Story, Michael D.

Abstract Background Radiation-induced heart disease (RIHD) may develop months to years following radiation therapy for cancers near the heart such as lung or breast cancer. Several mouse models of RIHD exist to study the pathogenesis of disease, but to our knowledge no studies have examined whether sex differences exist in RIHD in mice. Methods Female and male BALB/cJ mice received one whole heart dose of 22 Gray (Gy) radiation via a C5 collimator vs. sham controls that received 0 Gy, anesthesia and were placed in the X-ray machine for the same length of time. Mechanisms of cardiotoxicity were examined at 24 h (innate cardiotoxicity), day 10 (acute cardiotoxicity) and day 35 (chronic cardiotoxicity) post irradiation. Results Females and males developed dsDNA breaks from radiation at day 10 but females had more damage than males ( p < 0.001). Vessel area and cardiac hypertrophy were increased by radiation at day 10 and 35 but were higher in males than females at day 35 ( p < 0.001, p = 0.001, respectively). Bulk RNA sequencing of the heart at day 10 revealed that females and males developed similar gene pathway responses to radiation by upregulating cellular repair pathways and downregulated mitochondrial function. However, females upregulated the master regulator of mitochondrial function, Pgc1α ( p = 0.0001), suggesting improved mitochondrial repair in females. By day 35, males developed heart failure with reduced ejection fraction (HFrEF), inflammatory dilated cardiomyopathy (iDCM) and fibrosis while females developed heart failure with preserved ejection fraction (HFpEF) without inflammation or fibrosis. Conclusions We observed sex differences in nearly every cardiac parameter that we examined following radiation exposure. BALB/c males exposed to 22 Gy radiation developed HFrEF and iDCM by day 35 while females developed HFpEF. Further research is needed to better understand mechanisms driving sex differences in RIHD using translational animal models.

Abstract DAB2IP (Disabled homolog 2 interacting protein), a recognized tumor suppressor, plays a pivotal role in regulating various oncogenic pathways. Our previous research demonstrated that DAB2IP functions as a cell cycle regulator by facilitating PLK1-mediated mitosis progression. Here, we elucidate a novel function of DAB2IP in promoting DNA replication origin firing. Mechanistically, we identified that DAB2IP localizes to the nucleus, where it interacts with the histone acetyltransferase HBO1 and enhances the HBO1–PLK1 interaction. DAB2IP facilitates PLK1-mediated phosphorylation of HBO1, which subsequently promotes HBO1-directed acetylation of histone 3 at lysine 14 (H3K14Ac). This modification enables the loading of the minichromosome maintenance protein (MCM) complex onto chromatin, thereby supporting DNA replication and maintaining genome integrity. Additionally, we found that ATR regulates CDK1-mediated phosphorylation of DAB2IP, and that this phosphorylation is essential for the formation and activation of the HBO1-PLK1 complex. Ablation of DAB2IP phosphorylation results in increased genomic instability due to incomplete replication of genomic DNA, as evidenced by the accumulation of anaphase ultrafine bridges and 53BP1 nuclear bodies in G1 phase of the cell cycle. In summary, our findings underscore the critical regulatory role of DAB2IP in DNA replication initiation and genomic stability maintenance, providing new insights into its function in cellular homeostasis.

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 .

Abstract The clinical success of immune checkpoint inhibitors in treating metastatic and refractory cancers has generated significant interest in investigating their role in treating locally advanced diseases, thus requiring them to be combined with standard treatments in the hope of producing synergistic antitumor responses. Radiotherapy, in particular, has long been hypothesized to have actions complementary to those of immune checkpoint blockade, and a growing body of evidence indicates that cancer immunotherapy may also have radiosensitizing effects, which would provide unique benefit for locoregional treatments. Recent studies have demonstrated that when immune cells are activated by immunotherapeutics, they can reprogram the tumor microenvironment in ways that may potentially increase the radiosensitivity of the tumor. In this review, we highlight the evidence that supports reciprocal interactions between cancer immunotherapy and radiotherapy, where in addition to the traditional notion that radiation serves to enhance the activation of antitumor immunity, an alternative scenario also exists in which T-cell activation by cancer immunotherapy may sensitize tumors to radiation treatment through mechanisms that include normalization of the tumor vasculature and tissue hypoxia. We describe the empirical observations from preclinical models that support such effects and discuss their implications for future research and trial design.