Preclinical evaluation of the metabolism and disposition of RRx-001, a novel investigative anticancer agent

Coumarin-Furoxan Hybrid Suppressed the Proliferation and Metastasis of Triple-Negative Breast Cancer by Activating Mitochondrial Stress and Cell Apoptosis

Triple-negative breast cancer (TNBC) typically manifests as higher invasive carcinoma correlated with a worse prognosis that primarily relies on chemotherapy. There is growing evidence that nitric oxide (NO) donor drugs have the potential for anticancer therapy. On this basis, we constructed and evaluated a novel coumarin-furoxan hybrid 4A93 as an effective antitumor candidate drug. 4A93 exhibits low IC50 values in three TNBC cell lines and inhibits colony formation and DNA synthesis, probably due to the release of high concentrations of NO in mitochondria, which induces oxidative stress, mitochondrial dysfunction, and apoptosis. Further research suggests that 4A93 might destroy mitochondria by opening the mitochondrial permeability transition pore (mPTP), depolarizing the mitochondrial membrane potential (MMP), and promoting the release of cytochrome c into the cytoplasm. Intrinsic apoptosis is induced finally, along with Akt/Erk signaling suppression. Additionally, 4A93 underregulates the Epithelial-mesenchymal transition process to inhibit cell migration and invasion. In 4T1 subcutaneous and hematogenous models of mice, 4A93 therapy suppresses the tumor growth and prevented lung metastasis with favorable biosafety. Our results provide insights into 4A93 in TNBC treatment and validate the contribution of NO donors in tumor therapy.

RRx-001: a chimeric triple action NLRP3 inhibitor, Nrf2 inducer, and nitric oxide superagonist

RRx-001 is a shape shifting small molecule with Fast Track designation for the prevention/amelioration of chemoradiation-induced severe oral mucositis (SOM) in newly diagnosed Head and Neck cancer. It has been intentionally developed or "engineered" as a chimeric single molecular entity that targets multiple redox-based mechanisms. Like an antibody drug conjugate (ADC), RRx-001 contains, at one end a "targeting" moiety, which binds to the NLRP3 inflammasome and inhibits it as well as Kelch-like ECH-associated protein 1 (KEAP1), the negative regulator of Nrf2, and, at the other end, a conformationally constrained, dinitro containing 4 membered ring, which fragments under conditions of hypoxia and reduction to release therapeutically active metabolites i.e., the payload. This "payload", which is delivered specifically to hypoperfused and inflamed areas, includes nitric oxide, nitric oxide related species and carbon-centered radicals. As observed with ADCs, RRx-001 contains a backbone amide "linker" attached to a binding site, which correlates with the F_ab region of an antibody, and to the dinitroazetidine payload, which is microenvironmentally activated. However, unlike ADCs, whose large size impacts their pharmacokinetic properties, RRx-001 is a nonpolar small molecule that easily crosses cell membranes and the blood brain barrier (BBB) and distributes systemically. This short review is organized around the de novo design and in vivo pro-oxidant/pro-inflammatory and antioxidant/anti-inflammatory activity of RRx-001, which, in turn, depends on the reduced to oxidized glutathione ratio and the oxygenation status of tissues.

Technologies for Direct Detection of Covalent Protein-Drug Adducts

In the past two decades, drug candidates with a covalent binding mode have gained the interest of medicinal chemists, as several covalent anticancer drugs have successfully reached the clinic. As a covalent binding mode changes the relevant parameters to rank inhibitor potency and investigate structure-activity relationship (SAR), it is important to gather experimental evidence on the existence of a covalent protein-drug adduct. In this work, we review established methods and technologies for the direct detection of a covalent protein-drug adduct, illustrated with examples from (recent) drug development endeavors. These technologies include subjecting covalent drug candidates to mass spectrometric (MS) analysis, protein crystallography, or monitoring intrinsic spectroscopic properties of the ligand upon covalent adduct formation. Alternatively, chemical modification of the covalent ligand is required to detect covalent adducts by NMR analysis or activity-based protein profiling (ABPP). Some techniques are more informative than others and can also elucidate the modified amino acid residue or bond layout. We will discuss the compatibility of these techniques with reversible covalent binding modes and the possibilities to evaluate reversibility or obtain kinetic parameters. Finally, we expand upon current challenges and future applications. Overall, these analytical techniques present an integral part of covalent drug development in this exciting new era of drug discovery.

PREVLAR: Phase 2a Randomized Trial to Assess the Safety and Efficacy of RRx-001 in the Attenuation of Oral Mucositis in Patients Receiving Head and Neck Chemoradiotherapy

PURPOSE

No Food and Drug Administration-approved intervention exists for oral mucositis (OM) from chemoradiotherapy (CRT) used to treat head and neck cancers. RRx-001 is a hypoxia-activated, cysteine-directed molecule that affects key pathways involved in OM pathogenesis. This phase 2a, multi-institutional trial was designed to assess the safety and feasibility of 3 schedules of a fixed concentration of RRx-001; a standard-of-care arm was included to identify potential signals of efficacy for further study.

METHODS AND MATERIALS

This study enrolled patients with oral cavity and oropharynx squamous cell carcinoma receiving definitive or postoperative cisplatin-based CRT. Patients were randomized into 4 cohorts. In arms 1 to 3, RRx-001 was coinfused with patients' blood at differing intervals. Arm 4 was a control cohort of patients treated with CRT alone. Trained evaluators assessed OM using a standardized data collection instrument twice weekly during treatment and then until resolution. OM severity was scored centrally using World Health Organization criteria. Safety outcomes were assessed using National Cancer Institute - Common Terminology Criteriav4 benchmarks. Long-term tumor response was defined by Response evaluation criteria in solid tumors v1.1 criteria.

RESULTS

Fifty-three patients were enrolled, with 46 and 45 individuals contributing safety and efficacy data, respectively. There were no severe adverse events attributed to the study drug. Across all 3 active arms, the study drug was infused fully per protocol in 86% of patients. All 3 RRx-001 treatment cohorts appeared to demonstrate a similar or lower OM duration relative to control; arm 1 had the lowest median duration of severe oral mucositis (SOM), 8.5 days versus 24 days in controls among patients who developed at least 1 day of SOM. There were no locoregional failures in any patient.

CONCLUSIONS

Our results support the safety and feasibility of RRx-001 as an intervention to mitigate SOM. Additional studies are planned to confirm its efficacy.

RRx-001 and the "Right stuff": Protection and treatment in outer space

From antibiotics to aspirin to antimalarials and to anticancer agents, about half of the world's best-selling drugs are derived from nature. However, accelerating climatic disruption, habitat destruction, pollution, and biodiversity loss all negatively impact the potential of natural sources to continue to serve as repositories of novel pharmaceuticals. On that basis, the final frontier for drug development is perhaps not the rainforests, coral reefs, and other natural habitats but rather the aerospace industry with its virtually unlimited and inexhaustible man-made 'library' of potentially bioactive compounds. The first aerospace-sourced therapeutic to reach the clinic is RRx-001, an inhibitor of the NOD-like receptor - Nucleotide-binding oligomerization domain with Leucine rich Repeat and Pyrin domain (NLRP3) inflammasome in a Phase 3 trial for the treatment of small cell lung cancer (SCLC) and in a soon-to-start Phase 3 trial for protection against chemoradiotherapy-induced severe oral mucositis in first line head and neck cancer. As manned missions to the Moon, Mars, and asteroids as well as space tourism beckon, it is perhaps fitting that a compound like RRx-001, which is derived from 1,3,3-Trinitroazetidine (TNAZ), an explosive propellant for rockets, is a potential "all purpose" option to mitigate the major biomedical effects of space radiation exposures including cancer development and other tissue degenerations both within mission and after mission. This article highlights the promise of RRx-001 to attenuate the acute and late effects of radiation exposure on astronauts including the development of cancer.

Novel Nitric Oxide Donor Dinitroazetidine-Coumarin Hybrids as Potent Anti-Intrahepatic Cholangiocarcinoma Agents

Intrahepatic cholangiocarcinoma (iCC) is a serious liver cancer threatening human health. However, there are a few chemotherapeutic drugs for the treatment of iCC in the clinic. It is extremely urgent to develop new drugs for iCC. In this study, twenty dinitroazetidine and coumarin hybrids were synthesized and evaluated anti-iCC bioactivity as a new type of nitric oxide (NO) donors. Among them, compounds 2–5 and 21 showed a higher antiproliferative activity against RBE cell lines (human intrahepatic cholangiocarcinoma cell lines) and low cytotoxicity in nontumor cells (HOSEpiC and T29). The preliminary study of pharmacology mechanism indicated that compounds 2–5 and 21 could release effective concentration of NO in RBE cell lines, which leaded to inhibit the proliferation of RBE cell lines. The research results revealed that compound 3 inhibited the proliferation of RBE cell lines by inducing apoptosis and arresting cell cycle at G₂/M phase. Additionally, compound 3 had acceptable metabolic stability. Therefore, compound 3 was merited to further explore for developing a desirable NO donor lead with anti-iCC activity.

RRx-001 ameliorates inflammatory diseases by acting as a potent covalent NLRP3 inhibitor

The NLRP3 inflammasome plays a crucial role in innate immune-mediated inflammation and contributes to the pathogenesis of multiple autoinflammatory, metabolic and neurodegenerative diseases, but medications targeting the NLRP3 inflammasome are not available for clinical use. RRx-001 is a well-tolerated anticancer agent currently being investigated in phase III clinical trials, but its effects on inflammatory diseases are not known. Here, we show that RRx-001 is a highly selective and potent NLRP3 inhibitor that has strong beneficial effects on NLRP3-driven inflammatory diseases. RRx-001 inhibits the activation of the canonical, noncanonical, and alternative NLRP3 inflammasomes but not the AIM2, NLRC4 or Pyrin inflammasomes. Mechanistically, RRx-001 covalently binds to cysteine 409 of NLRP3 via its bromoacetyl group and therefore blocks the NLRP3-NEK7 interaction, which is critical for the assembly and activation of the NLRP3 inflammasome. More importantly, RRx-001 treatment attenuates the symptoms of lipopolysaccharide (LPS)-induced systemic inflammation, dextran sulfate sodium (DSS)-induced colitis and experimental autoimmune encephalomyelitis (EAE) in mice. Thus, our study identifies RRx-001 as a new potential therapeutic agent for NLRP3-driven diseases.

Vascular priming with RRx-001 to increase the uptake and accumulation of temozolomide and irinotecan in orthotopically implanted gliomas

Vascular normalisation refers to a 'remodeling' of the dysfunctional tumour capillary network, which regresses under the influence of anti-VEGF treatment, resulting in improved blood flow and oxygenation. RRx-001 is an anti-CD47-SIRPα small molecule with vascular normalising properties under investigation in clinical trials for the treatment of glioblastoma, brain metastases, lung cancer and colorectal cancer, with FDA Orphan Drug Designation in glioblastoma and other tumour types. This study investigated whether the improved oxygenation and perfusion that has been previously observed with RRx-001 both preclinically and clinically in the context of a brain metastasis trial was correlated with increased penetration and accumulation of the cytotoxic chemotherapies, irinotecan and temozolomide, in orthotopically implanted gliomas, priming tumours for improved response. The experiments demonstrate that administration of RRx-001 prior to temozolomide or irinotecan results in significantly increased uptake of irinotecan and temozolomide in orthotopic glioma tumours. Since the success of chemotherapy in the brain (and outside of it) is limited by subtherapeutic tumoral drug concentrations, vascular normalisation-enhanced delivery of standard cytotoxics as demonstrated with RRx-001 may mitigate or reverse clinical drug resistance and thereby improve the outcome of cancer therapy, particularly in the brain.

RRx-001 Increases Erythrocyte Preferential Adhesion to the Tumor Vasculature

Red blood cells (RBCs) serve a variety of functions beyond mere oxygen transport both in health and pathology. Notably, RRx-001, a minimally toxic pleiotropic anticancer agent with macrophage activating and vascular normalization properties currently in Phase III trials, induces modification to RBCs which could promote vascular adhesion similar to sickle cells. This study assessed whether RBCs exposed to RRx-001 adhere to the tumor microvasculature and whether this adhesion alters tumor viability. We next investigated the biomechanics of RBC adhesion in the context of local inflammatory cytokines after treatment with RRx-001 as a potential mechanism for preferential tumor aggregation. Human HEP-G2 and HT-29 tumor cells were subcutaneously implanted into nu/nu mice and were infused with RRx-001-treated and Technetium-99m (^99mTc)-labeled blood. RBC adhesion was quantified in an in vitro human umbilical vein endothelial cell (HUVEC) assay under both normoxic and hypoxic conditions with administration of either lipopolysaccharide (LPS) or Tumor necrosis alpha (TNFα) to mimic the known inflammation in the tumor microenvironment. One hour following administration of ^99mTc labeled RBCs treated with 10 mg/kg RRx-001, we observed an approximate 2.0-fold and 1.5-fold increase in ^99mTc-labeled RBCs compared to vehicle control in HEPG2 and HT-29 tumor models, respectively. Furthermore, we observed an approximate 40% and 36% decrease in HEP-G2 and HT-29 tumor weight, respectively, following treatment with RRx-001. To quantify RBC adhesive potential, we determined τ50, or the shear stress required for 50% disassociation of RBCs from HUVECs. After administration of TNF-α under normoxia, τ50 was determined to be 4.5 dynes/cm² (95% CI: 4.3-4.7 dynes/cm²) for RBCs treated with 10 μM RRx-001, which was significantly different (p < 0.05) from τ50 in the absence of treatment. Under hypoxic conditions, the difference of τ50 with (4.8 dynes/cm²; 95% CI: 4.6-5.1 dynes/cm²) and without (2.6 dynes/cm²; 95% CI: 2.4-2.8 dynes/cm²) 10 μM RRx-001 treatment was exacerbated (p = 0.05). In conclusion, we demonstrated that RBCs treated with RRx-001 preferentially aggregate in HEP-G2 and HT-29 tumors, likely due to interactions between RRx-001 and cysteine residues within RBCs. Furthermore, RRx-001 treated RBCs demonstrated increased adhesive potential to endothelial cells upon introduction of TNF-α and hypoxia suggesting that RRx-001 may induce preferential adhesion in the tumor but not in other tissues with endothelial dysfunction due to conditions prevalent in older cancer patients such as heart disease or diabetic vasculopathy.

The evolving landscape for cellular nitric oxide and hydrogen sulfide delivery systems: A new era of customized medications

Nitric oxide (NO) and hydrogen sulfide (H2S) are industrial toxins or pollutants; however, both are produced endogenously and have important biological roles in most mammalian tissues. The recognition that these gasotransmitters have a role in physiological and pathophysiological processes has presented opportunities to harness their intracellular effects either through inhibition of their production; or more commonly, through inducing their levels and or delivering them by various modalities. In this review article, we have focused on an array of NO and H2S donors, their hybrids with other established classes of drugs, and the various engineered delivery platforms such a fibers, polymers, nanoparticles, hydrogels, and others. In each case, we have reviewed the rationale for their development.

RRx-001, a first-in-class small molecule inhibitor of MYC and a downregulator of CD47, is an "erythrophagoimmunotherapeutic"

The main mechanism of action of RRx-001, a pharmaceutically unprecedented sui generis Phase 3 small molecule that is derived from the aerospace industry, is clarified. RRx-001 has demonstrated anticancer activity through antiangiogenic, immune, epigenetic, antioxidant, apoptotic and nitric oxide (NO) pathways, resulting in its pleiomorphic description as an antiangiogenic/vascular normalizer.

BRAINSTORM: A Multi-Institutional Phase 1/2 Study of RRx-001 in Combination With Whole Brain Radiation Therapy for Patients With Brain Metastases

PURPOSE

To determine the recommended phase 2 dose of RRx-001, a radiosensitizer with vascular normalizing properties, when used with whole-brain radiation therapy (WBRT) for brain metastases and to assess whether quantitative changes in perfusion magnetic resonance imaging (MRI) after RRx-001 correlate with response.

METHODS AND MATERIALS

Five centers participated in this phase 1/2 trial of RRx-001 given once pre-WBRT and then twice weekly during WBRT. Four dose levels were planned (5 mg/m², 8.4 mg/m², 16.5 mg/m², 27.5 mg/m²). Dose escalation was managed by the time-to-event continual reassessment method algorithm. Linear mixed models were used to correlate change in 24-hour T1, Ktrans (capillary permeability), and fractional plasma volume with change in tumor volume.

RESULTS

Between 2015 and 2017, 31 patients were enrolled. Two patients dropped out before any therapy. Median age was 60 years (range, 30-76), and 12 were male. The most common tumor types were melanoma (59%) and non-small cell lung cancer (18%). No dose limiting toxicities were observed. The most common severe adverse event was grade 3 asthenia (6.9%, 2 of 29). The median intracranial response rate was 46% (95% confidence interval, 24-68) and median overall survival was 5.2 months (95% confidence interval, 4.5-9.4). No neurologic deaths occurred. Among 10 patients undergoing dynamic contrast-enhanced MRI, a reduction in Vp 24 hours after RRx-001 was associated with reduced tumor volume at 1 and 4 months (P ≤ .01).

CONCLUSIONS

The addition of RRx-001 to WBRT is well tolerated with favorable intracranial response rates. Because activity was observed across all dose levels, the recommended phase 2 dose is 10 mg twice weekly. A reduction in fractional plasma volume on dynamic contrast-enhanced MRI 24 hours after RRx-001 suggests antiangiogenic activity associated with longer-term tumor response.

RRx-001 followed by platinum plus etoposide in patients with previously treated small-cell lung cancer

Background

This exploratory single-arm phase II study evaluated the efficacy and safety of RRx-001 followed by reintroduction of platinum plus etoposide in patients with previously treated small-cell lung cancer (SCLC).

Methods

Patients were treated with RRx-001 4 mg IV on day 1 of each week of a 21-day cycle followed at progression by re-challenge with etoposide 80–100 IV mg/m² on days 1, 2 and 3 and cisplatin 60–80 mg/m² IV on day 1 or carboplatin AUC 5–6 IV on day 1, every 21 days. The primary end points were overall survival (OS) and overall response rate to platinum regimen.

Results

Twenty-six patients were enroled and received at least one dose of RRx-001. The median number of prior lines of therapy was 2 (range 1–9) and 19 (73.1%) patients had platinum-resistant disease. In the intention-to-treat population, one patient (3.8%) had complete response and six (23.1%) had partial response on platinum plus etoposide. The estimated median and 12-month OS from enrolment were 8.6 months and 44.1%, respectively. The most common treatment-emergent adverse event from RRx-001 was mild discomfort at the infusion site (23%).

Conclusions

RRx-001 followed by re-challenge with platinum plus etoposide chemotherapy is feasible and associated with promising results.

Clinical trial registration

NCT02489903.

The dichotomous role of H2S in cancer cell biology? Déjà vu all over again

Nitric oxide (NO) a gaseous free radical is one of the ten smallest molecules found in nature, while hydrogen sulfide (H2S) is a gas that bears the pungent smell of rotten eggs. Both are toxic yet they are gasotransmitters of physiological relevance. There appears to be an uncanny resemblance between the general actions of these two gasotransmitters in health and disease. The role of NO and H2S in cancer has been quite perplexing, as both tumor promotion and inflammatory activities as well as anti-tumor and antiinflammatory properties have been described. These paradoxes have been explained for both gasotransmitters in terms of each having a dual or biphasic effect that is dependent on the local flux of each gas. In this review/commentary, I have discussed the major roles of NO and H2S in carcinogenesis, evaluating their dual nature, focusing on the enzymes that contribute to this paradox and evaluate the pros and cons of inhibiting or inducing each of these enzymes.

Magnetic resonance imaging of RRx-001 pharmacodynamics in preclinical tumors

RRx-001 is an anticancer agent that subjects cancer cells to reactive oxygen/nitrogen species (ROS/RNS) and acts as an epigenetic modifier. We have used a thiol-bearing MRI contrast agent, Gd-LC7-SH, to investigate the pharmacodynamics of RRx-001 in CHP-100 Ewing's Sarcoma, HT-29 colorectal carcinoma, and PANC-1 pancreatic carcinoma xenografts in SCID mice. Binding of Gd-LC7-SH to the Cys³⁴ residue on plasma albumin prolongs retention in the tumor microenvironment and increases tumor enhancement on MRI. Mice were imaged by MRI and in vivo T1 maps acquired 50 min (T1_{50 min}) after injection of 0.05 mmol/kg Gd-LC7-SH (i.v.) at baseline and 1, 24, and 72 h post-treatment with 10 mg/kg RRx-001 (i.v.). Consistent with an indirect thiol-modifying activity of RRx-001, tumor T1_{50 min} at 1 h post-drug was significantly longer than pre-drug tumor T1_{50 min} in all three tumor models, with the T1_{50 min} remaining significantly longer than baseline through 72 h post-drug in the HT-29 and PANC-1 tumors. The T1_{50 min} of CHP-100 tumors recovered to baseline by 24 h post-drug, suggesting a robust anti-oxidant response to the RRx-001 challenge that was presaged by a marked increase in perfusion at 1 h post-drug measured by DCE-MRI. MRI enhanced with Gd-LC7-SH provides a mechanistically rational biomarker of RRx-001 pharmacodynamics.

Nitric Oxide Donor-Based Cancer Therapy: Advances and Prospects

The increasing understanding of the role of nitric oxide (NO) in cancer biology has generated significant progress in the use of NO donor-based therapy to fight cancer. These advances strongly suggest the potential adoption of NO donor-based therapy in clinical practice, and this has been supported by several clinical studies in the past decade. In this review, we first highlight several types of important NO donors, including recently developed NO donors bearing a dinitroazetidine skeleton, represented by RRx-001, with potential utility in cancer therapy. Special emphasis is then given to the combination of NO donor(s) with other therapies to achieve synergy and to the hybridization of NO donor(s) with an anticancer drug/agent/fragment to enhance the activity or specificity or to reduce toxicity. In addition, we briefly describe inducible NO synthase gene therapy and nanotechnology, which have recently entered the field of NO donor therapy.

The macrophage stimulating anti-cancer agent, RRx-001, protects against ischemia-reperfusion injury

BACKGROUND

RRx-001, a clinical macrophage-stimulating anti-cancer agent that also produces nitric oxide (NO) was studied in a model of ischemia-reperfusion injury.

METHODS

The production of NO is dependent on the oxygen tension because nitric oxide synthases convert l-arginine to NO and l-citrulline in the presence of O₂. Since the P450 enzymes, which metabolize nitrate esters such as nitroglycerin are dependent on oxygen, the generation of 'exogenous' NO is also sensitive to alterations in tissue PO₂. I/R injury was studied in a hamster chamber window, with compression of the periphery of the window for 1 h to induce ischemia. Animals received RRx-001 (5 mg/kg) 24 h before ischemia and sodium nitrite (10 nmols/kg) was supplemented 10 min after the start of reperfusion. Vessel diameter, blood flow, adherent leukocytes, and functional capillary density were assessed by intravital microscopy at 0.5, 2, and 24 h following the release of the ischemia.

RESULTS

The results demonstrated that, compared to control, RRx-001 preconditioning increased blood flow and functional capillary density, and preserved tissue viability in the absence of side effects over a sustained time period.

CONCLUSION

Thus, RRx-001 may serve as a long-lived protective agent during postsurgical restoration of flow and other ischemia-reperfusion associated conditions, increasing blood flow and functional capillary density as well as preserving tissue viability in the absence of side effects.

RRx-001: a systemically non-toxic M2-to-M1 macrophage stimulating and prosensitizing agent in Phase II clinical trials

INTRODUCTION

According to Hanahan and Weinberg, cancer manifests as six essential physiologic hallmarks: (1) self-sufficiency in growth signals, (2) insensitivity to growth-inhibitory signals, (3) evasion of programmed cell death, (4) limitless replicative potential, (5) sustained angiogenesis, and (6) invasion and metastasis. As a facilitator of these traits as well as immunosuppression and chemoresistance, the presence of tumor-associated macrophages (TAMs) may serve as the seventh hallmark of cancer. Anticancer agents that successfully reprogram TAMs to target rather than support tumor cells may hold the key to better therapeutic outcomes. Areas covered: This article summarizes the characteristics of the macrophage-stimulating agent RRx-001, a molecular iconoclast, sourced from the aerospace industry, with a particular emphasis on the cell-to-cell transfer mechanism of action (RBCs to TAMs) underlying its antitumor activity as well as its chemo and radioprotective properties, consolidated from various preclinical and clinical studies. Expert opinion: RRx-001 is macrophage-stimulating agent with the potential to synergize with chemotherapy, radiotherapy and immunotherapy while simultaneously protecting normal tissues from their cytotoxic effects. Given the promising indications of activity in multiple tumor types and these normal tissue protective properties, RRx-001 may be used to treat a broad spectrum of malignancies, if it is approved in the future.

Epigenetic effects of RRx-001: a possible unifying mechanism of anticancer activity

RRx-001 is a novel aerospace-derived compound currently under investigation in several ongoing Phase II studies. In a Phase I trial, it demonstrated anti-cancer activity and evidence of resensitization to formerly effective therapies in heavily pre-treated patients with relapsed/refractory solid tumors. RRx-001 generates reactive oxygen and nitrogen species (ROS and RNS) and nitric oxide (NO), elicits changes in intracellular redox status, modulates tumor blood flow, hypoxia and vascular function and triggers apoptosis in cancer cells. We investigated the effect of RRx-001 on the epigenome of SCC VII cancer cells. RRx-001 at 0.5 and 2 μM significantly decreased global DNA methylation, i.e., 5-methylcytosine levels, in SCC VII cells. Consistently, 0.5-5 μM RRx-001 significantly decreased Dnmt1 and Dnmt3a protein expression in a dose- and time-dependent manner. In addition, global methylation profiling identified differentially methylated genes in SCC VII cells treated with 0.5, 2, and 5 μM RRx-001 compared to control cells. Twenty-three target sites were hypomethylated and 22 hypermethylated by >10% in the presence of at least two different concentrations of RRx-001. Moreover, RRx-001 at 2 μM significantly increased global acetylated histone H3 and H4 levels in SCC VII cells after 24 hour treatment, suggesting that RRx-001 regulates global acetylation in cancer cells. These results demonstrate that, in contrast to the traditional "one drug one target" paradigm, RRx-001 has multi(epi)target features, which contribute to its anti-cancer activity and may rationalize the resensitization to previously effective therapies observed in clinical trials and serve as a unifying mechanism for its anticancer activity.

Targeting tumor hypoxia with the epigenetic anticancer agent, RRx-001: a superagonist of nitric oxide generation

This study reveals a novel interaction between deoxyhemoglobin, nitrite and the non-toxic compound, RRx-001, to generate supraphysiologic levels of nitric oxide (NO) in blood. We characterize the nitrite reductase activity of deoxyhemoglobin, which in the presence of bound RRx-001 reduces nitrite at a much faster rate, leading to markedly increased NO generation. These data expand on the paradigm that hemoglobin generates NO via nitrite reduction during hypoxia and ischemia when nitric oxide synthase (NOS) function is limited. Here, we demonstrate that RRx-001 greatly enhances NO generation from nitrite reduction. RRx-001 is thus the first example of a functional superagonist for nitrite reductase. We hypothesize that physiologically this reaction releases the potentially cytotoxic effector NO selectively in hypoxic tumor regions. It may be that a binary NO-H2O2 trigger is indirectly responsible for the observed tumoricidal activity of RRx-001 since NO is known to inhibit mitochondrial respiration.

A look inside the mechanistic black box: Are red blood cells the critical effectors of RRx-001 cytotoxicity?

The therapeutic potential of epi-immunotherapeutic anticancer agent RRx-001 in cancer has been validated with preclinical and clinical studies, since RRx-001 has successfully completed a phase 1 trial and multiple single-agent and combination phase 2 trials with preliminary evidence of promising activity are underway. Previous experimental work has implicated diverse anticancer mechanisms such as oxidative stress, ATP and NADPH depletion, anti-angiogenesis and epigenetic modulation in the overall antitumor effect of RRx-001. The hypothesis of this study was that the RRx-001 red blood cells are the essential and de facto intermediaries responsible for the reprograming of tumor behavior via transfer of their intracellular and membrane contents. To test this hypothesis, and thereby resolve the "black box" incompleteness in the continuity of the mechanism, the fate of red blood cells incubated with RRx-001 was explored in vitro and in vivo both in healthy animals and in tumor-bearing mice. The collective results establish that RRx-001-derivatized red blood cells are the critical "missing links" to explain the specificity and anticancer activity of RRx-001, including its immunomodulatory effects on tumor-associated macrophages. These experimental results delineate a novel erythrocyte-based mechanism without precedent in the annals of oncology and open the door to rational combination strategies with RRx-001 both in cancer therapy and beyond, particularly in disease states that affect red blood cell and vascular function such as malaria, leishmaniasis, sickle-cell disease and hemorrhagic shock.

A novel hypoxia-selective epigenetic agent RRx-001 triggers apoptosis and overcomes drug resistance in multiple myeloma cells

The hypoxic bone-marrow (BM) microenvironment confers growth/survival and drug-resistance in multiple myeloma (MM) cells. Novel therapies targeting the MM cell in its hypoxic-BM milieu may overcome drug resistance. Recent studies led to the development of a novel molecule RRx-001 with hypoxia-selective epigenetic and Nitric Oxide-donating properties. Here we demonstrate that RRx-001 decreases the viability of MM cell lines and primary patient cells, as well as overcomes drug-resistance. RRx-001 inhibits MM cell growth in the presence of BM stromal cells. RRx-001 induced apoptosis is associated with: 1) activation of caspases; 2) release of ROS and nitrogen-species; 3) induction of DNA damage via ATM/γ-H2AX; and 4) decrease in DNA methytransferase (DNMT) and global methylation. RNA interference study shows a predominant role of DNMT1 in MM cell survival versus DNMT3a or DNMT3b. Deubiquitylating enzyme USP7 stimulates DNMT1 activity; and conversely, USP7-siRNA reduced DNMT1 activity and decreased MM cell viability. RRx-001 plus USP7 inhibitor P5091 triggered synergistic anti-MM activity. MM xenograft studies show that RRx-001 is well tolerated, inhibits tumor growth, and enhances survival. Combining RRx-001 with pomalidomide, bortezomib or SAHA induces synergistic anti-MM activity. Our results provide the rationale for translation of RRx-001, either alone or in combination, to clinical evaluation in MM.

Whole Brain Radiotherapy and RRx-001: Two Partial Responses in Radioresistant Melanoma Brain Metastases from a Phase I/II Clinical Trial: A TITE-CRM Phase I/II Clinical Trial

BACKGROUND: Kim et al. report two patients with melanoma metastases to the brain that responded to treatment with RRx-001 and whole brain radiotherapy (WBRT) without neurologic or systemic toxicity in the context of a phase I/II clinical trial. RRx-001 is an reactive oxygen and reactive nitrogen species (ROS/RNS)-dependent systemically nontoxic hypoxic cell radiosensitizer with vascular normalizing properties under investigation in patients with various solid tumors including those with brain metastases. SIGNIFICANCE: Metastatic melanoma to the brain is historically associated with poor outcomes and a median survival of 4 to 5 months. WBRT is a mainstay of treatment for patients with multiple brain metastases, but no significant therapeutic advances for these patients have been described in the literature. To date, candidate radiosensitizing agents have failed to demonstrate a survival benefit in patients with brain metastases, and in particular, no agent has demonstrated improved outcome in patients with metastatic melanoma. Kim et al. report two patients with melanoma metastases to the brain that responded to treatment with novel radiosensitizing agent RRx-001 and WBRT without neurologic or systemic toxicity in the context of a phase I/II clinical trial.

RRx-001, A novel dinitroazetidine radiosensitizer

The ‘holy grail’ in radiation oncology is to improve the outcome of radiation therapy (RT) with a radiosensitizer—a systemic chemical/biochemical agent that additively or synergistically sensitizes tumor cells to radiation in the absence of significant toxicity. Similar to the oxygen effect, in which DNA bases modified by reactive oxygen species prevent repair of the cellular radiation damage, these compounds in general magnify free radical formation, leading to the permanent “fixation” of the resultant chemical change in the DNA structure. The purpose of this review is to present the origin story of the radiosensitizer, RRx-001, which emerged from the aerospace industry. The activity of RRx-001 as a chemosensitizer in multiple tumor types and disease states including malaria, hemorrhagic shock and sickle cell anemia, are the subject of future reviews.

Nrf2 activity as a potential biomarker for the pan-epigenetic anticancer agent, RRx-001

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulatory transcription factor that plays an important role in the antioxidant response pathway against anticancer drug-induced cytotoxic effects. RRx-001 is a new anticancer agent that generates reactive oxygen and nitrogen species, and leads to epigenetic alterations in cancer cells. Here we report the RRx-001 mediated nuclear translocation of Nrf2 and the activation of expression of its downstream enzymes HO-1 and NQO1 in tumor cells. Inhibition of intrinsic Nrf2 expression by Nrf2-specific siRNA increased cell sensitivity to RRx-001. Molecular imaging of tumor cells co-expressing pARE-Firefly luciferase and pCMV-Renilla luciferase-mRFP in vitro and in vivo in mice revealed that RRx-001 significantly increased ARE-FLUC signal in cells in a dose- and time-dependent manner, suggesting that RRx-001 is an effective activator of the Nrf2-ARE signaling pathway. The pre-treatment level of ARE-FLUC signal in cells, reflecting basal activity of Nrf2, negatively correlated with the tumor response to RRx-001. The results support the concept that RRx-001 activates Nrf2-ARE antioxidant signaling pathways in tumor cells. Hence measurement of Nrf2-mediated activation of downstream target genes through ARE signaling may constitute a useful molecular biomarker for the early prediction of response to RRx-001 treatment, and thereby guide therapeutic decision-making.

Safety and activity of RRx-001 in patients with advanced cancer: a first-in-human, open-label, dose-escalation phase 1 study

BACKGROUND

Epigenetic alterations have been strongly associated with tumour formation and resistance to chemotherapeutic drugs, and epigenetic modifications are an attractive target in cancer research. RRx-001 is activated by hypoxia and induces the generation of reactive oxygen and nitrogen species that can epigenetically modulate DNA methylation, histone deacetylation, and lysine demethylation. The aim of this phase 1 study was to assess the safety, tolerability, and pharmacokinetics of RRx-001.

METHODS

In this open-label, dose-escalation, phase 1 study, we recruited adult patients (aged >18 years) with histologically or cytologically confirmed diagnosis of advanced, malignant, incurable solid tumours from University of California at San Diego, CA, USA, and Sarah Cannon Research Institute, Nashville, TN, USA. Key eligibility criteria included evaluable disease, Eastern Cooperative Group performance status of 2 or less, an estimated life expectancy of at least 12 weeks, adequate laboratory parameters, discontinuation of all previous antineoplastic therapies at least 6 weeks before intervention, and no residual side-effects from previous therapies. Patients were assigned to receive intravenous infusions of RRx-001 at increasing doses (10 mg/m(2), 16·7 mg/m(2), 24·6 mg/m(2), 33 mg/m(2), 55 mg/m(2), and 83 mg/m(2)) either once or twice-weekly for at least 4 weeks, with at least three patients per dose cohort and allowing a 2-week observation period before dose escalation. Samples for safety and pharmacokinetics analysis, including standard chemistry and haematological panels, were taken on each treatment day. The primary objective was to assess safety, tolerability, and dose-limiting toxic effects of RRx-001, to determine single-dose pharmacokinetics, and to identify a recommended dose for phase 2 trials. All analyses were done per protocol. Accrual is complete and follow-up is still on-going. This trial is registered with ClinicalTrials.gov, number NCT01359982.

FINDINGS

Between Oct 10, 2011, and March 18, 2013, we enrolled 25 patients and treated six patients in the 10 mg/m(2) cohort, three patients in the 16·7 mg/m(2) cohort, three patients in the 24·6 mg/m(2) cohort, four patients in the 33 mg/m(2) cohort, three patients in the 55 mg/m(2), and six patients in the 83 mg/m(2) cohort. Pain at the injection site, mostly grade 1 and grade 2, was the most common adverse event related to treatment, experienced by 21 (84%) patients. Other common drug-related adverse events included arm swelling or oedema (eight [32%] patients), and vein hardening (seven [28%] patients). No dose-limiting toxicities were observed. Time constraints related to management of infusion pain from RRx-001 resulted in a maximally feasible dose of 83 mg/m(2). Of the 21 evaluable patients, one (5%) patient had a partial response, 14 (67%) patients had stable disease, and six (29%) patients had progressive disease; all responses were across a variety of tumour types. Four patients who had received RRx-001 were subsequently rechallenged with a treatment that they had become refractory to; all four responded to the rechallenge.

INTERPRETATION

RRx-001 is a well-tolerated novel compound without clinically significant toxic effects at the tested doses. Preliminary evidence of activity is promising and, on the basis of all findings, a dose of 16·7 mg/m(2) was recommended as the targeted dose for phase 2 trials.

FUNDING

EpicentRx (formerly RadioRx).

NO to cancer: The complex and multifaceted role of nitric oxide and the epigenetic nitric oxide donor, RRx-001

The endogenous mediator of vasodilation, nitric oxide (NO), has been shown to be a potent radiosensitizer. However, the underlying mode of action for its role as a radiosensitizer – while not entirely understood – is believed to arise from increased tumor blood flow, effects on cellular respiration, on cell signaling, and on the production of reactive oxygen and nitrogen species (RONS), that can act as radiosensitizers in their own right. NO activity is surprisingly long-lived and more potent in comparison to oxygen. Reports of the effects of NO with radiation have often been contradictory leading to confusion about the true radiosensitizing nature of NO. Whether increasing or decreasing tumor blood flow, acting as radiosensitizer or radioprotector, the effects of NO have been controversial. Key to understanding the role of NO as a radiosensitizer is to recognize the importance of biological context. With a very short half-life and potent activity, the local effects of NO need to be carefully considered and understood when using NO as a radiosensitizer. The systemic effects of NO donors can cause extensive side effects, and also affect the local tumor microenvironment, both directly and indirectly. To minimize systemic effects and maximize effects on tumors, agents that deliver NO on demand selectively to tumors using hypoxia as a trigger may be of greater interest as radiosensitizers. Herein we discuss the multiple effects of NO and focus on the clinical molecule RRx-001, a hypoxia-activated NO donor currently being investigated as a radiosensitizer in the clinic.

•NO radiosensitizer activity is complex with variable results in clinical and non-clinical studies

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NO radiosensitizes by reaction with DNA radicals, by its metabolites and by impact on the vasculature.

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Understanding the local and context-specific activity of NO is key for radiosensitizer development

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RRx-001 induces NO production under hypoxia with promising radiosensitizing activity.

From METS to malaria: RRx-001, a multi-faceted anticancer agent with activity in cerebral malaria

BACKGROUND

The survival of malaria parasites, under substantial haem-induced oxidative stress in the red blood cells (RBCs) is dependent on the pentose phosphate pathway (PPP). The PPP is the only source of NADPH in the RBC, essential for the production of reduced glutathione (GSH) and for protection from oxidative stress. Glucose-6-phosphate dehydrogenase (G6PD) deficiency, therefore, increases the vulnerability of erythrocytes to oxidative stress. In Plasmodium, G6PD is combined with the second enzyme of the PPP to create a unique bifunctional enzyme, named glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase (G6PD-6PGL). RRx-001 is a novel, systemically non-toxic, epigenetic anticancer agent currently in Phase 2 clinical development for multiple tumour types, with activity mediated through increased nitric oxide (NO) production and PPP inhibition. The inhibition of G6PD and NO overproduction induced by RRx-001 suggested its application in cerebral malaria (CM).

METHODS

Plasmodium berghei ANKA (PbA) infection in C57BL/6 mice is an experimental model of cerebral malaria (ECM) with several similar pathological features to human CM. This study uses intravital microscopy methods with a closed cranial window model to quantify cerebral haemodynamic changes and leukocyte adhesion to endothelial cells in ECM.

RESULTS

RRx-001 had both single agent anti-parasitic activity and significantly increased the efficacy of artemether. In addition, RRx-001 preserved cerebral perfusion and reduced inflammation alone or combined with artemether. RRx-001's effects were associated with inhibition of PPP (G6PD and G6PD-6PGL) and by improvements in microcirculatory flow, which may be related to the NO donating properties of RRx-001.

CONCLUSION

The results indicate that RRx-001 could be used to potentiate the anti-malarial action of artemisinin, particularly on resistant strains, and to prevent infection.

Metabolic disposition of the anti-cancer agent [(14)C]laromustine in male rats

1. Laromustine (VNP40101M, also known as Cloretazine) is a novel sulfonylhydrazine alkylating (anticancer) agent. This article describes the use of quantitative whole-body autoradiography (QWBA) and mass balance to study the tissue distribution, the excretion mass balance and pharmacokinetics after intravenous administration of [(14)C]VNP40101M to rats. A single 10 mg/kg IV bolus dose of [(14)C]VNP40101M was given to rats. 2. The recovery of radioactivity from the Group 1 animals over a 7-day period was an average of 92.1% of the administered dose, which was accounted for in the excreta and carcass. Most of the radioactivity was eliminated within 48 h via urine (48%), with less excreted in feces (5%) and expired air accounted for (11%). The plasma half-life of [(14)C]laromustine was approximately 62 min and the peak plasma concentration (Cmax) averaged 8.3 μg/mL. 3. The QWBA study indicated that the drug-derived radioactivity was widely distributed to tissues through 7 days post-dose after a single 10 mg/kg IV bolus dose of [(14)C]VNP40101M to male pigmented Long-Evans rats. The maximum concentrations were observed at 0.5 or 1 h post-dose for majority tissues (28 of 42). The highest concentrations of radioactivity were found in the small intestine contents at 0.5 h (112.137 µg equiv/g), urinary bladder contents at 3 h (89.636 µg equiv/g) and probably reflect excretion of drug and metabolites. The highest concentrations in specific organs were found in the renal cortex at 1 h (28.582 µg equiv/g), small intestine at 3 h (16.946 µg equiv/g), Harderian gland at 3 h (12.332 µg equiv/g) and pancreas at 3 h (12.635 µg equiv/g). Concentrations in the cerebrum (1.978 µg equiv/g), cerebellum (2.109 µg equiv/g), medulla (1.797 µg equiv/g) and spinal cord (1.510 µg equiv/g) were maximal at 0.5 h post-dose and persisted for 7 days. 4. The predicted total body and target organ exposures for humans given a single 100 µCi IV dose of [(14)C]VNP40101M were well within the medical guidelines for maximum radioactivity exposures in human subjects.

Site of reactivity models predict molecular reactivity of diverse chemicals with glutathione

Drug toxicity is often caused by electrophilic reactive metabolites that covalently bind to proteins. Consequently, the quantitative strength of a molecule's reactivity with glutathione (GSH) is a frequently used indicator of its toxicity. Through cysteine, GSH (and proteins) scavenges reactive molecules to form conjugates in the body. GSH conjugates to specific atoms in reactive molecules: their sites of reactivity. The value of knowing a molecule's sites of reactivity is unexplored in the literature. This study tests the value of site of reactivity data that identifies the atoms within 1213 reactive molecules that conjugate to GSH and builds models to predict molecular reactivity with glutathione. An algorithm originally written to model sites of cytochrome P450 metabolism (called XenoSite) finds clear patterns in molecular structure that identify sites of reactivity within reactive molecules with 90.8% accuracy and separate reactive and unreactive molecules with 80.6% accuracy. Furthermore, the model output strongly correlates with quantitative GSH reactivity data in chemically diverse, external data sets. Site of reactivity data is nearly unstudied in the literature prior to our efforts, yet it contains a strong signal for reactivity that can be utilized to more accurately predict molecule reactivity and, eventually, toxicity.

Impact of hemoglobin nitrite to nitric oxide reductase on blood transfusion for resuscitation from hemorrhagic shock

Background:

Transfusion of blood remains the gold standard for fluid resuscitation from hemorrhagic shock. Hemoglobin (Hb) within the red blood cell transports oxygen and modulates nitric oxide (NO) through NO scavenging and nitrite reductase.

Aims:

This study was designed to examine the effects of incorporating a novel NO modulator, RRx-001, on systemic and microvascular hemodynamic response after blood transfusion for resuscitation from hemorrhagic shock in a hamster window chamber model. In addition, to RRx-001 the role of low dose of nitrite (1 × 10⁻⁹ moles per animal) supplementation after resuscitation was studied.

Materials and Methods:

Severe hemorrhage was induced by arterial controlled bleeding of 50% of the blood volume (BV) and the hypovolemic state was maintained for 1 h. The animals received volume resuscitation by an infusion of 25% of BV using fresh blood alone or with added nitrite, or fresh blood treated with RRx-001 (140 mg/kg) or RRx-001 (140 mg/kg) with added nitrite. Systemic and microvascular hemodynamics were followed at baseline and at different time points during the entire study. Tissue apoptosis and necrosis were measured 8 h after resuscitation to correlate hemodynamic changes with tissue viability.

Results:

Compared to resuscitation with blood alone, blood treated with RRx-001 decreased vascular resistance, increased blood flow and functional capillary density immediately after resuscitation and preserved tissue viability. Furthermore, in RRx-001 treated animals, both mean arterial pressure (MAP) and met Hb were maintained within normal levels after resuscitation (MAP >90 mmHg and metHb <2%). The addition of nitrite to RRx-001 did not significantly improve the effects of RRx-001, as it increased methemoglobinemia and lower MAP.

Conclusion:

RRx-001 alone enhanced perfusion and reduced tissue damage as compared to blood; it may serve as an adjunct therapy to the current gold standard treatment for resuscitation from hemorrhagic shock.

Development of methods for the bioanalysis of RRx-001 and metabolites

Background: Bioanalytical methods were required to study the novel anticancer drug, RRx-001 preclinically and for clinical pharmacokinetic analysis; however, RRx-001 quickly and completely disappeared on intravenous administration in preclinical species. Results: Quantification of RRx-001 directly or by derivatization was unsuccessful. On exposure to whole blood, RRx-001 formed the glutathione (GSH) adduct very rapidly, suggesting this metabolite as the bioanalyte. However, rapid enzymatic degradation in the blood matrix of RRx-001-GSH posed significant technical problems. Herein, we describe a novel and broadly applicable solution to stabilize GSH conjugates in blood samples by inhibiting the degrading enzyme. Liquid chromatography–tandem mass spectrometry methods for analysis of RRx-001-GSH in rat, dog and human plasma were developed and successfully validated to good laboratory practice standards. Conclusion: Extensive breakdown of RRx-001-GSH was effectively stopped by addition of the enzyme inhibitor, acivicin. The developed liquid chromatography–tandem mass spectrometry assay for RRx-001-GSH was validated for use in preclinical toxicology studies and the Phase I first-in-human clinical trial.

The implications of hyponitroxia in cancer

Tumors are spatially heterogeneous, with regions of relative hypoxia and normoxia. The tumor microenvironment is an important determinant of both tumor growth and response to a variety of cytotoxic and targeted therapies. In the tumor microenvironment, reactive oxygen species and nitric oxide (NO) are important mediators of the level of expression of many transcription factors and signaling cascades that affect tumor growth and responses to therapy. The primary objective of this review is to explore and discuss the seemingly dichotomous actions of NO in cancer biology as both a tumor promoter and suppressor with an emphasis on understanding the role of persistently low NO concentrations or hyponitroxia as a key mediator in tumor progression. This review will also discuss the potential role of hyponitroxia as a novel therapeutic target to treat cancer and outline an approach that provides new opportunities for pharmacological intervention.

Two Case Reports of Resensitization to Previous Chemotherapy with the Novel Hypoxia-Activated Hypomethylating Anticancer Agent RRx-001 in Metastatic Colorectal Cancer Patients

The development of chemoresistance is a persistent problem during the treatment of cancer. Although reversion or modification of acquired chemoresistance has been previously observed, no systematic exploration has been undertaken. Here, we report a case study of 2 male patients, 62 and 66 years old, both with histologically proven, radiologically progressing, extensively pretreated, metastatic and refractory (≥2 conventional regimens and drug therapy) colorectal adenocarcinoma that was previously treated with FOLFIRI. The patients were resensitized to FOLFIRI after exposure to RRx-001 in the context of a phase-1 study. RRx-001 is a novel, hypomethylating and free-radical-inducing anticancer agent that activates nitrite reduction to NO under hypoxia and has an impact on epigenetic pathways. The repression of DNA methyltransferase 1 by RRx-001 may lead to demethylation and reexpression of silenced tumor suppressor genes, leading to resensitization. These examples provide insight into a nascent strategy to improve the prognosis in heavily pretreated cancer patients and suggest routes for further exploration.

Real time dynamic imaging and current targeted therapies in the war on cancer: a new paradigm

In biology, as every science student is made to learn, ontology recapitulates phylogeny. In medicine, however, oncology recapitulates polemology, the science of warfare: The medical establishment is transitioning from highly toxic poisons that kill rapidly dividing normal and malignant cells with little specificity to tailored therapies that target the tumors with the lethality of the therapeutic warhead. From the advent of the information age with the incorporation of high-tech intelligence, reconnaissance, and surveillance has resulted in "data fusion" where a wide range of information collected in near real-time can be used to redesign most of the treatment strategies currently used in the clinic. The medical community has begun to transition from the 'black box' of tumor therapy based solely on the clinical response to the 'glass box' of dynamic imaging designed to bring transparency to the clinical battlefield during treatment, thereby informing the therapeutic decision to 'retreat or repeat'. The tumor microenvironment is dynamic, constantly changing in response to therapeutic intervention, and therefore the therapeutic assessment must map to this variable and ever-changing landscape with dynamic and non-static imaging capabilities. The path to personalized medicine will require incorporation and integration of dynamic imaging at the bedside into clinical practice for real-time, interactive assessment of response to targeted therapies. The application of advanced real time imaging techniques along with current molecularly targeted anticancer therapies which alter cellular homeostasis and microenvironment can enhance therapeutic interventions in cancer patients and further improve the current status in clinical management of patients with advanced cancers.