USE OF 6-THIO-dG TO TREAT THERAPY-RESISTANT TELOMERASEPOSITIVE PEDIATRIC BRAIN TUMORS

Abstract

Brain tumors remain the leading cause of cancer-related deaths in children and often are associated with long-term sequelae among survivors of current therapies. Telomerase and telomeres play important roles in cancer, representing attractive therapeutic targets to treat children with poor-prognosis brain tumors such as diffuse intrinsic pontine glioma (DIPG), high-grade glioma (HGG) and high-risk medulloblastoma (MB). It has shown that DIPG, HGG and MB frequently express telomerase activity. It is now shown that the telomerase-dependent incorporation of 6-thio-2′deoxyguanosine (6-thio-dG), a telomerase substrate precursor analog, into telomeres leads to telomere dysfunction-induced foci (TIFs) along with extensive genomic DNA damage, cell growth inhibition and cell death of primary stem-like cells derived from patients with DIPG, HGG and MB. Importantly, the effect of 6-thio-dG is persistent even after drug withdrawal. Treatment with 6-thio-dG elicits a sequential activation of ATR and ATM pathways and induces G2/M arrest. In vivo, treatment of mice bearing MB xenografts with 6-thio-dG delays tumor growth, increases in-tumor TIFs and apoptosis. Furthermore, 6-thio-dG crosses the blood-brain barrier and specifically targets tumor cells in an orthotopic mouse model of DIPG. Together, these findings suggest that 6-thio-dG is a promising approach to treat therapy-resistant telomerase-positive pediatric brain tumors.

1 . A method of treating a brain cancer in a pediatric subject, comprising administering a telomerase substrate precursor analog to a subject in need thereof, thereby treating pediatric brain cancer. 
     
     
         2 . The method of  claim 1 , wherein the subject's is age 1-21, 1-18 or 1-14. 
     
     
         3 . The method of  claim 1 , wherein the pediatric brain cancer is drug resistant. 
     
     
         4 . The method of  claim 1 , wherein the pediatric brain cancer is diffuse intrinsic pontine glioma (DIPG), high-grade glioma (HGG), or high-risk medulloblastoma (MB). 
     
     
         5 . The method of  claim 1 , wherein the brain cancer has telomerase activity. 
     
     
         6 . The method of  claim 1 , wherein the telomerase substrate precursor analog is 6-thio-2′ deoxyguanosine (6-thio-dG). 
     
     
         7 . The method of  claim 6 , wherein 6-thio-dG induces in vivo telomere dysfunction-induced foci (TIFs), apoptosis, and an inhibition of tumor growth. 
     
     
         8 . The method of  claim 1 , wherein the telomerase substrate precursor analog is administered in combination or sequentially with an immunotherapeutic agent, a targeted drug, an epigenetic modifier, a chemotherapeutic agent, radiotherapy, or any combination thereof. 
     
     
         9 . The method of  claim 1 , wherein the telomerase substrate precursor analog is administered in combination with an immune checkpoint inhibitor, such as an anti-PD-L1 or PD-1 antibody. 
     
     
         10 . The method of  claim 1 , further comprising the step of assessing telomerase activity in a brain cancer cell from said subject. 
     
     
         11 . A method of inducting G2/M cell cycle arrest in a cancer cell comprising contacting the cell with a telomerase substrate precursor analog and a telomerase inhibitor. 
     
     
         12 . The method of  claim 11 , wherein the cancer cell is a brain cancer cell. 
     
     
         13 . The method of  claim 12 , wherein the brain cancer cell is drug resistant. 
     
     
         14 . The method of  claim 11 , wherein the brain cancer cells is diffuse intrinsic pontine glioma (DIPG), high-grade glioma (HGG), or high-risk medulloblastoma (MB). 
     
     
         15 . The method of  claim 11 , wherein the cancer cell exhibits telomerase activity. 
     
     
         16 . The method of  claim 11 , wherein the telomerase substrate precursor analog is 6-thio-2′ deoxyguanosine (6-thio-dG). 
     
     
         17 . The method of  claim 16 , wherein 6-thio-dG induces in vivo telomere dysfunction-induced foci (TIFs), apoptosis, and an inhibition of tumor growth. 
     
     
         18 . The method of  claim 11 , wherein the telomerase substrate precursor analog is administered in combination or sequentially with an immunotherapeutic agent, a targeted drug, an epigenetic modifier, a chemotherapeutic agent, radiotherapy, or any combination thereof. 
     
     
         19 . The method of  claim 11 , further comprising the step of assessing telomerase activity in said cancer cell. 
     
     
         20 . The method of  claim 11 , wherein the cell cycle arrest induces the accumulation of genomic DNA damage.