Infantile neuronal ceroid lipofuscinosis (INCL) is a childhood neurodegenerative disease caused by the selective death of cortical and retinal neurons as the result of an inherited palmitoyl-protein thioesterase 1 (PPT1) deficiency. Neuronal death is common to many lysosomal storage diseases but it occurs very early in INCL and we show here that inhibition of PPT1 increases the susceptibility of these cells to apoptotic cell death. Thus transient transfection of LA-N-5 neuroblastoma cells with a reverse-oriented (antisense) PPT1 (AS-PPT1) reduced PPT1 enzyme activity (as measured by an in vitro assay) and increased the susceptibility to apoptosis induced by C2 ceramide. Similarly, inhibition of PPT1 with a synthetic inhibitor (AcG-palmitoyl diaminoproprionate-VKIKK) (DAP1) (100 microM) increased the susceptibility of the cells to apoptosis induced by either C2-ceramide or etoposide and Adriamycin (doxorubicin), common chemotherapeutic agents used in the treatment of solid tumours. In contrast, overexpression of PPT1 led to increased resistance to cell death induced by these drugs.