The Akt-inhibitor Erufosine induces apoptotic cell death in prostate cancer cells and increases the short term effects of ionizing radiation

Anticancer Effects of Mitoquinone via Cell Cycle Arrest and Apoptosis in Canine Mammary Gland Tumor Cells

Treating female canine mammary gland tumors is crucial owing to their propensity for rapid progression and metastasis, significantly impacting the overall health and well-being of dogs. Mitoquinone (MitoQ), an antioxidant, has shown promise in inhibiting the migration, invasion, and clonogenicity of human breast cancer cells. Thus, we investigated MitoQ's potential anticancer properties against canine mammary gland tumor cells, CMT-U27 and CF41.Mg. MitoQ markedly suppressed the proliferation and migration of both CMT-U27 and CF41.Mg cells and induced apoptotic cell death in a dose-dependent manner. Furthermore, treatment with MitoQ led to increased levels of pro-apoptotic proteins, including cleaved-caspase3, BAX, and phospho-p53. Cell cycle analysis revealed that MitoQ hindered cell progression in the G1 and S phases in CMT-U27 and CF41.Mg cells. These findings were supported using western blot analysis, demonstrating elevated levels of cleaved caspase-3, a hallmark of apoptosis, and decreased expression of cyclin-dependent kinase (CDK) 2 and cyclin D4, pivotal regulators of the cell cycle. In conclusion, MitoQ exhibits in vitro antitumor effects by inducing apoptosis and arresting the cell cycle in canine mammary gland tumors, suggesting its potential as a preventive or therapeutic agent against canine mammary cancer.

Micellar Curcumin Substantially Increases the Antineoplastic Activity of the Alkylphosphocholine Erufosine against TWIST1 Positive Cutaneous T Cell Lymphoma Cell Lines

Cutaneous T-cell lymphoma (CTCL) is a rare form of cancer with local as well as systemic manifestations. Concomitant bacterial infections increase morbidity and mortality rates due to impaired skin barrier and immune deficiency. In the current study, we demonstrated that the in vitro anti-lymphoma potential of erufosine is diminished by TWIST1 expression and micellar curcumin substantially increases its antineoplastic activity. Pharmacokinetic analysis showed that the micellar curcumin (MCRM) used in our study was characterized by low zeta potential, slow release of curcumin, and fast cell membrane penetration. The combination ratio 1:4 [erufosine:MCRM] achieved strong synergism by inhibiting cell proliferation and clonogenicity. The combined antiproliferative effects were calculated using the symbolic mathematical software MAPLE 15. The synergistic combination strongly decreased the expression of TWIST1 and protein kinase B/Akt as proven by western blotting. Significant reductions in NF-κB activation, induction of apoptosis, and altered glutathione levels were demonstrated by corresponding assays. In addition, the synergistic combination enhanced the anti-staphylococcal activity and prevented biofilm formation, as shown by crystal violet staining. Taken together, the above results show that the development of nanotechnological treatment modalities for CTCL, based on rational drug combinations exhibiting parallel antineoplastic and antibacterial effects, may prove efficacious.

Antineoplastic effects of erufosine on small cell and non-small cell lung cancer cells through induction of apoptosis and cell cycle arrest

BACKGROUND

Lung cancer (LC) is the most common types of cancer worldwide and is marked by high mortality rate. LC is classified into two major types due to their molecular and histological properties; non-small cell lung cancer (NSCLC) A549 and small cell lung cancer (SCLC). Currently, surgery, chemotherapy and radiation therapy are the most common treatment options of LC. However, the survival rate of LC is still very poor. Therefore, new treatment strategies are urgently needed. Erufosine (ErPC3) is a novel alkylphosphocholine and inhibits the translocation of Akt to the plasma membrane.

METHODS AND RESULTS

In the current study, the effects of ErPC3 in NSCLC cell line A549 and SCLC cell line DMS 114 in terms of cell viability, induction of apoptosis, cell cycle phase distribution, gene and protein expression levels, and migration capacity were investigated. 25 µM ErPC3 exhibited dose-dependent cytotoxicity against in both cancer cells. However, DMS 114 was more sensitive to ErPC3 than A549. Similarly, ErPC3 induced apoptotic cell ratio in DMS114 was significantly greater than A549. 25 µM ErPC3 caused the accumulation of both cell in G2/M phase. The levels of BCL-2 were downregulated and CASPASE 3-7 and BAX were upregulated while p-Akt levels were reduced in A549 and DMS 114 cells treated with 25 µM ErPC3. Besides, ErPC3 displayed anti-migratory effect on A549 and DMS 114.

CONCLUSION

These findings suggest that ErPC3 may be a promising novel therapeutic candidate for treatment of LC. ErPC3 treatment merits further investigation as potential agent against LC.

Dual Akt and Bcl-2 inhibition induces cell-type specific modulation of apoptotic and autophagic signaling in castration resistant prostate cancer cell lines

BACKGROUND

Cancer cell survival depends on the cross-regulation between apoptosis and autophagy which share common signaling pathways including PI3K/Akt/mTOR and Bcl-2. The aim of this study was to elucidate the modulation patterns between apoptosis and autophagy following dual inhibition by Akt inhibitor erufosine and Bcl-2 inhibitor ABT-737 in castration-resistant prostate cancer (CRPC) cell lines, PC-3 (Bax+) and DU-145 (Bax-).

METHODS AND RESULTS

Cell cycle progression, apoptotic and autophagic signaling were examined by flow cytometry, multi-caspase assay, Hoechst staining, acridine orange staining of acidic vesicular organelles (AVOs), qRT-PCR and Western Blot. Dual inhibition increased G2/M arrest in PC-3 and DU-145, but not in the healthy prostate epithelium cells, PNT-1A. Only in PC-3, dual inhibition induced synergistic apoptotic and additive autophagic effects. In DU-145 and PNT-1A cells, ABT-737 did not display any remarkable effect on multicaspase activity and erufosine and ABT-737, neither alone nor in combination induced AVOs. By dual inhibition, AKT, BCL-2 and NF-κB gene expressions were downregulated in PC-3, both ATG-5 and BECLIN-1 gene expressions were upregulated in DU-145 but Beclin-1 protein expression was substantially reduced in both CRPC cells. Dual inhibition-induced synergistic multicaspase activation in PC-3 degrades and disrupts autophagic activity of Beclin-1, enhancing caspase-dependent apoptosis. However, in DU-145, following dual inhibition, rate of multicaspase induction and apoptosis are lower but autophagy is completely abolished despite markedly increased BECLIN-1 gene expression.

CONCLUSION

In conclusion, antineoplastic drug combinations may display cell-type specific modulation of apoptotic and autophagic signaling and lack of protective autophagy may not necessarily indicate increased chemotherapeutic sensitivity in heterogenous tumor subpopulations.

Antineoplastic effects of erufosine on Graffi myeloid tumour in hamsters

Cancer has become one of the most significant health challenges for both human and veterinary medicine. The present study examined the antineoplastic and antimetastatic activity of the novel membrane-targeting anticancer agent erufosine. The antitumour effects of erufosine on Graffi virus-induced experimental myeloid tumour in hamsters was assessed by histopathological methods and evaluation of some biometric parameters of tumour growth. Two schemes of experimental antitumour therapy were applied - one that started simultaneously with the tumour transplantation and a second one that started after the appearance of palpable tumours. The results demonstrated protective antitumour effect of erufosine, expressed by decrease of transplantability, tumour growth inhibition, suppression of metastatic activity and extension of mean survival time. The effectivity of the experimental therapy was more pronounced when it was started simultaneously with the transplantation of the tumour cells. Presented results suggest that erufosine is a promising drug candidate for treatment of haematological malignances.

ABT-737 and erufosine combination against castration-resistant prostate cancer: a promising but cell-type specific response associated with the modulation of anti-apoptotic signaling

A deeper understanding of the molecular basis of castration-resistant prostate cancer (CRPC) paved the way for the rational design and development of targeted therapies, which yielded promising preclinical results. However, translation of these potentially promising agents into clinics has usually failed, partly because of tumor heterogeneity. In this study, anticancer activities of the Bcl-2 inhibitor ABT-737 and the Akt-inhibitor erufosine (ErPC3) alone and in combination were compared between CRPC (PC-3 and DU-145) and healthy (PNT-1A) cell lines. The combination of ABT-737 and ErPC3 showed synergistic antiproliferative, antimigratory, and apoptotic effects in PC-3 cells. In DU-145 cells, ErPC3 showed a resistant profile, with half-maximal inhibitory concentration (IC50) values more than two-fold of PC-3, and combining ErPC3 with ABT-737 yielded no added benefit for all the incubation periods compared with ErPC3 alone. In PNT-1A cells, ABT-737 and ErPC3 alone and in combination reduced cell survival slightly and only at the highest concentrations. Apoptosis analysis showed that ABT-737 induced increased Akt expression and ErPC3 induced increased Mcl-1 expression in DU-145 cells. In conclusion, the ABT-737 and ErPC3 combination seems to be promising against CRPC, with a favorable safety profile in healthy cells. However, CRPC cell-type-specific resistance may be induced by enhancement of antiapoptotic signaling.

Harnessing the potential of multimodal radiotherapy in prostate cancer

Radiotherapy in combination with androgen deprivation therapy (ADT) is a standard treatment option for men with localized and locally advanced prostate cancer. However, emerging clinical evidence suggests that radiotherapy can be incorporated into multimodality therapy regimens beyond ADT, in combinations that include chemotherapy, radiosensitizing agents, immunotherapy and surgery for the treatment of men with localized and locally advanced prostate cancer, and those with oligometastatic disease, in whom the low metastatic burden in particular might be treatable with these combinations. This multimodal approach is increasingly recognized as offering considerable clinical benefit, such as increased antitumour effects and improved survival. Thus, radiotherapy is becoming a key component of multimodal therapy for many stages of prostate cancer, particularly oligometastatic disease.

Multiple Facets of Autophagy and the Emerging Role of Alkylphosphocholines as Autophagy Modulators

Autophagy is a highly conserved multistep process and functions as passage for degrading and recycling protein aggregates and defective organelles in eukaryotic cells. Based on the nature of these materials, their size and degradation rate, four types of autophagy have been described, i.e. chaperone mediated autophagy, microautophagy, macroautophagy, and selective autophagy. One of the major regulators of this process is mTOR, which inhibits the downstream pathway of autophagy following the activation of its complex 1 (mTORC1). Alkylphosphocholine (APC) derivatives represent a novel class of antineoplastic agents that inhibit the serine-threonine kinase Akt (i.e. protein kinase B), which mediates cell survival and cause cell cycle arrest. They induce autophagy through inhibition of the Akt/mTOR cascade. They interfere with phospholipid turnover and thus modify signaling chains, which start from the cell membrane and modulate PI3K/Akt/mTOR, Ras-Raf-MAPK/ERK and SAPK/JNK pathways. APCs include miltefosine, perifosine, and erufosine, which represent the first-, second- and third generation of this class, respectively. In a high fraction of human cancers, constitutively active oncoprotein Akt1 suppresses autophagy in vitro and in vivo. mTOR is a down-stream target for Akt, the activation of which suppresses autophagy. However, treatment with APC derivatives will lead to dephosphorylation (hence deactivation) of mTOR and thus induces autophagy. Autophagy is a double-edged sword and may result in chemotherapeutic resistance as well as cancer cell death when apoptotic pathways are inactive. APCs display differential autophagy induction capabilities in different cancer cell types. Therefore, autophagy-dependent cellular responses need to be well understood in order to improve the chemotherapeutic outcome.

Alkylphospholipids are Signal Transduction Modulators with Potential for Anticancer Therapy

BACKGROUND

Alkylphospholipids (APLs) are synthetically derived from cell membrane components, which they target and thus modify cellular signalling and cause diverse effects. This study reviews the mechanism of action of anticancer, antiprotozoal, antibacterial and antiviral activities of ALPs, as well as their clinical use.

METHODS

A literature search was used as the basis of this review.

RESULTS

ALPs target lipid rafts and alter phospholipase D and C signalling cascades, which in turn will modulate the PI3K/Akt/mTOR and RAS/RAF/MEK/ERK pathways. By feedback coupling, the SAPK/JNK signalling chain is also affected. These changes lead to a G2/M phase cell cycle arrest and subsequently induce programmed cell death. The available knowledge on inhibition of AKT phosphorylation, mTOR phosphorylation and Raf down-regulation renders ALPs as attractive candidates for modern medical treatment, which is based on individualized diagnosis and therapy. Corresponding to their unusual profile of activities, their side effects result from cholinomimetic activity mainly and focus on the gastrointestinal tract. These aspects together with their bone marrow sparing features render APCs well suited for modern combination therapy. Although the clinical success has been limited in cancer diseases so far, the use of miltefosine against leishmaniosis is leading the way to better understanding their optimized use.

CONCLUSION

Recent synthetic programs generate congeners with the increased therapeutic ratio, liposomal formulations, as well as diapeutic (or theranostic) derivatives with optimized properties. It is anticipated that these innovative modifications will pave the way for the further successful development of ALPs.

Fatty Acid Inhibition Sensitizes Androgen-Dependent and -Independent Prostate Cancer to Radiotherapy via FASN/NF-κB Pathway

Elevated fatty acid synthase (FASN) has been reported in both androgen-dependent and -independent prostate cancers. Conventional treatment for prostate cancer is radiotherapy (RT); however, the following radiation-induced radioresistance often causes treatment failure. Upstream proteins of FASN such as Akt and NF-κB are found increased in the radioresistant prostate cancer cells. Nevertheless, whether inhibition of FASN could improve RT outcomes and reverse radiosensitivity of prostate cancer cells is still unknown. Here, we hypothesised that orlistat, a FASN inhibitor, could improve RT outcomes in prostate cancer. Orlistat treatment significantly reduced the S phase population in both androgen-dependent and -independent prostate cancer cells. Combination of orlistat and RT significantly decreased NF-κB activity and related downstream proteins in both prostate cancer cells. Combination effect of orlistat and RT was further investigated in both LNCaP and PC3 tumour-bearing mice. Combination treatment showed the best tumour inhibition compared to that of orlistat alone or RT alone. These results suggest that prostate cancer treated by conventional RT could be improved by orlistat via inhibition of FASN.

Induction of apoptosis in ovarian cancer cells by miR-493-3p directly targeting AKT2, STK38L, HMGA2, ETS1 and E2F5

Apoptosis is a form of directed programmed cell death with a tightly regulated signalling cascade for the destruction of single cells. MicroRNAs (miRNAs) play an important role as fine tuners in the regulation of apoptotic processes. MiR-493-3p mimic transfection leads to the induction of apoptosis causing the breakdown of mitochondrial membrane potential and the activation of Caspases resulting in the fragmentation of DNA in several ovarian carcinoma cell lines. Ovarian cancer shows with its pronounced heterogeneity a very high death-to-incidence ratio. A target gene analysis for miR-493-3p was performed for the investigation of underlying molecular mechanisms involved in apoptosis signalling pathways. Elevated miR-493-3p levels downregulated the mRNA and protein expression levels of Serine/Threonine Kinase 38 Like (STK38L), High Mobility Group AT-Hook 2 (HMGA2) and AKT Serine/Threonine Kinase 2 (AKT2) by direct binding as demonstrated by luciferase reporter assays. Notably, the protein expression of RAF1 Proto-Oncogene, Serine/Threonine Kinase (RAF1) was almost completely downregulated by miR-493-3p. This interaction, however, was indirect and regulated by STK38L phosphorylation. In addition, RAF1 transcription was diminished as a result of reduced transcription of ETS proto-oncogene 1 (ETS1), another direct target of miR-493-3p. Taken together, our observations have uncovered the apoptosis inducing potential of miR-493-3p through its regulation of multiple target genes participating in the extrinsic and intrinsic apoptosis pathway.

MiR-744-5p inducing cell death by directly targeting HNRNPC and NFIX in ovarian cancer cells

MicroRNAs (miRNAs) play an important role in the regulation of gene expression. The binding to target messenger RNAs (mRNAs) results in mRNA cleavage or inhibition of the translational machinery leading to decreased protein levels. Various signalling pathways, including apoptosis are modulated by miRNAs. Here, we investigated the role of miR-744-5p in apoptosis signalling in ovarian cancer cell lines. MiR-744-5p expression was reduced in the cancer cell lines independent of the host gene MAP2K4. Overexpression of miR-744-5p activated the intrinsic apoptotic pathway in SKOV3, OVCAR3 and Cisplatin resistant (A2780-cis) and non-resistant A2780 cells leading to cell death. Notably, miR-744-5p overexpression together with Carboplatin treatment led to at least additive pro-apoptotic effects. Investigation of the apoptotic signalling pathways mediated by miR-744-5p revealed that its elevated expression directly downregulated mRNA and protein expression of nuclear factor I X (NFIX) and heterogeneous nuclear ribonucleoprotein C (HNRNPC). HNRNPC caused diminished miR-21 expression and AKT phosphorylation, while NFIX decreased Bcl2 levels, leading to the detected pro-apoptotic effects. Finally, Kaplan-Meier-Plots showed a prolonged median disease-free survival in ovarian serous cystadenocarcinoma patients with high miR-744 expression.

New Insights into Protein Kinase B/Akt Signaling: Role of Localized Akt Activation and Compartment-Specific Target Proteins for the Cellular Radiation Response

Genetic alterations driving aberrant activation of the survival kinase Protein Kinase B (Akt) are observed with high frequency during malignant transformation and cancer progression. Oncogenic gene mutations coding for the upstream regulators or Akt, e.g., growth factor receptors, RAS and phosphatidylinositol-3-kinase (PI3K), or for one of the three Akt isoforms as well as loss of the tumor suppressor Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) lead to constitutive activation of Akt. By activating Akt, these genetic alterations not only promote growth, proliferation and malignant behavior of cancer cells by phosphorylation of various downstream signaling molecules and signaling nodes but can also contribute to chemo- and radioresistance in many types of tumors. Here we review current knowledge on the mechanisms dictating Akt’s activation and target selection including the involvement of miRNAs and with focus on compartmentalization of the signaling network. Moreover, we discuss recent advances in the cross-talk with DNA damage response highlighting nuclear Akt target proteins with potential involvement in the regulation of DNA double strand break repair.

Induction of ER and mitochondrial stress by the alkylphosphocholine erufosine in oral squamous cell carcinoma cells

Endoplasmic reticulum (ER) plays an essential role in cell function and survival. Accumulation of unfolded or misfolded proteins in the lumen of the ER activates the unfolded protein response (UPR), resulting in ER stress and subsequent apoptosis. The alkylphosphocholine erufosine is a known Akt-mTOR inhibitor in oral squamous cell carcinoma (OSCC). In the present study, we evaluate erufosine’s role to induce ER and mitochondrial stress leading to autophagy, apoptosis, and ROS induction. The cellular toxicity of erufosine was determined in two OSCC cell lines and gene expression and enrichment analyses were performed. A positive enrichment of ER stress upon erufosine exposure was observed, which was verified at protein levels for the ER stress sensors and their downstream mediators. Knockdown and pharmacological inhibition of the ER stress sensors PERK and XBP1 revealed their involvement into erufosine’s cellular effects, including proliferation, apoptosis, and autophagy induction. Autophagy was confirmed by increased acidic vacuoles and LC3-B levels. Upon erufosine exposure, calcium influx into the cytoplasm of the two OSCC cell lines was seen. Apoptosis was confirmed by nuclear staining, Annexin-V, and immunoblotting of caspases. The induction of mitochondrial stress upon erufosine exposure was predicted by gene set enrichment analysis (GSEA) and shown by erufosine’s effect on mitochondrial membrane potential, ATP, and ROS production in OSCC cells. These data show that ER and mitochondrial targeting by erufosine represents a new facet of its mechanism of action as well as a promising new framework in the treatment of head and neck cancers.

Investigation on tissue specific effects of pro-apoptotic micro RNAs revealed miR-147b as a potential biomarker in ovarian cancer prognosis

The development and progression of cancer can be ascribed to imbalances in gene regulation leading to aberrant cellular behavior. The loss of micro RNAs (miRNAs) exhibiting tumor-suppressive function has been demonstrated to be often causative for uncontrolled cell proliferation, migration or tissue infiltration. The installation of de novo tumor suppressive function by using pro-apoptotic miRNAs might be a promising therapeutic approach. In addition, there is a great demand for novel biomarkers for the prognosis of cancer, which prompted us to transfer a high content miRNA screening initially performed to identify bioprocess relevant miRNAs in Chinese hamster ovary (CHO) cells to human cancer cell lines . Analysis of screened miRNAs exhibiting strongest pro-apoptotic effects discovered globally and cross-species active candidates. The recovery rate of apoptosis inducing miRNAs was highest in the human ovarian carcinoma cell line SKOV3. Focusing on ovarian cell lines miR-1912, miR-147b and miR-3073a showed significant apoptosis induction in cell lines with different genetic background (SKOV3^p53null, OVCAR3^p53R248Q, TOV21G, TOV112D^p53R175H, A2780, A2780-cis^p53K351N) alone and additive effects in combination with carboplatin. While expression analysis revealed a low endogenous expression of miR-1912 and miR-147b in SKOV3, miRNA expression was highly upregulated upon apoptosis induction using chemotherapeutics. Ectopic introduction of these miRNAs lead to enhanced activation of caspase-dependent death signaling and an induction of the pro-apoptotic proteins Bak1 and Bax and a reduced expression of Bcl2 and Bcl-xL. Finally, analysis of The Cancer Genome Atlas data revealed the expression of hsa-miR-147b-5p to show a positive influence on the median survival of ovarian cancer patients.

Combination treatment with naftopidil increases the efficacy of radiotherapy in PC-3 human prostate cancer cells

PURPOSE

Clinically, radiotherapy (RT) often leads to the development of prostate cancer (PCa) resistance because of protective responses in cancer cells. One of the mechanisms includes the upregulation of RT-induced antioxidant enzymes. Thus, combination therapy with RT and certain pharmaceutical drugs targeting antioxidant enzymes may be ideal for increasing the efficacy of RT with minimum side effects. Naftopidil is a subtype-selective α1D-adrenoceptor antagonist used for the treatment of benign prostatic hyperplasia (BPH). In our drug repositioning study, naftopidil showed not only unique growth-inhibitory effects but also AKT phosphorylation-inhibitory effects in PC-3 human PCa cells. Here, we examined the efficacy of additive naftopidil treatment in combination with RT in PC-3 cells.

METHODS

The effects of combination therapy with RT plus naftopidil were analyzed using an animal model of PC-3 xenografts in BALB/c nude mice. The expression of the antioxidant enzyme manganese superoxide dismutase (MnSOD) was evaluated by western blotting.

RESULTS

Combination therapy with RT plus naftopidil induced a more efficacious delay in PC-3 xenograft tumor growth as compared with monotherapy with naftopidil or RT. In PC-3 tumors, combination therapy with RT plus naftopidil suppressed the upregulation of RT-induced MnSOD expression. In vitro, neither AKT inhibitor IV nor naftopidil directly altered MnSOD expression. Upregulation of RT-induced MnSOD expression was markedly suppressed by combination treatment with RT plus AKT inhibitor IV or naftopidil.

CONCLUSIONS

These results suggest that additive naftopidil treatment in combination with RT may increase the efficacy of RT for the treatment of PCa.

Activating Akt1 mutations alter DNA double strand break repair and radiosensitivity

The survival kinase Akt has clinical relevance to radioresistance. However, its contributions to the DNA damage response, DNA double strand break (DSB) repair and apoptosis remain poorly defined and often contradictory. We used a genetic approach to explore the consequences of genetic alterations of Akt1 for the cellular radiation response. While two activation-associated mutants with prominent nuclear access, the phospho-mimicking Akt1-TDSD and the clinically relevant PH-domain mutation Akt1-E17K, accelerated DSB repair and improved survival of irradiated Tramp-C1 murine prostate cancer cells and Akt1-knockout murine embryonic fibroblasts in vitro, the classical constitutively active membrane-targeted myrAkt1 mutant had the opposite effects. Interestingly, DNA-PKcs directly phosphorylated Akt1 at S473 in an in vitro kinase assay but not vice-versa. Pharmacological inhibition of DNA-PKcs or Akt restored radiosensitivity in tumour cells expressing Akt1-E17K or Akt1-TDSD. In conclusion, Akt1-mediated radioresistance depends on its activation state and nuclear localization and is accessible to pharmacologic inhibition.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

Akt inhibitors in cancer treatment: The long journey from drug discovery to clinical use (Review)

Targeted cancer therapies are used to inhibit the growth, progression, and metastasis of the tumor by interfering with specific molecular targets and are currently the focus of anticancer drug development. Protein kinase B, also known as Akt, plays a central role in many types of cancer and has been validated as a therapeutic target nearly two decades ago. This review summarizes the intracellular functions of Akt as a pivotal point of converging signaling pathways involved in cell growth, proliferation, apoptotis and neo‑angiogenesis, and focuses on the drug design strategies to develop potent anticancer agents targeting Akt. The discovery process of Akt inhibitors has evolved from adenosine triphosphate (ATP)‑competitive agents to alternative approaches employing allosteric sites in order to overcome the high degree of structural similarity between Akt isoforms in the catalytic domain, and considerable structural analogy to the AGC kinase family. This process has led to the discovery of inhibitors with greater specificity, reduced side-effects and lower toxicity. A second generation of Akt has inhibitors emerged by incorporating a chemically reactive Michael acceptor template to target the nucleophile cysteines in the catalytic activation loop. The review outlines the development of several promising drug candidates emphasizing the importance of each chemical scaffold. We explore the pipeline of Akt inhibitors and their preclinical and clinical examination status, presenting the potential clinical application of these agents as a monotherapy or in combination with ionizing radiation, other targeted therapies, or chemotherapy.

Simultaneous perturbation of the MAPK and the PI3K/mTOR pathways does not lead to increased radiosensitization

Background

The mitogen-activated protein kinases (MAPK) and the phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathways are intertwined on various levels and simultaneous inhibition reduces tumorsize and prolonges survival synergistically. Furthermore, inhibiting these pathways radiosensitized cancer cells in various studies. To assess, if phenotypic changes after perturbations of this signaling network depend on the genetic background, we integrated a time series of the signaling data with phenotypic data after simultaneous MAPK/ERK kinase (MEK) and PI3K/mTOR inhibition and ionizing radiation (IR).

Methods

The MEK inhibitor AZD6244 and the dual PI3K/mTOR inhibitor NVP-BEZ235 were tested in glioblastoma and lung carcinoma cells, which differ in their mutational status in the MAPK and the PI3K/mTOR pathways. Effects of AZD6244 and NVP-BEZ235 on the proliferation were assessed using an ATP assay. Drug treatment and IR effects on the signaling network were analyzed in a time-dependent manner along with measurements of phenotypic changes in the colony forming ability, apoptosis, autophagy or cell cycle.

Results

Both inhibitors reduced the tumor cell proliferation in a dose-dependent manner, with NVP-BEZ235 revealing the higher anti-proliferative potential. Our Western blot data indicated that AZD6244 and NVP-BEZ235 perturbed the MAPK and PI3K/mTOR signaling cascades, respectively. Additionally, we confirmed crosstalks and feedback loops in the pathways. As shown by colony forming assay, the AZD6244 moderately radiosensitized cancer cells, whereas NVP-BEZ235 caused a stronger radiosensitization. Combining both drugs did not enhance the NVP-BEZ235-mediated radiosensitization. Both inhibitors caused a cell cycle arrest in the G1-phase, whereas concomitant IR and treatment with the inhibitors resulted in cell line- and drug-specific cell cycle alterations. Furthermore, combining both inhibitors synergistically enhanced a G1-phase arrest in sham-irradiated glioblastoma cells and induced apoptosis and autophagy in both cell lines.

Conclusion

Perturbations of the MEK and the PI3K pathway radiosensitized tumor cells of different origins and the combination of AZD6244 and NVP-BEZ235 yielded cytostatic effects in several tumor entities. However, this is the first study assessing, if the combination of both drugs also results in synergistic effects in terms of radiosensitivity. Our study demonstrates that simultaneous treatment with both pathway inhibitors does not lead to synergistic radiosensitization but causes cell line-specific effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-015-0514-5) contains supplementary material, which is available to authorized users.

Targeting PI3K/Akt/mTOR signaling pathway in the treatment of prostate cancer radioresistance

The phosphatidylinositol-3-kinase/Akt and the mammalian target of rapamycin (PI3K/Akt/mTOR) pathway is one of the most frequently activated signaling pathways in prostate cancer (CaP) and other cancers, and responsible for the survival, metastasis and therapeutic resistance. Recent advances in radiation therapy indicate that activation of this pathway is closely associated with cancer radioresistance, which is a major challenge for the current CaP radiation treatment. Therefore, targeting this pathway by inhibitors to enhance radiosensitivity has great potential for clinical benefits of CaP patients. In this review, we summarize the recent findings in the PI3K/Akt/mTOR pathway in CaP radiotherapy research and discuss the potential use of the PI3K/Akt/mTOR pathway inhibitors as radiosensitizers in the treatment of CaP radioresistance in preclinical studies to explore novel approaches for future clinical trials.

Covalent-Allosteric Kinase Inhibitors

Targeting and stabilizing distinct kinase conformations is an instrumental strategy for dissecting conformation-dependent signaling of protein kinases. Herein the structure-based design, synthesis, and evaluation of pleckstrin homology (PH) domain-dependent covalent-allosteric inhibitors (CAIs) of the kinase Akt is reported. These inhibitors bind covalently to a distinct cysteine of the kinase and thereby stabilize the inactive kinase conformation. These modulators exhibit high potency and selectivity, and represent an innovative approach for chemical biology and medicinal chemistry research.

Marine lipopeptide Iturin A inhibits Akt mediated GSK3β and FoxO3a signaling and triggers apoptosis in breast cancer

Akt kinase is a critical component of the PI3K/Akt signaling pathway, which is frequently over expressed in human cancers including breast. Therapeutic regimens for inhibiting breast cancer with aberrant Akt activity are essential. Here, we evaluated antitumor effect of a marine bacteria derived lipopeptide ‘Iturin A’ on human breast cancer in vitro and in vivo through disrupting Akt pathway. Proliferation of MDA-MB-231 and MCF-7 breast cancer cells were significantly inhibited by Iturin A and it induced apoptosis as confirmed by increased Sub G₁ populations, DNA fragmentation, morphological changes and western blot analysis. Furthermore, Iturin A inhibited EGF induced Akt phosphorylation (Ser473 and Thr308) and its downstream targets GSK3β and FoxO3a. Iturin A inactivated MAPK as well as Akt kinase leading to the translocation of FoxO3a to the nucleus. Gene silencing of Akt in MDA-MB-231 and MCF-7 cells reduced the sensitivity of cancer cells to Iturin A. Interestingly, overexpression of Akt with Akt plasmid in cancer cells caused highly susceptible to induce apoptosis by Iturin A treatment. In a xenograft model, Iturin A inhibited tumor growth with reduced expressions of Ki-67, CD-31, P-Akt, P-GSK3β, P-FoxO3a and P-MAPK. Collectively, these findings imply that Iturin A has potential anticancer effect on breast cancer.

Dual PI3K/mTOR inhibitors, GSK2126458 and PKI-587, suppress tumor progression and increase radiosensitivity in nasopharyngeal carcinoma

Although combined chemoradiotherapy has provided considerable improvements for nasopharyngeal carcinoma (NPC), recurrence and metastasis are still frequent. The PI3K/Akt/mTOR pathway plays a critical role in tumor formation and tumor cell survival after radiation-induced DNA damage. In the present study, we evaluated whether inhibition of PI3K/mTOR by two novel dual inhibitors, GSK2126458 and PKI-587, could suppress tumor progression and sensitize NPC cells to radiation. Four NPC cell lines (CNE-1, CNE-2, 5-8F, and 6-10B) were used to analyze the effects of GSK216458 and PKI-587 on cell proliferation, migration, invasion, clonogenic survival, amount of residual γ-H2AX foci, cell cycle, and apoptosis after radiation. A 5-8F xenograft model was used to evaluate the in vivo effects of the two compounds in combination with ionizing radiation (IR). Both GSK216458 and PKI-587 effectively inhibited cell proliferation and motility in NPC cells and suppressed phosphorylation of Akt, mTOR, S6, and 4EBP1 proteins in a concentration- and time-dependent manner. Moreover, both compounds sensitized NPC cells to IR by increasing DNA damage, enhancing G2-M cell-cycle delay, and inducing apoptosis. In vivo, the combination of IR with GSK2126458 or PKI-587 significantly inhibited tumor growth. Antitumor effect was correlated with induction of apoptosis and suppression of the phosphorylation of mTOR, Akt, and 4EBP1. These new findings suggest the usefulness of PI3K/mTOR dual inhibition for antitumor and radiosensitizing. The combination of IR with a dual PI3K/mTOR inhibitor, GSK2126458 or PKI-587, might be a promising therapeutic strategy for NPC.

RNA-seq profiling of a radiation resistant and radiation sensitive prostate cancer cell line highlights opposing regulation of DNA repair and targets for radiosensitization

BACKGROUND

Radiotherapy is a chosen treatment option for prostate cancer patients and while some tumours respond well, up to 50% of patients may experience tumour recurrence. Identification of functionally relevant predictive biomarkers for radioresponse in prostate cancer would enable radioresistant patients to be directed to more appropriate treatment options, avoiding the side-effects of radiotherapy.

METHODS

Using an in vitro model to screen for novel biomarkers of radioresistance, transcriptome analysis of a radioresistant (PC-3) and radiosensitive (LNCaP) prostate cancer cell line was performed. Following pathway analysis candidate genes were validated using qRT-PCR. The DNA repair pathway in radioresistant PC-3 cells was then targeted for radiation sensitization using the PARP inhibitor, niacinimide.

RESULTS

Opposing regulation of a DNA repair and replication pathway was observed between PC-3 and LNCaP cells from RNA-seq analysis. Candidate genes BRCA1, RAD51, FANCG, MCM7, CDC6 and ORC1 were identified as being significantly differentially regulated post-irradiation. qRT-PCR validation confirmed BRCA1, RAD51 and FANCG as being significantly differentially regulated at 24 hours post radiotherapy (p-value =0.003, 0.045 and 0.003 respectively). While the radiosensitive LNCaP cells down-regulated BRCA1, FANCG and RAD51, the radioresistant PC-3 cell line up-regulated these candidates to promote cell survival post-radiotherapy and a similar trend was observed for MCM7, CDC6 and ORC1. Inhibition of DNA repair using niacinamide sensitised the radioresistant cells to irradiation, reducing cell survival at 2 Gy from 66% to 44.3% (p-value =0.02).

CONCLUSIONS

These findings suggest that the DNA repair candidates identified via RNA-seq hold potential as both targets for radiation sensitization and predictive biomarkers in prostate cancer.

Affinity of alkylphosphocholines to biological membrane of prostate cancer: studies in natural and model systems

The effectiveness of two alkylphosphocholines (APCs), hexadecylphosphocholine (miltefosine) and erucylphosphocholine to combat prostate cancer has been studied in vitro with artificial cancerous membrane, modelled with the Langmuir monolayer technique, and on cell line (Du-145). Studies performed with the Langmuir method indicate that both the investigated drugs have the affinity to the monolayer mimicking prostate cancer membrane (composed of cholesterol:POPC = 0.428) and the drug-membrane interactions are stronger for erucylphosphocholine as compared to hexadecylphosphocholine. Moreover, both studied drugs were found to fluidize the model membrane, which may lead to apoptosis. Indeed, biological studies confirmed that in Du-145 cell line both investigated alkylphosphocholines cause cell death primarily by apoptosis while necrotic cells constitute only a small percentage of APC-treated cells.

Differential effects of erufosine on proliferation, wound healing and apoptosis in colorectal cancer cell lines

The alkylphosphocholine, erucylphospho-N,N, N-trimethylpropanolamine (erufosine), has demonstrated anticancer effects in various cell lines, including leukemia, multiple myeloma, bladder, breast and oral squamous cell carcinoma cells. The purpose of the present study was to investigate its antiproliferative, antimigratory and pro-apoptotic effects in colorectal cancer cell lines, SW480 and CC531. The antiproliferative effect was determined by (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) (MTT) dye reduction assay following exposure to erufosine (3.1-100 µM) for 24-72 h. The antimigratory effect of erufosine (1.6-6 µM) was investigated by a wound healing assay for 12-48 h. Caspase-3/-7 activity was measured to detect apoptotic cell death. Erufosine inhibited cell proliferation in a dose- and time-dependent manner. The IC50 values following 72 h of incubation were 3.4 and 25.4 µM for SW480 and CC531 cells, respectively. erufosine at concentrations of 50 and 100 µM induced caspase-3/-7 activity concentration-dependently in SW480 cells, but only at 100 µM in CC531 cells. Incubation of SW480 cells with erufosine (1.56 µM) for 48 h inhibited migration into the scratched area by 54% as compared to the untreated cells; whereas in CC531 cells, the wound width in the erufosine-treated (1.56-6.25 µM) cells following 48 h was closed 2-fold slower than the rate in the untreated group. Erufosine (25 µM) attenuated osteonectin expression and abolished COL1A1 expression in CC531 cells. Erufosine appears to be a promising treatment agent for colorectal cancer. Rat CC531 cells are less sensitive to erufosine than human SW480 cells.

The translocator protein radioligand 18F-DPA-714 monitors antitumor effect of erufosine in a rat 9L intracranial glioma model

On the one hand, the translocator protein (TSPO) radioligand N,N-diethyl-2-(2-(4-(2-(18)F-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide ((18)F-DPA-714) has been suggested to serve as an alternative radiotracer to image human glioma, and on the other hand the alkylphosphocholine erufosine (ErPC3) has been reported to induce apoptosis in otherwise highly apoptosis-resistant glioma cell lines. The induction of apoptosis by ErPC3 requires TSPO, a mitochondrial membrane protein highly expressed in malignant gliomas. In this preclinical study, we monitored the effect of ErPC3 treatment in vivo using (18)F-DPA-714 PET.

METHODS

In vitro studies investigated the antitumor effect of ErPC3 in 9L rat gliosarcoma cells. In vivo, glioma-bearing rats were imaged with (18)F-DPA-714 for the time of treatment.

RESULTS

A significant decrease in 9L cell proliferation and viability and a significant increase in apoptosis and caspase-3 activation were demonstrated on ErPC3 treatment in cell culture. In the rat model, ErPC3 administration resulted in significant changes in (18)F-DPA-714 tumor uptake over the course of the treatment. Immunohistochemistry revealed reduced tumor volume and increased cell death in ErPC3-treated animals accompanied by infiltration of the tumor core by CD11b-positive microglia/macrophages and glial fibrillary acidic protein-positive astrocytes.

CONCLUSION

Our findings demonstrate a potent antitumor effect of ErPC3 in vitro, in vivo, and ex vivo. PET imaging of TSPO expression using (18)F-DPA-714 allows effective monitoring and quantification of disease progression and response to ErPC3 therapy in intracranial 9L gliomas.

Inhibition of the PI3K/AKT-NF-κB pathway with curcumin enhanced radiation-induced apoptosis in human Burkitt's lymphoma

The phosphatidylinositol-3-kinase (PI3K) / protein kinase B (AKT) signal transduction pathway is commonly misregulated in lymphoma and associated with tumorigenesis and enhanced resistance to radiotherapy. Curcumin has been shown to inhibit the PI3K/AKT signal transduction pathway in several tumor models. In this study, we found that curcumin inhibits constitutive and radiation-induced expression of the PI3K/AKT pathway and its downstream regulator nuclear factor kappaB (NF-κB) in human Burkitt's lymphoma, a high-grade non-Hodgkin's lymphoma (NHL). We further demonstrated that the blockage of radiation-induced activation of the PI3K/AKT pathway and its downstream regulator NF-κB by either curcumin or specific PI3/AKT inhibitors (LY294002 for PI3K or SH-5 for AKT) enhance apoptosis in three human Burkitt's lymphoma cell lines (Namalwa, Ramos, and Raji) that were treated with ionizing radiation. However, no synergic effect on radiation-induced apoptosis was found in the cells co-pretreated with curcumin combined with LY294002 or curcumin combined with SH-5. The results from this study suggest that curcumin might play an important role in radiotherapy of high-grade NHL through inhibition of the PI3K/AKT-dependent NF-κB pathway.

Targeting inhibitor 2 of protein phosphatase 2A as a therapeutic strategy for prostate cancer treatment

Inhibitor 2 of protein phosphatase 2A (I2PP2A), a biological inhibitor of the cellular serine/threonine protein phosphatase PP2A, is associated with numerous cellular processes that often lead to the formation and progression of cancer. In this study we hypothesized that targeting the inhibition of I2PP2A's multiple functions in prostate cancer cells might prevent cancer progression. We have investigated the effect of the small chain C6-ceramide, known to be a bioactive tumor suppressor lipid, on I2PP2A function, thereby affecting c-Myc signaling and histone acetylation in cells. Our data indicated that C6-ceramide treatment of prostate cancer cells induces cell death in PC-3, DU145, and LNCaP cells, but not normal prostate epithelial cells. C6-ceramide was able to disrupt the association between PP2A and I2PP2A. C6-ceramide inhibits I2PP2A's upregulation of c-Myc and downregulation of histone acetylation in prostate cancer cells. Our data indicated that targeting cancer related signaling pathways through I2PP2A using ceramide as an anti-I2PP2A agent could have beneficial effects as a therapeutic approach to prevent prostate cancer.

Reciprocal complementation of the tumoricidal effects of radiation and natural killer cells

The tumor microenvironment is a key determinant for radio-responsiveness. Immune cells play an important role in shaping tumor microenvironments; however, there is limited understanding of how natural killer (NK) cells can enhance radiation effects. This study aimed to assess the mechanism of reciprocal complementation of radiation and NK cells on tumor killing. Various tumor cell lines were co-cultured with human primary NK cells or NK cell line (NK-92) for short periods and then exposed to irradiation. Cell proliferation, apoptosis and transwell assays were performed to assess apoptotic efficacy and cell viability. Western blot analysis and immunoprecipitation methods were used to determine XIAP (X-linked inhibitor of apoptosis protein) and Smac (second mitochondria-derived activator of caspase) expression and interaction in tumor cells. Co-culture did not induce apoptosis in tumor cells, but a time- and dose-dependent enhancing effect was found when co-cultured cells were irradiated. A key role for caspase activation via perforin/granzyme B (Grz B) after cell-cell contact was determined, as the primary radiation enhancing effect. The efficacy of NK cell killing was attenuated by upregulation of XIAP to bind caspase-3 in tumor cells to escape apoptosis. Knockdown of XIAP effectively potentiated NK cell-mediated apoptosis. Radiation induced Smac released from mitochondria and neutralized XIAP and therefore increased the NK killing. Our findings suggest NK cells in tumor microenvironment have direct radiosensitization effect through Grz B injection while radiation enhances NK cytotoxicity through triggering Smac release.

Radiosensitization of Glioblastoma Cell Lines by the Dual PI3K and mTOR Inhibitor NVP-BEZ235 Depends on Drug-Irradiation Schedule

Previous studies have shown that the dual phosphatidylinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitor NVP-BEZ235 radiosensitizes tumor cells if added shortly before ionizing radiation (IR) and kept in culture medium thereafter. The present study explores the impact of inhibitor and IR schedule on the radiosensitizing ability of NVP-BEZ235 in four human glioblastoma cell lines. Two different drug-IR treatment schedules were compared. In schedule I, cells were treated with NVP-BEZ235 for 24 hours before IR and the drug was removed before IR. In schedule II, the cells were exposed to NVP-BEZ235 1 hour before, during, and up to 48 hours after IR. The cellular response was analyzed by colony counts, expression of marker proteins of the PI3K/AKT/mTOR pathway, cell cycle, and DNA damage. We found that under schedule I, NVP-BEZ235 did not radiosensitize cells, which were mostly arrested in G1 phase during IR exposure. In addition, the drug-pretreated and irradiated cells exhibited less DNA damage but increased expressions of phospho-AKT and phospho-mTOR, compared to controls. In contrast, NVP-BEZ235 strongly enhanced the radiosensitivity of cells treated according to schedule II. Possible reasons of radiosensitization by NVP-BEZ235 under schedule II might be the protracted DNA repair, prolonged G2/M arrest, and, to some extent, apoptosis. In addition, the PI3K pathway was downregulated by the NVP-BEZ235 at the time of irradiation under schedule II, as contrasted with its activation in schedule I. We found that, depending on the drug-IR schedule, the NVP-BEZ235 can act either as a strong radiosensitizer or as a cytostatic agent in glioblastoma cells.

Regulation of protein translation initiation in response to ionizing radiation

Background

Proliferating tumor cells require continuous protein synthesis. De novo synthesis of most proteins is regulated through cap-dependent translation. Cellular stress such as ionizing radiation (IR) blocks cap-dependent translation resulting in shut-down of global protein translation which saves resources and energy needed for the stress response. At the same time, levels of proteins required for stress response are maintained or even increased. The study aimed to analyze the regulation of signaling pathways controlling protein translation in response to IR and the impact on Mcl-1, an anti-apoptotic and radioprotective protein, which levels rapidly decline upon IR.

Methods

Protein levels and processing were analyzed by Western blot. The assembly of the translational pre-initiation complex was examined by Immunoprecipitation and pull-down experiments with 7-methyl GTP agarose. To analyze IR-induced cell death, dissipation of the mitochondrial membrane potential and DNA fragmentation were determined by flow cytometry. Protein levels of the different initiation factors were down-regulated using RNA interference approach.

Results

IR induced caspase-dependent cleavage of the translational initiation factors eIF4G1, eIF3A, and eIF4B resulting in disassembly of the cap-dependent initiation complex. In addition, DAP5-dependent initiation complex that regulates IRES-dependent translation was disassembled in response to IR. Moreover, IR resulted in dephosphorylation of 4EBP1, an inhibitor of cap-dependent translation upstream of caspase activation. However, knock-down of eIF4G1, eIF4B, DAP5, or 4EBP1 did not affect IR-induced decline of the anti-apoptotic protein Mcl-1.

Conclusion

Our data shows that cap-dependent translation is regulated at several levels in response to IR. However, the experiments indicate that IR-induced Mcl-1 decline is not a consequence of translational inhibition in Jurkat cells.

In vitro effect of molluscan hemocyanins on CAL-29 and T-24 bladder cancer cell lines

The aim of this study was to investigate the anti-tumor effects of molluscan hemocyanins (Hcs) isolated from the marine snail Rapana venosa (RvH) and the garden snail Helix lucorum (HlH) on human bladder cancer cell lines. The antitumor effect of the native molecules of the above-mentioned Hcs and their subunits were examined in comparison to keyhole limpet hemocyanin (KLH), which is the most thoroughly studied Hc. The experiments were conducted using 2 human bladder cancer cell lines: CAL-29 and T-24. Doxorubicin hydrochloride (DOX) and mitomycin-C (MIT-C), which are routinely used in clinical practice to treat bladder cancer, were used for comparison. The viability of the 2 bladder cancer cell lines, used at a concentration of 20,000 cells/well, was measured by WST-1 assay at 24, 48 and 72 h after treatment with the above-mentioned Hcs and their isoforms at a concentration ranging from 0.8 to 500 μg/ml. A direct growth inhibitory effect on the tumor cells was observed mainly after treatment with the native molecule of HlH and the structural subunit, RvH1, at a concentration of 500 μg/ml. The native molecule of RvH exhibited an efficacy similar to that of KLH. However, the observed growth inhibitory effect of HlH was superior to that observed for KLH and RvH, when used at the same concentration. These findings demonstrate the antitumor effect of other Hcs, apart from KLH. Our data suggest that the native molecule of HlH and the subunit, RvH1, are alternative candidates for the treatment of human superficial bladder cancer.

Microenvironment and radiation therapy

Dependency on tumor oxygenation is one of the major features of radiation therapy and this has led many radiation biologists and oncologists to focus on tumor hypoxia. The first approach to overcome tumor hypoxia was to improve tumor oxygenation by increasing oxygen delivery and a subsequent approach was the use of radiosensitizers in combination with radiation therapy. Clinical use of some of these approaches was promising, but they are not widely used due to several limitations. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is activated by hypoxia and induces the expression of various genes related to the adaptation of cellular metabolism to hypoxia, invasion and metastasis of cancer cells and angiogenesis, and so forth. HIF-1 is a potent target to enhance the therapeutic effects of radiation therapy. Another approach is antiangiogenic therapy. The combination with radiation therapy is promising, but several factors including surrogate markers, timing and duration, and so forth have to be optimized before introducing it into clinics. In this review, we examined how the tumor microenvironment influences the effects of radiation and how we can enhance the antitumor effects of radiation therapy by modifying the tumor microenvironment.

PI3K and Akt as molecular targets for cancer therapy: current clinical outcomes

The PI3K-Akt pathway is a vital regulator of cell proliferation and survival. Alterations in the PIK3CA gene that lead to enhanced PI3K kinase activity have been reported in many human cancer types, including cancers of the colon, breast, brain, liver, stomach and lung. Deregulation of PI3K causes aberrant Akt activity. Therefore targeting this pathway could have implications for cancer treatment. The first generation PI3K-Akt inhibitors were proven to be highly effective with a low IC(50), but later, they were shown to have toxic side effects and poor pharmacological properties and selectivity. Thus, these inhibitors were only effective in preclinical models. However, derivatives of these first generation inhibitors are much more selective and are quite effective in targeting the PI3K-Akt pathway, either alone or in combination. These second-generation inhibitors are essentially a specific chemical moiety that helps to form a strong hydrogen bond interaction with the PI3K/Akt molecule. The goal of this review is to delineate the current efforts that have been undertaken to inhibit the various components of the PI3K and Akt pathway in different types of cancer both in vitro and in vivo. Our focus here is on these novel therapies and their inhibitory effects that depend upon their chemical nature, as well as their development towards clinical trials.

Erufosine suppresses breast cancer in vitro and in vivo for its activity on PI3K, c-Raf and Akt proteins

PURPOSE

This study investigated the antineoplastic effect of the membrane active alkylphosphocholine erufosine in breast carcinoma models in vitro and in vivo and determined its influence on the PI3K/Akt and Ras/Raf/MAPK signaling pathways.

METHODS

The antiproliferative effect of erufosine in vitro was determined by the MTT dye reduction assay, and the antineoplastic efficacy on tumor growth was investigated by relating the mean total tumor volumes of treated and control rats. Immunoblot analysis was used for detecting changes in the expression level of the signal molecules p-PI3K (p-p85), p-Akt at Thr 308 and p-cRaf.

RESULTS

Based on their IC(50) (40 μM, respectively), the breast carcinoma cell lines MCF-7 and MDA-MB 231, which are estrogen receptor positive and negative, respectively, were equally sensitive to erufosine. In addition, erufosine caused dose-dependent decreases in the phosphorylation of PI3K (p85), Akt (PKB) at Thr 308 and cRaf in both cell lines. Moreover, administration of erufosine to rats bearing autochthonous methylnitrosourea-induced rat mammary carcinomas caused a significant dose-related tumor remission by more than 85 % (p < 0.05), which was well tolerated, as evidenced by a body weight loss of maximally 7 % and reduced tumor-related mortality (2 of 35 instead of 6 of 18 controls, p < 0.002).

CONCLUSIONS

The results clearly indicate that erufosine possesses high antineoplastic activity not only in human breast cancer cell lines in vitro but also in rat mammary carcinoma in vivo. In addition, it can be derived that the mechanism of action of erufosine involves influence on both, PI3K/Akt and Ras/Raf/MAPK signaling pathways.

Effects of ionizing radiation in combination with Erufosine on T98G glioblastoma xenograft tumours: a study in NMRI nu/nu mice

Background

Erufosine is a promising anticancer drug that increases the efficacy of radiotherapy in glioblastoma cell lines in vitro. Moreover, treatment of nude mice with repeated intraperitoneal or subcutaneous injections of Erufosine is well tolerated and yields drug concentrations in the brain tissue that are higher than the concentrations required for cytotoxic drug effects on glioblastoma cell lines in vitro.

Methods

In the present study we aimed to evaluate the effects of a combined treatment with radiotherapy and Erufosine on growth and local control of T98G subcutaneous glioblastoma xenograft-tumours in NMRI nu/nu mice.

Results

We show that repeated intraperitoneal injections of Erufosine resulted in a significant drug accumulation in T98G xenograft tumours on NMRI nu/nu mice. Moreover, short-term treatment with 5 intraperitoneal Erufosine injections caused a transient decrease in the growth of T98G tumours without radiotherapy. Furthermore, an increased radiation-induced growth delay of T98G xenograft tumours was observed when fractionated irradiation was combined with short-term Erufosine-treatment. However, no beneficial drug effects on fractionated radiotherapy in terms of local tumour control were observed.

Conclusions

We conclude that short-term treatment with Erufosine is not sufficient to significantly improve local control in combination with radiotherapy in T98G glioblastoma xenograft tumours. Further studies are needed to evaluate efficacy of extended drug treatment schedules.

Synthesis and characterization of a novel prostate cancer-targeted phosphatidylinositol-3-kinase inhibitor prodrug

The phosphatidylinositol-3-kinase/Akt (PI3K/Akt) pathway is constitutively activated in a substantial proportion of prostate tumors and is considered a key mechanism supporting progression toward an androgen-independent status, for which no effective therapy is available. Therefore, PI3K inhibitors, alone or in combination with other cytotoxic drugs, could potentially be used to treat cancer with a constitutive activated PI3K/Akt pathway. To selectively target advanced prostate tumors with a constitutive activated PI3K/Akt pathway, a prostate cancer-specific PI3K inhibitor was generated by coupling the chemically modified form of the quercetin analogue LY294002 (HO-CH(2)-LY294002, compound 8) with the peptide Mu-LEHSSKLQL, in which the internal sequence HSSKLQ is a substrate for the prostate-specific antigen (PSA) protease. The result is a water-soluble and latent PI3K inhibitor prodrug (compound 11), its activation being dependent on PSA cleavage. Once activated, the L-O-CH(2)-LY294002 (compound 10) can specifically inhibit PI3K in PSA-secreting prostate cancer cells and induce apoptosis with a potency comparable to that of the original LY294002 compound.

Radiation, inflammation, and immune responses in cancer

Chronic inflammation has emerged as one of the hallmarks of cancer. Inflammation also plays a pivotal role in modulating radiation responsiveness of tumors. As discussed in this review, ionizing radiation (IR) leads to activation of several transcription factors modulating the expression of numerous mediators in tumor cells and cells of the microenvironment promoting cancer development. Novel therapeutic approaches thus aim to interfere with the activity or expression of these factors, either in single-agent or combinatorial treatment or as supplements of the existing therapeutic concepts. Among them, NF-κB, STAT-3, and HIF-1 play a crucial role in radiation-induced inflammatory responses embedded in a complex inflammatory network. A great variety of classical or novel drugs including nutraceuticals such as plant phytochemicals have the capacity to interfere with the inflammatory network in cancer and are considered as putative radiosensitizers. Thus, targeting the inflammatory signaling pathways induced by IR offers the opportunity to improve the clinical outcome of radiation therapy by enhancing radiosensitivity and decreasing putative metabolic effects. Since inflammation and sex steroids also impact tumorigenesis, a therapeutic approach targeting glucocorticoid receptors and radiation-induced production of tumorigenic factors might be effective in sensitizing certain tumors to IR.

NVP-BEZ235 and NVP-BGT226, dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitors, enhance tumor and endothelial cell radiosensitivity

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is activated in tumor cells and promotes tumor cell survival after radiation-induced DNA damage. Because the pathway may not be completely inhibited after blockade of PI3K itself, due to feedback through mammalian target of rapamycin (mTOR), more effective inhibition might be expected by targeting both PI3K and mTOR inhibition.

MATERIALS AND METHODS

We investigated the effect of two dual PI3K/mTOR (both mTORC1 and mTORC2) inhibitors, NVP-BEZ235 and NVP-BGT226, on SQ20B laryngeal and FaDu hypopharyngeal cancer cells characterised by EGFR overexpression, on T24 bladder tumor cell lines with H-Ras mutation and on endothelial cells. Analysis of target protein phosphorylation, clonogenic survival, number of residual γH2AX foci, cell cycle and apoptosis after radiation was performed in both tumor and endothelial cells. In vitro angiogenesis assays were conducted as well.

RESULTS

Both compounds effectively inhibited phosphorylation of Akt, mTOR and S6 target proteins and reduced clonogenic survival in irradiated tumor cells. Persistence of DNA damage, as evidenced by increased number of γH2AX foci, was detected after irradiation in the presence of PI3K/mTOR inhibition, together with enhanced G2 cell cycle delay. Treatment with one of the inhibitors, NVP-BEZ235, also resulted in decreased clonogenicity after irradiation of tumor cells under hypoxic conditions. In addition, NVP-BEZ235 blocked VEGF- and IR-induced Akt phosphorylation and increased radiation killing in human umbilical venous endothelial cells (HUVEC) and human dermal microvascular dermal cells (HDMVC). NVP-BEZ235 inhibited VEGF-induced cell migration and capillary tube formation in vitro and enhanced the antivascular effect of irradiation. Treatment with NVP-BEZ235 moderately increased apoptosis in SQ20B and HUVEC cells but not in FaDu cells, and increased necrosis in both tumor and endothelial all cells tumor.

CONCLUSIONS

The results of this study demonstrate that PI3K/mTOR inhibitors can enhance radiation-induced killing in tumor and endothelial cells and may be of benefit when combined with radiotherapy.