Determination of tumor kinetics: strategies for the delivery of radiotherapy and chemotherapy.

Both clinical and laboratory evidence indicates that local control rates for many experimental and clinical human tumors decrease with protraction of the overall duration of radiation therapy and that a likely basis for this decrease is tumor cell repopulation during treatment. Such observations have stimulated interest in tumor kinetics, and a number of techniques have been developed that increase the potential for meaningful clinical study of the proliferative behavior of tumors. This review discusses the clinical and experimental evidence for proliferation during treatment, describes two potential approaches-accelerated fractionation and concurrent chemotherapy and radiotherapy-that can be employed to counteract such intratreatment proliferation, explores methods available for measuring tumor cell kinetics, and discusses how kinetics information may be used in the future to tailor therapy to a tumor's individual characteristics.     

Molecular Biology of the Cell Cycle: Potential for Therapeutic Applications in Radiation Oncology

The cell cycle was first described by radiation biologists more than 40 years ago. Since then, radiation oncologists have used information regarding the cell cycle, in particular cell cycle kinetics, to design various treatment protocols; these have resulted in only modest improvements in patient outcome. Over the past 10 to 15 years there has been an explosion of scientific knowledge regarding the cell cycle, in particular the molecular regulation of the cell cycle checkpoints. In this review we will discuss the genetic events involved in regulating the G1 and G2 checkpoints and how this information may lead to future therapeutic breakthroughs. In addition we will discuss the potential clinical impact of the recent cloning of the gene for ataxia telangiectasia.     

放射治疗结合EGFR靶向抑制剂的原理、现状及在非小细胞肺癌中的应用前景

放疗增敏作用是提高综合治疗疗效的主要方式。EGFR通路异常激活，酪氨酸激酶（EGFR-TK）活性增强会激活下游信号通路，肿瘤细胞增殖、侵袭、转移和血管生成的生物学特性得到强化，最终促进了肿瘤的发生和进展，且伴有放射抗拒。EGFR靶向抑制剂均具有明确的放射增敏作用，已经在临床中取得了不同程度的成功，并且有望在非小细胞肺癌的治疗中开拓新的领域。     

New approaches to cell kinetics in human tumors

Both clinical and laboratory evidence indicate that local control rates for many experimental and clinical human tumors decrease with protraction of the overall duration of radiation therapy. A likely basis for this is tumor cell repopulation during treatment. Such observations have stimulated interest in tumor kinetics, and a number of techniques have evolved to increase the potential for meaningful clinical study of the proliferative behavior of tumors. This review discusses the clinical and experimental evidence for proliferation during treatment, describes two potential approaches—accelerated fractionation and inhibition of proliferation—that could be employed in attempting to overcome such intratreatment proliferation, explores both past and newer, evolving methods available for measuring tumor cytokinetics, and discusses how such kinetic information could be used in the future to tailor therapy to a tumor's individual characteristics.     

A quantitative study of the effects of ionizing radiation on endothelial cells and capillary-like network formation

The initial events of angiogenesis comprise endothelial cell activation, migration, and proliferation. The characteristics of retinal endothelial cells and capillaries are significantly altered in a number of diseases including cancer. Since radiation has been shown as a useful tool in radiotherapy by altering the proliferative changes, it is important to evaluate the responses of the endothelial cells and the capillary network to radiation. We quantified functional and kinetic responses of endothelial cells and capillaries to radiation in an in vitro model. An in vitro angiogenesis model was introduced in our study with endothelial cells cultured on an extracellular matrix gel in which hollow tube-like structures could be rapidly formed. Vessel formation was quantified using stereological techniques. The cell cycle kinetics of endothelial cells and accumulation of DNA damage after radiation were measured using laser scanning cytometry. To study the response of proliferative capillary-like structures to radiation, the vessel network was irradiated with 2 gray (Gy). To evaluate functional and kinetic responses and differentiation of endothelial cells to radiation, cells were irradiated with 2 and 6 Gy. Progressive time- and dose-dependent loss of endothelial cells occurred starting 24 hours after radiation. Vessel growth was significantly retarded at the higher dose. A significant percentage of DNA breaks were detected dose-dependently. A large percentage of G1 cells were measured in the irradiated endothelial cell population when compared to the respective sham-treated control population. These results indicate that radiation-induced endothelial cell injuries destroy the integrity of vascular structure. We postulated that apoptosis may represent a biologically relevant mechanism of radiation-induced endothelial cell damage.     

L.H. Gray Medal lecture: cell kinetics and radiation oncology

Development of the study of human tumor cell kinetics during the past decades has deepened our understanding of the natural history of human cancers. Mathematical models based on the data which have been accumulated may help to evaluate, for the various types of human tumors, the time during their growth that the dissemination process occurred and to calculate the size distribution of the subclinical metastases at the time of treatment of the primary tumor. The perturbations caused by radiotherapy and chemotherapy are complex and include reassortment of surviving cells and repopulation. Currently it appears difficult in clinical practice to take advantage of cell reassortment while the differences in the rate and in the duration of repopulation between normal and neoplastic tissues are exploited in most therapeutic regimens. A better knowledge of cell and tissue kinetics following treatment may help to optimize the treatment scheduling in particular during combined administration of radiotherapy and chemotherapy. The study of the kinetics of proliferation in normal tissue has shown the existence of several types of inhibitory and stimulatory humoral factors. These, when purified, can be used to manipulate the proliferation of critical normal tissues in order to protect them during the administration of cell cycle specific drug or to accelerate their regeneration after treatment.     

Erlotinib (Tarceva): a promising drug targeting epidermal growth factor receptor tyrosine kinase

Overexpression of the epidermal growth factor receptor (EGFR) is correlated with a poor prognosis in several human malignancies. In addition, cancers overexpressing EGFR respond poorly to both chemotherapy and radiation therapy. Therefore, EGFR is a viable target for cancer therapy. This review will address how EGFR blockade modulates signal transduction, leading to alterations in the cell cycle progression with secondary inhibition of proliferation and differentiation of cancer cells. As a prototypical example, erlotinib (Tarceva), a reversible EGFR tyrosine kinase inhibitor will be discussed. This drug has demonstrated promising antitumor activity in Phase II trials in several solid tumors and definitive Phase III studies to demonstrate clinical benefit have completed accrual.     

Radiation-induced cell death mechanisms

The main goal when treating malignancies with radiation therapy is to deprive tumor cells of their reproductive potential. One approach to achieve this is by inducing tumor cell apoptosis. Accumulating evidences suggest that induction of apoptosis alone is insufficient to account for the therapeutic effect of radiotherapy. It has become obvious in the last few years that inhibition of the proliferative capacity of malignant cells following irradiation, especially with solid tumors, can occur via alternative cell death modalities or permanent cell cycle arrests, i.e., senescence. In this review, apoptosis and mitotic catastrophe, the two major cell deaths induced by radiation, are described and dissected in terms of activating mechanisms. Furthermore, treatment-induced senescence and its relevance for the outcome of radiotherapy of cancer will be discussed. The importance of p53 for the induction and execution of these different types of cell deaths is highlighted. The efficiency of radiotherapy and radioimmunotherapy has much to gain by understanding the cell death mechanisms that are induced in tumor cells following irradiation. Strategies to use specific inhibitors that will manipulate key molecules in these pathways in combination with radiation might potentiate therapy and enhance tumor cell kill.     

Erlotinib (Tarceva®): a promising drug targeting epidermal growth factor receptor tyrosine kinase

Overexpression of the epidermal growth factor receptor (EGFR) is correlated with a poor prognosis in several human malignancies. In addition, cancers overexpressing EGFR respond poorly to both chemotherapy and radiation therapy. Therefore, EGFR is a viable target for cancer therapy. This review will address how EGFR blockade modulates signal transduction, leading to alterations in the cell cycle progression with secondary inhibition of proliferation and differentiation of cancer cells. As a prototypical example, erlotinib (Tarceva^®), a reversible EGFR tyrosine kinase inhibitor will be discussed. This drug has demonstrated promising antitumor activity in Phase II trials in several solid tumors and definitive Phase III studies to demonstrate clinical benefit have completed accrual.     

Tumor response to ionizing radiation combined with antiangiogenesis or vascular targeting agents: exploring mechanisms of interaction.

Recent preclinical studies have suggested that radiotherapy in combination with antiangiogenic/vasculature targeting agents enhances the therapeutic ratio of ionizing radiation alone. Because radiotherapy is one of the most widely used treatments for cancer, it is important to understand how best to use these two modalities to aid in the design of rational patient protocols. The mechanisms of interaction between antiangiogenic/vasculature targeting agents and ionizing radiation are complex and involve interactions between the tumor stroma and vasculature and the tumor cells themselves. Vascular targeting agents are aimed specifically at the existing tumor vasculature. Antiangiogenic agents target angiogenesis or the new growth of tumor vessels. These agents can decrease overall tumor resistance to radiation by affecting both tumor cells and tumor vasculature, thereby breaking the codependent cycle of tumor growth and angiogenesis. The hypoxic microenvironment of the tumor also contributes to the mechanisms of interactions between antiangiogenic/vasculature targeting agents and ionizing radiation. Hypoxia stimulates up-regulation of angiogenic and tumor cell survival factors, giving rise to tumor proliferation, radioresistance, and angiogenesis. Preclinical evidence suggests that antiangiogenic agents reduce tumor hypoxia and provides a rationale for combining these agents with ionizing radiation. Optimal scheduling of combined treatment with these agents and ionizing radiation will ultimately depend on understanding how tumor oxygenation changes as tumors regress and regrow during exposure to these agents. This review article explores the complex interactions between antiangiogenic/vasculature targeting agents and radiation and offers insight into the mechanisms of interaction that may be responsible for improved tumor response to radiation.     

Role of cell cycle perturbations in the combination therapy of chemotherapeutic agents and radiation

The combination of radiotherapy with chemotherapeutic agents that sensitize tumor cells to ionizing radiation has long been regarded as a promising strategy to enhance cancer therapy. Many chemotherapeutic agents interact with radiation and enhance the cytotoxic or anti-tumor effect of radiation through a number of mechanisms. These include an increase in initial radiation damage, inhibition of cellular repair, cell cycle redistribution, enhancement of apoptosis, counteracting hypoxia and overcoming accelerated repopulation. This article focuses on the role of cell cycle perturbations in the radiosensitivity of cancer cells.     

Cell kinetic changes in human squamous cell carcinomas during radiotherapy studied using the in vivo administration of two halogenated pyrimidines

The aim of this study was to investigate cell cycle changes during radiation treatment and establish whether treatment intervention could be considered if these changes helped to predict outcome. 33 patients with head and neck cancer were administered iododeoxyuridine (IdUrd) prior to treatment and a second administration of bromodeoxyuridine (BrdUrd) prior to the fifth fraction of 2 Gy. Biopsies were taken several hours after each injection and flow cytometry was used to calculate changes in the cellular kinetics and cell cycle delay in vivo. The kinetic response of the tumour cells was variable; some showed an increase in proliferation during the first week of treatment, whilst the majority showed an inhibition of proliferation. Reduction in the labelling index (LI) and the pretreatment DNA ploidy status and not delays in G2 were the only parameters to correlate with clinical outcome. A lack of reduction in the LI after 1 week of radiotherapy and DNA aneuploidy predicted a group of patients where radiotherapy failed. This information could be helpful in planning future treatment interventions.     

放疗增敏PD-1/PD-L1抑制剂疗效的研究进展

程序性死亡受体-1(PD-1)/程序性死亡受体-配体(PD-L1)抑制剂治疗现已批准用于多种肿瘤,但其单药治疗疗效偏低。如何通过放疗来增敏PD-1/PD-L1抑制剂的疗效,是放疗业界研究的热点。放疗与PD-1/PD-L1抑制剂的联合应用,在多项研究中已显示出生存获益。然而电离辐射对于PD-1/PD-L1免疫治疗而言,是一把双刃剑。如何在充分发挥放疗免疫激活作用的同时,尽量避免放疗的免疫抑制效应,这与放疗的剂量选择、分割模式、治疗时机选择及治疗部位数目等密切相关。为此,本文针对晚期转移性肿瘤治疗中,如何优化放疗联合抗PD-1/PD-L1治疗做一综述。     

Flow cytometric analysis of cell proliferation kinetics using the anti-BrdUrd antibody

There is a growing interest in analysis of cell kinetics in a field of clinical oncology. The development of a monoclonal antibody to bromodeoxyuridine (BrdUrd), a thymidine analogue, is epoch making in the research of cell kinetics, and flow cytometry (FCM) combined with the antibody facilitates clinical use of information concerning cell kinetics of tumor cells. In this review article, we show flow cytometric analysis of cell kinetics using the antibody. Two color analysis of DNA-BrdUrd makes it easy and rapid to obtain cell kinetic data of both tumor and non-tumor cells, without the use of DNA precursors labeled with isotopes. A fraction of labeled cells in the mid S phase (FLSm) method provides more detail analysis of the cell cycle, although it needs multiple samplings after pulse labeling with BrdUrd. Alternatively, a short term continuous labeling method can roughly estimate cell kinetic parameters but this method very simple. Furthermore, effects of anticancer drugs and radiation to human malignant tumors can be rapidly evaluated with the above methods. The protocol of cancer treatment will be determined based on cell kinetic data from an individual patient.     

Targeting valosin‐containing protein enhances the efficacy of radiation therapy in esophageal squamous cell carcinoma

Overcoming resistance to radiation is a great challenge in cancer therapy. Here, we highlight that targeting valosin‐containing protein (VCP) improves radiation sensitivity in esophageal squamous cell carcinoma (ESCC) cell lines and show the potential of using VCP as a prognosis marker in locally advanced ESCC treated with radiation therapy. Esophageal squamous cell carcinoma cell lines with high VCP expression were treated with VCP inhibitor combined with radiotherapy. Cell proliferation, colony formation, cell death, and endoplasmic reticulum (ER) stress signaling were evaluated. Moreover, patients with newly diagnosed locally advanced ESCC who were treated with radiotherapy were analyzed. Immunohistochemistry was used to detect the expression of VCP. The correlation between overall survival and VCP was investigated. Esophageal squamous cell carcinoma cells treated with VCP inhibitor and radiotherapy showed attenuated cell proliferation and colony formation and enhanced apoptosis. Further investigation showed this combined strategy activated the ER stress signaling involved in unfolded protein response, and inhibited the ER‐associated degradation (ERAD) pathway. Clinical analysis revealed a significant survival benefit in the low VCP expression group. Targeting VCP resulted in antitumor activity and enhanced the efficacy of radiation therapy in ESCC cells in vitro. Valosin‐containing protein is a promising and novel target. In patients with locally advanced ESCC who received radiotherapy, VCP can be considered as a useful prognostic indicator of overall survival. Valosin‐containing protein inhibitors could be developed for use as effective cancer therapies, in combination with radiation therapy.     

Hedgehog: an attribute to tumor regrowth after chemoradiotherapy and a target to improve radiation response.

PURPOSE: Despite aggressive chemotherapy, radiotherapy, surgery, or combination approaches, the survival rate of patients with esophageal cancer remains poor. Recent studies have suggested that constitutive activation of the Hedgehog (Hh) pathway in cancers of the digestive tract may contribute to the growth and maintenance of cancer. However, the relationship between Hh signaling and therapeutic response is unknown. EXPERIMENTAL DESIGN: The expression and temporal kinetics of Hh signaling and proliferation biomarkers after chemoradiotherapy were examined in esophageal tumor xenografts. Additionally, immunohistochemical analysis of Sonic Hh (Shh) and Gli-1 expression were done on residual tumors from patients who received neoadjuvant chemoradiotherapy followed by surgery. The ability of Shh signaling to induce proliferation in esophageal cell lines was determined. Expression of cell cycle checkpoint proteins was analyzed in cells in which Hh signaling was activated or inhibited. We further determined the effect of inhibiting Hh signaling in sensitizing esophageal tumors to radiation. RESULTS: We showed that the Shh signaling pathway was extensively activated in esophageal cancer xenografts and residual tumors after chemoradiotherapy and the temporal kinetics of Hh signaling preceded increases in proliferation biomarker expression and tumor size during tumor regrowth. We further showed that Hh pathway activity influences proliferation rates of esophageal cancer cell lines through up-regulation of the G1-cyclin-Rb axis. Additionally, we found that blocking Hh signaling enhanced radiation cytotoxicity of esophageal cancer cells. CONCLUSIONS: These results suggest that activation of the Hh pathway may promote tumor repopulation after chemoradiotherapy and contribute to chemoradiation resistance in esophageal cancers.     

Contribution of radiation biology to the development of radiation therapy]

Results of radiation therapy for malignant tumors have steadily improved, and both radiation biology and radiation physics have contributed to this improvement. As examples of such contribution, radiobiologically-elaborated continuous hyperfractionated accelerated radiotherapy (CHART) has been proven to be superior to conventional radiotherapy against non-small cell lung cancer, and a hypoxic cell sensitizer nimorazole has been proven to be effective against pharyngeal and supraglottic laryngeal cancers. Based on laboratory studies, a combination of chemotherapy and radiotherapy has been shown to be superior to radiotherapy alone in many cancers. Radiation biology has also provided important fundamental data for clinical applications of heavy ion and proton beam therapy. In the future, useful predictive assays and radioprotectors are also expected to be developed. Radiation biology should continue to contribute to the further development of clinical radiation therapy.     

Enhancement of Fast Neutron Beams with Boron Neutron Capture Therapy: A mechanism for achieving a selective, concomitant tumor boost

Both fast neutron radiotherapy and boron neutron capture therapy (BNCT) have been utilized to treat malignant disease. Herein we discuss the potential of combining these treatments to enhance the effectiveness of fast neutron therapy through a concomitant BNCT boost. Using a fast neutron beam generated from a 50 MeV proton on beryllium reaction, we have determined that 0.1% of the beam per microgram of boron-10 per gram of tissue (μg/g) can be deposited via BNCT. Our mathematical modeling predicts that BNCT enhancement of our beam will lead to an additional 1-2 logs of tumor cell kill for boron-10 concentrations of 30-50 μg/g. We have validated this via V-79 cell line in vitro measurements. A Poisson model estimation of how this additional cell kill will influence local tumor control, predicts that BNCT enhancement of fast neutron radiation will lead to a clinically significant improvement in outcome.     

Effects of 2-deoxy-D-glucose on glycolysis,proliferation kinetics and radiation response of human cancer cells

The effects of 2-deoxy-D-glucose (2-DG) on energy metabolism, cell proliferation kinetics, radiation-induced DNA repair, and micronuclei formation in HeLa cells have been studied. Results show that the 2-DG induced modifications of the radiation effects are biphasic: (1) at high 2-DG conceentrations (>2.5 mM), DNA repair is inhibited and manifestation of radiation damage is enhanced as observed by an increase in the radiation (X ray) induced micronuclei formation; (2) lower concentrations of 2-DG (<2.5 mM) do not inhibit DNA repair and a decrease in the frequency of micronuclei formation is observed. These data, in correlation with the effects of 2-DG on glycolysis and cell proliferation kinetics, can be explained by the hypothesis that 2-DG induced modifications of radiation effects arise as a result of energy linked differential inhibitions of pathways of repair andfixation of DNA damage. Implications for cancer therapy are discussed.     

Incidence, risk factors, and pathogenesis of second malignancies in patients with non-Hodgkin lymphoma

Most Non-Hodgkin's Lymphoma patients will survive their diagnosis. High dose chemotherapy and autologous stem cell transplantation, and radiation therapy have all been implicated as risk factors to secondary cancer development. Herein, we will review the molecular biology, examine the epidemiologic findings, discuss the impact of both chemotherapy and radiotherapy, and focus on the special populations of pediatrics and high dose chemotherapy and autologous stem cell transplantation with regard to secondary cancer development.