Insights on Cancer Cell Inhibition, Subcellular Activities, and Kinase Profile of Phenylacetamides Pending 1H-Imidazol-5-One Variants

Structural changes of small-molecule drugs may bring interesting biological properties, especially in the field of kinase inhibitors. We sought to study tirbanibulin, a first-in-class dual Src kinase (non-ATP competitive)/tubulin inhibitor because there was not enough reporting about its structure–activity relationships (SARs). In particular, the present research is based on the replacement of the outer ring of the biphenyl system of 2-[(1,1′-biphenyl)-4-yl]-N-benzylacetamide, the identified pharmacophore of KX chemotype, with a heterocyclic ring. The newly synthesized compounds showed a range of activities in cell-based anticancer assays, agreeing with a clear SAR profile. The most potent compound, (Z)-N-benzyl-4-[4-(4-methoxybenzylidene)-2-methyl-5-oxo-4,5-dihydro-1H-imidazol-1-yl]phenylacetamide (KIM-161), demonstrated cytotoxic IC50 values at 294 and 362 nM against HCT116 colon cancer and HL60 leukemia cell lines, respectively. Profiling of this compound (aqueous solubility, liver microsomal stability, cytochrome P450 inhibition, reactivity with reduced glutathione, and plasma protein binding) confirmed its adequate drug-like properties. Mechanistic studies revealed that this compound does not depend on tubulin or Src kinase inhibition as a factor in forcing HL60 to exit its cell cycle and undergo apoptosis. Instead, KIM-161 downregulated several other kinases such as members of BRK, FLT, and JAK families. It also strongly suppresses signals of ERK1/2, GSK-3α/β, HSP27, and STAT2, while it downregulated AMPKα1 phosphorylation within the HL60 cells. Collectively, these results suggest that phenylacetamide-1H-imidazol-5-one (KIM-161) could be a promising lead compound for further clinical anticancer drug development.

Biobanked Glioblastoma Patient-Derived Organoids as a Precision Medicine Model to Study Inhibition of Invasion

Glioblastoma (GBM) is highly resistant to treatment and invasion into the surrounding brain is a cancer hallmark that leads to recurrence despite surgical resection. With the emergence of precision medicine, patient-derived 3D systems are considered potentially robust GBM preclinical models. In this study, we screened a library of 22 anti-invasive compounds (i.e., NF-kB, GSK-3-B, COX-2, and tubulin inhibitors) using glioblastoma U-251 MG cell spheroids. We evaluated toxicity and invasion inhibition using a 3D Matrigel invasion assay. We next selected three compounds that inhibited invasion and screened them in patient-derived glioblastoma organoids (GBOs). We developed a platform using available macros for FIJI/ImageJ to quantify invasion from the outer margin of organoids. Our data demonstrated that a high-throughput invasion screening can be done using both an established cell line and patient-derived 3D model systems. Tubulin inhibitor compounds had the best efficacy with U-251 MG cells, however, in ex vivo patient organoids the results were highly variable. Our results indicate that the efficacy of compounds is highly related to patient intra and inter-tumor heterogeneity. These results indicate that such models can be used to evaluate personal oncology therapeutic strategies.

A new role of low barrier hydrogen bond in mediating protein stability by small molecules

Low barrier hydrogen bond (LBHB) is a special type of hydrogen bond which occurs where two heteroatoms with similar pKa values share a single proton resulting in an unusually strong and short hydrogen bond. LBHBs in protein play important roles in enzyme catalysis and maintaining protein structural integrity but its other biochemical roles are unknown. Here we report a novel function of LBHB in selectively inducing tubulin protein degradation. A tubulin inhibitor, 3-(3-Phenoxybenzyl) amino-β-carboline (PAC), promotes selective degradation of αβ-tubulin heterodimers by binding to the colchicine site of β-tubulin. Biochemical studies have revealed that PAC specifically destabilizes tubulin, making it prone to aggregation that then predisposes it to ubiquitinylation and then degradation. Structural activity analyses have indicated that the destabilization is mediated by a single hydrogen bond formed between the pyridine nitrogen of PAC and βGlu198, which is identified as a LBHB. In contrast, another two tubulin inhibitors only forming normal hydrogen bonds with βGlu198 exhibit no degradation effect. Thus, the LBHB accounts for the degradation. Most importantly, we screened for compounds capable of forming LBHB with βGlu198 and demonstrated that BML284, a Wnt signaling activator, also promotes tubulin heterodimers degradation in a PAC-like manner as expected. Our study has identified a novel approach for designing tubulin degraders, providing a unique example of LBHB function and suggests that designing small molecules to form LBHBs with protein residues resulting in the highly specific degradation of a target protein could be a new strategy for drug development.

Dual Mechanism Inhibitor Control and Pharmacological Utility of Drug Resistance FLT3-ITD in Acute Myeloid Leukemia Cells

FLT3 mutations are among the most common genetic alterations in acute-myeloid leukemia (AML). They are associated with poor prognosis. Multiple FLT3 inhibitors have been in clinical evaluation at various stages. Resistance to FLT3 inhibitors due to acquired point mutations in the tyrosine-kinase domain (TKD), have limited the effectiveness of treatments. A “gatekeeper” mutation (F691L), is also resistant to most FLT3 inhibitors. New therapies are therefore needed. FLT3 inhibitors are needed to protect against FLT3-TKD mutations and FLT3 internal tandem duplicate (FLT3–ITD). We identified KX2-391, a dual FLT3/tubulin inhibitor, and examined its efficacy and mechanisms for overcoming drug-resistant FLT3ITD-TKD mutations. KX2-391 had potent growth inhibitory effects and apoptosis promoting effects on AML cell lines that harbor FLT3-ITD mutations. KX2-391 orally administered significantly prolonged the survival time of a murine model with leukemia caused by FLT3ITD-F691L. KX2-391 also inhibited growth of primary AML cells that express FLT3ITD-F691L and 2 primary cells that are FLT3ITD-D835Y. Preclinical data suggest that KX2-391 is a promising FLT3 inhibitor. The treatment of AML patients with FLT3 mutations, particularly refractory/relapsed patients suffering from F691L or other FLT3TKD mutations.

VERU-111: An Oral Tubulin Inhibitor That Suppresses Taxane-Sensitive and Taxane-Resistant Breast Cancer

Triple negative breast cancer (TNBC) patients have poorer overall prognosis relative to patients diagnosed with other molecular subtypes due to rapid onset of drug resistance to conventional chemotherapies and increased risk of visceral metastases. The microtubule inhibitor paclitaxel (Taxol, a taxane) is a frontline therapy for advanced breast cancer. We evaluated in TNBC models the preclinical safety and efficacy of a novel, potent, and orally bioavailable tubulin inhibitor, VERU-111, a tubulin inhibitor targeting the colchicine binding site. VERU-111 showed potent anti-proliferative and anti-migratory activity against several taxane-sensitive and taxane-resistant TNBC breast cancer cell lines. Based on these observations, taxane-resistant HER2+ cell lines were generated, and were also found to be responsive to VERU-111 treatment. In vivo, orally administered VERU-111 inhibited MDA-MB-231 tumor growth in a dose-dependent manner with antitumor potency similar to paclitaxel, and repressed metastases originating from the mammary fat pad or following tail vein injection. In contrast, in a MDA-MB-231 paclitaxel-resistant (TxR) subline, tumor growth was refractory to paclitaxel whereas VERU-111 significantly inhibited primary tumor growth and reduced lung and liver metastases. VERU-111 was then tested in a luciferase-labeled, multidrug resistant patient-derived xenograft (PDX) TNBC model. VERU-111 significantly inhibited HCI-10 PDX tumor growth and suppressed the expansion of axillary lymph node metastases present prior to initiation of therapy while suppressing lung, liver, bone and kidney metastases at study endpoint. Moreover, in contrast to paclitaxel, VERU-111 therapy did not cause a significant decrease in mouse body weight during treatment. Evaluation of efficacy of VERU-111 in taxane-sensitive and -resistant HER2+ xenograft models is in progress. Overall, we conclude that VERU-111 is a new generation orally bioavailable tubulin inhibitor that potently inhibits the growth of taxane-sensitive and taxane-resistant breast cancers with reduced adverse side effects relative to paclitaxel. Importantly, VERU-111 is well-tolerated in patients as evaluated in phase I/II clinical trials for advanced prostate cancer patients (NCT03752099). We propose that VERU-111 will be an effective second line therapy for patients with advanced breast cancer who progress on taxane-based therapeutic regimens.

The Tubulin Inhibitor VERU-111 in Combination With Vemurafenib Provides an Effective Treatment of Vemurafenib-Resistant A375 Melanoma

Melanoma is one of the deadliest skin cancers having a five-year survival rate around 15–20%. An overactivated MAPK/AKT pathway is well-established in BRAF mutant melanoma. Vemurafenib (Vem) was the first FDA-approved BRAF inhibitor and gained great clinical success in treating late-stage melanoma. However, most patients develop acquired resistance to Vem within 6–9 months. Therefore, developing a new treatment strategy to overcome Vem-resistance is highly significant. Our previous study reported that the combination of a tubulin inhibitor ABI-274 with Vem showed a significant synergistic effect to sensitize Vem-resistant melanoma both in vitro and in vivo. In the present study, we unveiled that VERU-111, an orally bioavailable inhibitor of α and β tubulin that is under clinical development, is highly potent against Vem-resistant melanoma cells. The combination of Vem and VERU-111 resulted in a dramatically enhanced inhibitory effect on cancer cells in vitro and Vem-resistant melanoma tumor growth in vivo compared with single-agent treatment. Further molecular signaling analyses demonstrated that in addition to ERK/AKT pathway, Skp2 E3 ligase also plays a critical role in Vem-resistant mechanisms. Knockout of Skp2 diminished oncogene AKT expression and contributed to the synergistic inhibitory effect of Vem and VERU-111. Our results indicate a treatment combination of VERU-111 and Vem holds a great promise to overcome Vem-resistance for melanoma patients harboring BRAF (V600E) mutation.

Dual Inhibition of γ-Tubulin and Plk1 Induces Mitotic Cell Death

α/β-Tubulin inhibitors that alter microtubule (MT) dynamics are commonly used in cancer therapy, however, these inhibitors also cause severe side effects such as peripheral neuropathy. γ-Tubulin is a possible target as antitumor drugs with low side effects, but the antitumor effect of γ-tubulin inhibitors has not been reported yet. In this study, we verified the antitumor activity of gatastatin, a γ-tubulin specific inhibitor. The cytotoxicity of gatastatin was relatively weak compared with that of the conventional MT inhibitors, paclitaxel and vinblastine. To improve the cytotoxicity, we screened the chemicals that improve the effects of gatastatin and found that BI 2536, a Plk1 inhibitor, greatly increases the cytotoxicity of gatastatin. Co-treatment with gatastatin and BI 2536 arrested cell cycle progression at mitosis with abnormal spindles. Moreover, mitotic cell death induced by the combined treatment was suppressed by the Mps1 inhibitor, reversine. These findings suggest that co-treatment with Plk1 and γ-tubulin inhibitors causes spindle assembly checkpoint-dependent mitotic cell death by impairing centrosome functions. These results raise the possibility of Plk1 and γ-tubulin inhibitor co-treatment as a novel cancer chemotherapy.

Recent Development in Indole Derivatives as Anticancer Agent: A Mechanistic Approach

Background: Cancer accounts for several deaths each year. There are multiple FDA approved drugs for cancer treatments. Due to the severe side effects and multiple drug resistance, the current drug therapies become ineffective. So, the newer moieties with fewer toxic effects are necessary for the development. Objective: The mechanism of indole derivatives as anti-cancer agents with their major target is explored in detail in this article. Methods: Recent advances and mechanism of indole derivatives as anti-cancer agents are reviewed. This review suggests a detailed explanation of multiple mechanisms of action of various indole derivatives: cell cycle arrest, aromatase inhibitor estrogen receptor regulator, tubulin inhibitor, a tyrosine kinase inhibitor, topoisomerase inhibitors, NFkB/PI3/Akt/mTOR pathway inhibitors, through which these derivatives have shown promising anti-cancer potential. Results: A full literature review showed that the indole derivatives are associated with the properties of inducing apoptosis, aromatase inhibition, regulation of estrogen receptor and inhibition of tyrosine kinase, tubulin assembly, NFkB/PI3/Akt/mTOR pathway, and HDACs. These derivatives have shown significant activity against cancer cell lines. Conclusion: Indole derivatives seem to be important in cancer via acting through various mechanisms. This review has shown that the indole derivatives can further be explored for the betterment of cancer treatment, and to discover the hidden potential of indole derivatives.