Antitumor activity of ME2303, a fluorine-containing anthracycline, against human tumors implanted in nude mice

A fluorine-containing anthracycline, ME2303, given intravenously once a week for 4 weeks at the maximum tolerated doses showed better therapeutic effects against 2 gastric, 3 lung and 2 human breast tumor xenografts than did adriamycin (ADM) at the maximum tolerated dose. Among the tumors, ME2303 showed a better effect against St-40, a well-differentiated human gastric adenocarcinoma, against which ADM showed only a marginal effect. Likewise, ME2303 was more effective against Lu-24 human small cell carcinoma and MX-1 human medullary tubular adenocarcinoma than ADM. Notably, the Lu-24 tumor, developed in nude mice, disappeared after the treatment in 3 out of 6 mice. ME2303 would be an interesting compound for phase I and II clinical studies in the future.     

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.     

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.     

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.     

Differential intracellular processing of the anthracycline drug ME2303 in doxorubicin-sensitive (A2780) and -resistant (A2780AD) human ovarian cancer cells as studied with confocal laser scanning microscopy and image analysis

Laser scanning confocal microscopy has been used to follow the uptake and efflux of the 2-fluoroglycoside of doxorubicin, ME2303, in live cultures of the human ovarian cancer cell line A2780 and its doxorubicin-resistant variant A2780AD. Our methods combine confocal laser scanning microscopy and image analysis to examine the dynamics of anthracycline drugs in cancer cells. Cytotoxicity determined by MTT dye reduction showed that A2780AD cells were more than 400 times less sensitive to doxorubicin compared to A2780 cells but almost 9 times more sensitive to ME2303 compared to doxorubicin. The naturally fluorescent drug was tracked within live cells at 37°C to provide time-course information in relation to nuclear and Golgi-associated cellular domains, as indicated by BODIPY FL ceramide-associated fluorescence. In both cell types, ME2303 was characterised by strong nuclear membrane and peri-nucleolar fluorescence and as a localised punctate pattern within the nucleus. A2780AD cells accumulated ME2303 in their nuclei at a much reduced rate compared to the doxorubicin-sensitive cells, and ME2303 efflux from resistant cell nuclei was approximately twice as fast as from A2780 cells. The relative uptake of ME2303 into Golgi-associated domains and the nucleus were monitored simultaneously during the initial 35 min of exposure to 10 μM ME2303 and during the first 45 min of a “chase” culture following exposure to 20 μM ME2303. ME2303 was detectable within the Golgi-associated domains of A2780 cells several minutes later and in less relative concentration than in A2780AD cells 15 min into a chase culture. Our results suggest the direct involvement of differences in drug processing via the Golgi apparatus in the expression of P-glycoprotein-related drug resistance.     

Antitumor activity and metabolism of a new anthracycline-containing fluorine (ME2303) in Lewis lung carcinoma-bearing mice.

(7-O-(2,6-Dideoxy-2-fluoro-alpha-L-talopyranosyl)adriamycinone-14- hemipimerate (ME2303) showed a more marked growth inhibition of Lewis lung carcinoma than adriamycin (ADM). When administered to s.c. Lewis lung carcinoma-bearing mice, ME2303 in the plasma and liver was rapidly metabolized and disappeared. However, ME2303 was incorporated into the tumor at higher concentrations and remained in the tumor for a longer period than in the plasma and liver. ME2303 was metabolized to 7-O-(2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl)adriamycinone (M1), the product of esterolysis, and its reduced derivative at the C-13 position (M2). Larger amounts of these metabolites were found in the analyzed tissues than in plasma. The maximum concentration of M1 in the tumor was observed at 2 h posttreatment, while the maxima in the plasma and liver were observed at 15 min. On the other hand, i.v. injection of M1 into mice showed a weaker antitumor effect than ME2303 injection, though M1 levels in the plasma and tumor were almost the same as those after administration of ME2303 at the maximum tolerated doses. Some metabolites of ME2303 were found in the tumor after administration of ME2303, but not after administration of M1. ADM remained in the analyzed tissues for a long period and ADM concentrations in the tumor were much higher than in the plasma but less than in the liver. M1 reached a concentration higher than that of ADM in the tumor, opposite to the pattern observed in the liver. The conversion process from ME2303 to M1, the metabolites and their locations in the tumor may be important for the marked antitumor effect of ME2303 in vivo.     

Antitumor activity of murine tumor necrosis factor (TNF) against transplanted murine tumors and heterotransplanted human tumors in nude mice

The antitumor activity of highly purified tumor necrosis factor (TNF) was tested against eight kinds of murine tumor and five kinds of human tumor heterotransplanted into nude mice. Mice were treated by intravenous or intratumoral injection of TNF, commencing when the tumors were well established. TNF showed an excellent curative effect against all kinds of murine and human tumors tested. Meth A sarcoma, Colon 26, Ehrlich, sarcoma 180, MM 46, MH 134, B16 melanoma, and Lewis lung tumors transplanted into mice underwent tumor necrosis and regression following a single injection of TNF. Sometimes a complete cure was observed in Meth A sarcoma, sarcoma 180, Ehrlich, and MM 46 tumors. Human cancers, SEKI, HMV-I, KATO-III, MKN 45, or KB, heterotransplanted into nude mice, also exhibited tumor necrosis and regression in size following several intratumoral injections of TNF. A great difference in curative effects of TNF was observed in Meth A sarcomas between those transplanted into BALB/c nu/+ and into BALB/c nu/nu mice: following a single intravenous administration the effect was stronger in BALB/c nu/+ than in nu/nu mice. In contrast, tumor necrosis was almost the same in nu/+ and nu/nu mice following intratumoral administration. The present results thus indicate that TNF from mice had an antitumor activity against not only murine tumors but also human tumors. In addition to direct cytotoxicity against tumor cells, TNF induced a host-mediated factor which contributed to the antitumor effects.     

Combined effect of PT-050 (recombinant human TNF) and antitumor drugs on syngeneic murine tumors

The combined effect of PT-050 (recombinant human TNF) and various antitumor drugs was investigated using murine colon 26 adenocarcinoma, Meth A sarcoma and B16 melanoma transplanted into syngeneic mice. When colon 26- or Meth A- bearing mice were intravenously given PT-050 in combination with mitomycin C (MMC), doxorubicin (DXR), cis-platinum (CDDP), 5-fluorouracil (5-FU) or cyclophosphamide (CPA), a significant synergistic effect was observed, that is, both the inhibition rate of tumor growth and the cured ratio were increased significantly when compared with those given each drug alone. Similarly, an augmentation of the antitumor effect was also observed in B16-bearing mice by a combined treatment with PT-050 and these antitumor drugs. These results suggest that the combination chemotherapy of PT-050 with various antitumor drugs may be useful for cancer therapy.     

Antitumor Activity and Metabolism of a New Anthracycline-containing Fluorine (ME2303) in Lewis Lung Carcinoma-bearing Mice

(7-O-(2,6-Dideoxy-2-fluoro-α-L-talopyranosyl)adriamycmone-14-hemipimerate (ME2303) showed a more marked growth inhibition of Lewis lung carcinoma than adriamycin (ADM). When administered to s.c. Lewis lung carcinoma-hearing mice, ME2303 in the plasma and liver was rapidly metabolized and disappeared. However, ME2303 was incorporated into the tumor at higher concentrations and remained in the tumor for a longer period than in the plasma and liver. ME2303 was metabolized to 7-O-(2,6-dideoxy-2-fluoro-α-L-talopyranosyl) adriamycinone (M1), the product of esterolysis, and its reduced derivative at the C-13 position (M2), Larger amounts of these metabolites were found in the analyzed tissues than in plasma. The maximum concentration of Ml in the tumor was observed at 2 h posttreatment, while the maxima in the plasma and liver were observed at 15 min. On the other hand, i.v. injection of M1 into mice showed a weaker antitumor effect than ME2303 injection, though Ml levels in the plasma and tumor were almost the same as those after administration of ME2303 at the maximum tolerated doses. Some metabolites of ME2303 were found in the tumor after administration of ME2303, but not after administration of M1. ADM remained in the analyzed tissues for a long period and ADM concentrations in the tumor were much higher than in the plasma but less than in the liver. M1 reached a concentration higher than that of ADM in the tumor, opposite to the pattern observed in the liver. The conversion process from ME2303 to M1, the metabolites and their locations in the tumor may be important for the marked antitumor effect of ME2303 in vivo.     

Enhancement of the antitumor effect of cyclophosphamide with the hypoxia-selective cytotoxin NLCQ-1 against murine tumors and human xenografts

The antitumor effect of cyclophosphamide (CPM) was investigated against SCCVII murine tumors and PC-3 human xenografts in combination with the hypoxia-selective cytotoxin 4-[3-(2-nitro-1-imidazolyl)-propylamino]-7-chloroquinoline hydrochloride (NLCQ-1). The in vivo-in vitro and the tumor regrowth assays were used, respectively, as end points. In certain cases the hypoxia-selective cytotoxin tirapazamine (TPZ) was included for comparison purposes. In the SCCVII/C3H model, bone marrow toxicity studies were performed in parallel by using a modified CFU-GM assay. In the SCCVII/C3H model, when NLCQ-1 (10 mg/kg i.p.) was given 1 h before cyclophosphamide (CPM; 75-200 mg/kg i.p.), dose-modification factors (DMFs) of 1.9 and 1.0 were achieved for the antitumor effect and bone marrow toxicity, respectively. The corresponding DMF values obtained with TPZ (23 mg/kg) given 2.5 h (optimal time) before CPM were 1.3 and 1.0, respectively. Thus, therapeutic indices (T.I.) of 1.9 and 1.3 were achieved with NLCQ-1 and TPZ, respectively. In the PC-3/athymic nude mouse model, NLCQ-1 (10 mg/kg) given 90 min before CPM (36 mg/kg), qd x 4, increased tumor regrowth delay by 8.7 days compared to CPM alone, at 16-fold the original tumor size. The corresponding log cell kill was 0.86 and -0.03 for NLCQ-1 + CPM and CPM alone, respectively. In general, NLCQ-1 in combination with nontoxic but inactive CPM doses (36 or 54 mg/kg, qd x 4) elicited good antitumor activity without subsequent additive systemic toxicity, whereas NLCQ-1 had minimal effect in combination with the active but toxic (> 10% mean net weight loss) CPM dose of 80 mg/kg. These results suggest a potential use of NLCQ-1 in the clinic as an adjuvant to chemotherapy with CPM.     

In vitro antitumor activity of the novel marine agent, Ecteinascidin-743 (ET-743, NSC-648766) against human tumors explanted from patients

Background: Ecteinascidin-743 (ET-743), a member of the ecteinascidin family selected for clinical development, is a tetrahydroisoquinolone alkaloid isolated from the marine ascidian, Ecteinascidia turbinata. This novel compound is a minor groove binding, guanine-specific alkylating agent which also interacts with the microtubule network and blocks cell cycle progression at late S/G2.Materials and methods: A soft agar cloning assay was used to determine the in vitro effects of ET-743 against primary human tumor specimens taken directly from patients. A total of 93 evaluable specimens were exposed to ET-743 for one-hour (n = 25) and/or 14-day continuous exposure (n = 92) at concentrations ranging from 0.1 nM to 1 µM. In vitro responses were defined as an inhibition 50% of human tumor colony forming units at a given concentration.Results: One-hour exposure to ET-743 at concentrations of 0.1 nM, 1 nM, 10 nM, 100 nM and 1 µM induced in vitro responses in 0% (0/17), 6% (1/17), 16% (4/25), 13% (1/8), and 25% (2/8) of specimens, respectively. Continuous exposure to ET-743 at concentrations of 0.1 nM, 1 nM, 10 nM, 100 nM and 1 µM, inhibited 0% (0/16), 13% (2/16), 49% (44/90), 62% (47/76), and 77% (58/75) of tumor specimens, respectively. Tumor-specific responses and concentration-dependent relationships were observed with a continuous exposure to ET-743. At 100 nM, the compound inhibited 79% (11/14) breast, 69% (9/13) non-small-cell lung, 58% (7/12) ovary, and 88% (7/8) melanoma specimens. At 1 µM, ET-743 inhibited 100% (14/14) breast specimens, 85% (11/13) non-small-cell lung, 67% (8/12) ovary and 86% (6/7) melanoma specimens. Activity of ET-743 at and above 10 nM was also observed against sarcoma and kidney tumors. At 10 nM concentration and continuous exposure ET-743 demonstrated incomplete cross-resistance with paclitaxel, alkylating agents, doxorubicin and cisplatin.Conclusions: Our data from the cloning assay indicate that the duration of exposure to ET-743 is an important factor in human tumors. Therefore, long-term exposure to ET-743 may be preferred in future clinical trials. The activity of ET-743 in breast, non-small-cell lung, and ovarian cancers as well as in melanoma may deserve further clinical evaluations. The potential of ET-743 in sarcoma and renal tumors might also be considered. In addition, our data indicate that a plasma concentration of 100 nM of ET-743 must be considered as a target during the clinical development of the compound; also the concept of continuous/protracted exposure in clinical trials with ET-743 has to be taken into account.     

Antitumor effects of a new antitumor agent, zinostatin stimalamer (YM881)--effects on experimental tumors in vitro and in vivo]

Zinostatin stimalamer (YM881) is an antitumor agent, chemically synthesized by coupling one molecule of neocarzinostatin (NCS), with 2 molecules of styrene maleic acid half-butylester copolymer. YM881 showed strong cytotoxicity to human (KB, ST4 and others) and mouse (P388, L1210) tumor cell lines and also drug-resistant tumor cell lines. The antitumor effects were observed in murine MM46, colon 26 and other tumor models. The antitumor activity was as effective as NCS or better than NCS at the effective dose ranges.     

GTI-2040, an antisense agent targeting the small subunit component (R2) of human ribonucleotide reductase,shows potent antitumor activity against a variety of tumors

GTI-2040 is a 20-mer oligonucleotide that is complementary to a coding region in the mRNA of the R2 small subunit component of human ribonucleotide reductase. In vitro studies using a number of human tumor cell lines have demonstrated that GTI-2040 decreases mRNA and protein levels of R2 in a sequence- and target-specific manner. In vivo studies have shown that GTI-2040 significantly inhibits growth of human colon tumors (adenocarcinoma), pancreatic tumors (adenocarcinoma), liver tumors, lung tumors, breast tumors (adenocarcinoma), renal tumors, ovarian tumors (adenocarcinoma), melanoma, brain glioblastoma-astrocytoma, prostatic tumors, and cervical tumors in nude and/or severe combined immunodeficient mice. Antitumor effects were not observed with an oligonucleotide containing four mismatches to the R2 sequence or with a scrambled sequence containing the same base content but not complementary to R2. This suggests that an antisense mechanism is responsible for the in vivo observations. In addition to tumor growth assays, GTI-2040 was tested in a murine model of human lymphoma. Treatment of severe combined immunodeficient mice bearing Burkitt's lymphoma with GTI-2040, but not control oligonucleotides, greatly extended the survival of mice, and survival extended well beyond the treatment period. Finally, GTI-2040 specifically inhibits metastasis of human melanoma cells to the lungs in nude mice. Taken together, the results of these studies indicate that GTI-2040 can act as a selective and specific anticancer agent against a broad range of human tumors.     

Antitumor activity of a new fluoropyrimidine derivative, 5'-deoxy-5-fluorouridine, against murine and human experimental tumors

5'-Deoxy-5-fluorouridine (5'-DFUR) was evaluated for antitumor activity against four murine tumors (L1210 leukemia, P388 leukemia, Lewis lung carcinoma, and B16 melanoma) and a human mammary carcinoma (MX-1) xenografted in athymic mice. Intraperitoneal administration of 5'-DFUR was ineffective against B16 melanoma implanted intraperitoneally and showed less marked antitumor activity against P388 and L1210 leukemias implanted intraperitoneally or intravenously as compared with that of 5-fluorouracil (5-FU) or 1-(2-tetrahydrofuryl)-5-fluorouracil (FT-207), while oral administration of 5'-DFUR showed a similar or superior antitumor activity to that of 5-FU or FT-207 against L1210 leukemia implanted subcutaneously. 5'-DFUR showed a marked antitumor activity against MX-1 implanted subcutaneously and also showed slight antitumor activity against Lewis lung carcinoma implanted subcutaneously, while 5-FU and FT-207 did not show any significant antitumor activity against these tumors. These results suggest that 5'-DFUR may be worthy of clinical trial against solid tumors, especially cancers of the breast.     

Cellular pharmacology and antitumor activity of N-(p-azidobenzoyl)-daunorubicin,a photoactive anthracycline analogue

Summary We have previously utilized N-(p-azidobenzoyl)daunorubicin (NABD), a photoactive analogue of daunorubicin (DNR), to identify unique anthracycline-binding polypeptides in rodent tissues and in tumor cells. Using cultured P388 tumor cells, we have now compared the cellular pharmacology and antitumor activity of NABD with that of DNR. Although rapidly accumulated by cells, the intracellular concentration of NABD was less than 20% that of DNR at steady-state levels. The cellular uptake of both drugs by P388 cells was dependent on extracellular drug concentration in the medium and on temperature. The rapid efflux of NABD and DNR from P388 cells in drug-free medium was reduced at lowered temperature (0 °C). Cytofluorescence microscopy demonstrated that NABD was predominantly localized in the cytoplasm, in contrast to the nuclear localization of DNR. NABD produced dose-dependent inhibition of [³H]thymidine (IC₅₀=10.0 M) and [³H]uridine (IC₅₀=1.60 M) incorporation in P388 cells to a lesser degree than DNR ([³H]thymidine, IC₅₀=0.15 M and [³H]uridine, IC₅₀=0.70 M). Continuous exposure to NABD inhibited P388 cell proliferation with an IC₅₀ of 0.27 M, compared with an IC₅₀ of 0.017 M for DNR. NABD is a pharmacologically active, photoactive analogue of DNR, which possesses properties different from those of the parent drug but similar to those of other anthracycline analogues. Photoaffinity labeling studies with NABD may identify important cytoplasmic constitutents which interact with this type of anthracycline and perhaps with the anthracycline antibiotics in general.Abbreviations used NABD N-(p-azidobenzoyl)daunorubicin - DNR daunorubicin - D₂ daunorubicinol - NABD₂ N-(p-azidobenzoyl)daunorubicinol - dDa 7-deoxydaunorubicin aglycone - dD_2a 7-deoxydaunorubicinol aglycone - TLC thin-layer chromatography - HPLC high-pressure liquid chromatography - THF tetrahydrofuran - PBS phosphate-buffered saline - DMSO dimethylsulfoxide     

Gold(III) complexes as a new family of cytotoxic and antitumor agents

In recent years, owing to the contributions of a few research groups, some new gold(III) compounds--either simple coordination complexes or organogold compounds--have been prepared that are sufficiently stable under physiological conditions and are promising candidates for pharmacological testing as cytotoxic and antitumor agents. In vitro pharmacological studies point out that some of these novel gold(III) complexes are highly cytotoxic toward cultured human tumor cell lines and are able to overcome resistance to platinum. Significant differences in the spectrum of action were observed compared with cisplatin. Studies are in progress to elucidate the mechanism of action of these compounds. The cellular effects of two representative gold(III) complexes are described. Preliminary results on binding to DNA in vitro are presented, pointing out that the interactions are generally weak. The implications of these results for the development of gold(III) complexes as a new family of cytotoxic and antitumor agents are discussed.     

Gold(III) complexes as a new family of cytotoxic and antitumor agents

In recent years, owing to the contributions of a few research groups, some new gold(III) compounds – either simple coordination complexes or organogold compounds – have been prepared that are sufficiently stable under physiological conditions and are promising candidates for pharmacological testing as cytotoxic and antitumor agents. In vitro pharmacological studies point out that some of these novel gold(III) complexes are highly cytotoxic toward cultured human tumor cell lines and are able to overcome resistance to platinum. Significant differences in the spectrum of action were observed compared with cisplatin. Studies are in progress to elucidate the mechanism of action of these compounds. The cellular effects of two representative gold(III) complexes are described. Preliminary results on binding to DNA in vitro are presented, pointing out that the interactions are generally weak. The implications of these results for the development of gold(III) complexes as a new family of cytotoxic and antitumor agents are discussed.     

Preclinical antitumor activity of an alpha-picoline derivative, penclomedine (NSC 338720), on human and murine tumors

Penclomedine, a synthetic alpha-picoline derivative, was identified as a potential antitumor agent in the P388 leukemia prescreen of the National Cancer Institute. Upon further evaluation in the National Cancer Institute in vivo tumor panel, the compound demonstrated good activity against two breast tumors. A single i.p. dose or five daily doses caused partial regressions of advanced-stage s.c. implanted mouse CD8F1 mammary adenocarcinomas. Also, penclomedine administered i.p. on Days 1,5, and 9 caused regression of the human MX-1 mammary carcinoma implanted under the renal capsule of athymic mice. In contrast, penclomedine demonstrated only marginal to moderate activity against the i.p. implanted L1210 leukemia and M5076 sarcoma and was inactive in three additional non-breast tumor models (i.p. B16 melanoma, i.v. Lewis lung carcinoma, and s.c. colon adenocarcinoma 38). Penclomedine administered p.o. and i.p. was equally effective against the subrenal capsule MX-1. Doses given p.o. every fourth day caused complete regression of 39 of 40 advanced-stage s.c. implanted MX-1 tumors but were much less effective against human H82 small cell lung carcinomas (13 of 80 complete regressions). Penclomedine p.o. also inhibited growth of the human MCF-7 and mouse 16/C breast adenocarcinomas. Further studies to support the development of penclomedine to clinical trial are in progress.