Plasma and cerebrospinal fluid pharmacokinetics of gemcitabine after intravenous administration in nonhuman primates

PURPOSE

Gemcitabine (dFdC) is a difluorine-substituted deoxycytidine analogue that has demonstrated antitumor activity against both leukemias and solid tumors. Pharmacokinetic studies of gemcitabine have been performed in both adults and children but to date there have been no detailed studies of its penetration into cerebrospinal fluid (CSF). The current study was performed in nonhuman primates to determine the plasma and CSF pharmacokinetics of gemcitabine and its inactive metabolite, difluorodeoxyuridine (dFdU) following i.v. administration.

METHODS

Gemcitabine, 200 mg/kg, was administered i.v. over 45 min to four nonhuman primates. Serial plasma and CSF samples were obtained prior to, during, and after completion of the infusion for determination of gemcitabine and dFdU concentrations. Gemcitabine and dFdU concentrations were measured using high-performance liquid chromatography (HPLC) and modeled with model-dependent and model-independent methods.

RESULTS

Plasma elimination was rapid with a mean t1/2 of 8 +/- 4 min (mean +/- SD) for gemcitabine and 83 +/- 8 min for dFdU. Gemcitabine total body clearance (ClTB) was 177 +/- 40 ml/min per kg and the Vdss was 5.5 +/- 1.0 l/kg. The maximum concentrations (Cmax) and areas under the time concentration curves (AUC) for gemcitabine and dFdU in plasma were 194 +/- 64 microM and 63.8 +/- 14.6 microM.h, and 783 +/- 99 microM and 1725 +/- 186 microM.h, respectively. The peak CSF concentrations of gemcitabine and dFdU were 2.5 +/- 1.4 microM and 32 +/- 41 microM, respectively. The mean CSF:plasma ratio was 6.7% for gemcitabine and 23.8% for dFdU.

CONCLUSIONS

There is only modest penetration of gemcitabine into the CSF after i.v. administration. The relatively low CSF exposure to gemcitabine after i.v. administration suggests that systemic administration of this agent is not optimal for the treatment of overt leptomeningeal disease. However, the clinical spectrum of antitumor activity and lack of neurotoxicity after systemic administration of gemcitabine make this agent an excellent candidate for further studies to assess the safety and feasibility of intrathecal administration.

Intrathecal chemotherapy

An unforeseen consequence of improved disease-free survival in many hematologic and solid tumor malignancies has been an increase in the incidence of disease recurrence in the leptomeninges. The recognition of the central nervous system (CNS) as a unique 'sanctuary' site has resulted in the development of therapeutic strategies specifically directed at the leptomeninges. Although therapeutic strategies have been successful in the prevention and treatment of CNS leukemia, there are still a paucity of therapeutic options for patients with neoplastic meningitis due to solid tumors or recurrent CNS leukemia. This article provides an overview of the pharmacology and toxicity of intrathecal agents that are commonly employed in the treatment and prevention of leptomeningeal disease, and describes new agents that are in the early stages of clinical development.

Gastrointestinal autonomic nerve tumors in the pediatric population: a report of four cases and a review of the literature

BACKGROUND

Gastrointestinal autonomic nerve tumors (GANTs) are a subpopulation of gastrointestinal stromal tumors (GISTs) that are characterized by ultrastructural features resembling enteric autonomic nerve cells, without epithelial, Schwannian, or smooth muscle differentiation. Delineation of the clinicopathologic features of GANT in the pediatric population is lacking.

METHODS

The clinicopathologic and outcome data for four pediatric patients with GANT are presented. The data from these patients and four previously reported pediatric patients are summarized and compared with data for GANT in adults.

RESULTS

All four cases occurred in females at a mean age of 12.5 years. The primary tumor site was the stomach in all cases, and the mean tumor size was 6.3 cm. Immunocytochemical and ultrastructural examination were essential in distinguishing GANT from GIST in all cases by identifying features of neural origin (neuron specific enolase in all four cases, NFP in three cases, S-100 in two cases, dense core neurosecretory granules in all four cases, and neuritelike processes in all four cases), while failing to identify features of myogenic origin (no desmin, smooth muscle actin, myofilaments, or dense bodies were found in any of the cases). Primary treatment was surgical, with chemotherapy administered to 1 patient at the time of recurrence. All patients are alive after a mean follow-up of 60 months (range, 8 months to 9 years).

CONCLUSIONS

Similarities of pediatric GANT to GANT in adults include the need for a high index of suspicion for diagnosis; comparable histopathologic, immunohistochemical, and ultrastructural features; and surgery as the primary therapy. Distinguishing features in children may be a prevalence among females in the second decade, a predominance of smaller gastric tumors, and a positive prognostic value of younger age.

Gastrointestinal autonomic nerve tumors in the pediatric population: a report of four cases and a review of the literature

BACKGROUND

Gastrointestinal autonomic nerve tumors (GANTs) are a subpopulation of gastrointestinal stromal tumors (GISTs) that are characterized by ultrastructural features resembling enteric autonomic nerve cells, without epithelial, Schwannian, or smooth muscle differentiation. Delineation of the clinicopathologic features of GANT in the pediatric population is lacking.

METHODS

The clinicopathologic and outcome data for four pediatric patients with GANT are presented. The data from these patients and four previously reported pediatric patients are summarized and compared with data for GANT in adults.

RESULTS

All four cases occurred in females at a mean age of 12.5 years. The primary tumor site was the stomach in all cases, and the mean tumor size was 6.3 cm. Immunocytochemical and ultrastructural examination were essential in distinguishing GANT from GIST in all cases by identifying features of neural origin (neuron specific enolase in all four cases, NFP in three cases, S-100 in two cases, dense core neurosecretory granules in all four cases, and neuritelike processes in all four cases), while failing to identify features of myogenic origin (no desmin, smooth muscle actin, myofilaments, or dense bodies were found in any of the cases). Primary treatment was surgical, with chemotherapy administered to 1 patient at the time of recurrence. All patients are alive after a mean follow-up of 60 months (range, 8 months to 9 years).

CONCLUSIONS

Similarities of pediatric GANT to GANT in adults include the need for a high index of suspicion for diagnosis; comparable histopathologic, immunohistochemical, and ultrastructural features; and surgery as the primary therapy. Distinguishing features in children may be a prevalence among females in the second decade, a predominance of smaller gastric tumors, and a positive prognostic value of younger age.