Tumor Cell Repopulation Research Articles

Abstract PO1-24-06: Prolactin Hormone-Induced Mammary Differentiation and Anti-tumorigenic Role in Breast Cancer

Abstract The premise of differentiation therapy in cancer is a strategy that aims at engaging-forward differentiation and cellular reprograming restricting the proliferative, tumor repopulation, stemness, EMT and metastatic capacities of tumor cells leading to the cessation of the aggressive tumor phenotype and offering the cancer patients improved survival for decades. Therefore, deciphering molecular mechanisms deriving differentiation in normal mammary and breast cancer cells may allow the discovery of innovative differentiation-based biomarkers and therapeutics in breast cancer. Lactation is an intricate process that results in the ability of the breast cells to produce a complex nutritious biological fluid to nurse the new-born. While the beneficial effects of breastfeeding to the infant is irrefutable, its effects on maternal health are less investigated especially in relation to breast cancer that still affects 1 in 8 women in high income countries and 1 in 20 globally. Importantly, epidemiological studies have linked breastfeeding to reduced risk of breast cancer by promoting terminal differentiation of the breast epithelial cells. While breastfeeding process is regulated by multiple hormones, growth factors, and transcriptional regulators, the lactation hormone prolactin (PRL) is known to be directly implicated in the hormonal control of breastfeeding. Extensive research including our own work has shown that PRL/PRL receptor (PRLR) pathway derives mammary gland development and importantly mammary epithelial cell terminal differentiation allowing successful lactation. In contrast the role of PRL in breast cancer is still to be fully defined. Importantly, we have accumulated compelling evidence using in-silico publicly available patient data sets and molecular data implicating this pathway as a clinically relevant pro-differentiation pathway driving differentiation and cellular reprograming suppressing stemness, EMT, metastasis and tumorigenesis in breast cancer. To better characterize PRL signaling mediating its pro-differentiation effects, we used large-scale unbiased proteomics analysis of PRLR/interacting proteins in breast cancer cells. Our analyses revealed several novel PRLR-interactors. We have further confirmed these interactions through co-immunoprecipitations/western blotting analyses in breast cancer cells representative the different breast cancer subtypes. We also examined their functional contributions to mammary differentiation and tumorigenesis using in vitro and in vivo assays. Moreover, we defined their potential clinical relevance using bioinformatics in silico databases of breast cancer. Together our study delineates novel PRL/PRLR-downstream signaling mediators important for mammary differentiation and tumorigenesis and may thus be useful as biomarkers and/or therapeutic targets in breast cancer. Citation Format: Dana Hamam, Suhad Ali. Prolactin Hormone-Induced Mammary Differentiation and Anti-tumorigenic Role in Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-24-06.

Mathematical modelling for spatial optimization of irradiation during proton radiotherapy with nanosensitizers

Abstract A spatially distributed mathematical model is presented that simulates the growth of a non-invasive tumour undergoing treatment by fractionated proton therapy with the use of non-radioactive tumour-specific nanosensitizers. Nanosensitizers are injected intravenously before each irradiation to increase the locally deposited dose via a chain of reactions with therapeutic protons. Modelling simulations show that the use of nanosensitizers allows increasing treatment efficacy. However, their effect is restricted by the necessity of decreasing the energy deposited in tumour in order to comply to the normal damage restrictions. Normalization of tumour microvasculature that accompanies the treatment, also compromises nanosensitizers effect as it impairs their inflow in tumour. It is shown that spatial optimization of irradiation, with conservation of total dose deposited in tumour, can increase tumour cell damage for each single irradiation. However, eventually it may not lead to the overall increase of treatment efficacy, in terms of minimization of the number of remaining viable tumour cells, due to the influence of tumour cell repopulation between irradiations. It is suggested that an efficient way towards minimization of tumour cell repopulation may be the faster suppression of angiogenesis by eradication of metabolically deprived tumour cells. This method can be efficient even despite the fact that it would also cause the decrease of supply of nanosensitizers into the tumour.

Autocrine regulation of tumor cell repopulation by Hsp70-HMGB1 alarmin complex

BackgroundCancer recurrence is regulated by a variety of factors, among which is the material of dying tumor cells; it is suggested that remaining after anti-cancer therapy tumor cells receive a signal from proteins called damage-associated molecular patterns (DAMPs), one of which is heat shock protein 70 (Hsp70).MethodsTwo models of tumor repopulation were employed, based on minimal population of cancer cells and application of conditioned medium (CM). To deplete the CMs of Hsp70 affinity chromatography on ATP-agarose and immunoprecipitation were used. Cell proliferation and the dynamics of cell growth were measured using MTT assay and xCELLigence technology; cell growth markers were estimated using qPCR and with the aid of ELISA for prostaglandin E detection. Immunoprecipitation followed by mass-spectrometry was employed to identify Hsp70-binding proteins and protein-protein interaction assays were developed to reveal the above protein complexes.ResultsIt was found that CM of dying tumor cells contains tumor regrowth-initiating factors and the removal of one of them, Hsp70, caused a reduction in the relapse-activating capacity. The pull out of Hsp70 alone using ATP-agarose had no effect on repopulation, while the immunodepletion of Hsp70 dramatically reduced its repopulation activity. Using proteomic and immunochemical approaches, we showed that Hsp70 in conditioned medium binds and binds another abundant alarmin, the High Mobility Group B1 (HMGB1) protein; the complex is formed in tumor cells treated with anti-cancer drugs, persists in the cytosol and is further released from dying tumor cells. Recurrence-activating power of Hsp70-HMGB1 complex was proved by the enhanced expression of proliferation markers, Ki67, Aurka and MCM-10 as well as by increase of prostaglandin E production and autophagy activation. Accordingly, dissociating the complex with Hsp70 chaperone inhibitors significantly inhibited the pro-growth effects of the above complex, in both in vitro and in vivo tumor relapse models.ConclusionsThese data led us to suggest that the abundance of the Hsp70-HMGB1 complex in the extracellular matrix may serve as a novel marker of relapse state in cancer patients, while specific targeting of the complex may be promising in the treatment of cancers with a high risk of recurrence.

TP53 and the Ultimate Biological Optimization Steps of Curative Radiation Oncology.

The new biological interaction cross-section-based repairable-homologically repairable (RHR) damage formulation for radiation-induced cellular inactivation, repair, misrepair, and apoptosis was applied to optimize radiation therapy. This new formulation implies renewed thinking about biologically optimized radiation therapy, suggesting that most TP53 intact normal tissues are low-dose hypersensitive (LDHS) and low-dose apoptotic (LDA). This generates a fractionation window in LDHS normal tissues, indicating that the maximum dose to organs at risk should be ≤2.3 Gy/Fr, preferably of low LET. This calls for biologically optimized treatments using a few high tumor dose-intensity-modulated light ion beams, thereby avoiding secondary cancer risks and generating a real tumor cure without a caspase-3-induced accelerated tumor cell repopulation. Light ions with the lowest possible LET in normal tissues and high LET only in the tumor imply the use of the lightest ions, from lithium to boron. The high microscopic heterogeneity in the tumor will cause local microscopic cold spots; thus, in the last week of curative ion therapy, when there are few remaining viable tumor clonogens randomly spread in the target volume, the patient should preferably receive the last 10 GyE via low LET, ensuring perfect tumor coverage, a high cure probability, and a reduced risk for adverse normal tissue reactions. Interestingly, such an approach would also ensure a steeper rise in tumor cure probability and a higher complication-free cure, as the few remaining clonogens are often fairly well oxygenated, eliminating a shallower tumor response due to inherent ion beam heterogeneity. With the improved fractionation proposal, these approaches may improve the complication-free cure probability by about 10-25% or even more.

Caspase-3 in glioma indicates an unfavorable prognosis by involving surrounding angiogenesis and tumor cell repopulation.

Effective biomarkers for estimating glioma prognosis are deficient. Canonically, caspase-3 acts as an "apoptosis executioner". However, its prognostic role in glioma and mechanistic effects on prognosis remain unclear. With glioma tissue microarrays, the prognostic roles of cleaved caspase-3 and its association with angiogenesis were explored. Next, by analyzing the mRNA microarray data from the CGGA, the prognostic role of CASP3 expression and correlations between CASP3 and markers of glioma angiogenesis and proliferation were investigated. To biologically interpret the prognostic role of caspase-3 in glioma, the influence of caspase-3 on surrounding angiogenesis and glioma cell repopulation was investigated with an in vitro cell co-culture model, which comprises irradiated U87 cells and un-irradiated firefly luciferase (Fluc)-labeled HUVEC (HUVEC-Fluc) or U87 (U87-Fluc) cells. The over-expressed dominant-negative caspase-3 was used to suppress normal caspase-3 activity. High levels of cleaved caspase-3 expression were associated with poor survival outcomes in glioma patients. Higher microvessel density was observed in patients with high levels of cleaved caspase-3 expression. By mining the microarray data in CGGA, it was revealed that higher CASP3 expression was found in glioma patients with lower Karnofsky Performance score, higher WHO grade, malignant histological subtype, wild-type IDH. Higher CASP3 expression indicated a worse survival rate in glioma patients. Patients with high CASP3 expression and negative IDH mutation showed the worst survival rate. Positive correlations were found between CASP3 and markers of tumor angiogenesis and proliferation. Subsequent data based on an in vitro cell co-culture model revealed that caspase-3 in irradiated glioma cells mediated pro-angiogenic and repopulation-promoting effects via regulating COX-2 signaling. With glioma tissue microarrays, high levels of COX-2 expression showed inferior survival outcomes in glioma patients. Glioma patients with high levels of cleaved caspase-3 and COX-2 expression showed the worst survival outcomes. This study innovatively identified an unfavorable prognostic role of caspase-3 in glioma. The pro-angiogenic and repopulation-prompting effects of caspase-3/COX-2 signaling may explain its unfavorable prognostic role and offer novel insights into therapy sensitization and curative effect prediction of glioma.

Cancer Cells Enter an Adaptive Persistence to Survive Radiotherapy and Repopulate Tumor.

Repopulation of residual tumor cells impedes curative radiotherapy, yet the mechanism is not fully understood. It is recently appreciated that cancer cells adopt a transient persistence to survive the stress of chemo- or targeted therapy and facilitate eventual relapse. Here, it is shown that cancer cells likewise enter a "radiation-tolerant persister" (RTP) state to evade radiation pressure in vitro and in vivo. RTP cells are characterized by enlarged cell size with complex karyotype, activated type I interferon pathway and two gene patterns represented by CST3 and SNCG. RTP cells have the potential to regenerate progenies via viral budding-like division, and type I interferon-mediated antiviral signaling impaired progeny production. Depleting CST3 or SNCG does not attenuate the formation of RTP cells, but can suppress RTP cells budding with impaired tumor repopulation. Interestingly, progeny cells produced by RTP cells actively lose their aberrant chromosomal fragments and gradually recover back to a chromosomal constitution similar to their unirradiated parental cells. Collectively, this study reveals a novel mechanism of tumor repopulation, i.e., cancer cell populations employ a reversible radiation-persistence by poly- and de-polyploidization to survive radiotherapy and repopulate the tumor, providing a new therapeutic concept to improve outcome of patients receiving radiotherapy.

Optimization of antitumor radiotherapy fractionation via mathematical modeling with account of 4 R’s of radiobiology

A spatially-distributed continuous mathematical model of solid tumor growth and treatment by fractionated radiotherapy is presented. The model explicitly accounts for the factors, widely referred to as 4 R’s of radiobiology, which influence the efficacy of radiotherapy fractionation protocols: tumor cell repopulation, their redistribution in cell cycle, reoxygenation and repair of sublethal damage of both tumor and normal tissues. With the use of special algorithm the fractionation protocols that provide increased tumor control probability, compared to standard clinical protocol, are found for various physiologically-based values of model parameters under the constraints of fixed overall normal tissue damage and maximum admissible fractional dose. In particular, it is shown that significant gain in treatment efficacy can be achieved for tumors of low malignancy by the use of protracted hyperfractionated protocols. The optimized non-uniform protocols are characterized by gradual escalation of fractional doses in their last parts, which start after the levels of oxygen and nutrients significantly elevate throughout the tumor and accelerated tumor proliferation manifests itself, which is a well-known experimental phenomenon.

The Dependence of Compensation Dose on Systematic and Random Interruption Treatment Time in Radiation Therapy

Introduction: In this work, we develop a multi-scale model to calculate corrections to the prescription dose to predict compensation required for the DNA repair mechanism and the repopulation of the cancer cells due to the occurrence of patient scheduling variabilities and the treatment time-gap in fractionation scheme. Methods: A system of multi-scale, time-dependent birth-death Master equations is used to describe stochastic evolution of double-strand breaks (DSBs) formed on DNAs and post-irradiation intra and inter chromosomes end-joining processes in cells, including repair and mis-repair mechanisms in microscopic scale, with an extension appropriate for calculation of tumor control probability (TCP) in macroscopic scale. Variabilities in fractionation time due to systematic shifts in patient’s scheduling and randomness in inter-fractionation treatment time are modeled. For an illustration of the methodology, we focus on prostate cancer. Results: We derive analytical corrections to linear-quadratic radiobiological indices α and β as a function of variabilities in treatment time and shifts in patient’s scheduling. We illustrate the dependence of the absolute value of the compensated dose on radio-biological sensitivity, α/β, DNA repair half-time, T1/2, tumor cells repopulation rate, and the time-gaps among treatment fractions due to inter-patient variabilities. At a given tumor size, delays between fractions totaling 24 h over the entire course of treatment, in a typical prostate cancer fractionation scheme, e.g., 81 Gy, 1.8 Gy per fraction and 45 treatment days, require up to 10% compensation dose if the sublethal DNA repair half-time, T1/2, spans over 10 h. We show that the contribution of the fast DNA repair mechanisms to the total dose is negligible. Instead, any compensation to the total dose stems from the tumor cell repopulation that may go up to a significant fraction of the original dose for a time gap of up to one week. Conclusions: We recommend implementation of time irregularities in treatment scheduling in the clinic settings to be taken into account. To achieve a clinical endpoint, corrections to the prescription dose must be assessed, in particular, if modern external beam therapy techniques such as IMRT/VMAT are used for the treatment of cancer.

Compensation for radiotherapy treatment interruptions due to a cyberattack: An isoeffective DVH‐based dose compensation decision tool

Unscheduled interruptions to radiotherapy treatments lead to decreased tumor control probability (TCP). Rapid cell repopulation in the tumor increases due to the absence of radiation dose, resulting in the loss of TCP. Compensation for this loss is required to prevent or reduce an extension of the patient's overall treatment time and regain the original TCP. The cyberattack on the Irish public health service in May 2021 prevented radiotherapy treatment delivery resulting in treatment interruptions of up to 12 days. Current standards for treatment gap calculations are performed using the Royal College of Radiologists (RCR) methodology, using a point‐dose for planning target volume (PTV) and the organs at risk (OAR).An in‐house tool, named EQD2VH, was created in Python to perform treatment gap calculations using the dose–volume histogram (DVH) information in DICOM data extracted from commercial treatment planning system plans. The physical dose in each dose bin was converted into equivalent dose in 2‐Gy fractions (EQD2), accounting for tumor cell repopulation. This EQD2‐based DVH provides a 2D representation of the impact of treatment gap compensation strategies on both PTV and OAR dose distributions compared to the intended prescribed treatment plan. This additional information can aid clinicians’ choice of compensation options. EQD2VH was evaluated using five high‐priority patients experiencing a treatment interruption when the cyberattack occurred. Compensation plans were created using the RCR methodology to evaluate EQD2VH as a decision‐making tool.The EQD2VH method demonstrated that the comparison of compensated treatment plans alongside the original intended treatment plans using isoeffective DVH analysis can be achieved. It enabled a visual and quantitative comparison between treatment plan options and provided an individual analysis of each structure in a patient's plan. It demonstrated potential to be a useful decision‐making tool for finding a balance between optimizing dose to PTV while protecting OARs.

Radiotherapy treatment interruptions during the Covid-19 pandemic: The UK experience and implications for radiobiology training

Unintended treatment interruptions during a course of radiotherapy can lead to extended overall treatment times which allow increased tumour cell repopulation to occur. Extra dose may therefore be required to offset any loss of tumour control. However, the manner in which the extra dose is delivered requires careful consideration in order to avoid the risk of increased normal tissue toxicity. Radiobiological modelling techniques can allow quantitative examination of such problems and may be used to derive revised pattens of radiation delivery which can help restore a degree of tumour control whilst limiting the likelihood of excess normal tissue morbidity. Unintended treatment interruptions can occur in any radiotherapy department but the rapid spread of the Covid-19 pandemic caused a major increase in the frequency of such interruptions due to staff and patient illness and the consequent self-isolation requirements. This article summarises the radiobiological considerations and caveats involved in assessing treatment interruptions and outlines the UK experience of dealing with the new challenges posed by Covid-19. The world-wide need for more education programmes in cancer radiobiology is highlighted.

Could Concurrent Capecitabine with Hypofractionated Radiotherapy in Elderly Patients with Muscle-Invasive Bladder Cancer be an Option?

Background:Repopulation of tumor cells during radiotherapy of transitional cell bladder carcinoma is believed to be a significant cause for treatment failure, and it was reported from clinical observations that the local control rate decreased with a prolonged treatment time, so accelerated hypofractionated radiotherapy with concurrent capecitabine may provide good local control in elderly patients unfit for surgery. The study aimed to evaluate the tolerability and efficacy of hypofractionated radiotherapy with capecitabine in elderly patients with urothelial carcinoma. Methods: Between October 2019 and September 2021, 30 patients with muscle-invasive bladder cancer staged T2-4aN0M0, underwent transurethral resection of bladder tumor followed by capecitabine (825 mg/m2 orally, 2 times a day) and radiation therapy (55 Gy in 2.2 Gy per fraction). Results:Thirty patients with a median age of 73.5 years (range, 65-85) were included in our study. Most patients had T2N0, and T3N0 (28 patients), furthermore 73.3% had an intermediate-grade tumor, Transurethral resection of bladder tumor was incomplete in 43.3. No grade 4 toxicity was documented. Grade 3 urinary toxicities occurred in two patients requiring hospitalization and temporal radiation cessation. Regarding late toxicities, no grade 3 or 4 toxicity was reported. A complete response was obtained in 56.7% of patients. After a median follow-up of 16 months, the locoregional control rate was 63%. Overall survival, local failure-free survival, and event-free survival were 100%, 93.3%, 80% and 43.3%, 33.3%, 30% at one and two years respectively. Conclusion:Hypofractionated chemoradiation with capecitabine, appears to be an effective and well-tolerated curative treatment strategy in the selected elderly population with urothelial carcinoma.

Molecular alterations in the culture of lung cancer cells H1299 after exposure to high doses of ionizing radiation

Objective To study the copy number of genes-components of signaling cascades involved in DNA repair, cell cycle regulation and apoptosis under the influence of high doses of ionizing radiation.Material and Мethods The study was carried out on a culture of H1299 non-small cell lung cancer cells. Cell lines were cultured in a Binder incubator (Germany) for 24 h (at 37 °C, 5% CO2 ), and then the groups were divided into therapeutic and control. The first one was irradiated with a NovalisTx, Varian linear accelerator at doses from 18 to 24 Gy, the second was not exposed to radiation. During the study, we monitored cell viability and evaluated apoptotic activity, then each sample was amplified in two iterations. During the study, cell viability was monitored, apoptotic activity was assessed, and then each sample was amplified in two replicates. The relative copy number of genetic loci was determined by Real-Time qPCR (RT-qPCR).Results When comparing the relative copy number in the genetic loci of the H1299 non-small cell lung cancer cell culture after exposure to a high dose of ionizing radiation, a statistically significant decrease in the relative copy number of the CASP3 and RBBP8 genes was found, which may indicate a decrease in the potential of caspase-mediated tumor repopulation and an increase in the radiosensitivity of tumor cells.Conclusion Exposure to high doses of ionizing radiation leads to a detrimental effect on tumor cells and allows to overcome one of the mechanisms of radioresistance – tumor cell repopulation.

Theoretical investigation of the impact of different timing schemes in hypofractionated radiotherapy.

This study compares the effectiveness of three fractionation schemes of equal fraction size, comprising five fractions of SBRT over 5days, 10days, or 15days, respectively. This comparative study is based on two tumor-control-probability (TCP) models that take into account tumor cell re-sensitization and repopulation during treatment; the Zaider-Minerbo-Stavreva (ZMS) and the Ruggieri-Nahum (RN) models. The ZMS model is further modified to include also re-sensitization according to the β mechanism of the linear-quadratic (LQ) model of cell killing. The modified version of the ZMS model is verified through fitting to the experimental data set of Fisher and Moulder. The study applies an idea used in a plan ranking methodology developed for the case when the specific values of the model parameters are not known. The TCPs of the compared regimens are calculated for various values of the model parameters and for two different values of the dose per fraction. The TCPs are presented as 2-D functions of two of the model parameters for each model correspondingly. The differences between the TCPs of each of the prolonged regimens and the TCP of the every week day regimen are also calculated for each model. Both models predict that the prolonged regimens are superior in terms of TCP to the every week-day one for most of the studied cases; however this is shown to exist to a different degree by the two models. It is shown again to a different degree that reversed situations where the every week day schedule is better than the prolonged regimens are also possible. It is concluded that a 30% TCP difference observed in a clinical study in favor of the fifteen-day regimen is theoretically possible. However, the fifteen-day regimen is outperformed in terms of TCP by the every week day regimen in more cases than the regimen lasting ten days. Therefore the choice of a prolongation in time must be made with care.

Irradiation‐induced polyploid giant cancer cells are involved in tumor cell repopulation via neosis

Tumor repopulation occurs when residual tumor cells surviving therapies tenaciously proliferate and re‐establish the tumor. The cellular and molecular mechanisms underlying this process remain poorly understood. In this study, we propose that polyploid giant cancer cells (PGCCs) are involved in tumor repopulation via neosis following radiotherapy. We found that although the majority of PGCCs induced by irradiation underwent cell death, some PGCCs exhibited proliferative capacity. Utilizing time‐lapse microscopy and single‐cell cloning assays, we observed that proliferating PGCCs underwent neosis, thereby contributing to tumor cell repopulation after irradiation. Notably, HMGB1 released from dying tumor cells rather than intracellular HMGB1 could promote neosis‐based tumor repopulation, and the latter could be suppressed by the use of HMGB1 inhibitors. Taken together, our results indicate that PGCC can initiate tumor repopulation via neosis following radiation therapy.

Do TUNEL and Other Apoptosis Assays Detect Cell Death in Preclinical Studies?

The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay detects DNA breakage by labeling the free 3ʹ-hydroxyl termini. Given that genomic DNA breaks arise during early and late stages of apoptosis, TUNEL staining continues to be widely used as a measure of apoptotic cell death. The advantages of the assay include its relative ease of performance and the broad availability of TUNEL assay kits for various applications, such as single-cell analysis of apoptosis in cell cultures and tissue samples. However, as briefly discussed herein, aside from some concerns relating to the specificity of the TUNEL assay itself, it was demonstrated some twenty years ago that the early stages of apoptosis, detected by TUNEL, can be reversed. More recently, compelling evidence from different biological systems has revealed that cells can recover from even late stage apoptosis through a process called anastasis. Specifically, such recovery has been observed in cells exhibiting caspase activation, genomic DNA breakage, phosphatidylserine externalization, and formation of apoptotic bodies. Furthermore, there is solid evidence demonstrating that apoptotic cells can promote neighboring tumor cell repopulation (e.g., through caspase-3-mediated secretion of prostaglandin E2) and confer resistance to anticancer therapy. Accordingly, caution should be exercised in the interpretation of results obtained by the TUNEL and other apoptosis assays (e.g., caspase activation) in terms of apoptotic cell demise.

Radiation Treatment Breaks: Are They Detrimental to Outcomes for Oropharyngeal Carcinoma Treated with Definitive Chemoradiation?

Varying practices exist to account for radiation treatment breaks (rTBs) resulting from institutional holidays during treatment of oropharyngeal squamous cell carcinoma (OPSCC) cancer patients undergoing concurrent chemoradiation (CRT). Studies in radiation biology suggest that local therapy delays may result in accelerated repopulation of residual tumor cells, however the clinical effects of this model in the setting of concurrent systemic therapy are unclear. We, therefore, evaluated the effect of rTBs in patients who received CRT on disease-free survival (DFS) in a consecutive cohort of patients with OPSCC. Patients with recurrent OPSCC, M1 disease, less than 6 months follow-up, or those treated with surgery or RT alone were excluded. Data collected included age, sex, KPS, smoking status, T stage, N stage, p16 IHC or HPV ISH status, RT dose and fractions, systemic therapy, total treatment duration, number of total and cumulative rTBs, overall survival/local/regional/distant failure (calculated from start of RT). rTBs were defined as any breaks taken during RT. Cumulative rTBs were defined as largest number of consecutive rTBs, not including weekends. The Kaplan-Meier method was used to estimate time-to-event outcomes on univariate analysis (UVA) and the Cox proportional hazards model was used to determine the effects of covariates on multivariate analysis (MVA). 462 OPSCC patients meeting inclusion criteria treated between 1/1/2010 and 12/31/2015. Median follow up was 5 years (6 months -10 yrs). Median total treatment duration was 48 days (41-64 days). 457 (99%) patients received 70 Gy of RT, 1 patient received a 400 cGy boost, and 4 patients received 66-68 Gy. 54 (12%) patients received induction chemotherapy. 369 (80%) patients received a cisplatin-based regimen and 93 (20%) received a non-cisplatin regimen. 345 (75%) were HPV or p16 positive, 45 (10%) were negative, and 72 (15%) were unknown. Table 1 describes the rTBs experienced by our cohort and results of our analysis. On UVA, only cumulative rTBs of 3 days were found to be significant (p = 0.04). On MVA, however, treatment duration, total rTBs, and cumulative rTBs were not significantly associated with DFS. We did not find a significant decrease in DFS for patients who had rTBs of 3 days in the setting of CRT for OPSCC. However, extended consecutive breaks (>3 days) may be associated with poorer outcomes, warranting further investigation.Abstract 3986; TableResults of UVA and MVA for DFSn (%)UVAMVATotal Breaks (days) 0140 (30) 1166 (36)p = 0.21p = 0.63HR 1.68 [0.21-13.65] 279 (17)p = 0.72p = 0.71HR 1.48 [0.19-11.44] 329 (6)p = 0.95p = 0.96HR 0.93 [0.10-9.32] 417 (4)p = 0.41p = 0.51HR 0.42 [0.03-5.70] 5+*31 (7)p = 0.10p = 0.81HR 1.34 [0.12-15.24]Cumulative Breaks (days) 0147 (32) 1256 (55)p = 0.34p = 0.96HR 0.92 [0.12-7.03] 225 (5)p = 0.53p = 0.71HR 1.55 [0.16-14.59] 314 (3)p = 0.04p = 1.00HR 1.00 [0.10-10.03] 410 (2)p = 0.52p = 0.83HR 0.73 [0.04-13.08] 510 (2)p = 0.38p = 65HR 1.83 [0.14-24.79]*Range 5-14 days. Open table in a new tab

Study protocol: a multicentre, prospective, phase II trial of isotoxic hypofractionated concurrent chemoradiotherapy for non-small cell lung cancer

IntroductionConcurrent chemoradiotherapy with conventional fractionation has been acknowledged as one of the standard treatments for locally advanced non-small cell lung cancer (NSCLC). The radiotherapy dose of 60 Gy is far...

Optimization of Dose Fractionation for Radiotherapy of a Solid Tumor with Account of Oxygen Effect and Proliferative Heterogeneity

A spatially-distributed continuous mathematical model of solid tumor growth and treatment by fractionated radiotherapy is presented. The model explicitly accounts for three time and space-dependent factors that influence the efficiency of radiotherapy fractionation schemes—tumor cell repopulation, reoxygenation and redistribution of proliferative states. A special algorithm is developed, aimed at finding the fractionation schemes that provide increased tumor cure probability under the constraints of maximum normal tissue damage and maximum fractional dose. The optimization procedure is performed for varied radiosensitivity of tumor cells under the values of model parameters, corresponding to different degrees of tumor malignancy. The resulting optimized schemes consist of two stages. The first stages are aimed to increase the radiosensitivity of the tumor cells, remaining after their end, sparing the caused normal tissue damage. This allows to increase the doses during the second stages and thus take advantage of the obtained increased radiosensitivity. Such method leads to significant expansions in the curative ranges of the values of tumor radiosensitivity parameters. Overall, the results of this study represent the theoretical proof of concept that non-uniform radiotherapy fractionation schemes may be considerably more effective that uniform ones, due to the time and space-dependent effects.

Optimization of fractionation schemes and beamlet intensities in intensity-modulated radiation therapy with changing cancer tumor properties

Intensity-modulated radiation therapy (IMRT) is a type of external beam radiation therapy used in cancer treatment. In IMRT, the prescribed radiation dose can be administered such that it is maximized on the cancerous tumor while sparing the surrounding healthy tissues. The total dose is divided into fractions across time intervals, called a fractionation scheme. To find the best fractionation scheme and beamlet intensities for total dose, optimization models are used. In this paper, a non-convex mixed-integer nonlinear programming model has been proposed wherein the spatiotemporal changes of the biological properties of the tumor due to tumor cell re-oxygenation, redistribution, and re-population that occur as the treatment progresses have been considered. Also, the dose constraints over both cumulative limits and per-fraction limits have been considered in the model. The output of this model is called the fractionation scheme and beamlet intensities considering biological changes in tumor cells (FBBTs). When the FBBTs are compared with conventional fractionation scheme and beamlet intensities (CFB) which do not include the biological properties of the tumor, it is observed that the FBBTs are more efficacious than the CFBs. To get FBBTs for datasets that resemble realistic tumors, an algorithm based on simulated annealing has been developed and used.

Mitochondria break through cellular boundaries

In our recent research, we have used respiration-deficient tumour cells to challenge the dogma that mitochondria with their genome are constrained within cells in the body, and to question the concept that mitochondria are primarily the powerhouse of the cell. Our results have shown that mitochondria move from normal cells in the body to tumour cells without mitochondrial DNA (mtDNA), resulting in respiration recovery and the ability to grow as tumours [1, 2]. Almost a decade earlier, a similar phenomenon had been show in co-cultures of human tumour cells lacking mtDNA with mesenchymal stem cells [3]. The strength of both of these ground-breaking studies was that they used mtDNA polymorphisms to show repopulation of tumour cells with mtDNA, establishing the origin of mitochondria in the donor cells.