Jacek Bil

Statins impair antitumor effects of rituximab by inducing conformational changes of CD20.

Background Rituximab is used in the treatment of CD20+ B cell lymphomas and other B cell lymphoproliferative disorders. Its clinical efficacy might be further improved by combinations with other drugs such as statins that inhibit cholesterol synthesis and show promising antilymphoma effects. The objective of this study was to evaluate the influence of statins on rituximab-induced killing of B cell lymphomas. Methods and Findings Complement-dependent cytotoxicity (CDC) was assessed by MTT and Alamar blue assays as well as trypan blue staining, and antibody-dependent cellular cytotoxicity (ADCC) was assessed by a 51Cr release assay. Statins were found to significantly decrease rituximab-mediated CDC and ADCC of B cell lymphoma cells. Incubation of B cell lymphoma cells with statins decreased CD20 immunostaining in flow cytometry studies but did not affect total cellular levels of CD20 as measured with RT-PCR and Western blotting. Similar effects are exerted by other cholesterol-depleting agents (methyl-β-cyclodextrin and berberine), but not filipin III, indicating that the presence of plasma membrane cholesterol and not lipid rafts is required for rituximab-mediated CDC. Immunofluorescence microscopy using double staining with monoclonal antibodies (mAbs) directed against a conformational epitope and a linear cytoplasmic epitope revealed that CD20 is present in the plasma membrane in comparable amounts in control and statin-treated cells. Atomic force microscopy and limited proteolysis indicated that statins, through cholesterol depletion, induce conformational changes in CD20 that result in impaired binding of anti-CD20 mAb. An in vivo reduction of cholesterol induced by short-term treatment of five patients with hypercholesterolemia with atorvastatin resulted in reduced anti-CD20 binding to freshly isolated B cells. Conclusions Statins were shown to interfere with both detection of CD20 and antilymphoma activity of rituximab. These studies have significant clinical implications, as impaired binding of mAbs to conformational epitopes of CD20 elicited by statins could delay diagnosis, postpone effective treatment, or impair anti-lymphoma activity of rituximab.

Proteasome Inhibition Potentiates Antitumor Effects of Photodynamic Therapy in Mice through Induction of Endoplasmic Reticulum Stress and Unfolded Protein Response

Photodynamic therapy (PDT) is an approved therapeutic procedure that exerts cytotoxic activity toward tumor cells by inducing production of reactive oxygen species such as singlet oxygen. PDT leads to oxidative damage of cellular macromolecules, including proteins that undergo multiple modifications such as fragmentation, cross-linking, and carbonylation that result in protein unfolding and aggregation. Because the major mechanism for elimination of carbonylated proteins is their degradation by proteasomes, we hypothesized that a combination of PDT with proteasome inhibitors might lead to accumulation of carbonylated proteins in endoplasmic reticulum (ER), aggravated ER stress, and potentiated cytotoxicity toward tumor cells. We observed that Photofrin-mediated PDT leads to robust carbonylation of cellular proteins and induction of unfolded protein response. Pretreatment of tumor cells with three different proteasome inhibitors, including bortezomib, MG132, and PSI, gave increased accumulation of carbonylated and ubiquitinated proteins in PDT-treated cells. Proteasome inhibitors effectively sensitized tumor cells of murine (EMT6 and C-26) as well as human (HeLa) origin to PDT-mediated cytotoxicity. Significant retardation of tumor growth with 60% to 100% complete responses was observed in vivo in two different murine tumor models (EMT6 and C-26) when PDT was combined with either bortezomib or PSI. Altogether, these observations indicate that combination of PDT with proteasome inhibitors leads to potentiated antitumor effects. The results of these studies are of immediate clinical application because bortezomib is a clinically approved drug that undergoes extensive clinical evaluations for the treatment of solid tumors.

Cardiotoxicity of the Anticancer Therapeutic Agent Bortezomib

Recent case reports provided alarming signals that treatment with bortezomib might be associated with cardiac events. In all reported cases, patients experiencing cardiac problems were previously or concomitantly treated with other chemotherapeutics including cardiotoxic anthracyclines. Therefore, it is difficult to distinguish which components of the therapeutic regimens contribute to cardiotoxicity. Here, we addressed the influence of bortezomib on cardiac function in rats that were not treated with other drugs. Rats were treated with bortezomib at a dose of 0.2 mg/kg thrice weekly. Echocardiography, histopathology, and electron microscopy were used to evaluate cardiac function and structural changes. Respiration of the rat heart mitochondria was measured polarographically. Cell culture experiments were used to determine the influence of bortezomib on cardiomyocyte survival, contractility, Ca(2+) fluxes, induction of endoplasmic reticulum stress, and autophagy. Our findings indicate that bortezomib treatment leads to left ventricular contractile dysfunction manifested by a significant drop in left ventricle ejection fraction. Dramatic ultrastructural abnormalities of cardiomyocytes, especially within mitochondria, were accompanied by decreased ATP synthesis and decreased cardiomyocyte contractility. Monitoring of cardiac function in bortezomib-treated patients should be implemented to evaluate how frequently cardiotoxicity develops especially in patients with pre-existing cardiac conditions, as well as when using additional cardiotoxic drugs.

Zinc protoporphyrin IX, a heme oxygenase-1 inhibitor, demonstrates potent antitumor effects but is unable to potentiate antitumor effects of chemotherapeutics in mice

BackgroundHO-1 participates in the degradation of heme. Its products can exert unique cytoprotective effects. Numerous tumors express high levels of HO-1 indicating that this enzyme might be a potential therapeutic target. In this study we decided to evaluate potential cytostatic/cytotoxic effects of zinc protoporphyrin IX (Zn(II)PPIX), a selective HO-1 inhibitor and to evaluate its antitumor activity in combination with chemotherapeutics.MethodsCytostatic/cytotoxic effects of Zn(II)PPIX were evaluated with crystal violet staining and clonogenic assay. Western blotting was used for the evaluation of protein expression. Flow cytometry was used to evaluate the influence of Zn(II)PPIX on the induction of apoptosis and generation of reactive oxygen species. Knock-down of HO-1 expression was achieved with siRNA. Antitumor effects of Zn(II)PPIX alone or in combination with chemotherapeutics were measured in transplantation tumor models.ResultsZn(II)PPIX induced significant accumulation of reactive oxygen species in tumor cells. This effect was partly reversed by administration of exogenous bilirubin. Moreover, Zn(II)PPIX exerted potent cytostatic/cytotoxic effects against human and murine tumor cell lines. Despite a significant time and dose-dependent decrease in cyclin D expression in Zn(II)PPIX-treated cells no accumulation of tumor cells in G1 phase of the cell cycle was observed. However, incubation of C-26 cells with Zn(II)PPIX increased the percentage of cells in sub-G1 phase of the cells cycle. Flow cytometry studies with propidium iodide and annexin V staining as well as detection of cleaved caspase 3 by Western blotting revealed that Zn(II)PPIX can induce apoptosis of tumor cells. B16F10 melanoma cells overexpressing HO-1 and transplanted into syngeneic mice were resistant to either Zn(II)PPIX or antitumor effects of cisplatin. Zn(II)PPIX was unable to potentiate antitumor effects of 5-fluorouracil, cisplatin or doxorubicin in three different tumor models, but significantly potentiated toxicity of 5-FU and cisplatin.ConclusionInhibition of HO-1 exerts antitumor effects but should not be used to potentiate antitumor effects of cancer chemotherapeutics unless procedures of selective tumor targeting of HO-1 inhibitors are developed.

Molecular mechanisms of the antitumor effects of anti-CD20 antibodies.

Anti-CD20 monoclonal antibodies (mAbs) have become the mainstay in the treatment of non-Hodgkins lymphomas and have shown significant activity in patients with B-cell chronic lymphocytic leukemia. Antitumor action of these antibodies results from triggering of indirect effector mechanisms of the immune system that include activation of complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), or phagocytosis. Moreover, some studies indicate direct influence of anti-CD20 mAbs on tumor cells that leads to induction of various types of cell death. Despite the wealth of data on the mechanisms of cytotoxicity that accumulated over the last two decades their relative contribution to the therapeutic outcome is still difficult to predict in individual patients. Elucidation of molecular mechanisms of anti-CD20 mAbs action is necessary to deliver their maximal activity in rationally designed combinations with other therapeutic approaches and to design next generation anti-CD20 mAb with improved ability to eliminate tumor cells.

Bortezomib modulates surface CD20 in B-cell malignancies and affects rituximab-mediated complement-dependent cytotoxicity

Recent observations indicate that rituximab-resistant lymphoma cells exhibit upregulation of components of the ubiquitin-proteasome system (UPS). Therefore, proteasome inhibitors including the clinically approved bortezomib might influence the levels of CD20, a rituximab target antigen. We observed that incubation of tumor cells with rituximab leads to increased levels of ubiquitinated CD20. However, inhibition of the UPS is not associated with upregulation, but rather with a counterintuitive downregulation of surface CD20 levels that increases resistance of tumor cells to rituximab-mediated cytotoxicity. Although preliminary observations indicate that CD20 might be a substrate for two proteolytic systems, the mechanisms as well as significance of these findings require further studies.Unresponsiveness to rituximab treatment develops in many patients prompting elucidation of underlying molecular pathways. It was recently observed that rituximab-resistant lymphoma cells exhibit up-regulation of components of the ubiquitin-proteasome system (UPS). Therefore, we investigated in more detail the role of this system in the regulation of CD20 levels and the influence of proteasome inhibitors on rituximab-mediated complement-dependent cytotoxicity (R-CDC). We observed that incubation of Raji cells with rituximab leads to increased levels of ubiquitinated CD20. However, inhibition of the UPS was not associated with up-regulation of surface CD20 levels, although it significantly increased its ubiquitination. Short-term (24 hours) incubation of Raji cells with 10 or 20 nM bortezomib did not change surface CD20 levels, but sensitized CD20(+) lymphoma cells to R-CDC. Prolonged (48 hours) incubation with 20 nM bortezomib, or incubation with 50 nM bortezomib for 24 hours led to a significant decrease in surface CD20 levels as well as R-CDC. These effects were partly reversed by bafilomycin A1, an inhibitor of lysosomal/autophagosomal pathway of protein degradation. These studies indicate that CD20 levels are regulated by 2 proteolytic systems and that the use of proteasome inhibitors may be associated with unexpected negative influence on R-CDC.

Statins potentiate cytostatic/cytotoxic activity of sorafenib but not sunitinib against tumor cell lines in vitro.

The aim of this study was to investigate the potential cytostatic/cytotoxic effects of HMG-CoA reductase inhibitors and two orphan drugs registered for the treatment of advanced renal cell carcinoma, i.e. sorafenib and sunitinib against several different tumor cell lines. Cytostatic/cytotoxic effects were measured using crystal violet or MTT reduction assays. Cell cycle regulation was investigated using flow cytometry and Western blotting. The combination of lovastatin and sorafenib (but not sunitinib) produced synergistic cytostatic/cytotoxic effects against all tested tumor cell lines. In this study, an impairment of the protein prenylation, especially geranylgeranylation, resulted predominantly in the potentiation of the cytostatic/cytotoxic activity of sorafenib, in cell cycle arrest in G1 phase, and, in poor induction of apoptosis. Moreover, due to the fact that it has been well documented that sorafenib compromises the heart function, we studied the interaction of lovastatin and sorafenib using rat cardiomyoblast line H9c2. The combination showed strong synergistic cardiotoxic effects. Statins and tyrosine kinase inhibitors were used at doses that are achievable clinically, which makes the combination promising for future studies, especially in urooncology, bearing in mind possible cardiotoxic effects.

Dedicated Bifurcation Paclitaxel‐Eluting Stent BiOSS Expert® in the Treatment of Distal Left Main Stem Stenosis

OBJECTIVES The aim of this study was to assess prospectively the effectiveness and safety profile of distal left main stem (LMS) stenosis treatment with dedicated bifurcation paclitaxel-eluting stent BiOSS Expert®. BACKGROUND Angioplasty of distal LMS stenosis is always a high-risk procedure, and optimal treatment is uncertain. METHODS This was a prospective international 2-center study, which enrolled patients with non-ST-elevation acute coronary syndrome (NSTE-ACS) or stable angina with distal left main stenosis. All patients were treated with the dedicated bifurcation stent BiOSS Expert®. Provisional T-stenting was the obligatory strategy. Angiographic control was performed after 12 months. The primary end-point was cumulative rate of death, myocardial infarction (MI), and target lesion revascularization (TLR) at 12 months. Angiographic end-points included late lumen loss, percent diameter stenosis, and binary restenosis rate. RESULTS A total of 54 patients with distal LMS stenosis were enrolled. Seven patients (13%) were enrolled during NSTE-ACS, 77.8% were hypertensive, 27.8% were diabetic, 51.9% had previous MI, 53.7% underwent prior percutaneous coronary intervention, and 16.7% coronary artery bypass graft. The mean SYNTAX score was 21.52 ± 6.50. The device success rate was 100%. The mean BiOSS Expert stent parameters were as follows: 4.07 ± 0.26 mm × 3.36 ± 0.26 mm × 16.61 ± 1.72 mm and in side branch the other stent (classical drug-eluting stent) was implanted in 25.9% of cases. The overall TLR was 9.3%. There were no death, stent thrombosis, or acute MI. In the univariate regression analysis, the only factor associated with higher risk for TLR was the SYNTAX score value. CONCLUSIONS The dedicated bifurcation stent BiOSS Expert® proved to be a feasible device, with promising safety and long-term clinical effectiveness in the treatment of distal LMS stenosis.

Regular drug-eluting stents versus the dedicated coronary bifurcation sirolimus-eluting BiOSS LIM® stent: the randomised, multicentre, open-label, controlled POLBOS II trial.

AIMS The aim of the POLBOS II randomised trial was to compare any regular drug-eluting stents (rDES) with the dedicated bifurcation sirolimus-eluting stent BiOSS LIM for the treatment of coronary bifurcation lesions. The secondary aim was to study the effect of final kissing balloon inflation (FKBI) on clinical outcomes. METHODS AND RESULTS Between December 2012 and December 2013, 202 patients with stable coronary artery disease or non-ST-segment elevation acute coronary syndrome were randomly assigned 1:1 to treatment of the coronary bifurcation lesions either with the BiOSS LIM stent (n=102) or with an rDES (n=100). Coronary re-angiography was performed at 12 months. The primary endpoint was the composite of cardiac death, myocardial infarction (MI), and target lesion revascularisation (TLR) at 12 months. The target vessel was located in the left main in one third of the cases (35.3% in BiOSS and 38% in rDES). Side branch treatment was required in 8.8% (rDES) and 7% (BiOSS). At 12 months, the cumulative MACE incidence was similar in both groups (11.8% [BiOSS] vs. 15% [rDES, p=0.08]), as was the TLR rate (9.8% vs. 9% [p=0.8]). The binary restenosis rates were significantly lower in the FKBI subgroup of the BiOSS group (5.9% vs. 11.8%, p<0.05). CONCLUSIONS MACE rates as well as TLR rates were comparable between the BiOSS LIM and rDES. At 12 months, cumulative MACE incidence was similar in both groups (11.8% vs. 15%), as was the TLR rate (9.8% vs. 9%). Significantly lower rates of restenosis were observed in the FKBI subgroup of the BiOSS group.

Prenyltransferases Regulate CD20 Protein Levels and Influence Anti-CD20 Monoclonal Antibody-mediated Activation of Complement-dependent Cytotoxicity

Background: The influence of farnesyltransferase inhibitors (FTIs) on CD20 levels is unknown. Results: FTIs increase CD20 expression and improve rituximab-mediated activation of complement-dependent cytotoxicity. Conclusion: FTIs sensitize tumor cells to anti-CD20 mAbs. Significance: The combination of FTIs with anti-CD20 mAbs seems to be a reasonable therapeutic approach worth to be tested in patients with B-cell tumors. Anti-CD20 monoclonal antibodies (mAbs) are successfully used in the management of non-Hodgkin lymphomas and chronic lymphocytic leukemia. We have reported previously that statins induce conformational changes in CD20 molecules and impair rituximab-mediated complement-dependent cytotoxicity. Here we investigated in more detail the influence of farnesyltransferase inhibitors (FTIs) on CD20 expression and antitumor activity of anti-CD20 mAbs. Among all FTIs studied, L-744,832 had the most significant influence on CD20 levels. It significantly increased rituximab-mediated complement-dependent cytotoxicity against primary tumor cells isolated from patients with non-Hodgkin lymphomas or chronic lymphocytic leukemia and increased CD20 expression in the majority of primary lymphoma/leukemia cells. Incubation of Raji cells with L-744,832 led to up-regulation of CD20 at mRNA and protein levels. Chromatin immunoprecipitation assay revealed that inhibition of farnesyltransferase activity was associated with increased binding of PU.1 and Oct-2 to the CD20 promoter sequences. These studies indicate that CD20 expression can be modulated by FTIs. The combination of FTIs with anti-CD20 mAbs is a promising therapeutic approach, and its efficacy should be examined in patients with B-cell tumors.