Pharmacodynamic Study of Phase 1/2 Trial of the XIAP Antisense Oligonucleotide (AEG35156) in Combination with Chemotherapy in Patients with Relapsed/Refractory AML.

XIAP, a potent cellular inhibitor of caspases 3 and 9, is highly expressed in various malignant cells including AML cells and contributes to chemoresistance. A phase 1/2 trial of the XIAP antisense oligonucleotide AEG35156 in combination with chemotherapy in AML patients in first relapse after a short (< 6 months) initial CR or with primary refractory disease was conducted (Schimmer A et al., abstract #, ASH 2008). Here we report the pharmacodynamic studies of patients in this trial treated at M. D. Anderson Cancer Center. A total of 13 patients were treated at our institution: 5 in the phase 1 study with escalating doses of AEG35156 (12mg/m² to 350 mg/m²) and 8 in the phase 2 study with a fixed dose of AEG35156 (350 mg/m²). Patients in both phases were treated with AEG35156 on days 1–3 by IV infusion over 2 hours followed by idarubicin on days 4–6 (12mg/m² over 30 min) and cytarabine (1.5g/m² by continuous infusion) on days 4–7 (patients age < 65) and days 4–6 (patients ≥ 65 years). AEG35156 was continued weekly for 4 weeks following re-induction chemotherapy. Blood samples were collected from each patient at screening, days 1–5 before the daily treatment, and day 28–35 post chemotherapies. XIAP mRNA levels (patients 102, 105, 106, 107, 109, 110, and 111) were determined in CD3/CD19-depleted mononuclear cells by real time RT-PCR. Apoptosis induction in RBC-lysed whole blood (all the patients except 105, 109, 113, and 114) was measured by Annexin V positivity and/or changes in mitochondrial membrane potential (MMP) whenever samples were available. XIAP mRNA knockdown was evident with increasing doses of AEG35156. No decrease of XIAP mRNA was found in patient 102 (dose 24 mg/m²) who did not respond to the treatment, while more than 60% of XIAP mRNA reduction was detected in patient 105 (dose 165 mg/m²) who achieved CR. XIAP mRNA was knocked down significantly in all phase 2 patients analyzed. XIAP mRNA levels were reduced by 90% or more in patients 106, 107, 109, and 110 and about 50% in patient 111. Importantly, 3 of these 5 patients achieved CR (107, 110, and 111). No apoptosis induction was detected in patients 101 (dose 12 mg/m²) and 102. A large increase of MMP-low but not of Annexin V positive cells by AEG35156 alone was detected in patient 103 (dose 48 mg/m²) especially in the CD34+38- stem cell compartment. Interestingly, apoptosis was induced by AEG35156 alone in patient 104 (dose 48 mg/m²) measured by both Annexin V positivity (33.6% on day 3 versus 14.7% on day 1 before the treatment) and changes in MMP (45.3% on day 3 versus 31.0% on day 1 before the treatment). Again, the induction was more pronounced in CD34+38- stem cells than CD34+38+ progenitor cells and bulk leukemic cells. Among the phase 2 patients, no induction in apoptosis was found in patient 106. Although no apoptosis induction was detected in bulk leukemic cells and CD34+38+ progenitor cells in patients 107, 110, and 111, a major induction in apoptosis was found in CD34+38- stem cells of all these three patients on day 2, 24 hours after first AEG35156 infusion. It is noteworthy that all three patients achieved CR with the treatment. Profound apoptosis induction was observed on day 2 in bulk as well as progenitor and stem cells in patient 115 and the patient achieved CR after one induction course. In summary, AEG35156, at the dose of 350 mg/m², is effective in knocking down XIAP mRNA levels in circulating blasts. This is accompanied by the induction of apoptosis preferentially in the CD34+38- stem cell compartment. This observation needs to be further investigated when more patients are evaluated. Knockdown of XIAP has to be confirmed at the protein levels in future studies.