Abstract 3188: Examining “Her2 low” patient populations for prediction to Her2-targeting antibody-drug conjugate response in Her2 negative patients using a novel high sensitivity immunohistochemistry assay

The positive results for trastuzumab deruxtecan (DS-8201) in Her2+ breast cancer from the pivotal phase II DESTINY-Breast01 trial announced in May 2019 represents a pivotal change in approach to anti-Her2 therapy. Data from the phase 1 trial for DS-2801 has demonstrated tumor shrinkage even in patients with low Her2 expression (Her2 IHC 2+/1+) by Her2 immunohistochemistry using the Ventana HER2 (4B5) assay (Lancet Oncol. 2017 Nov;18(11):1512-1522). This is thought to be due to a strong bystander effect of deruxtecan (Int J Cancer. 2019 May 14. doi: 10.1002/ijc.32408) and a resulting enhancement of anti-tumor immunity (Mol Cancer Ther. 2018 Jul;17(7):1494-1503). Thus, prediction of patient response trastuzumab deruxtecan goes well beyond the past approaches of evaluating only Her2 over-expression or amplification, and potentially involves complex tumor and immune interactions which drive a potent response even in patients who do not have high Her2 expression.

This represents an emerging “Her2 low” strategy in drug development which seeks to use antibodies against Her2 to direct cytotoxic or immune-stimulating payloads to tumor cells which do not over-express Her2, but still retain some Her2 expression, even if considered diagnostically “Her2 negative” by the existing Her2 companion diagnostic strategies. Currently, there is no marketed approach to stratifying “Her2 low” patients for these therapies, as such an approach would require an improved method of Her2 detection or IHC interpretation strategy that allows better segmentation of patients with low Her2 expression. This demand is unlikely to be met through changing Her2 IHC interpretation, as the existing Her2 companion diagnostic strategy still remains challenging in clinical practice after nearly 15 years of improvements in scoring interpretations lead by ASCO/CAP for improved testing performance.

This study demonstrates how we can meet this challenge using a novel approach to Her2 protein detection in human formalin-fixed, paraffin embedded (FFPE) tissues, called Quanticell™. Quanticell™ relies on Konica-Minolta's Phosphor-Integrated Dot (PID) technology for ultra-sensitive, in situ detection of Her2 protein in FFPE tissues. This approach is capable of detecting Her2 expression in clinical tissues that are characterized as “Her2 negative” by current IHC approaches, facilitating the determination of a new approach to a diagnostic cutpoint to stratify patients between “her2 negative” and “Her2 low”; which is distinct from the current “Her2 high” paradigm.

Citation Format: Joseph S. Krueger, Kenneth Bloom, George Abe, Hisatake Okada, Hiroyuki Yokota, Naoya Saito. Examining “Her2 low” patient populations for prediction to Her2-targeting antibody-drug conjugate response in Her2 negative patients using a novel high sensitivity immunohistochemistry assay [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3188.

Abstract LB-230: Quantitative immunohistochemistry for melanocortin 1 receptor using phosphor integrated dots

Visual scoring of biomarkers by immunohistochemistry (IHC) on formalin-fixed paraffin embedded tissues constitutes a major part of histopathologic diagnosis and staging of several cancers. To improve sensitivity and linearity of IHC methods, we have developed a quantitative IHC technique using streptavidin coated phosphor integrated dot (PID) fluorescent nanoparticles (Gonda et al, Scientific Reports, 2017). In retrospective analysis of clinically established biomarkers (i.e., PD-L1, HER2, CSF-1R), IHC-PID has provided high-sensitivity quantitative detection of target proteins with a broad dynamic range. The present study examines the utility of IHC-PID in the biomarker discovery and validation process by evaluating melanocortin subtype 1 receptor (MC1R) in cell lines and clinical biopsy samples. MC1R is currently under investigation as a potential diagnostic and therapeutic target for malignant melanoma, a lethal cancer with poor long-term prognosis. MC1R is an endocytic cell-surface G-protein coupled receptor that exhibits relatively high expression in malignant melanoma tumors vs. normal tissues. Notably, current melanoma therapies, including MAPKi (e.g., vemurafenib, dabrafenib) increase MC1R expression pharmacologically on melanoma cells (unpublished results). MC1R expression was determined in cell lines by standard radio-ligand binding assay (125I-NDP-α-MSH). The SK-Mel-28 cell line showed 5-6 fold increased expression of endogenous MC1R when compared to the A375 cell line. Formalin fixed pellets of these two cell lines were used for analytical validation of PID-IHC. By utilizing dedicated image-processing algorithms, the readout of average PID score/cell was determined to be 285 and 98, for SK-Mel-28 and A375 cell lines, respectively. To confirm the increase in sensitivity with the PID technology, enabling quantitative IHC and improved detection of MC1R, de-identified melanoma samples from varying sites were collected by surgical biopsy at The University of Iowa Hospitals and Clinics and scored by a pathologist. Sister sections were stained by conventional IHC or IHC-PID. For IHC-PID, sections were counter stained by hematoxylin; tumor regions were hand annotated by a pathologist; and fluorescent images in 5 microscopic fields were captured and analyzed. Background PID threshold was determined by using no-primary antibody as controls. IHC-PID was performed on MS0759 (T1b N0 M0), MS0045 (T3a N1a M0) and MS0868 (T4b N3 M1a) samples and showed average PID score/cell of 217±38, 68±12, and 160±21, respectively. Ongoing studies are expanding on IHC-PID use to assess MC1R expression on a clinical melanoma panel (n=20) in late stage patients undergoing pharmacological interventions including MAPKi. The overall goal of this project is to develop PID-based quantitative IHC to support the development of MC1R as an imaging biomarker for patient stratification and monitoring clinical response to MC1R-targeted radionuclide therapy for malignant melanoma.

Note: This abstract was not presented at the meeting.

Citation Format: Apollina Goel, Kenji Nishikawa, Etsuko Futaya, Ildiko Poylak, Robert Holt, Mengshi Li, Edwin Sagastum, Brenna Marks, Aaron D. Bossler, Frances L. Johnson, Michael K. Schultz, Hideki Goda, Hisatake Okada, Kelly Orcutt, George Abe, Kenneth Bloom. Quantitative immunohistochemistry for melanocortin 1 receptor using phosphor integrated dots [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 LB-230.