Hetero-Multivalent Targeted Liposomal Drug Delivery to Treat Pseudomonas aeruginosa Infections

Pseudomonas aeruginosa is the leading nosocomial and community-acquired pathogen causing a plethora of acute and chronic infections. The Centers for Disease Control and Prevention has designated multidrug-resistant isolates of P. aeruginosa as a serious threat. A novel delivery vehicle capable of specifically targeting  P. aeruginosa, and encapsulating antimicrobials, may address the challenges associated with these infections. We have developed hetero-multivalent targeted liposomes functionalized with host cell glycans to increase the delivery of antibiotics to the site of infection. Previously, we have demonstrated that compared with monovalent liposomes, these hetero-multivalent liposomes bind with higher affinity to P. aeruginosa. Here, compared with nontargeted liposomes, we have shown that greater numbers of targeted liposomes are found in the circulation, as well as at the site of P. aeruginosa (PAO1) infection in the thighs of CD-1 mice. No significant difference was found in the uptake of targeted, nontargeted, and PEGylated liposomes by J774.A1 macrophages. Ciprofloxacin-loaded liposomes were formulated and characterized for size, encapsulation, loading, and drug release. In vitro antimicrobial efficacy was assessed using CLSI broth microdilution assays and time-kill kinetics. Lastly, PAO1-inoculated mice treated with ciprofloxacin-loaded, hetero-multivalent targeted liposomes survived longer than mice treated with ciprofloxacin-loaded, monovalent targeted, or nontargeted liposomes and free ciprofloxacin. Thus, liposomes functionalized with host cell glycans target P. aeruginosa resulting in increased retention of the liposomes in the circulation, accumulation at the site of infection, and increased survival time in a mouse surgical site infection model. Consequently, this formulation strategy may improve outcomes in patients infected with P. aeruginosa.

Synthesis, characterization, in vitro SAR study, and preliminary in vivo toxicity evaluation of naphthylmethyl substituted bis-imidazolium salts

A series of novel bis-imidazolium salts was synthesized, characterized, and evaluated in vitro against a panel of non-small cell lung cancer (NSCLC) cells. Two imidazolium cores were connected with alkyl chains of varying lengths to develop a structure activity relationship (SAR). Increasing the length of the connecting alkyl chain was shown to correlate to an increase in the anti-proliferative activity. The National Cancer Institute's NCI-60 human tumor cell line screen confirmed this trend. The compound containing a decyl linker chain, 10, was chosen for further in vivo toxicity studies with C578BL/6 mice. The compound was well tolerated by the mice and all of the animals survived and gained weight over the course of the study.

N-Acetyl cysteine abrogates silver-induced reactive oxygen species in human cells without altering silver-based antimicrobial activity

Silver-based antimicrobials are widely used topically to treat infections associated with multi-drug resistant (MDR) pathogens. Expanding this topical use to aerosols to treat lung infections requires understanding and preventing silver toxicity in the respiratory tract. A key mechanism resulting in silver-induced toxicity is the production of reactive oxygen species (ROS). In this study, we have verified ROS generation in silver-treated bronchial epithelial cells prompting evaluation of three antioxidants, N-acetyl cysteine (NAC), ascorbic acid, and melatonin, to identify potential prophylactic agents. Among them, NAC was the only candidate that abrogated the ROS generation in response to silver acetate exposure resulting in the rescue of these cells from silver-associated toxicity. Further, this protective effect directly translated to preservation of metabolic activity, as demonstrated by the normal levels of citric acid cycle metabolites in NAC-pretreated silver acetate-exposed cells. Because the citric acid cycle remained functional, silver-exposed cells pre-incubated with NAC demonstrated significantly higher levels of adenosine triphosphate levels compared with NAC-free controls. Moreover, we found that this prodigious capacity of NAC to rescue silver acetate-exposed cells was due not only to its antioxidant activity, but also to its ability to directly bind silver. Despite binding to silver, NAC did not alter the antimicrobial activity of silver acetate.

Abstract 6366: Novel imidazolium compounds as intravesical therapeutic agents for non-muscle invasive bladder cancer

Introduction: Intravesical therapy has critical role in the treatment of high-risk non-muscle invasive bladder cancer. Due to ongoing shortage of BCG and lack of effective alternatives, there is an urgent need for novel intravesical chemotherapeutic agents. In this study, we investigated novel imidazolium compounds on bladder cancer cell lines to characterize activity and mechanism of action and in a mouse model to assess their efficacy and toxicity as intravesical agents.

Methods: Three different imidazolium compounds (IS23, TPP1 and TCK1) were screened for their activity against six bladder cancer cell lines at various concentrations and different exposure time. The GI50s for each compound were then used to assess induction of apoptosis in vitro and to study mechanism of action. In vivo efficacy and toxicity of these compounds was studied in normal mice. The BBN mouse model was used to assess in vivo efficacy of these compounds, as it recapitulates the histological and genetic characteristics of human bladder tumors. The drinking water of 6 to 8 weeks old mice was supplemented with 0.05% BBN for 12 weeks, then switched to regular drinking water. Mice were randomly assigned into 5 intravesical treatment groups with 50:50 male:female make up in each group: 1) IS23; 2) TPP1; 3) TCK1; 4) Gemcitabine; 5) vehicle. Drugs and vehicle were instilled for four weeks. Each mouse was subjected to excretory computed tomography urogram to assess the filling defects in the bladder before treatment and every two weeks following the treatment. Mice were euthanized if size of filling defect in urograms exceeded 1/3 of the bladder, developed hydronephrosis, or 4 weeks after completion of intravesical treatment, whichever came first.

Results: All imidazolium compounds showed toxicity to bladder cancer cells, TCK1 and TPP1 being the most and least potent respectively. They were also highly effective in killing bladder cancer cells with a 15-min GI90-dose. They briskly induced apoptosis by directly causing Cytochrome C expulsion from isolated mitochondria. Intravesical imidazolium compounds did not cause significant histopathological changes in normal bladder compared to vehicle group, but TPP1 was found to be tumor specific in vivo. TPP1 induced apoptosis in tumor without affecting normal bladder urothelium. In BBN-induced mice, 4/4 IS23-treated mice had filling defects while 8/15, 5/6, 10/11, and 7/8 TPP1-, TCK1-, vehicle-, and gemcitabine-treated mice had filling defects on urograms consistent with tumor. TPP1- and TCK1-treated mice had smaller filling defects compared to vehicle group mice, which was also confirmed histopathologically.

Conclusions: TPP1 has a novel and potent mechanism and is worthy of further study as an intravesical agent for the treatment of high-grade superficial bladder cancer. It appears to work through a mitochondrial-centric mechanism and have cancer-specificity.

Citation Format: Uttam Satyal, Abhishek Srivastava, David J. Weader, Michael L. Stromyer, Marie R. Southerland, Wiley J. Youngs, Philip H. Abbosh. Novel imidazolium compounds as intravesical therapeutic agents for non-muscle invasive bladder cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6366.

Synthesis, characterization, and biological activity of a triphenylphosphonium-containing imidazolium salt against select bladder cancer cell lines

Imidazolium salts have shown great promise as anticancer materials. A new imidazolium salt (TPP1), with a triphenylphosphonium substituent, has been synthesized and evaluated for in vitro and in vivo cytotoxicity against bladder cancer. TPP1 was determined to have a GI50 ranging from 200 to 250 μM over a period of 1 h and the ability to effectively inhibit bladder cancer. TPP1 induces apoptosis, and it appears to act as a direct mitochondrial toxin. TPP1 was applied intravesically to a bladder cancer mouse model based on the carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). Cancer selectivity of TPP1 was demonstrated, as BBN-induced tumors exhibited apoptosis but normal adjacent urothelium did not. These results suggest that TPP1 may be a promising intravesical agent for the treatment of bladder cancer.

Synthesis, characterization, in vitro SAR and in vivo evaluation of N,N'bisnaphthylmethyl 2-alkyl substituted imidazolium salts against NSCLC

Alkyl- and N,N'-bisnaphthyl-substituted imidazolium salts were tested in vitro for their anti-cancer activity against four non-small cell lung cancer cell lines (NCI-H460, NCI-H1975, HCC827, A549). All compounds had potent anticancer activity with 2 having IC50 values in the nanomolar range for three of the four cell lines, a 17-fold increase in activity against NCI-H1975 cells when compared to cisplatin. Compounds 1-4 also showed high anti-cancer activity against nine NSCLC cell lines in the NCI-60 human tumor cell line screen. In vitro studies performed using the Annexin V and JC-1 assays suggested that NCI-H460 cells treated with 2 undergo an apoptotic cell death pathway and that mitochondria could be the cellular target of 2 with the mechanism of action possibly related to a disruption of the mitochondrial membrane potential. The water solubilities of 1-4 was over 4.4mg/mL using 2-hydroxypropyl-β-cyclodextrin as a chemical excipient, thereby providing sufficient solubility for systemic administration.

Synthesis, anti-proliferative activity, SAR study, and preliminary in vivo toxicity study of substituted N,N'-bis(arylmethyl)benzimidazolium salts against a panel of non-small cell lung cancer cell lines

A series of N,N'-bis(arylmethyl)benzimidazolium salts have been synthesized and evaluated for their in vitro anti-cancer activity against select non-small cell lung cancer cell lines to create a structure activity relationship profile. The results indicate that hydrophobic substituents on the salts increase the overall anti-proliferative activity. Our data confirms that naphthylmethyl substituents at the nitrogen atoms (N¹(N³)) and highly lipophilic substituents at the carbon atoms (C² and C⁵(C⁶)) can generate benzimidazolium salts with anti-proliferative activity that is comparable to that of cisplatin. The National Cancer Institute's Developmental Therapeutics Program tested 1, 3-5, 10, 11, 13-18, 20-25, and 28-30 in their 60 human tumor cell line screen. Results were supportive of data observed in our lab. Compounds with hydrophobic substituents have higher anti-cancer activity than compounds with hydrophilic substituents.

Anti-tumor activity of lipophilic imidazolium salts on select NSCLC cell lines

The anti-tumor activity of imidazolium salts is highly dependent upon the substituents on the nitrogen atoms of the imidazolium cation. We have synthesized and characterized a series of naphthalene-substituted imidazolium salts and tested them against a variety of non-smallcell lung cancer cell lines. Several of these complexes displayed anticancer activity comparable to cisplatin. These compounds induced apoptosis in the NCI-H460 cell line as determined by Annexin V staining, caspase-3, and PARP cleavage. These results strongly suggest that this class of compounds can serve as potent chemotherapeutic agents.