Effectiveness and toxicity of protracted nitric oxide synthesis inhibition during IL-2 treatment of mice
W E Samlowski1, C Y Yim, J R McGregor
1University of Utah Cancer Immunotherapy Program, University of Utah School of Medicine, Salt Lake City, USA.
Abstract:
The current study was designed to characterize nitric oxide (NO.) synthesis during interleukin-2 (IL-2) treatment of mice, and to determine whether NO. mediated IL-2-induced "vascular leak." We developed a technique for chronic subcutaneous infusion of the NO. synthase inhibitor N omega monomethyl-L-arginine (MLA) via osmotic minipump to aid in further study of these processes. After IL-2 administration to C3H/HeN mice (180,000 IU i.p. b.i.d. for 5 days), NO. synthesis increased two-to-three fold, peaking on days 5-8. Administration of MLA reduced NO. synthesis in both IL-2-treated mice (from 2.7 to 1 microM/mouse/day), and normal mice (from 1 to 0.5 microM/mouse/day). This agent decreased IL-2-induced radiolabeled albumin accumulation in the liver after i.p. IL-2 administration (p < 0.02). MLA infusions resulted in minimal systemic toxicity in mice, as reflected by complete blood counts or serum chemistries. MLA also did not impair lymphokine-activated killer cell induction in vitro or in vivo, or alter IL-2-induced tumor responses in a 3-day pulmonary metastasis model. These experiments demonstrated that NO. is a mediator involved in the genesis of vascular permeability induced by IL-2 treatment. Studies designed to further evaluate the toxicity and usefulness of MLA infusions to modify this IL-2 induced toxicity appear to be warranted.
Insights
Nitric oxide (NO) synthesis increases with interleukin-2 (IL-2) treatment, contributing to vascular leak. The NO synthase inhibitor N omega monomethyl-L-arginine (MLA) reduced this leak without significant toxicity or impacting anti-tumor effects.
Area of Science:
- Immunology and Pharmacology
- Vascular Biology
Background:
- Interleukin-2 (IL-2) is a cytokine used in cancer therapy.
- IL-2 treatment can induce significant vascular leak, a dose-limiting toxicity.
- The role of nitric oxide (NO) in IL-2-induced vascular permeability is not fully understood.
Purpose of the Study:
- To characterize NO synthesis during IL-2 treatment in mice.
- To determine if NO mediates IL-2-induced vascular leak.
- To evaluate the efficacy and safety of a NO synthase inhibitor, N omega monomethyl-L-arginine (MLA), in mitigating IL-2 toxicity.
Main Methods:
- Chronic subcutaneous infusion of MLA using osmotic minipumps in C3H/HeN mice.
- Measurement of NO synthesis levels before and after IL-2 administration.
- Assessment of IL-2-induced vascular permeability using radiolabeled albumin accumulation in the liver.
- Evaluation of MLA's systemic toxicity via complete blood counts and serum chemistries.
- Analysis of MLA's impact on lymphokine-activated killer (LAK) cell induction and IL-2-mediated anti-tumor responses in a metastasis model.
Main Results:
- IL-2 administration significantly increased NO synthesis (two-to-three fold) in mice.
- MLA administration effectively reduced NO synthesis in both normal and IL-2-treated mice.
- MLA significantly decreased IL-2-induced radiolabeled albumin accumulation in the liver (p < 0.02).
- MLA infusions exhibited minimal systemic toxicity and did not impair LAK cell induction or IL-2 anti-tumor efficacy.
Conclusions:
- NO is a key mediator of IL-2-induced vascular permeability.
- MLA is a promising agent for reducing IL-2-induced vascular leak with minimal toxicity.
- Further studies on MLA infusions to mitigate IL-2 toxicity are warranted.
