Exosomes or small extracellular vesicles are considered a new generation of bioinspired-nanoscale drug delivery system (DDS). Endogenous exosomes function as signalosomes since they convey signals via ligands or adhesion molecules located on the exosomal membrane, or packaged inside the exosome. Recently, exosome membrane modification, therapeutic payloads encapsulation, and modulation of in vivo disposition of exosomes have been extensively investigated, among which significant advances have been made to optimize exosome-mediated delivery to solid tumors. Exosomes, specifically tumor cell-derived exosomes, are presumed to have tumor-preferential delivery due to the homotypic features. However, quality attributes that dictate the tissue distribution, cell type-selective uptake, and intracellular payload release of the administered exosomes, as well as the spatiotemporal information regarding exosome fate in vivo, remain to be further investigated. This review summarizes recent advances in developing exosomes as drug delivery platforms with a focus on tumor targeting. The pharmacokinetic features of naive exosomes and factors influencing their intracellular fate are summarized. Recent strategies to improve tumor targeting of exosomes are also reviewed in the context of the biological features of tumor and tumor microenvironment (TME). Selected approaches to augment tumor tissue deposition of exosomes, as well as methods to enhance intracellular payload delivery, are summarized with emphasis on the underlying mechanisms (eg, passive or active targeting, endosomal escape, etc.). In conclusion, this review highlights recently reported tumor-targeting strategies of exosome-based drug delivery, and it’s in the hope that multiple approaches might be employed in a synergistic combination in the development of exosome-based cancer therapy.

Endoplasmic reticulum-associated degradation (ERAD) is a protein quality control mechanism that eliminates unwanted proteins from the endoplasmic reticulum (ER) through a ubiquitin-dependent proteasomal degradation pathway. gp78 is a previously described ER membrane-anchored ubiquitin ligase (E3) involved in ubiquitination of ER proteins. AAA ATPase (ATPase associated with various cellular activities) p97/valosin-containing protein (VCP) subsequently dislodges the ubiquitinated proteins from the ER and chaperones them to the cytosol, where they undergo proteasomal degradation. We now report that gp78 physically interacts with p97/VCP and enhances p97/VCP-polyubiquitin association. The enhanced association correlates with decreases in ER stress-induced accumulation of polyubiquitinated proteins. This effect is abolished when the p97/VCP-interacting domain of gp78 is removed. Further, using ERAD substrate CD3δ, gp78 consistently enhances p97/VCP-CD3δ binding and facilitates CD3δ degradation. Moreover, inhibition of endogenous gp78 expression by RNA interference markedly increases the levels of total polyubiquitinated proteins, including CD3δ, and abrogates VCP-CD3δ interactions. The gp78 mutant with deletion of its p97/VCP-interacting domain fails to increase CD3δ degradation and leads to accumulation of polyubiquitinated CD3δ, suggesting a failure in delivering ubiquitinated CD3δ for degradation. These data suggest that gp78-p97/VCP interaction may represent one way of coupling ubiquitination with retrotranslocation and degradation of ERAD substrates.

Background and Aims: Endoplasmic reticulum (ER) stress is associated with liver inflammation and hepatocellular carcinoma (HCC). However, how ER stress links inflammation and HCC remains obscure. Mesencephalic astrocyte‐derived neurotrophic factor (MANF) is an ER stress‐inducible secretion protein that inhibits inflammation by interacting with the key subunit of nuclear factor kappa light chain enhancer of activated B cells (NF‐κB) p65. We hypothesized that MANF may play a key role in linking ER stress and inflammation in HCC. Approach and Results: Here, we found that MANF mRNA and protein levels were lower in HCC tissues versus adjacent noncancer tissues. Patients with high levels of MANF had better relapse‐free survival and overall survival rates than those with low levels. MANF levels were also associated with the status of liver cirrhosis, advanced tumor‐node‐metastasis (TNM) stage, and tumor size. In vitro experiments revealed that MANF suppressed the migration and invasion of hepatoma cells. Hepatocyte‐specific deletion of MANF accelerated N‐nitrosodiethylamine (DEN)‐induced HCC by up‐regulating Snail1+2 levels and promoting epithelial‐mesenchymal transition (EMT). MANF appeared in the nuclei and was colocalized with p65 in HCC tissues and in tumor necrosis factor alpha (TNF‐α)‐treated hepatoma cells. The interaction of p65 and MANF was also confirmed by coimmunoprecipitation experiments. Consistently, knockdown of MANF up‐regulated NF‐κB downstream target genes TNF‐α, interleukin (IL)‐6 and IL‐1α expression in vitro and in vivo. Finally, small ubiquitin‐related modifier 1 (SUMO1) promoted MANF nuclear translocation and enhanced the interaction of MANF and p65. Mutation of p65 motifs for SUMOylation abolished the interaction of p65 and MANF. Conclusions: MANF plays an important role in linking ER stress and liver inflammation by inhibiting the NF‐κB/Snail signal pathway in EMT and HCC progression. Therefore, MANF may be a cancer suppressor and a potential therapeutic target for HCC.

Improperly folded proteins in the endoplasmic reticulum (ER) are eliminated via ER-associated degradation, a process that dislocates misfolded proteins from the ER membrane into the cytosol, where they undergo proteasomal degradation. Dislocation requires a subclass of ubiquitin ligases that includes gp78 in addition to the AAA ATPase p97/VCP and its cofactor, the Ufd1-Npl4 dimer. We have previously reported that gp78 interacts directly with p97/VCP. Here, we identify a novel p97/VCP-interacting motif (VIM) within gp78 that mediates this interaction. We demonstrate that the VIM of gp78 recruits p97/VCP to the ER, but has no effect on Ufd1 localization. We also show that gp78 VIM interacts with the ND1 domain of p97/VCP that was shown previously to be the binding site for Ufd1. To evaluate the role of Ufd1 in gp78-p97/VCP-mediated degradation of CD3delta, a known substrate of gp78, RNA interference was used to silence the expression of Ufd1 and p97/VCP. Inhibition of p97/VCP, but not Ufd1, stabilized CD3delta in cells that overexpress gp78. However, both p97/VCP and Ufd1 appear to be required for CD3delta degradation in cells expressing physiological levels of gp78. These results raise the possibility that Ufd1 and gp78 may bind p97/VCP in a mutually exclusive manner and suggest that gp78 might act in a Ufd1-independent degradation pathway for misfolded ER proteins, which operates in parallel with the previously established p97/VCP-Ufd1-Npl4-mediated mechanism.