Is the Fate of Clinical Candidate Arry-520 Already Sealed? Predicting Resistance in Eg5–Inhibitor Complexes

Binding patterns of inhibitors to different pockets of kinesin Eg5

The kinesin-5 family member, Eg5, plays very important role in the mitosis. As a mitotic protein, Eg5 is the target of various mitotic inhibitors. There are two targeting pockets in the motor domain of Eg5, which locates in the α2/L5/α3 region and the α4/α6 region respectively. We investigated the interactions between the different inhibitors and the two binding pockets of Eg5 by using all-atom molecular dynamics method. Combined the conformational analysis with the free-energy calculation, the binding patterns of inhibitors to the two binding pockets are shown. The α2/L5/α3 pocket can be divided into 4 regions. The structures and binding conformations of inhibitors in region 1 and 2 are highly conserved. The shape of α4/α6 pocket is alterable. The space of this pocket in ADP-binding state of Eg5 is larger than that in ADP·Pi-binding state due to the limitation of a hydrogen bond formed in the ADP·Pi-binding state. The results of this investigation provide the structural basis of the inhibitor-Eg5 interaction and offer a reference for the Eg5-targeted drug design.

Cancer on motors: How kinesins drive prostate cancer progression?

Prostate cancer causes numerous male deaths annually. Although great progress has been made in the diagnosis and treatment of prostate cancer during the past several decades, much about this disease remains unknown, especially its pathobiology. The kinesin superfamily is a pivotal group of motor proteins, that contains a microtubule-based motor domain and features an adenosine triphosphatase activity and motility characteristics. Large-scale sequencing analyses based on clinical samples and animal models have shown that several members of the kinesin family are dysregulated in prostate cancer. Abnormal expression of kinesins could be linked to uncontrolled cell growth, inhibited apoptosis and increased metastasis ability. Additionally, kinesins may be implicated in chemotherapy resistance and escape immunologic cytotoxicity, which creates a barrier to cancer treatment. Here we cover the recent advances in understanding how kinesins may drive prostate cancer progression and how targeting their function may be a therapeutic strategy. A better understanding of kinesins in prostate cancer tumorigenesis may be pivotal for improving disease outcomes in prostate cancer patients.

The mesenchymal morphology of cells expressing the EML4-ALK V3 oncogene is dependent on phosphorylation of Eg5 by NEK7

Echinoderm microtubule-associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) oncogenic fusion proteins are found in approximately 5% of non-small cell lung cancers. Different EML4-ALK fusion variants exist with variant 3 (V3) being associated with a significantly higher risk than other common variants, such as variant 1 (V1). Patients with V3 respond less well to targeted ALK inhibitors, have accelerated rates of metastasis, and have poorer overall survival. A pathway has been described downstream of EML4-ALK V3 that is independent of ALK catalytic activity but dependent on the NEK9 and NEK7 kinases. It has been proposed that assembly of an EML4-ALK V3-NEK9-NEK7 complex on microtubules leads to cells developing a mesenchymal-like morphology and exhibiting enhanced migration. However, downstream targets of this complex remain unknown. Here, we show that the microtubule-based kinesin, Eg5, is recruited to interphase microtubules in cells expressing EML4-ALK V3, whereas chemical inhibition of Eg5 reverses the mesenchymal morphology of cells. Furthermore, we show that depletion of NEK7 interferes with Eg5 recruitment to microtubules in cells expressing EML4-ALK V3 and cell length is reduced, but this is reversed by coexpression of a phosphomimetic mutant of Eg5, in a site, S1033, phosphorylated by NEK7. Intriguingly, we also found that expression of Eg5-S1033D led to cells expressing EML4-ALK V1 adopting a more mesenchymal-like morphology. Together, we propose that Eg5 acts as a substrate of NEK7 in cells expressing EML4-ALK V3 and Eg5 phosphorylation promotes the mesenchymal morphology typical of these cells.

Antibody-drug conjugates: Recent advances in payloads

Antibody‒drug conjugates (ADCs), which combine the advantages of monoclonal antibodies with precise targeting and payloads with efficient killing, show great clinical therapeutic value. The ADCs' payloads play a key role in determining the efficacy of ADC drugs and thus have attracted great attention in the field. An ideal ADC payload should possess sufficient toxicity, low immunogenicity, high stability, and modifiable functional groups. Common ADC payloads include tubulin inhibitors and DNA damaging agents, with tubulin inhibitors accounting for more than half of the ADC drugs in clinical development. However, due to clinical limitations of traditional ADC payloads, such as inadequate efficacy and the development of acquired drug resistance, novel highly efficient payloads with diverse targets and reduced side effects are being developed. This perspective summarizes the recent research advances of traditional and novel ADC payloads with main focuses on the structure-activity relationship studies, co-crystal structures, and designing strategies, and further discusses the future research directions of ADC payloads. This review also aims to provide valuable references and future directions for the development of novel ADC payloads that will have high efficacy, low toxicity, adequate stability, and abilities to overcome drug resistance.

Drug resistance dependent on allostery: A P-loop rigor Eg5 mutant exhibits resistance to allosteric inhibition by STLC

The mitotic kinesin Eg5 has emerged as a potential anti-mitotic target for the purposes of cancer chemotherapy. Whether clinical resistance to these inhibitors can arise is unclear. We exploited HCT116 cancer cell line to select resistant clones to S-trityl-L-cysteine (STLC), an extensively studied Eg5 loop-L5 binding inhibitor. The STLC resistant clones differed in their resistance to other loop-L5 binding inhibitors but remained sensitive to the ATP class of competitive Eg5 specific inhibitors. Eg5 is still necessary for bipolar spindle formation in the resistant clones since the cells were sensitive to RNAi mediated depletion of Eg5. One clone expressing Eg5(T107N), a dominant point mutation in the P-loop of the ATP binding domain of the motor, appeared to be not only resistant but also dependent on the presence of STLC. Eg5(T107N) expression was associated also with resistance to the clinical relevant loop-L5 Eg5 inhibitors, Arry-520 and ispinesib. Ectopic expression of the Eg5(T107N) mutant in the absence of STLC was associated with strong non-exchangeable binding to microtubules causing them to bundle. Biochemical assays showed that in contrast to the wild type Eg5-STLC complex, the ATP binding site of the Eg5(T107N) is accessible for nucleotide exchange only when the inhibitor is present. We predict that resistance can be overcome by inhibitors that bind to other than the Eg5 loop-L5 binding site having different chemical scaffolds, and that allostery-dependent resistance to Eg5 inhibitors may also occur in cells and may have positive implications in chemotherapy since once diagnosed may be beneficial following cessation of the chemotherapeutic regimen.

Effective Synthesis and Biological Evaluation of Natural and Designed Bis(indolyl)methanes via Taurine-Catalyzed Green Approach

An ecofriendly, inexpensive, and efficient route for synthesizing 3,3'-bis(indolyl)methanes (BIMs) and their derivatives was carried out by an electrophilic substitution reaction of indole with structurally divergent aldehydes and ketones using taurine and water as a green catalyst and solvent, respectively, under sonication conditions. Using water as the only solvent, the catalytic process demonstrated outstanding activity, productivity, and broad functional group tolerance, affording the required BIM natural products and derivatives in excellent yields (59-90%). Furthermore, in silico based structure activity analysis of the synthesized BIM derivatives divulges their potential ability to bind antineoplastic drug target and spindle motor protein kinesin Eg5. The precise binding mode of BIM derivatives with the ATPase motor domain of Eg5 is structurally reminiscent with previously reported allosteric inhibitor Arry520, which is under phase III clinical trials. Nevertheless, detailed analysis of the binding poses indicates that BIM derivatives bind the allosteric pocket of the Eg5 motor domain more robustly than Arry520; moreover, unlike Arry520, BIM binding is found to be resistant to drug-resistant mutations of Eg5. Accordingly, a structure-guided mechanism of Eg5 inhibition by synthesized BIM derivatives is proposed.

Optical Control of Mitosis with a Photoswitchable Eg5 Inhibitor

Eg5 is a kinesin motor protein that is responsible for bipolar spindle formation and plays a crucial role during mitosis. Loss of Eg5 function leads to the formation of monopolar spindles, followed by mitotic arrest, and subsequent cell death. Several cell-permeable small molecules have been reported to inhibit Eg5 and some have been evaluated as anticancer agents. We now describe the design, synthesis, and biological evaluation of photoswitchable variants with five different pharmacophores. Our lead compound Azo-EMD is a cell permeable azobenzene that inhibits Eg5 more potently in its light-induced cis form. This activity decreased the velocity of Eg5 in single-molecule assays, promoted formation of monopolar spindles, and led to mitotic arrest in a light dependent way.

A review on the treatment of multiple myeloma with small molecular agents in the past five years

Multiple myeloma is currently incurable, and the incidence rate is increasing year by year worldwide. Although in recent years the combined treatment plan based on proteasome inhibitors and immunomodulatory drugs has greatly improved the treatment effect of multiple myeloma, most patients still relapse and become resistant to current treatments. To solve this problem, scientists are committed to developing drugs with higher specificity, such as iberdomide, which is highly specific to ikaros and aiolos. This review aims to focus on the small molecular agents that are being researched/clinically used for the treatment of multiple myeloma, including the target mechanism, structure-activity relationship and application prospects of small molecular agents.

KIF11 inhibitors filanesib and ispinesib inhibit meningioma growth in vitro and in vivo

Treatment of aggressive meningiomas remains challenging due to a high rate of recurrence in higher-grade meningiomas, frequent subtotal resections, and the lack of effective systemic treatments. Substantial overexpression associated with a poor prognosis has been demonstrated for kinesin family member 11 (KIF11) in high-grade meningiomas. Due to anti-tumor activity for KIF11 inhibitors (KIF11i) filanesib and ispinesib in other cancer types, we sought to investigate their mode of action and efficacy for the treatment of aggressive meningiomas. Dose curve analysis of both KIF11i revealed IC50 values of less than 1 nM in anaplastic and benign meningioma cell lines. Both compounds induced G2/M arrest and subsequent subG1 increase in all cell lines. Profound induction of apoptosis was detected in the anaplastic cell lines determined by annexin V staining. KIF11i significantly inhibited meningioma growth in xenotransplanted mice by up to 83%. Furthermore, both drugs induced minor hematological side effects, which were less pronounced for filanesib. We identified substantial in vitro and in vivo anti-tumor effects of the KIF11 inhibitors filanesib and ispinesib, with filanesib demonstrating better tolerability, suggesting future use of filanesib for the treatment of aggressive meningioma.

Design, synthesis, and evaluation of a novel prodrug, a S-trityl-l-cysteine derivative targeting kinesin spindle protein

Kinesin spindle protein (KSP) is expressed only in cells undergoing cell division, and hence represents an attractive target for the treatment of cancer. Several KSP inhibitors have been developed and undergone clinical trial, but their clinical use is limited by their toxicity to rapidly proliferating non-cancerous cells. To create new KSP inhibitors that are highly selective for cancer cells, we optimized the amino acid moiety of S-trityl-_l-cysteine (STLC) derivative 1 using in silico modeling. Molecular docking and molecular dynamics simulation were performed to investigate the binding mode of 1 with KSP. Consistent with the structure activity relationship studies, we found that a cysteine amino moiety plays an important role in stabilizing the interaction. Based on these findings and the structure of GSH, a substrate of γ-glutamyltransferase (GGT), we designed and synthesized the prodrug N-γ-glutamylated STLC derivative 9, which could be hydrolyzed by GGT to produce 1. The KSP ATPase inhibitory activity of 9 was lower than that of 1, and LC-MS analysis indicated that 9 was converted to 1 only in the presence of GGT in vitro. In addition, the cytotoxic activity of 9 was significantly attenuated in GGT-knockdown A549 cells. Since GGT is overexpressed on the cell membrane of various cancer cells, these results suggest that compound 9 could be a promising prodrug that selectively inhibits the proliferation of GGT-expressing cancer cells.

Eg5 targeting agents: From new anti-mitotic based inhibitor discovery to cancer therapy and resistance

Eg5, the product of Kif11 gene, also known as kinesin spindle protein, is a motor protein involved in the proper establishment of a bipolar mitotic spindle. Eg5 is one of the 45 different kinesins coded in the human genome of the kinesin motor protein superfamily. Over the last three decades Eg5 has attracted great interest as a promising new mitotic target. The identification of monastrol as specific inhibitor of the ATPase activity of the motor domain of Eg5 inhibiting the Eg5 microtubule motility in vitro and in cellulo sparked an intense interest in academia and industry to pursue the identification of novel small molecules that target Eg5 in order to be used in cancer chemotherapy based on the anti-mitotic strategy. Several Eg5 inhibitors entered clinical trials. Currently the field is faced with the problem that most of the inhibitors tested exhibited only limited efficacy. However, one Eg5 inhibitor, Arry-520 (clinical name filanesib), has demonstrated clinical efficacy in patients with multiple myeloma and is scheduled to enter phase III clinical trials. At the same time, new trends in Eg5 inhibitor research are emerging, including an increased interest in novel inhibitor binding sites and a focus on drug synergy with established antitumor agents to improve chemotherapeutic efficacy. This review presents an updated view of the structure and function of Eg5-inhibitor complexes, traces the possible development of resistance to Eg5 inhibitors and their potential therapeutic applications, and surveys the current challenges and future directions of this active field in drug discovery.