Abstract 627: Custom Vectra® Polaris™ fluorescent multiplex IHC panel identifies mature tertiary lymphoid structures in colorectal cancer

Introduction: Tertiary lymphoid structures (TLS) are promising prognostic indicators of positive outcomes for patients with solid tumors including colorectal cancer (CRC) [1]. Large-scale retrospective analysis shows patients with mature TLS in particular respond to PD-1/PD-L1 antibody treatment with improved objective response, progression-free and overall survival [2]. Since not all patients respond to PD-1/PD-L1 antibody treatment, identifying patients with mature TLS is clinically relevant as it enables selection of patients likely to respond to immune checkpoint blockade. Mature TLS are composed of T cells (CD3+), follicular B cells (CD20+), germinal center B cells (CD23+), and follicular dendritic cells (CD21+) [3]. The ability to identify and evaluate TLS is limited by detection methods which traditionally employ hematoxylin and eosin (H&E) staining for visual quantification of immune aggregates, potentially significantly underestimating their quantity [4]. Multiplexed fluorescent immunohistochemistry (IHC) detection assays have the capability to precisely quantify mature TLS within the TME. Colorectal cancer specimens expressing a dynamic range of TLS are stained with a novel custom Vectra® Polaris™ multiplex immunofluorescence panel detecting CD20, CD21, CD23, CD3 and pan-cytokeratin. Identification of mature TLS with CD3+CD20+CD21+ and CD3+CD20+CD23+ expression in the TME is reported.

Results: Vectra® Polaris™ TLS multiplex immunofluorescence panel successfully identified mature TLS in the TME of colorectal cancer patient samples. TLS were quantified via custom analytics algorithms generated with Indica HALO software.

Conclusion: Characteristics of TME immunity in colorectal cancer differentially impact an individual patient’s odds of survival [5]. The novel Vectra® Polaris™ multiplex assay in this study shows a detailed picture of mature TLS in patient cancer samples. Future applications of this panel include investigations of TLS associated with successful anti-tumor immune development and therapeutic response to treatment. [1] Oncoimmunology. 2020; 9(1): 1724763 [2] Nat Cancer. 2, 794-802 (2021) [3] Oncoimmunology. 2021; 10(1): 1900508. [4] Mod Pathol 2017 Sep;30(9):1204-1212. doi: 10.1038/modpathol.2017.43. [5] Cell. 2020 Sep 3;182(5):1341-1359.e19. doi: 10.1016/j.cell.2020.07.005

Citation Format: Sara G. Pollan, Arezoo Hanifi, James Hargrove, Erinn A. Parnell, Jessica Lin, Josette William Ragheb, Qingyan Au. Custom Vectra® Polaris™ fluorescent multiplex IHC panel identifies mature tertiary lymphoid structures in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 627.

Loss of CDCP1 triggers FAK activation in detached prostate cancer cells

A major metastasis suppressing mechanism is the rapid apoptotic death of cancer cells upon detachment from extracellular matrix, a process called anoikis. Focal adhesion kinase (PTK2/FAK) is a key enzyme involved in evasion of anoikis. We show that loss of the Cub-domain containing protein-1 (CDCP1), paradoxically stimulates FAK activation in the detached state of prostate cancer cells. In CDCP1low DU145 and PC3 prostate cancer cells, detachment-activation of FAK occurs through local production of PI(4,5)P2. PI(4,5)P2 is generated by the PIP5K1c-201 splicing isoform of PIP5K1c, which contains a unique SRC phosphorylation site. In the detached state, reduced expression of CDCP1 and an alternative CDCP1-independent SRC activation mechanism triggers PIP5K1c-pY644 phosphorylation by SRC. This causes a switch of Talin binding from β1-integrin to PIP5K1c-pY644 and leads to activation of PIP5K1c-FAK. Reduced CDCP1 expression also inactivates CDK5, a negative regulator of PIP5K1c. Furthermore, immersion of prostate cancer cells in 10% human plasma or fetal bovine serum is required for activation of PIP5K1c-FAK. The PIP5K1c induced detachment-activation of FAK in preclinical models sensitizes CDCP1low prostate cancer cells to FAK inhibitors. In patients, CDCP1High versus CDCP1low circulating tumor cells differ in expression of AR-v7, ONECUT2 and HOXB13 oncogenes and TMPRSS2 and display intra-patient heterogeneity of FAK-pY397 expression. Taken together, CDCP1low and CDCP1high detached prostate cancer cells activate distinct cytoplasmic kinase complexes and targetable transcription factors, which has important therapeutic implications.

Abstract 5795: Loss of CDCP1 in patient prostate cancer metastasis leads to uncoupling of beta-1 integrin from its cytoplasmic signaling through FAK

The Cub-Domain Containing Protein - 1, CDCP1, is a transmembrane glycoprotein, which is able to sequester Src and PKCδ into unique microdomains within the plasma membrane. CDCP1 can either promote or suppress tumor metastasis, dependent on the cancer type and experimental system. How the loss of CDCP1 leads to tumor metastasis is not well understood. We demonstrated for the first time in patients with prostate cancer (PCA), a significant reduction of CDCP1 expression in circulating cancer cells (CTC) and tumor metastasis relative to primary tumors and concordant analytical results. To investigate how the loss of CDCP1 facilitates PCA metastasis, we determined the consequences of CDCP1 loss in non-adherent cancer cells, which provide an experimental model system of CTCs. In this system, CDCP1 silenced cells exhibit 3-fold higher proliferation, 4-fold greater anchorage independent growth with colonies exceeding 5 microns in diameter, and a 2-fold reduction in migration ability. In 10% human plasma, these cells up-regulate p-FAK, p-SRC, p-AKT and p-MAPK expression, and at the same time loose expression of activated β1-integrin. The loss of inside-out activation of β1-integrin occurs through prevention of TALIN phosphorylation. Upon loss of CDCP1, Talin is no longer phosphorylated by CDK5 and this causes the disassembly of the β1 integrin - Talin complex. In addition, β1-integrin dissociates from CDK5 and from the CDK5-regulatory subunit, p35, but remains bound to p-FAK. We determined the pathway by which the loss of CDCP1 arrests CDK5 kinase activity. Upon loss of CDCP1, SRC phosphorylates p35. This generates a binding site for the C2 domain of PKCδ and phosphorylation of CDK5-T77 by PKCδ. The subsequent dissociation of the regulatory subunit abolishes the activity of CDK5. We show that both SRC inhibition and silencing of PKCδ reestablish the inside-out activation of β1-integrin. Altogether we discovered a new mechanism of regulation of CDK5 in prostate cancer cells, which leads to the uncoupling of β1-integrin and FAK. The potential biological and clinical consequences of this mechanism are (1) a switch from cell-matrix to cell-cell adhesion, (2) increased sensitivity of CTCs to FAK inhibitors and (3) improved adaptation and survival of cancer cells in the circulation and at the metastatic sites.

Citation Format: Sara G. Pollan, Fangjin Huang, Joshua M. Lang, Jamie M. Sperger, Kavita Shah, Beatrice S. Knudsen. Loss of CDCP1 in patient prostate cancer metastasis leads to uncoupling of beta-1 integrin from its cytoplasmic signaling through FAK [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5795. doi:10.1158/1538-7445.AM2017-5795

Abstract 5474: The formin, DIAPH3, regulates response to MT stabilizing drugs in prostate and breast cancer

Diaphanous-related formin-3 (DIAPH3), a cytoskeletal regulator of the formin family, is lost at high frequency in metastatic breast and prostate cancers and has characteristics of a non-canonical metastasis suppressor. We previously showed that DIAPH3 silencing evokes a transition to an “amoeboid” phenotype, characterized by rapid motility, RhoA/ROCK and ERK pathway activation, dynamic membrane blebbing and increased shedding of microvesicles. Here we demonstrate that DIAPH3 loss reduces microtubule (MT) stability in prostate and breast cancer cell lines, and increases the cells' sensitivity to the taxanes, paclitaxel and docetaxel and the non-taxane, epothilone B. DIAPH3 silencing reduces membrane localization of the multidrug resistance-associated protein, MRP1, a regulator of taxane efflux, and increases intracellular accumulation of fluorescent paclitaxel. Baseline acetylation of tubulin, which is proportional to the number of stable MT, is lower in DIAPH3-silenced cells. In contrast, the fold-increase of tubulin acetylation after treatment with MT stabilizing drugs is greater in DIAPH3 knockdown compared to control cells. Further, cytotoxicity induced by paclitaxel, docetaxel or epothilone B is enhanced by DIAPH3 silencing. Analysis of gene expression profiles of breast cancer patients treated with chemotherapeutic regimens containing taxanes in a neoadjuvant phase-2 clinical trial revealed that low DIAPH3 expression is associated with increased relapse free survival. Collectively, the data demonstrate that DIAPH3 deficiency increases responsiveness to widely used MT stabilizing drugs. These findings have implications for the inclusion of DIAPH3 in biomarker panels that stratify patients for treatment with taxanes, in particular in the neoadjuvant setting.

Citation Format: Samantha Morley, Sara G. Pollan, Sungyong You, Beatrice S. Knudsen, Michael Freeman. The formin, DIAPH3, regulates response to MT stabilizing drugs in prostate and breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5474. doi:10.1158/1538-7445.AM2014-5474