Animal board invited review: advances in proteomics for animal and food sciences

Animal production and health (APH) is an important sector in the world economy, representing a large proportion of the budget of all member states in the European Union and in other continents. APH is a highly competitive sector with a strong emphasis on innovation and, albeit with country to country variations, on scientific research. Proteomics (the study of all proteins present in a given tissue or fluid - i.e. the proteome) has an enormous potential when applied to APH. Nevertheless, for a variety of reasons and in contrast to disciplines such as plant sciences or human biomedicine, such potential is only now being tapped. To counter such limited usage, 6 years ago we created a consortium dedicated to the applications of Proteomics to APH, specifically in the form of a Cooperation in Science and Technology (COST) Action, termed FA1002--Proteomics in Farm Animals: www.cost-faproteomics.org. In 4 years, the consortium quickly enlarged to a total of 31 countries in Europe, as well as Israel, Argentina, Australia and New Zealand. This article has a triple purpose. First, we aim to provide clear examples on the applications and benefits of the use of proteomics in all aspects related to APH. Second, we provide insights and possibilities on the new trends and objectives for APH proteomics applications and technologies for the years to come. Finally, we provide an overview and balance of the major activities and accomplishments of the COST Action on Farm Animal Proteomics. These include activities such as the organization of seminars, workshops and major scientific conferences, organization of summer schools, financing Short-Term Scientific Missions (STSMs) and the generation of scientific literature. Overall, the Action has attained all of the proposed objectives and has made considerable difference by putting proteomics on the global map for animal and veterinary researchers in general and by contributing significantly to reduce the East-West and North-South gaps existing in the European farm animal research. Future activities of significance in the field of scientific research, involving members of the action, as well as others, will likely be established in the future.

The microbiological quality of hot water-washed broccoli florets and cut green beans

AIMS

To determine the effect of hot water washing on the microbiological quality of cut broccoli florets and trimmed green beans.

METHODS AND RESULTS

Broccoli florets and trimmed beans were washed for 90 s in tap water at either 20 degrees C or 52 degrees C and stored at 7 and 10 degrees C. The numbers of naturally occurring aerobic mesophilic organisms, Pseudomonas spp., Enterobacteriaceae, yeast and moulds and lactobacilli or lactic acid bacteria were enumerated at intervals for up to 2 weeks. The ability of Listeria monocytogenes, Bacillus cereus and Escherichia coli O157:H7 inoculated onto the tissue post heat treatment to survive or grow was also measured to mimic the effect of postprocess contamination. Using a hot wash treatment improved the initial appearance of the vegetables and resulted in a small, but significant, reduction in populations of all groups of endogenous flora measured. The number of yeast and moulds on the vegetables washed at 52 degrees C remained below the levels observed on the 20 degrees C washed vegetables throughout the observation period, but Pseudomonas spp., lactobacilli and Enterobacteriaceae were better able to grow on the hot-washed vegetables such that the counts at the end of storage were greater on hot-washed than ambient-washed vegetables. All three of the pathogens tested were better able to grow on hot-washed broccoli and beans than on equivalent product washed at 20 degrees C.

CONCLUSIONS

Hot water washing can be used to control enzymic browning or yeast and moulds growth but it can also allow more rapid and extensive growth by pathogens and spoilage organisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

Reduced protection against growth by pathogens means that the hot wash treatment of vegetables should be used with caution and requires careful assessment of risk.

Use of a novel method to characterize the response of spores of non-proteolytic Clostridium botulinum types B, E and F to a wide range of germinants and conditions

AIMS

Limited information is available on the germination triggers for spores of non-proteolytic Clostridium botulinum. An automated system was used to study the effect of a large number of potential germinants, of temperature and pH, and aerobic and anaerobic conditions, on germination of spores of non-proteolytic Cl. botulinum types B, E and F.

METHODS AND RESULTS

A Bioscreen analyser was used to measure germination by decrease in optical density. Results were confirmed by phase-contrast light microscopy. Spores of strains producing type B, E and F toxin gave similar results. Optimum germination occurred in L-alanine/L-lactate, L-cysteine/L-lactate and L-serine/L-lactate (50 mmol l(-1) of each). A further 12 combinations of factors induced germination. Sodium bicarbonate, sodium thioglycollate and heat shock each enhanced germination, but were not essential. Germination was similar in aerobic and anaerobic conditions. The optimum pH range was 5.5-8.0, germination occurred at 1-40 degrees C, but not at 50 degrees C, and was optimal at 20-25 degrees C.

CONCLUSIONS

The automated system enabled a systematic study of germination requirements, and provided an insight into germination in spores of non-proteolytic Cl. botulinum.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results extend understanding of germination of non-proteolytic Cl. botulinum spores, and provide a basis for improving detection of viable spores.

Preclinical antitumor activity of bizelesin in mice

Bizelesin (U-77779, NSC 615291), a synthetic analogue of the cytotoxic antibiotic CC-1065, is a bifunctional alkylating agent that produces DNA interstrand cross-links. Bizelesin was evaluated for antitumor activity against a broad spectrum of syngeneic murine tumors and human tumor xenografts in mice. Systemic drug administration produced >6.7 log10 cell kill against i.p. implanted P388 and L1210 leukemias and 80% tumor-free survivors against s.c. implanted L1210. Against i.p. implanted B16 melanoma, i.p. drug administration produced a 158%; increase in life span with 25% tumor-free survivors, whereas i.v. drug administration produced only a 67% increase in life span with no tumor-free survivors. More than 1.0 log10 cell kill was observed at low microgram/kg doses in several human tumor models representing diverse histiotypes (CAKI-1 renal, LX-1 lung, HT-29 colon, LOX IMVI and UACC-62 melanomas, and MX-1 mammary). Less than 1.0 log10 cell kill was exhibited in other tumor models (Lewis lung, colon 38, pancreatic 02, MCF7 mammary, and SK-MEL-3 melanoma). Bizelesin was optimally active when administered i.v. Although antitumor activity was independent of the schedule of administration, greater total doses were tolerated on the more prolonged schedules in any given experiment. Therapeutic doses of bizelesin did not produce delayed deaths, which had previously been observed for the parent compound CC-1065. However, recovery of lost weight was not attained until 16-30 days posttherapy. Bizelesin was as active against murine leukemia sublines resistant to cisplatin, melphalan, and 1,3-bis-(2-chloroethyl)-1-nitrosourea as against the parental line but was totally inactive against a doxorubicin-resistant subline. The complete cross-resistance of the doxorubicin-resistant subline to bizelesin suggests that bizelesin may be a substrate for the efflux pump that causes multidrug resistance. Due to its breadth of antitumor activity, potency, unique mechanism of action, and lack of cross-resistance with other alkylating agents, bizelesin was selected for development in clinical trials by the National Cancer Institute and the Upjohn Company. Toxicological studies and pharmaceutical development have been completed, and clinical trials are planned to start in the summer of 1996.

Antitumor 2,3-dihydro-2-(aryl)-4(1H)-quinazolinone derivatives. Interactions with tubulin

A series of derivatives of 2,3-dihydro-2-(aryl)-4(1H)-quinazolinone (DHQZ) with known antitumor activity was re-evaluated in the National Cancer Institute cancer cell line screen. Analysis by the COMPARE algorithm suggested that their cytotoxicity derived from interactions with tubulin. Significant inhibition of tubulin assembly and of the binding of radiolabeled colchicine to tubulin was demonstrated with several of the compounds, particularly NSC 145669, 175635, and 175636. The DHQZ derivatives are structurally analogous to a number of antimitotic agents, flavonols and derivatives of 2-styrylquinazolin-4(3H)-one and of 2-phenyl-4-quinolone. Structure-activity analogies between these agents, the combretastatins, and the colchicinoids were analyzed and summarized.

Antiproliferative effect in vitro and antitumor activity in vivo of brefeldin A

PURPOSE

An empiric in vitro screen of human tumor cell lines found brefeldin A inhibited the growth of immortalized human cell lines, with particular sensitivity to brefeldin in a series of immortalized melanoma cell lines and nonimmortalized prostate carcinoma explants. Brefeldin A alters the morphology and function of the Golgi apparatus, endosomal, and trans-Golgi compartments in different cell types. The studies presented here sought to obtain evidence of in vivo antitumor activity by brefeldin A.

METHODS

Antiproliferative activity was studied in prostate carcinoma cells in vitro using cell counts, protein, and viable stains. Activity was also studied in vivo against subcutaneous and subrenal capsule melanoma models.

RESULTS

Protracted exposures in vitro (between 24 and 72 hours) are necessary to cause persistent growth inhibition of immortalized PC3 prostate carcinoma cells. In human melanoma athymic mouse xenografts, brefeldin A showed antitumor activity in vivo when given 16 to 64 mg/kg/injection intraperitoneally q 7 h x 2, daily for 5 days. Activity was also observed in the intraperitoneal LOX IMVI (65%-100% increase in life span, with 17%-50% day 60 survivors); early-stage subcutaneous LOX IMVI and SK-MEL-5 (86%-100% growth inhibition), and subrenal capsule SK-MEL-5 and M19-MEL models.

CONCLUSIONS

Brefeldin A possesses noteworthy antitumor activity in vivo and antiproliferative effects in vitro in certain cell types. Strategies to allow protracted exposure of tumor cells to brefeldin A while preserving a therapeutic index are needed to assess the clinical potential of brefeldin A.

Synthesis, antitumor activity, and chemical properties of silaplatin and related platinum (II) and platinum (IV) complexes derived from beta-silyl amines

Platinum (II) and platinum (IV) coordination complexes derived from beta-silyl-substituted amines were prepared. The solubility of selected complexes in water and physiological saline was measured, and the effect of the beta-silicon on the reactivity of the complex in aqueous solution was determined by HPLC. The stabilities of selected silyl complexes were compared to the carbon analogues. The cyclic complexes 2a ("silaplatin") and its Pt(IV) analogue, 2b, were very active against L1210 leukemia in vivo. Both the platinum (II) complex 2a and the platinum (IV) complex 2b produced a significant number of cures over the dose range 10-40 mg/kg. The platinum (II) complex 2a, silaplatin, was very active in vivo against an L1210 leukemia subline that was resistant to cisplatin; 2a was also active, when given ip, against ic implanted L1210. The cyclobutanedicarboxylic acid complex 3c was synthesized; this complex was active against both cisplatin sensitive and resistant L1210 leukemia but was less potent than the analogous dichloro compound 2a. The acyclic platinum (II) and platinum (IV) complexes 1a,b were synthesized and unexpectedly found to be inactive in vivo against L1210 leukemia. More lipophilic silaplatin analogues were prepared--Pt(II) complex 2c and Pt(IV) complex 2d have one additional methylene carbon compared to 2a,b, whereas Pt(II) complex 2e and Pt(IV) complex 2f have two additional methylene carbons. Cyclization of the alkyl groups attached to the silicon gave the spiro bicyclic Pt(II) complexes 10a and 11a and the Pt(IV) complexes 10b and 11b.

Efficacy of the quinocarmycins KW2152 and DX-52-1 against human melanoma lines growing in culture kand in mice

Quinocarmycin monicitrate (KW2152) and its analogue, DX-52-1, demonstrated specificity for melanomas in the National Cancer Institute in vitro human tumor cell line drug screen. In contrast to most cell lines, a 50% reduction in tumor cell burden (as measured protein) at the end of a 48-h drug incubation was produced in five of eight melanoma lines by KW2152 concentrations (LC50s) ranging from 0.49 to 10.93 microM and by DX-52-1 concentrations ranging from 0.71 to 7.33 microM. Using the COMPARE algorithm, the patterns of differential cytotoxicity for both agents at the LC50 level of effect most closely resembled those for actinomycin D, mithramycin, and Adriamycin. In in vivo studies, both KW2152 (40 mg/kg/day) and DX-52-1 (90 mg/kg/day) caused partial and complete regressions of staged s.c.-implanted LOX IMVI melanoma xenografts following i.p. administration on days 5, 9, and 13 and produced tumor growth delays of 231 and 181%, respectively (P < 0.001). Activity was augmented by more prolonged therapy. Statistically significant growth inhibition of SK-MEL-2, UACC-62, UACC-257, and M14, but not SK-MEL-5 and MALME-3M, melanoma xenografts also was observed following every fourth or seventh day i.p. treatments. Based on these findings, DX-52-1 has been selected by the National Cancer Institute for development to clinical trial especially against melanomas. This agent represents one of the first to be selected for preclinical development based on disease-panel specificity discovered in the National Cancer Institute cancer drug screen.

Reversal by cytidine of cyclopentenyl cytosine-induced toxicity in mice without compromise of antitumor activity

Among nine compounds surveyed, cytidine was found to be the most effective in reversing the antiproliferative effects of cyclopentenyl cytosine (CPEC) on human T-lymphoblasts (MOLT-4) in culture. Cytidine, at concentrations of 1-25 microM, enabled cells to maintain normal logarithmic growth when added up to 12 hr after exposure to a 200 nM concentration of the oncolytic nucleoside, CPEC. The most abundant CPEC metabolite, CPEC-5'-triphosphate, is a potent [K1 approximately 6 microM] inhibitor of CTP synthetase (EC 6.3.4.2). Accumulation of this inhibitor resulted in a depletion of CTP levels to 17% of their original cellular concentration. Exogenous cytidine reversed CPEC-induced cellular cytotoxicity by suppressing the formation of CPEC-5'-triphosphate by 70%, and by partially replenishing intracellular CTP to at least 60-70% of its original concentration. In vivo, cytidine (500 mg/kg) administered intraperitoneally 4 hr after each daily dose of CPEC (LD10-LD100) for 9 days reduced the toxicity and abolished the lethality of CPEC to non-tumored mice. Of greater practical importance is the finding that, under these experimental conditions, cytidine did not curtail the antineoplastic properties of CPEC in L1210 tumor-bearing mice. Moreover, the concentration range over which CPEC exhibited antineoplastic activity was extended with cytidine administration.

Preclinical antitumor activity of temozolomide in mice: efficacy against human brain tumor xenografts and synergism with 1,3-bis(2-chloroethyl)-1-nitrosourea

Temozolomide, a methylating agent with clinical activity against brain tumors, demonstrated excellent antitumor activity following p.o. administration to athymic mice bearing human brain tumor xenografts. In the early stage s.c. implanted SNB-75 astrocytoma model, a 400-mg/kg dose administered on Day 5 produced 10 of 10 Day 54 tumor-free mice. In later staged s.c. U251 and SF-295 glioblastoma models, a single 600-mg/kg dose produced 9 of 10 Day 86 and 2 of 10 Day 40 tumor-free mice, respectively. In the latter group, a tumor growth delay of > 315% was attained. Similar levels of activity were attained with equal total doses on schedules of daily for 5 doses and every fourth day for 3 doses. A single 40-mg/kg i.v. dose of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) also demonstrated excellent activity, producing 9 of 10 tumor-free mice in the SNB-75 model and growth delays of 283 and 301% in the U251 and SF-295 models, respectively. Temozolomide was also highly effective against intracerebral implants of the U251 and SF-295 glioblastomas. Administration of either 600 mg/kg on Day 1 or 200 mg/kg on Days 1, 5, and 9 produced 7 of 9 Day 90 tumor-free mice in the U251 model. In the SF-295 model, a single 400-mg/kg dose or three 200-mg/kg doses produced 3 and 4 of 10 Day 90 tumor-free mice, respectively, and prolonged survival by 127%. A single 40-mg/kg i.v. dose of BCNU was more effective than temozolomide in the intracerebral SF-295 model, and less effective in the intracerebral U251 model. The synergistic potential of temozolomide and BCNU in combination was evaluated in an advanced stage s.c. implanted SF-295 model. When temozolomide was administered 2 h after BCNU on a single treatment day, a dramatic synergistic therapeutic effect was observed in two experiments. For example, single agent doses of temozolomide (600 mg/kg) and BCNU (60 mg/kg) and a combination (400 mg/kg + 27 mg/kg) demonstrating equivalent toxicity produced growth delays of 190, 258, and > 492% (includes 5 of 10 Day 51 tumor-free mice), respectively. Analysis of the data by a quadratic dose response model indicated synergism with significance at P = 0.0001 in both experiments. Synergism also was demonstrated by the isobole method. The reverse sequence was more toxic, but at lower combination doses a synergistic effect was still observed (P = 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

Antitumor activity and biochemical effects of aphidicolin glycinate (NSC 303812) alone and in combination with cisplatin in vivo

Aphidicolin, an inhibitor of DNA polymerases alpha and delta, is cytotoxic in vitro against tumor cells. The poor solubility of aphidicolin has led to the development of aphidicolin glycinate (AG; NSC 303812), a water soluble ester currently in early clinical trials. The antitumor activity of AG was investigated in a series of transplantable murine tumors in vivo. The drug demonstrated activity against the i.p. implanted B16 melanoma, producing maximum increased life spans of 75% following i.p. administration every 3 h for three doses on days 1-9. Treatment schedules involving both single injections per day on days 1-9 and multiple injections per day on days 1, 5, and 9 were less effective, indicating that this antitumor activity is schedule dependent. Similarly, greater activity was observed against the i.p. M5076 sarcoma when three daily injections were given on days 1-9 (57% increased life span) than with a single injection either on days 1-9 (36% increased life span) or on days 1, 5, 9, and 13 (inactive). Further scheduling studies in the s.c. M5076 sarcoma model showed that a 7-day infusion was superior to both a 24-h infusion and a 7-day course of three bolus treatments per day. On the assumption that DNA polymerase inhibition is the basis for this antitumor activity, inhibition of DNA synthesis in BALB/c x DBA/2 F1 mice was investigated by measuring incorporation of [3H]thymidine (20 microCi, i.v.) into DNA of spleen and jejunum. At 2 h after administration of AG, inhibition of DNA synthesis was dose dependent (median inhibitory dose, 60 mg/kg in both tissues) and was > 99% at 300 mg/kg. The inhibition was rapid in onset; AG (100 mg/kg i.p.) produced maximal (> 98%) inhibition in both tissues at 30 min. Recovery occurred in the intestine within 16 h; in spleen recovery was delayed to 24 h, and was followed by a rebound incorporation at 48 h (203%). A comparison of the inhibition of thymidine incorporation in tumor cells (B16 melanoma and P388 leukemia) and normal jejunum revealed no significant differences in the extent of inhibition or the rapidity of recovery in these tissues. The rapid recovery of DNA synthesis inhibition supports the use of prolonged infusion schedules in clinical trials, but the lack of evidence of selectivity for tumor cells suggests that AG may be of limited therapeutic value as a single agent. Thus, we evaluated AG in combination with cisplatin in an in vivo model of cisplatin refractory human ovarian cancer.(ABSTRACT TRUNCATED AT 400 WORDS)

Chloroquinoxaline sulfonamide: a sulfanilamide antitumor agent entering clinical trials

Chloroquinoxaline sulfonamide (CQS) has been developed to the clinical trial stage based on its activity in the Human Tumor Colony Forming Assay (HTCFA). In the HTCFA, CQS demonstrated inhibition of colony formation against breast, lung, melanoma and ovarian carcinomas. The mechanism of action of CQS is unknown. It does not appear to inhibit folate metabolism as does the structurally similar sulfaquinoxaline. Preclinical toxicology studies in dogs and rats have shown that CQS is toxic to lymphoid organs, bone marrow, gastrointestinal tract, pancreas, CNS, adrenal glands and testes. Toxicity was generally reversible with the exception of testicular atrophy in dogs and rats which occurred late and was not reversible within the study time frame. The pharmacokinetic data indicate that CQS binds to serum proteins in a dose and species specific manner. Terminal half-lives appear to vary between species from 60 hours in mice, 15 hours in rats, and 45-132 hours in dogs. Preliminary data indicate a longer terminal half-life in humans. Two phase I trials are ongoing using a 60 min infusion schedule once every 28 days. The starting dose for each trial was 18 mg/m2.

2-(aminoalkyl)-5-nitropyrazolo[3,4,5-kl]acridines, a new class of anticancer agents

2-(Aminoalkyl)-5-nitropyrazolo[3,4,5-kl]acridines were prepared from substituted anilines via the 1-chloro-4-nitroacridones followed by condensation with [(alkylamino)alkyl]hydrazines. Impressive activity was demonstrated for the 9-hydroxy, 9-alkoxy, and 9-acyloxy analogs in vitro on a L1210 leukemia line and in vivo against the P388 leukemia. Advanced studies led to the selection of 3bbb for clinical trial.

Preclinical antitumour activity and animal toxicology studies of rhizoxin, a novel tubulin-interacting agent

Rhizoxin is a 16-membered antifungal macrocyclic lactone isolated from the plant pathogenic fungus Rhizopus chinensis. The compound binds to tubulin, preventing microtubule formation, and inhibiting mitosis. It possesses antitumour activity in vivo against various preclinical murine models, both leukaemias and solid tumours model, as well as in vincristine- and doxorubicin-resistant leukaemia lines. In the present study, cytotoxic activity was observed in human tumour cell lines in vitro at very low concentrations (+/- 10(-10) M) particularly against melanoma, colon, renal, non-small cell and small cell lung cancer. In vivo antitumour activity was demonstrated in murine P388 and L1210 murine leukaemias, solid tumour models B16 melanoma and M5076 sarcoma, and in 5 out of 9 human solid tumour xenografts: LOX melanoma, MX-1 breast cancer, non-small cell lung cancer A549, and small cell lung cancers LXFS 605 and LXFS 650. The absence of cross-resistance to vinca alkaloids was confirmed in vivo against the vincristine-resistant P388 leukaemia subline and the vincristine-resistant human small cell lung cancer LXFS 650. In addition, the antitumour activity of rhizoxin was improved by prolonged or repeated drug administration indicating a schedule dependency. In animal toxicology studies, transient changes in erythrocyte and leukocyte numbers, local phlebitis, diarrhea, and spermatogenic arrest were observed. The LD10 value of rhizoxin after a single intravenous injection was 2.8 mg/kg (8.4 mg/m2). One-tenth of the mouse equivalent LD10 (0.84 mg/m2), the starting dose for clinical phase I studies, was considered to be safe in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

L-histidinol: preclinical therapeutic studies in combination with antitumor agents and pharmacokinetic studies in mice

Therapeutic studies were conducted with L-histidinol, in combination with cyclophosphamide, bischloroethylnitrosourea, 5-fluorouracil, phenylalanine mustard, or cis-platinum(II)diammine dichloride, in several transplantable tumors in mice. These tumor types included murine L1210 P388 leukemias, M5076 sarcoma, mammary 16/C adenocarcinoma, human LOX melanoma, and colon HT-29 adenocarcinoma. Therapeutic benefits of adding L-histidinol to a regimen, compared to the regimen alone, were marginal. Pharmacokinetic studies indicated a rapid clearance of L-histidinol following a bolus dose (250 mg/kg i.p.), peak plasma concentration of 200 micrograms/ml (1.4 mM), and beta phase t1/2 of 12.6 min. Maximum tolerable plasma steady state concentrations with a 24-h infusion (2000 mg/kg/24 h) were no greater than 25 micrograms/ml (0.18 mM).

Antitumor activity and cross-resistance of carmethizole hydrochloride in preclinical models in mice

Carmethizole hydrochloride [1-methyl-2-methylthio-4,5-bis(hydroxymethyl)imidazole-4', 5'-bis(N-methylcarbamate)hydrochloride, NSC 602,668; hereafter called carmethizole] is a new antitumor drug that has shown relatively broad activity in initial evaluations against several murine tumors and human tumor xenografts in vivo. The present studies were designed to address questions about carmethizole's activity against established disease, its activity on different treatment schedules, and the extent of its cross-resistance with established drugs. Human MX-1 mammary carcinoma, human NCI-H82 small-cell lung carcinoma, and human LOX amelanotic melanoma xenografts in athymic mice were used to determine the drug's activity against established disease; the NCI-H82 lung-tumor xenograft in athymic mice was used to explore its schedule dependence; and a series of drug-resistant murine leukemias provided an in vivo cross-resistance profile. When injected i.p., carmethizole exhibited antitumor activity against advanced-stage s.c. MX-1 mammary, s.c. NCI-H82 lung, and i.p. LOX melanoma xenografts and was as effective against established disease (MX-1 and LOX) as it was against early-stage disease (no data are available for early-stage NCI-H82). The therapeutic effect of carmethizole was not route-dependent, as was evidenced by the similar delays observed in tumor growth following i.p. and i.v. administration. The use of a split-dose schedule on a single day instead of one bolus injection yielded an increase in the total dose delivered, resulting in an increased delay in tumor growth. Murine leukemias resistant to vincristine (VCR), amsacrine (AMSA), or methotrexate (MTX) were not cross-resistant to carmethizole. However, murine leukemias resistant to doxorubicin (ADR), melphalan (L-PAM), cisplatin (DDPt), 1-beta-D-ara-binofuranosylcytosine (ara-C), and 5-fluorouracil (5-FU) were cross-resistant to carmethizole, suggesting that patients who have previously been treated with any of these agents might be less likely to respond to carmethizole than those who have had no opportunity to develop resistance to any of these compounds. We anticipate that the information derived from these studies may be useful in the design of clinical trials of carmethizole and may stimulate additional basic research on the mechanism of action of this new agent.

Antitumor properties of 2(1H)-pyrimidinone riboside (zebularine) and its fluorinated analogues

2(1H)-Pyrimidinone riboside (zebularine, 1b) and its 5-fluoro (6b) and 2'-ara-fluoro (7b) analogues have been synthesized and evaluated in vivo as antitumor agents. Zebularine provides increase in life span (ILS) values of ca. 70% against intraperitoneal (ip) murine B16 melanoma and 50% against P388 leukemia. This compound is active when administered either ip or orally against ip or subcutaneously implanted L1210 leukemia, producing ILS values of about 100% at an optimum dose of 400 mg/kg. 1b is also active (60% ILS) against ara-C-resistant L1210. The analogous unsubstituted purine riboside nebularine (2) has modest activity against P388 leukemia (60% ILS). While 2'-ara-fluorozebularine (7b) is only marginally active (40% ILS) at high doses against L1210 leukemia, 5-fluoro analogue 6b is more active than zebularine and is ca. 100 times more potent. Although the activity of 6b is about the same as that of 1b against P388 leukemia, greater potency also is realized in this model. Zebularine is a strong inhibitor of cytidine deaminase, but in contrast to tetrahydrouridine, 1b is acid-stable. In an attempt to use this property to advantage in oral administration, 1b and ara-C have been orally coadministered to mice with ip L1210 leukemia. When zebularine is given in divided doses, up to a 2-fold increase in activity is realized, relative to treatment with the same dose of ara-C alone.

Terephthalamidine: past and future

Terephthalamidine (NSC 57155) is one of 800 terephthalanilides and related compounds which were synthesized and tested preclinically in the late 1950's and early 1960's. Based upon their activity against murine leukemias, some of these agents were tested briefly in clinical trials at that time. Despite the observation of responses, the compounds were dropped because of severe and unusual neurotoxicity. More recently, terephthalamidine has been screened for antitumor activity and chosen for further clinical investigation by the NCI's Project for the Review of Old Drugs (P.R.O.D.) because of its novel structure and spectrum of preclinical activity. The current availability of a plasma assay for the drug permits further study of its clinical pharmacokinetics and pharmacodynamics and, perhaps, the development of improved scheduling strategies.

Practical spontaneous metastasis model for in vivo therapeutic studies using a human melanoma

In vivo studies aimed at therapy of spontaneous human tumor metastases have been hampered by the lack of practical experimental models. The LOX amelanotic melanoma model described here represents a transplantation model which rapidly and reproducibly results in spontaneous pulmonary metastasis following s.c. inoculation into athymic mice. Pulmonary lesions can be detected using a simple bioassay procedure which is useful for estimation of metastatic cell killing. Using this model we demonstrate that systemic therapy with cyclophosphamide or dacarbazine can produce metastatic cell killing consistent with complete eradication of established pulmonary metastases. This model may also prove useful for future experimental therapeutic studies aimed at prevention of metastases by manipulating tumor staging interval and treatment schedule.

Preclinical antitumor activity of penclomedine in mice: cross-resistance, schedule dependence, and oral activity against tumor xenografts in brain

Penclomedine is 3,5-dichloro-2,4-dimethoxy-6-(trichloromethyl)pyridine (NSC 338720), an alpha-picoline derivative with p.o. antitumor activity in preclinical leukemia and solid tumor models. Described here are an in vivo cross-resistance profile of penclomedine, treatment schedule dependence studies, and studies exploring the effects of p.o. drug on human tumors xenografted into mouse brain. The latter studies exploited the apparent facile distribution of penclomedine to the central nervous system. Tumor models used included murine leukemia lines selected in vivo for acquired resistance to various antitumor drugs and the human mammary and lung tumor xenografts MX-1 and H82, respectively. The therapeutic effects of p.o. penclomedine against s.c. MX-1 and H82 xenografts were shown to be independent of treatment schedule. Therapeutic activity was comparable when p.o. and parenteral treatments were compared. Lines of P388 leukemia resistant to melphalan, cyclophosphamide, and carmustine were cross-resistant to penclomedine in vivo. Leukemia lines resistant to antimetabolites, DNA binders/intercalators, and vincristine were not cross-resistant to penclomedine. Intracerebrally implanted MX-1 xenografts retained their sensitivity to p.o. penclomedine, and therapeutic activity was at least comparable to that of carmustine, a drug known for its ability to cross the blood-brain barrier. These results demonstrate attributes of penclomedine that are relatively uncommon among currently available antitumor drugs and that are of interest for the anticipated clinical development of this drug.

Modulation of cytosine arabinoside toxicity by 3-deazauridine in a murine leukemia model

3-Deazauridine (DAUrd), a competitive inhibitor of CTP synthetase, inhibits both RNA and DNA synthesis. Murine leukemia cells resistant to cytosine arabinoside (ara-C) due to a deletion of deoxycytidine kinase are collaterally sensitive to DAUrd, which inhibits the de novo production of CTP and hence results in dCTP depletion. We evaluated DAUrd in combination with the palmitate derivative of ara-C (palmO-ara-C) in mice bearing L1210 leukemia cells with a subpopulation resistant to ara-C. Both simultaneous administration and a sequential schedule of palmO-ara-C at its maximally tolerated dose (MTD), followed by DAUrd treatment, failed to produce a therapeutic gain. We also studied whether non-toxic doses of DAUrd (15-250 mg/kg i.p. at h 0 and 6 on days 4 and 8) could modulate the antileukemic activity of palmO-ara-C (7.5-120 mg/kg i.p. at h 3 on days 4 and 8). The addition of DAUrd produced a modest (but statistically significant) prolongation of life span and a further 2-log10 reduction in tumor burden compared to the same dose of palmO-ara-C alone, and resulted in long-term survivors in five of 30 treated animals. Two-dimensional dose-response analysis of the survival data indicated a positive drug interaction (p less than or equal to 0.01) when the dosage of DAUrd was modeled to reflect an apparent threshold effect. Cyclopentenyl cytosine (CPE-C; 0.625-2.5 mg/kg i.p. at h 0 and 6 on days 4 and 8), a more potent inhibitor of CTP synthetase, was also given with palmO-ara-C. This combination resulted in an additional 2-6 log10 units of cell kill and occasional long-term survivors at palmO-ara-C dosages that alone resulted in no more than 2 log10 units of cell kill and no long-term survivors. However, DAUrd and CPE-C given with palmO-ara-C increased host toxicity, compromising the tolerable dose of palmO-ara-C. Single-agent palmO-ara-C given at its MTD produced a similar reduction in tumor burden and increase in life span compared to the highest palmO-ara-C dose that could be given in combination with either modulator.

Schedule dependence, activity against natural metastases, and cross-resistance of pyrazine diazohydroxide (sodium salt, NSC 361456) in preclinical models in vivo

Pyrazine diazohydroxide (sodium salt, NSC 361456; PZDH) is a new antitumor drug with relatively broad activity in initial evaluations against murine leukemias, solid tumors, and two human tumor xenografts in vivo. The present studies were designed to address questions about PZDH activity on different treatment schedules, its activity against metastases, and the extent of its cross-resistance with established drugs. Human LOX amelanotic melanoma xenografts in athymic mice were used to explore schedule dependence and activity against natural metastases, and a series of drug-resistant murine leukemias provided an in vivo cross-resistance profile. Single-dose treatment and prolonged treatment provided equivalent therapeutic responses to PZDH by both the i.p. and i.v. routes in the i.p. LOX model. A s.c. LOX model resulting in spontaneous pulmonary metastases was adapted for bioassay and quantitation of the numbers of LOX cells killed by PZDH among both primary and metastatic cell populations. It was demonstrated that PZDH afforded about 2-log10 orders of magnitude greater cell kill among pulmonary metastases than against primary s.c. LOX tumors in the same mouse. Murine leukemias resistant to doxorubicin (ADR), vincristine (VCR), cisplatin (DDPt), methotrexate (MTX), N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU), and cyclophosphamide (CPA) were not cross-resistant to PZDH. However, both P388 and L1210 leukemia sublines resistant to melphalan (L-PAM) were cross-resistant to PZDH, suggesting that patients previously treated with L-PAM might have less likelihood of response to PZDH than those who had had no opportunity to develop L-PAM resistance. Although these observations should not be applied to clinical studies without due caution, they support clinical evaluation of PZDH as well as continued investigation of its molecular pharmacology.

Oncolytic activity and mechanism of action of a novel L-cysteine derivative, L-cysteine, ethyl ester, S-(N-methylcarbamate) monohydrochloride

A study on the oncolytic activity of the L-cysteine derivative L-cysteine, ethyl ester, S-(N-methylcarbamate) monohydrochloride (NSC 303861), revealed that the drug caused complete regression of the MX-1 human mammary tumor xenograft. The compound also exhibited moderate antitumor activity against murine leukemia P388 (T/C value of 169% at a daily dose of 400 mg/kg) and against M5076 sarcoma (T/C value of 135% at a daily dose of 600 mg/kg). The drug was inactive against B16 melanoma, Lewis lung, colon 38 and CD8F1 mammary carcinomas. The compound exhibited significant cytotoxicity against hepatoma 3924A cells in culture (LC50 = 6 microM). Studies on the mechanism of action revealed that the cytotoxicity of the drug could be partially abrogated by protecting hepatoma 3924A cells in culture with L-glutamine. At 6 h after injection of the compound (400 mg/kg) into rats bearing hepatoma 3924A, the pools of L-glutamine and L-glutamate in the tumor decreased to 33% and 71%, respectively, of control levels; the drug selectively inhibited the activities of L-glutamine-requiring enzymes of purine nucleotide biosynthesis, amidophosphoribosyltransferase, FGAM synthase, and GMP synthase, to 21%, 1%, and 69%, respectively, without significantly altering the activities of pyrimidine biosynthetic enzymes, carbamoylphosphate synthase II and CTP synthase. Measurement of the nucleotide concentrations further corroborated the actions of the drug on the purine nucleotide biosynthetic enzyme activities. Drug injection (400 mg/kg) in the hepatoma 3924A-bearing rats reduced the concentrations of IMP in the tumor to 52%, those of total adenylates to 52%, those of total guanylates to 57%, and those of NAD to 73%, without significantly perturbing the pyrimidine nucleotide pools. Studies on the mechanism of action of the L-cysteine derivative suggested that the compound behaved as an L-glutamine antagonist, selectively acting on the enzymes of purine nucleotide biosynthesis.

Activity of batracylin (NSC-320846) against solid tumors of mice

Batracylin (NSC 320846) is a water insoluble, solid tumor active compound discovered by the Development Therapeutics Program of the National Cancer Institute (NCI). In vivo, the NCI found this compound to be highly active [median treated tumor mass/median control tumor mass (T/C) = 0 to 20%] both orally and intraperitoneally against colon 38. In a disk diffusion, soft agar colony formation assay (500 ug/disk), we found solid tumor selectively (compared to leukemia L1210) against colon adenocarcinoma 38 (0-170 zu:L1210 leukemia; greater than 950 zu:C8), colon adenocarcinoma 9 (0-170 zu:L1210; greater than 950 zu:C9), colon adenocarcinoma 7/A (0-170 zu:L1210; 250-400 zu:C7), and pancreas ductal carcinoma 03 (0-170 zu:L1210; greater than 950 zu:Panc 03 (200 zone units [zu] = 6.5 mm zone of inhibition of cultured tumor colonies from drug disk). In vivo we have tested batracylin against mammary adenocarcinoma 16/C, colon 9, colon 38, colon 51, Panc 03, and hepatoma 129. Upon oral administration, batracylin was effective against colon 9 (T/C = 2.4%) and marginally active against colon 38 (T/C = 39%). Batracylin was orally ineffective against Panc 03 (T/C greater than 100%), colon #51 (T/C = 77%) and hepatoma 129 (T/C greater than 100%). Upon subcutaneous administration, batracylin was effective against colon #9 (T/C = 0%), and Panc 03 (T/C = 15%) but ineffective against mammary 16/C (T/C greater than 100%). At efficacious doses, delayed neurotoxicity, hepatic toxicity and a significant host weight loss was noted (with slow recovery). Both our in vitro data and the NCI in vivo data confirm its scant activity against L1210 (%ILS = 8 to 16%). Although showing activity against selected murine solid tumors, it lacked curative potential with early stage disease [C38, C9, Panc 03] and has shown relative inactivity in vitro against human solid tumor cell lines (H-125, CX-1, HCT-8, HCT-116). Batracylin has entered large animal toxicology trials at the NCI, anticipating phase I clinical evaluation.

Display and analysis of patterns of differential activity of drugs against human tumor cell lines: development of mean graph and COMPARE algorithm

The objective of this study was to develop and investigate an approach to optimally detect, rank, display, and analyze patterns of differential growth inhibition among cultured cell lines. Such patterns of cellular responsiveness are produced by substances tested in vitro against disease-oriented panels of human tumor cell lines in a new anticancer screening model under development by the National Cancer Institute. In the first phase of the study, we developed a key methodological tool, the mean graph, which allowed the transformation of the numerical cell line response data into graphic patterns. These patterns were particularly expressive of differential cell growth inhibition and were conveniently amenable to further analyses by an algorithm we devised and implemented in the COMPARE computer program.

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.

Pyrazole: preclinical reassessment

Pyrazole (NSC-45410) is a low molecular weight, heterocyclic compound which has been considered for reevaluation in the clinic as a potential cytotoxic agent (Fig. 1). Discovered in 1893, pyrazole is best known as an inhibitor of liver alcohol dehydrogenase (ki = 0.2 uM), and as a result, has been used extensively in studies of alcohol metabolism. In 1960, pyrazole was identified as being active in preclinical antitumor models, which led to preliminary clinical testing. The early Phase I studies were not followed by disease specific Phase II trials, and the clinical activity of the drug has never been evaluated. This omission was noted by the National Cancer Institute's Project for the Review of Old Drugs (PROD), at which time it was also noted that pyrazole is selectively toxic to thyroid tissue in an animal model. Hence, interest in pyrazole was revived for two reasons: (a) failure to screen it for clinical activity in the 1960's, and (b) current interest in discovering drugs with selective toxicity to specific tissues for evaluation of their activity in malignancies arising in the target tissue. In this review, we summarize the evidence which has accumulated concerning pyrazole's potential role as an anticancer agent.

Preclinical antitumor activity of batracylin (NSC 320846)

Batracylin (NSC 320846, BAY H 2049), given ip on days 2 and 9 at a dose 400 mg/kg, inhibited tumor growth completely in 80-100% of mice with early-stage colon adenocarcinoma 38. Therapeutic efficacy against this subcutaneously implanted tumor was retained upon oral administration of Batracylin although, compared to ip treatment, larger doses were required. Batracylin also caused regression of advanced (400 mg) colon 38 tumors. Only modest activity was observed for this compound against P388 leukemia, but P388 sublines with acquired resistance to either adriamycin or cisplatin demonstrated collateral sensitivity. Batracylin currently is undergoing toxicological evaluation by NCI prior to clinical trials.

Cyclopentenylcytosine. A carbocyclic nucleoside with antitumor and antiviral properties

Cyclopentenylcytosine (CPE-C, 2), a pyrimidine analogue of the fermentation derived carbocyclic nucleoside neplanocin A, has been synthesized from the optically active cyclopentenylamine 3b by two synthetic routes. CPE-C demonstrates significant antitumor activity against both the sensitive and ara-C resistant lines of L1210 leukemia in vivo. Multiple long term survivors are produced in both tumor models. The compound also gives 100% growth inhibition of the solid human A549 lung and MX-1 mammary tumor xenografts grown in athymic mice. Good activity is also observed against a third human tumor xenograft model, metastatic LOX melanoma. CPE-C has significant activity against both DNA and RNA viruses in vitro. Potent activity is observed against HSV-1 (TK+ and TK-), HSV-2, vaccinia, cytomegalovirus, and varicella-zoster virus. Good activity is also found against a strain of influenza virus (Hong Kong flu), vesicular stomatitis virus, Japanese encephalitis virus, and Punta Toro virus.

N-methylformamide: cytotoxic, radiosensitizer, or chemosensitizer

N-methylformamide (NMF), a polar solvent, is currently being evaluated by the National Cancer Institute (NCI) as an antineoplastic agent because of its activity against colon, mammary, and lung tumor xenografts. Results from preclinical studies suggest that it has radiosensitizing, chemosensitizing, and differentiating activity. Its mechanism of action remains unknown, but may involve cellular depletion of glutathione, cell membrane changes, or modulation of proto-oncogene expression. Preclinical toxicology studies conducted in mice, rats, and beagle dogs showed reversible hepatotoxicity to be dose-limiting. Clinically, NMF is administered both orally and by intravenous (IV) injection. The bioavailability with oral administration is 90% to 95%. The highest reported plasma concentration of NMF is approximately 4 mmol/L in a patient who received a dose of 2,000 mg/m2 of IV NMF. Biphasic elimination with IV NMF is seen on both the daily for five days and weekly for 3 weeks schedule. Approximately 5% to 7% of the total administered IV dose is excreted in the urine. In phase I studies, dose-limiting toxicities included reversible hepatotoxicity, a generalized malaise syndrome, and nausea and vomiting. One partial response has been reported in the 111 patients treated on phase II trials in colorectal, head and neck, and renal carcinomas. Suggestions for the future development of this drug are presented.

Arabinosyl-5-azacytosine: a novel nucleoside entering clinical trials

Arabinosyl-5-azacytosine is a new compound which has been selected by the Division of Cancer Treatment, National Cancer Institute for clinical development as an antineoplastic agent based on its high degree of activity against a broad range of tumor types in preclinical studies. Therapeutic activity has been observed against murine and human leukemias, transplantable murine solid tumors, and human tumor xenografts. Arabinosyl-5-azacytosine exhibited a broader spectrum of activity against human solid tumors than cytosine arabinoside. Arabinosyl-5-azacytosine is phosphorylated to the nucleotide level by deoxycytidine kinase. Upon further anabolism to the triphosphate level, it can be incorporated into DNA. The mechanism of cytotoxicity is thought to be related to inhibition of DNA synthesis. Leukemic and solid tumor cell lines that are resistant to cytosine arabinoside due to deletion of deoxycytidine kinase activity are cross-resistant to arabinosyl-5-azacytosine. Unlike cytosine arabinoside, arabinosyl-5-azacytosine does not readily undergo deamination. Schedule dependence has been demonstrated in mice bearing L1210 leukemia, with superior activity seen with multiple doses administered on each treatment day compared to administration of larger but less frequently administered doses. From preliminary data in solid tumor models, however, antitumor activity did not appear to be superior with continuous infusion compared to that observed on a bolus schedule. Preclinical toxicology studies indicated that the bone marrow and gastrointestinal tract were the main target organs. A single large dose of arabinosyl-5-azacytosine could be tolerated by both mice and dogs. When administered as a continuous infusion, the toxicity was related to both the dose and duration of exposure, suggesting that toxicity resulted from a critical time above a threshold concentration as opposed to the total area under the concentration-time curve. Phase I clinical trials have been initiated to determine the maximum tolerated dose on a low dose continuous infusion schedule for 72 hours and also on a high dose short infusion daily times five schedule.

Synthesis, chemical stability and pre-clinical anti-tumor activity of pyrazine diazohydroxide, sodium salt (NSC-361456)

The synthesis, chemical stability and anti-tumor activity of pyrazine diazohydroxide, sodium salt, a compound that has been selected for development to clinical trials, are described. The compound shows a half-life of about 100 minutes at pH 7.4 and is active against a number of experimental tumors.

Experimental antitumor activity of the amsacrine analogue CI-921

CI-921 is a di-substituted analogue of amsacrine currently in phase 1 clinical trial. CI-921 was developed to clinical trial largely on the basis of a series of studies at five cancer research laboratories that demonstrated its improved spectrum and degree of activity relative to those of amsacrine against murine tumor models. The tumor models studied included lung, colon, and mammary carcinomas and encompassed a wide range of biologic properties and chemosensitivities. CI-921 had significant activity against 16 of 19 (84%) tumor models examined. The activity of CI-921 was superior to that of amsacrine in 10 of 14 tumor systems that were sensitive to at least one of the agents and for which comparable data existed. In the remaining four systems, CI-921 and amsacrine were equivalent in activity. CI-921 was found to be roughly equipotent with amsacrine on a milligram-per-kilogram (body wt) basis and was found to have significantly higher activity when given orally.

Flavone acetic acid (LM 975, NSC 347512). A novel antitumor agent

Flavone acetic acid (FAA) is a synthetic flavonoid compound which has recently begun clinical trials as an antitumor agent based on its striking activity in solid tumor model systems. The pharmacologic behavior of FAA in animals appears to be predictive of both its cytotoxic efficacy and its toxicity to normal tissues (principally the central nervous system and gastrointestinal tract). The design and conduct of phase I studies in man are based upon these principles, with the goal of maximizing their safety and efficacy.

Preclinical antitumor activity and pharmacological properties of deoxyspergualin

A new antibiotic, deoxyspergualin (DSG), demonstrated antitumor activity against L1210 leukemia in mice. The life span of mice bearing either i.p. or s.c.-implanted L1210 increased greater than 150% following i.p. administration of 25 mg/kg DSG on days 1-9. Activity obtained with i.p. bolus treatments was schedule dependent. The tumor burden in mice bearing the s.c. implanted L1210 was reduced by 4-6 log10 units at the end of treatment when DSG was administered every 3 h for 8 injections on days 1, 5, and 9. By contrast, single injections of DSG on days 1, 5, and 9 allowed the tumor burden to increase at least 100-fold during treatment and daily single injections for 9 days reduced the tumor burden by 2 log10 units. The therapeutic advantage for i.p.-implanted L1210 of maintaining plasma concentrations of DSG was indicated further by infusion studies using s.c.-implanted Alzet osmotic pumps. Tumor burden was reduced by 3.5 and 6 log10 units following s.c. bolus treatments every 3 h on day 1 and a 24 h-infusion, respectively. The optimal infusion time for an infusion rate in mice of 179 mg/kg/day appeared to be 72 h. Pharmacokinetic studies following bolus i.v. injection revealed a rapid plasma clearance of parent drug (20.8 ml/min/kg) and a beta half-life of approximately 12 min. The bolus dose kinetics was used to predict the steady state plasma concentrations resulting from s.c. infusion; good agreement was observed between predicted values and experimental results. Based on these preclinical data, DSG has been developed to clinical trial. Initial Phase I protocols involve a 120-h infusion schedule.

Enhanced melphalan cytotoxicity in human ovarian cancer in vitro and in tumor-bearing nude mice by buthionine sulfoximine depletion of glutathione

The development of acquired resistance to alkylating agents frequently limits the effectiveness of chemotherapy in the treatment of ovarian cancer. While the resistance to alkylating agents is multifactorial, the association of drug resistance with elevations in glutathione (GSH) is of potential clinical relevance since there exist pharmacologic means to lower intracellular GSH levels. We have used in vitro and in vivo models of human ovarian cancer to demonstrate that selective inhibition of GSH synthesis with L-buthionine-S,R-sulfoximine (L-BSO) leads to a lowering of GSH levels and an increase in cytotoxicity of the alkylating agent melphalan. In the human ovarian cancer cell line NIH:OVCAR-3, derived from a patient clinically refractory to alkylating agents, L-BSO resulted in a 3.6-fold enhancement of melphalan cytotoxicity. This cell line was also adapted for intraperitoneal growth in athymic nude mice. In this in vivo model, in which the mice die of massive ascites and intraabdominal carcinomatosis, L-BSO given orally in drinking water for 5 days decreased GSH levels in the tumor cells by 96% compared to a 79 and 86% reduction in GSH levels in the bone marrow and gastrointestinal mucosa respectively. Lowering of GSH levels with BSO was not accompanied by an increase in lethality for melphalan in non-tumored nude mice. However, in tumor-bearing nude mice, a single melphalan (5 mg/kg) treatment following GSH depletion with L-BSO was markedly superior to treatment with melphalan alone, producing a 72% increase in median survival time. Furthermore, L-BSO treatment of human bone marrow cells prior to melphalan exposure had little effect on melphalan toxicity as assessed in a CFUc-GM assay. These results suggest that treatment with the GSH synthesis inhibitor BSO may preferentially enhance the cytotoxic effects of alkylating agents against human ovarian cancer and overcome acquired resistance.

Merbarone: an antitumor agent entering clinical trials

Merbarone was developed to clinical trial stage on the basis of its 'curative' activity against P388 and L1210 leukemias and moderate activity against B16 melanoma and M5076 sarcoma. Its activity appears to be schedule-dependent favoring a longer duration of administration. The mechanism of action of merbarone is not yet established but it does induce single strand breaks in DNA apparently without binding to DNA. The pharmacokinetic data in the dog indicate that clearance mechanisms may be saturable. Merbarone is hydroxylated at the 4' position in the rat, mouse and dog, and glucuronidated in the dog. Parent drug and the hydroxy metabolite are excreted in the urine. If saturable clearance mechanisms also pertain to man, this will mean that infusion rate (and therefore steady state concentrations reached) may be a significant factor in determining acute toxicity. Preclinical toxicology studies revealed that major target tissues are in the lymphoid organs, bone marrow, gastrointestinal tract and kidney. Some behavioral signs of reversible central nervous system toxicity were observed. Phase I trials have commenced using only a 5-day continuous intravenous infusion schedule based on the preclinical data. The pharmacokinetic information from these trials will be crucial for further clinical development of the compound, including selection of the optimal schedule(s) for phase II/III evaluation.

Therapeutic and pharmacokinetic relationships of flavone acetic acid: an agent with activity against solid tumors

Flavone acetic acid is a novel structure which exhibits an interesting spectrum of antitumor activity in preclinical studies. It has little antitumor activity in the leukemias and pronounced antitumor activity in solid tumors. Preclinical therapeutic, toxicologic, and pharmacokinetic studies are summarized and considered together to introduce the concept of a therapeutic window of effective plasma concentrations and effective exposure times in attempts to maximize therapeutic effects and minimize toxic effects. Plasma concentrations, predicted to fall from 600 to 100 micrograms/ml over 10 hours resulting from 267 mg/kg ip bolus injections in mice are curative to sc implanted colon 38. Doses of 356 mg/kg and higher cause acute lethality in many mice. Iv doses cause acute lethality in mice more frequently than ip doses, which suggests a peak toxic effect. However, iv infusions in mice, which also can be curative to colon 38, can also result in a lethal effect, although more delayed, even though the predicted plasma concentrations are much below the peak plasma concentrations that appear to be necessary for acute lethality. Plasma concentrations, 100 to 600 micrograms/ml predicted to result from single doses that are therapeutic and not acutely lethal in mice, if maintained by infusion in dogs for 28 hours or longer result in delayed lethality. We conclude that relatively high plasma concentrations (greater than 100 micrograms/ml) are needed for therapeutic activity with this antitumor agent and that lethality can result from two distinctly different causes. An acute lethality can result from an excessively high peak plasma concentration (greater than 600 micrograms/ml). A delayed lethality can result from a too-long exposure (greater than 24 hrs) at therapeutically effective plasma concentrations (100-600 micrograms/ml). We also note that unexpected kinetic differences exist among the mouse, dog, and man. Whereas usually with antitumor agents plasma clearances are proportional to body surface area, and hence faster in small species, quite the opposite is true with flavone acetic acid. Mice exhibit a slower plasma clearance relative to dogs and man.

Arabinofuranosyl-5-azacytosine: antitumor and cytotoxic properties

Arabinofuranosyl-5-azacytosine (ara-AC), a nucleoside combining the structural elements of 5-azacytidine and arabinofuranosylcytosine, exhibited unusually wide therapeutic activity against several murine leukemias and all three human xenografts of the National Cancer Institute tumor panel. Activity was observed following either a daily or an intermittent regimen of treatment in the i.p. L1210 model. However, when multiple doses were administered on each treatment day, a greater therapeutic effect was produced and the total dose was reduced. Extensive necrosis was observed by light and electron microscopy in P388 tumors treated with ara-AC. Following s.c. administration, ara-AC caused regression of the mammary and lung xenografts (MX-1 and LX-1) and a 93% inhibition of the human colon tumor (CX-1); other analogues of this drug failed to demonstrate a comparably broad spectrum of activity. Morphological assessment of treated xenografts revealed a general loss of cell-to-cell contact and abundant necrosis 24 h after the administration of ara-AC. In culture, the 50% inhibitory concentrations of ara-AC for P388 and L1210 cells at 24 h were 1.9 and 4.5 microM, respectively, and the decline in replication rates was dependent on drug concentration. The cytocidal nature of the drug was demonstrated by cloning experiments in which it was observed that ara-AC abolished the clonogenicity of lymphoblasts but was only minimally cytotoxic to normal murine bone marrow progenitor cells. As adjudged by flow cytometry, the drug induced a distinct slowing of cell cycle traverse through S phase. Induction of the differentiation of HL-60 cells in culture was another cytotropic effect of this drug. At 44% differentiation (10 microM ara-AC), 50% of the cultured cells were viable. Its broad spectrum antitumor activity, its selective toxicity to tumor cells, and its ability to produce cytodifferentiation render ara-AC of interest as a potential antineoplastic agent in humans.

Didemnin B. The first marine compound entering clinical trials as an antineoplastic agent

A new class of marine compounds, the didemnins, with potent antitumor activity has been identified. They share the novel structure of a cyclic depsipeptide. Among three structurally related compounds, didemnin B is by far the most potent in its in vitro cytotoxicity and in vivo antitumor activity (0.001 microgram/ml inhibits the growth of L1210 leukemia cells by 50%). It also demonstrates good antitumor activity against B16 melanoma and moderate activity against M5076 sarcoma and P388 leukemia. The compound also has good antiviral and potent immunosuppressive properties. Although the precise mechanism of action for the cytotoxicity remains unknown, the agent inhibits protein synthesis more than DNA synthesis and the inhibition of protein synthesis is closely correlated with inhibition of L1210 cell growth. Toxicology studies in CD2F1 mice, Fischer 344 rats and beagle dogs reveal that major target organs are the lymphatics, gastrointestinal tract, liver and kidney. Phase I trials are currently in progress under the auspices of the National Cancer Institute.

Activity of flavone acetic acid (NSC-347512) against solid tumors of mice

Flavone acetic acid (FAA) is a new antitumor agent that has recently entered Phase I clinical trials. In preclinical studies, we have found that FAA was broadly active against a variety of transplantable solid tumors of mice (colon #51, #07, #10, #26; pancreatic ductal adenocarcinomas #02 and #03; mammary adenocarcinoma #16/C/Adr; M5076 reticulum cell sarcoma and Glasgow's osteosarcoma). FAA was curative for colon adenocarcinoma #10 and pancreatic ductal adenocarcinoma #03. Thus, for the first time an agent has been identified with very broad, perhaps nearly universal solid tumor activity. FAA was also found to be orally active and stable in solution at 37 degrees C for 48 h. FAA was selectively cytotoxic in vitro for solid tumors over leukemias L1210 and P388 (in a soft-agar colony formation assay), thus correlating cellular selectivity in vitro with in vivo antitumor activity. The finding that FAA was active in vitro, established that the agent did not need metabolism (activation) outside the tumor cell. The main drawback of FAA was an unusual 'threshold' behavior in which only a narrow range of doses were active and splitting the dose markedly decreased activity.

Activity of a novel 4-quinolinecarboxylic acid, NSC 368390 [6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarb oxylic acid sodium salt], against experimental tumors

A novel, substituted 4-quinolinecarboxylic acid (NSC 339768) demonstrated antitumor activity against L1210 leukemia and B16 melanoma in the National Cancer Institute's Developmental Therapeutics Program. An extensive analogue synthesis program was initiated; over 200 derivatives were synthesized and tested for anticancer activity. One of these compounds, 6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarboxylic acid sodium salt, NSC 368390 (DuP-785), was selected for further investigation because of its efficacy against a spectrum of human solid tumors and its water solubility. In initial studies with L1210 leukemia, the compound caused an increase in life span of greater than 80%. The activity was schedule dependent, and the compound was equally efficacious when administered i.p., i.v., s.c., or p.o. In tests against human tumors xenografted under the renal capsule of nude mice, NSC 368390 when injected i.p. in doses of 20-40 mg/kg daily for 9 days inhibited the growth of the MX-1 breast, LX-1 lung, BL/STX-1 stomach, and CX-1 colon carcinomas by greater than 90%. NSC 368390 also inhibited the growth of three distinct human colon carcinomas, the HCT-15, clone A, and DLD-2 tumors, growing s.c. in nude mice. An i.p. dose of 25 mg/kg given daily for 9 days inhibited the growth of the DLD-2 colon cancer by 98%. 1-beta-D-Arabinofuranosylcytosine and Adriamycin were ineffective, and fluorouracil was only moderately effective against these colon tumors. Because of its good activity against human colon tumors and other human carcinomas and its water solubility, NSC 368390 (DuP-785) is being developed as a Phase 1 anticancer agent.

Anthrapyrazoles, a new class of intercalating agents with high-level, broad spectrum activity against murine tumors

A series of 5-[(aminoalkyl)amino]-substituted anthra[1,9-cd] pyrazol-6(2H)ones (anthrapyrazoles) were synthesized. These compounds, which differ from the anthracenediones in that an additional pyrazole ring has been fused to the anthracene system in place of one carbonyl group, were evaluated in vivo for their anticancer activity in eight different mouse tumor systems. Compounds were selected for testing primarily on the basis of their high levels of activity P388 leukemia and occasionally for structural considerations. Sixty-seven % of the 21 analogues studied were curative in the National Cancer Institute P388 screen. Many of the compounds tested were highly active against each of the tumors of the National Cancer Institute panel. Thus 82, 73, 45, and 80% of the compounds tested were curative for L1210 leukemia, B16 melanoma, M5076 sarcoma, and the MX-1 mammary xenograft, respectively. Several of the compounds studied were curative against every tumor of the above panel. Because of the high activity of the anthrapyrazole series as a class in the National Cancer Institute tumor panel, additional testing was necessary to allow selection of clinical candidates. Twenty-one anthrapyrazoles were tested against mammary adenocarcinoma 16C, colon adenocarcinoma 11a, and the Ridgway osteogenic sarcoma. Four compounds, PD 113,309 (Cl-937), PD 113,785 (Cl-941), PD 111,815 (Cl-942), and PD 115,593, were judged superior to the rest on the basis of the expanded panel testing. The preclinical data to date suggest that these anthrapyrazoles are similar to doxorubicin in both degree and spectrum of activity. Each of these anthrapyrazoles were significantly more active than were the other synthetic intercalating agents, the anthracenediones mitoxantrone and ametantrone, against the tumors of the expanded panel. On the basis of their high level of broad spectrum activity in preclinical systems, ease of formulation, possible lack of cross-resistance with doxorubicin, and potential lack of cardiotoxicity, Cl-937, Cl-941, and Cl-942 have been selected for further preclinical evaluation and possible clinical development.