Electrochemotherapy: aspects of preclinical development and early clinical experience

Abstract

Objective: To develop an optimized, reproducible system of electrochemotherapy, and to investigate its clinical application in patients with cutaneous or subcutaneous recurrences of inoperable or progressive disease recalcitrant to current anticancer treatments.

Background: Electrochemotherapy is the application of electric pulses to tumor tissue, rendering the cell membranes permeable to otherwise impermeant or poorly permeant anticancer drugs. This facilitates a potent local cytotoxic effect.

Study design: The optimal parameters for electrical pulses and bleomycin concentration were obtained in vitro and then applied to tumors derived from 4 histologically distinct human cancer cell lines (7860, PC3, OE19, MCF-7) established in athymic nude mice. Comparison was made with tumors that received bleomycin alone, electric pulses alone, and untreated controls. The optimized electrochemotherapy was then applied to patients with cutaneous or subcutaneous tumors, of any histologic type, recurrent or metastatic and unresponsive to standard chemotherapy and/or radiotherapy regimens. Tumors were assessed at monthly intervals to determine response to the treatment.

Results: In vivo: Using the optimal parameters ascertained in vitro, all tumors treated by electrochemotherapy with bleomycin (n = 24) had significantly regressed (P < 0.001, all 4 lines) compared with control tumors (n = 72). Twelve tumors completely regressed (50%) following a single application, with 12 partial regressions (50%). Clinical: In 30 patients (111 tumors), none of the treated tumors progressed. Sixty percent of tumors (66 of 111) showed complete regression, 22% (24 of 111) partial response, and 18% (21 of 111) no change. Electrochemotherapy was more effective in smaller tumors (<3 cm), 71% (64 of 90) showing complete regression, 20% (18 of 90) partial response, and 9% (8 of 90) no change.

Conclusions: Electrochemotherapy parameters optimized in vitro are applicable in vivo. This treatment is effective in athymic nude mice for all histologic types indicating a nonimmunologic mode of action. In clinical application, electrochemotherapy is an effective, safe, and reproducible therapy. Patients with cutaneous or subcutaneous tumors previously refractory to surgical intervention, systemic chemotherapy, and/or radiotherapy responded successfully irrespective of histologic type.

Figures

FIGURE 1. In vitro determination of the optimal voltage and concentration of bleomycin which induces tumor cell killing. A, OE-19 esophageal adenocarcinoma. B, 786O renal cell carcinoma; C, MCF-7 breast carcinoma. D, PC-3 prostate carcinoma. Maximal cytocidal activity was achieved using similar parameters for all 4 cell lines: voltage 1400 V/cm and bleomycin concentration of 10 μg/mL.

FIGURE 2. Results of in vivo electrochemotherapy for 4 tumor cell lines growing in athymic nude mice (bleomycin 1 μg/100 mL) was injected into each tumor prior to application of a 1400 V/cm current. Only the combined administration of bleomycin and electric pulses inhibited tumor growth. P < 0.001 for all. A, OE-19 esophageal adenocarcinoma. B, 786O renal cell carcinoma. C, MCF-7 breast carcinoma. D, PC-3 prostate carcinoma.

FIGURE 3. Histology of MCF-7 tumors 24 hours following treatment demonstrates cell death by apoptosis in response to electrochemotherapy. A, Hematoxylin and eosin (H&E) staining of control tumor at 24 hours. B, H&E staining of tumor 24 hours after electrochemotherapy shows extensive denucleation indicating cell death. C, TUNEL staining of tumor 24 hours after treatment with electrochemotherapy. The luminescent cells are apoptotic. No apoptosis is detected in untreated control tumor at 24 hours.

FIGURE 4. Finite element modeling using FEMLAB software was used to simulate the electric fields generated by the electrodes for an applied voltage of 1400 V/cm. Both plate (A) and needle (B) electrodes were used during clinical application to ensure complete exposure of the electrical field to the full tumor mass. Between plate electrodes (A), there is a homogenous electrical field. In contrast, the electric field between the needle electrodes shows a marked reduction in voltage away from the tip head and is less homogeneous. Variability in tumor characteristics will further alter the electric field.

FIGURE 5. Images of the Cliniporator, electric pulse delivery unit (left) with the 2 electrode type used in this study, needle (top right) and plate (bottom right). The Cliniporator is CE-approved and has been applied clinically at the CCRC since 2003.

FIGURE 6. Chest wall recurrence of breast carcinoma in a 52-year-old woman 4 years after left mastectomy and axillary clearance and adjuvant radiation therapy. There was no response to systemic chemotherapy. Complete response to electrochemotherapy was seen 2 months after treatment, without recurrence within the treated area at the 14-month follow-up.

FIGURE 7. Inoperable squamous cell carcinoma of the left parotid with a complete left-sided facial palsy following initial response to systemic chemotherapy. The 59-year-old patient refused a further systemic treatment. Although nodal and pulmonary disease progressed, near-complete regression of the primary tumor was achieved by treatment with electrochemotherapy. The patient survived 15 months after treatment.