{
  "abstract": "Background Unleashing the immune anti-tumor response against metastatic melanoma through immune checkpoint blockade (ICB) therapies have redefined clinical care. ICB resistance is multifactorial, involving tumor cell-intrinsic and -extrinsic mechanisms and dynamic interactions within the tumor microenvironment. Many tumor-specific pathways are associated with ICB resistance, including those induced by TME stress and impacting release of immunomodulatory signaling biomolecules. We uncovered a previously unrecognized role for Activating Transcription Factor 6 (ATF6) in sensitizing melanoma cells to T cell killing (TCK). ATF6 is well-studied as a DNA-binding protein associated with both transcriptional activation and repression. ATF6 is commonly associated with the regulation of the unfolded protein response (UPR) to attenuate proteostatic collapse but is also linked to other pathways of cellular survival and homeostasis. Our data shows transcriptional regulation by ATF6 sensitizes melanoma cells to TCK.Methods To investigate ATF6-specific activation in melanoma, murine melanoma cell lines (B16F10 and Yumm1.7) were engineered to stably express either the full-length 90 kDa ATF6 (ATF6-WT) or the constitutively active 50 kDa form (ATF6-CA). In parallel, pharmacologic activation of endogenous ATF6 was achieved using the small molecule activator AA147. ATF6 pathway activation was validated by qPCR and immunoblotting. Functional effects on immune susceptibility were assessed using co-culture cytotoxicity assays and pre-clinical immunocompetent melanoma models. ATF6-driven transcriptional and proteomic alterations were profiled using RNA-seq and mass spectrometry to identify potential mechanisms.Results Both genetic and pharmacologic activation of ATF6 using the small molecule AA147 produced consistent results. Tumors (B16F10 and YUMM1.7) expressing constitutively active ATF6 (ATF6-CA) grew more slowly than control tumors. This ATF6-mediated tumor suppression was abolished by in vivo depletion of CD8 + T cells, indicating a T cell-dependent mechanism. In vitro, ATF6 activation increased tumor susceptibility to CD8+ TCK. When combined with immune checkpoint blockade (anti-CTLA4/anti-PD1), ATF6 activation significantly improved overall survival and led to complete tumor regression in some mice (figures 1 and 2). Multi-omic profiling revealed a loss of key negative immune regulators (e.g., Serpins and Galectins) in ATF6-activated melanoma cells, with the reduction of SerpinB9 being implicated as a potential mechanism of enhanced immune sensitivity.Conclusions We uncovered a previously unrecognized role for ATF6 in the potentiation of the anti-tumor immune response. ATF6 activation in melanoma cells promoted significant increases in TCK in vitro and conveyed a robust advantage in vivo. Combinatorial ATF6 activation and ICB therapy greatly improved overall survival and demonstrated a curative effect, nominating AA147 for translation as a neo-adjuvant or combinatorial therapeutic approach.Abstract 691 Figure 1Genetic ATF6 activation enhances melanoma ICB response. Tumor growth and survival of B16.Vec ± ICB are shown (pAbstract 691 Figure 2Pharmacological ATF6 activation enhances melanoma ICB response. Tumor growth and survival of B16.F10 ± AA147 ± ICB are shown (p",
  "authors": [
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Jacob L Edmondson"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Sanjay Adhikary"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Daniel Fil"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Megan R Reed"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Billie Heflin"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Katherine Wallis"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Sydnye L Shuttleworth"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Nathan Avaritt"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "lan J Tackett"
    },
    {
      "affiliations": [
        "University of Arkansas for Medical Sciences, Little Rock, AR, USA"
      ],
      "name": "Brian Koss"
    }
  ],
  "title": "691 ATF6 activation promotes ICB response in melanoma",
  "uid": "ac22414d-1813-5c3f-9d62-211739e1ca87"
}