Response to Comment on "Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply"

Tolstoy reports the existence of a characteristic 100 thousand year (ky) period in the bathymetry of fast-spreading seafloor but does not argue that sea level change is a first-order control on seafloor morphology worldwide. Upon evaluating the overlap between tectonic and Milankovitch periodicities across spreading rates, we reemphasize that fast-spreading ridges are the best potential recorders of a sea level signature in seafloor bathymetry.

Response to Comment on "Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply"

Huybers et al present new bathymetric spectra from an intermediate-spreading ridge as evidence for a primary contribution of sea level cycles to the morphology of the seafloor. Although we acknowledge the possibility that sea level-modulated magmatic constructions may be superimposed on a first-order tectonic fabric, we emphasize the difficulty of deciphering these different contributions in the frequency domain alone.

Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply

Recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid (23,000 to 100,000 years) fluctuations in ridge magma supply caused by sealevel changes that modulate melt production in the underlying mantle. Using quantitative models of faulting and magma emplacement, we demonstrate that, in fact, seafloor-shaping processes act as a low-pass filter on variations in magma supply, strongly damping fluctuations shorter than about 100,000 years. We show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input. This provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills, the most common topographic feature on Earth.

Loss of DNA mismatch repair due to knockout of MSH2 or PMS2 results in resistance to cisplatin and carboplatin

Loss of DNA mismatch repair is a common finding in hereditary nonpolyposis colon cancer as well as in many types of sporadic human tumors. The effect of loss of DNA mismatch repair activity on sensitivity to cisplatin and carboplatin was tested using MSH2 and PMS2 knockout cell lines. The knockout dMsh2 embryonic stem cell line was 2.1-fold more resistant to cisplatin and 1.7-fold more resistant to carboplatin when compared to the isogenic wild-type wt-2 cell line. Likewise, the PMS2(-/-) mouse fibroblasts were 1.9-fold more resistant to cisplatin and 1.5-fold more resistant to carboplatin when compared to the isogenic PMS2(+/+) fibroblasts. These findings demonstrate that loss of mismatch repair due to knockout of either MSH2 or PMS2 results in low-level resistance to cisplatin and carboplatin, drugs that form the same types of adducts in DNA. These data validate results previously obtained using non-isogenic mismatch repair-proficient and -deficient cell lines, and indicate that simple recognition of the cisplatin adduct by the MSH2/MSH6 heterodimer is not sufficient for full detector function, but that PMS2 is also required for the pro-apoptotic signal to be generated from this detector.

Association between hsp60 messenger-RNA levels and Cisplatin resistance in human head and neck-cancer cell-lines

Development of resistance to cisplatin (cDDP) is a major obstacle in the cure of many cancers. Recently, a cDNA from cDDP-resistant human ovarian carcinoma cells was identified as the mitochondrial hsp60 chaperonin. The aim of this study was to determine the changes in expression of hsp60 during selection for cDDP resistance in two head and neck cancer cell lines, UMSCC5 and UMSCC10b and whether the emergence of resistance could be correlated with the level of hsp60 expression. We have selected cDDP-resistant variants of two squamous cell carcinoma cell lines, the UMSCC5 and UMSCC10b with levels of resistance varying from 1.5 to 6-fold. Concomitant with the emergence of resistance, the basal level of hsp60 increased 2 to 3-fold. In addition, less cDDP resistance as well as lower hsp60 levels were detected in cDDP resistant variants of the UMSCC10b cell line when selected in the presence of tamoxifen, suggesting a correlation between the intrinsic level of hsp60 expression and cDDP resistance. Using linear regression analysis both UMSCC5 and UMSCC10b cell lines demonstrated a high degree of correlation with coefficients of 0.91 and 0.90, respectively. In conclusion, the expression of hsp60 was closely related to the development of cDDP resistance and could be used as a marker for the emergence of cDDP resistance.

The clinical effectiveness and cost-effectiveness of genotyping for CYP2D6 for the management of women with breast cancer treated with tamoxifen: a systematic review

BACKGROUND

Breast cancer is the most common cancer affecting women in the UK. Tamoxifen (TAM) is considered as the standard of care for many women with oestrogen receptor positive breast cancer. However, wide variability in the response of individuals to drugs at the same doses may occur, which may be a result of interindividual genetic differences (pharmacogenetics). TAM is known to be metabolised to its active metabolites N-desmethyl TAM and 4-hydroxytamoxifen by a number of CYP450 enzymes, including CYP2D6, CYP3A4, CYP2C9, CYP2C19 and CYP2B6. N-desmethyl TAM is further metabolised to endoxifen by CYP2D6. Endoxifen, which is also formed via the action of CYP2D6, is 30- to 100-fold more potent than TAM in suppressing oestrogen-dependent cell proliferation, and is considered an entity responsible for significant pharmacological effects of TAM. Thus, an association between the cytochrome P450 2D6 (CYP2D6) genotype and phenotype (expected drug effects) is believed to exist and it has been postulated that CYP2D6 testing may play a role in optimising an individual's adjuvant hormonal treatment.

OBJECTIVES

To determine whether or not testing for cytochrome P450 2D6 (CYP2D6) polymorphisms in women with early hormone receptor positive breast cancer leads to improvement in outcomes, is useful for health decision-making and is a cost-effective use of health-care resources.

DATA SOURCES

Relevant electronic databases and websites including MEDLINE, EMBASE and HuGENet [Centers for Disease Control and Prevention (Office of Public Health Genomics), Human Genome Epidemiology Network] were searched until July 2009. Further studies that became known to the authors via relevant conferences or e-mail alerts from an automatically updated search of the Scopus database were also included as the review progressed, up to March 2010.

REVIEW METHODS

A systematic review of the clinical effectiveness and cost-effectiveness of CYP2D6 testing was undertaken. As it was not possible to conduct meta-analyses, data were extracted into structured tables and narratively discussed. An exploratory analysis of sensitivity and specificity was undertaken. A review of economic evaluations and models of CYP2D6 testing for patients treated with TAM was also carried out.

RESULTS

A total of 25 cohorts were identified which examined clinical efficacy (overall survival and relapse/recurrence), adverse events and endoxifen plasma concentrations by genotype/phenotype. Significantly, six cohorts suggest extensive metabolisers (Ems) appear to have better outcomes than either poor metabolisers (PMs) or PMs + intermediate metabolisers in terms of relapse/recurrence; however, three cohorts report apparently poorer outcomes for EMs (albeit not statistically significant). There was heterogeneity across the studies in terms of the patient population, alleles tested and outcomes used and defined. One decision model proposing a strategy for CYP2D6 testing for TAM was identified, but this was not suitable for developing a model to examine the cost-effectiveness of CYP2D6 testing. It was not possible to produce a de novo model because of a lack of data to populate it.

CONCLUSION

This is a relatively new area of research that is evolving rapidly and, although international consortia are collaborating, the data are limited and conflicting. Therefore, it is not possible to recommend pharmacogenetic testing in this patient population. Future research needs to focus on which alleles (including, or in addition to, those related to CYP2D6) reflect patient response, the link between endoxifen levels and clinical outcomes, and the appropriate pathways for implementation of such pharmacogenetic testing in patient care pathways.

P1-12-16: HER-2 Testing and Treatment – Is Age a Factor?

Aims: Elderly breast cancer patients have a poorer prognosis due to late diagnosis and sub-optimal treatment. In the UK, HER-2 testing was introduced in 2005 and we sought to determine whether HER-2 testing was performed on patients of all ages and whether HER-2 positive patients of all ages subsequently received Herceptin, from implementation in 2005 until 2008.

Methods: Review of all newly diagnosed breast cancers in women over 50 in our Unit between January 2005 and December 2008 was performed. Cases were identified from the hospital pathology electronic database. Patients were considered HER-2 positive if tissue sections scored 3+ on immunohistochemical analysis (intense membranous staining) or if gene amplification was detected using fluorescence in-situ hybridisation (FISH). Patients were eligible for treatment with Herceptin if the tumour exceeded 1cm in size or if they had lymph-node positive disease, per UK guidelines. Herceptin treatment was determined for all patients.

Results: In total 703 patients with a median age of 68 years (range 56 to 98) were identified and 628 (89.3%) underwent definitive surgery (mastectomies: 246; wide local excisions: 382) and axillary surgery. In total 371 patients (52.8%) underwent HER-2 testing by immunohistochemistry or FISH. HER-2 tests performed by year: 2005 (51/131; 38.9%); 2006 (59/187; 31.6%); 2007 (71/189; 37.6%) and 2008 (190/196; 96.9%). Fifty six patients (15.1%) were HER-2 positive by immunohistochemistry or FISH. Median age of HER2 positive patients was 66 years (range 57 to 98); median age of HER2 negative patients was 68 years (range 56 to 96). Forty four HER-2 positive patients (78.6%) were eligible for treatment with Herceptin; of these 28 patients (63.6%) were treated with Herceptin. HER2 testing, treatment with Herceptin and overall 5-year mortality rate for patients between 50 to 69 years and patients aged 70 years or older is summarised in Table1.

A preliminary examination of the effects of genetic variants of redox enzymes on susceptibility to oedematous malnutrition and on percentage cytotoxicity in response to oxidative stress in vitro

BACKGROUND

The causes of oedematous vs non-oedematous childhood malnutrition (OM vs NOM) remain elusive. It is possible that inherited differences in handling oxidant stressors are a contributing factor.

AIMS

To test for associations between polymorphisms in five genes and (i) risk of OM, a case-control study, and (ii) percentage cytotoxicity in peripheral blood mononuclear cells (PBMCs) exposed to hydrogen peroxide (H(2)O(2)), an in vitro cell challenge study.

METHODS

Participants had been admitted previously for treatment of OM (cases, n = 74) or NOM (controls, n = 50), or were an independent set of healthy pregnant women (n = 47) who donated peripheral blood mononuclear cells. We tested for associations between genetic variation and outcome using single markers or a bivariate score constructed by counting numbers of deleterious alleles for each of 15 possible pairs of markers.

RESULTS

In the case-control study there were no significant single-marker associations with OM. We did find that higher bivariate scores were associated with OM for the pair of NAD(P)H:quinone oxidoreductase 1 and catalase (odds ratio 2·00, 95% CI 1·05-3·82). In the cell challenge experiments, there were no significant associations with percentage cytotoxicity.

CONCLUSIONS

Variation in this small set of genes seems unlikely to have a large impact on either risk of OM or cytotoxicity after H(2)O(2) exposure. The use of larger sample sizes to test the effects of a much larger set of genetic variants will be required in order to determine whether genetic variation contributes to the risk of OM. Such studies have potential for improving our understanding of causal pathways in OM.

Tamoxifen Resistance in Estrogen Receptor Positive (ER+) Breast Cancer Is Driven by Estrogen Receptor Negative (ER-) Cancer Stem-Like Cells

Introduction: Intrinsic and acquired resistance to endocrine therapy significantly reduces survival rates of women with ER+ breast cancer. In the normal breast, multipotent stem cells are ER-. We hypothesised that tumourigenic breast cancer stem-like cells (CSCs) are ER- and therefore function independently of estrogen, representing a novel mechanism of resistance to endocrine therapy.Methods: Three ER+ cell lines, MCF-7, T47D and BT474 were assessed for ER expression by immunocytochemistry (ICC) in monolayer and after CSC enrichment. Putative CSC number was assessed by the non-adherent mammosphere (MS) assay, in the presence and absence of tamoxifen, and by Fluorescence Activated Cell Sorting (FACS) for the markers CD44+/CD24-/low/epithelial specific antigen(ESA)+. The effect of acquired Tamoxifen resistance on the CSC population of two independent Tamoxifen-resistant (TAM-R) MCF-7 variants, from Cardiff (TAM-RCARD) and Copenhagen (TAM-RCOP) was compared to parental, tamoxifen sensitive (TAM-S) controls. In the MS assay both the number and size of colonies were assessed.Results: A small sub-population of ER_ cells were demonstrated in MCF7 (6.1 ± 1.4%), T47D (6.8± 0.5) and BT474 (3.7±1.3) cells by ICC. However, the majority of putative breast CSCs (CD44+/CD24-/low/ESA-) in MCF7 cells were ER_ (73.2 ± 4.6 % p= 0.0007). There was a significant increase in the proportion of ER- cells in TAM-R cell lines (TAM-RCARD 11.6 ± 1.4% p=0.01 and TAM-RCOP 22 ± 4.8% p=0.02 respectively) compared to the parental TAM-S controls. Both TAM-R cell lines demonstrated increased mammosphere forming efficiency (MFE) compared to TAM-S cells (TAM-RCARD 4% vs. 2.5% p=0.03, and TAM-RCOP 8% vs. 3% p=0.007). The putative CSC population (CD44+/CD24-/low/ESA+) was enriched more than 2.5 fold in TAM-R compared to TAM-S parental controls. Compared with controls, the absolute MFE was not affected by Tamoxifen treatment, although mammospheres formed were significantly smaller.Conclusions: The majority of the putative CSC populations in ER+ breast cancer do not express ER. There is an increase in the proportion of putative ER- CSCs in TAM-R MCF7 cell lines. The reduction in MS size suggests that Tamoxifen targets transit amplifying cells but does not reduce the absolute number of CSC in ER+ breast cancers. These findings demonstrate a novel mechanism of endocrine resistance in ER+ breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5125.