GP100 expression is variable in intensity in melanoma

Abstract

Drugs or cellular products that bind to gp100 are being investigated for treatment of cutaneous melanoma. The relative specificity of gp100 expression in melanocytes makes it an attractive target to harness for therapeutic intent. For example, Tebentafusp, a bispecific gp100 peptide-HLA-directed CD3 T cell engager, has generated significant enthusiasm in recent years due to its success in improving outcomes for uveal melanoma and is being studied in cutaneous melanoma. However, the extent and intensity of gp100 expression in advanced cutaneous melanoma has not been well studied. Here, we interrogated a large cohort of primary and metastatic melanomas for gp100 expression by immunohistochemistry. Expression in metastatic samples was globally higher and almost uniformly positive, however the degree of intensity was variable. Using a quantitative immunofluorescence method, we confirmed the variability in expression. As gp100-binding drugs are assessed in clinical trials, the association between activity of the drugs and the level of gp100 expression should be studied in order to potentially improve patient selection.

Keywords: Glycoprotein 100; ImmTAC; Melanoma; Targeted therapy; Tebentafusp.

Fig. 1

Detection of gp100 protein in melanoma cell lines and tissues. A Western blot showing expression of gp100 (100kD) in cell lines derived from cutaneous and uveal melanoma cell lines (left). Pixel intensity was quantitated for each band using ImageJ and displayed relative to loading control (right). “Strong expression” was defined as relative intensity > 20 and indicated by dashed line. Blue, cutaneous melanoma-derived; red, uveal melanoma-derived. B Representative images from immunohistochemical staining of the nevus and melanoma tissue microarrays showing scores from 0 to 3. Top left, nevus; top right, primary melanoma, lower left, metastatic melanoma; lower right, metastatic melanoma. C Intensity scores for nevus and melanoma tissue microarrays. *p < 0.01, ****p < 0.0001

Fig. 2

Immunofluorescence staining of gp100 in melanoma tissues. A Representative pseudo-color images for two metastatic melanoma histospots with high (top) and low (bottom) IF intensity scores. Staining target is indicated in lower right for each image. Tumor masks generated from analysis of S100 staining are shown for each histospot, and IF intensity score is determined for gp100 in the tumor compartment. B Box plot showing IF scores from histospots that received both a QIF score and an IHC score (Fig. 1). Histospots were grouped by IHC score as indicated. ****p < 0.0001. C Box plot showing IF scores for nevi, primary melanomas, and metastatic melanomas. *p < 0.01, ****p < 0.0001