Peptidomimetic Src/pretubulin inhibitor KX-01 alone and in combination with paclitaxel suppresses growth, metastasis in human ER/PR/HER2-negative tumor xenografts

Synthesis and evaluation of KX-01 analogs with an exploration of linker attachment points for antibody-drug conjugates

KX-01 (tirbanibulin, Klisyri®) is a recently FDA-approved drug for treating actinic keratosis, with a distinct dual mechanism of action combining microtubule disruption and non-ATP-competitive Src inhibition. This unique mechanism and novel chemotype highlight KX-01's potential as a payload for antibody-drug conjugates. In this study, we synthesized and evaluated KX-01 derivatives to enhance anticancer potency and explore functional groups suitable for antibody conjugation. Notably, replacing the morpholine group with an N-benzoylpiperazine scaffold resulted in an analog with significantly improved in vitro antiproliferative activity, attributed to enhanced microtubule disruption and Src inhibition. Furthermore, introducing a phenol or aniline functionality as a common linker attachment point preserved substantial cytotoxicity. These results suggest the potential of KX-01 derivatives for future use as ADC payloads.

Topical Pharmacological Treatment of Actinic Keratoses: Focus on Tirbanibulin 1% Ointment

Actinic keratosis (AK) is a frequent precancerous skin lesion that mostly affects chronically sun-exposed areas. Chronic sun damage leads to various mutations in onco-suppressor and oncogenic genes which cause an uncontrolled proliferation of atypical keratinocytes. Untreated AKs may evolve in cutaneous squamous cell carcinoma (cSCC), with the consequent need for dermato-surgical excision or even for systemic immunotherapy in case of invasive/metastatic cSCCs. Epidemiology data on AK prevalence are various, however, the literature unanimously reports an increasing prevalence due to the aging of the population. Clinically AKs appear as a scaly, erythematous macule or papule or hyperkeratotic plaque. Management of AKs and the field of cancerization is important to avoid the natural evolution into squamous cell carcinomas (SCCs). Both physical and topical treatments are approved for managing AKs. Patient compliance with topical regimens is usually low due to the length of the posology and frequent skin adverse events. A recently approved tirbanibulin-based ointment, showed potential for inhibiting cell proliferation and blocking SRC-kinases, implicated in the progression of AKs in SCCs. The advantage of this new treatment is the practical posology, with a daily application for 5 consecutive days on AKs of the face-scalp area. Local skin reactions are usually mild and do not require treatment discontinuation. The short course of this new therapy and its excellent tolerance massively increased patient compliance. This article reviews what is currently known about this new therapy from its mechanism of action to clinical trial outcomes regarding safety, effectiveness, and patient adherence to the treatment.

Single-cell and Bulk RNA-Seq reveal angiogenic heterogeneity and microenvironmental features to evaluate prognosis and therapeutic response in lung adenocarcinoma

Background

Angiogenesis stands as a pivotal hallmark in lung adenocarcinoma (LUAD), intricately shaping the tumor microenvironment (TME) and influencing LUAD progression. It emerges as a promising therapeutic target for LUAD, affecting patients' prognosis. However, its role in TME, LUAD prognosis, and its clinical applicability remain shrouded in mystery.

Methods

We employed integrated single-cell and bulk transcriptome sequencing to unravel the heterogeneity of angiogenesis within LUAD cells. Through "consensus clustering", we delineated distinct angiogenic clusters and deciphered their TME features. "Monocle2" was used to unravel divergent trajectories within malignant cell subpopulations of LUAD. Additionally, regulon submodules and specific cellular communication patterns of cells in different angiogenic states were analyzed by "pyscenic" and "Cellchat" algorithms. The "univariate Cox" and "LASSO" algorithms were applied to build angiogenic prognostic models. Immunohistochemistry (IHC) on clinical samples validated the role of model factors in LUAD angiogenesis. We utilized CTRP 2.0 and PRISM databases for pinpointing sensitive drugs against lung adenocarcinoma.

Results

Two clusters for the activation of angiogenesis were identified, with Cluster 1 showing a poor prognosis and a pro-cancerous TME. Three differentiated states of malignant epithelial LUAD cells were identified, which had different degrees of angiogenic activation, were regulated by three different regulon submodules, and had completely different crosstalk from other cells in TME. The experiments validate that SLC2A1 promotes angiogenesis in LUAD. ARS (Angiogenesis related score) had a high prognostic value; low ARSs showed immunotherapy benefits, whereas high ARSs were sensitive to 15 chemotherapeutic agents.

Conclusion

The assessment of angiogenic clusters helps to determine the prognostic and TME characteristics of LUAD. Angiogenic prognostic models can be used to assess the prognosis, immunotherapeutic response, and chemotherapeutic drug sensitivity of LUAD.

THY1 (CD90) Maintains the Adherens Junctions in Nasopharyngeal Carcinoma via Inhibition of SRC Activation

We had previously shown that THY1 (CD90) is a tumor suppressor in nasopharyngeal carcinoma (NPC) and that its down-regulation and loss of expression are associated with tumor metastasis, yet the mechanism leading to such effects remains unknown. In this study we show that tumor invasion could be suppressed by THY1 via adherens junction formation in a few NPC cell lines, and knockdown of THY1 would disrupt this cell-cell adhesion phenotype. Mechanistically, the activity of the SRC family kinase (SFK) member, SRC, and canonical Wnt signaling were dramatically reduced when THY1 was constitutively expressed. Previous studies by others have found that high levels of SRC activity in NPCs are associated with EMT and a poor prognosis. We hypothesized that THY1 can suppress tumor invasion in NPC via inhibition of SRC. By gene silencing of SRC, we found that the in vitro NPC cell invasion was significantly reduced and adherens junctions were restored. Through proteomic analysis, we identified that platelet-derived growth factor receptor β (PDGF-Rβ) and protein tyrosine phosphatase nonreceptor type 22 (PTPN22) are novel and potential binding partners of THY1, which were subsequently verified by co-immunoprecipitation (co-IP) analysis. The ligand of PDGF-Rβ (PDGF-BB) could highly induce SRC activation and NPC cell invasion, which could be almost completely suppressed by THY1 expression. On the other hand, the PTPN22 siRNA could enhance both the SRC activities and the cell invasion and could also disrupt the adherens junctions in the THY1-expressing NPC cells; the original THY1-induced phenotypes were reverted when the PTPN22 expression was reduced. Together, our results identified that PTPN22 is essential for THY1 to suppress cell invasion and SRC activity, maintain tight adherens junctions, and prevent NPC metastasis. These results suggested that PDGF-Rβ and SRC can be used as drug targets for suppressing NPC metastasis. Indeed, our in vivo assay using the SRC inhibitor KX2-391, clearly showed that inhibition of SRC signaling can prevent the metastasis of NPC, indicating that targeting SRC can be a promising approach to control the NPC progression.

Pharmacological Agents Used in the Prevention and Treatment of Actinic Keratosis: A Review

Actinic keratosis (AK) is among the most commonly diagnosed skin diseases with potentially life-threatening repercussions if left untreated. Usage of pharmacologic agents represents one of many therapeutic strategies that can be used to help manage these lesions. Ongoing research into these compounds continues to change our clinical understanding as to which agents most benefit particular patient populations. Indeed, factors such as past personal medical history, lesion location and tolerability of therapy only represent a few considerations that clinicians must account for when prescribing appropriate treatment. This review focuses on specific drugs used in either the prevention or treatment of AKs. Nicotinamide, acitretin and topical 5-fluorouracil (5-FU) continue to be used with fidelity in the chemoprevention of actinic keratosis, although some uncertainty persists in regard to which agents should be used in immunocompetent vs. immunodeficient/immunosuppressed patients. Topical 5-FU, including combination formulations with either calcipotriol or salicylic acid, as well as imiquimod, diclofenac and photodynamic light therapy are all accepted treatment strategies employed to target and eliminate AKs. Five percent of 5-FU is regarded as the most effective therapy in the condition, although the literature has conflictingly shown that lower concentrations of the drug might also be as effective. Topical diclofenac (3%) appears to be less efficacious than 5% 5-FU, 3.75-5% imiquimod and photodynamic light therapy despite its favorable side effect profile. Finally, traditional photodynamic light therapy, while painful, appears to be of higher efficacy in comparison to its more tolerable counterpart, daylight phototherapy.

Peptidomimetics in cancer targeting

The low efficiency of treatment strategies is one of the main obstacles to developing cancer inhibitors. Up to now, various classes of therapeutics have been developed to inhibit cancer progression. Peptides due to their small size and easy production compared to proteins are highly regarded in designing cancer vaccines and oncogenic pathway inhibitors. Although peptides seem to be a suitable therapeutic option, their short lifespan, instability, and low binding affinity for their target have not been widely applicable against malignant tumors. Given the peptides' disadvantages, a new class of agents called peptidomimetic has been introduced. With advances in physical chemistry and biochemistry, as well as increased knowledge about biomolecule structures, it is now possible to chemically modify peptides to develop efficient peptidomimetics. In recent years, numerous studies have been performed to the evaluation of the effectiveness of peptidomimetics in inhibiting metastasis, angiogenesis, and cancerous cell growth. Here, we offer a comprehensive review of designed peptidomimetics to diagnose and treat cancer.

Tirbanibulin for Actinic Keratosis: Insights into the Mechanism of Action

Actinic keratosis (AK) is a common pre-neoplastic skin lesion constituted by uncontrolled proliferation of atypical keratinocytes that may evolve to squamous cell carcinoma. With global prevalence increasing, AK is expected to be the most common carcinoma of the skin. Tirbanibulin is a reversible tubulin polymerization inhibitor with potent anti-proliferative and anti-tumoral effects. In-vivo and in-vitro studies have shown that tirbanibulin significantly inhibits cell proliferation, tumor growth and downregulates Src signaling with no overt toxicity. Early phase and Phase III trials have shown high lesion clearance, compliance, and few side effects of once daily tirbanibulin treatment. This review discusses tirbanibulin anti-cancer activity, focusing on tubulin polymerization and Src signaling inhibitory effects, highlighting relevant literature and novel preclinical results from the ATNXUS-KX01-001 study. Furthermore, we address the relevant findings obtained in recent clinical trials to evaluate the safety, efficacy, pharmacokinetics, clearance efficacy, and side effects of the 1% tirbanibulin ointment applied once daily. In summary, we highlight preclinical and clinical evidence on the use of tirbanibulin as an effective and safe treatment option for AK.

Topical Tirbanibulin, a Dual Src Kinase and Tubulin Polymerization Inhibitor, for the Treatment of Plaque-Type Psoriasis: Phase I Results

Plaque-type psoriasis is a common skin disorder. Tirbanibulin (KX01) is a new Src kinase inhibitor with potent antiproliferative activity against keratinocytes and has been approved for treatment of actinic keratosis. This Phase I study investigates the safety and activity of KX01 ointment in patients with plaque-type psoriasis. We recruited 28 patients from two medical centers in Taiwan. This study was performed in four stages. Double-blind treatments were randomized in stages I (KX01 0.01% + placebo, two rounds of two-week treatment) and II (KX01 0.1% + placebo, four weeks) and open-labelled in stages III (KX01 1%, five days) and IV (KX01 1%, five days weekly for four weeks). The safety, tolerability, KX01 concentration, target area score, physician global assessment, and disease relapse were determined. Most treatment-emergent adverse events were mild-to-moderate application site reactions. Three (50.0%) subjects from the stage IV group showed ≥50% reduction in the target area score (TAS50), while two subjects (33.3%) showed a clinically meaningful improvement in the physician global assessment score. KX01 0.01%, 0.1%, and 1% were safe and well-tolerated. KX01 1% at four weeks showed a promising activity for the treatment of plaque-type psoriasis.

KC-180-2 Exerts Anti-SCLC Effects via Dual Inhibition of Tubulin Polymerization and Src Signaling

In this study, a series of N-benzyl-2-(5-phenylpyridin-2-yl) acetamide-based derivatives were successfully designed and synthesized as anti-cancer agents. KC-180-2 was screened as a potentially leading compound with dual mechanisms of action: Src signaling and tubulin polymerization inhibition. It efficiently suppressed the proliferation of five cancer cell lines (MDA-MB-231, H446, SKOV-3, HepG2, and HT29), with IC₅₀ values ranging from 5 to 188 nM, especially small-cell lung cancer (SCLC) cells (IC₅₀, 5 nM). Correspondingly, it exerted a significant therapeutic effect on the H446 small-cell lung cancer xenograft model, significantly reducing the volume of tumors without obvious toxicity. Mechanistically, this compound significantly inhibited the polymerization of purified tubulin in vitro, inducing G2/M cell cycle arrest and binding to the kinase catalytic domain of the Src protein, which reduced the phosphorylation of Src. Thus, KC-180-2 is a potential lead compound for the further development of a new anti-tumor drug against SCLC.

Discovery of a Series of Hydroxamic Acid-Based Microtubule Destabilizing Agents with Potent Antitumor Activity

Hydroxamic acid group is one of the characteristic pharmacophores of histone deacetylase (HDAC) inhibitors. But here, we discovered a series of hydroxamic acid-based microtubule destabilizing agents (MDAs), which were derived from shortening the length of the linker in HDAC6 inhibitor SKLB-23bb. Interestingly, the low nanomolar antiproliferative activity of these MDAs depended on the presence of hydroxamic acid groups, but their inhibitory effects on HDAC were lost. Among them, 12b showed favorable metabolism stability, high bioavailability, and potent antitumor activity in multidrug-resistant cell lines and A2780/T xenograft model. More importantly, in the patient-derived xenograft models of triple-negative breast cancer and osimertinib-resistant non-small-cell lung cancer, both 20 mg/kg oral and 10 mg/kg intravenous administration of 12b could induce more than 70% tumor inhibition without obvious toxicity. Overall, we discovered that 12b, as a novel MDA based on hydroxamic acid, could serve as a potential MDA for further investigation.

Recent Progress on Tubulin Inhibitors with Dual Targeting Capabilities for Cancer Therapy

Microtubules play a crucial role in multiple cellular functions including mitosis, cell signaling, and organelle trafficking, which makes the microtubule an important target for cancer therapy. Despite the great successes of microtubule-targeting agents in the clinic, the development of drug resistance and dose-limiting toxicity restrict their clinical efficacy. In recent years, multitarget therapy has been considered an effective strategy to achieve higher therapeutic efficacy, in particular dual-target drugs. In terms of the synergetic effect of tubulin and other antitumor agents such as receptor tyrosine kinases inhibitors, histone deacetylases inhibitors, DNA-damaging agents, and topoisomerase inhibitors in combination therapy, designing dual-target tubulin inhibitors is regarded as a promising approach to overcome these limitations and improve therapeutic efficacy. In this Perspective, we discussed rational target combinations, design strategies, structure-activity relationships, and future directions of dual-target tubulin inhibitors.

Novel bone-targeted parathyroid hormone-related peptide antagonists inhibit breast cancer bone metastases

Patients with advanced breast cancer often develop bone metastases. Treatment is limited to palliative care. Parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) antagonists for bone metastases failed clinically due to short half-life and inadequate concentration in bone. We synthesized two novel PTHrP antagonists fused to an inert bacterial collagen binding domain (CBD) that directs drugs to bone. PTH(7-33)-CBD is an N-terminal truncated PTHrP antagonist. [W2]PTH(1-33)-CBD is an PTHrP inverse-agonist. The aim of this study was to assess PTH(7-33)-CBD to reduce breast cancer bone metastases and prevent osteolytic destruction in mice and to assess both drugs for apoptosis of breast cancer cells in vitro and inhibition of PTH receptor (PTHR1). PTH(7-33)-CBD (1000 µg/kg, subcutaneous) or vehicle was administered 24 h prior to MDA-MB-231 breast cancer cell inoculation into the tibia marrow. Weekly tumor burden and bone density were measured. Pharmacokinetic analysis of PTH(7-33)-CBD in rat serum was evaluated. Drug effect on cAMP accumulation in SaOS-2 osteosarcoma cells and apoptosis of MDA-MB-231 cells was assessed. PTH(7-33)-CBD reduced MDA-MB-231 tumor burden and osteolytic destruction in mice 4-5 weeks post-treatment. PTH(7-33)-CBD (1000 μg/kg i.v. and subcutaneous) in rats was rapidly absorbed with peak concentration 5-min and terminal half-life 3-h. Bioavailability by the subcutaneous route was 43% relative to the i.v. route. PTH(7-33)-CBD was detected only on rat periosteal bone surfaces that stained positive for collagen-1. PTH(7-33)-CBD and [W2]PTH(1-33)-CBD (10-8M) blocked basal and PTH agonist-induced cAMP accumulation in SaOS-2 osteosarcoma cells. Both drugs induced PTHR1-dependent apoptosis of MDA-MB-231 cells in vitro. Novel bone-targeted PTHrP antagonists represent a new paradigm for treatment of breast cancer bone metastases.

Dual Inhibitors as a New Challenge for Cancer Multidrug Resistance Treatment

BACKGROUND

Dual-targeting in cancer treatment by a single drug is an unconventional approach in relation to drug combinations. The rationale for the development of dualtargeting agents is to overcome incomplete efficacy and drug resistance frequently present when applying individual targeting agents. Consequently, -a more favorable outcome of cancer treatment is expected with dual-targeting strategies.

METHODS

We reviewed the literature, concentrating on the association between clinically relevant and/or novel dual inhibitors with the potential to modulate multidrug resistant phenotype of cancer cells, particularly the activity of P-glycoprotein. A balanced analysis of content was performed to emphasize the most important findings and optimize the structure of this review.

RESULTS

Two-hundred and forty-five papers were included in the review. The introductory part was interpreted by 9 papers. Tyrosine kinase inhibitors' role in the inhibition of Pglycoprotein and chemosensitization was illustrated by 87 papers. The contribution of naturalbased compounds in overcoming multidrug resistance was reviewed using 92 papers, while specific dual inhibitors acting against microtubule assembling and/or topoisomerases were described with 55 papers. Eleven papers gave an insight into a novel and less explored approach with hybrid drugs. Their influence on P-glycoprotein and multidrug resistance was also evaluated.

CONCLUSION

These findings bring into focus rational anticancer strategies with dual-targeting agents. Most evaluated synthetic and natural drugs showed a great potential in chemosensitization. Further steps in this direction are needed for the optimization of anticancer treatment.

Current advances of tubulin inhibitors as dual acting small molecules for cancer therapy

Microtubule (MT)-targeting agents are highly successful drugs as chemotherapeutic agents, and this is attributed to their ability to target MT dynamics and interfere with critical cellular functions, including, mitosis, cell signaling, intracellular trafficking, and angiogenesis. Because MT dynamics vary in the different stages of the cell cycle, these drugs tend to be the most effective against mitotic cells. While this class of drug has proven to be effective against many cancer types, significant hurdles still exist and include overcoming aspects such as dose limited toxicities and the development of resistance. Newer generations of developed drugs attack these problems and alternative approaches such as the development of dual tubulin and kinase inhibitors are being investigated. This approach offers the potential to show increased efficacy and lower toxicities. This review covers different categories of MT-targeting agents, recent advances in dual inhibitors, and current challenges for this drug target.

Discovery of Novel Dual Mechanism of Action Src Signaling and Tubulin Polymerization Inhibitors (KX2-391 and KX2-361)

The discovery of potent, peptide site directed, tyrosine kinase inhibitors has remained an elusive goal. Herein we describe the discovery of two such clinical candidates that inhibit the tyrosine kinase Src. Compound 1 is a phase 3 clinical trial candidate that is likely to provide a first in class topical treatment for actinic keratosis (AK) with good efficacy and dramatically less toxicity compared to existing standard therapy. Compound 2 is a phase 1 clinical trial candidate that is likely to provide a first in class treatment of malignant glioblastoma and induces 30% long-term complete tumor remission in animal models. The discovery strategy for these compounds iteratively utilized molecular modeling, along with the synthesis and testing of increasingly elaborated proof of concept compounds, until the final clinical candidates were arrived at. This was followed with mechanism of action (MOA) studies that revealed tubulin polymerization inhibition as the second MOA.

Dual Src Kinase/Pretubulin Inhibitor KX-01, Sensitizes ERα-negative Breast Cancers to Tamoxifen through ERα Reexpression

Unlike breast cancer that is positive for estrogen receptor-α (ERα), there are no targeted therapies for triple-negative breast cancer (TNBC). ERα is silenced in TNBC through epigenetic changes including DNA methylation and histone acetylation. Restoring ERα expression in TNBC may sensitize patients to endocrine therapy. Expression of c-Src and ERα are inversely correlated in breast cancer suggesting that c-Src inhibition may lead to reexpression of ERα in TNBC. KX-01 is a peptide substrate-targeted Src/pretubulin inhibitor in clinical trials for solid tumors. KX-01 (1 mg/kg body weight-twice daily) inhibited growth of tamoxifen-resistant MDA-MB-231 and MDA-MB-157 TNBC xenografts in nude mice that was correlated with Src kinase inhibition. KX-01 also increased ERα mRNA and protein, as well as increased the ERα targets progesterone receptor (PR), pS2 (TFF1), cyclin D1 (CCND1), and c-myc (MYC) in MDA-MB-231 and MDA-MB-468, but not MDA-MB-157 xenografts. MDA-MB-231 and MDA-MB-468 tumors exhibited reduction in mesenchymal markers (vimentin, β-catenin) and increase in epithelial marker (E-cadherin) suggesting mesenchymal-to-epithelial transition (MET). KX-01 sensitized MDA-MB-231 and MDA-MB-468 tumors to tamoxifen growth inhibition and tamoxifen repression of the ERα targets pS2, cyclin D1, and c-myc. Chromatin immunoprecipitation (ChIP) of the ERα promoter in KX-01-treated tumors demonstrated enrichment of active transcription marks (acetyl-H3, acetyl-H3Lys9), dissociation of HDAC1, and recruitment of RNA polymerase II. Methylation-specific PCR and bisulfite sequencing demonstrated no alteration in ERα promoter methylation by KX-01. These data demonstrate that in addition to Src kinase inhibition, peptidomimetic KX-01 restores ERα expression in TNBC through changes in histone acetylation that sensitize tumors to tamoxifen.Implications: Src kinase/pretubulin inhibitor KX-01 restores functional ERα expression in ERα^- breast tumors, a novel treatment strategy to treat triple-negative breast cancer. Mol Cancer Res; 15(11); 1491-502. ©2017 AACR.

Antitumor Effect of KX-01 through Inhibiting Src Family Kinases and Mitosis

PURPOSE

KX-01 is a novel dual inhibitor of Src and tubulin. Unlike previous Src inhibitors that failed to show clinical benefit during treatment of breast cancer, KX-01 can potentially overcome the therapeutic limitations of current Src inhibitors through inhibition of both Src and tubulin. The present study further evaluates the activity and mechanism of KX-01 in vitro and in vivo.

MATERIALS AND METHODS

The antitumor effect of KX-01 in triple negative breast cancer (TNBC) cell lines was determined by MTT assay. Wound healing and immunofluorescence assays were performed to evaluate the action mechanisms of KX-01. Changes in the cell cycle and molecular changes induced by KX-01 were also evaluated. A MDA-MB-231 mouse xenograft model was used to demonstrate the in vivo effects.

RESULTS

KX-01 effectively inhibited the growth of breast cancer cell lines. The expression of phospho-Src and proliferative-signaling molecules were down-regulated in KX-01-sensitive TNBC cell lines. In addition, migration inhibition was observed by wound healing assay. KX-01-induced G2/M cell cycle arrest and increased the aneuploid cell population in KX-01-sensitive cell lines. Multi-nucleated cells were significantly increased after KX-01 treatment. Furthermore, KX-01 effectively delayed tumor growth in a MDA-MB-231 mouse xenograft model.

CONCLUSION

KX-01 effectively inhibited cell growth and migration of TNBC cells. Moreover, this study demonstrated that KX-01 showed antitumor effects through the inhibition of Src signaling and the induction of mitotic catastrophe. The antitumor effects of KX-01 were also demonstrated in vivo using a mouse xenograft model.

Human Adipose Tissue-Derived Stromal/Stem Cells Promote Migration and Early Metastasis of Head and Neck Cancer Xenografts

BACKGROUND

Fat grafting has become popular for repair of postsurgical/postradiation defects after head/neck cancers resection. Fat graft supplementation with adipose tissue-derived stromal/stem cells (ASCs) is proposed to improve graft viability/efficacy, although the impact of ASCs on head/neck cancer cells is unknown.

OBJECTIVES

To determine whether ASCs affect growth, migration, and metastasis of human head/neck cancer.

METHODS

Human Cal-27 and SCC-4 head/neck cancer cells were co-cultured human ASCs, or treated with ASC conditioned medium (CM), and cancer cell growth/migration was assessed by MTT, cell count, and scratch/wound healing assays in vitro. Co-injection of 3 × 10(6) Cal-27/green fluorescent protein (GFP) cells and ASCs into the flank of NUDE mice assessed ASC effect on tumor growth/morphology. Quantitation of human chromosome 17 DNA in mouse organs assessed ASC effects on micrometastasis. Primary tumors were evaluated for markers of epithelial-to-mesenchymal transition, matrix metalloproteinases, and angiogenesis by immunohistochemistry.

RESULTS

Co-culture of Cal-27 or SCC-4 cells with ASCs from 2 different donors or ASC CM had no effect on cell growth in vitro. However, ASC CM stimulated Cal-27 and SCC-4 migration. Co-injection of ASCs from 2 different donors with Cal-27 cells did not affect tumor volume at 6 weeks, but increased Cal-27 micrometastasis to the brain. Evaluation of tumors sections from 1 ASC donor co-injection revealed that ASCs were viable and well integrated with Cal-27/GFP cells. These tumors exhibited increased MMP2, MMP9, IL-8, and microvessel density.

CONCLUSIONS

Human ASCs did not alter growth of human head/neck cancer cells or tumor xenografts, but stimulated migration and early micrometastasis to mouse brain.

Androgen receptor splice variants circumvent AR blockade by microtubule-targeting agents

Docetaxel-based chemotherapy is established as a first-line treatment and standard of care for patients with metastatic castration-resistant prostate cancer. However, half of the patients do not respond to treatment and those do respond eventually become refractory. A better understanding of the resistance mechanisms to taxane chemotherapy is both urgent and clinical significant, as taxanes (docetaxel and cabazitaxel) are being used in various clinical settings. Sustained signaling through the androgen receptor (AR) has been established as a hallmark of CRPC. Recently, splicing variants of AR (AR-Vs) that lack the ligand-binding domain (LBD) have been identified. These variants are constitutively active and drive prostate cancer growth in a castration-resistant manner. In taxane-resistant cell lines, we found the expression of a major variant, AR-V7, was upregulated. Furthermore, ectopic expression of two clinically relevant AR-Vs (AR-V7 and ARV567es), but not the full-length AR (AR-FL), reduced the sensitivities to taxanes in LNCaP cells. Treatment with taxanes inhibited the transcriptional activity of AR-FL, but not those of AR-Vs. This could be explained, at least in part, due to the inability of taxanes to block the nuclear translocation of AR-Vs. Through a series of deletion constructs, the microtubule-binding activity was mapped to the LBD of AR. Finally, taxane-induced cytoplasm sequestration of AR-FL was alleviated when AR-Vs were present. These findings provide evidence that constitutively active AR-Vs maintain the AR signaling axis by evading the inhibitory effects of microtubule-targeting agents, suggesting that these AR-Vs play a role in resistance to taxane chemotherapy.

Src signaling pathways in prostate cancer

Knowledge of the molecular events that contribute to prostate cancer progression has created opportunities to develop novel therapy strategies. It is now well established that c-Src, a non-receptor tyrosine kinase, regulates a complex signaling network that drives the development of castrate-resistance and bone metastases, events that signal the lethal phenotype of advanced disease. Preclinical studies have established a role for c-Src and Src Family Kinases (SFKs) in proliferation, angiogenesis, invasion and bone metabolism, thus implicating Src signaling in both epithelial and stromal mechanisms of disease progression. A number of small molecule inhibitors of SFK now exist, many of which have demonstrated efficacy in preclinical models and several that have been tested in patients with metastatic castrate-resistant prostate cancer. These agents have demonstrated provocative clinic activity, particularly in modulating the bone microenvironment in a therapeutically favorable manner. Here, we review the discovery and basic biology of c-Src and further discuss the role of SFK inhibitors in the treatment of advanced prostate cancer.

Multifunctional Polymeric Micelles Co-loaded with Anti-Survivin siRNA and Paclitaxel Overcome Drug Resistance in an Animal Model of Ovarian Cancer

Ovarian cancer is a dreadful disease estimated to be the second most common gynecologic malignancy worldwide. Its current therapy, based on cytoreductive surgery followed by the combination of platinum and taxanes, is frequently complicated by the onset of multidrug resistance (MDR). The discovery that survivin, a small antiapoptotic protein, is involved in chemoresistance provided a new prospect to overcome MDR in cancer, because siRNA could be used to inhibit the expression of survivin in cancer cells. With this in mind, we have developed self-assembly polymeric micelles (PM) able to efficiently co-load an anti-survivin siRNA and a chemotherapeutic agent, such as paclitaxel (PXL; survivin siRNA/PXL PM). Previously, we have successfully demonstrated that the downregulation of survivin by using siRNA-containing PM strongly sensitizes different cancer cells to paclitaxel. Here, we have evaluated the applicability of the developed multifunctional PM in vivo. Changes in survivin expression, therapeutic efficacy, and biologic effects of the nanopreparation were investigated in an animal model of paclitaxel-resistant ovarian cancer. The results obtained in mice xenografed with SKOV3-tr revealed a significant downregulation of survivin expression in tumor tissues together with a potent anticancer activity of survivin siRNA/PXL PM, while the tumors remained unaffected with the same quantity of free paclitaxel. These promising results introduce a novel type of nontoxic and easy-to-obtain nanodevice for the combined therapy of siRNA and anticancer agents in the treatment of chemoresistant tumors.

Small molecule substrate phosphorylation site inhibitors of protein kinases: approaches and challenges

Protein kinases are important mediators of cellular communication and attractive drug targets for many diseases. Although success has been achieved with developing ATP-competitive kinase inhibitors, the disadvantages of ATP-competitive inhibitors have led to increased interest in targeting sites outside of the ATP binding pocket. Kinase inhibitors with substrate-competitive, ATP-noncompetitive binding modes are promising due to the possibility of increased selectivity and better agreement between biochemical and in vitro potency. However, the difficulty of identifying these types of inhibitors has resulted in significantly fewer small molecule substrate phosphorylation site inhibitors being reported compared to ATP-competitive inhibitors. This review surveys reported substrate phosphorylation site inhibitors and methods that can be applied to the discovery of such inhibitors, including a discussion of the challenges inherent to these screening methods.

Meaningful prevention of breast cancer metastasis: candidate therapeutics, preclinical validation, and clinical trial concerns

The development of drugs to treat breast and other cancers proceeds through phase I dose finding, phase II efficacy, and phase III comparative studies in the metastatic setting, only then asking if metastasis can be prevented in adjuvant trials. Compounds without overt cytotoxic activity, such as those developed to inhibit metastatic colonization, will likely fail to shrink established lesions in the metastatic setting and never be tested in a metastasis prevention scenario where they were preclinically validated. We and others have proposed phase II primary and secondary metastasis prevention studies to address this need. Herein, we have asked whether preclinical metastasis prevention data agrees with the positive adjuvant setting trials. The data are limited but complimentary. We also review fundamental pathways involved in metastasis, including Src, integrins, focal adhesion kinase (FAK), and fibrosis, for their clinical progress to date and potential for metastasis prevention. Issues of inadequate preclinical validation and clinical toxicity profiles are discussed.

Src inhibition potentiates antitumoral effect of paclitaxel by blocking tumor-induced angiogenesis

The protein kinase Src is frequently over-activated in advanced cancers where it modulates the signaling transduction cascade of several growth factors. The feasibility of combination treatment of Src inhibitors with chemotherapy is currently under investigation. We evaluated the anti-tumoral effect of paclitaxel (PTX) in combination with S13, a tyrosine kinase inhibitor with a prevalent specificity for Src, in a hormone-insensible prostate cancer (PCa) cell model. In vivo, combination treatment with PTX and S13 reduced dramatically PCa tumor growth with a relevant difference in the density of new blood vessels with respect to control and single treatments. This reduction was determined by a concomitant impairment of endothelial cell migration and of VEGF release by cancer cells. In fact, S13, when used alone, was sufficient to reduce tubule formation in vivo, and to inhibit VEGFR2 activation and FAK expression in endothelial cells. In addition, the combination treatment determined a significant reduction in ROS production and HIF-1 stabilization in PCa cells respect to single treatments with S13 or PTX. In conclusion, Src-inhibition could be an effective therapeutic strategy aimed at supporting the anti-angiogenic action of PTX in aggressive PCa.

Identification of DW532 as a novel anti-tumor agent targeting both kinases and tubulin

AIM

7,8-Dihydroxy-4-(3-hydroxy-4-methoxyphenyl)-2H-chromen-2-one (DW532) is one of simplified analogues of hematoxylin that has shown broad-spectrum inhibition on tyrosine kinases and in vitro anti-cancer activities. The aim of this study was to identify DW532 as a agent targeting both kinases and tubulin, and to investigate its anti-cancer and anti-angiogenesis activities.

METHODS

In vitro tyrosine kinases activity was examined with ELISA, and tyrosine kinases activity in cells was evaluated with Western blot analysis. Tubulin turbidity assay, surface plasmon resonance and immunofluorescence technique were used to characterize the tubulin inhibitory activity. Cell proliferation was examined with SRB assay, and cell apoptosis and cell cycle distribution were analyzed with Annexin-V/PI staining and flow cytometry. Tube formation, aortic ring and chick chorioallantoic membrane assays were used to evaluate the anti-angiogenesis efficacy.

RESULTS

DW532 inhibited EGFR and VEGFR2 in vitro kinase activity (the IC50 values were 4.9 and 5.5 μmol/L, respectively), and suppressed their downstream signaling. DW532 dose-dependently inhibited tubulin polymerization via direct binding to tubulin, thus disrupting the mitotic spindle assembly and leading to abnormal cell division. In a panel of human cancer cells, DW532 (1 and 10 μmol/L) induced G2/M phase arrest and cell apoptosis, which subsequently resulted in cytotoxicity. Knockdown of BubR1 or Mps1, the two core proteins of the spindle assembly checkpoint dramatically decreased DW532-induced cell cycle arrest in MDA-MB-468 cells. Moreover, treatment with DW532 potently and dose-dependently suppressed angiogenesis in vitro and in vivo.

CONCLUSION

DW532 is a dual inhibitor against tubulin and tyrosine kinases, and deserves further development as a novel anti-cancer agent.

Human adipose tissue-derived stromal/stem cells promote migration and early metastasis of triple negative breast cancer xenografts

Background

Fat grafting is used to restore breast defects after surgical resection of breast tumors. Supplementing fat grafts with adipose tissue-derived stromal/stem cells (ASCs) is proposed to improve the regenerative/restorative ability of the graft and retention. However, long term safety for ASC grafting in proximity of residual breast cancer cells is unknown. The objective of this study was to determine the impact of human ASCs derived from abdominal lipoaspirates of three donors, on a human breast cancer model that exhibits early metastasis.

Methodology/Principal Findings

Human MDA-MB-231 breast cancer cells represents “triple negative” breast cancer that exhibits early micrometastasis to multiple mouse organs [1]. Human ASCs were derived from abdominal adipose tissue from three healthy female donors. Indirect co-culture of MDA-MB-231 cells with ASCs, as well as direct co-culture demonstrated that ASCs had no effect on MDA-MB-231 growth. Indirect co-culture, and ASC conditioned medium (CM) stimulated migration of MDA-MB-231 cells. ASC/RFP cells from two donors co-injected with MDA-MB-231/GFP cells exhibited a donor effect for stimulation of primary tumor xenografts. Both ASC donors stimulated metastasis. ASC/RFP cells were viable, and integrated with MDA-MB-231/GFP cells in the tumor. Tumors from the co-injection group of one ASC donor exhibited elevated vimentin, matrix metalloproteinase-9 (MMP-9), IL-8, VEGF and microvessel density. The co-injection group exhibited visible metastases to the lung/liver and enlarged spleen not evident in mice injected with MDA-MB-231/GFP alone. Quantitation of the total area of GFP fluorescence and human chromosome 17 DNA in mouse organs, H&E stained paraffin sections and fluorescent microscopy confirmed multi-focal metastases to lung/liver/spleen in the co-injection group without evidence of ASC/RFP cells.

Conclusions

Human ASCs derived from abdominal lipoaspirates of two donors stimulated metastasis of MDA-MB-231 breast tumor xenografts to multiple mouse organs. MDA-MB-231 tumors co-injected with ASCs from one donor exhibited partial EMT, expression of MMP-9, and increased angiogenesis.

Targeting SRC and tubulin in mucinous ovarian carcinoma

PURPOSE

To investigate the antitumor effects of targeting Src and tubulin in mucinous ovarian carcinoma.

EXPERIMENTAL DESIGN

The in vitro and in vivo effects and molecular mechanisms of KX-01, which inhibits Src pathway and tubulin polymerization, were examined in mucinous ovarian cancer models.

RESULTS

In vitro studies using RMUG-S and RMUG-L cell lines showed that KX-01 inhibited cell proliferation, induced apoptosis, arrested the cell cycle at the G2-M phase, and enhanced the cytotoxicity of oxaliplatin in the KX-01-sensitive cell line, RMUG-S. In vivo studies showed that KX-01 significantly decreased tumor burden in RMUG-S and RMUG-L mouse models relative to untreated controls, and the effects were greater when KX-01 was combined with oxaliplatin. KX-01 alone and in combination with oxaliplatin significantly inhibited tumor growth by reducing cell proliferation and inducing apoptosis in vivo. PTEN knock-in experiments in RMUG-L cells showed improved response to KX-01. Reverse phase protein array analysis showed that in addition to blocking downstream molecules of Src family kinases, KX-01 also activated acute stress-inducing molecules.

CONCLUSION

Our results showed that targeting both the Src pathway and tubulin with KX-01 significantly inhibited tumor growth in preclinical mucinous ovarian cancer models, suggesting that this may be a promising therapeutic approach for patients with mucinous ovarian carcinoma.

Disseminated breast cancer cells acquire a highly malignant and aggressive metastatic phenotype during metastatic latency in the bone

Background

Disseminated tumor cells (DTCs) in the bone marrow may exist in a dormant state for extended periods of time, maintaining the ability to proliferate upon activation, engraft at new sites, and form detectable metastases. However, understanding of the behavior and biology of dormant breast cancer cells in the bone marrow niche remains limited, as well as their potential involvement in tumor recurrence and metastasis. Therefore, the purpose of this study was to investigate the tumorigenicity and metastatic potential of dormant disseminated breast cancer cells (prior to activation) in the bone marrow.

Methodology/Principal Findings

Total bone marrow, isolated from mice previously injected with tumorspheres into the mammary fat pad, was injected into the mammary fat pad of NUDE mice. As a negative control, bone marrow isolated from non-injected mice was injected into the mammary fat pad of NUDE mice. The resultant tumors were analyzed by immunohistochemistry for expression of epithelial and mesenchymal markers. Mouse lungs, livers, and kidneys were analyzed by H+E staining to detect metastases. The injection of bone marrow isolated from mice previously injected with tumorspheres into the mammary fat pad, resulted in large tumor formation in the mammary fat pad 2 months post-injection. However, the injection of bone marrow isolated from non-injected mice did not result in tumor formation in the mammary fat pad. The DTC-derived tumors exhibited accelerated development of metastatic lesions within the lung, liver and kidney. The resultant tumors and the majority of metastatic lesions within the lung and liver exhibited a mesenchymal-like phenotype.

Conclusions/Significance

Dormant DTCs within the bone marrow are highly malignant upon injection into the mammary fat pad, with the accelerated development of metastatic lesions within the lung, liver and kidney. These results suggest the acquisition of a more aggressive phenotype of DTCs during metastatic latency within the bone marrow microenvironment.