What was the first chemotherapy agent studied in animals?

The first chemotherapy agent studied in animals was nitrogen mustard. This compound came to prominence during World War II when it was identified for its potential to inhibit rapidly dividing cells, which was particularly relevant for treating cancers. Researchers observed its effects after its application, noting its ability to induce cell death in cancerous tissues, leading to its development as a chemotherapeutic agent. This marked a significant turning point in oncological treatment, laying the groundwork for many more effective chemotherapy agents that followed. The exploration of nitrogen mustard as a chemotherapy drug was pivotal because it established the foundation for modern chemotherapy, demonstrating the feasibility of targeting cancer through the use of chemical agents.

In contrast, the other options listed were developed and evaluated in subsequent years, making nitrogen mustard significant as the first agent in this realm.