Abstract C048: Intrapatient heterogeneity and targeting microenvironment protection mechanisms in melanoma metastasis
Authors: Wilson Haley P. , Mersky Glenn L. , Haj Jelan I. , Teh Jessica L.F. , Cheng Phil F. , Caksa Signe , Mustafa Manal , Trachtenberg Isabella , Waltrich Francis J. , Stefanski Casey D. , Chua Vivian , Erkes Dan A. , Levesque Mitchell P. , Dummer Reinhard , Purwin Timothy J. , Capparelli Claudia , Aplin Andrew E. 
Published: November 2024

Abstract
Intrapatient tumor heterogeneity contributes to immunotherapy and targeted therapy resistance in cutaneous metastatic melanoma patients. More than 50% of melanoma patients develop brain metastases (MBM) during disease progressionand these patients have a very poor prognosis with a median overall survival of 4 months. To assess how tumors persist through treatments and adapt to and rely on organ-specific microenvironments, we utilized samples from a patient who had received anti-CTLA4, BRAFi/MEKi, and BRAFi/MEKi+CDK4/6i treatments during the LOGIC2 clinical trial. Eight short-term melanoma cultures (STMCs) were established from different metastatic site biopsies at chronological time points throughout the patient’s treatment and subsequent post-mortem resection of the bone, ovary, and brain metastatic sites. While the initial treatment naïve metastatic tumor in the breast was BRAF V600E mutant, NRAS Q61 mutations were acquired after treatment with CDK4/6i in the bone and ovary tumors. We performed single-cell RNA sequencing and identified that each STMC consists of 2-10 different subpopulations. By cell viability assay, we determined all STMCs were resistant to CDK4/6i, however had varying degrees of response to BRAFi and MEKi in vitro. Two STMCs (MM150604, MM150859) were sensitive to both BRAFi and MEKi. We identified HER3 was upregulated in the sensitive STMCs and more specifically, HER3 expression was elevated in the MBM STMC and in other MBM patient tumors in publicly available datasets. In publicly available data of the MBM tumor microenvironment (TME), neurons produce NRG1 and NRG2 while astrocytes and pericytes produce NRG2, exogenous sources of NRGs in the MBM TME that act as ligands for the HER3 receptor. Treatment with recombinant NRG1 partially rescued the growth of MBM cells and restored MAPK and AKT-mTOR signaling in the presence of BRAFi/MEKi suggesting that the brain microenvironment may play a role in drug tolerance. This novel finding demonstrates a unique role of HER3 in MBM and targeting the NRG-HER3 signaling axis could have therapeutic potential in melanoma patients with active brain metastases.
Citation Format: Haley P. Wilson, Glenn L. Mersky, Jelan I. Haj, Jessica L.F. Teh, Phil F. Cheng, Signe Caksa, Manal Mustafa, Isabella Trachtenberg, Francis J. Waltrich Jr, Casey D. Stefanski, Vivian Chua, Dan A. Erkes, Mitchell P. Levesque, Reinhard Dummer, Timothy J. Purwin, Claudia Capparelli, Andrew E. Aplin. Intrapatient heterogeneity and targeting microenvironment protection mechanisms in melanoma metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C048.