Orally bioavailable tubulin antagonists for paclitaxel-refractory cancer

VERU-111, an orally available tubulin inhibitor, suppresses ovarian tumor growth and metastasis

Ovarian cancer is the most lethal gynecological malignancy, with a 5-year survival rate of approximately 50%. The dismal prognosis is due in part to metastatic disease and acquired drug resistance to conventional chemotherapies such as taxanes. Colchicine binding site inhibitors (CBSIs) are attractive alternatives to taxanes because they could potentially achieve oral bioavailability and overcome drug resistance associated with the prolonged use of taxanes. VERU-111 is one of the most advanced CBSIs that is orally available, potent, and well tolerated and has shown good efficacy in several preclinical solid tumor models. Here, we demonstrate for the first time the in vitro potency of VERU-111 as well as its efficacy at inhibiting tumor growth and metastasis in an orthotopic ovarian cancer mouse model. VERU-111 has nanomolar potency against ovarian cancer cell lines and strongly inhibits colony formation, proliferation, invasion, and migration. VERU-111 disrupts microtubule formation to induce mitotic catastrophe and ultimately apoptosis in a concentration-dependent manner. The efficacy of VERU-111 was comparable with standard chemotherapy paclitaxel, the current first-line treatment of ovarian cancer, with no observed synergy with combination paclitaxel + VERU-111 treatment. In vivo, VERU-111 markedly suppressed ovarian tumor growth and completely suppressed distant organ metastasis. Together, these results support VERU-111 for its potential as a novel therapy for ovarian cancer, particularly for late-stage metastatic disease. SIGNIFICANCE STATEMENT: VERU-111 is an investigational new drug and has comparable efficacy as paclitaxel in suppressing tumor cell proliferation, colony formation, and migration in ovarian cancer models in vitro and has potent in vivo antitumor and antimetastatic activity in an orthotopic ovarian cancer mouse model. VERU-111 has low systemic toxicity and, unlike paclitaxel, is orally bioavailable and is not a substrate for the major drug efflux transporters, making it a promising and attractive alternative to taxane-based therapy.

Biological activity of a stable 6-aryl-2-benzoyl-pyridine colchicine-binding site inhibitor, 60c, in metastatic, triple-negative breast cancer

BACKGROUND

Improving survival for patients diagnosed with metastatic disease and overcoming chemoresistance remain significant clinical challenges in treating breast cancer. Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by a lack of therapeutically targetable receptors (ER/PR/HER2). TNBC therapy includes a combination of cytotoxic chemotherapies, including microtubule-targeting agents (MTAs) like paclitaxel (taxane class) or eribulin (vinca class); however, there are currently no FDA-approved MTAs that bind to the colchicine-binding site. Approximately 70 % of patients who initially respond to paclitaxel will develop taxane resistance (TxR). We previously reported that an orally bioavailable colchicine-binding site inhibitor (CBSI), VERU-111, inhibits TNBC tumor growth and treats pre-established metastatic disease. To further improve the potency and metabolic stability of VERU-111, we created next-generation derivatives of its scaffold, including 60c.

RESULTS

60c shows improved in vitro potency compared to VERU-111 for taxane-sensitive and TxR TNBC models, and suppress TxR primary tumor growth without gross toxicity. 60c also suppressed the expansion of axillary lymph node metastases existing prior to treatment. Comparative analysis of excised organs for metastasis between 60c and VERU-111 suggested that 60c has unique anti-metastatic tropism. 60c completely suppressed metastases to the spleen and was more potent to reduce metastatic burden in the leg bones and kidney. In contrast, VERU-111 preferentially inhibited liver metastases and lung metastasis repression was similar. Together, these results position 60c as an additional promising CBSI for TNBC therapy, particularly for patients with TxR disease.

Novel Brain-Penetrant, Small-Molecule Tubulin Destabilizers for the Treatment of Glioblastoma

Glioblastoma (GB) is the most lethal brain cancer in adults, with a 5-year survival rate of 5%. The standard of care for GB includes maximally safe surgical resection, radiation, and temozolomide (TMZ) therapy, but tumor recurrence is inevitable in most GB patients. Here, we describe the development of a blood-brain barrier (BBB)-penetrant tubulin destabilizer, RGN3067, for the treatment of GB. RGN3067 shows good oral bioavailability and achieves high concentrations in rodent brains after oral dosing (Cmax of 7807 ng/mL (20 μM), Tmax at 2 h). RGN3067 binds the colchicine binding site of tubulin and inhibits tubulin polymerization. The compound also suppresses the proliferation of the GB cell lines U87 and LN-18, with IC50s of 117 and 560 nM, respectively. In four patient-derived GB cell lines, the IC50 values for RGN3067 range from 148 to 616 nM. Finally, in a patient-derived xenograft (PDX) mouse model, RGN3067 reduces the rate of tumor growth compared to the control. Collectively, we show that RGN3067 is a BBB-penetrant small molecule that shows in vitro and in vivo efficacy and that its design addresses many of the physicochemical properties that prevent the use of microtubule destabilizers as treatments for GB and other brain cancers.

Synthesis and biological evaluation of structurally diverse 6-aryl-3-aroyl-indole analogues as inhibitors of tubulin polymerization

The synthesis and evaluation of small-molecule inhibitors of tubulin polymerization remains a promising approach for the development of new therapeutic agents for cancer treatment. The natural products colchicine and combretastatin A-4 (CA4) inspired significant drug discovery campaigns targeting the colchicine site located on the beta-subunit of the tubulin heterodimer, but so far these efforts have not yielded an approved drug for cancer treatment in human patients. Interest in the colchicine site was enhanced by the discovery that a subset of colchicine site agents demonstrated dual functionality as both potent antiproliferative agents and effective vascular disrupting agents (VDAs). Our previous studies led to the discovery and development of a 2-aryl-3-aroyl-indole analogue (OXi8006) that inhibited tubulin polymerization and demonstrated low nM IC50 values against a variety of human cancer cell lines. A water-soluble phosphate prodrug salt (OXi8007), synthesized from OXi8006, displayed promising vascular disrupting activity in mouse models of cancer. To further extend structure-activity relationship correlations, a series of 6-aryl-3-aroyl-indole analogues was synthesized and evaluated for their inhibition of tubulin polymerization and cytotoxicity against human cancer cell lines. Several structurally diverse molecules in this small library were strong inhibitors of tubulin polymerization and of MCF-7 and MDA-MB-231 human breast cancer cells. One of the most promising analogues (KGP591) caused significant G2/M arrest of MDA-MB-231 cells, disrupted microtubule structure and cell morphology in MDA-MB-231 cells, and demonstrated significant inhibition of MDA-MB-231 cell migration in a wound healing (scratch) assay. A phosphate prodrug salt, KGP618, synthesized from its parent phenolic precursor, KGP591, demonstrated significant reduction in bioluminescence signal when evaluated in vivo against an orthotopic model of kidney cancer (RENCA-luc) in BALB/c mice, indicative of VDA efficacy. The most active compounds from this series offer promise as anticancer therapeutic agents.

Molecular structure, spectral analysis and chemical activity of sabizabulin: A computational study

In this study, a detailed computational spectroscopic investigation of sabizabulin, a small molecule known as a tubulin inhibitor with potential antineoplastic, antiviral, and anti-inflammatory activities, has been presented. Our work utilizes Density Functional Theory (DFT) calculations to explore molecular optimization, thermodynamic characteristics, and the analysis of normal modes with vibrational assignments. We calculate essential properties such as standard zero-point vibrational energy, entropy, dipole moment, etc., based on data extracted from the optimized molecular structure. Additionally, we examine Mulliken charges and the Molecular Electrostatic Potential (MEP) plot to comprehend the electronic distribution and chemical activity of sabizabulin. Our findings provide valuable insights into the spectroscopic properties of sabizabulin, highlighting its potential therapeutic applications. Our work aims to explore future research directions that could expand the understanding of sabizabulin's actions and enhance its applicability in medical treatments.

Oral Sabizabulin for High-Risk, Hospitalized Adults with Covid-19: Interim Analysis

BACKGROUND: Sabizabulin is an oral, novel microtubule disruptor that has dual antiviral and anti-inflammatory activities in preclinical models. METHODS: A randomized, multicenter placebo-controlled phase 3 clinical trial was conducted with hospitalized patients with moderate to severe Covid-19 who were at high risk for acute respiratory distress syndrome (ARDS) and death. Patients were randomly assigned (2:1) to 9 mg of oral sabizabulin or placebo daily (up to 21 days). The primary end point was all-cause mortality up to day 60. Key secondary end points were days in the intensive care unit (ICU), days on mechanical ventilation, and days in the hospital. RESULTS: A total of 204 patients were randomly assigned to treatment: 134 to sabizabulin and 70 to placebo. Baseline characteristics were similar. Sabizabulin superiority was demonstrated by a planned interim analysis for the first 150 randomized patients. Sabizabulin treatment resulted in a 24.9 percentage point absolute reduction and a 55.2% relative reduction in deaths compared with placebo (odds ratio, 3.23; 95% CI confidence interval, 1.45 to 7.22; P=0.0042). The mortality rate was 20.2% (19 of 94) for sabizabulin versus 45.1% (23 of 51) for placebo. For the key secondary end points, sabizabulin treatment resulted in a 43% relative reduction in ICU days (P=0.0013), a 49% relative reduction in days on mechanical ventilation (P=0.0013), and a 26% relative reduction in days in the hospital (P=0.0277) versus placebo. Adverse and serious adverse events were lower in the sabizabulin group compared with the placebo group. CONCLUSIONS: Sabizabulin treatment resulted in a 24.9% absolute reduction in deaths compared with placebo in hospitalized patients with moderate to severe Covid-19 at high risk for ARDS and death, with a lower incidence of adverse and serious adverse events compared with placebo. (Funded by Veru, Inc.; ClinicalTrials.gov number, NCT04842747.)

Colchicine-Binding Site Agent CH-2-77 as a Potent Tubulin Inhibitor Suppressing Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive type of breast cancer. Unlike other subtypes of breast cancer, TNBC lacks hormone and growth factor receptor targets. Colchicine-binding site inhibitors (CBSI) targeting tubulin have been recognized as attractive agents for cancer therapy, but there are no CBSI drugs currently FDA approved. CH-2-77 has been reported to have potent antiproliferative activity against a panel of cancer cells in vitro and efficacious antitumor effects on melanoma xenografts, yet, its anticancer activity specifically against TNBC is unknown. Herein, we demonstrate that CH-2-77 inhibits the proliferation of both paclitaxel-sensitive and paclitaxel-resistant TNBC cells with an average IC50 of 3 nmol/L. CH-2-77 also efficiently disrupts the microtubule assembly, inhibits the migration and invasion of TNBC cells, and induces G2-M cell-cycle arrest. The increased number of apoptotic cells and the pattern of expression of apoptosis-related proteins in treated MDA-MB-231 cells suggest that CH-2-77 induces cell apoptosis through the intrinsic apoptotic pathway. In vivo, CH-2-77 shows acceptable overall pharmacokinetics and strongly suppresses the growth of orthotopic MDA-MB-231 xenografts without gross cumulative toxicities when administered 5 times a week. The in vivo efficacy of CH-2-77 (20 mg/kg) is comparable with that of CA4P (28 mg/kg), a CBSI that went through clinical trials. Importantly, CH-2-77 prevents lung metastasis originating from the mammary fat pad in a dose-dependent manner. Our data demonstrate that CH-2-77 is a promising new generation of tubulin inhibitors that inhibit the growth and metastasis of TNBC, and it is worthy of further development as an anticancer agent.

A Phase Ib/II Study of Sabizabulin, a Novel Oral Cytoskeleton Disruptor, in Men with Metastatic Castration-resistant Prostate Cancer with Progression on an Androgen Receptor-targeting Agent

PURPOSE

Sabizabulin, an oral cytoskeleton disruptor, was tested in a phase Ib/II clinical study in men with metastatic castration-resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

The phase Ib portion utilized a 3+3 design with escalating daily oral doses of 4.5-81 mg and increasing schedule in 39 patients with mCRPC treated with one or more androgen receptor-targeting agents. Prior taxane chemotherapy was allowed. The phase II portion tested a daily dose of 63 mg in 41 patients with no prior chemotherapy. Efficacy was assessed using PCWG3 and RECIST 1.1 criteria.

RESULTS

The MTD was not defined in the phase Ib and the recommended phase II dose was set at 63 mg/day. The most common adverse events (>10% frequency) at the 63 mg oral daily dosing (combined phase Ib/II data) were predominantly grade 1-2 events. Grade ≥3 events included diarrhea (7.4%), fatigue (5.6%), and alanine aminotransferase/aspartate aminotransferase elevations (5.6% and 3.7%, respectively). Neurotoxicity and neutropenia were not observed. Preliminary efficacy data in patients treated with ≥1 continuous cycle of 63 mg or higher included objective response rate in 6 of 29 (20.7%) patients with measurable disease (1 complete, 5 partial) and 14 of 48 (29.2%) patients had PSA declines. The Kaplan-Meier median radiographic progression-free survival was estimated to be 11.4 months (n = 55). Durable responses lasting >2.75 years were observed.

CONCLUSIONS

This clinical trial demonstrated that chronic oral daily dosing of sabizabulin has a favorable safety profile with preliminary antitumor activity. These data support the ongoing phase III VERACITY trial of sabizabulin in men with mCRPC.

Degradation of DRAK1 by CUL3/SPOP E3 Ubiquitin ligase promotes tumor growth of paclitaxel-resistant cervical cancer cells

Despite favorable responses to initial chemotherapy, drug resistance is a major cause limiting chemotherapeutic efficacy in many advanced cancers. However, mechanisms that drive drug-specific resistance in chemotherapy for patients with advanced cancers are still unclear. Here, we report a unique role of death-associated protein kinase-related apoptosis-inducing kinase 1 (DRAK1) associated with paclitaxel resistance in cervical cancer cells. Interestingly, DRAK1 protein level was markedly decreased in paclitaxel-resistant cervical cancer cells without affecting its mRNA expression, which resulted in an increase in tumor necrosis factor receptor-associated factor 6 (TRAF6) expression, as well as an activation of TRAF6-mediated nuclear factor-kappa B (NF-κB) signaling cascade, thereby promoting tumor progression. DRAK1 depletion markedly increased the chemotherapeutic IC₅₀ values of paclitaxel in cervical cancer cells. Ectopic expression of DRAK1 inhibited growth of paclitaxel-resistant cervical cancer cells in vitro and in vivo. Furthermore, DRAK1 was markedly underexpressed in chemoresistant cervical cancer patient tissues compared with chemosensitive samples. We found that DRAK1 protein was destabilized through K48-linked polyubiquitination promoted by the Cullin scaffold protein 3 (CUL3) / speckle-type POZ (poxvirus and zinc finger protein) protein (SPOP) E3 ubiquitin ligase in paclitaxel-resistant cells. Collectively, these findings suggest that DRAK1 may serve as a potential predictive biomarker for overcoming paclitaxel resistance in cervical cancer.

A novel orally active microtubule destabilizing agent S-40 targets the colchicine-binding site and shows potent antitumor activity

The tubulin colchicine binding site has been recognized as an attractive drug target to combat cancer, but none of the candidate drugs have been approved for medical treatment. We recently identified a structurally distinct small molecule S-40 as an oral potent tubulin destabilizing agent. Crystal structure analysis of S-40 in a complex with tubulin at a resolution of 2.4 Å indicated that S-40 occupies all 3 zones in the colchicine pocket with interactions different from known microtubule inhibitors, presenting unique effects on assembly and curvature of tubulin dimers. S-40 overcomes paclitaxel resistance and lacks neurotoxicity, which are the main obstacles limiting clinical applications of paclitaxel. Moreover, S-40 harbors the ability to inhibit growth of cancer cell lines as well as patient-derived organoids, induce mitotic arrest and cell apoptosis. Xenograft mouse models of human prostate cancer DU145, non-small cell lung cancer NCI-H1299 and paclitaxel-resistant A549 were strongly restrained without apparent side effects by S-40 oral administration once daily. These findings provide evidence for the development of S-40 as the next generation of orally effective microtubule inhibitors for cancer therapy.

Orally available tubulin inhibitor VERU-111 enhances antitumor efficacy in paclitaxel-resistant lung cancer

Lung cancer is the most common cause of cancer associated mortality. Chemotherapeutic agents, such as paclitaxel, are important treatment options but drug resistance often develops upon prolonged use. We report here the preclinical evaluation of a new orally available tubulin inhibitor, VERU-111, which can overcome several ABC-transporters mediated multi-drug resistance associated with taxane treatment. In vitro, VERU-111 prevents cell proliferation, invasion, migration and colony formation in both paclitaxel-sensitive and paclitaxel-resistant A549 lung cancer cells. VERU-111 effectively inhibits tubulin polymerization, arrests cells in G2/M phase, and induces cancer cell apoptosis. Further evaluation of various apoptotic proteins revealed that treatment of VERU-111 increases the expression of cleaved-PARP, cleaved-caspase-3 and p-histone H3 proteins. In vivo, orally administered VERU-111 in a paclitaxel-sensitive A549 xenograft model strongly inhibits tumor growth in a dose-dependent manner and is equally potent with paclitaxel. When tested in a highly paclitaxel-resistant A549/TxR tumor model, VERU-111 is as effective as the parental A549 model in significantly reducing the tumor volume, whereas paclitaxel is essentially ineffective. Collectively, this study showed that VERU-111 is a promising new generation of anti-tubulin agent for the treatment of taxane-resistant lung cancer.

An Orally Available Tubulin Inhibitor, VERU-111, Suppresses Triple-Negative Breast Cancer Tumor Growth and Metastasis and Bypasses Taxane Resistance

Triple-negative breast cancer (TNBC) accounts for approximately 15% of breast cancer cases in the United States. TNBC has poorer overall prognosis relative to other molecular subtypes due to rapid onset of drug resistance to conventional chemotherapies and increased risk of visceral metastases. Taxanes like paclitaxel are standard chemotherapies that stabilize microtubules, but their clinical efficacy is often limited by drug resistance and neurotoxicities. We evaluated the preclinical efficacy of a novel, potent, and orally bioavailable tubulin inhibitor, VERU-111, in TNBC models. VERU-111 showed potent cytotoxicity against TNBC cell lines, inducing apoptosis and cell-cycle arrest in a concentration-dependent manner. VERU-111 also efficiently inhibited colony formation, cell migration, and invasion. Orally administered VERU-111 inhibited MDA-MB-231 xenograft growth in a dose-dependent manner, with similar efficacies to paclitaxel, but without acute toxicity. VERU-111 significantly reduced metastases originating from the mammary fat pad into lung, liver, and kidney metastasis in an experimental metastasis model. Moreover, VERU-111, but not paclitaxel, suppressed growth of luciferase-labeled, taxane-resistant, patient-derived metastatic TNBC tumors. In this model, VERU-111 repressed growth of preestablished axillary lymph node metastases and lung, bone, and liver metastases at study endpoint, whereas paclitaxel enhanced liver metastases relative to vehicle controls. Collectively, these studies strongly suggest that VERU-111 is not only a potent inhibitor of aggressive TNBC phenotypes, but it is also efficacious in a taxane-resistant model of metastatic TNBC. Thus, VERU-111 is a promising new generation of tubulin inhibitor for the treatment of TNBC and may be effective in patients who progress on taxanes.Results presented in this study demonstrate the efficacy of VERU-111 in vivo and provide strong rationale for future development of VERU-111 as an effective treatment for metastatic breast cancer.

Polymeric Micellar Delivery of Novel Microtubule Destabilizer and Hedgehog Signaling Inhibitor for Treating Chemoresistant Prostate Cancer

Castration-resistant prostate cancer that has become resistant to docetaxel (DTX) represents one of the greatest clinical challenges in the management of this malignancy. There is an urgent need to develop novel therapeutic agents to overcome chemoresistance and improve the overall survival of patients. We have designed a novel microtubule destabilizer (2-(4-hydroxy-1H-indol-3-yl)-1H-imidazol-4-yl)(3,4,5-trimethoxyphenyl)methanone (QW-296) and combined it with a newly synthesized hedgehog (Hh) signaling pathway inhibitor 2-chloro-N 1-[4-chloro-3-(2-pyridinyl)phenyl]-N 4,N 4- bis(2-pyridinylmethyl)-1,4-benzenedicarboxamide (MDB5) to treat taxane-resistant (TXR) prostate cancer. The combination of QW-296 and MDB5 exhibited stronger anticancer activity toward DU145-TXR and PC3-TXR cells and suppressed tumor colony formation when compared with single-drug treatment. Because these drugs are hydrophobic, we synthesized the mPEG-p(TMC-MBC) [methoxy-poly(ethylene glycol)-block-poly(trimethylene carbonate-co-2-methyl-2-benzoxycarbonyl-propylene carbonate)] copolymer, which could self-assemble into micelles with loading capacities of 8.13% ± 0.75% and 9.12% ± 0.69% for QW-296 and MDB5, respectively. Further, these micelles provided controlled the respective drug release of 58% and 42% release of QW-296 and MDB5 within 24 hours when dialyzed against PBS (pH 7.4). We established an orthotopic prostate tumor in nude mice using stably luciferase expressing PC3-TXR cells. There was maximum tumor growth inhibition in the group treated with the combination therapy of QW-296 and MDB5 in micelles compared with their monotherapies or combination therapy formulated in cosolvent. The overall findings suggest that combination therapy with QW-296 and MDB5 has great clinical potential to treat TXR prostate cancer, and copolymer mPEG-p(TMC-MBC) could serve as an effective delivery vehicle to boost therapeutic efficacy in vivo.

Preclinical studies for the combination of paclitaxel and curcumin in cancer therapy (Review)

Cancer is one of the most common causes of death and remains the first in China and the second in the US. The common treatments for cancer include surgery, radiation, chemotherapy, targeted therapy and immunotherapy, while chemotherapy remains one of the most important treatments. However, the efficacy of chemotherapy is limited due to drug induced-toxicities and resistance, particularly multiple drug resistance (MDR). Therefore, discovery and development of novel therapeutic drugs and/or combination therapy are urgently needed to reduce toxicity and improve efficacy. Paclitaxel has been widely used to treat various cancers including cervical, breast, ovarian, brain, bladder, prostate, liver and lung cancers. However, its therapeutic efficacy is limited and MDR is a major obstacle. Recently, numerous preclinical studies have shown that the combination of paclitaxel and curcumin may be an ideal strategy to reverse MDR and synergistically improve their therapeutic efficacy in cancer therapy. This review mainly focuses on the current development and progress of the combination of paclitaxel and curcumin in cancer therapy preclinically.

Blood-brain barrier, cytotoxic chemotherapies and glioblastoma

INTRODUCTION

Glioblastomas (GBM) are the most common and aggressive primary malignant brain tumors in adults. The blood brain barrier (BBB) is a major limitation reducing efficacy of anti-cancer drugs in the treatment of GBM patients. Areas covered: Virtually all GBM recur after the first-line treatment, at least partly, due to invasive tumor cells protected from chemotherapeutic agents by the intact BBB in the brain adjacent to tumor. The passage through the BBB, taken by antitumor drugs, is poorly and heterogeneously documented in the literature. In this review, we have focused our attention on: (i) the BBB, (ii) the passage of chemotherapeutic agents across the BBB and (iii) the strategies investigated to overcome this barrier. Expert commentary: A better preclinical knowledge of the crossing of the BBB by antitumor drugs will allow optimizing their clinical development, alone or combined with BBB bypassing strategies, towards an increased success rate of clinical trials.

Synergistic combination of novel tubulin inhibitor ABI-274 and vemurafenib overcome vemurafenib acquired resistance in BRAFV600E melanoma

Acquired clinical resistance to vemurafenib, a selective BRAF(V600E) inhibitor, arises frequently after short-term chemotherapy. Because inhibitions of targets in the RAF-MEK-ERK pathway result in G(0)-G(1) cell-cycle arrest, vemurafenib-resistant cancer cells are expected to escape this cell-cycle arrest and progress to the subsequent G(2)-M phase. We hypothesized that a combined therapy using vemurafenib with a G(2)-M phase blocking agent will trap resistant cells and overcome vemurafenib resistance. To test this hypothesis, we first determined the combination index (CI) values of our novel tubulin inhibitor ABI-274 and vemurafenib on parental human A375 and MDA-MB-435 melanoma cell lines to be 0.32 and 0.1, respectively, suggesting strong synergy for the combination. We then developed an A375RF21 subline with significant acquired resistance to vemurafenib and confirmed the strong synergistic effect. Next, we studied the potential mechanisms of overcoming vemurafenib resistance. Flow cytometry confirmed that the combination of ABI-274 and vemurafenib synergistically arrested cells in the G(1)-G(2)-M phase, and significantly increased apoptosis in both parental A375 and the vemurafenib-resistant A375RF21 cells. Western blot analysis revealed that the combination treatment effectively reduced the level of phosphorylated and total AKT, activated the apoptosis cascade, and increased cleaved caspase-3 and cleaved PARP, but had no significant influence on the level of extracellular signal-regulated kinase (ERK) phosphorylation. Finally, in vivo coadministration of vemurafenib with ABI-274 showed strong synergistic efficacy in the vemurafenib-resistant xenograft model in nude mice. Overall, these results offer a rational combination strategy to significantly enhance the therapeutic benefit in patients with melanoma who inevitably become resistant to current vemurafenib therapy.

Discovery of 4-Aryl-2-benzoyl-imidazoles as tubulin polymerization inhibitor with potent antiproliferative properties

A series of 4-aryl-2-benzoyl-imidazoles were designed and synthesized based on our previously reported 2-aryl-4-benzoyl-imidazole (ABI) derivatives. The new structures reversed the aryl group and the benzoyl group of previous ABI structures and were named as reverse ABI (RABI) analogues. RABIs were evaluated for biological activity against eight cancer cell lines including multidrug-resistant cancer cell lines. In vitro assays indicated that several RABI compounds had excellent antiproliferative properties, with IC50 values in the low nanomolar range. The average IC50 of the most active compound 12a is 14 nM. In addition, the mechanism of action of these new analogues was investigated by cell cycle analysis, tubulin polymerization assay, competitive mass spectrometry binding assay, and molecular docking studies. These studies confirmed that these new RABI analogues maintain their mechanisms of action by disrupting tubulin polymerization, similar to their parental ABI analogues.