Synthesis of Mono- and Bisdihydrodipyridopyrazines and Assessment of Their DNA Binding and Cytotoxic Properties

Aminoalkyl-substituted monomeric and dimeric dihydrodipyridopyrazines have been synthesized and evaluated as antitumor agents. Potent cytotoxic compounds were identified in both series. Biochemical and biophysical studies indicated that all these compounds strongly stabilized the duplex structure of DNA and some of them elicited a selectivity for GC-rich sequences. Sequence recognition by of the dimeric dihydrodipyridopyrazines is reminiscent of that of certain antitumor bisnaphthalimides. Compared to monomers, corresponding dimeric derivatives showed higher affinity for DNA. This property was attributed to a bisintercalative binding to DNA. This assumption was indirectly probed by electric linear dichroism and DNA relaxation experiments. DNA provides a bioreceptor for these dihydrodipyridopyrazine derivatives, but no poisoning of human topoisomerases I or II was detected. Most of the compounds efficiently inhibited the growth of L1210 murine leukemia cells and perturbed the cell cycle progression (with a G2/M block in most cases). A weak but noticeable in vivo antitumor activity was observed with one of the dimeric compounds. This studies identifies monomeric and dimeric dihydrodipyridopyrazines as a new class of DNA-targeted antitumor agents.

Synthesis and biological evaluation of N-heterocyclic indolyl glyoxylamides as orally active anticancer agents

A series of N-heterocyclic indolyl glyoxylamides were synthesized and evaluated for in vitro and in vivo anticancer activities. They exhibited a broad spectrum of anticancer activity not only in murine leukemic cancer cells but also in human gastric, breast, and uterus cancer cells as well as their multidrug resistant sublines with a wide range of IC(50) values. They also induced apoptosis and caused DNA fragmentation in human gastric cancer cells. Among the compounds studied, 7 showed the most potent activity of growth inhibition (IC(50) = 17-1711 nM) in several human cancer cells. Given orally, compounds 7 and 13 dose-dependently prolonged the survival of animals inoculated with P388 leukemic cancer cells. N-Heterocyclic indolyl glyoxylamides may be useful as orally active chemotherapeutic agents against cancer and refractory cancerous diseases of multidrug resistance phenotype.

Reversal of P-glycoprotein-mediated multidrug resistance by ginsenoside Rg(3)

Multidrug resistance has been a major problem in cancer chemotherapy. In this study, in vitro and in vivo modulations of MDR by ginsenoside Rg(3), a red ginseng saponin, were investigated. In flow cytometric analysis using rhodamine 123 as an artificial substrate, Rg(3) promoted accumulation of rhodamine 123 in drug-resistant KBV20C cells in a dose-dependent manner, but it had no effect on parental KB cells. Additionally Rg(3) inhibited [3H]vinblastine efflux and reversed MDR to doxorubicin, COL, VCR, and VP-16 in KBV20C cells. Reverse transcriptase-polymerase chain reaction and immuno-blot analysis after exposure of KBV20C cells to Rg(3) showed that inhibition of drug efflux by Rg(3) was due to neither repression of MDR1 gene expression nor Pgp level. Photo-affinity labeling study with [3H]azidopine, however, revealed that Rg(3) competed with [3H]azidopine for binding to the Pgp demonstrating that Rg(3) competed with anticancer drug for binding to Pgp thereby blocking drug efflux. Furthermore, Rg(3) increased life span in mice implanted with DOX-resistant murine leukemia P388 cells in vivo and inhibited body weight increase significantly.

Fetal fetuin selectively induces apoptosis in cancer cell lines and shows anti-cancer activity in tumor animal models

An apoptosis-inducing protein with molecular weight of 60 kDa has been purified from fetal bovine serum. The N-terminal amino acid sequence of this protein (e.g. I-P-L-D-P-V-A-G-Y-K) reveals that it is bovine fetuin, a fetal protein functioning to control embryogenesis. The apoptosis-inducing activity of fetuin is totally dependent on zinc. Depletion of zinc ion from fetuin or substitution of zinc ion by barium ion completely abolished the apoptosis-inducing activity of fetuin. Interestingly, while the fetuin isolated from fetal serum selectively induces apoptosis in cancer without affecting normal cells, the fetuin isolated from mature serum is completely inactive. This suggests that the biological activity of fetuin is under developmental regulation. In vivo, tumor animal model studies showed that fetuin enhanced survival by up to 141% in P388 leukemia animal model in mice. Fetuin was also found to inhibit prostate cancer formation in a PC-3 prostate cancer model in mice.

Preclinical in vivo antitumor activity of vinflunine, a novel fluorinated Vinca alkaloid

Vinflunine, or 20',20'-difluoro-3',4'-dihydrovinorelbine, is a novel Vinca alkaloid obtained by hemisynthesis using superacidic chemistry. The most impressive structural modification of this vinorelbine derivative was the selective introduction of two fluorine atoms at the 20' position, a part of the molecule previously inaccessible by classic chemistry. The antitumor activity of vinflunine was evaluated against a range of transplantable murine and human tumors. Vinflunine exhibited marked activity against murine P388 leukemia grafted i.v. when given i.p. in single or multiple doses according to various schedules or in single i.v. or p.o. doses. Increases in life span achieved with vinflunine, as assessed by T/C ratios, ranged from 200% to 457% and proved markedly superior to those of 129-186% obtained with the other Vinca alkaloids tested. Against s.c.-implanted B16 melanoma, multiple i.p. administration of vinflunine proved active in terms of both survival prolongation and tumor growth inhibition, with optimal T/C values and relative areas under the tumor growth curves (rAUC) being 24% and 36%, respectively. The extent of this activity was superior to that noted for vinorelbine under the same experimental conditions. Growth inhibition of human tumor xenografts LX-1 (lung) and MX-1 (breast) was also observed following four weekly i.p. injections of vinflunine as reflected by optimal T/C values of 23% and 26%, respectively, and significant differences in the rAUCs noted for treated versus control animals. It was also noticeable that vinflunine induced considerably more prolonged inhibitory effects on tumor growth than did vinorelbine. These results demonstrate that vinflunine is well tolerated and is definitively active against a range of experimental animal tumor models. Vinflunine activity has been documented in terms of both survival prolongation and tumor growth inhibition, with definite superiority over vinorelbine being shown in each tumor model evaluated.

[Synthesis and biological properties of 3,5-cyclophosphates- and -amidophosphates of 1,2-O-alkylydene-6-deoxy-6-halogeno-alpha -D-glucofuranoses]

3,5-Cyclic phosphates and phosphoramides of 6-halogenated glucofuranoses were synthesized via interaction of 3,5,6-bicyclophosphites of 1,2-O-alkylidene-alpha-D-glucofuranoses with halogens (followed by treatment with nucleophilic reagents) and N-chloroamines. 3,5-Cyclic trans-dibutylphosphoramides of 6-chloro-6-deoxy-1,2-O-isopropylidene- and 6-chloro-6-deoxy-(R)-(2,2,2)-trichloroethylidene)-alpha-D-glucofuranoses were shown to possess antiproliferative activity against CaOv human ovarian carcinoma cells in vitro (CE50 of approximately 10(-5) M). Cyclic trans-dibutylphosphoramide of 6-chloro-6-deoxy-1,2,-O-isopropylidene-alpha-D-glucofuranose also displayed marked antitumor effect on P-388 transplantable murine leukemia in vivo (the maximum increase in life span of 100% was reached at the quintuple injection of 100 mg/kg daily).

Betamipron reduces cisplatin nephrotoxicity in rodents without modifying its antileukemic activity in mice

Protective effects of betamipron (BP, N-benzoyl-beta-alanine), one of a series of N-acyl amino acids, on cisplatin-induced nephrotoxicity were examined. Since the damage observed in the kidney is localized to the proximal tubule cells, we investigated the influence of BP on urinary enzymes and excreta. Male Wistar rats and ddY mice were injected i.p. with 6 mg/kg and 16 mg/kg, respectively, of cisplatin combined with an i.p. 250 mg/kg BP dose. The toxicity of cisplatin as indicated by body weight gain, blood urea nitrogen, and serum creatinine levels was significantly (p < 0.05) suppressed by administration of BP after cisplatin treatment. The increase in urinary N-acetyl-beta-D-glucosaminidase activity, increase and subsequent decrease in gamma-glutamyl transferase activities, and increase in beta 2-microglobulin level observed after treatment with cisplatin were suppressed by administration of BP after cisplatin treatment. The combination of cisplatin and BP had no apparent effect on the efficacy of cisplatin against P388 leukemic cells in mice.

Effect of the antiarrhythmic drug procainamide on the toxicity and antitumor activity of cis-diamminedichloroplatinum(II)

The class I antiarrhythmic drug procainamide (Pd) was tested on BDF1 mice for its chemoprotective activity against cis-diamminedichloroplatinum(II) (DDP) toxicity. Pd at the dose of 50 mg/kg protected mice against otherwise lethal doses of DDP (survivors at Day 14 after 25 mg/kg DDP or 25 mg/kg DDP-Pd treatment: 0% vs 100%) and greatly reduced the weight loss induced by DDP. Moreover, the increased plasma urea nitrogen levels caused by a single ip administration of DDP in water (8 or 16 mg/kg) as well as the tubular degenerative changes detected by light microscopy were prevented by Pd. Pd had no effect on the sensitivity of P388 leukemic cells to DDP in vitro, but the administration of DDP (16 mg/kg) and Pd (50 mg/kg) to BDF1 mice bearing P388 leukemic cells produced a significant increase in survivals compared to mice receiving ip DDP alone diluted in 0.9% NaCl solution. The increased efficacy of this combination therapy in P388 leukemic mice compared to a single DDP treatment at the same dose was observed both when the drugs were administered ip simultaneously (p = 0.042) and when DDP and Pd were given ip and iv, respectively (p = 0.018). Since procaine, which differs from Pd merely in the replacement of the amide by the ester linkage, has also been reported to significantly enhance DDP efficacy (M. Esposito et al., 1990, J. Natl. Cancer Inst. 82, 677-684.), a comparison of their effects in tumored mice exposed to DDP has been made. Although both drug combinations were superior to that of DDP alone, in terms of both survival time and numbers of cures, Pd treatment seems to offer better protection against DDP-induced lethality than did procaine.

Antitumor effect of erythromycin in mice

Oral administration of erythromycin in the dose range of 1-10 mg/kg increased the survival times of tumor-bearing mice in both allogeneic and syngeneic mouse systems by two- to three-fold as compared with those of vehicle control mice, with the maximum effect at a dose of 5 mg/kg/day. During the early phase of tumor transplantation, tumoricidal macrophages and natural killer cells were active in the antitumor resistance of erythromycin-treated mice. Thereafter, the tumoricidal activity of macrophages became stronger as serum levels of interleukin-4 (IL-4) rose. Furthermore, treatment of mice with anti-IL-4 monoclonal antibody abolished the antitumor resistance conferred by erythromycin. These results indicate that erythromycin exhibits an indirect antineoplastic activity by enhancing the production of IL-4 which augments the tumoricidal activity of macrophages.

Antitumor activity of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-2- isopropyl-1,3-dioxolane]platinum(II), a new platinum analogue, as an anticancer agent

The in vitro and in vivo antitumor activity of a new antitumor platinum complex, cis-malonato[(4R, 5R)-4,5- bis(aminomethyl)-2-isopropyl-1,3-dioxolane]platinum(II) (SKI2053R, NSC D644591), were evaluated and compared with those of cisplatin (CDDP) and carboplatin (CBDCA) using murine tumors. SKI 2053R was highly active in vitro against both L1210 murine leukemia and its CDDP-resistant subline, L1210/DDP; the relative resistances were 20.0-, 14.5-, and 2.7-fold for CDDP, CBDCA, and SKI 2053R, respectively. SKI 2053R showed activity comparable with or superior to either CDDP or CBDCA in mice implanted with L1210. In mice implanted with L1210/DDP, as compared with CBDCA, SKI 2053R showed high values for the percentage of treated survivors relative to controls and for numbers of cured mice, whereas CDDP had virtually no activity. In mice implanted with P388, all three drugs were highly active, but the intensity of activity was shown to be ranked in the following order: SKI 2053R > CDDP > CBDCA. The antitumor activity of SKI 2053R against Lewis lung carcinoma was comparable with that of both CDDP and CBDCA. The antitumor activity of SKI 2053R was further investigated against two human tumor xenografts, KATO III (stomach adenocarcinoma) and WiDr (colon adenocarcinoma), implanted s.c. in nude mice and was compared with that of CDDP. In SKI 2053R-treated groups, the time required for a mean tumor weight of 1,000 mg was 33.1 days in KATO III xenografts and 35.0 days in WiDr xenografts as compared with 30.2 and 27.2 days in CDDP-treated groups, respectively. SKI 2053R achieved growth-inhibition rates comparable with those of CDDP against KATO III (65% versus 59%) and WiDr xenografts (64% versus 54%) on day 35. These results indicate that SKI 2053R is an attractive candidate for further development as a clinically useful anticancer drug.

Liposomal vincristine which exhibits increased drug retention and increased circulation longevity cures mice bearing P388 tumors

Prolonged exposure to vincristine correlates with improved therapeutic activity. In this work, two methods are used to increase the circulation longevity of liposomal formulations of vincristine. The first involves incorporation of the ganglioside GM1, which acts to increase the circulation longevity of liposomal carriers, while the second approach relies on a modification of the vincristine encapsulation procedure which enhances drug retention. It is shown that these approaches are synergistic and increase the circulation half-life of vincristine from approximately 1 h to greater than 12 h. This results in a dramatic improvement in the therapeutic activity of liposomal vincristine as measured using a murine P388 lymphocytic leukemia model. At doses above 2 mg/kg, the optimized liposomal vincristine formulation cures greater than 50% of mice bearing the P388 tumor, whereas free vincristine results in no cures.

[The cross resistance to cytostatics of leukemia P388 cells with induced resistance to doxorubicin]

Using BDF1 mice it has been shown that P388 leukemia tumor cells with induced resistance to doxorubicin (P388/DX) were cross-resistant to daunomycin, carminomycin, actinomycin D, vincristine and mitomycin C. It has been shown that P388/DX leukemia tumor cells were sensitive to bleocina, bleomycitina, cyclophosphamide, 5 fluorouracil. It has been discussed the ways of cross-resistance of P388/DX leukemia tumor cells to cytostatic drugs.

Anti-leukaemic action of RuCl2 (DMSO)4 isomers and prevention of brain involvement on P388 leukaemia and on P388/DDP subline

Two ruthenium(II) complexes, characterised by the presence of dimethylsulphoxide ligands, were investigated in comparison to cisplatin on mouse P388 leukaemia and on a subline made resistant to cisplatin (P388/DDP). Both cis- and trans-RuCl2(DMSO)4 significantly prolonged the survival time of leukaemic mice, independently of the tumour line used. Unlike cisplatin, the prolongation of life-span of tumour-bearing hosts caused by ruthenium complexes was not supported by a parallel inhibition of the number of tumour cells in the treated hosts, as evidenced by tumour cell count in the peritoneal cavity and by vivo-vivo bioassays of blood samples and of whole brains. Thus, cis- and trans-RuCl2(DMSO)4 appear capable of preventing leukaemic spread into the central nervous system also when the number of tumour cells in the peritoneal cavity and in the blood stream is as high as in untreated controls. When the drug-induced DNA damage was investigated by modifying double stranded DNA and identifying the lesions able to inhibit DNA synthesis in vitro, trans-RuCl2(DMSO)4 and, to a lesser extent, cis-RuCl2(DMSO)4 formed blocking lesions at the same sites of cisplatin; nevertheless, the mechanism of antitumour activity of ruthenium complexes appears to be different from that of cisplatin for the absence of any relationship between cytotoxicity and prevention of leukaemic dissemination into the central nervous system. These data indicate that the activity of cis- and trans-RuCl2(DMSO)4 on the P388 leukaemia is characterised by the lack of cross-resistance with cisplatin and by the alteration of the metastasising behaviour of leukaemic cells which lose their natural capacity to invade the central nervous system.

Differential macrophage-mediated cytotoxicity to P388 leukemia cells and its drug-resistant cells examined by a new MTT assay

After activation by interferon-gamma (INF-gamma) and lipopolysaccharide(LPS), mouse peritoneal macrophages were cocultured with P388 parental cell line (P388/PRT) and its adriamycin (ADM)-, cisplatin(CDDP)-, cyclophosphamide(CPM)-, and mitomycin-C(MMC)-resistant cell lines for one day at effector:target ratios (E:T) of 10:1, 5:1, and 2:1. The direct 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) cleavage assay and a new indirect MTT assay as well as clonogenic assay were used to quantitate activated macrophage-mediated cytotoxicity to these non-adherent leukemia targets. The results revealed that all the P388 cell lines can be suppressed efficiently by activated macrophages, but P388 CPM- and MMC-resistant cell lines (P388/CPM, P388/MMC) were more susceptible than P388/PRT while P388 ADM- and CDDP-resistant cell lines (P388/ADM, P388/CDDP) shared equal level of survival rates with P388/PRT. This study also showed that both non-activated and activated macrophages can produce formazan in a high level, which can interfere with the final results of direct MTT assay. The new indirect MTT assay can avoid such interference by separating the effectors from the targets before performing the MTT assay and reflects the real viability of the targets so the indirect MTT assay developed in this study could be a better way to examine cytostatic and cytotoxic effect of activated macrophages on non-adherent tumor cells in vitro.

[The effect of ascitic fluid globulins on the growth of leukemia P388/DOX and Ehrlich's carcinoma in mice]

The study was performed to investigate the effect of ascitic fluid globulins of tumor on tumor growth and life span of mice. The globulins are shown to shorten the life span of Ehrlich tumor mice from 86.8 to 61.8 days, to increase 3-5-fold the growth rate of Ehrlich carcinoma and P388/DOX tumor. It was found that globulins of ascitic fluids and serum globulins of tumor have equal effects of tumor growth. It is proposed to use globulins of ascitic fluid to study the globulin role in tumor growth.

Doxorubicin-loaded nanospheres bypass tumor cell multidrug resistance

We have demonstrated that in vitro resistance of tumor cells to doxorubicin (Dox) can be fully circumvented by using doxorubicin-loaded nanospheres (Dox-NS), consisting of biodegradable polyisohexylcyanoacrylate polymers of 300 nm diameter and containing 2.83 mg of Dox per 31.5 mg of polymer. Five different multidrug-resistant cell lines, characterized by mdr1 amplification, were used in this study: Dox-R-MCF7, a human breast adenocarcinoma; SKVBL1, a human ovarian adenocarcinoma; K562-R, a human erythroleukemia; and two murine lines: P388-Adr-R, a monocytic leukemia of DBA2 mouse, and LR73MDR, a Chinese hamster ovarian cell line. These lines were 38.7, 210, 232, 143 and 20 times more resistant than their corresponding sensitive counterparts, respectively. Using Dox-NS, we obtained complete reversion of drug resistance in vitro, i.e. cell growth inhibition comparable with that obtained with sensitive cells exposed to free Dox. In vivo, we significantly prolonged the survival of DBA2 mice which had previously received P388-Adr-R cells by i.p. injections of Dox-NS, while free Dox injection was ineffective toward this rapidly growing tumor. (Prolongation of survival time: 115% vs 167% after Dox vs Dox-NS treatment, respectively.) Using the MCF7 cell line and its resistant variant, we studied the intracellular concentration and the cytoplasmic and nuclear distribution of Dox by laser microspectrofluorometry (LMSF). In sensitive cells, we observed a similar accumulation and distribution of Dox whatever the form of Dox delivery, i.e. whether free or carried by nanospheres. Analysis by LMSF showed that 99% of intranuclear Dox was bound to DNA after treatment with both forms of Dox. Of Dox, 81 and 83% were found in the intranuclear compartment of sensitive cells incubated with free Dox and Dox-NS, respectively. Resistant cells incubated with Dox-NS accumulated the same amount of Dox as sensitive cells incubated with free Dox or with Dox-NS. Dox, when loaded in nanospheres, bypasses the efflux mechanism responsible for multidrug resistance. LMSF analysis showed that Dox, transported and released by nanospheres, interacts with DNA identically in sensitive and resistant cells.

Cross-resistance of drug-resistant murine P388 leukemias to toxol in vivo

The antimicrotubule agent taxol (NSC 125973) has shown clinical antitumor activity against several classically refractory tumors. We developed a drug-resistance profile for taxol using ten drug-resistant P388 leukemias to identify potentially useful guides for patient selection for further clinical trials of taxol and possible non-cross-resistant drug combinations with taxol. Multidrug-resistant P388 leukemias exhibited either clear (leukemia resistant to amsacrine) or marginal cross-resistance (leukemias resistant to doxorubicin, actinomycin D, and mitoxantrone) to taxol. Leukemias resistant to vincristine (non-multidrug-resistant leukemia), camptothecin, melphalan, cisplatin, 1-beta-D-arabinofuranosylcytosine, and methotrexate were not cross-resistant to taxol. The data suggest that (1) it may be important to exclude or to monitor with extra care patients who have previously been treated with amsacrine, doxorubicin, actinomycin D, or mitoxantrone and (2) a combination of one of the non-cross-resistant drugs and taxol might exhibit therapeutic synergism.

Cyclosporin A potentiation of VP-16: production of long-term survival in murine acute lymphatic leukemia

Our prior in vitro studies on the correction of multidrug resistance by cyclosporin A (CsA) prompted us to investigate the effect of CsA and VP-16 in vivo. CsA given simultaneously at 2 or 10 mg/kg with VP-16 to BDF/1 mice bearing parental drug-sensitive P388 or L1210 lymphatic leukemia produced a 100% increase in survival as compared with VP-16 treatment alone. CsA-containing regimens also promoted 60-day survival in a significant number of P388 or L1210 leukemia-bearing mice as compared with animals receiving VP-16 in the absence of CsA (P < 0.02 and P < 0.001, respectively). CsA enhancement of the survival of mice bearing these lymphatic leukemias is restricted to VP-16, since the addition of CsA to therapeutic agents such as vincristine, daunorubicin, methotrexate, or cisplatin had no effect on survival.

Effect of coadministration of selenite on the toxicity and antitumor activity of cis-diamminedichloroplatinum (II) given repeatedly to mice

The effect of selenite coadministration on the toxicity and antitumor activity of repeated treatment with high doses of cis-diamminedichloroplatinum (cis-DDP) was examined in mice. Sodium selenite was injected s.c. into separate abdominal sites of mice together with cis-DDP at a molar ratio of 1:3.5 (selenite to cis-DDP) on day 0. The same amount of selenite was given daily for 4 subsequent days (days 1-4). This fixed administration schedule was repeated weekly for a total of 7 weeks. Under the experimental conditions used, the lethal toxicity, renal toxicity [indicated by an increase in blood urea nitrogen (BUN) and plasma creatinine levels], hepatic toxicity (indicated by an increase in plasma GPT and GOT activity), and myelotoxicity (indicated by a decrease in the numbers of leukocytes and platelets) observed in mice given repeated doses of cis-DDP alone (15 or 25 mumol/kg, s.c.) were significantly depressed by the coadministration of sodium selenite. Treatment with cis-DDP alone (15, 20, or 25 mumol/kg, s.c.) resulted in some dose-dependent prolongation of the life span of mice transplanted either s.c. with colon adenocarcinoma 38 (colon 38) or i.p. with P388 leukemia (P388) but did not completely depress the tumor growth, and the animals died of either progressive disease or cis-DDP-induced toxicity. However, following the coadministration of 7.1 mumol/kg selenite with 25 mumol/kg cis-DDP, all of the mice transplanted either s.c. with colon 38 or i.p. with P388 survived for as long as 4 months after the end of the treatment and showed no evidence of malignancy. These results indicate that selenite coadministration enables the use of increasing doses of cis-DDP and, consequently, enhances the antitumor effect of cis-DDP by depressing its side effects.

[The effect of thymalin on the count of large granular lymphocytes in the peripheral blood of mice with leukemia P388]

Effect of thymaline injections on peripheral blood natural killer cells in mice with p388 leukemia has been studied. The content of natural killers that have been identified as large granular lymphocytes decreased in blood of leukemia mice. Multiple thymaline injections (0.66 mg/kg) maintain the numbers of the lymphocytes at the level of control animals but did not increase the life span of leukemia mice.

In vitro and in vivo antitumoral activity of free, and encapsulated taxol

The anti-tumoral activity of taxol encapsulated either in liposomes or in nanocapsules was compared with that of free taxol, using the P388 and L1210 leukaemia test systems. The in vitro inhibition of cell growth was measured after 48 h and 96 h exposure to various concentrations of taxol. With P388 cells, the inhibitory activities of the three forms of the drug were similar. With the L1210 cells, however, the concentrations required for a 50 per cent inhibition of cell growth (IC50) after 48 h exposure to the drug were greater for nanocapsules than for liposomes or free taxol, the values being 0.060, 0.043 and 0.035 micrograms ml-1, respectively. However, a greater efficiency of nanocapsules was observed after 96 h exposure. Using cytomorphometric analysis, no difference was found between L1210 cells treated either with free or encapsulated taxol. In vivo, mice bearing P388 leukaemia, and treated either with taxol solubilized with 5 per cent DMSO + 5 per cent cremophor in saline solution, or with taxol encapsulated in liposomes (IP daily dose of 12.5 mg Kg-1 body weight x 4 days) showed ILS values of 65.8% and 67.9% respectively. Nanocapsules proved to be toxic, apparently due to their composition: this problem is currently under investigation.

[Combined effect of CDDP with various types of antitumor drugs against P 388 leukemia]

The combined effect of cisplatin (CDDP) with various types of antitumor drugs was examined in P 388 leukemia in vivo. Three representative drugs were chosen from every group of alkylating agents, antitumor antibiotics, antimetabolites, and plant originated drugs. According to their dependency on administration schedules, the dose-dependent and time-dependent drugs were administered once, and daily 5 times, respectively, before and after the single administration of CDDP. In addition to these sequential combinations, simultaneous treatment with CDDP was examined for the drugs which were singly administered. The combined effect was assessed by comparing ILS (increase in life span) in a combined group with the sum of ILS's of each of the 2 single-treatment groups. Synergistic effect was observed in the combination of CDDP with all drugs except MMC. Among them CYC, CQ, ACNU, ADR, PEP, ET, VCR, and VDS produced synergistic effect in any treatment schedules, irrespective of the combination sequences. In the cases of the combination with antimetabolites, the combined effect was depended on the treatment sequences; prior treatment of 5-FU, and posterior treatment of Ara-C and MTX to CDDP administration exhibited a synergistic effect, but the combination in reverse sequence remained almost additive.

Optimum schedule of selenium administration to reduce lethal and renal toxicities of cis-diamminedichloroplatinum in mice

The optimum conditions of selenium administration to reduce the side effects of a single dose of cis-diamminedichloroplatinum (cis-DDP) in mice were examined. The best effects against lethal toxicity of cis-DDP was obtained when sodium selenite was administered subcutaneously (s.c.) to mice simultaneously with s.c. injected cis-DDP at a molar ratio of 1 to 3.5 (sodium selenite to cis-DDP) on the first day and the same amount of selenite was given daily for four subsequent days. This coadministration of selenite completely depressed not only lethal toxicity of cis-DDP but also its renal toxicity (indicated by increased blood urea nitrogen values) and intestinal toxicity (indicated by the incidence of diarrhea) which were usually observed in the mice treated with cis-DDP alone. Furthermore, coadministration of selenite did not compromise the antitumor activity of cis-DDP against several transplantable tumors in mice. Therefore, the administration schedule of selenite with cis-DDP described above may be useful for cancer chemotherapy.

Protection against cisplatin nephrotoxicity by prochlorperazine

Prochlorperazine (Compazine; PCPZ) is often used to limit cisplatin (CDDP)-induced emesis. However, recent studies in mice have shown that PCPZ protects against renal injury produced by treatment with various nephrotoxicants (e.g., MethylCCNU, mercuric chloride). Because renal toxicity remains a serious limitation to the effective use of CDDP, we conducted the present study to determine whether PCPZ could also protect against CDDP-induced renal injury. PCPZ treatment was shown to ameliorate CDDP-induced renal lesions in both rats and mice at doses and treatment schedules that were comparable with those used for alleviating chemotherapy-induced emesis. A PCPZ dose of 10 mg/kg x 2 offered complete protection against CDDP-induced increases in blood urea nitrogen (BUN) levels in mice, with significant protection occurring at a PCPZ dose as low as 5 mg/kg. Similarly, PCPZ ameliorated CDDP-induced increases in BUN, glucosouria, and enzymuria in F344 rats. PCPZ treatment did not affect the urinary excretion or renal tissue levels of total platinum or the plasma pharmacokinetics of free platinum. However, it did cause a marked reduction in the concentration of total plasma platinum (free platinum + protein-bound platinum). PCPZ was not found to affect the in vivo antitumor activity of CDDP against P388 leukemia. The present study suggests that PCPZ may be of therapeutic benefit when used with CDDP and provides a rational basis for the selection of antiemetic therapy.

Overcoming drug resistance in cancer cells with synthetic isoprenoids

A cultured subline (P388/ADM) of mouse P388 leukemia resistant to doxorubicin, vinblastine, vincristine, dactinomycin, and daunorubicin became sensitive again when treated with noncytotoxic doses of either of two synthetic isoprenoids: N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) and N-(p-methylbenzyl)decaprenylamine X HCI (PMB-decaprenylamine). The isoprenoids also reversed resistance to doxorubicin and vincristine in a cultured vincristine-resistant P388 leukemia subline (P388/VCR). Median lethal doses (LD50) for PMB-decaprenylamine and SDB-ethylenediamine administered ip were 123 and 350 mg/kg against mice, whereas the LD50 for verapamil, another modifier of cellular drug resistance, was about 7.6 mg/kg. In vivo experiments with P388/VCR-bearing mice showed that both SDB-ethylenediamine and verapamil overcame vincristine resistance, but PMB-decaprenylamine showed only slight activity. SDB-ethylenediamine was especially effective, overcoming the vincristine resistance at 1 mg drug/kg. Since the structure of SDB-ethylenediamine resembles that of verapamil, a calcium-blocking agent that overcomes drug resistance, it was checked for calcium-blocking activity. However, calcium channel-blocking activity was not observed with 20 micrograms isoprenoid/ml, whereas calcium channel activity was completely blocked by 1 microgram verapamil/ml.

Antitumor activity of imidazolium-bisimidazole-tetrachlororuthenate (III). A representative of a new class of inorganic antitumor agents

The antitumor activity of imidazolium-bisimidazole-tetrachlororuthenate (III) against the P388 leukemia and against the B16 melanoma was investigated. The test compound showed high activity against these tumor models. The tumor inhibiting effect was in the range or better than the effects of the compounds cyclophosphamide, cisplatin, or 5-fluorouracil, which were tested as positive controls. The effective substance is a new, water soluble, anionic, nitrogen-heterocyclic coordinated, ruthenium species, exhibiting antitumor activity.

Lack of dexamethasone effect on the antitumor activity of cisplatin

High-dose glucocorticosteroids have proven to be effective antiemetic agents when used before and after cisplatin chemotherapy. To rule out a possible decrease in cisplatin antitumor activity by a direct effect of short-term glucocorticosteroid treatment, survival was studied in mice inoculated with P388 leukemia and then treated with cisplatin preceded by a single high dose (1.5 mg/kg) of dexamethasone (Dex). The median survival of animals treated with cisplatin-Dex was 19 days, and that of animals treated with cisplatin alone was 18 days. These survival durations were significantly longer (P less than 0.01) than the survival time of the controls (median, 12 days). A double-layer soft agar clonogenic assay was used to study the possible effect of Dex on cisplatin inhibition of tumor colony-forming units from two human tumor cell lines (HEC-1A, endometrial; and WiDr, colon). In this model, the addition of Dex to cisplatin showed no statistically significant effect. These data suggest that Dex has no inhibitory effect on the antitumor activity of cisplatin.

Biological effects and structure-activity relationships of 1,2-dihydropyrido[3,4-b]pyrazines

The effects of a number of 1,2-dihydropyrido[3,4-b]pyrazines (1-deaza-7,8-dihydropteridines) upon the proliferation and the mitotic index of cultured L1210 cells and upon the survival of mice bearing P388 leukemia were determined. The 1,2-dihydrostructure and amino groups or masked amino groups at positions 5 and 7 were necessary for activity, and various substituents at positions 2 and 3 had considerable influence upon the activity. A number of these pyrazines had significant activity against i.p. P388 leukemia in mice, and several pyrazines were more active than the corresponding oxazines or thiazines in both the in vitro and the in vivo systems. The effects of the pyrazines upon the cultured cells were reversible, and the rate and degree of reversibility were influenced by the substituents at positions 2 and 3. Tests performed with two of the pyrazines yielded results that indicate that these compounds, like the known agent nocodazole, might compete with colchicine for binding to tubulin. Synergistic killing of cultured L1210 cells was obtained with combinations of one of the pyrazines and vincristine.

Cimetidine enhancement of cyclophosphamide antitumour activity

Male DBA2 mice were given 10(6) P-388 leukaemic cells i.p. and cimetidine (CMT) at 100 mg/kg 1 day for 10 days, or as a single 100 mg/kg injection 30 min before cyclophosphamide (CTX). CMT significantly prolonged the survival of groups of mice receiving 50, 100 and 200 mg/kg of CTX 3 days after tumour inoculation. Median survival increased by 5.5 days (P less than 0.05), 10 days (P less than 0.05) and 13 days (P less than 0.05) respectively. The addition of CMT had the effect of roughly doubling the CTX dose, without increasing the lethality. CMT produced the only long-term survival seen in the study (1-2/10) CMT alone had no apparent antitumour activity. CMT significantly prolonged mean pentobarbital sleep to 28.6-60 min vs only 10 min for phenobarbital treated mice. Both CMT regimens increased the plasma concentration time products for CTX-induced metabolites (NBP) by about 1.3 fold (in contrast to a 33% reduction with phenobarbital). On average the single-dose CMT regimen produced the greatest effect on survival, on pentobarbital sleep duration and on total NBP reactive species. Probable mechanisms for the CMT-CTX interaction include competitive microsomal enzyme inhibition and/or acutely depressed hepatic blood flow. Caution should be used in combining CMT with full doses of CTX and any other highly metabolized antineoplastic agents in man.

Effect of thymidine on the toxicity and antitumor activity of ftorafur

The effects of thymidine (TdR) on the toxicity and antitumor activity of ftorafur (FT), a 5-FU analog, were determined. The LD10 of FT was 130, 430, and 680 mg/kg, respectively, when FT was administered ip in the following treatment schedules: (a) daily for 9 days, (b) every 4th day for three treatments, and (c) 1 day only. When FT was administered simultaneously with 250 mg/kg of TdR, the LD10 was 13, 62, and 630 mg/kg in the respective treatment schedules. Lethargy was observed in mice when the daily dose of FT was greater than or equal to 150 mg/kg. FT alone was active (% treated/control [T/C] = 153) against ascites P388 murine leukemia only at high, single doses. Simultaneous administration of FT and 250 mg/kg of TdR at or below the LD10 dose of FT resulted in an increase in the antitumor activity to a % T/C of 217 (daily, Days 1-9) and 188 (daily, Days 1, 5, and 9). The activity of FT administered simultaneously with TdR on Day 1 only (%T/C = 142) was lower than that for FT alone. Using a treatment schedule of Days 1, 5, and 9, a TdR/FT mol ratio of greater than or equal to 2.0 seems necessary to achieve an increase in therapeutic value against P388 murine leukemia. This may explain the lack of increase in activity against P388 when 250 mg/kg of TdR was coadministered with FT on Day 1 only. FT alone or coadministered with 250 mg/kg of TdR was equally active against L1210 ascites tumor at doses up to the LD10 with daily treatments on Days 1, 5, and 9 and on Days 1-9; the doses of FT, however, were below those which cause lethargy.

Potentiation of antitumor effect of virus-induced interferon by mouse immune interferon preparations

In inbred DBA/2 mice, the antitumor activities of separate and combined preparations of mouse immune interferon and mouse virus-induced interferon on the development of P388 tumors were studied. Immune interferon alone (25 U/day) did not affect tumor development. Virus-induced interferon alone (25,000 U/day) delayed tumor development and increased survival time. The mouse immune interferon preparations significantly enhanced or potentiated the antitumor effects of mouse virus-induced interferon when the interferons were used in combined therapy.

Enhancement of the antitumor-activity of Corynebacterium parvum by appropriate adjustment of dosage schedules

Single and multiple doses of Corynebacterium parvum ranging from 0.01 to 60 mg/kg as the total dose were tested at selected times against 10(6) P388 leukemia cells inoculated ip in BDF1 mice. The minimum dose needed for maximum protection was determined according to the ability of the treatment to produce an increase in the lifespan (ILS) of mice. The ip dose required after transplant for significant ILS was 40 mg/kg as the total dose. The administration of a single dose 2 days prior to implant produced maximum antitumor effects at 1 mg/kg, with all other doses above and below this level being significantly less effective. Protection was achieved before implant, with the following maximum ILS recorded for each dose and time: 1 mg/kg on Day -2 = 110%; 60 mg/kg on Day -5 = 70%; 10 mg/kg on Day -2 = 50%; and 0.1 and 0.01 mg/kg on either Day -2 or Day -5 = 25%-30%. Cytotoxicity studies demonstrated that 51Cr release after 1 mg/kg was more rapid in onset (peaking on Day 3 after treatment) than after 60 mg/kg (peaking on Day 5 after treatment). It was concluded that the proper adjustment of the dose and time of administration of C. parvum prior to tumor transplant enhanced antitumor activity of this immunopotentiator. Considerably higher doses were required after transplant for the desired effects to be achieved. The cytotoxicity studies demonstrated differences in tumor cell-killing which were dose-related and may be a contributing factor in the dose and time-related antitumor effects of C. parvum.