Radiation and checkpoint blockade immunotherapy: radiosensitisation and potential mechanisms of synergy

Checkpoint blockade immunotherapy has received mainstream attention as a result of striking and durable clinical responses in some patients with metastatic disease and a reasonable response rate in many tumour types. The activity of checkpoint blockade immunotherapy is not restricted to melanoma or lung cancer, and additional indications are expected in the future, with responses already reported in renal cancer, bladder cancer, and Hodgkin's lymphoma among many others. Additionally, the interactions between radiation and the immune system have been investigated, with several studies describing the synergistic effects on local and distant tumour control when radiation therapy is combined with immunotherapy. Clinical enthusiasm for this approach is strengthened by the many ongoing trials combining immunotherapy with definitive and palliative radiation. Herein, we discuss the biological and mechanistic rationale behind combining radiation with checkpoint blockade immunotherapy, with a focus on the preclinical data supporting this potentially synergistic combination. We explore potential hypotheses and important considerations for clinical trial designs. Finally, we reintroduce the notion of radiosensitising immunotherapy, akin to radiosensitising chemotherapy, as a potential definitive therapeutic modality.

Dosimetric predictors of sexual function decline following LDR brachytherapy for prostate cancer (PCa)

113

Background: Conventional dosimetric standards for implant quality do not adequately predict patient reported QoL measures following prostate brachytherapy. We used a dynamic learning knowledgebase (Oncospace) to explore relationships between dose and patient-reported outcomes. Methods: Patient reported quality of life outcomes were prospectively collected for 366 patients with stage cT1-T2 PCa over a 10 year interval. Patients received Pd-103 seed implantation under real-time ultrasound guidance, and completed a QoL instrument (IIEF-5) prior to treatment and at follow-up. Multivariate risk models were used to evaluate dose/toxicity relationships and the Oncospace learning environment generated prediction models using granular dose volume relationships. Results: Median follow-up was 36 months (SD 28.5). In the cohort, 23.7% (n = 87) received combined brachytherapy and EBRT; 14.7% (n = 54) had received prior androgen suppression therapy. Sexual QoL data at minimum of 2 years was available in 141 men. The mean decrement in sexual function per the IIEF-5 instrument was 3.76 points (SD 10.3), with 17.0% of men reporting a decrement of 10 points or greater. There was no significant association with prior androgen suppression (p = 0.20) or combined EBRT use (p = 0.69). DVH curves were queried and dichotomized according to stable sexual function vs significant decline ( > 10) at 2 years post-implant. A logistic regression model was used to generate probability surface maps of volumetric dose effects on outcomes. Logistic regression revealed a correlation between dose to the cavernosal nerves and total SHIM score throughout the high dose region of the DVH curve (p < 0.05). No similar dose/volume correlation with sexual function emerged for structures. Conclusions: Granular dose/volume and toxicity correlation using the Oncospace learning environment exposed a statistically significant relationship between volumetric dose to the cavernosal nerves and sexual function decline in patients undergoing LDR brachytheramarpy. Minimization of dose to the cavernosal nerves may preserve sexual function after permanent prostate seed brachytherapy.

Bromopyridone Nucleotide Analogues, Anoxic Selective Radiosensitizing Agents That Are Incorporated in DNA by Polymerases

Ionizing radiation is frequently used to kill tumor cells. However, hypoxic solid tumor cells are more resistant to this treatment, providing the impetus to develop molecules that sensitize cells to ionizing radiation. 5-Bromo-2'-deoxyuridine (BrdU) has been investigated as a radiosensitizing agent in the lab and clinic for almost 5 decades. Recent reports that BrdU yields DNA interstrand cross-links (ICLs) in non-base-paired regions motivated us to develop radiosensitizing agents that generate cross-links in duplex DNA selectively under anoxic conditions. 4-Bromo- and 5-bromopyridone analogues of BrdU were synthesized and incorporated into oligonucleotides via solid-phase synthesis. Upon irradiation, these molecules yield DNA interstrand cross-links under anaerobic conditions. The respective nucleotide triphosphates are substrates for some DNA polymerases. ICLs are produced upon irradiation under anoxic conditions when the 4-bromopyridone is present in a PCR product. Because the nucleoside analogue is a poor phosphorylation substrate for human deoxycytidine kinase, a pro-nucleotide form of the 4-bromopyridone was used to incorporate this analogue into cellular DNA. Despite these efforts, the 4-bromopyridone nucleotide was not detected in cellular DNA. Although these molecules are improvements over previously reported nucleotide analogues designed to be hypoxic radiosensitizing agents, additional advances are needed to create molecules that function in cells.

Systemic Administration and Targeted Radiosensitization via Chemically Synthetic Aptamer-siRNA Chimeras in Human Tumor Xenografts

Radiation therapy is a highly effective tool for treating all stages of prostate cancer, from curative approaches in localized disease to palliative care and enhanced survival for patients with distant bone metastases. The therapeutic index of these approaches may be enhanced with targeted radiation-sensitizing agents. Aptamers are promising nucleic acid delivery agents for short interfering RNAs (siRNA) and short hairpin RNAs (shRNA). We have previously developed a radiation-sensitizing RNA aptamer-shRNA chimera that selectively delivers DNA-PK targeting shRNAs to prostate-specific membrane antigen (PSMA) positive cells in the absence of transfection reagents. Although these chimera are effective, their synthesis requires in vitro transcription and their evaluation was limited to intratumoral administration. Here, we have developed a second-generation aptamer-siRNA chimera that can be assembled through the annealing of three separate chemically synthesized components. The resulting chimera knocked down DNA-PK in PSMA-positive prostate cancer cells, without the need of additional transfection reagents, and enhanced the efficacy of radiation-mediated cell death. Following intravenous injection, the chimera effectively knocked down DNA-PK in established subcutaneous PSMA-positive tumors. Systemic treatment with these radiation-sensitizing agents selectively enhanced the potency of external beam radiation therapy for established PSMA-positive tumors.

Monitoring nanoparticle-mediated cellular hyperthermia with a high-sensitivity biosensor

AIM

To develop and apply a heat-responsive and secreted reporter assay for comparing cellular response to nanoparticle (NP)- and macroscopic-mediated sublethal hyperthermia.

MATERIALS & METHODS

Reporter cells were heated by water bath (macroscopic heating) or iron oxide NPs activated by alternating magnetic fields (nanoscopic heating). Cellular responses to these thermal stresses were measured in the conditioned media by secreted luciferase assay.

RESULTS & CONCLUSION

Reporter activity was responsive to macroscopic and nanoparticle heating and activity correlated with measured macroscopic thermal dose. Significant cellular responses were observed with NP heating under doses that were insufficient to measurably change the temperature of the system. Under these conditions, the reporter response correlated with proximity to cells loaded with heated nanoparticles. These results suggest that NP and macroscopic hyperthermia may be distinctive under conditions of mild hyperthermia.

Magnetic nanoparticle hyperthermia enhances radiation therapy: A study in mouse models of human prostate cancer

PURPOSE

We aimed to characterise magnetic nanoparticle hyperthermia (mNPH) with radiation therapy (RT) for prostate cancer.

METHODS

Human prostate cancer subcutaneous tumours, PC3 and LAPC-4, were grown in nude male mice. When tumours measured 150 mm3 magnetic iron oxide nanoparticles (MIONPs) were injected into tumours to a target dose of 5.5 mg Fe/cm3 tumour, and treated 24 h later by exposure to alternating magnetic field (AMF). Mice were randomly assigned to one of four cohorts to characterise (1) intratumour MIONP distribution, (2) effects of variable thermal dose mNPH (fixed AMF peak amplitude 24 kA/m at 160 ± 5 kHz) with/without RT (5 Gy), (3) effects of RT (RT5: 5 Gy; RT8: 8 Gy), and (4) fixed thermal dose mNPH (43 °C for 20 min) with/without RT (5 Gy). MIONP concentration and distribution were assessed following sacrifice and tissue harvest using inductively coupled plasma mass spectrometry (ICP-MS) and Prussian blue staining, respectively. Tumour growth was monitored and compared among treated groups.

RESULTS

LAPC-4 tumours retained higher MIONP concentration and more uniform distribution than did PC3 tumours. AMF power modulation provided similar thermal dose for mNPH and combination therapy groups (CEM43: LAPC-4: 33.6 ± 3.4 versus 25.9 ± 0.8, and PC3: 27.19 ± 0.7 versus 27.50 ± 0.6), thereby overcoming limitations of MIONP distribution and yielding statistically significant tumour growth delay.

CONCLUSION

PC3 and LAPC-4 tumours represent two biological models that demonstrate different patterns of nanoparticle retention and distribution, offering a model to make comparisons of these effects for mNPH. Modulating power for mNPH offers potential to overcome limitations of MIONP distribution to enhance mNPH.

A functional screen identifies miRNAs that inhibit DNA repair and sensitize prostate cancer cells to ionizing radiation

MicroRNAs (miRNAs) have been implicated in DNA repair pathways through transcriptional responses to DNA damaging agents or through predicted miRNA regulation of DNA repair genes. We hypothesized that additional DNA damage regulating miRNAs could be identified by screening a library of 810 miRNA mimetics for the ability to alter cellular sensitivity to ionizing radiation (IR). A prostate cancer Metridia luciferase cell model was applied to examine the effects of individual miRNAs on IR sensitivity. A large percentage of miRNA mimetics were found to increase cellular sensitivity to IR, while a smaller percentage were protective. Two of the most potent IR sensitizing miRNAs, miR-890 and miR-744–3p, significantly delayed IR induced DNA damage repair. Both miRNAs inhibited the expression of multiple components of DNA damage response and DNA repair. miR-890 directly targeted MAD2L2, as well as WEE1 and XPC, where miR-744–3p directly targeted RAD23B. Knock-down of individual miR-890 targets by siRNA was not sufficient to ablate miR-890 radiosensitization, signifying that miR-890 functions by regulating multiple DNA repair genes. Intratumoral delivery of miR-890 mimetics prior to IR therapy significantly enhanced IR therapeutic efficacy. These results reveal novel miRNA regulation of DNA repair and identify miR-890 as a potent IR sensitizing agent.

End-of-radiation PSA as a novel prognostic factor in patients undergoing definitive radiation for prostate cancer

68

Background: In patients with localized prostate cancer undergoing radiation therapy (RT) +/- androgen deprivation therapy (ADT), an end of radiation (EOR) PSA obtained during the last week of RT may serve as an early post-treatment predictor of poor outcomes and identify patients in whom to pursue treatment intensification or novel therapies. Methods: We reviewed an IRB-monitored, prospectively acquired database of patients with prostate cancer treated with definitive RT at our institution from 1993-2007 (n=890). Patients with an available EOR PSA were divided into two cohorts and analyzed separately based on inclusion of ADT into the treatment regimen. EOR PSA thresholds of 0.5 ng/mL and 1.0 ng/mL were explored. Multivariate analysis was performed to determine prognostic factors for biochemical failure-free survival (BFFS, Phoenix criteria) and overall survival (OS). Kaplan-Meier survival curves were constructed, with stratification by EOR PSA thresholds. Results: Median age was 69 years, with an even distribution of NCCN low risk (33.5%), intermediate risk (34.0%), and high risk (32.5%) patients. Median RT dose was 7020 cGy, and 54.5% were treated with ADT. Median follow-up of the entire cohort was 11.7 yrs. EOR PSA level was available for the majority of patients (77.5%). On multivariate analysis, EOR PSA >0.5 ng/mL was significantly associated with worse BFFS (p<0.0001) and OS (p<0.0001). In the subset of patients undergoing RT with ADT for NCCN intermediate/high risk disease, 5 yr BFFS was more disparate based an EOR PSA threshold of 0.5 ng/mL (5 yr BFFS: 87.3% vs. 41.1%, p<0.001), than initial NCCN risk level (5 yr BFFS: 88.7% vs. 76.9%, p=0.038). In NCCN low risk patients undergoing definitive RT alone, an EOR PSA threshold of 1.0 ng/mL was significantly prognostic of outcome (5 yr BFFS: 100.0% vs. 88.6%, p=0.024). Conclusions: For NCCN intermediate/high risk patients undergoing RT with ADT, EOR PSA >0.5 ng/mL may represent a better surrogate for poor outcomes than initial risk group. In addition, NCCN low risk patients undergoing RT alone who obtained an EOR PSA ≤1.0 ng/mL experienced excellent BFFS. Prospective evaluation of the utility of EOR PSA should be explored.

Magnetic resonance imaging contrast of iron oxide nanoparticles developed for hyperthermia is dominated by iron content

PURPOSE

Magnetic iron oxide nanoparticles (MNPs) are used as contrast agents for magnetic resonance imaging (MRI) and hyperthermia for cancer treatment. The relationship between MRI signal intensity and cellular iron concentration for many new formulations, particularly MNPs having magnetic properties designed for heating in hyperthermia, is lacking. In this study, we examine the correlation between MRI T2 relaxation time and iron content in cancer cells loaded with various MNP formulations.

MATERIALS AND METHODS

Human prostate carcinoma DU-145 cells were loaded with starch-coated bionised nanoferrite (BNF), iron oxide (Nanomag® D-SPIO), Feridex™, and dextran-coated Johns Hopkins University (JHU) particles at a target concentration of 50 pg Fe/cell using poly-D-lysine transfection reagent. T2-weighted MRI of serial dilutions of these labelled cells was performed at 9.4 T and iron content quantification was performed using inductively coupled plasma mass spectrometry (ICP-MS). Clonogenic assay was used to characterise cytotoxicity.

RESULTS

No cytotoxicity was observed at twice the target intracellular iron concentration (∼100 pg Fe/cell). ICP-MS revealed highest iron uptake efficiency with BNF and JHU particles, followed by Feridex and Nanomag-D-SPIO, respectively. Imaging data showed a linear correlation between increased intracellular iron concentration and decreased T2 times, with no apparent correlation among MNP magnetic properties.

CONCLUSIONS

This study demonstrates that for the range of nanoparticle concentrations internalised by cancer cells the signal intensity of T2-weighted MRI correlates closely with absolute iron concentration associated with the cells. This correlation may benefit applications for cell-based cancer imaging and therapy including nanoparticle-mediated drug delivery and hyperthermia.

Low interrater reliability in grading of rectal bleeding using National Cancer Institute Common Toxicity Criteria and Radiation Therapy Oncology Group Toxicity scales: a survey of radiation oncologists

PURPOSE

To measure concordance among genitourinary radiation oncologists in using the National Cancer Institute Common Toxicity Criteria (NCI CTC) and Radiation Therapy Oncology Group (RTOG) grading scales to grade rectal bleeding.

METHODS AND MATERIALS

From June 2013 to January 2014, a Web-based survey was sent to 250 American and Canadian academic radiation oncologists who treat prostate cancer. Participants were provided 4 case vignettes in which patients received radiation therapy and developed rectal bleeding and were asked for management plans and to rate the bleeding according to NCI CTC v.4 and RTOG late toxicity grading (scales provided). In 2 cases, participants were also asked whether they would send the patient for colonoscopy. A multilevel, random intercept modeling approach was used to assess sources of variation (case, respondent) in toxicity grading to calculate the intraclass correlation coefficient (ICC). Agreement on a dichotomous grading scale (low grades 1-2 vs high grades 3-4) was also assessed, using the κ statistic for multiple respondents.

RESULTS

Seventy-two radiation oncologists (28%) completed the survey. Forty-seven (65%) reported having either written or been principal investigator on a study using these scales. Agreement between respondents was moderate (ICC 0.52, 95% confidence interval [CI] 0.47-0.58) when using NCI CTC and fair using the RTOG scale (ICC 0.28, 95% CI 0.20-0.40). Respondents who chose an invasive management were more likely to select a higher toxicity grade (P<.0001). Using the dichotomous scale, we observed moderate agreement (κ = 0.42, 95% CI 0.40-0.44) with the NCI CTC scale, but only slight agreement with the RTOG scale (κ = 0.19, 95% CI 0.17-0.21).

CONCLUSION

Low interrater reliability was observed among radiation oncologists grading rectal bleeding using 2 common scales. Clearer definitions of late rectal bleeding toxicity should be constructed to reduce this variability and avoid ambiguity in both reporting and interpretation.

Androgen withdrawal fails to induce detectable tissue hypoxia in the rat prostate

BACKGROUND

It has been reported that significant hypoxia may occur in the rat prostate following androgen deprivation (AD). It is well known that hypoxia substantially reduces radiation sensitivity of cells both in vitro and in vivo. Given that contemporary management of men with intermediate and high-risk prostate cancer includes the use of neoadjuvant androgen suppression and radiation, AD-induced hypoxia in the prostate could result in suboptimal therapeutic results. Given this concern, we fully investigate possible AD-induced hypoxia in the ventral prostate (VP) of adult rats by two independent methods.

METHODS

Tissue pO2 levels in the VP of adult Spraque-Dawley rats were evaluated prior to and at various time points following castration by two independent techniques. First, an Oxylab tissue oxygen monitor with a 240 μm probe was used for quantitative monitoring of global VP oxygenation. Second, fluorescence immunohistochemistry using the hypoxia marker EF5, known to be metabolically activated by hypoxic cells, was used to evaluate cell-to-cell variation in hypoxia at various days post-castration.

RESULTS

Neither the oxygen probe nor EF5 method demonstrate any substantive change in pO2 levels in the rat VP at any time point post-castration.

CONCLUSIONS

We find no evidence that the rat VP becomes hypoxic at any point following castration using an animal model that closely mimics the human prostate. These data are in contrast to previous reports suggesting prostatic hypoxia occurs following AD and provide assurance that our present therapeutic strategy of neoadjuvant AD followed by radiation is not compromised by AD-induced tissue hypoxia.

Radiosensitization of Pancreatic Cancer Cells In Vitro and In Vivo through Poly (ADP-ribose) Polymerase Inhibition with ABT-888

OBJECTIVES

To determine whether poly (ADP-ribose) polymerase-1/2 (PARP-1/2) inhibition enhances radiation-induced cytotoxicity of pancreatic adenocarcinoma in vitro and in vivo, and the mechanism by which this occurs.

METHODS

Pancreatic carcinoma cells were treated with ABT-888, radiation, or both. In vitro cell viability, apoptosis, and PARP activity were measured. Orthotopic xenografts were generated in athymic mice and treated with ABT-888 (25mg/kg), radiation (5Gy), both, or no treatment. Mice were monitored with bioluminescence imaging.

RESULTS

In vitro, treatment with ABT-888 and radiation led to higher rates of cell death after 8days (P < .01). Co-treatment with 5Gy and 1, 10 or 100μmol/l of ABT-888 led to dose enhancement factors of 1.29, 1.41 and 2.36, respectively. Caspase activity was not significantly increased when treated with ABT-888 (10 μmol/l) alone (1.28-fold, P = .08), but became significant when radiation was added (2.03-fold, P < .01). PARP activity increased post-radiation and was abrogated following co-treatment with ABT-888. In vivo, treatment with ABT-888, radiation or both led to tumor growth inhibition (TGI) of 8, 30 and 39days, and survival at 60days of 0%, 0% and 40%, respectively.

CONCLUSIONS

ABT-888 with radiation significantly enhanced tumor response in vitro and in vivo. ABT-888 inhibited PAR protein polymerization resulting in dose-dependent feedback up-regulation of PARP and p-ATM suggesting increased DNA damage. This translated into enhancement in TGI and survival with radiation in vivo. In vitro PAR levels correlated with levels of tumor apoptosis suggesting potential as a predictive biomarker. These data are being used to support a Phase I study in locally advanced pancreatic cancer.

Absorbable hydrogel spacer use in men undergoing prostate cancer radiotherapy: 12 month toxicity and proctoscopy results of a prospective multicenter phase II trial

BACKGROUND

Radiation therapy is one of the recommended treatment options for localized prostate cancer. In randomized trials, dose escalation was correlated with better biochemical control but also with higher rectal toxicity. A prospective multicenter phase II study was carried out to evaluate the safety, clinical and dosimetric effects of the hydrogel prostate-rectum spacer. Here we present the 12 months toxicity results of this trial.

METHODS

Fifty two patients with localized prostate cancer received a transperineal PEG hydrogel injection between the prostate and rectum, and then received IMRT to a dose of 78 Gy. Gastrointestinal and genitourinary toxicity were recorded during treatment and at 3, 6 and 12 months following irradiation by using the RTOG/EORTC criteria. Additionally, proctoscopy was performed 12 months after treatment and the results were scored using the Vienna Rectoscopy Scale (VRS).

RESULTS

Of the patients treated 39.6% and 12.5% experienced acute Grade 1 and Grade 2 GI toxicity, respectively. There was no Grade 3 or Grade 4 acute GI toxicity experienced in the study. Only 4.3% showed late Grade 1 GI toxicity, and there was no late Grade 2 or greater GI toxicity experienced in the study. A total of 41.7%, 35.4% and 2.1% of the men experienced acute Grade 1, Grade 2 and Grade 3 GU toxicity, respectively. There was no Grade 4 acute GU toxicity experienced in the study. Late Grade 1 and Grade 2 GU toxicity was experienced in 17.0% and 2.1% of the patients, respectively. There was no late Grade 3 or greater GU toxicity experienced in the study. Seventy one percent of the patients had a VRS score of 0, and one patient (2%) had Grade 3 teleangiectasia. There was no evidence of ulceration, stricture or necrosis at 12 months.

CONCLUSION

The use of PEG spacer gel is a safe and effective method to spare the rectum from higher dose and toxicity.

Development and screening of a series of antibody-conjugated and silica-coated iron oxide nanoparticles for targeting the prostate-specific membrane antigen

The prostate-specific membrane antigen (PSMA) is an established target for the delivery of cancer therapeutic and imaging agents due to its high expression on the surface of prostate cancer cells and within the neovasculature of other solid tumors. Here, we describe the synthesis and screening of antibody-conjugated silica-coated iron oxide nanoparticles for PSMA-specific cell targeting. The humanized anti-PSMA antibody, HuJ591, was conjugated to a series of nanoparticles with varying densities of polyethylene glycol and primary amine groups. Customized assays utilizing iron spectral absorbance and enzyme-linked immunoassay (ELISA) were developed to screen microgram quantities of nanoparticle formulations for immunoreactivity and cell targeting ability. Antibody and PSMA-specific targeting of the optimized nanoparticle was evaluated using an isogenic PSMA-positive and PSMA-negative cell line pair. Specific nanoparticle targeting was confirmed by iron quantification with inductively coupled plasma mass spectrometry (ICP-MS). These methods and nanoparticles support the promise of targeted theranostic agents for future treatment of prostate and other cancers.

Irreversible inhibition of DNA polymerase β by small-molecule mimics of a DNA lesion

Abasic sites are ubiquitous DNA lesions that are mutagenic and cytotoxic but are removed by the base excision repair pathway. DNA polymerase β carries out two of the four steps during base excision repair, including a lyase reaction that removes the abasic site from DNA following incision of its 5'-phosphate. DNA polymerase β is overexpressed in cancer cells and is a potential anticancer target. Recently, DNA oxidized abasic sites that are produced by potent antitumor agents were shown to inactivate DNA polymerase β. A library of small molecules whose structures were inspired by the oxidized abasic sites was synthesized and screened for the ability to irreversibly inhibit DNA polymerase β. One candidate (3a) was examined more thoroughly, and modification of its phosphate backbone led to a molecule that irreversibly inactivates DNA polymerase β in solution (IC50 ≈ 21 μM), and inhibits the enzyme's lyase activity in cell lysates. A bisacetate analogue is converted in cell lysates to 3a. The bisacetate is more effective in cell lysates, more cytotoxic in prostate cancer cells than 3a and potentiates the cytotoxicity of methyl methanesulfonate between 2- and 5-fold. This is the first example of an irreversible inhibitor of the lyase activity of DNA polymerase β that works synergistically with a DNA damaging agent.

Multidisciplinary clinic evaluation changes prostate cancer stage and risk stratification

91

Background: The use of multidisciplinary clinics (MDCs) for outpatient cancer evaluation is increasing. Data on whether MDCs improve prostate cancer (PCa) care are limited. We studied the frequency of changes in PCa grade and stage upon MDC evaluation. Methods: Between May 2008 and December 2012, 887 consecutive patients underwent consultation for newly diagnosed prostate cancer at the Johns Hopkins Hospital (JHH) MDC, which features real-time collaboration among urologists, radiation oncologists, and medical oncologists. Retrospective chart review identified presenting tumor characteristics, based on outside assessment (medical records sent upon referral to MDC), as compared with disease stage and grade as determined at MDC evaluation. All outside biopsy slides were reviewed by JHH pathologists, and all outside imaging (CT, MRI, bone scan) was reviewed by JHH radiologists. Results: The three most chosen treatments after MDC evaluation were external beam radiotherapy +/- androgen deprivation (39.3%), radical prostatectomy (32.0%) and active surveillance/expectant management (12.9%). Using the NCCN guidelines as a benchmark, many men were found to have undergone non-indicated imaging (bone scan 23.9%, CT/MRI 47.4%). Overall, 186/647 (28.7%) had a change in their NCCN risk classification or N or M stage. For example, 2.9% of men were down-classified as very-low-risk, rendering them eligible for active surveillance. 5.7% of men thought to have localized cancer were up-classified as metastatic, thus prompting systemic management approaches. Conclusions: Comprehensive evaluation of prostate cancer patients in a MDC is associated with critical changes in presenting disease classification from baseline in over one in four men. While questions about the long term costs and benefits of MDCs remain, these results lend credence to the growing belief that MDCs may dramatically impact management for a large number of men with prostate cancer. [Table: see text]

Combined treatment effects of radiation and immunotherapy: studies in an autochthonous prostate cancer model

PURPOSE

To optimize the combination of ionizing radiation and cellular immunotherapy using a preclinical autochthonous model of prostate cancer.

METHODS AND MATERIALS

Transgenic mice expressing a model antigen under a prostate-specific promoter were treated using a platform that integrates cone-beam CT imaging with 3-dimensional conformal therapy. Using this technology we investigated the immunologic and therapeutic effects of combining ionizing radiation with granulocyte/macrophage colony-stimulating factor-secreting cellular immunotherapy for prostate cancer in mice bearing autochthonous prostate tumors.

RESULTS

The combination of ionizing radiation and immunotherapy resulted in a significant decrease in pathologic tumor grade and gross tumor bulk that was not evident with either single-modality therapy. Furthermore, combinatorial therapy resulted in improved overall survival in a preventive metastasis model and in the setting of established micrometastases. Mechanistically, combined therapy resulted in an increase of the ratio of effector-to-regulatory T cells for both CD4 and CD8 tumor-infiltrating lymphocytes.

CONCLUSIONS

Our preclinical model establishes a potential role for the use of combined radiation-immunotherapy in locally advanced prostate cancer, which warrants further exploration in a clinical setting.

Patterns of palliative radiation near the end of life: A single-institution retrospective analysis

9636

Background: The care of patients who receive radiation therapy (RT) at the end of life (EOL) is under scrutiny to ensure effectiveness and value, with many patients not completing RT (Gripp, 2010; Toole, 2012). This retrospective analysis seeks to describe patterns of utilization of palliative RT, including rates of completion of RT offered at the EOL and the use of single fraction RT for bone metastases. Methods: Electronic medical records were used to create a database of 3,383 RT plans for brain, bone, lung, and other metastatic sites in patients treated at Johns Hopkins Hospital from 9/1/2007-7/15/2012. RT plans without palliative intent were excluded. T-tests and logistic regression compared patient and treatment characteristics between patients who died > 1 month versus ≤ 1 month after their last RT fraction. Results: A total of 983 patients were treated to 1,524 sites, with an average of 1.7 RT sites (SD 1.3) per patient. Of these, 872 (89%) patients had complete records and were included in analysis. At the time of analysis, 85% had died. The mean age of 62.1 years (SD 3.4) did not differ statistically based on time from RT to death. Death ≤ 1 month after RT was documented in 215 (24.7%) patients. Compared to patients living > 1 month after RT, patients receiving RT within the last month of life were more likely to be lung (17% versus 9%), less likely to be brain (34% versus 44%), and equally likely to be bone (45% versus 43%) sites. Patients who died ≤ 1 month after completing RT spent on average 5 days (16.6%) of the last month of life receiving RT, with no significant difference by disease site. Conclusions: Most patients receiving palliative RT finish therapy, with 25% dying ≤ 1 month after RT. Single fraction bone RT was relatively uncommon, with no significant difference in the rates of single fraction RT based on time from RT to death. These data provide a framework to match treatment patterns with national guidelines. Additionally, they provide context to model risk of death shortly after RT, which can aid in clinical decision-making. [Table: see text]

A multi-institutional clinical trial of rectal dose reduction via injected polyethylene-glycol hydrogel during IMRT for prostate cancer: Analysis of dosimetric outcomes

35

Background: To characterize the effect of a prostate-rectum spacer on dose to rectum during external beam radiotherapy for prostate cancer, and to assess for factors correlated with rectal dose reduction. Methods: Fifty-two patients at 4 institutions were enrolled onto a prospective pilot clinical trial. Patients underwent baseline scans, then were injected with perirectal spacing hydrogel and re-scanned. IMRT plans were created on both scans for comparison. Objectives were to establish rates of creation of ≥7.5mm of prostate-rectal separation, and decrease in rectal V70 of ≥25%. Multiple regression analysis was performed to evaluate associations between pre- vs. post-injection changes in rectal V70 and changes in plan conformity, rectal volume, bladder volume, bladder V70, PTV volume, as well as post-injection mid-gland separation, gel volume, gel thickness, length of PTV/gel contact, or gel left-to-right symmetry. Results: Hydrogel resulted in > 7.5mm prostate-rectal separation in 95.8% of patients; 95.7% had decreased rectal V70 of > 25%, with mean reduction of 8.0 Gy. There were no significant differences in pre- and post-injection prostate, PTV, rectal, and bladder volumes. Plan conformities were significantly different pre- vs. post-injection (P = 0.02). In multiple regression analysis, change in plan conformity was negatively associated with reduction in V70 (P=0.01); plans with worse conformity indexes post-injection compared to pre-injection (n=13) still had improvements in rectal V70. Reductions in V70 did not significantly vary by institution, despite significant inter-institutional variations in plan conformity. There were no significant relationships between reduction in V70 and the other characteristics analyzed. Conclusions: Injection of hydrogel into prostate-rectal interface resulted in dose reductions to rectum for > 90% of patients treated. Rectal sparing was statistically significant across a range of 10-75 Gy, and was demonstrated within the presence of significant inter-institutional variability in plan conformity, target definitions, and injection results.