Reversal by two dihydropyridine compounds of resistance to multiple anticancer agents in mouse P388 leukemia in vivo and in vitro

We investigated whether two representative 1,4-dihydropyridine derivatives, NK-250 and NK-252, could potentiate the antitumor activity of multiple anticancer agents including vincristine (VCR), vinblastine, vindesine and actinomycin D in drug-resistant tumor cells and their parental drug-sensitive tumor cells. NK-250 and NK-252 at 5-10 microM almost completely reversed VCR resistance in cultured VCR-resistant P388/VCR cells derived from the mouse drug-sensitive P388/S leukemia cell line and also potentiated the cytocidal activity of VCR in drug-sensitive P388/S cells. NK-250 and NK-252 at 1-10 microM inhibited the photoaffinity labeling by [3H]azidopine of the cell-surface 170,000-molecular-weight P-glycoprotein. In chemotherapeutic experiments with leukemia-bearing mice, NK-250 or NK-252 was orally administered in combination with different drugs of the MDR phenotype administered intraperitoneally. The antitumor activity of the various combinations was found to be augmented in mice bearing P388/S- and P388/VCR-leukemia. Among the combinations examined, the combination of NK-250 and VCR was the most effective. These two 1,4-dihydropyridines, NK-250 and NK-252, are unique compounds because they were effective not only in circumventing the drug resistance, but also in potentiating the action of antitumor drugs against drug-sensitive tumors.     

A benzophenazine derivative,N-β-dimethylaminoethyl 9-carboxy-5-hydroxy-10-methoxy-benzo[a]phenazine-6-carboxamide,as a new antitumor agent against multidrug-resistant and sensitive tumors

Summary NC-190, a benzophenazine derivative (N-β-dimethylaminoethyl 9-carboxy-5-hydroxy-10-methoxybenzo[a]phenazine-6-carboxamide), was effective against multidrug-resistant human and mouse tumor cells in vitro and in vivo. When vincristine (VCR)-resistant P388 leukemia-bearing mice were treated with an optimal dose of NC-190, four of six mice were cured, whereas treatment of mice with VCR resulted in only a marginal increase in life span. The compound also showed chemotherapeutic effect against Adriamycin-resistant P388 leukemia-bearing mice and was effective against various multidrug-resistant human and murine tumor cells in vitro. Its cytotoxicity to multidrug-resistant K562 cells was not enhanced by the addition of verapamil. The accumulation of NC-190 in multidrug-resistant K562 cells was slightly lower than that observed in sensitive K562 cells; the compound did not efficiently inhibit the binding of VCR to the plasma membrane of resistant cells, indicating that NC-190 has little affinity for P-glycoprotein. NC-190 inhibited the activity of DNA topoisomerase II. These observations suggest that NC-190 (1) is not transported out of resistant cells by P-glycoprotein and (2) inhibits DNA topoisomerase II activity in the cells, resulting in its likely effectiveness against various multidrug-resistant tumor cells.     

Reversal of multidrug resistance by novel nitrophenyl pyrones, SNF4435C and D.

SNF4435C and D, novel immunosuppressants produced by a strain of Streptomyces spectabilis, were examined for their reversing effects in vitro on various multidrug-resistant (MDR) tumor cells overexpressing P-glycoprotein. These two compounds in the range of 3-10 microM completely reversed the resistance of MDR variant cells, mouse leukemia P388 cells [vincristine (VCR)-resistant P388/VCR and adriamycin (ADM)-resistant P388/ADM], human myelogenous leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM) and human ovarian cancer A2780 cells (ADM-resistant AD(10)), against VCR. Both compounds moderately potentiated the sensitivity of the MDR cells to ADM but the reversal was not complete. SNF4435C and D significantly increased the intracellular accumulation of VCR in AD(10) cells as potently as verapamil, cyclosporin A (CysA) and FK506, whereas the compounds exerted no effect on the accumulation of VCR in the drug-sensitive parent cells. Moreover, SNF4435C improved the chemotherapeutic efficacy of VCR in the treatment of P388/VCR-bearing mice. When 10 mg/kg SNF4435C was administered intraperitoneally to the mice concurrently with 0.2 mg/kg VCR for every 5 days, a treated/control (T/C) value of 143% was obtained. These results suggest that the compounds are useful candidates or tools for MDR modification in cancer chemotherapy.     

Reversal of Multidrug Resistance by Novel Nitrophenyl Pyrones, SNF4435C and D

SNF4435C and D, novel immunosuppressants produced by a strain of Streptomyces spectabilis , were examined for their reversing effects in vitro on various multidrug-resistant (MDR) tumor cells overexpressing P-glycoprotein. These two compounds in the range of 3–10 [jM completely reversed the resistance of MDR variant cells, mouse leukemia P388 cells [vincristine (VCR)-resistant P388/ VCR and adriamycin (ADM)-resistant P388/ADM], human myelogenous leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM) and human ovarian cancer A2780 cells (ADM-resistant AD10), against VCR. Both compounds moderately potentiated the sensitivity of the MDR cells to ADM but the reversal was not complete. SNF4435C and D significantly increased the intracellular accumulation of VCR in AD10 cells as potently as verapamil, cyclosporin A (CysA) and FK506, whereas the compounds exerted no effect on the accumulation of VCR in the drug-sensitive parent cells. Moreover, SNF4435C unproved the chemotherapeutic efficacy of VCR in the treatment of P388/VCR-bearing mice. When 10 mg/kg SNF4435C was administered intra-peritoneally to the mice concurrently with 0.2 mg/kg VCR for every 5 days, a treated/control (T/C) value of 143% was obtained. These results suggest that the compounds are useful candidates or tools for MDR modification in cancer chemotherapy.     

Rhizoxin, a macrocyclic lactone antibiotic, as a new antitumor agent against human and murine tumor cells and their vincristine-resistant sublines

Rhizoxin, isolated from a plant pathogenic fungus which causes rice seedling blight, inhibits the mitosis of the tumor cells in a manner similar to that of Vinca alkaloids as revealed by morphological study and flow cytometry analysis. This new 16-membered macrocyclic lactone showed similar chemotherapeutic effects to those of vincristine against L1210 and P388 leukemia-bearing mice. The drug is also effective against B16 melanoma inoculated i.p. or s.c. Rhizoxin, in contrast to the ansamacrolide, maytansine, was effective against human and murine tumor cells resistant to vincristine and Adriamycin in vitro and in vivo. A maximum 60% increase in life span was obtained in mice inoculated with P388 leukemia resistant to vincristine. Rhizoxin showed greater cytotoxicity in cultured tumor cells than did vincristine. Rhizoxin seems to bear consideration for further development as a new chemotherapeutic agent.     

Reversal of multidrug resistance by a novel quinoline derivative,MS-209

MS-209, a novel quinoline derivative, was examined for its reversing effect on multidrug-resistant tumor cells. MS-209 at 1–10 M completely reversed resistance against vincristine (VCR) in vitro in multidrug-resistant variants of mouse leukemia P388 cells (VCR-resistant P388/VCR and Adriamycin (ADM)-resistant P388/ADM) and human leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM). MS-209 at 1–10 M also completely reversed resistance against ADM in vitro in P388/VCR cells, K562/VCR cells, and K562/ADM cells. In ADM-resistant P388 (P388/ADM) cells, however, ADM resistance was only partially reversed at the MS-209 concentrations tested. MS-209 enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. When MS-209 was given p.o. at 80 mg/kg twice a day (total dose, 160 mg/kg per day) with 100 g/kg VCR, a treated/control (T/C) value of 155% was obtained. MS-209 also enhanced the chemotherapeutic effect of ADM in P388/ADM-bearing mice. The most prominent effects were obtained when MS-209 was given with 2 mg/kg ADM, yielding T/C values of 150%–194% for the combined treatment at an MS-209 dose of 200–450 mg/kg. MS-209 inhibited [³H]-azidopine photolabeling of P-glycoprotein efficiently. Furthermore, the accumulation of ADM in K562/ADM cells was increased more eficiently by MS-209 than by verapamil. These results indicate that MS-209, like verapamil, directly interacts with P-glycoprotein and inhibits the active efflux of antitumor agents, thus overcoming multidrug resistance in vitro and in vivo.This work was supported by grants-in-aid from the Ministry of Education Science and Culture, Japan     

Circumvention of multidrug resistance by a newly synthesized quinoline derivative, MS-073.

Newly synthesized quinoline derivatives were investigated for their efficacy to reverse multidrug resistance (MDR). In this study, one of the most effective quinoline derivatives, MS-073, was compared with verapamil with regard to its ability to overcome MDR in vitro and in vivo. MS-073 at 0.1 microM almost completely reversed in vitro resistance to vincristine (VCR) in VCR-resistant P388 cells. The compound also reversed in vitro VCR, adriamycin (ADM), etoposide, and actinomycin D resistance in ADM-resistant human myelogenous leukemia K562 (K562/ADM) cells, ADM-resistant human ovarian carcinoma A2780 cells, and colchicine-resistant human KB cells. MS-073 administered i.p. daily for 5 days with VCR enhanced the chemotherapeutic effect of VCR in VCR-resistant P388-bearing mice. Increases in life span of 19-50% were obtained by the combination of 100 micrograms/kg of VCR with 3-100 mg/kg of MS-073, as compared to the control. The ability of MS-073 to reverse MDR was remarkably higher, especially at low MS-073 doses, than that of verapamil, both in vitro and in vivo. MS-073 enhanced accumulation of [3H]VCR in K562/ADM cells. Photolabeling of P-glycoprotein with 200 nM [3H]azidopine in K562/ADM plasma membranes was completely inhibited by 10 microM MS-073, indicating that MS-073 reverses MDR by competitively inhibiting drug binding to P-glycoprotein.     

Effects of quinidine and related compounds on cytotoxicity and cellular accumulation of vincristine and adriamycin in drug-resistant tumor cells

Quinidine, which has antiarrhythmic activity, greatly enhanced the cytotoxicity of vincristine (VCR) in tumor cells and especially in VCR-resistant sublines of P388 leukemia (P388/VCR) and human myelogenous leukemia. A nontoxic concentration of quinidine increased VCR cytotoxicity in these resistant tumor cells about 50 to 80 times, and the drug in combination with VCR could completely reverse VCR resistance of these cell lines. Quinidine also enhanced the cytotoxicity of Adriamycin, especially in the Adriamycin-resistant subline of P388 leukemia; this enhancement (8-fold) was less than that of VCR toxicity in the VCR-resistant tumor line. When administered daily for 10 days with VCR, quinidine at doses of 50 to 125 mg/kg significantly enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. Some other antiarrhythmic agents also showed similar effects in vitro, but these effects were considerably lower than that of quinidine. Quinidine increased the cellular levels of VCR and daunomycin in VCR-resistant sublines of mouse and human tumors and the ADM-resistant mouse tumor line in vitro, respectively. Quinidine also enhanced the cellular accumulation of VCR in P388/VCR cells in vivo. Thus, the therapeutic effect observed in P388/VCR-bearing mice might be due to the enhanced accumulation of VCR in P388/VCR cells by quinidine. The increase of cellular accumulation of VCR was partly explained by inhibition of efflux of VCR and daunomycin from the resistant tumor cells. The mechanism of this phenomenon is discussed in relation to previous findings on calcium channel blockers.     

Antitumor effects of TZT-1027, a novel dolastatin 10 derivative, on human tumor xenografts in nude mice

TZT-1027 was evaluated for its antitumor effects in sixteen human tumors xenografted in nude mice from gastric (H-81, H-106, H-30, H-154), breast (H-31, H-62), colon (H-110, H-143), lung (LC-376, H-74, Mqnu-1, LC-351), liver (H-181), renal cell (H-12) and ovarian (H-OC-3, SOC-4) cancer lines. In the latter three and lung (Mqnu-1, LC-351) cancers the results were compared with those obtained with CPT-11, VCR, CDDP, ADM. TZT-1027 showed effective antitumor activity (IR > or = 58%) against fifteen of the tumor lines, all but LC-351, and showed markedly effective activity (IR > or = 80%) against twelve tumor lines, including drug-resistant colon (H-110), lung (H-74) and ovarian (SOC-4) cancer lines. The complete regression was shown in five H-OC-3 tumor-bearing mice out of seven. Moreover, TZT-1027 was shown to be more potent in three cancer models (Mqnu-1, H-81, SOC-4) than CPT-11, and to have markedly effective antitumor activity in two cancers (H-12, H-OC-3) in which VCR was ineffective and in ovarian cancer (SOC-4) in which CPT-11, CDDP and ADM were ineffective. The administration of TZT-1027 induced fewer side effects; transient reduction of body weight was observed in four lines out of sixteen tested. These results suggest that TZT-1027 is an excellent candidate for clinical trials for the treatment of cancer.     

MX2, a morpholino anthracycline, as a new antitumor agent against drug-sensitive and multidrug-resistant human and murine tumor cells

MX2, a new morpholino anthracycline, showed similar or superior chemotherapeutic effects to Adriamycin (ADM) against several experimental murine tumors. i.v. administration of MX2 against L1210-bearing mice induced a prolongation of life-span by twice or more compared to ADM. MX2 was equally or slightly more effective against Lewis lung carcinoma and colon adenocarcinomas 26 and 38 than ADM when either drug was given i.v. The antitumor activity of MX2 against human tumor xenografts was similar to that of ADM, and the compound was effective against three out of four gastric adenocarcinomas, one out of two non-small-cell lung carcinomas, and two out of two mammary adenocarcinomas. In particular, this compound exhibited a marked effect against MX-1, a human mammary adenocarcinoma. MX2, in contrast to ADM, was effective against sublines of P388 leukemia resistant to ADM or aclacinomycin A in vivo as well as in vitro. A maximum percentage increase in life-span of about 90% was obtained in mice bearing these resistant tumors. MX2 is a unique anthracycline antibiotic effective on drug-sensitive as well as multidrug-resistant murine and human cells.     

A fluorine-containing anthracycline (ME2303) as a new antitumor agent against murine and human tumors and their multidrug-resistant sublines

A new fluorine-containing anthracycline derivative, ME2303, showed excellent antitumor activity against various experimental tumor models. The i.p. or i.v. administrations of ME2303 on Day 1 or on Days 1, 5, and 9 against i.p.-implanted L1210 leukemia cells rendered more than 50% of mice tumor free at wide ranges of nontoxic doses, whereas the incidence of cure obtained with Adriamycin (ADM) was less than that obtained with ME2303. ME2303 given i.p. or i.v. on Day 1 or Days 1, 5, and 9 was also effective against i.p.-implanted P388 leukemia cells, and higher incidences of cure were obtained than with ADM. ME2303 administered i.v. on Days 1, 8, 15, and 22 showed prominent antitumor activity against s.c.-implanted colon adenocarcinomas 26 and 38, Lewis lung carcinoma, B16 melanoma, and M5076 sarcoma. Against colon adenocarcinoma 26, ME2303 induced cure in 16 of 20 mice at doses of 35 to 71 mumol/kg, whereas no cure was observed with ADM. Significant growth inhibition of colon adenocarcinoma 38, Lewis lung carcinoma, B16 melanoma, and M5076 sarcoma cell lines was also observed at a dose of 18 to 106 mumol/kg. ME2303 was effective against human and murine multidrug-resistant cells in vitro. For example, human myelogenous leukemia K562 resistant to ADM (K562/ADM) was only 2.8-fold more resistant to ME2303, while the cells were 200-fold more resistant to ADM when the values for the concentration of drug required for 50% inhibition of cell growth were compared. ME2303 was also more effective than ADM against human leukemia CCRF-CEM resistant to vinblastine, human ovarian carcinoma A2780 resistant to ADM, human epidermoid carcinoma KB cells resistant to colchicine, and mouse leukemia P388 resistant to ADM and vincristine. Therapeutic effects were obtained in vivo against ADM- and, especially, vincristine-resistant P388 leukemia. ME2303 is one of the most interesting potential antitumor agents to be studied further.     

Reversal of multidrug resistance by an immunosuppressive agent FK-506

Summary FK-506, a novel immunosuppressive agent, was examined for its reversing effect on multidrug-resistant tumor cells. FK-506 at 3 M completely reversed the resistance against vincristine (VCR) in vitro in VCR-resistant mouse leukemia P388 cells (P388/VCR). FK-506 also enhanced the cytotoxicity of VCR in Adriamycin(ADM)-resistant human ovarian cancer A2780 cells (AD₁₀) and ADM-resistant human myelogenous leukemia K562 cells (K562/ADM) in vitro. FK-506 was also effective in modulating sensitivity to ADM in AD₁₀ cells in vitro. FK-506 enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. When 20 mg/kg FK-506 was combined with 200 g/kg VCR, a T/C value of 151% was obtained. Under the protocol used in this study, FK-506 was more potent than cyclosporin A (CsA) and verapamil. FK-506 inhibited [³H]azidopine binding to P-glycoprotein efficiently. The binding of VCR to K562/ADM plasma membrane was inhibited by FK-506 as effectively as by CsA. Moreover, the accumulation of VCR in AD₁₀ cells was increased by FK-506 as efficiently as that of CsA and verapamil. These results indicate that FK-506 directly interacts with P-glycoprotein like CsA and verapamil, inhibits the active efflux of vincristine from resistant cells, increases the vincristine accumulation in resistant cells, and thus overcomes multidrug resistance in vitro and in vivo.Abbreviations VCR vincristine - ADM Adriamycin - CsA cyclosporin A - MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (thiazolyl blue) - T/C mean survival time of treated group of mice divided by mean survival time of control group - T/V mean survival time of treated group of mice divided by mean survival time of the group of mice treated with vincristine alone This work was supported by grants-in-aid for cancer Research from the Ministry of Education, Science and Culture, and from the Ministry of Health and Welfare, Japan     

Antitumor activity and hematotoxicity of a new, substituted dihydrobenzoxazine, FK973, in mice

FK973, a new, substituted dihydrobenzoxazine (11-acetyl-8-carbamoyloxymethyl-4-formyl-14-oxa-1,11- diazatetracyclo[7.4.1.0.0]tetra-deca-2,4,6-trien-6,9-diyl diacetate), was obtained by chemical modification of a novel antibiotic which was isolated from the fermentation products of Streptomyces sandaensis No. 6897. FK973 had cytotoxic effects against in vitro cultured human and murine tumor cells. FK973 in doses of 0.032-5.6 mg/kg (i.p.) had stronger antitumor activities and higher chemotherapeutic ratio than mitomycin C against such murine ascitic tumors as P388 and L1210 leukemia, B16 melanoma, M5076 reticulum cell sarcoma of ovarian origin, Colon 26 carcinoma, Ehrlich carcinoma, and MH134 hepatoma. In tests against murine and human solid tumors implanted s.c. in normal mice and nude mice, respectively, FK973 (i.v.) inhibited growth of murine tumors (M5076 sarcoma, Colon 38 carcinoma, B16 melanoma, and Lewis lung carcinoma) by 66-100% and human tumors (LX-1 lung, MX-1 mammary, and SC-6 stomach carcinoma) by 84-99%. In studies with drug-resistant P388 leukemia, FK973 was also effective against vincristine-resistant P388, moderately effective against mitomycin C (MMC)- and adriamycin-resistant P388, and partially effective against cyclophosphamide-resistant P388 cells in mice. Leukopenic effects of FK973 and MMC in mice were comparable at doses which gave antitumor activity almost equally. FK973 had no effect on the numbers of platelets and red blood cells, whereas MMC markedly decreased both. FK973 decreased the numbers of colony forming units in spleen and in culture and the effect was less than that of MMC. Therefore, FK973 may give weaker myelosuppression than MMC. The results suggest that FK973 will be a beneficial drug for the treatment of cancer.     

Combination therapy of CPT-11, a camptothecin derivative, with various antitumor drugs against L 1210 leukemia

Antitumor effect of CPT-11 in combination with cyclophosphamide (CY), nimustin hydrochloride (AC-NU), thio-TEPA (TESPA), methotrexate (MTX), 5-fluorouracil (5-FU), cytosine arabinoside (ara-C), thioinosine (6-MPR), adriamycin (ADM), bleomycin (BLM), mitomycin C (MMC), actinomycin D (ACT-D), vincristine sulfate (VCR), etoposide (VP-16) or cisplatin (CDDP) against L 1210 murine leukemia was investigated. The combination treatment of CPT-11 with CY, ACNU, ADM, CDDP, TESPA and ACT-D showed synergistic effects and significantly prolonged the survival time of L 1210-inoculated mice compared with CPT-11 alone or antitumor drug alone. Although the combination with 5-FU, 6-MPR, VP-16, MMC or VCR had synergistic effect for some schedules exceptionally with ara-C, MTX or BLM had slight synergistic effect against L 1210.     

Potentiation of vincristine by vitamin A against drug-resistant mouse leukaemia cells

Vitamin A has been shown to potentiate the cytotoxic action of anticancer agents like vincristine (VCR) against drug resistant mouse P388 leukaemia cells. In vitro tests showed enhancement by retinyl acetate of cytocidal activities of VCR against drug-sensitive leukaemia (P388/S) and VCR-resistant leukaemia (P388/VCR) cells in culture; retinyl acetate rather specifically potentiated VCR against cultured P388/VCR cells than P388/S cells. The cellular accumulation of radioactive VCR was significantly enhanced in cultured P388/VCR cells when retinyl acetate was present. The efflux of VCR from drug-resistant cells was blocked by retinyl acetate. The effect of the combination of vitamin A and VCR was also tested in vivo on the life-span of mice bearing P388/S or P388/VCR. Intraperitoneal administration of retinyl palmitate at 41.75 or 83.5 mg kg-1 was effective to potentiate the antileukaemic activity of VCR against P388/S bearing mice, and it also overcame vincristine-resistance in P388/VCR bearing mice.     

Antitumor activity of a novel antitumor antibiotic, quinocarmycin citrate (KW2152)

A novel antitumor antibiotic, 2a,3,4,5,6,6a,7,11b-octahydro-11-methoxy-12-methyl-3,6-imino-1H-2-oxa-11 c- azanaphth(1,2,3-cd)azulene-5-carboxylic acid monocitrate (quinocarmycin citrate; KW2152) was selected for investigation in a number of experimental tumor systems because of its efficacy against P388 leukemia. In the initial studies with P388 leukemia (i.p.-i.p.), KW2152 gave an increase in life span of greater than 80%. The activity was schedule dependent and daily administration was the most effective. KW2152 caused marginal activity against L1210 leukemia, B16 melanoma, and M5076 sarcoma. The effect on cultured cells suggested that KW2152 was not cross-resistant to Adriamycin (ADM) but was cross-resistant to mitomycin C (MMC); however, KW2152 caused prolongation of life span against mice bearing P388/ADM or P388/MMC. In tests against human tumors xenografted s.c. in nude mice, KW2152 significantly inhibited the growth of MX-1 mammary carcinoma with all tumors cured at i.v. doses of 4.4 mg/kg/day and p.o. doses of 26.2 mg/kg/day given daily for 7 days. KW2152 also inhibited distinct human gastric carcinomas, St-4 and St-15 tumors, and colon carcinoma Co-3 by daily administration for 7 days. Against St-4, KW2152 gave a treated versus control percentage of 27, compared to 52 for cis-diamminedichloroplatinum. Against Co-3, KW2152 was at least as effective as MMC, ADM, cis-diamminedichloroplatinum, and bleomycin, giving a treated versus control percentage of 18 at a dose of 8.6 mg/kg/day given daily for 7 days. KW2152 showed growth inhibitory activity against cultured murine tumors and human cells. The order of in vitro efficacy of KW2152 against murine tumors, P388 leukemia greater than L1210 leukemia, B16 melanoma, correlated with the order of the sensitivity on the i.p.-i.p. systems of these tumors. The 50% inhibitory concentrations against P388 leukemia cells were 5.3 X 10(-6) and 1.1 X 10(-7) M after 1 and 72 h exposure, respectively. KW2152 caused significant inhibition of RNA synthesis after a short time exposure. In P388 leukemia cells exposed for 1 h with KW2152, the 50% inhibitory concentration for RNA synthesis was 10(-5) M, 30-fold less than that for DNA synthesis. White blood cell depression or platelet depression was not significant after administration of the i.v. 10% lethal dose given daily for 7 days. Because of its good activity against human mammary tumor MX-1 and some effectiveness against other gastric and colon carcinomas and its water solubility, a novel antitumor antibiotic, KW2152, is being developed as a Phase I anticancer agent.     

Cellular pharmacology of MX2, a new morpholino anthracycline, in human pleiotropic drug-resistant cells

We previously reported that MX2, a new morpholino anthracycline, showed marked effects on pleiotropic drug-resistant sublines of murine P388 leukemia in vivo as well as in vitro. In this study we examine the in vitro cytotoxicity against pleiotropic drug-resistant sublines of human tumor cell lines. MX2 was effective against multidrug-resistant sublines of four human tumor cell lines; these cells, having a 4.8- to 200-fold cross-resistance to Adriamycin (ADM) showed only a 0.7- to 2.3-fold resistance to MX2 compared with the sensitive cells. To elucidate the mechanism by which MX2 overcomes multidrug resistance, the intracellular pharmacology of MX2 in human myelogenous leukemia K562 and its ADM-resistant subline (K562/ADM) was examined. Both K562 and K562/ADM cells accumulated MX2 more easily than ADM, and the intracellular accumulation of MX2 attained a steady state in both cell lines within 30 min of incubation at 37 degrees C. The amount of MX2 that accumulated in K562/ADM at a steady state was only 1.3 times lower than that in K562. However, ADM was accumulated slowly in both cell lines compared with MX2, and the intercellular concentration reached a steady state in K562/ADM after 90 min of incubation and in K562 after more than 120 min. K562/ADM cells accumulated a 3.3-fold lower concentration of ADM than K562 after 120 min of exposure. The steady-state concentration of ADM in K562/ADM was 8.3 times lower than that of MX2. In addition, greater than 70% of MX2 was retained in both cell lines after 150 min of incubation in the absence of this drug. Verapamil, a calcium antagonist, hardly augmented the cytotoxicity of MX2 against K562/ADM, and no distinct effect of this drug on both the time course and the maximal level of accumulation of MX2 was observed. Interestingly, MX2 effectively inhibited ATP/Mg2(+)-dependent [3H]vincristine binding to K562/ADM membrane preparations, indicating that MX2 could be transported outside the cell by an active efflux pump. The high intracellular accumulation and retention of MX2 in K562/ADM through the rapid influx of the drug into the cells may be one of the reasons why MX2 circumvents pleiotropic drug resistance.     

Modulation of Multidrug Resistance by SDZ PSC 833 in Leukemic and Solid-tumor-bearing Mouse Models

P-Glycoprotein inhibitors, including the nonimmunosuppressive cyclosporin D analog SDZ PSC 833 (PSC 833), have been developed to circumvent multidrug resistance. In the present study, the potential of PSC 833 in reversing multidrug resistance was evaluated in various systemic treatment models with leukemic and solid-tumor-bearing mice. Having a relatively wide therapeutic window of daily p.o. doses from 12.5 to 75 mg/kg, PSC 833 significantly improved the antileukemic activity of the anticancer drugs adriamycin (ADM), vincristine (VCR) and etoposide (VP-16) given i.p. or i.v. against i.p.-inoculated vincristine-resistant P388 tumor (P388/VCR). PSC 833 in combination with i.p.-injected anticancer drugs in optimal schedule and dosage induced apparent cures in some leukemic mice, whereas no cures were obtained with the cyclosporin A/anticancer drug combinations. PSC 833 combined with i.v.-injected anticancer drugs was highly active, but not curative, against P388/VCR and parental P388 tumors (maximum T/C>175%). PSC 833 in combination with intravenous treatment with ADM showed prominent anti-solid-tumor activity against s.c.-inoculated colon adenocarcinoma 26 and human colorectal adenocarcinoma HCT-15. Against colon adenocarcinoma 26, the PSC 833/ADM combinations induced cure in two or three of six mice. PSC 833/ADM combinations significantly inhibited the growth of the tumor with maximum percent inhibitions of 83 and 73% in the early and advanced stages of the HCT-15 tumor models, respectively. The present study demonstrated that PSC 833 is highly active in potentiating the antitumor activity of systemically administered ADM, VCR and VP-16 against four murine and human tumors with a relatively wide therapeutic window of daily p.o. dose range of 12.5–100 mg/kg.     

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 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothec in, a novel water-soluble derivative of camptothecin, against murine tumors

The search for new water-soluble analogues of camptothecin (CPT) with higher activity and less toxicity has led to the development of a novel compound, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin (CPT-11), which showed significant antitumor activity against a broad spectrum of experimental tumor models by i.p., i.v., or oral administration. When its activity against L1210 was compared with that of CPT and known derivatives, CPT-11 was most effective, giving the highest maximum increase in life span (ILS) and showing good activity over a wide dose range. The antitumor activity of CPT-11 was shown against tumors not only in the ascites form but also in the solid form. Included among the more susceptible murine tumors are S180, Meth A fibrosarcoma, Lewis lung carcinoma, Ehrlich carcinoma, MH134 hepatoma, mammary carcinoma of C3H/HeN mice, L1210, and P388 leukemia. Probable cures of these tumors were induced frequently by CPT-11. The antitumor activity of CPT-11 against i.p.-implanted L1210 was superior to that of Adriamycin in maximum ILS, the number of cured mice, and the therapeutic ratio. CPT-11 at a dose of 100 mg/kg produced an ILS in excess of 300% with five of six mice surviving tumor free, and effected 100% tumor regression at 200 mg/kg, whereas the optimum dose of Adriamycin, 12.5-25 mg/kg, brought about 114-129% ILS with one of six mice surviving. The acute toxicity of CPT-11 was extremely low, particularly in the case of oral administration. CPT-11 is expected to be clinically useful.