Feasibility Study of a Dose Dense Induction Regimen of High Dose Cytarabine (HiDAC) and Gemtuzumab Ozogamicin (Mylotarg™) for Newly Diagnosed Elderly Patients with Acute Myeloid Leukemia.

Elderly patients with acute myeloid leukemia (AML) are known to have higher relapse rates due to the failure to overcome drug resistance. In an attempt to overcome this we conducted a Phase I study of a dose dense regimen of two cycles of HiDAC and Mylotarg^TM as sole therapy in newly diagnosed AML patient’s ≥60 years. HiDAC was administered in a dose escalation pattern: 3000mg/m² intravenously for 6 (cohort 1) and 9 (cohort 2)doses, and Mylotarg^TM was infused at 6mg/m² intravenously on days 1 and 8 of each cycle. All patients received G-CSF 5mcg/kg/day subcutaneously from days 11–14 until count recovery. Nine patients were enrolled, six patients in cohort 1 and three patients in cohort 2. The mean age in this study was 68 years, 90% patients were white, there were 6 male and 3 female patients. Four patients had de novo AML while 5 patients had secondary AML (four with prior MDS, one with prior alkylator therapy). Of these 9 patients, 6 patients achieved a CR or CR_P i.e. overall response rate of ~ 67%. The median duration of response was 6 months. Two patients who received 9 doses of HiDAC developed neurotoxicity after the sixth dose of HiDAC and thus required to have dose of cytarabine reduced to 100mg/m² for second cycle. All 9 patients had grade IV cytopenias as expected. Thrombocytopenia was a major issue with one patient developing hemorrhagic cystitis, two patients with broncho-alveolar hemorrhage and one patient with gastrointestinal bleeding. Only one patient died within 30 days of treatment from disseminated aspergillosis infection and multiorgan failure response was evaluable. No veno-occlusive disease was seen in any of these patents treated with two cycles of HiDAC and Mylotarg^TM. Given the profound hematologic and neurologic toxicity in this elderly group of patients the trial has been rewritten using prolonged infusion gemcitabine at 10mg/m²/min intravenously over 6,9,or 12 hours (depending on the cohort patient will be assigned to) after Mylotarg^TM 6mg/m² infusion. Currently we are evaluating the possible mechanisms for drug toxicity and resistance in these nine elderly AML treated with HiDAC and will present these data. Using primary leukemic cells obtained from these patients, real-time quantitative polymerase chain reaction is being utilised to measure mRNA levels of enzymes involved in the metabolism of cytarabine namely, deoxycytidine kinase, cytidine deaminase, 5′nucleotidase, ribonucleotide reductase, DNA polymerases alpha and beta, and also for levels of hENT1 transporter protein which is responsible for the intracellular transport of cytarabine. Western Blot technique will be utilized to determine the levels of expression of four major proteins, namely, LRP, MRP, GSTP1 and MRP-1, and of proteins associated with apoptosis and cell survival, such as, bcl-2, bax, p53. GSTP1 genetic polymorphism will be determined using an allele-specific TaqMan PCR assay. Apoptosis will be quantified using the TUNEL assay and by flow cytometry following propidium iodide staining.