The role of mitomycin antibiotics in the chemotherapy of solid tumors

Signalling and putative therapeutic molecules on the regulation of synoviocyte signalling in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by symmetrical and chronic polyarthritis. Fibroblast-like synoviocytes are mainly involved in joint inflammation and cartilage and bone destruction by inflammatory cytokines and matrix-degrading enzymes in RA. Approaches that induce various cellular growth alterations of synoviocytes are considered as potential strategies for treating RA. However, since synoviocytes play a critical role in RA, the mechanism and hyperplastic modulation of synoviocytes and their motility need to be addressed. In this review, we focus on the alteration of synoviocyte signalling and cell fate provided by signalling proteins, various antioxidant molecules, enzymes, compounds, clinical candidates, to understand the pathology of the synoviocytes, and finally to achieve developed therapeutic strategies of RA.

Cite this article: Bone Joint Res 2021;10(4):285–297.

Efficacy and safety of raltitrexed combinations with uracil- tegafur or mitomycin C as salvage treatment in advanced colorectal cancer patients: a multicenter study of Anatolian Society of Medical Oncology (ASMO)

BACKGROUND

There is no standard treatment for patients with colorectal cancer (CRC) progressing after irinotecan and oxaliplatin treatment. Here we aimed to retrospectively evaluate the efficacy and tolerability of raltitrexed in combination with oral 5-fluoropyrimidine (uracil tegafur-UFT) or mitomycin C as salvage therapy in mCRC patients.

MATERIALS AND METHODS

A total of 62 patients who had received raltitrexed combined with UFT or mitomycin C were identified between December 2008 and June 2013. They were given raltitrexed 2.6 mg/m2 (max 5 mg) i.v. on day 1 in combination with either oral UFT 500 mg/day on days 1-14 every 3 weeks (group A) or mitomycin C 6 mg/m2 i.v. on day every 3 weeks (group B).

RESULTS

Forty-two patients (67.7%) were in group A and 20 (32.2%) in group B. In 15 patients (24%) grade 3/4 toxicity was observed, resulting in dose reduction, and in 13 patients (20.9%) dose delay was necessary. The median progression free survival (PFS) was 3 months (95%CI 2.65-3.34) and median overall survival (OS) was 6 months (95%CI 2.09-9.90) in the whole group. Median PFS was 3 months (95%CI 2.60-3.39) in group A vs 3 months (95%CI 1.64-4.35) in group B (p=0.90). Median OS was 6 months (95%CI 2.47-9.53) in group A vs 12 months (95%CI 2.83-21.1) in group B (p=0.46).

CONCLUSIONS

The combination of raltitrexed with UFT or mitomycin C seem to be a salvage therapy option due to safety profile and moderate clinical activity in heavily-pretreated mCRC patients.

Enhancement of the efficacy of mitomycin C-mediated apoptosis in human colon cancer cells with RNAi-based thioredoxin reductase 1 deficiency

Thioredoxin reductase 1 (Trr1) is an antioxidant and redox regulator that functions in governing the cellular redox state and survival against oxidative insults in mammals. However, this selenoprotein is also overexpressed in various forms of malignant cancers, leading to the hypothesis that Trr1 may be a potential target for cancer therapy. A quinone anti-cancer drug, mitomycin C (MMC), has been clinically used in the treatment of several types of tumors, including those of the colon. MMC exerts its activity via ROS induction and further results in DNA cross-linkage. To evaluate the significant role of Trr1 in MMC resistance in human colon cancer (RKO) cells, specific reduction in the expression of Trr1 was achieved using short-hairpin RNA (shRNA)-based interference. Our results showed that stable Trr1 shRNA knockdown manifested higher cellular susceptibility to MMC in comparison to that in wild-type cells. In addition, increased intracellular ROS accumulation appeared in the Trr1 shRNA knockdown cells compared to the RKO wild-type cells, in proportion to a relatively higher fraction of the DNA damage reporter protein phosphorylated histone 'γ-H2AX'. Notably, a neutral comet assay demonstrated that DNA double-strand breaks were highly induced in the Trr1-deficient cancer cells in the presence of MMC, presumably stimulating cancer cell death. Our results also revealed that MMC-induced apoptosis was associated with enhancement of oxidative damage to DNA. These results suggest that the specific knockdown of Trr1 expression via shRNA vector interference technology may be a potent molecular strategy by which to enhance the effectiveness of MMC-mediated killing in human colon cancer cells, through acceleration of double-strand DNA damage-oxidative stress as a trigger for apoptosis. This implies that Trr1 may be a prime target for enhancing the effectiveness of MMC chemotherapy in combination with specific RNA interference.

Stereoselective synthesis of complex polycyclic aziridines: use of the Brønsted acid-catalyzed aza-Darzens reaction to prepare an orthogonally protected mitomycin C intermediate with maximal convergency

A concise synthesis of a highly functionalized intermediate lacking only C10 of the mitomycin backbone is described. The key to this development is the Brønsted acid-catalyzed aza-Darzens reaction used to forge the cis-aziridine. Additionally an oxidative ketalization fortuitously occurs during the quinone-enamine coupling step, leading to an orthogonally protected hydroquinone.

Effects of photochemically activated alkylating agents of the FR900482 family on chromatin

Bioreductive alkylating agents are an important class of clinical antitumor antibiotics that crosslink and monoalkylate DNA. Here, we use a synthetic, photochemically activated derivative of FR400482 to investigate the molecular mechanism of this class of drugs in a biologically relevant context. We find that the organization of DNA into nucleosomes effectively protects it against drug-mediated crosslinking, while permitting monoalkylation. This modification has the potential to lead to the formation of covalent crosslinks between chromatin and nuclear proteins. Using in vitro approaches, we found that interstrand crosslinking of free DNA results in a significant decrease in basal and activated transcription. Finally, crosslinked plasmid DNA is inefficiently assembled into chromatin. Our studies suggest pathways for the clinical effectiveness of this class of reagents.

Mitomycin C induces apoptosis via Fas/FasL dependent pathway and suppression of IL-18 in cervical carcinoma cells

Mitomycin C (MMC) is used fairly widely as an anticancer drug, as it possesses mechanisms of action which are preferable to other chemotherapeutic compounds, including cisplatin, docetaxel, and lovastatin. In the previous study, we established the RSV-luc promoter analysis system, which is used to screen drugs against cervical carcinomas caused by HPV infection. We then demonstrated the repression of HPV E6-activated RSV promoter activity by anticancer agents such as carboplatin (CA), cisplatin (CIS), and MMC. In these studies, we focused on the investigation of apoptotic mechanisms in MMC-treated cervical carcinoma cell lines, most notably SiHa/pRSV-luc (KCTC 0427BP) and SiHa. DNA fragmentation assays and TUNEL staining revealed that MMC and CIS, but not CA, resulted in apoptosis. MMC treatment induced a reduction in the expressions of the E6 oncogene and IL-18, in a p53-independent manner. MMC also increased FasL expression and induced the processing of caspases-8 and -3. Our results indicated that MMC induced apoptosis in SiHa/pRSV-luc and SiHa cells via caspase-8 and -3 processing, in a Fas/FasL-dependent manner. MMC also suppressed the expression of IL-18 in the same cells. MMC also down-regulated IkappaB expression, and up-regulated p65 expression. These results suggest that MMC induces apoptosis, not only through caspase-8 and -3 dependent Fas/FasL pathway, but also via the regulation of NF-kappaB activity and IL-18 expression.

Reduced Toxicity and Superior Therapeutic Activity of a Mitomycin C Lipid-Based Prodrug Incorporated in Pegylated Liposomes

PURPOSE

A lipid-based prodrug of mitomycin C [MMC; 2,3-(distearoyloxy)propane-1-dithio-4'-benzyloxycarbonyl-MMC] was designed for liposome formulation. The purpose of this study was to examine the in vitro cytotoxicity, pharmacokinetics, in vivo toxicity, and in vivo antitumor activity of this new lipid-based prodrug formulated in polyethylene glycol-coated (pegylated) liposomes.

EXPERIMENTAL DESIGN

MMC was released from the MMC lipid-based prodrug (MLP) by thiolytic-induced cleavage with a variety of thiol-containing reducing agents. MLP was incorporated with nearly 100% efficiency in cholesterol-free pegylated liposomes with hydrogenated phosphatidylcholine as the main component and a mean vesicle size of approximately 90 nm. This formulation was used for in vitro and in vivo tests in rodents.

RESULTS

In vitro, the cytotoxic activity of pegylated liposomal MLP (PL-MLP) was drastically reduced compared with free MMC. However, in the presence of reducing agents, such as cysteine or N-acetyl-cysteine, its activity increased to nearly comparable levels to those of free MMC. Intravenous administration of PL-MLP in rats resulted in a slow clearance indicating stable prodrug retention in liposomes and long circulation time kinetics, with a pharmacokinetic profile substantially different from that of free MMC. In vivo, PL-MLP was approximately 3-fold less toxic than free MMC. The therapeutic index and absolute antitumor efficacy of PL-MLP were superior to that of free MMC in the three tumor models tested. In addition, PL-MLP was significantly more active than a formulation of doxorubicin in pegylated liposomes (DOXIL) in the M109R tumor model, a mouse tumor cell line with a multidrug-resistant phenotype.

CONCLUSIONS

Delivery of MLP in pegylated liposomes is a potential approach for effective treatment of multidrug-resistant tumors while significantly buffering the toxicity of MMC.

NAD(P)H: quinone oxidoreductase 1 expression in kidney podocytes

NAD(P)H:quinone oxidoreductase 1 (NQO1; DT-diaphorase; DTD) is a cytosolic two-electron reductase, and compounds of the quinone family such as mitomycin C are efficiently bioactivated by this enzyme. The observation that DT-diaphorase is highly expressed in many cancerous tissues compared to normal tissues has provided us with a potentially selective target that can be exploited in the design of novel anticancer agents. Because of the relative lack of information about the cell-specific expression of DT-diaphorase, the purpose of this study was to map the distribution of this enzyme in normal human tissues. Fifteen tissue samples from normal human kidney were analyzed for expression of DT-diaphorase by immunohistochemistry (two-step indirect method). We found a specific high expression of DT-diaphorase in glomerular visceral epithelial cells (podocytes). These results suggest that a high expression of DT-diaphorase in podocytes could play a major role in the pathogenesis of renal toxicity and mitomycin C-induced hemolytic uremic syndrome, in which injury to the glomerular filtration mechanism is the primary damage, leading to a cascade of deleterious events including microangiopathic hemolytic anemia and thrombocytopenia. This observation has potential therapeutic implications because the DT-diaphorase metabolic pathway is influenced by many agents, including drugs, diet, and environmental cell factors such as pH and oxygen tension.

Immunologically specific activation of a cephalosporin derivative of mitomycin C by monoclonal antibody beta-lactamase conjugates

The syntheses of two cephalosporin derivatives 2 and 3 of mitomycin C (1) containing 7-phenylacetamido and 7-delta-carboxybutanamido side chains, respectively, are described. These compounds were prepared for evaluation as cephalosporin prodrugs capable of being activated by mAb-beta-lactamase conjugates. In vitro cytotoxicity assays performed on H2987 lung adenocarcinoma and clone 62 melanoma cell lines indicated that compound 2 was comparable in cytotoxicity to the parent drug. In an effort to improve upon the cytotoxic differential of 2, an alternative prodrug 3 containing a polar carboxyl group in the side chain of the cephalosporin moiety was prepared. Compound 3 consistently behaved as a prodrug and was approximately 40- and 10-fold less toxic than 1 toward H2987 and clone 62, respectively. Determination of kinetic constants for hydrolysis by beta-lactamase from Enterobacter cloacae P99 indicated kcat values of 476 +/- 170 and 248 +/- 15.1 s-1 for 2 and 3, respectively. The kcat/Km ratios for 2 and 3 were found to be approximately 9.7 and 2.1 microM/s, respectively. Comparison of these kcat/Km values with those obtained for similar cephalosporin derivatives of other antitumor agents demonstrated that compounds with delta-carboxybutanamido side chains generally have slightly diminished efficiency of enzymatic hydrolysis compared to the corresponding 7-phenylacetamido analog. It was also demonstrated that the less toxic prodrug 3 was activated in an immunologically specific manner by L6-F(ab')-beta-lactamase and 96.5-F(ab')-beta-lactamase conjugates, selective for H2987 and clone 62 cells, respectively.

FR900482, a close cousin of mitomycin C that exploits mitosene-based DNA cross-linking

BACKGROUND

The class of antitumor antibiotics that includes FR900482 has a very close structural analogy to the mitomycins, one of which, mitomycin C, has been in widespread clinical use for more than 20 years. Like mitomycin C, these antitumor antibiotics are reductively activated in vivo and covalently cross-link DNA as a result of activity of the mitosene moiety generated on reduction. Owing to differences in structure and the attendant mechanistic differences in bioreductive activation between the mitomycins and FR900482, FR900482 does not produce an adventitious superoxide radical anion during reductive activation and thus does not exhibit oxidative strand scission of DNA. It is postulated that the low clinical toxicity of FR900482 relative to mitomycin C is a direct manifestation of the mechanistic differences of bioreductive activation leading to the highly reactive DNA cross-linking mitosenes.

RESULTS

Using Fe(II)-EDTA footprinting, we showed that the two natural products FR900482 (1) and dihydro, FR66979 (3), and the semi-synthetically derived triacetate FK973 (2), display remarkable selectivity for 5' deoxy-CG sequences of DNA, and that this selectivity is abolished upon deletion of the exocyclic N2 amine of either participating guanosine residue. In addition, we investigated the mono alkylation abilities of FR66979 with respect to a number of inosine-substituted oligonucleotides and observed that the FR900482 class of compounds were able to give rise to easily separable orientation isomers of their respective cross-links.

CONCLUSIONS

The FR900482 class of antitumor antibiotics cross-link DNA in a fashion analogous to the mitomycins. The cross-linking reaction yields two orientation isomers which are of vastly different electrophoretic mobility and which also exhibit radically different DNA-protein recognition properties upon reaction with AluI restriction endonuclease. In addition, mono-alkylation of DNA by FR66979 shows little, if any, dependence upon pre-covalent interactions deemed necessary for the mitomycins. These insights support the proposal that the FR900482 class of compounds represents a compelling clinical replacement for mitomycin C, given its greatly reduced host toxicity and superior DNA interstrand cross-linking efficacy.

Development, pharmacology, role of DT-diaphorase and prospects of the indoloquinone EO9

1. The indoloquinone EO9 (3-hydroxymethyl-5-aziridinyl-1-methyl-2- (1H-indole-4,7-dione)-propenol; E85/053; NSC 382,459) is a synthetic bioreductive alkylating agent that is structurally related to mitomycin C (MMC). 2. EO9 does, however, show a different mechanism of action and a broader antitumour profile than MMC. It is also a more potent cytotoxic agent in vitro than MMC, probably because of its impressive efficient activation by reductive enzymes, particularly DT-Diaphorase. This enzyme is elevated in several tumours compared to normal tissues. 3. The preferential cytotoxicity of EO9 under hypoxic conditions makes it an interesting compound to combine with radiation. 4. In preclinical and the Phase I clinical studies, no myelosuppression was observed but reversible proteinuria was dose-limiting. Phase II clinical studies were started in the summer of 1994.

Enzymology of the reduction of the novel fused pyrazine mono-n-oxide bioreductive drug, RB90740 roles for P450 reductase and cytochrome b5 reductase

RB90740 is the lead compound in a series of fused pyrazine mono-N-oxide bioreductive drugs. Theses agents have potential application in cancer therapy, since they are more toxic to hypoxic than to aerobic cells as a consequence of their bioactivation by cellular reductase enzymes within the hypoxic regions of a tumour. In this study, mouse liver microsomes have been used to characterise the enzymology of the reductive activation of RB90740. Under hypoxic conditions, the reduction of RB90740 to its stable 2-electron reduced product RB92815 was supported by both NADH and NADPH, the former supporting a rate approximately 80% of the latter. Combining the two cofactors had no additive effect. Neither carbon monoxide nor metyrapone inhibited reduction of RB90740, indicating that P450 isozymes were not involved in the reduction of this compound. 2' AMP, and inhibitor of P450 reductase, did not inhibit formation of RB92815, whereas DPIC, another inhibitor but with a different mode of action, inhibited both the NADH, and NADPH-dependent reduction of RB90740. Similarly, two selective inhibitors of NADH: cytochrome b5 reductase, pHMB and PTU, completely inhibited both NADH and NADPH-dependent reduction of RB90740. Our findings implicate P450 reductase, cytochrome b5 reductase, and cytochrome b5 in the activation of the compound. However, there is no clear relationship between the intracellular levels of P450 reductase and cytochrome b5 reductase and the hypoxic toxicity of RB90740, which implies that other factors, in addition to drug activation, play a major role in controlling the toxicity of this particular bioreductive drug.

Hypoxia and drug resistance

Biologically and therapeutically important hypoxia occurs in many solid tumor masses. Hypoxia can be a direct cause of therapeutic resistance because some drugs and radiation require oxygen to be maximally cytotoxic. Cellular metabolism is altered under hypoxic conditions. Hypoxia can result in drug resistance indirectly if under this condition cells more effectively detoxify the drug molecules. Finally, there is evidence that hypoxia can enhance genetic instability in tumor cells thus allowing more rapid development of drug resistance cells. The current review describes the effects of hypoxia on tumor response to a variety of anti-cancer agents and also describes progress toward therapeutically useful methods of delivering oxygen to tumors in an effort to overcome therapeutic resistance due to hypoxia. Finally, the use of hypoxic cell selective cytotoxic agents as a means of addressing hypoxic 'drug resistance' is discussed.

Manipulation and exploitation of the tumour environment for therapeutic benefit

We describe aspects of the tumour microenvironment that are available as targets for manipulation. In particular, the question asked is whether hypoxia in tumours is a problem to be overcome, or a physiological abnormality to be exploited? Bioreductive drugs require metabolic reduction to generate cytotoxic metabolites. This process is facilitated by appropriate reductases and the lower oxygen conditions present in solid tumours compared with normal tissues. Because of their specificity, bioreductive drugs are used to help answer this question. Other aspects of tumour physiology and biochemistry that may be exploited include tissue dependent reductase expression, pH and angiogenesis.

Effect of hyperthermia on the activity of 1-[(4'-hydroxy-2'-butenoxy)methyl]-2-nitroimidazole, which is cytotoxic to hypoxic cells

The effect on EMT6/KU cells of a newly synthesized hypoxic cell sensitizer, 1-[(4'-hydroxy-2'-butenoxy)methyl]-2-nitroimidazole (RK28), combined with heat was determined in vitro under conditions of hypoxia. As compared with aerobic conditions, hypoxia produced a 1.30-fold increase in the cytotoxicity of the drug for mouse mammary EMT6/KU cells induced by 1 h heat treatment at 43 degrees C in medium with a normal pH. Hypoxia also reduced the surviving fraction of cells treated with both RK28 alone for 2 h and the same concentrations of RK28 and heat (43 degrees C) in combination. Those enhancement ratios corresponded to a 20.3- and > 345-fold increase, respectively. Moreover, concomitant treatment with RK28 and heat greatly inhibited the clonogenic activity of the EMT6/KU cells under conditions of in vitro hypoxia and in all experimental groups; there was a statistically significant difference in the time-response curves (P < 0.05). As hypoxic cells in a solid tumor are resistant to various anticancer drugs, RK28 combined with hyperthermia deserves further study for possible clinical applications.

Thiol oxidation coupled to DT-diaphorase-catalysed reduction of diaziquone. Reductive and oxidative pathways of diaziquone semiquinone modulated by glutathione and superoxide dismutase

DT-diaphorase [NAD(P)H:quinone oxidoreductase; EC 1.6.99.2] catalysed the two-electron reduction of the anti-tumour quinone 2,5-bis-(1-aziridinyl)-3,6-bis(ethoxycarbonylamino)-1,4-benzoquino ne (AZQ) to the hydroquinone form (AZQH2). Although DT-diaphorase catalysis of AZQ was not significantly affected by pH, the hydroquinone product was effectively stabilized by protonation at pH values below 7, whereas, above that pH, hyroquinone autoxidation, evaluated in terms of H2O2 production, increased exponentially. The autoxidation of AZQH2 entailed the formation of diverse radicals, such as O2-.,HO., and the semiquinone form of AZQ (AZQ-.), which contributed to different extents to the e.p.r. spectrum. Superoxide dismutase enhanced the autoxidation of AZQH2 and suppressed the e.p.r. signal ascribed to AZQ-., in agreement with a displacement of the equilibrium of the semiquinone autoxidation reaction (AZQ-.+O2 in equilibrium with AZQ+O2-.) upon enzymic withdrawal of O2-.. GSH increased the steady-state concentration of AZQH2 formed during DT-diaphorase catalysis and inhibited temporarily its autoxidation. This effect was accompanied by oxidation of the thiol to the disulphide within a process involving glutathionyl radical (GS.) formation, the relative contribution of which to the e.p.r. spectrum was enhanced by increasing GSH concentrations. GS. formation in this experimental model can be rationalized as originating from the reaction of GSH with AZQ-., rather than with O2-. or HO., for thiol oxidation was not affected significantly by superoxide dismutase, and GS. formation was insensitive to catalase. In addition, GSH suppressed the e.p.r. signal attributed to AZQ-.. No glutathionyl-quinone conjugate was detected during the DT-diaphorase-catalysed reduction of AZQ; although the chemical requirements for alkylation were partly fulfilled (quinone ring aromatization and acid-assisted aziridinyl ring opening), the negligible dissociation of GSH (GS(-)+H+ in equilibrium with GSH) at low pH prevented any nucleophilic addition to occur. Therefore the redox transitions of AZQ during DT-diaphorase catalysis seemed to be centred on the semiquinone species, the fate of which was inversely affected by catalytic amounts of superoxide dismutase and large amounts of GSH: the former enhanced AZQ-. autoxidation and the latter favoured AZQ-. reduction. Accordingly, superoxide dismutase and GSH suppressed the semiquinone e.p.r. signal. These results are discussed in terms of three interdependent redox transitions (comprising one-electron transfer reactions involving the quinone, oxygen and the thiol) and the thermodynamic and kinetic properties of the reactions involved.

Bioreductive activation of mitomycin C by DT-diaphorase

The role of DT-diaphorase (DTD, EC 1.6.99.2) in the bioreductive activation of mitomycin C was examined using purified rat hepatic DTD. The formation of adducts with reduced glutathione (GSH), binding of [3H]mitomycin C to DNA, and mitomycin C-induced DNA interstrand cross-linking were used as indicators of bioactivation. Mitomycin C was metabolized by DTD in a pH-dependent manner with increasing amounts of metabolism observed as the pH was decreased from 7.8 to 5.8. The major metabolite observed during DTD-mediated reduction of mitomycin C was 2,7-diaminomitosene. GSH adduct formation, binding of [3H]mitomycin C and mitomycin C-induced DNA interstrand cross-linking were observed during DTD-mediated metabolism. In agreement with the pH dependence of metabolism, increased bioactivation was observed at lower pH values. Temporal studies and experiments using authentic material showed that 2,7-diaminomitosene could be further metabolized by DTD resulting in the formation of mitosene adducts with GSH. DNA cross-linking during either chemical (sodium borohydride) or enzymatic (DTD) mediated reduction of mitomycin C could be observed at pH 7.4, but it increased as the pH was decreased to 5.8, showing the critical role of pH in the cross-linking process. These data provide unequivocal evidence that the obligate two-electron reductase DTD can bioactivate mitomycin C to reactive species which can form adducts with GSH and DNA and induce DNA cross-linking. The use of mitomycin C may be a viable approach to the therapy of tumors high in DTD activity, particularly when combined with strategies to lower tumor pH.

Potentiation of alkylating chemotherapy by dual function nitrofurans in multi-cell spheroids and solid tumors

The cytotoxicity and chemosensitizing potential of four dual function nitrofurans was determined in human HT-29 multi-cell spheroids and rodent KHT sarcoma solid tumors. Spheroids were treated with a range of doses of the bioreductive drugs for a period of up to 48 h and the extent of cell kill was assessed at various times after treatment. Cytotoxicity was determined using a clonogenic cell-survival assay. The results demonstrated that two of the nitrofurans were even more toxic to spheroid cells than was the potent bioreductive nitroimidazole aziridine RSU 1069. The dose of the nitrofuran which, after a 24-h exposure, led to a survival value between 0.5 and 1.0, then was chosen for subsequent studies aimed at assessing the ability of these agents to potentiate the efficacy of the nitrosourea CCNU. Exposure to this chemotherapeutic agent was for a period of 1 h. The results indicated that all four dual function nitrofurans enhanced the cell killing of the conventional chemotherapeutic agent by factors ranging from 1.1 to 1.7. Subsequent studies evaluated the therapeutic benefit of combining these bioreductive agents and CCNU in KHT sarcoma-bearing C3H/HeJ mice. The nitrofurans were administered i.p. 0.5 h prior to the chemotherapy and tumor response was assessed by measuring the survival of clonogenic KHT cells 22-24 h after treatment. Normal tissue toxicity was determined using a bone marrow stem cell (CFU-GM) assay. Combining these bioreductive agents with CCNU increased the tumor cell kill by factors of 1.2 to 1.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of mitomycin C on the uptake of photofrin II in a human colon adenocarcinoma cell line

Flow cytometry (FCM) was used to investigate the effect of mitomycin C (MC) on the cellular uptake of Photofrin II (PII) in a cultured human colon adenocarcinoma cell line (WiDr). The surface area of the cells increased as they passed through the cell cycle from G0/G1 to G2/M phase. MC retarded the cells in G2/M phase and enhanced the surface area of the cells. A 1.3-2.3-fold increase in the cell surface area and a 1.3-2.7-fold increase in the cellular uptake of PII in the tumor cells was observed after 2 h-8 h incubation with MC. Within each sample, an almost linear relationship between the intensity of PII fluorescence in the cells and the surface area of the cells was found. However, for the cells incubated with MC the surface area was not the only determinant of PII uptake. Effects of MC on the cell cycle, the cell surface area and the permeability of the cell membrane are suggested as possible reasons for the increase of cellular uptake of PII in the tumor cells.

Mitomycin-induced pulmonary toxicity: case report and review of the literature

OBJECTIVE

This report describes a case of mitomycin-induced pulmonary toxicity and reviews the incidence of this adverse effect, reported patterns of toxicity and associated dosages of the drug, and the use of corticosteroids in the management of pulmonary toxicity.

DATA SOURCES

Information about our patient was obtained in part from the medical chart; we had also treated him personally in the past. We conducted a MEDLINE search of the English language literature (restricted to human studies) from 1966 to 1991 and manually searched Index Medicus for current information.

STUDY SELECTION

All case reports that described pulmonary toxicity possibly associated with mitomycin were reviewed.

DATA EXTRACTION

Studies were evaluated for the dosages of mitomycin given to patients, the nature and onset of symptoms, management course, and corticosteroid use.

DATA SYNTHESIS

Our case is similar to others described in the literature. The incidence of mitomycin-induced pulmonary toxicity has been reported to range from 2 to 38 percent. Concurrent vinca alkaloid administration may potentiate the risk of an acute pulmonary insult secondary to mitomycin use. The toxicity is usually of slow onset and the average total dosage of drug implicated is 78 mg. A formal evaluation of corticosteroid treatment has not been performed, but various authors have reported success with different regimens.

CONCLUSIONS

The incidence of pulmonary toxicity associated with mitomycin is unpredictable, but more likely to occur at higher dosages. Treatment with corticosteroids is encouraged to improve pulmonary response.

Cytotoxicity of dual function nitrofurans in rodent and human tumor cells

The efficacy and selective hypoxic cell cytotoxicity of four dual function nitrofurans and two nitroimidazole-aziridines was determined in human (A549, HT-29) and rodent (KHT/iv) tumor cells. All bioreductive compounds were found to be less effective at killing human than mouse tumor cells (approximately 2-6-fold). This reduced cytotoxicity in the human tumor cells occurred irrespective of the state of oxygenation. In addition, the degree of selective toxicity toward hypoxic cells or the cytotoxicity factor (CF), defined as the ratio of the surviving fraction in air to that under hypoxic conditions, was (a) greater for the nitroimidazole-aziridines than for the nitrofurans and (b) less in the human than the rodent tumor cell lines investigated. For example, CF values in A549 or HT-29 cells typically were 2-4-fold lower than those determined in KHT/iv cells. This reduction in the CF in the human cells resulted from a greater loss in the hypoxic toxicity than in the aerobic toxicity when compared with the rodent cells.

Addition of mitomycin C to cis-diamminedichloroplatinum(II)/hyperthermia/radiation therapy in the FSaIIC fibrosarcoma

Hyperthermia (temperatures greater than or equal to 42 degrees C) is used clinically to improve the effectiveness of radiation therapy and, although therapeutic gains have been reported, efficacy is limited when tumours are large and/or radiation tolerance is reduced. In order to improve the utility of the hyperthermia/radiation combination we have tested the addition of cisplatin (CDDP) in the laboratory and in the clinic. Our clinical studies have shown that the CDDP/hyperthermia/radiation combination is tolerable and effective, but laboratory investigations demonstrated a relative lack of cytotoxicity in the hypoxic tumour subpopulation. In order to improve the effectiveness of the CDDP/hyperthermia/radiation combination against hypoxic cells we have evaluated the addition of mitomycin C, a hypoxic cell cytotoxic agent to this combination. Mitomycin C (5 mg/kg) i.p. produced a tumour growth delay (TGD) of about 5.3 days in the FSaIIC murine fibrosarcoma; hyperthermia (43 degrees C x 30 min) caused only about 1.4 day TGD and the combination of mitomycin C followed immediately by hyperthermia caused a TGD of about 8.6 days. CDDP (5 mg/kg) i.p. followed by hyperthermia and then 3 Gy on day 1 only of a 5 day x 3 Gy radiation protocol produced a TGD of about 25 days. With the addition of mitomycin C just before CDDP a TGD of about 44 days resulted. Whole tumour excision experiments demonstrated that mitomycin C was highly interactive with CDDP at 37 degrees C and was dose-modifying. When used with CDDP and hyperthermia, however, mitomycin C added little additional cytotoxicity. Hoechst 33342 dye diffusion-determined tumour subpopulation studies indicated a marked effect of the addition of mitomycin C in the dim (enriched in hypoxic cells) subpopulation and nearby equal cytotoxicity in both bright (enriched in euoxic cells) and dim cells resulted. These investigations suggest considerable potential therapeutic efficacy to the addition of mitomycin C to the CDDP/hyperthermia/radiation combination.

Glutathionyl- and hydroxyl radical formation coupled to the redox transitions of 1,4-naphthoquinone bioreductive alkylating agents during glutathione two-electron reductive addition

The kinetic parameters of the redox transitions subsequent to the two-electron transfer implied in the glutathione (GSH) reductive addition to 2- and 6-hydroxymethyl-1,4-naphthoquinone bioalkylating agents were examined in terms of autoxidation, GSH consumption in the arylation reaction, oxidation of the thiol to glutathione disulfide (GSSG), and free radical formation detected by the spin-trapping electron spin resonance method. The position of the hydroxymethyl substituent in either the benzenoid or the quinonoid ring differentially influenced the initial rates of hydroquinone autoxidation as well as thiol oxidation. Thus, GSSG- and hydrogen peroxide formation during the GSH reductive addition to 6-hydroxymethyl-1,4-naphthoquinone proceeded at rates substantially higher than those observed with the 2-hydroxymethyl derivative. The distribution and concentration of molecular end products, however, was the same for both quinones, regardless of the position of the hydroxymethyl substituent. The [O2]consumed/[GSSG]formed ratio was above unity in both cases, thus indicating the occurrence of autoxidation reactions other than those involved during GSSG formation. EPR studies using the spin probe 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) suggested that the oxidation of GSH coupled to the above redox transitions involved the formation of radicals of differing structure, such as hydroxyl and thiyl radicals. These were identified as the corresponding DMPO adducts. The detection of either DMPO adduct depended on the concentration of GSH in the reaction mixture: the hydroxyl radical adduct of DMPO prevailed at low GSH concentrations, whereas the thiyl radical adduct of DMPO prevailed at high GSH concentrations. The production of the former adduct was sensitive to catalase, whereas that of the latter was sensitive to superoxide dismutase as well as to catalase. The relevance of free radical formation coupled to thiol oxidation is discussed in terms of the thermodynamic and kinetic properties of the reactions involved as well as in terms of potential implications in quinone cytotoxicity.

Cytostatic synergism between bromodeoxyuridine, bleomycin, cisplatin and chlorambucil demonstrated by a sensitive cell kinetic assay

Bromodeoxyuridine/Hoechst flow cytometry was used to analyse the interference of common cytostatic agents with cell activation and cell cycle progression of human B-cell lines. Bleomycin impaired both cell activation and G2 transit, the latter effect being oxygen dependent. The DNA alkylating agents cyclophosphamide, chlorambucil and mitomycin C caused G2 arrest, whereas cisplatin arrested cells in both the S and G2 phase of the cell cycle. Vinblastin interfered with mitosis, but in addition arrested cells in all phases of the cell cycle. The growth inhibitory action of bleomycin, cisplatin and chlorambucil was dependent upon the bromodeoxyuridine (BrdU) concentration in the culture medium. No interaction was found between BrdU and cyclophosphamide, mitomycin C and vinblastin. The cell cycle kinetic mechanism of the interaction between BrdU and bleomycin, cisplatin and chlorambucil was a potentiation of the G2 arrest. In conclusion, BrdU may be useful in clinical chemotherapy as a chemosensitizer for selected cytostatic agents.

Enhancement of chemotherapy and nitroimidazole-induced chemopotentiation by the vasoactive agent hydralazine

Nitroimidazoles have been shown to be potent sensitisers of certain clinically active chemotherapeutic agents. This process of chemopotentiation has been shown to be hypoxia-mediated. The present studies evaluated whether increasing the level of hypoxia in the tumour tissue, by treatment with the vasoactive agent hydralazine, could modify the chemosensitising ability of nitroheterocyclics. Administering either misonidazole or RSU 1164 before, or hydralazine after, the chemotherapeutic agents melphalan, cyclophosphamide or the nitrosourea CCNU, increased the extent of cell kill in both the KHT sarcoma and RIF-1 tumour. However, even greater enhancements could be achieved when hydralazine was used in treatment protocols in which a nitroimidazole was combined with chemotherapy. For example, a 5.0 mg kg-1 dose of hydralazine given 30 min after melphalan, or a 2.5 mmol kg-1 dose of misonidazole administered 30 min before melphalan, increased, compared to melphalan alone, the resultant tumour cell kill by factors of approximately 1.9 and approximately 1.3, respectively. By comparison, when hydralazine was given after the melphalan plus misonidazole combination, treatment efficacy was enhanced approximately 3-fold compared to melphalan alone. Yet in contrast to the results of the tumour response studies, the inclusion of hydralazine did not increase the bone marrow toxicity associated with the chemotherapeutic agent when used alone or in conjunction with a nitroimidazole. The results, therefore, imply that the addition of hydralazine to the chemotherapy, or chemotherapy-sensitiser protocol, led to a therapeutic advantage.

Addition of a hypoxic cell selective cytotoxic agent (mitomycin C or porfiromycin) to Fluosol-DA/carbogen/radiation

In an effort to develop effective combination treatments for use with radiation against solid tumors, the cytotoxic effects of the addition of mitomycin C or porfiromycin on treatment with Fluosol-DA/carbogen (95% O2/5% CO2) breathing and radiation in the FSaIIC tumor system were studied. In vitro mitomycin C and porfiromycin were both preferentially cytotoxic toward hypoxic FSaIIC cells. After in vivo exposure, however, the cytotoxicity of mitomycin C toward single cell tumor suspensions obtained from whole tumors was exponential over the dose range studied, but for porfiromycin a plateau in cell killing was observed. With Fluosol-DA/carbogen breathing and single dose radiation, addition of either mitomycin C or porfiromycin increased the tumor cell kill achieved at 5 Gy by approximately 1.2 and 1.0 logs, respectively. Less effect was seen with addition of the drugs at the 10 and 15 Gy radiation doses. In tumor growth delay experiments, the addition of either mitomycin C or porfiromycin to Fluosol-DA/carbogen breathing and radiation resulted in primarily an additive increase in tumor growth delay. The survival of Hoechst 33342 dye-selected tumor cell subpopulations indicated that Fluosol-DA/carbogen breathing increased the cytotoxicity of radiation (10 Gy) more in the bright cell subpopulation (4-fold) than in the dim cell subpopulation (2-fold) resulting in an overall 4-fold sparing of the dim subpopulation. Mitomycin C and porfiromycin were both more toxic toward the dim cell subpopulations. Addition of mitomycin C or porfiromycin to Fluosol-DA/carbogen breathing and radiation (10 Gy) resulted in a primarily additive effect of the drugs and radiation killing in both tumor cell subpopulations. Thus, with mitomycin C/Fluosol-DA/carbogen and radiation there was a 2-fold sparing of dim cells and with porfiromycin in the combined treatment a 1.6-fold sparing of the dim cell population. Our results indicate that treatment strategies directed against both oxic and hypoxic tumor subpopulations can markedly increase the tumor cell kill achieved by radiation.

Reductive activation of potential antitumor bis(aziridinyl)benzoquinones by xanthine oxidase: competition between oxygen reduction and quinone reduction

The reduction of a series of 2,5-bis(1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives with various 3,6 substituents by the enzyme xanthine oxidase has been studied. The reduction rate has been assayed by measuring the rate of reduction of cytochrome c, which is very efficiently reduced by reduced BABQ species. Under nitrogen, the reduction rate correlated with the quinone reduction potential and steric parameters. Comparing reduction rates under nitrogen and air demonstrates that at BABQ concentrations greater than 25 microM the competition for electrons from xanthine oxidase between oxygen and the BABQ derivative is dominated by the latter. This is also confirmed by the effect of superoxide dismutase (SOD): in the presence of a BABQ derivative, cytochrome c reduction can be totally inhibited by SOD, although the required amount of SOD depends on the redox potential of the quinones. This indicates that SOD causes the equilibrium between semiquinone and superoxide to shift, resulting in a decrease of the semiquinone concentration. It is concluded that reduction by xanthine oxidase is a simple and effective method for reducing aziridinylbenzoquinones.

Trimodality therapy (drug/hyperthermia/radiation) with BCNU or mitomycin C

To develop multimodality treatment combinations with high curative potential in advanced local disease, BCNU (N,N'-bis(2-chloroethyl)-N-nitro-sourea) and mitomycin C were tested with hyperthermia and radiation in the FSaIIC fibrosarcoma system. Growth delay experiments demonstrated that, while neither BCNU nor mitomycin C produced dose modification of the radiation response, and hyperthermia (43 degrees C, 30 min) produced only a moderate dose modification (1.4 +/- 0.2), the combination of BCNU plus hyperthermia resulted in a radiation dose modifying factor (DMF) of 1.9 +/- 0.3, and mitomycin C plus hyperthermia a dose modifying factor of 2.1 +/- 0.4. Tumor cell survival over a range of BCNU doses administered i.p. immediately before hyperthermia resulted in a dose modifying factor of 1.8 +/- 0.2 versus drug alone. With mitomycin C however, giving the drug immediately prior to heating produced a dose modifying factor due to hyperthermia of only 1.2 +/- 0.10. Hoechst 33342 diffusion was used to separate tumor cells into predominately oxic and hypoxic subpopulations. Administration of the single, double and trimodality therapies showed that BCNU was 3.1-fold more toxic to the oxic versus the hypoxic cells whereas mitomycin C was 3.5-fold more toxic to the hypoxic compared to the oxic cells. Hyperthermia was 1.4-fold more toxic to the hypoxic versus the oxic cells whereas 10 Gy of radiation was 2.0-fold more toxic to the oxic compared to the hypoxic cells. The combination of hyperthermia plus radiation increased killing in both Hoechst dye defined subpopulations but relatively more in the hypoxic cells in which killing was 1.8-fold greater than in the oxic cells. When heat was delivered immediately after i.p. administration of the anticancer drugs, hyperthermia increased BCNU killing in the oxic cells by 17.2-fold versus 4.4-fold in the hypoxic cells and increased mitomycin-killing by 2.6-fold in the oxic cells versus 17-fold in the hypoxic cells. Use of the full trimodality treatment, given in the sequence drug (BCNU, 50 mg/kg or mitomycin-C 5 mg/kg)----heat (43 degrees C, 30 min)----radiation (10 Gy) produced a 3 log kill in the oxic cells versus a 2 log kill in the hypoxic cells with BCNU and a 2 log kill in the oxic cells versus a 3 log kill in the hypoxic cells with mitomycin C. These results indicate that the use of selected anticancer drugs with hyperthermia and radiation can produce highly cytotoxic interactions which markedly modify the effect of radiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Efficacy of mitomycin C against alveolar Echinococcus

Mitomycin C was tested against the metacestode stage of Echinococcus multilocularis in jirds. The efficacy of 61-76% was achieved within 1 month of treatment with a total dose of 0.04, 0.08 or 0.3 mg.

Covalent binding studies on the 14C-labeled antitumor compound 2,5-bis(1-aziridinyl)-1,4-benzoquinone. Involvement of semiquinone radical in binding to DNA, and binding to proteins and bacterial macromolecules in situ

2,5-Bis(1-aziridinyl)-1,4-benzoquinone (BABQ) is a compound from which several antitumour drugs are derived, such as Trenimone, Carboquone and Diaziquone (AZQ). The mechanism of DNA binding of BABQ was studied using 14C-labeled BABQ and is in agreement with reduction of the quinone moiety and protonation of the aziridine ring, followed by ring opening and alkylation. The one-electron reduced (semiquinone) form of BABQ alkylates DNA more efficiently than two-electron reduced or non reduced BABQ. Covalent binding to polynucleotides did not unambiguously reveal preference for binding to specific DNA bases. Attempts to elucidate further the molecular structure of DNA adducts by isolation of modified nucleosides from enzymatic digests of reacted DNA failed because of instability of the DNA adducts. The mechanism of covalent binding to protein (bovine serum albumin, BSA) appeared to be completely different from that of covalent binding to DNA. Binding of BABQ to BSA was not enhanced by reduction of the compound and was pH dependent in a way that is opposite to that of DNA alkylation. Glutathione inhibits binding of BABQ to BSA and forms adducts with BABQ in a similar pH dependence as the protein binding. The aziridine group therefore does not seem to be involved in the alkylation of BSA. Incubation of intact E. coli cells, which endogenously reduce BABQ, resulted in binding to both DNA and RNA, but also appreciable protein binding was observed.

Study of the redox properties of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) and its glutathionyl conjugate in biological reactions: one- and two-electron enzymatic reduction

Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone), the basic unit of several tetracyclic antitumor antibiotics, and its glutathione conjugate were reduced by the one- and two-electron transfer flavoproteins NADPH-cytochrome P450 reductase and DT-diaphorase to their semi- and hydroquinone forms, respectively. Kinetic studies performed on purified DT-diaphorase showed the following results: KNADPHm = 68 microM, KQuinonem = 0.92 microM, and Vmax 1300 nmol X min-1 X microgram enzyme-1. Similar studies performed on purified NADPH-cytochrome P450 reductase indicated a lower KNADPHm (10.5 microM) and higher KQuinonem (2.3 microM). The Vmax values were 20-fold lower (46 nmol X min-1 X micrograms enzyme-1) than those observed with DT-diaphorase. DT-diaphorase reduced the naphthazarin-glutathione conjugate with an efficiency 5-fold lower than that observed with the parent quinone. The nucleophilic addition of GSH to naphthazarin proceeded with GSH consumption at rates slower than those observed with 1,4-naphthoquinone and its monohydroxy derivative, 5-hydroxy-1,4-naphthoquinone. The initial rate of GSH consumption during these reactions did not vary whether the assay was carried out under anaerobic or aerobic conditions. Autoxidation accompanied the DT-diaphorase and NADPH-cytochrome P450 reductase catalysis of naphthazarin and its glutathionyl adduct as well as the 1,4-reductive addition of GSH to naphthazarin. Superoxide dismutase at catalytic concentrations (nM range) enhanced slightly (1.1- to 1.6-fold) the autoxidation following the enzymatic catalysis of naphthazarin. Autoxidation during the GSH reductive addition to 1,4-naphthoquinones decreased with increasing number of -OH substituents, 1,4-naphthoquinone greater than 5-hydroxy-1,4-naphthoquinone greater than 5,8-dihydroxy-1,4-naphthoquinone, thus revealing that the contribution of redox transitions other than autoxidation, e.g., cross-oxidation, to the decay of the primary product of nucleophilic addition increases with increasing number of -OH substituents. Superoxide dismutase enhanced substantially the autoxidation of glutathionyl-naphthohydroquinone adducts, thereby affecting only slightly the total GSH consumed and GSSG formed during the reaction. The present results are discussed in terms of the relative contribution of one- and two-electron transfer flavoproteins to the bioreductive activation of naphthazarin and its glutathionyl conjugate as well as the importance of autoxidation reactions in the mechanism(s) of quinone cytotoxicity.

Microsomal superoxide anion production and NADPH-oxidation in a series of 22 aziridinylbenzoquinones

Several 2,5-bis(1-aziridinyl)-1,4-benzoquinones (BABQs) can be activated to alkylating species by reduction of the quinone moiety. On the other hand, cytotoxicity of these compounds can be induced by redox cycling. A series of BABQs and their methylated analogues (BMABQs) with different substituents at the 3- and 6-position was synthesized in order to investigate the influence of the substituents on the reduction of the quinone moiety and on the generation of superoxide anion radicals with rat liver microsomes. Superoxide anion production (SAP) ranged from 3.7 +/- 0.1 to 742 +/- 74 nmoles/min/mg protein with quinone concentrations of 10 nmoles/ml. NADPH-oxidation was measured under the same conditions and it correlated well (r = 0.88, P less than 0.001) with SAP. It ranged from 1.4 +/- 0.2 to 494 +/- 60 nmoles/min/mg protein. SAP for 22 B(M) ABQs showed a good correlation with the summated electronic substituent constant sigma para.total (r = 0.86, P less than 0.001). It can be concluded that superoxide anion production by 22 B(M)ABQs in rat liver microsomes can be predicted from structural features of the compounds.

Randomized clinical trial of mitomycin C as an adjunct to radiotherapy in head and neck cancer

A randomized prospective clinical trial was carried out to assess the usefulness of the addition of mitomycin C to radiation therapy used alone or in combination with surgery for the treatment of squamous cell carcinoma of the head and neck region. One hundred and twenty patients with biopsy proven tumor of the oral cavity, oropharynx, larynx, hypopharynx, and nasopharynx were randomly assigned to receive or not receive mitomycin C; all other aspects were similar in the two treatment groups. One hundred and seventeen patients were evaluable with a median follow-up time of greater than 5 years. Acute and chronic normal tissue radiation reactions were equivalent in the two treatment groups. Hematologic and pulmonary toxicity were observed in the drug treated patients. Actuarial disease-free survival at 5 years was 49% in the radiation therapy group and 75% in the radiation therapy plus mitomycin C group, p less than 0.07. Local recurrence-free survival was 66% in the radiation therapy group and 87% in the radiation therapy plus mitomycin C group, p less than 0.02. The findings demonstrate that mitomycin C can be administered safely as an adjunct to radiation therapy in the treatment of head and neck cancer. The drug improves local tumor control without enhancing normal tissue radiation reactions.

The chemosensitizing and cytotoxic effects of RSU 1164 and RSU 1165 in a murine tumor model

RSU 1069, the lead compound in a series of nitroimidazoles containing an alkylating aziridine function, has been shown to be a potent radiosensitizer and chemopotentiator both in vitro and in vivo. However, this agent also demonstrates significant in situ toxicity. Recently it has been shown that less toxic analogues of RSU 1069 can be produced by the introduction of alkyl substituents to moderate the reactivity of the aziridine function. The present investigations were undertaken to evaluate the in vivo cytotoxicity and chemosensitizing efficacy of two such analogues, RSU 1164 and RSU 1165. All experiments were performed with KHT sarcomas grown intra-muscularly. In the cytotoxicity studies, a range of sensitizer doses was utilized whereas in the chemopotentiation investigations a fixed sensitizer exposure was combined simultaneously with a range of doses of the nitrosourea CCNU. In both studies, tumor cell survival was determined 22-24 hr after treatment using a soft agar clonogenic assay. Normal tissue toxicity in the chemopotentiation studies was assessed by bone marrow CFU-S assay. Both analogues were found to be significantly less cytotoxic to KHT sarcoma cells than RSU 1169 (a factor of 4-6 in dose at 50% cell survival). Combining a 1.0 to 2.0 mmol/kg dose of RSU 1164 or RSU 1165 with a range of doses of CCNU increased tumor cell killing by a factor of 1.5-1.6 but did not enhance bone marrow stem cell toxicity. The addition of either sensitizer to CCNU treatment therefore led to a significant therapeutic benefit.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

Modification of DNA by mitomycin C in cancer patients detected by 32P-postlabeling analysis

DNA adducts of mitomycin C (MMC) were detected by 32P-postlabeling analysis in both surgical specimens and an autopsy sample of the liver of patients with hepatocellular carcinoma who had received chemotherapy with MMC. Four kinds of adducts were detected in all 6 patients treated with MMC. These adducts had identical chromatographic mobilities to those of adducts in the liver of rats treated with MMC, but 1 additional adduct was detected in rat liver. In patients treated with MMC, about 3 adducts/10(8) nucleotides were found 4 days after MMC treatment, and 1 adduct/10(8) nucleotides 14 days after treatment and the latter level was maintained for up to 56 days. MMC-DNA adducts were also detected in peripheral blood leukocytes from a patient 1 and 7 days after MMC treatment, at levels of 1 and 0.6 adduct/10(8) nucleotides, respectively. These results suggest the tumor-initiating activity of MMC in humans.

Characterization of radiation resistant hypoxic cell subpopulations in KHT sarcomas. (II). Cell sorting

Hypoxic cells in KHT sarcomas were characterized using fluorescence activated cell sorting based on the diffusion properties of the fluorochrome Hoechst 33342. Tumour-bearing female C3H/HeJ mice were injected i.v. with 10 micrograms g-1 Hoechst 33342 and the cells derived from the tumours sorted on the basis of their staining intensities. For each sorted fraction the DNA histogram was evaluated using FCM analysis. The results indicated that the bright and dim cells were not equally distributed about the cell cycle. For example, a greater proportion of S phase cells were in the bright subpopulations whereas the dim subpopulations contained an increased proportion of cells in G1. When the tumours were irradiated with a single dose of radiation prior to cell sorting, the dim cells survived preferentially. Dose response curves for the 20% most dim and 20% most bright cells, sorted on the basis of fluorescence intensity, then were determined. The survival curves of the dim and bright cells were found to have slopes similar to those of KHT cells irradiated in situ in dead animals or in vitro under fully oxic conditions, respectively. In addition, when KHT sarcoma-bearing mice were given a 2.5 mmol kg-1 dose of misonidazole (MISO) prior to irradiation and cell sorting, the dim subpopulation was sensitized whereas the bright subpopulation was not. These findings suggest that (i) compared to well-oxygenated areas, hypoxic regions of KHT tumours contain a smaller percentage of cells actively proliferating and (ii) Hoechst 33342 sorting may allow the detailed in situ evaluation of agents acting directly against hypoxic cells in solid tumours.

Mechanism of monofunctional and bifunctional alkylation of DNA by mitomycin C

The relative amounts of monofunctional and bifunctional alkylation products of DNA with mitomycin C (MC) depend on whether one or both masked alkylating functions of MC are activated reductively; adduct 8 is the result of one function and adducts 7 and 9, formed as a pair, are the result of both functions being activated [Tomasz, M., Lipman, R., Chowdary, C., Pawlak, J., Verdine, G. L., & Nakanishi, K. (1987) Science (Washington, D.C.) 235, 1204-1208]. To determine the mechanism governing this differential reactivity of MC with DNA, MC-Micrococcus luteus DNA complexes formed under varying conditions in vitro were digested to nucleosides and adducts. Adduct distribution, analyzed by high-performance liquid chromatography, served as the measure of monofunctional and bifunctional activation. H2/PtO2 and xanthine oxidase/reduced nicotinamide adenine dinucleotide (NADH) activated MC mostly monofunctionally, and Na2S2O4 activated the drug bifunctionally under comparable conditions. Excess MC selectively suppressed, but excess PtO2 selectively promoted, bifunctional activation by H2/PtO2; excess xanthine oxidase and/or NADH also had promoting effects. O2 tested in the Na2S2O4 system was inhibitory. 10-Decarbamoyl-MC acted strictly monofunctionally under all conditions. Monoadducts bound to DNA were converted to bis adducts upon rereduction. A mechanism with the following features was derived: (i) Activation of MC at C-1 and C-10 is sequential (C-1 first). (ii) A one-time reduction is sufficient for both. (iii) Activation of the second function may be selectively inhibited by kinetic factors or O2. (iv) 7 and 9 are coproducts of bifunctional activation; their ratio depends on the DNA base sequence. (v) Activation of the second function involves an iminium intermediate. Direct applications to the action of MC in vivo are discussed.

Molecular mechanisms for the hypoxia-dependent activation of 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233)

The reduction of the hypoxic cell toxin 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) was investigated using pulse radiolysis, radiation chemical reduction, and xanthine oxidase. Evidence was found that the one-electron reduction product of the parent compound is an oxidizing radical that caused single- and double-strand breaks in plasmid DNA and that produced a malondialdehyde-like thiobarbituric acid adduct from 2-deoxy-D-ribose. Possible forms of the reactive radical, either carbon- or nitrogen-centered, are suggested. The "natural" lifetime of the radical was sufficiently long that it could diffuse over significant distances within hypoxic cells and thus inflict oxidative damage on cellular targets. The radical reacted with O2 at a rate comparable to those of the nitroimidazoles misonidazole and metronidazole. Thus, the selectivity for hypoxic cells is probably due to the elimination of "futile" reduction when the cellular oxygen concentration is sufficiently low.

Activation mechanisms to chemical toxicity

The pathobiology of chemical toxicity may involve "acute lethal injury" (necrosis), "autoxidative injury" (oxygen toxicity), "immunological injury" (neoantigen formation), and malignancy. Toxic chemicals may be activated by reduction, conjugation, radical formation, or oxidation. Oxidative activation may be effected by cytochromes P-450/P-448, flavoprotein monooxygenases, or hydroxyl radicals. The alternative pathways of oxidative metabolism of toxic chemicals, namely, detoxication and activation, are catalysed by the phenobarbital-induced cytochromes P-450 and by the 3-methylcholanthrene-induced cytochromes P-448 respectively. Oxidative metabolism by cytochromes P-450 is followed by conjugation and detoxication, whereas oxidative metabolism by cytochromes P-448 yields reactive intermediates which are not readily conjugated, and thus react with vital intracellular macromolecules, resulting in necrosis, redox cycling and oxygen radical formation, neoantigen production, and mutations. The molecular dimensions of specific substrates, inhibitors and inducers of the PB-cytochromes P-450 indicate that they are globular and are different from those of the cytochromes P-448 which are planar, suggesting that the active sites of the two families of enzymes are different. Oxidative metabolism of planar substrates of cytochromes P-448 results in conformationally-hindered oxygenations, which inhibits subsequent conjugations. Cytochrome P-448 activity may be quantified by the oxidative deethylation of 7-ethoxyresorufin which, unlike benzo(a)pyrene hydroxylation (AHH) is a specific reaction for this family of enzymes. Oxidative metabolism of chemicals varies inversely with the body weight of the animal species, so that chemical toxicity involving oxidative activation, redox cycling, and reactive oxygen is greater the smaller the animal species.

Isolation and structure of a covalent cross-link adduct between mitomycin C and DNA

A DNA cross-link adduct of the antitumor agent mitomycin C (MC) to DNA has been isolated and characterized; the results provide direct proof for bifunctional alkylation of DNA by MC. Exposure of MC to Micrococcus luteus DNA under reductive conditions and subsequent nuclease digestion yielded adducts formed between MC and deoxyguanosine residues. In addition to the two known monoadducts, a bisadduct was obtained. Reductive MC activation with Na2S2O4 (sodium dithionite) leads to exclusive bifunctional alkylation. The structure of the bisadduct was determined by spectroscopic methods that included proton magnetic resonance, differential Fourier transform infrared spectroscopy, and circular dichroism. Formation of the same bisadduct in vivo was demonstrated upon injection of rats with MC. Computer-generated models of the bisadduct that was incorporated into the center of the duplex B-DNA decamer d(CGTACGTACG)2 indicated that the bisadduct fit snugly into the minor groove with minimal distortion of DNA structure. A mechanistic analysis of the factors that govern monofunctional and bifunctional adduct formation is presented.

Increased anti-tumor effect of adriamycin-loaded albumin microspheres is associated with anaerobic bioreduction of drug in tumor tissue

Anti-tumor activity and fate of adriamycin incorporated into biodegradable albumin microspheres was examined in vivo after direct intratumoral injection. Adriamycin in microspherical form displayed superior anti-tumor activity to a comparable dose of drug in solution. This was associated at later time points (40 hr, 50 hr and 72 hr after injection) with higher median parent drug concentrations in tumor tissue (4.1, 3.6, 2.6 micrograms/g respectively for microspheres and 1.6, 1.7 and 1.0 micrograms/g for solution) and the consistent detection of 7-deoxyaglycone metabolites, end products of reduction of adriamycin under anaerobic conditions (1.1, 1.0, 1.0 micrograms/g respectively for microspheres and less than 0.1 micrograms/g at all time points for solution). It is generally considered that the redox properties of anthracyclines are responsible for their toxicity to normal tissues whereas other mechanisms are responsible for antineoplastic activity. In this study we show that inducing metabolism of Adriamycin via reductive pathways is associated with increased anti-tumor effect.