Dynamic bioluminescence and fluorescence imaging of the effects of the antivascular agent Combretastatin-A4P (CA4P) on brain tumor xenografts

Towards updated understanding of brain metastasis

Brain metastasis (BM) is a common complication in cancer patients with advanced disease and attributes to treatment failure and final mortality. Currently there are several therapeutic options available; however these are only suitable for limited subpopulation: surgical resection or radiosurgery for cases with a limited number of lesions, targeted therapies for approximately 18% of patients, and immune checkpoint inhibitors with a response rate of 20-30%. Thus, there is a pressing need for development of novel diagnostic and therapeutic options. This overview article aims to provide research advances in disease model, targeted therapy, blood brain barrier (BBB) opening strategies, imaging and its incorporation with artificial intelligence, external radiotherapy, and internal targeted radionuclide theragnostics. Finally, a distinct type of BM, leptomeningeal metastasis is also covered.

Non-Invasive Evaluation of Acute Effects of Tubulin Binding Agents: A Review of Imaging Vascular Disruption in Tumors

Tumor vasculature proliferates rapidly, generally lacks pericyte coverage, and is uniquely fragile making it an attractive therapeutic target. A subset of small-molecule tubulin binding agents cause disaggregation of the endothelial cytoskeleton leading to enhanced vascular permeability generating increased interstitial pressure. The resulting vascular collapse and ischemia cause downstream hypoxia, ultimately leading to cell death and necrosis. Thus, local damage generates massive amplification and tumor destruction. The tumor vasculature is readily accessed and potentially a common target irrespective of disease site in the body. Development of a therapeutic approach and particularly next generation agents benefits from effective non-invasive assays. Imaging technologies offer varying degrees of sophistication and ease of implementation. This review considers technological strengths and weaknesses with examples from our own laboratory. Methods reveal vascular extent and patency, as well as insights into tissue viability, proliferation and necrosis. Spatiotemporal resolution ranges from cellular microscopy to single slice tomography and full three-dimensional views of whole tumors and measurements can be sufficiently rapid to reveal acute changes or long-term outcomes. Since imaging is non-invasive, each tumor may serve as its own control making investigations particularly efficient and rigorous. The concept of tumor vascular disruption was proposed over 30 years ago and it remains an active area of research.

FB-15 inhibits MGC-803 cells growth by regulating energy metabolism

In this study, we scrutinized the anticancer effects of FB-15 on human gastric carcinoma MGC-803 cells in vitro and vivo, and its preliminary effect on tubulin and HIF-1α. We confirmed that FB-15 not only inhibited the proliferation of a large number of cells in a concentration and time-dependent manner but also inhibited proliferation of a single cell to form clones. FB-15 manifested little cytotoxicity for normal stomach cells GES-1. The flow cytometry analysis displayed that FB-15 induced apoptosis MGC-803 cells and mainly arrested cells in the S phase in a concentration-dependent manner. The results of the wound healing assay indicated that FB-15 suppressed cell migration. Furthermore, the western blotting showed that FB-15 down-regulated the expression of β3-tubulin and HIF-1α, consistent with Immunohistochemical assay. The binding modes of FB-15 with tubulin were clarified by molecular docking. FB-15 significantly suppressed the growth of MGC-803 gastric cancer tumors. The inhibitory effect of FB-15 on tumor growth was superior to 5-Fu. Taken together, these results provided evidence for FB-15 to be used as an effective anticancer drug candidate for gastric cancer.

LCRF-0006, a small molecule mimetic of the N-cadherin antagonist peptide ADH-1, synergistically increases multiple myeloma response to bortezomib

N-cadherin is a homophilic cell-cell adhesion molecule that plays a critical role in maintaining vascular stability and modulating endothelial barrier permeability. Pre-clinical studies have shown that the N-cadherin antagonist peptide, ADH-1, increases the permeability of tumor-associated vasculature thereby increasing anti-cancer drug delivery to tumors and enhancing tumor response. Small molecule library screens have identified a novel compound, LCRF-0006, that is a mimetic of the classical cadherin His-Ala-Val sequence-containing region of ADH-1. Here, we evaluated the vascular permeability-enhancing and anti-cancer properties of LCRF-0006 using in vitro vascular disruption and cell apoptosis assays, and a well-established pre-clinical model (C57BL/KaLwRij/5TGM1) of the hematological cancer multiple myeloma (MM). We found that LCRF-0006 disrupted endothelial cell junctions in a rapid, transient and reversible manner, and increased vascular permeability in vitro and at sites of MM tumor in vivo. Notably, LCRF-0006 synergistically increased the in vivo anti-MM tumor response to low-dose bortezomib, a frontline anti-MM agent, leading to regression of disease in 100% of mice. Moreover, LCRF-0006 and bortezomib synergistically induced 5TGM1 MM tumor cell apoptosis in vitro. Our findings demonstrate the potential clinical utility of LCRF-0006 to significantly increase bortezomib effectiveness and enhance the depth of tumor response in patients with MM.

Synthesis and biological evaluation of novel 5,6,7-trimethoxy flavonoid salicylate derivatives as potential anti-tumor agents

5,6,7-Trimethoxy flavonoid salicylate derivatives were designed by the joining of three important pharmacophores (TMP, flavonoid, and SA) according to the combination principle. A series of novel trimethoxy flavonoid salicylate derivatives were synthesized and their in vitro anti-tumor activities were evaluated. Among these derivatives, compound 7f exhibited excellent antiproliferative activity against HGC-27 cells and MGC-803 cells with IC₅₀ values of 10.26 ± 6.94 μM and 17.17 ± 3.03 μM, respectively. Subsequently, the effects on cell colony formation (clonogenic survival assay), cell migration (wound healing assay), cell cycle distribution (PI staining assay), cell apoptosis (Hoechst 33258 staining assay and annexin V-FITC/PI dual staining assay), lactate level (lactate measurement), microtubules disarrangement (immunofluorescence staining analysis) and docking posture (molecular docking simulation) were determined. Further western blot analysis confirmed that compound 7f could effectively down-regulate the expression of glycolysis-related proteins HIF-1α, PFKM and PKM2 and tumor angiogenesis-related proteins VEGF. Overall, these studies suggested that compound 7f, as the representative compound of those, might be a promising candidate for the treatment of gastric cancer and deserved the further studies.

Harnessing the Power of Optical Microscopic and Macroscopic Imaging for Natural Products as Cancer Therapeutics

Natural products (NPs) are an important source for new drug discovery over the past decades, which have been demonstrated to be effectively used in cancer prevention, treatment, and adjuvant therapy. Many methods, such as the genomic and metabolomic approaches, immunochemistry, mass spectrometry, and chromatography, have been used to study the effects of NPs on cancer as well as themselves. Because of the advantages in specificity, sensitivity, high throughput, and cost-effectiveness, optical imaging (OI) approaches, including optical microscopic imaging and macroscopic imaging techniques have also been applied in the studies of NPs. Optical microscopic imaging can observe NPs as cancer therapeutics at the cellular level and analyze its cytotoxicity and mechanism of action. Optical macroscopic imaging observes the distribution, metabolic pathway, and target lesions of NPs in vivo, and evaluates NPs as cancer therapeutics at the whole-body level in small living animals. This review focuses on the recent advances in NPs as cancer therapeutics, with particular emphasis on the powerful use of optical microscopic and macroscopic imaging techniques, including the studies of observation of ingestion by cells, anticancer mechanism, and in vivo delivery. Finally, we prospect the wider application and future potential of OI approaches in NPs as cancer therapeutics.

MicroRNA-330-3p promotes brain metastasis and epithelial-mesenchymal transition via GRIA3 in non-small cell lung cancer

Brain metastasis (BM) is associated with poor prognosis in patients with non-small cell lung cancer (NSCLC). We sought to identify microRNAs (miRNAs) that could serve as biomarkers to differentiate NSCLC patients with and without BM. Logistic regression was conducted with 122 NSCLC patients (60 without BM, 62 with BM) to assess the association between miRNAs and BM. We confirmed several risk factors for BM and revealed that serum miR-330-3p levels are higher in NSCLC patients with BM than that without BM. Overexpression of miR-330-3p promoted proliferation, migration, invasion and epithelial-mesenchymal transition (EMT) of NSCLC cells in vitro and NSCLC tumorigenesis in vivo. Knocking down miR-330-3p suppressed this metastatic phenotype. We identified putative miR-330-3p target genes by comparing mRNA microarray analysis data from A549 cells after miR-330-3p knockdown with candidate miR-330-3p target genes predicted by public bioinformatic tools and luciferase reporter assays. We found that GRIA3 is a target of miR-330-3p and that miR-330-3p stimulates EMT progress by mediating GRIA3-TGF-β1 interaction. Our results provide novel insight into the role of miR-330-3p in NSCLC metastasis, and suggest miR-330-3p may be a useful biomarker for identifying NSCLC with metastatic potential.

Targeting tumor cells and neovascularization using RGD-functionalized magnetoliposomes

Purpose

Magnetoliposomes (MLs) have shown great potential as magnetic resonance imaging contrast agents and as delivery vehicles for cancer therapy. Targeting the MLs towards the tumor cells or neovascularization could ensure delivery of drugs at the tumor site. In this study, we evaluated the potential of MLs targeting the αvβ3 integrin overexpressed on tumor neovascularization and different tumor cell types, including glioma and ovarian cancer.

Methods

MLs functionalized with a Texas Red fluorophore (anionic MLs), and with the fluorophore and the cyclic Arginine-Glycine-Aspartate (cRGD; cRGD-MLs) targeting the αvβ3 integrin, were produced in-house. Swiss nude mice were subcutaneously injected with 10⁷ human ovarian cancer SKOV-3 cells. Tumors were allowed to grow for 3 weeks before injection of anionic or cRGD-MLs. Biodistribution of MLs was followed up with a 7T preclinical magnetic resonance imaging (MRI) scanner and fluorescence imaging (FLI) right after injection, 2h, 4h, 24h and 48h post injection. Ex vivo intratumoral ML uptake was confirmed using FLI, electron paramagnetic resonance spectroscopy (EPR) and histology at different time points post injection.

Results

In vivo, we visualized a higher uptake of cRGD-MLs in SKOV-3 xenografts compared to control, anionic MLs with both MRI and FLI. Highest ML uptake was seen after 4h using MRI, but only after 24h using FLI indicating the lower sensitivity of this technique. Furthermore, ex vivo EPR and FLI confirmed the highest tumoral ML uptake at 4 h. Last, a Perl’s stain supported the presence of our iron-based particles in SKOV-3 xenografts.

Conclusion

Uptake of cRGD-MLs can be visualized using both MRI and FLI, even though the latter was less sensitive due to lower depth penetration. Furthermore, our results indicate that cRGD-MLs can be used to target SKOV-3 xenograft in Swiss nude mice. Therefore, the further development of this particles into theranostics would be of interest.

Chemiluminescence and Bioluminescence Imaging for Biosensing and Therapy: In Vitro and In Vivo Perspectives

Chemiluminescence (CL) and bioluminescence (BL) imaging technologies, which require no external light source so as to avoid the photobleaching, background interference and autoluminescence, have become powerful tools in biochemical analysis and biomedical science with the development of advanced imaging equipment. CL imaging technology has been widely applied to high-throughput detection of a variety of analytes because of its high sensitivity, high efficiency and high signal-to-noise ratio (SNR). Using luciferase and fluorescent proteins as reporters, various BL imaging systems have been developed innovatively for real-time monitoring of diverse molecules in vivo based on the reaction between luciferin and the substrate. Meanwhile, the kinetics of protein interactions even in deep tissues has been studied by BL imaging. In this review, we summarize in vitro and in vivo applications of CL and BL imaging for biosensing and therapy. We first focus on in vitro CL imaging from the view of improving the sensitivity. Then, in vivo CL applications in cells and tissues based on different CL systems are demonstrated. Subsequently, the recent in vitro and in vivo applications of BL imaging are summarized. Finally, we provide the insight into the development trends and future perspectives of CL and BL imaging technologies.

Photoacoustic microscopy for evaluating combretastatin A4 phosphate induced vascular disruption in orthotopic glioma

The use of an optical resolution photoacoustic microscopy (OR-PAM) system to evaluate the vascular disruptive effect of combretastatin A4 Phosphate (CA4P) on a murine orthotopic glioma with intact skull is described here. Second generation optical-resolution photoacoustic microscopy scanner with a 532 nm pulsed diode-pumped solid-state laser that specifically matches the absorption maximum of hemoglobin in tissues was used to image orthotopic glioma inoculated in mouse brain. Two-dimensional maps of brain vasculature with a lateral resolution of 5 μm and a depth of 700 μm at a field of view 5 × 4 mm were acquired on normal brain and glioma brain. Longitudinal imaging of the brain pre- and post-administration of CA4P, a FDA approved drug for solid tumors, enabled the monitoring of hemodynamic changes in tumor vasculature revealing the well documented vascular shutdown and recovery associated with this drug. Our study marks the beginning of potential prospects of this technology as an imaging tool for preclinical and clinical study of pathologies characterized by changes in the vasculature.

Noninvasive Anatomical and Functional Imaging of Orthotopic Glioblastoma Development and Therapy using Multispectral Optoacoustic Tomography

PURPOSE

Here we demonstrate the potential of multispectral optoacoustic tomography (MSOT), a new non-invasive structural and functional imaging modality, to track the growth and changes in blood oxygen saturation (sO2) in orthotopic glioblastoma (GBMs) and the surrounding brain tissues upon administration of a vascular disruptive agent (VDA).

METHODS

Nude mice injected with U87MG tumor cells were longitudinally monitored for the development of orthotopic GBMs up to 15 days and observed for changes in sO2 upon administration of combretastatin A4 phosphate (CA4P, 30 mg/kg), an FDA approved VDA for treating solid tumors. We employed a newly-developed non-negative constrained approach for combined MSOT image reconstruction and unmixing in order to quantitatively map sO2 in whole mouse brains.

RESULTS

Upon longitudinal monitoring, tumors could be detected in mouse brains using single-wavelength data as early as 6 days post tumor cell inoculation. Fifteen days post-inoculation, tumors had higher sO2 of 63 ± 11% (n = 5, P < .05) against 48 ± 7% in the corresponding contralateral brain, indicating their hyperoxic status. In a different set of animals, 42 days post-inoculation, tumors had lower sO2 of 42 ± 5% against 49 ± 4% (n = 3, P < .05) in the contralateral side, indicating their hypoxic status. Upon CA4P administration, sO2 in 15 days post-inoculation tumors dropped from 61 ± 9% to 36 ± 1% (n = 4, P < .01) within one hour, then reverted to pre CA4P treatment values (63 ± 6%) and remained constant until the last observation time point of 6 hours.

CONCLUSION

With the help of advanced post processing algorithms, MSOT was capable of monitoring the tumor growth and assessing hemodynamic changes upon administration of VDAs in orthotopic GBMs.

Preclinical Evaluation of Radioiodinated Hoechst 33258 for Early Prediction of Tumor Response to Treatment of Vascular-Disrupting Agents

This study aimed to explore the use of ¹³¹I-Hoechst 33258 (¹³¹I-H33258) for early prediction of tumor response to vascular-disrupting agents (VDAs) with combretastatin-A4 phosphate (CA4P) as a representative. Necrosis avidity of ¹³¹I-H33258 was evaluated in mouse models with muscle necrosis and blocking was used to confirm the tracer specificity. Therapy response was evaluated by ¹³¹I-H33258 SPECT/CT imaging 24 h after CA4P therapy in W256 tumor-bearing rats. Radiotracer uptake in tumors was validated ex vivo using γ-counting, autoradiography, and histopathological staining. Results showed that ¹³¹I-H33258 had predominant necrosis avidity and could specifically bind to necrotic tissue. SPECT/CT imaging demonstrated that an obvious “hot spot” could be observed in the CA4P-treated tumor. Ex vivo γ-counting revealed ¹³¹I-H33258 uptake in tumors was increased 2.8-fold in rats treated with CA4P relative to rats treated with vehicle. Autoradiography and corresponding H&E staining suggested that ¹³¹I-H33258 was mainly localized in necrotic tumor area and the higher overall uptake in the treated tumors was attributed to the increased necrosis. These results suggest that ¹³¹I-H33258 can be used to image induction of cell necrosis 24 h after CA4P therapy, which support further molecular design of probes based on scaffold H33258 for monitoring of tumor response to VDAs treatment.

Multi-targeting NGR-modified liposomes recognizing glioma tumor cells and vasculogenic mimicry for improving anti-glioma therapy

Like the anti-angiogenic strategy, anti-vascular mimicry is considered as a novel targeting strategy for glioma. In the present study, we used NGR as a targeting ligand and prepared NGR-modified liposomes containing combretastatin A4 (NGR-SSL-CA4) in order to evaluate their potential targeting of glioma tumor cells and vasculogenic mimicry (VM) formed by glioma cells as well as their anti-VM activity in mice with glioma tumor cells. NGR-SSL-CA4 was prepared by a thin-film hydration method. The in vitro targeting of U87-MG (human glioma tumor cells) by NGR-modified liposomes was evaluated. The in vivo targeting activity of NGR-modified liposomes was tested in U87-MG orthotopic tumor-bearing nude mice. The anti-VM activity of NGR-SSL-CA4 was also investigated in vitro and in vivo. The targeting activity of the NGR-modified liposomes was demonstrated by in vitro flow cytometry and in vivo biodistribution. The in vitro anti-VM activity of NGR-SSL-CA4 was indicated in a series of cell migration and VM channel experiments. NGR-SSL-CA4 produced very marked anti-tumor and anti-VM activity in U87-MG orthotopic tumor-bearing mice in vivo. Overall, the NGR-SSL-CA4 has great potential in the multi-targeting therapy of glioma involving U87-MG cells, and the VM formed by U87-MG cells as well as endothelial cells producing anti-U87-MG cells, and anti-VM formed by U87-MG cells as well as anti-endothelial cell activity.

The vascular disrupting agent combretastatin A-4 phosphate causes prolonged elevation of proteins involved in heme flux and function in resistant tumor cells

Vascular disrupting agents (VDAs) represent a promising class of anti-cancer drugs for solid tumor treatment. Here, we aim to better understand the mechanisms underlying tumor reccurrence and treatment resistance following the administration of a VDA, combretastatin A-4 phosphate (CA4P). Firstly, we used photoacoustic tomography to noninvasively map the effect of CA4P on blood oxygen levels throughout subcutaneous non-small cell lung cancer (NSCLC) tumors in mice. We found that the oxygenation of peripheral tumor vessels was significantly decreased at 1 and 3 hours post-CA4P treatment. The oxygenation of the tumor core reduced significantly at 1 and 3 hours, and reached anoxia after 24 hours. Secondly, we examined the effect of CA4P on the levels of proteins involved in heme flux and function, which are elevated in lung tumors. Using immunohistochemistry, we found that CA4P substantially enhanced the levels of enzymes involved in heme biosynthesis, uptake, and degradation, as well as oxygen-utilizing hemoproteins. Furthermore, measurements of markers of mitochondrial function suggest that CA4P did not diminish mitochondrial function in resistant tumor cells. These results suggest that elevated levels of heme flux and function contribute to tumor regrowth and treatment resistance post-VDA administration.

Multimodal imaging guided preclinical trials of vascular targeting in prostate cancer

The high mortality rate associated with castration-resistant prostate cancer (CRPC) underscores the need for improving therapeutic options for this patient population. The purpose of this study was to examine the potential of vascular targeting in prostate cancer. Experimental studies were carried out in subcutaneous and orthotopic Myc-CaP prostate tumors implanted into male FVB mice to examine the efficacy of a novel microtubule targeted vascular disrupting agent (VDA), EPC2407 (Crolibulin™). A non-invasive multimodality imaging approach based on magnetic resonance imaging (MRI), bioluminescence imaging (BLI), and ultrasound (US) was utilized to guide preclinical trial design and monitor tumor response to therapy. Imaging results were correlated with histopathologic assessment, tumor growth and survival analysis. Contrast-enhanced MRI revealed potent antivascular activity of EPC2407 against subcutaneous and orthotopic Myc-CaP tumors. Longitudinal BLI of Myc-CaP tumors expressing luciferase under the androgen response element (Myc-CaP/ARE-luc) revealed changes in AR signaling and reduction in intratumoral delivery of luciferin substrate following castration suggestive of reduced blood flow. This reduction in blood flow was validated by US and MRI. Combination treatment resulted in sustained vascular suppression, inhibition of tumor regrowth and conferred a survival benefit in both models. These results demonstrate the therapeutic potential of vascular targeting in combination with androgen deprivation against prostate cancer.

Acute changes in liver tumour perfusion measured non-invasively with arterial spin labelling

BACKGROUND

Non-invasive measures of tumour vascular perfusion are desirable, in order to assess response to vascular targeting (or modifying) therapies. In this study, hepatic arterial spin labelling (ASL) magnetic resonance imaging (MRI) was investigated to measure acute changes in perfusion of colorectal cancer in the liver, in response to vascular disruption therapy with OXi4503.

METHODS

SW1222 and LS174T tumours were established in the liver of MF1 nu/nu mice via intrasplenic injection. Perfusion and R2(*) MRI measurements were acquired with an Agilent 9.4T horizontal bore scanner, before and at 90 min after 40 mg kg(-1) OXi4503.

RESULTS

A significant decrease in SW1222 tumour perfusion was observed (-43±33%, P<0.005). LS174T tumours had a significantly lower baseline level of perfusion. Intrinsic susceptibility MRI showed a significant increase in R2(*) in LS174T tumours (28±25%, P<0.05). An association was found between the change in tumour perfusion and the proximity to large vessels, with pre-treatment blood flow predictive of subsequent response. Histological evaluation confirmed the onset of necrosis and evidence of heterogeneous response between tumour deposits.

CONCLUSIONS

Hepatic ASL-MRI can detect acute response to targeted tumour vascular disruption entirely non-invasively. Hepatic ASL of liver tumours has potential for use in a clinical setting.

Preclinical Activity of the Vascular Disrupting Agent OXi4503 against Head and Neck Cancer

Vascular disrupting agents (VDAs) represent a relatively distinct class of agents that target established blood vessels in tumors. In this study, we examined the preclinical activity of the second-generation VDA OXi4503 against human head and neck squamous cell carcinoma (HNSCC). Studies were performed in subcutaneous and orthotopic FaDu-luc HNSCC xenografts established in immunodeficient mice. In the subcutaneous model, bioluminescence imaging (BLI) along with tumor growth measurements was performed to assess tumor response to therapy. In mice bearing orthotopic tumors, a dual modality imaging approach based on BLI and magnetic resonance imaging (MRI) was utilized. Correlative histologic assessment of tumors was performed to validate imaging data. Dynamic BLI revealed a marked reduction in radiance within a few hours of OXi4503 administration compared to baseline levels. However, this reduction was transient with vascular recovery observed at 24 h post treatment. A single injection of OXi4503 (40 mg/kg) resulted in a significant (p < 0.01) tumor growth inhibition of subcutaneous FaDu-luc xenografts. MRI revealed a significant reduction (p < 0.05) in volume of orthotopic tumors at 10 days post two doses of OXi4503 treatment. Corresponding histologic (H&E) sections of Oxi4503 treated tumors showed extensive areas of necrosis and hemorrhaging compared to untreated controls. To the best of our knowledge, this is the first report, on the activity of Oxi4503 against HNSCC. These results demonstrate the potential of tumor-VDAs in head and neck cancer. Further examination of the antivascular and antitumor activity of Oxi4503 against HNSCC alone and in combination with chemotherapy and radiation is warranted.

The vascular disrupting activity of OXi8006 in endothelial cells and its phosphate prodrug OXi8007 in breast tumor xenografts

This study describes the vascular disrupting ability and the mechanism of action of the indole-based tubulin-binding compound, OXi8006, and its water-soluble phosphate prodrug OXi8007. Treatment of rapidly proliferating human umbilical vein endothelial cells (HUVECs), used as a model for the tumor vasculature, with OXi8006 or OXi8007, caused potent microtubule disruption followed by extensive reorganization of the cytoskeletal network. The mechanism of action involved an increase in focal adhesion formation associated with an increase in phosphorylation of both non-muscle myosin light chain and focal adhesion kinase. These effects were dramatically diminished by an inhibitor of RhoA kinase, a downstream effector of RhoA. Cell cycle blockade at G2/M and cytotoxicity toward rapidly proliferating HUVECs were also observed. Capillary-like networks of HUVECs were disrupted by the action of both OXi8006 and OXi8007. The prodrug OXi8007 exhibited potent and rapid dose-dependent antivascular activity assessed by dynamic bioluminescence imaging (BLI) in an MDA-MB-231-luc breast cancer xenograft mouse model. By 6 hours post treatment, over 93% of the BLI signal was abolished with only a slight recovery at 24 hours. These findings were confirmed by histology. The results from this study demonstrate that OXi8007 is a potent vascular disrupting agent acting through an anti-microtubule mechanism involving RhoA.