Continuous versus intermittent extended adjuvant letrozole for breast cancer: final results of randomized phase III SOLE (Study of Letrozole Extension) and SOLE Estrogen Substudy.

BACKGROUND: Late recurrences in postmenopausal women with hormone receptor-positive breast cancers remain an important challenge. Avoidance or delayed development of resistance represents the main objective in extended endocrine therapy (ET). In animal models, resistance was reversed with restoration of circulating estrogen levels during interruption of letrozole treatment. This phase III, randomized, open-label Study of Letrozole Extension (SOLE) studied the effect of extended intermittent letrozole treatment in comparison with continuous letrozole. In parallel, the SOLE estrogen substudy (SOLE-EST) analyzed the levels of estrogen during the interruption of treatment. PATIENTS AND METHODS: SOLE enrolled 4884 postmenopausal women with hormone receptor-positive, lymph node-positive, operable breast cancer between December 2007 and October 2012 and among them, 104 patients were enrolled in SOLE-EST. They must have undergone local treatment and have completed 4-6 years of adjuvant ET. Patients were randomized between continuous letrozole (2.5 mg/day orally for 5 years) and intermittent letrozole treatment (2.5 mg/day for 9 months followed by a 3-month interruption in years 1-4 and then 2.5 mg/day during all of year 5). RESULTS: Intention-to-treat population included 4851 women in SOLE (n = 2425 in the intermittent and n = 2426 in the continuous letrozole groups) and 103 women in SOLE-EST (n = 78 in the intermittent and n = 25 in the continuous letrozole groups). After a median follow-up of 84 months, 7-year disease-free survival (DFS) was 81.4% in the intermittent group and 81.5% in the continuous group (hazard ratio: 1.03, 95% confidence interval: 0.91-1.17). Reported adverse events were similar in both groups. Circulating estrogen recovery was demonstrated within 6 weeks after the stop of letrozole treatment. CONCLUSIONS: Extended adjuvant ET by intermittent administration of letrozole did not improve DFS compared with continuous use, despite the recovery of circulating estrogen levels. The similar DFS coupled with previously reported quality-of-life advantages suggest intermittent extended treatment is a valid option for patients who require or prefer a treatment interruption.

Characterization of male breast cancer: results of the EORTC 10085/TBCRC/BIG/NABCG International Male Breast Cancer Program.

Background: Male breast cancer (BC) is rare, managed by extrapolation from female BC. The International Male BC Program aims to better characterize and manage this disease. We report the results of part I, a retrospective joint analysis of cases diagnosed during a 20-year period. Methods: Patients with follow-up and tumor samples, treated between 1990 and 2010, in 93 centers/9 countries. Samples were centrally analyzed in three laboratories (the United Kingdom, the Netherlands and the United States). Results: Of 1822 patients enrolled, 1483 were analyzed; 63.5% were diagnosed between 2001 and 2010, 57 (5.1%) had metastatic disease (M1). Median age at diagnosis: 68.4 years. Of 1054 M0 cases, 56.2% were node-negative (N0) and 48.5% had T1 tumors; 4% had breast conserving surgery (BCS), 18% sentinel lymph-node biopsy; half received adjuvant radiotherapy; 29.8% (neo)adjuvant chemotherapy and 76.8% adjuvant endocrine therapy (ET), mostly tamoxifen (88.4%). Per central pathology, for M0 tumors: 84.8% ductal invasive carcinomas, 51.5% grade 2; 99.3% estrogen receptor (ER)-positive; 81.9% progesterone receptor (PR)-positive; 96.9% androgen receptor (AR)-positive [ER, PR or AR Allred score ≥3]; 61.1% Ki67 expression low (<14% positive cells); using immunohistochemistry (IHC) surrogates, 41.9% were Luminal-A-like, 48.6% Luminal-B-like/HER-2-negative, 8.7% HER-2-positive, 0.3% triple negative. Median follow-up: 8.2 years (0.0-23.8) for all, 7.2 years (0.0-23.2), for M0, 2.6 years (0.0-12.7) for M1 patients. A significant improvement over time was observed in age-corrected BC mortality. BC-specific-mortality was higher for men younger than 50 years. Better overall (OS) and recurrence-free survival (RFS) were observed for highly ER+ (P = 0.001), highly PR+ (P = 0.002), highly AR+ disease (P = 0.019). There was no association between OS/RFS and HER-2 status, Ki67, IHC subtypes nor grade. Conclusions: Male BC is usually ER, PR and AR-positive, Luminal B-like/HER2-negative. Of note, 56% patients had T1 tumors but only 4% had BCS. ER was highly positive in >90% of cases but only 77% received adjuvant ET. ER, PR and AR were associated with OS and RFS, whereas grade, Ki67 and IHC surrogates were not. Significant improvement in survival over time was observed.

Do all patients with advanced HER2 positive breast cancer need upfront-chemo when receiving trastuzumab? Randomized phase III trial SAKK 22/99.

Background: HER2-targeted therapy plus chemotherapy is standard treatment in advanced HER2+ breast cancer. Trastuzumab alone followed by addition of chemotherapy at disease progression versus upfront combination therapy has not been elucidated. Patients and methods: One-hundred seventy-five patients with measurable/evaluable HER2+ advanced disease without previous HER2-directed therapy were randomized to trastuzumab alone followed, at disease progression, by the combination with chemotherapy (Arm A) or upfront trastuzumab plus chemotherapy (Arm B). Chemotherapy could be stopped after ≥6 cycles in responding patients, trastuzumab was continued until progression. The primary endpoint of this superiority trial was time to progression (TTP) on combined trastuzumab-chemotherapy (Combination-TTP) in both arms. Secondary endpoints included response rate, TTP, overall survival, quality of life and toxicity. Results: Combination-TTP was longer than expected in both arms, 12.2 months in Arm A and 10.3 months in Arm B and not significantly different (hazard ratio [HR] 0.7; 95% CI 0.5-1.1; P =0.1). Overall survival was also not significantly different (HR 0.9; 95% CI 0.6-1.5; P = 0.55). In Arm A, the median TTP before introduction of chemotherapy was 3.7 months (95% CI 2.3-5.4), yet at 2 years 6% of patients were still on trastuzumab alone. Patients without visceral disease had a Combination-TTP of 21.8 months in arm A, compared with 10.1 months in arm B (unplanned analysis HR 2.1, 95% CI 1.1-4.2, P = 0.03). Patients with visceral disease showed no difference. Toxicity was chemotherapy-related. Conclusion: The outcome of patients receiving sequential trastuzumab-chemotherapy or upfront combination was similar. We failed to demonstrate superiority of the sequential approach. These results nevertheless suggest chemotherapy and its toxicity can be deferred, especially in patients with indolent, non-visceral disease. Despite a larger non-inferiority confirmatory study would be needed, these findings represent an additional proof of concept that de-escalation strategies can be discussed in individual patients.

The impact of ABCC11 polymorphisms on the risk of early-onset fluoropyrimidine toxicity.

A missense variant (c.1637C>T, T546M) in ABCC11 encoding the MRP8 (multidrug resistance protein 8), a transporter of 5-fluorodeoxyuridine monophosphate, has been associated with an increased risk of 5-fluorouracil-related severe leukopenia. To validate this association, we investigated the impact of the ABCC11 variants c.1637C>T, c.538G>A and c.395+1087C>T on the risk of early-onset fluoropyrimidine-related toxicity in 514 cancer patients. The ABCC11 variant c.1637C>T was strongly associated with severe leukopenia in patients carrying risk variants in DPYD, encoding the key fluoropyrimidine-metabolizing enzyme dihydropyrimidine dehydrogenase (odds ratio (OR): 71.0; 95% confidence interval (CI): 2.5-2004.8; Pc.1637C>T*DPYD=0.013). In contrast, in patients without DPYD risk variants, no association with leukopenia (OR: 0.95; 95% CI: 0.34-2.6) or overall fluoropyrimidine-related toxicity (OR: 1.02; 95% CI: 0.5-2.1) was observed. Our study thus suggests that c.1637C>T affects fluoropyrimidine toxicity to leukocytes particularly in patients with high drug exposure, for example, because of reduced fluoropyrimidine catabolism.

The effect of real-time electronic monitoring of patient-reported symptoms and clinical syndromes in outpatient workflow of medical oncologists: E-MOSAIC, a multicenter cluster-randomized phase III study (SAKK 95/06).

BACKGROUND: Patients with advanced, incurable cancer receiving anticancer treatment often experience multidimensional symptoms. We hypothesize that real-time monitoring of both symptoms and clinical syndromes will improve symptom management by oncologists and patient outcomes. PATIENTS AND METHODS: In this prospective multicenter cluster-randomized phase-III trial, patients with incurable, symptomatic, solid tumors, who received new outpatient chemotherapy with palliative intention, were eligible. Immediately before the weekly oncologists' visit, patients completed the palm-based E-MOSAIC assessment (Edmonton-Symptom-Assessment-Scale, ≤3 additional symptoms, estimated nutritional intake, body weight change, Karnofsky Performance Status, medications for pain, fatigue, nutrition). A cumulative, longitudinal monitoring sheet (LoMoS) was printed immediately. Eligible experienced oncologists were defined as one cluster each and randomized to receive the immediate print-out LoMoS (intervention) or not (control). Primary analysis limited to patients having uninterrupted (>4/6 visits with same oncologist) patient-oncologist sequences was a mixed model for the difference in patients global quality of life (G-QoL; items 29/30 of EORTC-QlQ-c30) between baseline (BL) and week 6. Intention-to-treat (ITT) analysis included all eligible patients. RESULTS: In 8 centers, 82 oncologists treated 264 patients (median 66 years; overall survival intervention 6.3, control 5.4 months) with various tumors. The between-arm difference in G-QoL of 102 uninterrupted patients (intervention: 55; control: 47) was 6.8 (P = 0.11) in favor of the intervention; in a sensitivity analysis (oncologists treating ≥2 patients; 50, 39), it was 9.0 (P = 0.07). ITT analysis revealed improvement in symptoms (difference last study visit-BL: intervention -5.4 versus control 2.1, P = 0.003) and favored the intervention for communication and coping. More patients with high symptom load received immediate symptom management (chart review, nurse-patient interview) by oncologists getting the LoMoS. CONCLUSION: Monitoring of patient symptoms, clinical syndromes and their management clearly reduced patients' symptoms, but not QoL. Our results encourage the implementation of real-time monitoring in the routine workflow of oncologist with a computer solution.

Brain metastases in gastro-oesophageal adenocarcinoma: insights into the role of the human epidermal growth factor receptor 2 (HER2).

BACKGROUND: Gastro-oesophageal adenocarcinomas rarely metastasize to the central nervous system (CNS). The role of the human epidermal growth factor receptor 2 (HER2) in patients with these cancers and CNS involvement is presently unknown. PATIENTS AND METHODS: A multicentre registry was established to collect data from patients with gastro-oesophageal adenocarcinomas and CNS involvement both retrospectively and prospectively. Inclusion in the study required a predefined clinical data set, a central neuro-radiological or histopathological confirmation of metastatic CNS involvement and central assessment of HER2 by immunohistochemistry (IHC) and in situ hybridisation (ISH). In addition, expression of E-cadherin and DNA mismatch repair (MMR) proteins were assessed by IHC. RESULTS: One hundred patients fulfilled the inclusion criteria. The population's median age was 59 years (interquartile range: 54-68), of which 85 (85%) were male. Twenty-five patients were of Asian and 75 of Caucasian origin. HER2 status was positive in 36% (95% CI: 26.6-46.2) of cases. Median time from initial diagnosis to the development of brain metastases (BMets) or leptomeningeal carcinomatosis (LC) was 9.9 months (95% CI: 8.5-15.0). Median overall survival from diagnosis was 16.9 months (95% CI: 14.0-20.7) and was not related to the HER2 status. E-cadherin loss was observed in 9% of cases and loss of expression in at least one DNA MMR proteins in 6%. CONCLUSIONS: The proportion of a positive HER2 status in patients with gastro-oesophageal adenocarcinoma and CNS involvement was higher than expected. The impact of anti-HER2 therapies should be studied prospectively.

Bone mineral density in breast cancer patients treated with adjuvant letrozole, tamoxifen, or sequences of letrozole and tamoxifen in the BIG 1-98 study (SAKK 21/07).

BACKGROUND: The risk of osteoporosis and fracture influences the selection of adjuvant endocrine therapy. We analyzed bone mineral density (BMD) in Swiss patients of the Breast International Group (BIG) 1-98 trial [treatment arms: A, tamoxifen (T) for 5 years; B, letrozole (L) for 5 years; C, 2 years of T followed by 3 years of L; D, 2 years of L followed by 3 years of T]. PATIENTS AND METHODS: Dual-energy X-ray absorptiometry (DXA) results were retrospectively collected. Patients without DXA served as control group. Repeated measures models using covariance structures allowing for different times between DXA were used to estimate changes in BMD. Prospectively defined covariates were considered as fixed effects in the multivariable models. RESULTS: Two hundred and sixty-one of 546 patients had one or more DXA with 577 lumbar and 550 hip measurements. Weight, height, prior hormone replacement therapy, and hysterectomy were positively correlated with BMD; the correlation was negative for letrozole arms (B/C/D versus A), known osteoporosis, time on trial, age, chemotherapy, and smoking. Treatment did not influence the occurrence of osteoporosis (T score < -2.5 standard deviation). CONCLUSIONS: All aromatase inhibitor regimens reduced BMD. The sequential schedules were as detrimental for bone density as L monotherapy.

Assessment of the management of carcinomatous meningitis from breast cancer globally: a study by the Breast International Group Brain Metastasis Task Force.

BACKGROUND: Carcinomatous meningitis (CM) is a severe complication of breast cancer. The Breast International Group (BIG) carried out a survey to describe the approach to CM internationally. PATIENTS AND METHODS: A questionnaire on the management of CM was developed by the Brain Metastases Task Force of BIG and distributed to its groups, requesting one answer per group site. RESULTS: A total of 241 sites responded, 119 from Europe, 9 from North America, 39 from Central/South America, 58 from Asia, and 16 in Australia/New Zealand, with 24.5% being general hospitals with oncology units, 44.4% university hospitals, 22.4% oncology centers, and 8.7% private hospitals. About 56.0% of sites reported seeing <5 cases annually with 60.6% reporting no increase in the number of cases of CM recently. Nearly 63.1% of sites investigate for CM when a patient has symptoms or radiological evidence, while 33.2% investigate only for symptoms. For diagnosis, 71.8% of sites required a positive cerebrospinal fluid cytology, while magnetic resonance imaging findings were sufficient in 23.7% of sites. Roughly 97.1% of sites treat CM and 51.9% also refer patients to palliative care. Intrathecal therapy is used in 41.9% of sites, mainly with methotrexate (74.3%). As many as 20 centers have a national registry for patients with breast cancer with central nervous system metastases and of those 5 have one for CM. Most (90.9%) centers would be interested in participating in a registry as well as in studies for CM, the latter preferably (62.1%) breast cancer subtype specific. CONCLUSIONS: This is the first study to map out the approach to CM from breast cancer globally. Although guidelines with level 1 evidence are lacking, there is a high degree of homogeneity in the approach to CM globally and great interest for conducting studies in this area.

Differential efficacy of three cycles of CMF followed by tamoxifen in patients with ER-positive and ER-negative tumors: long-term follow up on IBCSG Trial IX.

BACKGROUND: The benefit of adjuvant chemotherapy in postmenopausal patients with estrogen receptor (ER)-positive lymph node-negative breast cancer is being reassessed. PATIENTS AND METHODS: After stratification by ER status, 1669 postmenopausal patients with operable lymph node-negative breast cancer were randomly assigned to three 28-day courses of 'classical' CMF (cyclophosphamide, methotrexate, 5-fluorouracil) chemotherapy followed by tamoxifen for 57 months (CMF→tamoxifen) or to tamoxifen alone for 5 years. RESULTS: ERs were positive in 81% of tumors. At a median follow-up of 13.1 years, patients with ER-positive breast cancers did not benefit from CMF [13-year disease-free survival (DFS) 64% CMF→tamoxifen, 66% tamoxifen; P = 0.99], whereas CMF substantially improved the prognosis of patients with ER-negative breast cancer (13-year DFS 73% versus 57%, P = 0.001). Similarly, breast cancer-free interval (BCFI) was identical in the ER-positive cohort but significantly improved by chemotherapy in the ER-negative cohort (13-year BCFI 80% versus 63%, P = 0.001). CMF had no influence on second nonbreast malignancies or deaths from other causes. CONCLUSION: CMF is not beneficial in postmenopausal patients with node-negative ER-positive breast cancer but is highly effective within the ER-negative cohort. In the future, other markers of chemotherapy response may define a subset of patients with ER-positive tumors who may benefit from adjuvant chemotherapy.

PRO_10--a new tissue-based prognostic multigene marker in patients with early estrogen receptor-positive breast cancer.

BACKGROUND/AIMS: Clinicopathological and molecular factors determine the prognosis of breast cancer. PRO_10 is a prognostic score based on quantitative RT-PCR of 10 proliferation-associated genes obtained from formalin-fixed, paraffin-embedded breast cancer tissues. We revalidated PRO_10 in patients treated in a non-trial setting. METHODS: The charts of 315 patients with postmenopausal estrogen receptor (ER)-positive breast cancer between 1996 and 2004 were reviewed. Forty-eight cases relapsed within 5 years of diagnosis; they were paired with controls by matching the N and T stage, histological grade, percent ER-positive cells, human epidermal growth factor receptor 2, age, adjuvant chemo- and endocrine therapy. The score was tested by conditional logistic regression. RESULTS: Despite strict matching, PRO_10 remained prognostic for recurrence in the whole group (odds ratio, OR = 4.7, p = 0.005) and in subgroups of grade 2 (OR = 5.5, p = 0.009) and N0 cancers (OR = 15, p = 0.002). Five-year recurrence-free survival was 29% in patients with high and 67% in patients with low scores (p = 0.002). PRO_10 was prognostic for overall survival (5-year overall survival 71 vs. 91%). CONCLUSION: PRO_10 is an independent prognostic marker in postmenopausal ER-positive breast cancer. It is based on formalin-fixed, paraffin-embedded tissue and could be integrated easily into the routine diagnostic workflow.

The effect of endocrine responsiveness on high-risk breast cancer treated with dose-intensive chemotherapy: results of International Breast Cancer Study Group Trial 15-95 after prolonged follow-up.

BACKGROUND: The role of adjuvant dose-intensive chemotherapy and its efficacy according to baseline features has not yet been established. PATIENTS AND METHODS: Three hundred and forty-four patients were randomized to receive seven courses of standard-dose chemotherapy (SD-CT) or three cycles of dose-intensive epirubicin and cyclophosphamide (epirubicin 200 mg/m(2) plus cyclophosphamide 4 mg/m(2) with filgrastim and progenitor cell support). All patients were assigned tamoxifen at the completion of chemotherapy. The primary end point was disease-free survival (DFS). This paper updates the results and explores patterns of recurrence according to predicting baseline features. RESULTS: At 8.3-years median follow-up, patients assigned DI-EC had a significantly better DFS compared with those assigned SD-CT [8-year DFS percent 47% and 37%, respectively, hazard ratio (HR) 0.76; 95% confidence interval 0.58-1.00; P = 0.05]. Only patients with estrogen receptor (ER)-positive disease benefited from the DI-EC (HR 0.61; 95% confidence interval 0.39, 0.95; P = 0.03). CONCLUSIONS: After prolonged follow-up, DI-EC significantly improved DFS, but the effect was observed only in patients with ER-positive disease, leading to the hypothesis that efficacy of DI-EC may relate to its endocrine effects. Further studies designed to confirm the importance of endocrine responsiveness in patients treated with dose-intensive chemotherapy are encouraged.

Novel Genetic Variants in Carboxylesterase 1 Predict Severe Early-Onset Capecitabine-Related Toxicity.

An important concern with the anticancer drug capecitabine (Cp), an oral prodrug of 5-fluorouracil, are dose-limiting adverse effects, in particular hand-foot syndrome (HFS) and diarrhea. Here we evaluated the association of genetic variability in all enzymes of the Cp-activation pathway to 5-fluorouracil with Cp-related early-onset toxicity in 144 patients receiving Cp. We identified a haplotype encompassing five variants in the carboxylesterase 1 (CES1) gene region including an expression quantitative trait locus associated with early-onset Cp-toxicity (Haplotype A3: ORadditive = 2.2, 95% CI 1.2-4.0, Padjusted = 0.012; ORrecessive = 10.3, 95% CI 2.1-49.4, Padjusted = 0.0038). Furthermore, the association of two linked cytidine deaminase (CDA) promoter variants (c.1-451C>T: ORdominant = 4.3, 95% CI 1.3-14.2, Padjusted = 0.017; and c.1-92A>G: ORdominant = 4.4, 95% CI 1.3-14.5, Padjusted = 0.015) with Cp-related diarrhea was replicated. This first study identifying an association of genetic variation in CES1 with Cp-related toxicity provides further evidence for the existence of a functional noncoding CES1-variant with a possible regulatory impact.

Loss of DNA mismatch repair: effects on the rate of mutation to drug resistance.

BACKGROUND: The loss of the ability of cells to repair mismatches in double-stranded DNA is a common finding in human tumors. This defect results in genomic instability and in increased resistance to several of the drugs used in cancer chemotherapy. The human colon cancer cell line HCT116 is deficient in DNA mismatch repair (MMR) because of a genetic defect in the hMLH1 gene, which is located on chromosome 3. In this study, we investigated whether MMR-deficient HCT116+chr2 cells (i.e., HCT116 cells into which chromosome 2 has been transferred [as a control]) have a higher rate of mutation to resistance to commonly used chemotherapeutic agents (i.e., cisplatin, doxorubicin, paclitaxel [Taxol], and etoposide) than MMR-proficient HCT116+chr3 cells (i.e., HCT116 cells into which chromosome 3 has been transferred to provide a wild-type copy of the hMLH1 gene). METHODS: Spontaneous mutation rates were calculated from measurements of the mutant fractions of cells before and after their expansion through a known number of generations (also known as the technique of maximum likelihood estimation). Aliquots of 500000 cells were expanded in culture over a period of 2 weeks, and the mutant fractions were determined both before and after expansion of secondary cultures (each also with an initial 500000 cells) in drug concentrations that produced survival fractions of 0.0002%. RESULTS: Mutation rates in MMR-proficient and MMR-deficient cells did not differ on exposure to cisplatin, doxorubicin, or paclitaxel; however, the relative mutation rate was 2.4-fold higher in MMR-deficient cells exposed to etoposide (P=.002). CONCLUSION: These results suggest that genes involved in the control of cellular sensitivity to etoposide are targets for mutation when the loss of MMR destabilizes the genome. Tumors containing large fractions of MMR-deficient cells may demonstrate more rapid emergence of clinical resistance to etoposide.

Loss of DNA mismatch repair in acquired resistance to cisplatin.

Selection of cells for resistance to cisplatin, a well-recognized mutagen, could result in mutations in genes involved in DNA mismatch repair and thereby to resistance to DNA-alkylating agents. Parental cells of the human ovarian adenocarcinoma cell line 2008 expressed hMLH1 when analyzed with immunoblot. One subline selected for resistance to cisplatin (2008/A) expressed no hMLH1, whereas another (2008/C13*5.25) expressed parental levels. Microsatellite instability was readily demonstrated in 2008/A cells but not in 2008 and in 2008/C13*5.25 cells. In addition, the 2008/A cells were 2-fold resistant to methyl-nitro-nitrosoguanidine and had a 65-fold elevated mutation rate at the HPRT locus as compared to 2008 cells, both of which are consistent with the loss of DNA mismatch repair in these cells. To determine whether the loss of DNA mismatch repair itself contributes to cisplatin resistance, studies were carried out in isogenic pairs of cell lines proficient or defective in this function. HCT116, a human colon cancer cell line deficient in hMLH1 function, was 2-fold resistant to cisplatin when compared to a subline complemented with chromosome 3 and expressing hMLH1. Similarly, the human endometrial cancer cell line HEC59, which expresses no hMSH2, was 2-fold resistant to cisplatin when compared to a subline complemented with chromosome 2 that expresses hMSH2. Therefore, the selection of cells for resistance to cisplatin can result in the loss of DNA mismatch repair, and loss of DNA mismatch repair in turn contributes to resistance to cisplatin.

Differential induction of c-Jun NH2-terminal kinase and c-Abl kinase in DNA mismatch repair-proficient and -deficient cells exposed to cisplatin.

The c-Abl nonreceptor tyrosine kinase and the c-Jun NH2-terminal kinase (JNK/stress-activated protein kinase) are activated during the injury response to the DNA-damaging agent cisplatin. Loss of DNA mismatch repair activity results in resistance to cisplatin in human cancer cells, suggesting that the mismatch repair proteins function as a detector for cisplatin DNA adducts. To identify signaling pathways activated by this detector, we investigated the effect of the loss of DNA mismatch repair function on the ability of cisplatin to activate the JNK and c-Abl kinases. The results demonstrate that cisplatin activates JNK kinase 3.8 +/- 0.2-fold more efficiently in DNA mismatch repair-proficient than repair-deficient cells, and that activation of c-Abl is completely absent in the DNA mismatch repair-deficient cells. Furthermore, the results show that cisplatin-induced activation of JNK occurs through a stress-activated protein kinase/extracellular signal-regulated kinase kinase 1-independent mechanism. We conclude that activation of JNK and c-Abl by cisplatin is in part dependent upon the integrity of DNA mismatch repair function, suggesting that these kinases are part of the signal transduction pathway activated when mismatch repair proteins recognize cisplatin adducts in DNA.

In vitro and in vivo resistance to cisplatin in cells that have lost DNA mismatch repair.

In vitro studies have shown that loss of DNA mismatch repair due to lack of either hMSH2 or hMLH1 activity results in low-level resistance to cisplatin but not to oxaliplatin, an analogue that produces a different type of DNA adduct. No information is currently available on whether this low-level resistance is sufficient to result in enrichment of mismatch repair-deficient cells during drug exposure in vitro or to account for clinical failure of treatment in vivo. Mixed populations of cells containing a minority of DNA mismatch repair-deficient cells constitutively expressing green fluorescence protein were exposed repeatedly in vitro to cisplatin and oxaliplatin. Treatment with cisplatin resulted in a gradual enrichment for DNA mismatch repair-deficient cells, whereas treatment with oxaliplatin did not. MSH2-/- and MSH2+/+ embryonic stem cells were established as xenografts in athymic nude mice. Animals were treated 48 h after tumor implantation with a single LD10 dose of either cisplatin or oxaliplatin. MSH2-/- tumors were significantly less responsive to cisplatin than MSH2+/+ tumors, whereas there was no difference in sensitivity to oxaliplatin. These results demonstrate that the degree of cisplatin resistance conferred by loss of DNA mismatch repair is sufficient to produce both enrichment of mismatch repair-deficient cells during treatment in vitro and a large difference in clinical responsiveness in vivo. The results identify loss of DNA mismatch repair as a mechanism of resistance to cisplatin but not oxaliplatin.