Fluorescence-Guided Imaging of Brain Tumors: A Safety Study Using SBK2-ICG

Treating people with serious brain tumors is challenging, and the outlook for these people is poor. On average, people survive less than one year after their are diagnosed. How long someone lives after diagnosis and treatment may depend on how much of the tumor is able to be removed with surgery. However, it can be difficult for surgeons to tell the difference between where the tumor is and where healthy brain tissue is using standard white light surgical microscope illumination. Because of this, new methods to help surgeons see tumor borders more clearly during surgery could be valuable. Fluorescence imaging may be one method that can help surgeons see tumor borders more clearly. Previous studies have used fluorescence imaging to better visualize tumors, but no previous studies have used SBK2-ICG. In fact, the use of SBK2-ICG is conceptually different than other studies. Currently, the only FDA approved drug used in fluorescent imaging for visualizing brain tumors during surgery is called 5-aminolevulinic acid, or 5-ALA. 5-ALA is naturally metabolized in human cells to something called PpIX. When people are given 5-ALA before surgery, it gets turned into PpIX, which can then be excited by fluorescent light at wavelengths of 400-410 nm. Because tumor cells and healthy cells metabolize 5-ALA in different ways, PpIX tends to accumulate in epithelial and malignant cells, including brain tumor cells. In a review of previous studies, using 5-ALA was associated with better removal of tumor tissue, longer overall survival, and longer progression-free survival. However, 5-ALA only weakly detects tumor borders and does not identify infiltrative cells on the edges of tumors. Also, even thin barriers of normal cells can make it difficult for surgeons to see 5-ALA, which makes it difficult to tell the difference between tumor tissue and healthy tissue. Because of this, it would be helpful to use a drug that emits a light that more deeply penetrates brain tissue so that surgeons can see tumor tissue and healthy tissue better. SBK2-ICG is different than 5-ALA because it is not metabolized by the human body. Instead, SBK2-ICG attaches to a unique piece of cells that accumulates in tumors. SBK2-ICG can also be excited at a wavelength of 789 nm, rather than the wavelength of 400-410 nm that 5-ALA is excited at. SBK2-ICG gives off a near infrared light when it is excited, making it easier to see the borders of tumors. It also helps with seeing deep inside of the tumor. Using SBK2-ICG and fluorescent light has been shown to identify more than 99% of tumor cells in rodent xenograft models of human brain tumors in the lab. Researchers want to assess the safety of SBK2-ICG in people with brain tumors who are already planning to have surgery to remove their tumor and see how SBK2-ICG compares to standard practices in identifying tumor tissue versus healthy tissue.