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H Z Hill

Publications and source records attributed to H Z Hill.

At least 19 recordsLinked to original sources
PubMed2001

Transfection of nonmelanocytic cells with tyrosinase gene constructs for survival studies.

To better understand the role of melanin in the response of cells to radiation, the vector pcTYR containing the tyrosinase cDNA and a control vector pcTYW with no tyrosinase cDNA were transfected and expressed in nonpigmented CHOK1-A(L) 1282B5 cells. A pigmented clone was selected from the pcTYR transfectants and an antibiotic-resistant clone was selected from the controls. Melanin was assessed qualitatively by electron paramagnetic resonance (EPR) and quantitatively by a 14C-based assay. The EPR signal detectable in pcTYR-containing cells was at least twice that of pcTYW and parental CHOK1-A(L) cells and the tyrosinase activity was found to be at least six times greater. Melanin was classified to be eumelanin. Survivals of the transfectants were compared to those of the parent cells after irradiation by UVC from a germicidal lamp, UVB from TL01 lamps, UVA from Alisun lamps, UVB/UVA from FS20 lamps, and by gamma-rays from a 137Cs source. Compared to the pcTYW-containing cells, the pigmented cells were more sensitive to killing by UVC, and resistant to killing by UVA and gamma-rays. There were no significant differences in survival after the other irradiations. These results suggest that the pigment synthesized by the activity of tyrosinase alone, unmodified by the activities of TRP1 and TRP2, is protective against the types of reactive oxygen species produced by UVA and gamma-rays but not protective against lethal damage from photons in the UVB range and sensitizes to UVC photons.

Animals↗
PubMed2001

Four-way test of mortality: a useful tool for cancer education.

The use of a four-way test for the study of adverse outcomes in cancer, such as mortality and relapse, is described. This test facilitates a rapid, structured examination of patients' records that has been useful for teaching about the actual and apparent causes of treatment failure, and thus useful for teaching about how to achieve the best possible outcome for every patient. In this test, four questions are asked about factors identified: Was there evidence of 1) understaging, and/or 2) undertreatment, and/or 3) other factors, and/or 4) other causes? The use of the four-way test is illustrated by a review of 41 consecutive patients with Stage I colorectal cancer, 18 of whom had died at the time the study was conducted. One or more findings that contributed to either actual or apparent treatment failure were readily identified with the four-way test in 17 of the 18 fatal cases.

Adult↗
PubMed2001

Free radical-initiated and gap junction-mediated bystander effect due to nonuniform distribution of incorporated radioactivity in a three-dimensional tissue culture model.

To investigate the biological effects of nonuniform distribution of radioactivity in mammalian cells, we have developed a novel three-dimensional tissue culture model. Chinese hamster V79 cells were labeled with tritiated thymidine and mixed with unlabeled cells, and multicellular clusters (approximately 1.6 mm in diameter) were formed by gentle centrifugation. The short-range beta particles emitted by (3)H impart only self-irradiation of labeled cells without significant cross-irradiation of unlabeled bystander cells. The clusters were assembled in the absence or presence of 10% dimethyl sulfoxide (DMSO) and/or 100 microM lindane. DMSO is a hydroxyl radical scavenger, whereas lindane is an inhibitor of gap junctional intercellular communication. The clusters were maintained at 10.5 degrees C for 72 h to allow (3)H decays to accumulate and then dismantled, and the cells were plated for colony formation. When 100% of the cells were labeled, the surviving fraction was exponentially dependent on the mean level of radioactivity per labeled cell. A two-component exponential response was observed when either 50 or 10% of the cells were labeled. Though both DMSO and lindane significantly protected the unlabeled or bystander cells when 50 or 10% of the cells were labeled, the effect of lindane was greater than that of DMSO. In both cases, the combined treatment (DMSO + lindane) elicited maximum protection of the bystander cells. These results suggest that the bystander effects caused by nonuniform distributions of radioactivity are affected by the fraction of cells that are labeled. Furthermore, at least a part of these bystander effects are initiated by free radicals and are likely to be mediated by gap junctional intercellular communication.

Animals↗
PubMed2000

UVA, pheomelanin and the carcinogenesis of melanoma.

Cloudman S91 mouse melanoma cells vary in constitutive and inducible melanin levels. Survival, mutation induction and DNA damage were quantitated after exposure to UVB, UVA and FS20 lamps. Assuming that the observed differences are related to melanin, induced pigment is photo-protective for survival and mutation after UVB and FS20 exposure, and is photosensitizing for survival after UVA exposure. No changes in pyrimidine dimers could be measured. DNA damage in pigmented mouse melanocytes (melan-a and melan-b) was greater than that in albino melanocytes (melan-c) after UVB and FS20, and the pigmented cells were more sensitive to killing. Pigment appears to be protective for killing by UVA in these melanocytes. Human melanocytes from different skin types vary in both melanin amount and composition (eu- and pheomelanin). Effects of pigmentation on UVB responses are unclear. In UVA, heavily pigmented cells have more DNA damage than lightly pigmented cells, but are resistant to killing. Increased pheomelanin photosensitizes DNA damage in lightly pigmented cells. Since eumelanin predominates in the mouse melanoma cells and melanocytes, they are less likely than human cells to provide a satisfactory model for human solar melanomagenesis. In order to understand the mechanism of photocarcinogenesis of melanoma, melanins in human melanocytes from different pigment types should be carefully quantitated and characterized. Mutations induced in them by solar wavelength-emitting lamps with well-characterized spectra should be measured, and mutant DNA should be sequenced to determine the nature of the solar-induced lesions. Research should focus on UVA and pheomelanin.

Animals↗
PubMed2000

The degree of pigmentation modulates the radiosensitivity of human melanoma cells.

The relationship between cell pigmentation and radiosensitivity was investigated in two selected human melanoma cell lines with different melanin content (mixed type: eumelanin and pheomelanin, and pheomelanotic phenotypes). The same study was also done after stimulation of melanogenesis (1) by addition of the melanin precursor l-tyrosine to each of the cell lines separately and (2) by irradiation alone with doses ranging from 0 to 10 Gy. We found that a decrease in cell radiosensitivity was correlated with the type of melanin, with a clear involvement of eumelanin rather than pheomelanin. Increasing the intracellular content of both melanins promoted the growth of irradiated cells. Moreover, at a dose of 10 Gy, both tyrosinase activity and melanin cell content were significantly increased in the absence of any other melanogenesis promoter. Our data suggest that the amount of intracellular melanin is inversely related to the radiosensitivity of melanoma cells and may explain at least in part the controversial responses to ionizing radiations reported for melanoma.

Cell Survival↗
PubMed1999

Therapeutic resistance: characterization and inactivation by specific antiserum of a putative protein family produced by tumour cells.

A multitherapy resistance (MTR) factor produced by Cloudman S91 mouse melanoma cells rescues a responsive cell line after gamma-irradiation, short wavelength ultraviolet light, mitomycin C, vinblastine and actinomycin D. A similar activity with respect to ionizing radiation is now shown to be produced by human melanoma cells and by both human and mouse breast cancer cells but not by five normal cell lines. In these studies, the factor produced in serum-free conditioned medium (SFCM) by Cloudman S91/I3 cells is further characterized. Its activity in a clonogenic assay using related Cloudman S91/amel cells is destroyed by trypsin but not by DNase and is stable for at least 8 days at a variety of temperatures including 37 degrees C. Molecules greater than 30 kDa from SFCM collected from S91/I3 cells were concentrated and separated by preparative zonal electrophoresis (PZE). Bioactivity was present in both the cathode- and the anode-running fractions. The active acidic (anode) fractions were analysed by preparative isoelectric focusing. Bioactivity was present between pI 3.5 and 4.2. These PZE fractions were also used to immunize two rabbits, both of which produced antiserum that abrogated the bioactivity of SFCM and of the PZE cathode fractions. Antiserum also decreased the survival of irradiated S91/I3 producer cells that do not respond to SFCM but nonetheless must require MTR proteins for the expression of radiation resistance. These studies present a model for the production of rescue factors by non-clonogenic tumour cells that may persist in some tumours for considerable periods of time.

Amino Acid Transport Systems, Neutral↗
PubMed1997

Melanin: a two edged sword?

Melanin is both photosensitizer and photoprotector. Skin cancer rates decrease with increasing constitutive pigmentation, yet the pigment has been shown to be photoreactive and capable of producing damaging reactive oxygen species. We utilized model systems of related cells or similar cell type that vary in constitutive and in induced pigment. Induction of eumelanin in Cloudman S91 mouse melanoma cells leads to less UV-induced killing and to less mutation induction at the ouabain locus (Na+, K(+)-ATPase). Pigmented mouse melanocytes, melan-b (brown) and melan-a (black) were slightly less sensitive than melan-c (albino) melanocytes to killing after UVC and UVA but were more sensitive to killing after UVB and UVB + UVA. Pigment had a small sensitizing effect on pyrimidine dimer DNA damage in both the melanoma cells and the melanocytes. The lack of consistency in these results suggests that intracellular pigment may disregulate the milieu intérieur resulting in end effects that are unrelated to the original genomic damage.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Survival of Cloudman mouse melanoma cells after irradiation by solar wavelengths of light.

A number of variants of Cloudman S91 mouse melanoma cells that differ with respect to the amount of pigment produced are available for study. In this report, we compare the photobiological responses of S91/amel, which contains about 1 pg of melanin per cell, with S91/I3, which contains about 3 pg/cell. Earlier studies had shown that UVC induced more oxidative damage (in the form of thymine glycols) in cell line S91/I3 than in S91/amel and that cell line S91/amel was more resistant to killing by UVC than S91/I3. The present study finds that S91/amel cells are also relatively resistant to killing by near monochromatic UVB from a Philips TL01 fluorescent lamp and by near monochromatic UVA from a Philips HPW125 lamp. However, when the cells are irradiated with a Westinghouse FS20 polychromatic lamp, the S91/I3 cells are more resistant than the S91/amel cells. These findings cannot be explained on the basis of pigment induction because in S91/I3 this is about the same after UVB and FS20, although the maximum is reached earlier after UVB. Nor can our findings be explained on the basis of pyrimidine dimer formation, which is comparable in the two cell lines regardless of the type of irradiation. These results suggest that, with a pigment such as melanin, which absorbs light across the visible and ultraviolet ranges of the spectrum, cellular responses to monochromatic light do not necessarily predict responses to polychromatic mixtures.

Animals↗
PubMed1997

Comparative action spectrum for ultraviolet light killing of mouse melanocytes from different genetic coat color backgrounds.

The photobiology of mouse melanocyte lines with different pigment genotypes was studied by measuring colony-forming ability after irradiation. The cell lines were wild-type black (melan-a) and the mutants brown (melan-b) and albino (melan-c). Four lamps emitting various UV wavelengths were used. These were germicidal (UVC, 200-280 nm), 82.3% output at 254 nm, TL01 (UVB, 280-320 nm), 64.2% at 310-311 nm, FS20, broadband with peak output at 312 nm and Alisun-S (UVA, 320-400 nm), broadband with peak output at 350-354 nm. Appropriate filtration reduced the contaminating UVC to nonlethal levels for the longer waverange lamps. Wild-type melan-a was resistant to UVC and UVA compared to the other two cell lines, but the differences were small. The melan-c cell line was more resistant to UVB and markedly more resistant to FS20 than the pigmented lines. With the exception of FS20 responses, melan-b was more sensitive than melan-a to killing by the various UV lamps. There were more pyrimidine dimers (cyclobutane dimers and 6-4 photoproducts) produced in melan-a than in melan-c cells by UVC, UVB and FS20 lamps. Unlike melan-c, melan-a and melan-b showed a strong free radical signal of melanin character with a detectable contribution of pheomelanin-like centers. The contribution of pheomelanin was higher in melan-b than in melan-a, while the total melanin content in these two cell lines was comparable. The abundant melanin granules of wild-type melan-a melanocytes were well melanized and ellipsoidal, whereas those of melan-b melanocytes tended to be spherical. In the albino line (melan-c) the melanocytes contained only early-stage melanosomes, all of which were devoid of melanin. The results indicate that pigment does not protect against direct effect DNA damage in the form of pyrimidine dimers nor does it necessarily protect against cell death. High pigment content is not very protective against killing by UVC and UVA, and it may photosensitize in UVB the very wavelength range that is of greatest concern with respect to the rising incidence in skin cancer, especially melanoma. It is clear from these studies that, in pigment cells, monochromatic results cannot predict polychromatic responses and that cell death from solar irradiations is a complex phenomenon that depends on more than DNA damage.

Animals↗
PubMed1997

Induced melanin reduces mutations and cell killing in mouse melanoma.

When melanin absorbs light energy, it can produce potentially damaging active oxygen species. There is little doubt that constitutive pigment in dark-skinned individuals is photoprotective against skin cancer, but induced pigment-as in tanning-may not be. The first step in cancer induction is mutation in DNA. The most suitable systems for evaluating the role of melanin are those in which pigment can be varied and mutations can be measured. Several cell lines from Cloudman S91 mouse melanoma can be induced to form large quantities of melanin pigment after treatment with a number of different agents enabling comparison of mutant yields in the same cells differing principally in pigment concentration. In these studies, melanin was induced with synthetic alpha-melanocyte-stimulating hormone and with isobutyl methyl xanthine in the cell line S91/mel. The former inducer produced about 50% more pigment than the latter. Survival and mutation induction at the Na+/K(+)-ATPase locus were studied using ethyl methane sulfonate (EMS), a standard mutagen and five UV lamps emitting near monochromatic and polychromatic UV light in the three wave-length ranges of UV. There was greater protection against killing and mutation induction in the more heavily pigmented cells after exposure to EMS and after irradiation with monochromatic UVC and UVB. There was significant protection against killing by polychromatic UVB + UVA (FS20), but the small degree of protection against mutation was not significant. No significant change in killing and mutation using the same protocol was seen in S91/amel, a related cell line that does not respond to these inducers. No mutants were produced by either monochromatic or polychromatic UVA at doses that killed 50% of the cells. Our results show that induced pigment-shown earlier to be eumelanin (K. A. Cieszka et al., Exp. Dermatol. 4, 192-198, 1995)-is photo- and chemoprotective, but it is less effective in protection against mutagenesis by polychromatic UVB + UVA in a spectrum that more nearly approximates the solar spectrum.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Interference by cellular melanin with assay of DNA-protein crosslinks by the potassium dodecyl sulfate precipitation method.

The potassium dodecyl sulfate precipitation method was used to quantify DNA-protein crosslinks (DPCs) in lysates of melanoma cells exposed to ultraviolet radiation. Inducing melanin production in these cells before exposure to ultraviolet radiation decreased the apparent yield of DPCs. The decrease could also be produced by addition of melanin to lysates after exposure to crosslinking conditions. Experimental models could attribute this decrease to neither quenching of scintillations from the tritium label used nor to an effect of single strand breaks of DNA. This assay appears to be inappropriate for quantification of DPCs in melanized cells.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Breast cancer in the inner city: intensive efforts may be succeeding.

Breast cancer is a significant problem in a 518 bed government supported university hospital in New Jersey's largest city. The following records were reviewed: tumor registry abstracts of the 367 analytic breast cancer patients admitted from 1/1/91 to 12/31/92; the 455 participants in the Breast Cancer Detection Awareness Program (BCDAP) from 1987 to 1992; and the 460 breast biopsies performed from 1990 to 1992. Breast cancer is less common at this inner city hospital than in the U.S. in general; the stage is more advanced at presentation than in the U.S. overall; and the overall survival is only 54% at five years. Approximately 40% of the patients were African-American women from the inner city. Their median age was 53, seven years younger than the median age for diagnosis in the U.S. overall, and their five year survival was only 46%. Intensive efforts have recently produced improvement in the proportion of cases diagnosed at early stages (T0 and T1), but a decrease in mortality has not yet been seen.

Black or African American↗
PubMed1995

Growth and pigmentation in genetically related Cloudman S91 melanoma cell lines treated with 3-isobutyl-1-methyl-xanthine and beta-melanocyte-stimulating hormone.

4 clonal sublines of Cloudman S91 melanoma cells, S91/mel, S91/I3, S91/6 and S91/amel, were evaluated for changes in growth, pigment content and plating efficiency during and after treatment with a cyclic-AMP phosphodiesterase inhibitor-melanin-stimulating agent, 3-isobutyl-1-methyl-xanthine (IBMX) plus beta-melanocyte stimulating hormone (beta-MSH) or IBMX alone. After combined treatment, increases in melanin content on day 3 were 48, 27, 11, and 2 pg/cell in the four cell lines respectively. In each case IBMX alone was less effective than IBMX plus beta-MSH. Doubling time increased and plating efficiency decreased with increased melanization. The increases in doubling time and decreases in plating efficiency were cell line dependent. The greatest rate of increase in doubling time and decrease in plating efficiency as a function of melanin content were seen in S91/amel, which produced the least pigment. The lowest rates of increase/decrease were seen in S91/mel, which produced the most pigment. Melanin pigment induced in the cells was classified as eumelanin by EPR determination. The differential response to induction of pigmentation makes these cell lines suitable models for comparative studies on the role of melanin in pigment cell biology.

1-Methyl-3-isobutylxanthine↗
PubMed1995

A multitherapy resistance factor from melanoma reveals that killing by near UV is different from genotoxic agents.

A diffusible multitherapy resistance factor (MTRF) is produced by Cloudman S91 melanoma cells in vitro. The MTRF decreases sensitivity of the target cell line, S91/amel, to gamma-irradiation, UVC (200-280 nm) and mitomycin C (MMC). In the present study, we demonstrate that MTRF also increases the survival of S91/amel after exposure to actinomycin D (AMD) and vinblastine (VBL). The MTRF is thus effective when target cells have been exposed to five genotoxic agents that act by different mechanisms. It does not alter the response to the same five agents of the S91/I3 producer cells, which are presumably saturated with the factor. The factor has no effect on the survival of S91/amel cells that have been exposed to lethal doses of near monochromatic UVB (280-320 nm) or UVA (320-400 nm) or to polychromatic FS20 lamps. The lack of effectiveness of MTRF after cells have been exposed to near (300-400 nm) UV radiation indicates that in this wavelength range, S91 melanoma cells are killed by mechanisms that are different from the lethal effects of the five genotoxic agents (gamma-irradiation, UVC, MMC, AMD and VBL) to which the target cells demonstrate a response.

Animals↗
PubMed1994

Influence of an autocrine multitherapy resistance factor on radiation responses of melanoma cells.

An autocrine multitherapy resistance factor (MTRF) produced by a radioresistant subclone of S91 mouse melanoma (S91/I3) causes an increase in radioresistance of a radiosensitive subclone (S91/amel). MTRF has no effect on the survival of S91/I3, which is already relatively resistant to gamma-irradiation. In this study, we examined the effect of MTRF in the form of S91/I3 conditioned medium or as S91/I3 heavily-irradiated cells (I3-HRCells) on cellular responses of S91/amel cells after exposure to gamma-rays. Target S91/amel cells retained more than half of their ability to respond to rescue by MTRF on day 4 after exposure to 3 Gy. Continuous presence of MTRF during colony formation was necessary for maximum plating efficiency. Although the extent of double strand DNA breakage and repair was the same in S91/amel and S91/I3, split-dose recovery experiments with MTRF revealed previously undetected repair of sublethal damage in S91/amel cells. MTRF did not alter the extent of potentially lethal damage repair (PLDR) in S91/I3 or S91/amel. S91/amel cells were more responsive to MTRF if they had been harvested from confluent dishes, while S91/I3 cells produced a more effective factor if they had been harvested in exponential phase. These findings demonstrate that MTRF has unique properties. It does not appear to be involved in genome repair since it does not alter the extent of PLDR and it is effective when added to cells after complete split-dose recovery has occurred.

Animals↗
PubMed1994

Thioredoxin reductase induction coincides with melanin biosynthesis in brown and black guinea pigs and in murine melanoma cells.

X-rays were used to induce melanin biosynthesis in brown and black guinea pigs in vivo. During the course of pigmentation, the expression of thioredoxin reductase was increased, whereas for the other antioxidant enzymes, superoxide dismutase (cytosol Cu/Zn-enzyme), catalase, and glutathione reductase, levels and activities decreased. Isobutylmethylxanthine induced eumelanin biosynthesis in murine melanoma cells (Cloudman S-91). In these cells, thioredoxin reductase levels coincided with melanogenesis. Our results suggest that both tyrosinase and thioredoxin reductase respond to oxidative stress in the epidermis as well as in melanoma cells and react with superoxide anion radicals to stimulate melanogenesis and to prevent peroxidative damage, respectively.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Influence of an autocrine diffusible resistance factor on cell survival after exposure to therapeutic agents.

A subclone of Cloudman mouse melanoma cells (S91/I3) produces a resistance factor (RF) that increases the survival of a different but related subclone, S91/Amel, after exposure to either ultraviolet C (UVC) radiation or to mitomycin C (MMC). The presence of RF was deduced from experiments in which heavily irradiated S91/I3 cells were plated with the target S91/Amel cells. The effect of RF was also present in cell-free conditioned tissue culture medium (CM) from S91/I3 cultures. These results extend previous findings that both subclones produce an autocrine resistance factor (RF) that alters the radiation response of target S91/Amel cells making them less sensitive to death by low linear energy transfer (LET) ionizing radiation. S91/I3 cells are radioresistant relative to S91/Amel and produce the RF more effectively than S91/Amel. S91/I3 cells do not respond to the RF, being themselves, presumably, maximally stimulated. The significant findings are (1) the RF is effective at decreasing the killing of the target cells using cytotoxic agents that operate by different mechanisms; (2) The relative sensitivities of S91/Amel and S91/I3 to the toxic agents is not a factor in the responses of these cells to the RF: S91/Amel survivals are increased by the RF, those of S91/I3 are not; (3) the RF is elaborated by the melanoma cells whether or not they have been irradiated; it is, apparently, a normal cell product; (4) the RF is effective when added after the cytotoxic insult; its presence is not required during irradiation or drug treatment. The RF appears to act by novel mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗