Pharmacological and Pharmacokinetic Evaluation of AST-202, CD25-Targeted Aptamer Conjugated with Anti-Mitotic MMAE Warhead for the Treatment of Hematological Malignancies

CD25 is an alpha subunit of IL-2 receptor that is overexpressed in various hematological malignant conditions. Evidences for meta-analysis and literatures indicate that the abnormal expression of CD25 is closely associated with poorer outcome and prognosis in lymphoma and leukemia patients. AST-202 is the novel micellar aptamer-drug conjugate (ApDC) composed of CD25-targeting aptamer precisely conjugated with 3 anti-mitotic MMAE warhead which is delivered to eliminate CD25-expressing leukemic/lymphoblastic cells.

Strong amphiphilic nature due to add 3 hydrophobic drugs at the end of an aptamer led AST-202 to self-assemble into a spherical micellar structure with hydrodynamic radius ~180nm (hydrophobic drug core and hydrophilic aptamer surface).

Interestingly, when the in vitro plasma stability of aptamer-MMAE linkage was monitored by measuring the released MMAE over a 4-day period, the amount of MMAE released was only less than 1% in AST-202 while the aptamer with a single MMAE lost 50~60% of its payload within 4 days, suggesting the significant improvement of the metabolic stability of AST-202. ). This improvement of stability was found to translate to improved PK profile relative to AST-202(1), resulting in the dramatic increase of AUC and half-life as well as the decreased CL.

Cytotoxicity evaluation against a panel of human lymphoma and leukemia cell lines with different CD25-expression level revealed the correlation of the expression level of the target and CD25-negative Daudi and H929 cells (derived from B-cell lymphoma and multiple myeloma, respectively) were not affected in the range of treatment up to 1uM.

Comparative in vivo study with subcutaneous xenografts of AST-202 and single MMAE-conjugated aptamer demonstrated CD25-specific tumor targeting and the superior anti-tumor efficacy of AST202 relative to ApDC with a single payload. The following study with a disseminated tumor model showed dramatic extensions of survival in all treatment groups compared with vehicle and non-binding ApDC controls and survival difference between AST-202(1) and AST-202(3) was not observed at the tested dose range.

Consequently, based on the improved in vitro stability, PK profile, and efficacy, AST-202(3) which is a novel micellar aptamer-drug conjugate could be a potential candidate for further preclinical development as a therapeutic candidate against hematological malignancies.

No relevant conflicts of interest to declare.