A375 Melanoma Cells are Sensitized to Cisplatin-Induced Toxicity by a Synthetic Nitro-Flavone Derivative 2-(4-Nitrophenyl)-4H-Chromen-4-one Through Inhibition of PARP1

Background: Cisplatin has been extensively used in therapeutics for its broad-spectrum anticancer activity and frequently used for the treatment of solid tumors. However, it presents several side-effects and several cancers develop resistance. Combination therapy of cisplatin with poly (ADP-ribose) polymerase 1 (PARP1) inhibitors has been effective in increasing its efficacy at lower doses. Methods and Results: In this work, we have shown that the nitro-flavone derivative, 2-(4-Nitrophenyl)-4H-chromen-4-one (4NCO), can improve the sensitivity of cancer cells to cisplatin through inhibition of PARP1. The effect of 4NCO on cisplatin toxicity was studied through combination therapy in both exponential and density inhibited A375 melanoma cells. Combination index (CI) was determined from isobologram analysis. The mechanism of cell killing was assessed by lactate dehydrogenase (LDH) assay. Temporal nicotinamide adenine dinucleotide (NAD+) assay was done to show the inhibition of PARP1. We also performed in silico molecular modeling studies to know the binding mode of 4NCO to a modeled PARP1-DNA complex containing cisplatin-crosslinked adduct. The results from both in silico and in cellulo studies confirmed that PARP1 inhibition by 4NCO was most effective in sensitizing A375 melanoma cells to cisplatin. Isobologram analysis revealed that 4NCO reduced cell viability both in exponential and density inhibited A375 cells synergistically. The combination led to cell death through apoptosis. Conclusion: The synthetic nitro-flavone derivative 4NCO effectively inhibited the important nuclear DNA repair enzyme PARP1 and therefore, could complement the DNA-damaging anticancer drug cisplatin in A375 cells and thus, could act as a potential adjuvant to cisplatin in melanoma therapy.

48. DEVELOPING TUMOR-HOMING CYTOTOXIC HUMAN INDUCED NEURAL STEM CELLS AS AN ADJUVANT TREATMENT FOR RADIATION THERAPY OF BRAIN METASTASES

INTRODUCTION Non-small cell lung cancer (NSCLC) is the most common primary cancer to metastasize to the brain. Radiation is first-line for multifocal brain metastases, but recurrence is observed in 40% of patients. An adjuvant treatment to radiation is needed to effectively treat post-radiation tumor. Genetically engineered neural stem cells (NSCs) have the unique ability to seek out tumors and deliver therapeutic payloads that significantly reduce tumor burden. Here we have transdifferentiated human fibroblasts into induced neural stem cells (hiNSC) and explored the efficacy of hiNSCs therapy for NSCLC brain metastases. METHODS hiNSCs were infused intracerebroventricularly (ICV) into mice with bilateral intracranial H460 NSCLC tumors. Bioluminescent imaging (BLI) was used to determine hiNSCs persistence while fluorescent analysis of brain sections characterized tumor-homing migration. In vitro co-culture assays and isobologram analysis were used to determine the synergistic effect of the cytotoxic protein TRAIL and radiation therapy on NSCLC tumor cells. To determine efficacy in vivo, H460 cells were implanted in the brains of mice and treated with either hiNSC-TRAIL alone or in combination with 2 Gy radiation. Tumor volumes were then tracked via BLI. RESULTS/CONCLUSION hiNSCs persisted in the brain >1 week after ICV injection, and hiNSCs were found to co-localize with both bilateral tumor foci. Isobologram analysis showed a combination index of 0.64, suggesting radiation and TRAIL have a synergistic cytotoxic effect on NSCLC tumors. In vivo, radiation and hiNSC-TRAIL therapy reduced tumor volumes 90% compared to control-treated animals, while each therapy alone only reduced tumors 21% and 52%, respectively. While neither monotherapy significantly impacted survival, combination therapy demonstrated a 40% extension in survival, with treated mice surviving a median of 28 days while controls animals only survived 20 days. Together, these results demonstrate the therapeutic potential of hiNSC-TRAIL as an adjuvant to radiation for treatment of NSCLC brain metastases.