A simple and inexpensive method to control oxygen concentrations within physiological and neoplastic ranges

Traditional methods for regulating oxygen concentration ([O2]) in in vitro experiments over the range found in normal and tumor tissues require the use of expensive equipment to generate controlled gas atmospheres or the purchase of a range of gas cylinders with certified O2 percentages. Here we describe a simple and inexpensive enzymatic method for generating low, precise steady-state [O2] levels that are stable for several hours. This method is particularly applicable to the in vitro study of some classes of hypoxia-targeted antitumor prodrugs and bioreductively activated agents.

1,2-Bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (VNP40101M): II. Role of O 6 -alkylguanine-DNA alkyltransferase in cytotoxicity

PURPOSE

VNP40101M (1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine) is a sulfonylhydrazine prodrug that possesses broad spectrum antitumor efficacy in murine models. VNP40101M activation generates chloroethylating species that alkylate DNA at the O(6)-position of guanine, and a carbamoylating agent, methyl isocyanate, which inhibits O(6)-alkylguanine-DNA alkyltransferase (AGT) in model systems. We determined whether expression of AGT in Chinese hamster ovary (CHO) cells decreased sensitivity to VNP40101M and explored the mechanism of VNP40101M cytotoxicity by employing analogs of VNP40101M that generate reactive intermediates with either carbamoylating or chloroethylating activity.

METHODS

AGT was overexpressed in CHO cells by transfection with an expression vector containing the human AGT gene. Cell lines expressing AGT were employed in clonogenic assays to determine the cytotoxicity of VNP40101M and its analogs.

RESULTS

VNP40101M was more active against AGT-expressing CHO cells than 90CE (1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine), a chloroethylating generator devoid of carbamoylating activity. Furthermore, the greater the degree of AGT expression the more resistance to VNP40101M cytotoxicity. Combination chemotherapy experiments support the conclusions that methyl isocyanate and the chloroethylating species generated from the activation of VNP40101M function synergistically to kill cells.

CONCLUSIONS

The findings support the concept that alkylation of the O(6)-position of guanine residues in DNA is the predominant lesion created by VNP40101M, and that methyl isocyanate resulting from the base-catalyzed activation of VNP40101M inhibits AGT and presumably other enzymes involved in DNA repair, thereby enhancing the yield of the DNA G-C interstrand crosslinks responsible for the antitumor activity of this agent.

1,2-Bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (VNP40101M): I. Direct inhibition of O 6 -alkylguanine-DNA alkyltransferase (AGT) by electrophilic species generated by decomposition

PURPOSE

To investigate the interaction of the electrophilic species generated by the decomposition of the antineoplastic prodrug 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (VNP40101M) on the ability of O(6)-alkylguanine-DNA alkyltransferase (AGT) to repair alkylated O(6)-chloroethylguanine and/or N(1),O(6)-ethanoguanine DNA lesions.

MATERIALS AND METHODS

The contributions of inhibitory electrophilic species generated from VNP40101M towards AGT was assessed using analogues that selectively generated either the chloroethylating or the carbamoylating components of VNP40101M. The activity of AGT was determined from the inhibition of crosslink formation from O(6)-chloroethylguanine and/or N(1),O(6)-ethanoguanine lesions. The half-lives of sulfonylhydrazine derivatives and isocyanates were measured using an acidification assay which gives a change in absorbance proportional to the release or consumption of small quantities of protons.

RESULTS

Both of the reactive components produced by VNP40101M directly inactivated cloned human AGT; the carbamoylating moiety (IC(50) about 13 micro M) was approximately seven- to eight-fold more potent than the alkylating component(s) (IC(50) about 100 micro M). These inhibitory actions were moderated by the addition of naked T5 bacteriophage DNA. Thus, AGT bound to DNA was markedly more resistant than free AGT to these electrophilic species. DNA also blocked the spontaneous loss of AGT activity which occurred upon incubation of this protein under mild conditions.

CONCLUSIONS

The reaction of AGT with the methyl isocyanate generated from the decomposition of VNP40101M increased the net number of crosslinks generated by VNP40101M compared to a sulfonylhydrazine prodrug that formed the equivalent alkylating species in the absence of the cogeneration of methyl isocyanate. These actions may be of significance to the antineoplastic activity of VNP40101M.

Synthesis of halogen-substituted 3-deazaadenosine and 3-deazaguanosine analogues as potential antitumor/antiviral agents

Various 2-halogen-substituted analogues (38, 39, 43 and 44), 3-halogen-substituted analogues (51 and 52), and 2',3'-dihalogen-substituted analogues (57-60) of 3-deazaadenosine and 3-halogen-substituted analogues (61 and 62) of 3-deazaguanosine have been synthesized as potential anticancer and/or antiviral agents. Among these compounds, 3-deaza-3-bromoguanosine (62) showed significant cytotoxicity against L1210, P388, CCRF-CEM and B16F10 cell lines in vitro, producing IC50 values of 3, 7, 9 and 7 microM, respectively. Several 3-deazaadenosine analogues (38, 51, 57 and 59) showed moderate to weak activity against hepatitis B virus.

Inhibition of 20 S and 26 S proteasome activity by lithium chloride: impact on the differentiation of leukemia cells by all-trans retinoic acid

Lithium affects several enzymatic activities, however, the molecular mechanisms of lithium actions are not fully understood. We previously showed that LiCl interacts synergistically with all-trans-retinoic acid to promote terminal differentiation of WEHI-3B D(+) cells, a phenomenon accompanied by the recovery of the retinoid-induced loss of retinoic acid receptor alpha protein pools. Here, we demonstrate the effects of LiCl on proteasome-dependent degradation of retinoic acid receptor alpha proteins. LiCl alone, or in combination with all-trans-retinoic acid, increased cellular levels of ubiquitinated retinoic acid receptor alpha and markedly reduced chymotryptic-like activity of WEHI-3B D(+) 20 S and 26 S proteasome enzymes. Neither KCl nor all-trans-retinoic acid affected enzyme activity, whereas NaCl produced a modest reduction at relatively high concentrations. In addition, LiCl inhibited 20 S proteasome chymotryptic-like activity from rabbits but had no effect on tryptic-like activity of the 26 S proteasome. This effect has significant consequences in stabilizing the retinoic acid receptor alpha protein levels that are necessary to promote continued differentiation of leukemia cells in response to all-trans-retinoic acid. In support of this concept, combination of proteasome inhibitors beta-clastolactacystin or benzyloxycarbonyl-Leu-Leu-Phe with all-trans-retinoic acid increased differentiation of WEHI-3B D(+) cells in a manner that was analogous to the combination of LiCl and all-trans-retinoic acid.

Reversal of mitomycin C resistance by overexpression of bioreductive enzymes in Chinese hamster ovary cells

The clinical utility of antineoplastic agents is limited by the development of drug resistance by tumors. Mitomycin C (MC) is a bacterial product that must be enzymatically reduced to exert anticancer activity. We have demonstrated that expression of the bacterial MC resistance-associated (MCRA) protein in Chinese hamster ovary (CHO) cells confers profound resistance to this antibiotic under aerobic conditions, but not under hypoxia. MCRA produces resistance to MC by redox cycling of the activated hydroquinone intermediate back to the prodrug form. A CHO cell line developed by stepwise exposure to increasing concentrations of MC likewise expressed high level resistance to MC in air, but not under hypoxia. The overexpression of DT-diaphorase and NADPH:cytochrome c (P-450) reductase, two enzymes known to activate MC, restored sensitivity to MC in both MCRA-transfected and drug-selected cell lines. The level of sensitization was proportional to the quantity of enzyme activity expressed, supporting the concept that the levels of these two activating enzymes are important for sensitivity to MC. The findings of resistance to MC in air but not under hypoxic conditions and of restoration of sensitivity to MC by increasing levels of DT-diaphorase activity, properties not adequately explained by other resistance mechanisms (i.e., decreases in MC activation, repair of DNA lesions, and/or drug efflux), support the hypothesis that a functional mammalian homologue of MCRA may be involved in producing resistance to MC.

Erythrocyte membrane ATP binding cassette (ABC) proteins: MRP1 and CFTR as well as CD39 (ecto-apyrase) involved in RBC ATP transport and elevated blood plasma ATP of cystic fibrosis

In addition to the better-known roles of the erythrocyte in the transport of oxygen and carbon dioxide, the concept that the red blood cell is involved in the transport and release of ATP has been evolving (J. Luthje, Blut 59, 367, 1989; G. R. Bergfeld and T. Forrester, Cardiovasc. Res. 26, 40, 1992; M. L. Ellsworth et al., Am. J. Physiol. 269, H2155, 1995; R. S. Sprague et al., Am. J. Physiol. 275, H1726, 1998). Membrane proteins involved in the release of ATP from erythrocytes now appear to include members of the ATP binding cassette (ABC) family (C. F. Higgins, Annu. Rev. Cell Biol. 8, 67, 1992; C. F. Higgins, Cell 82, 693, 1995). In addition to defining physiologically the presence of ABC proteins in RBCs, accumulating gel electrophoretic evidence suggests that the cystic fibrosis transmembrane conductance regulator (CFTR) and the multidrug resistance-associated protein (MRP1), respectively, constitute significant proteins in the red blood cell membrane. As such, this finding makes the mature erythrocyte compartment a major mammalian repository of these important ABC proteins. Because of its relative structural simplicity and ready accessibility, the erythrocyte offers an ideal system to explore details of the physiological functions of ABC proteins. Moreover, the presence of different ABC proteins in a single membrane implies that interaction among these proteins and with other membrane proteins may be the norm and not the exception in terms of modulation of their functions.

Inhibition of DNA cross-linking by mitomycin C by peroxidase-mediated oxidation of mitomycin C hydroquinone

Mitomycin C requires reductive activation to cross-link DNA and express anticancer activity. Reduction of mitomycin C (40 microm) by sodium borohydride (200 microm) in 20 mm Tris-HCl, 1 mm EDTA at 37 degrees C, pH 7.4, gives a 50-60% yield of the reactive intermediate mitomycin C hydroquinone. The hydroquinone decays with first order kinetics or pseudo first order kinetics with a t(12) of approximately 15 s under these conditions. The cross-linking of T7 DNA in this system followed matching kinetics, with the conversion of mitomycin C hydroquinone to leuco-aziridinomitosene appearing to be the rate-determining step. Several peroxidases were found to oxidize mitomycin C hydroquinone to mitomycin C and to block DNA cross-linking to various degrees. Concentrations of the various peroxidases that largely blocked DNA cross-linking, regenerated 10-70% mitomycin C from the reduced material. Thus, significant quantities of products other than mitomycin C were produced by the peroxidase-mediated oxidation of mitomycin C hydroquinone or products derived therefrom. Variations in the sensitivity of cells to mitomycin C have been attributed to differing levels of activating enzymes, export pumps, and DNA repair. Mitomycin C hydroquinone-oxidizing enzymes give rise to a new mechanism by which oxic/hypoxic toxicity differentials and resistance can occur.

Reengineering granulocyte colony-stimulating factor for enhanced stability

Granulocyte colony-stimulating factor is a long-chain cytokine that has both biological and therapeutic applications. It is involved in the production and maturation of neutrophilic progenitor cells and neutrophils and is administered to stimulate the production of white blood cells to reduce the risk of serious infection in immunocompromised patients. We have reengineered granulocyte colony-stimulating factor to improve the thermodynamic stability of the protein, focusing on enhancing the alpha-helical propensity of residues in the antiparallel 4-helix bundle of the protein. These redesigns resulted in proteins with substantially enhanced stability while retaining wild-type levels of biological activity, measured as the ability of the reengineered proteins to stimulate the proliferation of murine myeloid cells transfected with the granulocyte colony-stimulating factor receptor.

Synthesis and biological evaluation of L- and D-configurations of 2',3'-dideoxy-4'-C-methyl-3'-oxacytidine analogues

Novel L- and D-configuration 2',3'-dideoxy-4'-C-methyl-3'-oxacytidine and their 5-fluoro analogues have been synthesized from 1-benzyloxy-2-propanone and L-ascorbic acid in eight steps and evaluated for biological activity.

Transport of fluorescein in MDCKII-MRP1 transfected cells and mrp1-knockout mice

The multidrug resistant-associated protein 1 (MRP1) is a membrane-bound transport protein that is involved in the efflux of organic anions and has been implicated in multidrug resistance in cancer. MRP1 has also been reported to be ubiquitously expressed in normal tissues, including the brain. The presence of functional organic anion transporters in the blood-brain and blood-CSF barriers that influence the distribution of various compounds to the brain has long been known. The purpose of this study was to examine the role of MRP1 in the brain distribution of a model organic anion, fluorescein. The substrate specificity of MRP1 for fluorescein was initially determined by examining the accumulation of fluorescein in MDCKII MRP1-transfected cells. The distribution of fluorescein in the brain was then examined in wild-type and mrp1 gene knockout mice. The results show that in MDCKII MRP1-transfected cells, the accumulation of fluorescein was significantly lower (about 40% lower) than that in wild-type MDCKII cells. MRP1 inhibitors such as probenecid, MK-571, and LY402913 enhanced fluorescein accumulation in MDCKII MRP1-transfected cells to a greater extent than in wild-type MDCKII cells. In an in vivo study, after intravenous injection of fluorescein, the fluorescein brain-to-plasma concentration ratio in mrp1 knockout mice was not significantly different than that in wild-type mice. However, when probenecid was co-administered with fluorescein in wild-type mice, the fluorescein brain-to-plasma ratio was significantly increased (1.5-fold). These findings suggest that fluorescein is a substrate for MRP1. Furthermore, the in vivo study also suggests that MRP1 has a limited role in the transport and distribution of fluorescein in the brain. Therefore, other organic anion transport proteins, including the various isoforms of the MRP family, may be responsible for the accumulation and transport of organic anions in the brain.

Bioreductive metabolism of mitomycin C in EMT6 mouse mammary tumor cells: cytotoxic and non-cytotoxic pathways, leading to different types of DNA adducts. The effect of dicumarol

The six DNA adducts formed in EMT6 mouse mammary tumor cells upon treatment with mitomycin C (MC) fall into two groups: (1) four guanine adducts of MC and (2) two guanine adducts derived from 2,7-diaminomitosene (2,7-DAM), the major reductive metabolite of MC. The two groups of adducts were proposed to originate from two pathways arising from reductive activation of MC: (a) direct alkylation of DNA and (b) formation of 2,7-DAM, which then alkylates DNA. The aim of this study was to test the validity of this proposal and to evaluate the significance of alkylation of DNA by 2,7-DAM. Treatment of the cells with 2,7-DAM itself yielded the same 2,7-DAM-guanine adducts as treatment with MC; however, 2,7-DAM was approximately 100-fold less cytotoxic than MC. The uptake and efflux of 2,7-DAM by EMT6 cells was comparable to that of MC, but 2,7-DAM alkylated DNA with higher efficiency than MC. These results validate the two proposed pathways and show that formation of 2,7-DAM-DNA adducts in MC-treated cells represents a relatively non-toxic pathway of reductive metabolism of MC. A selective stimulatory effect of dicumarol (DIC) on 2,7-DAM-DNA adduct formation in EMT6 cells treated with MC was also investigated. DIC had no effect on alkylation by MC in cell-free systems, nor did it have significant effects on adduct formation or cell survival for cells treated with 2,7-DAM. It is proposed that in the cell DIC stimulates a reductase enzyme located at subcellular sites where the activated MC species has no direct access to DNA and therefore is diverted into the non-cytotoxic pathway, which leads to the formation of 2,7-DAM and its adducts.

Transcriptional regulation of the vitamin D(3) receptor gene by ZEB

The hormone 1,25-dihydroxyvitamin D(3) influences the growth and differentiation of a number of cell types. The functions of 1,25-dihydroxyvitamin D(3) are mediated through the vitamin D(3) receptor (VDR); therefore, an understanding of the regulation of VDR expression is important when considering the molecular mechanisms of differentiation induced by vitamin D(3) and its analogues. ZEB, a Krüppel-type transcription factor known to repress the transcription of several genes, binds to two sites within the VDR promoter and activates the transcription of this receptor in a cell-specific manner. Transfection of ZEB into SW620 colon carcinoma cells results in an up-regulation of the expression of endogenous VDR, confirming the role of ZEB in the transcriptional activation of the VDR gene. The expression of VDR is also induced by c-MYB; thus, ZEB and c-MYB may modulate the levels of VDR expression during differentiation in embryonal development, as well as in cancer cells.

Structure-activity studies of novobiocin analogs as modulators of the cytotoxicity of etoposide (VP-16)

We have previously reported that the antibiotic novobiocin enhanced the toxicity of the anticancer agent etoposide (VP-16) to several drug-sensitive and -resistant tumor cell lines. The increase in VP-16 cytotoxicity produced by novobiocin was not due to the combined effects of these agents on topoisomerase II, but to inhibition by novobiocin of VP-16 efflux, which in turn led to increased accumulation of VP-16 and increased formation of potentially lethal VP-16-stabilized topoisomerase II-DNA covalent complexes. We have now identified novobiocin analogs that are essentially equivalent to novobiocin as inhibitors of the activity of topoisomerase II, but that are more potent than novobiocin (a) as modulators of the cytotoxicity of VP-16 to WEHI-3B leukemia and A549 lung carcinoma cells and (b) in increasing VP-16 accumulation in these cell lines. Thus, removal of the sugar moiety of novobiocin to form novobiocic acid enhanced the potency of the antibiotic as a modulator of VP-16, whereas the substituted coumarin ring alone (U-7587) was devoid of VP-16 modulatory activity. Modifications of the side chain of novobiocin significantly influenced modulatory activity, with cyclonovobiocic acid, which was formed from novobiocic acid by acid-catalyzed cycloaddition, being the most active in enhancing the cytotoxicity of VP-16. The increased potency of novobiocic acid and cyclonovobiocic acid as modulators of VP-16 activity was achieved with no change from novobiocin in the capacity of these analogs to inhibit the catalytic activity of mammalian topoisomerase II, indicating a change in the specificity of these analogs.

1,2-Bis(methylsulfonyl)-1-(2-chloroethyl)-2-(methylamino)carbonylhydrazine (101M): a novel sulfonylhydrazine prodrug with broad-spectrum antineoplastic activity

Our laboratory has synthesized and evaluated the anticancer activity of a number of sulfonylhydrazine DNA modifying agents. As a class, these compounds possess broad spectrum antitumor activity, demonstrating significant activity against a variety of experimental murine tumors, including the P388 and L1210 leukemias, B16 melanoma, M109 lung carcinoma, and M5076 reticulum cell sarcoma, as well as against the human LX-1 lung carcinoma xenograft. The current report describes the activity of a more recently synthesized member of this class, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-(methylamino)carbonylhydrazine (101M). 101M was active in mice against the i.p. implanted L1210 leukemia over a wide range of doses and produced long-term survivors when administered as a single i.p. bolus of 10, 20, 40, 60, or 80 mg/kg, demonstrating a wider margin of safety than the nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Curative therapy was achieved with doses of 101M that did not produce depression of the bone marrow. 101M was also highly effective against the L1210 leukemia when administered by the oral route. The ability of 101M to penetrate the blood-brain barrier and eradicate leukemia cells in the brain was remarkable (>6 log kill). This agent was also curative against L1210 variants resistant to cyclophosphamide, BCNU, or melphalan. Mice implanted with the murine C26 colon carcinoma were also cured by two injections of 10 or 20 mg/kg of 101M. Administration of 101M by two different well-tolerated regimens caused complete regression of established human glioblastoma U251 xenografts in 100% of treated mice, and significant responses were also obtained with 101M against advanced murine M109 lung carcinomas in mice. The broad spectrum of anticancer activity of the sulfonylhydrazine prodrug 101M coupled with the wide range of therapeutic safety exhibited by this agent, makes 101M particularly attractive for further development and clinical evaluation.

The pharmacological phenotype of combined multidrug-resistance mdr1a/1b- and mrp1-deficient mice

Two major classes of plasma membrane proteins that actively extrude a wide range of structurally diverse hydrophobic amphipathic antineoplastic agents from cells, with different mechanisms of action, lead to multidrug resistance. To study the importance of these ATP-binding cassette transporters to the toxicity of cancer chemotherapy agents, we have used mice genetically deficient in both the mdr1a and mdr1b genes [mdr1a/1b(-/-) mice], the mrp1 gene [mrp1(-/-) mice], and the combined genes mdr1a/1b and mrp1 [mdr1a/1b(-/-), mrp1(-/-) mice] and embryonic fibroblasts derived from wild-type mice and from the three gene knockout animals. The consequences of export pump deficiencies were evaluated primarily using vincristine and etoposide. Mice deficient in the three genes, mdr1a/1b and mrp1, exhibited a 128-fold increase in toxicity to vincristine and a 3-5-fold increase in toxicity to etoposide; increased toxicity to embryonic fibroblast cells from triple knockout mice also occurred with vincristine and etoposide. Vincristine, which normally does not express toxicity to the bone marrow and to the gastrointestinal mucosa when used at therapeutic doses, caused extensive damage to these tissues in mdr1a/1b(-/-), mrp1(-/-) mice. The findings indicate that the P-glycoprotein and mrpl are compensatory transporters for vincristine and etoposide in the bone marrow and the gastrointestinal mucosa and emphasize the potential for increased toxicities by the combined inhibition of these efflux pumps.

The leukotriene C(4) transporter MRP1 regulates CCL19 (MIP-3beta, ELC)-dependent mobilization of dendritic cells to lymph nodes

Adaptive immune responses begin after antigen-bearing dendritic cells (DCs) traffic from peripheral tissues to lymph nodes. Here, we show that DC migration from skin to lymph nodes utilizes the leukotriene C(4) (LTC(4)) transporter multidrug resistance-associated protein 1 (MRP1). DC mobilization from the epidermis and trafficking into lymphatic vessels was greatly reduced in MRP1(-/-) mice, but migration was restored by exogenous cysteinyl leukotrienes LTC(4) or LTD(4). In vitro, these cysteinyl leukotrienes promoted optimal chemotaxis to the chemokine CCL19, but not to other related chemokines. Antagonism of CCL19 in vivo prevented DC migration out of the epidermis. Thus, MRP-1 regulates DC migration to lymph nodes, apparently by transporting LTC(4), which in turn promotes chemotaxis to CCL19 and mobilization of DCs from the epidermis.

Synthesis and biological evaluation of L- and D-configuration 1,3-dioxolane 5-azacytosine and 6-azathymine nucleosides

Novel L- and D-configuration dioxolane 5-azacytosine and 6-azathymine nucleosides have been synthesized and evaluated for biological activity. (-)-(2S,4S)-1-[2-(Hydroxymethyl)-1,3-dioxolan-4-yl]-5-azacytosine (6) showed significant activity against HBV, whereas the D-configuration analogue (14) has been found to exhibit potent anti-HIV activity.

Maintenance of retinoic acid receptor alpha pools by granulocyte colony-stimulating factor and lithium chloride in all-trans retinoic acid-treated WEHI-3B leukemia cells: relevance to the synergistic induction of terminal differentiation

Previous studies have demonstrated that combinations of all-trans retinoic acid (ATRA) with either granulocyte-colony stimulating factor (G-CSF) or lithium chloride (LiCl) produced synergistic terminal differentiation of WEHI-3B myelomonocytic leukemia (D(+)) cells. It was found that steady-state retinoic acid receptor alpha (RARalpha) protein levels were markedly reduced in these cells after exposure to ATRA. Because the presence of receptors for a hormone ligand is required for its action, differentiation therapy with ATRA may be self-limiting. The combination of G-CSF with ATRA significantly attenuated the loss of RARalpha protein, and synergistic terminal differentiation occurred. LiCl was more effective than G-CSF in preserving RARalpha pools and synergized with ATRA more strongly than G-CSF. These findings suggested that the prevention of RARalpha protein loss by G-CSF or LiCl in ATRA-treated cells functioned to extend the differentiation response to the retinoid and was responsible, at least in part, for the observed synergism. D(+) cells transfected with an expression plasmid containing RARalpha cDNA had a 6- to 8-fold increase in steady-state RARalpha mRNA compared with vector-transfected cells and showed a 2- to 3-fold increase in RARalpha protein. ATRA caused a reduction, but not a complete loss, of RARalpha protein in these transfectants, which were considerably more responsive than parental D(+) cells to ATRA as a single agent, supporting the concept that the protection of RARalpha pools results in a heightened differentiation response to ATRA.

Interim results of a randomized trial of mitomycin C as an adjunct to radical radiotherapy in the treatment of locally advanced squamous-cell carcinoma of the cervix

The purpose of this study was to determine the efficacy of mitomycin C as an adjunct to radiotherapy for the treatment of locally advanced cervix cancer. Patients with squamous-cell carcinoma of the cervix, stages IB2-IVA, were randomized to receive radiotherapy alone or radiotherapy with concomitant mitomycin C. An initial cohort of 160 patients, having a mean follow-up of 46 months, is analyzed. Intravenous mitomycin C, 15 mg/M(2), was given on the first and sixth week of radiotherapy. The 78 patients in the radiotherapy with mitomycin C group and 82 patients in the radiotherapy alone group have a comparable distribution by age and stage (mean age 47 years; stage IB 3%, IIA 11%, IIB 48%, IIIA 1%, IIIB 36%, IVA 3%). The four-year actuarial survival rates for radiotherapy with mitomycin C and radiotherapy alone were 72% and 56%, respectively (P = 0.13). The four-year actuarial disease-free survival rates for radiotherapy with mitomycin C and radiotherapy alone were 71% and 44%, respectively, a statistically significant difference (P = 0.01). The four-year actuarial local recurrence-free survival rates for patients receiving radiotherapy with mitomycin C and radiotherapy alone were 78% and 63%, respectively (P = 0.11). Differences in four-year distant recurrence-free survival between radiotherapy plus mitomycin C and radiotherapy alone were significantly different at 85% vs. 61% (P = 0.01); this analysis is not adjusted for local failure. On subgroup analysis, stage III-IVA patients had a four-year actuarial disease-free survival of 75% for radiotherapy plus mitomycin C compared with 35% for radiotherapy alone (P = 0.03). There were no treatment- related deaths. Mild hematologic toxicity was seen only in the group treated with mitomycin C. No excess in non-hematologic toxicity has been observed thus far with combined mitomycin C and radiotherapy. In this open phase III trial of mitomycin C as an adjunct to radical radiotherapy for squamous-cell carcinoma of the cervix, there were minimal hematologic effects and no increase in acute radiation reactions. A statistically significant difference in favor of patients receiving mitomycin C is shown for disease-free survival. Thus far, there are trends in favor of those patients receiving mitomycin C for survival and local control. Patients with more advanced stage disease, predominantly stage IIIB, appear to have the most benefit. These preliminary results support the hypothesis that targeting hypoxic cells may lead to a therapeutic enhancement in the radiotherapy of cervix cancer. This trial continues to accrue patients and follow-up data. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 206-223 (2000).

Attenuation of the induced differentiation of HL-60 leukemia cells by mitochondrial chaperone HSP70

The HSP70 family of heat shock proteins, which are involved in development and cellular differentiation, is elevated in various tumor cell lines. To examine the role of these proteins in neoplastic cell differentiation, four members of the HSP70 multiple gene family (i.e., HSP70, HSC70, GRP78, and mtHSP70) were examined during the induced differentiation of HL-60 promyelocytic leukemia cells. Western analyses showed that continuous exposure for 48 h of HL-60 cells to the differentiation-inducing agents, all-trans retinoic acid, 1,25-dihydroxyvitamin D3, or N-methylformamide, resulted in decreases in mitochondrial HSP70 (mtHSP70), with little change in the levels of HSP70, HSC70, and GRP78. To gain information on the role of mtHSP70 in the differentiation process, HL-60 cells were transfected with either murine mthsp70 cDNA or vector alone. Slightly greater than twofold increases in mtHSP70 protein levels occurred in cells transfected with the mthsp70 cDNA. In vector-transfected HL-60 cells, myeloid differentiation, measured as an increase in CD31 expression and nitroblue tetrazolium positivity, was observed following 3-6 days of treatment with each of the three inducing agents. In contrast, cell differentiation induced by each agent was markedly attenuated in mthsp70-transfected HL-60 cells. These findings suggest that a decrease in mtHSP70 is important for the induced differentiation of HL-60 cells.

Phase I and pharmacokinetic study of novobiocin in combination with VP-16 in patients with refractory malignancies

PURPOSE

The coumarin antibiotic novobiocin potentiates the activity of etoposide (VP-16) in vitro by increasing intracellular accumulation of VP-16. The drug efflux pump inhibited by novobiocin appears to be distinct from both of the major proteins associated with the multidrug resistance phenotype in human cancers, the 170-kDa P-glycoprotein and the 190-kDa multidrug resistance protein. In a recent study, we found that novobiocin augmented VP-16 accumulation ex vivo in 16 of 24 fresh tumor samples at concentrations that could be achieved in vivo. Therefore, we conducted a clinical trial to determine the maximum tolerated dose and the pharmacokinetics of novobiocin when given in combination with VP-16.

PATIENTS AND METHODS

Patients with refractory cancer were treated with VP-16 on days 1, 3, and 5. Antiemetics, consisting of ondansetron and dexamethasone, were given 60 minutes before the VP-16 was administered. Novobiocin was given orally 30 minutes before the VP-16, and the dose was escalated in successive groups of patients according to a standard dose escalation design. Treatment cycles were repeated every 4 weeks. Plasma concentrations of novobiocin were determined during the first treatment cycle by high-performance liquid chromatography.

RESULTS

Thirty-three patients were treated for a total of 69 cycles. Eleven patients were treated with a starting dose of VP-16 of 120 mg/m2, and three of these patients experienced neutropenic fever. The dose of VP-16 was reduced to 100 mg/m2, and an additional 22 patients were enrolled. The dose of novobiocin ranged from 3 to 9 g. At a novobiocin dose of at least 5.5 g, plasma concentrations of at least 150 microM were sustained for 24 hours. Dose-limiting toxicities consisted of neutropenic fever and reversible hyperbilirubinemia. Nausea, which was a limiting toxicity in other trials of novobiocin, was well controlled with the use of serotonergic antiemetics. Diarrhea was common but mild in most patients.

DISCUSSION

In previously treated patients, the recommended dose of novobiocin in this schedule is 7 g/m2/day. Novobiocin does not appear to augment the toxicity of VP-16 to the bone marrow or the gastrointestinal mucosa. Plasma concentrations of novobiocin equivalent to the levels required to modulate VP-16 in vitro are readily achievable for total but not unbound free drug.

Structure of adduct X, the last unknown of the six major DNA adducts of mitomycin C formed in EMT6 mouse mammary tumor cells

Treatment of EMT6 mouse mammary tumor cells with mitomycin C (MC) results in the formation of six major MC-DNA adducts. We identified the last unknown of these ("adduct X") as a guanine N(2) adduct of 2, 7-diaminomitosene (2,7-DAM), in which the mitosene is linked at its C-10 position to guanine N(2). The assigned structure is based on UV and mass spectra of adduct X isolated directly from the cells, as well as on its difference UV, second-derivative UV, and circular dichroism spectra, synthesis from [8-(3)H]deoxyguanosine, and observation of its heat stability. These tests were carried out using 17 microg of synthetic material altogether. The mechanism of formation of adduct X involves reductive metabolism of MC to 2,7-DAM, which undergoes a second round of reductive activation to alkylate DNA, yielding adduct X and another 2,7-DAM-guanine adduct (adduct Y), which is linked at guanine N7 to the mitosene. Adduct Y has been described previously. Adduct X is formed preferentially at GpC, while adduct Y favors the GpG sequence. In contrast to MC-DNA adducts, the 2,7-DAM-DNA adducts are not cytotoxic.

Triapine (3-aminopyridine-2-carboxaldehyde- thiosemicarbazone): A potent inhibitor of ribonucleotide reductase activity with broad spectrum antitumor activity

Previous studies from our laboratories have shown that (a) Triapine() is a potent inhibitor of ribonucleotide reductase activity and (b) hydroxyurea-resistant L1210 leukemia cells are fully sensitive to Triapine. In an analogous manner, Triapine was similarly active against the wild-type and a hydroxyurea-resistant subline of the human KB nasopharyngeal carcinoma. Triapine was active in vivo against the L1210 leukemia over a broad range of dosages and was curative for some mice. This agent also caused pronounced inhibition of the growth of the murine M109 lung carcinoma and human A2780 ovarian carcinoma xenografts in mice. Optimum anticancer activity required twice daily dosing due to the duration of inhibition of DNA synthesis which lasted about 10 hr in L1210 cells treated with Triapine in vivo. DNA synthesis in normal mouse tissues (i.e. duodenum and bone marrow) uniformly recovered faster than that in L1210 leukemia cells, demonstrating a pharmacological basis for the therapeutic index of this agent. Triapine was more potent than hydroxyurea in inhibiting DNA synthesis in L1210 cells in vivo, and the effects of Triapine were more pronounced. In addition, the duration of the inhibition of DNA synthesis in leukemia cells from mice treated with Triapine was considerably longer than in those from animals treated with hydroxyurea. Combination of Triapine with various classes of agents that damage DNA (e.g. etoposide, cisplatin, doxorubicin, and 1-acetyl-1,2-bis(methylsulfonyl)-2-(2-chloroethyl)hydrazine) resulted in synergistic inhibition of the L1210 leukemia, producing long-term survivors of tumor-bearing mice treated with several dosage levels of the combinations, whereas no enhancement of survival was found when Triapine was combined with gemcitabine or cytosine arabinoside. The findings demonstrate the superiority of Triapine over hydroxyurea as an anticancer agent and further suggest that prevention by Triapine of repair of DNA lesions created by agents that damage DNA may result in efficacious drug combinations for the treatment of cancer.