New Acyclic Cytotoxic Jasplakinolide Derivative from the Marine Sponge Jaspis splendens.

A new acylic jasplakinolide congener (2), another acyclic derivative requiring revision (4), together with two jasplakinolide derivatives including the parent compound jasplakinolide (1) were isolated from the Indonesian marine sponge Jaspis splendens. The chemical structures of the new and known compounds were unambiguously elucidated based on HRESIMS and exhaustive 1D and 2D NMR spectral analysis as well as a comparison of their NMR data with those of jasplakinolide (1). The isolated jasplakinolides inhibited the growth of mouse lymphoma (L5178Y) cells in vitro with IC50 values in the low micromolar to nanomolar range.

Uptake and metabolism of mizoribine, an immunosuppressant, in L5178Y-R mouse lymphoma cells in vitro and peripheral blood mononuclear cells of rats and kidney transplant recipients in vivo.

The cellular uptake of mizoribine (MZR), an immunosuppressant, and metabolism of MZR to MZR-5'- monophosphate (MZRP), an active metabolite, were evaluated in L5178Y-R mouse lymphoma cells and peripheral blood mononuclear cells (PBMCs) of rats and kidney transplant recipients (KTRs, n = 22). Real-time PCR analysis revealed the expression of ENT1 and ENT2 mRNAs, but not of CNTs, in L5178Y-R cells and rat's PBMCs. In L5178Y-R cells, the uptake of MZR was suppressed by adenosine, a substrate for ENT1 and ENT2, but not by 5-(4-nitrobenzyl)-6-thioinosine (0.1 µM), an ENT1 inhibitor. Saturable metabolism of MZR to MZRP was observed. In rats, peak plasma concentrations of MZR and peak concentrations of MZR and MZRP in PBMCs were observed 3 h after oral administration. MZR disappeared from PBMCs in parallel with plasma MZR, but the disappearance of MZRP from PBMCs appeared to be slow. In KTRs, the mean plasma concentration of MZR 3-4 h after ingestion was 3.14 µg/ml and the mean MZRP concentration in PBMCs was 16.8% of MZR, reflecting the involvement of ENT in the uptake of MZR. A linear relationship was observed between plasma MZR concentrations ranging from 1 to 6 µg/ml and PBMC's MZRP concentrations ranging from 90 to 200 ng/ml.

From radioresistance to radiosensitivity: In vitro evolution of L5178Y lymphoma.

PURPOSE: To discuss the possible reasons for the loss of tumourigenicity and the acquisition of new phenotypic features (among them, sensitivity to X and UVC radiations) as a result of in vitro cultivation of L5178Y lymphoma cells. RESULTS: Ten years ago the phenotypic differences between LY-R (original L5178Y maintained in vivo and examined in vitro) and LY-S lines were reviewed in detail by the author. The loss of tumourigenicity of LY-R cells upon in vitro cultivation accompanying the acquirement of the LY-S phenotype had been described earlier by Beer et al. (1983). In spite of their common origin, the sublines were shown to differ in their relative sensitivity to a number of DNA damaging agents and in numerous other features. Here, selected differences between LY-R and LY-S lines are briefly reviewed. It is proposed that Wallace's concept (2010a) that mitochondria are the interface between environmental conditions and the genome may explain the LY-R-LY-S conversion under prolonged in vitro cultivation. CONCLUSION: The differences between the LY lines were probably of epigenetic rather than genetic character. The properties of LY-R cells changed as a result of exposure to an oxic in vitro milieu. The changes could be preconditioned by heteroplasmy and the selection of cells endowed with mitochondria best fitted to a high oxygen-low carbon dioxide environment.

Genetic damage, but limited evidence of oxidative stress markers in diethyl maleate-induced glutathione depleted mouse lymphoma L5178Y (TK(+/-)) cell cultures.

Depletion of glutathione (GSH) in cells exposed to certain xenobiotics has been proposed to result in oxidative stress, which could lead to damage of cellular macromolecules such as proteins, lipids, and DNA. Diethyl maleate (DEM) is known to conjugate with GSH and rapidly lower cellular GSH levels. The objective of this study was to investigate the influence of DEM-induced GSH depletion on various genotoxicity and gene expression end points in mouse lymphoma L5178Y (TK(+/-)) cell cultures. Cells were exposed to DEM for 4 h at concentrations of 0, 6.7, 13.5, 26.9, 53.8, 107.6, 215.3, and 430.6 µg/mL (0.039-2.5 mM). Genotoxicity was evaluated by examining the induction of in vitro micronuclei (20 h post-treatment) and DNA strand breaks as measured by comet (immediately following treatment), and correlating these observations to cellular GSH levels. In the current study, GSH was decreased more than 50% at the lowest test concentration (6.7 µg/mL) and more than 95% at ≥ 107.6 µg/mL. A significant increase in micronuclei and DNA strand breaks was observed at concentrations of ≥ 26.9 µg/mL. Gene expression of seven apoptosis and oxidative-stress related genes showed significant alterations in only three genes only at the highest test concentration. Quantifiable levels of 8-OH-dG (≥ 2 adducts per 1 × 10(8) NT) were not detected at any treatment concentration. These results demonstrate an association between DEM-induced genotoxicity and GSH depletion in mouse lymphoma L5178Y (TK(+/-)) cells, but not with other oxidative markers.

Activity of fourteen new hydantoin compounds on the human ABCB1 efflux pump.

BACKGROUND: Multidrug resistance (MDR) is one of the major concerns in the treatment of cancer and one of the major causes of therapy failure. The overexpression of an ABC transporter, the ABCB1, is often associated with MDR in cancer. Previously it was observed that hydantoin compounds can modulate the activity of the ABCB1 pump. MATERIALS AND METHODS: Fourteen hydantoin derivatives were synthesized and studied for their capacity to increase accumulation of ethidium bromide (EB) by mouse lymphoma cancer cells that were transfected with the human ABCB1 gene and overexpress the human ABCB1 pump. RESULTS: It was observed that the accumulation of EB by the cells in the presence of four of the newly synthesized hydantoins was strongly increased. Similar but milder effects were also observed for the other seven hydantoins; the remaining three had no activity. CONCLUSION: The 14 hydantoin compounds studied belong to three different structural groups. Structure-activity relationships were studied and important molecular substituents that were possibly responsible for increased the activity of the molecules were identified. This important information may lead to the continuation of our work and to the future synthesis of more active compounds.

Steroidal alkaloids of Veratrum lobelianum Bernh. and Veratrum nigrum L.

Twelve steroidal alkaloids were isolated from four populations of Veratrum lobelianum Bernh. and Veratrum nigrum L. Full NMR data for veralosinine (1), and extensive 1H NMR data for veralosine (3) and teinemine (5) are presented here for the first time. (+/-)-15-O-(2-Methylbutyroyl)germine (10) is undescribed up to now. The antiproliferative activities of veranigrine, veralosinine, and neogermitrine have shown that they are a perspective for further studies.

Multidrug resistance modulation and apoptosis induction of cancer cells by terpenic compounds isolated from Euphorbia species.

BACKGROUND: One of the most promising strategies to overcome multidrug resistance (MDR) is to use compounds that can modulate P-glycoprotein and restore the cytotoxicity of anticancer drugs. Furthermore, the search for compounds that regulate and overcome apoptosis deficiency of cancer cells is also of great therapeutic importance. MATERIALS AND METHODS: Seven known pentacyclic triterpenes and one steroid were isolated from Euphorbia lagascae methanolic extracts and identified by physical and spectroscopic methods. These compounds, together with eleven terpenoids previously isolated from Euphorbia lagascae and E. tuckeyana were tested for their MDR-reversing and/or apoptosis induction activities by flow cytometry on L5178 human MDR1 gene-transfected mouse lymphoma cells. RESULTS: Four taraxastane-type triterpenes: 21alpha-hydroxytaraxasterol, 21alpha-hydroxytaraxasterol acetate, 3beta,30-dihydroxy-20(21)-taraxastene and 3beta-hydroxy-20-taraxasten-30-al, and two steroids: stigmastane-3,6-dione and ergosterol peroxide exhibited a significant MDR-Pgp modulation activity. Some aspects of structure-activity relationships are discussed. Regarding apoptosis induction, the most significant results were obtained for the polycyclic diterpenes ent-16alpha,17-dihydroxykauran-3-one and ent-16alpha,17-dihydroxyatisan-3-one.

Antitumor activity of alkaloids derived from Amaryllidaceae species.

The aim of the present study was to investigate the anticancer properties of five alkaloids isolated from Amaryllidaceae, including the inhibitory effect on P-glycoprotein (P-gp) and the apoptosis-inducing capacity. The tested alkaloids were evaluated for their multidrug resistance (MDR)-reversing activity on human MDR1-gene-transfected L5178 mouse lymphoma cells, using the rhodamine-123 (Rh-123) assay. Trisphaeridine and pretazettine increased the intracellular Rh-123 concentration 30- and 50-fold, respectively, as compared to the non-treated cells, and 2-O-acetyllycorine and trisphaeridine were demonstrated by means of the checkerboard method to enhance the antiproliferative activity of doxorubicin on L5178 MDR mouse lymphoma cells. The MTT assay revealed that pretazettine, trisphaeridine and 2-O-acetyllycorine displayed excellent antiproliferative effects on both the human and the mouse cell lines. The apoptosis-inducing activities of selected agents (2-O-acetyllycorine and trisphaeridine) were measured via acridine orange and ethidium bromide dual staining and flow cytometry of the subG1 population.

Annexin A2 regulates the levels of plasmin, S100A10 and Fascin in L5178Y cells.

Annexin A2 (ANXA2) was reported as the receptor, activator, expression enhancer, or cooperator for plasmin, S100A10, and others. To delineate the effect of ANXA2 on the proteins that are probably associated with tumor development and metastasis by a credible experimental method, we generated an ANXA2 gene knockout tumor cell line, ANXA2(-/-) L5178Y, and compared the expression levels of plasmin, S100A10 and fascin in the generated cell line with in wild type of L5178Y at mRNA and protein levels. The results showed that the mRNA level of plasminogen (PLG) was not substantially changed in cultured ANXA2(-/-) cells, but the protein level of plasmin was significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. For S100A10 and fascin, their mRNA and protein levels were significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. Results indicate that ANXA2 introduces the generation or expression of plasmin, S100A10, and fascin in tumor cells. ANXA2 affects PLG/plasmin level by a way post transcription and may be an inducer or enhancer to fascin expression at transcription level. By the regulations, ANXA2 enhances the development, invasion, and metastasis of tumor. The detailed mechanism for the regulations above remains to be further investigated, but our results show the potential of ANXA2 as a new target molecule for the strategies of tumor biotherapy or tumor gene therapy.

Are so-called uremic toxins always toxic?

OBJECTIVE: Numerous substances qualify as uremic toxins by fulfilling all properties characterizing such compounds. However, their role in the development of uremic state maybe ambiguous. We followed these properties on the example of N-methyl-2-pyridone-5-carboxamide (Met2PY) from the nicotinamide end-products family. The aim of this study was to determine if these uremic compounds are toxic in all circumstances. METHODS: To establish a direct toxic effect, a cytotoxicity test was performed. The influence of Met2PY on DNA damage in cultured cells was measured, using a comet assay. For in vitro experiments, Moly (L5178Y), LLCPK-1, and A549 cell lines were used. We used 250 microM H2O2 and 200 ng/mL angiotensin II (ANGII) as damaging factors. RESULTS: A direct cytotoxic effect of Met2PY on Moly cells was observed. In LLC-PK1 cells, co-incubation with 0.03 mM Met2PY protected cells against the DNA damage caused by ANG II. In A549 cells, the action of Met2PY was ambiguous. At lower concentrations (1 and 3 mM), it showed protective effects, although 10 mM Met2PY increased the toxic effect of 250 microM H2O2. CONCLUSIONS: Our results suggest that Met2PY is not always toxic or harmful. In some circumstances, it may even express beneficial and protective properties.

Uncoupling of telomere length and radiosensitivity in mouse lymphoma cell lines of similar genetic background.

PURPOSE: To investigate the link between radiosensitivity and telomere length in murine lymphoid cell line stocks that have similar genetic backgrounds but different radiosensitivities. MATERIALS AND METHODS: We used two stocks from both the parental L5,178Y-R cell line and the repair-deficient radiosensitive subline, L5,178Y-S, to assess telomere length. We used terminal restriction fragment analysis and flow-fluorescence in situ hybridization (FISH) telomere length assessment to determine telomere lengths in the related radiosensitive and non-radiosensitive cell lines. Each cell line was further tested for retention of its original radiation response phenotype using cell growth assays after treatment with ionizing radiation. RESULTS: One stock of L5,178Y-R cells had long telomeres, whereas the other stock had short telomeres. Likewise, one stock of L5,178Y-S cells had long telomeres, whereas the other stock had short telomeres. Telomere lengths in these cell lines were relatively stable for over 80 divisions in culture. Each cell line was confirmed to have retained its original radiosensitivity phenotype. CONCLUSION: We conclude that radiosensitivity is independent of telomere length in these genetically similar cell lines.

Ochratoxin A-induced mutagenesis in mammalian cells is consistent with the production of oxidative stress.

Ochratoxin A (OTA) is a widespread mycotoxin in food and a powerful nephrocarcinogen in rats. The mutagenicity of OTA has been extensively investigated but with conflicting results, thus leaving open the mechanistic question for OTA carcinogenicity. Here, we examined the mutagenicity of OTA by using well-standardized mutation assays such as the hypoxanthine-guanine phosphoribosyltransferase (HPRT) assay in Chinese hamster V79 cells and the thymidine kinase assay in mouse lymphoma LY5178 cells. OTA-induced HPRT mutations were characterized at the molecular level. In V79 cells, OTA produced a dose- and time-related decrease in cell number as a consequence of the transitory cytostatic effect mediated by G2/M cell cycle arrest. In both mutation assays, OTA was weakly mutagenic and this effect was independent of biotransformation. OTA-induced mutations were characterized by point mutations (48%) and a lack of a detectable reverse-transcription polymerase chain reaction product (52%). The pattern of OTA-induced point mutations was similar to that of spontaneous mutants, suggesting that OTA induced an increase of the endogenous oxidative metabolism but not covalent DNA adducts. Our data support a model where OTA is mutagenic via oxidative DNA damage induction.

In vitro apoptotic activity of 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones in L5178Y cells.

Compounds containing B-N bonds have shown interesting biological activity. One class of such molecules is the 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones (3a-j), which contain a B-N bond, have an alpha-amino acid moiety in the heterocycle, and have an exocyclic moiety related to an amino acid. The purpose of this work was to determine the inhibitory effects of 3a-j on the proliferation of murine L5178Y lymphoma cells. A new five-membered heterocyclic nucleus with apoptotic activity was found. The target products showed potent cytotoxicity in the L5178Y cell line. Among them, 3a exhibited the highest antineoplastic activity in L5178Y cells with an IC(50) value of 22.5+/-0.2 microM.

In vitro cytotoxic and non-genotoxic effects of gutta-percha solvents on mouse lymphoma cells by single cell gel (comet) assay.

Chloroform and eucalyptol are widely used in clinical dentistry as gutta-percha solvents. However, these compounds may represent a hazard to human health, especially by causing injury to genetic apparatus and/or inducing cellular death. In this study, the genotoxic and cytotoxic potentials associated with exposure to chloroform and eucalyptol were assessed on mouse lymphoma cells in vitro by the single cell gel (comet) assay and trypan blue exclusion test, respectively. Both gutta-percha solvents proved to be cytotoxic at the same levels in concentrations of 2.5, 5 and 10 microL/mL (p<0.05). On the other hand, neither of the solvents induced DNA breakage. Taken together, these results suggest that although both tested compounds (chloroform and eucalyptol) are strong cytotoxicants, it seems that they are not likely to increase the level of DNA damage on mammalian cells.

A novel treatment for ocular tumors using membrane FasL vesicles to activate innate immunity and terminate immune privilege.

PURPOSE: Ocular immune privilege promotes tumor growth by hindering the development of innate and adaptive immunity. A prior study showed that ocular tumors expressing the membrane-only form of Fas ligand (FasL) terminate immune privilege, induce vigorous inflammation, undergo rejection, and induce systemic protective immunity. In these previous experiments the tumor cells used were genetically engineered to express membrane FasL. As an initial step toward developing an immunotherapy for intraocular tumors, the present study was conducted to examine whether injection of microvesicles expressing membrane FasL into ocular tumors (that are FasL negative) would have a similar effect. METHODS: Microvesicles expressing either no FasL or membrane-only Fas ligand were coinjected with L5178Y-R lymphoma cells into the anterior chambers (AC) of DBA/2 mice. RESULTS: Tumor cells coinjected with control vesicles grew progressively in the AC, and all mice died of metastatic disease by day 15. By contrast, a single injection of membrane FasL vesicles induced a potent inflammatory response characterized by GR1+ neutrophils and F4/80+ macrophages and significantly improved survival from 0% in untreated mice to 58% in mFasL-treated mice. Among the surviving mice, the ocular tumor was eliminated in 55%, and the mice exhibited systemic protection from a second tumor challenge. In the remaining 45%, the ocular tumor was not eliminated, but the mice were protected from liver metastases. CONCLUSIONS: Bioactive membrane FasL microvesicles coinjected with tumor cells induce a potent inflammatory response that terminates immune privilege, eliminates ocular tumors, and prevents metastatic disease.

Nitric oxide complexes in the interaction between primary and secondary tumor of L5178Y lymphoma.

Heme and non-heme Fe-NO complexes were observed in regard to the growth of primary and secondary solid tumors and ascites of murine L5178Y lymphoma. The complexes were detected by electron paramagnetic resonance spectroscopy at liquid nitrogen temperature. Primary solid tumors and secondary solid tumors or ascites were inoculated on the same day, or with a delay. The primary tumor inhibited growth of the secondary solid tumor only if the latter was inoculated with a delay, which did not correlate with the change of the types, nor with the increase in the level of Fe-NO complexes detected in the tissue, suggesting a "non-immunological" character of this inhibition. In some animals with solid tumors, spontaneous ascites developed. This process resulted in a marked decrease in the level of Fe-NO complexes in the solid tumor tissue. The primary solid tumor, however, did not influence the growth of secondary ascites, but intensified NO generation in the ascites of animals with partial removal of ascitic fluid. This experimental group survived 2.2 days longer than the control group without primary solid tumor. Our research revealed that the presence of Fe-NO complexes in the interaction between primary and secondary tumor strongly depends on the form of the tumor: solid or ascitic, and that murine L5178Y lymphoma may serve as a convenient model for the research on "concomitant immunity" against in vivo growing tumors. This is the first EPR study on "concomitant immunity" in regard to tumor-tumor and tumor-ascites interactions in vivo.

Contamination is a frequent confounding factor in toxicology studies with anthraquinone and related compounds.

Anthraquinone (AQ) (9,10-anthracenedione) is an important compound in commerce. Many structurally related AQ derivatives are medicinal natural plant products. Examples include 1-hydroxyanthraquinone (1-OH-AQ) and 2-hydroxyanthraquinone (2-OH-AQ), which are also metabolites of AQ. Some commercial AQ is produced by the oxidation of anthracene (AQ-OX). In the recent past, the anthracene used was distilled from coal tar and different lots of derived AQ often contained polycyclic aromatic hydrocarbon contaminants, particularly 9-nitroanthracene (9-NA). Many toxicology studies on AQ used contaminated anthracene-derived AQ-OX, including a National Toxicology Program (NTP) 2-year cancer bioassay that reported a weak to modest increase in tumors in the kidney and bladder of male and female F344/N rats and in the livers of male and female B6C3F1 mice. The AQ-OX used in that bioassay was mutagenic and contained 9-NA and other contaminants. In contrast, purified AQ is not genotoxic. The purpose of this paper is to provide additional information to help iterpret the NTP cancer bioassay. This paper describes a quantitative analytical study of the NTP anthracene-derived AQ-OX test material, and presents the results of mutagenicity studies with the 1-OH-AQ and 2-OH-AQ metabolites and the primary contaminant 9-NA. Purified 1-OH-AQ and 2-OH-AQ exhibited only weak mutagenic activity in selected strains of tester bacteria and required S9. Literature reports of potent mutagenic activity for 1-OH-AQ and 2-OH-AQ in bacteria minus S9 are, once again, very likely the result of the presence of contaminants in the test samples. Weak activity and limited production of the 1-OH-AQ and 2-OH-AQ metabolites are possible reasons that AQ fails to exhibit activity in numerous genotoxicity assays. 9-NA was mutagenic in tester strains TA98 and TA100 minus S9. This pattern of activity is consistent with that seen with the contaminated AQ-OX used in the NTP bioassay. Analysis of all the mutagenicity and analytical data, however, indicates that the mutagenic contamination in the NTP bioassay probably resides with compounds in addition to 9-NA. 9-NA exhibited potent mutagenic activity in the L5178Y mammalian cell mutagenicity assay in the presence of S9. The positive response was primarily associated with an increase in small colony mutants suggesting a predominance of a clastogenic mechanism. Quantitative mutagenicity and carcinogenicity potency estimates indicate that it is plausible that the contaminants alone in the NTP AQ-OX bioassay could have been responsible for all of the observed carcinogenic activity. Although AQ-OX is no longer commercially used in the United States, many of the reported genotoxicity and carcinogenicity results in the literature for AQ and AQ derivative compounds must be viewed with caution.

Coffee-mediated protective effects against directly acting genotoxins and gamma-radiation in mouse lymphoma cells.

The cytokinesis-block micronucleus test was performed using L5178Y mouse lymphoma cells to ascertain whether or not standard (caffeinated) instant coffee, the commonly consumed polyphenolic beverage with antioxidant activity can protect against chromosomal damage induced by the directly acting agents N-methyl-N-nitro-N-nitrosoguanidine (MNNG), mitomycin C (MMC), methyl methanesulfonate (MMS) and gamma radiation. Our results demonstrated significant reductions in the in vitro genotoxic effects of MNNG, MMC, and MMS following co-treatment of mouse lymphoma cells with standard instant coffee. Subsequently, the comet assay was carried out to assess the effect of coffee co-treatment on the level of DNA damage induced by MMS in mouse lymphoma cells. The results demonstrated a significant reduction in MMS-induced DNA damage following co-treatment with standard instant coffee. Protective effects were observed in mouse lymphoma cells which were treated with coffee immediately after exposure to gamma radiation (1 and 2 Gy). Another experiment showed protection when the mammalian cells were irradiated (0.5 and 1 Gy) midway (at 2 h) during a 4 h coffee treatment. However, the protective effect against the lower dose (0.5 Gy) was not significant. In addition we assessed the modulatory effect of coffee on MNNG-induced apoptotic frequency by flow cytometry. The results revealed only a minor influence of coffee on the frequency of apoptotic cells induced by the test compounds, rendering an increase in sensitivity for apoptosis as a reason for the reduced genomic damage an unlikely or at least incomplete explanation.

Loss of P53 heterozygosity is not responsible for the small colony thymidine kinase mutant phenotype in L5178Y mouse lymphoma cells.

The mouse lymphoma L5178Y Tk+/- 3.7.2C assay is a well-characterized in vitro system used for the study of somatic cell mutation. It was determined that this cell line has a heterozygous mutation in exon 5 of Trp53. Based on this assumption that the cell line is heterozygous for the Trp53 gene, it was postulated that the small colony thymidine kinase (Tk) mutant phenotype may be due to a newly induced mutation/deletion in both the Trp53 and Tk1 alleles. The resultant Tk-/- mutants would also be Trp53+/0 or Trp53+/+ and would lose their ability to grow at normal rates. Subsequently, we published our evaluation of the Trp53 status in L5178Y cells. This analysis included sequencing of Trp53 exon 4 and determined that the mouse lymphoma cell line has a mutation in both of the Trp53 alleles and, therefore, no wild-type Trp53 allele in either Tk+/- cells or Tk-/- mutants. Because the cells have no wild-type Trp53, it is not possible that the small colony phenotype results from a newly induced loss of both functional Trp53 and Tk. To determine whether small colonies might, however, include the deletion of both Trp53 and Tk we evaluated, using microsatellite marker analysis, a series of small colony mutants. We also utilized in situ hybridization to determine that the Trp53 alleles are, in fact, in their normal chromosome 11 location in Tk+/- 3.7.2C mouse lymphoma cells. From all of these analyses we can conclude that the small colony mutant phenotype is not caused by deletion of both Trp53 and Tk1.

Action spectra of apoptosis induction and reproductive cell death in L5178Y cells in the UV-B region.

We investigated the action spectra for the induction of apoptosis and reproductive cell death in mouse lymphoma L5178Y cells using a high-performance spectroirradiator, the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki. L5178Y cells were exposed to monochromatic light at different wavelengths in the UV-B and UV-A regions. The frequencies of apoptosis induction and reproductive cell death were determined by counting cells with chromatin condensation and by a semi-solidified agarose colony formation assay, respectively. The measured action spectra for the two end-points were similar. The sensitivity decreased steeply with an increase of wavelength in the UV-B region, but showed no further decrement in the UV-A region. The action spectra were slightly steeper than that for the minimum erythematic dose (MED), and were similar to the light-absorption spectrum of DNA in the UV-B region. On the other hand, in the UV-A region, the spectra for both endpoints were close to the MED, but not to DNA absorption spectra. The difference between the measured spectra and that for MED may have been caused by the absorption of the light by the skin. Differences in the time course and morphological difference of apoptosis were found between the UV-B and UV-A region. These results suggest that although DNA damage induced by UV-B light can trigger apoptosis, or lead to reproductive cell death, other damage (membrane, protein and so on) may trigger those effects in the UV-A region.