PE38-based gene therapy of HER2-positive breast cancer stem cells via VHH-redirected polyamidoamine dendrimers.

Breast cancer stem cells (BCSCs) resist conventional treatments and cause tumor recurrence. Almost 25% of breast cancers overexpress human epidermal growth factor receptor-2 (HER2). Here we developed a novel multi-targeted nanosystem to specifically eradicate HER2+ BCSCs. Plasmids containing CXCR1 promoter, PE38 toxin, and 5'UTR of the basic fibroblast growth factor-2 (bFGF 5'UTR) were constructed. Polyamidoamine (PAMAM) dendrimers functionalized with anti-HER2 VHHs were used for plasmid delivery. Stem cell proportion of MDA-MB-231, MDA-MB-231/HER2+ and MCF-10A were evaluated by mammosphere formation assay. Hanging drop technique was used to produce spheroids. The uptake, gene expression, and killing efficacy of the multi-targeted nanosystem were evaluated in both monolayer and spheroid culture. MDA-MB-231/HER2+ had higher ability to form mammosphere compared to MCF-10A. Our multi-targeted nanosystem efficiently inhibited the mammosphere formation of MDA-MB-231 and MDA-MB-231/HER2+ cells, while it was unable to prevent the mammosphere formation of MCF-10A. In the hanging drop culture, MDA-MB-231/HER+ generated compact well-rounded spheroids, while MCF-10A failed to form compact cellular masses. The multi-targeted nanosystem showed much better uptake, higher PE38 expression, and subsequent cell death in MDA-MB-231/HER2+ compared to MCF-10A. However, the efficacy of our targeted toxin gene therapy was lower in MDA-MB-231/HER2+ spheroids compared with that in the monolayer culture. the combination of the cell surface, transcriptional, and translational targeting increased the stringency of the treatment.