Ara-C cytotoxicity and Ara-CTP accumulation.

(A) Ara-C sensitivity (LC₅₀ Ara-C in μg/mL) of leukemic cells from infants (n = 9) and older children (noninfants) (n = 14) with newly diagnosed acute lymphoblastic leukemia (ALL). (B) Ara-CTP accumulation (pmol/10⁶ cells) in leukemic cells from infants (n = 15) and older children (n = 8) with ALL upon ex vivo exposure to 1 μM of Ara-C for 24 hours. The lines indicate the median values; and ○, individual patients.