Interleukin 12: still a promising candidate for tumor immunotherapy?

Interleukin 12 (IL-12) seemed to represent the ideal candidate for tumor immunotherapy, due to its ability to activate both innate (NK cells) and adaptive (cytotoxic T lymphocytes) immunities. However, despite encouraging results in animal models, very modest antitumor effects of IL-12 in early clinical trials, often accompanied by unacceptable levels of adverse events, markedly dampened hopes of the successful use of this cytokine in cancer patients. Recently, several clinical studies have been initiated in which IL-12 is applied as an adjuvant in cancer vaccines, in gene therapy including locoregional injections of IL-12 plasmid and in the form of tumor-targeting immunocytokines (IL-12 fused to monoclonal antibodies). The near future will show whether this renewed interest in the use of IL-12 in oncology will result in meaningful therapeutic effects in a select group of cancer patients.

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

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.

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.

Statins can modulate effectiveness of antitumor therapeutic modalities.

Despite significant, frequently very strong, antiproliferative and tumoricidal effects of statins demonstrated in vitro, their antitumor effects in animal models are modest, and their efficacy in clinical trials has not been proven. As such, statins seem unlikely to be ever regarded as antitumor agents. However, statins are regularly taken by many elderly cancer patients for the prevention of cardiovascular events. Owing to their pleiotropic effects in normal and tumor cells, statins interact in various ways with many antitumor treatment modalities, either potentiating or diminishing their effectiveness. Elucidation of these interactions might affect the choice of treatment to be planned in cancer patients as some combinations might be contraindicated, whereas others might elicit potentiated antitumor effects but at a cost of increased general toxicity. Some other combinations might induce either comparable or even stronger antitumor effects, but with a beneficial concomitant reduction of specific side effects. Most of the studies reviewed in this article have been carried in vitro or in experimental tumor models, but clinical relevance of the findings is also discussed.

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-beta-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.

Ciglitazone, an agonist of peroxisome proliferator-activated receptor gamma, exerts potentiated cytostatic/cytotoxic effects against tumor cells when combined with lovastatin.

Thiazolidinediones are ligands of PPAR-gamma, a member of the nuclear receptor family. These drugs have shown promising pre-clinical activity in tumor models but clinical studies failed to confirm their beneficial effect. We have studied the in vitro antitumor effects of a combination of ciglitazone, a thiazolidinedione drug, and lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. We observed a marked synergism in several different tumor cell lines resulting from both inhibition of cell proliferation and induction of apoptosis. These results strongly suggest that combining PPAR-gamma agonists with statins can produce significant antitumor effects.

Interleukin 15 augments antitumor activity of cytokine gene-modified melanoma cell vaccines in a murine model.

Many studies have demonstrated that interleukin 15 (IL-15) is a cytokine with strong antitumor properties and have suggested its potential use in tumor immunotherapy. IL-15 exerts its effect on innate and acquired immunity with the most prominent action in NK cells and CD8(+) memory T cells. Therefore, many authors have proposed that IL-15 could be a good candidate for augmenting the efficacy of vaccination strategies. In our experiments, in a model of B78-H1 murine transplantable melanoma, tumor-bearing mice were treated with different cytokine-gene modified tumor cell vaccines (producing TNF-alpha, GM-CSF, IL-12 or IL-6/sIL-6R) followed by a series of IL-15 injections. In order to investigate the infiltration of treated tumors by leukocytes, immunohistochemical staining was performed. In every case, the combined therapy was superior to the treatment with either a vaccine or IL-15 alone. Tumors treated with the combination of B78-H1 melanoma cells secreting IL-12 (B78/IL-12 vaccine) and IL-15 were heavily infiltrated by granulocytes. IL-15, either alone or in combination with the B78/IL-12 vaccine, influenced infiltration of tumors with CD3(+) lymphocytes, CD4(+)and CD8(+). To our knowledge, this is the first report that shows the universal genetically-modified tumor cell vaccine-augmenting properties of IL-15. The cytokine can be useful as an adjuvant in cancer gene therapy in humans.

Potentiated antitumor effects of the combination treatment with statins and pamidronate in vitro and in vivo.

The aim of the present study was to examine the potential antitumor activity of lovastatin and other statins together with pamidronate, a second generation bisphosphonate (BP), against tumor cell lines. Cytostatic/cytotoxic effects were measured using crystal violet assay. Regulation of the cell cycle and induction of apoptosis were evaluated using flow cytometry and Western blotting, migration of tumor cells was measured in a scratch wound assay and their invasiveness was measured with a Matrigel-invasion assay. Antitumor effects of the combination treatment were evaluated in a murine PANC 02 pancreatic adenocarcinoma model. Combination of pamidronate and lovastatin produced potentiated cytostatic/cytotoxic effects against breast and pancreatic cancer cell lines. The combination was also effective in inhibition of tumor cell adhesion to collagen IV and fibronectin and interfered with migration and invasiveness of tumor cells. Neither pamidronate nor lovastatin alone affected tumor growth in mice but the combination treatment resulted in retardation of tumor growth and prolongation of mouse survival. The combination of statins and pamidronate, a second generation bisphosphonate, demonstrates promising antitumor effects at doses readily achievable in patients. This combination holds promise for future clinical studies.

Erythropoietin reduces cisplatin-induced neurotoxicity without impairment of cytotoxic effects against tumor cells.

Cisplatin, a widely used chemotherapeutic is approved for the management of various solid tumors. Administration of cisplatin is associated with induction of significant toxicities that include neurotoxicity and nephrotoxicity, the latter leading to severe and debilitating anemia. Since erythropoietin, a hematopoietic growth factor that corrects chemotherapy-induced anemia, reduces transfusion requirements and seems to improve the patient's quality of life, has been shown to exert cytoprotective effects we decided to investigate its direct influence on cisplatin-induced neurotoxicity against primary cortical neurons isolated from rats. We observed that pre-treatment of neurons with erythropoietin significantly protects these cells from cisplatin-induced cytotoxicity. These effects correlated with amelioration of cisplatin-mediated activation of ERK1/2 kinases and decreased cleavage of caspase 3. Similarly to erythropoietin, a selective ERK1/2 inhibitor significantly reduced cisplatin-induced cytotoxicity against neuronal cells. Importantly, using the same experimental setting we did not observe any protection from cisplatin cytotoxicity against four established tumor cell lines. Altogether our studies confirm that erythropoietin might be an effective cytoprotective agent that reduces cisplatin-induced neurotoxicity.

Berberine, a natural cholesterol reducing product, exerts antitumor cytostatic/cytotoxic effects independently from the mevalonate pathway.

The aim of this study was to investigate the role of the mevalonate pathway in the cytostatic/cytotoxic effects of berberine, a natural plant alkaloid that reduces cholesterol concentration. Berberine as well as lovastatin, an inhibitor of the mevalonate pathway, exerted dose-dependent cytostatic/cytotoxic effects against human breast cancer cells (MDA-MB231). Although the mevalonate pathway metabolites (mevalonic acid, farnesyl pyrophosphate, geranylgeranyl pyrophosphate) effectively reversed cytostatic/cytotoxic effects of lovastatin against MDA-MB231 cells, they were not effective in influencing the cytostatic/cytotoxic effects of berberine. The cytostatic/cytotoxic effects of berberine do not seem to result from inhibition of the mevalonate pathway.

Erythropoietin restores the antitumor effectiveness of photodynamic therapy in mice with chemotherapy-induced anemia.

PURPOSE: The study was designed to examine the impact of anemia on the antitumor efficacy of photodynamic therapy (PDT) in a murine colon-26 adenocarcinoma model syngeneic with BALB/c mice. EXPERIMENTAL DESIGN: Acute hemolytic anemia was induced by a single i.p. injection of phenylhydrazine hydrochloride (150 mg/kg). Anemia induced by i.p. administration of carboplatin (100 mg/kg) was corrected by s.c. treatment with recombinant human erythropoietin (1000 units/kg/day). The effectiveness of PDT (10 mg/kg Photofrin, 150 J/cm2 laser dose) was evaluated by measurements of the footpad edema and tumor volume. All of the RBC-related parameters were measured from the tail vein. RESULTS: Phenylhydrazine hydrochloride injection resulted in a blunted response of normal tissues to Photofrin-mediated PDT-induced edema formation. Similarly, the antitumor response in mice with hemolytic anemia was nearly completely abrogated. The antitumor effectiveness of PDT was also significantly diminished in a more realistic clinical situation when anemia was induced by administration of carboplatin. Importantly, administration of recombinant human erythropoietin completely restored the sensitivity of the tumor to PDT in carboplatin-treated mice. CONCLUSIONS: These results indicate that anemia can negatively influence the therapeutic effectiveness of PDT. For optimal antitumor response anemia should be corrected before PDT procedure.

Interleukin 12-based immunotherapy improves the antitumor effectiveness of a low-dose 5-Aza-2'-deoxycitidine treatment in L1210 leukemia and B16F10 melanoma models in mice.

PURPOSE: Recent findings indicating that many genes related to cancer development are silenced by an aberrant DNA methylation suggest that inhibitors of this process may be effective cancer therapeutics. In this study we investigated the efficacy of low-dose 5-aza-2'-deoxycitydine (DAC), a methylation inhibitor, with interleukin (IL) 12, one of the most potent cytokines with antitumor activity. EXPERIMENTAL DESIGN: Mice inoculated with L1210 leukemia cells or with B16F10 melanoma cells were treated with 7 daily injections of low-dose DAC (0.2 mg/kg) and/or 7 daily doses of IL-12 (100 ng/dose). Scid/scid mice as well as monoclonal antibodies against CD4, CD8, and NK1.1 were used to investigate the mechanisms of the antitumor effects of the combination treatment. The activity of murine lymphocytes was measured with enzyme-linked immunospot and (51)Cr release assays. RESULTS: Treatment with DAC or IL-12 given alone produced moderate antitumor effects. In both tumor models combined treatment resulted in potentiated antitumor effects and produced 70% long-term survivors among mice inoculated with L1210 cells. The antitumor efficacy of combined treatment was abrogated in scid/scid mice, and after depletion of CD4(+) and CD8(+) T cells. Mice inoculated with B16F10 melanoma cells had significantly delayed tumor growth after combined treatment with DAC and IL-12. Strong antitumor effect correlated with a significant activation of lymph node-derived CD8(+) and CD4(+) cells. Transient neutropenia was observed in mice under treatment of DAC alone, but remarkably this effect was not potentiated by IL-12. CONCLUSIONS: This study provides the first evidence that antitumor effects of DAC can be strongly potentiated by IL-12 and could be beneficial in an effective low-dose-based antitumor therapy.

CpG immunostimulatory oligodeoxynucleotide 1826 enhances antitumor effect of interleukin 12 gene-modified tumor vaccine in a melanoma model in mice.

PURPOSE: The effectiveness of interleukin (IL)-12-secreting tumor vaccines in the treatment of mouse tumors could be enhanced by concurrent application of cytokines and costimulatory molecules. We investigated the therapeutic potential of IL-12 gene-transduced melanoma vaccine in combination with CpG immunostimulatory oligodeoxynucleotide (ODN) 1826, an adjuvant known to favor development of Th1-biased immune response, in a B78-H1 (B78) melanoma model in mice. EXPERIMENTAL DESIGN: Mice injected with B78 melanoma cells were treated with irradiated IL-12 gene-transduced B78 cells [B78/IL-12(X)] and/or ODN 1826. Mechanisms responsible for the antitumor effects of the treatment were investigated using fluorescence-activated cell sorter analysis, a standard (51)Cr releasing assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and ELISA. RESULTS: Single injection of B78/IL-12(X) cells had no effect on tumor growth, whereas seven consecutive daily injections of ODN 1826 markedly inhibited tumor progression with occasional curative effects. When used in combination, B78/IL-12(X) cells and ODN 1826 caused additional tumor growth reduction and eradication of tumors in 62% of treated mice. The combined treatment activated local inflammatory response against tumor but also induced systemic antitumor immunity. In vitro studies have shown that when used together, B78/IL-12(X) cells and ODN 1826 induced a potent Th1 response and suggested the role of IFN-gamma in activation of the host immune response. The antitumor effects in double-treated mice were accompanied by the development of cytotoxic effectors in the spleen and activation of macrophages. CONCLUSIONS: The results provided the evidence that the combination of IL-12 gene-modified melanoma vaccine and ODN 1826 induces synergistically systemic and local antitumor immunity.

Inhibition of cyclooxygenase-2 indirectly potentiates antitumor effects of photodynamic therapy in mice.

PURPOSE: The aim of the present study was to potentiate the antitumor effectiveness of photodynamic therapy (PDT). A cDNA microarray analysis was used to evaluate the gene expression pattern after Photofrin-mediated PDT to find more effective combination treatment with PDT and inhibitor(s) of the identified gene product(s) overexpressed in tumor cells. EXPERIMENTAL DESIGN: Atlas Mouse Stress Array was used to compare the expression profile of control and PDT-treated C-26 cells. The microarray results have been confirmed using Western blotting. Cytostatic/cytotoxic in vitro assay as well as in vivo tumor models were used to investigate the antitumor effectiveness of PDT in combination with cyclooxygenase (COX) 2 inhibitors. RESULTS: PDT induced the expression of 5 of 140 stress-related genes. One of these genes encodes for COX-2, an enzyme important in the tumor progression. Inhibition of COX-2 in vitro with NS-398, rofecoxib, or nimesulide, or before PDT with nimesulide did not influence the therapeutic efficacy of the treatment. Administration of a selective COX-2 inhibitor after PDT produced potentiated antitumor effects leading to complete responses in the majority of treated animals. CONCLUSIONS: COX-2 inhibitors do not sensitize tumor cells to PDT-mediated killing. However, these drugs can be used to potentiate the antitumor effectiveness of this treatment regimen when administered after tumor illumination.

Effective photoimmunotherapy of murine colon carcinoma induced by the combination of photodynamic therapy and dendritic cells.

PURPOSE: The unique mechanism of tumor destruction by photodynamic therapy (PDT), resulting from apoptotic and necrotic killing of tumor cells accompanied by local inflammatory reaction and induction of heat shock proteins (HSPs), prompted us to investigate the antitumor effectiveness of the combination of PDT with administration of immature dendritic cells (DCs). EXPERIMENTAL DESIGN: Confocal microscopy and Western blotting were used to investigate the influence of PDT on the induction of apoptosis and expression of HSP expression in C-26 cells. Confocal microscopy and flow cytometry studies were used to examine phagocytosis of PDT-treated C-26 cells by DCs. Secretion of interleukin (IL)-12 was measured with ELISA. Cytotoxic activity of lymph node cells was evaluated in a standard (51)Cr-release assay. The antitumor effectiveness of PDT in combination with administration of DCs was investigated in in vivo model. RESULTS: PDT treatment resulted in the induction of apoptotic and necrotic cell death and expression of HSP27, HSP60, HSP72/73, HSP90, HO-1, and GRP78 in C-26 cells. Immature DCs cocultured with PDT-treated C-26 cells efficiently engulfed killed tumor cells, acquired functional features of maturation, and produced substantial amounts of IL-12. Inoculation of immature DCs into the PDT-treated tumors resulted in effective homing to regional and peripheral lymph nodes and stimulation of cytotoxic activity of T and natural killer cells. The combination treatment with PDT and administration of DCs produced effective antitumor response. CONCLUSIONS: The feasibility and antitumor effectiveness demonstrated in these studies suggest that treatment protocols involving the administration of immature DCs in combination with PDT may have clinical potential.

The influence of photodynamic therapy on the immune response.

Photodynamic therapy (PDT) is a clinically approved therapeutic modality used for the management of several types of tumors as well as non-malignant diseases. Most of the effects of this treatment regimen result from direct action of singlet oxygen and reactive oxygen species. However, accumulating evidence indicates that antitumor effects are also mediated by indirect stimulation of inflammatory and immune responses. These responses include rapid local infiltration of tumors by neutrophils and macrophages accompanied by systemic release of inflammatory mediators. This early response can initiate and translate into a more precise immune reaction that involves activation of specific T lymphocytes that seem to be necessary for the ultimate control of residual tumor cells. Although still incompletely understood, PDT can not only activate but also suppress the immune response depending on several variables. This review summarizes the influence of PDT on the immune response and discusses its importance in the management of human diseases.

Topical ALA-PDT modifies neutrophils' chemiluminescence, lymphocytes' interleukin-1beta secretion and serum level of transforming growth factor beta1 in patients with nonmelanoma skin malignancies A clinical study.

BACKGROUND: Photodynamic therapy (PDT) has been recognized as a noninvasive therapeutic approach for the effective treatment of tumors. It has been shown in studies conducted on malignant cell lines and various animal tumor models, that the interaction of photosensitizing substances with light leads to the release of cytotoxic substances and stimulates the immune response. PURPOSE: The aim of our study was to analyze the immune system response in patients undergoing photodynamic therapy due to basal cell carcinoma (BCC). METHODS: Patients with skin malignancies have been treated by 10% delta-aminolevulinic acid (ALA) (Medac GmbH, Wedel, Germany) topically and light from a diode laser. Blood samples were obtained from each patient twice in the same day: before and 4h after photodynamic treatment procedure. In patients' serum the concentration of transforming growth factor beta1 (TGF-ß1) was determined. Additionally the study has been conducted on lymphocytes and granulocytes from peripheral blood. In cell culture supernatants the concentration of interleukin 1beta (IL-1ß), interleukin 2 (IL-2), interleukin 6 (IL-6), tumor necrosis factor alpha (TNFα), the percentile composition of patients' lymphocytes and the chemiluminescence of neutrophils have been measured. RESULTS: We have observed a significant increase (p=0.015) in the intensity of the neutrophil chemiluminescence and significant diminution (p=0.006) of IL-1ß concentration in supernatants. Similarly the serum level of TGF-ß1 has been significantly decreased (p<0.001). CONCLUSION: It is very likely that human immune system activity is modified by topical ALA-PDT and may potentially contribute to its final outcome.

Natural mechanisms protecting against cancer.

Carcinogenesis is a multistage process. At each step of this process, there are natural mechanisms protecting against development of cancer. The majority of cancers in humans is induced by carcinogenic factors present in our environment including our food. However, some natural substances present in our diet or synthesized in our cells are able to block, trap or decompose reactive oxygen species (ROS) participating in carcinogenesis. Carcinogens can also be removed from our cells. If DNA damage occurs, it is repaired in most of the cases. Unrepaired DNA alterations can be fixed as mutations in proliferating cells only and mutations of very few strategic genes can induce tumor formation, the most relevant are those activating proto-oncogenes and inactivating tumor suppressor genes. A series of mutations and/or epigenetic changes is required to drive transformation of a normal cell into malignant tumor. The apparently unrestricted growth has to be accompanied by a mechanism preserving telomeres which otherwise shorten with succeeding cell divisions leading to growth arrest. Tumor can not develop beyond the size of 1-2mm in diameter without the induction of angiogenesis which is regulated by natural inhibitors. To invade the surrounding tissues epithelial tumor cells have to lose some adhesion molecules keeping them attached to each other and to produce enzymes able to dissolve the elements of the basement membrane. On the other hand, acquisition of other adhesion molecules enables interaction of circulating tumor cells with endothelial cells facilitating extravasation and metastasis. One of the last barriers protecting against cancer is the activity of the immune system. Both innate and adaptive immunity participates in anti-tumor effects including the activity of natural killer (NK) cells, natural killer T cells, macrophages, neutrophils and eosinophils, complement, various cytokines, specific antibodies, and specific T cytotoxic cells. Upon activation neutrophils and macrophages are able to kill tumor cells but they can also release ROS, angiogenic and immunosuppressive substances. Many cytokines belonging to different families display anti-tumor activity but their role in natural anti-tumor defense remains largely to be established.

AAF-cmk sensitizes tumor cells to trail-mediated apoptosis.

TRAIL is a member of the tumor necrosis factor (TNF) superfamily. This cytokine is cytotoxic for a high proportion of tumor cells, but could be also toxic for normal cells. There is a need to find other agents able to potentiate the antitumor effects of this cytokine. In our study, we found that Ala-Ala-Phe-chloromethylketone (AAF-cmk) augmented cytotoxic activity of TRAIL or TNF against human leukemic cells. Flow cytometry studies and electron microscopy revealed that apoptosis was primarily responsible for this potentiation. Altogether, our studies indicate that AAF-cmk might effectively sensitize human leukemia cells to apoptosis induced by TRAIL and TNF.

Potential antitumor effects of statins (Review).

Statins, which have been introduced to the clinic for the treatment of hypercholesterolemia, are competitive inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the major rate-limiting enzyme that controls the conversion of HMG-CoA to mevalonic acid (MA). MA is the precursor in the biosynthesis of isoprenoid compounds including cholesterol, dolichol and ubiquinone. Furthermore, mevalonate-derived prenyl groups enable precise cellular localization and function of many proteins such as Ras and Rho proteins. Therefore, besides lowering cholesterol level, statins exert pleiotropic effects on many essential cellular functions including cell proliferation, differentiation, and survival but also participate in the regulation of cell shape and motility. Statins have been shown to inhibit proliferation and to induce apoptosis in a variety of tumor cells. They have also been found to display antitumor effects against melanoma, mammary carcinoma, pancreatic adenocarcinoma, fibrosarcoma, glioma, neuroblastoma, and lymphoma in animal tumor models resulting in retardation of tumor growth, and/or inhibition of the metastatic process. In preclinical studies statins have also been demonstrated to potentiate the antitumor effects of some cytokines and chemotherapeutics. The molecular mechanisms underlying antitumor activity of statins have not been fully elucidated but interference with the function of Ras and Rho family GTPases, inhibition of the activity of certain cyclin-dependent kinases (CDK), and activation of CDK inhibitors, all seem to participate in this activity. The results of several clinical studies of statins in cancer patients including phase I, phase I/II, and phase II trials have been published. Although evaluation of the therapeutic efficacy is not the purpose of early clinical trials and all conclusions might be premature at this stage, some preliminary conclusions have already been drawn. The results of these studies do not show any significant therapeutic effects of statins in cancer patients. However, the results of one of these studies suggest that statins could effectively strengthen the therapeutic activity of some chemotherapeutics. This observation seems to agree with the results of preclinical studies. However, as toxic side effects of statins have been particularly evident in their combination with some other drugs great caution should be advised while planning clinical trials based on combination therapy including statins in cancer patients.