Enhancement of interferon-induced 2-5 oligoadenylate synthetase activity by retinoic acid in human histiocytic lymphoma U937 cells and WISH cells

The GRIMs: a new interface between cell death regulation and interferon/retinoid induced growth suppression

Cytokines and vitamins play a central role in controlling neoplastic cell growth. The interferon (IFN) family of cytokines regulates antiviral, anti-tumor, antimicrobial, differentiation, and immune responses in mammals. Significant advances have been made with respect to IFN-induced signal transduction pathways and antiviral responses. However, the IFN-induced anti-tumor actions are poorly defined. Although IFNs themselves inhibit tumor growth, combination of IFNs with retinoids (a class of Vitamin A related compounds) strongly potentiates the IFN-regulated anti-tumor action in a number of cell types. To define the molecular mechanisms involved in IFN/retinoid (RA)-induced apoptosis we have employed a genetic approach and identified several critical genes. In this review, I provide the current picture of IFN- RA- and IFN/RA-regulated growth suppressive pathways. In particular, I focus on a novel set of genes, the genes-associated with retinoid-interferon induced mortality (GRIM). GRIMs may be novel types of tumor suppressors, useful as biological response markers and potentially novel targets for drug development.

Retinoic acid and interferon combination studies in human cancer

Retinoic acid and interferon-alpha have limited single-agent activity in advanced cancer. Cell culture data indicate that in combination these agents have enhanced activity (modulating growth and differentiation) in a number of malignant cell types. Recent clinical work in advanced squamous cell carcinoma reports major activity with this regimen. This paper reviews the preclinical and clinical data testing retinoic acid in combination with interferons and presents recent work integrating these agents with radiotherapy in locally advanced cervical cancer.

Effects of interferon-gamma and its interaction with retinoic acid on human neuroblastoma differentiation

Differentiation-promoting effects of interferon-gamma (IFN-gamma), both alone and in combination with retinoic acid (RA), were studied on the human neuroblastoma cell line, LA-N-5. The results show that IFN-gamma inhibited the growth and induced morphological differentiation in a dose- and time-dependent manner with measurable effects appearing at 20-40 IU/ml after 3 to 4 days of treatment in vitro. Acetylcholinesterase activity, used as a biochemical index of neuroblastoma differentiation, increased up to 2.5-fold in the presence of IFN-gamma with a half maximal concentration of approximately 100 IU/ml. Concomitantly, modest IFN-induced increases (less than or equal to 2-fold) in choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) activities were seen. Combination treatment of cells with IFN-gamma and RA resulted in synergistic effects on morphological differentiation, growth inhibition and induction of ChAT. Reversal of IFN-gamma's ability to influence neuroblastoma cell growth as well as potentiate the anti-tumor effects of RA was obtained in the presence of an antibody against the IFN-gamma receptor, implying receptor-mediated physiological events. Taken together, these data confirm the differentiating effects of IFN-gamma on human neuroblastoma cells and suggest that combination therapy with RA may be beneficial in the treatment of this disease.

Differential modulating effects of retinoic acid on interferon antiviral activity

The effect of retinoic acid (RA) on the antiviral activity of interferons (IFNs) alpha and beta in the U937 and WISH cells was examined to ascertain whether or not RA could reduce the effectiveness of IFN-induced resistance to viral infection. Our results indicate that in the U937 cells, RA (0.1-1.0 microM) had neither enhancing nor suppressive effect on the antiviral activity of IFN-alpha or beta against the Semliki Forest virus (SFV). However, in the WISH cells, RA had different effects on IFNs alpha and beta. Thus, while RA (0.1-50 microM) invariably suppressed the activity of IFN-alpha, it enhanced the action of IFN-beta at low dose (0.1-1.0 microM) but became suppressive at higher concentrations (greater than or equal to 10 microM). Furthermore, higher antiviral activity was consistently obtained when RA (0.1-10 microM) was added prior to either IFN-alpha or IFN-beta comparing to cultures with IFN alone. In addition, direct correlation between antiviral activity and the amplitude of 2-5 oligoadenylate (A) synthetase activity was not observed. These results suggest that modulation of IFN antiviral activity by RA varies with different systems and is dependent on the sequence of treatment.