Enhanced killing of SCC17B human head and neck squamous cell carcinoma cells after photodynamic therapy plus fenretinide via the de novo sphingolipid biosynthesis pathway and apoptosis

miR-31 Modulates Liver Cancer HepG2 Cell Apoptosis and Invasion via ROCK1/F-Actin Pathways

PURPOSE

Liver cancer is one of the most common malignant tumor in the world. miR-31 is downregulated in liver cancer and associated with tumor growth and metastasis. However, the underlying mechanism remains unclear.

METHODS

Cellular apoptosis was detected via MTT, TUNEL assay, LDH release and Annexin V/PI flow-cytometry analysis. Cellular migration and invasion were measured by the Transwell chamber assay. Mitochondrial functions were evaluated via mitochondrial membrane potential JC-1 staining and mPTP opening assessment. The mitophagy activity was examined via Western blots.

RESULTS

In the present study, our results confirm that miR-31 promotes apoptosis and inhibits proliferation and metastasis in liver cancer HepG2 cells. In vitro, miR-31 promotes HepG2 cell apoptosis through the mitochondrial pathway as indicated by mitochondrial potential reduction, increased mPTP opening time, cty-c release and imbalance of pro- and anti-apoptotic proteins. Furthermore, miR-31 reduces the energy generation by inhibiting mitochondrial respiratory function. At last, it is demonstrated that miR-31 triggers the mitochondrial damage via ROCK1/F-actin pathway. Inhibiting the ROCK1/F-actin pathway abolishes the effects of miR-31 mimic on mitochondrial injury, apoptosis, proliferation arrest and migration inhibition.

CONCLUSION

Our results reveal that miR-31 can inhibit HepG2 cell survival and metastasis by activating the ROCK1/F-actin pathway.

The involvement of M2 macrophage polarization inhibition in fenretinide-mediated chemopreventive effects on colon cancer

Clinical studies have shown that fenretinide (4-HPR) is an attractive chemopreventive agent for cancer treatment. However, to date, few studies have demonstrated the mechanism of the preventive effect of 4-HPR. In our current study, we revealed that 4-HPR could significantly suppress IL-4/IL-13 induced M2-like polarization of macrophages, which was demonstrated by the reduced expression of M2 surface markers, the down-regulation of M2 marker genes, and the inhibition of M2-like macrophages promoted angiogenesis. Mechanistically, our study suggested that the inhibition of the phosphorylation of STAT6, rather than the generation of oxidative stress, is involved in the 4-HPR-driven inhibition of M2 polarization. More intriguingly, by utilizing adenomatous polyposis coli (APC^min/+) transgenic mice, we demonstrated that the tumorigenesis was dramatically decreased by 4-HPR treatment accompanied with fewer M2-like macrophages in the tumor tissues, thereby profoundly blocking tumor angiogenesis. These findings, for the first time, reveal the involvement of M2 polarization inhibition in 4-HPR-mediated chemoprevention, which provides a new point of insight and indicates the potential mechanism underlying the chemopreventive effect of 4-HPR.

Interaction of acid ceramidase inhibitor LCL521 with tumor response to photodynamic therapy and photodynamic therapy-generated vaccine

Acid ceramidase has been identified as a promising target for cancer therapy. One of its most effective inhibitors, LCL521, was examined as adjuvant to photodynamic therapy (PDT) using mouse squamous cell carcinoma SCCVII model of head and neck cancer. Lethal effects of PDT, assessed by colony forming ability of in vitro treated SCCVII cells, were greatly enhanced when combined with 10 µM LCL521 treatment particularly when preceding PDT. When PDT-treated SCCVII cells are used to vaccinate SCCVII tumor-bearing mice (PDT vaccine protocol), adjuvant LCL521 treatment (75 mg/kg) resulted in a marked retardation of tumor growth. This effect can be attributed to the capacity of LCL521 to effectively restrict the activity of two main immunoregulatory cell populations (Tregs and myeloid-derived suppressor cells, MDSCs) that are known to hinder the efficacy of PDT vaccines. The therapeutic benefit with adjuvant LCL521 was also achieved with SCCVII tumors treated with standard PDT when using immunocompetent mice but not with immunodeficient hosts. The interaction of LCL521 with PDT-based antitumor mechanisms is dominated by immune system contribution that includes overriding the effects of immunoregulatory cells, but could also include a tacit contribution from boosting direct tumor cell kill.

Enhanced apoptotic cancer cell killing after Foscan photodynamic therapy combined with fenretinide via de novo sphingolipid biosynthesis pathway

We and others have shown that stresses, including photodynamic therapy (PDT), can disrupt the de novo sphingolipid biosynthesis pathway, leading to changes in the levels of sphingolipids, and subsequently, modulation of cell death. The de novo sphingolipid biosynthesis pathway includes a ceramide synthase-dependent reaction, giving rise to dihydroceramide, which is then converted in a desaturase-dependent reaction to ceramide. In this study we tested the hypothesis that combining Foscan-mediated PDT with desaturase inhibitor fenretinide (HPR) enhances cancer cell killing. We discovered that by subjecting SCC19 cells, a human head and neck squamous cell carcinoma cell line, to PDT+HPR resulted in enhanced accumulation of C16-dihydroceramide, not ceramide. Concomitantly, mitochondrial depolarization was enhanced by the combined treatment. Enhanced activation of caspase-3 after PDT+HPR was inhibited by FB. Enhanced clonogenic cell death after the combination was sensitive to FB, as well as Bcl2- and caspase inhibitors. Treatment of mouse SCCVII squamous cell carcinoma tumors with PDT+HPR resulted in improved long-term tumor cures. Overall, our data showed that combining PDT with HPR enhanced apoptotic cancer cell killing and antitumor efficacy of PDT. The data suggest the involvement of the de novo sphingolipid biosynthesis pathway in enhanced apoptotic cell killing after PDT+HPR, and identify the combination as a novel more effective anticancer treatment than either treatment alone.

Chlorin e6-mediated photodynamic effect diminishes therapeutic potential of 5-aza-2'-deoxycytidine-based whole-tumour-cell vaccine in mice bearing squamous cell carcinoma SCCVII

After years of setbacks, therapeutic cancer vaccines have become an alternative treatment option. Among the diversity of targeted tumour associated antigens (TAA), cancer-testis antigens (CTAs) are promising targets for cancer immunotherapy because they are highly immunogenic; meanwhile, they are expressed in human tumours of different histological origin but not in adult somatic tissues. Epigenetic modifications, such as DNA methylation, regulate CTAs expression both in normal and cancer cells. 5-Aza-2'-deoxycytidine (5-AZA-CdR), a DNA hypomethylating drug, induces the expression of CTAs in neoplastic cells. In these studies, we used 5-AZA-CdR-mediated up-regulation of CTAs and chlorin e6-mediated photodynamic effect in the production of a whole-tumour-cell vaccine against murine squamous cell carcinoma SCCVII in C3H/HeN mice. The results show that 5-AZA-CdR can be used to elevate levels of diverse CTAs in SCCVII cells. The 5-AZA-CdR-based vaccine, combined with the systemic administration of 5-AZA-CdR, delayed tumour growth. However, the treatment had no effect on survival in mice, most likely because of the toxicity of systemic treatment with 5-AZA-CdR. The photodynamic effect diminished therapeutic potential of 5-AZA-CdR-based vaccine. Chemo-immunotherapy with 5-AZA-CdR and therapeutic cancer vaccines may be an alternative approach to cancer therapy. However, further studies are needed to optimize treatment and vaccine preparation protocols.