Structural phase transformations in annealed Pt/Mn/Fe trilayers

Thermally-activated phase transitions in Pt/Mn/Fe thin films were investigated by a combination of x-ray diffraction, transmission electron microscopy, secondary neutral mass spectrometry depth profiling, atomic force microscopy, and magnetic properties measurements. Post-annealing was carried out in vacuum to different temperatures up to 620 °C. Initially, at temperatures between 280 °C-450 °C first L10-MnPt is formed at the Mn/Pt interface followed by the most likely formation of metastable bcc Fe3Pt, which gets transformed by further annealing to fcc Fe3Pt and eventually to chemically ordered L12-Fe3Pt. The final product after annealing at 620 °C consists of two interesting phases, which are relevant for spintronic applications, antiferromagnetic L10-MnPt with addition of Fe and ferromagnetic L12-Fe3Pt, consistent with the initial element composition.

Phase transformations in Pt/Fe bilayers during post annealing probed by resistometry

X-ray diffraction (XRD), secondary neutral mass spectrometry (SNMS) depth profiling, and electrical resistivity measurements were used to follow the phase transformations in Pt/Fe bi-layered thin films during annealing. Initially, the electrical resistivity increases linearly with temperature up to 150 °C due to the contribution of phonon scattering of the metallic Pt and Fe bilayer. Further increase of the annealing temperature leads to a steeper linear increase, which is associated with the initial formation of the chemically disordered A1-phase followed by the formation of the chemically ordered L1₀-FePt phase, as confirmed by XRD and SNMS studies. Finally, at about 620 °C the single L1₀-FePt phase has formed throughout the film. Moreover, the electrical resistivity contains also the magnetic contribution to the total resistivity. In this case, the loss in magnetic order is indicated by a change in temperature dependence of the resistivity at about 310 °C, representing the Curie temperature of the initially formed A1-FePt alloy, while the finally formed L1₀-FePt alloy reveals a higher magnetic transition temperature of about 410 °C. In this study, it has been demonstrated that resistometry in combination with structural and chemical analysis provides valuable information on diffusion processes, structural phase formations and its stability range, as well as on the magnetic transition temperature.

A phase II study of pemetrexed and doxorubicin in patients with advanced or metastatic breast cancer (MBC)

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Background: Pemetrexed has a single-agent activity in MBC while doxorubicin is an established agent in breast cancer chemotherapy. This phase II study investigated the combination in patients with advanced or MBC who had not been previously treated with anthracyclines. Primary objective was to evaluate the overall response rate. Methods: Patients received pemetrexed 500 mg/m2 (10-min intravenous infusion) followed by doxorubicin 50 mg/m2 on day 1 of six 21-day cycles. Additional cycles were permitted based upon: absence of progressive disease, adequate cardiac function, and a maximum cumulative limit of doxorubicin 450 mg/m2. Routine folic acid and vitamin B12 supplementation was given to all patients. Results: A total of 79 women with advanced or MBC were enrolled at 15 centers in 7 countries. Major racial groups were Caucasians (50.6%) and Hispanics (24.1%). Median age was 55 years (range, 26–79) and most (91.1%) had performance status of 0 or 1. Patients had either metastatic (72.2 %) or locally advanced disease (27.9%). Sixteen (20.3%) patients had received prior adjuvant chemotherapy. A median of 6 cycles (range, 1–9) was delivered. During the 438 cycles, no doses were omitted, and 7 doses were reduced (3 for pemetrexed, 4 for doxorubicin). A total of 129 doses (29.5%) were delayed, primarily due to scheduling conflicts (84 doses) and neutropenia (19 doses). The relative dose intensity for both drugs was 93%. Overall response rate was 60.8% (95% CI, 49.1–71.6) with complete response in 8 patients (10.1%), partial response in 40 patients (50.6%), and stable disease in 20 patients (25.3%). Maximum CTC grade 3 and 4 toxicities observed in >5% patients were neutropenia (19 patients, 24.1%), leukopenia (8 patients, 10.1%), and vomiting (5 patients, 6.3%). Five deaths occurred during study treatment, 2 of which had causes (diarrhea, pneumonia) possibly related to the study drugs. One patient had resting left ventricular ejection fraction decreased to <50% after 6 cycles and did not receive further treatment. Conclusions: The combination of pemetrexed and doxorubicin was well tolerated and had promising response in patients with advanced or MBC. Survival and time-to-event results are forthcoming.

No significant financial relationships to disclose.

Gemcitabine plus CI-994 offers no advantage over gemcitabine alone in the treatment of patients with advanced pancreatic cancer: results of a phase II randomized, double-blind, placebo-controlled, multicenter study

BACKGROUND

CI-994, an oral histone deacetylase inhibitor, has antineoplastic activity and synergism with gemcitabine preclinically. This randomized phase II trial explored whether CI-994 plus gemcitabine improves overall survival, objective response, duration of response, time to treatment failure and change in quality of life (QoL) or pain compared with gemcitabine alone.

PATIENTS AND METHODS

A total of 174 patients received CG (CI-994 6 mg/m(2)/day days 1-21 plus gemcitabine 1000 mg/m(2) days 1, 8 and 15 each 28-day cycle) or PG (placebo plus gemcitabine 1000 mg/m(2) days 1, 8 and 15 of each 28-day cycle days 1-21).

RESULTS

Median survival was 194 days (CG) versus 214 days (PG) (P = 0.908). The objective response rate with CG was 12% versus 14% with PG when investigator-assessed and 1% versus 6%, respectively, when assessed centrally. Time to treatment failure did not differ between the two arms (P = 0.304). QoL scores at 2 months were worse with CG than with PG. Pain response rates were similar between the two groups. There was an increased incidence of neutropenia and thrombocytopenia with CG.

CONCLUSIONS

Adding CI-994 to gemcitabine in advanced pancreatic carcinoma does not improve overall survival, response rate or time to progression; CG produced decreased QoL and increased hematological toxicity and appears inferior to single-agent gemcitabine.

Analysis of genomic integrity and p53-dependent G1 checkpoint in telomerase-induced extended-life-span human fibroblasts

Life span determination in normal human cells may be regulated by nucleoprotein structures called telomeres, the physical ends of eukaryotic chromosomes. Telomeres have been shown to be essential for chromosome stability and function and to shorten with each cell division in normal human cells in culture and with age in vivo. Reversal of telomere shortening by the forced expression of telomerase in normal cells has been shown to elongate telomeres and extend the replicative life span (H. Vaziri and S. Benchimol, Curr. Biol. 8:279-282, 1998; A. G. Bodnar et al., Science 279:349-352, 1998). Extension of the life span as a consequence of the functional inactivation of p53 is frequently associated with loss of genomic stability. Analysis of telomerase-induced extended-life-span fibroblast (TIELF) cells by G banding and spectral karyotyping indicated that forced extension of the life span by telomerase led to the transient formation of aberrant structures, which were subsequently resolved in higher passages. However, the p53-dependent G1 checkpoint was intact as assessed by functional activation of p53 protein in response to ionizing radiation and subsequent p53-mediated induction of p21(Waf1/Cip1/Sdi1). TIELF cells were not tumorigenic and had a normal DNA strand break rejoining activity and normal radiosensitivity in response to ionizing radiation.

Cell cycle responses of two X-ray sensitive mutants defective in DNA repair

Both the xrs and V-3 lines of Chinese hamster ovary cells exhibit marked sensitivity to ionizing radiation. They are also sensitive to agents such as bleomycin and H2O2 but exhibit normal responses to ultraviolet light and mitomycin C. Both cell lines are defective in split-dose repair and repair of double-strand breaks in DNA. Analysis of response to radiation as a function of age in the cell cycle indicates that both cell lines exhibit a marked sensitivity in late G1 and early S phase with more limited sensitization throughout the remainder of the cell cycle.

Toxicity of RSU-1069 for KHT cells treated in vivo or in vitro: evidence for a diffusible toxic product

RSU-1069 is a highly effective hypoxic cell cytotoxin in KHT sarcomas treated in vivo. However, relative to the hypoxic cells, the oxic cells in the tumor appear more sensitive to the drug than would have been predicted on the basis of results with CHO (AA8-4) cells treated in vitro with the drug under oxic and hypoxic conditions. To examine possible reasons for this difference, suspensions of KHT cells were prepared from tumors growing in vivo, and treated with RSU-1069 in vitro under oxic or hypoxic conditions. The sensitivity of the KHT cells was similar to that of AA8-4 cells, regardless of whether the cells were obtained from untreated tumors or from tumors given 15 Gy in vivo just prior to the preparation of the cell suspension. We observed, however, that the sensitivity of both AA8-4 cells and KHT cells to drug treatment under hypoxic conditions increased with the density of the cells in the treated suspension. This result suggests the possibility that a diffusible toxic product may be released from cells. Such a product could contribute to the toxicity of the drug for oxic cells in tumors in situ.

Studies on the toxicity of RSU-1069

RSU-1069 combines an aziridine function with a 2-nitroimidazole and has been reported to exhibit extraordinary radiosensitization both in vitro and in vivo. Such sensitization appears to be at variance with the electron affinity of the compound. In addition, recent experiments suggest that the compound is highly toxic to hypoxic tumor cells in vivo. On the assumption that the observed radiosensitizing ability may be a manifestation of toxicity and because of the high in vivo toxicity, we have investigated aerobic and hypoxic toxicity, both in wild type CHO cells and in mutants sensitive to a variety of DNA damaging agents. With wild type cells under aerobic conditions, the compound is approximately 50 times as toxic as misonidazole and under hypoxic conditions, approximately 250 times as toxic. The ratio of hypoxic to aerobic toxicity is approximately 80 times. Under aerobic conditions, repair-deficient mutants are 10 times as sensitive to RSU-1069 as wild type cells and approximately 100 times as sensitive under hypoxic conditions. The ratio of hypoxic to aerobic toxicity for the mutant cells is approximately 900. Based on these observations, we suggest that under aerobic conditions the aziridine function is primarily responsible for toxicity, whereas, under hypoxic conditions, the aziridine moiety combined with a reduced 2-nitroimidazole moiety produces a bifunctional agent.

Studies of the in vivo and in vitro cytotoxicity of the drug RSU-1069

The radiosensitizing and cytotoxic properties of the drug RSU-1069, (1-(2-nitro-1-imidazolyl)-3-(1-aziridino)-2-propanol) a 2-nitroimidazole with an aziridine ring in its side-chain, have been examined both in vivo and in vitro. Studies with the KHT Sarcoma or RIF1 tumour indicated that, at doses between 0.04 and 0.16 mg g-1 body wt, the drug was increasingly effective at killing tumour cells when combined with radiation. Cell survival in both tumours following combined RSU-1069 and radiation (1500 or 2000 cGy) treatment was similar when the drug was given 60 min before or immediately after irradiation suggesting that the effect observed was due to hypoxic cell cytotoxicity rather than radiosensitization. Studies with CHO cells in vitro indicated that RSU-1069 was equally as effective as a number of other 2-nitroimidazoles as a radiosensitizer when drug exposure and radiation treatment was given at 4 degrees C. It was substantially more toxic to hypoxic than to aerobic CHO cells (a factor of 90 in dose to give equivalent cell killing) and was much more toxic to CHO cells than misonidazole (a factor of approximately 100 in dose) at 37 degrees C. HeLa cells were more sensitive to RSU-1069 than CHO cells and, under hypoxic conditions, were approximately 20-fold more sensitive to the drug than when aerobic. Prior incubation of hypoxic CHO cells with RSU-1069 at toxic concentrations did not influence the sensitivity of the surviving cells to radiation treatment (i.e. there was no shoulder removal as is observed with misonidazole) nor did prior radiation treatment influence the sensitivity of the surviving cells to drug treatment. Overall the results indicate that RSU-1069 is a highly effective cytotoxic agent for hypoxic cells both in vivo and in vitro but, when drug exposure and radiation treatment are given at 4 degrees C, it is not a more effective sensitizer than other 2-nitroimidazoles.

Hypoxia-dependent reduction of 1-(2-nitro-1-imidazolyl)-3-methoxy-2-propanol by Chinese hamster ovary cells and KHT tumor cells in vitro and in vivo

Incubation of Chinese hamster ovary cells and KHT murine fibrosarcoma tumor cells in the absence of oxygen with 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol, one of the most effective radiation sensitizers of hypoxic cells, results in the preferential reduction of 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol. The radioactivity associated with the acid-insoluble precipitate from cells incubated in nitrogen is about four times higher than that of cells incubated in air. When aqueous extracts of tissues of a C3H mouse bearing the KHT tumor, after i.p. injection with 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol, are analyzed, a reduction product is found in relatively higher yields in the tumor than in normal tissues. The relative radioactivity in the pellet from the tumor homogenate is also high in comparison with those of most normal tissues. These results provide suggestive evidence for a higher degree of hypoxic in the tumor than in most normal tissues. The formation of reduction products and their subsequent binding to macromolecules may explain the preferential toxicity of nitro compounds to mammalian cells under hypoxia conditions. These results suggest that some nitro compounds may be useful for the treatment of tumors having a high fraction of hypoxic cells even in the absence of radiation.

Synchronization of mammalian cells with tritiated thymidine

Short exposures of mammalian cells to tritiated thymidine of high specific activity destroys the proliferative capacity of mammalian cells. Since the killing is limited to cells that have synthesized DNA in the presence of the labeled compound, an exposure duration of less than one generation can yield a synchronized population.