Antibody-
mertansine (DM1) conjugates (AMCs) are among the very few active targeting
therapeutics that are approved or clinically investigated for treating various
cancers including metastatic
breast cancer. However, none of the AMCs are effective for the treatment of
triple-negative breast cancers (TNBCs). Here, we show that cRGD-decorated, redox-activatable micellar
mertansine prodrug (cRGD-
MMP) can effectively target and deliver DM1 to αvβ3
integrin overexpressing MDA-MB-231 TNBC xenografts in nude mice, resulting in potent
tumor growth inhibition.
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays showed that cRGD-
MMP had obvious targetability to MDA-MB-231 cells with a low half-maximal inhibitory concentration (IC50) of 0.18 μM, which was close to that of free DM1 and 2.2-fold lower than that of micellar
mertansine prodrug (
MMP; nontargeting control). The confocal microscopy studies demonstrated that cRGD-
MMP mediated a clearly more efficient cellular uptake and intracellular release of
doxorubicin (used as a fluorescent anticancer
drug model) in MDA-MB-231 cells. Notably, cRGD-
MMP loaded with 1,1'-dioctadecyltetramethyl
indotricarbocyanine iodide (DiR; a hydrophobic near-infrared
dye) was shown to quickly accumulate in the MDA-MB-231
tumor with strong DiR fluorescence from 2 to 24 h post injection.
MMP loaded with DiR could also accumulate in the
tumor, although significantly less than cRGD-
MMP. The biodistribution studies revealed a high DM1 accumulation of 8.1%ID/g in the
tumor for cRGD-
MMP at 12 h post injection. The therapeutic results demonstrated that cRGD-
MMP effectively suppressed MDA-MB-231
tumor growth at 1.6 mg DM1 equiv./kg without causing noticeable side effects, as shown by little
body weight loss and histological analysis. This
MMP has appeared as a promising platform for potent treatment of TNBCs.