A PI3K gene expression signature predicts for recurrence in early-stage non-small cell lung cancer treated with stereotactic body radiation therapy

INTRODUCTION

Increasingly, early-stage non-small cell lung cancer (NSCLC) is treated with stereotactic body radiation therapy (SBRT). Although treatment is generally effective, a small subset of tumors will recur because of radioresistance. Preclinical studies suggested PI3K-AKT-mTOR activation mediates radioresistance. This study sought to validate this finding in tumor samples from patients who underwent SBRT for NSCLC.

METHODS

Patients with T1-3N0 NSCLC treated with SBRT at our institution were included. Total RNA of formalin-fixed paraffin-embedded tumor biopsy specimens (pretherapy) was isolated and analyzed using the Clariom D assay. Risk scores from a PI3K activity signature and four published NSCLC signatures were generated and dichotomized by the median. Kaplan-Meier curves and Cox regressions were used to analyze their association with recurrence and overall survival (OS). The PI3K signature was also tested in a data set of resected NSCLC for additional validation.

RESULTS

A total of 92 patients were included, with a median follow-up of 18.3 months for living patients. There was no association of any of the four published gene expression signatures with recurrence or OS. However, high PI3K risk score was associated with higher local recurrence (hazard ratio [HR], 11.72; 95% CI, 1.40-98.0; p = .023) and worse disease-free survival (DFS) (HR, 3.98; 95% CI, 1.57-10.09; p = .0035), but not OS (p = .49), regional recurrence (p = .15), or distant recurrence (p = .85). In the resected NSCLC data set (n = 361), high PI3K risk score was associated with decreased OS (log-rank p = .013) but not DFS (p = 0.54).

CONCLUSIONS

This study validates that higher PI3K activity, measured by gene expression, is associated with local recurrence and worse DFS in early-stage NSCLC patients treated with SBRT. This may be useful in prognostication and/or tailoring treatment, and merits further validation.

Quantitation of navtemadlin in human plasma and brain tissue by liquid chromatography-tandem mass spectrometry

Navtemadlin is an orally bioavailable small molecule that blocks the protein-protein interaction between murine double minute 2 protein (MDM2) and the tumor suppressor protein p53, leading to p53-mediated cell cycle arrest and apoptosis. It is being evaluated in clinical trials for a variety of malignancies, both as a single agent and in combination regimens. A sensitive, robust LC-tandem mass spectrometry (LC-MS/MS) method was developed to quantitate navtemadlin in plasma, and this method was also validated using brain tissue homogenate. Sample preparation involved protein precipitation of plasma or brain tissue homogenate using acetonitrile. Navtemadlin, navtemadlin glucuronide, and the internal standard, D6 -navtemadlin, were separated from microsomal incubation extracts using gradient elution and a ZORBAX XDB C18 column. Analytes were detected using a SCIEX 5500 triple quadrupole mass spectrometer in positive electrospray ionization mode. The assay range of 1-1000 ng/mL was shown to be accurate (96.1-102.0% and 95.7-104%) and precise (coefficient of variation ≤ 10.6% and ≤ 6.6%) in plasma and brain tissue homogenate, respectively. An 8000 ng/mL navtemadlin sample diluted 1:10 (v/v) with plasma was also accurately quantitated. Navtemadlin has been stable in frozen plasma at -70°C for at least 20 months. This validated LC-MS/MS method was applied to determine navtemadlin concentrations in plasma and brain tissue samples from two separate patients receiving 120 mg/day navtemadlin on protocol ABTC1604.

Circulating tumor DNA predicts neoadjuvant immunotherapy efficacy and recurrence-free survival in surgical non-small cell lung cancer patients

Background

There is currently a lack of effective biomarkers to evaluate efficacy of neoadjuvant therapy (NAT) for resectable non-small cell lung cancer (NSCLC) patients. Circulating tumor DNA (ctDNA) has been investigated as a non-invasive tool for the assessment of tumor burden and minimal residual disease (MRD). The utility of ctDNA profiling in reflecting NAT efficacy, however, has not been confirmed. This study explored the association of ctDNA change with treatment response to NAT and recurrence-free survival (RFS) after surgery.

Methods

Eligible patients with stage IB–IIIA NSCLC were retrospectively included if they had received neoadjuvant immunotherapy combined with chemotherapy (IO+Chemo), dual immunotherapy (IO+IO), or chemotherapy alone (Chemo). We conducted ctDNA profiling before and after NAT, after surgery, and during follow-ups using an ultra-deep lung cancer-specific MRD (LC-MRD) sequencing panel.

Results

A total of 22 patients who received NAT followed by surgery between August 2018 and July 2019 were included in this study. The major pathological response (MPR) rates were 58.33% (7/12) in the IO+Chemo group, 25.00% (1/4) in the IO+IO group, and 16.67% (1/6) in the Chemo group. The ctDNA dynamics during NAT were highly concordant with pathologic response, demonstrating 100% sensitivity and 83.33% specificity, for an overall accuracy of 91.67%. Pre-surgery detectable ctDNA (after NAT) trended to correlate with inferior RFS [hazard ratio (HR), 7.41; 95% confidence interval (CI): 0.91–60.22, log-rank P=0.03]. At 3-8 days after surgery, ctDNA was detectable in 31.8% of patients and was an independent risk factor for recurrence (HR, 5.37; 95% CI: 1.27–22.67; log-rank P=0.01). The presence of ctDNA at 3 months after surgery showed 83% sensitivity and 90% specificity for predicting relapse (C-index, 0.79; 95% CI: 0.62–0.95). During disease monitoring after surgery, molecular recurrence by means of ctDNA preceded radiographic relapse, with a median time of 6.83 months.

Conclusions

This study investigated the potential of ctDNA in evaluating NAT efficacy in NSCLC, implying the high concordance between ctDNA and pathological response. We also set out the prognostic value of perioperative ctDNA in predicting recurrence.

Phase I Trial of Definitive Concurrent Chemoradiotherapy and Trametinib for KRAS-Mutated Non-Small Cell Lung Cancer

OBJECTIVE

This phase I trial (NCT01912625) evaluated the safety and pharmacokinetics of definitive concurrent chemoradiotherapy (cCRT) and the radiosensitizer trametinib (MEK1/2 inhibitor) for KRAS-mutated nonmetastatic non-small cell lung cancer (NSCLC).

METHODS

Patients received cCRT (carboplatin/paclitaxel and 60 Gy/30 fractions radiotherapy); oral trametinib (7 days/week) commenced on day 1 and completed on the final day of radiotherapy. Dose-finding of trametinib was done using the time-to-event continual reassessment method (TiTE-CRM); dose levels were 0.5mg (level -1), 1mg (initial, level 1), 1.5mg (level 2), and 2mg (level 3). Progression-free (PFS) and overall survival (OS) times were also recorded.

RESULTS

Fifteen patients (stage III, variety of KRAS mutations) were treated, with 1/5/4/5 at dose levels -1/1/2/3, respectively. Five patients received dose reductions (n=2, levels 2 and 3; n=1, level 1). Twelve patients completed the full cCRT course. One patient (following 12d trametinib) was taken off protocol for an unrelated/unresolved grade 1 event and later experienced grade 5 sepsis/respiratory failure. There was one grade 4 retinal detachment; grade 3 events included skin rash (n=2) and ventricular dysfunction, pneumonitis, pain, fatigue, and diarrhea (n=1 each). The final dose selected by the TiTE-CRM of trametinib was 1.5 mg. Pharmacokinetic profiles were elucidated and extensively described. At median follow-up of 70 months, median PFS was 11 months and median OS was 38 months.

CONCLUSIONS

The MTD for trametinib when combined with cCRT is 1.5 mg, with encouraging preliminary outcomes. This combination merits further study to combine with consolidation durvalumab in non-metastatic KRAS mutant NSCLC.

Utility of circulating microRNA-150 for rapid evaluation of bone marrow depletion after radiation, and efficiency of bone marrow reconstitution

PURPOSE

Total body irradiation (TBI) is a common myeloablative preparative regimen used in acute myeloid and lymphoblastic leukemia patients prior to allogenic hematopoietic stem cell transplantation (HSCT). The inefficient clearance of tumor cells and radiation-induced toxicity to normal tissues is attributed to relapse and morbidity in a significant fraction of patients. Developing biomarkers that provide an individual's physiological response to radiation will allow personalized treatment and follow-up. We investigated the utility of circulating microRNA150-5p (miR150) for evaluation of radiation dose response.

MATERIALS AND METHODS

Age-, gender-, and strain-matched wild type and miR150 null (knock out, KO) mice were subjected to TBI and evaluated for the impact of circulating miR150 expression on survival and hematological endpoints. Dose- and time-dependent changes of the miR150 level in bone marrow were assessed using flow cytometry. The functional roles of miR150 in cellular response to radiation were evaluated using apoptosis assay. miR150 expression in leukemic cell lines and in blood collected from leukemia patients with diverse outcomes were evaluated by quantitative RT-PCR.

RESULTS

Absence of miR150 in mice conferred resistance to radiation injury and resulted in accelerated recovery of lymphoid and myeloid cells after ablative or partially ablative TBI in mice. Overexpression of miR150 resulted in a higher percentage of cells at G2/M phases of cell cycle which is associated with increased sensitivity and susceptibility to apoptotic cell death after radiation. Levels of circulating miR150 were found to be decreased after radiation in leukemia patients and exhibited an inverse correlation with recurrence.

CONCLUSION

Current study demonstrates the utility of a miR150-based blood test for rapid evaluation of the efficiency of marrow ablation and recovery following radiation and HSCT. The internally controlled blood test will potentially provide near real-time evaluation of functional marrow that will allow optimal dosing based on an individual's physiological response to radiation.

Two-miRNA-based finger-stick assay for estimation of absorbed ionizing radiation dose

Nuclear radiation and radioactive fallouts resulting from a nuclear weapon detonation or reactor accidents could result in injuries affecting multiple sensitive organs, defined as acute radiation syndrome (ARS). Rapid and early estimation of injuries to sensitive organs using markers of radiation response is critical for identifying individuals who could potentially exhibit ARS; however, there are currently no biodosimetry assays approved for human use. We developed a sensitive microRNA (miRNA)-based blood test for radiation dose reconstruction with ±0.5 Gy resolution at critical dose range. Radiation dose-dependent changes in miR-150-5p in blood were internally normalized by a miRNA, miR-23a-3p, that was nonresponsive to radiation. miR-23a-3p was not highly expressed in blood cells but was abundant in circulation and was released primarily from the lung. Our assay showed the capability for dose estimation within hours to 1 week after exposure using a drop of blood from mice. We tested this biodosimetry assay for estimation of absorbed ionizing radiation dose in mice of varying ages and after exposure to both improvised nuclear device (IND)-spectrum neutrons and gamma rays. Leukemia specimens from patients exposed to fractionated radiation showed depletion of miR-150-5p in blood. We bridged the exposure of these patients to fractionated radiation by comparing responses after fractionated versus single acute exposure in mice. Although validation in nonhuman primates is needed, this proof-of-concept study suggests the potential utility of this assay in radiation disaster management and clinical applications.

Let-7b-3p inhibits tumor growth and metastasis by targeting the BRF2-mediated MAPK/ERK pathway in human lung adenocarcinoma

Background

Lung cancer is a malignant tumor with the highest morbidity and mortality rates worldwide, of which lung adenocarcinoma (LUAD) is the most common subtype. Overall, current treatments of LUAD are not satisfactory; therefore, novel targets need to be explored. Let-7b-3p is an important member of the let-7 family of microRNAs (miRNAs), and has not been studied separately in LUAD. This study aimed to investigate the role and molecular mechanism of let-7b-3p in LUAD.

Methods

Herein, let-7b-3p expression was detected by quantitative real-time polymerase chain reaction (qRT-PCR) and fluorescence in situ hybridization (FISH) assays. MTT, colony formation assay, flow cytometry analysis, wound-healing, Transwell and in vivo experiments were conducted to assess let-7b-3p’s function in LUAD. The downstream target TFIIB-related factor 2 (BRF2) was predicted using bioinformatics analyses and confirmed by dual-luciferase reporter assay and rescue experiments. Additionally, BRF2 was found to affect the MAPK/ERK pathway through transcriptome sequencing analysis and western blot (WB) assay.

Results

Let-7b-3p is downregulated in LUAD cells and tissue samples and low let-7b-3p expression is correlated with a poor prognosis in LUAD patients. Let-7b-3p suppresses the proliferation and metastasis of LUAD cells both in vivo and in vitro by directly targeting the BRF2-mediated MAPK/ERK pathway.

Conclusions

Let-7b-3p inhibits the development of LUAD and is an ideal novel therapeutic target for the treatment of LUAD.

Prediction of neoadjuvant chemotherapy response in high-grade osteosarcoma: added value of non-tumorous bone radiomics using CT images

Background

This study aimed to determine the impact of including radiomics analysis of non-tumorous bone region of interest in improving the performance of pathological response prediction to chemotherapy in high-grade osteosarcomas (HOS), compared to radiomics analysis of tumor region alone.

Methods

This retrospective study included 157 patients diagnosed with HOS between November 2013 and November 2017 (age range, 5-44 years; mean age, 16.99 ±7.42 years), in which 69 and 88 patients were diagnosed as pathological good response (pGR) and non-pGR, respectively. Radiomics features were extracted from tumor and non-tumorous bone regions based on diagnostic CT images. Pathological response classifiers were developed and validated via leave-one-out cross validation (LOOCV) and independent validation methods by using the area under the receiver operating characteristic curve (AUC) value as the figure of merit.

Results

Using the LOOCV, the classifiers combining features from tumor and non-tumorous regions showed better prediction performance than those from tumor region alone (AUC, 0.8207±0.0043 vs. 0.7799±0.0044). The combined classifier also showed better performance than the tumor feature-based classifier in both training and validation datasets [training dataset: 0.791, 95% confidence interval (CI), 0.706-0.860 vs. 0.766, 95% CI, 0.679-0.840; validation dataset: 0.816, 95% CI, 0.662-0.920 vs. 0.766, 95% CI, 0.606-0.885].

Conclusions

Radiomics analysis of combined tumor and non-tumorous bone features showed improved performance of pathological response prediction to chemotherapy in HOS compared to that of tumor features alone. Moreover, the proposed classifier had the potential to predict pathological response to chemotherapy for HOS patients.

Association of Pre- and Posttreatment Neutrophil-Lymphocyte Ratio With Recurrence and Mortality in Locally Advanced Non-Small Cell Lung Cancer

Objectives

Neutrophil–lymphocyte ratio (NLR) has been associated with mortality in non-small cell lung cancer (NSCLC), but its association with recurrence in locally advanced NSCLC (LA-NSCLC), specifically, is less established. We hypothesized pre- and posttreatment NLR would be associated with recurrence and mortality.

Methods

We studied the association of pretreatment NLR (pre-NLR) and posttreatment NLR at 1 (post-NLR₁) and 3 months (post-NLR₃) with outcomes in patients with LA-NSCLC treated with chemoradiation. Pre-NLR was dichotomized by 5, an a priori cutoff previously shown to be prognostic in LA-NSCLC. Post-NLR₁ and post-NLR₃ were dichotomized by their medians.

Results

We identified 135 patients treated with chemoradiation for LA-NSCLC between 2007 and 2016. Median follow-up for living patients was 61.1 months. On multivariable analysis, pre-NLR ≥ 5 was associated with worse overall survival (HR = 1.82; 95% CI 1.15 – 2.88; p = 0.011), but not with any recurrence, locoregional recurrence, or distant recurrence. Post-NLR₁ ≥ 6.3 was not associated with recurrence or survival. Post-NLR₃ ≥ 6.6 was associated with worse overall survival (HR = 3.27; 95% CI 2.01– 5.31; p < 0.001), any recurrence (HR = 2.50; 95% CI 1.53 – 4.08; p < 0.001), locoregional recurrence (HR = 2.50; 95% CI 1.40 – 4.46; p = 0.002), and distant recurrence (HR = 2.53; 95% CI 1.49 – 4.30; p < 0.001).

Conclusion

Pretreatment NLR is associated with worse overall survival and posttreatment NLR is associated with worse survival and recurrence. These findings should be validated independently and prospectively studied.

Recurrence After Stereotactic Body Radiation Therapy Versus Lobectomy for Non-Small Cell Lung Cancer

BACKGROUND

Although lobectomy remains the standard of care for early-stage non-small cell lung cancer, several studies suggest equipoise between lobectomy and stereotactic body radiation therapy (SBRT). However randomized evidence is lacking. We compared outcomes of early-stage non-small cell lung cancer patients treated with lobectomy or SBRT.

METHODS

We included clinical T1-2N0 non-small cell lung cancer treated with lobectomy or SBRT to a biologically effective dose of ≥100 Gy₁₀. We used Cox proportional hazards and nearest-neighbor propensity score (2:1) matching to adjust for confounders. Kaplan-Meier curves were used to assess survival and recurrence.

RESULTS

We identified 554 patients treated with lobectomy (n = 389) or SBRT (n = 165) at our institution between 2008 and 2018. After propensity score matching, there were 132 SBRT patients and 85 lobectomy patients. SBRT was associated with increased local recurrence (hazard ratio [HR], 6.80; 95% confidence interval [CI], 1.92-24.10; P = .003) and regional nodal recurrence (HR, 2.58; 95% CI, 1.17-5.68; P = .018), and with worse overall survival (HR, 2.00; 95% CI, 1.21-3.32; P = .007) and progression-free survival (HR, 2.34; 95% CI, 1.50-3.67; P < .001). There was no difference in distant recurrence (HR, 1.19; 95% CI, 0.57-2.52; P = .64).

CONCLUSIONS

We found superior outcomes in patients with early-stage non-small cell lung cancer treated with lobectomy compared with SBRT, including locoregional control. These findings should be interpreted with caution because of selection bias but underscore the importance of robust randomized prospective data to clarify the relative efficacy of these modalities.

Pre-treatment neutrophil-lymphocyte ratio is associated with overall mortality in localized non-small cell lung cancer treated with stereotactic body radiotherapy

BACKGROUND

Neutrophil-lymphocyte ratio (NLR) has been associated with mortality in several disease sites. We hypothesized that NLR is associated with inferior outcomes in localized non-small cell lung cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT).

METHODS

We evaluated the association of pre-treatment NLR, obtained within 6 months of starting SBRT, with overall survival, as well as primary tumor, regional, and distant recurrence. Multivariate Cox regression was then used to assess pre-treatment NLR as a predictor of mortality. We validated our findings in an independent cohort of patients treated at two other institutions. In a secondary analysis, we also evaluated the association of post-treatment NLR with mortality in the training cohort.

RESULTS

A total of 156 patients and 166 tumors were included in the training cohort with a median follow-up of 13.4 months. After dichotomization by median, NLR > 3.6 was associated with mortality on univariate (p = 0.010) and multivariate analysis (p = 0.023). In the validation cohort, NLR > 3.6 was similarly associated with mortality on univariate (p = 0.031) and multivariate (p = 0.007) analysis. In a secondary analysis in the training cohort, we found post-treatment NLR was significantly increased compared to pre-treatment NLR (p < 0.001) and associated with mortality on univariate analysis (p = 0.005) and multivariate analysis (p = 0.010).

CONCLUSIONS

Pre-treatment NLR > 3.6 is associated with mortality in patients treated with SBRT. This finding was validated in an independent cohort of patients treated at two other institutions. Additionally, post-treatment NLR was significantly increased from pre-treatment and associated with overall survival.

Identifying patterns of care for elderly patients with non-surgically treated stage III non-small cell lung cancer: an analysis of the national cancer database

Background

To compare patterns of care for elderly patients versus non-elderly patients with non-surgically treated stage III non-small cell lung cancer (NSCLC) using the National Cancer Database (NCDB). We hypothesize that elderly patients are less likely to receive curative treatments, including concurrent chemoradiation (CCRT), compared to non-elderly patients.

Methods

We identified patients from the NCDB between 2003 and 2014 with non-surgically treated stage III NSCLC. We defined elderly as ≥70 years old and non-elderly <70 years old. Treatment categories included: no treatment, palliative treatment (chemotherapy alone, radiation (RT) alone <59.4 Gy or chemoradiation (CRT) <59.4 Gy), or definitive treatment (RT alone ≥59.4 Gy or CRT ≥59.4 Gy). Differences in treatment between elderly and non-elderly were tested using the χ² test.

Results

We identified 57,602 elderly and 55,928 non-elderly patients. More elderly patients received no treatment (24.5% vs. 13.2%, P < 0.0001) and the elderly were less likely to receive definitive treatment (48.5% vs. 56.3%, P < 0.0001). CCRT was delivered in a significantly smaller proportion of elderly vs. non-elderly patients (66.0% vs. 78.9%, P < 0.0001 in patients treated with definitive intent; 32.0% vs. 44.5%, P < 0.0001 in patients receiving any treatment; and 24.2% vs. 38.6%, P < 0.0001 amongst all patients).

Conclusions

In this large study of patients with non-surgically treated stage III NSCLC, elderly patients were less likely to receive any treatment or treatment with definitive intent compared to the non-elderly. The lack of use of concurrent or sequential chemotherapy in the elderly with stage III NSCLC suggests that the optimal treatment approach for this vulnerable population remains undefined.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1142-7) contains supplementary material, which is available to authorized users.

Stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC): contemporary insights and advances

The standard-of-care treatment for early-stage non-small cell lung cancer (NSCLC) continues to be surgery in the form of lobectomy or pneumonectomy. Stereotactic body radiation therapy (SBRT) has evolved as a viable alternative to surgery for medically inoperable patients, achieving excellent local control (LC) with relatively minimal toxicity in standard-risk patients. Nevertheless, the maturation of SBRT has fostered debate regarding its use, technique, dose, and fractionation, particularly in the context of patient- and disease-specific characteristics such as tumor size and location. This review will cover the recent trends and future directions of SBRT as it becomes an increasingly individualized modality in the treatment of early-stage NSCLC.

The Addition of Chemotherapy to Radiation Therapy Improves Survival in Elderly Patients with Stage III Non-Small Cell Lung Cancer

INTRODUCTION

Elderly patients account for the majority of lung cancer diagnoses but are poorly represented in clinical trials. We evaluated the overall survival (OS) of elderly patients with stage III NSCLC treated with definitive radiation compared with that of patients treated with definitive chemoradiation.

METHODS

We conducted a comparative effectiveness study of radiation therapy versus chemoradiation in elderly (≥70 years old) patients with stage III NSCLC not treated surgically diagnosed from 2003 to 2014; the patients were identified by using the National Cancer Database. Two cohorts were evaluated: patients (n = 5023) treated with definitive radiation (≥59.4 Gy) and patients (n = 18,206) treated with definitive chemoradiation. Chemoradiation was further defined as concurrent (radiation and chemotherapy started within 30 days of each other) or sequential (radiation started >30 days after chemotherapy). We compared OS between the treatment groups by using the Kaplan-Meier method and Cox proportional hazards regression before and after propensity score matching (PSM).

RESULTS

Treatment with chemoradiation was associated with improved OS versus that with radiation both before PSM (hazard ratio [HR] = 0.66, 95% confidence interval [CI]: 0.64-0.68, p < 0.001) and after PSM (HR = 0.67, 95% CI: 0.64-0.70, p < 0.001). Relative to concurrent chemoradiation, sequential chemoradiation was associated with a 9% reduction in the risk for death (HR = 0.91, 95% CI: 0.85-0.96, p = 0.002).

CONCLUSIONS

We found that definitive chemoradiation resulted in a survival advantage compared with definitive radiation in elderly patients. Sequential chemotherapy and radiation was superior to concurrent chemoradiation. Although prospective trials are needed, this analysis suggests that chemoradiation should be strongly considered for elderly patients and the optimal sequencing of chemotherapy and radiation remains an unanswered question for this patient population.

Blood-based biomarkers in lung cancer: prognosis and treatment decisions

Despite recent advances, non-small cell lung cancer (NSCLC) remains a devastating disease with overall poor prognosis. Major contributing factors include obstacles to diagnosing the disease early in its course during the asymptomatic stage as well as diversity and complexity of its biology underlying tumorigenesis and tumor progression. Advances in molecularly targeted therapies which drives the development of personalized cancer care require precise and comprehensive understanding of tumor biology, not only at the time of diagnosis but also during treatment course and surveillance. As lung tumor tissue can be difficult to obtain without invasive and potentially risky procedures, it is difficult to monitor treatment response with serial tissue biopsies. Development of non-invasive but reliable blood based tumor markers has become an important research area. In this review, we focus on the following circulating biomarkers that have been identified in recent years: circulating tumor cells (CTCs); circulating cell-free nucleic acids, such as circulating tumor DNA (ctDNA) and microRNA (miR); and other biomarkers such as genomic and proteomic features. These biomarkers not only have prognostic values, but also can help guild treatment decisions by monitoring tumor burden, detecting minimal residual disease and/or recurrent disease, as well as monitoring evolution of genetic alterations throughout the treatment course.

Radiation Dose to the Thoracic Vertebral Bodies Is Associated With Acute Hematologic Toxicities in Patients Receiving Concurrent Chemoradiation for Lung Cancer: Results of a Single-Center Retrospective Analysis

PURPOSE

To test the hypothesis that increasing radiation therapy (RT) dose to the thoracic vertebral bodies (TVBs) contributes to the development of hematologic toxicities (HTs) in patients with lung cancer.

METHODS AND MATERIALS

Cases of non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) treated with definitive chemoradiation with concurrent platinum-based doublet chemotherapy at our institution from 2007 to 2016 were identified. Mean TVB dose and the volume of TVBs receiving at least 5 to 60 Gy (V₅-V₆₀) were retrospectively recorded. Logistic regression was used to test associations between grade ≥3 HT (HT3+) and dosimetric/clinical parameters. Normal tissue complication probability was evaluated using the Lyman-Kutcher-Burman (LKB) model for HT3+, and receiver operating characteristics analysis was used to determine dosimetric cut-points.

RESULTS

We identified 201 patients, the majority having NSCLC (n=162, 81%) and stage III to IV disease (n=179, 89%). All patients received either cisplatin/etoposide (n=107, 53%) or carboplatin/paclitaxel (n=94, 47%). Median RT dose was 60 Gy (range, 60-70 Gy). The rate of HT3+ was 49% (n=99). Increasing mean TVB dose (per Gy) was associated with higher odds of developing HT3+ (odds ratio 1.041, 95% confidence interval 1.004-1.080, P=.032), as were increasing TVB V₅ to V₂₀. These dosimetric correlates to HT3+ persisted on multivariate analysis. Constrained optimization of the LKB model for HT3+ yielded the parameters: n=1, m=1.79, and TD₅₀=21.4 Gy. Optimal cut-points identified were V₅=65%, V₁₀=60%, V₂₀=50%, and mean dose=23.5 Gy. Patients with values above these cut-points had an approximately 2-fold increased risk of HT3+.

CONCLUSIONS

We found that mean TVB dose and low-dose parameters (V₅-V₂₀) were associated with HT3+ in chemoradiation for lung cancer. Per the LKB model, bone marrow behaves like a parallel organ (n=1), implying that mean TVB dose is a useful predictor for toxicity. These data suggest that efforts to spare dose to the TVBs may reduce rates of severe HT.

Urinary miRNAs as Biomarkers for Noninvasive Evaluation of Radiation-Induced Renal Tubular Injury

Radiation nephropathy is one of the common late effects in cancer survivors who received radiotherapy as well as in victims of radiation accidents. The clinical manifestations of radiation nephropathy occur months after exposure. To date, there are no known early biomarkers to predict the future development of radiation nephropathy. This study focuses on the development of urinary biomarkers providing readout of acute responses in renal tubular epithelial cells. An amplification-free hybridization-based nCounter assay was used to detect changes in mouse urinary miRNAs after irradiation. After a single LD₅₀ of total-body irradiation (TBI) or clinically relevant fractionated doses (2 Gy twice daily for 3 days), changes in urinary levels of microRNAs followed either an early pattern, peaking at 6-8 h postirradiation and gradually declining, or later pattern, peaking from 24 h to 7 days. Of 600 miRNAs compared, 12 urinary miRNAs showed the acute response and seven showed the late response, common to both irradiation protocols. miR-1224 and miR-21 were of particular interest, since they were the most robust acute and late responders, respectively. The early responding miR-1224 also exhibited good dose response after 2, 4, 6 and 8 Gy TBI, indicating its potential use as a biomarker for radiation exposure. In situ hybridization of irradiated mouse kidney sections and cultured mouse primary renal tubular cells confirmed the tubular origin of miR-1224. A significant upregulation in hsa-miR-1224-3p expression was also observed in human proximal renal tubular cells after irradiation. Consistent with mouse urine data, a similar expression pattern of hsa-miR-1224-3p and hsa-miR-21 were observed in urine samples collected from human leukemia patients preconditioned with TBI. This proof-of-concept study shows the potential translational utility of urinary miRNA biomarkers for radiation damage in renal tubules with possible prediction of late effects.

Extranodal NK/T Cell Lymphoma, Nasal Type (ENKTL-NT): An Update on Epidemiology, Clinical Presentation, and Natural History in North American and European Cases

PURPOSE OF REVIEW

Extranodal NK/T cell lymphoma, nasal type (ENKTL-NT) is an aggressive extranodal non-Hodgkin lymphoma most commonly occurring in East Asia and Latin America but with increasing incidence in the United States. Data on epidemiology, disease presentation, and outcome for European and North American ("Western") cases are very limited. We review published landmark clinical studies on ENKTL-NT in the West and report in detail recent data, including our institutional experience.

RECENT FINDINGS

We highlight key observations in its epidemiology, natural history, and trends in clinical management. In the USA, ENKTL-NT is more common among Asian Pacific Islanders (API) and Hispanics compared to non-Hispanic whites. Published studies indicate less heterogeneity in clinical presentation in Western ENKTL-NT compared to Asian patients. While there is variation in age at diagnosis, presence of antecedent lymphoproliferative disorders, and outcomes among racial/ethnic groups, the universal association of ENKTL-NT with EBV and the poor response of this neoplasm to anthracycline-based therapy is consistent across all geographic areas. Data on epidemiology, disease presentation, and clinical outcomes in mature T cell and NK cell (T/NK cell) neoplasms, including ENKTL-NT, in Europe and North America are very limited. As the classification and diagnostic characterization of the currently recognized T/NK cell lymphoma disease entities continue to evolve, gaps and inconsistencies in data reporting across different studies are being recognized. Despite these limitations, several studies from the USA suggest that the incidence of ENKTL-NT is higher in Asian Pacific Islanders (API) and non-white Hispanics and that outcomes may be worse in non-whites. However, the universal association of ENKTL-NT with Epstein-Barr virus (EBV) across all ethnic groups suggests a common pathogenesis. Given the overlap between the entities included in the category of T/NK cell neoplasms, there is a need to further define biological and clinical differences that may affect diagnosis, treatment, and outcome.

Prognostic Value of Primary Tumor Volume Changes on kV-CBCT during Definitive Chemoradiotherapy for Stage III Non-Small Cell Lung Cancer

INTRODUCTION

Kilovoltge cone beam computed tomography (kV-CBCT) allows for tumor localization and response assessment during definitive chemoradiotherapy for locally advanced NSCLC. We hypothesize that significant tumor volume loss occurs early during radiotherapy and that the extent of volume loss correlates with clinical outcomes.

METHODS

A total of 52 patients with locally advanced NSCLC treated with definitive chemoradiotherapy were reviewed. kV-CBCT images were used to contour primary gross tumor volumes at four time points during treatment. Patients were dichotomized according to absolute and relative volume changes at each time point. Statistical analyses were performed to evaluate correlations between volume changes and clinical outcomes.

RESULTS

The median gross tumor volumes were 77.1, 48.3, 42.5, and 29.9 cm³ for fractions 1, 11, 21, and final, respectively. Greater relative volume loss between fractions 1 and 21 correlated with improved distant control (hazard ratio [HR] = 0.35, 95% confidence interval [CI]: 0.13-0.94, p = 0.038) and overall survival (HR = 0.40, 95% CI: 0.16-0.98, p = 0.046). Greater relative volume loss between fractions 11 and 21 correlated with improved progression-free survival (HR = 0.39, 95% CI: 0.17-0.88, p = 0.02) and trended toward improved overall survival (HR = 0.43, 95% CI: 0.17-1.06, p = 0.07). On multivariate analysis, greater relative volume loss between fractions 11 and 21 correlated with improved progression-free survival (HR = 0.39, 95% CI: 0.16-0.97, p = 0.041) and overall survival (HR = 0.31, 95% CI: 0.11-0.88, p = 0.027).

CONCLUSIONS

Significant primary tumor volume loss occurs early during radiotherapy for locally advanced NSCLC. Greater relative tumor volume loss during treatment correlates with improved disease control and overall survival. Thus, kV-CBCT has potential to be used as a practical prognostic imaging marker.

Patterns of major wound complications following multidisciplinary therapy for lower extremity soft tissue sarcoma

BACKGROUND AND OBJECTIVES

The purpose of this study was to determine the pattern and timing of major wound complications (MWCs) in patients at our institution who received multimodality treatment for lower extremity soft tissue sarcoma (LE-STS) and to evaluate the impact of MWCs on tumor control and patient outcomes.

METHODS

The medical records of 102 LE-STS patients treated with limb-sparing surgery and radiation therapy were reviewed. MWCs were defined as secondary operations with anesthesia, seroma/hematoma aspiration, admission for IV antibiotics, or persistent deep packing.

RESULTS

MWCs occurred in 22% of patients, with 45% of events occurring >120 days after resection. On multivariate analysis, preoperative external beam radiation therapy (EBRT) (OR 4.29, 95% CI 1.06-17.40, P = 0.042) and skin graft placement (OR 6.39, 95% CI 1.37-29.84, P = 0.018) were found to be independent predictors of MWCs. MWC occurrence did not predict for chronic toxicity and did not impact tumor control or survival.

CONCLUSIONS

A considerable proportion of MWCs occur >120 days from surgical resection with preoperative EBRT and skin graft placement independent predictors for MWCs. While an additional source of morbidity, MWC occurrence did not impact tumor control, nor did it predict for chronic toxicity. J. Surg. Oncol. 2016;114:385-391. © 2016 Wiley Periodicals, Inc.

Inter-Fraction Tumor Volume Response during Lung Stereotactic Body Radiation Therapy Correlated to Patient Variables

Purpose

Analyze inter-fraction volumetric changes of lung tumors treated with stereotactic body radiation therapy (SBRT) and determine if the volume changes during treatment can be predicted and thus considered in treatment planning.

Methods and Materials

Kilo-voltage cone-beam CT (kV-CBCT) images obtained immediately prior to each fraction were used to monitor inter-fraction volumetric changes of 15 consecutive patients (18 lung nodules) treated with lung SBRT at our institution (45–54 Gy in 3–5 fractions) in the year of 2011–2012. Spearman's (ρ) correlation and Spearman's partial correlation analysis was performed with respect to patient/tumor and treatment characteristics. Multiple hypothesis correction was performed using False Discovery Rate (FDR) and q-values were reported.

Results

All tumors studied experienced volume change during treatment. Tumor increased in volume by an average of 15% and regressed by an average of 11%. The overall volume increase during treatment is contained within the planning target volume (PTV) for all tumors. Larger tumors increased in volume more than smaller tumors during treatment (q = 0.0029). The volume increase on CBCT was correlated to the treatment planning gross target volume (GTV) as well as internal target volumes (ITV) (q = 0.0085 and q = 0.0039 respectively) and could be predicted for tumors with a GTV less than 22 mL. The volume increase was correlated to the integral dose (ID) in the ITV at every fraction (q = 0.0049). The peak inter-fraction volume occurred at an earlier fraction in younger patients (q = 0.0122).

Conclusions

We introduced a new analysis method to follow inter-fraction tumor volume changes and determined that the observed changes during lung SBRT treatment are correlated to the initial tumor volume, integral dose (ID), and patient age. Furthermore, the volume increase during treatment of tumors less than 22mL can be predicted during treatment planning. The volume increase remained significantly less than the overall PTV expansion, and radiation re-planning was therefore not required for the purpose of tumor control. The presence of the studied correlations suggests that the observed volumetric changes may reflect some underlying biologic process rather than random fluctuations.

Imaging across the life span: innovations in imaging and therapy for gynecologic cancer

The focus of this article is radiation therapy for gynecologic cancers, with emphasis on imaging-based treatment planning and delivery. For the various gynecologic cancers, radiation oncologists rely on essential clinical information to triage treatment options, and various imaging studies are performed for treatment planning and radiation therapy delivery. A practical approach is provided to help radiologists tailor their reports for the needs of their radiation oncology and gynecologic oncology colleagues, to optimize multidisciplinary care for patients with gynecologic cancer. Template radiology reports are proposed to address the specific information needs of oncologists at each phase-before, during, and after treatment. Fueled by the rapid progress in engineering and computer sciences during the past 2 decades, remarkable advances have been made in anatomic, functional, and molecular imaging and in radiation treatment planning and delivery in patients with gynecologic cancer. Radiation therapy has evolved from a nontargeted approach to a precisely targeted, highly conformal treatment modality, to further improve treatment outcomes and reduce morbidity. High-quality imaging has become essential for staging of the disease, delineation of tumor extent for treatment planning and delivery, and monitoring therapy response. Anatomic and functional imaging has also been shown to provide prognostic information that allows clinicians to tailor therapy on the basis of personalized patient information. This field is an area of active research, and future clinical trials are warranted to validate preliminary results in the field.

Primary Cutaneous B-Cell Lymphoma: Management and Patterns of Recurrence at the Multimodality Cutaneous Lymphoma Clinic of The Ohio State University

BACKGROUND

The increasing incidence of primary cutaneous B-cell lymphomas (PCBCLs) presents new challenges for clinicians. Despite advances in the clinical and pathologic characterization of PCBCL, the significance of the current staging approach as a risk profiling tool and the effect of various treatments on outcome remain unclear.

MATERIALS AND METHODS

We retrospectively reviewed patients who presented with a diagnosis of PCBCL seen at The Ohio State University between 1998 and 2012. We reviewed the initial presentation and treatment modality. We then assessed whether the treatment modality (conservative skin-directed vs. definitive radiation with or without systemic therapy), stage (T1 or ≥T2), or histologic subtype (primary cutaneous follicle center lymphoma [PCFCL] vs. primary cutaneous marginal zone B-cell lymphoma [PCMZL]) affected the risk of recurrence.

RESULTS

We identified 67 patients referred with an initial diagnosis of PCBCL. After imaging, 12 did not meet the criteria for PCBCL and were classified as having systemic B-cell lymphoma with cutaneous involvement. The remaining 55 patients included 25 with PCMZL, 24 with PCFCL, 2 with primary cutaneous large B-cell lymphoma leg type, and 4 with unclassifiable disease. According to the International Society of Cutaneous Lymphoma-European Organization for Research and Treatment of Cancer staging, 30 cases were T1 (55%), 14 T2 (25%), and 11 T3 (20%). Comparing the time to first recurrence (TFR) by indolent PCBCL subtypes, we found no difference in the recurrence risk for either stage (T1, p = .51 vs. T2/T3, p = .30). Comparing TFR by treatment modality, we found no difference in TFR within T1 patients (p = .34) or T2/T3 patients (p = .44).

CONCLUSION

Our limited analysis highlights the importance of complete staging at diagnosis and suggests that the treatment modality does not affect the risk of recurrence in T1 indolent PCBCL.

Minimal Inter-Fractional Fiducial Migration during Image-Guided Lung Stereotactic Body Radiotherapy Using SuperLock Nitinol Coil Fiducial Markers

Objectives

Stereotactic body radiotherapy (SBRT) is being increasingly used for the treatment of patients with lung cancer or lung metastasis who are medically unfit to undergo resection. In order to improve accuracy and confidence in targeting tumors, many centers rely on fiducial implantation. We evaluated the migration of a novel fiducial marker specifically designed for lung tissue implanted via electromagnetic navigation bronchoscopy (ENB).

Methods

We retrospectively quantified the individual and group migrations of SuperLock nitinol coil fiducials for 15 patients receiving lung stereotactic body radiotherapy (SBRT), in order to evaluate the reliability of using these fiducials as a target surrogate for cases where tumors cannot be clearly delineated on cone beam CTs (CBCTs). For each fraction, we compared the individual and group migrations of the fiducials between the planning CT and the acquired CBCT. The group migration was defined as the distance between the centroids of the fiducial group and GTV.

Results

A total of 16 lung targets were included in our study for these 15 patients (one patient with two targets). Of 55 fiducials placed, we observed a 100% retention rate. The mean individual migration was 1.87 mm (range, 0.63–5.25 mm) with a standard deviation of 1.26 mm. The mean group migration was 1.94 mm (range, 0.03–6.19 mm) with a standard deviation of 1.45 mm. Overall, there was minimal change in the relative locations of the markers with respect to each other, as well as to the target.

Conclusions

We found that the SuperLock nitinol coil fiducial marker positions are stable throughout the radiation treatment, and can be used as a reliable surrogate to target, and to avoid geometric misses during gated treatments.

Treating cutaneous T-cell lymphoma with highly irregular surfaces with photon irradiation using rice as tissue compensator

PURPOSE

Cutaneous T-cell lymphoma (CTCL) is known to have an excellent response to radiotherapy, an important treatment modality for this disease. In patients with extremity and digit involvement, the irregular surface and depth variations create difficulty in delivering a homogenous dose using electrons. We sought to evaluate photon irradiation with rice packing as tissue equivalence and determine clinical tolerance and response.

MATERIALS AND METHODS

Three consecutive CTCL patients with extensive lower extremity involvement including the digits were treated using external beam photon therapy with rice packing for tissue compensation. The entire foot was treated to 30-40 Gy in 2-3 Gy per fraction using 6 MV photons prescribed to the mid-plane of an indexed box filled with rice in which the foot was placed. Treatment tolerance and response were monitored with clinical evaluation.

RESULTS

All patients tolerated the treatment without treatment breaks. Toxicities included grade 3 erythema and desquamation with resolution within 4 weeks. No late toxicities were observed. All patients had a partial response by 4 weeks after therapy with two patients achieving a complete response. Patients reported improved functionality after treatment. No local recurrence has been observed.

CONCLUSION

Tissue compensation with rice packing offers a convenient, inexpensive, and reproducible method for the treatment of CTCL with highly irregular surfaces.

Downregulation of peroxiredoxin-1 by β-elemene enhances the radiosensitivity of lung adenocarcinoma xenografts

β-elemene, the active component of elemene (1-methyl-1-vinyl-2,4-diisopropenyl-cyclohexane), is a naturally occurring compound isolated from the traditional Chinese medicinal herb Curcuma wenyujin. Studies have confirmed that β-elemene enhances the radiosensitivity of lung cancer cell lines such as A549, by multiple pathways; however, their underlying mechanisms and pathways are yet to be elucidated. In the present study, two-dimensional differential in-gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry were used to profile the different proteins in A549 cell xenograft models of both treatment groups. The protein/mRNA expression was assessed by reverse transcription-polymerase chain reaction and western blotting techniques in tumor samples from all treatment groups. As a critical player in redox regulation of cancer cells, inhibition of peroxiredoxin-1 (Prx-1) may be an effective option for enhancing the tumor response to radiation. We further verified Prx-1 expression at the transcription and translation levels. β-elemene at a dose of 45 mg/kg had little effect on the Prx-1 protein expression, which was correlated with a moderate antitumor effect. However, a 45 mg/kg dose of β-elemene significantly inhibited the Prx-1 mRNA expression, thereby suggesting a possible influence on the transcriptional process, and radiation significantly increased the Prx-1 mRNA/protein expression compared to the control group (p<0.01). Notably, Prx-1 mRNA/protein expression was significantly lower in the β-elemene/radiation co-treatment group compared to the baseline levels in the control group (p<0.01). These results suggest that radiation-induced Prx-1 expression is directly or indirectly suppressed by β-elemene, thus suggesting a new pathway by which to reverse radioresistance.

The role of modern radiation therapy in the management of extremity sarcomas

For nearly half a decade, surgery and radiation therapy have been used in combination to achieve the goal of limb preservation in extremity soft tissue sarcoma, with success rates in excess of 90%. Common decision points in therapeutic radiation delivery for sarcoma are discussed, including preoperative versus postoperative irradiation, the postoperative boost, and when irradiation might be unnecessary. We describe specialized techniques, such as brachytherapy and intraoperative irradiation. The data driving current practice is summarized.

Combining targeted agents with modern radiotherapy in soft tissue sarcomas

Improved understanding of soft-tissue sarcoma (STS) biology has led to better distinction and subtyping of these diseases with the hope of exploiting the molecular characteristics of each subtype to develop appropriately targeted treatment regimens. In the care of patients with extremity STS, adjunctive radiation therapy (RT) is used to facilitate limb and function, preserving surgeries while maintaining five-year local control above 85%. In contrast, for STS originating from nonextremity anatomical sites, the rate of local recurrence is much higher (five-year local control is approximately 50%) and a major cause of death and morbidity in these patients. Incorporating novel technological advancements to administer accurate RT in combination with novel radiosensitizing agents could potentially improve local control and overall survival. RT efficacy in STS can be increased by modulating biological pathways such as angiogenesis, cell cycle regulation, cell survival signaling, and cancer-host immune interactions. Previous experiences, advancements, ongoing research, and current clinical trials combining RT with agents modulating one or more of the above pathways are reviewed. The standard clinical management of patients with STS with pretreatment biopsy, neoadjuvant treatment, and primary surgery provides an opportune disease model for interrogating translational hypotheses. The purpose of this review is to outline a strategic vision for clinical translation of preclinical findings and to identify appropriate targeted agents to combine with radiotherapy in the treatment of STS from different sites and/or different histology subtypes.

Abstract 854: Inhibition of PRMT5 results in radiosensitization in lung cancer cell lines

Background: Protein arginine methylation is a post translational modification that influences signal transduction, mRNA splicing, gene transcription and DNA repair. Among the PRMT family members, PRMT5 is a type II enzyme that symmetrically methylates histone H4 at Arginine 3 and histone H3 at Arginine 8. Studies have recently linked this modification to carcinogenesis and metastasis. The function of PRMT5 in carcinogenesis is related to cell proliferation through modulation of E2F1, p53, EGFR, and CRAF. It is known to accelerate progression through the G1 phase of cell cycle by influencing proteins like CDK4 and CDK6. Previous work on human lung cancer specimens has demonstrated an overexpression of PRMT5 in cancerous tissue when compared to normal lung parenchyma. Suppression of PRMT5 significantly inhibits cell proliferation in lung cancer cell lines A549 and H1299. We hypothesized inhibition of PRMT5 can lead to increased radiosensitivity in lung cancer cells.

Method: Several lung cancer cell lines were used in the experiments, including A549, H1299 and H23. SiRNA (Dharmacon) and lentiviral shRNA (Sigma) were used to knock down (KD) PRMT5 levels transiently or stably in A549 cell line in which p53 is present in its wild type form. Forty eight hours after transient transfection, cells were plated for clonogenic survival assay and subsequently exposed to ionizing radiation at 0, 2, and 8 Gy. Cellular PRMT5 protein levels were estimated by western blotting analysis for PRMT5 KD and scramble control cell lines. The scramble control and siRNA knockdown cells were subjected to cell cycle analysis by flow cytometry. We also tested specific PRMT5 inhibitors with and without radiation therapy in the lung cancer cell lines to see if PRMT5 inhibitors could lead to increased radiosensitivity.

Results: We observed a &gt;90% PRMT5 KD in transiently transfected cells at 48 h and 72 h post transfection as verified by western blot analysis. This transient KD lead to a small but significant decrease in colony survival after radiation. This radiosensitization was not observed in cells selected for stable KD of PRMT5 protein by lentiviral RNA transfection. There is an increase of cell population in G1 arrest in PRMT5 transient KD cells but not in stable KD cells. Additionally, cells treated with PRMT5 specific inhibitors (“cpd5” or “cpd65”) demonstrated increased radiosensitivity in A549 cells but not in H1299 suggesting that this effect may be p53-dependent.

Conclusion: PRMT5 inhibition by siRNA or its specific inhibitors lead to radiosensitivity in A549 lung cancer cell line. This effect may be partially dependent on p53-dependent cell cycle arrest. Further work to inhibit PRMT5 in other lung cancer cell lines with different p53 activities will be investigated.

Citation Format: Smitha Sharma, X Wu, P Smith, N Denko, C Li, H Lai, F Yan, K Shilo, A Chakravarti, S Sif, R Baiocchi, G Otterson, Meng Xu-Welliver. Inhibition of PRMT5 results in radiosensitization in lung cancer cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 854. doi:10.1158/1538-7445.AM2014-854

Dosimetric consequences of pancreatic tumor motion when predetermined treatment margins are employed during intensity-modulated radiation therapy

PURPOSE

To quantify the dosimetric consequences of pancreatic tumor motion on the pancreatic intensity-modulated radiation therapy (IMRT) plans.

METHODS

Dose map of IMRT plans for 5 patients with pancreatic cancer were measured using a 2D diode array placed on a computer-controlled platform to simulate 2D pancreatic tumor motion. Dosimetric analysis was then performed to obtain IMRT quality assurance (QA) passing rates. The convolution method, which used a motion kernel to simulate 2D pancreatic motion, was also applied to the treatment and phantom verification plans for a wide range of magnitudes of motion (0.8-2.0 cm). The resulting motion-convolved verification dose maps (VDMs) were compared with the dynamic measurements to evaluate IMRT QA passing rates as well as the dose-volume histogram, the V95% of the planning target volume (PTV) and V98% of the clinical target volume (CTV).

RESULTS

While CTV coverage was maintained when the simulated pancreatic tumor drifted inside the PTV with magnitudes of 1.0 cm and 1.5 cm, the V95% of the PTV was reduced by 10% and 17%, respectively. We also found that the differences between the measurements and the static VDMs increased proportional to the amplitude of motion, while the agreement between the measurements and the motion-convolved VDMs was excellent for any magnitude of motion.

CONCLUSIONS

When the 4D technique is not available, predetermined margins must be used carefully to avoid possible under-dose to the target. Additionally, the phantom results show that the kernel convolution method provides an accurate evaluation of the dosimetric impact due to tumor motion and it should be employed in the planning process.

Down-regulation of survivin and hypoxia-inducible factor-1 α by β-elemene enhances the radiosensitivity of lung adenocarcinoma xenograft

Elemene (1-methyl-1-vinyl-2,4-diisopropenyl-cyclohexane) is a naturally occurring compound that can be isolated from the traditional Chinese medicinal herb Curcuma wenyujin. β-elemene, its active component, has recently been demonstrated to enhance the radiosensitivity of human cancer cell lines in vitro and of one animal tumor in vivo. The underlying mechanism, however, is still unclear. In this study, we demonstrated for the first time that β-elemene significantly improves the radiosensitivity of A549 lung adenocarcinoma xenograft in vivo as measured by tumor regrowth delay experiments. Our results showed that β-elemene, at 45 mg/kg, significantly inhibited radiation-induced expression of survivin and hypoxia-inducible factor (HIF)-1 α proteins. Because HIF-1 α is known to regulate survivin transcription and acts as upstream regulator of survivin, it is possible that β-elemene regulates the transcription of survivin through HIF-1 α. Our study suggests that β-elemene is a promising drug to enhance tumor radioresponse, and survivin and HIF-1 α are novel targets of β-elemene.

The adaptive imbalance in base excision-repair enzymes generates microsatellite instability in chronic inflammation

Chronic infection and associated inflammation are key contributors to human carcinogenesis. Ulcerative colitis (UC) is an oxyradical overload disease and is characterized by free radical stress and colon cancer proneness. Here we examined tissues from noncancerous colons of ulcerative colitis patients to determine (a) the activity of two base excision-repair enzymes, AAG, the major 3-methyladenine DNA glycosylase, and APE1, the major apurinic site endonuclease; and (b) the prevalence of microsatellite instability (MSI). AAG and APE1 were significantly increased in UC colon epithelium undergoing elevated inflammation and MSI was positively correlated with their imbalanced enzymatic activities. These latter results were supported by mechanistic studies using yeast and human cell models in which overexpression of AAG and/or APE1 was associated with frameshift mutations and MSI. Our results are consistent with the hypothesis that the adaptive and imbalanced increase in AAG and APE1 is a novel mechanism contributing to MSI in patients with UC and may extend to chronic inflammatory or other diseases with MSI of unknown etiology.

The adaptive imbalance in base excision-repair enzymes generates microsatellite instability in chronic inflammation

Chronic infection and associated inflammation are key contributors to human carcinogenesis. Ulcerative colitis (UC) is an oxyradical overload disease and is characterized by free radical stress and colon cancer proneness. Here we examined tissues from noncancerous colons of ulcerative colitis patients to determine (a) the activity of two base excision-repair enzymes, AAG, the major 3-methyladenine DNA glycosylase, and APE1, the major apurinic site endonuclease; and (b) the prevalence of microsatellite instability (MSI). AAG and APE1 were significantly increased in UC colon epithelium undergoing elevated inflammation and MSI was positively correlated with their imbalanced enzymatic activities. These latter results were supported by mechanistic studies using yeast and human cell models in which overexpression of AAG and/or APE1 was associated with frameshift mutations and MSI. Our results are consistent with the hypothesis that the adaptive and imbalanced increase in AAG and APE1 is a novel mechanism contributing to MSI in patients with UC and may extend to chronic inflammatory or other diseases with MSI of unknown etiology.

The role of p53 in base excision repair following genotoxic stress

The p53 tumor suppressor protein is involved in apoptosis and cell cycle checkpoints. We have shown recently that p53 also facilitates base excision repair (BER). To further examine p53 involvement in the regulation of BER we chose to focus on 3-methyladenine DNA glycosylase (3-MeAde DNA glycosylase), the first enzyme acting in the BER pathway. 3-MeAde DNA glycosylase activity was found to be modulated by the p53 protein. This modulation was dependent on the type of genotoxic stress used. Gamma-irradiation damage resulted in activation of glycosylase, which was enhanced by p53. Doxorubicin and hydrogen peroxide (H2O2) treatment, although inducing p53 stabilization, did not cause the activation of glycosylase. Nitric oxide (NO) resulted in activation of 3-MeAde DNA glycosylase. Surprisingly this activation was down regulated by wild-type p53. The down regulation of 3-MeAde DNA glycosylase activity was due to trans repression of glycosylase mRNA by p53. Furthermore, we found that AP endonuclease (APE) activity was not altered by NO. Our study provides evidence for a possible antimutagenic role for p53 following exposure of cells to NO species. In the absence of p53, NO exposure results in elevation of 3-MeAde DNA glycosylase activity that results in elevation in the number of AP sites in DNA. At the same time, APE activity does not rise and removal of the AP sites is not further processed resulting in a mutator phenotype. When p53 is present, it down regulates the transcription of 3-MeAde DNA glycosylase. This provides a new model by which p53 prevents the creation of a mutator phenotype.

Inactivation and degradation of O(6)-alkylguanine-DNA alkyltransferase after reaction with nitric oxide

O(6)-Alkylguanine-DNA alkyltransferase (AGT) plays a critical role in protection from the carcinogenic effects of simple alkylating agents by repairing O(6)-alkylguanine adducts via a direct transfer reaction. Nitric oxide (NO) or species derived from it are known to be able to initiate neoplastic growth and cannot only damage DNA, either directly or via the formation of intermediates such as nitrosamines, but can also inhibit some DNA repair processes. We have studied the inactivation of AGT by NO in detail in vitro and in vivo using wild-type human AGT (hAGT) and mutants at key residues. Our results show that hAGT is readily but reversibly inactivated by the formation of S-nitrosylcysteine at Cys-145, which is the alkyl acceptor site. The facile reaction of this cysteine residue with NO is attributable to its interaction with other residues in hAGT including His-146 and Glu-172 that activate the sulfhydryl group of Cys-145 to allow its nucleophilic attack on DNA adducts. Although the S-nitrosylcysteine adduct in hAGT is readily reversible by reaction with other cellular thiols, the formation of S-nitrosocysteine at Cys-145 was found to lead to the rapid degradation of the hAGT protein in vivo. This degradation is brought about by the ubiquitin/proteasomal system. The formation of an S-nitrosylcysteine at Cys-145 in hAGT in response to NO led to a large increase in the ubiquitination of the protein. This NO-mediated increase did not occur with the C145S or C145A mutants. A conformational change in hAGT, which involves opening of an asparagine hinge, normally occurs after alkylation of the protein in its role in DNA repair and causes degradation of the alkylated hAGT. Our results indicate that a similar effect occurs after reaction of the protein with NO. Thus, exposure to NO causes an irreversible loss of DNA repair capacity for alkylation adducts. This may contribute toward the potential development of tumors in cells upon chronic exposure to NO because of inflammation or infection. This may be of particular importance because such exposure may also lead to the formation of N-nitroso compounds that can act as alkylating agents.

Degradation of the alkylated form of the DNA repair protein, O(6)-alkylguanine-DNA alkyltransferase

O(6)-Alkylguanine-DNA alkyltransferase (AGT) is a DNA repair protein that removes alkyl groups from DNA by transferring them to an internal Cys-145 residue. As the S-alkylcysteine is not converted back to cysteine, the protein can only act once and the resulting alkylated AGT molecule is rapidly degraded. The mechanism underlying the disappearance of the alkylated AGT has been studied in vivo in CHO cells and in vitro in reticulocyte lysates by using the pseudosubstrate O(6)-benzylguanine (BG) and mutant forms of AGT. The wild-type AGT was stable but was ubiquitinated and degraded rapidly by the proteasome after treatment with BG or with an oligodeoxyribonucleotide, which contained O(6)-methylguanine. Mutants C145F (and other mutants with bulky substituents at position 145), which have alterations that cause a steric alteration at the active site and also prevent hydrogen bonding involving Cys-145 resembled the alkylated AGT and were ubiquitinated and degraded rapidly irrespective of treatment with BG. Mutant M134F, which causes a steric alteration without interfering directly with the hydrogen-bonding network involving Cys-145, partially destabilized AGT and its degradation was increased further by reaction with BG. Mutant C145S, which maintains the hydrogen-binding network and causes no distortion, was not rapidly degraded. The results indicate that the conformational change resulting in the opening of the asparagine hinge region in the structure, which is brought about by formation of an S-alkyl adduct, leads to an increased recognition by a ubiquitin ligase targeting the protein for degradation. This is a novel type of post-translational modification causing ubiquitination.

Effect of O6-benzylguanine on alkylating agent-induced toxicity and mutagenicity. In Chinese hamster ovary cells expressing wild-type and mutant O6-alkylguanine-DNA alkyltransferases

The DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) has been shown to protect cells from the toxic and mutagenic effect of alkylating agents by removing lesions from the O6 position of guanine. O6-Benzylguanine (BG) is a potent inactivator of AGT, resulting in an increase in the sensitivity of cells to the toxic effects of chemotherapeutic alkylating agents. Chinese hamster ovary (CHO) cells and CHO cells transfected with wild-type AGT (CHOWTAGT) and a mutant AGT [P138 M/V139I/P140K (CHOMIK)] known to be resistant to BG were treated with BG and various alkylating agents. BG treatment alone dramatically decreased AGT activity in CHOWTAGT cells but resulted in no depletion in AGT activity in CHOMIK cells. In the absence of AGT, these cells are highly sensitive to the toxic and mutagenic effects of temozolomide and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), and no further sensitization occurs in the presence of BG. In contrast, CHOWTAGT cells are resistant to temozolomide and BCNU, and treatment with BG resulted in a significantly higher cell killing and mutation frequency. CHOMIK cells were completely resistant to temozolomide or BCNU in the presence and absence of BG. Both cell killing and mutation frequency of 4-hydroperoxycyclophosphamide (4-HC) in CHO, CHOWTAGT, and CHOMIK cells were increased in the presence of BG. 4-HC generates two active metabolites, phosphoramide mustard (PM) and acrolein. BG had no effect on 4hydroperoxydidechlorocyclophosphamide (which generates acrolein and a nonalkylating form of PM) in CHO cells and CHOMIK cells, but enhancement of toxicity was observed with PM in both these cell lines. Therefore, we attribute the enhancement to the PM metabolite of 4-HC. Our results demonstrate that wild-type AGT plays an important role in protecting against the toxic and mutagenic effect of O6 alkylating agents and that a mutant AGT resistant to inactivation by BG effectively prevents BG-enhanced toxicity and mutagenicity induced by these agents. Expression of the AGT protein contributes to resistance of 4-HC. BG also enhances the toxicity of 4-HC and PM by a mechanism that may not involve the AGT repair protein.

Direct reversal of DNA damage by mutant methyltransferase protein protects mice against dose-intensified chemotherapy and leads to in vivo selection of hematopoietic stem cells

Direct reversal of O6 adducts caused by chemotherapy agents is accomplished in mammalian cells by the protein O6-methylguanine DNA methyltransferase (MGMT). Some tumors overexpress MGMT and are resistant to alkylator therapy. One future approach to treatment of these tumors may rely on concurrent pharmacological depletion of tumor MGMT with O6-benzylguanine (6-BG) and protection of sensitive tissues, such as hematopoietic stem and progenitor cells, using genetic modification with 6-BG-resistant MGMT mutants. We have used retroviral-mediated gene transfer to transduce murine hematopoietic bone marrow cells with MGMT point mutants showing resistance to 6-BG depletion in vitro. These mutants include proline to alanine and proline to lysine substitutions at the 140 position (P140A and P140K, respectively), which show 40- and 1000-fold resistance to 6-BG compared with wild-type (WT) MGMT. Lethally irradiated mice were reconstituted with murine stem cells transduced with murine stem cell virus retrovirus expressing each mutant, WT MGMT, or mock-infected cells and then treated with a combination of 30 mg/kg 6-BG and 10 mg/kg 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or with 40 mg/kg BCNU alone. Compared with mice treated with BCNU alone, significant myeloid toxicity and death occurred in mice reconstituted with mock-infected or WT MGMT (<0.1 probability of survival) or the P140A mutant (0.13 probability of survival) MGMT cDNAs. In contrast, after an initial period of mild cytopenia, mice reconstituted with the P140K mutant (0.83 probability of survival) recovered nearly normal blood counts, even during continued treatment. Comparison of peripheral blood neutrophils after completion of 5 weekly treatments in these animals showed a direct correlation between the treatment and in vivo selection for progeny of transduced cells (pretreatment, approximately 8-12% transduced cells; no treatment, approximately 6% transduced cells; BCNU only, 51% transduced cells; 6-BG/BCNU, 93% transduced cells). To determine whether this selection occurred at the stem cell level, bone marrow from each treatment group was infused into secondary recipients. Whereas animals that received bone marrow from untreated animals reconstituted with 2% transduced cells, animals receiving marrow from 6-BG/BCNU-treated animals reconstituted with 94% transduced cells, demonstrating nearly complete selection for stem cells in the primary animals. Mice reconstituted with marrow from animals treated with BCNU only demonstrated 23% transduced cells, consistent with partial selection of stem cells in the primary mice. The levels of transduced cells also correlated with survival during a second round of intensive combination chemotherapy (probability of survival: 6-BG/BCNU, 1.0; BCNU alone, >0.70; no treatment, <0.1). These data demonstrate that mutant MGMT expressed in the bone marrow can protect mice from time- and dose-intensive chemotherapy and that the combination of 6-BG and BCNU leads to uniform selection of transduced stem cells in vivo in mice.

The role of human O(6)-alkylguanine-DNA alkyltransferase in promoting 1,2-dibromoethane-induced genotoxicity in Escherichia coli

The expression of the DNA repair protein human O(6)-alkylguanine-DNA alkyltransferase (AGT) in Escherichia coli strains GWR109 or TRG8 that lack endogenous AGT greatly increased the toxicity and mutagenicity of 1,2-dibromoethane (DBE). Pretreatment of strain TRG8 expressing human AGT, which is permeable to exogenous drugs, with the AGT inhibitor O(6)-benzylguanine (BG) abolished the lethal and mutagenic effects of DBE, indicating that an active AGT is required for promoting DBE genotoxicity. This was confirmed by the observation that E. coli expressing either the C145A AGT mutant, which is inactive due to loss of the alkyl acceptor site, or mutants Y114E and R128A, which are inactive due to alteration of the DNA binding domain, did not enhance the action of DBE. However, the AGT mutant protein P138M/V139L/P140K, which is active in repairing methylated DNA but is totally resistant to inactivation by BG due to alterations in the active site pocket, was unable to enhance the genotoxicity of DBE. Similarly, other mutants, G156P, Y158H and K165R that are strongly resistant to BG, were much less effective than wild type AGT in mediating the genotoxicity of DBE. Mutant P140A, which is moderately resistant to BG, did increase mutations in response to DBE but was less active than wild type. These results suggest that human AGT is able to interact with a DNA lesion produced by DBE but, instead of repairing it, converts it to a more genotoxic adduct. This interaction is prevented by mutations that modify the active site of AGT to exclude BG.