Circulating tumor cells reveal early predictors of disease progression in patients with stage III NSCLC undergoing chemoradiation and immunotherapy

Circulating tumor cells (CTCs) are early signs of metastasis and can be used to monitor disease progression well before radiological detection by imaging. Using an ultrasensitive graphene oxide microfluidic chip nanotechnology built with graphene oxide sheets, we were able to demonstrate that CTCs can be specifically isolated and molecularly characterized to predict future progression in patients with stage III non-small cell lung cancer (NSCLC). We analyzed CTCs from 26 patients at six time points throughout the treatment course of chemoradiation followed by immune checkpoint inhibitor immunotherapy. We observed that CTCs decreased significantly during treatment, where a larger decrease in CTCs predicted a significantly longer progression-free survival time. Durvalumab-treated patients who have future progression were observed to have sustained higher programmed death ligand 1+ CTCs compared to stable patients. Gene expression profiling revealed phenotypically aggressive CTCs during chemoradiation. By using emerging innovative bioengineering approaches, we successfully show that CTCs are potential biomarkers to monitor and predict patient outcomes in patients with stage III NSCLC.

Combined cytotoxic and immune-stimulatory gene therapy for primary adult high-grade glioma: a phase 1, first-in-human trial

BACKGROUND

High-grade gliomas have a poor prognosis and do not respond well to treatment. Effective cancer immune responses depend on functional immune cells, which are typically absent from the brain. This study aimed to evaluate the safety and activity of two adenoviral vectors expressing HSV1-TK (Ad-hCMV-TK) and Flt3L (Ad-hCMV-Flt3L) in patients with high-grade glioma.

METHODS

In this dose-finding, first-in-human trial, treatment-naive adults aged 18-75 years with newly identified high-grade glioma that was evaluated per immunotherapy response assessment in neuro-oncology criteria, and a Karnofsky Performance Status score of 70 or more, underwent maximal safe resection followed by injections of adenoviral vectors expressing HSV1-TK and Flt3L into the tumour bed. The study was conducted at the University of Michigan Medical School, Michigan Medicine (Ann Arbor, MI, USA). The study included six escalating doses of viral particles with starting doses of 1×1010 Ad-hCMV-TK viral particles and 1×109 Ad-hCMV-Flt3L viral particles (cohort A), and then 1×1011 Ad-hCMV-TK viral particles and 1×109 Ad-hCMV-Flt3L viral particles (cohort B), 1×1010 Ad-hCMV-TK viral particles and 1×1010 Ad-hCMV-Flt3L viral particles (cohort C), 1×1011 Ad-hCMV-TK viral particles and 1×1010 Ad-hCMV-Flt3L viral particles (cohort D), 1×1010 Ad-hCMV-TK viral particles and 1×1011 Ad-hCMV-Flt3L viral particles (cohort E), and 1×1011 Ad-hCMV-TK viral particles and 1×1011 Ad-hCMV-Flt3L viral particles (cohort F) following a 3+3 design. Two 1 mL tuberculin syringes were used to deliver freehand a mix of Ad-hCMV-TK and Ad-hCMV-Flt3L vectors into the walls of the resection cavity with a total injection of 2 mL distributed as 0·1 mL per site across 20 locations. Subsequently, patients received two 14-day courses of valacyclovir (2 g orally, three times per day) at 1-3 days and 10-12 weeks after vector administration and standad upfront chemoradiotherapy. The primary endpoint was the maximum tolerated dose of Ad-hCMV-Flt3L and Ad-hCMV-TK. Overall survival was a secondary endpoint. Recruitment is complete and the trial is finished. The trial is registered with ClinicalTrials.gov, NCT01811992.

FINDINGS

Between April 8, 2014, and March 13, 2019, 21 patients were assessed for eligibility and 18 patients with high-grade glioma were enrolled and included in the analysis (three patients in each of the six dose cohorts); eight patients were female and ten were male. Neuropathological examination identified 14 (78%) patients with glioblastoma, three (17%) with gliosarcoma, and one (6%) with anaplastic ependymoma. The treatment was well-tolerated, and no dose-limiting toxicity was observed. The maximum tolerated dose was not reached. The most common serious grade 3-4 adverse events across all treatment groups were wound infection (four events in two patients) and thromboembolic events (five events in four patients). One death due to an adverse event (respiratory failure) occurred but was not related to study treatment. No treatment-related deaths occurred during the study. Median overall survival was 21·3 months (95% CI 11·1-26·1).

INTERPRETATION

The combination of two adenoviral vectors demonstrated safety and feasibility in patients with high-grade glioma and warrants further investigation in a phase 1b/2 clinical trial.

FUNDING

Funded in part by Phase One Foundation, Los Angeles, CA, The Board of Governors at Cedars-Sinai Medical Center, Los Angeles, CA, and The Rogel Cancer Center at The University of Michigan.

Radiation biology workforce in the United States

In recent decades, the principal goals of participants in the field of radiation biologists have included defining dose thresholds for cancer and non-cancer endpoints to be used by regulators, clinicians and industry, as well as informing on best practice radiation utilization and protection applications. Importantly, much of this work has required an intimate relationship between "bench" radiation biology scientists and their target audiences (such as physicists, medical practitioners and epidemiologists) in order to ensure that the requisite gaps in knowledge are adequately addressed. However, despite the growing risk for public exposure to higher-than-background levels of radiation, e.g. from long-distance travel, the increasing use of ionizing radiation during medical procedures, the threat from geopolitical instability, and so forth, there has been a dramatic decline in the number of qualified radiation biologists in the U.S. Contributing factors are thought to include the loss of applicable training programs, loss of jobs, and declining opportunities for advancement. This report was undertaken in order to begin addressing this situation since inaction may threaten the viability of radiation biology as a scientific discipline.

NIMG-21. INTERIM ANALYSIS OF A PHASE II STUDY OF MULTIPARAMETRIC MR-GUIDED HIGH-DOSE RESPONSE-ADAPTIVE RADIOTHERAPY WITH CONCURRENT TEMOZOLOMIDE IN PATIENTS WITH NEWLY DIAGNOSED GLIOBLASTOMA

BACKGROUND

Biologically-informed radiotherapy (RT) targeting an adversely prognostic hypercellular/hyperperfused imaging phenotype in patients with newly diagnosed glioblastoma (GBM) may improve outcomes by identifying emerging regions of treatment resistance associated with survival (OS), and is under investigation in an ongoing Phase II trial (NCT04574856) of individualized, response-adaptive RT.

METHODS

In this single-arm phase II study, patients with newly diagnosed GBM following resection undergo dose-intensified chemoradiation targeting the residual hypercellular (TVHCV, mean contralateral normal brain+2SD) and hyperperfused tumor volume (TVCBV, contralateral normal frontal grey matter+1SD) identified using high b-value diffusion-weighted and dynamic contrast-enhanced perfusion MRI. The combination of TVHCVCBV (TVHCVCBV) is treated to 50 Gy in 20 fractions (2.5 Gy/fraction), and following mid-RT reassessment, the persistent and developing TVHCVCBV is treated to 30 Gy in 10 fractions (3 Gy/fraction). The primary endpoint is improvement in OS, with planned interim safety analysis.

RESULTS

Since October 2020, 16 of 30 patients have been enrolled. Median age was 58 years (range, 29-75) and 69% were male. No patient underwent biopsy only, and 50% had gross total resection; 23% had MGMT methylated tumors. Median TVHCV/TVCBV was 6.9 cc (range, 1.9-42.8) pre-RT and 30% (range, 1-72%) was nonenhancing. By mid-RT, TVHCVCBV was reduced to 4.2 cc (range, 0.8-34.3) and 47% (range, 3-74%) was nonenhancing. The TVHCVCBV persisting from pre- to mid-RT was 2.3 cc (range, 0-24.2), with an additional 1.8 cc (range, 0.3-20.6) newly developing outside the initial region. All patients underwent adaptive replanning for boost without interruption. Planned interim analysis determined an acceptable rate of neurologic toxicity and safety to continue enrollment.

CONCLUSION

Individualized, response adaptive RT using an advanced imaging biomarker to assess emerging and especially non-enhancing regions of treatment resistance in patients with GBM is feasible, with short term safety in an early cohort and longer-term efficacy outcomes anticipated with ongoing accrual.

Quantification of 3-dimensional structure and properties of flocculated natural suspended sediment

Natural sediment flocs are fragile and highly heterogeneous aggregates of biogenic and minerogenic material typically with high porosity and low density. In aquatic environments dominated by fine, cohesive or mixed sediments they can dominate suspended sediment flux. Consequently, monitoring and modelling the behaviour, transport and distribution of flocs is very important for many aquatic industries, maintenance of waterways and conservation and management of aquatic waterbodies. Mathematical models that predict the behaviour of flocs rely on the accurate assessments of the size, shape, density, porosity and fractal dimension of flocs. These inherently 3-dimensional (3D) characteristics are typically derived from 2-dimensional (2D) data, largely due to the challenges associated with sampling, capturing, imaging and quantifying these fragile aggregates. We have developed new volumetric microscopy techniques which can quantify 3D internal and external structures and characteristics of sediment flocs. Here, these techniques were applied to quantify the 3D size (volume), shape and fractal dimension of natural and artificial sediment flocs and compare them to standard 2D approaches. Our study demonstrates that 2D approaches are under-estimating shape complexity and over-estimating the size and mass settling flux of flocs by up to two orders of magnitude, and the discrepancy between 2D and 3D is most marked for natural, organic rich macroflocs. Our study has significant implications for estimations of sediment flux at local to global scales within in aquatic environments. These new data and approaches offer the potential to improve the current parameterisation of sediment transport models and to improve the accuracy of current field-monitoring techniques.

NEIM-08 A PHASE II STUDY OF MULTIPARAMETRIC MR-GUIDED HIGH DOSE ADAPTIVE RADIOTHERAPY WITH CONCURRENT TEMOZOLOMIDE IN PATIENTS WITH NEWLY DIAGNOSED GLIOBLASTOMA

BACKGROUND

Biologically-informed radiotherapy (RT) targeting an adversely prognostic hypercellular/hyperperfused imaging phenotype in patients with newly diagnosed glioblastoma (GBM) may improve outcomes by identifying emerging regions of treatment resistance associated with survival (OS), and is under investigation as a target for individualized, adaptive RT in an ongoing Phase II trial (NCT04574856).

METHODS

In this single-arm study, patients with newly diagnosed GBM following resection undergo dose-intensified chemoRT targeting the residual hypercellular (TV_HCV, mean contralateral normal brain+2SD) and hyperperfused tumor volume (TV_CBV, contralateral normal frontal grey matter+1SD) identified using high b-value diffusion-weighted and dynamic contrast-enhanced perfusion MRI. TV_HCV/TV_CBV is treated to 50 Gy in 20 fractions (2.5 Gy/fraction), and following mid-RT reassessment, the persistent and developing TV_HCV/TV_CBV is treated to 30 Gy in 10 fractions (3 Gy/fraction). The primary endpoint is improvement in OS, with planned interim safety analysis.

RESULTS

Since October 2020, 16 of 30 patients have been enrolled. Median age was 58 years (range, 29-75) and 69% were male. No patient underwent biopsy, and 50% had gross total resection; 23% had MGMT methylated tumors, and all except 2 were IDHwt. Median TV_HCV/TV_CBV was 6.9 cc (range, 1.9-42.8) pre-RT and 30% (range, 1-72%) was nonenhancing. By mid-RT, TV_HCV/TV_CBV was reduced to 4.2 cc (range, 0.8-34.3) and 47% (range, 3-74%) was nonenhancing. The TV_HCV/TV_CBV persisting from pre- to mid-RT was 2.3 cc (range, 0-24.2), with an additional 1.8 cc (range, 0.3-20.6) newly developing outside of the initial region. All patients underwent adaptive replanning for boost without interruption. Planned interim analysis determined an acceptable rate of neurologic toxicity and safety to continue enrollment.

CONCLUSION

Individualized, adaptive radiotherapy using an advanced imaging biomarker to assess emerging and especially non-enhancing regions of treatment resistance in patients with GBM is feasible, with short term safety in an early cohort and longer-term efficacy outcomes anticipated with ongoing accrual.

A surgical protocol for sinogenic brain abscess: the Oxford experience and a review of the literature

BACKGROUND

Rhinosinusitis-induced brain abscesses are rare but can result in devastating long-term sequalae and mortality; they require a high index of suspicion with early imaging to start early empiric parenteral antibiotic treatment covering aerobes and anaerobes.

METHODOLOGY

Our study was a retrospective analysis on 32 patients who were treated at Oxford University Hospitals for rhinosinusitis-induced brain abscess between February 2013 and June 2020.

RESULTS

Mean age of presentation was 45.83 for adults and 11.14 for children. Subdural collection was the most frequent abscess but 25% of patients had multiple sites of collection; the majority were in the frontal lobe. The most commonly identified pathogens were Streptococcus milleri group and Staphylococcus aureus; 93.75% of the patients were treated with combined Ceftriaxone and Metronidazole for an average of 8 weeks.

CONCLUSIONS

In our series most patients received also a prompt and aggressive surgical treatment with combined neurosurgical and ENT procedures in the majority; this was especially important in case of subdural empyema, Streptococcus milleri infection and direct intracranial spread of infection. More than half of the patients were treated with a single surgical procedure. Despite aggressive treatment, one third of patients experienced long-term neurological sequelae; there were no deaths.

CTNI-15. PHASE 0/I TRIAL OF MYCOPHENOLATE MOFETIL COMBINED WITH RADIATION TO OVERCOME GLIOBLASTOMA TREATMENT RESISTANCE BY TARGETING DE-NOVO PURINE METABOLISM: INTERIM REPORT

BACKGROUND

De novo purine synthesis promotes glioblastoma growth and stemness, invasiveness, and resistance to chemoradiation. Mycophenolate mofetil (MMF) is an FDA-approved inhibitor of de novo purine synthesis that sensitizes glioblastoma to radiation and chemotherapy in mice. This Phase 0/I trial of MMF with Radiotherapy in Recurrent Glioblastoma (NCT04477200) aims to determine the maximum-tolerated dose of MMF that can be combined with radiation,and the extent to which the active metabolite of MMF accumulates in brain tumors and inhibits de novo purine synthesis.

METHODS

Key eligibility criteria are age ≥18, KPS score ≥60%, and recurrent glioblastoma or gliosarcoma with clinical indication for re-irradiation (phase I) or re-resection/biopsy (phase 0). Patients with tumors involving ≥3 lobes or leptomeningeal space or bevacizumab use within 8 weeks are excluded. MMF 500-2000mg PO BID is given one week pre-operatively in Phase 0 (N=8), and up to 2000mg PO BID (starting 1000mg) on TITE-CRM dose escalation on Phase 1 cohort (N=30).

RESULTS

Since 7/2020, three Phase 0 and six Phase I subjects have been enrolled. On the phase I cohort, 1500mg BID dose has been reached. Studyrelated toxicities have been limited to mainly grade 1-2 nausea and fatigue. No notable study related hematotoxicity have been noted. Additionally, mass spectrometry-based correlative measurements of the activity of de novo GTP synthesis are ongoing.

CONCLUSION

MMF has been well tolerated up to 1500mg BID combined with radiotherapy in recurrent glioblastoma patients in this interim analysis. An additional upfront glioblastoma cohort with MMF with standard of care will activate in 2021. These studies will determine the maximum tolerated dose of MMF in combination with radiation and chemotherapy and provide a preliminary efficacy estimate at that dose. Encouraging results would support a randomized clinical trial to determine efficacy of MMF combined with chemoradiation in glioblastoma, and to define potential biomarkers for effectiveness.

LMD-09. Outcomes and symptom benefit from palliative radiotherapy for leptomeningeal disease in breast cancer patients

Objective

The benefit of radiotherapy (RT) in patients with leptomeningeal disease (LMD) is poorly characterized. This study assessed the overall survival (OS) and clinical improvement of a largely symptomatic cohort of breast cancer patients with LMD, to identify patient subsets most likely to benefit from palliative RT.

Methods

Patients with breast cancer-related classic radiographic LMD (36% cytology-confirmed) were treated with palliative whole brain and/or partial spine RT between 2000–2020 at a single academic institution in this retrospective analysis. OS was calculated from date of LMD diagnosis using the Kaplan-Meier method. A multivariate logistic regression model incorporating ER/PR status, HER2 status, ECOG and steroid use was developed to identify factors associated with symptom benefit, which was ascertained retrospectively by chart review.

Results

Among 64 patients, the radiographic distribution of LMD was in the brain (58%), spine (22%), or both (20%). A total of 63% had brain metastases, and 57% of patients had ER+ and/or PR+, 22% HER2+, and 38% triple-negative disease. Of the symptomatic patients (94%), primary symptom domains included cranial nerve deficits (34%), sensory/motor deficits from intracranial disease (25%) or spinal disease (27%), and headaches/nausea (14%), with 42% of patients reporting >1 symptom domain. Two-thirds of patients were on steroids prior to RT, and 13% of patients received intrathecal therapy. OS was 3.75 months. Following a median dose of 30Gy in 10 fractions, 59% of symptomatic patients experienced symptom improvement, with similar improvement rate across domains (12%, 15%, 19%, 14%, respectively); 21% of patients had improvement in >1 symptom domain. Hormone receptor positivity was independently associated with symptom improvement following RT (OR 3.5, 95% CI 1.2–11, p=0.029).

Conclusions

In this poor-prognosis cohort of breast cancer patients with LMD, palliative RT yielded symptomatic improvement, and may be particularly beneficial among better-prognosis patients with hormone receptor-positive disease.

Abstract PO-046: Combining PARP inhibition with radiation to sensitize homologous recombination proficient pancreatic cancer to immunotherapy

Pancreatic cancer is notoriously resistant to most cancer therapeutics including immunotherapy. We have previously shown that inhibition of the DNA damage response (DDR) enhances radiation-induced Type I interferon (T1IFN) and sensitizes pancreatic cancers to immunotherapy. In this study, we investigated the efficacy of radiation in combination with the poly (ADP-ribose) polymerase (PARP)inhibitor olaparib and programmed death ligand 1 (PD-L1) immune checkpoint blockade in otherwise resistant homologous recombination (HR) proficient pancreatic cancer. Initial studies demonstrated, in contrast to olaparib alone, that the combination of olaparib and radiation induced innate immune signaling in HR proficient pancreatic cancer cells marked by increases in pTBK1, T1IFN and pSTAT1. In animal tumor models, we found that the therapeutic efficacy of olaparib and radiation was greater in immune competent versus immune deficient hosts. In addition to the positive immune effects of olaparib and radiation, we also observed increased expression of PD-L1, a negative immune regulatory mechanism that likely restrains T1IFN-mediated innate immunity. We therefore went on to test the combined efficacy of PD-L1 blocking antibody with olaparib and radiation in syngeneic pancreatic tumor models. We found that monotherapy was ineffective in controlling tumor growth while doublet therapy with olaparib and radiation produced an intermediate tumor growth response. Importantly, maximal tumor growth inhibition was achieved following combined treatment with olaparib, radiation, and anti-PD-L1 which was significant relative to doublet therapy with olaparib-radiation or anti-PD-L1-radiation, and associated with a 20% complete response rate. Given that advances in therapy of pancreatic cancer require improvements in both local and systemic disease control, we examined the efficacy of combined therapy against tumors outside of the radiation field. In addition to the effects on tumors in the radiation field, we found that combined therapy with olaparib, radiation and anti-PD-L1 significantly delayed the growth of contralateral tumors outside of the radiation field, suggesting an adaptive immune response. Taken together, these studies illustrate the potential efficacy of combined therapy with olaparib, radiation, and anti-PD-L1 on both local and systemic pancreatic cancer and support our proposed clinical trial in patients with pancreatic cancer.

Citation Format: Qiang Zhang, Long Jiang, Yawen Zheng, Theodore Lawrence, Vaibhav Sahai, Michael D. Green, Meredith Morgan. Combining PARP inhibition with radiation to sensitize homologous recombination proficient pancreatic cancer to immunotherapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-046.

DDRE-28. MECHANISTIC AND THERAPEUTIC LINKS BETWEEN PURINE BIOSYNTHESIS AND DNA DAMAGE IN GLIOBLASTOMA

Glioblastoma (GBM) is the most common and aggressive adult brain cancer. Radiation therapy (RT) is a critical treatment modality, and development of RT resistance is the predominant cause of recurrence and mortality in GBM patients. Using cell line models as well as patient-derived xenografts and neurospheres in orthotopic brain tumor models, we have identified increased rates and dependence upon de novo purine biosynthesis as a hallmark of GBM RT resistance. More recently, we have discovered that radiation treatment acutely stimulates flux through de novo purine synthesis in cell line and neurosphere models of GBM. This RT-induced increase in de novo purine synthesis is dependent on signaling through the DNA damage response and thus appears to be an adaptive mechanism to supply purines to repair radiation-induced DNA damage. To determine whether this regulatory mechanism also exists in vivo, we have used advanced metabolomic and metabolic tracing techniques with ¹³C-labeled glucose and ¹⁵N-labeled glutamine in mice bearing RT-resistant GBM patient-derived orthotopic brain tumors. We found that that orthotopic GBM PDXs had elevated activity of de novo purine synthesis that increased further after RT, while normal cortex had little activity even after RT. These observations have therapeutic relevance, as targeting this metabolic pathway with the FDA-approved purine biosynthesis inhibitor mycophenolate mofetil (MMF) overcomes GBM radiation resistance in mouse models in vivo. The lack of de novo purine synthesis in normal cortex suggests that targeting this pathway may be tumor specific. Collectively our data suggest that de novo synthesis of purines mediates RT resistance in GBM and that treatment of brain tumors with MMF in combination with RT may be a promising therapeutic strategy in patients.

DDRE-19. PHASE 0/I TRIAL OF MYCOPHENOLATE MOFETIL COMBINED WITH RADIATION TO OVERCOME GLIOBLASTOMA TREATMENT RESISTANCE BY TARGETING DE-NOVO PURINE METABOLISM

BACKGROUND

Radiation resistance is one of the major limitations for effective control of glioblastoma. Guanosine triphosphate (GTP) supplementation promotes glioblastoma radioresistance. Conversely, GTP depletion overcomes glioblastoma radioresistance by slowing the repair of radiation-induced DNA damage. Mycophenolate mofetil (MMF) inhibits de novo GTP synthesis by inhibiting the key enzyme, inosine-5′-monophosphate dehydrogenase, and radiosensitizes glioblastoma in mice. These pre-clinical findings have led to Phase 0/I Dose Escalation Study of Mycophenolate Mofetil Combined with Radiation Therapy in Recurrent Glioblastoma (NCT04477200) to measure the concentration of active metabolite of MMF in glioblastoma, and to determine the safe dose of MMF when given in combination with radiation.

METHODS

Key eligibility criteria are age ≥18, patients with Karnofsky Performance Scale score ≥60, and recurrent glioblastoma or gliosarcoma with clinical indication for re-irradiation (phase I) or re-resection or biopsy (phase 0). Those with tumor involving ≥3 lobes or leptomeningeal space or bevacizumab use within 8 weeks are excluded. Eight participants will receive MMF 500–2000 mg PO BID for one week before surgery (phase 0). Approximately 30 subjects will receive MMF 250–2000 mg PO BID (starting: 1000mg) on TITE-CRM dose escalation model (phase I).

RESULTS

From 7/2020 to 11/2020, two phase 0 and three phase I subjects have completed MMF treatment without notable toxicity. Additionally, correlative measurements of the activity of de novo GTP synthesis are explored. The anticipated study duration is 48 months.

CONCLUSION

The results of this trial will aid in designing a randomized clinical trial to determine the efficacy of MMF combined with chemoradiation in glioblastoma, and to define potential biomarkers for effectiveness. MMF is widely available and inexpensive, so if positive efficacy result is observed, a brisk acceptance of MMF combined with the standard of care is anticipated.

DDRE-24. TARGETING PURINE METABOLISM TO OVERCOME GLIOBLASTOMA THERAPY RESISTANCE

Intratumoral genomic heterogeneity in glioblastoma (GBM) is a barrier to overcoming radiation (RT) resistance. To discover genotype-independent mediators of RT resistance, we correlated RT resistance with the concentration of approximately 700 metabolites across 23 GBM cell lines. Purine metabolites, especially those containing the base guanine, were most correlated with RT resistance. Similarly, increased abundance of tumor purines was associated with decreased survival in GBM patients treated with RT. This relationship is causal. Purine supplementation protected RT-sensitive GBMs from RT and promoted the repair of RT-induced double strand DNA breaks (DSBs). In vitro and in vivo stable isotope tracing confirmed that GBM cell lines and orthotopic patient-derived xenografts primarily generated purines through the de novo synthetic pathway. RT treatment further increased de novo purine synthesis in GBM through signaling via the DNA damage response. Inhibition of de novo GTP synthesis with mycophenolic acid (MPA) sensitized multiple GBM cell lines and neurospheres to RT by slowing the repair of RT-induced DSBs. MPA-induced radiosensitization was GTP-dependent as it was rescued by nucleoside supplementation. Modulating pyrimidine metabolism affected neither RT resistance nor DSB repair, suggesting these GTP-specific effects are due to active signaling rather than its ability to act as a physical substrate for DNA repair and candidate signaling molecules have been identified. These results were recapitulated in vivo with mycophenolate mofetil (MMF), the orally bioavailable FDA-approved prodrug of MPA. MMF potentiated RT efficacy, reduced tumor guanylates and slowed the repair of RT-induced DSBs across multiple models. Because de novo purine synthesis is activated by many of the oncogenic alterations that drive GBM, its inhibition is a promising genotype-independent strategy to overcome GBM RT resistance. We have now begun a clinical trial to determine whether combining MMF and RT is safe and potentially efficacious in patients with GBM.

Time to definitive care within major trauma networks in England

BACKGROUND

Significant mortality improvements have been reported following the implementation of English trauma networks. Timely transfer of seriously injured patients to definitive care is a key indicator of trauma network performance. This study evaluated timelines from emergency service (EMS) activation to definitive care between 2013 and 2016.

METHODS

An observational study was conducted on data collected from the UK national clinical audit of major trauma care of patients with an Injury Severity Score above 15. Outcomes included time from EMS activation to: arrival at a trauma unit (TU) or major trauma centre (MTC); to CT; to urgent surgery; and to death.

RESULTS

Secondary transfer was associated with increased time to urgent surgery (median 7·23 (i.q.r. 5·48-9·28) h versus 4·37 (3·00-6·57) h for direct transfer to MTC; P < 0·001) and an increased crude mortality rate (19·6 (95 per cent c.i. 16·9 to 22·3) versus 15·7 (14·7 to 16·7) per cent respectively). CT and urgent surgery were performed more quickly in MTCs than in TUs (2·00 (i.q.r. 1·55-2·73) versus 3·15 (2·17-4·63) h and 4·37 (3·00-6·57) versus 5·37 (3·50-7·65) h respectively; P < 0·001). Transfer time and time to CT increased between 2013 and 2016 (P < 0·001). Transfer time, time to CT, and time to urgent surgery varied significantly between regional networks (P < 0·001).

CONCLUSION

Secondary transfer was associated with significantly delayed imaging, delayed surgery, and increased mortality. Key interventions were performed more quickly in MTCs than in TUs.

1 vs 3 days laparoscopic suturing courses: is it feasible to design a valid training curriculum?

BACKGROUND

Laparoscopic skills are unlikely to be achieved exclusively in the operating theatre, so simulation training has become mandatory to acquire specific psychomotor skills to be merged in a more complex procedure.

OBJECTIVE

To compare 3-day vs. 1-day laparoscopic suturing courses and to better address participants' needs according to their level of experience.

METHODS

Observational cohort study conducted between January 2017 and December 2018 including 107 participants amongst which 61 attended a 3-day and 46 the 1-day suturing course.

RESULTS

Data analysis showed no significant difference in the pre-test suturing scores between the two groups. On each course, when comparing the pre- and post-tests results, the participants reached a statistically significant improvement in both precision and knotting score (p< 0.01). However, when comparing the two types of courses, the data showed a better performance in the post-session test for those attending the 3-day course (p<0.05), as well as a higher mean score improvement (4.7 vs. 2.8; p<0.05) and time needed to complete exercises (-270s vs. -150s; p<0.05). Furthermore, grouping the participants according to their experience, the experts achieved a significantly better improvement attending the 3-day course, when compared to the beginners.

CONCLUSIONS

Both 3 and 1-day course are successful in improving laparoscopic suturing skills regardless of the participant's experience. However experienced participants benefit more from a longer course while the 1-day one should be dedicated to pre-surgical competences acquisition.

Abstract 6273: TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination

Background: Basal-like breast cancer (BC) has the highest rates of local recurrence despite the use of radiation therapy. Therefore, approaches for radiosensitization are critically needed for patients with this subtype of BC.

Methods: Four independent datasets were used to correlate gene expression with local recurrence (LR) and Kaplan-Meier analysis validated the impact of TTK expression on LR. The METABRIC dataset was used to determine TTK expression in BC subtypes. Clonogenic survival assays were used to determine the radiosensitization of cell lines after TTK inhibition (TTKi). Mouse models were used to assess TTKi in combination with RT in vivo. DNA damage was quantified using γH2AX staining. HR and NHEJ efficiency assays were performed using HR/NHEJ specific reporter systems. HR competency was also assessed using Rad51 foci formation assays. Rescue experiments were performed using wild-type (WT) and kinase-dead (KD) TTK plasmids in combination with siRNA targeting the UTR region of TTK.

Results: Ten genes were found to significantly correlate with early LR (≤3 years) after surgery and radiation across 4 independent datasets (N=896 pts), with TTK, a cell cycle kinase, ranked the highest. Kaplan-Meier survival analysis in multiple cohorts demonstrated that higher than median TTK expression correlates with decrease LR free survival after RT (HR 1.70-2.42, p&lt;0.01 for all 3 cohorts). Subtype association analysis demonstrated that TTK expression was most elevated in basal-like BC. Using inducible shRNA, the combination of TTK knockdown and RT increases radiosensitivity in multiple basal-like BC cell lines (rER 1.21-1.63). Additionally, TTKi using, Bayer 1161909 (B909), enhanced radiosensitivity in multiple cell lines (rER 1.10-2.27). In vivo, TTKi, using shRNA or B909, in combination with RT led to delayed tumor growth and a significant increase in time to tumor tripling (Placebo: 9 days vs. B909+RT: undefined [&gt;35 days], p&lt;0.0001) in both cell line and PDX models. Increased DNA damage was found after combination treatment of TTKi and RT compared to RT alone, indicating that DNA damage repair mechanisms may be compromised by TTKi. The efficiency of the double strand DNA damage repair mechanism, homologous recombination (HR), but not non-homologous end joining (NHEJ), was reduced upon TTKi in HR/NHEJ specific reporter systems. Additionally, Rad51 foci formation was reduced by TTKi after RT compared to RT alone. Reintroduction of WT TTK, after knockdown of endogenous TTK, rescued radioresistance and HR efficiency, however, reintroduction of kinase-dead (KD) TTK was unable to do so in multiple cell lines. WT TTK also rescued Rad51 foci formation after knockdown of endogenous TTK while KD TTK did not.

Conclusion: These data support TTKi as a radiosensitizing strategy for clinical development in basal-like BC patients and that radiosensitization is mediated, at least in part, through impaired HR repair.

Citation Format: Benjamin Chandler, Leah Moubadder, Cassandra Ritter, Meilan Liu, Meleah Cameron, Kari Wilder-Romans, Amanda Zhang, Andrea Pesch, Anna Michmerhuizen, Nicole Hirsh, Marlie Androsiglio, Tanner Ward, Eric Olsen, Yashar Niknafs, Sofia Merajver, Dafydd Thomas, Powel Brown, Theodore Lawrence, Shyam Nyati, Lori Pierce, Arul Chinnaiyan, Corey Speers. TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6273.

MR1 in combination with tumor mutational burden and PD-1/PD-L1 expression as a potentially novel clinical predictor for T cell exhaustion and immune checkpoint inhibitor response

3109

Background: Immune checkpoint inhibitors (ICIs) restore T cell function by reversing T cell exhaustion. Variable response to ICIs warrants the development of precise predictive biomarkers, which is challenging due to difficulty in capturing the interplay of factors involved with tumor cell immune recognition. High intratumoral expression of MR1, the MHC-I related protein basally expressed on cancer cells, may drive T cell exhaustion through presentation of cancer-specific antigens. Here, we construct a database to study the relationship between MR1, tumor mutational burden (TMB), the PD-1/PD-L1 axis and T cell exhaustion across 8,975 sequenced tumors and 27 cancer types. Methods: RNA Seq by expectation maximization (RSEM) values from the TCGA were collected and normalized along with expression data for markers of interest (Table). TMB was defined as the number of non-synonymous somatic mutations per sample. For each cancer, 5 cohorts were created based on ascending mean expression levels of MR1, PD-1, PD-L1, and increasing TMB. For each cancer, an “immunogenicity score” for these factors was computed, and its relationship with T cell exhaustion signatures was assessed via linear regression. Data is presented as adjusted R2 and p-value. Results: While PD-1 and T cell exhaustion marker expression were correlated across cancers, the “immunogenicity score” (IS) correlated with exhaustion markers specifically in cancers with FDA-approved ICIs. Excluding MR1 from the score weakened the correlation with EOMES and TBET expression (Table). Each component of the score analyzed independently failed to show a statistically significant correlation for both EOMES and TBET expression. Conclusions: In this cross-cancer analysis, we support the hypothesis that presentation of metabolic intermediates in cancer cells via MR1 may drive T cell exhaustion. Also, the novel “immunogenicity score”, which incorporates MR1 into standard biomarkers for response to ICIs may convey the global picture of cancer cell recognition by the immune system and warrants further investigation as a tool for predicting clinical response. [Table: see text]

RTHP-34. IMPROVED SURVIVAL IN CNS LYMPHOMA WITH SALVAGE LOW-DOSE WHOLE-BRAIN RADIOTHERAPY WITH FOCAL BOOST AND CONCURRENT TEMOZOLOMIDE

OBJECTIVE

There is no standard salvage radiotherapy (RT) regimen, nor a consensus on the concurrent chemotherapy use in CNS lymphoma. We assessed the efficacy of low-dose whole-brain radiotherapy (WBRT) with focal-boost to the area of disease and concurrent temozolomide for the salvage treatment of CNS lymphoma.

METHODS

A single center retrospective study of CNS lymphoma patients seen between 01/2004 and 02/2019. The inclusion criteria were: diagnosis of CNS lymphoma, age > 18 years at diagnosis, radiation treatment to the brain, and formulation of plan at University of Michigan with at least one follow-up. Overall survival (OS) was determined by Kaplan Meier method.

RESULTS

Out of 93 patients (median age 58, 45% female), 73% were diagnosed with primary CNS lymphoma (n=68), and the remainder with secondary CNS lymphoma. Radiation modalities were WBRT alone (n=52), low-dose WBRT + focal boost (n=33) and focal RT alone (n=8). Twenty-six patients (28%) received concurrent temozolomide with radiation. Those who received WBRT+boost achieved complete response at a significantly higher rate than those who received WBRT alone (36% vs 17% respectively, p=0.047). The median OS among all groups was 45 months. There was a significant improvement in OS in patients receiving low-dose WBRT+boost compared to WBRT alone (median 65 vs 14 months respectively, p=0.016). OS was significantly longer in patients who received concurrent temozolomide than in those who did not (median 86 vs 23 months respectively, p=0.0287).

CONCLUSIONS

In CNS lymphoma salvage RT, a longer survival was observed with low-dose WBRT with focal-boost compared to WBRT alone, as well as with concurrent temozolomide. This result is limited by the selection bias to each of the treatment groups; however, the low-dose WBRT with focal-boost and concurrent temozolomide is a useful salvage alternative to standard WBRT as it may reduce long-term neurocognitive toxicity.

NIMG-77. RESPONSE ASSESSMENT USING MULTIPARAMETRIC MRI DURING CHEMORADIATION PREDICTS OVERALL SURVIVAL IN PATIENTS WITH NEWLY DIAGNOSED GLIOBLASTOMA

INTRODUCTION

Identifying both aggressive hypercellular (HCV) and hyperperfused (hCBV) regions of glioblastoma (GBM) prior to radiation (RT) using multiparametric MRI (mpMRI) predicts PFS and recurrence better than either technique alone, and is under investigation in a phase II trial as a novel target for dose-intensified RT. We hypothesized that early response in combined HCV/hCBV could be assessed using mpMRI and predict OS better than baseline assessment.

METHODS

Forty-three patients with newly diagnosed GBM underwent prospective high b-value (b=3000 s/mm2) DW-MRI and DCE-MRI pre-RT and 3 weeks into RT. Twenty patients were treated on a dose-escalation trial specifically targeting HCV/hCBV identified by mpMRI. An automated threshold method was used to generate HCV (mean contralateral normal brain+2SD) and hCBV (contralateral normal frontal grey matter+1SD). Survival was calculated using Kaplan-Meier method and compared using log-rank test. Age, gender, performance status, RT dose, extent of surgery, MGMT methylation, and imaging characteristic were tested in Cox proportional hazards models for survival.

RESULTS

Most patients had gross total (47%) or subtotal resection (37%), and 25% were MGMT methylated. Significant volumetric reduction during RT was observed in the Gd-enhanced volume (4.4 cc reduction, 95%CI 1.1–7.7, 17%), as well as HCV (1.8 cc reduction, 95%CI 0.2–3.4, 19%) and hCBV (1.1 cc reduction, 95%CI -0.4–2.6, 10%). No difference was observed between MGMT subgroups, but patients treated on protocol specifically targeting the mpMRI volume had significant reduction in combined HCV/hCBV (-4.4 cc, 95%CI -6.6,-2.3) vs non-protocol patients (-0.3 cc, 95%CI -2.6,2.0, p=0.006). A reduction in combined HCV/hCBV was associated with superior OS (AHR 0.60, 95%CI 0.40–0.89, p=0.01), while baseline imaging (all p< 0.90) and change in Gd-enhanced volume (p=0.61) were not.

CONCLUSIONS

Significant early response in HCV/hCBV during treatment is observed when targeted with dose-intensified RT, and is associated with improved OS with potential for adaptive strategies in future trials.

TRLS-07. BRAINSTORM: OUTCOMES FROM A MULTI-INSTITUTIONAL PHASE I/II STUDY OF RRx-001 IN COMBINATION WITH WHOLE BRAIN RADIATION THERAPY FOR PATIENTS WITH BRAIN METASTASES

INTRODUCTION: To determine the recommended Phase II dose of RRx-001, a radiosensitizer with vascular normalizing properties, when used with whole-brain radiation therapy (WBRT) for brain metastases, and to assess whether quantitative changes in perfusion MRI after RRx-001 correlate with response. METHODS AND MATERIALS: Five centers participated in this phase I/II trial of RRx-001 given once pre-WBRT then twice weekly during WBRT (30 Gy/10 fractions). Four dose levels were planned (5 mg/m2, 8.4 mg/m2, 16.5 mg/m2, 27.5 mg/m2). Dose-escalation was managed by the Time-to-Event Continual Reassessment Model (TITE-CRM). Correlative DCE-MRI was performed in a subset of patients and linear mixed models used to correlate change in 24-hour T1, Ktrans (capillary permeability) and Vp (plasma volume) with change in tumor volume. RESULTS: Between 2015–2017, 31 patients were enrolled. Two patients dropped out prior to any therapy and 7 were treated with concurrent temozolomide following a study amendment. Median age was 60 years (range, 30–76) and 17 were male. The most common tumor types were melanoma (58%) and non-small cell lung cancer (20%). No dose-limiting toxicities were observed. The most common severe adverse event was grade 3 asthenia in 6.9% (2/29). The median intracranial response rate was 46% (95%CI 24–68) and median overall survival was 5.2 months (95%CI 4.5–9.4). No neurologic deaths occurred. Among 10 evaluable patients undergoing DCE-MRI, a reduction in Vp 24 hours after RRx-001 was associated with reduced tumor volume at 1 month and 4 months (p≤0.01). CONCLUSION: The addition of RRx-001 to WBRT is safe and well-tolerated with favorable intracranial response rates. Because activity was observed across all dose levels, and in the absence of a dose response, the recommended Phase 2 dose is 10 mg administered twice weekly. A reduction in Vp by DCE-MRI 24 hours after RRx-001 suggests anti-angiogenic activity that is associated with longer-term tumor response.

CD8+ T cells regulate tumor ferroptosis by targeting the system xc− during cancer immunotherapy

Cytotoxic T cells recognize specific antigens expressed on tumor cells and mediate tumor cell apoptosis mainly through perforin–granzyme-mediated and FAS-mediated pathways. Ferroptosis is a recently discovered form of cell death that differs from apoptosis and results from iron-dependent lipid peroxide accumulation. The potential contribution of CD8+ T cell-mediated cytotoxic activity and immunotherapy to tumor ferroptosis remains unknown. Here, we find that immunotherapy-activated CD8+ T cells sensitize tumor cell ferroptosis. Mechanistically, IFNγ released from CD8+ T cells downregulates expression of SLC3A2 and SLC7A11, two subunits of glutamate-cystine antiporter system xc−, restrains tumor cell cystine uptake, and as a consequence, promotes tumor cell lipid peroxidation and ferroptosis. In preclinical models, depletion of cyst(e)ine by cyst(e)inase in combination with checkpoint blockade synergistically enhances T cell-mediated anti-tumor immunity and induces tumor cell ferroptosis. Expression of glutamate-cystine antiporter system xc− is negatively associated with CD8+ T cell signature, IFNγ expression, and cancer patient outcome. Transcriptome analyses before and during nivolumab therapy reveal that clinical benefits correlate with reduced expression of SLC3A2 and increased IFNγ and CD8. Thus, T cell-promoted tumor ferroptosis is a novel anti-tumor mechanism. Targeting tumor ferroptosis pathway constitutes a therapeutic approach in combination with checkpoint blockade.

Development of a Fully Cross-Validated Bayesian Network Approach for Local Control Prediction in Lung Cancer

The purpose of this study is to demonstrate that a Bayesian network (BN) approach can explore hierarchical biophysical relationships that influence tumor response and predict tumor local control (LC) in non-small-cell lung cancer (NSCLC) patients before and during radiotherapy from a large-scale dataset. Our BN building approach has two steps. First, relevant biophysical predictors influencing LC before and during the treatment are selected through an extended Markov blanket (eMB) method. From this eMB process, the most robust BN structure for LC prediction was found via a wrapper-based approach. Sixty-eight patients with complete feature information were used to identify a full BN model for LC prediction before and during the treatment. Fifty more recent patients with some missing information were reserved for independent testing of the developed pre- and during-therapy BNs. A nested cross-validation (N-CV) was developed to evaluate the performance of the two-step BN approach. An ensemble BN model is generated from the N-CV sampling process to assess its similarity with the corresponding full BN model, and thus evaluate the sensitivity of our BN approach. Our results show that the proposed BN development approach is a stable and robust approach to identify hierarchical relationships among biophysical features for LC prediction. Furthermore, BN predictions can be improved by incorporating during treatment information.

Application of Next Generation Sequencing for Diagnostic Testing of Tree Fruit Viruses and Viroids

Conventional detection of viruses and virus-like diseases of plants is accomplished using a combination of molecular, serological, and biological indexing. These are the primary tools used by plant virologists to monitor and ensure trees are free of known viral pathogens. The biological indexing assay, or bioassay, is considered to be the "gold standard" as it is the only method of the three that can detect new, uncharacterized, or poorly characterized viral disease agents. Unfortunately, this method is also the most labor intensive and can take up to three years to complete. Next generation sequencing (NGS) is a technology with rapidly expanding possibilities including potential applications for the detection of plant viruses. In this study, comparisons are made between tree fruit testing by conventional and NGS methods, to demonstrate the efficacy of NGS. A comparison of 178 infected trees, many infected with several viral pathogens, demonstrated that conventional and NGS were equally capable of detecting known viruses and viroids. Comparable results were obtained for 170 of 178 of the specimens. Of the remaining eight specimens, some discrepancies were observed between viruses detected by the two methods, representing less than 5% of the specimens. NGS was further demonstrated to be equal or superior for the detection of new or poorly characterized viruses when compared with a conventional bioassay. These results validated both the effectiveness of conventional virus testing methods and the use of NGS as an additional or alternative method for plant virus detection.

Morphological Measurements of the Proximal Interphalangeal Joint

The morphology of the proximal interphalangeal joint was determined using a photographic technique. The head of the proximal phalanx, viewed end on, has a complex trapezoid appearance characteristic for each named digit. The asymmetric condyles diverge from one another and are separated by an intercondylar groove that increases in depth from the dorsal to the palmar surface. Saggital sections of the head of the proximal phalanx are not circular, but, sections taken in the plane of maximum dimensions of the condyle are circular with a radius of curvature of approximately one half of the height of the condyles.

The articular surface of the base of the middle phalanx is not circular in outline in either the saggital or coronal plane. In coronal sections the articular surface is biconcave convex with a prominent median ridge separating the two adjacent concave articular surfaces.

The implications of this varied morphology on implant design are discussed.

Emerging therapies for the treatment of relapsed or refractory follicular lymphoma

With no treatment standard having been established for relapsed and refractory follicular lymphoma, a number of therapeutic approaches are used in Canada. In patients who relapse early or who eventually become resistant to subsequent treatment, prognosis is poor, and new approaches are needed. A number of novel therapies are being examined in this setting, including monoclonal antibodies, immunoconjugates, immunomodulatory agents, and signal transduction inhibitors. With the body of evidence for those emerging therapies accumulating and the standard upfront treatment changing from rituximab and chop (cyclophosphamide-doxorubicin-vincristine-prednisone) or rituximab and cvp (cyclophosphamide-vincristine-prednisone) to bendamustine and rituximab, treatment decisions in the relapsed and refractory setting have become more complex. The choice of subsequent treatment must consider type of upfront treatment; duration of remission; and patient-related factors such as age, comorbidities, and treatment preferences. This paper summarizes the evidence for novel therapies and proposes recommendations for subsequent treatment options by remission duration after induction and maintenance.

Traumatic brain injury in England and Wales: prospective audit of epidemiology, complications and standardised mortality

OBJECTIVES

To provide a comprehensive assessment of the management of traumatic brain injury (TBI) relating to epidemiology, complications and standardised mortality across specialist units.

DESIGN

The Trauma Audit and Research Network collects data prospectively on patients suffering trauma across England and Wales. We analysed all data collected on patients with TBI between April 2014 and June 2015.

SETTING

Data were collected on patients presenting to emergency departments across 187 hospitals including 26 with specialist neurosurgical services, incorporating factors previously identified in the Ps14 multivariate logistic regression (Ps14ⁿ) model multivariate TBI outcome prediction model. The frequency and timing of secondary transfer to neurosurgical centres was assessed.

RESULTS

We identified 15 820 patients with TBI presenting to neurosurgical centres directly (6258), transferred from a district hospital to a neurosurgical centre (3682) and remaining in a district general hospital (5880). The commonest mechanisms of injury were falls in the elderly and road traffic collisions in the young, which were more likely to present in coma. In severe TBI (Glasgow Coma Score (GCS) ≤8), the median time from admission to imaging with CT scan is 0.5 hours. Median time to craniotomy from admission is 2.6 hours and median time to intracranial pressure monitoring is 3 hours. The most frequently documented complication of severe TBI is bronchopneumonia in 5% of patients. Risk-adjusted W scores derived from the Ps14ⁿ model indicate that no neurosurgical unit fell outside the 3 SD limits on a funnel plot.

CONCLUSIONS

We provide the first comprehensive report of the management of TBI in England and Wales, including data from all neurosurgical units. These data provide transparency and suggests equity of access to high-quality TBI management provided in England and Wales.

Abstract B76: Targeting Mcl-1 for radiosensitization of pancreatic cancers

In order to identify targets whose inhibition may enhance the efficacy of chemoradiation in pancreatic cancer and, thus, improve survival in patients with locally advanced pancreatic cancer, we conducted an siRNA library screen of 8,800 genes. We identified Mcl-1 (myeloid cell leukemia-1), an anti-apoptotic member of the Bcl-2 family, as a target for sensitizing pancreatic cancer cells to gemcitabine-radiation. Thus, we investigated Mcl-1 inhibition by genetic (siRNA) and pharmacological (small molecule) approaches as a radiosensitizing strategy in pancreatic cancer cells. Mcl-1 depletion by siRNA radiosensitized BxPC-3, Panc-1, and MiaPaCa-2 cells with radiation enhancement ratios (RER) of 1.5±0.06, 1.4±0.03, and 1.3±0.01, respectively, and caused Caspase-3 activation and PARP cleavage. We next tested the ability of the recently identified, selective, small molecule inhibitor of Mcl-1, UMI-77 (Abulwerdi F et al., Mol Cancer Ther, 2014), to inhibit the anti-apoptotic functions of Mcl-1 and radiosensitize in pancreatic cancer cells. Consistent with inhibition of Mcl-1 anti-apoptotic function, UMI-77 (1-5uM) caused dissociation of Mcl-1 from the pro-apoptotic protein Bak. Under these same conditions, UMI-77 produced significant radiosensitization in BxPC-3 and Panc-1 cells (RER: 1.5±0.1 and 1.3±0.04, respectively; P&lt;0.05) with minimal radiosensitization of MiaPaCa-2 cells (1.2±0.07). Since Mcl-1 expression levels are highest in BxPC-3 and Panc-1 cells and lowest in MiaPaCa-2 cells, these results suggest that elevated Mcl-1 protein levels may be a biomarker for radiosensitization by Mcl-1 inhibition. In addition, radiosensitization by UMI-77 was associated with Caspase-3 activation, PARP cleavage, and increased sub-G1 DNA content. In contrast, ABT-737, a well-established inhibitor of Bcl-2, Bcl-XL, and Bcl-w, failed to radiosensitize pancreatic cancer cells suggesting the unique importance of Mcl-1 in radiation survival. Taken together, these results validate Mcl-1 as a target for radiosensitization of pancreatic cancer cells and demonstrate the efficacy of small molecules which displace Mcl-1 from Bak/Bax as radiosensitizers in pancreatic cancer. Furthermore, these results support continued investigation of UMI-77 and its analogues in animal models and in combination with gemcitabine-radiation as a strategy for radiation and chemoradiation sensitization of pancreatic cancers.

Citation Format: Qiang Zhang, Dongping Wei, Jason Schreiber, Tasneem Kausar, Theodore Lawrence, Yi Sun, Zaneta Nikolovska-Coleska, Meredith A. Morgan. Targeting Mcl-1 for radiosensitization of pancreatic cancers. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B76.