Streptavidin expressed gene fusions and methods of use thereof

A fusion protein, comprising at least a first and a second polypeptide joined end to end, wherein said first polypeptide comprises at least 129 amino acids of streptavidin, as set forth in SEQ ID NO:

• 2, or functional variants, said variants comprising at least 90% amino acid identity with the native sequences thereof, wherein said variants retain the ability to bind biotin, and wherein said second polypeptide comprises anti-CD25 antibody or antigen-binding fragment thereof.

A method for targeting a tumor cell comprising the administration of a fusion protein and a sensitizing agent, wherein said fusion protein comprises at least a first and a second polypeptide joined end to end, wherein said first polypeptide comprises at least 129 amino acids of streptavidin, as set forth in SEQ ID NO:

• 2, or conservatively substituted variants thereof, wherein said second polypeptide is a targeting agent that binds a cell surface protein, or a cell-associated stromal or matrix protein, on a tumor cell, wherein the streptavidin portion of the fusion protein is capable of binding biotin, and wherein said sensitizing agent is a radiation-sensitizing agent.

A method for targeting a tumor cell comprising the administration of a fusion protein, further comprising a sensitizing agent, wherein said fusion protein comprises at least a first and a second polypeptide joined end to end, wherein said first polypeptide comprises at least 129 amino acids of streptavidin, as set forth in SEQ ID NO:

• 2, or conservatively substituted variants thereof, wherein said second polypeptide is an anti-CD25 antibody or antigen binding fragment thereof, wherein the streptavidin portion of the fusion protein is capable of binding biotin, and wherein said sensitizing agent is a radiation-sensitizing agent.

A composition comprising a fusion protein comprising a first and a second polypeptide joined end to end, wherein said first polypeptide comprises at least 129 amino acids of streptavidin, as set forth in SEQ ID NO:

• 2, or functional variants comprising at least 90% amino acid identity with the native sequences thereof, wherein said variants retain the ability to bind biotin, and wherein said second polypeptide comprises a polypeptide that specifically binds a cell surface protein, or a cell-associated stromal or matrix protein, and a radiation-sensitizing agent.