following compound withdrawal and arrest release. This apoptotic response was significantly higher for AK301 than for other mitotic inhibitors tested (colchicine, vincristine, and BI 2536). AK301-treated cells exhibited a robust mitosis-associated DNA damage response, including ATM activation, γH2AX phosphorylation and p53 stabilization. The association between mitotic signaling and the DNA damage response was supported by the finding that Aurora B inhibition reduced the level of γH2AX staining. Confocal imaging of AK301-treated cells revealed multiple γ-tubulin microtubule organizing centers attached to microtubules, but with limited centrosome migration, raising the possibility that aberrant microtubule pulling may underlie DNA breakage. AK301 selectively targeted APC-mutant colonocytes and promoted TNF-induced apoptosis in p53-mutant colon cancer cells. Our findings indicate that AK301 induces a mitotic arrest state with a highly active DNA damage response. Together with a reversible arrest state, AK301 is a potent promoter of a mitosis-to-apoptosis transition that can target cancer cells with mitotic defects.

MTORC1 and DNA-PKcs as novel molecular determinants of sensitivity to Chk1 inhibition

BackgroundChk1 inhibitors are currently under clinical evaluation as single agents and in combination with cytotoxic chemotherapy. Understanding determinants of sensitivity and novel combinations is critical for further clinical development. MethodsPotentiation of mTOR inhibitor cytotoxicity by the Chk1 inhibitor V158411 was determined in p53 mutant colon cancer cells. DNA damage response, expression levels of repair proteins, cell cycle effects and the contribution of alternative DSB repair pathways were further evaluated by western blotting and high content analysis. ResultsmTOR inhibitors AZD8055, RAD-001, rapamycin and BEZ235 induced synergistic cytotoxicity with the Chk1 inhibitor V158411 in p53 mutant colon cancer cells. Reduced FANCD2, RAD51 and RPA70, core proteins in homologous recombination repair (HRR) and interstrand crosslink repair (ICLR), following inhibition of mTOR was associated with increased V158411 induced DSBs and caspase 3-independent cell death. Dual mTOR and Chk1 inhibition activated DNA-PKcs. Cells defective in DNA-PKcs exhibited increased resistance to V158411 with Chk1 expression closely correlated to DNA-PKcs expression in various types of cancer. ConclusionsDown regulation of proteins involved in HRR or ICLR by mTOR inhibitors is associated with increased sensitivity of human tumours to Chk1 inhibitors such as V158411. High levels of DNA-PKcs may be a potential biomarker to stratify patients to Chk1 inhibitor therapy alone or in combination with mTOR inhibitors.

γH2AX and Chk1 phosphorylation as predictive pharmacodynamic biomarkers of Chk1 inhibitor-chemotherapy combination treatments.

BackgroundChk1 inhibitors are currently in clinical trials in combination with a range of cytotoxic agents and have the potential to potentiate the clinical activity of a large number of standard of care chemotherapeutic agents. Utilizing pharmacodynamic biomarkers to optimize drug dose and scheduling in these trials could greatly enhance the likelihood of clinical success.MethodsIn this study, we evaluated the in vitro potentiation of the cytotoxicity of a range of cytotoxic chemotherapeutic drugs by the novel Chk1 inhibitor V158411 in p53 mutant colon cancer cells. Pharmacodynamic biomarkers were evaluated in vitro.ResultsV158411 potentiated the cytotoxicity of a range of chemotherapeutic agents with distinct mechanisms of action in p53 mutant colon cancer cell lines grown in anchorage dependent or independent culture conditions. Analysis of pharmacodynamic biomarker changes identified dependencies on the chemotherapeutic agent, the concentration of the chemotherapeutic and the duration of time between combination treatment and biomarker analysis. A reduction in total Chk1 and S296/S317/S345 phosphorylation occurred consistently with all cytotoxics in combination with V158411 but did not predict cell line potentiation. Induction of γH2AX levels was chemotherapeutic dependent and correlated closely with potentiation of gemcitabine and camptothecin in p53 mutant colon cancer cells.ConclusionsOur results suggest that Chk1 phosphorylation could be a useful biomarker for monitoring inhibition of Chk1 activity in clinical trials involving a range of V158411-chemotherapy combinations and γH2AX induction as a predictor of potentiation in combinations containing gemcitabine or camptothecin.

Effects of ΔNp73β on cisplatin treatment in colon cancer cells

p73 can activate transcription of p53-responsive genes, thereby inhibiting cell growth. An alternative promoter in the TP73 gene gives rise to an N-terminally truncated isoform of p73, ΔNp73, which lacks the transactivation domain of the full length TAp73 protein. TAp73 is considered pro-apoptotic, and ΔNp73 anti-apoptotic. In this study, we overexpressed ΔNp73β in p53 wild type and p53 mutant colon cancer cell lines and further exposed the cells to cancer therapeutic drug cisplatin. The results showed that cisplatin decreased the protein expression levels of ΔNp73β in a dose-dependent manner, and both TAp73 and p53 were upregulated after cisplatin treatment. Further, clonogenic potential and cell viability were decreased, and apoptotic cells increased, in p53 mutant and in p53 wild type cells. Cellular viability was significantly higher in ΔNp73β-cells than mock-transfected cells. However, ΔNp73β overexpression did not affect the cellular susceptibility to cisplatin. In conclusion, the overexpression of ΔNp73β increases viability in p53 wild type and p53 mutant colon cancer cells, and cisplatin induces the degradation of ΔNp73β in a dose-dependent manner.

A New Isoquinolinium Derivative, Cadein1, Preferentially Induces Apoptosis in p53-defective Cancer Cells with Functional Mismatch Repair via a p38-dependent Pathway

We screened a protoberberine backbone derivative library for compounds with anti-proliferative effects on p53-defective cancer cells. A compound identified from this small molecule library, cadein1 (cancer-selective death inducer 1), an isoquinolinium derivative, effectively leads to a G(2)/M delay and caspase-dependent apoptosis in various carcinoma cells with non- functional p53. The ability of cadein1 to induce apoptosis in p53-defective colon cancer cells was tightly linked to the presence of a functional DNA mismatch repair (MMR) system, which is an important determinant in chemosensitivity. Cadein1 was very effective in MMR(+)/p53(-) cells, whereas it was not effective in p53(+) cells regardless of the MMR status. Consistently, when the function of MMR was blocked with short hairpin RNA in SW620 (MMR(+)/p53(-)) cells, cadein1 was no longer effective in inducing apoptosis. Besides, the inhibition of p53 increased the pro-apoptotic effect of cadein1 in HEK293 (MMR(+)/p53(+)) cells, whereas it did not affect the response to cadein1 in RKO (MMR(-)/p53(+)) cells. The apoptotic effects of cadein1 depended on the activation of p38 but not on the activation of Chk2 or other stress-activated kinases in p53-defective cells. Taken together, our results show that cadein1 may have a potential to be an anti-cancer chemotherapeutic agent that is preferentially effective on p53-mutant colon cancer cells with functional MMR.

Mirk Regulates the Exit of Colon Cancer Cells from Quiescence

Mirk/Dyrk1B is a serine/threonine kinase widely expressed in colon cancers. Serum starvation induced HD6 colon carcinoma cells to enter a quiescent G0 state, characterized by a 2N DNA content and a lower RNA content than G1 cells. Compared with cycling cells, quiescent cells exhibited 16-fold higher levels of the retinoblastoma protein p130/Rb2, which sequesters E2F4 to block entry into G1, 10-fold elevated levels of the CDK inhibitor p27kip1, and 10-fold higher levels of Mirk. However, depletion of Mirk did not prevent entry into G0, but enabled quiescent HD6, SW480, and colo320 colon carcinoma cells to acquire some biochemical characteristics of G1 cells, including increased levels of cyclin D1 and cyclin D3 because of slower turnover, increased activity of their CDK4/cyclin D complexes, and increased phosphorylation and decreased E2F4 sequestering ability of the CDK4 target, p130/Rb2. As a result, depletion of Mirk allowed some cells to escape quiescence and enabled cells released from quiescence to traverse G1 more quickly. The kinase activity of Mirk was increased by the chemotherapeutic drug 5-fluorouracil (5-FU). Treatment of p53 mutant colon cancer cells with 5-FU led to an elongated G1 in a Mirk-dependent manner, as G1 was shortened by ectopic overexpression of cyclin D1 mutated at the Mirk phosphorylation site (T288A), but not by wild-type cyclin D1. Mirk, through regulating cyclin D turnover, and the CDK inhibitor p27, as shown by depletion studies, functioned independently and additively to regulate the exit of tumor cells from quiescence.

Non-genotoxic anti-neoplastic effects of ellipticine derivative NSC176327 in p53-deficient human colon carcinoma cells involve stimulation of p73

We previously performed a high-throughput screen using real-time noninvasive bioluminescence imaging of p53 transcriptional activity and identified a group of small molecules that trigger p53-like transcriptional responses in p53-deficient tumor cells. Here we further examined the anti-tumor effects of selected compounds in vitro and showed that NSC176327, a derivative of the cytotoxic plant alkaloid ellipticine, exhibited strong anti-neoplastic effects in wild-type p53, p53-mutant or p53-deficient human colon cancer cells. NSC176327 was more potent at inhibiting tumor cell growth as compared with chemotherapeutic drugs and other ellipticine derivatives and induced cell cycle arrest and apoptosis. Surprisingly, unlike what is observed with the parent compound ellipticine, a DNA damage signaling response was not observed with NSC176327 as evidenced by lack of phosphorylated histone H2AX foci in NSC176327-treated tumor cells. NSC176327 treatment caused a significant increase in p53-activated reporter signal in HCT116, SW620 and HCT116 p53−/− cells and upregulated DR5 and p21 protein expression. NSC176327 treatment also resulted in increased p73 protein expression and knockdown of transactivating isoforms of p73 in HCT116 p53−/− cells showed significant resistance to drug treatment. These results demonstrate an important role of p73 in the anti-tumor effects of NSC176327, and suggest that a close analog of ellipticine may act by a non-genotoxic mechanism targeting the p53/p73 pathway as compared with the original parent compound that targets the same pathway.

Sanguinarine causes DNA damage and p53-independent cell death in human colon cancer cell lines

The benzophenanthridine alkaloid sanguinarine has antimicrobial and possibly anticancer properties but it is not clear to what extent these activities involve DNA damage. Thus, we studied its ability to cause DNA single and double strand breaks, as well as increased levels of 8-oxodeoxyguanosine, in human colon cancer cells and found DNA damage consistent with oxidation. Since the tumor suppressor p53 is frequently involved in inducing apoptosis following DNA damage we investigated the effect of sanguinarine in wild type, p53-mutant and p53-null colon cancer cell lines. We found them to be equally sensitive to this plant compound, indicating that cell death is not mediated by p53 in this case. In addition, our observation that apoptosis induced by sanguinarine is initiated very rapidly raised the question whether there is enough time for cellular signaling in response to DNA damage. Moreover, the abundance of double strand breaks is not consistent with only oxidative damage to DNA. We conclude that the majority of DNA double strand breaks in sanguinarine-treated cells are likely the result, rather than the cause, of apoptotic cell death and that apoptosis induced by sanguinarine is independent of p53 and most likely independent of DNA damage.

Docosahexaenoic acid enhances the susceptibility of human colorectal cancer cells to 5-fluorouracil.

Powerful growth-inhibitory action has been shown for n-3 polyunsaturated fatty acids against colon cancer cells. We have previously described their ability to inhibit proliferation of colon epithelial cells in patients at high risk of colon cancer. In the work reported here we investigated the ability of docosahexaenoic acid (DHA) to potentiate the antineoplastic activity of 5-fluorouracil (5-FU) in p53-wildtype (LS-174 and Colo 320) and p53-mutant (HT-29 and Colo 205) human colon cancer cells. When in combination with DHA, 5-FU was used at concentrations ranging from 0.1 to 1.0 microM, much lower than those currently found in plasma patients after infusion of this drug. Similarly, the DHA concentrations (< or =10 microM) used in combination with 5-FU were lower than those widely used in vitro and known to cause peroxidative effects in vivo. Whereas the cells showed different sensitivity to the growth-inhibitory action of 5-FU, DHA reduced cell growth independently of p53 cellular status. DHA synergized with 5-FU in reducing colon cancer cell growth. The potentiating effect of DHA was attributable to the enhancement of the proapoptotic effect of 5-FU. DHA markedly increased the inhibitory effect of 5-FU on the expression of the antiapoptotic proteins BCL-2 and BCL-XL, and induced overexpression of c-MYC which has recently been shown to drive apoptosis and, when overexpressed, to sensitize cancer cells to the action of proapoptotic agents, including 5-FU. Our results indicate that DHA strongly increases the antineoplastic effects of low concentrations of 5-FU. Overall, the results suggest that combinations of low doses of the two compounds could represent a chemotherapeutic approach with low toxicity.

The roles of thymidylate synthase and p53 in regulating Fas-mediated apoptosis in response to antimetabolites.

Fas (CD95/Apo-1) is a member of the tumor necrosis factor receptor family. Receptor binding results in activation of caspase 8, leading to activation of proapoptotic downstream molecules. We found that expression of Fas was up-regulated >10-fold in MCF-7 breast and HCT116 and RKO colon cancer cell lines after treatment with IC(60) doses of 5-fluorouracil (5-FU) and raltitrexed (RTX). Combined treatment with the agonistic Fas antibody CH-11 and either 5-FU or RTX resulted in a highly synergistic induction of apoptosis in these cell lines. Similar results were obtained for another antifolate, Alimta. Induction of thymidylate synthase expression inhibited Fas induction in response to RTX and Alimta, but not in response to 5-FU. Furthermore, thymidylate synthase induction abrogated the synergy between CH-11 and both antifolates but had no effect on the synergistic interaction between 5-FU and CH-11. Inactivation of p53 in MCF-7 and HCT116 cell lines blocked 5-FU- and antifolate-mediated up-regulation of Fas. Furthermore, Fas was not up-regulated in response to 5-FU or antifolates in the p53-mutant H630 colon cancer cell line. Lack of Fas up-regulation in the p53-null and -mutant lines abolished the synergistic interaction between 5-FU and CH-11. Interestingly, synergy was still observed between the antifolates and CH-11 in the p53-null HCT116 and p53-mutant H630 cell lines, although this was significantly reduced compared with the p53 wild-type cell lines. Our results indicate that Fas is an important mediator of apoptosis in response to both 5-FU and antifolates.

Mechanism of resistance to chemoradiation in p53 mutant human colon cancer

To understand one of the mechanisms of resistance to chemoradiation in colon cancer cells, we investigated whether 5-fluorouracil (5-FU) mediated the expression of epidermal growth factor receptor (EGFR) and modified repair of radiation-induced DNA damage, especially in a p53 independent pathway. Cytotoxicity was determined for 5-FU combined with radiation for three colon cancer cell lines that contain mutant p53 (SW480, HT29 and WiDr), using the WST-8 colorimetric assay. EGFR and the excision repair cross complementation group 1 (ERCC1) proteins during chemoradiation were measured by Western blot analysis. SW480 cells were significantly resistant to chemoradiation compared to the other mutant p53 cell lines. The alteration of EGFR and ERCC1 proteins during chemoradiation in SW480 was apparently inversely related to that of the other radiosensitive cell lines. 5-FU-induced activation of EGFR followed by radiation in SW480 cells resulted in up-regulation of ERCC1. In contrast, 5-FU-induced degradation of EGFR followed by radiation in the other radiosensitive cell lines resulted in down-regulation of ERCC1. This suggested a complementary interaction between EGFR and ERCC1, and that 5-FU-induced EGFR activation conferred protection against radiation, through activation of DNA repair. Interaction of EGFR and ERCC1 might correlate with radiation-induced DNA damage when p53 mutant colon cancer cell lines are exposed to 5-FU followed by radiation.