Lipid rafts are tightly packed, cholesterol-and sphingolipid-enriched microdomains within the plasma membrane that play important roles in many pathophysiological processes. Rafts have been strongly implicated as master regulators of signal transduction in cancer, where raft compartmentalization can promote transmembrane receptor oligomerization, shield proteins from enzymatic degradation, and act as scaffolds to enhance intracellular signaling cascades. Cancer cells have been found to exploit these mechanisms to initiate oncogenic signaling and promote tumor progression. This review highlights the roles of lipid rafts within the metastatic cascade, specifically within tumor angiogenesis, cell adhesion, migration, EMT, and transendothelial migration. Additionally, the interplay between lipid rafts and different modes of cancer cell death, including necrosis, apoptosis, and anoikis will be described. The clinical role of lipid raft-specific proteins caveolin and flotillin in assessing patient prognosis and evaluating metastatic potential of various cancers will be presented. Collectively, elucidation of the complex roles of lipid rafts and raft components within the metastatic cascade may be instrumental for therapeutic discovery to curb pro-metastatic processes. Research.

Colorectal cancer (CRC) remains a leading cause of cancer death, and its mortality is associated with metastasis and chemoresistance. We demonstrate that oxaliplatin-resistant CRC cells are sensitized to TRAIL-mediated apoptosis. Oxaliplatin-resistant cells exhibited transcriptional downregulation of caspase-10, but this had minimal effects on TRAIL sensitivity following CRISPR-Cas9 deletion of caspase-10 in parental cells. Sensitization effects in oxaliplatin-resistant cells were found to be a result of increased DR4, as well as significantly enhanced DR4 palmitoylation and translocation into lipid rafts. Raft perturbation via nystatin and resveratrol significantly altered DR4/raft colocalization and TRAIL sensitivity. Blood samples from metastatic CRC patients were treated with TRAIL liposomes, and a 57% reduction of viable circulating tumor cells (CTCs) was observed. Increased DR4/lipid raft colocalization in CTCs was found to correspond with increased oxaliplatin resistance and increased efficacy of TRAIL liposomes. To our knowledge, this is the first study to investigate the role of lipid rafts in primary CTCs.

Colorectal cancer (CRC) remains the second leading cause of cancer related death in the United States. Clinical studies show combination chemotherapy cocktails increase Stage IV patient progression free survival when containing 5-fluorouracil, leucovorin and oxaliplatin (FOLFOX). Despite an initial response rate of 40-50%, patients undergoing FOLFOX have a low median overall survival of 18-months. Treatment induced chemoresistance is in part responsible for this high morbidity, as subpopulations of surviving cells develop resistance mechanisms to induce a more aggressive, metastatic phenotype. Consequently, there exists an urgent need to develop new therapies for metastatic cancers that have become chemoresistant. We hypothesized that Tumor Necrosis factor - α Related Apoptosis Inducing Ligand (TRAIL) based therapeutics would be efficacious in treating oxaliplatin resistant CRC, providing an adjuvant for patients who have exhausted conventional treatment modalities. Four different CRC cell lines were chosen for this study: SW620, SW480, HCT116 and HT29 cells as they all have varying sensitivities to TRAIL. Briefly, oxaliplatin resistant (OxR) derivatives of these cell lines were developed by treating with oxaliplatin and subjecting surviving subpopulations to many rounds of increasing concentrations of chemotherapy. Resistant cells show increased expression of mesenchymal markers along with increased invasiveness. Metastatic CRC patient blood samples were obtained from Guthrie Clinic. Interestingly, SW620 OxR and HCT116 OxR cells show increased sensitization to soluble TRAIL compared to their parental counterparts. Flow cytometry and confocal microscopy demonstrate these sensitized cell lines have increased expression of death receptor 4 (Dr4). Previous studies have demonstrated that combination treatment with oxaliplatin and TRAIL sensitize cancer cells via localization of death receptors into lipid rafts. In our study, we observe a similar phenomenon where oxaliplatin resistant cells have a higher degree of lipid raft-Dr4 colocalization. Induction of death receptor-lipid raft complexes using resveratrol enhances parental SW620 cell sensitivity to TRAIL by 70%, whereas inhibition of lipid rafts via cholesterol sequestration using nystatin decreases sensitization of SW620 OxR cells by 30%. Circulating tumor cells (CTCs) from metastatic CRC patients who have undergone FOLOFX or oxaliplatin based chemotherapy exhibited colocalization of Dr4 and Dr5 into lipid rafts. Additionally, treating whole blood samples from patients with TRAIL-conjugated nanoparticles decreased the number of viable CTCs in circulation 4-fold compared to oxaliplatin monotherapy. These results demonstrate the utility of TRAIL based therapeutics to treat chemoresistant and metastatic CRC. Additionally, this mechanism of apoptosis signal propagation via lipid raft-death receptor complexes can be explored further to probe possible drug targets to augment receptor localization. Citation Format: Joshua Dale Greenlee, Nerymar Ortiz-Otero, Tejas Subramanian, Kevin Liu, Michael King. TRAILing chemoresistance: Oxaliplatin resistance sensitizes colorectal cancer to TRAIL via death receptor localization [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-069.

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