In vitro chemosensitivity of lymphoblasts at relapse in childhood leukemia using the MTT assay.

Lymphoblasts from 21 previously untreated patients with acute lymphoblastic leukemia (ALL) and 31 patients in relapse were tested for chemosensitivity. Blast cells were cultured with 22 anticancer drugs for 4 days and assayed by MTT dye using a scanning microplate photometer. The percent cytotoxicity index (%CI) and LD50 (micrograms/ml) were calculated for each drug. The mean absorbances (+/- S.D.) of 1 x 10(5) cells in the untreated group and relapsed groups in control wells were 0.219 (+/- 0.126) and 0.385 (+/- 0.147), respectively (p less than 0.01). Cells in the untreated group were more sensitive in vitro to vincristine, prednisolone, L-asparaginase (L-ASP), vinblastine, 5-fluorouracil, epirubicin, bleomycin (BLM), and etoposide (VP16) with respect to the %CI value and to L-ASP, VP16, BLM, and mitoxantrone with respect to the LD50 value than those in the relapsed groups. In contrast, no significant differences were observed for the other 13 drugs. There was also a significant difference in sensitivity within the relapsed group--13 having good clinical response and 15 showing no response to chemotherapy--with regard to four drugs, mitomycin C, neocarzinostatin, L-ASP, and teniposide. Cells in the relapsed group had more heterogeneous chemosensitivity than those in the untreated group, and divided into sensitive and resistant types, but large interindividual differences existed. The MTT assay and LD50-drug resistance percentile curves are useful for the selection of effective drugs in both untreated and relapsed patients with acute leukemia.