Molecular fingerprinting of radiation resistant tumors: can we apprehend and rehabilitate the suspects?

Assessment of Proliferation and Apoptosis in Testes of Rats after Experimental Localized Electron Irradiation

BACKGROUND AND PURPOSE

With the emergence of linear accelerators in radiotherapy, it becomes necessary to accurately select new dosing regimens. The purpose of this study was to assess the morphological changes of spermatogenesis after radiation exposure.

MATERIALS AND METHODS

Male Wistar rats (n = 40) were subjected to targeted ionizing radiation on a pulsed electron accelerator "NOVAC-11" with doses of 2, 8 and 12 Gy. Spermatogenesis was assessed a week later using light microscopy and immunohistochemical method (antibodies to Ki-67, Bcl-2, p53, Caspase 3).

RESULTS

A decrease in the number of normal germ cells was seen in all experimental groups, while radioresistant Sertoli and Leydig cells were barely affected. The most serious damage to the tubules and germ cells was observed in 8 and 12 Gy irradiation groups. IHC analysis of testes after irradiation showed a shift in the proliferative-apoptotic balance toward apoptosis of germ cells: a decrease in the expression levels of Ki-67 and Bcl-2, an increase in p53-positive and caspase 3-positive cells by the end of the experiment.

CONCLUSION

Dose-dependent progressive pathomorphological changes in histoarchitectonics of the testes are traced, and a decrease in the number of germ cells is seen on the seventh day after irradiation with a pulsed electron accelerator "NOVAC-11".

Venetoclax cooperates with ionizing radiation to attenuate Diffuse Midline Glioma tumor growth

PURPOSE

Tumor relapse after radiation therapy (RT) is a major hurdle in treating pediatric H3K27M-mutant diffuse midline gliomas (DMGs). RT-induced stress increases association of BCL2 family of proteins with BH3 pro-apoptotic activators preventing apoptosis. We hypothesized that inhibition of RT-induced BCL2 with a clinically relevant inhibitor, venetoclax, will block BCL2 activity leading to increased apoptosis. BCL2 has never been implicated in DMG as a RT-induced resistant mechanism.

EXPERIMENTAL DESIGN

We performed an integrated genomic analysis to determine genes responsible for radioresistance and a targeted drug screen to identify drugs that synergize with radiation in DMG. Effect of venetoclax on radiation-na�ve and 6Gy radiation on cells was evaluated by studying cell death, changes in BCL2 phosphorylation, reactive oxygen species (ROS), and apoptosis, as well as BCL2 association with BH3 apoptosis initiators. The efficacy of combining venetoclax with radiation was evaluated in vivo using orthotopic xenograft models.

RESULTS

BCL2 was identified as a key regulator of tumor growth after radiation in DMGs. Radiation sensitizes DMGs to venetoclax treatment independent of p53 status. Venetoclax as a monotherapy was not cytotoxic to DMG cells. Post-radiation venetoclax treatment significantly increased cell death, reduced BCL2-BIM association and augmented mitochondrial ROS leading to increased apoptosis. Combining venetoclax with RT significantly enhanced the survival of mice with DMG tumors.

CONCLUSIONS

This study shows that venetoclax impedes the anti-apoptotic function of radiation-induced BCL2 in DMG leading to increased apoptosis. Results from these pre-clinical studies demonstrate the potential use of the BCL2 inhibitor, venetoclax, combined with RT for pediatric DMG.

Apigenin Enhanced Radiation-Induced Apoptosis/Necrosis by Sensitization of LNCaP Prostate Cancer Cells to 6 MV Photon Beams

OBJECTIVE

Whereas prostate cancer (PrCa) may be unresponsive or moderately responsive to radiation therapy (RT)- most common modality for treatment of PrCa- patients must receive a high dose of RT In order to achieve appropriate tumour control. However, this increase in radiation dose may lead to severe adverse effects in normal tissues. Sensitization of PrCa to radiation provides an alternate approach to improve the therapeutic efficacy of RT. This study aims to assess the radiosensitisation effect of apigenin (Api) on a prostate cancer cell line (LNCaP).

MATERIALS AND METHODS

In this experimental study, LNCaP cells were treated with 0-80 μM Api to investigate its effect on LNCaP cell viability and determine its half-maximal inhibitory concentration (IC₅₀). Next, the cells were divided into four groups: i. Control, ii. Cells treated with the IC₅₀ concentration of Api, iii. Cells treated with 2 Gy ionizing radiation (IR), and cells co-treated with Api and IR. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, real-time polymerase chain reaction (PCR), and an Annexin V-FITC/PI assay were performed to assess cell survival, Bax and Bcl-2 expressions, and presence of apoptosis and necrosis.

RESULTS

Api inhibited cell survival in a dose-dependent, but not time-dependent manner. Cells treated with Api had increased amounts of early apoptosis, late apoptosis, and secondary necrosis compared to the control group. This group also had decreased Bcl-2 gene expression and up-regulated Bax gene expression. Co-treatment with Api and IR significantly inhibited cell survival, and increased early apoptosis, late apoptosis and secondary necrosis compared to the other groups. There was a significant decrease in Bcl-2 gene expression along with up-regulation of Bax gene expression, and Bax/Bcl-2 ratio changes that favoured apoptosis.

CONCLUSION

Api inhibited PrCa cell survival and induced apoptosis as a single agent. In addition, Api significantly sensitized the LNCaP cells to IR and enhanced radiation-induced apoptosis.

Damage-associated molecular patterns in tumor radiotherapy

Radiotherapy is one of the most common modalities for the treatment of cancer. One of the most promising effects of radiotherapy is immunologic cell death and the release of danger alarms, which are known as damage-associated molecular patterns (DAMPs). DAMPs are able to trigger cancer cells and other cells within tumor microenvironment (TME), either for suppression or promotion of tumor growth. Heat shock proteins (HSPs) including HSP70 and HSP90, high mobility group box 1 (HMGB1), and adenosine triphosphate (ATP) and its metabolites such as adenosine are the most common danger alarms that are released after radiotherapy-induced immunologic cell death. Some DAMPs including adenosine is able to interact with both cancer cells as well as other cells in TME to promote tumor growth and resistance to radiotherapy. However, others are able to trigger anti-tumor immunity or both tumor suppressive and immunosuppressive mechanisms depending on affected cells. In this review, we explain the mechanisms behind the release of radiation-induced DAMPs, and its consequences on cells within tumor. Targeting of these mechanisms may be in favor of tumor control in combination with radiotherapy and radioimmunotherapy.

Synergistic Effect of a Mesothelin-Targeted 227Th Conjugate in Combination with DNA Damage Response Inhibitors in Ovarian Cancer Xenograft Models

Targeted ²²⁷Th conjugates (TTCs) represent a new class of therapeutic radiopharmaceuticals for targeted α-therapy. They comprise the α-emitter ²²⁷Th complexed to a 3,2-hydroxypyridinone chelator conjugated to a tumor-targeting monoclonal antibody. The high energy and short range of the α-particles induce antitumor activity, driven by the induction of complex DNA double-strand breaks. We hypothesized that blocking the DNA damage response (DDR) pathway should further sensitize cancer cells by inhibiting DNA repair, thereby increasing the response to TTCs. Methods: This article reports the evaluation of the mesothelin (MSLN)-TTC conjugate (BAY 2287411) in combination with several DDR inhibitors, each of them blocking different DDR pathway enzymes. MSLN is a validated cancer target known to be overexpressed in mesothelioma, ovarian, lung, breast, and pancreatic cancer, with low expression in normal tissue. In vitro cytotoxicity experiments were performed on cancer cell lines by combining the MSLN-TTC with inhibitors of ataxia telangiectasia mutated, ataxia telangiectasia and Rad3-related (ATR), DNA-dependent protein kinase, and poly[adenosine diphosphate ribose] polymerase (PARP) 1/2. Further, we evaluated the antitumor efficacy of the MSLN-TTC in combination with DDR inhibitors in human ovarian cancer xenograft models. Results: Synergistic activity was observed in vitro for all tested inhibitors (inhibitors are denoted herein by the suffix “i”) when combined with MSLN-TTC. ATRi and PARPi appeared to induce the strongest increase in potency. Further, in vivo antitumor efficacy of the MSLN-TTC in combination with ATRi or PARPi was investigated in the OVCAR-3 and OVCAR-8 xenograft models in nude mice, demonstrating synergistic antitumor activity for the ATRi combination at doses demonstrated to be nonefficacious when administered as monotherapy. Conclusion: The presented data support the mechanism-based rationale for combining the MSLN-TTC with DDR inhibitors as new treatment strategies in MSLN-positive ovarian cancer.

Cyclooxygenase‑2‑mediated upregulation of heme oxygenase 1 mitigates the toxicity of deuterium‑tritium fusion radiation

Utilizing the energy released from the nuclear fusion of deuterium with tritium (D-T) may be an important method of supplying energy in the future. The ionizing radiation emitted from nuclear fusion is a potential health risk to humans, including scientists who are currently performing nuclear fusion experiments and the employees of fusion nuclear plants, in the future. However, there have been few reports on the biological effects of fusion radiation. In the present study, using the High Intensity D-T Fusion Neutron Generator, the DNA damage and its regulation in normal human fibroblasts exposed to fusion radiation were investigated. Heme oxygenase 1 (HO-1), which is reported to induce anti-inflammatory activity, was upregulated in the irradiated cells. Pretreatment with the HO-1 inhibitor, protoporphyrin IX zinc (II), exacerbated double strand break formation following exposure to fusion radiation. The expression of cyclooxygenase-2 (COX-2) contributed to the upregulation of HO-1, as demonstrated by the result that its inhibitor, NS-398, inhibited the induction of HO-1 in irradiated cells. It was further clarified that the ataxia telangiectasia mutated DNA damage response was activated and it stimulated the phosphorylation of p38 mitogen-activated protein kinase, which was responsible for the upregulation of COX-2 and HO-1. These results provide novel information on fusion radiation-induced biological effects and potential targets for decreasing the associated health risks.

Cathepsin B and L inhibitors: a patent review (2010 - present)

INTRODUCTION

Cathepsins play an important role in protein degradation and processing. Aberrant cathepsin B or L is closely associated with many serious diseases such as cancer, osteoporosis and autoimmune disorders. Therefore, development of potent and selective cathepsin B and L inhibitors has aroused much attention in recent years. Although several classes of cathepsin inhibitors are presently available, there are still some problems to solve, such as broad-spectrum inhibition to protease, specially cysteine proteases, which lead to unpredictable side effects in clinical trials. Therefore, it is very necessary to discovery new scaffolds and new application of cathepsin B and L inhibitors for developing therapeutic agents for treating diseases mediated by cathepsin B or L. Areas covered: This updated review summarizes new patents on cathepsin B and L inhibitors from 2010 to present. Expert opinion: The review gives the latest development in the area of inhibitors of cathepsin B and L, which have been considered key therapeutic targets for the development of drugs treating related diseases. This review puts emphasis on the discovery of novel small molecule inhibitors of cathepsin B and L, as well as their new application as new therapeutic agents.

Disruption of STAT3 by niclosamide reverses radioresistance of human lung cancer

A major challenge affecting the outcomes of patients with lung cancer is the development of acquired radioresistance. However, the mechanisms underlying the development of resistance to therapy are not fully understood. Here, we discovered that ionizing radiation induces phosphorylation of Janus-associated kinase (JAK)-2 and STAT3 in association with increased levels of Bcl2/Bcl-XL in various human lung cancer cells. To uncover new mechanism(s) of radioresistance of lung cancer, we established lung cancer cell model systems with acquired radioresistance. As compared with radiosensitive parental lung cancer cells (i.e., A549, H358, and H157), the JAK2/STAT3/Bcl2/Bcl-XL survival pathway is significantly more activated in acquired radioresistant lung cancer cells (i.e., A549-IRR, H358-IRR, and H157-IRR). Higher levels of STAT3 were found to be accumulated in the nucleus of radioresistant lung cancer cells. Niclosamide, a potent STAT3 inhibitor, can reduce STAT3 nuclear localization in radioresistant lung cancer cells. Intriguingly, either inhibition of STAT3 activity by niclosamide or depletion of STAT3 by RNA interference reverses radioresistance in vitro. Niclosamide alone or in combination with radiation overcame radioresistance in lung cancer xenografts. These findings uncover a novel mechanism of radioresistance and provide a more effective approach to overcome radioresistance by blocking the STAT3/Bcl2/Bcl-XL survival signaling pathway, which may potentially improve lung cancer outcome, especially for those patients who have resistance to radiotherapy.

Effects of the monoamine oxidase inhibitors pargyline and tranylcypromine on cellular proliferation in human prostate cancer cells

Chemotherapy is one of the therapeutic strategies that has been used for the inhibition of cancer cell proliferation in several types of cancer, including prostate cancer. Although monoamine oxidase (MAO) inhibitors, phytoestrogen and antioxidants used in chemotherapy have been systematically studied, their effects on cancer cell growth remain to be fully understood. The purpose of this study was to investigate the effects of the MAO inhibitors, pargyline and tranylcypromine on cell survival in human prostate carcinoma (LNCaP-LN3) cells. After treating LNCaP-LN3 cells with pargyline or tranylcypromine, we examined cell proliferation, cell cycle pattern, apoptosis and the expression levels of apoptosis-related genes. The proliferation of cells exposed to pargyline decreased in a dose- and time-dependent manner, while tranylcypromine-treated cells showed the opposite results. Treatment with pargyline significantly induced cell cycle arrest at the G1 phase compared to the control and tranylcypromine-treated cells. In addition, pargyline induced an increase in the cell death rate by promoting apoptosis; however, tranylcypromine had no effect on LNCaP-LN3 cells. Based on our results, we suggest that pargyline is more powerful than tranylcypromine for the treatment of human prostate cancer.

Targeting the Bcl-2 family for cancer therapy

INTRODUCTION

Programmed cell death is well-orchestrated process regulated by multiple pro-apoptotic and anti-apoptotic genes, particularly those of the Bcl-2 gene family. These genes are well documented in cancer with aberrant expression being strongly associated with resistance to chemotherapy and radiation.

AREAS COVERED

This review focuses on the resistance induced by the Bcl-2 family of anti-apoptotic proteins and current therapeutic interventions currently in preclinical or clinical trials that target this pathway. Major resistance mechanisms that are regulated by Bcl-2 family proteins and potential strategies to circumvent resistance are also examined. Although antisense and gene therapy strategies are used to nullify Bcl-2 family proteins, recent approaches use small molecule inhibitors (SMIs) and peptides. Structural similarity of the Bcl-2 family of proteins greatly favors development of inhibitors that target the BH3 domain, called BH3 mimetics.

EXPERT OPINION

Strategies to specifically identify and inhibit critical determinants that promote therapy resistance and tumor progression represent viable approaches for developing effective cancer therapies. From a clinical perspective, pretreatment with novel, potent Bcl-2 inhibitors either alone or in combination with conventional therapies hold significant promise for providing beneficial clinical outcomes. Identifying SMIs with broader and higher affinities for inhibiting all of the Bcl-2 pro-survival proteins will facilitate development of superior cancer therapies.

Factors implicated in radiation therapy failure and radiosensitization of prostate cancer

Tissue markers may be helpful in enhancing prediction of radiation therapy (RT) failure of prostate cancer (PCa). Among the various biomarkers tested in Phase III randomized trials conducted by the Radiation Therapy Oncology Group, p16, Ki-67, MDM2, COX-2, and PKA yielded the most robust data in predicting RT failure. Other pathways involved in RT failure are also implicated in the development of castration-resistant PCa, including the hypersensitive androgen receptor, EGFR, VEGF-R, and PI3K/Akt. Most of them are detectable in PCa tissue even at the time of initial diagnosis. Emerging evidence suggests that RT failure of PCa results from a multifactorial and heterogeneous disease process. A number of tissue markers are available to identify patients at high risk to fail RT. Some of these markers have the promise to be targeted by drugs currently available to enhance the efficacy of RT and delay disease progression.