Phosphoproteomic evaluation of pharmacological inhibition of leucine-rich repeat kinase 2 reveals significant off-target effects of LRRK-2-IN-1

Genetic mutations in leucine-rich repeat kinase 2 (LRRK2) have been linked to autosomal dominant Parkinson's disease. The most prevalent mutation, G2019S, results in enhanced LRRK2 kinase activity that potentially contributes to the etiology of Parkinson's disease. Consequently, disease progression is potentially mediated by poorly characterized phosphorylation-dependent LRRK2 substrate pathways. To address this gap in knowledge, we transduced SH-SY5Y neuroblastoma cells with LRRK2 G2019S via adenovirus, then determined quantitative changes in the phosphoproteome upon LRRK2 kinase inhibition (LRRK2-IN-1 treatment) using stable isotope labeling of amino acids in culture combined with phosphopeptide enrichment and LC-MS/MS analysis. We identified 776 phosphorylation sites that were increased or decreased at least 50% in response to LRRK2-IN-1 treatment, including sites on proteins previously known to associate with LRRK2. Bioinformatic analysis of those phosphoproteins suggested a potential role for LRRK2 kinase activity in regulating pro-inflammatory responses and neurite morphology, among other pathways. In follow-up experiments, LRRK2-IN-1 inhibited lipopolysaccharide-induced tumor necrosis factor alpha (TNFα) and C-X-C motif chemokine 10 (CXCL10) levels in astrocytes and also enhanced multiple neurite characteristics in primary neuronal cultures. However, LRRK2-IN-1 had almost identical effects in primary glial and neuronal cultures from LRRK2 knockout mice. These data suggest LRRK2-IN-1 may inhibit pathways of perceived LRRK2 pathophysiological function independently of LRRK2 highlighting the need to use multiple pharmacological tools and genetic approaches in studies determining LRRK2 function.

Dclk1 Inhibition Cancels 5-FU-induced Cell-cycle Arrest and Decreases Cell Survival in Colorectal Cancer

BACKGROUND/AIM

5-Fluorouracil (5-FU) is frequently used in colorectal cancer treatment, but with limited success. The aim of the present study was to explore the cytotoxic effects of 5-FU, in combination with inhibition of doublecortin-like kinase 1 (Dclk1), a tumor stem cell marker that regulates pro-survival signaling in colorectal cancer cells, in the human colon cancer cell line, COLO-320.

MATERIALS AND METHODS

The effects of 5-FU treatment plus Dclk1 inhibition on the phosphorylation of checkpoint kinase 1 (Chk1), cell cycle, DNA damage, apoptosis, and cell survival in COLO-320 cells were evaluated.

RESULTS

Combined treatment with 5-FU and a Dclk1 inhibitor, LRRK2-IN-1 (LRRK), decreased 5-FU-induced phosphorylation of Chk1 and canceled 5-FU-induced cell-cycle arrest at the S phase. Combined treatment with 5-FU and LRRK failed to induce poly (ADP-ribose) polymerase 1 (PARP-1) cleavage, but tended to decrease cell survival compared to individual treatment with 5-FU or LRRK.

CONCLUSION

These results indicate that a combination of 5-FU and LRRK may be an effective, novel approach for colorectal cancer therapy.

Synthesis and In Vitro and In Vivo Evaluation of [3H]LRRK2-IN-1 as a Novel Radioligand for LRRK2

PURPOSE

LRRK2 (leucine-rich repeat kinase 2) has recently been proven to be a promising drug target for Parkinson's disease (PD) due to an apparent enhanced activity caused by mutations associated with familial PD. To date, there have been no reports in which a LRRK2 inhibitor has been radiolabeled and used for in in vitro or in vivo studies of LRRK2. In the present study, we radiolabeled the LRRK2 ligand, LRRK-IN-1, for the purposes of performing in vitro (IC50, K d , B max, autoradiography) and in vivo (biodistribution, and blocking experiments) evaluations in rodents and human striatum tissues.

PROCEDURES

[3H]LRRK2-IN-1 was prepared with high radiochemical purity (>99 %) and a specific activity of 41 Ci/mmol via tritium/hydrogen (T/H) exchange using Crabtree's catalyst. For IC50, K d , and B max determination, LRRK2-IN-1 was used as a competing drug for nonspecific binding assessment. The specific binding of the tracer was further evaluated via an in vivo blocking study in mice with a potent LRRK2 inhibitor, Pf-06447475.

RESULTS

In vitro binding studies demonstrated a saturable binding site for [3H]LRRK2-IN-1 in rat kidney, rat brain striatum and human brain striatum with K d of 26 ± 3 and 43 ± 8, 48 ± 2 nM, respectively. In rat, the density of LRRK2 binding sites (B max) was higher in kidney (6.4 ± 0.04 pmol/mg) than in brain (2.5 ± 0.03 pmol/mg), however, in human brain striatum, the B max was 0.73 ± 0.01 pmol/mg protein. Autoradiography imaging in striatum of rat and human brain tissues gave results consistent with binding studies. In in vivo biodistribution and blocking studies in mice, co-administration with Pf-06447475 (10 mg/kg) reduced the uptake of [3H]LRRK2-IN-1 (%ID/g) by 50-60% in the kidney or brain.

CONCLUSION

The high LRRK2 brain density observed in our study suggests the feasibility for positron emission tomography imaging of LRRK2 (a potential target) with radioligands of higher affinity and specificity.