Abstract
These studies investigated the toxicological effects of 1,2-bis (methylsulfonyl)-1-(2-chloroethyl)-2-(methylaminocarbonyl) hydrazine, VNP40101M, a novel alkylating antitumor agent, in animals. Speague-Dawley rats (2–10/sex/time point at each dose) and Beagle dogs (1–3/sex/time point at each dose) were treated with VNP40101M (0 [vehicle], 1, 3, 10, and 20 mg/kg in rats and 0, 0.3, 1, and 3 mg/kg in dogs), given intravenously (IV, bolus via the tail or slow push via the cephalic or saphenous vein, respectively) once daily for 5 consecutive days. Clinical signs, mortality, body weight, clinical pathology, gross necropsy, organ weights, and histopathology were evaluated for as long as 43 days in rats and 50 days in dogs. In rats, the toxic doses were found to be at 10 and 20 mg/kg, which induced mainly pulmonary toxicity and mortality. The pulmonary toxicity was reflected by an increase in lung weight; clear, pink or red fluid within the thoracic cavity observed at necropsy; and histopathological evidence of alveolar edema, vascular congestion, alveolar histiocytosis, and vascular thrombi. Although some of these effects were observed in rats treated with 3 mg/kg, the incidence was low (∼7%-30%) and may be reversible (based on the time-dependent reduction in the magnitude of lung weight increases). Therefore, the maximum tolerated dose (MTD, or the maximum dose that did not induce significant toxicity or induced reversible toxicity) was 3 mg/kg. VNP40101M at 1 mg/kg did not induce any toxicity, other than low incidence of alveolar edema (2/30 rats), and increased incidences of capillary ectasis/congestion and alveolar histocytosis (2–6/30 rats vs. 1/30–36 in control rats). Therefore, the low effect level (LOEL) is considered to be 1 mg/kg in rats when given IV for 5 days. In dogs, LOEL, MTD, and toxic dose levels were comparable (based on a body weight/surface area conversion) to those in rats, except for some gastrointestinal (GI) effects (i.e., red lesion in the ileum) observed at 0.3 mg/kg (equivalent to 1 mg/kg, or similar to the LOEL in rats) and the associated effects (slight body weight loss and inappetence). For dogs treated with 1 mg/kg (equivalent to ∼3 mg/kg, or MTD, in rats), VNP40101M induced the same GI effects seen in dogs treated with 0.3 mg/kg of VNP40101M. Additionally, a transient reduction in white blood cell counts was also observed. Three mg/kg (equivalent to ∼10 mg/kg, or toxic dose level, in rats) was toxic to dogs, as reflected by the poor clinical condition of these dogs, which subsequently required euthanasia. In conclusion, VNP40101M, when given IV once daily for 5 consecutive days, has a LOEL of 1 mg/kg, a MTD of 3 mg/kg, and toxic doses at 10 mg/kg in rats. The primary toxicity of VNP40101M was pulmonary toxicity and mortality. Based on an interspecies body weight/surface area conversion, VNP40101M had comparable LOEL (0.3 mg/kg), MTD (1 mg/kg), and toxic doses (3 mg/kg) in dogs, except that dogs appeared to be more sensitive to the GI effects of VNP40101M.