Development of Hibernomas in Rats Dosed with Phentolamine Mesylate During the 24-Month Carcinogenicity Study

Phentolamine is a reversible competitive α-adrenergic antagonist with similar affinities for α1 and α2 receptors. It has a long history of safe clinical use, and was developed as a potential therapy for male erectile dysfunction because of its capacity to increase the arteriolar blood flow to the corpora cavernosa. Phentolamine mesylate was administered to rats by oral gavage at daily doses of 10, 50, and 150 mg/kg for 24 months. A dose-related increase in mortality, ascribed to an exaggerated pharmacologic effect, was seen at high doses. Systemic exposure as measured by plasma drug concentration increased with dose and duration of dosing and slight drug accumulation occurred, particularly in high-dose males. In the treated groups, 10 males and 1 female were diagnosed with hibernomas, neoplasms of brown adipose tissue, which appeared in the thoracic cavity or retroperitoneal area as circumscribed, tan to reddish-brown lobulated masses. Histologically, the masses were well circumscribed with variably sized lobules defined by a rich capillary network and consisted of closely apposed oval to polygonal cells with large amounts of cytoplasm and a centrally located nucleus. The cytoplasm's appearance varied from multivacuolated to univacuolated to granular eosinophilic. In a few cases, neoplastic emboli were observed in capsular vessels. Ultrastructurally, the neoplastic cells contained numerous mitochondria with transverse parallel cristae that occupied over 60% of the cytoplasm and lipid droplets. This study documents the previously unreported development of hibernomas in rats treated with phentolamine mesylate.

Dermatotoxicology: Safety Evaluation of Topical Products in Minipigs: Study Designs and Practical Considerations

The minipig has long been identified as the nonrodent animal of choice for preclinical safety evaluation of topically applied materials. This article reviews types of topical applications, study designs, and practical considerations. Dermal administration to the minipig presents multiple challenges. Issues to be considered are the area of exposure, the nature of the test article, the need for covering of the dose site, preparation of the dose site, and procedures for administration. The potential for cross-contamination (exposure of control animals to test article) is very high in topical studies and appropriate safeguards to prevent this are discussed. Topical administration to the intact skin is the most commonly utilized form of safety evaluation, but procedures have also been developed for intradermal administration and for the use of nonintact/wounded skin; these will be discussed. Evaluation of local (topical) effects is critical and can become complicated. Considerations in evaluations of the skin are interobserver variability, use of different scoring systems and discrepancies betweenin vivoobservations, necropsy observations, and microscopic pathology findings. Causes for apparent discrepancies and suggestions for practical resolution through appropriate procedures are discussed. Practical issues in necropsy and histotechnology procedures and techniques to optimize preservation of skin are also discussed.

Oxcarbazepine monotherapy in postherpetic neuralgia unresponsive to carbamazepine and gabapentin

OBJECTIVES

We present the results of a preliminary, open-label trial to evaluate the efficacy and tolerability of oxcarbazepine in postherpetic neuralgia (PHN) unresponsive to treatment with antiepileptic drugs (carbamazepine and gabapentin) and local anesthetic blocks.

MATERIALS AND METHODS

Twenty-four patients were treated with oxcarbazepine monotherapy for 8 weeks. Starting dose was 150 mg/day, subsequently increased by 150 mg/day every 2 days until a maintenance dose of 900 mg/day. Pain was assessed using a visual analog scale (VAS).

RESULTS

There was a significant decrease in the mean VAS score following 8 weeks of treatment (Delta=5.33; paired t-test: P <0.0001) compared with baseline. Oxcarbazepine was effective from the first week of treatment. There was a significant reduction in allodynia, leading to improvements in patients' functioning and quality of life. Oxcarbazepine was generally well tolerated.

CONCLUSION

Oxcarbazepine appears to be a promising alternative monotherapeutic approach for patients affected by PHN.

Evaluation of apomorphine HCl effects on reproductive endpoints: studies in male rats and dogs

Apomorphine HCl is currently in phase III clinical trials for the treatment of erectile dysfunction. The potential for reproductive toxicity in males was assessed based on a 13-week rat study--a fertility study in male rats--and a 6-month study in dogs. The subcutaneous (s.c.) route was selected to simulate the sublingual route in humans. Dosages of apomorphine were 0.0 (vehicle), 0.8, 2, and 8 mg/kg/day in the 13-week study in rats (20/group), with 8 mg/kg/day used for only 9 weeks. In the fertility study, 24 males/group were cohabited with females, and doses were 0.0, 0.2, 0.8, and 2 mg/kg/day. Males were treated for 4 weeks prior to cohabitation and for 5 weeks throughout cohabitation. Organ weights, including testis and left epididymis, sperm count and morphology in the epididymis, and sperm motility in the vas deferens were evaluated. Male fertility index, and in females, the numbers of fetuses, implantation sites, and corpora lutea were counted. Male dogs (five/group) were dosed with 0.04, 0.1, or 0.4 mg/kg/day for 6 months. Epididymal and prostate weight, and testicular and epididymal histology were evaluated. Daily morbidity/mortality, weekly clinical observations, body weight, and food consumption were evaluated in all studies. No adverse effect was observed in any of the reproductive parameters in the studies. The NOEL for reproductive toxicity was approximately equal to 0.4 mg/kg/day in dogs and > or = 2 mg/kg/day in rats. These doses in rats and dogs correlated with plasma levels of approximately 240 and 130 ng/mL, and AUCs of 200 and 100 ng.h/mL, respectively. These levels suggest a safety margin for the evaluated male reproductive endpoints of at least 104 times based on the Cmax, and 44 times based on AUC of the clinical dose.

Inhibition of coagulation by a phosphorothioate oligonucleotide

In the development of antisense therapeutics, there have been a number of hybridization-independent effects characterized for phosphorothioate oligodeoxynucleotides. One such effect is the transient prolongation of clotting times following intravenous infusion of high doses. In this study, inhibition of clotting times was characterized by determining the time course of both APTT and plasma oligonucleotide following intravenous infusion of ISIS 2302 in cynomolgus monkeys. Prolongation of APTT was also achieved by addition of ISIS 2302 to citrated blood from untreated monkeys, allowing the investigation of the mechanism of inhibition in vitro. Results from this study clearly indicate that the intrinsic pathway (APTT) was more sensitive to inhibition than the extrinsic pathway (PT). The prolongation of APTT was also shown to be transient and closely correlated with plasma oligonucleotide concentrations. The extent of APTT prolongation can be controlled by minimizing peak plasma oligonucleotide concentrations through lowering the dose or prolonging infusion duration. Direct addition of ISIS 2302 to blood produced quantitatively similar inhibition of clotting times. This effect was similar for a number of different phosphorothioate oligodeoxynucleotides, but oligonucleotides containing phosphodiester linkages and 2'-propoxy linkages were much less inhibitory. Additional in vitro studies indicated that the mechanism of inhibition was independent of that of heparin and possibly involved selective inhibition of the intrinsic pathway as well as the common clotting pathway. Investigation of selective clotting factors indicated that there was no direct inhibition of the enzymatic activity of factor Xa, XIa, or thrombin using chromogenic substrates. However, ISIS 2302 did produce a concentration-dependent increase in clotting time when fibrinogen was used as the substrate for thrombin.

Evaluation of the toxicity of ISIS 2302, a phosphorothioate oligonucleotide, in a four-week study in cynomolgus monkeys

The toxicity of ISIS 2302, a phosphorothioate oligonucleotide with antisense activity against human ICAM-1 mRNA, was investigated in cynomolgus monkeys (young adult). The oligonucleotide was administered by slow bolus injection every other day for 28 days (14 doses) at dose levels of 0, 2, 10, and 50 mg/kg/injection. The basic group size consisted of three male and three female monkeys which were sacrificed 2 days after the last dose. An additional 2 monkeys/sex in the vehicle control and 50 mg/kg dose groups remained on study for a 28-day treatment-free period. No treatment-related deaths occurred during this study, however, one monkey in the 10 mg/kg dose group was markedly lethargic after the first dose. Other clinical observations included periocular swelling (> or = 10 mg/kg) on the first day of the study, and bruising in all dose groups throughout the study. Bruising was associated with a dose-dependent prolongation of clotting times, particularly activated partial thromboplastin times (APTT), that was transient in nature. Bruises occurred around site of intravenous dosing or blood collection, and were manifested as subcutaneous hemorrhages upon microscopic evaluation. There were no corresponding alterations in hematology parameters including RBC or platelet counts. Other treatment-related microscopic alterations noted were intracytoplasmic eosinophilic granules and vacuolation in proximal tubular epithelial cells at 10 and 50 mg/kg, with free RBC in renal proximal tubular lumens at 50 mg/kg. Serum chemistry parameters including BUN and creatinine levels were normal in all dose groups and there were no notable alterations in urinalysis parameters. Granules and vacuolations in kidneys were reversed following a 4-week treatment free period. In general, 10 and 50 mg/kg ISIS 2302 produced dose-dependent changes in clotting times and the kidney that were reversible, while 2 mg/kg ISIS 2302 produced no remarkable alterations.

Activation of the alternative pathway of complement by a phosphorothioate oligonucleotide: potential mechanism of action

Intravenous infusion of high doses of phosphorothioate oligonucleotides in monkeys has been associated with transient alterations in hematologic and hemodynamic parameters, which appear to be secondary to complement activation. ISIS 2302, a phosphorothioate oligonucleotide specific for human intracellular adhesion molecule-1, was used to further characterize complement activation in monkeys. Complement activation occurred selectively through the alternative pathway resulting in increased plasma concentrations of the complement split products Bb, C3a and C5a. Marked fluctuations in circulating neutrophil counts and reductions in cardiac output were closely associated with peak production of anaphylatoxins C3a and C5a. Changing both dose and infusion duration revealed that complement activation is related to plasma levels of oligonucleotide, and that there is a minimum threshold concentration of approximately 50 micrograms/ml of ISIS 2302 that is required to activate complement. Dose regimens in which plasma concentrations do not exceed this threshold do not result in complement activation. Further investigation reveals that plasma concentrations of a key regulatory component of the alternative pathway, Factor H, were also decreased after administration of ISIS 2302. Decreases in Factor H levels are suggestive of a possible mechanism of complement activation. Direct interaction between ISIS 2302 and Factor H was demonstrated in a competition assay, where increasing concentrations of ISIS 2302 eluted Factor H from a heparin-sepharose column. These data demonstrate a clear correlation between plasma oligonucleotide concentrations and complement activation. Interactions between ISIS 2302 and Factor H may lead to activation of the alternative complement pathway.