Building upon Nature's Framework: Overview of Key Strategies Toward Increasing Drug-Like Properties of Natural Product Cyclopeptides and Macrocycles

The pharmaceutical industry has focused mainly in the development of small-molecule entities intended for oral administration for the past decades. As a result, the majority of existing drugs address only a narrow range of biological targets. In the era of post-genomics, transcriptomics, and proteomics, there is an increasing interest on larger modulators of proteins that can span larger surfaces, access new therapeutic mechanisms of action, and provide greater target specificity. Traditional drug-like molecules developed using "rule-of-five" (Ro5) guidelines have been proven ineffective against a variety of challenging targets, such as protein-protein interactions, nucleic acid complexes, and antibacterial modalities. However, natural products are known to be effective at modulating such targets, leading to a renewed focus by medicinal chemists on investigating underrepresented chemical scaffolds associated with natural products. Here we describe recent efforts toward identification of novel natural cyclopeptides and macrocycles as well as selected medicinal chemistry strategies to increase drug-like properties or further exploration of their activity.

Phase I study of the halichondrin B analogue eribulin mesylate in combination with cisplatin in advanced solid tumors

BACKGROUND

Eribulin mesylate is a synthetic macrocyclic ketone analogue of Halichondrin B that has demonstrated high antitumor activity in preclinical and clinical settings. This phase I study aimed to determine the maximum tolerated dose (MTD), dose-limiting toxicities (DLTs), and pharmacokinetics in combination with cisplatin (CP) in patients with advanced solid tumours.

METHODS

Thirty-six patients with advanced solid tumours received eribulin mesylate 0.7-1.4 mg m(-2) and CP 60-75 mg m(-2). Eribulin mesylate was administered on days 1, 8, and 15 in combination with CP day 1 every 28-day cycle. The protocol was amended after dose level 4 (eribulin mesylate 1.4 mg m(-2), CP 60 mg m(-2)) when it was not feasible to administer eribulin mesylate on day 15 because of neutropenia; the treatment schedule was changed to eribulin mesylate on days 1 and 8 and CP on day 1 every 21 days.

RESULTS

On the 28-day schedule, three patients had DLT during the first cycle: grade (G) 4 febrile neutropenia (1.0 mg m(-2), 60 mg m(-2)); G 3 anorexia/fatigue/hypokalemia (1.2 mg m(-2), 60 mg m(-2)); and G 3 stomatitis/nausea/vomiting/fatigue (1.4 mg m(-2), 60 mg m(-2)). On the 21-day schedule, three patients had DLT during the first cycle: G 3 hypokalemia/hyponatremia (1.4 mg m(-2), 60 mg m(-2)); G 4 mucositis (1.4 mg m(-2), 60 mg m(-2)); and G 3 hypokalemia (1.2 mg m(-2), 75 mg m(-2)). The MTD and recommended phase II dose was determined as eribulin mesylate 1.2 mg m(-2) (days 1, 8) and CP 75 mg m(-2) (day 1), on a 21-day cycle. Two patients had unconfirmed partial responses (PR) (pancreatic and breast cancers) and two had PR (oesophageal and bladder cancers).

CONCLUSIONS

On the 21-day cycle, eribulin mesylate 1.2 mg m(-2), administered on days 1 and 8, in combination with CP 75 mg m(-2), administered on day 1 is well tolerated and showed preliminary anticancer activity.

Natural Products in Drug Discovery and Development. 27-28 June 2005, London, UK

The meeting covered many aspects of the use of natural products in drug discovery and development. The historical and current contributions of natural products to the main classes of medicines, technical improvements to the supply of marine microbial products by fermentation and molecular biology and the value of natural chemical diversity for providing patentable, drug-like lead molecules were among the topics discussed. Several compounds in current clinical trials were described; these included several anticancer compounds and two compounds in development by Phytopharm plc, PYM-50028 (Cogane) and PYM-50018 (Myogane), for the treatment of neurodegenerative disease.

A novel cytotoxic oxetane ent-kauranoid from Isodon japonicus

A novel ll,20: 1,20-diepoxy-ent-kaurane diterpenoid, maoyecrystal 1 (1), was isolated from Isodan japonicus, and its structure was elucidated by spectroscopic methods and comparison with another new ent-kauranoid, rubescensin W (2) from Isodon rubescens var. taihangensis. The structure of 2 was determined by single crystal X-ray diffraction analysis. A bioassay of their cytotoxity against K562 cells showed that the oxetane group of 1 might be a bioactive moiety.

Nitric oxide donor increases the efficiency of cytostatic therapy and retards the development of drug resistance

The potentiality to increase the chemotherapeutic effectiveness of some cytostatics in low, subtherapeutic doses in combination with nitric oxide (NO) donor has been shown. This type of combined therapy results in significant increase in life span and number of survivors among mice bearing leukemias P388 and L-1210. A similar effect was observed for intracerebral leukemia P388 transplantation. In this case the life span of mice treated with cyclophosphamide and NO donor increased by three times in comparison to therapy with cyclophosphamide alone. The coinjection of nitric oxide donor and cytostatics improved the antimetastatic activity of the cytostatics: the index of melanoma B16 metastasis inhibition at the cyclophosphamide monotherapy is 50%; on addition of NO donor the index is over 80%. Comparative studies of NO donor (organic nitrate) and a similar compound in which ONO(2) moieties were replaced by OH groups demonstrated that the presence of NO(2) is required for adjuvant activity of compounds and confirmed that nitric oxide modifies the antitumor effects of cytostatics. It is shown also that nitric oxide donor retards the development of drug resistance to cyclophosphamide.

Potent antimalarial activities of polyether antibiotic, X-206

In the course of our screening program to discover antimalarial antibiotics, which are active against drug resistant Plasmodium falciparum in vitro and rodents infected with P. berghei in vivo, from the culture broth of microorganisms, we found a selective and potent active substance produced by an actinomycete strain K99-0413. It was identified as a known polyether antibiotic, X-206. We also compared the in vitro antimalarial activities and cytotoxicities of 12 known polyethers with X-206. Among them, X-206 showed the most selective and potent inhibitory effect against both drug resistant and sensitive strains of P. falciparum. Comparison of biological activities and ion-affinities of the above antibiotics suggests that monovalent cations play an important biological role for the intracellular growth of P. falciparum in parasitized erythrocytes. Moreover, X-206 showed potent in vivo antimalarial activity on the rodent model, though the therapeutic window was narrow compared with its selective toxicity in vitro. These observations are the first report of antimalarial activity of X-206.

Synthesis of multiply substituted, ion channel forming octi(p-phenylene)s: theme and variations

[reaction: see text] To facilitate the access to unique models for biological processes, we examined six different synthetic routes to octi(p-phenylene) rods with lateral and terminal substituents R(L) and R(T). This systematic study allowed us to increase to overall yield for the synthesis of a new class of oligo(p-phenylene) ionophores about 20 times and to provide general insights into the practicability of synthetic routes to multiply substituted molecular rods.

Clonal preservation of human pancreatic cell line derived from primary pancreatic adenocarcinoma

Adenocarcinoma of the pancreas generally remains an incurable disease by available treatment modalities, demanding the development of a suitable cell-culture/animal model and the discovery and evaluation of novel therapeutic agents. We report the clonal preservation of a human pancreatic cell line (KCI-MOH1) established from a 74-year-old African-American man diagnosed with pancreatic cancer. Initially the human primary tumor was grown as a xenograft in SCID mice and, subsequently, a cell line was established from tumors grown as a xenograft as reported in our earlier publication. The molecular characterization of the primary tumor, the tumors grown as xenograft, and the cell line all revealed similar genotypic properties. By using an automated DNA sequencer, a K-ras mutation (codon 12, GGT to CGT, Gly to Arg) was detected in the pancreatic tumor tissue taken from the patient, whereas no p53 mutation was detected. The same K-ras mutation and unaltered p53 was also found in the xenograft tumor and in the KCI-MOH1 cell line. Chromosome analysis of the cultured cells revealed: 42,XY,add(3)(p11.2),der(7)t(7;12) (p22;q12),-10,-12,add (14)(p11),-18,add (20)(q13),-22/84, idemx2, which is the same chromosome complement found in xenograft tumors. The KCI-MOH1 cell line grows well in tissue culture and forms tumors in the SCID mice when implanted subcutaneously, as well as in orthotopic sites. The KCI-MOH1 cell line-derived SCID mouse xenograft model was used for efficacy evaluation of bryostatin 1, auristatin-PE, spongistatin 1, and gemcitabine alone and in combination. Tumor growth inhibition (T/C expressed as percentage), tumor growth delay (T - C), and log 10 kill for these agents were 38%, 22 days, and 0.53; 15%, 30 days, and 0.80; 24%, 25 days, and 0.66; and 10%, 33 days, and 0.90, respectively. When given in combination, two of seven gemcitabine + auristatin-PE-treated animals were free of tumors for 150 days and were considered cured. Animals treated with a combination of bryostatin 1 and gemcitabine and a combination of spongistatin and gemcitabine produced remissions in only one of seven mice. From these results, we conclude that (a) this is the first study illustrating that clonal characteristics of primary pancreatic tumors remained unchanged when implanted in mice and as a permanent cell line grown in vitro; and (b) there is a synergistic effect between gemcitabine and selected marine products tested in this study, which is more apparent in the gemcitabine and auristatin-PE combination. The results of this preliminary study suggest that these agents should be explored clinically in the treatment of pancreatic cancer.

Differential sensitivity of human prostatic cancer cell lines to the effects of protein kinase and phosphatase inhibitors

We investigated the effect of protein kinase and phosphatase inhibitors on the growth of six human prostatic cancer cell lines: DU145, PC3, ND1, LNCaP, ALVA31 and JCA1. We studied okadaic acid and sodium orthovanadate as serine/threonine and tyrosine protein phosphatase inhibitors, respectively, and staurosporin and genistein as a serine/threonine and tyrosine protein kinase inhibitors, respectively. All inhibitors examined exhibited a dose-dependent growth inhibitory effect on prostatic cancer cell lines. Our data indicate that prostatic cancer cell lines express unique biochemical properties since the degree of growth inhibition varied greatly and was dependent on the specific cell line and inhibitor studied. In addition, we found that surface expression of endoglin (CD105) changed by treatment with all inhibitors in most of the cell lines. These data also indicate that endoglin appears to be involved both in protein phosphatase and kinase mediated phosphoprotein turnover.

Comparative study of the antitumor activity of bistramides A, D and K against a non-small cell broncho-pulmonary carcinoma

Bistramides A, D and K are substances extracted from the marine ascidian Lissoclinum bistratum Sluiter that are capable of inducing in vitro terminal differentiation (G1DT) of cells from a non-small cell broncho-pulmonary carcinoma (NSCLCN6), but present different in vitro toxicities. This study shows that only the least toxic bistramides D and K possess an antitumor activity. These two substances could be administered as a continuous treatment which would induce terminal differentiation of stem cells at their entry into the cell cycle, thereby causing their destruction.

[The anti-ischemic properties of crown ether derivatives]

Experiments on open-chest anaesthetized cats were made to test derivatives of crown ethers, such as benzylase-15-crown-5 and dibenzylase-15-crown-5 for their effects on myocardial ischemia and the functional status of a myocardial ischemic focus in temporary coronary occlusion during coronary spasm induced by dihydroergotamine and during coronary microthrombosis caused by ADP. When intravenously administered in doses of 0.5-15 mg/kg, the tested agents were found to enhance myocardial tolerance to ischemia, depressed ST segment in ischemia induced by coronary occlusion and administration of ATP, and prevented ST-segment depression during coronary spasm.

CP-72,588, a semisynthetic analog of the polyether ionophore UK-58,582 with increased anticoccidial potency

We have employed semisynthesis to enhance the anticoccidial potency of a polyether ionophore. CP-72,588 is the alpha-methyl analog of the fermentation-derived polyether ionophore UK-58,852. The parent ionophore required a dose of 15 ppm to achieve anticoccidial efficacy in chickens equivalent to that of salinomycin at 60 ppm. CP-72,588 demonstrated substantially improved potency, with efficacy at 5 to 7.5 ppm. The intrinsic antimicrobial potencies of the two ionophores are similar; however, CP-72,588 was found in chicken tissues at higher levels than those of the parent ionophore when each was administered at the same dose (8 ppm). The enhanced potency of CP-72,588 may be partially due to enhanced uptake into tissues.

Comparative effects of protein phosphatase inhibitors (okadaic acid and calyculin A) on human leukemia HL60, HL60/ADR and K562 cells

Inhibitors of protein phosphatases 1/2A (okadaic acid and calyculin A) exhibited differential cytotoxicity toward three human leukemia cell lines, in an increasing order of resistance, HL60 less than HL60/ADR less than K562 cells. Cytotoxicity of the toxins was associated with marked mitotic arrest of the cells, characterized by chromatid scattering/overcondensation and abnormal mitotic spindles. In all cases, calyculin A was more potent than okadaic acid. Protein phosphorylation experiments in intact cells revealed that HL60/ADR, the adriamycin-resistant variant, showed a higher overall phosphorylation of nuclear proteins than the drug-sensitive parental HL60, and that phorbol ester (protein kinase C activator) and calyculin A appeared to more specifically stimulate phosphorylation of p66 and p60, respectively. It was suggested that the toxins might be useful in delineating mechanisms underlying certain properties of cancer cells (such as multidrug resistance, mitosis and differentiation) related to protein phosphorylation/dephosphorylation reactions.

Lack of effectiveness of several chelators in removing internally deposited strontium from mice following repeated parenteral strontium administration

Diethylenetriaminepentaacetic acid (DTPA), ethylenglycolbis-(beta-amino-ethylether)-N,N-tetraacetic acid (EGTA), tartaric acid, KRYPTOFIX 222, and KRYPTOFIX 5 were evaluated for their efficacy in mobilization of strontium from the body of mice which had received 20 sc injections of strontium nitrate (95 mg/kg/injection) for 4 w. Twenty-four hours after the last strontium injection, ip administration of 1 of the various chelators or 0.9% saline was initiated and continued daily for 5 d. Mice were housed in metabolic cages, and urine and feces were collected daily for 5 d. After this period, the animals were killed and tissues removed. Tartaric acid, KRYPTOFIX 222, and KRYPTOFIX 5 had no effect on urinary or fecal strontium elimination, whereas DTPA and EGTA significantly decreased the fecal strontium excretion. The concentration of strontium in bone was only lowered in tartaric-treated mice. This study indicates the use of the above chelators is not an effective treatment to enhance the removal of strontium following repeated parenteral strontium administration.

Effect of the fatty acid oxidation inhibitor methyl palmoxirate (methyl 2-tetradecylglycidate) on recovery from insulin-induced hypoglycemia in diabetic dogs

Methyl palmoxirate, an effective hypoglycemic agent administered p.o., has been shown to decrease hepatic glucose production secondary to inhibition of mitochondrial fatty acid oxidation. Because the ability to increase hepatic glucose production is an important counter-regulatory defense against hypoglycemia, we compared the ability of streptozotocin/alloxan-induced diabetic dogs treated p.o. with vehicle or methyl palmoxirate (2.5 mg/kg/day X 7 days) to recover from insulin-induced hypoglycemia. Hepatic glucose production and glucose utilization were determined by isotope dilution before and after acute reduction of plasma glucose by i.v. insulin injection (0.10 or 0.13 U/kg). Diabetic dogs treated with methyl palmoxirate for 6 days had lower overnight fasting plasma glucose levels than vehicle-treated animals (158 +/- 7 vs. 171 +/- 11, respectively, P less than .05). Plasma glucose at 4 hr after the last dose of drug decreased to 115 +/- 5 mg/dl, whereas glucose in the vehicle-treated dogs was unchanged (172 +/- 8 mg/dl). Recovery from insulin-induced hypoglycemia (nadirs of 58 +/- 5 and 42 +/- 4 mg/dl in the vehicle- and methyl palmoxirate-treated groups, respectively) was not significantly different between the two groups of dogs. Restoration of plasma glucose was primarily due to increased hepatic glucose production in both treatment groups, as glucose utilization did not fall significantly below baseline levels. Plasma glucagon levels increased in both vehicle- and methyl palmoxirate-treated dogs in response to hypoglycemia, indicating that release of an important counter-regulatory hormone was not compromised by drug treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Prophylaxis of early ventricular fibrillation by inhibition of acylcarnitine accumulation

Hypoxia in isolated myocytes results in accumulation of long-chain acylcarnitines (LCA) in sarcolemma. Inhibition of carnitine acyltransferase I (CAT-I) with sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA) prevents both the accumulation of LCA in the sarcolemma and the initial electrophysiologic derangements associated with hypoxia. Another amphiphilic metabolite, lysophosphatidylcholine (LPC), accumulates in the ischemic heart in vivo, in part because of inhibition of its catabolism by accumulating LCA. It induces electrophysiologic alterations in vitro analogous to early changes induced by ischemia in vivo. The present study was performed to determine whether POCA could prevent accumulation of both LCA and LPC induced by ischemia in vivo and if so, whether attenuation of early arrhythmogenesis would result. LAD coronary artery occlusions were induced for 5 min in chloralose-anesthetized cats. Coronary occlusion in untreated control animals elicited prompt, threefold increases of LCA (73 +/- 8 to 286 +/- 60 pmol/mg protein) and twofold increase of LPC (3.3 +/- 0.4 to 7.5 +/- 0.9 nmol/mg protein) selectively in the ischemic zone, associated with ventricular tachycardia (VT) or ventricular fibrillation (VF) occurring within the 5-min interval before acquisition of myocardial samples in 64% of the animals. POCA prevented the increase of both LCA and LPC. It also prevented the early occurrence of VT or VF (within 5 min of occlusion) in all animals studied. The antiarrhythmic effect of POCA was not attributable to favorable hemodynamic changes or to changes in myocardial perfusion measured with radiolabeled microspheres. Thus, inhibition of CAT-I effectively reduced the incidence of lethal arrhythmias induced early after the onset of ischemia. Accordingly, pharmacologic inhibition of this enzyme provides a promising approach for prophylaxis of sudden cardiac death, that typically occurs very soon after the onset of acute ischemia, in man.

Etomoxir, a carnitine palmitoyltransferase I inhibitor, protects hearts from fatty acid-induced ischemic injury independent of changes in long chain acylcarnitine

Fatty acids are known to increase the severity of injury during acute myocardial ischemia. In this study, we determined the effects of a carnitine palmitoyltransferase I inhibitor, ethyl 2-[6-(4-chlorophenoxy)hexyl]oxirane-2-carboxylate (Etomoxir) on reperfusion recovery of fatty acid perfused hearts. Following a 25-minute period of global ischemia, isolated working hearts reperfused with 1.2 mM palmitate, 11 mM glucose exhibited depressed function compared to hearts perfused with 11 mM glucose alone. A low dose of Etomoxir (10(-9) M) decreased long chain acylcarnitine and long chain acyl-coenzyme A (CoA) levels but did not prevent depressed function. In contrast, a high dose of Etomoxir (10(-6) M) prevented the palmitate-induced depression of function but did not decrease myocardial long chain acylcarnitine or long chain acyl-CoA levels. At this high dose of Etomoxir, oxygen consumption per unit work was decreased during reperfusion recovery, and ATP and creatine-phosphate levels were significantly higher after reperfusion. In aerobic hearts not subjected to ischemia, Etomoxir (10(-6) M) increased glucose oxidation both in the presence and absence of palmitate, while 10(-9) M Etomoxir had no effect. In these aerobic hearts, only the low dose of Etomoxir decreased long chain acylcarnitine and long chain acyl-CoA levels. These data demonstrate that Etomoxir (10(-6) M) increases functional recovery of fatty acid perfused ischemic hearts. This protection is unrelated to changes in levels of long chain acylcarnitines but may be due to increased glucose use by the reperfused heart, resulting in decreased oxygen consumption per unit work.

Additive hypoglycemic effects of drugs that modify free-fatty acid metabolism by different mechanisms in rats with streptozocin-induced diabetes

In this study the effect of two drugs [etomoxir and nicotinic acid (NA)] on plasma glucose, free-fatty acid (FFA), and triglyceride (TG) concentrations was determined in rats with streptozocin (STZ)-induced diabetes. The two compounds modify FFA metabolism by different mechanisms, etomoxir (ethyl-2-[6-(4-cholorophenoxyl)-hexyl]oxirane-2-carboxylate) by inhibiting hepatic fatty acid oxidation, and NA by inhibiting lipolysis in adipose tissue. Diabetes was induced in male Sprague-Dawley rats, weighing approximately 400 g, by STZ injection (30 mg/kg i.v.), and the metabolic effects of the two drugs were studied 7-10 days later. The acute administration of either etomoxir or NA lowered plasma glucose concentrations in diabetic rats by approximately 150 mg/dl (P less than .001) in 4 h. However, the two drugs differed dramatically in their effects on plasma FFA and TG concentrations. Specifically, etomoxir produced striking increases in plasma FFA and TG concentrations, whereas NA administration caused a marked decrease. However, when NA was given in conjunction with etomoxir, NA prevented the increase in plasma FFA and TG concentration seen with etomoxir; the combination of NA and etomoxir approximately doubled the decrease in plasma glucose concentration produced by NA or etomoxir when given alone. Because plasma insulin concentrations did not change in response to either drug, whether administered singly or in combination, these metabolic effects do not result from a change in insulin secretion. These results suggest that modulation of FFA metabolism at the level of the adipocyte or the liver can have dramatic effects on carbohydrate and lipid metabolism.

Prevention of diabetes-induced myocardial dysfunction in rats by methyl palmoxirate and triiodothyronine treatment

Diabetes results in myocardial functional alterations which are accompanied by a depression of biochemical parameters such as myosin ATPase and calcium uptake in the sarcoplasmic reticulum. Methyl palmoxirate, a fatty acid analog, is reported to decrease circulating glucose levels by inhibiting fatty acid metabolism, thus forcing carbohydrate utilization. In the present study, we attempted to prevent streptozotocin diabetes-induced myocardial alterations in the rat. Using the isolated working heart preparation, we observed a depression of myocardial function in rats 6 weeks after the induction of diabetes, which was characterized by the inability of these hearts to develop left ventricular pressures and rates of ventricular contraction and relaxation as well as control hearts at higher left atrial filling pressures. Methyl palmoxirate treatment (25 mg kg-1 day-1 po daily) was unable to control diabetes-induced changes in plasma glucose, triglycerides, insulin, and total lipids. Also, the functional depression seen in diabetic rat hearts was present despite the treatment. However, depression of calcium uptake and elevation of long chain acyl carnitines seen in sarcoplasmic reticulum (SR) prepared from diabetic rat hearts could be prevented by the treatment. As triiodothyronine (T3) treatment has been shown to normalize depression of cardiac myosin ATPase in diabetic rats, we repeated the study using a combination of T3 (30 micrograms kg-1 day-1 sc daily) and methyl palmoxirate. While diabetic rats treated with T3 alone did not show significant improvement of myocardial function when compared with untreated diabetics, the function of those treated with both T3 and methyl palmoxirate was not significantly different from that in control rat hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of the metabolic effects of 2-tetradecylglycidate by octanoic acid in the genetically diabetic mouse (db/db)

2-Tetradecylglycidate is a specific inhibitor of the enzyme carnitine palmitoyl transferase, the rate-limiting step in long chain fatty acid oxidation. We previously showed that chronic administration of TDGA to genetically diabetic mice caused a dose-dependent decrease in blood glucose, retarded the development of renal immunopathologic lesions, and resulted in significant cardiomegaly. The present study was designed to evaluate whether all the observed consequences of chronic TDGA administration resulted from inhibition of long chain fatty acid oxidation or whether the drug exerted other nonspecific effects. To circumvent the effects of LCFAO inhibition, diabetic mice were dosed with TDGA and given a diet containing 9% octanoic acid. Octanoic acid is a medium chain fatty acid, whose oxidation is not dependent on the carnitine transferase system and is not inhibited by TDGA. Administration of the octanoate diet to diabetics receiving TDGA abrogated all the drug effects, including lowering of blood glucose and prevention of renal immunopathology. Cardiomegaly, a consequence of increased protein accretion associated with TDGA dosing, did not occur in the octanoate-fed animals. These results indicate that all the actions of TDGA are mediated via its inhibitory effects on long chain fatty acid oxidation. The cardiac changes resulting from chronic TDGA administration suggest that long chain fatty acid oxidation and its relationship with myocardial energetics may exert a regulatory role on protein synthesis in the myocardium.

Mechanism of hyperglycemia and response to treatment with an inhibitor of fatty acid oxidation in a patient with insulin resistance due to antiinsulin receptor antibodies

Severe hyperglycemia and insulin resistance due to antiinsulin receptor antibodies developed over a period of 3 months in a 50-yr-old insulin-requiring diabetic patient. The hyperglycemia resulted from overproduction of glucose due to excessive rates of glycogenolysis and gluconeogenesis rather than decreased glucose utilization. Treatment with methyl-2-tetradecylglycidate, an inhibitor of fatty acid oxidation, resulted in a decrease in plasma glucose concentration. This was associated with a decrease in the rate of glucose production due to decreases in both gluconeogenesis and glycogenolysis rates, as well as an increase in the respiratory quotient. Plasma glucose concentrations continued to respond to the drug for the next 2 months until the sudden development of terminal hypoglycemia. The hypoglycemic action of the drug is consistent with the existence of an insulin-independent effect of fatty acid oxidation on glucose metabolism in man.

[Search for and study of antiarrhythmic substances among crown ethers]

The authors studied antiarrhythmic properties of macrocyclic polyesters. Some of the esters exhibited antiarrhythmic activity coupled with low toxicity. It was found that antiarrhythmic action of these substances is not mediated via acetylcholine and/or catecholamine system responsible for nervous regulation of the cardiac activity. The compounds under study were found to have marked antifibrillar properties. Experiments on an isolated rat heart demonstrated calcium specificity of the antifibrillar action of cyclolactones. It is assumed that macrocyclic polyesters represent a new class of antiarrhythmic agents having a direct cardiotropic action.

Preclinical evaluation of the anti tumour activity of new epoxyde derivatives

As a follow-up to our initial results on the antineoplastic activity of alpha-1,3,5-triglycidyl-s-triazinetrione (alpha TGT, NSC-296934, Teroxirone), many new epoxyde derivatives were tested against murine tumours, mostly against P388 leukaemia, to determine their antineoplastic role and to characterize their specific effect against tumour cells in vivo, as well as to select an analogue with higher anti-cancer properties and superior pharmacological properties. Triglycidyl urazol (TGU, NSC-332488) showed the highest therapeutic activity and a good level of water-solubility which makes this agent a good candidate for phase-one clinical trials.

Anticoccidial activity of crown polyethers

Anticoccidial activity in vitro against Eimeria tenella is reported for crown polyethers with ring sizes from 14 to 30 atoms. The most potent compounds, 4 and 9, were found active at 0.33 ppm, but none were active in vivo. Test results are discussed in terms of lipophilic shielding of complexed cations.

Metabolic control of prevention of nephropathy by 2-tetradecylglycidate in the diabetic mouse (db/db)

The genetically diabetic mouse (db/db) exhibits hyperphagia, progressive weight gain, hyperglycemia, and hyperinsulinemia during the first few months of life during which time characteristic pathologic changes occur in several organ systems including the kidney. The extent to which long chain fatty acid oxidation (LCFAO) contributes to excessive gluconeogenesis and hyperglycemia in these animals in unknown. Therefore, the synthetic fatty acid analogue 2-tetradeclyglycidate (TDHA), a potent inhibitor of LCFAO, was given orally to db/db mice to evaluate its capacity to control the blood glucose and prevent their diabetic nephropathy. Five groups of diabetic mice (N = 6) were assigned to receive TDGA in a dose of 5, 10, and 25 mg/kg/day, vehicle (tragacanth), or nothing (control). TDGA had no observable effects on food intake or growth patterns. Drug-treated animals had significant lowering of fasting glucose at 0 and 4 h after dosing during the midportion of the study (2-6 wk). In the latter part of the study (wk 8-11), blood glucose 4 h after dosing was lowered in mice given 10 and 25 free fatty acids. Animals receiving TDGA 25 mg/kg/day exhibited significant inhibition of immunopathologic changes in the kidney. Heart weight was significantly increased in mice receiving TDGA 25 mg/kg/day, and the total amount of myocardial carnitine content was increased in all three drug-treated groups. Increased tissue deposition of lipid was not apparent on histologic examination of liver in drug-treated animals. Inhibition of long chain fat oxidation in the db/db mouse results in significant lowering of blood glucose, and decreased the renal immunopathologic features of diabetic nephropathy in this animal model.

Phase II studies of dianhydrogalactitol and VP-16-213 in colorectal cancer

Phase II chemotherapy trials of dianhydrogalactitol and VP-16-213 were conducted in patients with metastatic colorectal cancer who had measurable malignant disease which served as indicators of response to therapy. Dianhydrogalactitol was given in a 5-day course at a dosage of 30 mg/m2/day. Toxic reactions included nausea, vomiting, leukopenia, thrombocytopenia, and anemia. There was a definite tendency to a compounding of hematologic toxicity with repeated courses. No evidence of objective therapeutic response was observed among 30 patients treated. VP-16-213 was given at a dosage of 130 mg/m2 on Days 1, 3, and 5. Toxic reactions included nausea, vomiting, alopecia, leukopenia, thrombocytopenia, and anemia. Hematologic toxicity was more severe in patients with elevated serum bilirubin levels. No evidence of objective therapeutic response was observed among 28 patients treated.

Phase I trial of dianhydrogalactitol administered Iv in a weekly schedule

Dianhydrogalactitol was given to 28 patients with a variety of advanced solid tumors on a weekly schedule in iv doses ranging from 2 to 80 mg/m2. No significant toxicity was encountered at doses up to 40 mg/m2/week for 4 weeks. At higher doses mild-to-moderate nausea and vomiting and hematologic toxicity were noted. Thrombocytopenia was more common than granulocytopenia and frequently resolved more slowly. No adverse drug-realted effects on liver, renal, coagulation, or cardiac function were seen. Although no patient had significant antitumor response (as strictly defined), objective improvement was noted in two patients, one with hypernephroma and the other with malignant melanoma. for phase II studies, a weekly dose of 70 mg/m2 is recommended for patients with normal hematopoiesis, with reduction by 25% (55 mg/m2) in patients with extensive prior radiation therapy, prior chemotherapy, and/or widespread metastasis to the bone.

Phase I evaluation of dianhydrogalactitol (NSC-132313)

A toxicologic evaluation of dianhydrogalactitol in man was completed for a 5- and a 10-day schedule. The maximum tolerated dose was 30 mg/m2/day for the 5-day schedule and 21 mg/m2/day for the 10-day schedule. Dose-limiting myelosuppression occurred with both schedules, with leukopenia and thrombocytopenia being observed at median Days 15 and 19 respectively for the 5-day course and median Days 22 and 26 of the 10-day course. Nausea was infrequent and mild. Responses were obtained in one patient with laryngeal carcinoma and in one patient with adenocarcinoma of the lung.

Phase I study of a five-day intermittent schedule for 1,2:5,6-dianhydrogalactitol (NSC-132313)

Because 1,2:5,6-dianhydrogalactitol (NSC-132313 (DAG; the main conversion reaction product of the treatment of dibromodulcitol by mild akali or human serum) showed considerable antitumor activity in various mouse and rat tumor systems, a phase I study in 50 patients was conducted with five daily iv treatments repeated every 6 weeks. Thrombocytopenia was the dose-limiting toxicity. At a dose of 40 mg/m2/day for 5 days, the median platelet nadir was 31,000/mm3 and occurred on day 20; the plate count returned to normal within 8 days. At the same dose, the median white blood cell (WBC) nadir was 2,300/mm3 also on day 20-, the WBC count returned to normal within 7 days. Anemia, nausea, and vomiting were usually mild to moderate. No renal, hepatic, central nervous system, cardiac, or pulmonary toxicity was identified. Antitumor effects of DAG were observed in patients with renal, bladder, and small-cell lung cancers. An iv dose of 20-30 mg/m2/day for 5 consecutive days, repeated every 5-6 weeks, was recommended for phase II studies.

Colestipol hydrochloride, a new hypolipidemic drug: a two-year study

Colestipol hydrochloride is an insoluble, nonabsorbable copolymer with bile-acid-binding capacity. It prevents reabsorption of cholates from the intestinal tract into the enterohepatic circulation causing a net loss of bile acids, and therefore of cholesterol. Sixty subjects with cholesterol levels over 250 mg/100 ml were studied for 104 weeks. Patients with normal phenotypes, types 2,3, and 4, were given 5 gm three times daily and experienced an average drop of 40 mg/100 ml (14%). While patients with types 2,3, and 4 hyperlipidemia responded effectively, cholesterol levels in type 2 patients dropped earliest and most consistently with an average decrease of 58 mg/100 ml (19%). A comparable group of patients with hyperlipidemia taking placebo showed on average no change in serum cholesterol. Serum triglyceride values were not altered significantly. The resin is not absorbed from the gastrointestinal tract and produces a slight increase in fecal volume. Results of chemistries, enzyme assays, prothrombin times, hematology, and urinalysis and body weights wer unaltered. There was no evidence of lithogenic bile production. Colestipol is a tasteless and ordorless copolymer with high acceptability. Side effects were limited to occasional bloating, gas, and constipation. The drug is a safe, effective, palatable hypolipedmic agent.

Long-term treatment of hypercholesterolemia with colestipol hydrochloride

Colestipol hydroxhloride (15 gm/day) (an anion exchange resin that binds bile acids) of placebo was administered to 92 patients with hypercholesterolemia who were followed for periods up to 36 months. There was a prompt (1 month), significant (p smaller than 0.05 minus 0.001), and sustained (36 months) lowering of serum cholesterol in the colestipol HCl-treated group, but no significant change in the placebo group. Serum triglycerides increased in both treatment groups in parallel; the reason was not apparent. Side effects were equally distributed between colestipol HCl and placebo and were primarily gastrointestinal (upper abdominal distress, constipation). Colestipol HCl appears to be a safe and effective treatment for hypercholesterolemia; tolerance does not seem to develop.

Changes in plasma lipoprotein lipids in hypercholesterolaemic patients treated with the bile acid-sequestering resin, colestipol

1. Seven patients with type II hyperlipoproteinaemia were treated with the bile acid-sequestering resin, colestipol (5 g three times daily), after a prolonged period of taking placebo.

2. After 8–9 weeks of treatment, the plasma concentration of the non-esterified cholesterol of very-low-density lipoprotein (VLDL) had risen by a mean of 0.09 mmol/l (43% increase, P < 0.001), that of the esterified cholesterol of VLDL had risen by a mean of 0.11 mmol/l (38% increase, P < 0.01), and that of the triglyceride of VLDL had risen by a mean of 0.40 mmol/l (53% increase, P<0.001). During the same period, the plasma concentration of the non-esterified cholesterol of low-density lipoprotein (LDL) decreased by a mean of 0.44 mmol/l (26% decrease, P < 0.01), that of the esterified cholesterol of LDL decreased by a mean of 1.28 mmol/l (30% decrease, P< 0.001), and that of the triglyceride of LDL decreased by a mean of 0.04 mmol/l (8% decrease, P < 0.01). No significant changes occurred in the plasma concentration of either the cholesterol or triglyceride of high-density lipoprotein (HDL) during treatment.

3. During the early period of treatment with colestipol, changes took place in the specific radioactivity of plasma cholesterol (labelled by intravenous injection of [3H]cholesterol), which, together with the changes in the mass of cholesterol within the individual plasma lipoproteins, were consistent with an increased influx into plasma of non-esterified cholesterol within VLDL, and an increased efflux of cholesterol from plasma within LDL.

Isosorbide in the medical treatment of infantile hydrocephalus

✓ The author reports the methods, results and complications of isosorbide therapy in 60 patients with various types of infantile hydrocephalus. Treatment was monitored by serial measurements of head circumference, assessment of fontanel tension, air ventriculography, and echoencephalography. Frequent estimation of plasma electrolytes, urea, and Astrup figures were found essential to guard against serious hypernatremia and acidosis, especially if higher doses were used. Infants with moderate hydrocephalus and those whose shunt was removed temporarily because of infection did particularly well under isosorbide. Cases of severe hydrocephalus rarely responded to therapy and in these, at best, only a delay before surgical therapy was achieved.