P10.04.A The development of a potent, tumour-specific heptamethine cyanine dye-palbociclib conjugate with novel mechanisms of action for the treatment of glioblastoma

Abstract

Abstract Background Glioblastoma is the most common and aggressive primary brain tumour in adults. The development of anti-cancer agents for brain tumours is challenged by the blood-brain barrier and the resistance conferred by the local tumour microenvironment. Heptamethine cyanine dyes (HMCDs) are a class of near-infrared fluorescence compounds that have recently emerged as promising agents for drug delivery Material and Methods We conjugated palbociclib, a cyclin-dependent kinase 4/6 inhibitor to the HMCD, MHI 148 for the treatment of GBM. Patient-derived GBM cell lines were established from surgically resected biopsy GBM tissue. Results High-throughput drug screening revealed an almost 100-fold increase in cytotoxicity of the palbociclib-MHI 148 conjugate compared to palbociclib alone. Moreover, the palbociclib-MHI 148 conjugate was synergistic with radiation, but not with temozolomide. Further analysis revealed the palbociclib-MHI 148 conjugate was superior to other cyclin-dependent kinase inhibitors in vitro. The shift of palbociclib from cytostatic to cytotoxic when conjugated to MHI 148 prompted further investigation. We revealed that palbociclib-MHI 148-dependent inhibition of cell-cycle progression resulted in increased DNA damage. This preceded increased transcription of key extrinsic apoptosis genes and caused a time-dependent upregulation of TNFR1 endocytosis-dependent cell death signalling. Notably, inhibition of endocytosis and siRNA knockdown of TNFR1 prevented palbociclib-MHI 148-induced cell death. Conclusion: These results highlight a novel mechanism of action of palbociclib when conjugated to MHI-148 that induced autocrine-driven TNFR1-mediated apoptosis. In addition, we highlight the potential application of HMCDs in repurposing tyrosine kinase inhibitors, to overcome the current limitations preventing the expansion of second-line treatment options for GBM.