Single domain antibody (SBT-100) crosses the blood brain barrier (BBB) and inhibits human glioblastoma by selectively targeting KRAS and P-STAT3.

e13547 Background: Glioblastoma is difficult to treat malignancy that has a high incidence of KRAS mutations ( > 90%) and hyper-expression of P-STAT3 ( > 90%). Most chemotherapeutic agents and large biologics (four chain heterotetrameric IgG) cannot cross the BBB. Therefore Singh Biotechnology’s (SBT) propriety technology has developed a novel targeted therapy and engineered SBT-100 a 15 kD single domain antibody (sdAb) that is bispecific for KRAS and STAT3, which can cross the BBB to target gliablastomas. Methods: Human glioblastoma (U87MG) cell line was used and obtained from ATCC. Biacore affinity assay was used to demonstrate SBT-100 binding to KRAS, KRAS (G12D), and STAT3. The glioblastoma cells were incubated with 0µg/ml to 200µg/ml of SBT-100. MTT assay was performed after 3 days of treatment with SBT-100 and the growth inhibition was calculated. Xenograft (athymic nude mouse) with a well established tumor growing for 6 weeks was injected with SBT-100 intraperitoneally (IP). After 15 minutes the brain of this animal was harvested for immunohistochemical staining. Results: Biacore studies showed SBT-100 binds KRAS with affinity constant of 10-9M, KRAS (G12D) at 10-8M, and STAT3 at 10-8M. MTT assay reveals 62% (p < 0.01) growth inhibition of U87MG within 3 days. A xenograft mouse with a well established tumor ( > 150mm3), when injected IP with 5mg/kg of SBT-100 showed localization in the brain within 15 minutes. Therefore SBT-100 (sdAb) crosses the BBB, and shows intracellular localization in the animal’s neurons and glial cells. Conclusions: SBT-100 significantly inhibits the growth of glioblastoma. KRAS mutations and/or over expression of P-STAT3 in glioblastomas are promising targets for sdAbs like SBT-100, which is bispecific for KRAS and STAT3. SBT-100 crosses the BBB and localizes within the neurons and glial cells of the brain. SBT’s proprietary single domain antibody technology platform used to engineer SBT-100 holds promise for targeting primary brain malignancies, metastatic cancers that go to the brain, and for neurologic disease amenable to targeted therapy. Many chemo-resistant and radiation-resistant cancers use STAT3 as an escape mechanism.