Safety study of induction chemotherapy and synchronous radiotherapy (RT) and cetuximab in stage III non-small cell lung cancer (NSCLC): SCRATCH (Cohort I)

18032

Background: The addition of cetuximab can increase the efficacy of chemotherapy for advanced NSCLC. Concomitant cetuximab and RT is superior to RT alone for locally advanced squamous cell head & neck carcinoma. The SCRATCH study (cohort I) is a phase I study to assess the safety of synchronous cetuximab and radical RT in patients with Stage III NSCLC. Methods: Cohort I will contain 12 patients with inoperable stage III NSCLC. Inclusion criteria are performance status 0–1, adequate organ function, and disease encompassable within a radical RT volume. Exclusion criteria are previous malignancy, thoracic RT or treatment with EGFR targeted therapy. Patients receive platinum-based induction chemotherapy, followed by weekly intravenous cetuximab (initial dose 400mg/m2; maintenance dose 250mg/m2) and concomitant RT (64Gy/32fractions/45days). The primary end-point is toxicity. NCI Common Toxicity Criteria (CTC) V3.0 assessments are performed weekly during radiotherapy, and at regular follow-up visits. Results: Data from the first 9 patients is available. 2 patients stopped receiving cetuximab early due to toxicity. 1 experienced grade 3 fatigue following the initial dose, and the other declined further treatment after developing grade 2 skin toxicity. 2 patients have died, 1 from disease progression and 1 from thromboembolic disease. Both deaths occurred between months 2 and 4 post RT and were not attributed to the cetuximab therapy. Of the 7 living patients, 2 have survived 1 year (measured from the first day of induction chemotherapy). The maximum NCI CTC V3.0 scores are summarised in the table below. Conclusions: The results suggest that the early and late toxicities of synchronous cetuximab and radical RT are acceptable. Data on all 12 patients will be available by June 2007. SCRATCH Study cohorts II-IV follow on and will recruit sequentially. They will assess the safety of adding concomitant cisplatin (±vinorelbine) to cetuximab and radical RT.

[Table: see text]

No significant financial relationships to disclose.

Phase I evaluation of OXi4503, a vascular disrupting agent, in patients with advanced solid tumours

14146

Background: OXi4500, the active product of OXi4503, is a vascular disrupting agent acting at the colchicine binding site on the β subunit of tubulin. OXi4503 has greater anti-tumour activity in human cancer cell lines, causes a greater reduction in tumour blood flow than combretastatin A4P and has single agent activity in human tumour xenograft models. A phase I trial has commenced to examine the safety, tolerability and pharmacokinetics of OXi4503, with the primary objective being determination of MTD. FDG-PET scans were performed prior to and 28 days after the first infusion of OXi4503. Several other pharmacodynamic endpoints are also being assessed including DCE & BOLD MRI, circulating endothelial progenitor cells and cytokeratin 18. Methods: OXi4503 is administered by 3 weekly iv infusions to a maximum of 6 cycles. Starting dose was 0.06mg/m2. 100% dose escalation in single patient cohorts proceeded to 3.84mg/m2, when cohorts were expanded to three patients and 30% escalation due to emergence of grade 2 drug-related toxicity (thrombocytopaenia). Results: 11 patients have so far received OXi4503 (5F 6M, median age 54, range 33–68); median cycles received was 2 (range 1–4). Common AE’s include hypertension, pyrexia and anaemia. PK profiles show a dose-dependent linear increase in peak plasma concentrations and AUC of both OXi4503 and OXi4500. OXi4500 concentrations at current dosing (5 mg/m2) are close to that seen at the MTD in rats and dogs. DCE-MRI showed significant reduction in Ktrans in one patient (0.24mg/m2). In the 2 patients studied to date, PET images showed a decrease in the standardised uptake value (SUV) in 3 out of 4 metastases for one subject (1.92mg/m2) and in 5 out of 7 metastases for the other subject (3.84mg/m2) demonstrating a reduction in FDG uptake following drug treatment. Of 10 patients assessed, 2 have stable disease and 8 disease progression. Conclusions: OXi4503 has been tolerated at doses up to 5mg/m2 with no DLT observed, but changes in functional activity have been seen in 3 patients. MTD has not been reached and recruitment is ongoing.

[Table: see text]

Effect of sperm cryopreservation and supplementing semen doses with seminal plasma on the establishment of a sperm reservoir in gilts

Frozen-thawed (FT) boar sperm have a reduced fertile life, due in part to a capacitation-like status induced by cooling. Reversal of this cryocapacitation in vitro by exposure to boar seminal plasma (SP) has been demonstrated. The objective of these studies was to determine the effect of SP on the ability of FT sperm to create an oviductal sperm reservoir following artificial insemination (AI). In Experiment one, 35 pre-pubertal gilts were injected (IM) with 400 IU eCG plus 200 IU hCG to induce oestrus. At detection of oestrus, gilts were inseminated with 3 x 10(9) live sperm, either fresh (FS; n = 13), FT (n = 10), or FT supplemented with 10% v/v SP (n = 12). Gilts were killed 8 h later, their reproductive tracts recovered and the uterotubal junctions (UTJs) flushed to recover sperm. Fewer (p < 0.01) sperm were recovered following FT, compared to FS, inseminations, and there was no evident effect of SP. In Experiment two, 30 pre-pubertal gilts received IM injections of 1000 IU eCG followed by 5 mg pLH 80 h later to control time of ovulation. Gilts were inseminated with 3 x 10(9) live FS sperm (n = 6), FT sperm (n = 15) or FT sperm plus 10% SP (n = 9) at 12 h before ovulation and then sacrificed 8 h later. The UTJs were dissected and flushed for sperm recovery. Fewest (p < 0.001) sperm were recovered following FT insemination and there was no evident effect of SP. These data demonstrate that the size of the sperm reservoir is markedly reduced in gilts inseminated with FT sperm. However, the lack of effect of SP suggested that either it did not reverse cryocapacitation or that such a reversal does not impact the in vivo ability to create a sperm reservoir.

Intra arterial hepatic chemotherapy for unresectable colorectal metastases: (review)

BACKGROUND

Hepatic arterial infusion (HAI) chemotherapy is based on the idea that liver metastases are perfused almost exclusively by the hepatic artery. This approach has been extensively investigated in 1970s and 1980s. Currently, there is a worldwide growing interest in intraarterial therapeutic approaches for hepatic metastases. The principal aim of this review was to define current role of HAI in the management of metastatic colorectal cancer.

METHODS

Data for this review were identified by searches of MEDLINE using the search terms "hepatic arterial infusion", "colorectal cancer" and "chemotherapy". Abstracts and reports from meetings were included only when they related directly to previously published work. Only papers published in English between 1966 and 2005 were included.

RESULTS AND CONCLUSION

There are 10 published randomised clinical trials comparing fluoropyrimidine-based HAI with systemic route. Two meta-analyses of the earlier 7 trials confirmed a statistically significant response rate and improved disease-free survival with HAI. However, the cost and complication rates were of primary concern. The last decade witnessed the introducztion of new chemotherapeutic regimens including biologically targeted agents for the management of metastatic colorectal cancer patients and advancement in radiological and surgical techniques. These led to reconsideration of HAI-based therapeutic modalities with many running trials addressing its value in this new era. The results of these trials may help to clarify the role of HAI in the near future.

Genomic diversity of cultivable Lactobacillus populations residing in the neonatal and adult gastrointestinal tract

The objective of this study was to investigate the cultivable Lactobacillus population in adult and infant faecal material to identify strains shared across a number of individuals. A range of lactobacilli isolated on Lactobacillus-selective agar from faeces of 16 infants and 11 adults were genetically fingerprinted and further characterized by 16S rRNA gene sequencing. The relatedness of all the Lactobacillus strains isolated to known species was also determined both genetically and phenotypically. This study revealed that the human intestine is initially colonized by only a few (1-2) different cultivable strains whereas in adults the pattern becomes more complex with a higher diversity of strains. The adult samples contained three genetically distinct Lactobacillus strains in some cases, while infant samples generally harboured only one dominant Lactobacillus strain. Moreover, the species in general appeared to differ with Lactobacillus rhamnosus and Lactobacillus casei/paracasei found mainly in adults, whereas Lactobacillus gasseri and Lactobacillus salivarius were more commonly isolated in infant samples. The data reaffirm the differences in Lactobacillus populations both between individual subjects and between the infant and adult, with an overall change in the diversity and complexity from early stages of life to adulthood.

EXIBIT: An international multicenter phase II trial of gemcitabine and oxaliplatin (GEMOX) in patients with advanced biliary tract cancer

4135

Background: Biliary tract carcinomas (BTC) are often diagnosed at an advanced/metastatic stage and have a poor prognosis. The combination of gemcitabine and oxaliplatin (GEMOX) showed promising activity in a French Phase II study (4 centers) in advanced BTC (André. Ann Oncol 2004;15:1339–1343). The objective of this study is to further evaluate the efficacy and safety of GEMOX as first-line therapy in patients (pts) with advanced BTC. Methods: Eligible pts were >18 years of age with histologically proven and measurable, locally advanced or metastatic BTC, had an ECOG PS ≤ 2, adequate renal and hematologic functions, bilirubin < 2.5 × upper limit of normal, and no prior malignancy or brain metastases. Gemcitabine 1000 mg/m2 (Day 1) and oxaliplatin 100 mg/m2 (Day 2) were administered every 2 weeks. The primary objective was response rate (RR) by RECIST (one dimension); secondary objectives were progression-free survival (PFS), overall survival (OS), and safety. Here we report an interim analysis of OS and safety. Results: A total of 70 pts were enrolled between April 2003 and April 2005. The median age was 62 years (range 30–83), 40.0% of pts were male, 94.3% had ECOG PS 0–1. Tumor sites were intrahepatic bile ducts (37.1%), gallbladder (31.4%), extrahepatic bile ducts (12.9%), ampulla of Vater (1.4%), intra/extrahepatic bile ducts (1.4%), missing data (15.7%); 98.6% of pts had no prior radiotherapy and 50% had no prior surgery for BTC. Median OS is 8.25 months (68% of pts are dead and 32% have censored data). Sixty-seven pts were evaluable for safety. Grade 3/4 (NCI-CTC v. 2) hematologic toxicities (% of pts) included thrombocytopenia 10.4%, anemia 9.0%, and neutropenia 9.0%. One pt had febrile neutropenia. Grade 3/4 nonhematologic toxicities included pain 10.4%, ALT elevation 9.0%, fatigue 9.0%, infection 10.4%, vomiting 9.0%, sensory neuropathy 4.5%, nausea 4.5%, and diarrhea 3.0%. One patient died during treatment (cause unknown). Conclusions: GEMOX has acceptable toxicity in pts with BTC. Updated efficacy data (RR, PFS, and OS for the entire population and also by tumor sites) will be presented at the meeting.

[Table: see text]

The mode of action of the lantibiotic lacticin 3147--a complex mechanism involving specific interaction of two peptides and the cell wall precursor lipid II

Lacticin 3147 is a two-peptide lantibiotic produced by Lactococcus lactis in which both peptides, LtnA1 and LtnA2, interact synergistically to produce antibiotic activities in the nanomolar concentration range; the individual peptides possess marginal (LtnA1) or no activity (LtnA2). We analysed the molecular basis for the synergism and found the cell wall precursor lipid II to play a crucial role as a target molecule. Tryptophan fluorescence measurements identified LtnA1, which is structurally similar to the lantibiotic mersacidin, as the lipid II binding component. However, LtnA1 on its own was not able to substantially inhibit cell wall biosynthesis in vitro; for full inhibition, LtnA2 was necessary. Both peptides together caused rapid K(+) leakage from intact cells; in model membranes supplemented with lipid II, the formation of defined pores with a diameter of 0.6 nm was observed. We propose a mode of action model in which LtnA1 first interacts specifically with lipid II in the outer leaflet of the bacterial cytoplasmic membrane. The resulting lipid II:LtnA1 complex is then able to recruit LtnA2 which leads to a high-affinity, three-component complex and subsequently inhibition of cell wall biosynthesis combined with pore formation.

Polymorphisms within the lactoferrin gene promoter in various cattle breeds

Lactoferrin (Lf) is an iron-binding protein and belongs to the serum transferrin family. It has broad spectrum antimicrobial action, and it is found in exocrine secretions including milk. The sequence of the bovine lactoferrin gene promoter was analyzed in five different cattle breeds (Holstein Friesian, New Zealand Holstein, Montebéliard, Normande, and Norwegian Red) to determine the extent of polymorphic variation, which exists in this region both within and across cattle breeds. Fifteen different single nucleotide polymorphisms (SNPs) were identified throughout this region. Numerous polymorphisms were found throughout the Holstein Friesian, New Zealand Holstein, Montebéliard, and Normande populations. The most frequently encountered polymorphism found in all breeds was at position -28, which is immediately proximal to the TATA box of the promoter. The most variable base position was -131, which included three types of heterozygotes including a single base deletion in one allele, and three homozygote variants. This polymorphism occurs in a putative transcription factor binding site, for the nuclear factor of activated T cells (NF-ATc). A unique polymorphism was identified in one Normande animal, and three polymorphisms were found in one Montebéliard animal. In general, Norwegian Red cattle displayed fewer SNPs than other breeds. Most nucleotide changes in these animals were within the 190 base pairs of the transcription start point, with the exception of an insertion seen in three animals at position -478. In conclusion, SNPs were found in abundance throughout this regulatory region. Whether or not these polymorphisms have an effect on the regulation of the bovine lactoferrin gene is yet to be elucidated. However, the identification of lactoferrin promoter variants may serve as a marker for healthier animals, thereby accelerating the improvement of animals through breeding.

184 EFFECT OF LIVE CONFOCAL FLUORESCENCE IMAGING ON EMBRYONIC DEVELOPMENT

The aim of this study was to examine the effects of fluorescent confocal imaging on embryo development. DNA damage, caspase activation, and reactive oxygen species (ROS) production were also measured. In vitro-generated bovine 8-cell embryos and in vivo-produced mouse 2-cell embryos were stained with Mitotracker Red and individually imaged using a spinning-disc confocal module (CARV) attached to a Nikon TE2000-U microscope. The sample was excited with a 120 W metal halide lamp (X-Cite 120) using a fluorescent filter set (Excitation: 575 nm; Emission: 640 nm). A variety of number and durations of exposures were tested. Continuous variables were analyzed by t-test, whereas categorical data were analyzed using the homogeneity chi square test. Bovine embryos showed no differences in blastocyst development (Day 7.5; Day 0 = IVF) or hatched blastocysts (Day 11) between groups of imaged and non-imaged embryos (Table 1). Despite numerous attempts, we were unable to find a level of exposure that disturbed embryo development, indicating that bovine embryos have a high degree of tolerance to the imaging system. After exposure, mouse embryos were cultured in vitro to the blastocyst stage and transferred into surrogate synchronized females. Embryos subjected to five exposures of 50 ms developed normally both in vitro and in vivo (Table 1). However, exposing the embryos 30 times significantly affected in vitro and in vivo development. Subsequently, we examined the effect of confocal imaging on DNA damage (Comet assay), ROS production (dichlorofluoresceindiacetate, DCF), and caspase 3 activation (PhiPhiLux®-G1D2). Bovine embryos were exposed to 60z–50 ms or 60z–500 ms, and mouse embryos to 5z–50 ms or 30z–50 ms after Mitotracker Red staining. We observed that caspase 3 was not activated when measured 1.5 h after imaging. Similarly, DNA damage was not different among embryos exposed at different levels of imaging. However, ROS production significantly increased in both bovine and mouse embryos after exposure to confocal imaging, and this increase correlated with fluorescence exposure level. We conclude that imaging bovine pre-implantation embryos with this system increased ROS production but did not disturb in vitro development (even at unnecessary high levels of exposure). In mouse embryos, in vitro development after imaging directly correlated with in vivo development. It remains to be determined whether the increase in ROS production and decreased developmental potential is due to the fluorescence exposure alone or the combined effect of fluorescence exposure and Mitotracker labeling. Table 1. Embryonic development after confocal fluorescence imaging

24 GLOBAL TRANSCRIPT PROFILING OF CLONED BOVINE BLASTOCYSTS USING AFFYMETRIX GENECHIP TECHNOLOGY

Identification of genes implicated in the biological processes of somatic cell nuclear transfer will improve our understanding of reprogramming events, i.e. the transformation of a lineage-committed cell into a pluripotent one. In addition, the gene expression profile of cloned embryos can help explain the widely reported developmental failures in cloned animals. In this study, we investigated global gene expression profiles of bovine in vitro-fertilized and cloned embryos using Gene Chip Bovine Genome Arrays (Affymetrix, Inc., Santa Clara, CA, USA). For the generation of cloned bovine blastocysts from two adult fibroblast lines (C and D), we employed methods previously proven to generate live offspring and compared these offspring to in vitro-produced blastocysts. Total RNA isolated from groups of 10 blastocysts was amplified by a template-switching PCR. Amplified cDNAs were used to synthesize biotin-labeled antisense RNAs (aRNAs) during and in vitro transcription reaction. Labeled aRNAs were hybridized to microarrays as described by the manufacturer. Experiments were performed in four replicates. Expression data were analyzed using the Significance Analysis of Microarrays (SAM; Tusher et al. 2001 Proc. Natl. Acad. Sci. 98, 5116-5121) procedure and software. Overall, 48.4% and 46% of 23 000 bovine transcripts spotted on the arrays were present in cloned and in in vitro-produced control blastocysts, respectively. The SAM procedure identified 43 genes that changed at least 1.5-fold, with an estimated false discovery rate (FDR) of 20%. Comparison of gene expression between NT embryos produced from two different cell lines and IVF controls with the same criteria revealed 6 (clones from cell line C vs. IVF) and 46 (clones from cell line D vs. IVF) differentially expressed genes. The number of transcripts expressed differentially between the cloned embryos with different donor cell origin was 437. Of the 43 differentially expressed transcripts in cloned blastocysts, 13 have unknown functions and the rest of the genes related to cell structure (tuftelin, desmoplakin), cell cycle/mitosis (Kinesin like 4, katanin, stathmin, PCNA), energy metabolism (lactate dehydrogenase, ATPsynthase, lipid-binding protein, keto acid dehydrogenase E1, metallothionein), and cell signaling (GTP-binding protein1, GTP binding stimulatory protein). Our results indicate that expression profiles of cloned blastocysts could be affected by somatic donor cell.

Characteristics of primary biliary cirrhosis in British Columbia's First Nations population

Primary biliary cirrhosis (PBC) is a rare, autoimmune liver disorder characterized by progressive destruction of intrahepatic bile ducts, that results in portal inflammation, scarring, cirrhosis and, eventually, liver failure. Although considered rare in Canadian populations, it is the leading indication for referral for liver transplantation in British Columbia's First Nations population. Previously, an expanded review of all cases referred to the British Columbia Transplant Society for PBC was carried out comparing the demographics of those of First Nations descent with those not of First Nations descent. The review suggested that the rate of referral for transplantation was eight times higher for those of First Nations descent compared with those of other descent (P=0.0001), and a disproportionate number of the First Nations cases lived on Vancouver Island (48% of cases versus 18% expected, P<0.05). Additionally, the age of referral was significantly younger (45.9 versus 54.3 years) for those of First Nations descent and there are fewer First Nations men referred (1:34) than expected. For the purpose of the present report, 28 symptomatic cases were ascertained separately and reviewed in a clinical study to delineate the features of this population.

RESULTS

Although available liver biopsy reports were consistent with PBC, not all cases were antimitochondrial antibody-positive (18% negative). There was a family history of PBC confirmed by medical records in 33% of cases. There were five multiplex families identified, one with seven affected individuals. Detailed family histories revealed a recurrence risk of 4% for PBC for all first-degree relatives older than 21 years of age, but 10% when considering only women. Other autoimmune conditions coexisted in PBC patients in 79% of all cases. Arthritis was most frequent (60%), with thyroid disease (16%) and systemic lupus erythematosus (12%) also present. Additionally, a history of autoimmune diseases (arthritis, systemic lupus erythematosus and thyroid disease) was present in 21% of first-degree relatives. A strong genetic predisposition to PBC and other autoimmune diseases, combined with common environmental factors, is postulated in this population. Further study is underway to identify these factors.

The lantibiotic lacticin 3147 produced in a milk-based medium improves the efficacy of a bismuth-based teat seal in cattle deliberately infected with Staphylococcus aureus

A preparation of the bacteriocin lacticin 3147 (prepared from a demineralized whey protein fermentation liquor) was combined as a powder with a bismuth-based intramammary teat seal and evaluated for its potential as an antimicrobial in non-lactating cows. The lacticin/teat seal formulation enabled significant bacteriocin release from the seal without the requirement for a surfactant. Studies in vivo in lactating cows demonstrated that this formulation was effective in reducing bacterial recoveries (approximately 20-fold) from teats deliberately inoculated with Staphylococcus aureus after infusion. Moreover, this formulation also significantly reduced the numbers of Staph. aureus recovered from teats that were exposed to the challenge bacterium before the infusion of the teat seal preparation. The powdered preparation of lacticin 3147 did, however, cause some teat irritation as evidenced by associated rises in somatic cell count (SCC). However, this effect was short-lived and when the mean SCC readings pre-infusion and the final two readings post-infusion were compared, there was no significant difference in the immunological acceptance between treatments.

Efficacy of 5-fluorouracil-based chemotherapy in elderly patients with metastatic colorectal cancer: a pooled analysis of clinical trials

BACKGROUND

Recently published population-based investigations showed elderly patients to be underrepresented in clinical trials and less often treated according to the standard therapy. Although there is evidence that elderly patients benefit from adjuvant (radio-) chemotherapy to the same extent as younger patients, no large series describes the influence of age on efficacy of chemotherapy in metastatic colorectal cancer.

PATIENTS AND METHODS

We carried out a retrospective analysis using source data of 3825 patients who received 5-fluorouracil (5-FU)-containing treatment in 22 European trials and identified 629 patients with an age of > or = 70 years.

RESULTS

We found an equal overall survival in elderly patients [10.8 months, 95% confidence interval (CI) 9.7-11.8] and in younger patients (11.3 months, 95% CI 10.9-11.7; P = 0.31). Response rate did not differ between age groups > or = 70 and <70 years (23.9% and 21.1%; respectively; P = 0.14). Progression-free survival was marginally prolonged in elderly patients (5.5 months, 95% CI 5.2-5.8; compared with 5.3 months, 95% CI 5.1-5.5; P = 0.01). In both age groups, infusional 5-FU resulted in significantly increased response rates, overall survival and progression-free survival compared with bolus 5-FU.

CONCLUSIONS

'Fit' elderly patients benefit at least to the same extent from palliative chemotherapy with 5-FU as younger patients. Infusional 5-FU was shown to be more effective than bolus 5-FU in both age groups. Therefore, standardized palliative chemotherapy should generally be offered to elderly patients and they should not be excluded from clinical trials.

The mystery of primary biliary cirrhosis in British Columbia's First Nations people

OBJECTIVES

Primary biliary cirrhosis (PBC) is a rare chronic, progressive liver disorder leading to transplantation or death, with a known autoimmune basis. Although it has been estimated to have a prevalence of between 2-5 cases per 100,000 worldwide, it is not rare in British Columbia's (BC) First Nations (FN) peoples, where it is the leading indication for liver transplant in that population. A study of indications for liver transplant from 1989 to 1998 demonstrated that although just 3.9% of the population of BC is of FN descent, 25% of those requiring transplantation for PBC were of FN descent. From this, it can be calculated that PBC is about 8 times more common than in the non-native population.

METHODS

We studied the prevalence of PCB on Vancouver Island, where about 50% of the cases on the transplant Society List are reported.

RESULTS AND DISCUSSION

As with many autoimmune diseases, PBC affects women predominantly. Genetic predisposition and environmental factors are thought to contribute to the development of PBC. A strong genetic component is postulated in the BC population where 6 affected individuals are all related through common great grandparents. Nonetheless, both genetic and environmental components are being explored in this unique population.

272 OOCYTE SPONTANEOUS ACTIVATION IN DIFFERENT RAT STRAINS

Oocyte spontaneous activation (OSA) has been reported to occur during in vitro culture of ovulated rat eggs. Approximately 1.5 h after isolation and culture, unfertilized oocytes extrude the second polar body and enter a metaphase arrest, and by 3 h individual chromatids separate and scatter throughout the egg's cytoplasm. The objective of this study was to compare the proportion of OSA and the level of maturation promoting factor (MPF) activity in oocytes from different strains. Twelve strains were selected from two commercial sources based on litter size. Mature female rats (9 to 12 weeks old) were superovulated using 20 IU eCG s.c. followed by 30 IU eCG s.c. 5 h later. After 48 h, a dose of 50 IU hCG was administered intraperitonealy and females were mated with vasectomized males. Oocytes were collected 17 h after hCG injection and cumulus cells were removed by transfer to M2 medium containing hyaluronidase (1 mg mL−1). Denuded oocytes were cultured in 50 μ­L drops of M16 medium under oil at 37°C and 5% CO2 in air. In order to assess OSA, oocytes were mounted in glycerol containing Hoechst 33342 (10 μg mL−1) on a glass slide after 6 h of in vitro culture. The proportion of activated oocytes was determined by epifluorescence microscopy. Oocytes were considered to be in metaphase II if they presented a compact group of chromosomes at the metaphase plate, and were considered activated when chromosome dispersion at different degrees was observed. Data were analyzed by ANOVA, considering each animal as an experimental unit. Significant differences were observed between strains (P < 0.01, Table). In order to determine MPF activity of each strain, 10 oocytes were removed from culture at 0, 1.5, and 3 h after oocyte collection and immediately stored in kinase buffer in LN2 for posterior analysis using an ELISA based kit (MESACUP cdc2 Kinase Assay Kit, MBL, Nagoya, Japan). The log ratio of the MPF activity at 1.5 and 3 h relative to 0 h for each animal (5 per strain) was analyzed by ANOVA. There were no MPF differences between or within strains (P > 0.3 and P > 0.05, respectively). We did not observe the expected decrease in MPF activity that allows for the exit of metaphase II arrest. This could imply that OSA is not associated with a decrease in MPF, or that MPF decreased rapidly and returned to metaphase levels by 1.5 h after culture. In conclusion, different levels of OSA were observed between strains, however, no differences in MPF activity were detected at the analyzed time points.