Aileron (United States)

e21547 Background: The incidence of metastatic melanoma is on the rise, and 40-60% of patients will develop melanoma brain metastases (MBM). Frontline treatment consists of stereotactic radiosurgery given concurrently with immune checkpoint inhibition (ICI) or BRAF/MEK inhibition in BRAF mutated patients. While this therapy is effective at local control, the immune-suppressive nature of the CNS creates a permissive environment that facilitates distal intracranial relapse in over half of patients within 1 year. An improved understanding of the CNS tumor microenvironment (TME) is critical for designing effective treatments that improve MBM response to ICI. MyD88 is part of the inflammasome complex downstream of toll-like receptor or IL-1R receptor activation, and is aberrantly activated in the MBM TME. While critical for mediating innate immune activation, unrelenting stimulation of this pathway can trigger immune suppression through the reflexive recruitment of suppressive myeloid cells. Emavusertib (CA-4948) is a CNS permeable inhibitor of IRAK-4, a rate-limiting factor in the myddosome cascade. Thus, emavusertib may recondition the immunologic landscape of MBM through inhibition of myddosome induced myeloid infiltration, improving tumor response to ICI. Materials and Methods: Patient MBM tissues were examined by IHC to validate myddosome activation in the TME. Immunologic profiling of preclinical MBM tumors and PBMCs was performed via flow cytometry in response to anti-PD-1 ICI alone and in combination with emavusertib. Geospatial profiling of lymphocyte and myeloid cell distribution in single and combination treated MBM tumors was done using 3D imaging of cleared brain tissue. Overall survival was assessed in response to anti-PD-1 ICI treatment in combination with emavusertib. Results: In addition to promoting lymphocyte recruitment to MBM tumors, anti-PD-1 ICI significantly increases tumor infiltration by myeloid cells. Surface expression of PD-L1 was also elevated on myeloid cells in response to anti-PD-1 ICI. Microglia demonstrated no change in overall PD-L1 expression in response to either therapy, suggesting that peripheral myeloid cells are the principle target of therapy. Concomitant treatment with emavusertib alleviated ICI induced peripheral myeloid recruitment and reduced PD-L1 expression in MBM tumors while preserving effector lymphocyte infiltration. Emavusertib treatment also improved overall survival of mice when treated in combination with anti-PD-1 as compared to anti-PD-1 therapy alone. Conclusions: Emavusertib reconditions the MBM TME by mitigating the recruitment of infiltrating suppressive myeloid cells that likely confer resistance to anti-PD-1 ICI. This improves the anti-tumor efficacy of anti-PD-1 ICI, resulting in increased overall survival. Thus, emavusertib may be an effective adjuvant for improving treatment response to ICI in patients with MBM.

Abstract BACKGROUND: TP53 mutations are rare across pediatric cancers. Recent work using CRISPR-Cas9 screens has demonstrated that MDM2 and MDMX are strong dependencies in a range of TP53-wildtype pediatric malignancies. Increased expression of MDM2 and MDMX is a common mechanism for suppressing p53 in pediatric malignancies and can occur by copy number gain or amplification, as has been reported in retinoblastoma and hepatoblastoma. In pediatric high-grade gliomas, activating PPM1D mutations drive p53 suppression, likely through MDM2 stabilization. ALRN-6924 is a novel, first-in-class, cell-permeating stapled peptide that disrupts the inhibitory interactions between MDM2/MDMX(MDM4) and p53. ALRN-6924 has been evaluated in two adult Phase I trials, with good tolerability and evidence of clinical activity across a range of cancer subtypes. Given the oncogenic roles of MDM2 and MDMX in pediatric malignancies, we developed a Phase I clinical trial designed to evaluate the tolerability, pharmacokinetics, and pharmacodynamic and antitumor activity of ALRN-6924. METHODS: This is a Phase I, open-label, investigator-initiated multicenter study of ALRN-6924 in children 1-21 years of age with relapsed/refractory cancer (NCT03654716). The primary objectives are to determine the recommended phase 2 dose, and to describe toxicities and pharmacokinetic parameters of ALRN-6924 in this population. The monotherapy arm consists of two cohorts: Cohort A for patients with TP53-wildtype solid tumors and lymphomas; and Cohort B for patients with retinoblastoma, or TP53-wildtype tumors that meet any of the following criteria: hepatoblastoma, malignant rhabdoid tumor, MDM2 or MDMX amplification, TET2 loss, or PPM1D activating mutations. Patients with CNS primary tumors are only eligible for Cohort B. In Cohorts A and B, patients receive ALRN-6924 intravenously on Days 1, 4, 8 and 11 of a 21-day cycle starting at a dose of 2.2 mg/kg. An expansion cohort for patients eligible for Cohort B will open following completion of monotherapy dose escalation. Patients with relapsed/refractory leukemias enroll to Cohort C and receive ALRN-6924 in combination with low-dose cytarabine on days 1, 8 and 15 of a 28-day cycle starting at a dose of 2.7 mg/kg. Pharmacokinetic sampling and pharmacodynamic testing (serum MIC-1 modulation) is required for all patients. Correlative biology studies will include evaluation of circulating tumor DNA for TP53 mutations in patients with solid tumors and serial assessment of leukemic blasts in patients with relapsed leukemia. Enrollment began in October 2018. Up to 69 patients will be enrolled. Citation Format: David S. Shulman, Kieuhoa T. Vo, Elizabeth Fox, Jodi A. Muscal, Loren D. Walensky, Yana Pikman, Kimberly Stegmaier, Alanna Church, Brian D. Crompton, Andrew E. Place, Susan N. Chi, Allison F. O'Neill, Junne Kamihara, Suzanne Ezrre, Cecilia Carlowicz, Dawn Pinchasik, Hasan Al-Sayegh, Clement Ma, Wendy B. London, Steven G. DuBois. A Phase I multicenter trial of the dual MDM2/MDMX inhibitor ALRN-6924 in children and young adults with relapsed/refractory pediatric cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT112.

Abstract Hypoxia-inducible transcription factors (HIF) are key regulators of cellular adaptation to hypoxia in solid tumors, and HIF-1α controls the expression of genes involved in anaerobic metabolism, angiogenesis, cell growth and survival. Hydrocarbon cross-linked alpha helical peptides (Stapled Peptides) are a breakthrough approach to create new class of drugs that modulate intracellular protein-protein interactions. Here, we have mimicked the structure and function of the CITED2 protein, an endogenous negative regulator of the interaction between HIF-1α and p300 proteins, by designing a Stapled Peptide derived from CITED2 to generate the first example of a potent and selective Stapled Peptide inhibitor of HIF-1α-dependent transcription. ATSP-9172 bound to the CH1 domain of p300 and disrupted the HIF-1α C-TAD/CH1 interaction in biochemical assays and inhibited HIF-dependent reporter gene activity in ME-180 cells. Examination of endogenous transcript levels in ME-180 cells revealed that ATSP-9172 down-regulated the transcription of HIF-1α target genes, such as adolase C, angiopoietin-like 4, and carbonic anhydrase 9 in a dose-dependent manner, but did not affect the expression of non-HIF target genes, verifying a specific and on-target mechanism of action. ATSP-9172 exhibited a dramatic improvement in solubility and plasma stability profile relative to the linear peptide, and demonstrated favorable pharmacokinetic properties in mice by providing high systemic exposure, low plasma clearance and long elimination half-life. Finally, intravenous administration of ATSP-9172 on an every other day schedule significantly inhibited tumor growth in a PC-3 human prostate tumor xenograft model (p < 0.05); this inhibition was found to be dose-dependent. Our results demonstrate that a Stapled Peptide mimicking the HIF inhibitory function of the native CITED2 protein provides a novel and specific strategy to suppress HIF-1α-dependent gene expression for cancer therapy. Citation Format: Kaiming Sun, Steven J. DeMarco, Vincent Guerlavais, Aditi Mukherjee, Sean Irwin, Eric Shi, Hongliang Cai, Krzysztof Darlak, Solimar Santiago, Jessica Pero, Karen A. Olson, Huw M. Nash, Yong Chang. ATSP-9172, a novel Stapled Peptide inhibitor of HIF-dependent transcriptional activity with in vivo antitumor efficacy in a preclinical model of prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-304. doi:10.1158/1538-7445.AM2013-LB-304