Preparation of bisphosphonate-modified doxorubicin and evaluation of its antitumor activity in vitro

Using the heterobifunctional crosslinker 3-(2-pyridinedithio) propionate N-succinimidyl ester (SPDP) as a coupling agent, doxorubicin (DOX) was coupled with pamidronate sodium via a chemical cross-linking method to prepare bisphosphonate-modified doxorubicin (P-DOX). The obtained product was characterized by Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. To evaluate the in vitro bone targeting of the drugs, the binding amount of drugs onto calcium phosphate was measured, and the in vitro drug release behavior was measured under different pH values and in the presence of cysteine. Finally, to evaluate the effect of phosphorylated doxorubicin on the cellular activity of normal bone tissue and its inhibitory ability on the growth of tumor cells, the drug was co-cultured with osteogenic precursor cells, prostate cancer cells, and osteosarcoma cells, respectively. Infrared spectra analysis showed that DOX/bisphosphonate complex was successfully synthesized. The drug adsorption experiments showed that the adsorption rate of modified doxorubicin onto hydroxyapatite was increased by about one time, and effective release was achieved in a cysteine-rich environment and acidic environment. Cell co-culture experiments showed that compared with traditional doxorubicin, phosphorylated doxorubicin accumulated less in osteogenic precursor cells, effectively reducing the toxicity of chemotherapeutic drugs to normal bone tissue cells. In addition, phosphorylated doxorubicin could be effectively taken up by tumor cells, which effectively inhibit the proliferation, migration, and invasion of tumor cells, and promote apoptosis and necrosis of tumor cells. Thus, the synthesis of doxorubicin-bisphosphonate conjugates provides a new solution for the treatment of malignant bone tumors and provides an important reference for the development of more targeted antitumor drugs.