In vitro chemosensitivity assessed with the MTT assay in childhood acute non-lymphoblastic leukemia.

Cellular drug resistance is supposed to play a major role in chemotherapy failures which frequently occur in childhood acute non-lymphoblastic leukemia (ANLL). Therefore, we determined in vitro chemosensitivity to daunorubicin, doxorubicin, mitoxantrone, 6-thioguanine, etoposide, and cytosine arabinoside (Ara-C) in childhood ANLL using the colorimetric MTT assay. The 4-day MTT assay was successfully performed in 62/73 samples obtained from 53 children with ANLL. We obtained comparable results from bone marrow or peripheral blood samples, and from fresh or cryopreserved samples. In vitro chemosensitivity was not related to clinical features such as sex, age, white blood cell count, or FAB-types. The group of poor responders to chemotherapy was median 3-fold more resistant to Ara-C than the group of good responders, but identification of a threshold for Ara-C sensitivity predictive for individual responses was limited due to the great overlap of in vitro chemosensitivities between both groups. Children with relapsed ANLL were in vitro median 3-fold more resistant to Ara-C than the initial ANLL group. No significant differences for the other drugs were observed with respect to clinical response or disease status. These results suggest that in vitro resistance to Ara-C plays an important role in chemotherapy failures in childhood ANLL, but larger studies are necessary to establish the predictive value of Ara-C sensitivity assessed with the MTT assay.