Germinal center hypoxia in tumor-draining lymph nodes negatively regulates tumor-induced humoral immune responses in mouse models of breast cancer

Hypoxia develops in germinal centers (GCs) induced by model antigens; however, it is unknown whether tumor-reactive GCs are also hypoxic. We identified GC hypoxia in lymph nodes (LNs) draining murine mammary tumors and lethally irradiated tumor cells, and found that hypoxia is associated with the levels of antibody-secreting B cells. Hypoxic culture conditions impaired the proliferation of activated B cells, and inhibited class-switching to IgG1 and IgA immunoglobulin isotypes in vitro. To assess the role of the hypoxic response in tumor-reactive GCs in vivo, we deleted von Hippel-Lindau factor (VHL) in class-switched B cells and found decreased GC B cells in tumor-draining LNs, reduced class-switched and tumor-specific antibodies in the circulation, and modified phenotypes of tumor-infiltrating T cells and macrophages. We also detected the hypoxia marker carbonic anhydrase IX in the GCs of LNs from breast cancer patients, providing evidence that GC hypoxia develops in humans. We conclude that GC hypoxia develops in TDLNs, and that the hypoxic response negatively regulates tumor-induced humoral immune responses in preclinical models.

Abstract PO-033: The angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient tumour hypoxia and improves response to ionizing radiation therapy

Poorly oxygenated (hypoxic) cells are key components of the solid tumour microenvironment that drive tumour heterogeneity. Hypoxia regulates a variety of processes that promote tumour cell survival and metastasis, and hypoxic tumour cells are resistant to therapy. Patients with tumours that contain hypoxic cells have worse outcome after radiotherapy, chemotherapy, and even surgery, underscoring the therapeutic relevance of hypoxia in driving more aggressive tumour phenotypes. Hypoxic tumour cells result from deficiencies in the delivery of oxygen relative to the high oxygen demand of tumour cells. “Chronic” hypoxia develops due to the limited diffusion distance of oxygen through tumour tissue, while “transient” hypoxia occurs due to fluctuations in microregional tumour perfusion and oxygen delivery over time. Transiently hypoxic cells are more resistant to radiation therapy and are more metastatic than chronically hypoxic cells although, despite decades of work in this area, there are no effective long-term strategies to specifically target transiently hypoxic cells in solid tumours. Angiotensin II type 1 receptor (AT1R) blockers (ARBs) are widely prescribed anti-hypertensive agents that can also exhibit anti-fibrotic activity. Recent evidence indicates that the ARB losartan can inhibit collagen I (Col1) deposition in tumours by cancer-associated fibroblasts (CAFs), reduce blood vessel constriction, and increase net tumour blood flow, although the influence of losartan or other ARBs on transient hypoxia and tumour radiation response is unknown. We hypothesized that ARB-mediated inhibition of Col1 deposition from CAFs increases tumour blood flow by stabilizing microregional fluctuations in tumour perfusion and that ARBs will reduce transient tumour hypoxia. We tested the ARBs losartan and telmisartan in human tumour xenografts using positron emission tomography and intravenously injected fluorescent perfusion dyes to quantify tumour perfusion, and a combination of exogenous hypoxia markers and the hemorheological agent pentoxifylline to assess transient tumour hypoxia. We found that CAF-containing tumours had reduced Col1 levels in response to telmisartan, but not losartan, consistent with the improved pharmacokinetics and AT1R binding affinity of telmisartan. Telmisartan increased net tumour blood flow and stabilized microregional fluctuations in tumour perfusion. Importantly, telmisartan decreased overall hypoxia in the tumours by specifically targeting transient tumour hypoxia, which translated into a significant improvement in radiation response. These data indicate that telmisartan reduces a therapeutically-relevant population of transiently hypoxic tumour cells. Understanding how the solid tumour microenvironment influences cancer therapy is central to improving treatment outcome. Our work underscores the importance of transient tumour hypoxia and supports future clinical studies to evaluate telmisartan as a neoadjuvant for radiation therapy.

Citation Format: Brennan J. Wadsworth, Rachel A. Cederberg, Che-Min Lee, Natalie S. Firmino, S. Elizabeth Franks, Jinhe Pan, Nadine Colpo, Kuo-Shyan Lin, Francois Benard, Kevin L. Bennewith. The angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient tumour hypoxia and improves response to ionizing radiation therapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-033.

Angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient hypoxia and improves tumour response to radiation

Hypoxic tumour cells are radiation-resistant and are associated with poor therapeutic outcome. A poorly understood source of tumour hypoxia is unstable perfusion, which exposes tumour cells to varying oxygen tensions over time creating "transiently" hypoxic cells. Evidence suggests that angiotensin II type 1 receptor blockers (ARBs) can improve tumour perfusion by reducing collagen deposition from cancer associated fibroblasts (CAFs). However, the influence of ARBs on transient hypoxia and tumour radiation response is unknown. We tested how the ARBs losartan and telmisartan affected the solid tumour microenvironment, using fluorescent perfusion dyes and positron emission tomography to quantify tumour perfusion, and a combination of hypoxia markers and the hemorheological agent pentoxifylline to assess transient tumour hypoxia. We found CAF-containing tumours have reduced collagen I levels in response to telmisartan, but not losartan. Telmisartan significantly increased tumour blood flow, stabilized microregional tumour perfusion, and decreased tumour hypoxia by reducing the development of transient hypoxia. Telmisartan-treated tumours were more responsive to radiation, indicating that telmisartan reduces a therapeutically important population of transiently hypoxic tumour cells. Our findings indicate telmisartan is capable of modifying the tumour microenvironment to stabilize tumour perfusion, reduce transient hypoxia, and improve tumour radiation response.

Liposomal Formulations to Modulate the Tumour Microenvironment and Antitumour Immune Response

Tumours are complex systems of genetically diverse malignant cells that proliferate in the presence of a heterogeneous microenvironment consisting of host derived microvasculature, stromal, and immune cells. The components of the tumour microenvironment (TME) communicate with each other and with cancer cells, to regulate cellular processes that can inhibit, as well as enhance, tumour growth. Therapeutic strategies have been developed to modulate the TME and cancer-associated immune response. However, modulating compounds are often insoluble (aqueous solubility of less than 1 mg/mL) and have suboptimal pharmacokinetics that prevent therapeutically relevant drug concentrations from reaching the appropriate sites within the tumour. Nanomedicines and, in particular, liposomal formulations of relevant drug candidates, define clinically meaningful drug delivery systems that have the potential to ensure that the right drug candidate is delivered to the right area within tumours at the right time. Following encapsulation in liposomes, drug candidates often display extended plasma half-lives, higher plasma concentrations and may accumulate directly in the tumour tissue. Liposomes can normalise the tumour blood vessel structure and enhance the immunogenicity of tumour cell death; relatively unrecognised impacts associated with using liposomal formulations. This review describes liposomal formulations that affect components of the TME. A focus is placed on formulations which are approved for use in the clinic. The concept of tumour immunogenicity, and how liposomes may enhance radiation and chemotherapy-induced immunogenic cell death (ICD), is discussed. Liposomes are currently an indispensable tool in the treatment of cancer, and their contribution to cancer therapy may gain even further importance by incorporating modulators of the TME and the cancer-associated immune response.

Non-coding RNAs predict recurrence-free survival of patients with hypoxic tumours

Hypoxia promotes tumour aggressiveness and reduces patient survival. A spectrum of poor outcome among patients with hypoxic tumours suggests that additional factors modulate how tumours respond to hypoxia. PIWI-interacting RNAs (piRNAs) are small non-coding RNAs with a pivotal role in genomic stability and epigenetic regulation of gene expression. We reported that cancer type-specific piRNA signatures vary among patients. However, remarkably homogenous piRNA profiles are detected across patients with renal cell carcinoma, a cancer characterized by constitutive upregulation of hypoxia-related signaling induced by common mutation or loss of von Hippel-Lindau factor (VHL). By investigating >3000 piRNA transcriptomes in hypoxic and non-hypoxic tumors from seven organs, we discovered 40 hypoxia-regulated piRNAs and validated this in cells cultured under hypoxia. Moreover, a subset of these hypoxia-regulated piRNAs are regulated by VHL/HIF signaling in vitro. A hypoxia-regulated piRNA-based score (PiSco) was associated with poor RFS for hypoxic tumours, particularly Stage I lung adenocarcinomas, suggesting that hypoxia-regulated piRNA expression can predict tumour recurrence even in early-stage tumours and thus may be of clinical utility.

Small non-coding RNA transcriptome of the NCI-60 cell line panel

Only 3% of the transcribed human genome is translated into protein, and small non-coding RNAs from these untranslated regions have demonstrated critical roles in transcriptional and translational regulation of proteins. Here, we provide a resource that will facilitate cell line selection for gene expression studies involving sncRNAs in cancer research. As the most accessible and tractable models of tumours, cancer cell lines are widely used to study cancer development and progression. The NCI-60 panel of 59 cancer cell lines was curated to provide common models for drug screening in 9 tissue types; however, its prominence has extended to use in gene regulation, xenograft models, and beyond. Here, we present the complete small non-coding RNA (sncRNA) transcriptomes of these 59 cancer cell lines. Additionally, we examine the abundance and unique sequences of annotated microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs), small nuclear RNAs (snRNAs), and small nucleolar RNAs (snoRNAs), and reveal novel unannotated microRNA sequences.