Recently, the eye drug delivery system has received increasing attention. The in situ ophthalmic gel is a semisolid ophthalmic preparation that can be changed in the eyes immediately after the solution is administered, showing unique advantages as a new drug delivery system. Although there are still some problems to be solved, the in situ ophthalmic gel is a promising drug delivery system to treat ocular diseases, due to its properties in improving the bioavailability, prolonging the retention time of the drug, producing a sustained-release effect, and possessing little toxicity and irritation. In this review, the characteristics, classification, ocular barrier, and route of administration of in situ ophthalmic gel have been introduced in detail for expanding the horizon of nanoscale technologies in the treatment of ocular diseases in the foreseeable future.

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Metastasis, the spread of a tumor or cancer from the primary site of the body to a secondary site, is a multi-step process in cancer progression, accounting for various obstacles in cancer treatment and most cancer-related deaths. Metabolic reprogramming refers to adaptive metabolic changes that occur in cancer cells in the tumor microenvironment (TME) to enhance their survival ability and metastatic potential. Stromal cell metabolism also changes to stimulate tumor proliferation and metastasis. Metabolic adaptations of tumor and non-tumor cells exist not only in the TME but also in the pre-metastatic niche (PMN), a remote TME conducive for tumor metastasis. As a novel mediator in cell-to-cell communication, small extracellular vesicles (sEVs), which have a diameter of 30–150 nm, reprogram metabolism in stromal and cancer cells within the TME by transferring bioactive substances including proteins, mRNAs and miRNAs (microRNAs). sEVs can be delivered from the primary TME to PMN, affecting PMN formation in stroma rewriting, angiogenesis, immunological suppression and matrix cell metabolism by mediating metabolic reprogramming. Herein, we review the functions of sEVs in cancer cells and the TME, how sEVs facilitate PMN establishment to trigger metastasis via metabolic reprogramming, and the prospective applications of sEVs in tumor diagnosis and treatment.