The anti-sortilin 11H8-MMAE and anti-syndecan-1 6D11-MMAE conjugates had a significant effect on cell viability and morphology in metastatic prostate cancer cells, when compared to an isotype control 10A3-MMAE conjugated antibody directed against an intracellular epitope on syndecan-1. Here, SDC1 is linked to prostate cancer.