Bortezomib proteasome inhibition

Richardson PG, Mitsiades C, Hideshima T et al (2006) Bortezomib proteasome inhibition as an effective anticancer therapy. Annu Rev Med 57 33-47... 

Bortezomib. Bortezomib (Velcade) inhibits pro-teasome activity in mammalian cells.11 Mammalian proteasome is responsible for degrading certain cellular proteins affecting cell function and division. By prolonging the activity of these proteins, bortezomib brings about complex changes in cell function that lead to cell dysfunction and death. Certain types of cancer, such as multiple myeloma, are more sensitive to impaired proteasome regulation, hence the use of this drug in these cancers. 

Figure 12.2 Pharmacodynamic profiles of NPI-0052 and bortezomib after a single IV administration in mice or rats. (A) Inhibition of CT-L, T-L and C-L 205 proteasome activities in packed whole blood (PWB) lysates after a single IV administration of NPI-0052 (0.15 mg/kg) or bortezomib (1 mg/kg) in mice. NPI-0052 exhibits a broader and longer 20>S proteasome inhibition profile than bortezomib.14 (B) CT-L 205 proteasome activity recovers more quickly in peripheral blood mononuclear cell (PBMQ lysates compared with PWB lysates after NPI-0052 administration to rats at 0.05 mg/kg or 0.1 mg/kg.

More importantly, proof-of-mechanism with proteasome inhibition levels in packed whole blood (inhibition of CT-L activity increasing with time and dose up to 100% Figure 12.4) reaching and exceeding those reported with therapeutic doses of bortezomib was attained at lower doses, suggesting potential for a significantly improved therapeutic ratio. Of particular interest, the profile of adverse events associated with NPI-0052 was quite different from those generally reported with bortezomib. 

The inhibition of multifunctional enzymes can also have therapeutic interest. The 26S proteasome is a mul-ticatalytic intracellular protease complex expressed in eukaryotic cells. This complex is responsible for selective degradation of intracellular proteins that are responsible for cell proliferation, growth, regulation of apoptosis and transcription of genes. Thus, proteasome inhibition is a potential treatment option for cancer and diseases due to aberrant inflammation conditions. Bortezomib and PS-519 are the first proteasome inhibitors that have entered clinical trials. In multiple myeloma, both the FDA (United States... 

Bortezomib (velcade) (1R)-3-methyl-l-[[(2S)-1 -oxo-3-phenyl-2-[pyrazinylcarbonyl)amino] propyl]butyl]boronic acid binds to the 20S core of the 26S proteasome and reversibly inhibits its chymotrypsin-like activity. Inhibition of the proteasome disrupts multiple signaling cascades within the cell, often leading to cell death. The most important consequences of proteasome inhibition are believed to result from downregulation of NF-kB, a key transcription factor that promotes cell survival. In a similar manner, bortezomib disrupts ubiquitin-proteasome regulation of p2I, p27, and p53, which are key regulatory proteins in the cell cycle and initiators of apoptosis. 

After intravenous administration of I—1.3 mg/rrf of bortezomib in patients without renal or hepatic impairment, there is a rapid distribution phase (<10 minutes), followed by a longer elimination phase of 5—15 hours. Plasma protein binding averaged 83%. The mean terminal elimination in preclinical studies was 5.4 hours, with an average clearance of 66 Uh. Peak pharmacodynamic activity (proteasome inhibition) occurred at I hour with a mean of 61% inhibition and a tyi of 24 hours. Inhibition of the 20S subunit was 10—30% at 96 hours. Proteasome inhibition is highly concentration dependent. 

Like bortezomib, MLN9708 is also a peptide boronate (Fig. 13.5) but it is orally active, shows greater tissue penetration, and has a shorter half-hfe. The drug is primarily an inhibitor of the chymotrypsin-like activity of the 20S proteasome core and, like bortezomib, it inhibits NF-kB activation and has antitumor activity in multiple myeloma and some other hematologic mahgnan-cies. Besides peptide boronates like bortezomib, other synthetic compounds tested as proteasome inhibitors include peptide aldehydes, peptide epoxyketones, and peptide vinyl sulfones. 

Bortezomib is the hrst therapeutic proteasome inhibitor. It inhibits the activity of the 26S-proteasoom protein complex which regulates protein expression and function and thus plays a role for cell homeostasis. It is used for the treatment of relapsed mulh-ple myeloma. Following intravenous administrahon bortezomib is mainly metabolised with an elimina-hon halflife of 5-15 h. It is frequently associated with somehmes irreversable neuropathy. Myelosuppression may be dose limiting. 

Our initial findings that NPI-0052 inhibited all three proteolytic functions of the IDS proteasome vide supra) led us to compare its profile with other proteasome inhibitors (Figure 12.1) such as bortezomib,14 carfilzomib (PR-171)31 and CEP-187 70.30 These agents inhibit the CT-L activity to a similar degree as NPI-0052 but exhibit different inhibition profiles for the T-L and C-L activities. In addition, NPI-0052 exhibits a different recovery profile of proteasome functions in whole blood, normal organs, tumour and peripheral blood mononuclear cell preparations compared with other agents.52... 

Our studies clearly differentiate NPI-0052 from other proteasome inhibitors in the speed and duration of action and the inhibition profile of the 20S proteasome. These differences and the possible off-target activities of bortezomib indicate that NPI-0052 may provide a greater therapeutic index and greater activity in diseases where bortezomib shows minimal activity.64... 

The pharmacodynamic profile of NPI-0052 is different from other proteasome inhibitors (bortezomib and carfilzomib) in that upon a single IV administration to mice, a sustained inhibition ( > 72 hours) of the main three 20.S proteolytic activities is observed in packed whole blood lysates (Figure 12.2A). Bortezomib has been reported to either have no effect on or to enhance the T-L activity, while carfilzomib specifically inhibits the CT-L 20V proteasome activity.14,31 Repeated NPI-0052 administration to rodents and monkeys leads to sustained dose-dependent inhibition of whole blood 20V proteasome activity, with higher inhibition observed after subsequent administrations and with partial recovery between consecutive NPI-0052 treatments. 

Besides their fundamental interest, proteasomes are relevant therapeutic targets. The peptide boronic acid, bortezomib (Velcade, Figure 12.2) is the first proteasome inhibitor to have reached the clinic and is used to treat late-stage multiple myeloma [4]. Originally developed as a p5-specific inhibitor, it was later on found to target also pi, pSi, and pii and, moreover, it became clear that exclusive inhibition of p5 is not sufficiently effective for tumor eradication. 

Fig. 13.5 Proteasome inhibitors used (or intended) for the treatment of relapsed multiple myeloma, mantle cell lymphoma, and some other tumors. Structures of the peptide boronates bortezomib and the orally active MLN9708, the peptide epoxyketone carfilzomib, and the y-lactam-p-lactone bicyclics sallnosporamide A (marizomib) and omuralide (P-clastolactacystin), both derived from natural sources. The drugs inhibit normal proteasome action by binding to the p-subunit proteolytic sites in the 20S core (see Fig. 13.4)...

Bortezomib, an A-protected dipeptide that contains a boron atom, inhibits proteasomes by binding via the boron atom to the catalytic site of the 26S proteasome with high affinity. This ultimately leads to the killing of multiple myeloma cells. 

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