ENHANCING EFFECT OF NEW BIOLOGICAL RESPONSE MODIFIER SULFOETHYLATED (1→3)-β-D-GLUCAN ON ANTITUMOR ACTIVITY OF CYCLOPHOSPHAMIDE IN THE TREATMENT OF EXPERIMENTAL MURINE LEUKOSES
Aim: One of the advanced methodologies of the tumor therapy is the application of the so-called biological response modifiers used for activation of the endogenous antitumor mechanisms and combined with classical cytotoxic agents. The aim of this work was the investigation of the effect of sulfoethylated (1→3)-β-D-glucan (SEG) in the treatment of experimental murine leukoses in combination with cyclophosphamide (CPA) and its ability to modulate the activity of lysosomal enzymes in tumor tissues. Materials and Methods: The solid forms of inoculated murine leukoses P388 and L1210/1 were transplantated to male DBA/2 mice. The therapy was performed by treating animals with CPA (Biokhimik, Saransk, Russia) alone or in combination with SEG (Institute of Chemistry, Slovak Academy of Sciences, Slovakia). CPA was administered in saline as a single intraperitoneal (ip) injection on the 10th day after tumor transplantation; SEG was administered to mice ip 3 days after tumor transplantation with the intervals in 3 days. The therapy effect was estimated by measuring of solid tumor volume. Activity of the cysteine proteases — cathepsins B and L — was measured fluorometrically using fluorescent substrates Z-Arg-Arg-MCA and Z-Phe-Arg-MCA (Sigma, USA), respectively. The apoptosis was estimated evaluating the number of cells with fragmented nuclei using optical microscope. Results: It has been demonstrated that application SEG leads to inhibition of tumor growth and potentiates therapeutic action of CPA, especially at repeated administrations during the whole treatment/observation At addition of SEG, therapeutic effect of a one-half reduced dose of CPA is equal or higher than that of the full dose. Therapeutic action of CPA and SEG on the studied tumors is realized predominantly through induction of apoptosis and is accompanied by a substantial increase of the activity of cysteine proteases cathepsins B and L in tumor tissues. The highest cathepsin B and cathepsin L activity in tumor tissue accompanied with the strongest inhibition of tumor growth. It is suggested that this phenomenon is due to the infiltration of the macrophages rich in the named enzymes into the tumor, where they phagocytize the apoptotic cells and tissue debris. Conclusion: Utilization of this polysaccharide BRM, sulfoethylated (1→3)-β-D-glucan, might potentially enhance efficiency of antitumor therapy with standard cytostatics without a need of substantial increase of their dosage and hence avoiding their toxic side-effects.
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