LTX-315 is a novel oncolytic peptide that has been designed de novo based on the structure–activity relationship of host defense peptides. The oncolytic effect of LTX-315 involves a unique immunogenic cell death targeting the mitochondria with subsequent release of danger-associated molecules. This initial targeting of the mitochondria is followed by disintegration of other cytoplasmic organelles resulting in the effective release of additional danger signals and a broad repertoire of tumor antigens leading to lysis of plasma membrane (necrosis). Through this mode of action, LTX 315 creates an essential premise for tumour specific polyclonal T cell responses.
Figure 1: LTX-315 trigger necrotic cell death. U2OS osteosarcoma cells treated with LTX-315 adopted a necrotic morphology with absent plasma membranes and vacuolated cyto-plasms (Forveille et al, Cell Cycle. 2015)
Figure 2: LTX-315 induces immunogenic cell death in cancer cells. When treated with LTX-315, dying cancer cells release damage-associated molecular patterns (DAMP) such as calreticulin, ATP, HMGB1, mitochondria-derived DNA (mtDNA) and formyl peptides (FMIT). DAMPs bind to specific receptors on antigen-presenting cells such as dendritic cells (DC) and promotes their maturation and engulfment of tumor-antigens with subsequent presentation to T cells and execution of effective immune response (Zhou et al, and Eike et al, Oncotarget, 2015, Zhou et al, Cell Death and Disease, 2016, Sveinbjørnsson et al, Future Medicinal Chemistry, 2017)
Figure 3: A proposed mechanism of action for intratumoral treatment with LTX-315
In vivo studies
Preclinical and clinical studies have demonstrated LTX-315`s unique ability to reshape the tumor microenvironment by inducing effective release of danger signals, chemokines and a broad range of tumor antigens. The treatment with LTX-315 also reprograms the tumor microenvironment by decreasing the local abundance of immunosuppressive T-regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs) (Yamazaki et al. Cell Death and Differentiation, 2016) and enhanced infiltration of polyclonal CD8T cells (Figure 4).
Figure 4: LTX-315 induce clonal expansion of T cells in both blood and treated lesion.
Preclinical studies have also confirmed LTX-315’s ability to induce systemic anticancer immune response when injected locally into tumors resulting in complete or partial regression of injected and non-injected tumors (i.e. abscopal effect). In addition, long-term protective immune responses have been demonstrated in cured animals (Nestvold et al, OncoImmunology, 2017).
Furthermore, a strong synergy with immune-checkpoint blockade has been demonstrated. Immune-checkpoint inhibitors have shown survival benefit in a small proportion of cancer patients with pre-existing T cells, indicating that combination therapies are needed. Since intratumoral administration of LTX-315 enhances tumor infiltration of T cells, both in number and diversity in cancer patients (personalized in situ vaccination), it is an ideal candidate for combination with other types of immunotherapy and provides the scientific rationale for initiating combination studies with immune checkpoint inhibitors in cancer patients (Figure 5).
Figure 5: LTX-315 works in synergy with immune checkpoint therapy. LTX-315 treatment caused regressions in tumors that were resistant to anti-CTLA4. (Murine MCA205 sarcoma; Yamazaki et al 2016)
LTX-315 as a T cell primer is ideal for combination therapy
An efficient T cell mediated tumor specific immune response requires two phases: the priming phase (generation of tumor specific T cells) and the effector phase (systemic destruction of tumor cells by the T cells). The effector phase is dependent on pre-existing or therapies that generate tumor specific T cells.
LTX-315 effectively exposes the patient`s unique neo-antigens and tumor associated antigens to the innate immune system and hence represents a first critical step in a priming phase (particularly in patients with no/low number of pre-existing tumor specific T cells). In order to further enhance antigen presentation and priming of T cells, local administration of immune checkpoint inhibitors (“release the brakes”) and/or immunostimulants (“push the gas pedal”) could be ideal combinations with LTX-315.
LTX-315 is an oncolytic immunotherapy. Time lapse study with confocal microscopy shows that the human melanoma cell (A547) is killed within minutes by LTX-315. (Courtesy of L.M. Eike and B. Sveinbjørnsson, UiT)
Presentation of LTX-315 – the discovery and its mode of action