THER-08. SGT53 – A NOVEL p53 NANOMEDICINE INDUCES SIGNIFICANT RESPONSES IN CHILDREN WITH RECURRENT MEDULLOBLASTOMA AND CHOROID PLEXUS CARCINOMA: A REPORT OF TWO CASES

BACKGROUND: Abnormal p53 function commonly defines high-risk CNS tumors, but functional restoration has eluded investigators. SGT-53 is a targeted nanomedicine encapsulating a plasmid DNA encoding wild-type human p53 with a transferrin receptor-targeting scFv on the nanocomplex surface resulting in efficient delivery across the BBB and robust tumor binding/uptake. Data generated by collaborators demonstrated synergy with irradiation and chemotherapy. REPORT: Two children with recurrent CNS malignancies have been treated with SGT-53, each receiving greater than 50 infusions in combination with irradiation and chemotherapy with no grade 3/4 AEs positively attributed to SGT-53. The first was an 11yo male with recurrent disseminated p53+ SHH medulloblastoma, with bulky intracranial/thoracolumbar disease. He received irradiation followed by biweekly doses of SGT-53 and temozolomide, bevacizumab and irinotecan given one week out of four. This patient exhibited a complete response of all disease on his first follow-up scan 8 weeks after therapy initiation and remained in remission for 8 months. The second patient was a 3yo male with disseminated recurrent choroid plexus carcinoma. He received CSI with SGT-53, followed by SGT-53, temozolomide and irinotecan as described above, again with no related grade 3/4 AEs. He experienced a partial response to all sites of disease and completed therapy after six months, progressing 7.8 months after initiating treatment. CONCLUSIONS: SGT-53 was well tolerated in two heavily-pretreated patients despite aggressive combinatorial strategies. The majority of the AEs experienced were mild and manageable. Each patient had significant responses, suggesting that SGT-53 should be evaluated in a clinical trial for similar patients.