Biodistribution of NX211, liposomal lurtotecan, in tumor-bearing mice.

Prolonging tumor exposure to topoisomerase I inhibitors has been correlated to enhance the efficacy of those agents. Lurtotecan, a water-soluble camptothecin analog, was formulated as a liposomal drug, NX211, to enhance the delivery of drug to tumors. Tumor-bearing mice were treated with either [14C]NX211 containing [14C]lurtotecan, [3H]NX211 containing [3H]phosphatidylcholine or [14C]lurtotecan, euthanized at selected times post-injection, and tissues, plasma, urine and feces were collected. These studies demonstrated that KB tumors of [14C]NX211-treated mice had approximately 70-fold greater concentrations of [14C]lurtotecan at 24 h, respectively, compared to concentrations of [14C]lurtotecan of the KB tumors of [14C]lurtotecan-treated mice. The area under curve (AUC) from 0 to 48 h of [14C]lurtotecan for the KB tumors of [14C]NX211-treated animals was over 17-fold greater than the AUC of [14C]lurtotecan for the tumors of [14C]lurtotecan-treated animals. Treatment with [3H]NX211 demonstrated that the lipid component continually accumulated over 24 h in the tissues. HPLC analysis of extracted material from tumors of [14C]NX211-treated mice showed that more than 95% of the radioactive material was intact [14C]lurtotecan. These findings are one of the keys justifying the development of a liposomal formulation of lurtotecan, which has the intent to increase tumor exposure and increase antitumor efficacy.

Pharmacokinetics and safety of an anti-vascular endothelial growth factor aptamer (NX1838) following injection into the vitreous humor of rhesus monkeys.

PURPOSE: The objective of this study was to determine the pharmacokinetics and safety for NX1838 following injection into the vitreous humor of rhesus monkeys. METHODS: Plasma and vitreous humor pharmacokinetics were determined following a single bilateral 0.25, 0.50, 1.0, 1.5, or 2.0 mg/eye dose. In addition, the pharmacokinetics and toxicological properties of NX1838 were determined following six biweekly bilateral injections of 0.25 or 0.50 mg/eye or following four biweekly bilateral injections of 0.10 mg per eye followed by two biweekly bilateral injections of 1.0 mg per eye. RESULTS: Plasma and vitreous humor NX1838 concentrations were linearly related to the dose administered. NX1838 was cleared intact from the vitreous humor into the plasma with a half-life of approximately 94 h, which was in agreement with the plasma terminal half-life. Vascular endothelial growth factor (VEGF)-binding assays demonstrated that the NX1838 remaining in the vitreous humor after 28 days was fully active. No toxicological effects or antibody responses were evident. CONCLUSIONS: The no observable effect level was greater than six biweekly bilateral 0.50 mg/eye doses or two biweekly bilateral 1.0 mg/eye doses. These pharmacokinetic and safety data support monthly 1 or 2 mg/eye dose regimens in human clinical trials.

An evaluation of the toxicities of 2'-fluorouridine and 2'-fluorocytidine-HCl in F344 rats and woodchucks (Marmota monax).

The toxicities of 2'-fluorouridine (2'-FU) and 2'-fluorocytidine-HCl (2'-FC) were separately evaluated in 2 species, male Fischer 344 (F334) rats and woodchucks. Particular attention was focused on the ability of these nucleosides to induce toxicities similar to those induced by the antiviral drug fialuridine (FIAU). 2'-FU or 2'-FC was administered to F344 male rats by intravenous injection at doses of 5, 50, and 500 mg/kg/day for 90 consecutive days and to male and female woodchucks at doses of 0.75 and 7.5 mg/kg/day for 90 consecutive days. Clinical chemistry, hematology, and urinalysis (woodchuck only) profiles were assessed during and at the termination of the study. At necropsy, organs were weighed and tissues collected for routine histologic analysis. Cytochrome c oxidase activity, citrate synthase activity, and mitochondrial DNA content were measured, and micronucleus formation in the bone marrow (rats only) was evaluated. No adverse clinical effects were observed in either species. Rats treated with high doses of either 2'-FU or 2'-FC had body weights that were 90% of those of controls. 2'-FU and 2'-FC both induced a moderate decrease in the median lymphocyte count, and 2'-FC and 2'-FU induced a mild increase in mean corpuscular hemoglobin and mean corpuscular volume. Both compounds caused slight to moderate, reversible, histologic changes in the spleen and thymus. In the woodchuck, 2'-FC caused a slight increase in mean absolute lymphocytes, and 2'-FC and 2'-FU slightly increased hepatic periportal vacuolation and/or mononuclear cell infiltration. In summary, neither compound showed evidence of the toxicity induced by fialuridine in either species. Although compound effects were observed, none of these effects were considered to be adverse, and the no-observed adverse effect level was determined to be 500 mg/kg/day for both compounds in the male F344 rat and 7.5 mg/kg/day in the woodchuck.

Derivation of RNA aptamer inhibitors of human complement C5.

Specific aptamer inhibitors of the human complement C5 component were produced by the SELEX methodology of directed evolution of nucleic acid ligands. The SELEX procedure started with a pool of random-sequence, 2'F-pyrimidine-modified nuclease-stabilized RNA, and after twelve rounds of iterative C5 binding and nucleic acid amplification an evolved RNA pool was obtained which contained the highest affinity binders to the C5 protein. The evolved RNA pool was then cloned and sequenced, and individual clones were analyzed for binding and function. Twenty-eight clones (out of sixty) were identified which bound C5 (termed aptamers). Seven of these aptamers formed a closely related sequence homology family; these aptamers bound C5 with a Kd 20-40 nM and also inhibited human serum hemolytic activity. In addition, these aptamers inhibited zymosan-induced generation of C5a. Aptamer inhibition of both C5b and C5a suggests that aptamer binding inhibits cleavage of C5 by the C5 convertase of both pathways. One of the inhibitory aptamer sequences was truncated to yield a 38-mer 2'F RNA aptamer which retained C5 binding and inhibitory activity. The structure of this aptamer is predicted to be a stem-loop containing thirteen base pairs, and also containing two bulges. The affinity of this aptamer was improved by performing a second biased SELEX experiment, where the randomized starting RNA pool uses a template where the individual base compositions are biased toward a specific sequence. This second SELEX experiment produced an aptamer with a Kd of 2-5 nM which retained functional activity. Another SELEX to rat C5 produced an aptamer with binding and inhibitory properties virtually identical with the human aptamer. The human and rat aptamers are being evaluated for complement inhibition in vitro and in vivo as potential therapeutics for treatment of human disease.

Regulatory decision strategy for entry of a novel biological therapeutic with a clinically unmonitorable toxicity into clinical trials: pre-IND meetings and a case example.

The following material was derived from a synthesis of case histories taken from investigational new drug (IND) applications and drug sponsors' experiences, utilizing fictionalized data to avoid any resemblance to any proprietary information; any such resemblance is accidental. These examples are used as an instructional scenario to illustrate appropriate handling of a difficult toxicology issue. In this scenario, a drug caused a toxicity in animals that was detected only by histopathologic analysis; if it were to develop in patients, no conventional clinical methods could be identified to monitor for it. It is not unusual for a firm to cancel clinical development plans for a lead drug candidate that causes such a toxicity, especially if such a drug is intended for use as a chronic therapeutic in a population of patients with a chronic disease. This case synthesis was inspired by a Food and Drug Administration (FDA) agreement to allow such a product to proceed into clinical trials after substantive pre-IND discussions and agreement on well-considered toxicology program designs. The scientists most closely involved in the strategy development included the sponsor's toxicologist, veterinary toxicologic pathologist, and pharmacokineticist, as well as the FDA's reviewing pharmacologist. The basis of this decision was thorough toxicity characterization (1-month studies in 2 species); correlating toxicities with a particular cumulative area under the curve (AUC) in both species; identification of the most sensitive species (the species that showed the lower AUC correlating with toxicity); allometric assessment of clearance of the drug in 3 nonhuman species; construction of a model of human kinetics (based on extrapolation from animal kinetics); and finally, estimation of clinical safety factors (ratios of the human estimated cumulative AUC at the proposed clinical doses, over the animal cumulative AUC that correlated with the no adverse effect levels). Industry and FDA scientists negotiated a joint assessment of risk and benefit in patients, resulting in the FDA permitting such a compound to enter into clinical trials for a serious autoimmune disease. Such constructive, early communication starts with the pre-IND meeting, and the conduct and planning for this meeting can be very important in establishing smooth scientific and regulatory groundwork for the future of a drug under IND investigation.

Liposome-anchored vascular endothelial growth factor aptamers.

Nuclease-resistant aptamers identified from randomized nucleic acid libraries represent a novel class of drug candidates. Aptamers are synthesized chemically and therefore can be readily modified with functional groups that modulate their properties. We report here on the preparation, initial characterization, and functional properties of a nuclease-resistant vascular endothelial growth factor (VEGF) aptamer anchored in liposome bilayers through a lipid group on the aptamer. While the high-affinity binding to VEGF is maintained, the plasma residence time of the liposome-anchored aptamer is considerably improved compared with that of the free aptamer. The lipid group attachment and/or liposome anchoring leads to a dramatic improvement in inhibitory activity of the aptamer toward VEGF-induced endothelial cell proliferation in vitro and vascular permeability increase and angiogenesis in vivo.

Anthracycline Efficacy in vitro: Cytotoxicity of Liposomal/Nonliposomal Daunorubicin and Doxorubicin for Multiple Tumor Cell Types.

Anthracyclines, including daunorubicin (DnR) and doxorubicin (DoX), have shown clinical chemotherapeutic utility, albeit in association with cumulative dose-associated cardiotoxicities. Despite structural similarity, however, DnR and DoX treatments have been directed toward leukemias and solid tumor types, respectively. Due to a paucity of in vitro data regarding differential use of DnR or DoX, we assessed the cytotoxicity of these compounds against solid and hematological tumor cell types. In addition, we examined liposomal formulations of DnR (L-DnR) and DoX (PEG-DoX), which, in contrast to DnR or DoX, demonstrate antineoplastic activity with reduced cardiotoxicity in vivo. Accordingly, cytotoxicity testing (with [methyl/-(3)H]thymidine incorporation) of DnR, DoX, L-DnR, and PEG-DoX on a range of different human tumor cell lines (e.g., breast, lung, ovarian, prostate, melanoma, lymphoma, and leukemia tumor cell types) was performed. Our data indicate comparable activity for DnR, DoX, or L-DnR in all tumor cell types examined [e.g., SK-BR-3 (breast adenocarcinoma) cells: IC50 values = 5.9, 9.1, and 4.7 ng/mL for DnR, DoX, and L-DnR respectively]. In addition, several solid tumor cell types were more responsive to DnR than DoX [e.g., DU-145 (prostate carcinoma) cells: IC50 values = 10.4 and 41.2 ng/mL for DnR and DoX, respectively; p >. 001]. Interestingly, PEG-DoX was substantively less effective for all tumor cells (IC50 values were about 100-10,000 times greater for PEG-DoX than for DnR, DoX, or L-DnR; p >. 001, all cases). Reduced PEG-DoX activity in vitro may be related to polyethylene glycol (PEG) moieties present on the liposomal exterior of PEG-DoX, which are not present on L-DnR. Nonetheless, taken together, these data suggest that DnR and DoX demonstrate comparable efficacy in vitro and that specific liposomal encapsulation (L-DnR) does not mitigate DnR efficacy in vitro.

Safety assessment programs for U.S. regulatory agencies: a perspective of requirements and compliance.

Regulatory agencies and components within agencies in the United States have been established at different times but with the same basic charge: to protect the health and welfare of the citizenry by regulating the manufacture and use of chemicals and devices that might constitute a threat to the environment or a health hazard for individuals, groups of individuals, or the population as a whole. The character of each agency differs because of the political climate in which it has evolved, the personalities of the leadership, and the internal philosophies concerning how the agency's charge under the letter of the law should be accomplished in keeping with the congressional intent for establishment of the agency. The current safety assessment program requirements/guidelines and some aspects of their interpretation and application are discussed for the Environmental Protection Agency and for components of the Food and Drug Administration, including the Center for Drug Evaluation and Research, the Center for Biologics Evaluation and Research, and the Center for Veterinary Medicine.

Hepatocellular proliferation in ibuprofen-treated mice.

Female B6C3F1 mice were treated with ibuprofen for 2 wk or 90 days to monitor effects on hepatocellular proliferation during acute and subchronic exposure. Proliferation was assessed by bromodeoxyuridine labeling. Mice treated with 100, 200, or 400 mg/kg ibuprofen for 2 wk had significantly increased liver weights. A dose-related increase in the number of labeled hepatocytes per 1,000 hepatocytes suggested that the weight increases were in part a result of hepatocellular proliferation. Hepatocellular hypertrophy also contributed to the increased liver size as indicated by decreases in the number of hepatocytes per high power field. Ultrastructural evaluation indicated that hepatocyte peroxisome size increased significantly in treated mice. Mice treated with 100 or 200 mg/kg ibuprofen for 90 days and given bromodeoxyuridine during the last 2 wk of ibuprofen exposure had statistically significant increases in relative liver weights. However, the number of labeled hepatocytes per 1,000 hepatocytes was not increased, and there was no evidence of hepatocellular hypertrophy. Mice given 200 mg/kg ibuprofen for 90 days had significantly decreased serum triglycerides. These findings indicate that ibuprofen treatment of mice results in hepatomegaly characterized by hepatocellular hypertrophy and hyperplasia. Peroxisomal changes may be contributory to the pathogenesis of this lesion.

Comparisons of protein changes in human and rodent hepatocytes induced by the rat-specific carcinogen, methapyrilene.

There is a growing concern that the rodent bioassay may not always serve as an appropriate model to assess the carcinogenic risk for humans exposed to certain compounds. Mechanistic research that examines the effects of a compound in rodent and man could help in the interpretation of bioassay results. This paper reports a novel use of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) technology to assess similarities and differences in the response of rodents and humans to the rat-specific hepatocarcinogen, methapyrilene (MP). A sequential examination of rodent and human hepatic proteins was conducted following in vivo exposure of rats and mice and in vitro exposure of rat, mouse, and human hepatocytes to MP. Results showed that covalent modifications observed in rats and mice in vivo were duplicated both qualitatively and quantitatively in the corresponding in vitro systems and that these modifications correlated with carcinogenic susceptibility. Covalent modifications in human hepatocytes were minimal despite exposure to concentrations of MP that were 6-fold higher than those used in rodent hepatocytes. These studies suggest that in the case of MP the rat is not the most appropriate model for assessing the human situation. Furthermore, these data show that in vitro-in vivo comparisons based on 2-D PAGE may provide adjunctive information for extrapolating rodent toxicity/bioassay results to human risk assessment.

Carcinogenicity studies of fluoxetine hydrochloride in rats and mice.

The antidepressant drug fluoxetine HCl was tested for carcinogenicity in three well designed and controlled studies in Fischer rats and C57BL/6 x C3H F1 mice. The compound was administered to the animals for 24 months at dietary doses of approximately 0, 0.5, 2.0, or 10.0 mg/kg body weight in rats and 1.0, 5.0, or 10.0 mg/kg in mice. The highest dose tested was a maximum tolerated dose for both species as evidenced by clinical signs (rats and mice) and some mortality (mice) referable to central nervous system pharmacological effects, decreased weight gain (rats), and histopathological changes of phospholipidosis (rats) and hepatic fatty change (mice). There was no evidence of an increased incidence of any type of unusual or commonly occurring spontaneous neoplasm in either rats or mice. There were statistically significant decreases in a few commonly occurring neoplasms. The data reported herein provide convincing evidence that fluoxetine is neither a complete carcinogen nor a tumor promoter.

Covalent protein modifications and gene expression changes in rodent liver following administration of methapyrilene: a study using two-dimensional electrophoresis.

The effect of methapyrilene (MP), a mitochondrial proliferator and presumed nongenotoxic carcinogen, has been examined in rodent liver by means of high-resolution two-dimensional electrophoretic analysis of total proteins. Using this approach, we have discovered protein modifications in rat liver resulting from 1 week MP treatment that suggest the involvement of a reactive drug metabolite. The restriction of these molecular charge modifications to mitochondrial proteins indicates that such a reactive metabolite must be generated and confined within the mitochondrion. Quantitative changes in numerous nonmitochondrial proteins are also observed. Following a 4-week recovery period, almost all the 1-week treatment changes are reversed, reestablishing a protein pattern close to that of the controls. At the end of a 10-week exposure, the mitochondrial protein modifications are increased and are accompanied by a variety of quantitative protein changes indicative of a large shift in gene expression and/or cell type composition. When a 4-week untreated recovery period follows the 10-week treatment, small quantitative changes persist. In the mouse, where MP appears not to induce mitochondrial proliferation or tumorigenesis, 1 week treatment nevertheless produces mitochondrial protein changes in vivo consistent with attack by a reactive metabolite, but at a level substantially lower than that seen in the rat. Features of the mitochondrial protein modification indicate that it is covalent, does not involve cysteine or tryptophan, and results from binding of a negatively charged adduct. The possibility that the putative reactive metabolite could also attack mitochondrial (but not nuclear) DNA suggests that MP could be genotoxic in an unconventional way. Detection of protein modification by two-dimensional gel analysis appears to offer a general method for the detection and characterization of processes generating reactive metabolites.