RRx-001, A novel dinitroazetidine radiosensitizer

Development of small molecule drugs targeting immune checkpoints

Immune checkpoint inhibitors (ICIs) are used to relieve and refuel anti-tumor immunity by blocking the interaction, transcription, and translation of co-inhibitory immune checkpoints or degrading co-inhibitory immune checkpoints. Thousands of small molecule drugs or biological materials, especially antibody-based ICIs, are actively being studied and antibodies are currently widely used. Limitations, such as anti-tumor efficacy, poor membrane permeability, and unneglected tolerance issues of antibody-based ICIs, remain evident but are thought to be overcome by small molecule drugs. Recent structural studies have broadened the scope of candidate immune checkpoint molecules, as well as innovative chemical inhibitors. By way of comparison, small molecule drug-based ICIs represent superior oral bioavailability and favorable pharmacokinetic features. Several ongoing clinical trials are exploring the synergetic effect of ICIs and other therapeutic strategies based on multiple ICI functions, including immune regulation, anti-angiogenesis, and cell cycle regulation. In this review we summarized the current progression of small molecule ICIs and the mechanism underlying immune checkpoint proteins, which will lay the foundation for further exploration.

Epigenetic regulation of enhancer of zeste homolog 2 (EZH2) -Yin Yang 1 (YY1) axis in cancer

In accordance with the World Health Organization, cancer is the second leading cause of death in patients. In recent years, the number of cancer patients has been growing, and the occurrence of cancer in people is becoming more common, primarily due to lifestyle factors. Yin Yang 1 (YY1) is a transcription factor that is widespread throughout. It is a zinc finger protein, falling under the GLI-Kruppel class. YY1 is known to regulate transcriptional activation and repression of various genes associated with different cellular processes such as DNA repair, autophagy, cell survival and apoptosis, and cell division. Meanwhile, EZH2 is a histone-lysine N-methyltransferase enzyme encoded by gene 7 in humans. Its main function involves catalyzing the addition of methyl groups to histone H3 at lysine 27 (H3K27me3), and it is involved in regulating CD8 + T cell fate and function. It is a subunit of a Polycomb repressor complex 2 (PRC2). The EZH2 gene encodes for an enzyme that is involved in histone methylation and transcriptional repression. It adds methyl groups to lysine 27 on histone H3 (H3K27me3) with the help of the cofactor S-adenosyl-L-methionine. In addition to its role in epigenetic regulation, EZH2 also acts as a regulator of CD8+ T cell fate and function. EZH2 has been implicated in T Cell Receptor (TCR) signaling via the regulation of actin polymerization. In fact, EZH2 is involved in numerous signaling pathways that lead to tumorigenesis. EZH2 is mutated in cancer and shows overexpression. Due to its mutation and overexpression, the cells that help combat cancer are suppressed and carcinogenicity is promoted. The association of EZH2 and YY1 poses an intriguing mechanism in relation to cancer.

Targeting Transcription Factor YY1 for Cancer Treatment: Current Strategies and Future Directions

Cancer represents a significant and persistent global health burden, with its impact underscored by its prevalence and devastating consequences. Whereas numerous oncogenes could contribute to cancer development, a group of transcription factors (TFs) are overactive in the majority of tumors. Targeting these TFs may also combat the downstream oncogenes activated by the TFs, making them attractive potential targets for effective antitumor therapeutic strategy. One such TF is yin yang 1 (YY1), which plays crucial roles in the development and progression of various tumors. In preclinical studies, YY1 inhibition has shown efficacy in inhibiting tumor growth, promoting apoptosis, and sensitizing tumor cells to chemotherapy. Recent studies have also revealed the potential of combining YY1 inhibition with immunotherapy for enhanced antitumor effects. However, clinical translation of YY1-targeted therapy still faces challenges in drug specificity and delivery. This review provides an overview of YY1 biology, its role in tumor development and progression, as well as the strategies explored for YY1-targeted therapy, with a focus on their clinical implications, including those using small molecule inhibitors, RNA interference, and gene editing techniques. Finally, we discuss the challenges and current limitations of targeting YY1 and the need for further research in this area.

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.

Bi-DTPA, a potential CT-guided radiation sensitizer

The therapeutic effects and application of radiotherapy are restricted to some extent due to low radiosensitivity of tumor tissues and adverse effects by excess dosage. Current radiosensitizers are confronted with problems in clinical translation because of complicated manufacture technique and high cost. In this research, we have synthesized a radiosensitizer with advantages in low cost and mass production, which could be applied to CT imaging and enhanced radiotherapy in breast cancer, namely Bi-DTPA. It not only enhanced tumor CT imaging which resulted in better therapeutic accuracy, but also realized radiotherapy sensitization by producing massive ROS and inhibit tumor proliferation, providing a sound perspective in the clinical translation of the radiosensitizer.

A Review of RRx-001: A Late-Stage Multi-Indication Inhibitor of NLRP3 Activation and Chronic Inflammation

Chronic unresolving inflammation is emerging as a key underlying pathological feature of many if not most diseases ranging from autoimmune conditions to cardiometabolic and neurological disorders. Dysregulated immune and inflammasome activation is thought to be the central driver of unresolving inflammation, which in some ways provides a unified theory of disease pathology and progression. Inflammasomes are a group of large cytosolic protein complexes that, in response to infection- or stress-associated stimuli, oligomerize and assemble to generate a platform for driving inflammation. This occurs through proteolytic activation of caspase-1-mediated inflammatory responses, including cleavage and secretion of the proinflammatory cytokines interleukin (IL)-1β and IL-18, and initiation of pyroptosis, an inflammatory form of cell death. Several inflammasomes have been characterized. The most well-studied is the nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome, so named because the NLRP3 protein in the complex, which is primarily present in immune and inflammatory cells following activation by inflammatory stimuli, belongs to the family of nucleotide-binding and oligomerization domain (Nod) receptor proteins. Several NLRP3 inflammasome inhibitors are in development, all with multi-indication activity. This review discusses the current status, known mechanisms of action, and disease-modifying therapeutic potential of RRx-001, a direct NLRP3 inflammasome inhibitor under investigation in several late-stage anticancer clinical trials, including a phase 3 trial for the treatment of third-line and beyond small cell lung cancer (SCLC), an indication with no treatment, in which RRx-001 is combined with reintroduced chemotherapy from the first line, carboplatin/cisplatin and etoposide (ClinicalTrials.gov Identifier: NCT03699956). Studies from multiple independent groups have now confirmed that RRx-001 is safe and well tolerated in humans. Additionally, emerging evidence in preclinical animal models suggests that RRx-001 could be effective in a wide range of diseases where immune and inflammasome activation drives disease pathology.

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.

Role of nitric oxide in hyper-aggressiveness of tumor cells that survive various anti-cancer therapies

Low level nitric oxide (NO) produced by inducible NO synthase (iNOS) in many malignant tumors is known to play a key role in the survival and proliferation of tumor cells. NO can also induce or augment resistance to anti-tumor treatments such as platinum-based chemotherapy (CT), ionizing radiotherapy (RT), and non-ionizing photodynamic therapy (PDT). In each of these treatments, tumor cells that survive the challenge may exhibit a striking increase in NO-dependent proliferative, migratory, and invasive aggressiveness compared with non-challenged controls. Moreover, NO from cells directly targeted by PDT can often stimulate aggressiveness in non- or poorly targeted bystander cells. Although NO-mediated resistance to many of these therapies is fairly-well recognized by now, the hyper-aggressiveness of surviving cells and bystander counterparts is not. We will focus on these negative aspects in this review, citing examples from the PDT, CT, and RT publications. Increased aggressiveness of cells that escape therapeutic elimination is a concern because it could enhance tumor progression and metastatic dissemination. Pharmacologic approaches for suppressing these negative responses will also be discussed, e.g., administering inhibitors of iNOS activity or iNOS expression as therapeutic adjuvants.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

Small Molecules and Immunotherapy Agents for Enhancing Radiotherapy in Glioblastoma

Glioblastoma (GBM) is an aggressive primary brain tumor that is associated with a poor prognosis and quality of life. The standard of care has changed minimally over the past two decades and currently consists of surgery followed by radiotherapy (RT), concomitant and adjuvant temozolomide, and tumor treating fields (TTF). Factors such as tumor hypoxia and the presence of glioma stem cells contribute to the radioresistant nature of GBM. In this review, we discuss the current treatment modalities, mechanisms of radioresistance, and studies that have evaluated promising radiosensitizers. Specifically, we highlight small molecules and immunotherapy agents that have been studied in conjunction with RT in clinical trials. Recent preclinical studies involving GBM radiosensitizers are also discussed.

RRx-001 Exerts Neuroprotection Against LPS-Induced Microglia Activation and Neuroinflammation Through Disturbing the TLR4 Pathway

Neuroinflammation plays an important role in the pathogenesis of many central nervous system diseases. Here, we investigated the effect of an anti-cancer compound RRx-001 on neuroinflammation and its possible new applications. BV2 cells and primary microglia cells were used to evaluate the role of RRx-001 in LPS-induced microglial activation and inflammatory response in vitro. And, we found that the increase in the synthesis and release of cytokines and the up-regulation of pro-inflammatory factors in LPS-treated microglial cells were significantly reduced by RRx-001 pretreatment. As the most classical inflammatory pathways, NF-κB and MAPK signaling pathways were activated by LPS, but were inhibited by RRx-001. Transcription of NLRP3 was also reduced by RRx-001. In addition, LPS induced oxidative stress by increasing the expression of Nox mediated by transcription factors NF-κB and AP-1, while RRx-001 pretreatment ameliorated Nox-mediated oxidative stress. LPS-induced activation of TAK1, an upstream regulator of NF-κB and MAPK pathways, was significantly inhibited by RRx-001 pretreatment, whereas recruitment of MyD88 to TLR4 was not affected by RRx-001. LPS-primed BV2 condition medium induced injury of primary neurons, and this effect was inhibited by RRx-001. Furthermore, we established a neuroinflammatory mouse model by stereotactic injection of LPS into the substantia nigra pars compacta (SNpc), and RRx-001 dose-dependently reduced LPS-induced microglial activation and loss of TH + neurons in the midbrain. In conclusion, the current study found that RRx-001 suppressed microglia activation and neuroinflammation through targeting TAK1, and may be a candidate for the treatment of neuroinflammation-related brain diseases.

Formulation Comprising Arsenic Trioxide and Dimercaprol Enhances Radiosensitivity of Pancreatic Cancer Xenografts

OBJECTIVE

To investigate the efficacy of a formula comprising arsenic trioxide and dimercaprol (BAL-ATO) as a radiosensitizing agent in model mice with pancreatic cancer xenografts.

METHODS

Female BALB/c nude mice bearing SW1990 human pancreatic cancer xenografts were divided into four treatment arms, including control, radiotherapy (RT), BAL-ATO, and RT + BAL-ATO groups. Survival and tumor volume were analyzed. We also assessed apoptosis in tumor samples by live imaging and detected hypoxia by confocal laser microscope observation. We further investigated the mechanisms of BAL-ATO action in RT by detecting affected proteins by western blot and immunohistochemistry assays.

RESULTS

Median survival was significantly longer in the RT + BAL-ATO group (64.5 days) compared with the control (49.5 days), RT (39 days), and BAL-ATO (48 days) groups (P < 0.001). RT + BAL-ATO inhibited the growth of tumors in mice by 73% compared with the control group, which was significantly higher than the rate of inhibition following RT alone (59%) (P < 0.01). Further analysis showed an improved microenvironment in terms of hypoxia in tumors treated with BAL-ATO alone or RT + BAL-ATO. Expression of signaling molecules associated with pancreatic cancer stem cells, including CD24, CD44, ALDH1A1, Gli-1, and Nestin, was detected in tumors treated with BAL-ATO alone or in combination with RT.

CONCLUSION

These data suggest that BAL-ATO function as a radiosensitizer in mice with pancreatic cancer xenografts, via mechanisms involving hypoxia reduction and inhibition of signaling pathways associated with pancreatic cancer stem cells. BAL-ATO may thus be a promising radiosensitizing agent in patients with pancreatic cancer.

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

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.

Discovery of RRx-001, a Myc and CD47 Downregulating Small Molecule with Tumor Targeted Cytotoxicity and Healthy Tissue Cytoprotective Properties in Clinical Development

After extensive screening of aerospace compounds in an effort to source a novel anticancer agent, RRx-001, a first-in-class dinitroazetidine small molecule, was selected for advancement into preclinical and clinical development. RRx-001 is a minimally toxic small molecule with a distinct chemical structure and mechanism of action. The paradox of RRx-001 is that it mediates both antitumor cytotoxicity and normal tissue protection. The question of exactly how RRx-001 does this, and by means of what mechanism(s), depending on the route of delivery, intravenous or intratumoral, are explored. RRx-001 is currently in phase 2 and 3 clinical trials for the treatment of multiple solid tumor malignancies and as a supportive care drug.

Application of Radiosensitizers in Cancer Radiotherapy

Radiotherapy (RT) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. Although great success has been achieved on radiotherapy, there is still an intractable challenge to enhance radiation damage to tumor tissue and reduce side effects to healthy tissue. Radiosensitizers are chemicals or pharmaceutical agents that can enhance the killing effect on tumor cells by accelerating DNA damage and producing free radicals indirectly. In most cases, radiosensitizers have less effect on normal tissues. In recent years, several strategies have been exploited to develop radiosensitizers that are highly effective and have low toxicity. In this review, we first summarized the applications of radiosensitizers including small molecules, macromolecules, and nanomaterials, especially those that have been used in clinical trials. Second, the development states of radiosensitizers and the possible mechanisms to improve radiosensitizers sensibility are reviewed. Third, the challenges and prospects for clinical translation of radiosensitizers in oncotherapy are presented.

The Role of Metabolic Enzymes in the Regulation of Inflammation

Immune cells undergo dramatic metabolic reprogramming in response to external stimuli. These metabolic pathways, long considered as simple housekeeping functions, are increasingly understood to critically regulate the immune response, determining the activation, differentiation, and downstream effector functions of both lymphoid and myeloid cells. Within the complex metabolic networks associated with immune activation, several enzymes play key roles in regulating inflammation and represent potential therapeutic targets in human disease. In some cases, these enzymes control flux through pathways required to meet specific energetic or metabolic demands of the immune response. In other cases, key enzymes control the concentrations of immunoactive metabolites with direct roles in signaling. Finally, and perhaps most interestingly, several metabolic enzymes have evolved moonlighting functions, with roles in the immune response that are entirely independent of their conventional enzyme activities. Here, we review key metabolic enzymes that critically regulate inflammation, highlighting mechanistic insights and opportunities for clinical intervention.

Radioresistance in Glioblastoma and the Development of Radiosensitizers

Ionizing radiation is a common and effective therapeutic option for the treatment of glioblastoma (GBM). Unfortunately, some GBMs are relatively radioresistant and patients have worse outcomes after radiation treatment. The mechanisms underlying intrinsic radioresistance in GBM has been rigorously investigated over the past several years, but the complex interaction of the cellular molecules and signaling pathways involved in radioresistance remains incompletely defined. A clinically effective radiosensitizer that overcomes radioresistance has yet to be identified. In this review, we discuss the current status of radiation treatment in GBM, including advances in imaging techniques that have facilitated more accurate diagnosis, and the identified mechanisms of GBM radioresistance. In addition, we provide a summary of the candidate GBM radiosensitizers being investigated, including an update of subjects enrolled in clinical trials. Overall, this review highlights the importance of understanding the mechanisms of GBM radioresistance to facilitate the development of effective radiosensitizers.

The epigenetics of brain tumors and its modulation during radiation: A review

The brain tumor is the abnormal growth of heterogeneous cells around the central nervous system and spinal cord. Most clinically prominent brain tumors affecting both adult and pediatric are glioblastoma, medulloblastoma, and ependymoma and they are classified according to their origin of tissue. Chemotherapy, radiotherapy, and surgery are important treatments available to date. However, these treatments fail due to multiple reasons, including chemoresistance and radiation resistance of cancer cells. Thus, there is a need of new therapeutic designs to target cell signaling and molecular events which are responsible for this resistance. Recently epigenetic changes received increased attention because it helps in understanding chromatin-mediated disease mechanism. The epigenetic modification alters chromatin structure that affects the docking site of many drugs which cause chemo-resistance of cancer therapy. This review centers the mechanism of how epigenetic changes affect the transcription repression and activation of various genes including Polycomb gene, V-Myc avian myelocytomatosis viral oncogene (MYCN). This review also put forth the pathway of radiation-induced reactive oxygen species generation and its role in epigenetic changes in the cellular level and its impact on tissue physiology. Additionally, there is a strong relationship between the behavior of an individual and environment-induced epigenetic regulation of gene expression. The review also discusses Transcriptome heterogeneity and role of tumor microenvironment in glioblastoma. Overall, this review emphasis important and novel epigenetic targets that could be of therapeutic benefit, which helps in overcoming the unsolved chromatin alteration in brain cancer.

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.

N-Dihydrogalactochitosan Potentiates the Radiosensitivity of Liver Metastatic Tumor Cells Originated from Murine Breast Tumors

Radiation is a widely used therapeutic method for treating breast cancer. N-dihydrogalactochitosan (GC), a biocompatible immunostimulant, is known to enhance the effects of various treatment modalities in different tumor types. However, whether GC can enhance the radiosensitivity of cancer cells remains to be explored. In this study, triple-negative murine 4T1 breast cancer cells transduced with multi-reporter genes were implanted in immunocompetent Balb/C mice to track, dissect, and identify liver-metastatic 4T1 cells. These cells expressed cancer stem cell (CSC) -related characteristics, including the ability to form spheroids, the expression of the CD44 marker, and the increase of protein stability. We then ex vivo investigated the potential effect of GC on the radiosensitivity of the liver-metastatic 4T1 breast cancer cells and compared the results to those of parental 4T1 cells subjected to the same treatment. The cells were irradiated with increased doses of X-rays with or without GC treatment. Colony formation assays were then performed to determine the survival fractions and radiosensitivity of these cells. We found that GC preferably increased the radiosensitivity of liver-metastatic 4T1 breast cancer cells rather than that of the parental cells. Additionally, the single-cell DNA electrophoresis assay (SCDEA) and γ-H2AX foci assay were performed to assess the level of double-stranded DNA breaks (DSBs). Compared to the parental cells, DNA damage was significantly increased in liver-metastatic 4T1 cells after they were treated with GC plus radiation. Further studies on apoptosis showed that this combination treatment increased the sub-G1 population of cells, but not caspase-3 cleavage, in liver-metastatic breast cancer cells. Taken together, the current data suggest that the synergistic effects of GC and irradiation might be used to enhance the efficacy of radiotherapy in treating metastatic tumors.

Nitric Oxide-Mediated Enhancement and Reversal of Resistance of Anticancer Therapies

In the last decade, immune therapies against human cancers have emerged as a very effective therapeutic strategy in the treatment of various cancers, some of which are resistant to current therapies. Although the clinical responses achieved with many therapeutic strategies were significant in a subset of patients, another subset remained unresponsive initially, or became resistant to further therapies. Hence, there is a need to develop novel approaches to treat those unresponsive patients. Several investigations have been reported to explain the underlying mechanisms of immune resistance, including the anti-proliferative and anti-apoptotic pathways and, in addition, the increased expression of the transcription factor Yin-Yang 1 (YY1) and the programmed death ligand 1 (PD-L1). We have reported that YY1 leads to immune resistance through increasing HIF-1α accumulation and PD-L1 expression. These mechanisms inhibit the ability of the cytotoxic T-lymphocytes to mediate their cytotoxic functions via the inhibitory signal delivered by the PD-L1 on tumor cells to the PD-1 receptor on cytotoxic T-cells. Thus, means to override these resistance mechanisms are needed to sensitize the tumor cells to both cell killing and inhibition of tumor progression. Treatment with nitric oxide (NO) donors has been shown to sensitize many types of tumors to chemotherapy, immunotherapy, and radiotherapy. Treatment of cancer cell lines with NO donors has resulted in the inhibition of cancer cell activities via, in part, the inhibition of YY1 and PD-L1. The NO-mediated inhibition of YY1 was the result of both the inhibition of the upstream NF-κB pathway as well as the S-nitrosylation of YY1, leading to both the downregulation of YY1 expression as well as the inhibition of YY1-DNA binding activity, respectively. Also, treatment with NO donors induced the inhibition of YY1 and resulted in the inhibition of PD-L1 expression. Based on the above findings, we propose that treatment of tumor cells with the combination of NO donors, at optimal noncytotoxic doses, and anti-tumor cytotoxic effector cells or other conventional therapies will result in a synergistic anticancer activity and tumor regression.

Gaseous signaling molecules and their application in resistant cancer treatment: from invisible to visible

Multidrug resistance (MDR) in cancer remains a critical obstacle for efficient chemotherapy. Many MDR reversal agents have been discovered but failed in clinical trials due to severe toxic effects. Gaseous signaling molecules (GSMs), such as oxygen, nitric oxide, hydrogen sulfide and carbon monoxide, play key roles in regulating cell biological function and MDR. Compared with other toxic chemosensitizing agents, GSMs are endogenous and biocompatible molecules with little side effects. Research show that GSM modulators, including pharmaceutical formulations of GSMs (combined with conventional chemotherapeutic drugs) and GSM-donors (small molecules with GSMs releasing property), can overcome or reverse MDR. This review discusses the roles of these four GSMs in modulating MDR, and summarizes GSMs modulators in treating cancers with drug resistance.

Cancer Radiosensitizers

Radiotherapy (RT) is a mainstay treatment for many types of cancer, although it is still a large challenge to enhance radiation damage to tumor tissue and reduce side effects to healthy tissue. Radiosensitizers are promising agents that enhance injury to tumor tissue by accelerating DNA damage and producing free radicals. Several strategies have been exploited to develop highly effective and low-toxicity radiosensitizers. In this review, we highlight recent progress on radiosensitizers, including small molecules, macromolecules, and nanomaterials. First, small molecules are reviewed based on free radicals, pseudosubstrates, and other mechanisms. Second, nanomaterials, such as nanometallic materials, especially gold-based materials that have flexible surface engineering and favorable kinetic properties, have emerged as promising radiosensitizers. Finally, emerging macromolecules have shown significant advantages in RT because these molecules can be combined with biological therapy as well as drug delivery. Further research on the mechanisms of radioresistance and multidisciplinary approaches will accelerate the development of radiosensitizers.

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 protects against cisplatin-induced toxicities

PURPOSE

RRx-001, a minimally toxic tumor-associated macrophage and neutrophil-repolarizing agent, is under investigation in Phase II clinical trials as a sensitizer/resensitizer to cisplatin and carboplatin. On the basis of anecdotal clinical observations of improved platinum tolerability following a priming period with RRx-001 as well as preclinical studies that have previously demonstrated radioprotection of intestinal stem cells and cardioprotection from doxorubicin, the in vivo cytoprotective potential of RRx-001 pretreatment against cisplatin-induced bone marrow suppression and renal toxicity was investigated.

METHODS

BALB/c mice were divided into three groups: (1) no treatment, (2) vehicle and cisplatin only, and (3) RRx-001 and cisplatin. RRx-001 treatment (5 mg/kg every other day for 3 days) was initiated 3 days prior to cisplatin administration. Blood was collected from the femoral vein at different intervals to measure total hemoglobin and leukocyte counts as well as renal functional markers (serum urea, creatinine and creatinine clearance). Metaphase spreads were prepared from whole bone marrow cells as markers of clastogenicity.

RESULTS

RRx-001 pretreatment significantly decreased (P < 0.05) the blood urea nitrogen and creatinine levels. A statistically significant (P < 0.05) reduction in the mean total chromosome aberration frequency per metaphase in the RRx-001 and cisplatin group compared to the cisplatin-only group was observed.

CONCLUSIONS

This study is the first to demonstrate that RRx-001 has nephro-, geno- and myeloprotective effects in vivo. Importantly, RRx-001 did not protect sarcoma-180 solid tumor xenografts against cisplatin-induced cytotoxicity. These results potentially support the use of RRx-001 as a chemoprotector against cisplatin-induced toxicities.

Partial Response in an RRx-001-Primed Patient with Refractory Small-Cell Lung Cancer after a Third Introduction of Platinum Doublets

Small-cell lung cancer (SCLC), initially exquisitely sensitive to first-line cisplatin/etoposide, invariably relapses and acquires a multidrug chemoresistant phenotype that generally renders retreatment with first-line therapy both futile and counterproductive. This report presents the case of a 77-year-old Caucasian male with extensive-stage refractory SCLC who was restarted on platinum doublets as part of a clinical trial called TRIPLE THREAT (NCT02489903) involving pretreatment with the epi-immunotherapeutic agent RRx-001, and who achieved a partial response after only 4 cycles. The patient had received a platinum drug twice before, in 2009 for a diagnosis of non-small-cell lung cancer (squamous cell carcinoma) and in 2015 for SCLC, suggesting that RRx-001 pretreatment may sensitize or resensitize refractory SCLC patients to first-line chemotherapy.