(137b) Novel Cytostatic Annexin A5-Drug Conjugates for Cancer Treatment

One of the problems with treating patients with cancer is that serious side effects often occur during treatment, and death can occur as a result of overtreatment. The chemotherapy that is commonly used to treat cancer often has negative effects on normal body organs and tissue, such as nausea, vomiting, hair loss, cognitive dysfunction, fatigue, changes in sexual functioning, and reductions in quality of life ratings. In the research reported here, novel protein-drug conjugates were developed that are targeted to the cancer cells and are needed in much reduced doses for the same effect as the free drug.

The novel conjugates we developed consist of the protein annexin A5 (ANXA5) linked to either chlorambucil (CMB) or emtansine (DM1). ANXA5 binds specifically to the anionic aminophospholipid phosphatidylserine (PS) on the outer membrane of cancer cells. PS is not expressed on normal cells, so the conjugate will not bind to them. CMB, an aromatic nitrogen mustard derivative, is an alkylating agent that interferes with DNA replication and induces cellular apoptosis via the accumulation of cytosolic p53 and subsequent activation of Bax, an apoptosis promoter. DM1 is a tubulin inhibitor that inhibits the assembly of microtubules by binding to tubulin, leading to mitotic arrest and apoptosis.

The two conjugates have been tested in vitro for their effectiveness against two mouse breast cancer cell lines and two mouse leukemia cell lines. Compared to the free drugs for 4T1 and EMT6 breast cancer cells, the conjugates were 42 to 377 times more effective when comparing the IC50 (concentration where the viability is by 50%) values obtained. For P388 and L1210 leukemia cells, the conjugates were 17 to 353 times more effective compared to the free drugs.

The ANXA5-CMB conjugate was tested for treating mice with syngeneic orthotopic 4T1 breast tumors at a dose of CMB in the conjugate of 0.5 mg/kg mouse weight. At this dose administered daily, the tumors were significantly smaller (approximately 5 times) compared to treating at this same dose of free drug after 9 days of treatment. Research is continuing to optimize the dosage.