NME1 and breast cancer: To investigate whether His6-NDPK-A can be delivered into the cytosol of MDA-MB-231 breast cancer cells via the PA63 transporter, we first confirmed that this cell line is susceptible for the PA63-mediated protein transport using a well-established His6-tagged cargo protein, His6-DTA, the recombinant enzyme domain of diphtheria toxin (DT).