Urolithin A Nanoparticle Therapy for Cisplatin-Induced Acute Kidney Injury

Increasing the efficacy of cytotoxic drugs without compromising off-target tissue safety is a critical issue in the field of oncology. The use of cytotoxic drugs is still a major therapeutic approach to treating both localized and metastasized cancers. Since its approval for human use in 1978, cisplatin continues to be one of the frontline cytotoxic drugs used in treating a wide variety of cancers. Despite significant toxicities, and development of chemoresistance, cisplatin either alone or in combination is currently tested in over 700 clinical trials (clinicaltrials.gov). The cancer treatment plan typically consists of repeated cycles of cisplatin at maximum tolerated doses by intravenous administration, and acute kidney injury (AKI) is one of the most serious off-target toxicities [1]. Currently, there is no FDA-approved drug for prevention or treatment of AKI. The pathophysiology of cisplatin-induced AKI is complex and involves multiple pathways that includes but not limited to oxidative stress-driven inflammation, necrosis, apoptosis, and vascular injury in the kidneys [1‒3]. Therefore, careful regulation of oxidative stress should offer off-target protection, without compromising on-target efficacy [4, 5]. In this context, natural and synthetic antioxidants that fall under supplement category are reported to alleviate cisplatin-induced AKI [6]. Recently, urolithin A (UA), a gastrointestinal metabolite of ellagic acid found in various berries, exhibited promising antioxidant and anti-inflammatory effects, maintaining, and promoting overall health and well-being [7]. Though a recent study suggests that UA complies with Lipinski’s rule of 5 for drug-likeness [8], yet UA is poorly bioavailable owing to the fact that everything absorbed may not necessarily be bioavailable. Nano-encapsulation of small or large molecules is a promising approach to improving bioavailability and clinical efficacy [9, 10]. Therefore, we have encapsulated UA in polymer particles with a view to improving oral bioavailability and clinical efficacy.

In general, polyester nanoparticle encapsulation of UA improves UA oral bioavailability, and ligand-decorated nanoparticles further this effect [11]. In healthy rats, nanoparticles with no ligand led to 2-fold increase, while those with ligand presented a 7-fold increase in UA bioavailability compared to unformulated UA [11]. Therefore, ligand-decorated UA nanoparticles were further tested in mouse model of AKI [11]. The UA nanoparticles were dosed at 50 mg/kg UA equivalent, 3 doses/week, significantly attenuating the histopathological hallmarks of cisplatin-induced AKI and reduced mortality by 63%, while untreated mice began dying by day 8 with 100% mortality on day 15. The mice that survived in the treatment group were terminated on day 19 and were found healthy and displayed better overall health in weight loss, blood urea nitrogen, and plasma creatinine [11]. UA nanoparticles ameliorated cisplatin-induced interstitial expansion and prevented acute tubular necrosis and atrophy. Quantification of H&E-stained images using ImageJ revealed that 37% of the cortical and medullar area was occupied by interstitial space, and UA nanoparticle treatment showed a ∼3-fold decrease in the expansion. PAS staining further revealed that UA nanoparticles successfully negated compensatory glomerular hypertrophy reflected by minimum to no tubular dilation, apoptotic bodies, renal casts within tubular lumens, thickening of glomerular basement membranes, and cross-sectional glomerular diameter [11]. UA nanoparticles also prevented apoptotic cells in renal cortex and medulla regions. We found that UA nanoparticles exert its action through Nrf2/antioxidant response element and p53 pathways that are implicated in cisplatin-induced AKI. UA nanoparticle treatment led to downregulation of Nrf2-inducible genes (metallothionein 1, thioredoxin reductase 1, and sulfiredoxin 1 homolog) by at least 8-fold, 7-fold, and 4-fold, respectively. Similarly, the treatment led to downregulation of p53-inducible genes (cyclin-dependent kinase inhibitor 1A, activating transcription factor 3, and transformation-related protein 53-inducible nuclear protein 1) by at least 7-fold, 3-fold, and 9-fold, respectively, suggesting the potential of UA nanoparticles as AKI therapeutics.

To date, cisplatin-induced AKI remains a major unmet medical need without any pharmacological interventions. There is significant ongoing research in mitigating cisplatin-induced toxicities by reformulation strategies or the use of adjuvant therapies. While reformulating cisplatin may partially address toxicity, the clinical effectiveness of the new dosage forms yet to be proven and, in this context, small molecule adjuvant therapies that do not compromise cisplatin efficacy would prove beneficial. In support, our un-published data suggest that UA sensitizes cisplatin-resistant cells to cisplatin, while UA or cisplatin alone at same concentrations is ineffective. In general, studies by our and other groups have been using models of AKI induced in healthy subjects, but healthy individuals do not take cisplatin. Therefore, it is important to test the potential of adjuvant therapies in cancer setting to rule out the possibilities of adjuvant therapies interfering with cisplatin efficacy. In addition, it is also important to consider the differences between organisms to their respective body size, as interspecies difference will have significant influence on clinical translation. Very recently, we have found that the ligand-decorated particles offered 5-fold increase in oral bioavailability compared to unformulated UA in healthy canine and closely match [12] with the reported human PK that used 28 daily doses of UA [13]. We remain highly optimistic that testing of the UA nanoparticles in a combination of models considering gender, dose, and age-dependent cisplatin-induced AKI, in healthy and cancer setting, including body size, will pave the way for clinical translation.

The author has no conflict of interest to declare.

This work is supported in part by National Institutes of Health grants (No. R01DK128597, R01 AI155908, R01DK125372).