Phosphorylation and Stabilization of PIN1 by JNK Promote Intrahepatic Cholangiocarcinoma Growth.

BACKGROUND AND AIMS: Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive type of liver cancer in urgent need of treatment options. Aberrant activation of the c-Jun N-terminal kinase (JNK) pathway is a key feature in ICC and an attractive candidate target for its treatment. However, the mechanisms by which constitutive JNK activation promotes ICC growth, and therefore the key downstream effectors of this pathway, remain unknown for their applicability as therapeutic targets. Our aim was to obtain a better mechanistic understanding of the role of JNK signaling in ICC that could open up therapeutic opportunities. APPROACH AND RESULTS: Using loss-of-function and gain-of-function studies in vitro and in vivo, we show that activation of the JNK pathway promotes ICC cell proliferation by affecting the protein stability of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1), a key driver of tumorigenesis. PIN1 is highly expressed in ICC primary tumors, and its expression positively correlates with active JNK. Mechanistically, the JNK kinases directly bind to and phosphorylate PIN1 at Ser115, and this phosphorylation prevents PIN1 mono-ubiquitination at Lys117 and its proteasomal degradation. Moreover, pharmacological inhibition of PIN1 through all-trans retinoic acid, a Food and Drug Administration-approved drug, impairs the growth of both cultured and xenografted ICC cells. CONCLUSIONS: Our findings implicate the JNK-PIN1 regulatory axis as a functionally important determinant for ICC growth, and provide a rationale for therapeutic targeting of JNK activation through PIN1 inhibition

Anti-PD-1/anti-CTLA-4 efficacy in melanoma brain metastases depends on extracranial disease and augmentation of CD8+ T cell trafficking

Inhibition of immune checkpoints programmed death 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) on T cells results in durable antitumor activity in melanoma patients. Despite high frequency of melanoma brain metastases (BrM) and associated poor prognosis, the activity and mechanisms of immune checkpoint inhibitors (ICI) in metastatic tumors that develop within the “immune specialized” brain microenvironment, remain elusive. We established a melanoma tumor transplantation model with intracranial plus extracranial (subcutaneous) tumor, mimicking the clinically observed coexistence of metastases inside and outside the brain. Strikingly, intracranial ICI efficacy was observed only when extracranial tumor was present. Extracranial tumor was also required for ICI-induced increase in CD8+ T cells, macrophages, and microglia in brain tumors, and for up-regulation of immune-regulatory genes. Combined PD-1/CTLA-4 blockade had a superior intracranial efficacy over the two monotherapies. Cell depletion studies revealed that NK cells and CD8+ T cells were required for intracranial anti–PD-1/anti–CTLA-4 efficacy. Rather than enhancing CD8+ T cell activation and expansion within intracranial tumors, PD-1/CTLA-4 blockade dramatically (∼14-fold) increased the trafficking of CD8+ T cells to the brain. This was mainly through the peripheral expansion of homing-competent effector CD8+ T cells and potentially further enhanced through up-regulation of T cell entry receptors intercellular adhesion molecule 1 and vascular adhesion molecule 1 on tumor vasculature. Our study indicates that extracranial activation/release of CD8+ T cells from PD-1/CTLA-4 inhibition and potentiation of their recruitment to the brain are paramount to the intracranial anti–PD-1/anti–CTLA-4 activity, suggesting augmentation of these processes as an immune therapy-enhancing strategy in metastatic brain cancer

Immune checkpoint blockade – how does it work in brain metastases?

Immune checkpoints restrain the immune system following its activation and their inhibition unleashes anti-tumor immune responses. Immune checkpoint inhibitors revolutionized the treatment of several cancer types, including melanoma, and immune checkpoint blockade with anti-PD-1 and anti-CTLA-4 antibodies is becoming a frontline therapy in metastatic melanoma. Notably, up to 60% of metastatic melanoma patients develop metastases in the brain. Brain metastases (BrM) are also very common in patients with lung and breast cancer, and occur in ∼20–40% of patients across different cancer types. Metastases in the brain are associated with poor prognosis due to the lack of efficient therapies. In the past, patients with BrM used to be excluded from immune-based clinical trials due to the assumption that such therapies may not work in the context of “immune-specialized” environment in the brain, or may cause harm. However, recent trials in patients with BrM demonstrated safety and intracranial activity of anti-PD-1 and anti-CTLA-4 therapy. We here discuss how immune checkpoint therapy works in BrM, with focus on T cells and the cross-talk between BrM, the immune system, and tumors growing outside the brain. We discuss major open questions in our understanding of what is required for an effective immune checkpoint inhibitor therapy in BrM

Tumor Microenvironment in the Brain

In addition to malignant cancer cells, tumors contain a variety of different stromal cells that constitute the tumor microenvironment. Some of these cell types provide crucial support for tumor growth, while others have been suggested to actually inhibit tumor progression. The composition of tumor microenvironment varies depending on the tumor site. The brain in particular consists of numerous specialized cell types such as microglia, astrocytes, and brain endothelial cells. In addition to these brain-resident cells, primary and metastatic brain tumors have also been shown to be infiltrated by different populations of bone marrow-derived cells. The role of different cell types that constitute tumor microenvironment in the progression of brain malignancies is only poorly understood. Tumor microenvironment has been shown to be a promising therapeutic target and diagnostic marker in extracranial malignancies. A better understanding of tumor microenvironment in the brain would therefore be expected to contribute to the development of improved therapies for brain tumors that are urgently required due to a poor availability of treatments for these malignancies. This review summarizes some of the known interactions between brain tumors and different stromal cells, and also discusses potential therapeutic approaches within this context

In vitro selection of high-affinity nucleic acid ligands to parasite target molecules.

The logic of using nucleic acids as pharmaceutical reagents is in part based on their capacity to interact with high affinity and specificity with other biological components. Considerable progress has been made over the past 10 years in the development of nucleic acid-based drug molecules using a variety of different technologies. One approach is a combinatorial technology that involves an iterative Darwinian-type in vitro evolution process, which has been termed SELEX for 'systematic evolution of ligands by exponential enrichment'. The procedure is a highly efficient method of identifying rare ligands from combinatorial nucleic acid libraries of very high complexity. It allows the selection of nucleic acid molecules with desired functions and it has been instrumental in the identification of a number of synthetic DNA and RNA molecules, so-called aptamers that recognise ligands of different chemical origin. The method is fast, it does not require special equipment and the selected aptamers typically bind their target with high affinity and high specificity. Here we summarise the recent examples of the SELEX technique within the context of identifying high-affinity ligands against parasite target molecules

Targeting the Variable Surface of African Trypanosomes with Variant Surface Glycoprotein-Specific, Serum-Stable RNA Aptamers

African trypanosomes cause sleeping sickness in humans and Nagana in cattle. The parasites multiply in the blood and escape the immune response of the infected host by antigenic variation. Antigenic variation is characterized by a periodic change of the parasite protein surface, which consists of a variant glycoprotein known as variant surface glycoprotein (VSG). Using a SELEX (systematic evolution of ligands by exponential enrichment) approach, we report the selection of small, serum-stable RNAs, so-called aptamers, that bind to VSGs with subnanomolar affinity. The RNAs are able to recognize different VSG variants and bind to the surface of live trypanosomes. Aptamers tethered to an antigenic side group are capable of directing antibodies to the surface of the parasite in vitro. In this manner, the RNAs might provide a new strategy for a therapeutic intervention to fight sleeping sickness