This compound 66 not only proved to inhibit both proteasome (IC50 of 1.1 nM) and HDAC (IC50 of 255 nM), but also showed antiproliferative activity against different multiple myeloma cell lines (RPMI-8226, IC50 of 6.66 nM; U266, IC50 of 4.31 nM; KM3, IC50 of 10.1 nM) including a cell line associated with multiple myeloma drug resistance to bortezomib (KM3/BTZ, IC50(66) of 8.98 nM; IC50(bortezomib) of 226 nM) [57]. This evidence concerns the gene HDAC9 and plasma cell myeloma.