Interferons: Pleiotropic cellular modulators

The Role of Mesenchymal Stem Cells and Exosomes in Tumor Development and Targeted Antitumor Therapies

Mesenchymal stem cells (MSCs) can be isolated from various tissues in adults and differentiated into cells of the osteoblasts, adipocytes, chondrocytes, and myocytes. Recruitments of MSCs towards tumors have a crucial contribution to tumor development. However, the role of MSCs in the tumor microenvironment is uncertain. In addition, due to its tropism to the tumor and low immunogenic properties, more and more pieces of evidence indicate that MSCs may be an ideal carrier for antitumor biologics such as cytokines, chemotherapeutic agents, and oncolytic viruses. Here, we review the existing knowledge on the anti- and protumorigenic effect of MSCs and their extracellular vesicles and exosomes, the role of MSCs, and their extracellular vesicles and exosomes as antitumor vectors.

Contributions for classification of platelet rich plasma - proposal of a new classification: MARSPILL

Platelet-rich plasma (PRP) has emerged as a significant therapy used in medical conditions with heterogeneous results. There are some important classifications to try to standardize the PRP procedure. The aim of this report is to describe PRP contents studying celular and molecular components, and also propose a new classification for PRP. The main focus is on mononuclear cells, which comprise progenitor cells and monocytes. In addition, there are important variables related to PRP application incorporated in this study, which are the harvest method, activation, red blood cells, number of spins, image guidance, leukocytes number and light activation. The other focus is the discussion about progenitor cells presence on peripherial blood which are interesting due to neovasculogenesis and proliferation. The function of monocytes (in tissue-macrophages) are discussed here and also its plasticity, a potential property for regenerative medicine treatments.

Antibody therapies for melanoma: new and emerging opportunities to activate immunity (Review)

The interface between malignant melanoma and patient immunity has long been recognised and efforts to treat this most lethal form of skin cancer by activating immune responses with cytokine, vaccine and also antibody immunotherapies have demonstrated promise in limited subsets of patients. In the present study, we discuss different antibody immunotherapy approaches evaluated in the context of melanoma, each designed to act on distinct targets and to employ different mechanisms to restrict tumour growth and spread. Monoclonal antibodies recognising melanoma-associated antigens such as CSPG4/MCSP and targeting elements of tumour-associated vasculature (VEGF) have constituted long-standing translational approaches aimed at reducing melanoma growth and metastasis. Recent insights into mechanisms of immune regulation and tumour-immune cell interactions have helped to identify checkpoint molecules on immune (CTLA4, PD-1) and tumour (PD-L1) cells as promising therapeutic targets. Checkpoint blockade with antibodies to activate immune responses and perhaps to counteract melanoma-associated immunomodulatory mechanisms led to the first clinical breakthrough in the form of an anti-CTLA4 monoclonal antibody. Novel modalities to target key mechanisms of immune suppression and to redirect potent effector cell subsets against tumours are expected to improve clinical outcomes and to provide previously unexplored avenues for therapeutic interventions.

Influence of interferons corneal angiogenesis induced by basic fibroblast growth factor and lipopolysaccharide

A controlled and reproducible angiogenic stimulus was induced in the rabbit cornea by Elvax-40 implants sequestering either 500 ng of lipopolysaccharide (LPS) or 500 ng of basic fibroblast growth factor (bFGF). The effect of IFNα and IFN(β) on angiogenesis was studied by inserting implants sequestering 500 ng of these cytokines (approximately 10(4) Units/implant) adjacent to the LPS or bFGF implants. Interferon-α or γ did not inhibit the bFGF-induced angiogenesis, and in most of these experiments an enhancing effect was observed. This enhancement was not statistically significant. The LPS-induced angiogenesis, however, was slightly inhibited in the presence of either interferon-α or γ but these differences were not statistically significant with p=0.1 only. Both cytokines were non angiogenic and there was no detectable difference between them regarding their effect on the angiogenic process induced by either bFGF or LPS.

Therapeutic potential of mesenchymal stem cells producing interferon-alpha in a mouse melanoma lung metastasis model

Adult stem cells represent a potential source for cell-based therapy of cancer. The present study evaluated the potential of bone marrow-derived mesenchymal stem cells (MSC), genetically modified to express interferon (IFN)-alpha, for the treatment of lung metastasis in an immunocompetent mouse model of metastatic melanoma. A recombinant adeno-associated virus (rAAV) 6 vector encoding IFN-alpha was used to transduce mouse bone marrow-derived MSC ex vivo. Expression and bioactivity of the transgenic protein from rAAV-transduced MSC were confirmed prior to in vivo studies. A lung metastasis model of melanoma was developed by i.v. injection of B16F10 cells into 8-week-old C57BL/6 mice. Ten days later, MSC transduced with rAAV-IFN-alpha or green fluorescent protein were intravenously injected. One cohort of mice was sacrificed to determine the effects of the therapy at an earlier time point, and another cohort was observed for long-term survival. Results indicated that systemic administration of MSC producing IFN-alpha reduced the growth of B16F10 melanoma cells and significantly prolonged survival. Immunohistochemistry analysis of the tumors from MSC-IFN-alpha-treated animals indicated an increase in apoptosis and a decrease in proliferation and blood vasculature. These data demonstrate the potential of adult MSC constitutively producing IFN-alpha to reduce the growth of lung metastasis in melanoma.

Phase 2 trial of the continuous IV administration of interferon-beta in patients with disseminated malignant melanoma

BACKGROUND

Interferons have been reported to significantly contribute to tumor suppression via both induction of p53 gene expression and inhibition of angiogenesis.

OBJECTIVE

The assessment of treatment toxicity and antitumoral effectiveness of continuous IV administration of interferon-beta based on an overall evaluation of laboratory, radiographic, and clinical parameters observed during the trial.

METHODS

The authors treated patients with advanced malignant melanoma with continuous IV infusions of 1 x 10(6) IU interferon-beta daily ( approximately 0.6 x 10(6) IU interferon-beta/m2 daily).

RESULTS

Continuous IV administration of interferon-beta had no significant effect on overall patient outcome. Interferon side effects were not a reason for treatment discontinuation in any of the patients observed during this trial.

CONCLUSIONS

Continuous IV interferon-beta had no significant effect on overall patient outcome in a group of patients with advanced malignant melanoma. To our knowledge, this is the first report on the continuous IV administration of interferon-beta in patients with advanced malignant melanoma.

Cutaneous melanoma: interferon alpha adjuvant therapy for patients at high risk for recurrent disease

Systemic adjuvant therapy in melanoma patients is the systemic treatment that is administered with the goal of eradicating micrometastatic deposits in patients who are clinically free of disease after surgical removal of the primary melanoma, but with a high risk of systemic recurrence. Interferon-alpha (IFN-alpha) is one of the most frequently used adjuvant therapies. Several randomized trials evaluated the efficacy of IFN-alpha in melanoma patients. However, results from conducted trials are controversial. Twelve randomized IFN-alpha trials are discussed in detail. All trials, including meta-analysis, failed to demonstrate a clear impact of IFN-alpha therapy on overall survival in melanoma patients. Based on currently available evidence, IFN-alpha therapy in the adjuvant setting should not be considered standard of care for patients who have melanoma. Results from ongoing studies are awaited. Further research for this therapy is required.

Melatonin and immunomodulation: connections and potential clinical applications

Melatonin is the main hormone secreted by the pineal gland in the human brain. It has a strong impact on the sleep-wake cycle and is considered a general modulator of the human circadian rhythm. Apart from these well-established properties, melatonin possesses immunomodulatory, antioxidative and antiinflammatory properties. The potential ability of this hormone to act synergistically with several cytokines by enhancing their antitumoral activity and dramatically decreasing their adverse effects has placed melatonin among the new and promising agents in cancer immunotherapy. The use of the neurohormone alone or in combination with cytokines and traditional chemotherapeutic drugs is currently under vigorous investigation. Experimental and clinical trials have already depicted some of the immunomodulatory and antitumor effects of melatonin, delineating the need for further research in this field.

Lymphocyte subset distribution and cytokine secretion in third trimester decidua in normal pregnancy and preeclampsia

BACKGROUND

Excessive Th1 activity in peripheral blood plays a probable role in the pathogenesis of preeclampsia. The aim of the study was to investigate whether disturbed local immune reactions are also present in decidua.

METHODS

Flow cytometric analysis of CD3, CD19, CD56/CD16, CD4, CD8, CD4/CD29, CD4/CD45RA, CD4/CD45RO, CD8/CD28, CD3/CD69 lymphocyte subsets isolated from third trimester decidua of pregnants with preeclampsia (n=21) and pregnant controls (n=11) subjected to elective caesarean sections. Spontaneous and phytohemaglutynine stimulated "in vitro" secretion of IL-2, IL-4, IL-6, IL-10, IL-12, IFN-gamma and TGF-beta by decidual lymphocytes was studied by ELISA. For the statistical significance of differences between the groups the U Mann-Whitney test was performed (confidence interval P<0.05).

RESULTS

Preeclamptic patients were characterized with an increased percentage of the CD3-/CD56+CD16+, CD8+/CD28+ and decreased percentage of CD3+, CD19+, CD4+/CD45RA+ lymphocytes. The profile of secreted cytokines shifts in favor of Th1 activity (extremely high IFN-gamma and low IL-6 and IL-10 secretion). Decidual IL-12 secretion in preeclamptic patients is decreased compared to controls.

CONCLUSION

Changes in NK and T lymphocyte subsets followed with Th1 cytokine IFN-gamma over-activity, could affect local immunoregulatory mechanisms in third trimester decidua of preeclamptic patients.

Immune-endocrine interactions and Leydig cell function: the role of cytokines

Inflammatory disease is known to affect male reproductive function and fertility. Male accessory gland infections (MAGI) account for almost 15% of all cases of male infertility seen in infertility clinics. Infections of the male accessory glands are associated with increased counts of white blood cells in semen and elevated levels of pro-inflammatory cytokines in the semen and the testis. Numerous studies have underscored the importance of cytokines in the regulation of testicular and glandular function during pathophysiological events as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this paper is to particularly review the role of cytokines in the regulation of Leydig cell function in the testis primarily under pathophysiological conditions, and also considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Antiviral therapy: respiratory infections, chronic hepatitis

This review focuses on the activity, clinical pharmacology, and clinical indications of antiviral agents used in the management of influenza, respiratory syncytial virus infections, and chronic hepatitis B and C. Two neuraminidase inhibitors, a new class of antiviral agents, were recently approved for the treatment of influenza A and B in children.

Modulation of the IL-10/IL-12 cytokine circuit by interferon-beta inhibits the development of epitope spreading and disease progression in murine autoimmune encephalomyelitis

IFN-beta has been shown to be effective in the treatment of multiple sclerosis (MS). However, the primary mechanism by which IFN-beta mediates its therapeutic effect remains unclear. Recent studies indicate that under defined conditions, IFN-beta may downregulate DC expression of IL-12. We and others have shown that IFN-beta may also downregulate IL-10. In light of the recently proposed paradigm that an IL-10/IL-12 immunoregulatory circuit controls susceptibility to autoimmune disease, we examined the effect of IFN-beta on the development and behavior of the autoreactive T cell repertoire during experimental autoimmune encephalomyelitis (EAE), an animal model sharing many features with MS. SWXJ mice were immunized with the immunodominant p139-151 determinant of myelin proteolipid protein (PLP), and at onset of EAE were treated every other day with IFN-beta. After eight weeks of treatment, we assessed autoreactivity and observed no significant IFN-beta effect on splenocyte proliferation or splenocyte production of IFN-gamma, IL-2, IL-4, or IL-5 in response to the priming determinant used to initiate disease. However, in IFN-beta treated mice, the cytokine profile in response to the priming immunogen was significantly skewed toward an increased production of IL-10 and a concurrent decreased production of IL-12. Moreover, the in vivo modulation of the IL-10/IL-12 immunoregulatory circuit in response to the priming immunogen was accompanied by an aborted development of epitope spreading. Our results indicate that IFN-beta induces a reciprocal modulation of the IL-10/IL-12 cytokine circuit in vivo. This skewed autoreactivity establishes an inflammatory microenvironment that effectively prevents endogenous self-priming thereby inhibiting the progression of disease associated with epitope spreading.

Short-term treatment with interferon-alpha/beta promotes remyelination, whereas long-term treatment aggravates demyelination in a murine model of multiple sclerosis

The mechanisms by which type I interferons (IFN) reduce the rate and severity of exacerbations in multiple sclerosis are unknown. We utilized a model of multiple sclerosis to determine the extent of demyelination and remyelination in Theiler's murine encephalomyelitis virus (TMEV)-infected SJL/J mice treated with mouse IFN-alpha/beta for a short (5 weeks) or a long (16 weeks) period. All mice were chronically infected with TMEV to simulate the clinical situation in multiple sclerosis. Short-term IFN-alpha/beta treatment increased the percent of remyelinated spinal cord white matter by threefold when compared with phosphate-buffered saline (PBS) treatment (P < 0.02), but it did not affect the extent of demyelination. In contrast, long-term IFN-alpha/beta treatment increased the extent of demyelination by twofold (P < 0.03). Long-term treatment increased the absolute area of remyelination, but the percent remyelination as a function of area of demyelination was not changed because of increased demyelination. An immunomodulatory mechanism may have contributed to the effect of IFN-alpha/beta on white matter pathology because treated mice had higher anti-TMEV IgGs in serum and demonstrated decreased numbers of B and T lymphocytes infiltrating the central nervous system (CNS). There was no correlation between the level of anti- IFN-alpha/beta antibodies and the extent of demyelination or remyelination. These results indicate that the length of type I IFN treatment may have paradoxical effects on demyelination and remyelination.

Interferon beta-1a prevents the effects of lipopolysaccharide on embryonic brain microvessels

By means of light and electron microscopy we have studied the effect of interferon beta-1a (IFNbeta-1a) in the optic tecta of 20-day-old chick embryos under normal conditions and after exposure to lipopolysaccharide (LPS) which mimics the blood-brain barrier (BBB) disruption in meningoencephalitis. Optic tecta were examined for: (i) ultrastructure by means of transmission electron microscopy; (ii) the immunohistochemical localization of HT7 antigen, a specific marker of differentiation of the brain microvessels; (iii) the brain microvessel permeability, by means of horseradish peroxidase (HRP) tracer; (iv) the expression of microvessel glycoconjugates, by means of lectin histochemistry, using Ricinus communis agglutinin-I (RCA-I), specific for beta-D-galactosyl moieties and Wheat Germ agglutinin (WGA) specific for sialyl and N-acetylglucosaminyl moieties. A morphometric evaluation of brain microvessel permeability and of glycoconjugate expression was also performed. In control- and in IFNbeta-1a-treated embryos, HRP was confined to the vessel lumina which were sealed by the interendothelial tight junctions. RCA-I binding sites were recognizable both in the basal membranes and in the tight junctions, while WGA sites were present on the luminal side of the endothelial cells. HRP was blocked in the vessels lumina by the interendothelial tight junctions. After LPS treatment, HRP showed an extravascular localization and the labeling of microvessels by anti-HT7 antibodies disappeared. RCA-I binding was only found ultrastructurally and appeared as irregularly clustered gold particles, in the cleft of damaged tight junctions, but were no longer detectable in the endothelial basement membranes. After pretreatment of LPS-treated embryos with IFNbeta-1a, the vessel permeability to HRP strongly decreased and the vessels showed the normal pattern of HT7 protein and of the RCA-I binding sites. These results indicate that the changes induced by LPS in the endothelial cells are prevented by IFNbeta-1a.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Pharmacodynamics of recombinant IFN-beta during long-term treatment of malignant melanoma

The pharmacodynamics and biologic activities of recombinant human interferon-beta (rHuIFN-beta) derived from chinese hamster ovary (CHO) cells were examined during long-term therapy in 7 melanoma patients. The CHO-derived rHuIFN-beta was given s.c. in a dose of 3 x 10(6) U three times per week for 24 weeks. Serum levels of IFN could not be detected before and 48 h after the s.c. injections. 2'-5'-Oligoadenylate synthetase (2-5 OAS), beta 2-microglobulin, and neopterin levels increased significantly 48 h after application, with a maximum after 96 h. Subsequently, the values decreased and remained only slightly elevated during the long-term therapy. Natural killer (NK) cell activity increased in the first 96 h significantly and fell below pretreatment values after 4 weeks. The decrease of biologic response could not be attributed to the occurrence of anti-IFN-beta antibodies because only 2 of the 7 patients developed neutralizing antibodies after 16 and 24 weeks of treatment, respectively. This trial confirms the biologic potency of CHO-derived rHuIFN-beta. However, the selected parameters demonstrate that immunostimulation is only possible over a short treatment period.

The interferons

OBJECTIVE

To provide a review of the biology, pharmacology, clinical application, and toxic effects of interferon and strategies for nursing management.

DATA SOURCES

Research studies, review articles, and book chapters pertaining to interferons.

CONCLUSIONS

Interferons are active therapeutic agents for hairy cell leukemia, chronic myelogenous leukemia, melanoma, and acquired immunodeficiency syndrome-related Kaposi's sarcoma. Clinical trials continue to investigate the clinical application of interferons.

IMPLICATIONS FOR NURSING PRACTICE

Oncology nurses can facilitate patient self-care in managing side effects of interferon therapy, provide patient and family education, and assist with reimbursement concerns.

In vitro lymphocyte blastogenic responses and cytokine production in sickle cell disease patients with acute pneumonia

BACKGROUND

Pulmonary infections continue to be a major cause of morbidity and mortality in patients with sickle cell disease (SCD).

METHODS

In this study cell-mediated immunity in vitro was evaluated in 62 SCD patients (62 steady state and 16 with acute pneumonia) and compared with 44 normal controls (30 healthy and 14 with acute pneumonia). Lymphocyte blastogenic responses to phytohemagglutinin, tetanus toxoid and Candida albicans antigen were assessed in all subjects. In addition production of tumor necrosis factor, alpha- and gamma-interferon (IFN) were assayed.

RESULTS

The results revealed comparable blastogenic responses to all three stimuli in all subjects except SCD patients with pneumonia. This group showed poor responses to all stimuli. The mean counts per minute were decreased 65 to 90% when compared with the other patients. Cytokine production of IFN-alpha and TNF was equivalent in all subjects. Conversely IFN-gamma production in both SCD groups, steady state (35 +/- 6 U/ml) and SCD with pneumonia (14 +/- 6 U/ml), was significantly decreased when compared with those in normal healthy controls (65 +/- 14 U/ml) and with pneumonia (48 +/- 17 U/ml). On analysis of individual titers 15 of 62 (24%) steady state and 10 of 16 (63%) SCD patients with pneumonia were deficient in IFN-gamma production in vitro.

CONCLUSIONS

Acute pulmonary infections seem to have a profound effect on cell-mediated immunity in SCD. IFN-gamma deficiency, along with quantitative and qualitative T cell abnormalities, may represent significant factors to explain the frequent and severe infections seen in SCD.

Interferon-beta inhibits progression of relapsing-remitting experimental autoimmune encephalomyelitis

The results of two phase III clinical trials have recently shown that interferon-beta (IFNbeta) is effective in the treatment of relapsing-remitting multiple sclerosis (RRMS). Treatment with IFNbeta results in a significant decrease in the rate of clinical relapse and a marked delay in progression to disability compared to placebo-treated control patients. In the present study, we demonstrate similar therapeutic effects after treating (SWR X SJL)F1 mice with IFNbeta at the onset of clinical signs of experimental autoimmune encephalomyelitis (EAE), a disease animal model widely used in MS studies. EAE was actively induced by immunization of (SWR X SJL)F1 mice with the immunodominant encephalitogenic peptide 139-151 of myelin proteolipid protein (PLP). In blinded testing, mice treated with IFNbeta at EAE onset showed a delay in progression to clinical disability as determined by marked improvement with time in mean clinical score, significant delay in onset of relapse, and significant decrease in exacerbation frequency compared to placebo-treated control mice. The therapeutic effect of IFNbeta was accompanied by a significant inhibition of delayed-type hypersensitivity (DTH) but not proliferation in response to the priming PLP 139-151. In addition, IFNbeta treatment resulted in an overall decrease in severity of both inflammation and demyelination in the central nervous system. These results mimic in an autoimmune animal model the effectiveness of IFNbeta treatment observed in MS. Moreover, our study suggests that anti-viral properties of IFNbeta are not essential for producing therapeutic effects in autoimmune demyelinating disease, and that the efficacy of IFNbeta in the treatment of MS may be due to inhibition of autoreactivity.

Effects of type I-interferons on human thyroid epithelial cells derived from normal and tumour tissue

Long term interferon (IFN) therapy is frequently associated with side effects which affect the thyroid gland such as hypothyroidism and thyroiditis. We have therefore tested the ability of type I-IFNs to exert direct effects on primary cultures of human thyroid epithelial cells: (i) Type I-IFNs (IFN-alpha 2b and IFN-omega) inhibit cell proliferation as determined by [3H]thymidine incorporation with a half-maximal effect at approximately 1 ng/ml (50 pM). Inhibition of cell growth is observed in cells derived from normal thyroid as well as neoplastic tissue (autonomous and non-secreting adenoma; follicular, papillary and anaplastic carcinoma). (ii) Over a similar concentration range, type I-IFNs suppressed thyroglobulin release by thyroid cells. (iii) IFN-alpha 2b stimulated surface expression of major histocompatibility class (MHC) I but not MHC II molecules, while IFN-gamma enhanced the expression of both MHC I and MHC II molecules. This effect of IFN-gamma, but not that of IFN-alpha 2b was antagonized by suramin. (iv) Incubation of thyroid cells with IFN-alpha 2b also resulted in increased cell surface levels of the intercellular adhesion molecule 1 (ICAM-1). These findings demonstrate that type I-IFNs directly affect thyroid function and explain related side effects of these cytokines. In addition, our results provide a rational basis for the possible use of type I-IFNs in the treatment of patients with advanced thyroid cancer for whom no therapeutic alternative exists.

Deterioration of mixed cryoglobulinemia during treatment with interferon-alpha-2a

A 60-year-old female developed mixed cryoglobulinemia associated with liver cirrhosis caused by the hepatitis C virus. During treatment with rIFN-alpha-2a, deterioration of cryoglobulinemia was recognized. The possible mechanisms underlying the deterioration are discussed.

Interferon-gamma inhibits DNA synthesis and insulin-like growth factor-II expression in human neuroblastoma cells

Interferon-gamma (IFN-gamma) is known to be an antiproliferative, differentiating agent in many cell types, including neuroblastoma. In this study, we determined the effects of IFN-gamma on cellular growth and expression of insulin-like growth factor II (IGF-II) and IGF receptors in the human neuroblastoma cell line SH-SY5Y. Incubation of SH-SY5Y cells in IFN-gamma (20-100 U/ml) induced the formation of long neuritic processes. IFN-gamma treatment also induced decreases in [3H]TdR incorporation, as well as serum-dependent changes in cell number. Treatment with IFN-gamma reduced cell number 33% in the presence of serum but had no effect on cell number in the absence of serum. IGF-II mRNA content was 60% inhibited by IFN-gamma, and was not serum dependent. The concentration of immunoreactive IGF-II in SH-SY5Y conditioned medium was also reduced in the presence of IFN-gamma, to less than half of control levels. In contrast, type I IGF receptor mRNA content was increased more than three-fold after treatment with IFN-gamma and serum. Co-incubation in IFN-gamma (20-100 U/ml) and IGF-II (3-10 nM) prevented the inhibitory effects of IFN-gamma on [3H]TdR incorporation in serum-free media. Our results suggest that IFN-gamma may inhibit DNA synthesis and cell growth by interfering with an IGF-II/type I IGF receptor autocrine growth or survival mechanism.

Interferon-gamma modulates retinoblastoma gene mRNA in monocytoid cells

To study the effect of interferon gamma (IFN-gamma) on the expression of the retinoblastoma (RB) susceptibility gene, we performed Northern-blot analysis on RNA extracted from Wish, HEL and monocytoid cell lines U-937 and THP-1 treated with 1,000 IU/ml of recombinant IFN-gamma. In U-937 and THP-1 cells, IFN-gamma increased the abundance of RB mRNA. In Wish and HEL cells, co-treatment with cycloheximide was required for IFN-gamma to increase the level of RB mRNA. Pre-treatment of THP-1 cells with cycloheximide prior to IFN-gamma treatment augmented the effects of IFN-gamma on RB gene expression. The effect of IFN-gamma in THP-1 cells was observed after 3 hr of treatment, being more pronounced after 6 hr and persisting until at least 18 hr, although at a lower level. These results suggest that IFN-gamma regulates the level of RB mRNA by different mechanisms in the different cell types. This cytokine increases the abundance of RB mRNA in monocytoid cell lines, reinforced by prior treatment with cycloheximide. Inhibition of protein synthesis is required in Wish and HEL cell lines before IFN-gamma has an effect on RB gene expression.

Cytotoxic and cytostatic effects of antitumor agents induced at the plasma membrane level

A variety of antitumor agents inhibit cell proliferation by interacting with the plasma membrane. They act as growth factor antagonists, growth factor receptor blockers, interfere with mitogenic signal transduction or exert direct cytotoxic effects. The P-glycoprotein encoded by the MDR1 gene represents a transmembrane protein which catalyzes the efflux of various antitumor agents. This membrane protein is the target of compounds acting as Multi-Drug Resistance (MDR)-modulators. Finally, several established antitumor agents which are considered to represent DNA-targeted drugs, including anthracyclines, platinum complexes and alkylating agents, cause a variety of membrane lesions. Their contribution to the antitumor activity of these drugs is discussed.