Targeting the proteasome as a therapeutic strategy against haematological malignancies

Discovery of novel 20S proteasome subunit β5 PROTAC degraders as potential therapeutics for pharyngeal carcinoma and Bortezomib-resistant multiple myeloma

Resistance to proteasome inhibitors like Bortezomib is a major challenge in the treatment of multiple myeloma (MM). Proteolysis targeting chimeras (PROTACs), an emerging therapeutic approach that induces selective degradation of target proteins, offer a promising solution to overcome drug resistance. In this study, we designed and synthesized novel small-molecule PROTACs that induce 20S proteasome subunit β5 degradation as a strategy to overcome Bortezomib resistance. These 20S proteasome subunit β5 PROTACs demonstrated considerable binding affinity to 20S proteasome subunit β5 and cereblon (CRBN), effectively induced 20S proteasome subunit β5 degradation, and exhibited potent antiproliferative activity against a panel of cancer cell lines. Notably, PROTACs 12f and 14 displayed robust antitumor effects against both the pharyngeal carcinoma cell line FaDu and the Bortezomib-resistant MM cell line KM3/BTZ in vitro and in vivo with excellent safety profiles. Taken together, our findings highlight the potential of PROTACs 12f and 14 as novel 20S proteasome subunit β5-degrading agents for the treatment of pharyngeal carcinoma and overcoming Bortezomib resistance in MM.

SEL1L, an UPR response protein, a potential marker of colonic cell transformation

BACKGROUND

SEL1L gene product is implicated in the endoplasmic reticulum (ER)-associated protein degradation and Unfolded Protein Response pathways. This gene and associated miRNAs have been indicated as predictive and prognostic markers of pancreatic cancer.

AIM

Explore the role of SEL1L in colorectal cancer (CRC) progression.

METHODS

SEL1L expression was analysed immunohistochemically in 153 adenomas and 71 CRCs from African American and North Italian patients. The distribution of stained cells was determined by computing median and inter quartile range. The receiver operating characteristics plot was used as discriminate power of SEL1L expression, CRC diagnosis and the effects on patient survival.

RESULTS

SEL1L was low in normal mucosa and confined to few scattered cells at the base crypt of the villi and in the foveolar glandular compartment. The highest levels were in Paneth cells within the lysosomes. The enterocytic progenitor cells and mature enterocytes showed less cytoplasmic staining. In CRCs, SEL1L expression significantly correlated with the progression from adenoma to carcinoma (P = 0.0001) being stronger in well-to-moderately differentiated cancers. No correlation was found with other clinicopathological characteristics or ethnicity.

CONCLUSIONS

SEL1L expression is a potential CRC tissue biomarker since its expression is significantly higher in adenoma cells with respect to normal mucosa. The levels of expression decrease sensibly in undifferentiated CRC cancers. Interestingly, Paneth cells contain high levels of SEL1L protein that could indicate pre-neoplastic mucosa undergoing neoplastic transformation. Since SEL1L's major function lies within ER stress and active ERAD response, it may identify CRCs with differentiated secretory phenotype and acute cellular stress.

Scytonemides A and B, cyclic peptides with 20S proteasome inhibitory activity from the cultured cyanobacterium Scytonema hofmanii

Two cyclic peptides, scytonemides A (1) and B (2), were isolated from the cultured fresh water cyanobacterium Scytonema hofmannii (UTEX 1834) by bioassay-guided fractionation using a proteasome inhibition assay. The planar structures of the compounds were determined by a combination of MS and 1D and 2D NMR spectroscopy. The advanced Marfey's method was used to determine the absolute configuration of both peptides. Scytonemide A possesses an unusual imino linkage, while scytonemide B is a depsipeptide containing 3-hydroxyoctanoic acid in the macrocycle. Both isolates were evaluated for their inhibition of the 20S proteasome, and scytonemide A displayed an IC(50) value of 96 nM, while scytonemide B was inactive at 50 μM.

Synthesis, in vitro and in vivo biological evaluation, docking studies, and structure--activity relationship (SAR) discussion of dipeptidyl boronic acid proteasome inhibitors composed of beta-amino acids

A series of novel dipeptidyl boronic acid proteasome inhibitors composed of beta-amino acids were synthesized, in vitro and in vivo biologically evaluated, and theoretically modeled for the first time. From the screened racemic compounds in enzyme, 4i was the most active. The IC(50) value of its pure enantiomer 4q was 9.6 nM, 36-fold more active than its isomer 4p and as active as the marketed bortezomib in inhibiting human 20S proteasome. This candidate also showed good activities with IC(50) values nearly less than 5 microM against several human solid and hematologic tumor cell lines. Safety evaluation in vivo with zebrafish and Sprague-Dawley (SD) rats showed that the candidate 4q was less toxic than bortezomib. Pharmacokinetic profiles suggested candidate 4q showed a more plasma exposure and longer half-life than bortezomib. Docking results indicated that 4q nearly interacted with 20S proteasome in a similar way as bortezomib.

Design, synthesis, biological evaluation, and structure-activity relationship (SAR) discussion of dipeptidyl boronate proteasome inhibitors, part I: comprehensive understanding of the SAR of alpha-amino acid boronates

New series of dipeptidyl boronate inhibitors of 20S proteasome were designed and synthesized. The comprehensive understanding of the SAR was obtained by utilizing the variation of four substituents. From the screened compounds in enzyme, novel inhibitors 49 and 50 were identified to be highly potent druglike candidates with IC(50) values of 1.2 and 1.6 nM, respectively, which showed better activities than the drug bortezomib on the market. Two hematologic human tumor cell lines, HL-60 and U266, were significantly sensitive to both candidates and showed nearly the same potency as the standard bortezomib with IC(50) values less than 10 nM. But as for most of the eight human solid tumor cell lines, both candidates were more potent than the standard with the IC(50) value range of 9.8-70 nM. The activity evaluation of the stereoisomers showed that changing R-isomers to S-isomers greatly reduced the potency and even induced inactivity.

Advances in and applications of proteasome inhibitors

With the recent US Food and Drug Administration approval of bortezomib (Velcade) for the treatment of relapsed multiple myeloma, the proteasome has emerged as a new therapeutic target with diverse pathology. Drug discovery programs in academia and the pharmaceutical industry have developed a range of low nanomolar synthetic and natural inhibitors of the 20S proteasome core particle that have entered human clinical trials as significant anti-cancer and anti-inflammatory leads. Moreover, proteasome inhibitors continue to serve as valuable research tools in cellular biology through the elucidation of important biological processes associated with the ubiquitin-proteasome pathway of protein degradation. This review will highlight recent advances in the development and application of proteasome inhibitors.

Effects of proteasome inhibitor, MG132, on proteasome activity and oxidative status of rat liver

In vivo effects of N-benzyloxycarbonyl (Cbz)-Leu-Leu-leucinal (MG132) on chymotryptic-like (ChT-L), tryptic-like, and post-glutamyl peptide hydrolytic-like proteasome activities, protein oxidation, lipid peroxidation (LP), glutathione (GSH) level, as well as on the activity of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione-reductase) in the rat liver were studied. The possibility of MG132 provoking the formation of free oxygen radicals was also assayed in primary hepatocytes. The following results were obtained: (1) In vivo, MG132 did not change the spontaneous LP, but increased Fe-induced LP and the amount of oxidized proteins; it decreased the GSH level in liver. From the proteasome activities studied in liver cytosol only ChT-L activity was significantly decreased after MG132 administration. Furthermore, MG132 increased antioxidant enzyme activities of SOD, CAT, and GSH-Px. (2) In vitro, MG132 increased free radical oxygen species in hepatocytes; this effect disappeared in the presence of CAT or mannitol. In conclusion, since nowadays proteasome inhibitors are entering into the swing of laboratory and clinical practice, the present data could provide useful information for MG132 action. Consequently, future in vivo experiments with MG132 could highlight the possibility of its use at different pathological conditions.

Role of the ubiquitin system and tumor viruses in AIDS-related cancer

Tumor viruses are linked to approximately 20% of human malignancies worldwide. This review focuses on examples of human oncogenic viruses that manipulate the ubiquitin system in a subset of viral malignancies; those associated with AIDS. The viruses include Kaposi's sarcoma herpesvirus, Epstein-Barr virus and human papilloma virus, which are causally linked to Kaposi's sarcoma, certain B-cell lymphomas and cervical cancer, respectively. We discuss the molecular mechanisms by which these viruses subvert the ubiquitin system and potential viral targets for anti-cancer therapy from the perspective of this system.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

A phase I/II study of arsenic trioxide/bortezomib/ascorbic acid combination therapy for the treatment of relapsed or refractory multiple myeloma

PURPOSE

This multicenter, open-label, phase I/II dose escalation study assessed the safety/tolerability and initial efficacy of arsenic trioxide/bortezomib/ascorbic acid (ABC) combination therapy in patients with relapsed/refractory multiple myeloma.

EXPERIMENTAL DESIGN

Enrolled in six cohorts, patients were given arsenic trioxide (0.125 or 0.250 mg/kg), bortezomib (0.7, 1.0, or 1.3 mg/m(2)), and a fixed dose of ascorbic acid (1 g) i.v. on days 1, 4, 8, and 11 of a 21-day cycle for a maximum of eight cycles. The primary end point was safety/tolerability of the ABC regimen.

RESULTS

Twenty-two patients (median age, 63 years) were enrolled, having failed a median of 4 (range, 3-9) prior therapies. One occurrence of grade 4 thrombocytopenia was observed. One patient had asymptomatic arrhythmia and withdrew from the study. Objective responses were observed in 6 (27%) patients, including two partial responses and four minor responses. Median progression-free survival was 5 months (95% confidence interval, 2-9 months), and median overall survival had not been reached. The 12-month progression-free survival and overall survival rates were 34% and 74%, respectively. One (minor response) of six patients receiving the lowest dose of bortezomib (0.7 mg/m(2)) and 5 (2 partial responses and 3 minor responses) of 16 patients receiving the higher doses (1.0 or 1.3 mg/m(2)) responded.

CONCLUSIONS

The ABC regimen was well tolerated by most patients, and it produced preliminary signs of efficacy with an objective response rate of 27% in this heavily pretreated study population. These findings warrant further clinical evaluation of the ABC combination for treatment of relapsed/refractory multiple myeloma.

Hypoxia-inducible transcription factor–1 alpha determines sensitivity of endothelial cells to the proteosome inhibitor bortezomib

Angiogenesis is a complex, orchestrated process that plays a critical role in several conditions and has special relevance in the progression of cancer. Hypoxia is the major stimulus for angiogenesis, and hypoxia-inducible transcription factor–1 alpha (HIF-1α) is its key mediator. We set up a novel in vitro model of HIF-1α up-regulation by treating human umbilical vein endothelial cells (HUVECs) with the hypoxia-mimicking deferoxamine (DFO) and found that this condition was sufficient to promote angiogenesis, like the well-known HUVEC model cultured under low pO2. The proteasome inhibitor bortezomib, which induces strong apoptosis in cancer cells, abrogated proliferation and angiogenesis of HUVECs when used at a high concentration (100 nM), yet promoted both functions at a low dosage (10 nM). This double-edged effect appeared to be mediated by differential effects exerted by the different concentrations of bortezomib on 2 master regulators of tumor-associated angiogenesis, HIF-1α and nuclear factor kappa B (NF-kB). Significantly, when HUVECs were induced to express HIF-1α prior to bortezomib treatment, proliferative and angiogenic responses were abolished, and a greatly enhanced proapoptotic effect was promoted with both concentrations of the drug. These findings indicate that HIF-1α up-regulation may sensitize endothelial cells to the antiangiogenic and proapoptotic effects of bortezomib and might be exploited to target tumor-associated vessels in the course of antiangiogenic therapies.

Beyond single-agent bortezomib: combination regimens in relapsed multiple myeloma

PURPOSE OF REVIEW

Bortezomib-based combinations are being investigated in relapsed or refractory multiple myeloma with the aim of improving outcomes. This review presents recent data from clinical trials of these combinations and discusses their implications.

RECENT FINDINGS

Preclinical findings indicating additive or synergistic activity of bortezomib plus conventional and novel agents for multiple myeloma appear to be supported by clinical studies of bortezomib-based combinations. Bortezomib combined with a broad set of active agents results in enhanced response rates, including high complete response rates. Encouraging responses to bortezomib and its combinations are also seen in elderly patients, patients with adverse prognostic factors such as refractory disease and increased beta2-microglobulin, patients with cytogenetic abnormalities such as chromosome 13 deletion, advanced bone disease, extramedullary involvement, and patients with renal impairment, including patients with renal failure requiring dialysis. Toxicities are predictable and manageable and comparable to those seen with bortezomib monotherapy.

SUMMARY

Bortezomib-based combinations show promising activity in relapsed or refractory multiple myeloma, including reversal of chemoresistance to previously used agents. As high complete and overall response rates translate into longer survival, bortezomib-based combinations appear likely to have a significant impact on the multiple myeloma treatment algorithm and on the course of the disease itself.