Ezatiostat HCl Liposomes for Injection (TLK199) Mechanism of Action. 1. Esterase action on the diester prodrug, ezatiostat liberates the active moiety, the tripeptide diacid; 2. Binding of diacid to GST P1-1 leads to release of JNK; 3. JNK phosphorylated c-JUN; 4. Phosphorylated C-Jun translocates to the nucleus and participates in transcription of growth and differentiation genes; 5. Trilineage growth and differentiation results.