Development of MeCCNU-resistance in clonally derived lines of Lewis lung carcinoma

Establishment of drug resistance in human gastric and colon carcinoma xenograft lines

We established multidrug-resistant human gastric and colon xenograft lines by means of intratumoral injections of four agents, doxorubicin (DXR), cisplatin (CDDP), 5-fluorouracil (5-FU) and mitomycin C (MMC), into subcutaneous SC1NU and SW480 tumors once a week or less. Such intermittent drug exposure is commonly used in clinical chemotherapeutic protocols. All xenograft lines acquired resistance to the injected drugs as evaluated by in vivo drug-resistance tests. Many of the drug-resistant lines showed various patterns of cross resistance to other drugs. In order to analyze the mechanism of resistance in vivo, we investigated the expression of drug resistance gene, which has been extensively studied in vitro. We used four complementary DNAs (cDNAs) for multidrug resistance (MDR1), glutathione S-transferase-pi (GST-pi), thymidylate synthase (TS) and dehydrofolate reductase (DHFR), as probes. We observed GST-pi, DHFR and TS mRNA expression at various levels, but MDR1 mRNA expression was found only in SW480/DXR by the method of poly (A+) RNA selection. Four resistant SW480 lines had higher TS mRNA expressions. Six resistant lines had stronger GST-pi mRNA expression. Five resistant lines had higher DHFR mRNA expression. Drug resistance genes related to the treated drug were also expressed in this in vivo model; MDR1 in SW480/DXR, GST-pi in SW480/CDDP and in SC1NU/CDDP and TS in SW480/5-FU. In contrast to in vitro resistant lines which have been reported as models of drug resistance, the expression of drug resistance genes in vivo was not always correlated to the acquisition of cross resistance. These resistant xenograft lines and the methods developed to induce drug resistance in vivo should be useful for studies on the mechanism of drug resistance in the clinical setting.

Development of drug resistance in a human epidermoid lung carcinoma xenograft line

The development of resistance to vincristine, actinomycin D and cisplatin has been examined in a human epidermoid lung carcinoma xenograft line (HXL 55) growing in nude mice. Treatment of HXL 55 with 1 mg kg-1 vincristine or 0.5 mg kg-1 actinomycin D once in each in vivo passage resulted in a rapid reduction in tumour responsiveness to these drugs. A partial resistance was already acquired at the 2nd transplant generation. In contrast, a gradual decrease in therapeutic response was observed with 10 mg kg-1 cisplatin. Irradiation with a local dose of 10 Gy induced no resistance. The three induced drug-resistant sublines were characterized in terms of the time course of development of resistance, the degree of induced resistance, cross-resistance, growth rate and stability of the phenotype.