Abstract 696: Phototheranostics of epithelioid sarcoma by targeting CD44 or EGFR

Abstract

Abstract Introduction: Epithelioid sarcoma (ES) is a rare yet high-grade and highly aggressive soft tissue neoplasm first identified by Enzinger in 1970.1 ES has high reported recurrence and metastasis rates (around 70% and 50%, respectively).2 Unresectable locally advanced and metastatic ES are usually chemoresistant and generally fatal.3 Here, we extended our previous near-infrared photoimmunotherapy (NIR-PIT) study,4 to develop antibody photosensitizer conjugates based on two monoclonal antibodies (mAbs) binding to CD44 or EGFR, both overexpressed on ES tumor cell surface. We conducted cellular studies and established animal models to evaluate the specificity and efficacy of the two mAb conjugates in binding, detecting and eliminating ES. Method: CD44, EGFR mAb or its IgG isotype control was conjugated with a NIR phthalocyanine dye, IR700, to form CD44-IR700, EGFR-IR700 and IgG-IR700, respectively. A bilateral ES tumor model was established by inoculating 1×106 VAESBJ cells in 0.05 ml of Hank's balanced salt solution on either flank of athymic Balb/c (nu/nu) female mouse. Subsequently, 100 μg of CD44-IR700 or EGFR-IR700 or IgG-IR700 was injected intravenously (i.v.), and NIR fluorescence images of IR700 in mice were obtained over a 24-h period (n = 4 per group). For PIT, tumor-bearing mice (n = 4 or 5 per group) received two i.v. injections of 100 μg of CD44-IR700 or EGFR-IR700 at a one-week interval, and tumors were exposed to NIR light exposure at 200 J/cm2 at 24h p.i. Tumor diameters were measured over 3 weeks. IgG-IR700 and PBS-injected mice were used as controls. Results and Discussion: We confirmed CD44 and EGFR overexpression in VAESBJ cells by flow cytometry. Both CD44-IR700 and EGFR-IR700 demonstrated target-specific binding to VAESBJ and cell death when activated by NIR light. Compared to EGFR-IR700, CD44-IR700 exhibited a higher potency in cellular PIT and had a much lower IC50 value. CD44-IR700 and EGFR-IR700 both exhibited preferential accumulation in VAESBJ tumors and showed approximately two to threefold higher retention compared to IgG-IR700. CD44-IR700 or EGFR-IR700 injection combined with NIR light exposure resulted in significant tumor growth delay in VAESBJ tumors compared to the IgG-IR700 or PBS group. Reduction of CD44 and EGFR levels were observed in the corresponding CD44-IR700 or EGFR-IR700-treated tumors as evidenced by flow cytometry and western blotting studies. Our data collectively demonstrate the specificity and efficacy of CD44 or EGFR-based PIT as novel therapeutic approaches that can be integrated into an intraoperative setting for achieving clear tumor margins in localized ES or applied as a standalone therapy for inoperable locally advanced and recurrent ES.