Intrinsic radiosensitivity of human cell lines is correlated with radioresponsiveness of human tumors: analysis of 101 published survival curves

Radiogenomics and radiotherapy response modeling

Advances in patient-specific information and biotechnology have contributed to a new era of computational medicine. Radiogenomics has emerged as a new field that investigates the role of genetics in treatment response to radiation therapy. Radiation oncology is currently attempting to embrace these recent advances and add to its rich history by maintaining its prominent role as a quantitative leader in oncologic response modeling. Here, we provide an overview of radiogenomics starting with genotyping, data aggregation, and application of different modeling approaches based on modifying traditional radiobiological methods or application of advanced machine learning techniques. We highlight the current status and potential for this new field to reshape the landscape of outcome modeling in radiotherapy and drive future advances in computational oncology.

The evolution of brachytherapy for prostate cancer

Brachytherapy (BT), using low-dose-rate (LDR) permanent seed implantation or high-dose-rate (HDR) temporary source implantation, is an acceptable treatment option for select patients with prostate cancer of any risk group. The benefits of HDR-BT over LDR-BT include the ability to use the same source for other cancers, lower operator dependence, and - typically - fewer acute irritative symptoms. By contrast, the benefits of LDR-BT include more favourable scheduling logistics, lower initial capital equipment costs, no need for a shielded room, completion in a single implant, and more robust data from clinical trials. Prospective reports comparing HDR-BT and LDR-BT to each other or to other treatment options (such as external beam radiotherapy (EBRT) or surgery) suggest similar outcomes. The 5-year freedom from biochemical failure rates for patients with low-risk, intermediate-risk, and high-risk disease are >85%, 69-97%, and 63-80%, respectively. Brachytherapy with EBRT (versus brachytherapy alone) is an appropriate approach in select patients with intermediate-risk and high-risk disease. The 10-year rates of overall survival, distant metastasis, and cancer-specific mortality are >85%, <10%, and <5%, respectively. Grade 3-4 toxicities associated with HDR-BT and LDR-BT are rare, at <4% in most series, and quality of life is improved in patients who receive brachytherapy compared with those who undergo surgery.

Outcome and prognostic factors in patients with brain metastases from small-cell lung cancer treated with whole brain radiotherapy

The purpose of this study was to evaluate prognostic factors associated with overall survival (OS) and neurological progression free survival (nPFS) in small-cell lung cancer (SCLC) patients with brain metastases who received whole-brain radiotherapy (WBRT). From 2003 to 2015, 229 SCLC patients diagnosed with brain metastases who received WBRT were analyzed retrospectively. In this cohort 219 patients (95%) received a total photon dose of 30 Gy in 10 fractions. The prognostic factors evaluated for OS and nPFS were: age, Karnofsky Performance Status (KPS), number of brain metastases, synchronous versus metachronous disease, initial response to chemotherapy, the Radiation Therapy Oncology Group recursive partitioning analysis (RPA) class and thoracic radiation. Median OS after WBRT was 6 months and the median nPFS after WBRT was 11 months. Patients with synchronous cerebral metastases had a significantly better median OS with 8 months compared to patients with metachronous metastases with a median survival of 3 months (p < 0.0001; HR 0.46; 95% CI 0.31-0.67). Based on RPA classification median survival after WBRT was 17 months in RPA class I, 7 months in class II and 3 months in class III (p < 0.0001). Karnofsky performance status scale (KPS < 70%) was significantly associated with OS in both univariate (HR 2.84; p < 0.001) and multivariate analyses (HR 2.56; p = 0.011). Further, metachronous brain metastases (HR 1.8; p < 0.001), initial response to first-line chemotherapy (HR 0.51, p < 0.001) and RPA class III (HR 2.74; p < 0.001) were significantly associated with OS in univariate analysis. In multivariate analysis metachronous disease (HR 1.89; p < 0.001) and initial response to chemotherapy (HR 0.61; p < 0.001) were further identified as significant prognostic factors. NPFS was negatively significantly influenced by poor KPS (HR 2.56; p = 0.011), higher number of brain metastases (HR 1.97; p = 0.02), and higher RPA class (HR 2.26; p = 0.03) in univariate analysis. In this series, the main prognostic factors associated with OS were performance status, time of appearance of intracranial disease (synchronous vs. metachronous), initial response to chemotherapy and higher RPA class. NPFS was negatively influenced by poor KPS, multiplicity of brain metastases, and higher RPA class in univariate analysis. For patients with low performance status, metachronous disease or RPA class III, WBRT should be weighed against supportive therapy with steroids alone or palliative chemotherapy.

Integrating Biological Covariates into Gene Expression-Based Predictors of Radiation Sensitivity

The use of gene expression-based classifiers has resulted in a number of promising potential signatures of patient diagnosis, prognosis, and response to therapy. However, these approaches have also created difficulties in trying to use gene expression alone to predict a complex trait. A practical approach to this problem is to integrate existing biological knowledge with gene expression to build a composite predictor. We studied the problem of predicting radiation sensitivity within human cancer cell lines from gene expression. First, we present evidence for the need to integrate known biological conditions (tissue of origin, RAS, and p53 mutational status) into a gene expression prediction problem involving radiation sensitivity. Next, we demonstrate using linear regression, a technique for incorporating this knowledge. The resulting correlations between gene expression and radiation sensitivity improved through the use of this technique (best-fit adjusted R² increased from 0.3 to 0.84). Overfitting of data was examined through the use of simulation. The results reinforce the concept that radiation sensitivity is not driven solely by gene expression, but rather by a combination of distinct parameters. We show that accounting for biological heterogeneity significantly improves the ability of the model to identify genes that are associated with radiosensitivity.

Decision support systems for personalized and participative radiation oncology

A paradigm shift from current population based medicine to personalized and participative medicine is underway. This transition is being supported by the development of clinical decision support systems based on prediction models of treatment outcome. In radiation oncology, these models 'learn' using advanced and innovative information technologies (ideally in a distributed fashion - please watch the animation: http://youtu.be/ZDJFOxpwqEA) from all available/appropriate medical data (clinical, treatment, imaging, biological/genetic, etc.) to achieve the highest possible accuracy with respect to prediction of tumor response and normal tissue toxicity. In this position paper, we deliver an overview of the factors that are associated with outcome in radiation oncology and discuss the methodology behind the development of accurate prediction models, which is a multi-faceted process. Subsequent to initial development/validation and clinical introduction, decision support systems should be constantly re-evaluated (through quality assurance procedures) in different patient datasets in order to refine and re-optimize the models, ensuring the continuous utility of the models. In the reasonably near future, decision support systems will be fully integrated within the clinic, with data and knowledge being shared in a standardized, dynamic, and potentially global manner enabling truly personalized and participative medicine.

Melanoma central nervous system metastases: current approaches, challenges, and opportunities

Melanoma central nervous system metastases are increasing, and the challenges presented by this patient population remain complex. In December 2015, the Melanoma Research Foundation and the Wistar Institute hosted the First Summit on Melanoma Central Nervous System (CNS) Metastases in Philadelphia, Pennsylvania. Here, we provide a review of the current status of the field of melanoma brain metastasis research; identify key challenges and opportunities for improving the outcomes in patients with melanoma brain metastases; and set a framework to optimize future research in this critical area.

Radiotherapy and immunotherapy: Can this combination change the prognosis of patients with melanoma brain metastases?

Brain metastases are a common occurrence in patients with melanoma. Prognosis is poor. Radiotherapy is the main local treatment for brain metastases. Recently, immunotherapy (i.e. immune checkpoints inhibitors) showed a significant impact on the prognosis of patients with metastatic melanoma, also in the setting of patients with brain metastases. Despite various possible treatments, survival of patients with melanoma brain metastases is still unsatisfactory; new treatment modalities or combination of therapies need to be explored. Being immunotherapy and radiotherapy alone both efficient in the treatment of melanoma brain metastases, the combination of these two therapies seems logical. Moreover radiotherapy can improve the efficacy of immunotherapy and the immune system plays a relevant role in the action of radiotherapy. Preclinical data support this combination. Clinical data are more contradictory. In this review, we will discuss available therapies for melanoma brain metastases, focusing on the preclinical and clinical available data supporting the possible synergism between radiotherapy and immunotherapy.

The changing paradigm of tumour response to irradiation

Tumours contain multiple different cell populations, including cells derived from the bone marrow as well as cancer-associated fibroblasts and various stromal populations including the vasculature. The microenvironment of the tumour cells plays a significant role in the response of the tumour to radiation treatment. Low levels of oxygen (hypoxia) caused by the poorly organized vasculature in tumours have long been known to affect radiation response; however, other aspects of the microenvironment may also play important roles. This article reviews some of the old literature concerning tumour response to irradiation and relates this to current concepts about the role of the tumour microenvironment in tumour response to radiation treatment. Included in the discussion are the role of cancer stem cells, radiation damage to the vasculature and the potential for radiation to enhance immune activity against tumour cells. Radiation treatment can cause a significant influx of bone marrow-derived cell populations into both normal tissues and tumours. Potential roles of such cells may include enhancing vascular recovery as well as modulating immune reactivity.

Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy in the Treatment of Uveal Melanoma

Uveal melanoma is the most common primary intraocular malignant tumor. Radiation therapy has now replaced enucleation as the treatment of choice, with radioactive eye plaques and proton therapy being the two most studied radiotherapy modalities. More recently, stereotactic radiosurgery and fractionated stereotactic radiotherapy have emerged as promising, non-invasive treatments for uveal melanoma. This review summarizes the available literature on these newer treatment modalities.

Biologically effective dose in fractionated molecular radiotherapy--application to treatment of neuroblastoma with (131)I-mIBG

In this work, the biologically effective dose (BED) is investigated for fractionated molecular radiotherapy (MRT). A formula for the Lea-Catcheside G-factor is derived which takes the possibility of combinations of sub-lethal damage due to radiation from different administrations of activity into account. In contrast to the previous formula, the new G-factor has an explicit dependence on the time interval between administrations. The BED of tumour and liver is analysed in MRT of neuroblastoma with (131)I-mIBG, following a common two-administration protocol with a mass-based activity prescription. A BED analysis is also made for modified schedules, when due to local regulations there is a maximum permitted activity for each administration. Modifications include both the simplistic approach of delivering this maximum permitted activity in each of the two administrations, and also the introduction of additional administrations while maintaining the protocol-prescribed total activity. For the cases studied with additional (i.e. more than two) administrations, BED of tumour and liver decreases at most 12% and 29%, respectively. The decrease in BED of the tumour is however modest compared to the two-administration schedule using the maximum permitted activity, where the decrease compared to the original schedule is 47%.

Advances in Radiation Therapy in Pediatric Neuro-oncology

Radiation therapy remains a highly effective therapy for many pediatric central nervous system tumors. With more children achieving long-term survival after treatment for brain tumors, late-effects of radiation have become an important concern. In response to this problem, treatment protocols for a variety of pediatric central nervous system tumors have evolved to reduce radiation fields and doses when possible. Recent advances in radiation technology such as image guidance and proton therapy have led to a new era of precision treatment with significantly less exposure to healthy tissues. These developments along with the promise of molecular classification of tumors and targeted therapies point to an optimistic future for pediatric neuro-oncology.

Viability of Non-Coplanar VMAT for Liver SBRT as Compared to Coplanar VMAT and Beam Orientation Optimized 4π IMRT

Purpose

The 4π static noncoplanar radiation therapy delivery technique has demonstrated better normal tissue sparing and dose conformity than the clinically used volumetric modulated arc therapy (VMAT). It is unclear whether this is a fundamental limitation of VMAT delivery or the coplanar nature of its typical clinical plans. The dosimetry and the limits of normal tissue toxicity constrained dose escalation of coplanar VMAT, noncoplanar VMAT and 4π radiation therapy are quantified in this study.

Methods and materials

Clinical stereotactic body radiation therapy plans for 20 liver patients receiving 30 to 60 Gy using coplanar VMAT (cVMAT) were replanned using 3 to 4 partial noncoplanar arcs (nVMAT) and 4π with 20 intensity modulated noncoplanar fields. The conformity number, homogeneity index, 50% dose spillage volume, normal liver volume receiving >15 Gy, dose to organs at risk (OARs), and tumor control probability were compared for all 3 treatment plans. The maximum tolerable dose yielding a normal liver normal tissue control probability <1%, 5%, and 10% was calculated with the Lyman-Kutcher-Burman model for each plan as well as the resulting survival fractions at 1, 2, 3, and 4 years.

Results

Compared with cVMAT, the nVMAT and 4π plans reduced liver volume receiving >15 Gy by an average of 5 cm³ and 80 cm³, respectively. 4π reduced the 50% dose spillage volume by ∼23% compared with both VMAT plans, and either significantly decreased or maintained OAR doses. The 4π maximum tolerable doses and survival fractions were significantly higher than both cVMAT and nVMAT (P < .05) for all normal liver normal tissue control probability limits used in this study.

Conclusions

The 4π technique provides significantly better OAR sparing than both cVMAT and nVMAT and enables more clinically relevant dose escalation for tumor local control. Therefore, despite the current accessibility of nVMAT, it is not a viable alternative to 4π for liver SBRT.

Radiotherapy with BRAF inhibitor therapy for melanoma: progress and possibilities

The introduction of small molecule BRAFV600 kinase inhibitors represents a milestone in the targeted therapy of patients with metastatic melanoma by a significant increase in therapeutic efficacy in terms of overall and progression-free survival compared with conventional chemotherapy. Beside BRAFV600 inhibitor treatment, radiotherapy is a further mainstay for the therapy of metastatic melanoma and thus a concomitant or sequential application of BRAFV600 inhibitors and radiotherapy is inevitable. Recent reports show a significant radiosensitization of the irradiated healthy tissue in patients with melanoma after the combination of radiotherapy and BRAFV600 inhibitors, evoking concern in clinical practice. We review interactions of BRAFV600 inhibitors and radiation with regard to antitumor effects and an increased radiotoxicity in the healthy tissue.

Treatment of Melanoma CNS Metastases

The discovery of the BRAFV600 mutation and the development of targeted therapies directed against this mutation as well as effective immunotherapies with durable benefits have revolutionized the treatment of patients with melanoma. Nonetheless, the frequent occurrence of brain metastases in patients with advanced melanoma represents a significant obstacle to long-term, high quality survival. The application of stereotactic radiation therapy has provided an opportunity to control brain metastases in the majority of patients with metastatic melanoma reducing the impact of these lesions on morbidity and mortality and enabling patients to receive and potentially benefit from these novel systemic treatments. Encouragingly, several of these novel new therapies have shown antitumor activity against CNS metastases that approach that seen against extracranial disease. As a consequence, several effective treatment options are now available for patients with melanoma brain metastases. With these tools in hand, it is anticipated that further investigation into the optimal sequence and/or combination of systemic therapies and local therapies along with multidisciplinary team practice will continue to improve the outcome of patients with this previously life-limiting disease complication.

Radioembolization of hepatocarcinoma with (90)Y glass microspheres: development of an individualized treatment planning strategy based on dosimetry and radiobiology

PURPOSE

The aim of this study was to optimize the dosimetric approach and to review the absorbed doses delivered, taking into account radiobiology, in order to identify the optimal methodology for an individualized treatment planning strategy based on (99m)Tc-macroaggregated albumin (MAA) single photon emission computed tomography (SPECT) images.

METHODS

We performed retrospective dosimetry of the standard TheraSphere® treatment on 52 intermediate (n = 17) and advanced (i.e. portal vein thrombosis, n = 35) hepatocarcinoma patients with tumour burden < 50% and without obstruction of the main portal vein trunk. Response was monitored with the densitometric radiological criterion (European Association for the Study of the Liver) and treatment-related liver decompensation was defined ad hoc with a time cut-off of 6 months. Adverse events clearly attributable to disease progression or other causes were not attributed to treatment. Voxel dosimetry was performed with the local deposition method on (99m)Tc-MAA SPECT images. The reconstruction protocol was optimized. Concordance of (99m)Tc-MAA and (90)Y bremsstrahlung microsphere biodistributions was studied in 35 sequential patients. Two segmentation methods were used, based on SPECT alone (home-made code) or on coregistered SPECT/CT images (IMALYTICS™ by Philips). STRATOS™ absorbed dose calculation was validated for (90)Y with a single time point. Radiobiology was used introducing other dosimetric variables besides the mean absorbed dose D: equivalent uniform dose (EUD), biologically effective dose averaged over voxel values (BEDave) and equivalent uniform biologically effective dose (EUBED). Two sets of radiobiological parameters, the first derived from microsphere irradiation and the second from external beam radiotherapy (EBRT), were used. A total of 16 possible methodologies were compared. Tumour control probability (TCP) and normal tissue complication probability (NTCP) were derived. The area under the curve (AUC) of the receiver-operating characteristic (ROC) curve was used as a figure of merit to identify the methodology which gave the best separation in terms of dosimetry between responding and non-responding lesions and liver decompensated vs non-decompensated liver treatment.

RESULTS

MAA and (90)Y biodistributions were not different (71% of cases), different in 23% and uncertain in 6%. Response correlated with absorbed dose (Spearman's r from 0.48 to 0.69). Responding vs non-responding lesion absorbed doses were well separated, regardless of the methodology adopted (p = 0.0001, AUC from 0.75 to 0.87). EUBED gave significantly better separation with respect to mean dose (AUC = 0.87 vs 0.80, z = 2.07). Segmentation on SPECT gave better separation than on SPECT/CT. TCP(50%) was at 250 Gy for small lesion volumes (<10 cc) and higher than 1,000 Gy for large lesions (>10 cc). Apparent radiosensitivity values from TCP were around 0.003/Gy, a factor of 3-5 lower than in EBRT, as found by other authors. The dose-rate effect was negligible: a purely linear model can be applied. Toxicity incidence was significantly larger for Child B7 patients (89 vs 14%, p < 0.0001), who were therefore excluded from dose-toxicity analysis. Child A toxic vs non-toxic treatments were significantly separated in terms of dose averaged on whole non-tumoural parenchyma (including non-irradiated regions) with AUC from 0.73 to 0.94. TD50 was ≈ 100 Gy. No methodology was superior to parenchyma mean dose, which therefore can be used for planning, with a limit of TD15 ≈ 75 Gy.

CONCLUSION

A dosimetric treatment planning criterion for Child A patients without complete obstruction of the portal vein was developed.

[Radioresistance parameters in head and neck cancers and methods to radiosensitize]

Head and neck cancers have been widely studied concerning their sensitivity to radiation therapy. Several parameters affect tumour response to radiation therapy. Some parameters are linked to the tumour. Large or invasive tumours, localization, such as oral cavity or adenopathy, are factors of radioresistance. Others parameters are linked to the patients themselves. Tobacco intoxication during radiotherapy and a low hemoglobin level contribute to radioresistance. More recently, a positive human papilloma virus (HPV) status has been reported to positively affect radiosensitivity. Finally, other parameters are related to tumour biology. Hypoxia, intrinsic radiosensitivity of tumour cells, tumour differentiation and repopulation (provided by Ki-67 index or EGFR level) are components of radiosensitivity. Currently, concurrent chemoradiotherapy is one of the gold standard treatments to overcome clinical outcome of locally advanced head and neck cancer. This combination increases locoregional control and survival. Taxane-based induction chemotherapy can also be an alternative. Another validated approach is the association of radiotherapy with cetuximab (EGFR targeting) but only one randomized study has been published. Fractionation modifications, especially hyperfractionation, have given positive results on both tumour control and survival. Strategies targeting hypoxia improve locoregional control but have less clinical impact.

Spatial mapping of the biologic effectiveness of scanned particle beams: towards biologically optimized particle therapy

The physical properties of particles used in radiation therapy, such as protons, have been well characterized, and their dose distributions are superior to photon-based treatments. However, proton therapy may also have inherent biologic advantages that have not been capitalized on. Unlike photon beams, the linear energy transfer (LET) and hence biologic effectiveness of particle beams varies along the beam path. Selective placement of areas of high effectiveness could enhance tumor cell kill and simultaneously spare normal tissues. However, previous methods for mapping spatial variations in biologic effectiveness are time-consuming and often yield inconsistent results with large uncertainties. Thus the data needed to accurately model relative biological effectiveness to guide novel treatment planning approaches are limited. We used Monte Carlo modeling and high-content automated clonogenic survival assays to spatially map the biologic effectiveness of scanned proton beams with high accuracy and throughput while minimizing biological uncertainties. We found that the relationship between cell kill, dose, and LET, is complex and non-unique. Measured biologic effects were substantially greater than in most previous reports, and non-linear surviving fraction response was observed even for the highest LET values. Extension of this approach could generate data needed to optimize proton therapy plans incorporating variable RBE.

Development and Validation of a Novel Radiosensitivity Signature in Human Breast Cancer

PURPOSE

An unmet clinical need in breast cancer management is the accurate identification of patients who will benefit from adjuvant radiotherapy. We hypothesized that integration of postradiation clonogenic survival data with gene expression data across breast cancer cell (BCC) lines would generate a radiation sensitivity signature (RSS) and identify patients with tumors refractive to conventional therapy.

EXPERIMENTAL DESIGN

Using clonogenic survival assays, we identified the surviving fraction (SF-2Gy) after radiation across a range of BCC lines. Intrinsic radiosensitivity was correlated to gene expression using Spearman correlation. Functional analysis was performed in vitro, and enriched biologic concepts were identified. The RSS was generated using a Random Forest model and was refined, cross-validated, and independently validated in additional breast cancer datasets.

RESULTS

Clonogenic survival identifies a range of radiosensitivity in human BCC lines (SF-2Gy 77%-17%) with no significant correlation to the intrinsic breast cancer subtypes. One hundred forty-seven genes were correlated with radiosensitivity. Functional analysis of RSS genes identifies previously unreported radioresistance-associated genes. RSS was trained, cross-validated, and further refined to 51 genes that were enriched for concepts involving cell-cycle arrest and DNA damage response. RSS was validated in an independent dataset and was the most significant factor in predicting local recurrence on multivariate analysis, outperfoming all clinically used clinicopathologic features.

CONCLUSIONS

We derive a human breast cancer-specific RSS with biologic relevance and validate this signature for prediction of locoregional recurrence. By identifying patients with tumors refractory to standard radiation this signature has the potential to allow for personalization of radiotherapy.

Survival patterns following brain metastases for patients with melanoma in the MAP-kinase inhibitor era

Survival with BRAF-mutant metastatic melanoma is prolonged with MAP-kinase pathway inhibitors (MAPKi). Among patients with brain metastases (BM), however, the clinical course of MAPKi-treated patients is not well described. We therefore explored these patients' survival patterns compared to contemporary patients not treated with MAPKi. We analyzed 106 patients who developed melanoma BM between 2007 and 2013. Of these, 37 (35%) received de novo MAPKi for BRAF-mutant disease, which preceded BM in 49%. Immunotherapy was given to 54% of MAPKi-treated patients and 94% of those who did not receive MAPKi. We evaluated the potential influence of patient characteristics, systemic therapies, and BM-directed treatments on time to appearance of new BM and overall survival. With a median follow-up of 8.0 months after initial BM, MAPKi use was an independent predictor of prolonged survival after BM diagnosis (median 14.1 vs 7.0 months, P = 0.03, adjusted hazard ratio 0.39). This survival advantage was driven by the 16.6-month median survival of patients who initiated MAPKi after BM were diagnosed, versus 5.6 months if initiated prior to BM development (P = 0.03). Median survival from the onset of any systemic metastases was 22 months regardless of the timing of MAPKi relative to BM appearance. Time to in-brain progression was longer among patients whose MAPKi course was started after BM diagnosis, but MAPKi initiation prior to BM diagnosis was associated with longer time to intracranial involvement. These findings are consistent with potential MAPKi activity in intracranial melanoma.

The actin depolymerizing factor (ADF)/cofilin signaling pathway and DNA damage responses in cancer

The actin depolymerizing factor (ADF)/cofilin protein family is essential for actin dynamics, cell division, chemotaxis and tumor metastasis. Cofilin-1 (CFL-1) is a primary non-muscle isoform of the ADF/cofilin protein family accelerating the actin filamental turnover in vitro and in vivo. In response to environmental stimulation, CFL-1 enters the nucleus to regulate the actin dynamics. Although the purpose of this cytoplasm-nucleus transition remains unclear, it is speculated that the interaction between CFL-1 and DNA may influence various biological responses, including DNA damage repair. In this review, we will discuss the possible involvement of CFL-1 in DNA damage responses (DDR) induced by ionizing radiation (IR), and the implications for cancer radiotherapy.

Immunological effects of a tumor necrosis factor alpha-armed oncolytic adenovirus

For long it has been recognized that tumor necrosis factor alpha (TNFa) has anticancer characteristics, and its use as a cancer therapeutic was proposed already in the 1980s. However, its systemic toxicity has limited its usability. Oncolytic viruses, selectively cancer-killing viruses, have shown great potency, and one of their most useful aspects is their ability to produce high amounts of transgene products locally, resulting in high local versus systemic concentrations. Therefore, the overall magnitude of tumor cell killing results from the combination of oncolysis, transgene-mediated direct effect such as TNFa-mediated apoptosis, and, perhaps most significantly, from activation of the host immune system against the tumor. We generated a novel chimeric oncolytic adenovirus expressing human TNFa, Ad5/3-D24-hTNFa, whose efficacy and immunogenicity were tested in vitro and in vivo. The hTNFa-expressing adenovirus showed increased cancer-eradicating potency, which was shown to be because of elevated apoptosis and necrosis rates and induction of various immune responses. Interestingly, we saw increase in immunogenic cell death markers in Ad5/3-d24-hTNFa-treated cells. Moreover, tumors treated with Ad5/3-D24-hTNFa displayed enhanced presence of OVA-specific cytotoxic T cells. We thus can conclude that tumor eradication and antitumor immune responses mediated by Ad5/3-d24-hTNFa offer a new potential drug candidate for cancer therapy.

Role for radiation therapy in melanoma

Although melanoma is generally considered a relative radioresistant tumor, radiation therapy (RT) remains a valid and effective treatment option in definitive, adjuvant, and palliative settings. Definitive RT is generally only used in inoperable patients. Despite a high-quality clinical trial showing adjuvant RT following lymphadenectomy in node-positive melanoma patients prevents local and regional recurrence, the role of adjuvant RT in the treatment of melanoma remains controversial and is underused. RT is highly effective in providing symptom palliation for metastatic melanoma. RT combined with new systemic options, such as immunotherapy, holds promise and is being actively evaluated.

Determinates of tumor response to radiation: tumor cells, tumor stroma and permanent local control

BACKGROUND AND PURPOSE

The causes of tumor response variation to radiation remain obscure, thus hampering the development of predictive assays and strategies to decrease resistance. The present study evaluates the impact of host tumor stromal elements and the in vivo environment on tumor cell kill, and relationship between tumor cell radiosensitivity and the tumor control dose.

MATERIAL AND METHODS

Five endpoints were evaluated and compared in a radiosensitive DNA double-strand break repair-defective (DNA-PKcs(-/-)) tumor line, and its DNA-PKcs repair competent transfected counterpart. In vitro colony formation assays were performed on in vitro cultured cells, on cells obtained directly from tumors, and on cells irradiated in situ. Permanent local control was assessed by the TCD50 assay. Vascular effects were evaluated by functional vascular density assays.

RESULTS

The fraction of repair competent and repair deficient tumor cells surviving radiation did not substantially differ whether irradiated in vitro, i.e., in the absence of host stromal elements and factors, from the fraction of cells killed following in vivo irradiation. Additionally, the altered tumor cell sensitivity resulted in a proportional change in the dose required to achieve permanent local control. The estimated number of tumor cells per tumor, their cloning efficiency and radiosensitivity, all assessed by in vitro assays, were used to predict successfully, the measured tumor control doses.

CONCLUSION

The number of clonogens per tumor and their radiosensitivity govern the permanent local control dose.

Earlier and sustained response with incidental use of cardiovascular drugs among patients with low- to medium-grade meningiomas treated with radiosurgery (SRS) or stereotactic radiotherapy (SRT)

BACKGROUND AND PURPOSE

Beneficial outcome for cancer treated with radiotherapy (RT) and β-blockers has been reported. We hypothesize a potential combined impact of stereotactic RT with incidental use of cardiovascular drugs also in meningiomas.

MATERIALS AND METHODS

In 64 patients with 70 intracranial meningiomas (male/female=17/53; median follow-up=2 years) from a prospective database with sustained RT/cardiovascular drug therapy tumor response (progression, stable disease, regression) was evaluated at predefined follow-up intervals of 3, 12 and 24 months based on MR-imaging. For this retrospective cohort analysis stepwise univariate and multivariate analyses for group comparison were performed. Between groups analysis and stepwise uni- and multivariate analysis was performed.

RESULTS

At one year follow-up there was a significant better tumor response for patients with antihypertensives use (p=0.008) and radiosurgery (SRS) (p=0.054), the difference between patients with and without antihypertensive medication remains significant in multivariate analysis. Two years after RT, only patients with β-blocker use had a significant better response to RT (p=0.032). Additionally, for the use of β-blockers a trend toward significance for early tumor response at 3 months compared to the control group was observed (p(one tailed)=0.059).

CONCLUSIONS

Our data suggest that concomitant antihypertensive medication (especially β-blockers) may lead to an earlier and sustained response in stereotactic irradiated low- to medium-grade intracranial meningiomas by affecting the β-adrenergic pathways.

Investigation of radiosensitivity gene signatures in cancer cell lines

Intrinsic radiosensitivity is an important factor underlying radiotherapy response, but there is no method for its routine assessment in human tumours. Gene signatures are currently being derived and some were previously generated by expression profiling the NCI-60 cell line panel. It was hypothesised that focusing on more homogeneous tumour types would be a better approach. Two cell line cohorts were used derived from cervix [n = 16] and head and neck [n = 11] cancers. Radiosensitivity was measured as surviving fraction following irradiation with 2 Gy (SF2) by clonogenic assay. Differential gene expression between radiosensitive and radioresistant cell lines (SF2 median) was investigated using Affymetrix GeneChip Exon 1.0ST (cervix) or U133A Plus2 (head and neck) arrays. There were differences within cell line cohorts relating to tissue of origin reflected by expression of the stratified epithelial marker p63. Of 138 genes identified as being associated with SF2, only 2 (1.4%) were congruent between the cervix and head and neck carcinoma cell lines (MGST1 and TFPI), and these did not partition the published NCI-60 cell lines based on SF2. There was variable success in applying three published radiosensitivity signatures to our cohorts. One gene signature, originally trained on the NCI-60 cell lines, did partially separate sensitive and resistant cell lines in all three cell line datasets. The findings do not confirm our hypothesis but suggest that a common transcriptional signature can reflect the radiosensitivity of tumours of heterogeneous origins.

HLA-G1 increases the radiosensitivity of human tumoral cells

Different molecules regulate the response of tumoral tissues to ionizing radiation. The objective of this work was to determine if HLA-G1 expression modulates the radiosensitivity of human tumoral cell lines. To this end, human melanoma M8 and human erythroleukemia K562 cell lines, with their correspondent HLA-G1 negative and positive variants, were gamma irradiated and the survival frequency was determined by clonogenic assay. The survival fraction of HLA-G1 expressing cells was around 60% of HLA-G1 negative cells. The generation of acidic vesicular organelles was higher in HLA-G1 positive cells. Apoptosis levels showed statistically significant differences only in K562 cells, whereas the variation in G2/M cycle progression was only significant in M8 cells. In addition, irradiation diminished cell-surface HLA-G1 and increased soluble HLA-G1 levels. Soluble HLA-G1 has no influence on cell survival in any cell line. In summary, we could demonstrate that HLA-G1 confers higher radiosensitivity to HLA-G1 expressing cells.

The role of radiotherapy in the overall treatment of melanoma

Radiotherapy has become an effective treatment in the management of melanoma patients. It has its place beneath surgical treatment options in a tumor entity that has only limited response to systemic medical therapies. New therapies, such as ipilimumab and vemurafenib, may prolong survival for several months but will cure only a few patients. Radiotherapy will still be required in adjuvant settings to reduce the local recurrence rate and in palliative situations, particularly in brain and bone metastasis. We review several indications for radiotherapy in the management of malignant melanoma with an effect on the guidelines in our clinical practice.

The use of systemic therapies for the treatment of brain metastases in metastatic melanoma: opportunities and unanswered questions

The development of brain metastases is common in patients with metastatic melanoma and heralds a particularly poor prognosis. The development of the immunological agent ipilimumab and targeted treatments such as the selective BRAF inhibitor vemurafenib have revolutionised the treatment of metastatic disease. Evidence from clinical trials suggest these drugs may be effective in the treatment of brain metastases from melanoma. However efficacy may be limited by a lack of penetration of the blood brain barrier (BBB) and by multi substrate efflux pumps expressed on the BBB. The role and sequencing of radiotherapy, both whole brain and stereotactic radiotherapy, is yet to be determined but combinations of radiotherapy and systemic therapies may further increase the effects of these drugs on brain metastases. Considering the impact of brain metastases on morbidity and mortality in metastatic melanoma, future research into systemic drug therapy for the treatment of brain metastases and improvements in BBB penetrance should be a priority.

Utilitarian prioritization of radiation oncology patients based on maximization of population tumour control

An objective method for establishing patient prioritization in the context of a radiotherapy waiting list is investigated. This is based on a utilitarian objective, being the greatest probability of local tumour control in the population of patients. A numerical simulation is developed and a clinical patient case-mix is used to determine the influence of the characteristics of the patient population on resulting optimal patient scheduling. With the utilitarian objective, large gains in tumour control probability (TCP) can be achieved for individuals or cohorts by prioritizing patients for that fraction of the patient population with relatively small sacrifices in TCP for a smaller fraction of the population. For a waiting list in steady state with five patients per day commencing treatment and leaving the list (and so with five patients per day entering the list), and a mean wait time of 35 days and a maximum of 90 days, optimized wait times ranged from a mean of one day for patients with tumour types with short effective doubling times to a mean of 66.9 days for prostate cancer patients. It is found that, when seeking the optimal daily order of patients on the waiting list in a constrained simulation, the relative rather than absolute value of TCP is the determinant of the resulting optimal waiting times. An increase in the mean waiting time mostly influences (increases) the optimal waiting times of patients with fast-growing tumours. The proportional representation of groups (separated by tumour type) in the patient population has an influence on the resulting distribution of optimal waiting times for patients in those groups, though has only a minor influence on the optimal mean waiting time for each group.

The radio-sensitizing effect of xanthohumol is mediated by STAT3 and EGFR suppression in doxorubicin-resistant MCF-7 human breast cancer cells

BACKGROUND

Chemotherapeutic drug resistance remains a clinical obstacle in cancer management. Drug-resistant cancer cells usually exhibit cross-resistance to ionizing radiation, which has devastating consequences for patients. With a better understanding of the molecular mechanisms, it will be possible to develop strategies to overcome this cross-resistance and to increase therapeutic sensitivity.

METHODS

Natural and synthetic flavonoid compounds including xanthohumol, the principal flavonoid in hops, were investigated for its radio-sensitizing activity on human breast cancer MCF-7 and adriamycin-resistant MCF-7 (MCF-7/ADR) cells. Chemo-sensitizing or radio-sensitizing effect was analyzed by tetrazolium-based colorimetric assay and flow cytometry. Western blot analysis, confocal microscopy, gene silencing with siRNA transfection and luciferase reporter gene assay were performed to examine signaling molecule activation.

RESULTS

Among the tested flavonoid compounds, pretreatment of the cells with xanthohumol significantly sensitized MCF-7/ADR cells to the radiation treatment by inducing apoptosis. In MCF-7/ADR cells, treatment with xanthohumol alone or with gamma-rays significantly decreased levels of anti-apoptotic proteins. Multi-drug resistance 1 (MDR1), epidermal growth factor receptor (EGFR) and signal transducer and activator of transcription 3 (STAT3) expression levels in MCF-7/ADR cells were suppressed by xanthohumol treatment. In addition, xanthohumol treatment increased death receptor (DR)-4 and DR5 expression. The xanthohumol-induced changes of these resistance-related molecules in MCF-7/ADR cells were synergistically increased by gamma-ray treatment.

CONCLUSIONS

Xanthohumol restored sensitivity of MCF-7/ADR cells to doxorubicin and radiation therapies.

GENERAL SIGNIFICANCE

Our results suggest that xanthohumol may be a potent chemo- and radio-sensitizer, and its actions are mediated through STAT3 and EGFR inhibition.

Systematic analysis of RBE and related quantities using a database of cell survival experiments with ion beam irradiation

For tumor therapy with light ions and for experimental aspects in particle radiobiology the relative biological effectiveness (RBE) is an important quantity to describe the increased effectiveness of particle radiation. By establishing and analysing a database of ion and photon cell survival data, some remarkable properties of RBE-related quantities were observed. The database consists of 855 in vitro cell survival experiments after ion and photon irradiation. The experiments comprise curves obtained in different labs, using different ion species, different irradiation modalities, the whole range of accessible energies and linear energy transfers (LETs) and various cell types. Each survival curve has been parameterized using the linear-quadratic (LQ) model. The photon parameters, α and β, appear to be slightly anti-correlated, which might point toward an underlying biological mechanism. The RBE values derived from the survival curves support the known dependence of RBE on LET, on particle species and dose. A positive correlation of RBE with the ratio α/β of the photon LQ parameters is found at low doses, which unexpectedly changes to a negative correlation at high doses. Furthermore, we investigated the course of the β coefficient of the LQ model with increasing LET, finding typically a slight initial increase and a final falloff to zero. The observed fluctuations in RBE values of comparable experiments resemble overall RBE uncertainties, which is of relevance for treatment planning. The database can also be used for extensive testing of RBE models. We thus compare simulations with the local effect model to achieve this goal.

Role of transcriptional corepressor CtBP1 in prostate cancer progression

Transcriptional repressors and corepressors play a critical role in cellular homeostasis and are frequently altered in cancer. C-terminal binding protein 1 (CtBP1), a transcriptional corepressor that regulates the expression of tumor suppressors and genes involved in cell death, is known to play a role in multiple cancers. In this study, we observed the overexpression and mislocalization of CtBP1 in metastatic prostate cancer and demonstrated the functional significance of CtBP1 in prostate cancer progression. Transient and stable knockdown of CtBP1 in prostate cancer cells inhibited their proliferation and invasion. Expression profiling studies of prostate cancer cell lines revealed that multiple tumor suppressor genes are repressed by CtBP1. Furthermore, our studies indicate a role for CtBP1 in conferring radiation resistance to prostate cancer cell lines. In vivo studies using chicken chorioallantoic membrane assay, xenograft studies, and murine metastasis models suggested a role for CtBP1 in prostate tumor growth and metastasis. Taken together, our studies demonstrated that dysregulated expression of CtBP1 plays an important role in prostate cancer progression and may serve as a viable therapeutic target.

Melanoma brain metastasis: overview of current management and emerging targeted therapies

The high rate of brain metastasis in patients with advanced melanoma has been a clinical challenge for oncologists. Despite considerable progress made in the management of advanced melanoma over the past two decades, improvement in overall survival has been elusive. This is due to the high incidence of CNS metastases, which progress relentlessly and which are only anecdotally responsive to systemic therapies. Surgery, stereotactic radiosurgery and whole-brain radiotherapy with or without cytotoxic chemotherapy remain the mainstay of treatment. However, new drugs have been developed based on our improved understanding of the molecular signaling mechanisms responsible for host immune tolerance and for melanoma growth. In 2011, the US FDA approved two agents, one antagonizing each of these processes, for the treatment of advanced melanoma. The first is ipilimumab, an anti-CTLA-4 monoclonal antibody that enhances cellular immunity and reduces tolerance to tumor-associated antigens. The second is vemurafenib, an inhibitor that blocks the abnormal signaling for melanoma cellular growth in tumors that carry the BRAF(V600E) mutation. Both drugs have anecdotal clinical activity for brain metastasis and are being evaluated in clinical trial settings. Additional clinical trials of newer agents involving these pathways are also showing promise. Therefore, targeted therapies must be incorporated into the multimodality management of melanoma brain metastasis.

A Comparison of In Vivo Cellular Responses to Cs-137 Gamma Rays And 320-kV X Rays

Research reported here relates to comparing the relative effectiveness of 320-kV X rays compared to Cs-137 gamma rays for two in vivo endpoints in C.B-17 mice after whole-body exposure: (1) cytotoxicity to bone marrow cells and splenocytes evaluated at 24-hours post exposure and (2) bone marrow and spleen reconstitution deficits (repopulation shortfalls) evaluated at 6 weeks post exposure. We show that cytotoxicity dose-response relationships for bone marrow cells and splenocytes are complex, involving negative curvature (decreasing slope as dose increases), presumably implicating a mixed cell population comprised of large numbers of hypersensitive, modestly radiosensitive, and resistant cells. The radiosensitive cells appear to respond with 50% being killed by a dose < 0.5 Gy. The X-ray relative biological effectiveness (RBE), relative to gamma rays, for destroying bone marrow cells in vivo is > 1, while for destroying splenocytes it is < 1. In contrast, dose-response relationships for reconstitution deficits in the bone marrow and spleen of C.B-17 mice at 6 weeks after radiation exposure were of the threshold type with gamma rays being more effective in causing reconstitution deficit.

Predicting outcomes in radiation oncology--multifactorial decision support systems

With the emergence of individualized medicine and the increasing amount and complexity of available medical data, a growing need exists for the development of clinical decision-support systems based on prediction models of treatment outcome. In radiation oncology, these models combine both predictive and prognostic data factors from clinical, imaging, molecular and other sources to achieve the highest accuracy to predict tumour response and follow-up event rates. In this Review, we provide an overview of the factors that are correlated with outcome-including survival, recurrence patterns and toxicity-in radiation oncology and discuss the methodology behind the development of prediction models, which is a multistage process. Even after initial development and clinical introduction, a truly useful predictive model will be continuously re-evaluated on different patient datasets from different regions to ensure its population-specific strength. In the future, validated decision-support systems will be fully integrated in the clinic, with data and knowledge being shared in a standardized, instant and global manner.

Malignant melanoma and radiotherapy: past myths, excellent local control in 146 studied lesions at Georgetown University, and improving future management

Introduction: Once thought to be radioresistant, emerging cellular and clinical evidence now suggests melanoma can respond to large radiation doses per fraction. Materials and Methods: We conducted a retrospective study of all patients treated with stereotactic radiosurgery and stereotactic body radiotherapy at Georgetown University Hospital from May 2002 through November 2008 and studied the classic extrapolated total dose corrected for volume (ETD_vol) model for predicting melanoma tumor response. Region-specific tumor outcomes were categorized by RECIST criteria and local control curves were estimated and analyzed when stratified by ETD_vol thresholds by use of the Kaplan–Meier method. Results: Follow-up information was available for 78 lesions (49 intracranial, 8 spinal, and 21 body) with mean follow-up period of 9.2 (range, 2–36) months. 1-year local control rates for intracranial, spinal, and body tumors were 84, 100, and 72%, respectively. Treatments in general were well-tolerated. Increased ETD_vol (p < 0.001) among intracranial sites resulted from larger (p < 0.001) doses per fraction combined with smaller (p < 0.001) tumor diameters. Intracranial 6-, 12-, and 24-month local control rates when treated above ETD_vol threshold of 230 Gy were all 90 vs. 89, 80, and 53% below this threshold. Body 6- and 12-month local control rates when treated above ETD_vol threshold of 100 Gy were 100 and 80% vs. 74 and 59% below this threshold. Discussion: By tailoring to melanoma’s unique radiobiology with large radiation doses per fraction, favorable local control was safely achieved. The ETD_vol model combines the important factor of dose per fraction in melanoma treatment with a volume correction factor to predict tumor response. Although limited sample size may have prevented reaching statistical significance for local control improvements using ETD_vol thresholds, optimal thresholds may exist to improve future tumor responses and further research is required.

Zoledronic acid enhances the effect of radiotherapy for bone metastases from renal cell carcinomas: more than a 24-month median follow-up

BACKGROUND

Renal cell carcinoma (RCC) is thought to respond unreliably to radiotherapy (RT). Zoledronic acid significantly reduces the risk of skeletal complications. This study investigated whether RT with zoledronic acid prolonged the time to bone-lesion progression in comparison with RT alone.

METHOD

Twenty-seven patients (34 lesions) with bone metastases secondary to RCC undergoing treatment with RT with or without zoledronic acid were retrospectively evaluated at two institutions between 1999 and 2009. Twelve patients were treated with RT alone from 1999 to 2008 (RT group). Fifteen patients were treated with RT and zoledronic acid from 2006 to 2009 (RT + Z group). The time to skeletal-related events and pain progression were assessed from patients' medical records.

RESULTS

The median (range) follow-up was 26 (3-75) and 24 (3-55) months in the RT and RT + Z groups, respectively. Three patients (three lesions) in the RT + Z group had skeletal-related events (SREs). In contrast, six patients (eight lesions) in the RT group had SREs. SREs comprised pathological fractures in five, additional surgeries in three, spinal cord or cauda equine compression in two, and repeat RT in one. There was a significant difference in SRE-free survival time and duration of site-specific pain response between groups.

CONCLUSIONS

RT combined with zoledronic acid significantly prolonged SRE-free survival and duration of pain response compared with RT alone in the treatment of osseous metastases from RCC.

Dosimetry study of [I-131] and [I-125]- meta-iodobenz guanidine in a simulating model for neuroblastoma metastasis

The physical properties of I-131 may be suboptimal for the delivery of therapeutic radiation to bone marrow metastases, which are common in the natural history of neuroblastoma. In vitro and preliminary clinical studies have implied improved efficacy of I-125 relative to I-131 in certain clinical situations, although areas of uncertainty remain regarding intratumoral dosimetry. This prompted our study using human neuroblastoma multicellular spheroids as a model of metastasis. 3D dose calculations were made using voxel-based Medical Internal Radiation Dosimetry (MIRD) and dose-point-kernel (DPK) techniques. Dose distributions for I-131 and I-125 labeled mIBG were calculated for spheroids (metastases) of various sizes from 0.01 cm to 3 cm diameter, and the relative dose delivered to the tumors was compared for the same limiting dose to the bone marrow. Based on the same data, arguments were advanced based upon the principles of tumor control probability (TCP) to emphasize the potential theoretical utility of I-125 over I-131 in specific clinical situations. I-125-mIBG can deliver a higher and more uniform dose to tumors compared to I-131 mIBG without increasing the dose to the bone marrow. Depending on the tumor size and biological half-life, the relative dose to tumors of less than 1 mm diameter can increase several-fold. TCP calculations indicate that tumor control increases with increasing administered activity, and that I-125 is more effective than I-131 for tumor diameters of 0.01 cm or less. This study suggests that I-125-mIBG is dosimetrically superior to I-131-mIBG therapy for small bone marrow metastases from neuroblastoma. It is logical to consider adding I-125-mIBG to I-131-mIBG in multi-modality therapy as these two isotopes could be complementary in terms of their cumulative dosimetry.

Radiosurgery for melanoma brain metastases in the ipilimumab era and the possibility of longer survival

OBJECT

A prospectively collected cohort of 77 patients who underwent definitive radiosurgery between 2002 and 2010 for melanoma brain metastases was retrospectively reviewed to assess the impact of ipilimumab use and other clinical variables on survival.

METHODS

The authors conducted an institutional review board-approved chart review to assess patient age at the time of brain metastasis diagnosis, sex, primary disease location, initial radiosurgery date, number of metastases treated, performance status, systemic therapy and ipilimumab history, whole-brain radiation therapy (WBRT) use, follow-up duration, and survival at the last follow-up. The Diagnosis-Specific Graded Prognostic Assessment (DSGPA) score was calculated for each patient based on performance status and the number of brain metastases treated.

RESULTS

Thirty-five percent of the patients received ipilimumab. The median survival in this group was 21.3 months, as compared with 4.9 months in patients who did not receive ipilimumab. The 2-year survival rate was 47.2% in the ipilimumab group compared with 19.7% in the nonipilimumab group. The DS-GPA score was the most significant predictor of overall survival, and ipilimumab therapy was also independently associated with an improvement in the hazard for death (p = 0.03).

CONCLUSIONS

The survival of patients with melanoma brain metastases managed with ipilimumab and definitive radiosurgery can exceed the commonly anticipated 4-6 months. Using ipilimumab in a supportive treatment paradigm of radiosurgery for brain oligometastases was associated with an increased median survival from 4.9 to 21.3 months, with a 2-year survival rate of 19.7% versus 47.2%. This association between ipilimumab and prolonged survival remains significant even after adjustment for performance status without an increased need for salvage WBRT.