Animal Model of Drug‐Resistant Tumor Progression

Abstract

Experimental animal model of tumor progression based on mice lymphosarcoma (LS) and resistant lymphosarcoma (RLS) has been developed. LS tumor displays high sensitivity to cyclophosphamide, which is widely used in anticancer therapy. RLS tumor was derived from LS by passaging in mice receiving low concentration of cyclophosphamide (20 mg/kg) and display resistance to cyclophosphamide (up to dose 150 mg/kg). The primary cultures of LS and RLS tumors display different expression levels of the genes related to apoptosis and multiple drug-resistant phenotype: in RLS tumor high levels of mdr1b and bcl-2 genes and low level of p53 gene expression were found. A total of 10% of cells in RLS primary culture display multiple drug-resistant phenotype and survive even at high dose of cytostatics. Cultivation of RLS primary culture in the presence of increasing vinblastine concentrations gives RLS(40) cell culture, which exhibits high levels of mdr1a/1b genes expression as compared to RLS and 20-fold increase of resistance to cytostatics. Drug-resistant RLS(40) cells were transplanted into CBA mice and sensitivity of the tumors to anticancer drugs was tested. RLS(40) tumors were resistant to a number of cytostatics used in anticancer therapy (cyclophosphamide, cysplatin, vinblastine, rubomycinum). Thus, RLS(40) tumor can be used as model, which corresponds to tumor status observed in patients after one or several courses of chemotherapy and can be useful for testing conventional therapy alone or together with newly developed gene-targeted therapeutics.

Ribonuclease binase inhibits primary tumor growth and metastases via apoptosis induction in tumor cells

“…26 Cytotoxic effect of binase on the RLS 40 cells is manifested in a similar way, and a lower percentage of apoptotic cells in a population of the RLS 40 cells may be associated with increased expression of the genes bcl-2 and mdr-1b. 27 Obtained data shows that there is a direct correlation between the sensitivity of tumor cell and inhibition of metastases development up to 50% on LLC and RLS 40 and up to 70% on B-16 melanoma models (Figs. 1, 2 and 4).…”

“…To elucidate the binase potential against tumors of various histological types, lymphosarcoma RLS 40 exhibiting MDR phenotype, 27 which forms the primary tumor site and is capable of metastasizing the liver, was further studied. One of the important objectives of this experiment was to assess whether the observed therapeutic effect of binase can be enhanced with the increase in a dosage of the enzyme up to 5 mg/kg.…”

Morphologic Changes in the Tumor and Liver in Mice with Transplanted RLS40 Lymphosarcoma during Increase of Its Drug Resistance

“…Drug-resistant murine lymphosarcoma RLS 40 was transplanted to animals. This tumor initially exhibits the MDR phenotype corresponding to the tumor status in patients after chemotherapy or to the status of a tumor initially resistant to standard PCT protocols used as the fi rst line therapy in the majority of hematological malignancies [7].…”

“…The resistance of tumor cell to PCT can result from a variety of processes from reduced intracellular concentration of antitumor drug because of substance release into extracellular space by P-glycoprotein (Pgp; ATP-dependent transmembrane protein), MDR1 gene product, to disorders in the apoptosis mechanisms in tumor cells (p53 gene mutation or defi cit, impairing its proapoptotic function) and/or hyperexpression of bcl-2 gene, causing insensitivity of cells to proapoptotic stimuli [7].…”

Cyclophosphamide metabolite inducing apoptosis in RLS mouse lymphosarcoma cells is a substrate for P-glycoprotein

“…P-glycoprotein, a product of mdr1a/1b genes, acts as a transmembrane pump and participates in the formation of the multiple drug resistance phenotype due to active drug elimination from tumor cells. However, the expression of mdr1a/1b genes belonging to ABS transporter gene family in RLS tumor cells 6-fold surpasses that in the parent LS cells [13]. However, during repeated in vivo passages of the tumor, bcl-2 + phenotype was lost and the expression of this gene returned to the level observed in LS cells.…”