Proteasome inhibition and its therapeutic potential in multiple myeloma

Figures & data

Figure 1A Structure of 26S proteasome: the 26S proteasome is formed when the 20S catalytic core is capped by 19S regulatory subunits at both ends in an ATP dependent fashion.

Figure 1B Cross section of the β ring of the 20S subunit of the proteasome: the post-glutamyl, tryptic, and chymotryptic sites are comprised of the threonine residues of the β1, β2, and β5 subunits respectively. Bortezomib inhibits the chymotryptic site.

Figure 2 Chemical structure of bortezomib.

Figure 3 Grade 3/4 adverse events of bortezomib and dexamethasone in the APEX trial.

Figure 4 Median levels of alkaline phosphatase levels of patients with multiple myeloma who responded to treatment with bortezomib and dexamethasone in the APEX trial. Reproduced with permission from Zangari M, Esseltine D, Lee CK, et al. Response to bortezomib is associated to osteoblastic activation in patients with multiple myeloma. Br J Haematol. 2005;131(1):71–73.¹⁴ Copyright © 2005 John Wiley and Sons.

Figure 5A Dexamethasone sensitive myeloma cells (MM.1S) cultured with 0.001 to 0.625 × 10⁻⁶ M. Dexamethasone in control media (□) and with bortezomib 0.0025 (▧) or 0.005 (■) × 10⁻⁶ M. Reproduced with permission from Hideshima T, Richardson P, Chauhan D, et al. The proteasome inhibitor PS-341 inhibits growth, induces apoptosis, and overcomes drug resistance in human multiple myeloma cells. Cancer Res. 2001;61(7): 3071–3076.⁶ Copyright © 2001 American Association for Cancer Research.

Figure 5B The addition of bortezomib to chemotherapeutic agents results in synergistic cytotoxicity in multiple myeloma cells: A) Melphalan-resistant cell line (RPMI8228/LR) treated for 24 hours with varying concentrations of melphalan alone or in combination with a noncytotoxic dose of bortezomib; B) Doxorubicin-resistant cell line (U266/dox4) treated for 24 hours with varying concentrations of doxorubicin alone or in combination with a noncytotoxic dose of bortezomib. C) Fresh myeloma cells treated with varying concentrations of melphalan alone or in combination with a noncytotoxic dose of bortezomib. Reproduced with permission from Ma MH, Yang HH, Parker K, et al. The proteasome inhibitor PS-341 markedly enhances sensitivity of multiple myeloma tumor cells to chemotherapeutic agents. Clin Cancer Res. 2003;9(3):1136–1144.¹⁸ Copyright © 2003 American Association for Cancer Research.

Table 1 Clinical trials of bortezomib in doublet-drug combination regimens

Study	Phase	Regimen	n	CR/nCR	ORR
Berenson et al^Citation20	I/II	Vel/Mel	46	15%	70%
Popat et al^Citation21	I/II	Vel/Mel ± Dex	53	23%	68%
Pineda-Roman et al^Citation22	I/II	VT ± Dex	85	22%	63%

Abbreviations: n, number of evaluable patients; Cr, complete remission; nCR, near complete remission; ORR, overall response rate; V el/Mel, velcade, melphalan; VT, velcade, thalidomide.

Table 2 Clinical trials of bortezomib in triplet-drug combination regimens

Study	Phase	Regimen	n/N	CR/nCR	ORR
Reece et al^Citation23	I/II	VCP	37/37	27%	68%
Kropff et al^Citation24	II	VCD	50/54	16% CR	82%
Hajek et al^Citation25	II		39/40	–	51%
Lee et al^Citation26	II	PAD→TD	30/39	70%	90%
Palumbo et al^Citation27		PAD	64/64	25%	67%
Richardson et al^Citation28	II	VRD	62/24	21%	84% (≥MR)
Poensich et al^Citation29	II	VBP	46/46	15%	61%

Abbreviations: n/N, number of evaluable patients/total number of enrolled patients; VCP, bortezomib, cyclophosphamide, prednisone; VCD, bortezomib, cyclophosphamide, dex; PAD, bortezomib, adriamycin, dex; TD, thalidomide, dex; VRD: bortezomib, lenalidomide, dex; VBP, bortezomib, bendamustine, prednisone.

Table 3 Clinical trials of bortezomib in multiple drug combination regimens

Study	Phase	Regimen	n	Cr/nCR	ORR
Palumbo et al^Citation30	I/II	VMPT	30/30	44%a	67%
Terpos et al^Citation31	II	VMDT	62a	–	66%
Ciolli et al^Citation32	II	VTDD	42/42	52%	74%
Kim et al^Citation33	II	VCTD	56/35	53% CR	92%

a number of evaluable patients unknown.

Abbreviations: n, number of evaluable patients; Cr, complete remission; nCR, near complete remission; ORR, overall response rate; V MPT, bortezomib, melphalan, prednisone, thalidomide; VMDT, bortezomib, melphalan, dex, thalidomide; VTDD, bortezomib, thalidomide, dex, liposomal doxorubicin; V CTD, bortezomib, cyclophosphamide, thalidomide, dex.

Figure 6 Chemotherapy schedule of bortezomib, melphalan, and prednisone (VMP) and melphalan and prednisone (MP) in the VISTA trial.

Abbreviations: VMP, velcade, melphalan, prednisone; MP, melphalan, prednisone.

Table 4 Summary of phase II trials in previously untreated MM

Trial	Regimen	N/N^†	CR/nCR	VGPR	PR	ORR
IFM 2005-01: Harousseau et al^Citation36	Vel/Dex (vs VAD)	424/482	19% (vs 8%)	24%	43%	83%
HOVON-655/GMMG-H4: Sonneveld et al^Citation37	PAD (vs VAD)	300/300	23% (vs 9%)	37%	–	83%
GIMEMA: Cavo et al^Citation35	VTD (vs TD)	460/474	55% (vs 32%)	30%	32%	94%
PETHEMA/GEM: Rosinol et al^Citation47	VTD vs (TD vs VBMCP/VBAD/Vel)	183/190	41% (vs 12% vs 28%)	–	39%	80%
VISTA: San Miguel et al^Citation34,Citation44	VMP (vs MP)	668/682	30% CR (vs 4%)	N/A	40%	71%
GEM05MAS65: Mateos et al^Citation45	VMPT (vs VTP)	206/260	41% (vs 37%)	–	40%	81%
GIMEMA: Palumbo et al^Citation46	VMPT (vs VMP)	354/393	39% CR (vs 21%)	16%	32%	87%

Abbreviations: V GPR, very good partial remission; V MP, bortezomib, melphalan, prednisone; MP, melphalan, predisone; V MPT, bortezomib, melphalan, prednisone, thalidomide; VTP, bortezomib, thalidomide, prednisone; V AD, vincristine, adriamycin, doxorubicin; PAD, bortezomib, doxorubicin, dexamethasone; V TD, velcade, thalidomide, dexamethasone; TD, thalidomide, dexamethasone; V BMCP, BCNU, vincristine, melphalan, prednisone; VBAD, vincristine, BCNU, doxorubicin, dexamethasone.

Table 5 Phase I/II and II combination trials in untreated myeloma

Trial	Regimen	n/N	CR/nCR	VGPR	PR	ORR
Harousseau et al^Citation51	Vel/Dex	48/52	21% CR	10%	35%	67%
Corso et al^Citation52		54/54	50%	20%	16%	86%
Rosinol et al^Citation53	Vel alternating with Dex	40/40	13% CR	10%	43%	65%
Jagannath et al^Citation54	Vel ± Dex	49/49	18%	20%	49%	88%
Orlowski et al^Citation55	Vel ± PLD	29/63	28%	–	52%	79%
Jakubowiak et al^Citation56	VDD	30/30	40% CR	23%	30%	93%
Palumbo et al^Citation57		102/102	13% CR	47%	36%	96%
Belch et al^Citation58		50/50	18%	–	60%	78%
Landau et al^Citation59	VDD→TD	31/31	29%	10%	42%	81%
Wang et al^Citation60	VTD	38/38	16%	–	71%	87%
Kaufman et al^Citation61		34/34	27% CR	32%	35%	94%
Yoon et al^Citation62	VAD→VTD	55/71	51%	10%	35%	96%
Richardson et al^Citation50	VRD	65/68	38%	30%	25%	100%
Berenson et al^Citation63	VAM	31/35	16% CR	10%	13%	39%
Bensinger et al^Citation64	VCD→VTD	43/44	35%	21%	40%	96%
Reeder et al^Citation65	VCD	33/33	39%	21%	27%	88%
Knop et al^Citation66		100/100	11% CR	–	68%	79
Barlogie et al^Citation67,Citation68	VTD-PACE	480–480	–	–	–	NR

Abbreviations: PLD, liposomal doxorubicin; VDD, Velcade, liposomal doxorubicin, dex; TD, thalidomide, dexamethasone; VTD, Velcade, thalidomide, dexamethasone; VAD, vincristine, adriamycin, doxorubicin; VR D, Velcade, revlimid dexamethasone; V AM, velcade, arsenic trioxide, melphalan; V CD, Velcade, cyclophosphamide, thalidomide; VDT-PACE, Velcade, dexamethasone, thalidomide, cisplatin, doxorubicin, cyclophosphamide, etoposide.

Figure 7 NF-κB activation pathway. The inhibitor protein I-κB, when bound to NF-κB in the cytoplasm, renders NF-κB inactive. A variety of cellular stimuli result in the phosphorylation and ubiquitination of I-κB, thereby targeting it for proteasome mediated degradation. Bortezomib, by inhibiting the proteasome, results in increased I-κB inhibition of NF-κB, thus resulting in inhibition of tumor growth. Reproduced with permission from Adams J. Potential for proteasome inhibition in the treatment of cancer. Drug Discov Today. 2003;8(7):307–315.³ Copyright © 2003 Elsevier.

Figure 8 Alteration in levels of Mcl-1 and NOXA results in apoptosis. Proteasome inhibiton increases levels of the proapoptoic factor NOXA, which then can override the concurrent increase in the anti-apoptic factor Mcl-1, thereby inducing the activation of caspases, and resulting in apoptosis.

Figure 9 The unfolded protein response. If misfolded proteins accumulate in endoplastic reticulum, the sensing mechanism IRE1α activates the transcription factor XBP-1 via IRE 1 kinase. XBP-1, in turn, activates the unfolded protein response (UPR) and results in apoptosis.

Figure 10 Kinetics of thrombocytopenia associated with bortezomib therapy. Reproduced with permission from Lonial S, Waller EK, Richardson PG, et al. Risk factors and kinetics of thrombocytopenia associated with bortezomib for relapsed, refractory multiple myeloma. Blood. 2005;106(12):3777–3784.⁸⁰ Copyright © 2005 American Society of Hematololgy.

Figure 11 Protein ubiquitination that earmarks proteins for proteasome degradation requires three classes of enzymes: E1 for activation of ubiquitin, E2 carrier protein for conjugation, and finally the E3 ligase that transfers ubiquitin to a lysine residue on the target protein. Reproduced with permission from Adams J. Potential for proteasome inhibition in the treatment of cancer. Drug Discov Today. 2003;8(7):307–315.³ Copyright © 2003 Elsevier.

Table 6 Recommended dose modification for bortezomib-related neuropathic pain and/or peripheral sensory neuropathy⁸⁷

Severity of peripheral neuropathy signs and symptoms	Modification of dose and regimen
Grade I (paresthesias and/or loss of reflexes)	No action
Grade I with pain or Grade 2 (interfering with function but not with activities of daily living)	Reduce bortezomib to 1.0 mg/m^2
Grade 2 with pain or Grade 3 (interfering with activities of daily living)	Withold bortezomib therapy until toxicity resolves. When toxcicity resolves reinitiate with a reduced dose of bortezomib at 0.7 mg/m^2 and change treatment schedule to once per week
Grade 4 (disabling)	Discontinue bortezomib

Grading based on NCI Common Toxicity Criteria CTCAE 3.0

Table 7 Classes of proteasome inhibitors

Class	Compounds
Peptide aldehydes	MG132
Peptide boronates	Bortezomib, CEP-18770
Peptide vinyl sulfones
Peptide epoxyketones	Epoxomicin, carfilzomib
β lactone inhibitors	Lactacystin, MLN 519, NPI-0052

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