Tumor senescence and radioresistant tumor-initiating cells (TICs): let sleeping dogs lie!

Ultralong circulating choline phosphate liposomal nanomedicines for cascaded chemo-radiotherapy

Cancer radiation therapy (RT) is limited by endogenous DNA repair of tumor cells and microenvironmental hypoxia in tumor tissues. Herein, we demonstrated an effective cancer chemo-radiotherapy strategy based on choline phosphate liposomal nanomedicines, which inhibit the intrinsic radioresistance of RT and concomitantly harness the RT-induced hypoxia to produce additional toxicity to overcome post-RT radioresistance. To achieve this strategy, a radiotherapy sensitizer, vorinostat, and a hypoxia-activated banoxantrone dihydrochloride (AQ4N) were simultaneously delivered to a tumor using liposomes composed of an inverted polarity lipid 2-((2,3-bis(oleoyloxy)propyl)dimethylammonio)ethyl ethyl phosphate (DOCPe). The DOCPe liposomes exhibited a longer blood circulation time and enhanced tumor accumulation, compared to their zwitterionic phosphocholine counterpart. The RT was sensitized by vorinostat to kill non-tolerant normoxic tumor cells efficiently. The irradiation aggravated hypoxia-activated AQ4N to further potentiate RT treatment. This chemo-radiotherapy combination showed excellent tumor treatment efficacy and is promising for future clinical translation.

Opportunities and challenges of radiotherapy for treating cancer

The past 20 years have seen dramatic changes in the delivery of radiation therapy, but the impact of radiobiology on the clinic has been far less substantial. A major consideration in the use of radiotherapy has been on how best to exploit differences between the tumour and host tissue characteristics, which in the past has been achieved empirically by radiation-dose fractionation. New advances are uncovering some of the mechanistic processes that underlie this success story. In this Review, we focus on how these processes might be targeted to improve the outcome of radiotherapy at the individual patient level. This approach would seem a more productive avenue of treatment than simply trying to increase the radiation dose delivered to the tumour.

HDAC inhibitor confers radiosensitivity to prostate stem-like cells

Background:

Radiotherapy can be an effective treatment for prostate cancer, but radiorecurrent tumours do develop. Considering prostate cancer heterogeneity, we hypothesised that primitive stem-like cells may constitute the radiation-resistant fraction.

Methods:

Primary cultures were derived from patients undergoing resection for prostate cancer or benign prostatic hyperplasia. After short-term culture, three populations of cells were sorted, reflecting the prostate epithelial hierarchy, namely stem-like cells (SCs, α₂β₁integrin^hi/CD133⁺), transit-amplifying (TA, α₂β₁integrin^hi/CD133⁻) and committed basal (CB, α₂β₁integrin^lo) cells. Radiosensitivity was measured by colony-forming efficiency (CFE) and DNA damage by comet assay and DNA damage foci quantification. Immunofluorescence and flow cytometry were used to measure heterochromatin. The HDAC (histone deacetylase) inhibitor Trichostatin A was used as a radiosensitiser.

Results:

Stem-like cells had increased CFE post irradiation compared with the more differentiated cells (TA and CB). The SC population sustained fewer lethal double-strand breaks than either TA or CB cells, which correlated with SCs being less proliferative and having increased levels of heterochromatin. Finally, treatment with an HDAC inhibitor sensitised the SCs to radiation.

Interpretation:

Prostate SCs are more radioresistant than more differentiated cell populations. We suggest that the primitive cells survive radiation therapy and that pre-treatment with HDAC inhibitors may sensitise this resistant fraction.

COX-2 promotes breast cancer cell radioresistance via p38/MAPK-mediated cellular anti-apoptosis and invasiveness

Radioresistance is one of the major barriers to improve the survival rate of breast cancer patients. Cyclooxygenase 2 (COX-2) is usually overexpressed in highly invasive and metastatic breast cancer, which may indicate an association with breast cancer radioresistance. The function role of COX-2 was investigated by using a radioresistant breast cancer cell line MDA-MB-231/RR10 and its parental cell line MDA-MB-231 cells before or after COX-2 was silenced by a specific small hairpin RNA (shRNA). The cell proliferation, migration, invasion, colony formation, and apoptosis were measured by CCK-8, scratch-wound, transwell, clone formation assay, and flow cytometry. Protein and mRNA expression were analyzed by Western blot and quantitative reverse transcriptase-polymerase chain reaction. COX-2 is upregulated in MDA-MB-231/RR10 cells compared with in MDA-MB-231 cells, and silencing of COX-2 expression by shRNA in MDA-MB-231/RR10 cells decreases the expression of Bcl-2 and Bcl-XL, but increases the proapoptotic protein BAK, leading to the increased apoptosis following treatment with γ-irradiation in comparison with those in control cells. Silencing of COX-2 also increases the expression of β-catenin and E-cadherin, two anti-invasion proteins, resulting in reduced cell migration and invasion tested by transwell chambers and wound-healing assays. Further study demonstrated that COX-2-induced radioresistance is negatively regulated through the phosphorylation of p38 at Tyr182, and that the phosphorylation of p38 induced by TNF-alpha reduces the expression of Bcl-2, BCL-XL, but increases β-catenin and E-cadherin, leading to the decreased invasiveness of cells. Our data suggest that COX-2, p38, Bcl-2, Bcl-XL, β-catenin, and E-cadherin may be considered as potential therapeutic targets against radioresistant breast cancer.

NKX3.1 haploinsufficiency is prognostic for prostate cancer relapse following surgery or image-guided radiotherapy

BACKGROUND

Despite the use of prostate specific antigen (PSA), Gleason-score, and T-category as prognostic factors, up to 40% of patients with intermediate-risk prostate cancer will fail radical prostatectomy or precision image-guided radiotherapy (IGRT). Additional genetic prognosticators are needed to triage these patients toward intensified combination therapy with novel targeted therapeutics. We tested the role of the NKX3.1 gene as a determinant of treatment outcome given its reported roles in tumor initiating cell (TIC) renewal, the DNA damage response, and cooperation with c-MYC during prostate cancer progression.

METHODS

Using high-resolution array comparative genomic hybridization (aCGH), we profiled the copy number alterations in TIC genes using tumor DNA from frozen needle biopsies derived from 126 intermediate-risk patients who underwent IGRT. These data were correlated to biochemical relapse-free rate (bRFR) by the Kaplan-Meier method and Cox proportional hazards models.

RESULTS

A screen of the aCGH-IGRT data for TIC genes showed frequent copy number alterations for NKX3.1, PSCA, and c-MYC. NKX3.1 haploinsufficiency was associated with increased genomic instability independent of PSA, T-category, and Gleason-score. After adjusting for clinical factors in a multivariate model, NKX3.1 haploinsufficiency was associated with bRFR when tested alone (HR = 3.05, 95% CI: 1.46-6.39, P = 0.0030) or when combined with c-MYC gain (HR = 3.88, 95% CI: 1.78-8.49, P = 0.00067). A similar association was observed for patients following radical prostatectomy with a public aCGH database. NKX3.1 status was associated with positive biopsies post-IGRT and increased clonogen radioresistance in vitro.

CONCLUSIONS

Our results support the use of genomic predictors, such as NKX3.1 status, in needle biopsies for personalized approaches to prostate cancer management.

DNA damage and breast cancer

Cancer is intimately related to the accumulation of DNA damage, and repair failures (including mutation prone repair and hyperactive repair systems). This article relates current clinical categories for breast cancer and their common DNA damage repair defects. Information is included on the potential for accumulation of DNA damage in the breast tissue of a woman during her lifetime and the role of DNA damage in breast cancer development. We then cover endogenous and exogenous sources of DNA damage, types of DNA damage repair and basic signal transduction pathways for three gene products involved in the DNA damage response system; namely BRCA1, BRIT1 and PARP-1. These genes are often considered tumor suppressors because of their roles in DNA damage response and some are under clinical investigation as likely sources for effective new drugs to treat breast cancers. Finally we discuss some of the problems of DNA damage repair systems in cancer and the conundrum of hyper-active repair systems which can introduce mutations and confer a survival advantage to certain types of cancer cells.

Side population cells isolated from hepatic carcinoma cell lines escape being killed by NK cells from NOD/SCID mice

AIM: To examine whether side population (SP) cells isolated from hepatic carcinoma cell lines can escape being killed by NK cells from NOD/SCID mice.

METHODS: Sorted natural killer (NK) cells from NOD/SCID mice were seeded in dishes and cultured for three days in the presence of 25 ng/mL IL-2 and IL-15 to activate cells. SP cells and main population (MP) cells were sorted with the FACSAria from Huh7 and PLC/REF/5 cell lines and co-cultured with activated NK cells for 12 hours. Cell apoptosis was evaluated by annexin V/7-AAD staining and flow cytometry.

RESULTS: There are no significant differences in cell viability and apoptosis between MP cells and SP cells from Huh7 and PLC/REF/5 cell lines (all P > 0.05). However, the proportions of annexin V+/7-AAD+ cells in MP cells co-cultured with NK cells were significantly higher than those in MP cells cultured alone and SP cells co-cultured with NK cells (Huh7: 8.43 ± 1.56 vs4.33 ± 1.36, 4.41 ± 0.70; PLC/PRF/5: 7.89 ± 1.53 vs 5.47 ± 1.04, 4.94 ± 0.95, all P < 0.05).

CONCLUSION: SP cells isolated from Huh7 and PLC/REF/5 cells could probably escape being killed by activated NK cells from NOD/SCID mice.