Project 1: Novel TRTs for Dosimetry-Guided Immunomodulation

Leader: Jamey Weichert, PhD

Professor
Department of Radiology
Director of the Contrast Agent Laboratory
University of Wisconsin

Co-leader: Bryan Bednarz, PhD

Associate Professor
Departments of Medical Physics and Human Oncology
University of Wisconsin

Summary

Our immune system protects us from the majority of invasive diseases but cancer cells are often able to avoid detection by our immune system. It has recently been discovered that combining radiotherapy with immunotherapy is more effective than either treatment alone. Conventional radiation therapy typically cannot treat all tumor sites in patients with metastatic disease because of potential side effects and because of its inability to target small tumors that are not seen on imaging scans. We have overcome these limitations by combining radioactive tumor-seeking molecules with different types of immunotherapy, and our goal is to determine how this type of treatment renders tumors more responsive to immunotherapy and to ultimately use imaging to optimize this treatment approach for cancer patients.

Specific Aims

Characterize the tumor uptake and bio-distribution over time for each therapeutic NM600 chelate (⁹⁰Y, ¹⁷⁷Lu, ²²⁵Ac) and for selected alternative TRT vectors (¹³¹I-MIBG, ⁹⁰Y-αGD2 mAb, ²²⁵Ac-αGD2 mAb, ¹³¹I-NM404, ⁹⁰Y-αSNPR-Fab, ⁹⁰Y-PSMA-617) in syngeneic murine tumor models.
Compare the dynamic dose-dependent effects of RT on tumor immune infiltrate and the host immune system using syngeneic murine tumor models for each therapeutic NM600 chelate and selected alternative TRT vectors.
Demonstrate that the ranges of tumor-absorbed doses necessary for immunomodulation can be safely translated to larger species by testing each therapeutic NM600 chelate in companion canines with spontaneous cancers. For this, we will characterize dosimetry, radionuclide bio-distribution, and effect on tumor immune infiltrate and immune cell counts in peripheral blood.

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Mounting preclinical and clinical evidence demonstrates that external beam radiation therapy (EBRT) can enhance the systemic anti-tumor response to immunotherapies (ImmRx) by modifying the tumor microenvironment (TME) in ways that enhance tumor immune susceptibility. Others and we have observed that in the setting of multifocal or metastatic disease this capacity of focal EBRT to elicit in situ vaccination (optimal at doses of 8-12 Gy) may be further enhanced by delivering low dose radiation (RT; 2-4 Gy) to all tumor sites. In this capacity, low dose RT may play a critical role in overcoming tumor-specific immune suppression from RT-sensitive immune lineages [e.g. regulatory T cells (Tregs)] and may also enhance the immune susceptibility of tumor cells at these disseminated sites by cGAS/STING activation of a type I interferon (IFN) response. The limited ability of EBRT to target all tumor sites without considerable risk of toxicity is a major hurdle that limits the capacity of EBRT to modulate the collective TME in this manner. In the setting of microscopic or metastatic disease, it is not possible to treat all TMEs with EBRT at the doses required for immunomodulation without also incurring lymphopenia. Consequently, a radiotherapy modality is needed that can deliver immunomodulatory RT doses to all tumor sites without triggering systemic immunosuppression. To meet this need, we hypothesize that molecularly targeted radionuclide therapy (TRT), a systemic form of radiotherapy combining a tumor-selective vector with a therapeutic radioisotope, will deliver immunomodulatory RT to all metastatic tumor sites resulting in significant tumor responses without systemic immune suppression.

To effectively study these broad mechanisms requires a TRT agent with 1) selective uptake across a breadth of malignancy, 2) a theranostic capacity for delivery of paired isotopes that can be used for therapy and diagnostic imaging (e.g. 90Y and 86Y, respectively) to facilitate personalized dosimetry, and 3) the ability to bind and deliver diverse radionuclides to study the differential capacity of these to immunomodulate the TME of micro and macro-metastases. Current FDA-approved TRTs are limited in their capacity to achieve this vision. We have developed a novel TRT vector, NM600, which is optimally suited for this broad application in dose-dependent immunomodulation and which has produced many complete responses including tumor specific immune memory induction in syngeneic murine tumor models when used in combination with checkpoint inhibition (Project 2), immunocytokine (Project 3), and DNA vaccine (Project 4) immunotherapies. Project 1 will investigate how the properties of different TRT vectors and radionuclides (e.g. linear energy transfer (LET), dose rate, and dose distribution) influence the TME and the host immune system in syngeneic mouse models relevant to each Project and also in companion canine cancer patients to assess whether parallel effects can be translated to a larger species. In Projects 2-4, this knowledge will be utilized to optimize the combination of TRT with each type of ImmRx and to elucidate biological mechanisms of observed synergies.