A 42-year-old woman with newly diagnosed acute myeloid leukaemia (AML) is started on chemotherapy with daunorubicin and cytarabine. After 5 days of therapy, peripheral blood shows a marked reduction in blast cells. A bone marrow biopsy reveals numerous apoptotic bodies within myeloid precursors. Which of the following best explains the mechanism of chemotherapy-induced apoptosis in these leukaemic cells?