Fascaplysin, particularly in its chloride form, is primarily recognized for its role as a selective CDK4 inhibitor. This compound has shown significant potential in cancer research, where it is used to study cell cycle regulation and proliferation. By inhibiting CDK4, fascaplysin can effectively halt the progression of the cell cycle at the G1 phase, making it a valuable tool in understanding and potentially treating cancers that are driven by CDK4 overactivity. Its application extends to preclinical studies where it is used to evaluate the efficacy of targeting CDK4 in various cancer models, including breast cancer, glioblastoma, and melanoma. Additionally, fascaplysin's ability to induce apoptosis in cancer cells further underscores its therapeutic potential. Researchers are also exploring its use in combination therapies, where it may enhance the effects of other anticancer agents, providing a multifaceted approach to cancer treatment.