Chemotherapeutic agents for colorectal cancer with a defective mismatch repair system: The state of the art

A review of the sensitivity of metastatic colorectal cancer patients with deficient mismatch repair to standard-of-care chemotherapy and monoclonal antibodies, with recommendations for future research

In 5% of metastatic colorectal cancer (mCRC) patients, tumours display a deficient mismatch repair (dMMR) system. Immunotherapy is beneficial in dMMR mCRC patients and has recently been approved by the Food and Drug Administration for patients with unresectable or metastatic dMMR CRC. Although dMMR and proficient MMR (pMMR) CRC tumours are biologically distinct, they are commonly treated with the same chemotherapy and monoclonal antibodies. This includes dMMR mCRC patients who did not respond to immunotherapy (20-30%). However, it is unclear if these treatments are equally beneficial in dMMR mCRC. Of note, dMMR mCRC patients have a worse prognosis compared to pMMR, which may in part be caused by a lower response to treatment. To avoid unnecessary exposure to ineffective treatments and their associated toxicity, it is important to identify which systemic treatments are most beneficial in dMMR mCRC patients, thus improving their outcome. Indeed, future treatment strategies are likely to involve combinations of immunotherapy, chemotherapy and monoclonal antibodies. In this evidence-based review, we summarize clinical trials reporting treatment efficacy of different types of chemotherapy and monoclonal antibodies in dMMR mCRC patients. We also review the biological rationale behind a potential differential benefit of chemotherapy with or without monoclonal antibodies in dMMR mCRC patients. A barrier in the interpretation of preclinical results is the choice of model systems. They largely comprise traditional models, including cell lines and xenografts, rather than more representative models, such as patient-derived organoids. We provide concrete recommendations for clinical investigators and fundamental researchers to accelerate research regarding which systemic therapy is most effective in dMMR mCRC patients.

Discovery of steroidal lactam conjugates of POPAM-NH2 with potent anticancer activity

Aim: Steroidal prodrugs of nitrogen mustards such as estramustine and prednimustine have proven effective anticancer agents in clinical use since the 1970s. In this work, we aimed to develop steroidal prodrugs of the novel nitrogen mustard POPAM-NH2. POPAM-NH2 is a melphalan analogue that was coupled with three different steroidal lactams. Methodology: The new conjugates were preclinically tested for anticancer activity against nine human and one rodent cancer experimental models, in vitro and in vivo. Results & conclusion: All the steroidal alkylators showed high antitumor activity, in vitro and in vivo, in the experimental systems tested. Moreover, these hybrid compounds showed by far superior anticancer activity compared with the alkylating agents, melphalan and POPAM-NH2.

Low Concentration of 5-Fluorouracil Increases the Effectiveness of Tumor RNA to Activate Murine Dendritic Cells

AIM

Considering the central role of dendritic cells (DCs) on the development of an antitumor immune response, in this study we used a murine model to evaluate how DC transfection with drug-treated tumor cell RNA changes their phenotype, and whether transfection enhances the in vivo effectiveness of a DC-based antitumor vaccine.

MATERIALS AND METHODS

MC-38 colorectal tumor cells were pretreated with the minimum effective concentration of 5-fluorouracil (5-FU), then their total RNA was extracted and transfected into DCs. These DCs were inoculated into C57Bl/6 mice bearing subcutaneous MC-38 tumor.

RESULTS

DC transfection with drug-treated tumor RNA increases the percentages of CD40⁺ (from 37.6% to 61.4%), CD86⁺ (from 39.8% to 53.4%), and major histocompatibility complex class II⁺ (from 51.2% to 75.3%) cells, whereas significantly increases the in vivo generation of interferon-γ producer lymphocytes.

CONCLUSION

These results reinforce our view that treatment of tumor cells with 5-FU induces transcriptional changes that can be transferred to DCs by RNA transfection, enhancing their ability to stimulate an antitumor response.

The mutational profile and infiltration pattern of murine MLH1-/- tumors: concurrences, disparities and cell line establishment for functional analysis

Mice lines homozygous negative for one of the four DNA mismatch repair (MMR) genes (MLH1, MSH2, PMS2, MSH6) were generated as models for MMR deficient (MMR-D) diseases. Clinically, hereditary forms of MMR-D include Lynch syndrome (characterized by a germline MMR gene defect) and constitutional MMR-D, the biallelic form. MMR-D knockout mice may be representative for both diseases. Here, we aimed at characterizing the MLH1^-/- model focusing on tumor-immune microenvironment and identification of coding microsatellite mutations in lymphomas and gastrointestinal tumors (GIT).

All tumors showed microsatellite instability (MSI) in non-coding mononucleotide markers. Mutational profiling of 26 coding loci in MSI⁺ GIT and lymphomas revealed instability in half of the microsatellites, two of them (Rfc3 and Rasal2) shared between both entities. MLH1^-/- tumors of both entities displayed a similar phenotype (high CD71, FasL, PD-L1 and CTLA-4 expression). Additional immunofluorescence verified the tumors’ natural immunosuppressive character (marked CD11b/CD200R infiltration). Vice versa, CD3⁺ T cells as well as immune checkpoints molecules were detectable, indicative for an active immune microenvironment. For functional analysis, a permanent cell line from an MLH1^-/- GIT was established. The newly developed MLH1^-/- A7450 cells exhibit stable in vitro growth, strong invasive potential and heterogeneous drug response. Moreover, four additional MSI target genes (Nktr1, C8a, Taf1b, and Lig4) not recognized in the primary were identified in this cell line.

Summing up, molecular and immunological mechanisms of MLH1^-/- driven carcinogenesis correlate well with clinical features of MMR-D. MLH1^-/- knockout mice combine characteristics of Lynch syndrome and constitutional MMR-D, making them suitable models for preclinical research aiming at MMR-D related diseases.

Clinicopathological significance of CHFR methylation in non-small cell lung cancer: a systematic review and meta-analysis

Checkpoint with Forkhead-associated and Ring finger domains (CHFR) is a G2/M checkpoint and tumor-suppressor gene. Recent publications showed the correlation of CHFR promoter methylation with clinicopathological significance of non-small cell lung cancer (NSCLC), however, the results remain inconsistent. The aim of this study is to investigate the Clinicopathological significance of CHFR promoter methylation in NSCLC with a meta-analysis. A total of nine studies were included in the meta-analysis that 816 patients were involved. Our data indicated that the frequency of CHFR promoter methylation was higher in NSCLC than in normal lung tissue, Odd Ratios (OR) was 9.92 with 95% corresponding confidence interval (CI) 2.17-45.23, p = 0.003. Further subgroup analysis revealed that CHFR promoter was more frequently methylated in squamous cell carcinoma (SCC) than in adenocarcinoma (ADC), OR was 4.46 with 95% CI 1.65-12.05, p = 0.003, suggesting the mechanism of SCC pathogenesis is different from ADC. Notably, CHFR promoter methylation was correlated with smoking behavior in NSCLC. In conclusion, CHFR could be a biomarker for diagnosis of NSCLC, and a promising drug target for development of gene therapy in SCC. CHFR promoter methylation is potentially associated with poor overall survival, additional studies need to be carried out for confirmation in future.

The diagnostic and prognostic value of CHFR hypermethylation in colorectal cancer, a meta-analysis and literature review

The Checkpoint with Forkhead-associated and Ring finger domains (CHFR) is a mitotic checkpoint and tumor-suppressor gene, its loss contributes tumorigenesis of epithelial cancers including colorectal carcinoma (CRC). The diagnostic and prognostic value of CHFR promoter hypermethylation in CRC remains unclear. This study aimed to conduct a meta-analysis and literature review and investigate clinicopathological significance of CHFR promoter hypermethylation in CRC. The following online database were used: PubMed, EMBASE, and Web of Science up to March 2017. Odds Ratios (OR) and Hazard Ratios (HR) with 95% corresponding confidence intervals (CIs) were calculated. A total of seven relevant articles were available for meta-analysis which included 966 patients. The frequency of CHFR promoter hypermethylation significantly increased in CRC compared to normal colorectal mucosa tissue, pooled OR was 8.35, p < 0.00001. CHFR promoter hypermethylation was not significantly correlated to stage, OR was 1.16, p = 0.63. However, CHFR promoter hypermethylation was more frequently observed in CRC with positive lymph nodes metastasis than CRC with negative lymph nodes metastasis, OR was 0.46, p = 0.03. Additionally CHFR promoter hypermethylation was significantly related to poor overall survival in patients with CRC, HR was 0.62, p = 0.008. Based on these results, tumor CHFR promoter hypermethylation is not only a diagnostic biomarker for CRC, but also a prognostic marker. CHFR promoter hypermethylation is significantly associated with worse overall survival in patients with CRC. Our data suggested that CHFR could be a potential drug target for development of demethylation treatment for patients with CRC.

DNA mismatch repair and its many roles in eukaryotic cells

DNA mismatch repair (MMR) is an important DNA repair pathway that plays critical roles in DNA replication fidelity, mutation avoidance and genome stability, all of which contribute significantly to the viability of cells and organisms. MMR is widely-used as a diagnostic biomarker for human cancers in the clinic, and as a biomarker of cancer susceptibility in animal model systems. Prokaryotic MMR is well-characterized at the molecular and mechanistic level; however, MMR is considerably more complex in eukaryotic cells than in prokaryotic cells, and in recent years, it has become evident that MMR plays novel roles in eukaryotic cells, several of which are not yet well-defined or understood. Many MMR-deficient human cancer cells lack mutations in known human MMR genes, which strongly suggests that essential eukaryotic MMR components/cofactors remain unidentified and uncharacterized. Furthermore, the mechanism by which the eukaryotic MMR machinery discriminates between the parental (template) and the daughter (nascent) DNA strand is incompletely understood and how cells choose between the EXO1-dependent and the EXO1-independent subpathways of MMR is not known. This review summarizes recent literature on eukaryotic MMR, with emphasis on the diverse cellular roles of eukaryotic MMR proteins, the mechanism of strand discrimination and cross-talk/interactions between and co-regulation of MMR and other DNA repair pathways in eukaryotic cells. The main conclusion of the review is that MMR proteins contribute to genome stability through their ability to recognize and promote an appropriate cellular response to aberrant DNA structures, especially when they arise during DNA replication. Although the molecular mechanism of MMR in the eukaryotic cell is still not completely understood, increased used of single-molecule analyses in the future may yield new insight into these unsolved questions.

Treatment of colon cancer cells with 5-fluorouracil can improve the effectiveness of RNA-transfected antitumor dendritic cell vaccine

Non-cytotoxic concentrations of selected chemotherapeutic agents amplify the antigen presentation capacity of dendritic cells (DCs) and are able to increase the immunogenicity of the colon cancer cell lineage HCT‑116, as previously demonstrated by our group. Since this functional alteration was associated with changes in gene expression, we aimed to evaluate whether transcriptional changes of tumor cells can be transferred to DCs, increasing their ability to induce a specific antitumor response. Therefore, HCT‑116 cells were treated with two different concentrations of 5-fluorouracil (5-FU), and their total RNA was transfected into human monocyte-derived DC, which function was evaluated through their ability to stimulate the proliferation of normal allogeneic T lymphocytes (MLR), and to generate cytolytic T cells. The transfected DCs demonstrated an increased percentage of CD83+, HLA-DR+, CD80+ and CD86+ cells. These phenotypical changes were followed by functional improvement demonstrated by the increased capacity of these DC to induce allogeneic T cell proliferation and to generate specific anti-HCT‑116 cytolytic T cells, as demonstrated by IFN-γ production following in vitro challenge with tumor cells. Our results allow us to conclude that treatment of tumor cells with a non-toxic concentration of 5-FU induces immunogenic changes that are transferred to DC by transfection of total RNA.

Impact of DNA mismatch repair system alterations on human fertility and related treatments

DNA mismatch repair (MMR) is one of the biological pathways, which plays a critical role in DNA homeostasis, primarily by repairing base-pair mismatches and insertion/deletion loops that occur during DNA replication. MMR also takes part in other metabolic pathways and regulates cell cycle arrest. Defects in MMR are associated with genomic instability, predisposition to certain types of cancers and resistance to certain therapeutic drugs. Moreover, genetic and epigenetic alterations in the MMR system demonstrate a significant relationship with human fertility and related treatments, which helps us to understand the etiology and susceptibility of human infertility. Alterations in the MMR system may also influence the health of offspring conceived by assisted reproductive technology in humans. However, further studies are needed to explore the specific mechanisms by which the MMR system may affect human infertility. This review addresses the physiological mechanisms of the MMR system and associations between alterations of the MMR system and human fertility and related treatments, and potential effects on the next generation.

YB-1 disrupts mismatch repair complex formation, interferes with MutSα recruitment on mismatch and inhibits mismatch repair through interacting with PCNA

Y-box binding protein-1 (YB-1) is highly expressed in tumors and it participates in various cellular processes. Previous studies indicated that YB-1 binds to mispaired DNA and interacts with several mismatch repair (MMR)-related factors. However, its role in the MMR system remains undefined. Here, we found that YB-1 represses mutS homolog 6 (MSH6)-containing MMR complex formation and reduces MutSα mismatch binding activity by disrupting interactions among MMR-related factors. In an effort to elucidate how YB-1 exerts this inhibitory effect, we have identified two functional proliferating cell nuclear antigen (PCNA)-interacting protein (PIP)-boxes that mediate YB-1/PCNA interaction and locate within the C-terminal region of YB-1. This interaction is critical for the regulatory role of YB-1 in repressing MutSα mismatch binding activity, disrupting MutSα/PCNA/G/T heteroduplex ternary complex formation and inhibiting in vitro MMR activity. The differential regulation of 3' and 5' nick-directed MMR activity by YB-1 was also observed. Moreover, YB-1 overexpression is associated with the alteration of microsatellite pattern and the enhancement of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced and spontaneous mutations. Furthermore, upregulation of other PIP-box-containing proteins, such as myeloid cell leukemia-1 (Mcl-1) and inhibitor of growth protein 1b (ING1b), has no impact on MMR complex formation and mutation accumulation, thus revealing the significant effect of YB-1 on regulating the MMR system. In conclusion, our study suggests that YB-1 functions as a PCNA-interacting factor to exert its regulatory role on the MMR process and involves in the induction of genome instability, which may partially account for the oncogenic potential of YB-1.

Selective cytotoxicity of rhodium metalloinsertors in mismatch repair-deficient cells

Mismatches in DNA occur naturally during replication and as a result of endogenous DNA damaging agents, but the mismatch repair (MMR) pathway acts to correct mismatches before subsequent rounds of replication. Rhodium metalloinsertors bind to DNA mismatches with high affinity and specificity and represent a promising strategy to target mismatches in cells. Here we examine the biological fate of rhodium metalloinsertors bearing dipyridylamine ancillary ligands in cells deficient in MMR versus those that are MMR-proficient. These complexes are shown to exhibit accelerated cellular uptake which permits the observation of various cellular responses, including disruption of the cell cycle, monitored by flow cytometry assays, and induction of necrosis, monitored by dye exclusion and caspase inhibition assays, that occur preferentially in the MMR-deficient cell line. These cellular responses provide insight into the mechanisms underlying the selective activity of this novel class of targeted anticancer agents.

Drug therapy for hereditary cancers

Tumors arising in patients with hereditary cancer syndromes may have distinct drug sensitivity as compared to their sporadic counterparts. Breast and ovarian neoplasms from BRCA1 or BRCA2 mutation carriers are characterized by deficient homologous recombination (HR) of DNA, that makes them particularly sensitive to platinum compounds or inhibitors of poly (ADP-ribose) polymerase (PARP). Outstandingly durable complete responses to high dose chemotherapy have been observed in several cases of BRCA-related metastatic breast cancer (BC). Multiple lines of evidence indicate that women with BRCA1-related BC may derive less benefit from taxane-based treatment than other categories of BC patients. There is virtually no reports directly assessing drug response in hereditary colorectal cancer (CRC) patients; studies involving non-selected (i.e., both sporadic and hereditary) CRC with high-level microsatellite instability (MSI-H) suggest therapeutic advantage of irinotecan. Celecoxib has been approved for the treatment of familial adenomatous polyposis (FAP). Hereditary medullary thyroid cancers (MTC) have been shown to be highly responsive to a multitargeted tyrosine kinase inhibitor vandetanib, which exerts specific activity towards mutated RET receptor. Given the rapidly improving accessibility of DNA analysis, it is foreseen that the potential predictive value of cancer-associated germ-line mutations will be increasingly considered in the future studies.

Biology of colorectal cancer

Significant advances have been made in understanding the biology of colorectal cancer. In this chapter, we review the key signaling pathways that play key roles in maintaining the growth and proliferation of colorectal cancer. The pathways that will be discussed include Wnt/beta-catenin, TGF-beta/SMAD, Notch, Hedgehog, epidermal growth factor receptor, Ras, and PI3K/Akt. In addition, we review the growing role of colon cancer stem cells in mediating cellular drug resistance and cancer recurrence. This enhanced understanding of cancer biology provides important insights for developing novel therapies that target specific growth factor receptors and/or certain critical signal transduction pathways. These targeted therapies can then be used alone or in combination with standard cytotoxic chemotherapy regimens.

DNA mismatch repair deficiency in endometrial carcinoma

Microsatellite instability (MSI) is the hallmark of a molecular pathway to carcinogenesis due to sporadic or inherited abnormalities of DNA mismatch repair genes. Inherited mutations are seen in hereditary nonpolyposis colorectal cancer syndrome. Endometrial carcinoma shows as high an incidence of MSI as does colorectal carcinoma. This review provides a framework for the gynecologic pathologist to understand the complexities of MSI in endometrial carcinoma, by discussing the basic mechanisms of mismatch repair and carcinogenesis, testing, the morphologic features of MSI endometrial cancer and the contradictory data regarding prognosis.

Chemomodulation of human dendritic cell function by antineoplastic agents in low noncytotoxic concentrations

The dose-delivery schedule of conventional chemotherapy, which determines its efficacy and toxicity, is based on the maximum tolerated dose. This strategy has lead to cure and disease control in a significant number of patients but is associated with significant short-term and long-term toxicity. Recent data demonstrate that moderately low-dose chemotherapy may be efficiently combined with immunotherapy, particularly with dendritic cell (DC) vaccines, to improve the overall therapeutic efficacy. However, the direct effects of low and ultra-low concentrations on DCs are still unknown. Here we characterized the effects of low noncytotoxic concentrations of different classes of chemotherapeutic agents on human DCs in vitro. DCs treated with antimicrotubule agents vincristine, vinblastine, and paclitaxel or with antimetabolites 5-aza-2-deoxycytidine and methotrexate, showed increased expression of CD83 and CD40 molecules. Expression of CD80 on DCs was also stimulated by vinblastine, paclitaxel, azacytidine, methotrexate, and mitomycin C used in low nontoxic concentrations. Furthermore, 5-aza-2-deoxycytidine, methotrexate, and mitomycin C increased the ability of human DCs to stimulate proliferation of allogeneic T lymphocytes. Thus, our data demonstrate for the first time that in low noncytotoxic concentrations chemotherapeutic agents do not induce apoptosis of DCs, but directly enhance DC maturation and function. This suggests that modulation of human DCs by noncytotoxic concentrations of antineoplastic drugs, i.e. chemomodulation, might represent a novel approach for up-regulation of functional activity of resident DCs in the tumor microenvironment or improving the efficacy of DCs prepared ex vivo for subsequent vaccinations.

Sporadic colorectal carcinomas with low-level microsatellite instability in Korea: do they form a distinct subgroup with distinguished clinicopathological features?

BACKGROUND

The biologic significance of low-level microsatellite instability (MSI) in colorectal cancers (CRCs) remains unclear. This study aimed to elucidate whether sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological characteristics from microsatellite stable (MSS) and MSI-high CRCs.

METHODS

We consecutively enrolled 657 patients who underwent their first surgical resections for stage I-IV sporadic CRCs and compared their clinicopathological features and prognosis after resection according to MSI status (574 MSS, 30 MSI-low and 53 MSI-high CRCs).

RESULTS

When compared with MSS CRCs, MSI-low CRCs showed significantly more frequent association with poorly differentiated histology, mucinous carcinoma, and large tumour size. In addition, MSI-low CRCs demonstrated significantly less frequent lymph node metastasis and advanced tumour stage than MSS CRCs. When compared with MSI-high CRCs, MSI-low CRCs were significantly more frequently located in distal colon. Three-year overall and disease-free survival rates of MSS, MSI-low and MSI-high CRCs were 83.5%, 90.0% and 91.7% and 82.0%, 89.1% and 87.5%, respectively and neither demonstrated significant difference between three groups.

CONCLUSIONS

These results indicated that sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological features and might form a distinct subgroup especially from MSS CRCs. Further large studies are required to evaluate the impact of MSI-low status on prognosis.

DNA mismatch binding and antiproliferative activity of rhodium metalloinsertors

Deficiencies in mismatch repair (MMR) are associated with carcinogenesis. Rhodium metalloinsertors bind to DNA base mismatches with high specificity and inhibit cellular proliferation preferentially in MMR-deficient cells versus MMR-proficient cells. A family of chrysenequinone diimine complexes of rhodium with varying ancillary ligands that serve as DNA metalloinsertors has been synthesized, and both DNA mismatch binding affinities and antiproliferative activities against the human colorectal carcinoma cell lines HCT116N and HCT116O, an isogenic model system for MMR deficiency, have been determined. DNA photocleavage experiments reveal that all complexes bind to the mismatch sites with high specificities; DNA binding affinities to oligonucleotides containing single base CA and CC mismatches, obtained through photocleavage titration or competition, vary from 10(4) to 10(8) M(-1) for the series of complexes. Significantly, binding affinities are found to be inversely related to ancillary ligand size and directly related to differential inhibition of the HCT116 cell lines. The observed trend in binding affinity is consistent with the metalloinsertion mode where the complex binds from the minor groove with ejection of mismatched base pairs. The correlation between binding affinity and targeting of the MMR-deficient cell line suggests that rhodium metalloinsertors exert their selective biological effects on MMR-deficient cells through mismatch binding in vivo.

Microsatellite instability, mismatch repair deficiency, and BRAF mutation in treatment-resistant germ cell tumors

PURPOSE

Mismatch repair (MMR) deficiency and microsatellite instability (MSI) are associated with cisplatin resistance in human germ cell tumors (GCTs). BRAF mutation (V600E) is found in MSI colorectal cancers. The role of RAS/RAF pathway mutations in GCT treatment response is unknown.

PATIENTS AND METHODS

Two patient cohorts were investigated: 100 control GCTs (50 seminomas and 50 nonseminomas) and 35 cisplatin-based chemotherapy-resistant GCTs. MMR proteins were analyzed by immunohistochemistry, and eight microsatellite loci were examined for MSI. Tumors were assessed for specific BRAF and KRAS mutations.

RESULTS

Resistant tumors showed a higher incidence of MSI than controls: 26% versus 0% in two or more loci (P < .0001). All resistant tumors were wild-type KRAS, and two controls (2%) contained a KRAS mutation. There was a significantly higher incidence of BRAF V600E mutation in resistant tumors compared with controls: 26% versus 1% (P < .0001). BRAF mutations were highly correlated with MSI (P = .006), and MSI and mutated BRAF were correlated with weak or absent staining for hMLH1 (P = .017 and P = .008). Low or absent staining of hMLH1 was correlated with promoter hypermethylation (P < .001). Tumors lacking expression of hMLH1 or MSH6 were significantly more frequent in resistant GCTs than in controls (P = .001 and 0.0036, respectively). Within the subgroup of resistant tumors, patients with MSI showed a trend to longer progression-free survival (P = .068).

CONCLUSION

We report for the first time a correlation between a gene mutation--BRAF V600E--and cisplatin resistance in nonseminomatous GCTs. Furthermore, a correlation between MMR deficiency, MSI, and treatment failure is confirmed.

Cost analysis of biomarker testing for mismatch repair deficiency in node-positive colorectal cancer

Background

Microsatellite instability (MSI) in colorectal cancer is caused by defective DNA mismatch repair (MMR). It is present in 15 per cent of sporadic colorectal cancers owing to epigenetic mutL homologue 1 (MLH1) inactivation. The evidence suggests that patients with tumours caused by defective DNA MMR do not benefit from 5-fluorouracil (5-FU)-based chemotherapy.

Methods

The proportion of cancers with defective DNA MMR identified by MSI analysis or immunohistochemistry was calculated from published data. The cost of analysis was compared with the potential savings if 5-FU-based chemotherapy was not administered to these patients.

Results

Some 16·3 per cent of sporadic colorectal cancers had defective DNA MMR. Immunostaining for MLH1 and mutS homologue 2 (MSH2) had a sensitivity of 92·4 per cent and a specificity of 99·6 per cent for identifying MSI-high tumours. The strongest predictive variable was right-sidedness, with positive and negative predictive values of 0·329 and 0·948 respectively. If 5-FU-based chemotherapy were not administered, potential savings of up to £1·2 million per 1000 patients tested could be made. Costs would be higher if alternative chemotherapeutic regimens were substituted as a result of testing.

Conclusion

Knowledge of MMR status may enable participation in trials of non-5-FU-based chemotherapy. The cost of MMR testing may be offset by more efficient use of chemotherapy.

DNA damage and repair: from molecular mechanisms to health implications

DNA is subjected to several modifications, resulting from endogenous and exogenous sources. The cell has developed a network of complementary DNA-repair mechanisms, and in the human genome, >130 genes have been found to be involved. Knowledge about the basic mechanisms for DNA repair has revealed an unexpected complexity, with overlapping specificity within the same pathway, as well as extensive functional interactions between proteins involved in repair pathways. Unrepaired or improperly repaired DNA lesions have serious potential consequences for the cell, leading to genomic instability and deregulation of cellular functions. A number of disorders or syndromes, including several cancer predispositions and accelerated aging, are linked to an inherited defect in one of the DNA-repair pathways. Genomic instability, a characteristic of most human malignancies, can also arise from acquired defects in DNA repair, and the specific pathway affected is predictive of types of mutations, tumor drug sensitivity, and treatment outcome. Although DNA repair has received little attention as a determinant of drug sensitivity, emerging knowledge of mutations and polymorphisms in key human DNA-repair genes may provide a rational basis for improved strategies for therapeutic interventions on a number of tumors and degenerative disorders.

Large proportion of low frequency microsatellite-instability and loss of heterozygosity in pheochromocytoma and endocrine tumors detected with an extended marker panel

PURPOSE

Pheochromocytoma (PCC) is a usually benign tumor originated in the majority of patients from the adrenal medulla. Regarding sporadic forms of PCC, mechanisms of pathogenesis are largely unknown. Recently, microsatellite-instability (MSI) was discussed as genetic factor contributing to PCC development. Since microsatellite markers used for MSI detection have only been recommended for colorectal carcinoma (CRC), we established an extended marker set for MSI detection in PCC.

METHODS

Twenty-two PCC patients were analyzed applying 11 microsatellite markers. Our marker set comprised the reference panel for CRC and six additional markers, which have already been described to detect MSI in tumors other than CRC. Moreover, 23 endocrine tumors with gastrointestinal origin were examined in order to test the applicability of this marker panel.

RESULTS

Microsatellite-instability was detected in 41% of PCCs. Twenty-seven percent showed loss of heterozygosity (LOH) events affecting different chromosomal regions. Among the 23 patients with endocrine tumors, only three (one pancreatic endocrine tumor, one duodenal neuro-endocrine tumor, one hepatic metastasis of a primary tumor with unknown origin) demonstrated MSI.

CONCLUSIONS

The extended microsatellite panel is qualified to detect MSI in PCC. Nine percent of MSI-positive cases would have not been noticed by the use of the reference panel alone. PCCs are characterized by low frequency MSI pointing to failures in factors involved in DNA replication.

Targeting DNA repair as a promising approach in cancer therapy

An increased DNA-repair activity in tumour cells has been associated with resistance to treatment to DNA-directed drugs, while defects in DNA repair pathways result in hypersensitivity to these agents. In the past years the unravelling of the molecular basis of these DNA pathways, with a better understanding of the DNA damage caused by different anticancer agents, has provided the rationale for the use of some DNA repair inhibitors to optimise the therapeutic use of DNA-damaging agents currently used in the treatment of tumours. In addition, the possibility to specifically target the differences in DNA repair capacity between normal and tumour cells has recently emerged as an exciting possibility. The present review will mainly cover those approaches that are currently under clinical investigation.