Effect of the proteasome inhibitor ALLnL on cisplatin sensitivity in human ovarian tumor cells

PID1 increases chemotherapy-induced apoptosis in medulloblastoma and glioblastoma cells in a manner that involves NFκB

Phosphotyrosine Interaction Domain containing 1 (PID1; NYGGF4) inhibits growth of medulloblastoma, glioblastoma and atypical teratoid rhabdoid tumor cell lines. PID1 tumor mRNA levels are highly correlated with longer survival in medulloblastoma and glioma patients, suggesting their tumors may have been more sensitive to therapy. We hypothesized that PID1 sensitizes brain tumors to therapy. We found that PID1 increased the apoptosis induced by cisplatin and etoposide in medulloblastoma and glioblastoma cell lines. PID1 siRNA diminished cisplatin-induced apoptosis, suggesting that PID1 is required for cisplatin-induced apoptosis. Etoposide and cisplatin increased NFκB promoter reporter activity and etoposide induced nuclear translocation of NFκB. Etoposide also increased PID1 promoter reporter activity, PID1 mRNA, and PID1 protein, which were diminished by NFκB inhibitors JSH-23 and Bay117082. However, while cisplatin increased PID1 mRNA, it decreased PID1 protein. This decrease in PID1 protein was mitigated by the proteasome inhibitor, bortezomib, suggesting that cisplatin induced proteasome dependent degradation of PID1. These data demonstrate for the first time that etoposide- and cisplatin-induced apoptosis in medulloblastoma and glioblastoma cell lines is mediated in part by PID1, involves NFκB, and may be regulated by proteasomal degradation. This suggests that PID1 may contribute to responsiveness to chemotherapy.

BRCA1 as a Therapeutic Target in Sporadic Epithelial Ovarian Cancer

In sporadic epithelial ovarian cancer (EOC), the inactivation of BRCA1 through various mechanisms is a relatively common event. BRCA1 protein dysfunction results in the breakdown of various critical pathways in the cell, notably, the DNA damage response and repair pathway. Tumors from patients with BRCA1 germline mutations have an increased sensitivity to DNA damaging chemotherapeutic agents, such as cisplatin, due to defective DNA repair. Thus, inhibiting BRCA1 in sporadic EOC using novel targeted therapies is an attractive strategy for the treatment of advanced or recurrent EOC. Several classes of small molecule inhibitors that affect BRCA1 have now been tested in preclinical and clinical studies suggesting that this is a rational therapeutic approach. The aim of this paper is to provide an understanding of how BRCA1 has evolved into a promising target for the treatment of sporadic disease and to outline the main potential small molecule inhibitors of BRCA1 in EOC.

Enhanced delivery of cisplatin to intraperitoneal ovarian carcinomas mediated by the effects of bortezomib on the human copper transporter 1

PURPOSE

The copper transporter 1 (CTR1) is a major influx transporter for platinum drugs. However, the accumulation of cisplatin in human ovarian carcinoma cells is limited by the fact that cisplatin triggers the down-regulation and proteasomal degradation of CTR1, thereby limiting its own uptake. We sought to determine whether proteasome inhibition using bortezomib would prevent human CTR1 (hCTR1) degradation and increase platinum accumulation in ovarian cancer cells.

EXPERIMENTAL DESIGN

The effects of bortezomib on human hCTR1 expression and cisplatin accumulation were measured by Western blot, flow cytometric, and confocal digital imaging analyses. Platinum accumulation was measured by inductively coupled plasma mass spectrometry and bortezomib concentrations by liquid chromatography/mass spectrometry.

RESULTS

Bortezomib blocked the cisplatin-induced down-regulation of hCTR1 in a concentration-dependent manner and increased cisplatin uptake 1.6- to 2.4-fold. Median effect analysis showed a combination index of 0.37 at 50% cell kill, indicating a high level of synergy. The effect of bortezomib was muted in cells lacking both alleles of CTR1, showing that bortezomib was working primarily through its effect on blocking hCTR1 degradation. I.p. administration of bortezomib produced a peritoneal/plasma area under the curve ratio of 252 in a murine model. I.p. administration of bortezomib before i.p. cisplatin increased platinum accumulation in peritoneal tumors by 33% (P = 0.006).

CONCLUSIONS

Proteasomal inhibition prevented cisplatin-induced down-regulation of hCTR1 in ovarian cancer cells and enhanced drug uptake and cell killing in a synergistic manner. Bortezomib shows a large pharmacologic advantage when administered i.p. There is a strong rationale for the combined i.p. administration of bortezomib and cisplatin.

Perturbation of DNA repair pathways by proteasome inhibitors corresponds to enhanced chemosensitivity of cells to DNA damage-inducing agents

Purpose

Breast cancer treatment often employs DNA double-strand breaks (DSBs), such as that induced by irradiation or anticancer agents. Ubiquitination is required at the site of DNA damage and plays a crucial role in the DSB repair pathway. We investigated the effect of proteasome inhibitors on the pathway after exposure to chemotherapeutic agents and examined its correlation with cytotoxicity.

Methods

Cells were exposed for 1 h to DNA damage-inducing chemotherapeutic agents. After DNA damage, nuclear foci formation of conjugated ubiquitin (Ub-foci) and cell viability were examined in the absence or presence of proteasome inhibitors MG132 and epoxomicin.

Results

Proteasome inhibitors trapped conjugated ubiquitin in the cytosol and blocked irinotecan (CPT-11)- and epirubicin-induced Ub-foci formation in MCF10A cells and HeLa cells, but not in MCF7 cells. MG132 sensitized MCF10A cells to CPT-11 and epirubicin treatment, demonstrating a synergistic effect. This synergistic effect is likely due to the failure to repair DNA, because a significant rise in unrepaired DNA damage was observed in the cells treated with MG132. On the other hand, no synergy was observed in MCF7 cells or when MG132 was combined with docetaxel.

Conclusions

The synergistic effect of proteasome inhibitors in combination with DNA damage-inducing agents warrants further investigating into its effectiveness in the treatment of breast cancer.

Incorporating bortezomib into the treatment of lung cancer

Bortezomib, a small-molecule proteasome inhibitor, has activity in lung cancer both as a single agent and in combination with agents commonly used in lung cancer. The ability of bortezomib to favorably modulate the expression of apoptosis-associated proteins, along with its moderate toxicity as a single agent, provides the basis for its combination with cytotoxic agents in the treatment of lung cancer. In non-small cell lung cancer, bortezomib as a single agent has limited activity but in combination with chemotherapy has shown encouraging activity without significantly adding to toxicity. Bortezomib as a single agent has shown minimal activity in small cell lung cancer. Although the role of bortezomib in lung cancer is uncertain, it is likely to have its greatest clinical benefit when given in combination with other therapeutics. Ongoing studies are focused on optimizing the scheduling of bortezomib with chemotherapy, investigating its combination with targeted agents and radiation, and examining its efficacy in a specific subgroup, bronchioloalveolar carcinoma.

Proteasome function is required for DNA damage response and fanconi anemia pathway activation

Proteasome inhibitors sensitize tumor cells to DNA-damaging agents, including ionizing radiation (IR), and DNA cross-linking agents (melphalan and cisplatin) through unknown mechanisms. The Fanconi anemia pathway is a DNA damage-activated signaling pathway, which regulates cellular resistance to DNA cross-linking agents. Monoubiquitination and nuclear foci formation of FANCD2 are critical steps of the Fanconi anemia pathway. Here, we show that proteasome function is required for the activation of the Fanconi anemia pathway and for DNA damage signaling. Proteasome inhibitors (bortezomib and MG132) and depletion of 19S and 20S proteasome subunits (PSMD4, PSMD14, and PSMB3) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, whereas depletion of DSS1/SHFM1, a subunit of the 19S proteasome that also directly binds to BRCA2, did not inhibit FANCD2 monoubiquitination or foci formation. On the other hand, DNA damage-signaling processes, such as IR-induced foci formation of phosphorylated ATM (phospho-ATM), 53BP1, NBS1, BRCA1, FANCD2, and RAD51, were delayed in the presence of proteasome inhibitors, whereas ATM autophosphorylation and nuclear foci formation of gammaH2AX, MDC1, and RPA were not inhibited. Furthermore, persistence of DNA damage and abrogation of the IR-induced G(1)-S checkpoint resulted from proteasome inhibition. In summary, we showed that the proteasome function is required for monoubiquitination of FANCD2, foci formation of 53BP1, phospho-ATM, NBS1, BRCA1, FANCD2, and RAD51. The dependence of specific DNA damage-signaling steps on the proteasome may explain the sensitization of tumor cells to DNA-damaging chemotherapeutic agents by proteasome inhibitors.

Bortezomib sensitizes pancreatic cancer cells to endoplasmic reticulum stress-mediated apoptosis

Bortezomib (PS-341, Velcade) is a potent and selective inhibitor of the proteasome that is currently under investigation for the treatment of solid malignancies. We have shown previously that bortezomib has activity in pancreatic cancer models and that the drug induces endoplasmic reticulum (ER) stress but also suppresses the unfolded protein response (UPR). Because the UPR is an important cytoprotective mechanism, we hypothesized that bortezomib would sensitize pancreatic cancer cells to ER stress-mediated apoptosis. Here, we show that bortezomib promotes apoptosis triggered by classic ER stress inducers (tunicamycin and thapsigargin) via a c-Jun NH(2)-terminal kinase (JNK)-dependent mechanism. We also show that cisplatin stimulates ER stress and interacts with bortezomib to increase ER dilation, intracellular Ca(2+) levels, and cell death. Importantly, combined therapy with bortezomib plus cisplatin induced JNK activation and apoptosis in orthotopic pancreatic tumors resulting in a reduction in tumor burden. Taken together, our data establish that bortezomib sensitizes pancreatic cancer cells to ER stress-induced apoptosis and show that bortezomib strongly enhances the anticancer activity of cisplatin.