Poster S20 - Evaluating the distribution and chemical agent retention of LASEIT: a novel ablative combination therapy for hepatocellular carcinoma

Introduction: Hepatocellular carcinoma (HCC) is the second most common cause of cancer deaths globally with around 800,000 deaths per year. The HCC standards of care, organ transplant and surgical resection, are not feasible for approximately 80% of HCC patients because of organ shortages and underlying liver damage(1). Percutaneous ablative therapies offer an appealing option for the treatment of inoperable HCC. However, many forms of ablation are based on heat and have challenges with safety and efficacy, for example, collateral damage to surrounding tissue and incomplete ablation of the tumor due to the heat sink effect from nearby flowing blood(2,3). To address the limited treatment options for HCC, our group recently developed the chemical ablative therapy, Light Activatable Sustained-exposure Ethanol technology (LASEIT). LASEIT combines two forms of chemical ablation –ethanol ablation and photodynamic therapy. Our formulation includes ethanol, the photosensitizer benzoporphyrin derivative (BPD), and ethyl cellulose (EC), a polymer that gels under aqueous conditions. An initial study demonstrated that LASEIT significantly reduced tumor burden compared to its respective monotherapies in a murine model of pancreatic cancer(4). However, the impact of EC concentration on the distribution area in tissue-mimicking phantoms and the release kinetics of each drug remains unclear. Thus, this study investigates how EC content in LASEIT affects its distribution and release profiles of ethanol and BPD.

Materials and

Methods: To determine the relationship between EC concentration and LASEIT distribution, 300 uL of LASEIT made with different concentrations of EC-ethanol (0, 6, and 12% EC:ethanol w/v) were injected into tissue-mimicking agarose phantoms, which mimic the mechanical properties of liver tissue and enable high throughput characterization of the injectate. The resulting depots (i.e., the distribution that forms around the needle tip) were sectioned and imaged using a custom widefield fluorescence microscope tuned to image the fluorescent properties of BPD. ImageJ was used to quantify the distribution area and solidity (i.e., the area of the depot divided by its convex hull area).

To evaluate the effects of EC on chemical agent retention under static conditions, 250 uL of LASEIT 6% and 12% were mixed into a beaker containing 50 mL of 10% fetal bovine serum in phosphate-buffered saline (FBS-PBS) to form a gel depot. The depots were then removed from the beaker and transferred to a conical tube with fresh FBS-PBS. The tubes were stored at 37°C, and the FBS-PBS was extracted at various time points from time zero to seven days, replacing the extracted media with new FBS-PBS. The release of BPD and ethanol from the depots was quantified by measuring fluorescence intensity via a microplate reader. Fluorescence intensity was converted to concentration through standard curves with known concentrations that were measured in the microplate reader. The percent release was then calculated by dividing the amount released by the total amount of chemical agents present in the depot at time zero.

Results, Conclusions, and Discussions: Representative fluorescence and binary images of 0, 6, and LASEIT 12% injections into phantoms are shown in Figure 1A. The average area and solidity of LASEIT 6% were 1.8 cm2 and 68.1% respectively (Fig 1B). LASEIT 12% depots, on the other hand, exhibited significantly larger distribution areas and greater solidity with 2.1 cm2 and 89.6%, respectively (Fig 1B). In the model of chemical agent release, within the first hour, there is a rapid increase in the BPD and ethanol released, before plateauing by the end of the first day. The total release of BPD and ethanol from LASEIT 12% was lower than what was observed in LASEIT 6%. LASEIT 12% release of BPD was 13.8% and ethanol release was 2.6%. While LASEIT 6% BPD release was 17.8% and ethanol release was 4.3%.

In conclusion, LASEIT 12% demonstrated increased distribution areas and chemical agent retention than LASEIT 6%. Increased distribution area and retention of BPD and ethanol in LASEIT depots could increase tumor ablation zones and minimize damage to surrounding healthy tissue. Future in vivo studies will elucidate LASEIT distribution in a mouse model.

Acknowledgements (Optional):

References:
1. Cha C, DeMatteo RP, Blumgart LH. Surgery and ablative therapy for hepatocellular carcinoma. J Clin Gastroenterol. 2002;35(5 Suppl 2):S130-137. doi:10.1097/00004836-200211002-00009
2. Shiina S, Sato K, Tateishi R, et al. Percutaneous Ablation for Hepatocellular Carcinoma: Comparison of Various Ablation Techniques and Surgery. Can J Gastroenterol Hepatol. 2018;2018:e4756147. doi:10.1155/2018/4756147
3. Li D, Kang J, Madoff DC. Locally ablative therapies for primary and metastatic liver cancer. Expert Rev Anticancer Ther. 2014;14(8):931-945. doi:10.1586/14737140.2014.911091
4. Yang J, Ma CH, Quinlan J, et al. Light-Activatable Minimally Invasive Ethyl Cellulose Ethanol Ablation: Biodistribution and Potential Applications. Published online Under review.