Dual Targeting of Akt and mTORC1 Impairs Repair of DNA Double-Strand Breaks and Increases Radiation Sensitivity of Human Tumor Cells

Pilot clinical trial and phenotypic analysis in chemotherapy-pretreated, metastatic triple-negative breast cancer patients treated with oral TAK-228 and TAK-117 (PIKTOR) to increase DNA damage repair deficiency followed by cisplatin and nab paclitaxel

BACKGROUND

A subset of triple-negative breast cancers (TNBCs) have homologous recombination deficiency with upregulation of compensatory DNA repair pathways. PIKTOR, a combination of TAK-228 (TORC1/2 inhibitor) and TAK-117 (PI3Kα inhibitor), is hypothesized to increase genomic instability and increase DNA damage repair (DDR) deficiency, leading to increased sensitivity to DNA-damaging chemotherapy and to immune checkpoint blockade inhibitors.

METHODS

10 metastatic TNBC patients received 4 mg TAK-228 and 200 mg TAK-117 (PIKTOR) orally each day for 3 days followed by 4 days off, weekly, until disease progression (PD), followed by intravenous cisplatin 75 mg/m2 plus nab paclitaxel 220 mg/m2 every 3 weeks for up to 6 cycles. Patients received subsequent treatment with pembrolizumab and/or chemotherapy. Primary endpoints were objective response rate with cisplatin/nab paclitaxel and safety. Biopsies of a metastatic lesion were collected prior to and at PD on PIKTOR. Whole exome and RNA-sequencing and reverse phase protein arrays (RPPA) were used to phenotype tumors pre- and post-PIKTOR for alterations in DDR, proliferation, and immune response.

RESULTS

With cisplatin/nab paclitaxel (cis/nab pac) therapy post PIKTOR, 3 patients had clinical benefit (1 partial response (PR) and 2 stable disease (SD) ≥ 6 months) and continued to have durable benefit in progression-free survival with pembrolizumab post-cis/nab pac for 1.2, 2, and 3.6 years. Their post-PIKTOR metastatic tissue displayed decreased mismatch repair (MMR), increased tumor mutation burden, and significantly lower levels of 53BP1, DAG Lipase β, GCN2, AKT Ser473, and PKCzeta Thr410/403 compared to pre-PIKTOR tumor tissue.

CONCLUSIONS

Priming patients' chemotherapy-pretreated metastatic TNBC with PIKTOR led to very prolonged response/disease control with subsequent cis/nab pac, followed by pembrolizumab, in 3 of 10 treated patients. Our multi-omics approach revealed a higher number of genomic alterations, reductions in MMR, and alterations in immune and stress response pathways post-PIKTOR in patients who had durable responses.

TRIAL REGISTRATION

This clinical trial was registered on June 21, 2017, at ClinicalTrials.gov using identifier NCT03193853.

The effects of PKI-402 on breast tumor models' radiosensitivity via dual inhibition of PI3K/mTOR

PURPOSE

PI3K/Akt/mTOR pathway activation causes relapse and resistance after radiotherapy in breast cancer (BC). We aimed to radiosensitize BC cell lines to irradiation (IR) by PKI-402, a dual PI3K/mTOR inhibitor.

METHODS

We performed cytotoxicity, clonogenicity, hanging drop, apoptosis and double-strand break detection, and phosphorylation of 16 essential proteins involved in the PI3K/mTOR pathway.

RESULTS

Our findings showed that PKI-402 has cytotoxic efficiency in all cell lines. Clonogenic assay results showed that PKI-402 plus IR inhibited the colony formation ability of MCF-7 and breast cancer stem cell lines. Results showed that PKI-402 plus IR causes more apoptotic cell death than IR alone in the MCF-7 cells but did not cause significant changes in the MDA-MB-231. γ-H2AX levels were increased in MDA-MB-231 in PKI-402 plus IR groups, whereas we did not observe any apoptotic and γ-H2AX induction in BCSCs and MCF-10A cells in all treatment groups. Some pivotal phosphorylated proteins of the PI3K/AKT pathway decreased, several proteins increased and others did not change.

CONCLUSION

In conclusion, if the combined use of PKI-402 with radiation is supported by in vivo studies, it can contribute to the treatment options and the course of the disease.

18F-FDG and 18F-FLT Uptake Profiles for Breast Cancer Cell Lines Treated with Targeted PI3K/Akt/mTOR Therapies

Background: To evaluate ¹⁸F-fluoro-2-deoxy-glucose (¹⁸F-FDG) and ¹⁸F-fluorothymidine (¹⁸F-FLT) as early-response biomarkers for phosphoinositide-3-kinase/Akt/mammalian-target-of-rapamycin (PI3K/Akt/mTOR) inhibition in breast cancer (BC) models. Materials and Methods: Two human epidermal growth factor receptor 2 (HER2)-positive (trastuzumab-sensitive SKBR3; trastuzumab-resistant JIMT1) and one triple-negative BC cell line (MDA-MB-231, trastuzumab, and everolimus resistant) were treated with trastuzumab (HER2 antagonist), PIK90 (PI3K inhibitor), or everolimus (mTOR inhibitor). Radiotracer uptake was measured before, 24, and 72 h after drug exposure and correlated with changes in cell number, glucose transporter 1 (GLUT1), cell cycle phase, and downstream signaling activation. Results: In responsive cells, cell number correlated with ¹⁸F-FLT at 24 h and ¹⁸F-FDG at 72 h of drug exposure, except in JIMT1 treated with everolimus, where both radiotracers failed to detect response owing to a temporary increase in tracer uptake. This flare can be caused by reflex activation of Akt combined with a hyperactive insulin-like growth factor I receptor (IGF-1R) signaling, resulting in increased trafficking of GLUTs to the cell membrane (¹⁸F-FDG) and enhanced DNA repair (¹⁸F-FLT). In resistant cells, no major changes were observed, although a nonsignificant flair for both tracers was observed in JIMT1 treated with trastuzumab. Conclusion: ¹⁸F-FLT positron emission tomography (PET) detects response to PI3K-targeting therapy earlier than ¹⁸F-FDG PET in BC cells. However, therapy response can be underestimated after trastuzumab and everolimus owing to negative feedback loop and crosstalk between pathways.

The 'stealth-bomber' paradigm for deciphering the tumour response to carbon-ion irradiation

Numerous studies have demonstrated the higher biological efficacy of carbon-ion irradiation (C-ions) and their ballistic precision compared with photons. At the nanometre scale, the reactive oxygen species (ROS) produced by radiation and responsible for the indirect effects are differentially distributed according to the type of radiation. Photon irradiation induces a homogeneous ROS distribution, whereas ROS remain condensed in clusters in the C-ions tracks. Based on this linear energy transfer-dependent differential nanometric ROS distribution, we propose that the higher biological efficacy and specificities of the molecular response to C-ions rely on a 'stealth-bomber' effect. When biological targets are on the trajectories of the particles, the clustered radicals in the tracks are responsible for a 'bomber' effect. Furthermore, the low proportion of ROS outside the tracks is not able to trigger the cellular mechanisms of defence and proliferation. The ability of C-ions to deceive the cellular defence of the cancer cells is then categorised as a 'stealth' effect. This review aims to classify the biological arguments supporting the paradigm of the 'stealth-bomber' as responsible for the biological superiority of C-ions compared with photons. It also explains how and why C-ions will always be more efficient for treating patients with radioresistant cancers than conventional radiotherapy.

Androgen and oestrogen receptor co-expression determines the efficacy of hormone receptor-mediated radiosensitisation in breast cancer

PURPOSE

Radiation therapy (RT) and hormone receptor (HR) inhibition are used for the treatment of HR-positive breast cancers; however, little is known about the interaction of the androgen receptor (AR) and estrogen receptor (ER) in response to RT in AR-positive, ER-positive (AR+/ER+) breast cancers. Here we assessed radiosensitisation of AR+/ER+ cell lines using pharmacologic or genetic inhibition/degradation of AR and/or ER.

METHODS

Radiosensitisation was assessed with AR antagonists (enzalutamide, apalutamide, darolutamide, seviteronel, ARD-61), ER antagonists (tamoxifen, fulvestrant) or using knockout of AR.

RESULTS

Treatment with AR antagonists or ER antagonists in combination with RT did not result in radiosensitisation changes (radiation enhancement ratios [rER]: 0.76-1.21). Fulvestrant treatment provided significant radiosensitisation of CAMA-1 and BT-474 cells (rER: 1.06-2.0) but not ZR-75-1 cells (rER: 0.9-1.11). Combining tamoxifen with enzalutamide did not alter radiosensitivity using a 1 h or 1-week pretreatment (rER: 0.95-1.14). Radiosensitivity was unchanged in AR knockout compared to Cas9 cells (rER: 1.07 ± 0.11), and no additional radiosensitisation was achieved with tamoxifen or fulvestrant compared to Cas9 cells (rER: 0.84-1.19).

CONCLUSION

While radiosensitising in AR + TNBC, AR inhibition does not modulate radiation sensitivity in AR+/ER+ breast cancer. The efficacy of ER antagonists in combination with RT may also be dependent on AR expression.

Combining radiation with PI3K isoform-selective inhibitor administration increases radiosensitivity and suppresses tumor growth in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a malignant lung tumor with a dismal prognosis. The activation of the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway is common in many tumor types including NSCLC, which results in radioresistance and changes in the tumor microenvironment. Although pan-PI3K inhibitors have been tested in clinical trials to overcome radioresistance, concerns regarding their excessive side effects led to the consideration of selective inhibition of PI3K isoforms. In this study, we assessed whether combining radiation with the administration of the PI3K isoform-selective inhibitors reduces radioresistance and tumor growth in NSCLC. Inhibition of the PI3K/AKT pathway enhanced radiosensitivity substantially, and PI3K-α inhibitor showed superior radiosensitizing effect similar to PI3K pan-inhibitor, both in vitro and in vivo. Additionally, a significant increase in DNA double-strand breaks (DSB) and a decrease in migration ability were observed. Our study revealed that combining radiation and the PI3K-α isoform improved radiosensitivity that resulted in a significant delay in tumor growth and improved survival rate.

Caffeic acid phenethyl ester induces radiosensitization via inhibition of DNA damage repair in androgen-independent prostate cancer cells

In the present study, we evaluated the radiomodulatory potential of caffeic acid phenethyl ester (CAPE), an active component of traditional herbal medicine propolis. CAPE has been identified as a potent anticancer agent in multiple cancer types and is reported to have the dual role of radioprotection and radiosensitization. However, the radiomodulatory potential of CAPE in prostate cancer (PCa), which eventually becomes radioresistant is not known. Therefore, we studied the effect of co-treatment of CAPE and gamma radiation on androgen-independent DU145 and PC3 cells. The combination treatment sensitized PCa cells to radiation in a dose-dependent manner. The radiosensitizing effect of CAPE was observed in both cell lines. CAPE enhanced the level of ionizing radiation (IR)-induced gamma H2AX foci and cell death by apoptosis. The combination treatment also decreased the migration potential of PCa cells. This was confirmed by increased expression of E-cadherin and decrease in vimentin expression. CAPE sensitized PCa cells to radiation in vitro and induced apoptosis, augmented phosphorylation of Akt/mTOR, and hampered cell migration. At the mechanistic level, co-treatment of CAPE and IR inhibited cell growth by decreasing RAD50 and RAD51 proteins involved in DNA repair. This resulted in enhanced DNA damage and cell death. CAPE might represent a promising new adjuvant for the treatment of hormone-refractory radioresistant PCa.

Translation Initiation Machinery as a Tumor Selective Target for Radiosensitization

Towards improving the efficacy of radiotherapy, one approach is to target the molecules and processes mediating cellular radioresponse. Along these lines, translational control of gene expression has been established as a fundamental component of cellular radioresponse, which suggests that the molecules participating in this process (i.e., the translational machinery) can serve as determinants of radiosensitivity. Moreover, the proteins comprising the translational machinery are often overexpressed in tumor cells suggesting the potential for tumor specific radiosensitization. Studies to date have shown that inhibiting proteins involved in translation initiation, the rate-limiting step in translation, specifically the three members of the eIF4F cap binding complex eIF4E, eIF4G, and eIF4A as well as the cap binding regulatory kinases mTOR and Mnk1/2, results in the radiosensitization of tumor cells. Because ribosomes are required for translation initiation, inhibiting ribosome biogenesis also appears to be a strategy for radiosensitization. In general, the radiosensitization induced by targeting the translation initiation machinery involves inhibition of DNA repair, which appears to be the consequence of a reduced expression of proteins critical to radioresponse. The availability of clinically relevant inhibitors of this component of the translational machinery suggests opportunities to extend this approach to radiosensitization to patient care.

Activated ERK Signaling Is One of the Major Hub Signals Related to the Acquisition of Radiotherapy-Resistant MDA-MB-231 Breast Cancer Cells

Breast cancer is one of the major causes of deaths due to cancer, especially in women. The crucial barrier for breast cancer treatment is resistance to radiation therapy, one of the important local regional therapies. We previously established and characterized radio-resistant MDA-MB-231 breast cancer cells (RT-R-MDA-MB-231 cells) that harbor a high expression of cancer stem cells (CSCs) and the EMT phenotype. In this study, we performed antibody array analysis to identify the hub signaling mechanism for the radiation resistance of RT-R-MDA-MB-231 cells by comparing parental MDA-MB-231 (p-MDA-MB-231) and RT-R-MDA-MB-231 cells. Antibody array analysis unveiled that the MAPK1 protein was the most upregulated protein in RT-R-MDA-MB-231 cells compared to in p-MDA-MB-231 cells. The pathway enrichment analysis also revealed the presence of MAPK1 in almost all enriched pathways. Thus, we used an MEK/ERK inhibitor, PD98059, to block the MEK/ERK pathway and to identify the role of MAPK1 in the radio-resistance of RT-R-MDA-MB-231 cells. MEK/ERK inhibition induced cell death in both p-MDA-MB-231 and RT-R-MDA-MB-231 cells, but the death mechanism for each cell was different; p-MDA-MB-231 cells underwent apoptosis, showing cell shrinkage and PARP-1 cleavage, while RT-R-MDA-MB-231 cells underwent necroptosis, showing mitochondrial dissipation, nuclear swelling, and an increase in the expressions of CypA and AIF. In addition, MEK/ERK inhibition reversed the radio-resistance of RT-R-MDA-MB-231 cells and suppressed the increased expression of CSC markers (CD44 and OCT3/4) and the EMT phenotype (β-catenin and N-cadherin/E-cadherin). Taken together, this study suggests that activated ERK signaling is one of the major hub signals related to the radio-resistance of MDA-MB-231 breast cancer cells.

Knockdown of AKT3 Activates HER2 and DDR Kinases in Bone-Seeking Breast Cancer Cells, Promotes Metastasis In Vivo and Attenuates the TGFβ/CTGF Axis

Bone metastases frequently occur in breast cancer patients and lack appropriate treatment options. Hence, understanding the molecular mechanisms involved in the multistep process of breast cancer bone metastasis and tumor-induced osteolysis is of paramount interest. The serine/threonine kinase AKT plays a crucial role in breast cancer bone metastasis but the effect of individual AKT isoforms remains unclear. Therefore, AKT isoform-specific knockdowns were generated on the bone-seeking MDA-MB-231 BO subline and the effect on proliferation, migration, invasion, and chemotaxis was analyzed by live-cell imaging. Kinome profiling and Western blot analysis of the TGFβ/CTGF axis were conducted and metastasis was evaluated by intracardiac inoculation of tumor cells into NOD scid gamma (NSG) mice. MDA-MB-231 BO cells exhibited an elevated AKT3 kinase activity in vitro and responded to combined treatment with AKT- and mTOR-inhibitors. Knockdown of AKT3 significantly increased migration, invasion, and chemotaxis in vitro and metastasis to bone but did not significantly enhance osteolysis. Furthermore, knockdown of AKT3 increased the activity and phosphorylation of pro-metastatic HER2 and DDR1/2 but lowered protein levels of CTGF after TGFβ-stimulation, an axis involved in tumor-induced osteolysis. We demonstrated that AKT3 plays a crucial role in bone-seeking breast cancer cells by promoting metastatic potential without facilitating tumor-induced osteolysis.

A New Twist in Protein Kinase B/Akt Signaling: Role of Altered Cancer Cell Metabolism in Akt-Mediated Therapy Resistance

Cancer resistance to chemotherapy, radiotherapy and molecular-targeted agents is a major obstacle to successful cancer therapy. Herein, aberrant activation of the phosphatidyl-inositol-3-kinase (PI3K)/protein kinase B (Akt) pathway is one of the most frequently deregulated pathways in cancer cells and has been associated with multiple aspects of therapy resistance. These include, for example, survival under stress conditions, apoptosis resistance, activation of the cellular response to DNA damage and repair of radiation-induced or chemotherapy-induced DNA damage, particularly DNA double strand breaks (DSB). One further important, yet not much investigated aspect of Akt-dependent signaling is the regulation of cell metabolism. In fact, many Akt target proteins are part of or involved in the regulation of metabolic pathways. Furthermore, recent studies revealed the importance of certain metabolites for protection against therapy-induced cell stress and the repair of therapy-induced DNA damage. Thus far, the likely interaction between deregulated activation of Akt, altered cancer metabolism and therapy resistance is not yet well understood. The present review describes the documented interactions between Akt, its target proteins and cancer cell metabolism, focusing on antioxidant defense and DSB repair. Furthermore, the review highlights potential connections between deregulated Akt, cancer cell metabolism and therapy resistance of cancer cells through altered DSB repair and discusses potential resulting therapeutic implications.

The influence of PI3K inhibition on the radiotherapy response of head and neck cancer cells

Radiotherapy has a central role in the treatment of head and neck squamous cell carcinoma (HNSCC). Activation of the PI3K/AKT/mTOR pathway can decrease the efficiency of radiotherapy via the promotion of cell survival and DNA repair. Here, the influence of PI3K pathway inhibition on radiotherapy response was investigated. Two PI3K inhibitors were investigated and both BKM120 and GDC0980 effectively inhibited cellular and clonogenic growth in 6 HNSCC cells, both HPV-positive as well as HPV-negative. Despite targeted inhibition of the pathway and slight increase in DNA damage, PI3K inhibition did not show significant radiosensitization. Currently only one clinical trial is assessing the effectiveness of combining BKM120 with RT in HNSCC (NCT02113878) of which the results are eagerly awaited.

Simultaneous Targeting of RSK and AKT Efficiently Inhibits YB-1-Mediated Repair of Ionizing Radiation-Induced DNA Double-Strand Breaks in Breast Cancer Cells

PURPOSE

Y-box binding protein 1 (YB-1) overexpression is associated with chemotherapy- and radiation therapy resistance. Ionizing radiation (IR), receptor tyrosine kinase ligands, and mutation in KRAS gene stimulate activation of YB-1. YB-1 accelerates the repair of IR-induced DNA double-strand breaks (DSBs). Ribosomal S6 kinase (RSK) is the main kinase inducing YB-1 phosphorylation. We investigated the impact of RSK targeting on DSB repair and radiosensitivity.

MATERIALS AND METHODS

The triple negative breast cancer (TNBC) cell lines MDA-MB-231, MDA-MB-468, and Hs 578T, in addition to non-TNBC cell lines MCF7, HBL-100, and SKBR3, were used. MCF-10A cells were included as normal breast epithelial cells. The RSK inhibitor LJI308 was used to investigate the role of RSK activity in S102 phosphorylation of YB-1 and YB-1-associated signaling pathways. The activation status of the underlying pathways was investigated by Western blotting after treatment with pharmacologic inhibitors or transfection with siRNA. The impact of LJI308 on DSB repair and postirradiation cell survival was tested by the γH2AX foci and the standard clonogenic assays, respectively.

RESULTS

LJI308 inhibited the phosphorylation of RSK (T359/S363) and YB-1 (S102) after irradiation, treatment with EGF, and in cells expressing a KRAS mutation. LJI308 treatment slightly inhibited DSB repair only in some of the cell lines tested. This was shown to be due to PI3K-dependent stimulation of AKT or constitutive AKT activity mainly in cancer cells but not in normal breast epithelial MCF-10A cells. Simultaneous targeting of AKT and RSK strongly blocked DSB repair in all cancer cell lines, independent of TNBC status or KRAS mutation, with a minor effect in MCF-10A cells. Cotargeting of RSK- and AKT-induced radiation sensitivity in TNBC MDA-MB-231 and non-TNBC MCF7 cells but not in MCF-10A cells.

CONCLUSIONS

Simultaneous targeting of RSK and AKT might be an efficient approach to block the repair of DSBs after irradiation and to induce radiosensitization of breast cancer cells.

Improving the Efficacy of Tumor Radiosensitization Through Combined Molecular Targeting

Chemoradiation, either alone or in combination with surgery or induction chemotherapy, is the current standard of care for most locally advanced solid tumors. Though chemoradiation is usually performed at the maximum tolerated doses of both chemotherapy and radiation, current cure rates are not satisfactory for many tumor entities, since tumor heterogeneity and plasticity result in chemo- and radioresistance. Advances in the understanding of tumor biology, a rapidly growing number of molecular targeting agents and novel technologies enabling the in-depth characterization of individual tumors, have fuelled the hope of entering an era of precision oncology, where each tumor will be treated according to its individual characteristics and weaknesses. At present though, molecular targeting approaches in combination with radiotherapy or chemoradiation have not yet proven to be beneficial over standard chemoradiation treatment in the clinical setting. A promising approach to improve efficacy is the combined usage of two targeting agents in order to inhibit backup pathways or achieve a more complete pathway inhibition. Here we review preclinical attempts to utilize such dual targeting strategies for future tumor radiosensitization.

MAPK4 deletion enhances radiation effects and triggers synergistic lethality with simultaneous PARP1 inhibition in cervical cancer

BACKGROUND

Cervical cancer is one of the most common cancers among females worldwide and advanced patients have extremely poor prognosis. However, adverse reactions and accumulating resistance to radiation therapy require further investigation.

METHODS

The expression levels of mitogen-activated protein kinase 4 (MAPK4) mRNA were analyzed by real-time PCR and its association with overall survival was analyzed using Kaplan-Mier method. Colony formation, immunofluorescence and western blotting were used to examine the effects of MAPK4 knockout or over-expression on cervical cancer cells after radiation treatment. Drug-sensitivity of cervical cancer cells to PARP1 inhibitors, olaparib or veliparib, was analyzed by CCK-8 cell viability assays, and the 50% inhibitory concentration (IC50) was quantified using GraphPad Prism. The functional effects of MAPK4 knockout on the sensitivity of cervical cancer to radiation treatment and PARP1 inhibitors were further examined using xenograft tumor mouse models in vivo.

RESULTS

Cervical cancer patients with high MAPK4 mRNA expression have lower survival rate. After radiation treatment, the colony number of MAPK4 knockout cells was markedly reduced, and the markers for DNA double-chain breakage were significantly up-regulated. In addition, MAPK4 knockout reduced protein kinase B (AKT) phosphorylation, whereas its over-expression resulted in opposite effects. In MAPK4 KO cells with irradiation treatment, inhibition of AKT phosphorylation promoted DNA double-chain breakage. Constitutive activation of AKT (CA-AKT) increased the levels of phosphorylated-AKT (p-AKT), and DNA repair-related proteins, phosphorylated-DNA-dependent protein kinase (p-DNA-PK) and RAD51 recombinase (RAD51). Furthermore, MAPK4 knockout was found to affect the sensitivity of cervical cancer cells to poly ADP-ribose polymerase 1 (PARP1) inhibitors by activating the phosphorylation of AKT. Moreover, in vivo results demonstrated that MAPK4 knockout enhanced the sensitivity of cervical cancer to radiation and PARP1 inhibitors in mouse xenograft models.

CONCLUSIONS

Collectively, our data suggest that combined application of MAPK4 knockout and PARP1 inhibition can be used as therapeutic strategy in radiation treatment for advanced cervical carcinoma.

Preliminary study on radiosensitivity to carbon ions in human breast cancer

The aim of the study was to investigate the various effects of high linear energy transfer (LET) carbon ion (12C6+) and low LET X-ray radiation on MDA-MB-231 and MCF-7 human breast cancer cells and to explore the underlying mechanisms of radiation sensitivity. Cell proliferation, cell colony formation, cell cycle distribution, cell apoptosis and protein expression levels [double-strand break marker γ-H2AX, cell cycle-related protein cyclin B1, apoptosis-related proteins Bax and Bcl-2, and the Akt/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase B1 (p70S6K) pathway] were detected after irradiation with carbon ions or X-rays at doses of 0, 2, 4 and 8 Gy. Our results showed that the inhibition of cell proliferation and cell colony formation and the induction of G2/M phase arrest, DNA lesions and cell apoptosis/necrosis elicited by carbon ion irradiation were more potent than the effects elicited by X-ray radiation at the same dose. Simultaneously, compared with X-ray radiation, carbon ion radiation induced a marked increase in Bax and prominent decreases in cyclin B1 and Bcl-2 in a dose-dependent manner. Furthermore, the Akt/mTOR/p70S6K pathway was significantly inhibited by carbon ion radiation in both breast cancer cell lines. These results indicate that carbon ion radiation kills MDA-MB-231 and MCF-7 breast cancer cells more effectively than X-ray radiation, which might result from the inhibition of the Akt/mTOR/p70S6K pathway.

Radiosensitising Cancer Using Phosphatidylinositol-3-Kinase (PI3K), Protein Kinase B (AKT) or Mammalian Target of Rapamycin (mTOR) Inhibitors

Radiotherapy is routinely used as a neoadjuvant, adjuvant or palliative treatment in various cancers. There is significant variation in clinical response to radiotherapy with or without traditional chemotherapy. Patients with a good response to radiotherapy demonstrate better clinical outcomes universally across different cancers. The PI3K/AKT/mTOR pathway upregulation has been linked to radiotherapy resistance. We reviewed the current literature exploring the role of inhibiting targets along this pathway, in enhancing radiotherapy response. We identified several studies using in vitro cancer cell lines, in vivo tumour xenografts and a few Phase I/II clinical trials. Most of the current evidence in this area comes from glioblastoma multiforme, non-small cell lung cancer, head and neck cancer, colorectal cancer, and prostate cancer. The biological basis for radiosensitivity following pathway inhibition was through inhibited DNA double strand break repair, inhibited cell proliferation, enhanced apoptosis and autophagy as well as tumour microenvironment changes. Dual PI3K/mTOR inhibition consistently demonstrated radiosensitisation of all types of cancer cells. Single pathway component inhibitors and other inhibitor combinations yielded variable outcomes especially within early clinical trials. There is ample evidence from preclinical studies to suggest that direct pharmacological inhibition of the PI3K/AKT/mTOR pathway components can radiosensitise different types of cancer cells. We recommend that future in vitro and in vivo research in this field should focus on dual PI3K/mTOR inhibitors. Early clinical trials are needed to assess the feasibility and efficacy of these dual inhibitors in combination with radiotherapy in brain, lung, head and neck, breast, prostate and rectal cancer patients.

Integrin αvβ3-Akt signalling plays a role in radioresistance of melanoma

Melanoma is a deadly type of skin cancer that is particularly difficult to treat owing to its resistance to radiation therapy. Here, we attempted to determine the key proteins responsible for melanoma radioresistance, with the aim of improving disease response to radiation therapy. Two melanoma cell lines, SK-Mel5 and SK-Mel28, with different radiosensitivities were analysed via RNA-Seq (Quant-Seq) and target proteins with higher abundance in the more radioresistant cell line, SK-Mel28, identified. Among these proteins, integrin αvβ3, a well-known molecule in cell adhesion, was selected for analysis. Treatment of SK-Mel28 cells with cilengitide, an integrin αvβ3 inhibitor, as well as γ-irradiation resulted in more significant cell death than γ-irradiation alone. In addition, Akt, a downstream signal transducer of integrin αvβ3, showed high basic activation in SK-Mel28 and was significantly decreased upon co-treatment with cilengitide and γ-irradiation. MK-2206, an Akt inhibitor, exerted similar effects on the SK-Mel28 cell line following γ-irradiation. Our results collectively demonstrate that the integrin αvβ3-Akt signalling pathway contributes to radioresistance in SK-Mel28 cells, which may be manipulated to improve therapeutic options for melanoma.

Enhancing the therapeutic effects of in vitro targeted radionuclide therapy of 3D multicellular tumor spheroids using the novel stapled MDM2/X-p53 antagonist PM2

BACKGROUND

Precision therapeutics continuously make advances in cancer therapy, and a field of growing interest is the combination of targeted radionuclide therapy (TRNT) with potential radiosensitizing agents. This study evaluated whether the effects of in vitro TRNT, using the 177Lu-labeled anti-CD44v6 antibody AbN44v6, were potentiated by the novel stapled MDM2/X-p53 antagonist PM2.

MATERIALS AND METHODS

Two wt p53 cell lines, HCT116 (colorectal carcinoma) and UM-SCC-74B (head and neck squamous cell carcinoma), expressing different levels of the target antigen, CD44v6, were used. Antigen-specific binding of 177Lu-AbN44v6 was initially verified in a 2D cell assay, after which the potential effects of unlabeled AbN44v6 on downstream phosphorylation of Erk1/2 were evaluated by western blotting. Further, the therapeutic effects of unlabeled AbN44v6, 177Lu-AbN44v6, PM2, or a combination (labeled/unlabeled AbN44v6 +/- PM2) were assessed in 3D multicellular tumor spheroid assays.

RESULTS

Radiolabeled antibody bound specifically to CD44v6 on both cell lines. Unlabeled AbN44v6 binding did not induce downstream phosphorylation of Erk1/2 at any of the concentrations tested, and repeated treatments with the unlabeled antibody did not result in any spheroid growth inhibition. 177Lu-AbN44v6 impaired spheroid growth in a dose-dependent and antigen-dependent manner. A single modality treatment with 20 μM of PM2 significantly impaired spheroid growth in both spheroid models. Furthermore, the combination of TRNT and PM2-based therapy proved significantly more potent than either monotherapy. In HCT116 spheroids, this resulted in a two- and threefold spheroid growth rate decrease for the combination of PM2 and 100 kBq 177Lu-AbN44v6 compared to monotherapies 14-day post treatment. In UM-SCC-74B spheroids, the combination therapy resulted in a reduction in spheroid size compared to the initial spheroid size 10-day post treatment.

CONCLUSION

TRNT using 177Lu-AbN44v6 proved efficient in stalling spheroid growth in a dose-dependent and antigen-dependent manner, and PM2 treatment demonstrated a growth inhibitory effect as a monotherapy. Moreover, by combining TRNT with PM2-based therapy, therapeutic effects of TRNT were potentiated in a 3D multicellular tumor spheroid model. This proof-of-concept study exemplifies the strength and possibility of combining TRNT targeting CD44v6 with PM2-based therapy.

Targeting AKT/PKB to improve treatment outcomes for solid tumors

The serine/threonine kinase AKT, also known as protein kinase B (PKB), is the major substrate to phosphoinositide 3-kinase (PI3K) and consists of three paralogs: AKT1 (PKBα), AKT2 (PKBβ) and AKT3 (PKBγ). The PI3K/AKT pathway is normally activated by binding of ligands to membrane-bound receptor tyrosine kinases (RTKs) as well as downstream to G-protein coupled receptors and integrin-linked kinase. Through multiple downstream substrates, activated AKT controls a wide variety of cellular functions including cell proliferation, survival, metabolism, and angiogenesis in both normal and malignant cells. In human cancers, the PI3K/AKT pathway is most frequently hyperactivated due to mutations and/or overexpression of upstream components. Aberrant expression of RTKs, gain of function mutations in PIK3CA, RAS, PDPK1, and AKT itself, as well as loss of function mutation in AKT phosphatases are genetic lesions that confer hyperactivation of AKT. Activated AKT stimulates DNA repair, e.g. double strand break repair after radiotherapy. Likewise, AKT attenuates chemotherapy-induced apoptosis. These observations suggest that a crucial link exists between AKT and DNA damage. Thus, AKT could be a major predictive marker of conventional cancer therapy, molecularly targeted therapy, and immunotherapy for solid tumors. In this review, we summarize the current understanding by which activated AKT mediates resistance to cancer treatment modalities, i.e. radiotherapy, chemotherapy, and RTK targeted therapy. Next, the effect of AKT on response of tumor cells to RTK targeted strategies will be discussed. Finally, we will provide a brief summary on the clinical trials of AKT inhibitors in combination with radiochemotherapy, RTK targeted therapy, and immunotherapy.

Combination Therapy With Charged Particles and Molecular Targeting: A Promising Avenue to Overcome Radioresistance

Radiotherapy plays a central role in the treatment of cancer patients. Over the past decades, remarkable technological progress has been made in the field of conventional radiotherapy. In addition, the use of charged particles (e.g., protons and carbon ions) makes it possible to further improve dose deposition to the tumor, while sparing the surrounding healthy tissues. Despite these improvements, radioresistance and tumor recurrence are still observed. Although the mechanisms underlying resistance to conventional radiotherapy are well-studied, scientific evidence on the impact of charged particle therapy on cancer cell radioresistance is restricted. The purpose of this review is to discuss the potential role that charged particles could play to overcome radioresistance. This review will focus on hypoxia, cancer stem cells, and specific signaling pathways of EGFR, NFκB, and Hedgehog as well as DNA damage signaling involving PARP, as mechanisms of radioresistance for which pharmacological targets have been identified. Finally, new lines of future research will be proposed, with a focus on novel molecular inhibitors that could be used in combination with charged particle therapy as a novel treatment option for radioresistant tumors.

PIM1 (Moloney Murine Leukemia Provirus Integration Site) Inhibition Decreases the Nonhomologous End-Joining DNA Damage Repair Signaling Pathway in Pulmonary Hypertension

OBJECTIVE

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by the narrowing of pulmonary arteries (PAs). It is now established that this phenotype is associated with enhanced PA smooth muscle cells (PASMCs) proliferation and suppressed apoptosis. This phenotype is sustained in part by the activation of several DNA repair pathways allowing PASMCs to survive despite the unfavorable environmental conditions. PIM1 (Moloney murine leukemia provirus integration site) is an oncoprotein upregulated in PAH and involved in many prosurvival pathways, including DNA repair. The objective of this study was to demonstrate the implication of PIM1 in the DNA damage response and the beneficial effect of its inhibition by pharmacological inhibitors in human PAH-PASMCs and in rat PAH models. Approach and Results: We found in vitro that PIM1 inhibition by either SGI-1776, TP-3654, siRNA (silencer RNA) decreased the phosphorylation of its newly identified direct target KU70 (lupus Ku autoantigen protein p70) resulting in the inhibition of double-strand break repair (Comet Assay) by the nonhomologous end-joining as well as reduction of PAH-PASMCs proliferation (Ki67-positive cells) and resistance to apoptosis (Annexin V positive cells) of PAH-PASMCs. In vivo, SGI-1776 and TP-3654 given 3× a week, improved significantly pulmonary hemodynamics (right heart catheterization) and vascular remodeling (Elastica van Gieson) in monocrotaline and Fawn-Hooded rat models of PAH.

CONCLUSIONS

We demonstrated that PIM1 phosphorylates KU70 and initiates DNA repair signaling in PAH-PASMCs and that PIM1 inhibitors represent a therapeutic option for patients with PAH.

The Combination of MK-2206 and WZB117 Exerts a Synergistic Cytotoxic Effect Against Breast Cancer Cells

Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death in women. Hormone receptor-positive breast cancer is usually subjected to hormone therapy, while triple-negative breast cancer is more formidable and poses a therapeutic challenge. Glucose transporters are potential targets for the development of anticancer drugs. In search of anticancer agents whose effect could be enhanced by a GLUT1 inhibitor WZB117, we found that MK-2206, a potent allosteric Akt inhibitor, when combined with WZB117, showed a synergistic effect on growth inhibition and apoptosis induction in breast cancer cells, including ER(+) MCF-7 cells and triple-negative MDA-MB-231 cells. The combination index values at 50% growth inhibition were 0.45 and 0.21, respectively. Mechanism studies revealed that MK-2206 and WZB117 exert a synergistic cytotoxic effect in both MCF-7 and MDA-MB-231 breast cancer cells by inhibiting Akt phosphorylation and inducing DNA damage. The combination may also compromise DNA damage repair and ultimately lead to apoptosis. Our findings suggest that the combination of Akt inhibitors and GLUT1 inhibitors could be a novel strategy to combat breast cancer.

Differential effects of the Akt inhibitor MK-2206 on migration and radiation sensitivity of glioblastoma cells

Background

Most tumor cells show aberrantly activated Akt which leads to increased cell survival and resistance to cancer radiotherapy. Therefore, targeting Akt can be a promising strategy for radiosensitization. Here, we explore the impact of the Akt inhibitor MK-2206 alone and in combination with the dual PI3K and mTOR inhibitor PI-103 on the radiation sensitivity of glioblastoma cells. In addition, we examine migration of drug-treated cells.

Methods

Using single-cell tracking and wound healing migration tests, colony-forming assay, Western blotting, flow cytometry and electrorotation we examined the effects of MK-2206 and PI-103 and/or irradiation on the migration, radiation sensitivity, expression of several marker proteins, DNA damage, cell cycle progression and the plasma membrane properties in two glioblastoma (DK-MG and SNB19) cell lines, previously shown to differ markedly in their migratory behavior and response to PI3K/mTOR inhibition.

Results

We found that MK-2206 strongly reduces the migration of DK-MG but only moderately reduces the migration of SNB19 cells. Surprisingly, MK-2206 did not cause radiosensitization, but even increased colony-forming ability after irradiation. Moreover, MK-2206 did not enhance the radiosensitizing effect of PI-103. The results appear to contradict the strong depletion of p-Akt in MK-2206-treated cells. Possible reasons for the radioresistance of MK-2206-treated cells could be unaltered or in case of SNB19 cells even increased levels of p-mTOR and p-S6, as compared to the reduced expression of these proteins in PI-103-treated samples. We also found that MK-2206 did not enhance IR-induced DNA damage, neither did it cause cell cycle distortion, nor apoptosis nor excessive autophagy.

Conclusions

Our study provides proof that MK-2206 can effectively inhibit the expression of Akt in two glioblastoma cell lines. However, due to an aberrant activation of mTOR in response to Akt inhibition in PTEN mutated cells, the therapeutic window needs to be carefully defined, or a combination of Akt and mTOR inhibitors should be considered.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5517-4) contains supplementary material, which is available to authorized users.

Nanog Signaling Mediates Radioresistance in ALDH-Positive Breast Cancer Cells

Recently, cancer stem cells (CSCs) have been identified as the major cause of both chemotherapy and radiotherapy resistance. Evidence from experimental studies applying both in vitro and in vivo preclinical models suggests that CSCs survive after conventional therapy protocols. Several mechanisms are proposed to be involved in CSC resistance to radiotherapy. Among them, stimulated DNA double-strand break (DSB) repair capacity in association with aldehyde dehydrogenase (ALDH) activity seems to be the most prominent mechanism. However, thus far, the pathway through which ALDH activity stimulates DSB repair is not known. Therefore, in the present study, we investigated the underlying signaling pathway by which ALDH activity stimulates DSB repair and can lead to radioresistance of breast cancer cell lines in vitro. When compared with ALDH-negative cells, ALDH-positive cells presented significantly enhanced cell survival after radiation exposure. This enhanced cell survival was associated with stimulated Nanog, BMI1 and Notch1 protein expression, as well as stimulated Akt activity. By applying overexpression and knockdown approaches, we clearly demonstrated that Nanog expression is associated with enhanced ALDH activity and cellular radioresistance, as well as stimulated DSB repair. Akt and Notch1 targeting abrogated the Nanog-mediated radioresistance and stimulated ALDH activity. Overall, we demonstrate that Nanog signaling induces tumor cell radioresistance and stimulates ALDH activity, most likely through activation of the Notch1 and Akt pathways.

Dual-Targeting of miR-124-3p and ABCC4 Promotes Sensitivity to Adriamycin in Breast Cancer Cells

AIMS

Increasing evidence links the abnormal expression of microRNAs and ATP-binding cassette subfamily C member 4 (ABCC4) with tumor development and progression, as well as with chemoresistance. Our aims were to determine the therapeutic potential of targeting both miR-124-3p and ABCC4 in breast cancer cells and to determine if duel targeting increased their sensitivity to chemotherapeutic drugs, in vitro.

MATERIALS AND METHODS

The expression of the ABCC4 protein and miR-124-3p were detected, respectively, by immunohistochemical staining and quantitative real-time polymerase chain reaction in breast cancer tumor tissue, MCF-7 and MCF-7-ADR cell lines. Suppression of ABCC4 expression and miR-124-3p overexpression were performed in MCF-7-ADR cell lines. Western blot assays were used to detect expression of ABCC4 and permeability glycoprotein 1/multi-drug resistance protein 1 (P-gp) in cells. Cell Counting Kit-8, flow cytometry, transwell, and scratch assays were conducted to detect cell proliferation, cell cycle, invasion, and migration of cells.

RESULTS

We found that ABCC4 protein expression was significantly increased, while the miR-124-3p level was significantly decreased in breast cancer tissue and cell lines. Tumor size and clinical tumor node metastasis stage were significantly correlated with elevated expression of ABCC4 and decreased expression of miR-124-3p. Interestingly, ABCC4 expression was significantly increased in MCF-7-ADR cells, while miR-124-3p level was significantly decreased compared with MCF-7 cells. The inhibition of ABCC4 and miR-124-3p overexpression both led to a significant decrease in cell proliferation, invasion, and migration of MCF-7-ADR cells, and combination of suppression of ABCC4 with miR-124-3p overexpression had a synergistic inhibitory effect. Our results further demonstrated that inhibition of ABCC4 expression and overexpression of miR-124-3p significantly enhanced the sensitivity to adriamycin (ADR) in MCF-7-ADR cells, and that simultaneous dual-targeting of miR-124-3p and ABCC4 had a stronger promotive effect on the sensitivity to ADR in MCF-7-ADR cells. Moreover, western blot analysis showed that miR-124-3p overexpression significantly inhibited P-gp expression in MCF-7-ADR cells.

CONCLUSION

Our data demonstrate that the combination of downregulation of ABCC4 with overexpression of miR-124-3p significantly increased sensitivity to ADR in MCF-7-ADR cells. This finding suggests that similar dual targeting may serve as a means to enhance therapies for drug-resistant breast cancers.

Targeting DNA Double-Strand Break Repair Pathways to Improve Radiotherapy Response

More than half of cancer patients receive radiotherapy as a part of their cancer treatment. DNA double-strand breaks (DSBs) are considered as the most lethal form of DNA damage and a primary cause of cell death and are induced by ionizing radiation (IR) during radiotherapy. Many malignant cells carry multiple genetic and epigenetic aberrations that may interfere with essential DSB repair pathways. Additionally, exposure to IR induces the activation of a multicomponent signal transduction network known as DNA damage response (DDR). DDR initiates cell cycle checkpoints and induces DSB repair in the nucleus by non-homologous end joining (NHEJ) or homologous recombination (HR). The canonical DSB repair pathways function in both normal and tumor cells. Thus, normal-tissue toxicity may limit the targeting of the components of these two pathways as a therapeutic approach in combination with radiotherapy. The DSB repair pathways are also stimulated through cytoplasmic signaling pathways. These signaling cascades are often upregulated in tumor cells harboring mutations or the overexpression of certain cellular oncogenes, e.g., receptor tyrosine kinases, PIK3CA and RAS. Targeting such cytoplasmic signaling pathways seems to be a more specific approach to blocking DSB repair in tumor cells. In this review, a brief overview of cytoplasmic signaling pathways that have been reported to stimulate DSB repair is provided. The state of the art of targeting these pathways will be discussed. A greater understanding of the underlying signaling pathways involved in DSB repair may provide valuable insights that will help to design new strategies to improve treatment outcomes in combination with radiotherapy.

Restraining Akt1 Phosphorylation Attenuates the Repair of Radiation-Induced DNA Double-Strand Breaks and Reduces the Survival of Irradiated Cancer Cells

The survival kinase protein kinase B (Akt) participates in the regulation of essential subcellular processes, e.g., proliferation, growth, survival, and apoptosis, and has a documented role in promoting resistance against genotoxic stress including radiotherapy, presumably by influencing the DNA damage response and DNA double-strand break (DSB) repair. However, its exact role in DSB repair requires further elucidation. We used a genetic approach to explore the consequences of impaired phosphorylation of Akt1 at one or both of its key phosphorylation sites, Threonine 308 (T308) or Serine 473 (S473), on DSB repair and radiosensitivity to killing. Therefore, we overexpressed either the respective single or the double phosphorylation-deficient mutants (Akt1-T308A, Akt1-S473A, or Akt1-T308A/S473A) in TRAMPC1 murine prostate cancer cells (TrC1) and measured the DSB repair kinetics and clonogenic cell survival upon irradiation. Only the expression of the Akt1-T308A/S473A induced a significant delay in the kinetics of DSB repair in irradiated TrC1 as determined by the γH2A.X (H2A histone family, member X) assay and the neutral comet assay, respectively. Moreover, Akt1-T308A/S473A-expressing cells were characterized by increased radiosensitivity compared to Akt1-WT (wild type)-expressing cells in long-term colony formation assays. Our data reveal that Akt1’s activation state is important for the cellular radiation response, presumably by modulating the phosphorylation of effector proteins involved in the regulation of DSB repair.

Enhancing radiosensitivity of melanoma cells through very high dose rate pulses released by a plasma focus device

Radiation therapy is a useful and standard tumor treatment strategy. Despite recent advances in delivery of ionizing radiation, survival rates for some cancer patients are still low because of recurrence and radioresistance. This is why many novel approaches have been explored to improve radiotherapy outcome. Some strategies are focused on enhancement of accuracy in ionizing radiation delivery and on the generation of greater radiation beams, for example with a higher dose rate. In the present study we proposed an in vitro research of the biological effects of very high dose rate beam on SK-Mel28 and A375, two radioresistant human melanoma cell lines. The beam was delivered by a pulsed plasma device, a "Mather type" Plasma Focus for medical applications. We hypothesized that this pulsed X-rays generator is significantly more effective to impair melanoma cells survival compared to conventional X-ray tube. Very high dose rate treatments were able to reduce clonogenic efficiency of SK-Mel28 and A375 more than the X-ray tube and to induce a greater, less easy-to-repair DNA double-strand breaks. Very little is known about biological consequences of such dose rate. Our characterization is preliminary but is the first step toward future clinical considerations.

mTORC1 pathway in DNA damage response

Living organisms have evolved various mechanisms to control their metabolism and response to various stresses, allowing them to survive and grow in different environments. In eukaryotes, the highly conserved mechanistic target of rapamycin (mTOR) signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of cellular metabolism, proliferation and survival. A growing body of evidence indicates that mTOR signaling is closely related to another cellular protection mechanism, the DNA damage response (DDR). Many factors important for the DDR are also involved in the mTOR pathway. In this review, we discuss how these two pathways communicate to ensure an efficient protection of the cell against metabolic and genotoxic stresses. We also describe how anticancer therapies benefit from simultaneous targeting of the DDR and mTOR pathways.

hTERT peptide fragment GV1001 demonstrates radioprotective and antifibrotic effects through suppression of TGF‑β signaling

GV1001 is a 16‑amino acid peptide derived from the human telomerase reverse transcriptase (hTERT) protein (616‑626; EARPALLTSRLRFIPK), which lies within the reverse transcriptase domain. Originally developed as an anticancer vaccine, GV1001 demonstrates diverse cellular effects, including anti‑inflammatory, tumor suppressive and antiviral effects. In the present study, the radioprotective and antifibrotic effects of GV1001 were demonstrated through suppressing transforming growth factor‑β (TGF‑β) signaling. Proliferating human keratinocytes underwent premature senescence upon exposure to ionizing radiation (IR), however, treatment of cells with GV1001 allowed the cells to proliferate and showed a reduction in senescent phenotype. GV1001 treatment notably increased the levels of Grainyhead‑like 2 and phosphorylated (p‑)Akt (Ser473), and reduced the activation of p53 and the level of p21/WAF1 in irradiated keratinocytes. It also markedly suppressed the level of TGF‑β signaling molecules, including p‑small mothers against decapentaplegic (Smad)2/3 and Smad4, and TGF‑β target genes, including zinc finger E‑box binding homeobox 1, fibronectin, N‑cadharin and Snail, in irradiated keratinocytes. Furthermore, GV1001 suppressed TGF‑β signaling in primary human fibroblasts and inhibited myofibroblast differentiation. Chromatin immunoprecipitation revealed that GV1001 suppressed the binding of Smad2 on the promoter regions of collagen type III α1 chain (Col3a1) and Col1a1. In a dermal fibrosis model in vivo, GV1001 treatment notably reduced the thickness of fibrotic lesions and the synthesis of Col3a1. These data indicated that GV1001 ameliorated the IR‑induced senescence phenotype and tissue fibrosis by inhibiting TGF‑β signaling and may have therapeutic effects on radiation‑induced tissue damage.

Exploiting Radiation-Induced Signaling to Increase the Susceptibility of Resistant Cancer Cells to Targeted Drugs: AKT and mTOR Inhibitors as an Example

Implementing targeted drug therapy in radio-oncologic treatment regimens has greatly improved the outcome of cancer patients. However, the efficacy of molecular targeted drugs such as inhibitory antibodies or small molecule inhibitors essentially depends on target expression and activity, which both can change during the course of treatment. Radiotherapy has previously been shown to activate prosurvival pathways, which can help tumor cells to adapt and thereby survive treatment. Therefore, we aimed to identify changes in signaling induced by radiation and evaluate the potential of targeting these changes with small molecules to increase the therapeutic efficacy on cancer cell survival. Analysis of "The Cancer Genome Atlas" database disclosed a significant overexpression of AKT1, AKT2, and MTOR genes in human prostate cancer samples compared with normal prostate gland tissue. Multifractionated radiation of three-dimensional-cultured prostate cancer cell lines with a dose of 2 Gy/day as a clinically relevant schedule resulted in an increased protein phosphorylation and enhanced protein-protein interaction between AKT and mTOR, whereas gene expression of AKT, MTOR, and related kinases was not altered by radiation. Similar results were found in a xenograft model of prostate cancer. Pharmacologic inhibition of mTOR/AKT signaling after activation by multifractionated radiation was more effective than treatment prior to radiotherapy. Taken together, our findings provide a proof-of-concept that targeting signaling molecules after activation by radiotherapy may be a novel and promising treatment strategy for cancers treated with multifractionated radiation regimens such as prostate cancer to increase the sensitivity of tumor cells to molecular targeted drugs. Mol Cancer Ther; 17(2); 355-67. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Ataxia-Telangiectasia Mutated Modulation of Carbon Metabolism in Cancer

The ataxia-telangiectasia mutated (ATM) protein kinase has been extensively studied for its role in the DNA damage response and its association with the disease ataxia telangiectasia. There is increasing evidence that ATM also plays an important role in other cellular processes, including carbon metabolism. Carbon metabolism is highly dysregulated in cancer due to the increased need for cellular biomass. A number of recent studies report a non-canonical role for ATM in the regulation of carbon metabolism. This review highlights what is currently known about ATM's regulation of carbon metabolism, the implication of these pathways in cancer, and the development of ATM inhibitors as therapeutic strategies for cancer.

Akt1 Stimulates Homologous Recombination Repair of DNA Double-Strand Breaks in a Rad51-Dependent Manner

Akt1 is known to promote non-homologous end-joining (NHEJ)-mediated DNA double-strand break (DSB) repair by stimulation of DNA-PKcs. In the present study, we investigated the effect of Akt1 on homologous recombination (HR)-dependent repair of radiation-induced DSBs in non-small cell lung cancer (NSCLC) cells A549 and H460. Akt1-knockdown (Akt1-KD) significantly reduced Rad51 protein level, Rad51 foci formation and its colocalization with γH2AX foci after irradiation. Moreover, Akt1-KD decreased clonogenicity after treatment with Mitomycin C and HR repair, as tested by an HR-reporter assay. Double knockdown of Akt1 and Rad51 did not lead to a further decrease in HR compared to the single knockdown of Rad51. Consequently, Akt1-KD significantly increased the number of residual DSBs after irradiation partially independent of the kinase activity of DNA-PKcs. Likewise, the number of residual BRCA1 foci, indicating unsuccessful HR events, also significantly increased in the irradiated cells after Akt1-KD. Together, the results of the study indicate that Akt1 seems to be a regulatory component in the HR repair of DSBs in a Rad51-dependent manner. Thus, based on this novel role of Akt1 in HR and the previously described role of Akt1 in NHEJ, we propose that targeting Akt1 could be an effective approach to selectively improve the killing of tumor cells by DSB-inducing cytotoxic agents, such as ionizing radiation.

Akt1 and Akt3 but not Akt2 through interaction with DNA-PKcs stimulate proliferation and post-irradiation cell survival of K-RAS-mutated cancer cells

Akt1 through the C-terminal domain interacts with the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and stimulates the repair of DNA double-strand breaks (DSBs) in K-RAS-mutated (K-RASmut) cells. We investigated the interactions of distinct domain(s) of DNA-PKcs in binding to full-length Akt1. Similarly, we analyzed potential interactions of DNA-PKcs with Akt2 and Akt3. Finally the effect of Akt isoforms in cell proliferation and tumor growth was tested. We demonstrated that Akt1 preferentially binds to the N-terminal domain of DNA-PKcs using pull-down studies with distinct eGFP-tagged DNA-PKcs fragments that were expressed by plasmids in combination with mCherry-tagged full-length Akt isoforms. These binding studies also indicated an interaction with the intermediate and C-terminal domains of DNA-PKcs. In contrast, Akt3 interacted with all four DNA-PKcs fragments without a marked preference for any specific domain. Notably, we could not see binding of Akt2 to any of the tested DNA-PKcs fragments. In subsequent studies, we demonstrated that Akt inhibition interferes with binding of Akt1 to the N-terminal domain of DNA-PKcs. This indicated a correlation between Akt1 activity and the Akt1/DNA-PKcs complex formation. Finally, knockdown studies revealed that the depletion of endogenous Akt1 and Akt3, but not Akt2, inhibit clonogenic activity and repair of ionizing radiation (IR)-induced DNA DSBs, leading to radiosensitization. Furthermore, in a xenograft study the expression of shAkt1 or shAkt3, but not shAkt2 in K-RASmut breast cancer cell line MDA-MB-231 showed major tumor growth delay. Together, these data indicate that Akt1 and Akt3, but not Akt2, physically interact with DNA-PKcs, thus stimulating the repair of DSBs and therefore protecting K-RASmut cells against IR. Likewise, interaction of Akt isoforms with DNA-PKcs could be crucial for their role in regulating tumor growth.

Combined inhibition of AKT and HSF1 suppresses breast cancer stem cells and tumor growth

Breast cancer is the most common cancer in women and the second leading cause of cancer deaths in women. Over 90% of breast cancer deaths are attributable to metastasis. Our lab has recently reported that AKT activates heat shock factor 1 (HSF1), leading to epithelial-to-mesenchymal transition in HER2-positive breast cancer. However, it is unknown whether the AKT-HSF1 pathway plays an important role in other breast cancer subtypes, breast cancer stem cells, or breast cancer growth and metastasis. Herein, we showed AKT and HSF1 to be frequently co-activated in breast cancer cell lines and specimens across different subtypes. Activated AKT (S473) and HSF1 (S326) are strongly associated with shortened time to metastasis. Inhibition of the AKT-HSF1 signaling axis using small molecule inhibitors, HSF1 knockdown or the dominant-negative HSF1 mutant (S326A) reduced the growth of metastatic breast cancer cells and breast cancer stem cells. The combination of small molecule inhibitors targeting AKT (MK-2206) and HSF1 (KRIBB11) resulted in synergistic killing of breast cancer cells and breast cancer stem cells across different molecular subtypes. Using an orthotopic xenograft mouse model, we found that combined targeting of AKT and HSF1 to significantly reduce tumor growth, induce tumor apoptosis, delay time to metastasis, and prolong host survival. Taken together, our results indicate AKT-HSF1 signaling mediates breast cancer stem cells self-renewal, tumor growth and metastasis, and that dual targeting of AKT and HSF1 resulted in synergistic suppression of breast cancer progression thereby supporting future testing of AKT-HSF1 combination therapy for breast cancer patients.