Biomedical subjects
Publications and source records attributed to M Pellarin.
Electron-lattice energy exchanges are investigated in gold and silver nanoparticles with sizes ranging from 30 to 2.2 nm embedded in different environments. Femtosecond pump-probe experiments performed in the low-perturbation regime demonstrate a strong increase of the intrinsic electron-phonon interaction for nanoparticles smaller than 10 nm due to a confinement effect.
The internal thermalization dynamics of the conduction electrons is investigated in silver nanoparticles with radius ranging from 13 to 1.6 nm using a femtosecond IR pump-UV probe absorption saturation technique. A sharp increase of the electron energy exchange rate is demonstrated for nanoparticles smaller than 5 nm. The results are consistent with electron-electron scattering acceleration due to surface induced reduction of the Coulomb interaction screening by the conduction and core electrons.
BACKGROUND: Intracranial primitive neuroectodermal tumors (PNETs) occur in the supratentorial and infratentorial regions of the brain. Although histologically similar, the natural history of the tumor at each site differs. The study goal was to determine whether there was evidence of a genetic difference between supratentorial and infratentorial PNETs. METHODS: Using comparative genomic hybridization (CGH), 53 PNETs were analyzed to determine copy number aberrations. Forty-three tumors were located in the cerebellum (IPNETs), and ten were supratentorial PNETs (SPNETs). All samples were reviewed to confirm the diagnosis. Each specimen had at least 50% tumor. RESULTS: Six of the 43 cases of IPNET had no copy number aberrations. In contrast, each case of SPNET had copy number aberrations detected by CGH. Statistically significant differences in copy number aberrations of chromosomes 14, 17, and 19 were detected in the two groups. The most common copy number aberration in the IPNETs was gain of chromosome 17q, which was observed in 16 of 43 cases (37%). However, no case of SPNET had gain of 17q. Loss of 14q was detected in four of ten SPNETs but was not detected in any of the IPNET cases. Loss of 19q was detected in 4 of 10 SPNETs and in only 1 of 43 IPNETs. CONCLUSIONS: These results indicate that the genetic aberrations of IPNETs differ from the genetic aberrations of SPNETs. Although they are similar histologically, SPNETs and IPNETs appear to be biologically distinct entities.
Neuroblastoma behavior is variable and outcome partially depends on genetic factors. However, tumors that lack high-risk factors such as MYCN amplification or 1p deletion may progress, possibly due to other genetic aberrations. Comparative genomic hybridization summarizes DNA copy number abnormalities in a tumor by mapping them to their positions on normal metaphase chromosomes. We analyzed 29 tumors from nearly equal proportions of children with stage I, II, III, IV, and IV-S disease by comparative genomic hybridization. We found two classes of copy number abnormalities: whole chromosome and partial chromosome. Whole chromosome losses were frequent at 11, 14, and X. The most frequent partial chromosome losses were on 1p and 11q. Gains were most frequent on chromosome 17 (72% of cases). The two patterns of gain for this chromosome were whole 17 gain and 17q gain, with 17q21-qter as a minimal common region of gain. Other common gains were on chromosomes 7, 6, and 18. High level amplifications were detected at 2p23-25 (MYCN region), at 4q33-35, and at 6p11-22. Chromosome 17q gains were associated with 1p and/or 11q deletions and advanced stage. The high frequency of chromosome 17 gain and its association with bad prognostic factors suggest an important role for this chromosome in the development of neuroblastoma.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1,14-Bis-(ethyl)-amino-5,10-diazatetradecane N1,N11-bis(ethyl)norspermine (BE-4-4-4) and 1,19-bis-(ethylamino)-5,10,15 triazanonadecane (BE-4-4-4-4) are two relatively new polyamine analogs synthesized for use as antineoplastic agents. In human brain tumor cell lines U-251 MG and SF-767, both agents inhibited cell growth, were cytotoxic, induced a variable G1/S block, and depleted intracellular polyamines. Since intracellular polyamine depletion did not always correlate with growth inhibition, cell survival, or cell cycle progression, it cannot completely explain the effects of these agents on growth, survival, and cell cycle progression in U-251 MG and SF-767 cells.
We designed three polyamine analogues, 1,14-diamino-N5-methyl-5,10- diazatetradecane (5me-4-4-4), 1,14-diamino-N5,N5-dimethyl-5,10-diazatetradecane (Q-Amm-4-4-4), and 1,14-bis-(ethylamino)-N5,N5-dimethyl-5,10-diazatetradecane (BE-Q-Amm-4-4-4), on the basis of computer modeling and physical-chemical studies of polyamine-DNA interactions. These analogues differ from natural polyamines and from one another in the charge distribution on their aliphatic backbone. We found that 10 microM 5me-4-4-4 did not inhibit growth and was not cytotoxic to the human brain tumor cell lines SF-767 and SF-126. The same concentrations of Q-Amm-4-4-4 and BE-Q-Amm-4-4-4 inhibited cell growth and killed more than 90% of each cell type on day 7 of the experiment. BE-Q-Amm-4-4-4 was slightly more toxic than Q-Amm-4-4-4 in both cell lines. All three agents either decreased or completely depleted intracellular putrescine and spermidine. Q-Amm-4-4-4 and BE-Q-Amm-4-4-4 each also lowered spermine. The fact that 5me-4-4-4 was nontoxic but that Q-Amm-4-4-4 was cytotoxic and inhibited growth suggests that the charge distribution along the surface of the aliphatic backbone of polyamines is important in determining growth inhibition and cytotoxicity.
Explore the source record for details and available documents.
We studied whether pretreatment of U-251 MG human brain tumor cells with the polyamine analog 1,19-bis-(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) affected the cytotoxicity of the topoisomerase II inhibitor etoposide. We found that BE-4-4-4-4 protected cells from the cytotoxic effects of etoposide. Possible mechanisms for this protection may be related to enhanced DNA-nuclear matrix association in analog-treated cells.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Computer graphics modeling and physicochemical studies of spermine-DNA interactions, as well as experiments in cell culture, indicate that a polyamine analogue with strong affinity for nucleic acids but poor ability to condense and aggregate DNA in vitro should act as an antiproliferative agent if it can enter cells. On the basis of our studies of polyamine-DNA interactions, we designed a pentamine, 1,19-bis(ethylamino)-5,10,15- triazanonadecane (BE-4-4-4-4), that had these characteristics. Measurement of melting temperature and ultraviolet light scattering studies show that the affinity of this analogue for calf-thymus DNA is about 4 times higher than that of spermine, whereas its ability to aggregate DNA is slightly poorer than that of spermine. Studies in U-87 MG, U-251 MG, SF-126, SF-188, SF-763, SF-767, and DAOY human brain tumor cells in tissue culture showed that treatment for more than 96 h with concentrations of 5 microM BE-4-4-4-4 or greater inhibited growth; decreased levels of putrescine, spermidine, and spermine; and decreased colony-forming ability in all cell lines. The cytotoxicity of the analogue varied among cell lines; DAOY and SF-767 were the most sensitive and the most resistant lines, respectively. In SF-763 cells, growth inhibition by BE-4-4-4-4 could be partially reversed by the addition of putrescine, spermidine, or spermine 1 day after BE-4-4-4-4 addition, but in U-251 MG cells, growth inhibition was reversed only by spermine and not by other polyamines. When any of the naturally occurring polyamines was added simultaneously with BE-4-4-4-4, growth inhibition was completely blocked. The data suggest that a threshold intracellular concentration of BE-4-4-4-4 is needed to manifest the growth-inhibitory and cytotoxic effects. In most cell lines, once that threshold level is reached, the growth-inhibitory and cytotoxic properties of the analogue are manifest irrespective of cellular polyamine levels. Further increases in the BE-4-4-4-4 concentration or incubation time reduce the intracellular polyamine levels but do not significantly increase growth inhibition. In U-87 MG and DAOY cells, however, prolonged incubation with higher concentrations of BE-4-4-4-4 causes additional growth inhibition along with depletion of intracellular polyamines.(ABSTRACT TRUNCATED AT 400 WORDS)
Explore the source record for details and available documents.
We studied the effects of the spermine analogue N1,N14-bis-(ethyl)-homospermine (BE-4-4-4) on growth, survival and polyamine levels in cultured U-251 MG and SF-188 human brain tumor cells. After 48 hr of treatment at concentrations of 1 microM or higher, BE-4-4-4 accumulated in cells with a concomitant decrease in intracellular putrescine, spermidine and spermine concentrations. Growth inhibition by 10 microM BE-4-4-4 began at 6 hr and peaked between 16 and 24 hr. The analogue was also increasingly cytotoxic with doses between 1 and 10 microM and with treatment times between 16 and 48 hr. Polyamines added 1 day after BE-4-4-4 lowered the intracellular concentrations of the analogue but did not reverse its growth-inhibitory activity. When added simultaneously with the analogue, however, polyamines caused a decrease in analogue concentration that was accompanied by a block to the growth inhibition. BE-4-4-4 has a higher affinity for DNA than spermine has, but is less able to aggregate DNA. Its growth-inhibitory and cytotoxic effects support our hypothesis that polyamine analogues that enter cells and replace natural polyamines at DNA binding sites, without fulfilling their biologic functions, should act as antiproliferative agents.
Explore the source record for details and available documents.