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Background We have previously demonstrated adaptive antibody responses targeting public tumor antigens in cancer patients. ATRC-101, a clinical stage, engineered version of an antibody identified in such a patient, displays robust single-agent activity in syngeneic tumor models requiring Fc receptors (FcRs) expressed by innate immune cells and the presence of CD8+ T cells. The novel target of ATRC-101 was found to be a tumor-restricted ribonucleoprotein (RNP) complex, and because RNP complexes drive T cell responses in infectious and autoimmune disease via innate immune cells, we further characterized the mechanism-of-action of ATRC-101. Here we describe changes in immune cell populations in a tumor model proximal to treatment initiation with ATRC-101. Methods Mice bearing EMT6 tumors received ATRC-101 beginning on day 7 post-tumor inoculation. Tissues were harvested between days 7 and 14 and analyzed by flow cytometry and immunohistochemistry. Transcriptome analysis was performed using RNA sequencing on whole tumors taken on days 7, 9, and 12. Results The earliest significant changes induced by ATRC-101, relative to vehicle, were noted just 24 hours after dosing: increased numbers of cDC1 cells in blood, and decreased numbers of cDC2 cells in blood and M-MDSCs in tumor. A significant increase of CD8+ T cells was observed in blood 48 hours after dosing and in tumor 96 hours after dosing. Increased numbers of NK cells were also observed in blood and tumor at this later time. Multiplex analysis of circulating cytokines demonstrated a very early increase in myeloid chemo-attractants, such as MCP1 and MIP1a.Whole exome sequencing of tumor samples showed that ATRC-101 dosing drives a significant increase, relative to vehicle, in the expression of interferon-stimulated genes. Co-culturing experiments demonstrated that induced, bone marrow-derived dendritic cells are activated by ATRC-101 and its target in a dose-dependent fashion. Conclusions Dosing with ATRC-101 in the EMT6 syngeneic tumor model, in which ATRC-101 displays notable single-agent activity, leads to changes in immune cell composition in the blood and tumor, with the earliest changes observed in myeloid or myeloid-derived cell populations, and to the early appearance of myeloid chemo-attractants. We believe these data indicate that ATRC-101 acts proximally on the myeloid cell populations in the tumor, leading to a remodeling of the tumor environment and an adaptive immune response that includes CD8+ T cells driving tumor regression. Our data demonstrate that ATRC-101, bound to its target which is an RNP complex, can activate myeloid cells and are consistent with this activation occurring via FcR and Toll-like receptor (TLR) pathways.

Background We have previously described ATRC-101, a fully human, engineered IgG1 antibody binding a tumor-restricted ribonucleoprotein (RNP) complex as its target. ATRC-101 is currently under evaluation in the clinic as a monotherapy for solid tumors. Following target engagement, ATRC-101 functions in an Fc-mediated fashion to deliver the target to the innate immune system, which modifies the tumor microenvironment and generates an adaptive immune response involving CD8+ T cells leading to anti-tumor activity in syngeneic mouse models. Binding of ATRC-101 appears restricted to malignant tissues in both mouse models and human, across a range of cancer histologic phenotypes, including carcinomas that are known candidates for anti-PD-1 treatment. In the EMT6 mouse model, representing a T cell-excluded phenotype in which anti-PD-1 agents display limited activity, ATRC-101 monotherapy was uniformly vigorous with persistent anti-tumor memory. When co-administered at a lower dose with anti-PD-1, the combination of therapy demonstrated a robust and heightened anti-tumor response relative to either agent dosed as monotherapy at similar concentrations. Methods To gain insight into the mechanisms that contribute to the anti-tumor effect with combination therapy, in vivo experiments in the EMT6 syngeneic mouse model were performed to determine temporal and spatial patterns of infiltrates and assessed tumors by using whole exome sequencing following administration of ATRC-101 vs. vehicle control. Within naive human tumor samples, coincident immunoreactivities of ATRC-101 and PD-L1 were also characterized. Results In mice treated with ATRC-101, analysis by immunofluorescence revealed a significant increase in the percentage of PD-1 reactive T cells within the tumor microenvironment. Elevated transcripts for PD-L1 also were detected in tumors from mice administered ATRC-101 vs baseline levels or vehicle control. When human tumor tissues were characterized for coincident expression of these targets, a high prevalence of ATRC-101 immunoreactivity was noted in both PD-L1 reactive and non-reactive tumor cores. Across multiple indications, ATRC-101 immunoreactivity was apparent in > 50% of PD-L1+ cores. Conclusions In situ studies suggest the target of ATRC-101 may co-locate with PD-L1, and in vivo studies indicate that ATRC-101 administration increases PD-L1 transcripts and PD-1-positive infiltrates in mouse tumor. Altogether, our data support studies to combine ATRC-101 with agents targeting PD-1 in the clinical treatment of solid tissue malignancies. Acknowledgements We acknowledge the significant effort and contributions of our colleagues from the clinical, in vivo pharmacology, translational sciences, in vitro pharmacology, and cell biology groups. This includes Mark Armanini, Erin Brosey, Chantia Carroll, Sean M. Carroll, Nicole Haaser, Benjamin Haugen, Dongkyoon Kim, Beatriz Millare, Yann Chong Tan, Danhui Zhang, and Patricia Zuno. Trial Registration NCT04244552 Ethics Approval The study was approved by WIRB (Western Institutional Review Board) on Jun 11, 2013. The WIRB study number is 20130121. Reference DeFalco J, Harbell M, Manning-Bog A, et al. Non-progressing cancer patients have persistent B cell responses expressing shared antibody paratopes that target public tumor antigens. Clinical Immunology 2018; 187:37–45.

Malignant gliomas are highly aggressive primary brain tumors with few treatment options and invariably fatal outcomes. The receptor tyrosine kinase epidermal growth factor receptor (EGFR) is hyperactivated through gene amplification or mutation in many cancers. EGFR activity is associated with increased cell proliferation, disease progression and therapeutic resistance. Intratumoral heterogeneity of EGFR arises as a signature pathogenetic events in the highly aggressive and invariably fatal brain tumor glioblastoma multiforme (GBM). Functional blockade of the EGFR kinase activity alone does not achieve maximal therapeutic benefit to support the role for EGFR kinase-independent functions. We performed a high-throughput, pharmacologic screening to identify EGFR-targeted therapeutics in glioma cells engineered to overexpress either a high or low copy number of EGFR wildtype (WT), a constitutively active mutant EGFR-vIII or an EGFR kinase-dead (KD) mutant. We discovered that the heat shock protein (HSP)90 inhibitor ganetespib selectively and potently killed glioma cells that overexpressed either the WT, vIII or KD forms of EGFR (IC50 ∼20-40nM). Real-time measurements demonstrated that ganetespib reduced proliferation, induced caspase-dependent apoptosis and inhibited glioma migration. Overexpression of the EGFR-WT, vIII or KD forms significantly increased intracellular ATP levels and WT, vIII and KI EGFR all translocalized to the mitochondria. Ganetespib addition rapidly reduced ATP in cells that overexpressed either kinase-active or kinase-inactive forms. Ganetespib reduced the proliferation of human patient GBM patient-derived tumor stem cells and effectively impaired the growth of subcutaneously placed glioma implants in nude mouse models. Ganetespib impairs the EGFR kinase-(in)dependent activities with the potential benefit to overcome intratumoral heterogeneity benefit and improve GBM patient outcome.

Small molecules that modulate cancer stem cell (CSC) fate and function offer therapeutic potential to improve patient outcome. Malignant gliomas are highly aggressive primary brain tumors with few treatment options and an invariably fatal outcome. High-throughput screening and structure-guided design identified a novel, dual phosphatidylinositol-3-kinase (PI3K)/mammaliam target of rapamycin (mTOR) inhibitor that potently induced apoptosis in glioma cells and glioma patient-derived CSCs. The compound, designated DT61, inhibited PI3K, mTORC1 and mTORC2 kinase activities at nanomolar concentrations in a dose-dependent manner. DT61 dramatically reduced the level of the PI3-K α and β isoforms and led to a reduction in the site-specific phosphorylation and activity of the pro-survival serine-threonine kinase Akt/Protein Kinase B (PKB). DT61 inhibition of PI3K activity prevented the inactivation of glycogen synthase kinase (GSK-3beta) to enhance site-specific phosphorylation and proteasomal degradation of the c-myc oncoprotein that drives gliomagenesis. The apoptotic effect of DT61 on CSCs was synergistically enhanced when combined with radiation treatment, a standard-of-care modality for glioma treatment. Taken together, the results demonstrate that DT61 is a novel, highly effective dual PI3K/mTOR inhibitor that is cytotoxic to brain CSC under normoxia and hypoxia with potential benefit for glioma patients.

The aim of this study was to identify a phenolic prodrug compound that is minimally metabolized by rat liver microsomes, but yet could form quinone reactive intermediates in melanoma cells as a result of its bioactivation by tyrosinase. In current work, we investigated 24 phenolic compounds for their metabolism by tyrosinase, rat liver microsomes and their toxicity towards murine B16-F0 and human SK-MEL-28 melanoma cells. A linear correlation was found between toxicities of phenolic analogs towards SK-MEL-28 and B16-F0 melanoma cells, suggesting similar mechanisms of toxicity in both cell lines. 4-HEB was identified as the lead compound. 4-HEB (IC(50) 48h, 75muM) showed selective toxicity towards five melanocytic melanoma cell lines SK-MEL-28, SK-MEL-5, MeWo, B16-F0 and B16-F10, which express functional tyrosinase, compared to four non-melanoma cells lines SW-620, Saos-2, PC3 and BJ cells and two amelanotic SK-MEL-24, C32 cells, which do not express functional tyrosinase. 4-HEB caused significant intracellular GSH depletion, ROS formation, and showed significantly less toxicity to tyrosinase specific shRNA transfected SK-MEL-28 cells. Our findings suggest that presence of a phenolic group in 4-HEB is critical for its selective toxicity towards melanoma cells.