Affibody-conjugated 5-fluorouracil prodrug system preferentially targets and inhibits HER2-expressing cancer cells.

Overexpression of HER2 is associated with cancer phenotypes, such as proliferation, survival, metastasis and angiogenesis, and has been validated as a therapeutic target. However, only a portion of patients benefited from anti-HER2 treatments, and many would develop resistance. A more effective HER2 targeted therapeutics is needed. Here, we adopted a prodrug system that uses 5-fluorocytosine (5-FC) and a HER2-targeting scaffold protein, Z HER2:2891 , fused with yeast cytosine deaminase (Fcy) to target HER2-overexpressing cancer cells and to convert 5-FC to a significantly more toxic chemotherapeutic, 5-fluorouracil (5-FU). We cloned the coding gene of Z HER2:2891 and fused with those of ABD (albumin-binding domain) and Fcy. The purified Z HER2:2891 -ABD-Fcy fusion protein specifically binds to HER2 with a Kd value of 1.6 nM Z HER2:2891 -ABD-Fcy binds to MDA-MB-468, SKOV-3, BT474, and MC38-HER2 cells, which overexpress HER2, whereas with a lower affinity to HER2 non-expresser, MC38. Correspondingly, the viability of HER2-expressing cells was suppressed by relative low concentrations of Z HER2:2891 -ABD-Fcy in the presence of 5-FC, and the IC 50 values of Z HER2:2891 -ABD-Fcy for HER2 high-expresser cells were approximately 10–1000 fold lower than those of non-HER2-targeting Fcy, and ABD-Fcy. This novel prodrug system, Z HER2:2891 -ABD-Fcy/5-FC, might become a promising addition to the existing class of therapeutics specifically target HER2-expressing cancers. • HER2 is a valid cancer therapeutic target. • Resistance to current treatments occurs in significant portion of patients. • Z HER2:2891 -ABD-Fcy with HER2-targeting and 5-FC converting activities could be purified. • Z HER2:2891 -ABD-Fcy/5-FC potently inhibits viability of HER2-expressing cells. [ABSTRACT FROM AUTHOR]