Panobinostat

By inhibiting HDACs across the board, panobinostat leaves histones and many non-histone proteins in a hyper-acetylated state, which reopens silenced genes, throws cancer cells into cell-cycle arrest, and triggers apoptosis (programmed cell death) ^[1][2]. In multiple myeloma there is a second, elegant angle: myeloma cells churn out huge amounts of protein and depend on getting rid of the defective ones. Bortezomib blocks the proteasome, one disposal route; panobinostat interferes with the other, the aggresome/HDAC6-linked pathway that hauls protein junk away for recycling. Hitting both routes at once overwhelms the cell with toxic protein garbage, which is the rationale for the combination ^[1][3].

The pivotal PANORAMA 1 phase III trial showed that adding panobinostat to bortezomib and dexamethasone extended progression-free survival by roughly four months versus placebo, which was enough for approval in relapsed or relapsed-and-refractory disease ^[2][3][4]. But independent reviewers were blunt that this came at a steep price; the drug caused frequent severe diarrhea, low blood counts, infections, fatigue, heart-rhythm and other organ toxicities, drove hospital admissions and treatment discontinuations, and did not clearly lengthen overall survival, leading some to judge it "more toxic than useful" ^[5]. It is also part of a wider wave of HDACenzymes that switch genes off by tightening DNA packaging inhibitors being explored across cancers ^[6]. The manufacturer later withdrew the U.S. approval, so its practical footing today is limited.