Cancer Ablation

While surgery and radiation is at the foundation for cancer treatment in developed countries, they are often not viable options for many in developing countries due to shortages in infrastructure, personnel and cost. Because of these obstacles, nine out of ten people in developing countries do not have access to local cancer treatment. Ethanol ablation is especially appealing for use in developing countries because it can be locally available and ultra-low-cost (<$5 per treatments), requires no specialized equipment, is highly portable, and can effectively treat relatively large lesions up to 5 cm in diameter. In high-resource settings ethanol ablation is sometimes preferred over radiofrequency ablation or surgery because it requires less operating time, fewer supplies, and results in fewer complications.

 

However, ethanol ablation’s clinical use has been limited to certain tumor locations due to the unpredictable delivery of pure ethanol. Pure ethanol can leak into porous tissue and vasculature leading to non-specific toxicity and incomplete tumor necrosis. We have developed a method for delivering ethanol that results in more precise delivery and greater safety than pure ethanol ablations. The beauty of our solution lies in its simplicity: combining ethanol, a cytotoxic agent, with ethyl cellulose, a water-insoluble/ethanol-soluble polymer, and intratumorally injecting the solution results in a slow-release ethanol-rich gel. We use intratumoral injections of ethanol and the polymer ethyl-cellulose delivered at a controlled injection rate to further control the size and distribution of the gel. Thus, ethyl cellulose creates a high concentration ethanol cavity, or depot, at the injection site.

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When a mixture of ethanol and ethylcellulose (EECF) is mixed with water, the solution undergoes a liquid to solid phase transition resulting in an ethanol-rich, cotton-like gel.

When we translated this to localized treatment of tumors, the ethyl cellulose-ethanol mixture was completely retained within the tumor, i.e., no leakage was observed. The ethanol and ethyl cellulose treatment completely annihilated the tumors one week after a single injection. In fact, 7/7 tumors injected with ethanol-ethyl cellulose completely regressed seven days after the initial injection, while none of the tumors regressed in the control (ethanol only) group.

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Spontaneously grown tumors in a hamster cheek pouch were treated with an intratumoral injection of either ethanol alone or ethanol plus ethyl cellulose (gel ethanol). Representative images of the effect of ethanol only and gel ethanol injections on a tumor are shown over 7 days. By day 7, all tumors treated with gel ethanol were completely gone, while tumors treated with ethanol-only showed little response.

For local tumor control, the goal is to kill as much of the diseased tissue as possible while preserving nearby healthy tissue. Ablation modalities are characterized by their zone of necrosis and the degree of peripheral damage compared to surgery. In order to produce a consistent well defined ablation zone we have developed an ethanol-ethyl cellulose mixture termed “gel ethanol” which is both low-cost and easily accessible. Ethylcellulose has unique physical properties that make it liquid when dissolved in pure ethanol and solid once injected into tissue which limits ethanol leakage into peripheral vessels and tissues. Fluorescein was added to an mixture of gel ethanol and to ethanol alone (control) to allow visualization of the injectate. Twenty-four hours after injection, tumors were excised and stained for cell viability. A mouse was considered to have an adverse event if it showed signs of functional impairment, bleeding, or inflammation/edema at any time during a 4-week monitoring period. In preliminary experiments, we demonstrated that gel ethanol distributed over a volume roughly twice the injection volume (Fig. 1A,B) and achieved a zone of necrosis of a volume similar to the distribution volume(Fig. 1 C,D). Importantly, and collateral tissue damage, bleeding, and inflammation were reduced (Fig. 1E) when using gel ethanol compared to using ethanol alone.

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A) Tumor cross-section following injection of liquid or gel ethanol with fluorescein added. 

B) The fluorescent volume is largest for gel ethanol. 

C) Cell viability staining of large tumors after treatment with liquid or gel ethanol compared with no treatment. 

D) The necrotic volume is greatest following treatment with gel ethanol. 

E) Percent of mice with adverse events within four weeks of treatment.

Most recently, we have found that gel ethanol can activate the immune system to fight cancer both at the primary tumor site and distant metastatic sites through a single treatment at the primary tumor site. Mice with highly metastatic 4T1 breast tumors were treated with either gel ethanol, surgery, or a saline control. After euthanasia, the lungs were removed from each mouse and examined for the presence of metastases. Mice receiving gel ethanol ablation had significantly fewer lung metastases than mice receiving either surgery or saline. These findings suggest that gel ethanol ablation has an antimetastatic, abscopal treatment effect.

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A) Mice bearing 4T1 tumors were treated with either gel ethanol, saline, or surgery 10 days after tumor implant.

B) Comparable survival was observed across all three groups.

C) Histology-stained lungs from mice treated with gel ethanol, saline, or surgery show that mice receiving gel ethanol treatment have a lower metastatic burden.

D) Quantifying the metastatic burden for gel ethanol, saline, and surgery reveals that mice treated with gel ethanol have a significantly lower metastatic burden than either saline or surgery.

Gel ethanol can be readily integrated with standard therapies, like surgery and checkpoint inhibitors (CPI), and combined with ubiquitous, low-cost agents like sodium bicarbonate (bicarb) and chemotherapies on the WHO essential medicines to modulate the local tumor microenvironment to produce a robust local and systemic antitumor immune response. 4T1 tumors are resistant to treatment with surgery and CPI, showing little survival advantage to saline treated mice. Combining surgery and CPI with gel ethanol greatly improves overall survival. In fact, 4T1 tumors treated with a combination of gel ethanol, cyclophosphamide (CP), bicarb, and surgery resulted in a 90% cure rate compared with 0% cure rate for CPI and surgery alone.

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Mice were treated with either saline, checkpoint inhibitor (CPI), surgery, gel ethanol + CPI, gel ethanol + cyclophosphamide (CP) + bicarb, gel ethanol + CP + bicarb + CPI, or gel ethanol + CP + bicarb + surgery. Gel ethanol integrates nicely with both CPI and surgery, showing significant survival improvement compared to CPI or surgery alone. The combination of gel ethanol with CP, bicarb, and surgery resulted in the greatest survival advantage, with around 90% of mice disease free by 60 days post treatment.

We are currently optimizing the delivery strategy for gel ethanol by examining how injectate infusion rate and formulation affect ethanol depot formation and tumor growth in pre-clinical models. We are also focusing on clinical translation of gel ethanol into a phase I clinical trial.