Apoptosis resistance in tumor cells

Proton Sponge Nanocomposites for Synergistic Tumor Elimination via Autophagy Inhibition-Promoted Cell Apoptosis and Macrophage Repolarization-Enhanced Immune Response

Cytoprotective autophagy and an immunosuppressive tumor microenvironment (TME) are two positive promoters for tumor proliferation and metastasis that severely hinder therapeutic efficacy. Inhibiting autophagy and reconstructing TME toward macrophage activation simultaneously are of great promise for effective tumor elimination, yet are still a huge challenge. Herein, a kind of dendrimer-based proton sponge nanocomposites was designed and constructed for tumor chemo/chemodynamic/immunotherapy through autophagy inhibition-promoted cell apoptosis and macrophage repolarization-enhanced immune response. These obtained nanocomposites contain a proton sponge G5AcP dendrimer, a Fenton-like agent Cu(II), and chemical drug doxorubicin (DOX). When accumulated in tumor regions, G5AcP can act as an immunomodulator to realize deacidification-promoted macrophage repolarization toward antitumoral type, which then secretes inflammatory cytokines to activate T cells. They also regulate intracellular lysosomal pH to inhibit cytoprotective autophagy. The released Cu(II) and DOX can induce aggravated damage through a Fenton-like reaction and chemotherapeutic effect in this autophagy-inhibition condition. Tumor-associated antigens are released from these dying tumor cells to promote the maturity of dendritic cells, further activating T cells. Effective tumor elimination can be achieved by this dendrimer-based therapeutic strategy, providing significant guidance for the design of a promising antitumor nanomedicine.

Eriodictyol mediated selective targeting of the TNFR1/FADD/TRADD axis in cancer cells induce apoptosis and inhibit tumor progression and metastasis

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Eriodictyol induces Selective Cytotoxicity to tumor cells.

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Eriodictyol enhances TNFR1 expression in cancer cells.

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Eriodictyol targets TNFR1 to selectively mediate apoptosis and cytotoxicity to cancer cells.

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Eriodictyol reduces tumour burden in experimentally induced lung metastasis in vivo.

While the anti-inflammatory activities of Eriodictyol, a plant-derived flavonoid is well-known, reports on its anti-cancer efficacy and selective cytotoxicity in cancer cells are still emerging. However, little is known regarding its mechanism of selective anti-cancer activities. Here, we show the mechanism of selective cytotoxicity of Eriodictyol towards cancer cells compared to normal cells. Investigation reveals that Eriodictyol significantly upregulates TNFR1 expression in tumor cells (HeLa and SK-RC-45) while sparing the normal cells (HEK, NKE and WI-38), which display negligible TNFR1 expression, irrespective of the absence or presence of Eriodictyol. Further investigation of the molecular events reveal that Eriodictyol induces apoptosis through expression of the pro-apoptotic DISC components leading to activation of the caspase cascade. In addition, CRISPR-Cas9 mediated knockout of TNFR1 completely blocks apoptosis in HeLa cells in response to Eriodictyol, confirming that Eriodictyol induced cancer cell apoptosis is indeed TNFR1-dependent. Finally, in vivo data demonstrates that Eriodictyol not only impedes tumor growth and progression, but also inhibits metastasis in mice implanted with 4T1 breast cancer cells. Thus, our study has identified Eriodictyol as a compound with high selectivity towards cancer cells through TNFR1 and suggests that it can be further explored for its prospect in cancer therapeutics.

PINK1-induced phosphorylation of mitofusin 2 at serine 442 causes its proteasomal degradation and promotes cell proliferation in lung cancer and pulmonary arterial hypertension

Impaired mitochondrial fusion, due in part to decreased mitofusin 2 (Mfn2) expression, contributes to unrestricted cell proliferation and apoptosis-resistance in hyperproliferative diseases like pulmonary arterial hypertension (PAH) and non-small cell lung cancer (NSCLC). We hypothesized that Mfn2 levels are reduced due to increased proteasomal degradation of Mfn2 triggered by its phosphorylation at serine 442 (S442) and investigated the potential kinase mediators. Mfn2 expression was decreased and Mfn2 S442 phosphorylation was increased in pulmonary artery smooth muscle cells from PAH patients and in NSCLC cells. Mfn2 phosphorylation was mediated by PINK1 and protein kinase A (PKA), although only PINK1 expression was increased in these diseases. We designed a S442 phosphorylation deficient Mfn2 construct (PD-Mfn2) and a S442 constitutively phosphorylated Mfn2 construct (CP-Mfn2). The effects of these modified Mfn2 constructs on Mfn2 expression and biological function were compared with those of the wildtype Mfn2 construct (WT-Mfn2). WT-Mfn2 increased Mfn2 expression and mitochondrial fusion in both PAH and NSCLC cells resulting in increased apoptosis and decreased cell proliferation. Compared to WT-Mfn2, PD-Mfn2 caused greater Mfn2 expression, suppression of proliferation, apoptosis induction, and cell cycle arrest. Conversely, CP-Mfn2 caused only a small increase in Mfn2 expression and did not restore mitochondrial fusion, inhibit cell proliferation, or induce apoptosis. Silencing PINK1 or PKA, or proteasome blockade using MG132, increased Mfn2 expression, enhanced mitochondrial fusion and induced apoptosis. In a xenotransplantation NSCLC model, PD-Mfn2 gene therapy caused greater tumor regression than did therapy with WT-Mfn2. Mfn2 deficiency in PAH and NSCLC reflects proteasomal degradation triggered by Mfn2-S442 phosphorylation by PINK1 and/or PKA. Inhibiting Mfn2 phosphorylation has potential therapeutic benefit in PAH and lung cancer.

Novel microtubule-targeting agents, pyrrolo-1,5-benzoxazepines, induce apoptosis in multi-drug-resistant cancer cells

PURPOSE

The development of multi-drug resistance (MDR) due to the expression of members of the ATP binding cassette (ABC) transporter family is a major obstacle in cancer treatment. The broad range of substrate specificities associated with these transporters leads to the efflux of many anti-cancer drugs from tumour cells. Therefore, the development of new chemotherapeutic agents that are not substrates of these transporters is important. We have recently demonstrated that some members of a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds are microtubule-depolymerising agents that potently induce apoptosis in several cancer cell lines and impair growth of mouse breast tumours. The aim of this current study was to establish whether PBOXs were capable of inducing apoptosis in cancer cells expressing either P-glycoprotein or breast cancer resistance protein (BCRP), two of the main ABC transporters associated with MDR.

METHODS

We performed in vitro studies to assess the effects of PBOXs on cell proliferation, cell cycle and apoptosis in human cancer cell lines and their drug-resistant substrains expressing either P-glycoprotein or BCRP. In addition, we performed a preliminary molecular docking study to examine interactions between PBOXs and P-glycoprotein.

RESULTS

We established that three representative PBOXs, PBOX-6, -15 and -16 were capable of inducing apoptosis in drug-resistant HL60-MDR1 cells (expressing P-glycoprotein) and HL60-ABCG2 cells (expressing BCRP) with similar potencies as in parental human promyelocytic leukaemia HL60 cells. Likewise, resistance to PBOX-6 and -16 was not evident in P-glycoprotein-expressing A2780-ADR cells in comparison with parent human ovarian carcinoma A2780 cells. Finally, we deduced by molecular docking that PBOX-6 is not likely to form favourable interactions with the substrate binding site of P-glycoprotein.

CONCLUSION

Our results suggest that pro-apoptotic PBOX compounds may be potential candidates for the treatment of P-glycoprotein- or BCRP-associated MDR cancers.

Phenylpropanoid glycoside reverse multidrug resistance of colon carcinoma LoVo/Adr cells through induction of apoptosis

AIM: To investigate the relationship between the reversing effect of phenylpropanoid glycoside (PPG) on multidrug resistance of colon carcinoma LoVo/Adr cells and apoptosis.

METHODS: LoVo/Adr cells were divided into three groups: non-treatment (negative control) group, PPG treatment group (treated with 40 mg/L PPG) and verapamil treatment (positive control) group (treated with 5 mg/L VP). The effects of PPG on multidrug resistance of LoVo/Adr cells were examined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. The effects of PPG on cell apoptosis were detected by flow cytometry. The effects of PPG on the activity of Caspase-3 were evaluated by determining pNA release rate.

RESULTS: PPG could decrease the half maximal inhibitory concentration (IC50) of adriamycin in LoVo cells and reverse their resistance to adriamycin. The reversal index was 9.93. PPG could significantly induce the apoptosis of LoVo cells when compared with the non-treatment group (P < 0.01). The rate of pNA release in the PPG treatment group was significantly higher than that in the non-treatment group (31.75 ± 4.34 pmol/min vs 18.45 ± 2.39 pmol/min, P < 0.01). Caspase-3 inhibitor Z-VAD-FMK could significantly inhibit PPG-induced pNA release (17.69 ± 2.68 pmol/min vs 31.75 ± 4.34 pmol/min, P < 0.01).

CONCLUSION: PPG reverse multidrug resistance of LoVo/Adr cells perhaps through induction of Caspase 3-dependent apoptosis.

Altered expression of mRNAs for apoptosis-modulating proteins in a low level multidrug resistant variant of a human lung carcinoma cell line that also expresses mdr1 mRNA

An in vitro model that might be relevant to cancer cell chemoresistance in vivo was generated by exposing the human lung carcinoma clonal cell line DLKP-SQ to 10 sequential pulses of pharmacologically attainable doses of doxorubicin. The resistant variant, DLKP-SQ/10p, was found to be cross-resistant to doxorubicin (10x), vincristine (43x), etoposide (3x), sodium arsenate (3x), paclitaxel (38x) [which could imply overexpression of P-glycoprotein (P-gp) and possibly increased multidrug resistance-associated protein activity] and 5-fluorouracil (4x), but slightly sensitized to carboplatin. Analysis of mRNA levels in the resistant variant revealed overexpression of mdr1 mRNA without significant alteration in mrp, Topo. IIalpha, GSTpi, dhfr or thymidylate synthase mRNA levels. Overexpression of the anti-apoptotic bcl-xL transcript and the pro-apoptotic bax mRNA was also detected but no alterations in bcl-2 or bag-1 mRNA levels were observed. Resistance to a P-gp-associated drug, doxorubicin, could be reversed with P-gp circumventing agents such as cyclosporin A and verapamil, but these substances had no effect on resistance to 5-fluorouracil. Overexpression of the pro-apoptotic bcl-xS gene in the DLKP-SQ/10p line partially reversed resistance not only to P-gp-associated drugs but also to 5-fluorouracil, indicating that the ratio of bcl family members may be important in determining sensitivity to chemotherapeutic drug-induced apoptosis.