Discovery and Structure-Based Optimization of Novel Atg4B Inhibitors for the Treatment of Castration-Resistant Prostate Cancer

Inhibition of aldo-keto reductase 1C3 overcomes gemcitabine/cisplatin resistance in bladder cancer

Systemic chemotherapy with gemcitabine and cisplatin (GC) has been used for the treatment of bladder cancer in which androgen receptor (AR) signaling is suggested to play a critical role. However, its efficacy is often limited, and the prognosis of patients who develop resistance is extremely poor. Aldo-keto reductase 1C3 (AKR1C3), which is responsible for the production of a potent androgen, 5α-dihydrotestosterone (DHT), by the reduction of 5α-androstane-3α,17β-dione (5α-Adione), has been attracting attention as a therapeutic target for prostate cancer that shows androgen-dependent growth. By contrast, the role of AKR1C3 in bladder cancer remains unclear. In this study, we examined the effect of an AKR1C3 inhibitor on androgen-dependent proliferation and GC sensitivity in bladder cancer cells. 5α-Adione treatment induced the expression of AR and its downstream factor ETS-domain transcription factor (ELK1) in both T24 cells and newly established GC-resistant T24GC cells, while it did not alter AKR1C3 expression. AKR1C3 inhibitor 2j significantly suppressed 5α-Adione-induced AR and ELK1 upregulation, as did an AR antagonist apalutamide. Moreover, the combination of GC and 2j in T24GC significantly induced apoptotic cell death, suggesting that 2j could enhance GC sensitivity. Immunohistochemical staining in surgical specimens further revealed that strong expression of AKR1C3 was associated with significantly higher risks of tumor progression and cancer-specific mortality in patients with muscle-invasive bladder cancer. These results suggest that AKR1C3 inhibitors as adjunctive agents enhance the efficacy of GC therapy for bladder cancer.

Targeted Protein Degradation via Lysosomes

In the scope of targeted protein degradation (TPD), proteolysis-targeting chimeras (PROTACs), leveraging the ubiquitin-proteasome system, have been extensively studied. However, they are limited to the degradation of soluble and membrane proteins, excluding the aggregated and extracellular proteins and dysfunctional organelles. As an alternative protein degradation pathway, lysosomes serve as a feasible tool for accessing these untouched proteins and/or organelles by proteosomes. Here, we focus on reviewing the emerging lysosome-mediated TPD, such as AUTAC, ATTEC, AUTOTAC, LYTAC, and MoDE-A. Intracellular targets, such as soluble and aggregated proteins and organelles, can be degraded via the autophagy-lysosome pathway. Extracellular targets, such as membrane proteins, and secreted extracellular proteins can be degraded via the endosome-lysosome pathway. In addition, we summarize the mechanism and regulation of autophagy, available methods and assays for monitoring the autophagy process, and the recently developed chemical probes for perturbing the autophagy pathways.

Discovery and mechanism studies of a novel ATG4B inhibitor Ebselen by drug repurposing and its anti-colorectal cancer effects in mice

Cysteine protease ATG4B, a key autophagy protein, is an attractive target for colorectal cancer therapy. However, ATG4B inhibitors with higher efficiency, safety, and clear mechanism are still limited. In this study, we discovered ATG4B inhibitors based on the FDA-approved drug library through FRET-based high-throughput screening and gel-based analysis. Among the nine hits, compound Ebselen showed the most potent ATG4B inhibitory activity (IC₅₀ = 189 nM) and exhibited controllable selectivity and structural optimizable possibility against ATG4A and caspases. We then performed mass spectrometry assay and cysteine mutations to confirm that Ebselen could covalently bind to ATG4B at Cys74. Moreover, Cys292 and Cys361 instead of Cys74 are responsible for the redox-oligomerization and efficient activity inhibition of ATG4B. Ultimately through cell culture and mouse xenograft tumor models, we established the impact of Ebselen on autophagy and tumor suppression via ATG4B inhibition other than apoptosis. These results suggest that old drug Ebselen as an ATG4B inhibitor through oxidative modification may be repurposed as a promising anti-colorectal cancer drug.

Monitoring of Current Cancer Therapy by Positron Emission Tomography and Possible Role of Radiomics Assessment

Evaluation of cancer therapy with imaging is crucial as a surrogate marker of effectiveness and survival. The unique response patterns to therapy with immune-checkpoint inhibitors have facilitated the revision of response evaluation criteria using FDG-PET, because the immune response recalls reactive cells such as activated T-cells and macrophages, which show increased glucose metabolism and apparent progression on morphological imaging. Cellular metabolism and function are critical determinants of the viability of active cells in the tumor microenvironment, which would be novel targets of therapies, such as tumor immunity, metabolism, and genetic mutation. Considering tumor heterogeneity and variation in therapy response specific to the mechanisms of therapy, appropriate response evaluation is required. Radiomics approaches, which combine objective image features with a machine learning algorithm as well as pathologic and genetic data, have remarkably progressed over the past decade, and PET radiomics has increased quality and reliability based on the prosperous publications and standardization initiatives. PET and multimodal imaging will play a definitive role in personalized therapeutic strategies by the precise monitoring in future cancer therapy.