BTZ is a proteasome inhibitor, used for treatment of various cancers like multiple myeloma and mantle cell lymphoma . Like DSA and VOR, upon Ra calculation, the hydrophilic pMeOx supposedly exhibits a higher compatibility for BTZ in comparison to hydrophobic blocks. Amongst those, , the estimated compatibility was in the order of pBuOx > pPentOx > pBuOzi ≈ pPrOzi (Figure ). Previously, Schulz et al. reported the A-pBuOx-A based formulations are capable to solubilize around 3.1 g/L BTZ . Here, we obtained similar results for the A-pBuOx-A triblock (i.e. 3.1 g/L soluble BTZ at 6 g/L feed). At 8 g/L BTZ feed, A-pBuOx-A gave BTZ solubility of around 3.9 g/L. However, the A-PentOx-A, its higher homologue, was found to be the best solubilizer, giving a BTZ solubility of 4.7 g/L (at 10 g/L feed) (LC ≈ 32 wt.% and LE ≈ 47%) (Figure ). The BTZ solubility in plain water was found to be relatively high with 0.75 g/L (Table ). A-pBuOzi-A showed a similar performance like A-pBuOx-A and gave a BTZ solubility of 3.8 g/L (at 10 g/L feed). Compared to other drugs, A-pPrOzi-A performed better in solubilizing BTZ, but the achieved solubility (≈ 2.7 g/L) was less than other polymers in the series. The suggested compatibility profile was not corroborated by formulation experiments, instead of A-pBuOx-A, the A-pPentOx-A was found to be best solubilizer and A-pPrOzi-A and A-pBuOzi-A showed differences in solubilizing BTZ, which became more apparent at higher BTZ feed.