James C. Cusack

Control of inducible chemoresistance: Enhanced anti-tumor therapy throughincreased apoptosis by inhibition of NF-κB

Programmed cell death (apoptosis) seems to be the principal mechanism whereby anti-oncogenic therapies such as chemotherapy and radiation effect their responses. Resistance to apoptosis, therefore, is probably a principal mechanism whereby tumors are able to overcome these cancer therapies. The transcription factor NF-κB is activated by chemotherapy and by irradiation in some cancer cell lines. Furthermore, inhibition of NF-κB in vitro leads to enhanced apoptosis in response to a variety of different stimuli. We show here that inhibition of NF-κB through the adenoviral delivery of a modified form of IκBα, the inhibitor of NF-κB, sensitizes chemoresistant tumors to the apoptotic potential of TNFκ and of the chemotherapeutic compound CPT-11, resulting in tumor regression. These results demonstrate that the activation of NF-κB in response to chemotherapy is a principal mechanism of inducible tumor chemoresistance, and establish the inhibition of NF-κB as a new approach to adjuvant therapy in cancer treatment.

Wild-Type Human p53 and a Temperature-Sensitive Mutant Induce Fas/APO-1 Expression

Fas/APO-1 is a cell surface protein known to trigger apoptosis upon specific antibody engagement. Because wild-type p53 can activate transcription as well as induce apoptosis, we queried whether p53 might upregulate Fas/APO-1. To explore this possibility, we examined human p53-null (H358 non-small-cell lung adenocarcinoma and K562 erythroleukemia) and wild-type p53-containing (H460 non-small-cell lung adenocarcinoma) cell lines. When H358 or H460 cells were transduced with a replication-deficient adenovirus expression construct containing the human wild-type p53 gene but not with vector alone, a marked upregulation (approximately a three-to fourfold increase) of cell surface Fas/APO-1 was observed by flow cytometry. Similarly, K562, cells stably transfected with a plasmid vector containing the temperature-sensitive human p53 mutant Ala-143 demonstrated a four- to sixfold upregulation of Fas/APO-1 by flow-cytometric analysis at the permissive temperature of 32.5 degrees C. Temperature-sensitive upregulation of Fas/APO-1 in K562 Ala-143 cells was verified by immunoprecipitation and demonstrated to result from enhanced mRNA production by nuclear run-on and Northern (RNA) analyses. Stably transfected K562 cells expressing temperature-insensitive, transcriptionally inactive p53 mutants (His-175, Trp-248, His-273, or Gly-281) failed to upregulate Fas/APO-1 at either 32.5 degrees or 37.5 degrees C. The temperature-sensitive transcription of Fas/APO-1 occurred in the presence of cycloheximide, indicating that de novo protein synthesis was not required and suggested a direct involvement of p53. Collectively, these observations argue that Fas/APO-1 is a target gene for transcriptional activation by p53.

Enhancement of radiosensitivity by proteasome inhibition: Implications for a role of NF-κB

PURPOSE NF-kappaB is activated by tumor necrosis factor, certain chemotherapeutic agents, and ionizing radiation, leading to inhibition of apoptosis. NF-kappaB activation is regulated by phosphorylation of IkappaB inhibitor molecules that are subsequently targeted for degradation by the ubiquitin-proteasome pathway. PS-341 is a specific and selective inhibitor of the proteasome that inhibits NF-kappaB activation and enhances cytotoxic effects of chemotherapy in vitro and in vivo. The objective of this study was to determine if proteasome inhibition leads to enhanced radiation sensitivity. METHODS AND MATERIALS Inhibition of NF-kappaB activation in colorectal cancer cells was performed by treatment of LOVO cells with PS-341 or infection with an adenovirus encoding IkappaB super-repressor, a selective NF-kappaB inhibitor. Cells were irradiated at 0, 2, 4, 6, 8, and 10 Gy with or without inhibition of NF-kappaB. NF-kappaB activation was determined by electrophoretic mobility gel shift assay, and apoptosis was evaluated using the TUNEL assay. Growth and clonogenic survival data were obtained to assess effects of treatment on radiosensitization. In vitro results were tested in vivo using a LOVO xenograft model. RESULTS NF-kappaB activation was induced by radiation and inhibited by pretreatment with either PS-341 or IkappaBalpha super-repressor in all cell lines. Inhibition of radiation-induced NF-kappaB activation resulted in increased apoptosis and decreased cell growth and clonogenic survival. A 7-41% increase in radiosensitivity was observed for cells treated with PS-341 or IkappaBalpha. An 84% reduction in initial tumor volume was obtained in LOVO xenografts receiving radiation and PS-341. CONCLUSIONS Inhibition of NF-kappaB activation increases radiation-induced apoptosis and enhances radiosensitivity in colorectal cancer cells in vitro and in vivo. Results are encouraging for the use of PS-341 as a radiosensitizing agent in the treatment of colorectal cancer.

Rationale for en bloc vein resection in the treatment of pancreatic adenocarcinoma adherent to the superior mesenteric-portal vein confluence

OBJECTIVE Tumor invasion of the superior mesenteric-portal vein (SMPV) confluence is often considered a contraindication to pancreaticoduodenectomy for patients with malignant tumors of the pancreas or periampullary region. The authors sought to determine whether pancreaticoduodenectomy with en bloc resection of the SMPV confluence could be safely performed and whether tumors involving the SMPV confluence were associated with pathologic parameters suggesting poor prognosis. SUMMARY BACKGROUND DATA Several centers have reported high rates of retroperitoneal margin positivity after pancreaticoduodenectomy for tumors of the pancreatic head and periampullary region. Positive-margin or incomplete resection is associated with early tumor recurrence and no survival benefit compared with palliative therapy. Tumor adherence to the lateral of posterior wall of the SMPV confluence often represents the only barrier to complete tumor resection at the time of pancreaticoduodenectomy. METHODS Data on all patients undergoing pancreaticoduodenectomy for adenocarcinoma of the pancreas or periampullary region over a 3.5-year period were entered prospectively in a pancreatic tumor database. To be considered for surgery, patients were required to fulfill the following computed tomography criteria for resectability: 1) the absence of extrapancreatic disease, 2) no tumor encasement of the superior mesenteric artery or celiac axis, and 3) a patent SMPV confluence. Tumor adherence to the superior mesenteric vein or SMPV confluence was assessed intraoperatively, and en bloc venous resection was performed when necessary to achieve complete tumor extirpation. Data on operative characteristics, morbidity, mortality, tumor size, nodal metastases, margin positivity, perineural invasion, and tumor DNA content were compared for patients who did and did not receive venous resection. RESULTS Fifty-nine patients underwent pancreaticoduodenectomy, 36 without venous resection and 23 with en bloc resection of the SMPV confluence. No differences in median hospital stay, morbidity, mortality, tumor size, margin positivity, nodal positivity, or tumor DNA content were observed between groups. CONCLUSIONS When necessary, segmental resection of the SMPV confluence may be performed safely during pancreaticoduodenectomy for periampullary malignant tumors. Tumors invading the SMPV confluence are not associated with histologic parameters suggesting a poor prognosis. Our data suggest that venous involvement is a function of tumor location rather than an indicator of aggressive tumor biology.

Marizomib, a Proteasome Inhibitor for All Seasons: Preclinical Profile and a Framework for Clinical Trials

The proteasome has emerged as an important clinically relevant target for the treatment of hematologic malignancies. Since the Food and Drug Administration approved the first-in-class proteasome inhibitor bortezomib (Velcade) for the treatment of relapsed/refractory multiple myeloma (MM) and mantle cell lymphoma, it has become clear that new inhibitors are needed that have a better therapeutic ratio, can overcome inherent and acquired bortezomib resistance and exhibit broader anti-cancer activities. Marizomib (NPI-0052; salinosporamide A) is a structurally and pharmacologically unique β-lactone-γ-lactam proteasome inhibitor that may fulfill these unmet needs. The potent and sustained inhibition of all three proteolytic activities of the proteasome by marizomib has inspired extensive preclinical evaluation in a variety of hematologic and solid tumor models, where it is efficacious as a single agent and in combination with biologics, chemotherapeutics and targeted therapeutic agents. Specifically, marizomib has been evaluated in models for multiple myeloma, mantle cell lymphoma, Waldenstroms macroglobulinemia, chronic and acute lymphocytic leukemia, as well as glioma, colorectal and pancreatic cancer models, and has exhibited synergistic activities in tumor models in combination with bortezomib, the immunomodulatory agent lenalidomide (Revlimid), and various histone deacetylase inhibitors. These and other studies provided the framework for ongoing clinical trials in patients with MM, lymphomas, leukemias and solid tumors, including those who have failed bortezomib treatment, as well as in patients with diagnoses where other proteasome inhibitors have not demonstrated significant efficacy. This review captures the remarkable translational studies and contributions from many collaborators that have advanced marizomib from seabed to bench to bedside.

Rationale for the treatment of solid tumors with the proteasome inhibitor bortezomib

Given its role in cellular metabolism, the proteasome could prove to be a critical target that can be exploited in treating cancer. In preclinical studies, several mechanisms for bortezomibs activity in multiple myeloma cells have been identified (e.g., NF-kappaB inhibition); antitumor activity with bortezomib has been seen in myeloma patients, thereby supporting the validity of the preclinical work. Similar mechanisms may be in play in solid tumors, and cell culture and xenograft data suggest bortezomib may be active in a wide range of tumor types. One promising possibility is the use of bortezomib for the treatment of chemoresistant tumors. Chemoresistance can be caused by a number of cellular factors; NF-kappaB is a prominent instigator of chemoresistance, and proteasome inhibition was an effective means of preventing NF-kappaB activation in myeloma and several solid tumor laboratory studies. However, the inhibition of NF-kappaB may not be the only mechanism for antitumor activity. This review explores the use of proteasome inhibitors to subvert intrinsic resistance mechanisms, disrupt inducible chemoresistance, or augment the mechanisms of action of standard chemotherapeutics. Thus, in addition to providing another target for anticancer treatment, proteasome inhibition may also provide a means to treat refractory tumors.

Potentiation of chemotherapeutic agents following antagonism of nuclear factor kappa B in human gliomas

Future success using chemotherapy against human gliomas may result from exploiting unique molecular vulnerabilities of these tumors. Chemotherapy frequently results in DNA damage. When such damage is sensed by the cell, programmed cell death, or apoptosis, may be initiated. However, chemotherapy-induced DNA damage may activate nuclear factor kappa B (NF-κB) and block apoptosis. We inhibited NF-κB using a gene therapy approach to determine whether this would render human glioma cells more susceptible to chemotherapy. U87 and U251 glioma cell lines were infected with either treatment adenovirus containing the gene for a mutant non-degradable form of IκBα, which is an inhibitor of NF-κB nuclear translocation, or empty control virus. Following viral infection, cells were treated either with BCNU, carboplatin, tumor necrosis factor alpha (TNF-α), or SN-38.Chemotherapy resulted in a marked increase in active intranuclear NF-κB. This response was greatly decreased by insertion of the mutant repressor gene. Similarly, a significant increase in cell killing by all chemotherapy age was demonstrated following infection with treatment virus. Expression of the mutant repressor gene also resulted in increased apoptosis by TUNEL assay following chemotherapy.Numerous genes are responsible for glioma chemoresistance. DNA damage by chemotherapy may induce the antiapoptotic factor NF-κB and prevent programmed cell death. Insertion of a mutant inhibitor of NF-κB strips cells of this antiapoptotic defense and renders them more susceptible to killing by chemotherapy via increased apoptosis.

NPI-0052 Enhances Tumoricidal Response to Conventional Cancer Therapy in a Colon Cancer Model

Purpose: In the current study, we examine the effects of a novel proteasome inhibitor, NPI-0052 (salinosporamide A), on proteasome function and nuclear factor-κB activation and evaluate its ability to enhance treatment response in colon cancer xenografts when administered orally. Experimental Design: The effects of treatment on nuclear factor-κB activation, cell cycle regulation, and apoptosis were determined. The pharmacodynamic effect of NPI-0052 on 20S proteasome function was assayed in vivo following oral and i.v. drug administration and compared with treatment with bortezomib. The effect of combined treatment with chemotherapy was determined in a colon cancer xenograft model. Results: We found that NPI-0052 is a potent, well-tolerated proteasome inhibitor that has pharmacodynamic properties distinct from bortezomib in that it achieves significantly higher and more sustained levels of proteasome inhibition. When combined with chemotherapy, NPI-0052 increases apoptosis and shifts cells toward G2 cell cycle arrest. When added to chemotherapy in vivo [using combinations of 5-fluorouracil (5-FU), CPT-11, Avastin (bevacizumab), leucovorin, and oxaliplatin], NPI-0052 significantly improved the tumoricidal response and resulted in a 1.8-fold increased response to CPT-11, 5-FU, and leucovorin triple-drug combination (P = 0.0002, t test), a 1.5-fold increased response to the oxaliplatin, 5-FU, and leucovorin triple-drug combination (P = 0.013, t test), and a 2.3-fold greater response to the CPT-11, 5-FU, leucovorin, and Avastin regimen (P = 0.00057). Conclusions: The high level of proteasome inhibition achieved by NPI-0052 is well tolerated and significantly improves the tumoricidal response to multidrug treatment in a colon cancer xenograft model. Further evaluation of this novel proteasome inhibitor in clinical trials is indicated.

Managing unsuspected tumor invasion of the superior mesenteric-portal venous confluence during pancreaticoduodenectomy

Most surgeons believe that tumor invasion of the superior mesenteric-portal venous (SMPV) confluence is a contraindication to pancreaticoduodenectomy for adenocarcinoma of the pancreas or periampullary region. Traditional techniques for performing pancreaticoduodenectomy have emphasized the importance of establishing a tumor-free plane between the SMPV confluence and the neck of the pancreas. However, this maneuver does not reveal tumor invasion of the lateral wall of the superior mesenteric vein (SMV) until after gastric and pancreatic transection--a point at which the surgeon has committed to resection. This unexpected but not uncommon finding likely contributes to the high incidence of margin-positive resections and subsequent local tumor recurrence. We describe our technique for segmental resection of the SMPV confluence at the time of pancreaticoduodenectomy. Routine ligation of the splenic vein and primary anastomosis of the SMV and portal vein have been abandoned in favor of an interposition graft using internal jugular vein.

Heparin-binding EGF-like growth factor is an early response gene to chemotherapy and contributes to chemotherapy resistance

We have shown that one of the principle mechanisms of chemotherapy resistance involves the activation of nuclear factor kappa-B (NF-κB). In an effort to identify NF-κB-regulated chemotherapy response genes, we performed a microarray assay and observed that heparin-binding EGF-like growth factor (HB-EGF) was significantly upregulated by SN38 (a strong inducer of NF-κB activity) in colon cancer cells. Further studies revealed that HB-EGF was rapidly induced following a variety of chemotherapy treatments. Using RNA interference, we demonstrated that the chemotherapy-induced HB-EGF was largely dependent on activator protein-1 (AP-1) and NF-κB activation. Constitutive HB-EGF expression rescued AP-1/NF-κB small interfering RNA (siRNA) cells from chemotherapy-induced apoptosis. Meanwhile, we found that the enzymatic shedding of HB-EGF was also regulated by chemotherapy treatment, resulting in the elevated release of soluble HB-EGF from the cellular membrane. Induction of HB-EGF expression and ectodomain shedding synergistically led to robust epidermal growth factor receptor (EGFR) phosphorylation, whereas inhibition of HB-EGF expression by use of the HB-EGF inhibitor (CRM197) or siRNA resulted in the suppression of chemotherapy-induced EGFR phosphorylation. These results suggest that the chemotherapy-induced EGFR activation is regulated by HB-EGF. Finally, we demonstrated that overexpression of HB-EGF led to apoptotic resistance to chemotherapy, whereas suppression of HB-EGF expression by siRNA resulted in a dramatic increase in cell death. In summary, our study suggests that chemotherapy-induced HB-EGF activation represents a critical mechanism of inducible chemotherapy resistance. Therefore, therapeutic intervention aimed at inhibiting HB-EGF activity may be useful in cancer prevention and treatments.