Riminophenazine compounds: pharmacology and anti-neoplastic potential

Investigation of Clofazimine Resistance and Genetic Mutations in Drug-Resistant Mycobacterium tuberculosis Isolates

Recently, as clofazimine (CFZ) showed a good therapeutic effect in treating multi-drug-resistant tuberculosis (MDR-TB), the anti-tuberculosis activity and resistance were re-focused. Here, we investigated the CFZ resistance and genetic mutations of drug-resistant Mycobacterium tuberculosis (DR-Mtb) isolates to improve the diagnosis and treatment of drug-resistant TB patients. The minimal inhibitory concentration (MIC) of CFZ was examined by resazurin microtiter assay (REMA) with two reference strains and 122 clinical isolates from Korea. The cause of CFZ resistance was investigated in relation to the therapeutic history of patients. Mutations of Rv0678, Rv1979c and pepQ of CFZ resistant isolates were analyzed by PCR and DNA sequencing. The rate of CFZ resistance with MIC > 1 mg/L was 4.1% in drug-resistant Mtb isolates. The cause of CFZ resistance was not related to treatment with CFZ or bedaquiline. A CFZ susceptibility test should be conducted regardless of dugs use history. The four novel mutation sites were identified in the Rv0678 and pepQ genes related to CFZ resistance in this study.

Riminophenazine Derivatives as Potential Antituberculosis Agents: Synthesis, Biological, and Electrochemical Evaluations

A series of novel riminophenazine derivatives, having ionizable alkyl substituents at N-5 and a variety of substituents on the C-3 imino nitrogen, at C-8 and on the pendant aryl group, have been designed and synthesized. Preliminary investigations into the relationship between lipophilicity, redox potential, and antimycobacterial activity were conducted, using the in vitro activity against Mycobacterium tuberculosis H₃₇Rv, mammalian cytotoxicity, and the redox potential of the compounds determined by cyclic voltammetry as measures. Results revealed an activity “cliff” associated with C-8 substitution (10l and 10m) that, along with defined redox activity, point to a new class of riminophenazines as potential anti-tuberculosis agents having reasonable activity (MIC₉₉ ~1 µM).

Realizing the Clinical Potential of Immunogenic Cell Death in Cancer Chemotherapy and Radiotherapy

Immunogenic cell death (ICD), which is triggered by exposure of tumor cells to a limited range of anticancer drugs, radiotherapy, and photodynamic therapy, represents a recent innovation in the revitalized and burgeoning field of oncoimmunnotherapy. ICD results in the cellular redistribution and extracellular release of damage-associated molecular patterns (DAMPs), which have the potential to activate and restore tumor-targeted immune responses. Although a convincing body of evidence exists with respect to the antitumor efficacy of ICD in various experimental systems, especially murine models of experimental anticancer immunotherapy, evidence for the existence of ICD in the clinical setting is less compelling. Following overviews of hallmark developments, which have sparked the revival of interest in the field of oncoimmunotherapy, types of tumor cell death and the various DAMPs most prominently involved in the activation of antitumor immune responses, the remainder of this review is focused on strategies which may potentiate ICD in the clinical setting. These include identification of tumor- and host-related factors predictive of the efficacy of ICD, the clinical utility of combinatorial immunotherapeutic strategies, novel small molecule inducers of ICD, novel and repurposed small molecule immunostimulants, as well as the critical requirement for validated biomarkers in predicting the efficacy of ICD.

Towards the first targeted therapy for triple-negative breast cancer: Repositioning of clofazimine as a chemotherapy-compatible selective Wnt pathway inhibitor

Wnt signaling is overactivated in triple-negative breast cancer (TNBC) and several other cancers, and its suppression emerges as an effective anticancer treatment. However, no drugs targeting the Wnt pathway exist on the market nor in advanced clinical trials. Here we provide a comprehensive body of preclinical evidence that an anti-leprotic drug clofazimine is effective against TNBC. Clofazimine specifically inhibits canonical Wnt signaling in a panel of TNBC cells in vitro. In several mouse xenograft models of TNBC, clofazimine efficiently suppresses tumor growth, correlating with in vivo inhibition of the Wnt pathway in the tumors. Clofazimine is well compatible with doxorubicin, exerting additive effects on tumor growth suppression, producing no adverse effects. Its excellent and well-characterized pharmacokinetics profile, lack of serious adverse effects at moderate (yet therapeutically effective) doses, its combinability with cytotoxic therapeutics, and the novel mechanistic mode of action make clofazimine a prime candidate for the repositioning clinical trials. Our work may bring forward the anti-Wnt targeted therapy, desperately needed for thousands of patients currently lacking targeted treatments.

Clofazimine encapsulation in nanoporous silica particles for the oral treatment of antibiotic-resistant Mycobacterium tuberculosis infections

Aim: First extensive reformulation of clofazimine (CLZ) in nanoporous silica particles (NSPs) for tackling antibiotic-resistant tuberculosis (TB) infections. Materials & methods: Solid-state characterization of several CLZ-encapsulated NSP formulations was followed by in vitro drug solubility, Caco-2 intestinal cells drug permeability and TB antibacterial activity. Results: NSPs stabilize the amorphous state of CLZ (shelf stability >6 months) and dramatically increase the drug solubility in simulated gastric fluid (up to 20-fold) with different dissolution kinetics depending on the NSPs used. CLZ encapsulation in NSP substantially enhances the permeation through model intestinal cell layer, achieving effective antimicrobial concentrations in TB-infected macrophages. Conclusion: Promising results toward refurbishment of an approved marketed drug for a different indication suitable for oral anti-TB formulation.

In vitro investigation of clofazimine analogues for antiplasmodial, cytotoxic and pro-oxidative activities

BACKGROUND

Tetramethyl-piperidine-substituted, B4119 and B4158 have been shown to exhibit antiplasmodial activity.

OBJECTIVES

The in vitro antiplasmodial, cytotoxic and oxidative activities of clofazimine and its analogues, all TMP (tetramethylpiperidyl)-substituted phenazines except B669, were evaluated in this study.

METHODS

The antiplasmodial activity of the compounds against RB-1 and pfUP10 laboratory strains of Plasmodium falciparum was investigated by flow cytometry. The cytotoxic activity against HeLa cells and oxidative activity were studied employing colorimetric and cytochrome C reduction assays respectively.

RESULTS

The riminophenazine agents exhibited antiplasmodial action of varying degrees: B669, B4100 and B4103 showed the best activity while B4121 and B4169 exhibited significant activity at 2µg/ml. Clofazimine had no antiplasmodial activity. The compounds B4100, B4103, B4121 and B4169 exhibited significant cytotoxic activity against HeLa cells at concentrations of 0.5µg/ml and above while B669 was active at 2µg/ml. Clofazimine and B669 tested at a concentration of 0.5µg/ml caused enhancement (p ≤ 0.05) of neutrophil superoxide production when compared to the FMLP control while all the other TMP-derivatives had no effect (p ≥ 0.05).

CONCLUSION

Tetramethylpiperidyl-subsituted phenazines may potentially be useful antimalarial/antitumor agents with no pro-oxidative properties. In vivo studies on the agents relative to these properties are recommended.

Anti-cancer effect of clofazimine as a single agent and in combination with cisplatin on U266 multiple myeloma cell line

Multiple Myeloma (MM) is a malignant neoplasm of bone marrow plasma B cells with high morbidity. Clofazimine (CLF) is an FDA-approved leprostatic, anti-tuberculosis, and anti-inflammatory drug that was previously shown to have growth suppression effect on various cancer types such as hepatocellular, lung, cervix, esophageal, colon, and breast cancer as well as melanoma, neuroblastoma, and leukemia. The objective of this study was to evaluate the anticancer effect and mechanism of CLF on U266 MM cell line. CLF (10μM, 24h) treatment resulted up to 72% growth suppression on a panel of hematological cell lines. Dose-response study conducted on U266 MM cell line revealed an IC₅₀ value of 9.8±0.7μM. CLF also showed a synergistic inhibition effect in combination with cisplatin. In mechanistic assays, CLF treatment caused mitochondrial membrane depolarization, change in cell membrane asymmetry and increase in caspase-3 activity; indicating to an intrinsic apoptosis mechanism. This study provides new evidence for the anticancer effect of CLF on U266 cell line. Further in vivo and clinical studies are warranted to evaluate its therapeutic potential for MM treatment.

Mechanisms of action and therapeutic efficacies of the lipophilic antimycobacterial agents clofazimine and bedaquiline

Drug-resistant (DR)-TB is the major challenge confronting the global TB control programme, necessitating treatment with second-line anti-TB drugs, often with limited therapeutic efficacy. This scenario has resulted in the inclusion of Group 5 antibiotics in various therapeutic regimens, two of which promise to impact significantly on the outcome of the therapy of DR-TB. These are the 're-purposed' riminophenazine, clofazimine, and the recently approved diarylquinoline, bedaquiline. Although they differ structurally, both of these lipophilic agents possess cationic amphiphilic properties that enable them to target and inactivate essential ion transporters in the outer membrane of Mycobacterium tuberculosis. In the case of bedaquiline, the primary target is the key respiratory chain enzyme F₁/F₀-ATPase, whereas clofazimine is less selective, apparently inhibiting several targets, which may underpin the extremely low level of resistance to this agent. This review is focused on similarities and differences between clofazimine and bedaquiline, specifically in respect of molecular mechanisms of antimycobacterial action, targeting of quiescent and metabolically active organisms, therapeutic efficacy in the clinical setting of DR-TB, resistance mechanisms, pharmacodynamics, pharmacokinetics and adverse events.

A far-red fluorescent probe for flow cytometry and image-based functional studies of xenobiotic sequestering macrophages

Clofazimine (CFZ) is an optically active, red-colored chemotherapeutic agent that is FDA approved for the treatment of leprosy and is on the World Health Organization's list of essential medications. Interestingly, CFZ massively accumulates in macrophages where it forms crystal-like drug inclusions (CLDIs) after oral administration of the drug in animals and humans. The analysis of the fluorescence spectra of CLDIs formed by resident tissue macrophages revealed that CFZ, when accumulated as CLDIs, undergoes a red shift in fluorescence excitation (from Ex: 540-570 to 560-600 nm) and emission (Em: 560-580 to 640-700 nm) signal relative to the soluble and free-base crystal forms of CFZ. Using epifluorescence microscopy, CLDI(+) cells could be identified, relative to CLDI(-) cells, based on a >3-fold increment in mean fluorescence signal at excitation 640 nm and emission at 670 nm. Similarly, CLDI(+) cells could be identified by flow cytometry, based on a >100-fold increment in mean fluorescence signal using excitation lasers at 640 nm and emission detectors >600 nm. CLDI's fluorescence excitation and emission was orthogonal to that of cell viability dyes such as propidium iodide and 4,6-diamidino-2-phenylindole dihydrochloride (DAPI), cellular staining dyes such as Hoechst 33342 (nucleus) and FM 1-43 (plasma membrane), as well as many other fluorescently tagged antibodies used for immunophenotyping analyses. In vivo, >85% of CLDI(+) cells in the peritoneal exudate were F4/80(+) macrophages and >97% of CLDI(+) cells in the alveolar exudate were CD11c(+). Most importantly, the viability of cells was minimally affected by the presence of CLDIs. Accordingly, these results establish that CFZ fluorescence in CLDIs is suitable for quantitative flow cytometric phenotyping analysis and functional studies of xenobiotic sequestering macrophages.

Anticancer efficacy and toxicokinetics of a novel paclitaxel-clofazimine nanoparticulate co-formulation

Contemporary chemotherapy is limited by disseminated, resistant cancer. Targeting nanoparticulate drug delivery systems that encapsulate synergistic drug combinations are a rational means to increase the therapeutic index of chemotherapeutics. A lipopolymeric micelle co-encapsulating an in vitro optimized, synergistic fixed-ratio combination of paclitaxel (PTX) and clofazimine (B663) has been developed and called Riminocelles™. The present pre-clinical study investigated the acute toxicity, systemic exposure, repeat dose toxicity and efficacy of Riminocelles in parallel to Taxol® at an equivalent PTX dose of 10 mg/kg. Daily and weekly dosing schedules were evaluated against Pgp-expressing human colon adenocarcinoma (HCT-15) xenografts implanted subcutaneously in athymic mice. Riminocelles produced statistically significant (p <  .05) tumor growth delays of 3.2 and 2.7 days for the respective schedules in contrast to Taxol delaying growth by 0.5 and 0.6 days. Using the control tumor doubling time of 4.2 days, tumor-cell-kill values of 0.23 for Riminocelles and 0.04 for Taxol following daily schedules were calculated. A significant weight loss of 5.7% after 14 days (p < 0.05) relative to the control group (n = 8) was observed for the daily Taxol group whereas Riminocelles did not incur significant weight loss neither were blood markers of toxicity elevated after acute administration (n = 3). The safety and efficacy of Riminocelles is statistically superior to Taxol. However, passive tumor targeting was not achieved and the tumor burden progressed quickly. Prior to further animal studies, the in vivo thermodynamic instability of the simple lipopolymeric micellular delivery system requires improvement so as to maintain and selectively deliver the fixed-ratio drug combination.

Comparative study of the effects of antituberculosis drugs and antiretroviral drugs on cytochrome P450 3A4 and P-glycoprotein

Predicting drug-drug interactions (DDIs) related to cytochrome P450 (CYP), such as CYP3A4 and one of the major drug transporters, P-glycoprotein (P-gp), is crucial in the development of future chemotherapeutic regimens to treat tuberculosis (TB) and TB/AIDS coinfection cases. We evaluated the effects of 30 anti-TB drugs, novel candidates, macrolides, and representative antiretroviral drugs on human CYP3A4 activity using a commercially available screening kit for CYP3A4 inhibitors and a human hepatocyte, HepaRG. Moreover, in order to estimate the interactions of these drugs with human P-gp, screening for substrates was performed. For some substrates, P-gp inhibition tests were carried out using P-gp-expressing MDCK cells. As a result, almost all the compounds showed the expected effects on human CYP3A4 both in the in vitro screening and in HepaRG cells. Importantly, the unproven mechanisms of DDIs caused by WHO group 5 drugs, thioamides, and p-aminosalicylic acid were elucidated. Intriguingly, clofazimine (CFZ) exhibited weak inductive effects on CYP3A4 at >0.25 μM in HepaRG cells, while an inhibitory effect was observed at 1.69 μM in the in vitro screening, suggesting that CFZ autoinduces CYP3A4 in the human liver. Our method, based on one of the pharmacokinetics parameters in humans, provides more practical information associated with not only DDIs but also with drug metabolism.

Anti-leprosy drug clofazimine inhibits growth of triple-negative breast cancer cells via inhibition of canonical Wnt signaling

Research on existing drugs often discovers novel mechanisms of their action and leads to the expansion of their therapeutic scope and subsequent remarketing. The Wnt signaling pathway is of the immediate therapeutic relevance, as it plays critical roles in cancer development and progression. However, drugs which disrupt this pathway are unavailable despite the high demand. Here we report an attempt to identify antagonists of the Wnt-FZD interaction among the library of the FDA-approved drugs. We performed an in silico screening which brought up several potential antagonists of the ligand-receptor interaction. 14 of these substances were tested using the TopFlash luciferase reporter assay and four of them identified as active and specific inhibitors of the Wnt3a-induced signaling. However, further analysis through GTP-binding and β-catenin stabilization assays showed that the compounds do not target the Wnt-FZD pair, but inhibit the signaling at downstream levels. We further describe the previously unknown inhibitory activity of an anti-leprosy drug clofazimine in the Wnt pathway and provide data demonstrating its efficiency in suppressing growth of Wnt-dependent triple-negative breast cancer cells. These data provide a basis for further investigations of the efficiency of clofazimine in treatment of Wnt-dependent cancers.

Sterilizing activities of novel combinations lacking first- and second-line drugs in a murine model of tuberculosis

Novel oral regimens composed of new drugs with potent activity against Mycobacterium tuberculosis and no cross-resistance with existing agents are needed to shorten and simplify treatment for both drug-susceptible and drug-resistant tuberculosis. As part of a continuing effort to evaluate novel drug combinations for treatment-shortening potential in a murine model, we performed two long-term, relapse-based experiments. In the first experiment, several 3- and 4-drug combinations containing new agents currently in phase 2/3 trials (TMC207 [bedaquiline], PA-824 and PNU-100480 [sutezolid], and/or clofazimine) proved superior to the first-line regimen of rifampin, pyrazinamide, and isoniazid. TMC207 plus PNU-100480 was the most effective drug pair. In the second experiment, in which 3- and 4-drug combinations composed of TMC207 and pyrazinamide plus rifapentine, clofazimine, PNU-100480, or both rifapentine and clofazimine were evaluated, the rank order of drugs improving the sterilizing activity of TMC207 and pyrazinamide was as follows: rifapentine plus clofazimine ≥ clofazimine ≥ rifapentine > PNU-100480. The results revealed potential new building blocks for universally active short-course regimens for drug-resistant tuberculosis. The inclusion of pyrazinamide against susceptible isolates may shorten the duration of treatment further.

Drug repositioning in the treatment of malaria and TB

The emergence and spread of drug resistance in the malaria parasite Plasmodium falciparum as well as multi- and extremely drug-resistant forms of Mycobacterium tuberculosis, the causative agent of TB, could hamper the control of these diseases. For instance, there are indications that the malaria parasite is becoming resistant to artemisinin derivatives, drugs that form the backbone of antimalarial combination therapy. Likewise, Mycobacterium tuberculosis strains that are multidrug-resistant or extremely drug-resistant to first- and second-line drugs have been associated with increased mortality. Thus, more than ever, new antimalarials and anti-TB drugs are needed. One of the strategies to discover new drugs is to reposition or repurpose existing drugs, thus reducing the cost and time of drug development. In this review, we discuss how this concept has been used in the past to discover antimalarial and anti-TB drugs, and summarize strategies that can lead to the discovery and development of new drugs.

Clofazimine: current status and future prospects

Clofazimine, a lipophilic riminophenazine antibiotic, possesses both antimycobacterial and anti-inflammatory activities. However, its efficacy has been demonstrated only in the treatment of leprosy, not in human tuberculosis, despite the fact that this agent is impressively active in vitro against multidrug-resistant strains of Mycobacterium tuberculosis. Recent insights into novel targets and mechanisms of antimicrobial and anti-inflammatory activity coupled with the acquisition of innovative drug delivery technologies have, however, rekindled interest in clofazimine as a potential therapy for multidrug- and extensively multidrug-resistant tuberculosis in particular, as well as several autoimmune diseases. The primary objective of this review is to critically evaluate these recent developments and to assess their potential impact on improving the therapeutic efficacy and versatility of clofazimine.

Regression of Novikoff rat hepatocellular carcinoma following locoregional administration of a novel formulation of clofazimine in lipiodol

We report here that, clofazimine (CFZ) treatment (0.1-10 microM) led to inhibition of in vitro proliferation of hepatocellular carcinoma (HCC) cell lines Hep3-beta, HuH-7, HepG2, SKHEP-1, PLC/PRF-5 and Novikoff. A 24 h exposure of human HuH-7 cells to various concentrations of CFZ dissolved in lipiodol (CFZ-L 10-160 microM), followed by 4 days treatment with medium alone, also led to dose-dependant inhibition of post-treatment cell growth. In vivo, direct intratumoural and intrahepatic arterial injection (IHA) of CFZ-L led to profound inhibition of orthotopic growth of rat Novikoff liver tumours (P < 0.0001 and P < 0.005, respectively). On the contrary, daily oral administration of 150 mg/kg CFZ for 7 days, did not influence the rate of Novikoff tumour growth. Histological examination of rat tumours, revealed the presence of lipiodol in tumour cells, 7 days after treatment with a single IHA dose. Histopathology did not show any abnormality in liver, lung or bowel sections taken from animals 1 week after IHA administration of CFZ-L. Similarly, liver function tests were all normal compared to saline treated animals. Deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labelling revealed the presence of large numbers of apoptotic cells in the CFZ-L treated tumours. Thus, intraarterial administration of the highly lipophilic antiproliferative agent CFZ in lipiodol solution may represent an effective and yet safe strategy for the regional treatment of HCCs.

Tetramethylpiperidine-substituted phenazines inhibit the proliferation of intrinsically multidrug resistant carcinoma cell lines

The effects of nine new tetramethylpiperidine (TMP)-substituted phenazines on the growth of a human esophageal cancer cell line (WHCO3), two human hepatocellular carcinoma cell lines (PLC and HepG2) and three human colon cancer cell lines (CaCo2, COLO 320DM and HT29) were compared to those of clofazimine, B669 and five standard chemotherapeutic agents. The three most active TMP-substituted phenazines against these cell lines were B3962, B4126 and B4125 with mean IC50 values for all the cancer cell lines tested of 0.36, 0.47 and 0.48 microg/ml respectively. B3962 and B4126, but not B4125 were also the most active against a semi-continuous human fibroblast culture (MRC5). The compound with the highest tumor specificity relative to the fibroblast culture, was B4125. Importantly, there was minimal variation in sensitivity of the different cell lines, including a multidrug resistant cell line (COLO 320DM) expressing high levels of P-glycoprotein, to the TMP-substituted phenazines. This was not the case with the standard chemotherapeutic agents. The efficacy of compounds such as B4125 against a broad spectrum of multidrug resistant cancer cell lines, together with their relatively high tumor specificity, suggests that these agents may be useful in the treatment of intrinsically resistant cancers such as colon and liver cancer.