Radiosensitizing Pancreatic Cancer via Effective Autophagy Inhibition

Abstract

Despite aggressive treatments, pancreatic ductal adenocarcinoma (PDAC) remains an intractable disease, largely because it is refractory to therapeutic interventions. To overcome its nutrient-poor microenvironment, PDAC heavily relies on autophagy for metabolic needs to promote tumor growth and survival. Here, we explore autophagy inhibition as a method to enhance the effects of radiotherapy on PDAC tumors. Hydroxychloroquine is an autophagy inhibitor at the focus of many PDAC clinical trials, including in combination with radiotherapy. However, its acid-labile properties likely reduce its intratumoral efficacy. Here, we demonstrate that EAD1, a synthesized analogue of HCQ, is a more effective therapeutic for sensitizing PDAC tumors of various KRAS mutations to radiotherapy. Specifically, in vitro models show that EAD1 is an effective inhibitor of autophagic flux in PDAC cells, accompanied by a potent inhibition of proliferation. When combined with radiotherapy, EAD1 is consistently superior to HCQ not only as a single agent, but also in radiosensitizing PDAC cells, and perhaps most importantly, in decreasing the self-renewal capacity of PDAC cancer stem cells (PCSC). The more pronounced sensitizing effects of autophagy inhibitors on pancreatic stem over differentiated cells points to a new understanding that PCSCs may be more dependent on autophagy to counter the effects of radiation toxicity, a potential mechanism explaining the resistance of PCSCs to radiotherapy. Finally, in vivo subcutaneous tumor models demonstrate that combination of radiotherapy and EAD1 is the most successful at controlling tumor growth. The models also confirmed a similar toxicity profile between EAD1 and Hydroxychloroquine.

KRAS Mutations in Solid Tumors: Characteristics, Current Therapeutic Strategy, and Potential Treatment Exploration

“…M-LIP-CLT, a hybrid nanoplatform capable of fusing Celastrol (CLT)-Loaded PEGylated lipids with the DC2.4 cell membrane, is an effective drug delivery system for PDAC-targeted therapy [ 91 ]. EAD1 is a synthesized analogue of hydroxychloroquine (HCQ) that is found to make KRAS-mutant PDAC more sensitive to radiotherapy [ 92 ]. A study reported that cetuximab (CTX)-conjugated maleimide-polyethylene glycol-chlorin e6 (CMPC) is an immune-stimulating antibody-photosensitizer conjugate, and it can be used for KRAS-mutant PDAC, the mechanism of which is Fc-mediated dendritic cell phagocytosis and immunogenic cell death triggered by light [ 93 ].…”

Autophagy: A Key Player in Pancreatic Cancer Progression and a Potential Drug Target

“…Currently, CQ and HCQ have been approved by the FDA for rheumatoid arthritis, malaria and assessed in a range of clinical trials involving cancer treatment [ 330 , 331 ]. Interestingly, there is a recent report of a novel, more efficacious analog, EAD1, capable of increasing the sensitivity of PDAC neoplasms and stem cells to radiation therapy [ 332 ]. Additionally, EAD1 was shown to be more efficacious in KRAS G12D mutant cell lines, indicating its potential as a treatment option for PDAC [ 332 ].…”

“…Interestingly, there is a recent report of a novel, more efficacious analog, EAD1, capable of increasing the sensitivity of PDAC neoplasms and stem cells to radiation therapy [332]. Additionally, EAD1 was shown to be more efficacious in KRAS G12D mutant cell lines, indicating its potential as a treatment option for PDAC [332]. The study by Wolpin et al demonstrated that HCQ as a monotherapy against chemoresistant PDAC patients was inconsistent and inefficacious [333].…”

Role of autophagy in tumor response to radiation: Implications for improving radiotherapy

“…The autophagy-related genes, especially ATG5 play a critical role in the EMT process as indicated by a study on cervical cancer cells ( 119 ). In radio-resistant cancer cells, like pancreatic ductal adenocarcinoma cells and NSCLC stem cells, autophagy has found to be essential in promoting tumor growth and invasiveness ( 120 ) as well as maintaining the stem cell-like properties ( 121 ) of the cells. as a result autophagy inhibitors, either individually or with combination with other traditional methods of cancer therapy, have been able to block proliferation, colony and, spheroid formation (in pancreatic CSC populations) in cancer cells ( 122 ).…”