Abstract
Abstract 2049
Poster Board II-26
Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to calechiamycin, gemtuzumab ozogamicin (GO), is used for the treatment of AML. We demonstrated that the response of AML cells to GO treatment also depends on Syk and SHP-1 expression (Leukemia 20:2093, 2006). Syk upregulation by the demethylating agent 5-azacytidine (5-aza) induced re-expression of Syk in some cases, resulting in enhanced GO and anti-CD33-mediated inhibition of leukemia cell growth. Thus, the cytotoxicity of both GO and anti-CD33 in primary AML samples was associated with Syk expression. 5-Aza restored Syk and increased the sensitivity of originally Syk-negative, non-responsive cells to CD33 ligation to levels of Syk-positive cells. We designed a clinical trial examining if treatment with 5-aza prior to GO is safe, efficacious, and whether in vivo responses to GO correlated with Syk expression and induction by 5-aza. Here we report the interim results of this trial. In Phase I, 14 patients (9 males [7 Caucasian, 1 Asian, 1 Hispanic], 5 females [2 Caucasian, 3 Asian], age range: 39-82 years [median: 66]) were treated with 75mg/m2 5-aza and GO in a dose-escalation manner: the first cohort (n=3) received 5-aza for 2 days followed by GO at 3 mg/m2 on days 3 and 17; the second cohort (n=3) received 5-aza for 2 days followed by GO at 6 mg/m2 on days 3 and 17; the third cohort (n=4) received 5-aza for 4 days followed by GO at 6 mg/m2 on days 5 and 19; and the fourth cohort (n=4) at 5-aza for 6 days followed by GO at 6 mg/m2 on days 7 and 21. No dose-limiting toxicities have been encountered. There were no responses in the first two cohorts (5 patients in 1st rel, 1 in 2nd rel at start of treatment); one patient in cohort 3 achieved a CR (in 1st relapse), two in cohort 4 have achieved CR (1 in 1st rel and 1 in 2nd rel). We are in Phase II of the study: Cohort 4 dose 5-aza for 6 days followed by GO at 6 mg/m2 on days 7 and 21. Patients remained on study until ANC recovered to 1000/mm3 for 3 consecutive days and were assessed for response to treatment. Average time to ANC recovery (n=6) 30 days (range 15-42) (median 33 days). Average length of time on study: 46 days. Prior to therapy, Syk was expressed in 10 of the 13 cases (baseline data not available on one case). After 5-aza treatment, Syk was re-expressed in each of the 3 negative cases, and increased over baseline in one case that was previously Syk +. SHP-1 was positive in 10 of the 13 cases and was re-expressed in each of the 3 negative cases. The leukemia cells from the patients who achieved CR were Syk+ in 2 of 3 cases. Syk was re-expressed in the one negative case after 5-aza. SHP-1 was expressed in 2 of 3 cases at baseline, and re-expressed in the one negative case after 5-aza. In vitro we analyzed inhibition of proliferation (for patients 1-6) or colony formation (for patients 7-14) induced by 5-aza and GO treatment. In all cases 5-azacytidine alone mediated about 50%, and GO alone about 40% cytotoxicity. Together they killed about 80% of leukemia cells. We also compared pre- and post 5-aza samples from the same patients: in all cases 5-aza treatment increased the GO-mediated cytotoxicity. These initial data show that in vivo exposure to 5-aza can induce the expression of two biomarkers involved in the intracellular response to GO. Correlations with response will be made in the Phase II portion of the study now underway.
Disclosures:
Ball: Celgene: Research Funding. Off Label Use: 5-azacytidine used in treatment of AML.
Genomic Encyclopedia of Type Strains, Phase I: The one thousand microbial genomes (KMG-I) project