The TAM family as a therapeutic target in combination with radiation therapy

The immunogenic radiation and new players in immunotherapy and targeted therapy for head and neck cancer

Although treatment modalities for head and neck cancer have evolved considerably over the past decades, survival rates have plateaued. The treatment options remained limited to definitive surgery, surgery followed by fractionated radiotherapy with optional chemotherapy, and a definitive combination of fractionated radiotherapy and chemotherapy. Lately, immunotherapy has been introduced as the fourth modality of treatment, mainly administered as a single checkpoint inhibitor for recurrent or metastatic disease. While other regimens and combinations of immunotherapy and targeted therapy are being tested in clinical trials, adapting the appropriate regimens to patients and predicting their outcomes have yet to reach the clinical setting. Radiotherapy is mainly regarded as a means to target cancer cells while minimizing the unwanted peripheral effect. Radiotherapy regimens and fractionation are designed to serve this purpose, while the systemic effect of radiation on the immune response is rarely considered a factor while designing treatment. To bridge this gap, this review will highlight the effect of radiotherapy on the tumor microenvironment locally, and the immune response systemically. We will review the methodology to identify potential targets for therapy in the tumor microenvironment and the scientific basis for combining targeted therapy and radiotherapy. We will describe a current experience in preclinical models to test these combinations and propose how challenges in this realm may be faced. We will review new players in targeted therapy and their utilization to drive immunogenic response against head and neck cancer. We will outline the factors contributing to head and neck cancer heterogeneity and their effect on the response to radiotherapy. We will review in-silico methods to decipher intertumoral and intratumoral heterogeneity and how these algorithms can predict treatment outcomes. We propose that (a) the sequence of surgery, radiotherapy, chemotherapy, and targeted therapy should be designed not only to annul cancer directly, but to prime the immune response. (b) Fractionation of radiotherapy and the extent of the irradiated field should facilitate systemic immunity to develop. (c) New players in targeted therapy should be evaluated in translational studies toward clinical trials. (d) Head and neck cancer treatment should be personalized according to patients and tumor-specific factors.

The paradox of radiation and T cells in tumors

In this review we consider what appears to be a paradox in immunotherapies based around radiation therapy. The paradox is based on three main points. 1. That T cells are needed for radiation's efficacy; 2. That tumor-specific T cells are enriched in the field of treatment; and 3. That radiation kills T cells in the treatment field. We discuss evidence of the effect of radiation on T cells in the field given their ongoing movement in and out of tissues and the tumor, and how the movement of T cells impacts the treated primary tumor and untreated distant metastases. Given this evidence, we revisit the paradox to understand how the extraordinary efficacy of radiation and immunity in preclinical models is dependent on this radiation sensitive cell.

Review of Experimental Studies to Improve Radiotherapy Response in Bladder Cancer: Comments and Perspectives

Bladder cancer is among the top ten most common cancer types in the world. Around 25% of all cases are muscle-invasive bladder cancer, for which the gold standard treatment in the absence of metastasis is the cystectomy. In recent years, trimodality treatment associating maximal transurethral resection and radiotherapy combined with concurrent chemotherapy is increasingly used as an organ-preserving alternative. However, the use of this treatment is still limited by the lack of biomarkers predicting tumour response and by a lack of targeted radiosensitising drugs that can improve the therapeutic index, especially by limiting side effects such as bladder fibrosis. In order to improve the bladder-preserving treatment, experimental studies addressing these main issues ought to be considered (both in vitro and in vivo studies). Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews, we conducted a literature search in PubMed on experimental studies investigating how to improve bladder cancer radiotherapy with different radiosensitising agents using a comprehensive search string. We made comments on experimental model selection, experimental design and results, formulating the gaps of knowledge still existing: such as the lack of reliable predictive biomarkers of tumour response to chemoradiation according to the molecular tumour subtype and lack of efficient radiosensitising agents specifically targeting bladder tumour cells. We provided guidance to improve forthcoming studies, such as taking into account molecular characteristics of the preclinical models and highlighted the value of using patient-derived xenografts as well as syngeneic models. Finally, this review could be a useful tool to set up new radiation-based combined treatments with an improved therapeutic index that is needed for bladder preservation.

Targeting MerTK Enhances Adaptive Immune Responses After Radiation Therapy

PURPOSE

The role of MerTK, a member of the Tyro3-Axl-MerTK family of receptor tyrosine kinase, in the immune response to radiation therapy (RT) is unclear. We investigated immune-mediated tumor control after RT in murine models of colorectal and pancreatic adenocarcinoma using MerTK wild-type and knock-out hosts and whether inhibition of MerTK signaling with warfarin could replicate MerTK knock-out phenotypes.

METHODS AND MATERIALS

Wild-type and MerTK^-/- BALB/c mice were grafted in the flanks with CT26 tumors and treated with computed tomography guided RT. The role of macrophages and CD8 T cells in the response to radiation were demonstrated with cell depletion studies. The role of MerTK in priming immune responses after RT alone and with agonist antibodies to the T cell costimulatory molecule OX40 was evaluated in a Panc02-SIY model antigen system. The effect of warfarin therapy on the in-field and abscopal response to RT was demonstrated in murine models of colorectal adenocarcinoma. The association between warfarin and progression-free survival for patients treated with SABR for early-stage non-small cell lung cancer was evaluated in a multi-institutional retrospective study.

RESULTS

MerTK^-/- hosts had better tumor control after RT compared with wild-type mice in a macrophage and CD8 T cell-dependent manner. MerTK^-/- mice showed increased counts of tumor antigen-specific CD8 T cells in the peripheral blood after tumor-directed RT alone and in combination with agonist anti-OX40. Warfarin therapy phenocopied MerTK^-/- for single-flank tumors treated with RT and improved abscopal responses for RT combined with anti-CTLA4. Patients on warfarin therapy when treated with SABR for non-small cell lung cancer had higher progression-free survival rates compared with non-warfarin users.

CONCLUSIONS

MerTK inhibits adaptive immune responses after SABR. Because warfarin inhibits MerTK signaling and phenocopies genetic deletion of MerTK in mice, warfarin therapy may have beneficial effects in combination with SABR and immune therapy in patients with cancer.

Role of the immunosuppressive microenvironment in immunotherapy

Immunotherapy is reshaping cancer treatment paradigms; however, response rates to immune therapies are low and depend on the host's pre-existing antitumor immunity. The tumor microenvironment is comprised of malignant cells, stroma, and extracellular molecules and can hinder immune control of tumors. Herein, we review how anti-tumor immune responses are formed and how tumors avoid immune destruction. We also outline potential therapeutic targets in the immunosuppressive tumor microenvironment to promote immune control of tumors.