CASC3 and neoplasm: Tumours treated with BTZ, as monotherapy or in combination with NK cells, displayed significantly reduced 1 and 5 subunit activity compared to vehicle control (P < 0.0001, both) or NK monotherapy (P < 0.01 for BTZ and P < 0.001 for combination, Figure 6A), indicating that the drug sufficiently crossed the blood–brain barrier to inhibit the catalytic subunits of the 20S proteasome.