Abstract PD10-06: PD10-06 Clinical outcomes and exploratory gene expression analysis of OPPORTUNE: a phase II window-of-opportunity study to evaluate pictilisib+anastrozole versus anastrozole alone in ER-positive breast cancer

Background: Endocrine therapy (ET) is the mainstay of ER+ BC treatment. However; up to 20% of ER+ BC tumors progress into metastatic disease and develop ET resistance, underscoring the need for combination therapies. Preclinical data suggest that combining phosphatidylinositol 3-kinase (PI3K) inhibitors with ET may overcome resistance. OPPORTUNE, a preoperative phase II window trial, evaluated whether the combination of the PI3K inhibitor pictilisib with anastrozole (PIC+ANA) can increase the antitumor effect of ANA in newly diagnosed operable ER+ BC. Early results showed greater suppression of tumor Ki67 in patients treated with PIC+ANA versus ANA alone. Here, we present gene expression analysis from tumors collected pre- and post-treatment, and their associations with Ki67 outcomes. Methods: Postmenopausal women with newly diagnosed operable ER+/HER2-negative BC were randomly allocated (2:1, favoring the combination) to 2 weeks of preoperative treatment with ANA 1 mg once per day (n = 47) or the combination of ANA 1 mg with PIC 260 mg once per day (n = 89). The primary end point was inhibition of tumor cell proliferation measured by change in Ki67 protein expression via IHC between tumor samples taken pre- and post-treatment. Samples were analyzed by RNA-sequencing—ER pathway activity, PAM50 intrinsic subtypes, and pathway analyses were assessed by Ki67 outcomes. Elastic net regression analysis and transcription factor activity inference with Dorothea were performed to identify features strongly associated with Ki67 outcomes. Results: 124 patients (ANA, n=43; PIC+ANA, n=81) had paired tumor samples at baseline/week 2 that were evaluable for both Ki67 and RNA-seq. PIC+ANA showed improved suppression of Ki67 compared to ANA alone (-83.78% vs -73.85%, p=0.012) and a greater proportion of patients achieved complete cell cycle arrest (CCCA, as defined by Ki67< 2.7%) in the PIC+ANA arm (45.68% vs 36.59%). ER pathway activity suppression was comparable between treatments. PAM50 classification based on RNA-seq showed that 83.0% of tumors were luminal (Lum) A at baseline and 12.9% were LumB, with the remainder being classified as Normal-like. PIC+ANA showed greater suppression of Ki67 in LumB tumors compared to LumA (-92.29% vs -81.62%). This effect was much greater in the PIC+ANA arm compared to LumB tumors treated with ANA alone (-92.29% vs -37.87%); however, given the low number of LumB tumors in the ANA arm (n=3), we could not determine statistical significance. Bioinformatic analysis of RNA-seq from baseline specimens showed that MYBL2 activity was associated with resistance to ANA (as defined by Ki67≥7.5% at week2). Tumors in the top quartile of MYBL2 activity at baseline showed improved Ki67 outcomes in the PIC+ANA arm compared to ANA alone (-91.71% vs -51.44%), while no differences were observed between treatments for tumors with lower MYBL2 activity (-79.16% vs -76.72%). Single-nucleus (sn)-RNA-seq from untreated ER+ BC tumors showed that MYBL2 was enriched in a single cluster of tumor cells, which also had the highest expression of a subset of actionable targets (including CDK1, CDK2, CDK4, EZH2, and AKT1), as compared to other tumor cells. Expression data from DepMap and drug-sensitivity data from ER+ BC cell lines show a positive trend between high MYBL2 expression and sensitivity to the ER degrader, giredestrant. Conclusions: PIC exhibited greater antiproliferative effects in combination with ANA in ER+/HER2- early BC compared to ANA alone, particularly in LumB and MYBL2-high tumors. Furthermore, the transcriptional profile and in vitro response of tumor cells with high MYBL2 expression suggest potential sensitivity to other combination therapies.

Citation Format: Alejandro Martinez Chibly, Alice Shia, Radia Johnson, Michael S. Hwang, Marc Hafner, Ciara Metcalfe, Kalpit Shah, Michal Slyper, Chris Bolen, Sarah E. Pinder, Alastair M. Thompson, Steven Gendreau, Peter Schmid. PD10-06 Clinical outcomes and exploratory gene expression analysis of OPPORTUNE: a phase II window-of-opportunity study to evaluate pictilisib+anastrozole versus anastrozole alone in ER-positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD10-06.

Enteric viruses replicate in salivary glands and infect through saliva

Enteric viruses like norovirus, rotavirus and astrovirus have long been accepted as spreading in the population through fecal-oral transmission: viruses are shed into feces from one host and enter the oral cavity of another, bypassing salivary glands (SGs) and reaching the intestines to replicate, be shed in feces and repeat the transmission cycle1. Yet there are viruses (for example, rabies) that infect the SGs2,3, making the oral cavity one site of replication and saliva one conduit of transmission. Here we report that enteric viruses productively and persistently infect SGs, reaching titres comparable to those in the intestines. We demonstrate that enteric viruses get released into the saliva, identifying a second route of viral transmission. This is particularly significant for infected infants, whose saliva directly transmits enteric viruses to their mothers' mammary glands through backflow during suckling. This sidesteps the conventional gut-mammary axis route4 and leads to a rapid surge in maternal milk secretory IgA antibodies5,6. Lastly, we show that SG-derived spheroids7 and cell lines8 can replicate and propagate enteric viruses, generating a scalable and manageable system of production. Collectively, our research uncovers a new transmission route for enteric viruses with implications for therapeutics, diagnostics and importantly sanitation measures to prevent spread through saliva.

Salivary Gland Function, Development and Regeneration

Salivary glands produce and secrete saliva, which is essential for maintaining oral health and overall health. Understanding both the unique structure and physiological function of salivary glands, as well as how they are affected by disease and injury will direct the development of therapy to repair and regenerate them. Significant recent advances, particularly in the OMICS field, increase our understanding of how salivary glands develop at the cellular, molecular and genetic levels; the signaling pathways involved, the dynamics of progenitor cell lineages in development, homeostasis and regeneration and the role of the extracellular matrix microenvironment. These provide a template for cell and gene therapies as well as bioengineering approaches to repair or regenerate salivary function.

Insulin-Like Growth Factor-1-Mediated DNA Repair in Irradiated Salivary Glands Is Sirtuin-1 Dependent

Ionizing radiation is one of the most common cancer treatments; however, the treatment leads to a wide range of debilitating side effects. In patients with head and neck cancer (HNC), the surrounding normal salivary gland is extremely sensitive to therapeutic radiation, and damage to this tissue results in various oral complications and decreased quality of life (QOL). In the current study, mice treated with targeted head and neck radiation showed a significant increase in double-stranded breaks (DSB) in the DNA of parotid salivary gland cells immediately after treatment, and this remained elevated 3 h posttreatment. In contrast, mice pretreated with insulin-like growth factor-1 (IGF-1) showed resolution of the same amount of initial DNA damage by 3 h posttreatment. At acute time points (30 min to 2 h), irradiated parotid glands had significantly decreased levels of the histone deactylase Sirtuin-1 (SirT-1) which has been previously shown to function in DNA repair. Pretreatment with IGF-1 increased SirT-1 protein levels and increased deacetylation of SirT-1 targets involved in DNA repair. Pharmacological inhibition of SirT-1 activity decreased the IGF-1-mediated resolution of DSB. These data suggest that IGF-1 promotes DNA repair in irradiated parotid glands through the maintenance and activation of SirT-1.

Palliative Care for Salivary Gland Dysfunction Highlights the Need for Regenerative Therapies: A Review on Radiation and Salivary Gland Stem Cells

Radiotherapy remains the major course of treatment for Head and Neck cancer patients. A common consequence of radiation treatment is dysfunction of the salivary glands, which leads to a number of oral complications including xerostomia and dysphagia, for which there is no existent cure. Here, we briefly describe the current palliative treatments available for patients undergoing these conditions, such as oral lubricants, saliva substitutes, and saliva stimulants. None of these options achieves restoration of normal quality of life due to their limited effectiveness, and in some cases, adverse side effects of their own. Other therapies under development, such as acupuncture and electrostimulation have also yielded mixed results in clinical trials. Due to the ineffectiveness of palliative care to restore quality of life, it is reasonable to aim for the development of regenerative therapies that allow restoration of function of the salivary epithelium following radiation treatment. Adult stem cells are a necessary component of wound healing, and play important roles in preserving normal function of adult tissues. Thus, the present review mainly focuses on the effects of radiation on adult stem cells in a variety of tissues, which may be at play in the response of salivary glands to radiation treatment. This is of clinical importance because progenitor cells of the salivary glands have shown partial regenerative potential in mouse transplantation assays. Therefore, understanding how these progenitor cells are affected by radiation offers potential for development of new therapies for patients with xerostomia.

Impact of targeting insulin-like growth factor signaling in head and neck cancers

The IGF system has been shown to have either negative or negligible impact on clinical outcomes of tumor development depending on specific tumor sites or stages. This review focuses on the clinical impact of IGF signaling in head and neck cancer, the effects of IGF targeted therapies, and the multi-dimensional role of IRS 1/2 signaling as a potential mechanism in resistance to targeted therapies. Similar to other tumor sites, both negative and positive correlations between levels of IGF-1/IGF-1-R and clinical outcomes in head and neck cancer have been reported. In addition, utilization of IGF targeted therapies has not demonstrated significant clinical benefit; therefore the prognostic impact of the IGF system on head and neck cancer remains uncertain.

Deletion of ATG5 shows a role of autophagy in salivary homeostatic control

Autophagy is a catabolic pathway utilized to maintain a balance among the synthesis, degradation, and recycling of cellular components, thereby playing a role in cell growth, development, and homeostasis. Previous studies revealed that a conditional knockout of essential member(s) of autophagy in a variety of tissues causes changes in structure and function of these tissues. Acinar cell-specific expression of knocked-in Cre recombinase through control of aquaporin 5 (Aqp5) promoter/enhancer (Aqp5-Cre) allows us to specifically inactivate Atg5, a protein necessary for autophagy, in salivary acinar cells of Atg5(f/f);Aqp5-Cre mice. There was no difference in apoptotic or proliferation levels in salivary glands of Atg5/Cre mice from each genotype. However, H&E staining and electron microscopy studies revealed modestly enlarged acinar cells and accumulated secretory granules in salivary glands of Atg5(f/f);Aqp5-Cre mice. Salivary flow rates and amylase contents of Atg5/Cre mice indicated that acinar-specific inactivation of ATG5 did not alter carbachol-evoked saliva and amylase secretion. Conversely, autophagy intersected with salivary morphological and secretory manifestations induced by isoproterenol administration. These results identified a role for autophagy as a homeostasis control in salivary glands. Collectively, Atg5(f/f);Aqp5-Cre mice would be a useful tool to enhance our understanding of autophagy in adaptive responses following targeted head and neck radiation or Sjögren syndrome.