ALDH7A1 and glioblastoma: The relatively low antiproliferative potency of some PDE inhibitors was unlikely to be caused by the lack of expression of the corresponding PDE targets in glioblastoma cells, as our RT-PCR experiments revealed detectable transcription of the majority of PDEs in all three of the glioblastoma lines tested, except for some PDE6 isoforms (Figure 2).