Enrichment for DNA mismatch repair-deficient cells during treatment with cisplatin

Revisiting the Anti-Cancer Toxicity of Clinically Approved Platinating Derivatives

Cisplatin (CDDP), carboplatin (CP), and oxaliplatin (OXP) are three platinating agents clinically approved worldwide for use against a variety of cancers. They are canonically known as DNA damage inducers; however, that is only one of their mechanisms of cytotoxicity. CDDP mediates its effects through DNA damage-induced transcription inhibition and apoptotic signalling. In addition, CDDP targets the endoplasmic reticulum (ER) to induce ER stress, the mitochondria via mitochondrial DNA damage leading to ROS production, and the plasma membrane and cytoskeletal components. CP acts in a similar fashion to CDDP by inducing DNA damage, mitochondrial damage, and ER stress. Additionally, CP is also able to upregulate micro-RNA activity, enhancing intrinsic apoptosis. OXP, on the other hand, at first induces damage to all the same targets as CDDP and CP, yet it is also capable of inducing immunogenic cell death via ER stress and can decrease ribosome biogenesis through its nucleolar effects. In this comprehensive review, we provide detailed mechanisms of action for the three platinating agents, going beyond their nuclear effects to include their cytoplasmic impact within cancer cells. In addition, we cover their current clinical use and limitations, including side effects and mechanisms of resistance.

Platinum Complexes in Colorectal Cancer and Other Solid Tumors

Simple Summary

Cisplatin is successfully used for the treatment of various solid cancers. Unfortunately, it shows no activity in colorectal cancer. The resistance phenotype of colorectal cancer cells is mainly caused by alterations in p53-controlled DNA damage signaling and/or defects in the cellular mismatch repair pathway. Improvement of platinum-based chemotherapy in cisplatin-unresponsive cancers, such as colorectal cancer, might be achieved by newly designed cisplatin analogues, which retain activity in unresponsive tumor cells. Moreover, a combination of cisplatin with biochemical modulators of DNA damage signaling might sensitize cisplatin-resistant tumor cells to the drug, thus providing another strategy to improve cancer therapy.

Abstract

Cisplatin is one of the most commonly used drugs for the treatment of various solid neoplasms, including testicular, lung, ovarian, head and neck, and bladder cancers. Unfortunately, the therapeutic efficacy of cisplatin against colorectal cancer is poor. Various mechanisms appear to contribute to cisplatin resistance in cancer cells, including reduced drug accumulation, enhanced drug detoxification, modulation of DNA repair mechanisms, and finally alterations in cisplatin DNA damage signaling preventing apoptosis in cancer cells. Regarding colorectal cancer, defects in mismatch repair and altered p53-mediated DNA damage signaling are the main factors controlling the resistance phenotype. In particular, p53 inactivation appears to be associated with chemoresistance and poor prognosis. To overcome resistance in cancers, several strategies can be envisaged. Improved cisplatin analogues, which retain activity in resistant cancer, might be applied. Targeting p53-mediated DNA damage signaling provides another therapeutic strategy to circumvent cisplatin resistance. This review provides an overview on the DNA repair pathways involved in the processing of cisplatin damage and will describe signal transduction from cisplatin DNA lesions, with special attention given to colorectal cancer cells. Furthermore, examples for improved platinum compounds and biochemical modulators of cisplatin DNA damage signaling will be presented in the context of colon cancer therapy.

The mismatch repair-dependent DNA damage response: Mechanisms and implications

An important role for the DNA mismatch repair (MMR) pathway in maintaining genomic stability is embodied in its conservation through evolution and the link between loss of MMR function and tumorigenesis. The latter is evident as inheritance of mutations within the major MMR genes give rise to the cancer predisposition condition, Lynch syndrome. Nonetheless, how MMR loss contributes to tumorigenesis is not completely understood. In addition to preventing the accumulation of mutations, MMR also directs cellular responses, such as cell cycle checkpoint or apoptosis activation, to different forms of DNA damage. Understanding this MMR-dependent DNA damage response may provide insight into the full tumor suppressing capabilities of the MMR pathway. Here, we delve into the proposed mechanisms for the MMR-dependent response to DNA damaging agents. We discuss how these pre-clinical findings extend to the clinical treatment of cancers, emphasizing MMR status as a crucial variable in selection of chemotherapeutic regimens. Also, we discuss how loss of the MMR-dependent damage response could promote tumorigenesis via the establishment of a survival advantage to endogenous levels of stress in MMR-deficient cells.

Linking arsenite- and cadmium-generated oxidative stress to microsatellite instability in vitro and in vivo

Mismatch repair (MMR) corrects replicative errors and minimizes DNA damage that occurs frequently in microsatellites. MMR deficiency is manifested as microsatellite instability (MSI), which contributes to hypermutability and cancer pathogenesis. Genomic instability, including MSI and chromosomal instability, appears to be responsible for the carcinogenesis of arsenic and cadmium, common contaminants in our environment. However, few studies have addressed arsenic- or cadmium-induced MSI, especially its potential link with arsenic- or cadmium-generated oxidative stress, due to the lack of quantifiable MSI assays and cost-effective animal models. Here, using a dual-fluorescent reporter, we demonstrate that sub-lethal doses of cadmium or arsenite, but not arsenate, increased the MSI frequency in human colorectal cancer cells. Arsenite- and cadmium-induced MSI occurred concomitantly with increased levels of reactive species and oxidative DNA damage, and with decreased levels of MMR proteins. However, N-acetyl-l-cysteine (NAC) suppressed arsenite- and cadmium-induced MSI and oxidative stress while restoring the levels of MMR proteins in the cells. Similarly, MSI was induced separately by arsenite and cadmium, and suppressed by NAC, in zebrafish in a fluorescinated PCR-based assay with newly-developed microsatellite markers and inter-segmental comparisons. Of five selected antioxidants examined, differential effects were exerted on the MSI induction and cytotoxicity of both arsenite and cadmium. Compared to MMR-proficient cells, MMR-deficient cells were more resistant to arsenic-mediated and cadmium-mediated cytotoxicity. Our findings demonstrate a novel linkage between arsenite-generated and cadmium-generated oxidative stress and MSI induction. Our findings also caution that antioxidants must be individually validated before being used for preventing arsenite- and cadmium-induced MSI that is associated with cancer development.

Mismatch repair defects and Lynch syndrome: The role of the basic scientist in the battle against cancer

We have currently entered a genomic era of cancer research which may soon lead to a genomic era of cancer treatment. Patient DNA sequencing information may lead to a personalized approach to managing an individual's cancer as well as future cancer risk. The success of this approach, however, begins not necessarily in the clinician's office, but rather at the laboratory bench of the basic scientist. The basic scientist plays a critical role since the DNA sequencing information is of limited use unless one knows the function of the gene that is altered and the manner by which a sequence alteration affects that function. The role of basic science research in aiding the clinical management of a disease is perhaps best exemplified by considering the case of Lynch syndrome, a hereditary disease that predisposes patients to colorectal and other cancers. This review will examine how the diagnosis, treatment and even prevention of Lynch syndrome-associated cancers has benefitted from extensive basic science research on the DNA mismatch repair genes whose alteration underlies this condition.

YY1 suppresses FEN1 over-expression and drug resistance in breast cancer

Background

Drug resistance is a major challenge in cancer therapeutics. Abundant evidence indicates that DNA repair systems are enhanced after repetitive chemotherapeutic treatments, rendering cancers cells drug-resistant. Flap endonuclease 1 (FEN1) plays critical roles in DNA replication and repair and in counteracting replication stress, which is a key mechanism for many chemotherapeutic drugs to kill cancer cells. FEN1 was previously shown to be upregulated in response to DNA damaging agents. However, it is unclear about the transcription factors that regulate FEN1 expression in human cancer. More importantly, it is unknown whether up-regulation of FEN1 has an adverse impact on the prognosis of chemotherapeutic treatments of human cancers.

Methods

To reveal regulation mechanism of FEN1 expression, we search and identify FEN1 transcription factors or repressors and investigate their function on FEN1 expression by using a combination of biochemical, molecular, and cellular approaches. Furthermore, to gain insights into the impact of FEN1 levels on the response of human cancer to therapeutic treatments, we determine FEN1 levels in human breast cancer specimens and correlate them to the response to treatments and the survivorship of corresponding breast cancer patients.

Results

We observe that FEN1 is significantly up-regulated upon treatment of chemotherapeutic drugs such as mitomycin C (MMC) and Taxol in breast cancer cells. We identify that the transcription factor/repressor YY1 binds to the FEN1 promoter and suppresses the expression of FEN1 gene. In response to the drug treatments, YY1 is dissociated from the FEN1 promoter region leading over-expression of FEN1. Overexpression of YY1 in the cells results in down-regulation of FEN1 and sensitization of the cancer cells to MMC or taxol. Furthermore, we observe that the level of FEN1 is inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.

Conclusion

Altogether, our current data indicate that YY1 is a transcription repressor of FEN1 regulating FEN1 levels in response to DNA damaging agents. FEN1 is up-regulated in human breast cancer and its levels inversely correlated with cancer drug and radiation resistance and with survivorship in breast cancer patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1043-1) contains supplementary material, which is available to authorized users.

Guidelines for surveillance of individuals with constitutional mismatch repair-deficiency proposed by the European Consortium "Care for CMMR-D" (C4CMMR-D)

Lynch syndrome (LS) is an autosomal dominant disorder caused by a defect in one of the DNA mismatch repair genes: MLH1, MSH2, MSH6 and PMS2. In the last 15 years, an increasing number of patients have been described with biallelic mismatch repair gene mutations causing a syndrome referred to as 'constitutional mismatch repair-deficiency' (CMMR-D). The spectrum of cancers observed in this syndrome differs from that found in LS, as about half develop brain tumours, around half develop digestive tract cancers and a third develop haematological malignancies. Brain tumours and haematological malignancies are mainly diagnosed in the first decade of life, and colorectal cancer (CRC) and small bowel cancer in the second and third decades of life. Surveillance for CRC in patients with LS is very effective. Therefore, an important question is whether surveillance for the most common CMMR-D-associated cancers will also be effective. Recently, a new European consortium was established with the aim of improving care for patients with CMMR-D. At a workshop of this group held in Paris in June 2013, one of the issues addressed was the development of surveillance guidelines. In 1968, criteria were proposed by WHO that should be met prior to the implementation of screening programmes. These criteria were used to assess surveillance in CMMR-D. The evaluation showed that surveillance for CRC is the only part of the programme that largely complies with the WHO criteria. The values of all other suggested screening protocols are unknown. In particular, it is questionable whether surveillance for haematological malignancies improves the already favourable outcome for patients with these tumours. Based on the available knowledge and the discussions at the workshop, the European consortium proposed a surveillance protocol. Prospective collection of all results of the surveillance is needed to evaluate the effectiveness of the programme.

Claudin-3 and claudin-4 regulate sensitivity to cisplatin by controlling expression of the copper and cisplatin influx transporter CTR1

Claudin-3 (CLDN3) and claudin-4 (CLDN4) are the major structural molecules that form tight junctions (TJs) between epithelial cells. We found that knockdown of the expression of either CLDN3 or CLDN4 produced marked changes in the phenotype of ovarian cancer cells, including an increase in resistance to cisplatin (cDDP). The effect of CLND3 and CLDN4 on cDDP cytotoxicity, cDDP cellular accumulation, and DNA adduct formation was compared in the CLDN3- and CLDN4-expressing parental human ovarian carcinoma 2008 cells and CLDN3 and CLDN4 knockdown sublines (CLDN3KD and CLDN4KD, respectively). Knockdown of CLDN3 or CLDN4 rendered human ovarian carcinoma 2008 cells resistant to cDDP in both in vitro culture and in vivo xenograft model. The net accumulation of platinum (Pt) and the Pt-DNA adduct levels were reduced in CLDN3KD and CLDN4KD cells. The endogenous mRNA levels of copper influx transporter CTR1 were found to be significantly reduced in the knockdown cells, and exogenous expression of CTR1 restored their sensitivity to cDDP. Reexpression of an shRNAi-resistant CLDN3 or CLDN4 up-regulated CTR1 levels, reversed the cDDP resistance, and enhanced TJ formation in the knockdown cells. Baseline copper (Cu) level, Cu uptake, and Cu cytotoxicity were also reduced in CLDN3KD and CLDN4KD cells. Cu-dependent tyrosinase activity was also markedly reduced in both types of CLDN knockdown cells when incubated with the substrate l-DOPA. These results indicate that CLDN3 and CLDN4 affect sensitivity of the ovarian cancer cells to the cytotoxic effect of cDDP by regulating expression of the Cu transporter CTR1.

Head and neck squamous cell carcinoma: mismatch repair immunohistochemistry and promoter hypermethylation of hMLH1 gene

Squamous cell carcinomas of the head and neck are the sixth most frequently occurring cancers and the seventh leading cause of cancer-related deaths worldwide. Epigenetic alteration, using promoter hypermethylation of hMLH1 gene, is important for the development of head and neck squamous cell carcinoma (HNSCC). AIM OF THIS WORK: The aim of the present study is to analyze the relationship between protein expression and promoter hypermethylation of the hMLH1 gene in HNSCC and correlating inactivation of this gene with clinical parameters.

MATERIALS AND METHODS

Paired normal and tumor specimens from 49 patients with HNSCC were collected from Otolaryngology Department, Minia University Hospital, from 2006 to 2009. We analyzed hMLH1 protein expression and promoter hypermethylation by immunohistochemical and methylation-specific polymerase chain reaction (MSP).

RESULTS

Decreased hMLH1 protein expression and hMLH1 promoter hypermethylation were shown in 15 (30.6%) and 14 (28.6%) cases, respectively. Eleven cases showed dysplasia and or carcinoma in situ in the surface squamous epithelia, and all were positively stained for the hMLH1 protein. hMLH1 promoter hypermethylation was detected in 10 (20.4%) cases of normal-appearing squamous mucosa adjacent to invasive carcinoma. Thirteen (86.7%) of 15 cases that were negative for the hMLH1 protein showed promoter hypermethylation, whereas 33 (97%) of 34 cases positive for the protein were negative of promoter methylation. Promoter hypermethylation was detected in 1 (7.1%) case in which invasive tumor cells were moderately positive for the hMLH1 protein. No significant correlation was observed between hMLH1 protein expression or hMLH1 promoter hypermethylation and any of clinicopathologic parameters.

CONCLUSIONS

hMLH1 gene may be detected early in head and neck squamous carcinogenesis. Promoter hypermethylation is an important mechanism for hMLH1 gene inactivation in HNSCC.

Mechanisms of multidrug resistance in cancer

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Resistance exists against every effective anticancer drug and can develop by numerous mechanisms including decreased drug uptake, increased drug efflux, activation of detoxifying systems, activation of DNA repair mechanisms, evasion of drug-induced apoptosis, etc. In the first part of this chapter, we briefly summarize the current knowledge on individual cellular mechanisms responsible for MDR, with a special emphasis on ATP-binding cassette transporters, perhaps the main theme of this textbook. Although extensive work has been done to characterize MDR mechanisms in vitro, the translation of this knowledge to the clinic has not been crowned with success. Therefore, identifying genes and mechanisms critical to the development of MDR in vivo and establishing a reliable method for analyzing clinical samples could help to predict the development of resistance and lead to treatments designed to circumvent it. Our thoughts about translational research needed to achieve significant progress in the understanding of this complex phenomenon are therefore discussed in a third section. The pleotropic response of cancer cells to chemotherapy is summarized in a concluding diagram.

MLH1 expression sensitises ovarian cancer cells to cell death mediated by XIAP inhibition

BACKGROUND

The X-linked inhibitor of apoptosis protein (XIAP), an endogenous apoptosis suppressor, can determine the level of caspase accumulation and the resultant response to apoptosis-inducing agents such as cisplatin in epithelial ovarian cancer (EOC). In addition, the mismatch repair protein, hMLH1, has been linked to DNA damage-induced apoptosis by cisplatin by both p53-dependent and -independent mechanisms.

METHODS

In this study, hMLH1 expression was correlated with clinical response to platinum drugs and survival in advanced stage (III-IV) EOC patients. We then investigated whether MLH1 loss was a determinant in anti-apoptosis response to cisplatin mediated by XIAP in isogenic and established EOC cell lines with differential p53 status.

RESULTS

The percentage of cells undergoing cisplatin-induced cell killing was higher in MLH1-proficient cells than in MLH1-defective cells. In addition, the presence of wild-type hMLH1 or hMLH1 re-expression significantly increased sensitivity to 6-thioguanine, a MMR-dependent agent. Cell-death response to 6-thioguanine and cisplatin was associated with significant proteolysis of MLH1, with XIAP destabilisation and increased caspase-3 activity. The siRNA-mediated inhibition of XIAP increased MLH1 proteolysis and cell death in MLH1-proficient cells but not in MLH1-defective cells.

CONCLUSION

These data suggest that XIAP inhibitors may prove to be an effective means of sensitising EOC to MLH1-dependent apoptosis.

Methylation and protein expression of DNA repair genes: association with chemotherapy exposure and survival in sporadic ovarian and peritoneal carcinomas

Background

DNA repair genes critically regulate the cellular response to chemotherapy and epigenetic regulation of these genes may be influenced by chemotherapy exposure. Restoration of BRCA1 and BRCA2 mediates resistance to platinum chemotherapy in recurrent BRCA1 and BRCA2 mutated hereditary ovarian carcinomas. We evaluated BRCA1, BRCA2, and MLH1 protein expression in 115 sporadic primary ovarian carcinomas, of which 31 had paired recurrent neoplasms collected after chemotherapy. Additionally, we assessed whether promoter methylation of BRCA1, MLH1 or FANCF influenced response to chemotherapy or explained alterations in protein expression after chemotherapy exposure.

Results

Of 115 primary sporadic ovarian carcinomas, 39 (34%) had low BRCA1 protein and 49 (42%) had low BRCA2 expression. BRCA1 and BRCA2 protein expression were highly concordant (p < 0.0001). MLH1 protein loss occurred in 28/115 (24%) primary neoplasms. BRCA1 protein loss in primary neoplasms was associated with better survival (p = 0.02 Log Rank test) and remained significant after accounting for either stage or age in a multivariate model (p = 0.04, Cox proportional hazards). In paired specimens, BRCA1 protein expression increased in 13/21 (62%) and BRCA2 protein expression increased in 15/21 (71%) of recurrent carcinomas with low or intermediate protein in the paired primary. In contrast MLH1 expression was rarely decreased in recurrent carcinomas (1/33, 3%). Similar frequencies of MLH1, BRCA1, and FANCF promoter methylation occurred in primary carcinomas without previous chemotherapy, after neoadjuvant chemotherapy, or in recurrent neoplasms.

Conclusion

Low BRCA1 expression in primary sporadic ovarian carcinoma is associated with prolonged survival. Recurrent ovarian carcinomas commonly have increased BRCA1 and/or BRCA2 protein expression post chemotherapy exposure which could mediate resistance to platinum based therapies. However, alterations in expression of these proteins after chemotherapy are not commonly mediated by promoter methylation, and other regulatory mechanisms are likely to contribute to these alterations.

Platinum resistance: the role of DNA repair pathways

Although platinum chemotherapeutic agents such as carboplatin, cisplatin, and oxaliplatin are used to treat a broad range of malignant diseases, their efficacy in most cancers is limited by the development of resistance. There are multiple factors that contribute to platinum resistance but alterations of DNA repair processes have been known for some time to be important in mediating resistance. Recently acquired knowledge has provided insight into the molecular mechanisms of DNA repair pathways and their effect on response to chemotherapy. This review will discuss the most important DNA repair pathways known to be involved in the platinum response, i.e., nucleotide excision repair (NER) and mismatch repair (MMR), and will briefly touch on the role of BRCA in DNA repair. The therapeutic implications of alterations in DNA repair which affect response to platinum in the treatment of patients with malignant disease, such as excision repair cross-complementation group 1 (ERCC1) deficiency and mismatch repair deficiency, will be reviewed.

Newer cytotoxic agents: attacking cancer broadly

The plasticity and instability of the cancer genome is impressive and is characterized by gene amplifications and deletions, rearrangements, and many silent and active mutations. Although targeted therapeutics have had effect in some diseases, there remains a large role for new cytotoxic agents that have the potential to be broadly active across multiple cancers. Platinum-based regimens are the basis for treatment of several common tumors. Satraplatin and picoplatin are newer platinum complexes that form bulkier lesions in DNA than their forerunners. Microtubules are a key target for anticancer agents. Vinca alkaloid and similar compounds fragment these critical structures, whereas taxanes stabilize them. Vinflunine is a new fluorinated Vinca alkaloid derivative with vascular disrupting effects, as well as antitumor effects. Epothilones are a new class of microtubule stabilizers. Mitosis has been targeted directly and indirectly by many anticancer agents. The aurora kinases are new targets in this class. Inhibitors of aurora kinases are likely to be cytotoxic. Finally, protein regulation is essential for cellular integrity. With the approval of bortezomib (Velcade, PS-341), the proteosome, a master protein regulator, has been validated as an anticancer target. The five articles in this issue of CCR Focus present the current status of these next generation cytotoxic agents.

Hsp27, Hsp70 and mismatch repair proteins hMLH1 and hMSH2 expression in peripheral blood lymphocytes from healthy subjects and cancer patients

Mismatch repair (MMR) deficiency and higher expression levels of heat shock proteins (Hsps) have been implicated with drug resistance to topoisomerase II poisons (doxorubicin) and to platinum compounds (cisplatin). This study was designed to determine individual influences of doxorubicin and cisplatin treatment on the expression of Hsp27, Hsp70, hMLH1 and hMSH2 proteins and in the DNA damage status in peripheral blood lymphocytes (PBLs). In addition, we studied whether these proteins and the DNA damage correlated with the survival of cancer patients. PBLs from 10 healthy donors and 25 cancer patients (before and after three cycles of chemotherapy) were exposed to in vitro treatments: C (control), HS (heat shock at 42 degrees C), Do or Pt (doxorubicin or cisplatin alone), and HS+Do or HS+Pt (heat shock+doxorubicin or heat shock+cisplatin). PBLs were collected at time 0 (T0: immediately after drug treatment) and after 24h of repair (T24). Hsp27, Hsp70, hMLH1 and hMSH2 were studied by immunocytochemistry and the DNA damage by alkaline comet assay. Immunofluorescence studies and confocal microscopy revealed that hMLH1 and hMSH2 colocalized with Hsp27 and Hsp72 (inducible form of Hsp70). hMLH1 and hMSH2 were significantly induced by Pt and HS+Pt at T24 in cancer patients, but only modestly influenced by Do. Cancer patients presented higher basal expression of total and nuclear Hsp27 and Hsp70 than controls, and these proteins were also increased by HS, Do and HS+Do. The Hsp70 induction by Pt and HS+Pt was noted in cancer patients, especially nuclear Hsp70. In cancer patients, basal DNA damage was slightly higher than in healthy persons; and after Pt and HS+Pt treatments, DNA migration and number of apoptotic cells were higher than controls. Hsps accomplished a cytoprotective function in pre-chemotherapy PBLs (HS before Do or Pt), but not in post-chemotherapy samples. In Pt-treated patients the ratio N/C (nuclear/cytoplasmic) of Hsp27 was related to disease free survival and overall survival, and hMSH2 correlated with overall survival. The results point to the utility of these molecules and of the comet assay as possible predictive markers.

Medulloblastoma, acute myelocytic leukemia and colonic carcinomas in a child with biallelic MSH6 mutations

Background A 13-year-old girl presented with rectal bleeding and was found to have two colonic carcinomas (stage Dukes' C) and multiple colonic polyps. At the age of 7 years she had widespread hyperpigmented and hypopigmented skin lesions, and had developed medulloblastoma, which was treated with chemotherapy and craniospinal irradiation. At the age of 10 years she had developed acute myelocytic leukemia, M5. She was treated with chemotherapy including sibling bone marrow transplant with busulfan/cyclophosphamide conditioning. A three-generation family history identified no relatives with colonic carcinomas or polyposis. Investigations Immunohistochemical analysis was performed on a sample of colonic adenoma. Staining for MLH1 and MSH2 was normal but was absent for MSH6. Direct sequencing of MSH6 was performed in the proband and both parents. Diagnosis Constitutional biallelic mutations in the mismatch repair gene MSH6 were identified in the proband. Both parents are carriers of one mutation. This is the first individual with biallelic MSH6 mutations reported with either medulloblastoma or acute myelocytic leukemia. Management Cascade genetic testing and colonoscopic screening for colorectal carcinoma has been offered to relatives carrying one mutation. The proband underwent panproctocolectomy and received adjuvant capecitabine. Identification of constitutional biallelic mismatch repair gene mutations allows the avoidance of chemotherapeutic agents likely to be ineffective and mutagenic in the context of the underlying mismatch repair deficiency. It is important to consider this diagnosis in children presenting with malignancy and abnormal skin pigmentation, even in the absence of a strong family history of tumors.

DNA mismatch repair and p53 function are major determinants of the rate of development of cisplatin resistance

As opposed to factors that control sensitivity to the acute cytotoxic effect of cisplatin, little is known about the factors that determine the rate at which resistance develops. This study examined how loss of p53 or DNA mismatch repair (MMR) function affected the rate of development of resistance to cisplatin in human colon carcinoma cells during sequential cycles of cisplatin exposure that mimic the way the drug is used in the clinic. We used a panel of sublines molecularly engineered to express either the MMR- and p53-proficient phenotype or singly or doubly deficient phenotypes. Loss of either MMR or p53 alone increased the rate of development of resistance to cisplatin by 1.8- and 2.4-fold, respectively; however, loss of both MMR and p53 increased the rate by 4.8-fold. Inhibition of DNA polymerase zeta by suppression of the expression of its REV3 subunit eliminated the increased rate of development of resistance observed in the MMR-deficient cells. Loss of p53 or MMR increased the steady-state level of REV3 and of REV1 mRNA; loss of both functions increased these levels much further by a factor of 20.2-fold for REV3 and 10.3-fold for REV1. The basal level of homologous recombination measured using a reporter vector was 1.3- to 1.7-fold higher in cells that had lost either p53 or MMR function, and 2.6-fold higher in cells that had lost both. In the p53- and MMR-proficient cells, cisplatin induced a 17-fold increase in homologous recombination even when the recombining sequences that did not contain cisplatin adducts; the magnitude of induction was even greater in cells that had lost either one or both functions. We conclude that separate from effects on sensitivity to the acute cytotoxic effect of cisplatin, loss of MMR, especially when combined with loss of p53, results in rapid evolution of cisplatin resistance during sequential rounds of drug exposure that is likely mediated by enhanced mutagenic translesion synthesis. The DNA damage response activated by cisplatin is accompanied by a p53- and MMR-dependent increase in homologous recombination even between adduct-free sequences.

A phase II study of a paclitaxel and oxaliplatin combination in platinum-sensitive recurrent advanced ovarian cancer patients

PURPOSE

A multicentric, phase II study to evaluate the efficacy and safety of the combination paclitaxel and oxaliplatin in patients with platinum-sensitive recurrent ovarian cancer.

PATIENTS AND METHODS

Patients received 175 mg/m(2) paclitaxel (over 3 h) followed by 130 mg/m(2) oxaliplatin (over 2 h) every 21 days for up to nine cycles without hydration or primary granulocyte colony-stimulating factor prophylaxis. Patients had to have an Eastern Cooperative Oncology Group performance status of 0-2 and to have received no more than one prior cisplatin- and/or carboplatin-containing chemotherapy regimen with a platinum-progression-free interval > or =6 months.

RESULTS

Of the 105 patients enrolled and treated, 98 were eligible. An overall response rate of 81% (79 of 98 patients) (95% confidence interval 71% to 88%) was observed according to RECIST criteria (third party reviewed), and 88% (86 of 98) when this was complemented with CA-125 response. With a median follow up of 43.6 months (range 30.2-64.2) the median progression-free survival was 10.2 months (range 0.3-21.4) and the overall survival 32.4 months. Seven hundred and eight cycles were administered (median seven per patient; range one to nine). A total of 67% of patients experienced National Cancer Institute Common Toxicity Criteria grade 3-4 neutropenia, including 8% with concomitant febrile episode, without treatment-related deaths. Ninety-three per cent of patients experienced neuropathy of grade 1 or more, including 25% with cumulative reversible peripheral neuropathy of grade 3-4. Oxaliplatin doses were reduced in 30 patients due to neurotoxicity.

CONCLUSIONS

The oxaliplatin/paclitaxel combination can be administered in an outpatient setting every 3 weeks without specific measures. The high level of activity and its duration observed warrants further evaluation of this combination in pretreated platinum-sensitive advanced ovarian cancer patients.

Profiling of proteins associated with cisplatin resistance in ovarian cancer cells

Resistance to cisplatin is a major impediment to the successful treatment of ovarian cancer, but the precise nature of the resistance is still unclear. In the current study, we aimed to investigate and compare the protein expression profiles in cisplatin-sensitive and cisplatin-resistant ovarian cancer cell lines. We employed the recent development of surface-enhanced laser desorption/ionization ProteinChip technology to measure protein expression in three human ovarian cancer cell lines (KF-1, MN-1, and A2780) and their sublines (KF-r, MN-r, and A2780cp) resistant to cisplatin. The ProteinChip Arrays were analyzed using the ProteinChip Reader. We did not find any regularity in protein expressions in secretions of cisplatin-sensitive and cisplatin-resistant cells. But on the IMAC3 array, we captured 12 identical expressions which represent a subset of proteins whose expression levels are different between parent ovarian cancer cells and their cisplatin-resistant cells. In particular, at the molecular weight of 7829 d, three kinds of parent cell lines exhibited an elevated expression and their cisplatin-resistant sublines revealed a lowered expression. At the molecular weight of 6881 d, for KF and MN cell lines, opposite protein expressions were seen in the parent cell line and its cisplatin-resistant subline. We think the interesting protein expressions perhaps suggest some mechanisms involved in cisplatin resistance.

Multiple genetic and epigenetic interacting mechanisms contribute to clonally selection of drug-resistant tumors: Current views and new therapeutic prospective

Successful treatment of cancer requires a clear understanding of drug-resistance mechanism. Cancer patient are often treated with standard protocols without considering individual difference in chemosensitivity, whereas the efficacy of anticancer drug varies widely among individual patients. Since chemosensitivity involves multiple interacting factors, it is not sufficient to investigate a single gene or factor to fix chemoresistance. Along with affecting disease progression, the synergism between genetic and epigenetic abnormalities can contribute to convert a sensible tumor cell in a resistant one. Unlike genetic changes, epigenetic changes are potentially reversible. Therefore, treatment with DNA methylation inhibitors can reactivate the expression of genes improperly methylated and can reverse many aspect of cancer phenotype such as drug resistance. The demethylating agents are used in the treatment of several kind of tumor, but toxicity and the potential outcome on the normal methylation patterns have always been concern of researchers and clinicals. It is necessary to create individual chemosensitivity-chemoresistance maps in order to identify the combination of drugs for optimized treatments. An overview on genetic and epigenetic events contributing to clonally selection of chemotherapeutic-resistant tumors is discussed.

Signalling cell cycle arrest and cell death through the MMR System

Loss of DNA mismatch repair (MMR) in mammalian cells, as well as having a causative role in cancer, has been linked to resistance to certain DNA damaging agents including clinically important cytotoxic chemotherapeutics. MMR-deficient cells exhibit defects in G2/M cell cycle arrest and cell killing when treated with these agents. MMR-dependent cell cycle arrest occurs, at least for low doses of alkylating agents, only after the second S-phase following DNA alkylation, suggesting that two rounds of DNA replication are required to generate a checkpoint signal. These results point to an indirect role for MMR proteins in damage signalling where aberrant processing of mismatches leads to the generation of DNA structures (single-strand gaps and/or double-strand breaks) that provoke checkpoint activation and cell killing. Significantly, recent studies have revealed that the role of MMR proteins in mismatch repair can be uncoupled from the MMR-dependent damage responses. Thus, there is a threshold of expression of MSH2 or MLH1 required for proper checkpoint and cell-death signalling, even though sub-threshold levels are sufficient for fully functional MMR repair activity. Segregation is also revealed through the identification of mutations in MLH1 or MSH2 that provide alleles functional in MMR but not in DNA damage responses and mutations in MSH6 that compromise MMR but not in apoptotic responses to DNA damaging agents. These studies suggest a direct role for MMR proteins in recognizing and signalling DNA damage responses that is independent of the MMR catalytic repair process. How MMR-dependent G2 arrest may link to cell death remains elusive and we speculate that it is perhaps the resolution of the MMR-dependent G2 cell cycle arrest following DNA damage that is important in terms of cell survival.

Mechanisms of therapy-related carcinogenesis

Therapy-related cancers, defined as second primary cancers that arise as a consequence of chemotherapy and/or radiotherapy, are unusual in that they have a well-defined aetiology. Knowledge of the specific nature of the initiating exposure and exactly when it occurred has made it easier to identify crucial genetic events and to model these in vitro and in vivo. As such, the study of therapy-related cancers has led to the elucidation of discrete mechanisms of carcinogenesis, including DNA double-strand-break-induced gene translocation and genomic instability conferred by loss of DNA repair. Unsurprisingly, some of these mechanisms seem to operate in the development of sporadic cancers.

No significant role for beta tubulin mutations and mismatch repair defects in ovarian cancer resistance to paclitaxel/cisplatin

Background

The mechanisms of chemoresistance in ovarian cancer patients remain largely to be elucidated. Paclitaxel/cisplatin combination is the standard chemotherapeutic treatment for this disease, although some patients do not respond to therapy. Our goals were to investigate whether TUBB mutations and mismatch repair defects underlie paclitaxel and cisplatin resistance.

Methods

Thirty-four patients with primary ovarian carcinomas (26 serous and eight clear cell carcinomas) treated with paclitaxel/cisplatin were analysed. TUBB exon 4 was analysed by nested PCR after a first round PCR using intronic primers. Microsatellite analysis was performed with the quasimonomorphic markers BAT 26 and BAT 34.

Results

Twenty-two of the 34 ovarian cancers (64.7%) presented residual tumour after surgery, seven of which (7/22; 31.8%) were shown to be chemoresistant (five serous and two clear cell tumours). Sequence analysis did not find any mutation in TUBB exon 4. Microsatellite instability was not detected in any of the ovarian carcinomas.

Conclusion

We conclude that TUBB exon 4 mutations and mismatch repair defects do not play a significant role in paclitaxel/cisplatin resistance.

MSH2 missense mutations alter cisplatin cytotoxicity and promote cisplatin-induced genome instability

Defects in the mismatch repair protein MSH2 cause tolerance to DNA damage. We report how cancer-derived and polymorphic MSH2 missense mutations affect cisplatin cytotoxicity. The chemotolerance phenotype was compared with the mutator phenotype in a yeast model system. MSH2 missense mutations display a strikingly different effect on cell death and genome instability. A mutator phenotype does not predict chemotolerance or vice versa. MSH2 mutations that were identified in tumors (Y109C) or as genetic variations (L402F) promote tolerance to cisplatin, but leave the initial mutation rate of cells unaltered. A secondary increase in the mutation rate is observed after cisplatin exposure in these strains. The mutation spectrum of cisplatin-resistant mutators identifies persistent cisplatin adduction as the cause for this acquired genome instability. Our results demonstrate that MSH2 missense mutations that were identified in tumors or as polymorphic variations can cause increased cisplatin tolerance independent of an initial mutator phenotype. Cisplatin exposure promotes drug-induced genome instability. From a mechanistical standpoint, these data demonstrate functional separation between MSH2-dependent cisplatin cytotoxicity and repair. From a clinical standpoint, these data provide valuable information on the consequences of point mutations for the success of chemotherapy and the risk for secondary carcinogenesis.

Microsatellite instability is not related to response to cisplatin-based chemotherapy in cervical cancer

This study investigates whether microsatellite instability (MSI) due to defects of the mismatch repair (MMR) system could be associated with response to cisplatin-based neoadjuvant chemotherapy (NACT) and if cisplatin exposure could select MSI-positive cell clones in cervical cancer. Microsatellite analysis was performed by polymerase chain reactions using six microsatellite markers, while hMLH1 protein expression was investigated by immunohistochemistry. We found that 1 tumor out of 20 (5%) NACT-responding patients and 1 tumor out of 18 (6%) nonresponding patients showed MSI. The analysis of tumor specimens collected after NACT revealed no change in the banding pattern as compared to each corresponding pre-NACT tumor at each locus tested. hMLH1 staining was observed in at least > or =80% of cells in all tumors examined except the two exhibiting MSI. Our data showed that MSI due to defects of the MMR system seems not to play a crucial role in the biology of human cervical cancer cells and that MSI seems not to be related to response to chemotherapy. Moreover, cisplatin exposure did not seem to select for MMR-deficient tumor clones in cervical cancer.

Mismatch repair and DNA damage signalling

Postreplicative mismatch repair (MMR) increases the fidelity of DNA replication by up to three orders of magnitude, through correcting DNA polymerase errors that escaped proofreading. MMR also controls homologous recombination (HR) by aborting strand exchange between divergent DNA sequences. In recent years, MMR has also been implicated in the response of mammalian cells to DNA damaging agents. Thus, MMR-deficient cells were shown to be around 100-fold more resistant to killing by methylating agents of the S(N)1type than cells with functional MMR. In the case of cisplatin, the sensitivity difference was lower, typically two- to three-fold, but was observed in all matched MMR-proficient and -deficient cell pairs. More controversial is the role of MMR in cellular response to other DNA damaging agents, such as ionizing radiation (IR), topoisomerase poisons, antimetabolites, UV radiation and DNA intercalators. The MMR-dependent DNA damage signalling pathways activated by the above agents are also ill-defined. To date, signalling cascades involving the Ataxia telangiectasia mutated (ATM), ATM- and Rad3-related (ATR), as well as the stress-activated kinases JNK/SAPK and p38alpha have been linked with methylating agent and 6-thioguanine (TG) treatments, while cisplatin damage was reported to activate the c-Abl and JNK/SAPK kinases in MMR-dependent manner. MMR defects are found in several different cancer types, both familiar and sporadic, and it is possible that the involvement of the MMR system in DNA damage signalling play an important role in transformation. The scope of this article is to provide a brief overview of the recent literature on this subject and to raise questions that could be addressed in future studies.

Confocal microscopic analysis of the interaction between cisplatin and the copper transporter ATP7B in human ovarian carcinoma cells

Some cisplatin (DDP)-resistant cells overexpress the copper export transporter ATP7B, and cells molecularly engineered to overexpress ATP7B are resistant to DDP. The interaction of Cu with ATP7B normally triggers its relocalization from the perinuclear region to more peripheral vesicles. To investigate the interaction of DDP with ATP7B, we examined the effect of DDP on the subcellular localization of ATP7B using human ovarian carcinoma cells expressing a cyan fluorescent protein (ECFP)-tagged ATP7B (2008/ECFP-ATP7B). ATP7B expression was confirmed in 2008/ECFP-ATP7B cells by Western blotting, and its functionality was documented by showing that it rendered the cells 1.9-fold resistant to CuSO(4) and 4.1-fold resistant to DDP and also reduced the accumulation of both drugs. There was greater sequestration of Pt into intracellular vesicles in the 2008/ECFP-ATP7B cells than in the 2008/ECFP cells. Confocal digital microscopy revealed that ECFP-ATP7B localized in the perinuclear region in absence of drug exposure and that both Cu and DDP triggered relocalization to more peripheral vesicular structures. A fluorescein-labeled form of DDP that retained cytotoxicity and was subject to the same mechanisms of resistance as DDP colocalized with ECFP-ATP7B in the 2008/ECFP-ATP7B cells, whereas the same fluorochrome lacking the DDP moiety did not. These results provide evidence that DDP directly interacts with ATP7B to trigger its relocalization and that ATP7B mediates resistance to DDP by sequestering it into vesicles of the secretory pathway for export from the cell.

Characterization of palindromic loop mismatch repair tracts in mammalian cells

Single- and multi-base (loop) mismatches can arise in DNA by replication errors, during recombination, and by chemical modification of DNA. Single-base and loop mismatches of several nucleotides are efficiently repaired in mammalian cells by a nick-directed, MSH2-dependent mechanism. Larger loop mismatches (> or =12 bases) are repaired by an MSH2-independent mechanism. Prior studies have shown that 12- and 14-base palindromic loops are repaired with bias toward loop retention, and that repair bias is eliminated when five single-base mismatches flank the loop mismatch. Here we show that one single-base mismatch near a 12-base palindromic loop is sufficient to eliminate loop repair bias in wild-type, but not MSH2-defective mammalian cells. We also show that palindromic loop and single-base mismatches separated by 12 bases are repaired independently at least 10% of the time in wild-type cells, and at least 30% of the time in MSH2-defective cells. Palindromic loop and single-base mismatches separated by two bases were never repaired independently. These and other data indicate that loop repair tracts are variable in length. All tracts extend at least 2 bases, some extend <12 bases, and others >12 bases, on one side of the loop. These properties distinguish palindromic loop mismatch repair from the three known excision repair pathways: base excision repair which has one to six base tracts, nucleotide excision repair which has approximately 30 base tracts, and MSH2-dependent mismatch repair, which has tracts that extend for several hundred bases.

Measurement of DNA adducts in cells exposed to cisplatin

The two main cisplatin-induced DNA lesions, G--G and A--G, have been measured in cells exposed to the drug. (G--G and A--G denote the intrastrand bifunctional adducts formed between adjacent purine bases.) It has proven feasible, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), observe the G--G and A--G lesions in mouse fibroblast cells exposed for 1 h to a 120 microM concentration of cisplatin. After extraction of the DNA from the cells, the lesions were enzymatically isolated from the DNA in the form of modified dinucleoside monophosphates with the phosphodiester bond intact. MS/MS detection of the modified dinucleoside monophosphates in the negative ion mode manifests two transitions; from the negative ion to the loss of one NH(3) group and from the ion less one NH(3) group to the loss of both NH(3) groups. The multiple reaction monitoring capability of LC-MS/MS was used to measure the three most abundant isotopes of the two main lesions for both transitions of each lesion (i.e., 12 MS/MS values in toto). Ion currents could be detected for all 12 pairs of MS/MS values in the DNA from exposed cells. Although this protocol results in some overlap of MS/MS values between the two lesions, a slight difference in elution times clearly distinguishes between them.

Phase I and pharmacokinetic study of the multitargeted antifolate pemetrexed in combination with oxaliplatin in patients with advanced solid tumors

BACKGROUND

This phase I and pharmacokinetic study of pemetrexed in combination with oxaliplatin was performed to determine the maximum tolerated dose (MTD), and to evaluate safety and pharmacokinetics in patients with metastatic solid tumors.

PATIENTS AND METHODS

Pemetrexed was administered as a 10- min i.v. infusion followed 30 min later by oxaliplatin as a 2- h infusion, once every 21 days. Up to two previous chemotherapy regimens were allowed. Vitamin B(12) supplementation and folic acid were not included in this study.

RESULTS

Thirty-six patients were treated in six escalating dose levels. Dose-limiting toxicities at dose level 6 (pemetrexed 500 mg/m(2) plus oxaliplatin 130 mg/m(2)) were febrile neutropenia, grade 3-4 diarrhea and grade 3 paresthesia. The MTD was not reached. The most common toxicity was neutropenia, with grade 3-4 occurring in 61% of patients. The pharmacokinetics of this pemetrexed-oxaliplatin combination are consistent with those following single-agent administration. Five responses (all partial) were observed over a broad range of solid tumors.

CONCLUSIONS

This pemetrexed-oxaliplatin combination (without vitamin supplementation) every 21 days can be administered using full therapeutic doses of each agent with acceptable tolerability and no overlapping toxicity. The recommended regimen for phase II studies is pemetrexed 500 mg/m(2) plus oxaliplatin 120 mg/m(2).

Alterations in p53 predict response to preoperative high dose chemotherapy in patients with gastric cancer

AIMS

To evaluate the usefulness of molecular markers in predicting histopathological and clinical response to preoperative high dose chemotherapy (HDCT) and survival of patients with advanced gastric cancer.

METHODS

In a phase II trial, 25 patients with metastatic gastric cancer received preoperative tandem HDCT consisting of etoposide, cisplatin, and mitomycin, followed by autologous bone marrow transplantation to achieve surgical resectability. Samples before and after treatment, from normal and tumour tissue, were characterised histopathologically, and both p53 and BAX expression was analysed by immunohistochemistry. Pretreatment formalin fixed, paraffin wax embedded samples from normal and tumour tissue were microdissected, and the extracted DNA was preamplified using improved primer extension preamplification polymerase chain reaction. Detection of microsatellite instability (MSI) or loss of heterozygosity (LOH) was performed using markers for p53, BAX, BAT25, BAT26, D2S123, D17S250, and APC. Exons 5-9 of the p53 gene were sequenced directly on ABI 373.

RESULTS

Four parameters were significantly associated with response to chemotherapy and prolonged overall survival: positive p53 immunostaining, positive p53 mutation status before chemotherapy, strong histological regression induced by preoperative HDCT, and surgical treatment. Patients's sex or age, tumour location or stage, lymph node status, Lauren classification, MSI, or LOH did not influence duration of survival significantly in this high risk population.

CONCLUSION

Positive p53 immunostaining and p53 mutation status in pretreatment tumour biopsies might be useful molecular predictors of response and prognosis in patients with advanced gastric cancer treated by preoperative HDCT.

Mismatch repair and response to DNA-damaging antitumour therapies

Most antitumour therapies damage tumour cell DNA either directly or indirectly. DNA damage responses, and particularly DNA repair, influence the outcome of therapy. Because DNA repair normally excises lethal DNA lesions, it is intuitive that efficient repair will contribute to intrinsic drug resistance. Indeed, in certain circumstances reduced levels of DNA nucleotide excision repair are associated with a good therapeutic outlook (Curr Biol 9 (1999) 273). A paradoxical relationship between DNA mismatch repair (MMR) and drug sensitivity has been revealed by model studies in cell lines. This suggests that connections between MMR and tumour therapy might be more complex. Here, we briefly review how MMR deficiency can affect drug resistance and the extent to which loss of MMR is a prognostic factor in certain cancer therapies. We also consider how the inverse relationship between MMR activity and drug resistance might influence the development of treatment-related malignancies which are increasingly linked to MMR defects.

Shaping of tumor and drug-resistant genomes by instability and selection

Tumors with defects in mismatch repair (MMR) show fewer chromosomal changes by cytogenetic analyses than most solid tumors, suggesting that a greater proportion of the alterations required for malignancy occur in genes with nucleotide sequences susceptible to errors normally corrected by MMR. Here, we used genome-wide microarray comparative genomic hybridization to carry out a higher resolution evaluation of the effect of MMR competence on genomic alterations occurring in 20 cell lines and to determine if characteristic aberrations arise in MMR-proficient and -deficient HCT116 cells undergoing selection for methotrexate resistance. We observed different spectra of aberrations in MMR-proficient compared to -deficient cell lines, as well as among cell lines with different types of MMR-deficiency. We also observed different genetic routes to drug resistance. Resistant MMR-deficient cells most frequently displayed no copy number alterations (16/29 cell pools), whereas all MMR-proficient cells had unique abnormalities involving chromosome 5, including amplicons centered on the target gene, DHFR and/or a neighboring novel locus (7/13 pools). These observations support the concept that tumor genomes are shaped by selection for alterations that promote survival and growth advantage, as well as by the particular dysfunctions in genes responsible for maintenance of genetic integrity.

Tumour-inhibiting platinum complexes--state of the art and future perspectives

Thirty years after the onset of the first clinical studies with cisplatin, the development of antineoplastic platinum drugs continues to be a productive field of research. This article reviews the current preclinical and clinical status, including a discussion of the molecular basis for the activity of the parent drug cisplatin and platinum drugs of the second and third generation, in particular their interaction with DNA. Further emphasis is laid on the development of third generation platinum drugs with activity in cisplatin-resistant tumours, particularly on chelates containing 1,2-diaminocyclohexane (DACH) and on the promising and more recently evolving field of non-classic ( trans- and multinuclear) platinum complexes. The development of oral platinum drugs and drug targeting strategies using liposomes, polymers or low-molecular-weight carriers in order to improve the therapeutic index of platinum chemotherapy are also covered.

Promoter hypermethylation and inactivation of hMLH1, a DNA mismatch repair gene, in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a multistage process during which adverse genetic alterations accumulate resulting in loss of cell cycle control, selective cell overgrowth, and ultimately formation of malignancy. Among various genetic alterations in HNSCC is increased microsatellite instability (MSI). hMLH1 is one of the major mismatch DNA repair genes, the inactivation of which caused increased MSI in a variety of human cancers including HNSCC. While somatic mutation is a major mechanism of the hMLH1 gene inactivation in hereditary form of human cancer, promoter hypermethylation appears to be primarily involved in the inactivation of the hMLH1 gene in sporadic form of human cancers. In the current study, we analyzed 78 cases of HNSCC for hMLH1 protein expression and promoter hypermethylation by IHC and methylation-specific PCR (MSP). Twenty-four of 78 cases (31%) of HNSCC contained markedly reduced levels of the hMLH1 protein. Based on the IHC results, 8 cases without and 8 with hMLH1 protein expression (total of 16) were further analyzed by MSP. Seven of 8 cases (88%) that were negative for the hMLH1 protein displayed promoter hypermethylation, whereas 7 of 7 cases (100%) strongly positive for the protein were free of promoter methylation. This study confirms our previous conclusion that promoter hypermethylation represents a major mechanism of the hMLH1 gene inactivation in HNSCC.

Mismatch repair genes and microsatellite instability as molecular markers for gynecological cancer detection

Due to major developments in genetics over the past decade, molecular biology tests are serving promising tools in early diagnosis and follow-up of cancer patients. Recent epidemiological studies revealed that the risk for each individual to develop cancer is closely linked to his/her own genetic potentialities. Some populations that are defective in DNA repair processes, for example in Xeroderma pigmentosum or in the Lynch syndrome, are particularly prone to cancer due to the accumulation of mutations within the genome. Such populations would benefit from the development of tests aimed at identifying people who are particularly at risk. Here, we review some data suggesting that the inactivation of mismatch repair is often found in endometrial cancer and we discuss molecular-based strategies that would help to identify the affected individuals in families with cases of glandular malignancies.

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.

Multicentre phase II study of oxaliplatin as a single-agent in cisplatin/carboplatin +/- taxane-pretreated ovarian cancer patients

BACKGROUND

This multicentre phase II open-label study evaluated safety and antitumour activity of oxaliplatin in cisplatin or carboplatin (cis/carboplatin) +/- taxane-pretreated advanced ovarian cancer (AOC) patients.

PATIENTS AND METHODS

Forty-eight patients received oxaliplatin 130 mg/M2 intravenously every 3 weeks, 94% having a performance status (PS) 0-1. All were pretreated with cis/carboplatin and 21 (44%) with paclitaxel. The median number of involved organs was two, 18 (38%) had liver metastasis, 23 (48%) were platinum-resistant and 14 (29%) were taxane-resistant. Forty-two patients were evaluable for a response, 18 (43%) were platinum-resistant and 11 (26%) were taxane-resistant.

RESULTS

A total of 253 cycles was administered (median: 5.5/patient). Median cumulative oxaliplatin dose was 666 mg/m2. National Cancer Institute-Common Toxicity Criteria toxicity analysis showed that seven patients (15%) had grade 3/4 thrombocytopenia, two patients (4%) had grade 3 neutropenia, and one patient had grade 3 anaemia. Eleven patients (23%) experienced grade 3 neurosensory toxicity. Of the 29 patients with peripheral neuropathy at the end of treatment, 55% had recovered or improved 1 month later. Eleven objective responses (two complete) were obtained in the 42 evaluable patients [ORR 26%, 95% confidence interval (CI) 14% to 42%], with 10/24 (42%, 95% CI 22% to 63%) in platinum-sensitive, and 1 of 18 (5.6%, 95% CI 0% to 27%) in platinum-resistant patients. Median response duration was 9.2 months (95% CI 6.6% to 11.8%), and median progression-free and overall survival in all treated patients were 4.3 months (95% CI 3.0% to 5.7%) and 15.0 months (95% CI 11.1% to 18.8%), respectively.

CONCLUSION

Oxaliplatin has a good safety profile and is active in cis/carboplatin +/- paclitaxel-pretreated AOC patients.

Tumor attenuation by combined heparan sulfate and polyamine depletion

Cells depend on polyamines for growth and their depletion represents a strategy for the treatment of cancer. Polyamines assemble de novo through a pathway sensitive to the inhibitor, alpha-difluoromethylornithine (DFMO). However, the presence of cell-surface heparan sulfate proteoglycans may provide a salvage pathway for uptake of circulating polyamines, thereby sparing cells from the cytostatic effect of DFMO. Here we show that genetic or pharmacologic manipulation of proteoglycan synthesis in the presence of DFMO inhibits cell proliferation in vitro and in vivo. In cell culture, mutant cells lacking heparan sulfate were more sensitive to the growth inhibitory effects of DFMO than wild-type cells or mutant cells transfected with the cDNA for the missing biosynthetic enzyme. Moreover, extracellular polyamines did not restore growth of mutant cells, but completely reversed the inhibitory effect of DFMO in wild-type cells. In a mouse model of experimental metastasis, DFMO provided in the water supply also dramatically diminished seeding and growth of tumor foci in the lungs by heparan sulfate-deficient mutant cells compared with the controls. Wild-type cells also formed tumors less efficiently in mice fed both DFMO and a xylose-based inhibitor of heparan sulfate proteoglycan assembly. The effect seemed to be specific for heparan sulfate, because a different xyloside known to affect only chondroitin sulfate did not inhibit tumor growth. Hence, combined inhibition of heparan sulfate assembly and polyamine synthesis may represent an additional strategy for cancer therapy.

Multicenter phase II-III study of oxaliplatin plus cyclophosphamide vs. cisplatin plus cyclophosphamide in chemonaive advanced ovarian cancer patients

PURPOSE

A phase II-III randomised study to compare safety and efficacy of an oxaliplatin/cyclophosphamide (OXAC) combination, vs. the reference combination of cisplatin/cyclophosphamide (CPC), in untreated advanced ovarian cancer patients.

PATIENTS AND METHODS

182 patients were enrolled, of whom 177 were treated: 86 with OXAC (130 mg/m2 oxaliplatin two-hour intravenous (i.v.) infusion, 1,000 mg/m2 cyclophosphamide two-hour i.v. infusion), and 91 with CPC (100 mg/m2 cisplatin one-hour i.v. infusion. 1,000 mg/m2 cyclophosphamide two-hour i.v. infusion). Treatment cycles were repeated every three weeks (maximum of six cycles).

RESULTS

The main toxicities, which were significantly less severe in the OXAC arm, were myelosuppression and vomiting, including (OXAC vs CPC, % patients): grade 3-4 leukopenia (37% vs. 56%), and anaemia (7% vs. 32%), with blood transfusions in 8% vs. 21%. In the OXAC arm, 64% of surgically assessable patients and 33% of clinically assessable patients achieved an objective response. In the CPC arm, 67% patients achieved a surgical response and 42% achieved an objective clinical response. In the OXAC and CPC arms, median progression free-survival was 13.0 and 13.3 months, and overall survival was 36.0 and 25.1 months respectively, without statistically significant difference.

CONCLUSION

The activity and time-related parameters of the OXAC and CPC combinations in advanced ovarian cancer patients, are comparable. Combined with the better safety profile of the oxaliplatin-containing regimen, this confirms the interest of oxaliplatin combined with active new agents in this indication.

Resistance to topoisomerase poisons due to loss of DNA mismatch repair

Sporadic breast carcinomas demonstrate microsatellite instability, reflecting the presence of DNA mismatch repair-deficient cells, in about one fourth of cases at the time of diagnosis. Loss of DNA mismatch repair has been reported to result in resistance not only to cisplatin and alkylating agents but also to the topoisomerase II poison doxorubicin, suggesting an association between DNA mismatch repair and topoisomerase II poison-induced cytotoxicity. Our study investigates the relationship between loss of MSH2 or MLH1 function and sensitivity to the topoisomerase I and II poisons, and to the taxanes, 2 classes of cytotoxic drugs commonly used in breast cancer. Two pairs of cell lines proficient and deficient in mismatch repair due to loss of either MSH2 or MLH1 function were used. Loss of either MSH2 or MLH1 function resulted in resistance to the topoisomerase II poisons doxorubicin, epirubicin and mitoxantrone, whereas only loss of MLH1 function was associated with low-level resistance to the topoisomerase I poisons camptothecin and topotecan. In contrast, there was no resistance to docetaxel and paclitaxel. Our data support the hypothesis that both MSH2 and MLH1 are involved in topoisomerase II poison-mediated cytotoxicity, whereas only MLH1 is involved in topoisomerase I poison-mediated cytotoxicity. Since our study shows that loss of DNA mismatch repair does not result in resistance to the taxanes, these drugs can be recommended for use in breast cancer deficient in mismatch repair.

DNA mismatch repair and cancer

Five human DNA mismatch repair genes have been identified that, when mutated, cause susceptibility to hereditary nonpolyposis colorectal cancer (HNPCC). Mutational inactivation of both copies of a DNA mismatch repair gene results in a profound repair defect and progressive accumulation of mutations throughout the genome. Some of the mutations confer selective advantage on the cells, giving rise to cancer. Recent discoveries suggest that apart from postreplication repair, DNA mismatch repair proteins have several other functions that are highly relevant to carcinogenesis. These include DNA damage surveillance, prevention of recombination between nonidentical sequences and participation in meiotic processes (chromosome pairing). A brief overview of these different features of the human DNA mismatch repair system will be provided, with the emphasis in their implications in cancer development.

Highlights in ovarian cancer

The ovarian cancer presentations at the 2000 ASCO meeting did not yield any major paradigm shifts in the treatment of women with epithelial ovarian cancer. Emphasis at this year's meeting focused on the potential incorporation of drugs such as topotecan, oxaliplatin, doxil, and gemcitabine into the initial treatment strategies of women with advanced ovarian cancer. These studies included the introduction of several active and tolerable regimens that are potentially worthy of direct comparison to the carboplatin and paclitaxel combination. In the woman with recurrent or persistent ovarian cancer there was a greater focus on phase III studies directly comparing various chemotherapy strategies in the treatment of women with recurrent disease. This included the comparisons of single-versus two-drug salvage regimens, alternate salvage schedules, and direct comparison of agents active in taxane- and platinum-resistant disease. Finally, several early studies of novel non-chemotherapeutic strategies were presented.

Pilot study of the paclitaxel, oxaliplatin, and cisplatin combination in patients with advanced/recurrent ovarian cancer

To determine the feasibility of the paclitaxel, oxaliplatin, cisplatin combination in advanced ovarian cancer (AOC), 15 patients with AOC (8 chemonaive, and 7 second-line, disease-free interval > or = 12 months) received paclitaxel 135 mg/m2 at day 1, with oxaliplatin 100 mg/m2 and cisplatin 75 mg/m2 at day 2, every 3 weeks for 6 cycles. Pretreated patients received prophylactic granulocyte colony-stimulating factor (5 microg/kg/d, days 6-13). Seventy cycles were administered; median 5 (range: 2-6 cycles) in chemonaive, and 4 (range: 2-6) in pretreated patients. There were grades III to IV neutropenia in 77%, febrile neutropenia in 24%, and grades III to IV thrombocytopenia in 4% of the cycles. Besides neutropenia, cumulative neurosensory toxicity was also limiting although reversible, with National Cancer Institute Common Toxicity Criteria grades II to III observed in 13 patients. Three of the pretreated patients had complete responses (43%), three had partial responses, and one had disease stabilization. Six of the 8 chemonaive patients had complete responses (75%), 1 had disease stabilization, and 1 had disease progression. The median follow-up is 17 months (range: 9-20 months) in chemonaive and 41 months (range: 13-58 months) in pretreated patients, and time to progression has been consistently more than 12 months, with 6 patients (5 chemonaive) still progression free (range: 15+ to 22+ months). This active combination shows acceptable hematologic toxicity, and reversible cumulative neurosensory toxicity. Further clinical exploration of the present combination appears warranted.

DNA damage after chemotherapy correlates with tumor response and survival in small cell lung cancer patients

To explore the induction of chemotherapy (CT) DNA damage and its correlation with tumor response and patient survival, we undertook the present study in 20 small cell lung cancer (SCLC) patients. All patients underwent the same treatment based on CT courses of carboplatin and etoposide. Blood samples were taken before and immediately after CT and every 12 weeks during follow-up. Nuclear DNA damage was determined through the variations in three mitochondrial pseudogene mutations in DNA of peripheral blood mononuclear cells. They were detected by mutation-specific PCR and assessed by a semiquantitative method. The relative level of mutation rose after chemotherapy in all cases. Among the 11 patients (55%) with higher relative levels of mutations, 9 (82%) of them achieved a complete response. In contrast, of the 9 patients (45%) with lower relative levels of mutations, only 2 (18%) achieved a complete response, displaying a statistically significant difference (P=0.02). The overall survival for patients with marked genomic damage was 18 months (range 10-24), and for patients with low degree of DNA damage, it was 12 months (range 5-15) (P=0.002). Genomic damage detected after chemotherapy treatment correlates positively with tumor response and patient survival.

Molecular basis for resistance to the anticancer drug cisplatin in Dictyostelium

The efficacy of the widely used chemotherapeutic drug cisplatin is limited by the occurrence of drug-resistant tumour cells. To fully exploit the potential of this drug in cancer therapy, it is imperative to understand the molecular basis of cisplatin resistance. Using an insertional mutagenesis technique in cells of Dictyostelium discoideum, we have identified six genes which are involved in cisplatin resistance. None of these genes has been previously linked to resistance to this drug. Several of these genes encode proteins that are involved in signal transduction pathways which regulate cell death, cell proliferation or gene regulation. The resistance of these mutant strains is specific for cisplatin, since deletion of these genes does not confer resistance to other DNA-damaging agents. Significantly, the disruption of three of these genes, encoding the sphingosine-1-phosphate lyase, the RegA cAMP phosphodiesterase and a phosphatidylinositol-4-phosphate 5-kinase, also results in abnormalities in the multicellular development of this organism, although there is no change in the rate of mitotic cell growth. This study has identified previously unsuspected molecular pathways which function in the cellular response to cisplatin and are required for normal morphogenesis, and underscores the complexity of the cellular response to cisplatin. These pathways provide potential targets for modulating the response to this important drug.

Oxaliplatin clinical activity: a review

Oxaliplatin (Eloxatin), a recently developed third-generation cisplatin analogue with a 1,2-diaminocyclohexane (DACH) carrier ligand, has displayed preclinical and clinical activity in a wide variety of tumour types. Synergistic with 5-FU in colorectal cancer (CRC), the combination has proven efficacy in 5-FU-resistant advanced disease and in previously untreated CRC, as demonstrated in controlled phase III trials, while evaluation in the adjuvant setting is ongoing. Due to its excellent safety profile, its unique mechanism of action and lack of cross-resistance with other active agents in CRC, oxaliplatin has also been combined with CPT-11 and Raltitrexed with promising results. Trials in pretreated and untreated advanced ovarian cancer (AOC), as a single agent or in combination with cisplatin, cyclophosphamide or paclitaxel, indicate a yet to be defined role in AOC and confirm its lack of cross-resistance with cis/carboplatin. Clinical investigations of single agent and combination therapies in breast, lung, prostate and germ-cell carcinomas, non-Hodgkin's lymphoma and malignant mesothelioma are being pursued. While the role of oxaliplatin in medical oncology is yet to be fully defined, it appears to be an important new anticancer agent.

Decreased UV sensitivity, mismatch repair activity and abnormal cell cycle checkpoints in skin cancer cell lines derived from UVB-irradiated XPA-deficient mice

Xeroderma pigmentosum group A gene (XPA)-deficient mice are defective in nucleotide excision repair (NER) and are therefore highly sensitive to ultraviolet (UV)-induced skin carcinogenesis. We established cell lines from skin cancers of UVB-irradiated XPA-deficient mice to investigate the phenotypic changes occurring during skin carcinogenesis. As anticipated, the skin cancer cell lines were devoid of NER activity but were less sensitive to killing by UV-irradiation than the XPA(-/-) fibroblast cell line. The lines were also more resistant to 6-thioguanine (6-TG) than XPA(-/-) and XPA(+/+) fibroblasts, which was suggestive of a mismatch repair (MMR) defect. Indeed, in vitro mismatch binding and MMR activity were impaired in several of these cell lines. Moreover, these cell lines displayed cell cycle checkpoint derangements following UV-irradiation and 6-TG exposure. The above findings suggest that MMR downregulation may help cells escape killing by UVB, as was seen previously for methylating agents and cisplatin, and thus that MMR deficient clones are selected for during the tumorigenic transformation of XPA(-/-) cells.