17-DMAG Tested Again in CLL

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[2101] The Geldanamycin Derivative DMAG Demonstrates Improved

Cytotoxicity and Down-Modulation of Hsp90 Client Proteins Relative to

17-AAG in Chronic Lymphocytic Leukemia (CLL) Cells: Justification for

Clinical Trials in CLL. Session Type: Poster Session, Board #279-II

Amy J. , Amy J. Wagner, L. , M. Lucas,

D. De Lay, M. , S. Percy Ivy, S. Lin, C.

Byrd Comprehensive Cancer Center, The Ohio State University,

Columbus, OH; Cancer Therapy Evaluation Program, National Cancer

Institute, Rockville, MD

The heat shock protein Hsp90 functions to stabilize important cell

survival- and proliferation-related kinases such as AKT, IKK, c-Src,

Raf-1, and cdk9. Cancer cells have activated Hsp90 as compared to

normal cells, making this a relevant therapeutic target to eliminate

these kinases.

The semi-synthetic geldanamycin derivative 17-allylamino-17-

demethoxygeldanamycin (17-AAG) binds to and inhibits the activity of

Hsp90, and previous work demonstrated the ability of 17-AAG to

deplete AKT in several cancer types in vitro. A newer geldanamycin

derivative, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin

(DMAG) has improved pharmacological properties including solubility

and oral bioavailability, and was shown to be more effective than 17-

AAG in melanoma and pancreatic carcinoma mouse xenograft mouse

models.

We therefore examined the effects of 17-AAG and DMAG against CD19-

positive tumor cells from CLL patients. Cell viability was examined

by the MTT assay, and AKT and IKK protein expression was examined by

immunoblot analysis. In samples from seven CLL patients, 1.0uM DMAG

resulted in 31.5% viability (95% CI: 13.1-50.0%), compared to 61.5%

viability (95% CI: 45.0-78.0%) using the same concentration of 17-

AAG. In four CLL patient samples treated with 1.0uM DMAG for 24

hours, AKT was decreased an average of 72.5% (95% CI: 57.7-87.3%)

relative to the untreated controls. This is in comparison to 1.0uM 17-

AAG, which caused a 52.7% decrease in AKT (95%CI: 39.7-65.6%). IKK

protein was also decreased at similar levels in all patient samples

examined. This data indicates that in CLL cells, DMAG has superior

activity both in cytotoxicity and in reduction of relevant Hsp90

client proteins. 17-AAG is currently undergoing Phase I clinical

testing in CLL, and DMAG is completing phase I clinical development

in solid tumor malignancies.

Overall, our data and that of others support clinical development of

DMAG in CLL, based on the improved pharmacologic properties, enhanced

efficacy relative to 17-AAG, and expected down-regulation of target

proteins. In addition, our in vitro observations support using

measurement of protein down-regulation of AKT and IKK as

pharmacodynamic biomarkers of activity in patients undergoing therapy

with these agents.