Image-guided radiation therapy of tumors in preclinical models.

Image-guided radiation therapy (IGRT) platforms for preclinical research represent an important advance for radiation research. IGRT-based platforms more accurately model the delivery of therapeutic ionizing radiation as delivered in clinical practice which permits more translationally and clinically relevant radiation biology research. Fundamentally, IGRT allows for precise delivery of ionizing radiation in order to (1) ensure that the tumor and/or target of interest is adequately covered by the prescribed radiation dose, and (2) to minimize the radiation dose delivered to adjacent nontargeted or normal tissues. Here, we describe the techniques and outline a general workflow employed for IGRT in preclinical in vivo tumor models.

LTX-315-enabled, radiotherapy-boosted immunotherapeutic control of breast cancer by NK cells.

LTX-315 is a nonameric oncolytic peptide in early clinical development for the treatment of solid malignancies. Preclinical and clinical evidence indicates that the anticancer properties of LTX-315 originate not only from its ability to selectively kill cancer cells, but also from its capacity to promote tumor-targeting immune responses. Here, we investigated the therapeutic activity and immunological correlates of intratumoral LTX-315 administration in three syngeneic mouse models of breast carcinoma, with a focus on the identification of possible combinatorial partners. We found that breast cancer control by LTX-315 is accompanied by a reconfiguration of the immunological tumor microenvironment that supports the activation of anticancer immunity and can be boosted by radiation therapy. Mechanistically, depletion of natural killer (NK) cells compromised the capacity of LTX-315 to limit local and systemic disease progression in a mouse model of triple-negative breast cancer, and to extend the survival of mice bearing hormone-accelerated, carcinogen-driven endogenous mammary carcinomas. Altogether, our data suggest that LTX-315 controls breast cancer progression by engaging NK cell-dependent immunity.

Radiation-activated secretory proteins of Scgb1a1+ club cells increase the efficacy of immune checkpoint blockade in lung cancer.

Radiation therapy (RT) in combination with immune checkpoint inhibitor (ICI) represents a promising regimen for non-small cell lung cancer (NSCLC), however, the underlying mechanisms are poorly characterized. We identified a specific dose of RT that conferred tumor regression and improved survival in NSCLC models when combined with ICI. The immune-modulating functions of RT was ascribed to activated lung-resident Scgb1a1+ club cells. Importantly, mice with club cell-specific knockout of synaptosome-associated protein 23 failed to benefit from the combination treatment, indicating a pivotal role of club cell secretome. We identified 8 club cells secretory proteins, which inhibited immunosuppressive myeloid cells, reduced pro-tumor inflammation, and enhanced anti-tumor immunity. Notably, CC10, a member of club cell secretome was increased in plasma of NSCLC patients responding to the combination therapy. By revealing an immune-regulatory role of club cells, our studies have the potential to guide future clinical trials of ICI in NSCLC.

Activin A Promotes Regulatory T-cell-Mediated Immunosuppression in Irradiated Breast Cancer.

Increased regulatory T cells (Treg) after radiotherapy have been reported, but the mechanisms of their induction remain incompletely understood. TGFß is known to foster Treg differentiation within tumors and is activated following radiotherapy. Thus, we hypothesized that TGFß blockade would result in decreased Tregs within the irradiated tumor microenvironment. We found increased Tregs in the tumors of mice treated with focal radiotherapy and TGFß blockade. This increase was mediated by upregulation of another TGFß family member, activin A. In vitro, activin A secretion was increased following irradiation of mouse and human breast cancer cells, and its expression was further enhanced upon TGFß blockade. In vivo, dual blockade of activin A and TGFß was required to decrease intratumoral Tregs in the context of radiotherapy. This resulted in an increase in CD8+ T-cell priming and was associated with a reduced tumor recurrence rate. Combination of immune checkpoint inhibitors with the dual blockade of activin A and TGFß led to the development of tumor-specific memory responses in irradiated breast cancer. Supporting the translational value of activin A targeting to reduce Treg-mediated immunosuppression, retrospective analysis of a public dataset of patients with breast cancer revealed a positive correlation between activin A gene expression and Treg abundance. Overall, these results shed light on an immune escape mechanism driven by activin A and suggest that dual targeting of activin A and TGFß may be required to optimally unleash radiation-induced antitumor immunity against breast cancer.

PTEN as a Guardian of the Genome: Pathways and Targets.

Faithful transmission of genetic information is only possible with the structural and functional integrity of the genome. PTEN has been recognized as a guardian of the genome since the identification of its noncanonical localization and function in the nucleus. Yet, the role of PTEN in guarding the genome relies on integration of diverse mechanisms elicited by its canonical activity in antagonizing PI3K as well as emerging noncanonical functions. In the nucleus, PTEN maintains the structural integrity of chromosomes and the architecture of heterochromatin by physically interacting with chromosomal and nucleosomal components. PTEN also controls the functional integrity of key genetic transmission machineries by promoting proper assembly of the replisome and mitotic spindles. Deregulation of PTEN signaling impairs genome integrity, leading to spontaneous replication/mitotic stress and subsequent stress tolerance. Identification of novel targets of PTEN signaling and illumination of the interplay of diverse PTEN pathways in genome maintenance will help us better understand mechanisms underlying tumor evolution and therapeutic resistance.

Converging focal radiation and immunotherapy in a preclinical model of triple negative breast cancer: contribution of VISTA blockade.

Antibodies targeting the co-inhibitory receptor programmed cell death 1 (PDCD1, best known as PD-1) or its main ligand CD274 (best known as PD-L1) have shown some activity in patients with metastatic triple-negative breast cancer (TNBC), especially in a recent Phase III clinical trial combining PD-L1 blockade with taxane-based chemotherapy. Despite these encouraging findings, however, most patients with TNBC fail to derive significant benefits from PD-L1 blockade, calling for the identification of novel therapeutic approaches. Here, we used the 4T1 murine mammary cancer model of metastatic and immune-resistant TNBC to test whether focal radiation therapy (RT), a powerful inducer of immunogenic cell death, in combination with various immunotherapeutic strategies can overcome resistance to immune checkpoint blockade. Our results suggest that focal RT enhances the therapeutic effects of PD-1 blockade against primary 4T1 tumors and their metastases. Similarly, the efficacy of an antibody specific for V-set immunoregulatory receptor (VSIR, another co-inhibitory receptor best known as VISTA) was enhanced by focal RT. Administration of cyclophosphamide plus RT and dual PD-1/VISTA blockade had superior therapeutic effects, which were associated with activation of tumor-infiltrating CD8+ T cells and depletion of intratumoral granulocytic myeloid-derived suppressor cells (MDSCs). Overall, these results demonstrate that RT can sensitize immunorefractory tumors to VISTA or PD-1 blockade, that this effect is enhanced by the addition of cyclophosphamide and suggest that a multipronged immunotherapeutic approach may also be required to increase the incidence of durable responses in patients with TNBC.

Radiotherapy Cooperates with IL15 to Induce Antitumor Immune Responses.

Focal radiotherapy can promote cross-presentation of tumor antigens to T cells, but by itself, it is insufficient to induce therapeutically effective T-cell responses. The common gamma-chain cytokine IL15 promotes and sustains the proliferation and effector function of CD8+ T cells but has limited activity against poorly immunogenic tumors that do not elicit significant spontaneous T-cell responses. Here, we show that radiotherapy and subcutaneous IL15 had complementary effects and induced CD8+ T-cell-mediated tumor regression and long-term protective memory responses in two mouse carcinoma models unresponsive to IL15 alone. Mechanistically, radiotherapy-induced IFN type I production and Batf3-dependent conventional dendritic cells type 1 (cDC1) were required for priming of tumor-specific CD8+ T cells and for the therapeutic effect of the combination. IL15 cooperated with radiotherapy to activate and recruit cDC1s to the tumor. IL15 alone and in complex with a hybrid molecule containing the IL15α receptor have been tested in early-phase clinical trials in patients with cancer and demonstrated good tolerability, especially when given subcutaneously. Expansion of natural killer (NK) cells and CD8+ T cells was noted, without clear clinical activity, suggesting further testing of IL15 as a component of a combinatorial treatment with other agents. Our results provide the rationale for testing combinations of IL15 with radiotherapy in the clinic.