A major goal of cancer immunotherapy has been to re-activate quiescent tumor-associated T-cells to enhance their detection and killing of cancer cells in tumor microenvironments. It is well established that with persistent activation of T- cells, in chronic inflammation and cancer, immune suppressive checkpoints exist that inhibit T- cell activation to limit collateral damage to host tissues. Building on this knowledge cancer therapies have been developed that block T-cell checkpoints using monoclonal antibodies. Checkpoint blocking strategies that have targeted the inhibition of two T-cell checkpoints, PD-1 and CTLA-4, have been curative for some cancers. However, a majority of patients either do not respond or the responses are not durable. A likely reason for this is the presence of other immune regulatory systems that suppress T-cell function in tumors, including T regulatory cells and myeloid derived suppressor cells that perhaps must also be eliminated. Recently there has been a growing awareness that nano-sized extracellular vesicles present in tumors are able to arrest T-cell function. We have isolated micro-vesicles called exosomes (EX) from human tumors that bind to and internalize into T-cells resulting in a rapid and reversible blockade in the activation potential of these cells. The immunosuppressive EX represents a new T- cell checkpoint that results in an arrest of the activation the T-cell signaling cascade. The suppression of T-cells has been causally linked to phosphatidylserine (PS) expressed on the surface of the EX. Several non-toxic water soluble organic molecules that bind PS have been synthesized by our collaborators at MTTI, and have been screened and shown by us at IMT LLC, to block/reverse the immune suppressive activity of tumor-associated EX. One of the PS binding molecules, Zn- T-DPA, significantly inhibits the T-cell immune suppression of the tumor-associated EX in vitro. .
In Aim 1 the pharmacokinetics (PK), the bio-availability and toxicity of Zn-T-DPA, will be addressed in globally immune deficient NSG naive mice, and in these mice bearing human ovarian tumor xenografts.
In Aim 2 we will determine the pharmacodynamics (PD) of this molecule in vivo. We predict, and will test here, that treatment in vivo with Zn-T-DPA (at a dose determined in Aim 1) of NSG mice bearing human ovarian tumor xenografts will block or reverse the T-cell suppression by the tumor-associated exosomes, re-activate patients? tumor- associated T-cells, and enhance tumor killing in the tumor microenvironment. With our novel xenograft model (that includes tumor stroma, the tumor-associated T-cells, and exosomes) we are able to quantify several matrices including changes in tumor cell number, serum levels of human cytokines, and in the number and activation potential of the tumor- associated T-cells. Our in vivo studies in Phase 1 of this application are expected to provide a rationale and underpinning for a Phase II application to study the PK, PD and efficacy of the Zn-T-DPA in combination with currently used checkpoint inhibition therapies, and provide for a scale up development of the Zn-T-DPA for a Phase I clinical trial.
Small vesicles have been identified in human ovarian tumors that inhibit the anti-tumor responses of patients? white blood cells (called T cells). A drug has been discovered that selectively blocks the immune suppressive vesicles. We predict that by blocking the vesicles? effect in the tumors we will be able to reactivate quiescent T cells, and thereby enhance their tumor killing activity and prevent tumor spreading. This is to be tested in this grant using novel techniques that have made it possible to study human tumors and tumor-associated T cells that are established as grafts in immune deficient mice.
