Patterns of Locoregional Failure After Ablative 5-Fraction Stereotactic MR-Guided on-Table Adaptive Radiation Therapy for Pancreatic Cancer

PURPOSE/OBJECTIVE(S)

SBRT for pancreatic ductal adenocarcinoma (PDAC) is routinely delivered with non-ablative dose to only gross disease resulting in locoregional failure (LRF) rates of >50%, most commonly near the celiac artery (CA) and/or superior mesenteric artery (SMA). It is unclear whether an alternative approach of prescribing ablative dose to gross disease plus elective coverage prevents and/or delays LRF. The study objective was to describe the incidence and anatomic distribution of LRF using this treatment approach.

MATERIALS/METHODS

A single institution retrospective analysis was performed of non-metastatic PDAC patients who received ablative stereotactic MR-guided on-table adaptive radiation therapy (A-SMART) on a 0.35T MR-Linac from 2018-2022. Median prescribed dose was 50 Gy/5 fractions. Elective coverage (EC), including a margin around the primary tumor, CA, and SMA, to 33-35 Gy/5 fractions became routine in 2019 using a simultaneous integrated boost; the porta hepatis was not routinely covered. LRFs were contoured and defined as out-of-field (OOF), marginal (M), or in-field (IF) if >80%, 20-80%, or <20% of it was outside of the most peripheral prescription isodose line.

RESULTS

One hundred four patients were evaluated (87% head tumors). 94% had induction chemotherapy (median 4 months), usually FOLFIRINOX (66%) or gemcitabine/nab-paclitaxel (27%). 88% received EC. Median GTV, CTV, PTVgrosstumor, and PTVelective volumes were 29 cc, 90 cc, 64 cc, and 127 cc, respectively. 16 patients (15%) had LRF after a median of 17 months (range: 2.4-30.8) from A-SMART; 13 had scans available for delineating LRF. Median follow-up from A-SMART for the entire cohort vs. LRF was 12 vs. 24 months. LRF involved the primary tumor (31%), retroperitoneal lymph nodes (25%), SMA (19%), porta hepatis (19%), and CA (6%). LRF was OOF, M, or IF in 30.8% (n = 4), 61.5% (n = 8), and 7.7% (n = 1). Distance from the 3 SMA failures to SMA origin was 10 cm (EC used), 9.3 cm (EC used), and 3 cm (no EC). The 1 CA failure involved the CA origin (no EC). Median mean, maximum, and minimum dose of the contoured LRF region on the original plan was 33.3 Gy (range: 9.7-50.3 Gy), 56 Gy (range: 44.2-71.4 Gy), and 11.4 Gy (range: 1.2-22.7 Gy), respectively. Median V20, V25, V30, V35, and V40 of the contoured LRF was 84.3% (range: 16.1-100%), 69.2% (range: 12.5-99.7%), 57.5% (range: 9.3-95.5%), 41.2% (range: 6.8-84.0%), and 32.7% (range: 4.8-71.8%).

CONCLUSION

This study represents the first patterns of LRF analysis after ablative 5-fraction SBRT for PDAC. Although EC is not currently endorsed by published pancreas SBRT guidelines, our low LRF incidence especially involving the CA/SMA demonstrates that EC should be considered, even when delivering ablative dose. Furthermore, given that nearly all LRF were M or OOF we have considered expanding our institutional elective volumes. While the optimal EC dose is uncertain, 33-35 Gy appears effective in limiting IF LRF and therefore has been standardized within ongoing ablative SBRT trials for PDAC at our institution.

Ablative 5-Fraction CT vs. MR-Guided Pancreatic SBRT: Evaluation of Interfraction Anatomic Changes on Dosimetric Constraints

PURPOSE/OBJECTIVE(S)

CT-guided SBRT for locally advanced pancreatic cancer (LAPC) is usually non-ablative (BED < 100 Gy10) to minimize grade 3+ toxicity risks given the concern of interfraction anatomic changes (IACs) in GI anatomy and imaging quality associated with kV-CBCT. Emerging data demonstrate that MR guidance facilitates 5-fraction (fx) dose escalation due to superior soft tissue contrast, continuous intrafraction imaging, automatic beam gating, and on-table adaptive replanning capability. Treatment outcomes for ablative 5-fx CT- vs. MR-guided SBRT are not well characterized, nor are differences in predicted GI OAR doses when accounting for IACs.

MATERIALS/METHODS

Weevaluated 40 plans (20 CT, 20 MR) for 20 LAPC patients (pts) previously treated in breath hold (BH) on a 0.35 T MR-Linac. Prescribed dose was 50 Gy (gross disease) and 33 Gy (elective) in 5 fx using a simultaneous integrated boost technique. CT plans were retrospectively created using 2-3 VMAT arcs with the same prescription dose, target volumes (assuming BH), and constraints (prioritizing OARs over target coverage) as the MR IMRT plans (∼20-40 fields). CT planners were blinded to MR plans. We compared predicted GI OAR dose of CT vs. MR plans across each of the 5 fx for all 20 patients to evaluate the dosimetric impact of IACs by coregistering CT plans to the anatomy of the day based on 0.35T MR scans acquired for GI OAR segmentation and treatment delivery.

RESULTS

MedianV100% of the GTV, CTV, PTV50, and PTV33 across the original CT vs. MR plans were 97.5% vs. 91.3% (p = 0.017), 99.9% vs. 98.2% (p<0.01), 86.2% vs. 79.3% (p = 0.39), and 97.2% vs. 93.0% (p<0.01), respectively. GI OAR constraints were met for all original CT/MR plans although it was predicted that 1+ GI OAR constraint would be violated (most commonly duodenum) for 88/100 CT vs. 85/100 MR fractions. Across the 88 violated CT fractions, the median predicted GI OAR doses were duodenum V35: 3.3 cc (range: 0.16-18.0cc), duodenum V40: 1.2 cc (range: 0.01-11.9cc), small bowel V35: 1.2 cc (range: 0.4-10.9cc), small bowel V40: 0.2 cc (range: 0.04-7.0cc), stomach V35: 1.5 cc (range: 0.52-6.8cc), stomach V40: 0.3 cc (range: 0.05-2.8cc). GI OAR doses across the 85 violated MR fractions were similar. Median fxs per pt with 1+ predicted GI OAR violation was 5 (range: 1-5) for both CT and MR plans.

CONCLUSION

This isthe first evaluation of IAC effects on predicted GI OAR dose for 5-fx CT- vs. MR-guided SBRT. Although VMAT arcs facilitated higher target coverage in the initial CT plans, GI OAR constraint violations were observed in 85-88% of CT/MR plans. Although on-table adaptive replanning is routine on MR-guided Linacs it is not commonly available on CT-guided Linacs. As such, ablative 5-fx SBRT delivered with CT guidance is expected to result in significant toxicity due to exceeding GI OAR constraints for most delivered fractions.

Chikungunya Virus Vaccine Candidate Incorporating Synergistic Mutations Is Attenuated and Protects Against Virulent Virus Challenge

BACKGROUND

Chikungunya virus (CHIKV) is an arbovirus that periodically emerges to cause large epidemics of arthritic disease. Although the robust immunity elicited by live-attenuated virus (LAV) vaccine candidates makes them attractive, CHIKV vaccine development has been hampered by a high threshold for acceptable adverse events.

METHODS

We evaluated the vaccine potential of a recently described LAV, skeletal muscle-restricted virus (SKE), that exhibits diminished replication in skeletal muscle due to insertion of target sequences for skeletal muscle-specific miR-206. We also evaluated whether these target sequences could augment safety of an LAV encoding a known attenuating mutation, E2 G82R. Attenuation of viruses containing these mutations was compared with a double mutant, SKE G82R.

RESULTS

SKE was attenuated in both immunodeficient and immunocompetent mice and induced a robust neutralizing antibody response, indicating its vaccine potential. However, only SKE G82R elicited diminished swelling in immunocompetent mice at early time points postinoculation, indicating that these mutations synergistically enhance safety of the vaccine candidate.

CONCLUSIONS

These data suggest that restriction of LAV replication in skeletal muscle enhances tolerability of reactogenic vaccine candidates and may improve the rational design of CHIKV vaccines.

Molecular Basis for Antiviral Action of EDP‐235: A Potent and Selective SARS‐CoV‐2 3CLpro Inhibitor for the Treatment of Covid 19

To date, there are no approved oral antiviral therapies that can be administered early in the course of COVID‐19 to suppress progression of the disease or for prophylaxis. EDP‐235 is a potent and selective inhibitor of SARS‐CoV‐2 3C‐like protease (3CLpro). EDP‐235 inhibits SARS‐CoV‐2 3CLpro protease activity with an IC₅₀ of 5.8 ± 3.7 nM and retains its activity against variant 3CLpro proteins from multiple SARS‐CoV‐2 lineages (IC₅₀range of 2.8­–5.8 nM). 3CLpro protease activity progress curves showed significant curvature in a time‐ and EDP‐235‐concentration‐dependent manner indicative of slow‐onset inhibition. Slow reversal of inhibition of SARS‐CoV‐2 3CLpro enzyme activity was observed in a jump dilution experiment. Michaelis‐Menten kinetic studies with a FRET peptide substrate in the presence of EDP‐235 indicated that EDP‐235 is a substrate‐competitive inhibitor of SARS‐CoV‐2 3CLpro with an overall dissociation constant K_iof 3.0 ± 1.6 nM. SARS‐CoV‐2 3CLpro was crystallized bound to a close analog of EDP‐235 and structure elucidation revealed that the ligand bound at the active site and interacted with side chains of conserved residues Cys‐145, His‐163, and Glu‐166. EDP‐235 also potently inhibits 3CLpro enzymes from other α‐coronaviruses (IC₅₀range of 2–4 nM) and β‐coronaviruses (SARS‐CoV IC₅₀ of 5.4 nM, MERS‐CoV IC₅₀ of 70 nM) which cause disease in humans to date. EDP‐235 resistance mutations in HCoV‐229E map to the active site of 3CLpro close to the predicted binding site and offer additional support to the mechanism of inhibition. EDP‐235 also showed a favorable selectivity profile (>300 selectivity index) when tested against a panel of 30 mammalian proteases. In summary, EDP‐235 acts as a slow‐onset, slow‐reversible, substrate‐competitive inhibitor of SARS‐CoV‐2 3CLpro. The outstanding preclinical profile of EDP‐235 supports its further evaluation as an oral therapeutic for the management of COVID‐19.

Chikungunya virus replication in skeletal muscle cells is required for disease development

Chikungunya virus (CHIKV) is an arbovirus capable of causing a severe and often debilitating rheumatic syndrome in humans. CHIKV replicates in a wide variety of cell types in mammals, which has made attributing pathologic outcomes to replication at specific sites difficult. To assess the contribution of CHIKV replication in skeletal muscle cells to pathogenesis, we engineered a CHIKV strain exhibiting restricted replication in these cells via incorporation of target sequences for skeletal muscle cell-specific miR-206. This virus, which we term SKE, displayed diminished replication in skeletal muscle cells in a mouse model of CHIKV disease. Mice infected with SKE developed less severe disease signs, including diminished swelling in the inoculated foot and less necrosis and inflammation in the interosseous muscles. SKE infection was associated with diminished infiltration of T cells into the interosseous muscle as well as decreased production of Il1b, Il6, Ip10, and Tnfa transcripts. Importantly, blockade of the IL-6 receptor led to diminished swelling of a control CHIKV strain capable of replication in skeletal muscle, reducing swelling to levels observed in mice infected with SKE. These data implicate replication in skeletal muscle cells and release of IL-6 as important mediators of CHIKV disease.

667. Preclinical Pharmacokinetic and Pharmacodynamic Characterization of EDP-938, a Novel and Potent NonFusion Replication Inhibitor of Respiratory Syncytial Virus

Background

Respiratory syncytial virus (RSV) infection presents a significant health challenge in young children, elderly and immunocompromised patients. To date, there are no effective treatments available. EDP-938 was designed to meet this unmet medical need and is currently in Phase 2 clinical trials. Herein we report its preclinical pharmacokinetic (PK) and pharmacodynamic (PD) properties.

Methods

The pharmacokinetics of EDP-938 following single intravenous and oral doses were determined in mice, rats, dogs, and monkeys. In vitro cellular permeability and metabolic stability were assayed using Caco-2 cells and human liver microsomes, respectively. In vivo pharmacodynamic efficacy of EDP-938 was conducted in the African green monkey model, in which animals experimentally challenged with RSV were orally dosed twice daily with 100 mg/kg EDP-938 for 6 days starting 24 hours prior to infection.

Results

EDP-938 was well absorbed in the preclinical species with oral bioavailability values ranging from 27.1% in dogs, 35.4% in mice, 35.7% in rats, and 39.5% in monkeys, after a single oral dose when formulated in 0.5% methylcellulose. EDP-938 showed a moderate in vitro permeability of 3.6 x 10^–6 cm/sec in Caco-2 cells. Based on the outcome of these absorption studies, EDP-938 was projected to have good oral absorption in humans. EDP-938 had low intrinsic clearance of 5 mL/minute/mg in human liver microsomes. Moreover, EDP-938 demonstrated potent antiviral efficacy in an African green monkey model of RSV infection. In untreated monkeys the RSV RNA viral load in the bronchoalveolar lavage fluid peaked at 10⁶ copies/mL on day 5 post-infection, by comparison in animals treated with EDP-938 the viral load was below the limit of detection by day 3 post-infection. The PK/PD modeling suggested that plasma trough concentrations ≥10 × EC₉₀ led to >4-log viral load reduction in EDP-938 treated monkeys.

Conclusion

The favorable preclinical PK and PD properties of EDP-938 support its further clinical development as a novel treatment for RSV infection.

Disclosures

All authors: No reported disclosures.

A soil bacterium alters sex determination and rhizoid development in gametophytes of the fern Ceratopteris richardii

Gametophytes of the fern Ceratopteris richardii develop into either hermaphrodites or males. As hermaphrodites develop, they secrete antheridiogen, or A_CE, into the environment, inducing male development in undifferentiated gametophytes. Hermaphrodites are composed of archegonia, antheridia, rhizoids and a notch meristem, while males consist of antheridia and rhizoids. Much of the research on sexual and morphological development concerns gametophytes grown in sterile environments. Using biochemical and molecular techniques we identify a soil bacterium and explore its effects on sexual and rhizoid development. Hermaphrodite and male gametophytes were exposed to this bacterium and the effects on sexual development, rhizoid length and rhizoid number were explored. The bacterium was identified as a pseudomonad, Pseudomonas nitroreducens. Gametophytes grown in the presence of the pseudomonad were more likely to develop into hermaphrodites across all gametophyte densities. Across all gametophyte sizes, hermaphrodites had rhizoids that were 2.95× longer in the presence of the pseudomonad while males had rhizoids that were 2.72× longer in the presence of the pseudomonad. Both hermaphrodite and male gametophytes developed fewer rhizoids in the presence of the pseudomonad. Control hermaphrodites produced 1.23× more rhizoids across all gametophyte sizes. For male gametophytes grown in the absence of the pseudomonad, the rate of increase in the number of rhizoids was greater with increasing size in the control than the rate of increase in males grown in the presence of the pseudomonad. The pseudomonad may be acting on gametophyte sexual development via several potential mechanisms: degradation of A_CE, changes in nutrient availability or phytohormone production. The pseudomonad may also increase rhizoid number through production of phytohormones or changes in nutrient availability.

Reovirus infection triggers inflammatory responses to dietary antigens and development of celiac disease

Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (T_H1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pT_reg) conversion and promoting T_H1 immunity to dietary antigen. Initiation of T_H1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pT_reg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.

Comparative evaluation of the performance of the Abbott real-time human immunodeficiency virus type 1 (HIV-1) assay for measurement of HIV-1 plasma viral load following automated specimen preparation

The performance of the new Abbott real-time human immunodeficiency virus type 1 (HIV-1) assay for HIV-1 RNA load determination in plasma was compared to that of the Abbott LCx HIV-1 RNA quantitative assay following automated RNA isolation by the Abbott m1000 extractor. The measured viral loads of 89 clinical specimens differed by mean 0.19 log10 copies/ml (95% confidence interval, 0.12 to 0.26 log10 copies/ml). Although the difference in viral load determinations was positively skewed in favor of the LCx assay, it did not reach statistical significance (P = 0.42). Results were linearly associated (R2 = 0.94) and strongly correlated (R = 0.96). Good performance was observed with HIV-1 subtypes other than B and circulating recombinant forms, although results obtained with two subtype G specimens and one H specimen showed a more substantial difference.