MLH1-deficient HCT116 colon tumor cells exhibit resistance to the cytostatic and cytotoxic effect of the poly(A) polymerase inhibitor cordycepin (3'-deoxyadenosine) in vitro

Cordycepin (3'-deoxyadenosine) is an inhibitor of poly(A) polymerase (PAP), an enzyme crucial to mRNA 3'-end processing, which produces the shortening of poly(A) tails, leading to the destabilization of mRNAs. Cordycepin inhibits proliferation and induces apoptosis in tumor cells, indicating its antitumor activity. Defective 3'-end processing is associated with hypersensitivity to UV treatment. We investigated the effects of cordycepin on proliferation and apoptosis in MLH1-deficient and MLH1-proficient HCT116 colon tumor cells. MLH1 is a DNA mismatch repair (MMR) protein involved in the processing of damaged DNA. Cells with defective MMR show resistance to certain anticancer drugs. The results showed that MLH1-deficient HCT116 cells are 2-fold less sensitive to the cytostatic effect of cordycepin, as compared to MLH1-proficient cells. This reduced sensitivity to cordycepin in MLH1-deficient cells was associated with reduced upregulation of the cell cycle inhibitor p21. MLH1-deficient cells also exhibited reduced susceptibility to apoptosis upon treatment with cordycepin, as demonstrated by the reduced PARP-1 cleavage. Our findings showed that MLH1-deficient HCT116 colon tumor cells are resistant to the cytostatic and cytotoxic effect of cordycepin, indicating a possible involvement of MMR in mRNA polyadenylation. The findings also suggest that cordycepin is not suitable to therapeutically encounter tumor cells lacking MLH1 expression

Glucosylceramide synthase inhibitors differentially affect expression of glycosphingolipids

Glucosylceramide synthase (GCS) catalyzes the first committed step in the biosynthesis of glucosylceramide (GlcCer)-related glycosphingolipids (GSLs). Although inhibitors of GCS, PPMP and PDMP have been widely used to elucidate their biological function and relevance, our comprehensive literature review revealed that the available data are ambiguous. We therefore investigated whether and to what extent GCS inhibitors affect the expression of lactosylceramide (LacCer), neolacto (nLc4 and P1), ganglio (GM1 and GD3) and globo (Gb3 and SSEA3) series GSLs in a panel of human cancer cell lines using flow cytometry, a commonly applied method investigating cell-surface GSLs after GCS inhibition. Their cell-surface GSL expression considerably varied among cell lines and more importantly, sublethal concentrations (IC10) of both inhibitors preferentially and significantly reduced the expression of Gb3 in the cancer cell lines IGROV1, BG1, HT29 and T47D, whereas SSEA3 was only reduced in BG1. Unexpectedly, the neolacto and ganglio series was not affected. LacCer, the precursor of all GlcCer-related GSL, was significantly reduced only in BG1 cells treated with PPMP. Future research questions addressing particular GSLs require careful consideration; our results indicate that the extent to which there is a decrease in the expression of one or more particular GSLs is dependent on the cell line under investigation, the type of GCS inhibitor and exposure duratio

Cost-effectiveness of trastuzumab in the adjuvant treatment of early breast cancer: a model-based analysis of the HERA and FinHer trial

BACKGROUND: Routine adjuvant administration of trastuzumab (T) has been implemented in most centers, but its economic impact has not yet been well examined. METHODS: A Markov model was constructed based on clinical data of the Herceptin Adjuvant (HERA) and the Finland Herceptin (FinHer) trials. Costs from the perspective of a Swiss health care provider were calculated based on resource use. RESULTS: On the basis of HERA data, our model yielded an overall survival rate of 71.8% for the T group versus 62.8% for the control group [risk ratio (RR) = 0.87) after 10 years and 62.9% versus 52.7% (RR = 0.84) after 15 years. Cost-effectiveness resulted in 40505 Euros (EUR) per life years gained (LYG) after 10 years and 19673 EUR per LYG after 15 years. For the FinHer regimen, overall survival after 10 and 15 years resulted in 81.8% versus 66.1% (RR = 0.81) and 73.6% versus 57.0% (RR = 0.77). Costs of 8497 EUR per patient could be saved after 10 years and 9256 EUR after 15 years compared with the control group. CONCLUSION: In a long-term perspective, adjuvant T based on the HERA regimen can be considered cost-effective. The regimen used in the FinHer trial is even cost saving, but estimations are based on a single small tria

Loss of atm sensitises p53-deficient cells to topoisomerase poisons and antimetabolites

Background: Ataxia-telangiectasia is a pleiotropic autosomal recessive disorder caused by mutations in the ATM gene. In addition to a profound cancer predisposition, another hallmark of ataxia-telangiectasia is radiosensitivity. Recently, p53-null mouse fibroblasts have been reported to be radiosensitised by the concurrent loss of ATM. Materials and methods: We compared the sensitivity of atm+/+/p53-/- and atm-/-/p53-/- mouse embryonic fibroblasts to different classes of chemotherapeutic agents using the MTT assay, Trypan Blue exclusion and fluorescence-activated cell sorting for cell cycle and apoptosis analyses. Results: Loss of ATM function in p53-deficient cells resulted in a 2- to 4-fold increase in sensitivity to the topoisomerase I poisons camptothecin and topotecan, to the topoisomerase II poisons doxorubicin, epirubicin and etoposide, and to the antimetabolites 5-fluorouracil and gemcitabine, but not to the platinum compounds cisplatin, carboplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, or to busulfan. Loss of ATM function did not result in increased apoptosis, but resulted in increased Trypan Blue staining in response to epirubicin, suggesting that processes other than apoptosis may mediate cytotoxicity. ATM deficiency did not alter the extent of G1/S or G2/M cell cycle phase accumulation produced by epirubicin, suggesting that enhanced sensitivity was not due to failure of checkpoint activation. Conclusions: We provide further evidence that ATM is involved in regulating cellular defences against some cytotoxic agents in the absence of p53. Tumour-targeted functional inhibition of ATM may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancer

Increased sensitivity of p53-deficient cells to anticancer agents due to loss of Pms2

A large fraction of human tumours carries mutations in the p53 gene. p53 plays a central role in controlling cell cycle checkpoint regulation, DNA repair, transcription, and apoptosis upon genotoxic stress. Lack of p53 function impairs these cellular processes, and this may be the basis of resistance to chemotherapeutic regimens. By virtue of the involvement of DNA mismatch repair in modulating cytotoxic pathways in response to DNA damaging agents, we investigated the effects of loss of Pms2 on the sensitivity to a panel of widely used anticancer agents in E1A/Ha-Ras-transformed p53-null mouse fibroblasts either proficient or deficient in Pms2. We report that lack of the Pms2 gene is associated with an increased sensitivity, ranging from 2–6-fold, to some types of anticancer agents including the topoisomerase II poisons doxorubicin, etoposide and mitoxantrone, the platinum compounds cisplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, and the antimetabolite gemcitabine. In contrast, no change in sensitivity was found after treatment with 5-fluorouracil. Cell cycle analysis revealed that both, Pms2-deficient and -proficient cells, retain the ability to arrest at the G2/M upon cisplatin treatment. The data indicate that the concomitant loss of Pms2 function chemosensitises p53-deficient cells to some types of anticancer agents, that Pms2 positively modulates cell survival by mechanisms independent of p53, and that increased cytotoxicity is paralleled by increased apoptosis. Tumour-targeted functional inhibition of Pms2 may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancers

MyCTC chip: microfluidic-based drug screen with patient-derived tumour cells from liquid biopsies

Cancer patients with advanced disease are characterized by intrinsic challenges in predicting drug response patterns, often leading to ineffective treatment. Current clinical practice for treatment decision-making is commonly based on primary or secondary tumour biopsies, yet when disease progression accelerates, tissue biopsies are not performed on a regular basis. It is in this context that liquid biopsies may offer a unique window to uncover key vulnerabilities, providing valuable information about previously underappreciated treatment opportunities. Here, we present MyCTC chip, a novel microfluidic device enabling the isolation, culture and drug susceptibility testing of cancer cells derived from liquid biopsies. Cancer cell capture is achieved through a label-free, antigen-agnostic enrichment method, and it is followed by cultivation in dedicated conditions, allowing on-chip expansion of captured cells. Upon growth, cancer cells are then transferred to drug screen chambers located within the same device, where multiple compounds can be tested simultaneously. We demonstrate MyCTC chip performance by means of spike-in experiments with patient-derived breast circulating tumour cells, enabling >95% capture rates, as well as prospective processing of blood from breast cancer patients and ascites fluid from patients with ovarian, tubal and endometrial cancer, where sensitivity to specific chemotherapeutic agents was identified. Together, we provide evidence that MyCTC chip may be used to identify personalized drug response patterns in patients with advanced metastatic disease and with limited treatment opportunities

Photodynamic therapy of DNA mismatch repair-deficient and -proficient tumour cells

Loss of DNA mismatch repair is a common finding in hereditary nonpolyposis colon cancer as well as in many types of sporadic human tumours. DNA mismatch repair-deficient cells have been reported to be resistant to many chemotherapeutic agents and to radiotherapy, and to have the potential of rapidly acquiring additional mutations leading to tumour progression. Photodynamic therapy is a new treatment modality using light to activate a photosensitiser that preferentially localises in tumour cells. An oxygen dependent photochemical reaction ensues, resulting in selective tumour necrosis. The effect of loss of DNA mismatch repair activity on the sensitivity to photodynamic therapy was tested using pairs of cell lines proficient or deficient in mismatch repair due to loss of either MLH1 or MSH2 protein function. Cells were incubated with the photosensitiser 5,10,15,20-meta-tetra(hydroxyphenyl)chlorin and exposed to laser light at 652 nm with various optical doses ranging from 0–1 J cm−2. Cell survival was assessed using the clonogenic assay. Loss of MLH1 or MSH2 function was not associated with resistance to photodynamic therapy. MCF-7 cells repeatedly treated with photodynamic therapy expressed parental levels of MLH1, MSH2, MSH6, and PMS2. DNA mismatch repair-deficient and -proficient cells showed similar subcellular distributions of meta-tetra(hydroxyphenyl)chlorin as analysed by laser scanning and fluorescence microscopy. Therefore, repeated exposure of tumour cells to photodynamic therapy does not seem to result in loss of DNA mismatch repair, and loss of mismatch repair, in turn, does not seem to contribute to resistance to photodynamic therapy. Our results suggest recommending photodynamic therapy as a strategy for circumventing resistance due to loss of DNA mismatch repair

Dissociation of minor groove binders from DNA: insights from metadynamics simulations

We have used metadynamics to investigate the mechanism of noncovalent dissociation from DNA by two representatives of alkylating and noncovalent minor groove (MG) binders. The compounds are anthramycin in its anhydrous form (IMI) and distamycin A (DST), which differ in mode of binding, size, flexibility and net charge. This choice enables to evaluate the influence of such factors on the mechanism of dissociation. Dissociation of IMI requires an activation free energy of ∼12 kcal/mol and occurs via local widening of the MG and loss of contacts between the drug and one DNA strand, along with the insertion of waters in between. The detachment of DST occurs at a larger free energy cost, ∼16.5 or ∼18 kcal/mol depending on the binding mode. These values compare well with that of 16.6 kcal/mol extracted from stopped-flow experiments. In contrast to IMI, an intermediate is found in which the ligand is anchored to the DNA through its amidinium tail. From this conformation, binding and unbinding occur almost at the same rate. Comparison between DST and with kinetic models for the dissociation of Hoechst 33258 from DNA uncovers common characteristics across different classes of noncovalent MG ligands

Microsatellite instability due to hMLH1 deficiency is associated with increased cytotoxicity to irinotecan in human colorectal cancer cell lines

Around 15% of colorectal cancers (CRCs) show microsatellite instability (MSI) due to dysfunction of the mismatch repair system (MMR). As a consequence of this, MSI tumours tend to accumulate errors in mononucleotide repeats as those in genes implicated in repairing double-strand breaks (DSBs). Previous studies have shown that irinotecan (CPT-11), a chemotherapy agent inducing DSB, is more active in MSI than in microsatellite stable (MSS) CRC. The purpose of this study was to compare the sensitivity to CPT-11 in a series of CRC cell lines with either proficient or deficient MMR and to assess the mutational status of two DSB repair genes, MRE11 and RAD50, in these cell lines. hMLH1-deficient cell lines due to either epigenetic silencing or mutation showed very similar IC50 and were four- to nine-fold more sensitive to CPT-11 than the MSS line. Cell lines harbouring mutations in both MRE11 and RAD50 were most sensitive to CPT-11. We conclude that MSI cell lines display higher sensitivity to CPT-11 than MSS cells. Mutation of MRE11 and RAD50 could account for this difference in response to CPT-11. Future clinical trials tailoring chemotherapy regimens based on microsatellite status are warranted