A phase I–II study on the combination of rapamycin and short course radiotherapy in rectal cancer

PI3K/AKT/mTOR Targeting in Colorectal Cancer Radiotherapy: A Systematic Review

BACKGROUND

Radioresistance is a major challenge in the treatment of patients with colorectal cancer (CRC) and impairs the efficacy of radiotherapy. The PI3K/AKT/mTOR signaling pathway plays a critical role in CRC and contributes to the development of radioresistance. Accordingly, targeting this signaling pathway may be a promising strategy to improve oncotherapy.

METHODS

We performed a systematic search of Scopus, PubMed, Web of Science, Embase, and Medline databases. We included articles that investigated the effects of PI3K/AKT/mTOR pathway inhibitors on improving the efficacy of radiotherapy.

RESULT

Of the 32 articles included in our review, 27 were preclinical studies and 5 were clinical trials. We examined the effects of various signaling pathway inhibitors in combination with radiotherapy. While the efficacy of these therapies when used alone is limited, their combination is associated with reduced survival, induction of apoptosis, and cell cycle arrest, which may increase radiosensitivity. Despite the limited number of studies, this combination therapy has shown favorable treatment outcomes in patients with CRC.

CONCLUSION

PI3K/AKT/mTOR is a critical signaling pathway for cancer cell survival. By inhibiting this pathway, we can increase the efficacy of radiotherapy. These results provide valuable insights for the further development of research and clinical practice in the treatment of colorectal cancer.

Exploring the interactions of rapamycin with target receptors in A549 cancer cells: insights from molecular docking analysis

Rapamycin, a macrocyclic antibiotic derived from the actinomycetes Streptomyces hygroscopicus, is a widely used immunosuppressant and anticancer drug. Even though rapamycin is regarded as a multipotent drug acting against a broad array of anomalies and diseases, the mechanism of action of rapamycin and associated pathways have not been studied and reported clearly. Also reports on the binding of rapamycin to cancer cell receptors are limited to the serine/threonine protein kinase mTORC1. Hence, to uncover the exact potential of rapamycin in cancer therapy, a series of cell culture and in silico studies were conducted to identify other receptors capable of binding to rapamycin. Through molecular docking and simulations, it was found that the receptors EGFR, FKBP12, MET, FGFR, ROS1 and ALK were capable of binding with rapamycin. The findings from the current study provides new insights in modern cancer research and therapy. This could also facilitate in understanding the possible action mechanisms of rapamycin in other diseases such as neurovegetative diseases, autoimmune diseases, etc.

Novel radiation and targeted therapy combinations for improving rectal cancer outcomes

Neoadjuvant radiotherapy (RT) is commonly used as standard treatment for rectal cancer. However, response rates are variable and survival outcomes remain poor, highlighting the need to develop new therapeutic strategies. Research is focused on identifying novel methods for sensitising rectal tumours to RT to enhance responses and improve patient outcomes. This can be achieved through harnessing tumour promoting effects of radiation or preventing development of radio-resistance in cancer cells. Many of the approaches being investigated involve targeting the recently published new dimensions of cancer hallmarks. This review article will discuss key radiation and targeted therapy combination strategies being investigated in the rectal cancer setting, with a focus on exploitation of mechanisms which target the hallmarks of cancer.

PI3K/Akt/mTOR Signaling Pathway as a Target for Colorectal Cancer Treatment

In the last decade, pathway-specific targeted therapy has revolutionized colorectal cancer (CRC) treatment strategies. This type of therapy targets a tumor-vulnerable spot formed primarily due to an alteration in an oncogene and/or a tumor suppressor gene. However, tumor heterogeneity in CRC frequently results in treatment resistance, underscoring the need to understand the molecular mechanisms involved in CRC for the development of novel targeted therapies. The phosphatidylinositol 3-kinase/protein kinase B/mammalian target of the rapamycin (PI3K/Akt/mTOR) signaling pathway axis is a major pathway altered in CRC. The aberrant activation of this pathway is associated with CRC initiation, progression, and metastasis and is critical for the development of drug resistance in CRC. Several drugs target PI3K/Akt/mTOR in clinical trials, alone or in combination, for the treatment of CRC. This review aims to provide an overview of the role of the PI3K/Akt/mTOR signaling pathway axis in driving CRC, existing PI3K/Akt/mTOR-targeted agents against CRC, their limitations, and future trends.

Regulation of Eukaryotic Translation Initiation Factor 4E as a Potential Anticancer Strategy

Eukaryotic translation initiation factors (eIFs) are highly expressed in cancer cells, especially eIF4E, the central regulatory node driving cancer cell growth and a potential target for anticancer drugs. eIF4E-targeting strategies primarily focus on inhibiting eIF4E synthesis, interfering with eIF4E/eIF4G interactions, and targeting eIF4E phosphorylation and peptide inhibitors. Although some small-molecule inhibitors are in clinical trials, no eIF4E inhibitors are available for clinical use. We provide an overview of the regulatory mechanisms of eIF4E and summarize the progress in developing and discovering eIF4E inhibitor strategies. We propose that interference with eIF4E/eIF4G interactions will provide a new perspective for the design of eIF4E inhibitors and may be a preferred strategy.

Interactions of radiation therapy with common and innovative systemic treatments: Antidiabetic treatments, antihypertensives, lipid-lowering medications, immunosuppressive medications and other radiosensitizing methods

The invention and approval of innovative anticancer therapies in the last decade have revolutionized oncology treatment. Radiotherapy is one of the three traditional pillars in oncology treatment with surgery and systemic therapies. Some standard-of-care combinations of chemoradiotherapy widened the therapeutic window of radiation, while some other chemotherapies such as gemcitabine caused unacceptable toxicities when combined with radiation in lung cancers. Fast-paced progress are specially focused on immunotherapies, targeted-therapies, anti-angiogenic treatment, DNA repair inhibitors, hormonotherapy and cell cycle inhibitors. New anticancer therapeutic arsenals provided new possibilities of combined oncological treatments. The interactions of the radiotherapy with other systemic treatments, such as non-anticancer immunomodulatory/immunosuppressive medications are sometimes overlooked even though they could offer a real therapeutic benefit. In this review, we summarize the new opportunities and the risks of historical and novel combined therapies with radiation: non-anticancer immunomodulatory/immunosuppressive drugs, systemic reoxygenation, new therapies such as nanoparticles and SMAC mimetics. Key biological mechanisms, pre-clinical and available clinical data will be provided to demonstrate the promising opportunities in the years to come.

Programmed death-ligand 1 and mammalian target of rapamycin signaling pathway in locally advanced rectal cancer

PURPOSE

To evaluate the role of programmed death-ligand 1 (PD-L1) and mammalian target of rapamycin (mTOR) signaling pathway in locally advanced rectal cancer (LARC).

METHODS

Between February 2012 and February 2018, 103 patients with LARC treated by neoadjuvant chemoradiotherapy (neoCRT) and total mesorectal excision (TME) were included. PD-L1, mTOR and p-mTOR of pair-matched pre-neoCRT biopsies and post-neoCRT surgical tissue were evaluated by immunohistochemistry.

RESULTS

The mean combined positive score (CPS), tumor proportion score (TPS) and immune cell score (IC) of pre-neoCRT were 2.24 (0-70), 1.87 (0-70) and 0.67 (0-10), respectively. The mean CPS, TPS and IC of post-neoCRT were 2.19 (0-80), 1.38 (0-80) and 1.60 (0-20), respectively. Significant difference was observed in terms of IC between pre-neoCRT and post-neoCRT (p = 0.010). The 5-year disease-free survival (DFS) rate of the whole group was 62.4%. Multivariate analysis by Cox model indicated that pre-neoCRT TPS [hazard ratio (HR) 1.052, 95% confidence interval (CI) 1.020-1.086, p = 0.001] and post-neoCRT CPS (HR 0.733, 95% CI 0.555-0.967, p = 0.028) were associated with DFS. In the 89 patients without pathological complete response, p-mTOR and IC were upregulated after neoCRT.

CONCLUSIONS

For patients with LARC treated by neoCRT and TME, p-mTOR and IC were upregulated after neoCRT. Pre-neoCRT TPS and post-neoCRT CPS were independent prognostic predictors of DFS.

Common Pathogenetic Mechanisms Underlying Aging and Tumor and Means of Interventions

Recently, there has been an increase in the incidence of malignant tumors among the older population. Moreover, there is an association between aging and cancer. During the process of senescence, the human body suffers from a series of imbalances, which have been shown to further accelerate aging, trigger tumorigenesis, and facilitate cancer progression. Therefore, exploring the junctions of aging and cancer and searching for novel methods to restore the junctions is of great importance to intervene against aging-related cancers. In this review, we have identified the underlying pathogenetic mechanisms of aging-related cancers by comparing alterations in the human body caused by aging and the factors that trigger cancers. We found that the common mechanisms of aging and cancer include cellular senescence, alterations in proteostasis, microbiota disorders (decreased probiotics and increased pernicious bacteria), persistent chronic inflammation, extensive immunosenescence, inordinate energy metabolism, altered material metabolism, endocrine disorders, altered genetic expression, and epigenetic modification. Furthermore, we have proposed that aging and cancer have common means of intervention, including novel uses of common medicine (metformin, resveratrol, and rapamycin), dietary restriction, and artificial microbiota intervention or selectively replenishing scarce metabolites. In addition, we have summarized the research progress of each intervention and revealed their bidirectional effects on cancer progression to compare their reliability and feasibility. Therefore, the study findings provide vital information for advanced research studies on age-related cancers. However, there is a need for further optimization of the described methods and more suitable methods for complicated clinical practices. In conclusion, targeting aging may have potential therapeutic effects on aging-related cancers.

The PI3K/AKT/mTOR signaling pathway inhibitors enhance radiosensitivity in cancer cell lines

INTRODUCTION

Radiotherapy is one of the most common types of cancer treatment modalities. Radiation can affect both cancer and normal tissues, which limits the whole delivered dose. It is well documented that radiation activates phosphatidylinositol 3-kinase (PI3K) and AKT signaling pathway; hence, the inhibition of this pathway enhances the radiosensitivity of tumor cells. The mammalian target of rapamycin (mTOR) is a regulator that is involved in autophagy, cell growth, proliferation, and survival.

CONCLUSION

The inhibition of mTOR as a downstream mediator of the PI3K/AKT signaling pathway represents a vital option for more effective cancer treatments. The combination of PI3K/AKT/mTOR inhibitors with radiation can increase the radiosensitivity of malignant cells to radiation by autophagy activation. Therefore, this review aims to discuss the impact of such inhibitors on the cell response to radiation.

Biomarkers and cell-based models to predict the outcome of neoadjuvant therapy for rectal cancer patients

Rectal cancer constitutes approximately one-third of all colorectal cancers and contributes to considerable mortality globally. In contrast to colon cancer, the standard treatment for localized rectal cancer often involves neoadjuvant chemoradiotherapy. Tumour response rates to treatment show substantial inter-patient heterogeneity, indicating a need for treatment stratification. Consequently researchers have attempted to establish new means for predicting tumour response in order to assist in treatment decisions. In this review we have summarized published findings regarding potential biomarkers to predict neoadjuvant treatment response for rectal cancer tumours. In addition, we describe cell-based models that can be utilized both for treatment prediction and for studying the complex mechanisms involved.

PET Imaging of Tumor Perfusion: A Potential Cancer Biomarker?

Perfusion, as measured by imaging, is considered a standard of care biomarker for the evaluation of many tumors. Measurements of tumor perfusion may be used in a number of ways, including improving the visual detection of lesions, differentiating malignant from benign findings, assessing aggressiveness of tumors, identifying ischemia and by extension hypoxia within tumors, and assessing treatment response. While most clinical perfusion imaging is currently performed with CT or MR, a number of methods for PET imaging of tumor perfusion have been described. The inert PET radiotracer 15O-water PET represents the recognized gold standard for absolute quantification of tissue perfusion in both normal tissue and a variety of pathological conditions including cancer. Other cancer PET perfusion imaging strategies include the use of radiotracers with high first-pass uptake, analogous to those used in cardiac perfusion PET. This strategy produces more visually pleasing high-contrast images that provide relative rather than absolute perfusion quantification. Lastly, multiple timepoint imaging of PET tracers such as 18F-FDG, are not specifically optimized for perfusion, but have advantages related to availability, convenience, and reimbursement. Multiple obstacles have thus far blocked the routine use of PET imaging for tumor perfusion, including tracer production and distribution, image processing, patient body coverage, clinical validation, regulatory approval and reimbursement, and finally feasible clinical workflows. Fortunately, these obstacles are being overcome, especially within larger imaging centers, opening the door for PET imaging of tumor perfusion to become standard clinical practice. In the foreseeable future, it is possible that whole-body PET perfusion imaging with 15O-water will be able to be performed in a single imaging session concurrent with standard PET imaging techniques such as 18F-FDG-PET. This approach could establish an efficient clinical workflow. The resultant ability to measure absolute tumor blood flow in combination with glycolysis will provide important complementary information to inform prognosis and clinical decisions.

Is Host Metabolism the Missing Link to Improving Cancer Outcomes?

For the past 100 years, oncologists have relentlessly pursued the destruction of tumor cells by surgical, chemotherapeutic or radiation oncological means. Consistent with this focus, treatment plans are typically based on key characteristics of the tumor itself such as disease site, histology and staging based on local, regional and systemic dissemination. Precision medicine is similarly built on the premise that detailed knowledge of molecular alterations of tumor cells themselves enables better and more effective tumor cell destruction. Recently, host factors within the tumor microenvironment including the vasculature and immune systems have been recognized as modifiers of disease progression and are being targeted for therapeutic gain. In this review, we argue that—to optimize the impact of old and new treatment options—we need to take account of an epidemic that occurs independently of—but has major impact on—the development and treatment of malignant diseases. This is the rapidly increasing number of patients with excess weight and its’ attendant metabolic consequences, commonly described as metabolic syndrome. It is well established that patients with altered metabolism manifesting as obesity, metabolic syndrome and chronic inflammation have an increased incidence of cancer. Here, we focus on evidence that these patients also respond differently to cancer therapy including radiation and provide a perspective how exercise, diet or pharmacological agents may be harnessed to improve therapeutic responses in this patient population.

Effect of Rapamycin on the Radio-Sensitivity of Cultured Tumor Cells Following Boron Neutron Capture Reaction

Background

Mammalian target of rapamycin (mTOR) signaling pathway has been implicated in multiple mechanisms of resistance to anticancer drugs and poor treatment outcomes in various human cancers. Meanwhile, clinical boron neutron capture therapy (BNCT) has been carried out for patients with malignant gliomas, melanomas, inoperable head and neck tumors and oral cancers. This study aimed to evaluate the effect of mTOR inhibition on radio-sensitivity of cultured tumor cells in BNCT, employing p-boronophenylalanine-¹⁰B (BPA) as a ¹⁰B-carrier.

Methods

Cultured SAS cells had been incubated for 48 h at RPMI medium with mTOR inhibitor, rapamycin at the dose of 1 µM, and then continuously incubated for 2 more hours at RPMI medium containing both BPA at the ¹⁰B concentration of 10 ppm and rapamycin (1 µM). Subsequently, the SAS cells received reactor neutron beams, and then surviving fraction and micronucleus frequency were determined.

Results

SAS cells incubated with rapamycin showed resistance to γ-rays compared with no treatment with rapamycin. The efficiency of delivery of ¹⁰B from BPA into cultured SAS cells was reduced through combining with rapamycin, leading to reduced sensitivity following boron neutron capture reaction.

Conclusions

Since many tumors are characterized by deregulated PI3K/AKT/mTOR pathway, rapamycin is thought to inhibit the pathway and tumor growth. However, it was revealed that rapamycin can also inhibit the transport of ¹⁰B for BNCT into tumor cells. When BNCT is combined with mTOR inhibitor, the efficiency as cancer treatment can be reduced by repression of distributing ¹⁰B in tumor cells, warranting precaution when the two strategies are combined.

Targeting Protein Synthesis in Colorectal Cancer

Under physiological conditions, protein synthesis controls cell growth and survival and is strictly regulated. Deregulation of protein synthesis is a frequent event in cancer. The majority of mutations found in colorectal cancer (CRC), including alterations in the WNT pathway as well as activation of RAS/MAPK and PI3K/AKT and, subsequently, mTOR signaling, lead to deregulation of the translational machinery. Besides mutations in upstream signaling pathways, deregulation of global protein synthesis occurs through additional mechanisms including altered expression or activity of initiation and elongation factors (e.g., eIF4F, eIF2α/eIF2B, eEF2) as well as upregulation of components involved in ribosome biogenesis and factors that control the adaptation of translation in response to stress (e.g., GCN2). Therefore, influencing mechanisms that control mRNA translation may open a therapeutic window for CRC. Over the last decade, several potential therapeutic strategies targeting these alterations have been investigated and have shown promising results in cell lines, intestinal organoids, and mouse models. Despite these encouraging in vitro results, patients have not clinically benefited from those advances so far. In this review, we outline the mechanisms that lead to deregulated mRNA translation in CRC and highlight recent progress that has been made in developing therapeutic strategies that target these mechanisms for tumor therapy.

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.

Emerging trends in the treatment of rectal cancer

The conventional treatment for cT3-T4 or node-positive clinically resectable rectal cancer is long course preoperative chemoradiation followed by surgery and postoperative adjuvant chemotherapy. Disadvantages of this approach include possible overtreatment of patients, 6 weeks of daily radiation treatment, and undetected metastatic disease. There are a number of emerging trends which are changing this approach to treatment. Selected topics included in this manuscript include the selective use of pelvic radiation, the role of radiation for a positive radial margin, the interval between radiation and surgery, non-operative management, new chemoradiation regimens, short vs. long course radiation, and the role of postoperative adjuvant chemotherapy.

mTORC Inhibitors as Broad-Spectrum Therapeutics for Age-Related Diseases

Chronological age represents the greatest risk factor for many life-threatening diseases, including neurodegeneration, cancer, and cardiovascular disease; ageing also increases susceptibility to infectious disease. Current efforts to tackle individual diseases may have little impact on the overall healthspan of older individuals, who would still be vulnerable to other age-related pathologies. However, recent progress in ageing research has highlighted the accumulation of senescent cells with chronological age as a probable underlying cause of pathological ageing. Cellular senescence is an essentially irreversible proliferation arrest mechanism that has important roles in development, wound healing, and preventing cancer, but it may limit tissue function and cause widespread inflammation with age. The serine/threonine kinase mTOR (mechanistic target of rapamycin) is a regulatory nexus that is heavily implicated in both ageing and senescence. Excitingly, a growing body of research has highlighted rapamycin and other mTOR inhibitors as promising treatments for a broad spectrum of age-related pathologies, including neurodegeneration, cancer, immunosenescence, osteoporosis, rheumatoid arthritis, age-related blindness, diabetic nephropathy, muscular dystrophy, and cardiovascular disease. In this review, we assess the use of mTOR inhibitors to treat age-related pathologies, discuss possible molecular mechanisms of action where evidence is available, and consider strategies to minimize undesirable side effects. We also emphasize the urgent need for reliable, non-invasive biomarkers of senescence and biological ageing to better monitor the efficacy of any healthy ageing therapy.

Potential of memory T cells in bridging preoperative chemoradiation and immunotherapy in rectal cancer

The management of locally advanced rectal cancer has passed a long way of developments, where total mesorectal excision and preoperative radiotherapy are crucial to secure clinical outcome. These and other aspects of multidisciplinary strategies are in-depth summarized in the literature, while our mini-review pursues a different goal. From an ethical and medical standpoint, we witness a delayed implementation of novel therapies given the cost/time consuming process of organizing randomized trials that would bridge an already excellent local control in cT3-4 node-positive disease with long-term survival. This unfortunate separation of clinical research and medical care provides a strong motivation to repurpose known pharmaceuticals that suit for treatment intensification with a focus on distant control. In the framework of on-going phase II-III IG/IMRT-SIB trials, we came across an intriguing translational observation that the ratio of circulating (protumor) myeloid-derived suppressor cells to (antitumor) central memory CD8+ T cells is drastically increased, a possible mechanism of tumor immuno-escape and spread. This finding prompts that restoring the CD45RO memory T-cell pool could be a part of integrated adjuvant interventions. Therefore, the immunocorrective potentials of modified IL-2 and the anti-diabetic drug metformin are thoroughly discussed in the context of tumor immunobiology, mTOR pathways and revised Warburg effect.

Radiotherapy-Activated Cancer-Associated Fibroblasts Promote Tumor Progression through Paracrine IGF1R Activation

Preoperative radiotherapy (RT) is a mainstay in the management of rectal cancer, a tumor characterized by desmoplastic stroma containing cancer-associated fibroblasts (CAF). Although CAFs are abundantly present, the effects of RT to CAF and its impact on cancer cells are unknown. We evaluated the damage responses of CAF to RT and investigated changes in colorectal cancer cell growth, transcriptome, metabolome, and kinome in response to paracrine signals emerging from irradiated CAF. RT to CAF induced DNA damage, p53 activation, cell-cycle arrest, and secretion of paracrine mediators, including insulin-like growth factor-1 (IGF1). Subsequently, RT-activated CAFs promoted survival of colorectal cancer cells, as well as a metabolic switch favoring glutamine consumption through IGF1 receptor (IGF1R) activation. RT followed by IGF1R neutralization in orthotopic colorectal cancer models reduced the number of mice with organ metastases. Activation of the downstream IGF1R mediator mTOR was significantly higher in matched (intrapatient) samples and in unmatched (interpatient) samples from rectal cancer patients after neoadjuvant chemoradiotherapy. Taken together, our data support the notion that paracrine IGF1/IGF1R signaling initiated by RT-activated CAF worsens colorectal cancer progression, establishing a preclinical rationale to target this activation loop to further improve clinical responses and patient survival.Significance: These findings reveal that paracrine IGF1/IGF1R signaling promotes colorectal cancer progression, establishing a preclinical rationale to target this activation loop. Cancer Res; 78(3); 659-70. ©2017 AACR.

Neoadjuvant Treatment Strategies: Advanced Radiation Alternatives

Long-course chemoradiation therapy (CRT) has been the standard approach for locally advanced rectal tumors. Neoadjuvant CRT is associated to improved local disease control, with less toxicity when compared with adjuvant CRT, as well as the chance for pathologic complete response. The CRT regimens have improved over the past years. This article will examine selected controversies, including novel chemoradiation regimens, duration of radiation (short vs. long course), and radiation techniques such as intensity-modulated radiation therapy (IMRT).