SINEs work by binding to CRM1, a karyopherin which performs nuclear transport of hundreds of proteins—including tumor suppressors, oncogenes, and proteins involved in governing cell growth—from the cell nucleus to the cytoplasm. CRM1 it is often overexpressed and misregulated in cancer, and is the sole transporter of many proteins essential for cancer cell proliferation and spread.[1] By restoring nuclear transport of these proteins to normal, SINEs lead to a buildup of tumor suppressors in the nucleus of malignant cells and reduce levels of oncogene products which drive cell growth, ultimately triggering apoptosis.[1][2]In vitro, this effect appears to spare normal (non-malignant) cells.[1] Nevertheless, because CRM1 is a pleiotropicgene, inhibiting it affects many different systems in the body, which causes a high rate of adverse reactions.[2]