Initial evaluation of the antitumour activity of KGP94, a functionalized benzophenone thiosemicarbazone inhibitor of cathepsin L

Design and synthesis of dual cathepsin L and S inhibitors and antimetastatic activity evaluation in pancreatic cancer cells

Currently, the migration and invasion of cancer cells remain the main factors of poor prognosis in the majority of cancer patients. Developing an effective antimetastatic agent is crucial for cancer therapy. Our recent research revealed that Cat L and S are expressed concurrently in metastatic pancreatic cancer cells. Asperphenamate analog ASPER-29, which exhibits dual Cat L and S inhibitory potency, showed a definite antimetastatic effect on pancreatic cancer BxPC-3 and PANC-1 cells. To further improve the antimetastatic ability of asperphenamate-type molecules, 24 derivatives were designed and synthesized by a scaffold-hopping strategy. The cathepsin inhibitory activity assay results showed that most of the derivatives exhibited dual inhibitory effects on Cat L and S. Among all derivatives, Compound B1a showed the strongest inhibitory activity, with IC50 values of 4.10 ± 0.14 μM and 1.79 ± 0.11 μM, which were 1.5-fold and 2.8-fold more potent than those of positive drugs against Cat L and S, respectively. Further wound-healing and transwell chamber assays demonstrated that B1a presented significant antimetastatic ability in vitro.

A Novel Ibuprofen Derivative and Its Complexes: Physicochemical Characterization, DFT Modeling, Docking, In Vitro Anti-Inflammatory Studies, and DNA Interaction

A novel derivative of ibuprofen and salicylaldehyde N′-(4-hydroxybenzylidene)-2-(4-isobutylphenyl) propane hydrazide (HL) was synthesized, followed by its complexation with Cu, Ni, Co, Gd, and Sm. The compounds obtained were characterized by ¹HNMR, mass spectrometry, UV-Vis spectroscopy, FT-IR spectroscopy, thermal analysis (DTA and TGA), conductivity measurements, and magnetic susceptibility measurements. The results indicate that the complexes formed were [Cu(L)(H₂O)]Cl·2H₂O, [Ni(L)₂], [Co(L)₂]·H₂O, [Gd(L)₂(H₂O)₂](NO₃)·2H₂O and [Sm(L)₂(H₂O)₂](NO₃)·2H₂O. The surface characteristics of the produced compounds were evaluated by DFT calculations using the MOE environment. The docking was performed against the COX2 targeting protein (PDB code: 5IKT Homo sapiens). The binding energies were −7.52, −9.41, −9.51, −8.09, −10.04, and −8.05 kcal/mol for HL and the Co, Ni, Cu, Sm, and Gd complexes, respectively, which suggests the enhancement of anti-inflammatory behaviors compared with the binding energy of ibuprofen (−5.38 kcal/mol). The anti-inflammatory properties of the new compounds were assessed in vitro using the western blot analysis method and the enzyme-linked immunosorbent assay (ELISA), consistent with the outcomes obtained from docking. The half-maximal inhibitory concentration (IC₅₀) values are 4.9, 1.7, 3.7, 5.6, 2.9, and 2.3 µM for HL and the Co, Ni, Cu, Sm, and Gd complexes, respectively, showing that they are more effective inhibitors of COX2 than ibuprofen (IC₅₀ = 31.4 µM). The brain or intestinal estimated permeation method (BOILED-Egg) showed that HL and its Co complex have high gastrointestinal absorption, while only the free ligand has high brain penetration. The binding constants of Co, Cu, and Gd complexes with DNA were recorded as 2.20 × 10⁴, 2.27 × 10^6, and 4.46 × 10³ M⁻¹, respectively, indicating the intercalator behavior of interaction. The newly synthesized ibuprofen derivative and its metal complexes showed greater anti-inflammatory activity than ibuprofen.

Targeting lysosomes in human disease: from basic research to clinical applications

In recent years, accumulating evidence has elucidated the role of lysosomes in dynamically regulating cellular and organismal homeostasis. Lysosomal changes and dysfunction have been correlated with the development of numerous diseases. In this review, we interpreted the key biological functions of lysosomes in four areas: cellular metabolism, cell proliferation and differentiation, immunity, and cell death. More importantly, we actively sought to determine the characteristic changes and dysfunction of lysosomes in cells affected by these diseases, the causes of these changes and dysfunction, and their significance to the development and treatment of human disease. Furthermore, we outlined currently available targeting strategies: (1) targeting lysosomal acidification; (2) targeting lysosomal cathepsins; (3) targeting lysosomal membrane permeability and integrity; (4) targeting lysosomal calcium signaling; (5) targeting mTOR signaling; and (6) emerging potential targeting strategies. Moreover, we systematically summarized the corresponding drugs and their application in clinical trials. By integrating basic research with clinical findings, we discussed the current opportunities and challenges of targeting lysosomes in human disease.

An efficient and concise synthesis of a selective small molecule non-peptide inhibitor of cathepsin L: KGP94

KGP94 is a potent, selective, and competitive inhibitor of the lysosomal endopeptidase enzyme (Cathepsin L) currently in preclinical trials for the treatment of metastatic cancer, which is a leading cause of cancer-associated death. Herein, we report two new synthetic routes for synthesizing the target compound through four consecutive steps, using a Weinreb amide approach starting from a common 3-bromobenzoyl chloride. A key step in the approach is a coupling reaction of a readily available Grignard reagent with amide 4 to produce 6, a previously unreported coupling pattern. These new strategies offer an efficient and alternative approach to synthesis of target compound with an excellent overall yield.

Cysteine Cathepsins: Potential Applications in Diagnostics and Therapy of Malignant Tumors

Cysteine cathepsins are proteolytic enzymes involved in protein degradation in lysosomes and endosomes. Cysteine cathepsins have been also found in the tumor microenvironment during carcinogenesis, where they are implicated in proliferation, invasion and metastasis of tumor cells through the degradation of extracellular matrix, suppression of cell-cell interactions, and promotion of angiogenesis. In this regard, cathepsins can have a diagnostic value and represent promising targets for antitumor drugs aimed at inhibition of these proteases. Moreover, cysteine cathepsins can be used as activators of novel targeted therapeutic agents. This review summarizes recent discovered roles of cysteine cathepsins in carcinogenesis and discusses new trends in cancer therapy and diagnostics using cysteine cathepsins as markers, targets, or activators.

Cathepsin L secretion by host and neoplastic cells potentiates invasion

The presence of macrophages within breast tumors correlates with metastatic potential. These tumor-associated macrophages often take on a pro-tumorigenic (M2-like) phenotype resulting in the secretion of growth factors and proteases, including the lysosomal protease cathepsin L. Since cathepsin L also is frequently secreted by breast cancer cells and contributes to tumor invasion, metastasis, and angiogenesis, we hypothesized that secretion of cathepsin L by both tumor-associated macrophages and neoplastic cells would facilitate the metastatic phenotype. Our results showed that the novel cathepsin L/K inhibitors KGP94 and KGP207 could inhibit in vitro M2 macrophage invasion and reduce the macrophage-stimulated invasion of 4T1 murine breast cancer cells. KGP94 and KGP207 treatment also reduced the expression of several M2-associated markers, suggesting that cathepsin L activity may be important for IL-4-driven M0 to M2 differentiation. In addition, cathepsin L shRNA knockdown studies revealed that cathepsin L from both the tumor cell and the macrophage population is important for tumor cell invasion. Thus our data suggest that tumor cells and macrophages may both contribute to the cathepsin L-driven metastatic phenotype of breast cancer. Taken together, these studies highlight the importance of cathepsin L in macrophage functions and suggest that cathepsin inhibition strategies may be therapeutically beneficial by impairing the progression of tumors with high infiltration of M2 macrophages.

Cysteine cathepsins as a prospective target for anticancer therapies-current progress and prospects

Cysteine cathepsins (CTS), being involved in both physiological and pathological processes, play an important role in the human body. During the last 30 years, it has been shown that CTS are highly upregulated in a wide variety of cancer types although they have received a little attention as a potential therapeutic target as compared to serine or metalloproteinases. Studies on the increasing problem of neoplastic progression have revealed that secretion of cell-surface- and intracellular cysteine proteases is aberrant in tumor cells and has an impact on their growth, invasion, and metastasis by taking part in tumor angiogenesis, in apoptosis, and in events of inflammatory and immune responses. Considering the role of CTS in carcinogenesis, inhibition of these enzymes becomes an attractive strategy for cancer therapy. The downregulation of natural CTS inhibitors (CTSsis), such as cystatins, observed in various types of cancer, supports this claim. The intention of this review is to highlight the relationship of CTS with cancer and to present illustrations that explain how some of their inhibitors affect processes related to neoplastic progression.

Synthesis and biological evaluation of a water-soluble phosphate prodrug salt and structural analogues of KGP94, a lead inhibitor of cathepsin L

The magnitude of expression of cathepsin L, often upregulated in the tumor microenvironment, correlates with the invasive and metastatic nature of certain tumors. Inhibition of cathepsin L represents an emerging strategy for the treatment of metastatic cancer. A potent, small-molecule inhibitor (referred to as KGP94) of cathepsin L, and new KGP94 analogues were synthesized. (3,5-Dibromophenyl)-(3-hydroxyphenyl) ketone thiosemicarbazone (22), with an IC₅₀ value of 202nM, exhibited similar inhibitory activity against cathepsin L compared to KGP94 (IC₅₀=189nM). Due to limited aqueous solubility of KGP94, a water-soluble phosphate salt (KGP420) was prepared in order to facilitate future in vivo studies. Enzymatic hydrolysis with alkaline phosphatase (ALP) demonstrated that the phosphate prodrug, KGP420, was readily converted to the parent compound, KGP94.

Cathepsin L in tumor angiogenesis and its therapeutic intervention by the small molecule inhibitor KGP94

A significant proportion of breast cancer patients harbor clinically undetectable micrometastases at the time of diagnosis. If left untreated, these micro-metastases may lead to disease relapse and possibly death. Hence, there is significant interest in the development of novel anti-metastatic agents that could also curb the growth of pre-established micrometastases. Like primary tumor, the growth of metastases also is driven by angiogenesis. Although the role of cysteine protease Cathepsin L (CTSL) in metastasis associated tumor cell functions such as migration and invasion is well recognized, its role in tumor angiogenesis remains less explored. The present study examines the contribution of CTSL to breast cancer angiogenesis and evaluates the anti-angiogenic efficacy of CTSL inhibitor KGP94. CTSL semi-quantitative RT-PCR analysis on breast tissue panels revealed significant upregulation of CTSL in breast cancer patients which strongly correlated with increased relapse and metastatic incidence and poor overall survival. Preclinically, CTSL ablation using shRNA or KGP94 treatment led to a significant reduction in MDA-MB-231 tumor cell induced angiogenesis in vivo. In-vitro assessments demonstrated a significant decrease in various angiogenic properties such as endothelial cell sprouting, migration, invasion, tube formation and proliferation in the presence of KGP94. Microarray analyses revealed a significant upregulation of cell cycle related genes by CTSL. Western blot analyses further confirmed upregulation of members of the cyclin family by CTSL. Collectively, these data indicate that CTSL is an important contributor to tumor angiogenesis and that the CTSL inhibition may have therapeutic utility in the treatment of breast cancer patients.

Synthesis and biochemical evaluation of benzoylbenzophenone thiosemicarbazone analogues as potent and selective inhibitors of cathepsin L

Upregulation of cathepsin L in a variety of tumors and its ability to promote cancer cell invasion and migration through degradation of the extracellular matrix suggest that cathepsin L is a promising biological target for the development of anti-metastatic agents. Based on encouraging results from studies on benzophenone thiosemicarbazone cathepsin inhibitors, a series of fourteen benzoylbenzophenone thiosemicarbazone analogues were designed, synthesized, and evaluated for their inhibitory activity against cathepsins L and B. Thiosemicarbazone inhibitors 3-benzoylbenzophenone thiosemicarbazone 1, 1,3-bis(4-fluorobenzoyl)benzene thiosemicarbazone 8, and 1,3-bis(2-fluorobenzoyl)-5-bromobenzene thiosemicarbazone 32 displayed the greatest potency against cathepsin L with low IC50 values of 9.9 nM, 14.4 nM, and 8.1 nM, respectively. The benzoylbenzophenone thiosemicarbazone analogues evaluated were selective in their inhibition of cathepsin L compared to cathepsin B. Thiosemicarbazone analogue 32 inhibited invasion through Matrigel of MDA-MB-231 breast cancer cells by 70% at 10 μM. Thiosemicarbazone analogue 8 significantly inhibited the invasive potential of PC-3ML prostate cancer cells by 92% at 5 μM. The most active cathepsin L inhibitors from this benzoylbenzophenone thiosemicarbazone series (1, 8, and 32) displayed low cytotoxicity toward normal primary cells [in this case human umbilical vein endothelial cells (HUVECs)]. In an initial in vivo study, 3-benzoylbenzophenone thiosemicarbazone (1) was well-tolerated in a CDF1 mouse model bearing an implanted C3H mammary carcinoma, and showed efficacy in tumor growth delay. Low cytotoxicity, inhibition of cell invasion, and in vivo tolerability are desirable characteristics for anti-metastatic agents functioning through an inhibition of cathepsin L. Active members of this structurally diverse group of benzoylbenzophenone thiosemicarbazone cathepsin L inhibitors show promise as potential anti-metastatic, pre-clinical drug candidates.

G2/M Cell Cycle Arrest and Tumor Selective Apoptosis of Acute Leukemia Cells by a Promising Benzophenone Thiosemicarbazone Compound

Anti-mitotic therapies have been considered a hallmark in strategies against abnormally proliferating cells. Focusing on the extensively studied family of thiosemicarbazone (TSC) compounds, we have previously identified 4,4'-dimethoxybenzophenone thiosemicarbazone (T44Bf) as a promising pharmacological compound in a panel of human leukemia cell lines (HL60, U937, KG1a and Jurkat). Present findings indicate that T44Bf-mediated antiproliferative effects are associated with a reversible chronic mitotic arrest caused by defects in chromosome alignment, followed by induced programmed cell death. Furthermore, T44Bf selectively induces apoptosis in leukemia cell lines when compared to normal peripheral blood mononuclear cells. The underlying mechanism of action involves the activation of the mitochondria signaling pathway, with loss of mitochondrial membrane potential and sustained phosphorylation of anti-apoptotic protein Bcl-xL as well as increased Bcl-2 (enhanced phosphorylated fraction) and pro-apoptotic protein Bad levels. In addition, ERK signaling pathway activation was found to be a requisite for T44Bf apoptotic activity. Our findings further describe a novel activity for a benzophenone thiosemicarbazone and propose T44Bf as a promising anti-mitotic prototype to develop chemotherapeutic agents to treat acute leukemia malignancies.

Cathepsin L targeting in cancer treatment

Proteolytic enzymes may serve as promising targets for novel therapeutic treatment strategies seeking to impede cancer progression and metastasis. One such enzyme is cathepsin L (CTSL), a lysosomal cysteine protease. CTSL upregulation, a common occurrence in a variety of human cancers, has been widely correlated with metastatic aggressiveness and poor patient prognosis. In addition, CTSL has been implicated to contribute to cancer-associated osteolysis, a debilitating morbidity affecting both life expectancy and the quality of life. In this review, we highlight the mechanisms by which CTSL contributes to tumor progression and dissemination and discuss the therapeutic utility of CTSL intervention strategies aimed at impeding metastatic progression and bone resorption.

Design, synthesis, computational calculation and biological evaluation of some novel 2-thiazolyl hydrazones

In the present study a novel series of 1-(1-(4-isobutylphenyl)ethylidene)-2-(4-phenylthiazol-2-yl)hydrazine 2a and its derivatives 2b-2f have been synthesized by the cyclization of 1-(1-(4-isobutylphenyl)ethylidene)thiosemicarbazide with 2-bromoacetophenone/ 4-substituted 2-bromoacetophenones. The structures of the synthesized thiazolyl hydrazones 2a-2f were characterized by FT-IR, (1)H, (13)C NMR, 2D NMR and mass spectral techniques. The molecular geometries were also investigated theoretically using B3LYP functional with 6-311G(d,p) basis set. To explain the molecular properties energy gap (Eg), electronegativity (χ), hardness (g), electrophilicity (ω) and softness (S) were computed, natural bonding orbital (NBO) analysis and molecular electrostatic potential (MEP) were also performed at the same level of theory. All the synthesized thiazolyl hydrazones 2a-2f were screened for their in vitro antimicrobial activity against selected bacterial and fungal strains. The results showed that the heterocyclic thiazolyl hydrazone derivatives exhibit a promising selective inhibitory activity against various bacterial and fungal strains.

Mechanistic insights into mode of action of novel natural cathepsin L inhibitors

Background

Development of a cancerous cell takes place when it ceases to respond to growth-inhibiting signals and multiplies uncontrollably and can detach and move to other parts of the body; the process called as metastasis. A particular set of cysteine proteases are very active during cancer metastasis, Cathepsins being one of them. They are involved in tumor growth and malignancy and have also been reported to be overexpressed in tumor cell lines. In the present study, a combinatorial approach comprising three-dimensional quantitative structure-activity relationship (3D QSAR), ligand-based pharmacophore modelling and search followed by cathepsin L structure-based high throughput screening was carried out using an initial set of 28 congeneric thiosemicarbazone derivatives as cathepsin L inhibitors. A 3D QSAR was derived using the alignment of a common thiosemicarbazone substructure. Essential structural features responsible for biological activity were taken into account for development of a pharmacophore model based on 29 congeneric thiosemicarbazone derivatives. This model was used to carry out an exhaustive search on a large dataset of natural compounds. A further cathepsin L structure-based screen identified two top scoring compounds as potent anti-cancer leads.

Results

The generated 3D QSAR model showed statistically significant results with an r² value of 0.8267, cross-validated correlation coefficient q² of 0.7232, and a pred_r² (r² value for test set) of 0.7460. Apart from these, a high F test value of 30.2078 suggested low probability of the model's failure. The pharmacophoric hypothesis chosen for searching the natural compound libraries was identified as DDHRR, where two Ds denote 2 hydrogen donors, H represents a hydrophobic group and two Rs represent aromatic rings, all of which are essential for the biological activity. We report two potential drug leads ZINC08764437 (NFP) and ZINC03846634 (APQ) obtained after a combined approach of pharmacophore-based search and structure-based virtual screen. These two compounds displayed extra precision docking scores of -7.972908 and -7.575686 respectively suggesting considerable binding affinity for cathepsin L. High activity values of 5.72 and 5.75 predicted using the 3D QSAR model further substantiated the inhibitory potential of these identified leads.

Conclusion

The present study attempts to correlate the structural features of thiosemicarbazone group with their biological activity by development of a robust 3D QSAR model. Being statistically valid, this model provides near accurate values of the activities predicted for the congeneric set on which it is based. These predicted activities are good for the test set compounds making it indeed a statistically sound 3D QSAR model. The identified pharmacophore model DDHRR.8 comprised of all the essential features required to interact with the catalytic triad of cathepsin L. A search for natural compounds based on this pharmacophore followed by docking studies further screened out two top scoring candidates: NFP and AFQ. The high binding affinity and presence of essential structural features in these two compounds make them ideal for consideration as natural anti-tumoral agents. Activity prediction using 3D QSAR model further validated their potential as worthy drug candidates against cathepsin L for treatment of cancer.

Cathepsin L inhibition by the small molecule KGP94 suppresses tumor microenvironment enhanced metastasis associated cell functions of prostate and breast cancer cells

Metastasis remains the major cause of therapeutic failure, poor prognosis and high mortality in breast and prostate cancer patients. Aberrant microenvironments including hypoxia and acidic pH are common features of most solid tumors that have been long associated with enhanced metastasis and poor patient outcomes. Novel approaches to reduce metastatic incidences and improve overall survival of cancer patients clearly are needed. The crucial role of Cathepsin L (CTSL) in the dissemination of tumor cells has led to the development of novel cathepsin L inhibition strategies. The present study evaluated the ability of KGP94, a small molecule inhibitor of CTSL, to impair the metastatic phenotype of prostate (PC-3ML) and breast (MDA-MB-231) cancer cells both under normal and aberrant microenvironmental conditions. To assess the role of CTSL in hypoxia and acidosis triggered metastasis associated cell functions, secreted CTSL levels were determined under conditions pertinent to the tumor microenvironment. Acute exposures to hypoxic or acidic conditions significantly elevated secreted CTSL levels either through an increase in intracellular CTSL levels or through activation of lysosomal exocytosis or both, depending on the tumor type. Increases in CTSL secretion closely paralleled enhanced tumor cell migration and invasion suggesting that CTSL could be an essential factor in tumor microenvironment triggered metastasis. Importantly, KGP94 treatment led to marked attenuation of tumor cell invasion and migration under both normal and aberrant microenvironmental conditions suggesting that it may have significant utility as an anti-metastatic agent.