Hypoxia is one of the defining characteristics of the tumor microenvironment (TME) in solid cancers. It has a major impact on the growth and spread of malignant cells as well as their resistance to common treatments like radiation and chemotherapy. Here, we explore the complex functions of hypoxia in the TME and investigate its effects on angiogenesis, immunological evasion, and cancer cell metabolism. For prognostic and therapeutic reasons, hypoxia identification is critical, and recent developments in imaging and molecular methods have enhanced our capacity to precisely locate underoxygenated areas inside tumors. Furthermore, targeted therapies that take advantage of hypoxia provide a potential new direction in the treatment of cancer. Therapeutic approaches that specifically target hypoxic conditions in tumors without causing adverse effects are being led by hypoxia-targeted nanocarriers and hypoxia-activated prodrugs (HAPs). This review provides an extensive overview of this dynamic and clinically significant area of oncology research by synthesizing current knowledge about the mechanisms of hypoxia in cancer, highlighting state-of-the-art detection methodologies, and assessing the potential and efficacy of hypoxia-targeted therapies.

Immunotherapy is one of the most promising anti-cancer treatment. It involves activating the host's own immune system to eliminate cancer cells. Activation of cGAS-STING pathway is promising therapeutic approach for cancer immunotherapy. However, in human clinical trials, targeting cGAS-STING pathway results in insufficient or unsustainable anti-tumor response. To enhance its effectiveness, combination with other anti-cancer therapies seems essential to achieve synergistic systemic anti-tumor response.The aim of this study was to evaluate whether the combination of STING agonist-cGAMP with anti-vascular RGD-(KLAKLAK)₂ peptide results in a better anti-tumor response in poorly immunogenic tumors with various STING protein and α_vβ₃ integrin status.Combination therapy inhibited growth of murine breast carcinoma more effectively than melanoma. In melanoma, the administration of STING agonist alone was sufficient to obtain a satisfactory therapeutic effect. In both tumor models we have noted stimulation of innate immune response following cGAMP administration alone or in combination. The largest population of immune cells infiltrating the TME after therapy were activated NK cells. Increased infiltration of cytotoxic CD8⁺ T lymphocytes within the TME was only observed in melanoma tumors. However, they also expressed the “exhaustion” PD-1 receptor. In contrast, in breast carcinoma tumors each therapy caused the drop in the number of infiltrating CD8⁺ T cells.The obtained results indicate an additional therapeutic benefit from combining STING agonist with an anti-vascular agent. However, this effect depends on the type of tumor, the status of its microenvironment and the expression of specific proteins such as STING and α_vβ₃ family integrin.

Imiquimod (IMQ), a drug from aminoquinoline group, is the toll-like receptor 7 (TLR7) agonist. It acts as an immunostimulant and radio-sensitizing agent. IMQ stimulates both innate and adaptive immune response. Despite studies conducted, there are no unambiguous data showing how IMQ affects the condition of tumor blood vessels. Tumor vasculature plays the main role in tumor progression. Formation of abnormal blood vessels increases area of hypoxia which recruits suppressor cells, blocks tumor infiltration by CD8⁺ T lymphocytes, inhibits efficacy of chemoterapeutic drug and leads to cancer relapse. Normalization is a type of therapy targeted at abnormal tumor blood vessels. Here, we demonstrated that 50 µg of IMQ inhibits the growth of melanoma tumors more efficiently, compared to other tested doses and the control group. Dose escalation did not improve the therapeutic antitumor potential of TLR7 agonist. A dose of 50 µg of IMQ most effectively reduced tumor blood vessel density. Imiquimod normalized tumor vasculature both structurally (by reducing vessel tortuosity and increasing pericyte coverage) and functionally (by improving tumor perfusion) in a dose-dependent manner. Hypoxia regions in tumors of treated mice were significantly reduced after IMQ administration. A dose of 50 µg of IMQ had also the greatest impact on the changes in tumor-infiltrating T lymphocytes levels. TLR7 agonist inhibited angiogenesis in treated mice. Functional vascular normalization by IMQ increases the effectiveness of low dose of doxorubicin. Higher dose of IMQ showed worse effects than lower doses including decreased tumor perfusion, increased tumor hypoxia and immunosuppression. This knowledge may help to optimize the combination of the selected IMQ dose with e.g. chemotherapy or radiotherapy to elicit synergistic effect in cancer treatment. To conclude, we outline IMQ repurposing as a vascular normalizing agent. Our research results may contribute to expanding the therapeutic indications for the use of IMQ in anticancer therapy in the future.

Nanoparticles (NPs) dual-targeted with folic acid (FA) and biotin (BIO) are developed to overcome problems associated with conventional chemotherapy and tumor heterogeneity. Although some preliminary studies have been conducted to develop dual-targeted micelles for delivery of docetaxel (Dtx), a more detailed analysis is needed to discover their pharmaceutical potential. Therefore, this manuscript is focused on a comprehensive analysis of the influence of the type and density of targeting ligand on micelles' morphology, physicochemical properties, drug loading and release, cell internalization, cytotoxicity in vitro against several kinds of cells and in vivo on two mice cancer models. For this purpose, three kinds of micelles were obtained: decorated with one type of ligand (FA or BIO) and dual-targeted. The micelles contained different amounts of FA- and/or BIO-functionalized polymer (10, 25, and 50%). Additionally, the dual-targeted micelles were compared with a mixture of two kinds of single-targeted micelles. The study showed that the cytotoxic effect of micelles strongly depends on the type of cancer cells and their surface characteristics. The micelles with a higher density of ligands may have higher efficiency against cells with lower expression of cell surface receptors (SK-BR-3 and MCF-7). Conversely, micelles with lower ligand density may be advantageous against cancer cells with overexpression of surface receptors (HeLa, 4T1). Interestingly, the drug delivered in FA-targeted micelles showed higher cytotoxicity compared to dual-targeted micelles in which two ligands are present on the same NP. However, Dtx delivered in a mixture of micelles single-targeted with FA and BIO showed the highest cytotoxic effect, which was confirmed in vitro and in vivo on the mice model.

Hypoxia is a hallmark of solid tumors that reduces chemotherapy efficacy and enhances systemic toxicity. This study evaluated hypoxia-sensitive polymersomes as a delivery system for doxorubicin (DOX) to improve antitumor efficacy and reduce side effects. Methods: Polymersomes were synthesized, loaded with DOX, and tested on cancer and healthy cells under normoxic and hypoxic conditions. Cytotoxicity, cellular uptake, apoptosis induction, and potential mechanism of degradation were assessed. In vivo efficacy was investigated in 4T1 tumor-bearing mice treated intravenously with free DOX or DOX-loaded hypoxia-sensitive polymersomes (three times 5 mg/kg). Tumor volume, body weight, histology, and immunochemistry were analyzed. In vitro, both free DOX and DOX-loaded polymersomes induced significant cytotoxicity and apoptosis. The effect was enhanced under hypoxia, consistent with elevated NQO1 expression. In vivo, both formulations suppressed tumor growth to a comparable degree; however, polymersome-treated mice exhibited markedly reduced weight loss, indicating lowered systemic toxicity. Histological examination showed extensive necrosis and architectural disruption in tumors from both treatment groups. Hypoxia-sensitive polymersomes effectively deliver doxorubicin to hypoxic regions, achieving tumor growth inhibition comparable to that of the free drug while reducing treatment-associated toxicity. These findings support encapsulated DOX as a promising strategy for safer chemotherapy in hypoxic cancers.