Accessing Combinatorial Effect of PARP Inhibitor with DNA Damaging Agent in Rhabdomyosarcoma at Single Cell Resolution
Background: Combination therapies using cytotoxic drugs have revolutionized the treatment of pediatric rhabdomyosarcoma (RMS). However, cure rates have largely remained stagnant since their implementation. We have recently generated an optically-clear, immune-deficient zebrafish that can engraft human RMS tumors, with growth kinetics and histological features similar to those grown in immune-deficient murine models. However, the zebrafish model has additional powerful attributes including high fecundity, low maintenance cost and the ability to assess growth kinetics at single-cell resolution. PARP inhibitors (PARPi) are now used in the clinic for the treatment of triple negative breast cancer and ovarian cancer. More recently, it has been demonstrated that the addition of DNA-damaging agents potentiates PARPi cytotoxicity in a variety of cancer types, including Ewing sarcoma. To date, preclinical modeling of PARPi and DNA-damaging agents has yet to be studied in RMS.
Project Goals: Given that PARPi are now in clinical evaluation in children, are well-known to induce apoptosis in human RMS cell lines and potently synergize with DNA-damaging agents to elevate cancer cell killing in other sarcomas, this project aims to study if the combination of PARPi and DNA-damaging agents will be an effective therapy for pediatric RMS patients. Aim 1 will elucidate an optimal combination of PARPi and DNA-damaging agents for human RMS cells using xenograft studies into immune-deficient zebrafish. Aim 2 will investigate mechanism(s) of drug action at single cell resolution. Aim 3 will validate the most efficient combination of PARPi and DNA-damaging agents for effects in human PDX models of RMS.
Project Update 2022: I have developed an immune compromised zebrafish xenograft model that enables efficient long-term engraftment of a variety of human RMS tumors. Kinetics and histology of the human RMS cells grown in the zebrafish are largely similar to that observed when grown in immune compromised mice. It has been well documented that PARP inhibitors (PARPi), in addition of the DNA damaging agent, Temozolomide, can further potentiate PARPi cytotoxicity in a variety of cancer types, including Ewing’s Sarcoma, glioma and leiomyosarcoma etc. Over the past 3 years, our preclinical modeling in zebrafish and mice RMS models uncovered combination olaparib PARPi and temozolomide DNA damaging agent as a potent therapy for the elimination of human RMS tumor cells in vivo. Remarkably, both ERMS and ARMS were responsive to combination treatment, despite transformation by different oncogenic drivers. Even more remarkable, all models tested showed response to combination therapy, suggesting that our preclinical modeling may have identified a potent drug combination for the treatment of a wide array of RMS. Our work, together with help from clinical trial teams at the MGH and Dana-Farber Cancer Institute has resulted in an ongoing phase I clinical trial using olaparib and temozolomide for relapsed RMS pediatric patients.
