The exponentially growing acute lymphoblastic leukemia cell line, MOLT-4 cells, was cultured with or without a CDK2 inhibitor, GW8510 or Chk2 inhibitor II, for 6 h, and phosphorylation of pRB was evaluated by site-specific phospho-serine/threonine antibodies (Fig. 3B). Here, RB1 is linked to acute lymphoblastic leukemia.