Intrathecal ACNU treatment of B16 melanoma leptomeningeal metastasis in a new athymic rat model

Summary To evaluate new cytotoxic drugs for intrathecal treatment we developed an experimental model of leptomeningeal metastasis by intracisternal injection of 10⁴B16-F10 melanoma cells in nude rats. One hour in vitro incubation with 20 g/ml ACNU (area under the drug concentration-time curve = 1200 gxmin/ml) induced a 4-log kill of B16 melanoma cells. A single or repeated non-toxic dose of 1 mg/kg was injected into the cisterna magna of rats inoculated with tumor (area under the drug concentration-time curve assuming an even cerebrospinal fluid distribution > 7000 gxmin/ml). Median survival free of symptoms was 16 days (range 14–27) for controls (n = 9) and 18 days (range 17–23) for rats treated with ACNU on day 4 (n = 9). Animals treated both on day 2 and 8 (n = 8) developed symptoms on day 21 (range 13–35). Neurological symptoms and neuropathological examination in animals with increased survival indicated local suppression of tumor growth in the cisterna magna but increased spinal seeding and mass growth. From these results and the available pharmacokinetic data on ACNU it is concluded that bolus injection of ACNU — although locally effective — is not a sufficient treatment of widespread leptomeningeal metastasis. An increased therapeutic efficacy might be achieved by ventriculolumbar perfusion.