Abstract
Molecular targeted therapy has been proved effective in treatment of rectal cancer. Up-regulated expression of programmed death ligand-1 (PD-L1) was observed after the management of molecular targeted therapy, which made the therapeutic effect discounted. Tumors with higher PD-L1 expression were more sensitive and responsive to treatment of PD-L1 inhibitor. Therefore, the combination of molecular targeted therapy and immune checkpoint blockade makes sense. In this study, the copolymers of poly (ethylene glycol)-block-poly (L-leucine) (PEG-PLLeu) were synthesized as a thermosensitive hydrogel composite for consecutive release of regorafenib (REG) and BMS202. The mechanical properties of PEG-PLLeu were investigated, confirming that PEG-PLLeu (5 wt.%) was suitable for in situ injection as drug-delivery composite at low temperature and stable after sol-gel transition at body temperature. Importantly, the double drug loaded hydrogel showed superior antitumour activity over single drugs in an orthotopic rectal cancer model (CT26-Luc). Further analysis of the tumor tissues suggested that REG upregulated the expression of PD-L1 in tumor tissues. In addition, the immunosuppressive tumor microenvironment of CT26-Luc tumor was distinctly relieved under the effect of BMS202, as characterized by increased infiltration of CD8+ T cells in tumors and enhanced secretion of antitumour cytokines (IFN-γ and TNF-α). Moreover, the drug-loaded composite showed no obvious toxicity in histological analysis. Taken together, the administration of REG and BMS202 in the PEG-PLLeu composite could induce a synergistic effect in in situ treatment of rectal cancer without obvious toxicity, and thus represented a potential strategy for enhanced in situ therapeutic modality.
Highlights
Rectal cancer is a common malignant tumor with high morbidity and mortality (Bray et al, 2018)
Once uncontrolled angiogenesis is ceased, the abnormal blood vessels in TME tend to be normalized to cope with sufficient oxygen supply, increased migration of antitumour immune cells, and enhanced penetration of antitumour agents into the tumor which contributed to the suppression thereof; it was found that molecular targeted therapy boosted upregulation of programmed death ligand-1 (PD-L1) in tumor tissues (Liu et al, 2015)
We propose that the combination of locally applied molecular targeted therapy and checkpoint blockade immunotherapy may be meaningful as a therapy for rectal cancer
Summary
Rectal cancer is a common malignant tumor with high morbidity and mortality (Bray et al, 2018). Once uncontrolled angiogenesis is ceased, the abnormal blood vessels in TME tend to be normalized to cope with sufficient oxygen supply, increased migration of antitumour immune cells, and enhanced penetration of antitumour agents into the tumor which contributed to the suppression thereof; it was found that molecular targeted therapy boosted upregulation of programmed death ligand-1 (PD-L1) in tumor tissues (Liu et al, 2015). This immune accommodation of a tumor may hamper the molecular targeted agent-based antitumour efficiency. The combination of molecular targeted therapy and checkpoint blockade immunotherapy makes sense
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