Impediments to enhancement of CPT-11 anticancer activity by E. coli directed beta-glucuronidase therapy

Targeted bacteria-mediated therapy of mouse colorectal cancer using baicalin, a natural glucuronide compound, and E. coli overexpressing β-glucuronidase

The side effects of common chemotherapeutic drugs that damage healthy tissues account for one of the most important problems in cancer research that needs careful addressing. Bacterial-Directed Enzyme Prodrug Therapy (BDEPT) is a promising strategy that uses bacteria to direct a converting enzyme to the tumor site and activate a systemically injected prodrug selectively within the tumor; so that the side effects of the therapy would significantly decrease. In this study, we evaluated the efficacy of baicalin, a natural compound, as a glucuronide prodrug in association with an engineered strain of Escherichia coli DH5α harboring the pRSETB-lux/βG plasmid in a mouse model of colorectal cancer. E. coli DH5α-lux/βG was designed to emit luminescence and overexpress the β-glucuronidase. Unlike the non-engineered bacteria, E. coli DH5α-lux/βG showed the ability to activate baicalin, and the cytotoxic effects of baicalin on the C26 cell line were increased in the presence of E. coli DH5α-lux/βG. Analyzing the tissue homogenates of mice bearing C26 tumors inoculated with E. coli DH5α-lux/βG indicated the specific accumulation and multiplication of bacteria in the tumor tissues. While both baicalin and E. coli DH5α-lux/βG could inhibit tumor growth as monotherapy, an enhanced inhibition was observed when animals were subjected to combination therapy. Moreover, no significant side effects were observed after histological investigation. The results of this study indicate that baicalin has the capability of being used as a suitable prodrug in the BDEPT, however further research is required before it can be applied in the clinic.

Application of bacterial directed enzyme prodrug therapy as a targeted chemotherapy approach in a mouse model of breast cancer

Cancer is the second leading cause of death in the world. Some of the usual cancer treatments include surgery, chemotherapy, and radiotherapy. However, due to low efficacy and side effects of these treatments, novel targeted therapeutic methods are needed. One of the common drawbacks of cancer chemotherapy is off-target toxicity. In order to overcome this problem, many investigations have been conducted. One of the new targeted therapy methods known as bacterial directed enzyme-prodrug therapy (BDEPT) employs bacteria as enzyme carriers to convert a pro-drug to a drug specifically within the tumor site. In the present study, we used Escherichia coli DH5α carrying luxCDABE gene cluster and overexpressing β-glucuronidase for luminescent emission and enzyme expression, respectively. Enzyme expression can lead to the conversion of glycyrrhizic acid as a prodrug to glycyrrhetinic acid, a potent anti-cancer agent. DH5α-lux/βG was characterized and its stability was also evaluated. Bacteria colonization in the tumor site was measured by tissue homogenate preparation and colony counting method. Histopathological studies on the liver, spleen, and tumor were also conducted. According to the results, co-treatment of 4T1, a highly metastatic mouse breast cancer cell line, with GL and DH5α-lux/βG could significantly decrease the IC₅₀ values. Moreover, increased number of bacteria could lead to a dramatic drop in IC₅₀ value. Specific colonization of DH5α-lux/βG was observed in the tumor site compared with other tissues (p< 0.0001). Moreover, the biocompatibility evaluation proved that DH5α-lux/βG had no adverse effects on normal tissues. Furthermore, concurrent usage of GL and bacteria in the treatment of induced 4T1 tumors in BALB/c mice significantly delayed tumor growth (p<0.001) during 16 days of investigation. Based on these findings, BDEPT might be useful for targeted breast cancer therapy, although further investigations are required to confirm this.

Newly Obtained Apple Pectin as an Adjunct to Irinotecan Therapy of Colorectal Cancer Reducing E. coli Adherence and β-Glucuronidase Activity

Colorectal cancer (CRC) is the second cause of cancer death worldwide. The composition and enzymatic activity of colonic microbiota can significantly affect the effectiveness of CRC chemotherapy. Irinotecan is a drug widely used to treat colon cancer. However, the transformation of a drug-glucuronide (SN-38G) back to its active form (SN-38) by bacterial β-glucuronidase (GUS) constitutes the primary reason for the observed intestinal toxicity of irinotecan. It was demonstrated that novel enzymatically extracted apple pectin (PC) might be a promising candidate for an adjunct to irinotecan therapy. PC itself reduced the viability of HCT 116 and Caco-2 colorectal cancer cells, induced apoptosis, and increased intracellular reactive oxygen species production. Moreover, PC enhanced the cytotoxic and proapoptotic effect of irinotecan (at concentrations below its IC₅₀), i.e., synergistic effect was recorded. Additionally, PC exhibited potent anti-inflammatory properties and prevented adhesion of prototype adherent-invasive E. coli (AIEC) LF82 strain and laboratory K-12_C600 strain to colon cancer cells. PC was also identified to be an effective inhibitor of bacterial GUS activity. Altogether, novel apple pectin was identified as a promising candidate for a supplement to irinotecan therapy that might alleviate its side-effects via inhibition of bacterial GUS and thus increasing its therapeutic efficacy.

Use of a genetically engineered E. coli overexpressing β-glucuronidase accompanied by glycyrrhizic acid, a natural and anti-inflammatory agent, for directed treatment of colon carcinoma in a mouse model

Bacteria-directed enzyme prodrug therapy (BDEPT), is an emerging alternative directed and tumor-specific approach. The basis of this method is the conversion of a non-toxic prodrug by a bacterial enzyme to a toxic drug within the tumor-microenvironment (TME). In the present study, the therapeutic efficacy of BDEPT was investigated based on the ability of Escherichia coli DH5α-lux/βG in activation of glycyrrhizic acid (GL), a natural and non-toxic compound purified from licorice, to glycyrrhetinic acid (GA) only in TME. To do so, the anti-bacterial effects of GL on bacteria and the cytotoxic effects of the produced GA on survival rate of CT26 mouse colon carcinoma cells were evaluated. The IC₅₀ values of the produced GA and cisplatin were determined as 210 μM and 100 μM, respectively. Comparing these values to GL treatment (1305 μM) indicates that bacteria could have efficiently activated GL to GA to inhibit the growth of tumor cells. Afterward, the anti-cancer effects of bacteria used in combination with GL was investigated in a mouse model of colon carcinoma. Results were indicative of targeted homing and even proliferation of luminescent bacteria in TME. Moreover, combined treatment greatly inhibited tumor growth. Histopathological analysis of dissected tissues also demonstrated increased apoptosis rate in tumor cells after combined treatment and interestingly, showed no obvious damage to the spleen and liver of treated mice. Accordingly, this BDEPT approach could be considered as an effective alternative tumor-specific therapy utilizing prodrug-activating enzymes expressing from tumor-targeting bacteria to allow the development of new tumor-specific pharmacotherapy protocols.

Designer bacteria as intratumoural enzyme biofactories

Bacterial-directed enzyme prodrug therapy (BDEPT) is an emerging form of treatment for cancer. It is a biphasic variant of gene therapy in which a bacterium, armed with an enzyme that can convert an inert prodrug into a cytotoxic compound, induces tumour cell death following tumour-specific prodrug activation. BDEPT combines the innate ability of bacteria to selectively proliferate in tumours, with the capacity of prodrugs to undergo contained, compartmentalised conversion into active metabolites in vivo. Although BDEPT has undergone clinical testing, it has received limited clinical exposure, and has yet to achieve regulatory approval. In this article, we review BDEPT from the system designer's perspective, and provide detailed commentary on how the designer should strategize its development de novo. We report on contemporary advancements in this field which aim to enhance BDEPT in terms of safety and efficacy. Finally, we discuss clinical and regulatory barriers facing BDEPT, and propose promising approaches through which these hurdles may best be tackled.

Real-time imaging of intestinal bacterial β-glucuronidase activity by hydrolysis of a fluorescent probe

Intestinal bacterial β-glucuronidase (βG) hydrolyzes glucuronidated metabolites to their toxic form in intestines, resulting in intestinal damage. The development of a method to inhibit βG is thus important but has been limited by the difficulty of directly assessing enzyme activity in live animals. Here, we utilized a fluorescent probe, fluorescein di-β-D-glucuronide (FDGlcU), to non-invasively image the intestinal bacterial βG activity in nude mice. In vitro cell-based assays showed that the detection limit is 10⁴ colony-forming units/well of βG-expressing bacteria, and that 7.81 ng/mL of FDGlcU is enough to generate significant fluorescent signal. In whole-body optical images of nude mice, the maximum fluorescence signal for βG activity in intestines was detected 3 hours after gavage with FDGlcU. Following pretreatment with a bacterial βG inhibitor, the fluorescence signal was significantly reduced in abdomens and excised intestines images. For a 4-day antibiotic treatment to deplete intestinal bacteria, the FDGlcU-based images showed that the βG activity was decreased by 8.5-fold on day 4 and then gradually increased after treatment stopped. The results suggested that FDGlcU-based imaging revealed the in vitro and in vivo activity of intestinal bacterial βG, which would facilitate pharmacodynamic studies of specific bacterial βG inhibitors in animal studies.