Table 1.

Proteasome inhibitors that are approved or currently investigated in clinical trials.

Proteasome Inhibitor	Company	Phase	Structure Type	Targets	Mechanism	Administration Route	Covalent Bond
Bortezomib	Millennium	Approved by the FDA in 2003	Dipeptide boronic acid	β1, β5	Covalently bonds with the N-terminal threonine of the β subunit	Intravenous	Reversible
Carfilzomib	Kyprolis	Approved by the FDA in 2012	Epoxy-peptide	β5	Combines with threonine at the active site of the β5 subunit to form a stable morpholine ring [48]	Intravenous	Irreversible
Ixazomib	Takeda	Approved by the FDA in 2015	Dipeptide leucine	β5	Forms a covalent bond with the N-terminal threonine of the trypsin-like active site [49,50]	Intravenous /oral	Reversible
Oprozomib	Amgen	Phase I/II	Tripeptide epoxy ketone	β5	Combines with threonine at the active site of the β5 subunit to form a stable morpholine ring [51]	Oral	Irreversible
Delanzomib	Teva	Phase I/II	Threonine Boric Acid	β1, β5	Forms a covalent bond with the N-terminal threonine of the trypsin-like active site [52]	Intravenous	Reversible
Marizomib	Celgene	Phase III	β-lactone-γ-lactam	β1, β2, β5	Thr1O γ on the subunit is covalently bound to the carbonyl group derived from the β-lactone ring of the inhibitor [53]	Intravenous	Irreversible