Mouse Leukemia L1210 Cells Research Articles

Novel Acridine-Triazenes as Prototype Combilexins: Synthesis, DNA Binding, and Biological Activity

A series of bifunctional ligands has been developed as prototype DNA-binding combilexins using a DNA template-directed approach. These novel agents contain a 1,3-diaryltriazene linker moiety, present in the established DNA minor groove-binder berenil [1,3-bis(4'-amidinophenyl)-triazene], which is attached to an intercalating acridine chromophore by a functionalized thiazole residue. This 9-arylacridine is predicted to confer rotational freedom to the hybrid molecule and thus facilitate bifunctional interaction with double-stranded DNA through a combination of 'classical' intercalation and minor groove-binding processes. The noncovalent DNA-binding properties of these acridine-triazene combilexins, together with the component molecular fragments, have been examined by fluorescence quenching and thermal denaturation studies with calf thymus DNA and two oligonucleotides, [poly(dA-dT)]2 and [poly(dG-dC)]2. In addition, the binding behaviors of these acridine compounds are compared to those of proflavine (3,6-diaminoacridine) and its 9-phenyl derivative. The results indicate that the hybrid agents (i) are more DNA-affinic than either molecular component, (ii) retain the AT-preferential binding properties of the parent difunctionalized 1,3-diaryltriazene residues, despite weak GC-preferential behavior associated with the acridine chromophore, and (iii) have a reduced binding affinity at pH 7 that reflects the protonation status of the acridine. In contrast, the more basic proflavines show much greater binding affinity and a marked preference for GC-rich DNA sequences. In vitro cytotoxicity data with L1210 mouse leukemia and A2780 human colon cancer cell lines show that the conjugate molecules are approximately 10-40-fold more potent than the acridine or triazene subunits and have activities that compare favorably with those of other reported synthetic combilexins. Intercalative binding modes with a model d(GATACGATAC).d(GTATCGTATC) target duplex have been investigated using molecular modeling techniques. These studies provide a rational basis for the binding properties and suggest that the prototype combilexins can bind in a bimodal manner that induces little distortion of the host DNA duplex. Energy-minimized models for the possible dual interactions are discussed.

9-substituted acridine derivatives with long half-life and potent antitumor activity: synthesis and structure-activity relationships.

A series of DNA-intercalating 9-anilinoacridines, namely 9-phenoxyacridines, 9-(phenylthio)acridines, and 9-(3',5'-disubstituted anilino)acridines, were synthesized as potential antitumor agents with inhibitory effects on DNA topoisomerase II. Unlike amsacrine (m-AMSA), these agents were designed to avoid the oxidative metabolic pathway. These acridine derivatives were, therefore, expected to have long half-life in plasma. Both 9-phenoxyacridines and 9-(phenylthio)acridines were found to have moderate cytotoxicity against mouse leukemia L1210 and human leukemic HL-60 cell growth in culture. Among 9-(3',5'-disubstituted anilino)acridines, 3-(9-acridinylamino)-5-(hydroxymethyl)aniline (AHMA) was found to be a potent topoisomerase II inhibitor and exhibited significant antitumor efficacy both in vitro and in vivo. Chemotherapy of solid-tumor-bearing mice with 10, 10, and 5 mg/kg (QD x 4, ip) AHMA, VP-16, and m-AMSA, respectively, resulted in more tumor volume reduction by AHMA than by VP-16 or m-AMSA for E0771 mammary adenocarcinoma and B-16 melanoma. For Lewis lung carcinoma, AHMA was as potent as VP-16 but more active than m-AMSA. Structure-activity relationships of AHMA derivatives are discussed.

The dynamics of cobalamin utilization in L-1210 mouse leukemia cells: a model of cellular cobalamin metabolism

The uptake and metabolism of cobalamin (Cbl) has been studied in L-1210 murine leukemia cells propagating in vitro. Extracellular Cbl (protein bound and free) and intracellular Cbl (protein bound and free) were determined after culturing L-1210 cells in the presence of [ 57Co]cyanocobalamin (CN-Cbl) bound to transcobalamin II (transcobalamin, TC). The intracellular pool of free [ 57Co]Cbl increased during the first 24 h of culture and a substantial fraction of this free pool was effluxed from the cell to the medium. Upon depletion of extracellular TC-[ 57Co]CN-Cbl, the intracellular concentration of free Cbl decreased as did the efflux of Cbl to the medium. Internalized [ 57Co]CN-Cbl was converted to hydroxocobalamin (OH-Cbl), methylcobalamin (Me-Cbl) and 5′-deoxyadenosylcobalamin. These Cbl forms were found in both soluble (cytoplasmic) and insoluble (membrane) fractions. Intracellular protein-bound [ 57Co]Cbl fractionated with methionine synthase (MS) and methylmalonyl-CoA mutase (MU) activity. The major form of Cbl associated with the two enzymes was OH-Cbl. Cells propagated in medium containing N 5-methyltetrahydrofolate and homocysteine showed a substantial increase in MS activity which paralleled the increase in the intracellular concentration of Me-Cbl and the Cbl bound to the enzyme.

Wide difference between the cytotoxicity of the 11-α- and 11-β-cyano analogues of tilivalline and their epimeric conversion

Tilivalline (TV) possesses a pyrrolo[1,4]benzodiazepine nucleus and is cytotoxic toward mammalian cells. The 11-β-cyano TV analogue (1) is about one hundred times more cytotoxic to mouse leukemia L1210 cells than TV itself. In contrast, the 11-α-cyano TV analogue (2), an epimer of 1, has only about one-hundredth the cytotoxicity of 1. It was found that epimerization proceeded between 1 and 2 under physiological conditions, and the cytotoxicity of 2 is thought to be caused mainly by 1 that was formed from 2 during incubation in medium.

The stereospecific cytotoxic potency of (6R) and (6S)-5,10-dideazatetrahydrofolate correlates with cellular folylpolyglutamate synthetase levels

The de novo purine synthesis inhibitor 5,10-dideazatetrahydrofolate (DDATHF) has previously been shown to inhibit the growth of mouse L1210 and human CCRF-CEM leukemia cells. The present study demonstrates that both the 6 R and 6 S diastereomers of DDATHF are also cytotoxic to mammalian cells in a stereospecific manner. The cytotoxic potency of (6 R)-DDATHF (also known as Lometrexol) towards different cell lines varied by approximately 14-fold and that of (6 S)-DDATHF by as much as 156-fold. Compared to (6 R)-DDATHF, (6 S)-DDATHF was 6.0- and 7.2-fold more cytotoxic to human WiDr colon adenocarcinoma and Chinese hamster ovary (CHO) cells, respectively, and only 1.5- and 2.0-fold more cytotoxic to human T24 bladder carcinoma and mouse L1210 leukemia cells, respectively. However, compared to (6 S)-DDATHF, (6 R)-DDATHF was 8.7- and 6.9-fold more cytotoxic to C3H/10T1/2 clone 8 and clone 16 mouse fibroblasts, respectively. Weak inhibition of aminoimidazolecarboximide ribonucleotide formylransferase (AICARFT, EC 2.1.2.3) appeared to have little role in the cytotoxicity of DDATFH diastereomers to WiDr cells during a 24-h exposure. Although glycinamide ribonucleotide formyltransferase (GARFT, EC 2.1.21) is the main biochemical target of DDATHF, DDATHF stereoisomers' cytotoxic potency showed no clear negative correlation with cellular GARFT levels. However, cellular folylpolyglutamate synthetase (FPGS, EC 6.3.2.17) levels correlated with cytotoxic potency in a positive manner. Suprisingly, two enzyme-dose/DDATHF LD 90-response curves were observed for FPGS corresponding to differences in (6 R) and (6 S)-DDATHF cytotoxic potency among the six cell lines studied.

Urinary and urothelial effects of sodium salts in male rats.

The oxidative DNA damage induced by the renal carcinogen potassium bromate (KBrO3) in cultured mammalian cells and in a cell-free system was characterized by means of various repair endonucleases. Under cell-free conditions, no modifications were induced by KBrO3 alone, but extensive DNA damage was observed in the presence of glutathione (GSH). The DNA damage was found to consist mostly of base modifications sensitive to Fpg protein (formamidopyrimidine-DNA glycosylase). HPLC analysis demonstrated that many of the modifications were 7,8-dihydro-8-oxoguanine (8-hydroxyguanine) residues. Single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to endonuclease III (5,6-dihydropyrimidine derivatives) were formed in only low amounts. This ‘damage profile’ and experiments with various scavengers (catalase, superoxide dismutase, deferoxamine, azide, tert-butanol) and D2O as solvent excluded the involvement of hydroxyl radicals and singlet oxygen in the damage production, but were consistent with a radical mechanism involving bromine radicals. In L1210 mouse leukemia cells and LLC-PK1 porcine kidney cells, KBrO3 alone gave rise to a DNA damage profile similar to that observed after treatment of cell-free DNA with KBrO3 plus GSH, i.e. base modifications sensitive to Fpg protein were formed in high excess of all other lesions quantified. In LLC-PK1 cells (derived from the target organ of KBrO3 carcinogenesis) the level of DNA damage was twice that in the L1210 cells. DNA damage was partially prevented by depletion of intracellular GSH with diethylmaleate, indicating that GSH played an activating role in the cells similar to that seen under cell-free conditions. The Fpg-sensitive base modifications induced by KBrO3 were repaired with only moderate efficiency (38 ± 10% of the lesions were still present after 18 h in full medium) under conditions that did not influence cell proliferation.

Oxidative DNA damage induced by potassium bromate under cell-free conditions and in mammalian cells.

The oxidative DNA damage induced by the renal carcinogen potassium bromate (KBrO3) in cultured mammalian cells and in a cell-free system was characterized by means of various repair endonucleases. Under cell-free conditions, no modifications were induced by KBrO3 alone, but extensive DNA damage was observed in the presence of glutathione (GSH). The DNA damage was found to consist mostly of base modifications sensitive to Fpg protein (formamidopyrimidine-DNA glycosylase). HPLC analysis demonstrated that many of the modifications were 7,8-dihydro-8-oxoguanine(8-hydroxyguanine) residues. Single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to endonuclease III (5,6-dihydropyrimidine derivatives) were formed in only low amounts. This 'damage profile' and experiments with various scavengers (catalase, superoxide dismutase, deferoxamine, azide, tert-butanol) and D2O as solvent excluded the involvement of hydroxyl radicals and single oxygen in the damage production, but were consistent with a radical mechanism involving bromine radicals. In L1210 mouse leukemia cells and LLC-PK1 porcine kidney cells, KBrO3 alone gave rise to a DNA damage profile similar to that observed after treatment of cell-free DNA with KBrO3 plus GSH, i.e. base modifications sensitive to Fpg protein were formed in high excess of all other lesions quantified. In LLC-PK1 cells (derived from the target organ of KBrO3-induced carcinogenesis) the level of DNA damage was twice that in the L1210 cells. DNA damage was partially prevented by depletion of intracellular GSH with diethylmaleate, indicating that GSH played an activating role in the cells similar to that seen under cell-free conditions. The Fpg-sensitive base modifications induced by KBrO3 were repaired with only moderate efficiency (38 +/- 10% of the lesions were still present after 18 h in full medium) under conditions that did not influence cell proliferation.

Synergistic anti-tumor effects of mitomycin C and bile salts against L1210 cells.

The effects of various adjuvants on the cytotoxicity of mitomycin C (MMC) were studied in L1210 mouse leukemia cells. Adjuvants examined in this study were sodium glycocholate (Na-GC), sodium deoxycholate (Na-DC), O-n-dodecyl-beta-D-maltopyranoside (LM), and sodium salicylate. Among various additives, bile salts such as Na-GC and Na-DC were the most effective for increasing the cytotoxicity of MMC against L1210 cells. A dose-dependent increase in cytotoxic effect of MMC was observed in the presence of these bile salts. To elucidate a possible mechanism for enhancing the cytotoxic effect of MMC by the bile salts, the cellular uptake of MMC with or without Na-GC was examined using L1210 cells. The cellular concentration of MMC was determined by a reversed-phase HPLC. When Na-GC was coadministered with MMC, the uptake of MMC into L1210 cells was significantly enhanced as compared with MMC alone. Furthermore, the membrane fluidity of L1210 cells, as determined by fluorescence polarization, was increased in the presence of Na-GC. These results suggested that the enhancement of cytotoxicity of MMC by the addition of Na-GC could be attributed to the increasing cellular uptake of MMC due to the increasing membrane fluidity of L1210 cells.

An XPG DNA Repair Defect Causing Mutagen Hypersensitivity in Mouse Leukemia L1210 Cells

One of the most widely used antitumor drugs is cis-diamminedichloroplatinum(II) (cisplatin), and mechanisms of cisplatin resistance have been investigated in numerous model systems. Many studies have used mouse leukemia L1210/0 as a reference wild-type cell line, and cisplatin-resistant subclones have been derived from it. Increased DNA excision repair capacity is thought to play a key role in the acquired cisplatin resistance, and this has influenced development of drugs for clinical trials. We report here that the L1210/0 line is in fact severely deficient in nucleotide excision repair of damaged DNA in vivo and in vitro. L1210/0 cell extracts could be complemented by extracts from repair-defective human xeroderma pigmentosum (XP) or rodent excision repair cross-complementing (ERCC) mutant cells, except for XPG/ERCC5 mutants. Purified XPG protein could restore repair proficiency to L1210/0 extracts. Expression of mouse XPG mRNA was similar in all L1210 lines studied, suggesting a point mutation or small alteration of XPG in L1210/0 cells. The DNA repair capacity of a cisplatin-resistant subline, L1210/DDP10, is similar to that of type culture collection L1210 cells and to those of other normal mammalian cell lines. Nucleotide excision repair of DNA is thus clearly important in the intrinsic cellular defense against cisplatin. However, in contrast to what is generally believed, enhancement of DNA repair above the normal level in these rodent cells does not appear to be a mechanism of acquired resistance to the drug.

Antimicrotubule effects of the novel antitumor benzoylphenylurea derivative HO-221

The antitumor action of HO-221, a novel benzoylphenylurea derivative, was studied. The in vitro cytotoxic strength of HO-221 was investigated, as measured by IC50 values, compared with those of other drugs with different action mechanisms, using Chinese hamster lung (CHL) cells, mouse leukemia L1210 cells and human promyelocytic leukemia HL-60 cells. Morphological alterations following treatment were observed under a phase contrast microscope, and the mitotic index was determined at regular intervals to check for accumulation of metaphase cells. HO-221 was found to have a very strong toxic effect on all cell types, equal to that of the spindle poisons used as controls. HO-221 also produced the same specific morphological changes as the spindle poisons, with a significant accumulation of metaphase cells. A chromosome analysis of treated cells showed that HO-221 frequently induced polyploid and aneuploid cells, but without accompanying chromosome-breaking activity. An in vivo mouse bone marrow micronucleus assay was also carried out. The assay allowed the in vivo identification of a chromosome breaker or a spindle poison through the measurement of the relative sizes of micronuclei produced and erythrocytes. HO-221 was found frequently to induce relatively large micronuclei, an action regarded as specific to spindle poisons. It was thus demonstrated that HO-221 acts as a spindle poison both in vitro and in vivo. In order to investigate the mechanism of this action, a study of tubulin assembly using purified calf brain tubulin was carried out, which demonstrated clearly that HO-221 inhibits microtubule assembly. A detailed investigation of the action mechanism of HO-221 as a spindle poison is now called for.

Cytotoxic effects of several hopanoids on mouse leukemia L1210 and P388 cells.

The cytotoxic effects of hopanoids, including bacteriohopane-32, 33, 34, 35-tetrol (Tetrol), bacteriohopane-32-ol (Monol), diploptene, diplopterol and acetylated Monol (AcO-Monol) isolated from Acetobacter aceti, were tested against two leukemia cell lines. Tetrol and Monol have been shown to be toxic to mouse L1210 and P388 compared to the other hopanoids. By measuring the ESR spectra of the spin labeled membranes of these cells, it was shown that the incorporation of Monol resulted in a decrease in the fluidity of the membranes. The decrease in membrane fluidity may correlate, in part, with the cytotoxicity of hopanoids against the two cell lines.

Permeabilization of the plasma membrane of L1210 mouse leukemia cells using lithotripter shock waves.

Permeabilization of L1210 cells by lithotripter shock waves in vitro was monitored by evaluating the accumulation of fluorescein-labeled dextrans with a relative molecular mass ranging from 3,900-2,000,000. Incubation with labeled dextran alone caused a dose- and time-dependent increase in cellular fluorescence as determined by flow cytometry, with a vesicular distribution pattern in the cells consistent with endocytotic uptake. Shock wave exposure prior to incubation with labeled dextran revealed similar fluorescence intensities compared to incubation with labeled dextran alone. When cells were exposed to shock waves in the presence of labeled dextran, mean cellular fluorescence was further increased, indicating additional internalization of the probe. Confocal laser scanning microscopy confirmed intracellular fluorescence of labeled dextran with a diffuse distribution pattern. Fluorescence-activated cell sorting with subsequent determination of proliferation revealed that permeabilized cells were viable and able to proliferate. Permeabilization of the membrane of L1210 cells by shock waves in vitro allowed loading of dextrans with a relative molecular mass up to 2,000,000. Permeabilization of tumor cells by shock waves provides a useful tool for introducing molecules into cells which might be of interest for drug targeting in tumor therapy in vivo.

Hybrid anthracycline antibiotics: production of new anthracyclines by cloned genes from Streptomyces purpurascens in Streptomyces galilaeus.

A DNA segment cloned from Streptomyces purpurascens ATCC 25489 close to a region that hybridized to a probe containing part of the actinorhodin polyketide synthase caused S. galilaeus ATCC 31615 to produce new anthracyclines. When transformed with certain sub-clones of this segment, the host produced glycosides of epsilon-rhodomycinone, beta-rhodomycinone, 10-demethoxycarbonylaklavinone and 11-deoxy-beta-rhodomycinone in addition to those of aklavinone, the natural anthracyclines of S. galilaeus. The first two compounds are S. purpurascens products and the other two are novel compounds that conceptually are structural hybrids between S. galilaeus and S. purpurascens products. Three glycosides of one of the novel aglycones, 11-deoxy-beta-rhodomycinone, were purified and found to possess cytotoxic activity against L1210 mouse leukaemia cells. Separate regions of the cloned S. purpurascens DNA are responsible for modification of the S. galilaeus host product at the 10- and 11-positions.

Synthesis and biological activity of intercalator substituted bile steroids

Cholic acid has been functionalised at the 3 and 24 positions with quinoline and quinoxaline chromophores. The 24-quinoline monoester shows significant activity against L1210 mouse leukaemia cells compared to the 3,24-disubstituted quinoline and quinoxaline esters.

Synthesis and in vitro cytotoxicity of 6-vinyluridine and related compounds

The 6-alkenyluracil nucleosides ( 7a–e) and bases ( 14a–i) were synthesized and evaluated for their ability to inhibit the growth of mouse leukemia L1210 cells in vitro. While several of the free bases are cytotoxic, with IC 50 values in the 1 – 5 μM range, the corresponding β- d-ribofuranosyl nucleosides are not significantly active.

Visible light generates oxidative DNA base modifications in high excess of strand breaks in mammalian cells.

The DNA damage induced by visible light in L1210 mouse leukaemia cells was analysed by an alkaline elution assay with specific repair endonucleases. DNA single-strand breaks and DNA modifications sensitive to FPG protein (formamidopyrimidine-DNA glycosylase), endonuclease III and exonuclease III were quantified in parallel. The light-induced cellular DNA damage was found to consist of many base modifications sensitive to FPG protein, which most probably are predominantly 7,8-dihydro-8-oxoguanine (8-hydroxyguanine) residues. Base modifications sensitive to endonuclease III are virtually absent. The yield of the FPG-sensitive base modifications is 10-fold higher than that of single-strand breaks plus AP sites (sites of base loss). The described ratios of the various modifications indicate that the damage most probably results from a reaction of DNA with singlet oxygen (type II reaction) or directly with an excited endogenous photosensitizer (type I reaction) and is not mediated by hydroxyl radicals. Experiments with cut-off filters indicate that wavelengths between 400 and 500 nm are responsible for most of the modifications. The FPG-sensitive base modifications are repaired efficiently (t1/2 approximately 1 h at 37 degrees C). This is perhaps why the light-induced DNA damage is apparently associated with only low mutagenicity.

Thermal enhancement of drug uptake and DNA adducts as a possible mechanism for the effect of sequencing hyperthermia on cisplatin-induced cytotoxicity in L1210 cells

An optimal scheduling of hyperthermia and cis-diammine-dichloroplatinum(II) (cisplatin) may increase the therapeutic gain of the combination of these two modalities. In this study, intracellular platinum accumulation, total platinum binding to DNA, and DNA interstrand crosslinks (ISC) were assayed to investigate the molecular mechanisms responsible for the effect of sequencing hyperthermia on the thermal enhancement of cisplatin-induced cytotoxicity in mouse leukemia L1210 cells. Simultaneous treatment with heat (41.5 degrees C, 60 min) and cisplatin produced maximal cell killing with a 4-fold decrease in the 50% growth-inhibitory concentration (IC50) of the platinum complex. Super-additive cell killing was also shown when cells were exposed to heat before cisplatin treatment, whereas no thermal enhancement in cisplatin-mediated cytotoxicity was observed in cells given heat after exposure to cisplatin. These results correlated with the degree of formation of ISC observed in cells following various treatments. A 2- to 3-fold increase in ISC formation was observed in cells given heat before or during cisplatin exposure, whereas heat after cisplatin treatment did not alter either the formation or the reversal of ISC as compared with cisplatin alone. The increased ISC formation was associated with an increase in intracellular platinum accumulation and total platinum binding to DNA in cells given heat before or during cisplatin exposure. These data, showing that hyperthermia potentiates cisplatin cytotoxicity by increasing drug uptake and the formation of DNA adducts without inhibiting the repair of DNA lesions, demonstrate the potential utility of sequencing hyperthermia combined with cisplatin as a clinical anticancer therapy.

Induction of Apoptosis by Erbstatin in Mouse Leukemia L1210 Cells

Erbstatin, a tyrosine kinase inhibitor, has antitumor activity on L1210 mouse leukemia. We tried to find the mechanism of this cytotoxic effect of erbstatin. Erbstatin increased trypan blue exclusion in cultured LI210 cells. The cytotoxic action of erbstatin was accompanied with shrinking of the cells and internucleosomal DNA fragmentation, characteristics of apoptosis. The DNA fragmentation was induced with other tyrosine kinase inhibitors as well, methyl 2,5-dihydroxycinnamate and herbimycin A. In addition, intracellular tyrosine phosphorylation was inhibited by erbstatin before cell death. Erbstatin-induced DNA fragmentation was prevented by zinc ions, but not by cycloheximide or 12-O-tetradecanoylphorbol 13-acetate (TPA). Thus, erbstatin induced apoptotic cell death in L1210 cells by inhibiting tyrosine kinase.

Use of nucleoside kinase-deficient mouse leukemia L1210 cell lines to determine metabolic routes of activation of antitumor nucleoside analogs

Mouse leukemia L1210 cell lines that were selected for resistance to deoxyguanosine (dGuo-R) or lacked adenosine kinase activity (ED2) were used to evaluate the nature of the nucleoside kinase that was required to phosphorylate nucleoside analogs to their respective active nucleotide form. The dGuo-R cells had reduced levels of kinase activity toward araC, dGuo and 2-CldAdo as substrates with essentially no loss of activity toward dCyd. This cell line showed resistance to dGuo, araC, araG, FdAdo, and Fara A but not to dAdo or araA. The ED2 cell line was resistant to pyrazofurin and 6-methylmercaptopurine riboside and to araA/EHNA but not to 2-CldAdo or 2-Cl-2′-FaraA. The study of the effects of newer nucleoside analogs such as dFdCyd, MdAdo, MdCyd and MdGuo in these cell lines showed that some of these agents are primarily phosphorylated by deoxyribonucleoside kinase (dFdCyd) or by adenosine kinase (MdAdo) or in some instances by multiple kinases (FaraA). These cell lines will be useful in defining the nature of the kinase(s) responsible for activating new nucleoside analogs and defining cross-resistance patterns.

Nuclear factor kappa B binding activity in mouse L1210 cells following photofrin II-mediated photosensitization.

Clinical photodynamic therapy (PDT) uses the photosensitizer photofrin II to produce singlet molecular oxygen and other reactive oxygen intermediates for localized tumor tissue cytotoxicity. In this report, we show that PDT enhances the DNA binding activity of nuclear factor kappa B (NF kappa B), a transactivator of cytokine gene expression. Photosensitization following a 16 h incubation of photofrin II induced NF kappa B binding activity in mouse leukemia L1210 cells 10-fold above that observed in exponentially growing cultures. Serum starvation, as well as drug-alone and light-alone controls, elevated basal NF kappa B binding activity two- to three-fold. Upstream stimulatory factor binding activity was not modulated by any of the cell treatments and was used to standardize gel mobility shift data. This study identifies porphyrin-mediated PDT as an inducer of NF kappa B binding activity, extending recent findings that NF kappa B activation is a general response to oxidative stress.