oprozomib and Carcinoma--Squamous-Cell

Acquired resistance to proteasome inhibitors represents a considerable impediment to their effective clinical application. Carfilzomib and its orally bioavailable structural analog oprozomib are second-generation, highly-selective, proteasome inhibitors. However, the mechanisms of acquired resistance to carfilzomib and oprozomib are incompletely understood, and effective strategies for overcoming this resistance are needed. Here, we developed models of acquired resistance to carfilzomib in two head and neck squamous cell carcinoma cell lines, UMSCC-1 and Cal33, through gradual exposure to increasing drug concentrations. The resistant lines R-UMSCC-1 and R-Cal33 demonstrated 205- and 64-fold resistance, respectively, relative to the parental lines. Similarly, a high level of cross-resistance to oprozomib, as well as paclitaxel, was observed, whereas only moderate resistance to bortezomib (8- to 29-fold), and low level resistance to cisplatin (1.5- to 5-fold) was seen. Synergistic induction of apoptosis signaling and cell death, and inhibition of colony formation followed co-treatment of acquired resistance models with carfilzomib and the histone deacetylase inhibitor (HDACi) vorinostat. Synergism was also seen with other combinations, including oprozomib plus vorinostat, or carfilzomib plus the HDACi entinostat. Synergism was accompanied by upregulation of proapoptotic Bik, and suppression of Bik attenuated the synergy. The acquired resistance models also exhibited elevated levels of MDR-1/P-gp. Inhibition of MDR-1/P-gp with reversin 121 partially overcame carfilzomib resistance in R-UMSCC-1 and R-Cal33 cells. Collectively, these studies indicate that combining carfilzomib or oprozomib with HDAC or MDR-1/P-gp inhibitors may be a useful strategy for overcoming acquired resistance to these proteasome inhibitors.

Topics: Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Boronic Acids; Bortezomib; Carcinoma, Squamous Cell; Cell Line, Tumor; Cisplatin; Drug Resistance, Neoplasm; Drug Synergism; Head and Neck Neoplasms; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Membrane Proteins; Mitochondrial Proteins; Oligopeptides; Proteasome Inhibitors; Pyrazines; Vorinostat

The proteasome inhibitor bortezomib has shown remarkable clinical success in the treatment of multiple myeloma. However, the efficacy and mechanism of action of bortezomib in solid tumor malignancies is less well understood. In addition, the use of this first-in-class proteasome inhibitor is limited by several factors, including off-target effects that lead to adverse toxicities. We recently reported the impact and mechanisms of carfilzomib and oprozomib, second-in-class proteasome inhibitors with higher specificities and reduced toxicities, against head and neck squamous cell carcinoma (HNSCC). Carfilzomib and oprozomib potently inhibit HNSCC cell survival and the growth of HNSCC tumors. Both compounds promote upregulation of proapoptotic BIK and antiapoptotic MCL1, which serves to mediate and attenuate, respectively, the killing activities of these proteasome inhibitors. Both compounds also induce complete autophagic flux that is partially dependent on activation of the unfolded protein response (UPR) and upregulation of ATF4. Carfilzomib- and oprozomib-induced autophagy acts to promote HNSCC cell survival. Our study indicates that the therapeutic benefit of these promising proteasome inhibitors may be improved by inhibiting MCL1 expression or autophagy.

Topics: Activating Transcription Factor 4; Autophagy; Boronic Acids; Bortezomib; Carcinoma, Squamous Cell; Cell Line, Tumor; Cell Survival; Head and Neck Neoplasms; Humans; Models, Biological; Oligopeptides; Proteasome Inhibitors; Pyrazines; Squamous Cell Carcinoma of Head and Neck; Unfolded Protein Response