Analysis of the high-dose-range radioresistance of prostate cancer cells, including cancer stem cells, based on a stochastic model

Quantitative analysis of radiosensitizing effect for magnetic hyperthermia-radiation combined therapy on prostate cancer cells

BACKGROUND

Magnetic hyperthermia (MHT) has emerged as a promising therapeutic approach in the field of radiation oncology due to its superior precision in controlling temperature and managing the heating area compared to conventional hyperthermia. Recent studies have proposed solutions to address clinical safety concerns associated with MHT, which arise from the use of highly concentrated magnetic nanoparticles and the strong magnetic field needed to induce hyperthermic effects. Despite these efforts, challenges remain in quantifying therapeutic outcomes and developing treatment plan systems for combining MHT with radiation therapy (RT).

PURPOSE

This study aims to quantitatively measure the therapeutic effect, including radiation dose enhancement (RDE) in the magnetic hyperthermia-radiation combined therapy (MHRT), using the equivalent radiation dose (EQD) estimation method.

METHODS

To conduct EQD estimation for MHRT, we compared the therapeutic effects between the conventional hyperthermia-radiation combined therapy (HTRT) and MHRT in human prostate cancer cell lines, PC3 and LNCaP. We adopted a clonogenic assay to validate RDE and the radiosensitizing effect induced by MHT. The data on survival fractions were analyzed using both the linear-quadradic model and Arrhenius model to estimate the biological parameters describing RDE and radiosensitizing effect of MHRT for both cell lines through maximum likelihood estimation. Based on these parameters, a new survival fraction model was suggested for EQD estimation of MHRT.

RESULTS

The newly designed model describing the MHRT effect, effectively captures the variations in thermal and radiation dose for both cell lines (R2 > 0.95), and its suitability was confirmed through the normality test of residuals. This model appropriately describes the survival fractions up to 10 Gy for PC3 cells and 8 Gy for LNCaP cells under RT-only conditions. Furthermore, using the newly defined parameter r, the RDE effect was calculated as 29% in PC3 cells and 23% in LNCaP cells. EQDMHRT calculated through this model was 9.47 Gy for PC3 and 4.71 Gy for LNCaP when given 2 Gy and MHT for 30 min. Compared to EQDHTRT, EQDMHRT showed a 26% increase for PC3 and a 20% increase for LNCaP.

CONCLUSIONS

The proposed model effectively describes the changes of the survival fraction induced by MHRT in both cell lines and adequately represents actual data values through residual analysis. Newly suggested parameter r for RDE effect shows potential for quantitative comparisons between HTRT and MHRT, and optimizing therapeutic outcomes in MHRT for prostate cancer.

Comparison of biochemical changes induced in radioresistant prostate cancer cells by X-rays, radiosensitizing drugs, and a combined therapy using Raman microspectroscopy

Cancer radioresistance is a major problem in radiotherapy. Many strategies have been proposed to overcome this process including the use of radiosensitizing drugs such as C75 or silibinin. The overall result of all treatments (radiotherapy, chemotherapy, and combined treatment) is cancer cell death. On the other hand, each treatment affects cancer cells differently at the molecular level. However, little is known about biochemical changes induced in cancer cells by these treatments (especially in combined therapy) at the submicroscale. In this study, Raman microspectroscopy was applied to follow such changes induced in radioresistant prostate cancer cells by X-rays, radiosensitizing drugs (C75, silibinin), and a combined treatment. The analysis was supported by the Partial Least Squares Regression method to reveal spectral changes induced by an increasing dose of X-rays and concentrations of the drugs. The obtained regression coefficient (β) plots were compared to each other using a correlation coefficient (R). Our results show that PC-3 cells exhibit dose- and concentration-dependent responses to the treatment with different biochemical changes induced by X-rays in the presence of C75 and silibinin. Moreover, both drugs affect the cells differently at the submicroscale and independently from the X-ray's presence. Finally, C75 shows significant efficiency in the reduction of cell radioresistance.

Generality Assessment of a Model Considering Heterogeneous Cancer Cells for Predicting Tumor Control Probability for Stereotactic Body Radiation Therapy Against Non-Small Cell Lung Cancer

The generality of a model for predicting tumor control probability from in vitro clonogenic survival considering of cancer stem-like cells, the so-called integrated microdosimetric-kinetic model, is presented by comparing the model to public data on stereotactic body radiation therapy for non-small cell lung cancer cells.

The soluble guanylyl cyclase pathway is inhibited to evade androgen deprivation-induced senescence and enable progression to castration resistance

Castration-resistant prostate cancer (CRPC) is fatal and therapeutically under-served. We describe a novel CRPC-restraining role for the vasodilatory soluble guanylyl cyclase (sGC) pathway. We discovered that sGC subunits are dysregulated during CRPC progression and its catalytic product, cyclic GMP (cGMP), is lowered in CRPC patients. Abrogating sGC heterodimer formation in castration-sensitive prostate cancer (CSPC) cells inhibited androgen deprivation (AD)-induced senescence, and promoted castration-resistant tumor growth. We found sGC is oxidatively inactivated in CRPC. Paradoxically, AD restored sGC activity in CRPC cells through redox-protective responses evoked to protect against AD-induced oxidative stress. sGC stimulation via its FDA-approved agonist, riociguat, inhibited castration-resistant growth, and the anti-tumor response correlated with elevated cGMP, indicating on-target sGC activity. Consistent with known sGC function, riociguat improved tumor oxygenation, decreasing the PC stem cell marker, CD44, and enhancing radiation-induced tumor suppression. Our studies thus provide the first evidence for therapeutically targeting sGC via riociguat to treat CRPC.

Statement of significance

Prostate cancer is the second highest cancer-related cause of death for American men. Once patients progress to castration-resistant prostate cancer, the incurable and fatal stage, there are few viable treatment options available. Here we identify and characterize a new and clinically actionable target, the soluble guanylyl cyclase complex, in castration-resistant prostate cancer. Notably we find that repurposing the FDA-approved and safely tolerated sGC agonist, riociguat, decreases castration-resistant tumor growth and re-sensitizes these tumors to radiation therapy. Thus our study provides both new biology regarding the origins of castration resistance as well as a new and viable treatment option.

DNA‑PKcs phosphorylation specific inhibitor, NU7441, enhances the radiosensitivity of clinically relevant radioresistant oral squamous cell carcinoma cells

Radioresistant cancer cells lead to poor prognosis after radiotherapy. However, the mechanisms underlying cancer cell radioresistance have not been fully elucidated. Thus, the DNA damage response of clinically relevant radioresistant oral squamous cell carcinoma HSC2-R cells, established by long-term exposure of parental HSC2 cells to fractionated radiation, was investigated. The DNA double-strand break (DSB) repair protein-specific inhibitor, NU7441, which targets DNA-dependent protein kinase catalytic subunit (DNA-PKcs) phosphorylation, and IBR2, which targets Rad51, were administered to HSC2 and HSC2-R cells. NU7441 administration eliminated colony formation in both cell lines under 6 Gy X-ray irradiation, whereas IBR2 did not affect colony formation. NU7441 and IBR2 significantly enhanced 6 Gy X-ray irradiation-induced apoptosis in HSC2-R cells. In HSC2-R cells, cell cycle arrest released earlier than in HSC2 cells, and phosphorylated-H2A histone family member X (γH2AX) expression rapidly decreased. Following NU7441 administration, γH2AX expression and the cell percentages of the G2/M phase were not decreased at 48 h after treatment in HSC2-R cells. DNA-PKcs has been demonstrated to regulate non-homologous end-joining (NHEJ) and homologous recombination (HR) repair, and the later phase of DSB repair is dominated by HR. Therefore, the results of the present study indicated that the DSB repair mechanism in HSC2-R cells strongly depends on NHEJ and loss of HR repair function. The present study revealed a potential mechanism underlying the acquired radioresistance and therapeutic targets in radioresistant cancer cells.

Application of Gold Nanoparticles as Radiosensitizer for Metastatic Prostate Cancer Cell Lines

More than 50% of all prostate cancer (PCa) patients are treated by radiotherapy (RT). Radioresistance and cancer recurrence are two consequences of the therapy and are related to dose heterogeneity and non-selectivity between normal and tumoral cells. Gold nanoparticles (AuNPs) could be used as potential radiosensitizers to overcome these therapeutic limitations of RT. This study assessed the biological interaction of different morphologies of AuNPs with ionizing radiation (IR) in PCa cells. To achieve that aim, three different amine-pegylated AuNPs were synthesized with distinct sizes and shapes (spherical, AuNP_sp-PEG, star, AuNP_st-PEG, and rods, AuNP_r-PEG) and viability, injury and colony assays were used to analyze their biological effect on PCa cells (PC3, DU145, and LNCaP) when submitted to the accumulative fraction of RT. The combinatory effect of AuNPs with IR decreased cell viability and increased apoptosis compared to cells treated only with IR or untreated cells. Additionally, our results showed an increase in the sensitization enhancement ratio by cells treated with AuNPs and IR, and this effect is cell line dependent. Our findings support that the design of AuNPs modulated their cellular behavior and suggested that AuNPs could improve the RT efficacy in PCa cells.

Translational study for stereotactic body radiotherapy against non-small cell lung cancer, including oligometastases, considering cancer stem-like cells enable predicting clinical outcome from in vitro data

BACKGROUND

Curative effects of stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) have been evaluated using various biophysical models. Because such model parameters are empirically determined based on clinical experience, there is a large gap between in vitro and clinical studies. In this study, considering the heterogeneous cell population, we performed a translational study to realize the possible linkage based on a modeling approach.

METHODS

We modeled cell-killing and tumor control probability (TCP) considering two populations: progeny and cancer stem-like cells. The model parameters were determined from in vitro survival data of A549 and EBC-1 cells. Based on the cellular parameters, we predicted TCP and compared it with the corresponding clinical data from 553 patients collected at Hirosaki University Hospital.

RESULTS

Using an all-in-one developed model, the so-called integrated microdosimetric-kinetic (IMK) model, we successfully reproduced both in vitro survival after acute irradiation and the 3-year TCP with various fractionation schemes (6-10 Gy per fraction). From the conventional prediction without considering cancer stem cells (CSCs), this study revealed that radioresistant CSCs play a key role in the linkage between in vitro and clinical outcomes.

CONCLUSIONS

This modeling study provides a possible generalized biophysical model that enables precise estimation of SBRT worldwide.

Spatio-temporal modelling of phenotypic heterogeneity in tumour tissues and its impact on radiotherapy treatment

We present a mathematical model that describes how tumour heterogeneity evolves in a tissue slice that is oxygenated by a single blood vessel. Phenotype is identified with the stemness level of a cell and determines its proliferative capacity, apoptosis propensity and response to treatment. Our study is based on numerical bifurcation analysis and dynamical simulations of a system of coupled, non-local (in phenotypic "space") partial differential equations that link the phenotypic evolution of the tumour cells to local tissue oxygen levels. In our formulation, we consider a 1D geometry where oxygen is supplied by a blood vessel located on the domain boundary and consumed by the tumour cells as it diffuses through the tissue. For biologically relevant parameter values, the system exhibits multiple steady states; in particular, depending on the initial conditions, the tumour is either eliminated ("tumour-extinction") or it persists ("tumour-invasion"). We conclude by using the model to investigate tumour responses to radiotherapy, and focus on identifying radiotherapy strategies which can eliminate the tumour. Numerical simulations reveal how phenotypic heterogeneity evolves during treatment and highlight the critical role of tissue oxygen levels on the efficacy of radiation protocols that are commonly used in the clinic.

A feasibility study of the therapeutic application of a mixture of 67/64 Cu radioisotopes produced by cyclotrons with proton irradiation

PURPOSE

64 Cu and 67 Cu radioisotopes have nuclear characteristics suitable for nuclear medicine applications. The production of 64 Cu is already well established. However, the production of 67 Cu in quantities suitable to conduct clinical trials is more challenging as it leads to the coproduction of other Cu isotopes, in particular 64 Cu. The aim of this study is to investigate the possibility of using a CuCl2 solution with a mixture of 67/64 Cu radioisotopes for therapeutic purposes, providing an alternative solution for the cyclotron production problem.

METHODS

Copper radioisotopes activities were calculated by considering proton beam irradiation of the following targets: (i) 70 Zn in the energy range 70-45 MeV; (ii) 68 Zn in the energy range 70-35 MeV; (iii) a combination of 70 Zn (70-55 MeV) and 68 Zn (55-35 MeV). The contribution of each copper radioisotope to the human-absorbed dose was estimated with OLINDA/EXM software using the biokinetic model for CuCl2 published by ICRP 53. The total absorbed dose generated by the 67/64 CuCl2 mixture, obtained through different production routes, was calculated at different times after the end of the bombardment (EOB). A simple spherical model was used to simulate tumors of different sizes containing uniformly distributed 67/64 Cu mixture and to calculate the absorbed dose of self-irradiation. The biological damage produced by 67 Cu and 64 Cu was also evaluated through cellular dosimetry and cell surviving fraction assessment using the MIRDcell code, considering two prostate cancer cell lines with different radiosensitivity.

RESULTS

The absorbed dose to healthy organs and the effective dose (ED) per unit of administered activity of 67 CuCl2 are higher than those of 64 CuCl2 . Absorbed dose values per unit of administered activity of 67/64 CuCl2 mixture increase with time after the EOB because the amount of 67 Cu in the mixture increases. Survival data showed that the biological damage caused per each decay of 67 Cu is greater than that of 64 Cu, assuming that radionuclides remain accumulated in the cell cytoplasm. Sphere model calculations demonstrated that 64 Cu administered activity must be about five times higher than that of 67 Cu to obtain the same absorbed dose for tumor mass between 0.01 and 10 g and about 10 times higher for very small spheres. Consequently, the 64 CuCl2 -absorbed dose to healthy organs will reach higher values than those of 67 CuCl2 . The supplemental activity of the 67/64 CuCl2 mixture, required to get the same tumor-absorbed dose produced by 67 CuCl2 , triggers a dose increment (DI) in healthy organs. The waiting time post-EOB necessary to keep this DI below 10% (t10% ) depends on the irradiation methods employed for the production of the 67/64 CuCl2 mixture.

CONCLUSIONS

A mixture of cyclotron produced 67/64 Cu radioisotopes proved to be an alternative solution for the therapeutic use of CuCl2 with minimal DI to healthy organs compared with pure 67 Cu. Irradiation of a 70 Zn+68 Zn target in the 70-35 MeV proton energy range for 185 h appears to be the best option from among all the production routes investigated, as it gives the maximum amount of activity, the shortest t10% (10 h), and less than 1% of 61 Cu and 60 Cu impurities.

Dissecting Tumor Growth: The Role of Cancer Stem Cells in Drug Resistance and Recurrence

Simple Summary

Cancer is one of the most debated problems all over the world. Cancer stem cells are considered responsible of tumor initiation, metastasis, drug resistance, and recurrence. This subpopulation of cells has been found into the tumor bulk and showed the capacity to self-renew, differentiate, up to generate a new tumor. In the last decades, several studies have been set on the molecular mechanisms behind their specific characteristics as the Wnt/β-catenin signaling, Notch signaling, Hedgehog signaling, transcription factors, etc. The most powerful part of CSCs is represented by the niches as “promoter” of their self-renewal and “protector” from the common oncological treatment as chemotherapy and radiotherapy. In our review article we highlighted the primary mechanisms involved in CSC tumorigenesis for the setting of further targets to control the metastatic process.

Abstract

Emerging evidence suggests that a small subpopulation of cancer stem cells (CSCs) is responsible for initiation, progression, and metastasis cascade in tumors. CSCs share characteristics with normal stem cells, i.e., self-renewal and differentiation potential, suggesting that they can drive cancer progression. Consequently, targeting CSCs to prevent tumor growth or regrowth might offer a chance to lead the fight against cancer. CSCs create their niche, a specific area within tissue with a unique microenvironment that sustains their vital functions. Interactions between CSCs and their niches play a critical role in regulating CSCs’ self-renewal and tumorigenesis. Differences observed in the frequency of CSCs, due to the phenotypic plasticity of many cancer cells, remain a challenge in cancer therapeutics, since CSCs can modulate their transcriptional activities into a more stem-like state to protect themselves from destruction. This plasticity represents an essential step for future therapeutic approaches. Regarding self-renewal, CSCs are modulated by the same molecular pathways found in normal stem cells, such as Wnt/β-catenin signaling, Notch signaling, and Hedgehog signaling. Another key characteristic of CSCs is their resistance to standard chemotherapy and radiotherapy treatments, due to their capacity to rest in a quiescent state. This review will analyze the primary mechanisms involved in CSC tumorigenesis, with particular attention to the roles of CSCs in tumor progression in benign and malignant diseases; and will examine future perspectives on the identification of new markers to better control tumorigenesis, as well as dissecting the metastasis process.

Tumor radioresistance caused by radiation-induced changes of stem-like cell content and sub-lethal damage repair capability

Cancer stem-like cells (CSCs) within solid tumors exhibit radioresistance, leading to recurrence and distant metastasis after radiotherapy. To experimentally study the characteristics of CSCs, radioresistant cell lines were successfully established using fractionated X-ray irradiation. The fundamental characteristics of CSCs in vitro have been previously reported; however, the relationship between CSC and acquired radioresistance remains uncertain. To efficiently study this relationship, we performed both in vitro experiments and theoretical analysis using a cell-killing model. Four types of human oral squamous carcinoma cell lines, non-radioresistant cell lines (SAS and HSC2), and radioresistant cell lines (SAS-R and HSC2-R), were used to measure the surviving fraction after single-dose irradiation, split-dose irradiation, and multi-fractionated irradiation. The SAS-R and HSC2-R cell lines were more positive for one of the CSC marker aldehyde dehydrogenase activity than the corresponding non-radioresistant cell lines. The theoretical model analysis showed that changes in both the experimental-based ALDH (+) fractions and DNA repair efficiency of ALDH (-) fractions (i.e., sub-lethal damage repair) are required to reproduce the measured cell survival data of non-radioresistant and radioresistant cell lines. These results suggest that the enhanced cell recovery in SAS-R and HSC2-R is important when predicting tumor control probability in radiotherapy to require a long dose-delivery time; in other words, intensity-modulated radiation therapy is ideal. This work provides a precise understanding of the mechanism of radioresistance, which is induced after irradiation of cancer cells.

Prospective Monitoring of Circulating Epithelial Tumor Cells (CETC) Reveals Changes in Gene Expression during Adjuvant Radiotherapy of Breast Cancer Patients

Circulating epithelial tumor cells (CETC) are considered to be responsible for the formation of metastases. Therefore, their importance as prognostic and/or predictive markers in breast cancer is being intensively investigated. Here, the reliability of single cell expression analyses in isolated and collected CETC from whole blood samples of patients with early-stage breast cancer before and after radiotherapy (RT) using the maintrac^® method was investigated. Single-cell expression analyses were performed with qRT-PCR on a panel of selected genes: GAPDH, EpCAM, NANOG, Bcl-2, TLR 4, COX-2, PIK3CA, Her-2/neu, Vimentin, c-Met, Ki-67. In all patients, viable CETC were detected prior to and at the end of radiotherapy. In 7 of the 9 (77.8%) subjects examined, the CETC number at the end of the radiotherapy series was higher than before. The majority of genes analyzed showed increased expression after completion of radiotherapy compared to baseline. Procedures and methods used in this pilot study proved to be feasible. The method is suitable for further investigation of the underlying molecular biological mechanisms occurring in cells surviving radiotherapy and possibly the development of radiation resistance.

Epigenetic mechanisms underlying prostate cancer radioresistance

Radiotherapy (RT) is one of the mainstay treatments for prostate cancer (PCa), a highly prevalent neoplasm among males worldwide. About 30% of newly diagnosed PCa patients receive RT with a curative intent. However, biochemical relapse occurs in 20–40% of advanced PCa treated with RT either alone or in combination with adjuvant-hormonal therapy. Epigenetic alterations, frequently associated with molecular variations in PCa, contribute to the acquisition of a radioresistant phenotype. Increased DNA damage repair and cell cycle deregulation decreases radio-response in PCa patients. Moreover, the interplay between epigenome and cell growth pathways is extensively described in published literature. Importantly, as the clinical pattern of PCa ranges from an indolent tumor to an aggressive disease, discovering specific targetable epigenetic molecules able to overcome and predict PCa radioresistance is urgently needed. Currently, histone-deacetylase and DNA-methyltransferase inhibitors are the most studied classes of chromatin-modifying drugs (so-called ‘epidrugs’) within cancer radiosensitization context. Nonetheless, the lack of reliable validation trials is a foremost drawback. This review summarizes the major epigenetically induced changes in radioresistant-like PCa cells and describes recently reported targeted epigenetic therapies in pre-clinical and clinical settings.

Phenotypic variation modulates the growth dynamics and response to radiotherapy of solid tumours under normoxia and hypoxia

In cancer, treatment failure and disease recurrence have been associated with small subpopulations of cancer cells with a stem-like phenotype. In this paper, we develop and investigate a phenotype-structured model of solid tumour growth in which cells are structured by a stemness level, which varies continuously between stem-like and terminally differentiated behaviours. Cell evolution is driven by proliferation and death, as well as advection and diffusion with respect to the stemness structure variable. Here, the magnitude and sign of the advective flux are allowed to vary with the oxygen level. We use the model to investigate how the environment, in particular oxygen levels, affects the tumour's population dynamics and composition, and its response to radiotherapy. We use a combination of numerical and analytical techniques to quantify how under physiological oxygen levels the cells evolve to a differentiated phenotype and under low oxygen level (i.e., hypoxia) they de-differentiate. Under normoxia, the proportion of cancer stem cells is typically negligible and the tumour may ultimately become extinct whereas under hypoxia cancer stem cells comprise a dominant proportion of the tumour volume, enhancing radio-resistance and favouring the tumour's long-term survival. We then investigate how such phenotypic heterogeneity impacts the tumour's response to treatment with radiotherapy under normoxia and hypoxia. Of particular interest is establishing how the presence of radio-resistant cancer stem cells can facilitate a tumour's regrowth following radiotherapy. We also use the model to show how radiation-induced changes in tumour oxygen levels can give rise to complex re-growth dynamics. For example, transient periods of hypoxia induced by damage to tumour blood vessels may rescue the cancer cell population from extinction and drive secondary regrowth.

4-Methylumbelliferone administration enhances radiosensitivity of human fibrosarcoma by intercellular communication

Hyaluronan synthesis inhibitor 4-methylumbelliferone (4-MU) is a candidate of radiosensitizers which enables both anti-tumour and anti-metastasis effects in X-ray therapy. The curative effects under such 4-MU administration have been investigated in vitro; however, the radiosensitizing mechanisms remain unclear. Here, we investigated the radiosensitizing effects under 4-MU treatment from cell experiments and model estimations. We generated experimental surviving fractions of human fibrosarcoma cells (HT1080) after 4-MU treatment combined with X-ray irradiation. Meanwhilst, we also modelled the pharmacological effects of 4-MU treatment and theoretically analyzed the synergetic effects between 4-MU treatment and X-ray irradiation. The results show that the enhancement of cell killing by 4-MU treatment is the greatest in the intermediate dose range of around 4 Gy, which can be reproduced by considering intercellular communication (so called non-targeted effects) through the model analysis. As supposed to be the involvement of intercellular communication in radiosensitization, the oxidative stress level associated with reactive oxygen species (ROS), which leads to DNA damage induction, is significantly higher by the combination of 4-MU treatment and irradiation than only by X-ray irradiation, and the radiosensitization by 4-MU can be suppressed by the ROS inhibitors. These findings suggest that the synergetic effects between 4-MU treatment and irradiation are predominantly attributed to intercellular communication and provide more efficient tumour control than conventional X-ray therapy.

Targeting Radiation-Resistant Prostate Cancer Stem Cells by B7-H3 CAR T Cells

Radiotherapy (RT) is a key treatment for prostate cancer. However, RT resistance can contribute to treatment failure. Prostate cancer stem cells (PCSCs) are radioresistant. We recently found that fractionated irradiation (FIR) upregulates expression of the immune checkpoint B7-H3 (CD276) on PCSCs and bulk cells in each prostate cancer cell line tested. These findings prompted us to investigate whether B7-H3 targeting chimeric antigen receptor (CAR) T cells, which may abrogate function of an immune checkpoint and mediate lysis of targeted cells, can target RT-resistant PCSCs in vitro and in vivo. B7-H3 expression is naturally higher on PCSCs than bulk prostate cancer cells and cytotoxicity of B7-H3 CAR T cells to PCSCs is more potent than to bulk prostate cancer cells. Furthermore, FIR significantly upregulates B7-H3 expression on PCSCs and bulk prostate cancer cells. The duration of FIR or single-dose irradiation-induced further upregulation of B7-H3 on bulk prostate cancer cells and PCSCs lasts for up to 3 days. B7-H3 CAR T-cell cytotoxicity against FIR-resistant PCSCs at a low effector to target ratio of 1:1 was assessed by flow cytometry and sphere formation assays. Further upregulation of B7-H3 expression by FIR made PCSCs even more sensitive to B7-H3 CAR T-cell-mediated killing. Consequently, the FIR and B7-H3 CAR T-cell therapy combination is much more effective than FIR or CAR T cells alone in growth inhibition of hormone-insensitive prostate cancer xenografts in immunodeficient mice. Our work provides a sound basis for further development of this unique combinatorial model of RT and B7-H3 CAR T-cell therapy for prostate cancer. SIGNIFICANCE: We demonstrate that FIR significantly upregulates B7-H3 expression by RT-resistant PCSCs and bulk cells; cytotoxicity of B7-H3 CAR T cells to FIR-treated PCSCs is potent and results in significantly improved antitumor efficacy in mice.

Influence of adjuvant radiotherapy on circulating epithelial tumor cells and circulating cancer stem cells in primary non-metastatic breast cancer

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CETCs have the same molecular properties as the cells in the primary tumor.

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Circulating cancer stem cells can be successfully identified in the blood of breast cancer patients and monitored during RT.

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Patients after neoadjuvant chemotherapy had the highest number of CETCs prior to RT but the CETC counts decreased significantly during RT indicating that this group of patients could most likely benefit from adjuvant RT.

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Increase in cCSC numbers during RT could be a predictor for early recurrence of cancer disease.

Background

: There is an unmet need to identify biomarkers that directly reflect response to adjuvant radiotherapy (RT). Circulating epithelial tumor cells (CETCs) represent the liquid component of solid tumors and are responsible for metastatic relapse. CETC subsets with cancer stem cell characteristics, circulating cancer stem cells (cCSCs), play a pivotal role in the metastatic cascade. Monitoring the most aggressive subpopulation of CETCs could reflect the aggressiveness of the remaining tumor burden. There is limited data on the detection and monitoring changes in CETC and cCSC numbers during RT in early breast cancer.

Methods

: CETC numbers were analyzed prior to, at midterm and at the end of RT in 52 primary non-metastatic breast cancer patients. Hormone receptor status was determined in CETCs prior to and at the end of RT. For the identification of cCSCs cell suspensions from the peripheral blood of patients were cultured in vitro under conditions favoring growth of tumorspheres.

Results

: Hormone receptor status in CETCs before RT was comparable to that in primary tumor tissue. Prior to RT numbers of CETCs correlated with aggressiveness of primary tumors. cCSCs could be successfully identified and monitored during RT. Prior to RT patients treated with neoadjuvant chemotherapy had significantly higher numbers of CETCs and tumorspheres compared to patients after adjuvant chemotherapy. During RT, the number of CETCs decreased continuously in patients after neoadjuvant chemotherapy but not after adjuvant chemotherapy.

Conclusion

: Monitoring the number of CETCs and the CETC subset with cancer stem cell properties during RT may provide additional clinically useful prognostic information.

Physicochemical damage and early-stage biological response to X-ray radiation studied in prostate cancer cells by Raman spectroscopy

Exposure to ionizing radiation significantly affects biochemistry of cancer cells. The effect of irradiation can be divided into two stages, that is, the physicochemical stage and the biological response. Both effects induce different biochemical changes in the cells and should be analyzed as two separate phenomena. Thus, in the current study, Raman spectroscopy of prostate cancer cells fixed before (the physicochemical damage model) and just after (the biological response model) irradiation was undertaken to compare biochemical composition of irradiated cancer cells at both stages. Spectroscopic analysis of the cells was performed separately for cytoplasmic and nuclear regions. Biochemical changes of irradiated cells were analyzed using partial least squares regression (PLSR) method on the basis of the collected Raman spectra. Regression coefficients were therefore used to describe differences and similarities between biochemical composition of cancer cells undergoing the physicochemical stage and biological response. Additionally, PLSR models of both phenomena were compared for linear dose-dependence and a cross prediction.

Low Dose Combined Treatment with Ultraviolet-C and Withaferin a Enhances Selective Killing of Oral Cancer Cells

Withaferin A (WFA), a Withania somnifera-derived triterpenoid, is an anticancer natural product. The anticancer effect of nonionizing radiation such as ultraviolet-C (UVC) as well as the combined treatment of UVC and WFA is rarely investigated. Low dose UVC and/or WFA treatments (12 J/m² and/or 1 μM) were chosen to evaluate antioral cancer cell line effects by examining cytotoxicity, cell cycle disruption, apoptosis induction, and DNA damage. For two cancer cell lines (Ca9-22 and HSC-3), single treatment (UVC or WFA) showed about 80% viability, while a combined treatment of UVC/WFA showed about 40% viability. In contrast, there was noncytotoxicity to normal oral cell lines (HGF-1). Compared to single treatment and control, low dose UVC/WFA shows high inductions of apoptosis in terms of flow cytometric detections for subG1, annexin V, pancaspase changes as well as Western blotting for detecting cleaved poly (ADP-ribose) polymerase (c-PARP) and caspase 3 (c-Cas 3) and luciferase assay for detecting Cas 3/7 activity. Low dose UVC/WFA also showed high inductions of oxidative stress and DNA damage in terms of flow cytometric detections of reactive oxygen species (ROS), mitochondrial superoxide (MitoSOX) generation, and membrane potential (MitoMP) destruction, γH2AX and 8-oxo-2’deoxyguanosine (8-oxodG) types of DNA damages. For comparison, low dose UVC/WFA show rare inductions of annexin V, Cas 3/7 activity, ROS, MitoSOX, and MitoMP changes to normal oral HGF-1 cells. Therefore, low dose UVC/WFA provides a novel selectively killing mechanism to oral cancer cells, suggesting that WFA is a UVC sensitizer to inhibit the proliferation of oral cancer cells.

CSC Radioresistance: A Therapeutic Challenge to Improve Radiotherapy Effectiveness in Cancer

Radiotherapy (RT) is a modality of oncologic treatment that can be used to treat approximately 50% of all cancer patients either alone or in combination with other treatment modalities such as surgery, chemotherapy, immunotherapy, and therapeutic targeting. Despite the technological advances in RT, which allow a more precise delivery of radiation while progressively minimizing the impact on normal tissues, issues like radioresistance and tumor recurrence remain important challenges. Tumor heterogeneity is responsible for the variation in the radiation response of the different tumor subpopulations. A main factor related to radioresistance is the presence of cancer stem cells (CSC) inside tumors, which are responsible for metastases, relapses, RT failure, and a poor prognosis in cancer patients. The plasticity of CSCs, a process highly dependent on the epithelial–mesenchymal transition (EMT) and associated to cell dedifferentiation, complicates the identification and eradication of CSCs and it might be involved in disease relapse and progression after irradiation. The tumor microenvironment and the interactions of CSCs with their niches also play an important role in the response to RT. This review provides a deep insight into the characteristics and radioresistance mechanisms of CSCs and into the role of CSCs and tumor microenvironment in both the primary tumor and metastasis in response to radiation, and the radiobiological principles related to the CSC response to RT. Finally, we summarize the major advances and clinical trials on the development of CSC-based therapies combined with RT to overcome radioresistance. A better understanding of the potential therapeutic targets for CSC radiosensitization will provide safer and more efficient combination strategies, which in turn will improve the live expectancy and curability of cancer patients.

Conventional Treatment of Glioblastoma Reveals Persistent CD44+ Subpopulations

Glioblastoma (GBM) is the most frequent and devastating primary tumor of the central nervous system with a median survival of 12 to 15 months after diagnosis. GBM is highly difficult to treat due to its delicate location, inter- and intra-tumoral heterogeneity, and high plasticity in response to treatment. In this study, we intracranially implanted primary GBM cells into mice which underwent conventional GBM treatments, including irradiation, temozolomide, and a combination. We obtained single cell suspensions through a combination of mechanical and enzymatic dissociation of brain tissue and investigated in detail the changes in GBM cells in response to conventional treatments in vivo using multi-color flow cytometry and cluster analysis. CD44 expression was elevated in all treatment groups, which was confirmed by subsequent immunohistochemistry. High CD44 expression was furthermore shown to correlate with poor prognosis of GBM and low-grade glioma (LGG) patients. Together, these results indicate a key role for CD44 in glioma pathogenesis.

A Model for Estimating Dose-Rate Effects on Cell-Killing of Human Melanoma after Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a type of radiation therapy for eradicating tumor cells through a ¹⁰B(n,α)⁷Li reaction in the presence of ¹⁰B in cancer cells. When delivering a high absorbed dose to cancer cells using BNCT, both the timeline of ¹⁰B concentrations and the relative long dose-delivery time compared to photon therapy must be considered. Changes in radiosensitivity during such a long dose-delivery time can reduce the probability of tumor control; however, such changes have not yet been evaluated. Here, we propose an improved integrated microdosimetric-kinetic model that accounts for changes in microdosimetric quantities and dose rates depending on the ¹⁰B concentration and investigate the cell recovery (dose-rate effects) of melanoma during BNCT irradiation. The integrated microdosimetric–kinetic model used in this study considers both sub-lethal damage repair and changes in microdosimetric quantities during irradiation. The model, coupled with the Monte Carlo track structure simulation code of the Particle and Heavy Ion Transport code System, shows good agreement with in vitro experimental data for acute exposure to ⁶⁰Co γ-rays, thermal neutrons, and BNCT with ¹⁰B concentrations of 10 ppm. This indicates that microdosimetric quantities are important parameters for predicting dose-response curves for cell survival under BNCT irradiations. Furthermore, the model estimation at the endpoint of the mean activation dose exhibits a reduced impact of cell recovery during BNCT irradiations with high linear energy transfer (LET) compared to ⁶⁰Co γ-rays irradiation with low LET. Throughout this study, we discuss the advantages of BNCT for enhancing the killing of cancer cells with a reduced dose-rate dependency. If the neutron spectrum and the timelines for drug and dose delivery are provided, the present model will make it possible to predict radiosensitivity for more realistic dose-delivery schemes in BNCT irradiations.

A theoretical cell-killing model to evaluate oxygen enhancement ratios at DNA damage and cell survival endpoints in radiation therapy

Radio-resistance induced under low oxygen pressure plays an important role in malignant progression in fractionated radiotherapy. For the general approach to predict cell killing under hypoxia, cell-killing models (e.g. the Linear-Quadratic model) have to be fitted to in vitro experimental survival data for both normoxia and hypoxia to obtain the oxygen enhancement ratio (OER). In such a case, model parameters for every oxygen condition needs to be considered by model-fitting approaches. This is inefficient for fractionated irradiation planning. Here, we present an efficient model for fractionated radiotherapy the integrated microdosimetric-kinetic model including cell-cycle distribution and the OER at DNA double-strand break endpoint (OER_DSB). The cell survival curves described by this model can reproduce the in vitro experimental survival data for both acute and chronic low oxygen concentrations. The OER_DSB used for calculating cell survival agrees well with experimental DSB ratio of normoxia to hypoxia. The important parameters of the model are oxygen pressure and cell-cycle distribution, which enables us to predict cell survival probabilities under chronic hypoxia and chronic anoxia. This work provides biological effective dose (BED) under various oxygen conditions including its uncertainty, which can contribute to creating fractionated regimens for multi-fractionated radiotherapy. If the oxygen concentration in a tumor can be quantified by medical imaging, the present model will make it possible to estimate the cell-killing and BED under hypoxia in more realistic intravital situations.

Platelet-Derived Growth Factor Receptor and Ionizing Radiation in High Grade Glioma Cell Lines

Treatment of high grade gliomas (HGGs) has remained elusive due to their high heterogeneity and aggressiveness. Surgery followed by radiotherapy represents the mainstay of treatment for HGG. However, the unfavorable location of the tumor that usually limits total resection and the resistance to radiation therapy are the major therapeutic problems. Chemotherapy with DNA alkylating agent temozolomide is also used to treat HGG, despite modest effects on survival. Disregulation of several growth factor receptors (GFRs) were detected in HGG and receptor amplification in glioblastoma has been suggested to be responsible for heterogeneity propagation through clonal evolution. Molecularly targeted agents inhibiting these membrane proteins have demonstrated significant cytotoxicity in several types of cancer cells when tested in preclinical models. Platelet-derived growth factor receptors (PDGFRs) and associated signaling were found to be implicated in gliomagenesis, moreover, HGG commonly display a Platelet-derived growth factor (PDGF) autocrine pathway that is not present in normal brain tissues. We have previously shown that both the susceptibility towards PDGFR and the impact of the PDGFR inactivation on the radiation response were different in different HGG cell lines. Therefore, we decided to extend our investigation, using two other HGG cell lines that express PDGFR at the cell surface. Here, we investigated the effect of PDGFR inhibition alone or in combination with gamma radiation in 11 and 15 HGG cell lines. Our results showed that while targeting the PDGFR represents a good means of treatment in HGG, the combination of receptor inhibition with gamma radiation did not result in any discernable difference compared to the single treatment. The PI3K/PTEN/Akt/mTOR and Ras/Raf/MEK/ERK pathways are the major signaling pathways emerging from the GFRs, including PDGFR. Decreased sensitivity to radiation-induced cell death are often associated with redundancy in these pro-survival signaling pathways. Here we found that Phosphoinositide 3-kinases (PI3K), Extracellular-signal-regulated kinase 1/2 (ERK1/2), or c-Jun N-terminal kinase 1/2 (JNK1/2) inactivation induced radiosensitivity in HGG cells.