Activation of M2 macrophage autophagy by rapamycin increases the radiosensitivity of colorectal cancer xenografts

BACKGROUND

Tumor-associated macrophages (TAMs) are intimately involved in cancer radiochemotherapy resistance. However, the mechanism by which macrophages affect radiosensitivity through autophagy remains unclear. The purpose of our study was to investigate how activating autophagy in type-II macrophages (M2) by using rapamycin (RAP) would affect the radiosensitivity of colorectal cancer (CRC) xenografts.

MATERIALS AND METHODS

A nude mouse CRC model was established by injecting LoVo CRC cells. After tumor formation, supernatant from M2 cells (autophagy-unactivated), autophagy-activated M2 cells, or autophagy-downregulated M2 cells was injected peritumorally. All tumor-bearing mice were irradiated with 8-Gy X-rays twice, and the radiosensitivity of CRC xenografts was analyzed in each group.

RESULTS

The mass, volume, and microvessel density (MVD) of tumors in the autophagy-unactivated M2 group significantly increased; however, supernatant from M2 cells that were autophagy-activated by rapamycin significantly decreased tumor weight, volume, and MVD compared with negative control. Combining bafilomycin A1 (BAF-A1) with RAP treatment restored the ability of the M2 supernatant to increase tumor mass, volume, and MVD. Immunohistochemical and Western blot results showed that compared with the negative control group, supernatant from M2 cells that were not activated by autophagy downregulated the expression of Livin and Survivin in tumor tissues; activation of M2 autophagy further downregulated the protein levels.

CONCLUSIONS

Therefore, autophagy-activated M2 supernatant can downregulate the expression of the antiapoptotic genes Livin and Survivin in CRC xenografts, improving the radiosensitivity of CRC by inducing apoptosis in combination with radiotherapy and inhibiting the growth of transplanted tumors.

BCG invokes superior STING-mediated innate immune response over radiotherapy in a carcinogen murine model of urothelial cancer

Radiation and bacillus Calmette-Guérin (BCG) instillations are used clinically for treatment of urothelial carcinoma, but the precise mechanisms by which they activate an immune response remain elusive. The role of the cGAS-STING pathway has been implicated in both BCG and radiation-induced immune response; however, comparison of STING pathway molecules and the immune landscape following treatment in urothelial carcinoma has not been performed. We therefore comprehensively analyzed the local immune response in the bladder tumor microenvironment following radiotherapy and BCG instillations in a well-established spontaneous murine model of urothelial carcinoma to provide insight into activation of STING-mediated immune response. Mice were exposed to the oral carcinogen, BBN, for 12 weeks prior to treatment with a single 15 Gy dose of radiation or three intravesical instillations of BCG (1 × 108  CFU). At sacrifice, tumors were staged by a urologic pathologist and effects of therapy on the immune microenvironment were measured using the NanoString Myeloid Innate Immunity Panel and immunohistochemistry. Clinical relevance was established by measuring immune biomarker expression of cGAS and STING on a human tissue microarray consisting of BCG-treated non-muscle-invasive urothelial carcinomas. BCG instillations in the murine model elevated STING and downstream STING-induced interferon and pro-inflammatory molecules, intratumoral M1 macrophage and T-cell accumulation, and complete tumor eradication. In contrast, radiotherapy caused no changes in STING pathway or innate immune gene expression; rather, it induced M2 macrophage accumulation and elevated FoxP3 expression characteristic of immunosuppression. In human non-muscle-invasive bladder cancer, STING protein expression was elevated at baseline in patients who responded to BCG therapy and increased further after BCG therapy. Overall, these results show that STING pathway activation plays a key role in effective BCG-induced immune response and strongly indicate that the effects of BCG on the bladder cancer immune microenvironment are more beneficial than those induced by radiation. © 2021 The Pathological Society of Great Britain and Ireland.

2-Hexyl-4-Pentylenic Acid (HPTA) Stimulates the Radiotherapy-induced Abscopal Effect on Distal Tumor through Polarization of Tumor-associated Macrophages

OBJECTIVE

The aim of this study was to explore the effects of 2-hexyl-4-pentylenic acid (HPTA) in combination with radiotherapy (RT) on distant unirradiated breast tumors.

METHODS

Using a rat model of chemical carcinogen (7,12-dimethylbenz[a]anthracene,DMBA)-induced breast cancer, tumor volume was monitored and treatment response was evaluated by performing HE staining, immunohistochemistry, immunofluorescence, qRT-PCR, and western blot analyses.

RESULTS

The results demonstrated that HPTA in combination with RT significantly delayed the growth of distant, unirradiated breast tumors. The mechanism of action included tumor-associated macrophage (TAM) infiltration into distant tumor tissues, M1 polarization, and inhibition of tumor angiogenesis by IFN-γ.

CONCLUSION

The results suggest that the combination of HPTA with RT has an abscopal effect on distant tumors via M1-polarized TAMs, and HPTA may be considered as a new therapeutic for amplifying the efficacy of local RT for non-targeted breast tumors.

The graphical abstract was available in the web of www.besjournal.com.

Mesoporous Bi-Containing Radiosensitizer Loading with DOX to Repolarize Tumor-Associated Macrophages and Elicit Immunogenic Tumor Cell Death to Inhibit Tumor Progression

Tumor-associated macrophages (TAMs) were a major component of tumor, which comprised up to 50% of tumor mass, and correlated with poor prognosis in more than 80% of cases. TAMs were resistant to radiotherapy and chemotherapy, and radiation could further activate TAMs to promote tumor progression. Herein, we explored a kind of Bi-based mesoporous upconversion nanophosphor (UCNP) loaded with doxorubicin (UCNP-DOX) to elicit immunogenic tumor cell death and repolarize TAMs to an antitumor M1-like type for strengthening the tumor-specific antitumor immune effects of X-ray radiotherapy. The repolarization effect of UCNP-DOX with X-ray was confirmed in THP-1 cell line, in vivo mouse model, and hydrothorax of a non-small-cell lung carcinoma patient. Moreover, the UCNP-DOX and X-ray radiation could elicit immunogenic tumor necrosis, presenting more tumor antigens for tumor-specific immune response. In a cell co-incubation system, activated macrophages could significantly inhibit cancer colony formation, migration, and invasion. After treatment, xenografted tumor in mice was also found to be significantly regressed and presented substantial CD8-positive T cells. This study opens the door to further enhance the abscopal effects and inhibit the metastasis in radiotherapy.