Tumor-derived apolipoprotein E confers resistance to temozolomide in pancreatic neuroendocrine tumors.

Temozolomide (TMZ) is a first-class clinical drug for patients with pancreatic neuroendocrine tumors (pNETs). However, the therapeutic effects of TMZ are limited because of the chemoresistance of pNET cells, which has not been fully elucidated. Here, we demonstrate that the reprogramming of lipid metabolism regulates TMZ resistance in patients with pNETs. Via integrated multiomics sequencing, apolipoprotein E (APOE), which is a critical lipid carrier, was identified to be highly increased in the tissue and blood plasma of patients in the TMZ treatment group compared with those in the control group. Further mechanistic studies revealed that TMZ treatment promotes the expression and secretion of APOE, which binds to its surface receptor known as scavenger receptor class B member 1 (SCARB1), thus leading to increased uptake of exogenous lipids to remodel cellular lipid metabolism and activation of the homologous recombination repair (HRR) pathway to repair DNA damage via the β-catenin-BRCA1/2 axis. The interruption of APOE-mediated lipid uptake via a SCARB1 inhibitor named as block lipid transport-1 (BLT-1), suppressed TMZ-induced HRR activation and sensitized tumor cells to TMZ treatment in preclinical models, including PDCs, PDOs, and PDXs. In addition, APOE expression levels were shown to be positively correlated with BRCA1/2 expression in clinical specimens and online databases. This study reveals a new functional role of APOE that leads to chemoresistance in patient treatment. Our findings suggest the potential of combined administration of BLT-1 to overcome TMZ chemoresistance and improve treatments for patients with pNETs.