Consensus diagnoses and mode of action for the formation of gastric tumors in rats treated with the chloroacetanilide herbicides alachlor and butachlor.

A panel of pathologists (Panel) was formed to evaluate the pathogenesis and human relevance of tumors that developed in the fundic region of rat stomachs in carcinogenicity and mechanistic studies with alachlor and butachlor. The Panel evaluated stomach sections stained with hematoxylin and eosin, neuron-specific enolase, and chromogranin A to determine the presence and relative proportion of enterochromaffin-like (ECL) cells in the tumors and concluded all tumors were derived from ECL cells. Biochemical and pathological data demonstrated the tumor formation involved a nongenotoxic threshold mode of action (MOA) initially characterized by profound atrophy of the glandular fundic mucosa that affected gastric glands, but not surface epithelium. This resulted in a substantial loss of parietal cells and a compensatory mucosal cell proliferation. The loss of parietal cells caused a marked increase in gastric pH (hypochlorhydria), leading to sustained and profound hypergastrinemia. The mucosal atrophy, together with the increased gastrin, stimulated cell growth in one or more ECL cell populations, resulting in neoplasia. ECL cell autocrine and paracrine effects led to dedifferentiation of ECL cell tumors. The Panel concluded the tumors develop via a threshold-dependent nongenotoxic MOA, under conditions not relevant to humans.

Local and systemic toxicity of intraoral submucosal injections of phentolamine mesylate (OraVerse).

OraVerse, an injectable formulation of phentolamine mesylate (PM), was recently approved by the U.S. Food and Drug Administration (FDA) for reversal of anesthesia of the lip and tongue and associated functional deficits resulting from an intraoral submucosal injection of a local anesthetic containing a vasoconstrictor. Because PM had not been approved previously for submucosal administration, 2 Good Laboratory Practices (GLP) studies in dogs designed to investigate systemic toxicity and the local effects of single and repeated dosing of OraVerse on the inferior alveolar nerve and branches of the superior alveolar nerve and adjacent soft tissues after local administration were conducted. Systemic toxicity was measured by preinjection and postinjection clinical examinations, clinical chemistry, and gross and microscopic examinations of major organs after necropsy. No evidence of systemic toxicity was detected. Local nerve and adjacent tissue damage was assessed by conventional histopathology. Nerve degeneration was evident in 1 animal. Mild perineural inflammation adjacent to the inferior alveolar nerve and inflammatory exudates were observed in submucosal tissues in several animals. No changes were observed in the nerves at injection sites of dogs from any dose group that were considered directly related to the test articles. These data reveal that single and repeated intraoral administrations of OraVerse are well tolerated in beagle dogs.

Concentrations of dapivirine in the rhesus macaque and rabbit following once daily intravaginal administration of a gel formulation of [14C]dapivirine for 7 days.

Dapivirine is a nonnucleoside reverse transcriptase inhibitor being developed as a topical microbicide for the prevention of human immunodeficiency virus infection. The distribution of radioactivity and drug in plasma and in vaginal, cervical, and draining lymph node tissues was investigated after daily application of a vaginal gel formulation of [14C]dapivirine to rhesus macaques. This was preceded by a preliminary study with rabbits. Following the intravaginal administration of [14C]dapivirine ( approximately 0.1 mg/ml [15 microCi/ml]) to rabbits (0.5 ml/day) and macaques (1 ml/day) for 7 days, the dapivirine levels associated with vaginal and cervical tissue samples 1 h after the final dose were high (quantities of microg/g of tissue) and remained detectable at 24 h (mean, >or=2.5 ng/g in rabbits) and 48 h (mean, >80 ng/g in macaques). Radioactivity levels were low in the plasma and very low or unquantifiable in the draining lymph nodes of the macaques. Microautoradiography identified drug-related material (DRM) on the surfaces of the vaginal and cervical tissues of the rabbits and macaques. Although DRM was primarily associated with the outermost layer of shedding cells in rabbits, two animals showed some evidence of small quantities in the mucosal epithelium of the cervix. In macaques, DRM was seen within the keratinized layer of the vaginal epithelium and and was found to extend into the superficial cellular layers, and in at least one animal it appeared to be present in the deepest (germinal) layer of the epithelium and in submucosal tissues. The persistence of biologically significant concentrations of dapivirine in vaginal and cervical tissues for >24 h supports the development of dapivirine as a microbicide for once daily application.