Hannan, Raquibul

Abstract The tumor landscape of pancreatic ductal adenocarcinoma (PDAC) is refractory to conventional photon radiotherapy (RT) because of a fibrotic tumor microenvironment (TME) that promotes chronic hypoxia and reduced immune surveillance. The radiobiological factors unique to carbon ion RT (CIRT), such as high linear energy transfer and less dependence on oxygen, make it well-suited to overcome the PDAC TME. In this study, we utilized clonal syngeneic KPC pancreatic tumor cell lines and tumors to examine this postulate and to identify underlying factors that affect the response of PDAC to CIRT. Although KPC cell lines exhibited radiobiological effectiveness greater than 3, subcutaneous tumors in the mouse hind leg showed lower radiobiological effectiveness—1.3 based on quintupling time—at a linear energy transfer between 70 and 80 keV/μm. Four days after CIRT, we observed widespread transcriptomic changes in the tumor immune microenvironment, suggesting increased infiltration of antitumor immune cells and elevated expression of antitumor T-cell cytokines, MHC class I molecules, and co-stimulatory signals. Fewer immunologic changes were observed following photon irradiation. By 7 days after CIRT, tumor-supportive transcriptomic programs characterized by protumor cytokines, M2 macrophages, and cancer-associated fibroblasts emerged, promoting resistance and limiting the durability of tumor growth delay. These findings suggest that CIRT may offer a favorable platform compared with conventional photon RT for combining with immunotherapies. Furthermore, these data highlight the risk of using in vitro survival data alone in treatment planning and indicate that underlying TME factors affect the response of PDAC in vivo.

Abstract The tumor landscape of pancreatic ductal adenocarcinoma (PDAC) is refractory to conventional photon radiotherapy (RT) due to a fibrotic tumor microenvironment (TME) that promotes chronic hypoxia and reduced immune surveillance. The radiobiological factors unique to carbon ion radiotherapy (CIRT), such as high linear energy transfer (LET) and less dependence on oxygen, make it well-suited to overcome the PDAC TME. Here, we utilized clonal syngeneic KPC pancreatic tumor cell lines and tumors to examine this postulate and to identify underlying factors that impact the response of PDAC to CIRT. While KPC cell lines exhibited radiobiologic effectiveness (RBE) greater than 3, subcutaneous tumors in the mouse hind leg showed lower RBEs – 1.3 based on quintupling time – at a LET of 75 keV/μm. Four days after CIRT, we observed widespread transcriptomic changes in the tumor immune microenvironment (TME), suggesting increased infiltration of anti-tumor immune cells, elevated expression of anti-tumor T cell cytokines, MHC class I molecules, and co-stimulatory signals. Fewer immunologic changes were observed following photon irradiation. By seven days after CIRT, tumor-supportive transcriptomic programs characterized by pro-tumor cytokines, M2 macrophages, and cancer-associated fibroblasts (CAFs) emerged, promoting resistance and limiting the durability of tumor growth delay. These findings suggest that CIRT may offer a favorable platform compared to conventional photon radiation therapy for combining with immunotherapies. Furthermore, these data highlight the risk of using in vitro survival data alone in treatment planning and indicate that underlying TME factors impact the response of PDAC in vivo .

387 Background: Level 1 evidence supports treatment of high-risk and node positive PCa using 4-9 weeks of radiotherapy (RT) combined with 18-36 months of androgen deprivation therapy (ADT) with or without abiraterone acetate plus prednisone (AAP). While effective, some cancers recur, and this prolonged treatment is associated with inconvenience and variable morbidity. We aimed to determine whether the biological synergy of stereotactic body radiotherapy (SBRT) with a 6-month combination of ADT, AAP, and the PARP inhibitor niraparib, could enable a shorter intensified, yet safe and effective, therapeutic alternative. Methods: ASCLEPIuS (NCT04194554) is a multicenter investigator-initiated phase I/II trial in high-risk or node positive, homologous recombination unselected, PCa. Patients received 6 months of ADT, AAP, niraparib and SBRT to the prostate (37.5-40 Gy) +/- pelvic lymph nodes (25 Gy). Focal prostate/nodal boosting was permitted. The phase I primary endpoint was the maximum tolerated dose (MTD) of niraparib using the time-to-event continuous reassessment method (3 dose levels: 100 mg and 200 mg held during SBRT, or 200 mg concurrent with SBRT). Dose limiting toxicities (DLT) were any persistent grade 4+ hematologic toxicity or any grade 3+ rectal/urinary toxicity at least possibly related to treatment as assessed by CTCAE v5.0. Patient reported quality of life (QOL) was assessed with the EPIC-26 short form. Linear mixed models were used to compare scores over time. Results: Accrual began in Nov. 2020 with a transition from phase I to phase II in May 2023 after enrolling 54 men. Median follow-up of the phase I cohort is 12.1 months (IQR 9.4-18.9), 80% (n=43) had Grade Group 4-5, median PSA was 17 ng/mL (range, 1-73), 15% (n=8) had cN+ disease, and 76% (n=41) received nodal RT. There were 0 DLTs to date, no grade 3+ rectal or urinary toxicities, and 5 serious adverse events at least possibly attributable to study treatment (anemia, non-rectal gastrointestinal, syncope, infection, musculoskeletal). The most common grade 3 toxicities were hypertension (n = 11, 21%) and leukopenia (n=6, 11%). Transient dose reductions or holds of AAP or niraparib occurred in 10 and 11 patients, respectively. There were no statistically significant declines in patient reported urinary QOL at 6- or 12-months post-treatment compared to baseline (all p >0.15). A transient decline in bowel QOL at 6-months occurred (p<0.01), which improved by 12-months (p=0.16). Conclusions: Our phase I findings support the short-term safety and tolerability of the combination of SBRT to the prostate and nodes, ADT, AAP, and niraparib at an MTD of 200 mg in men with high-risk or node positive PCa. Our trial completed phase II enrollment in May 2024, and longer-term safety, efficacy, and genomic correlations will be presented in the future. Clinical trial information: NCT04194554 .