In vitro and in vivo effects of a recombinant anti-PSMA immunotoxin in combination with docetaxel against prostate cancer

// Marta Michalska 1 , Susanne Schultze-Seemann 1 , Lioudmila Bogatyreva 2 , Dieter Hauschke 2 , Ulrich Wetterauer 1 , Philipp Wolf 1 1 Department of Urology, Medical Center, University of Freiburg, Freiburg, Germany 2 Institute for Medical Biometry and Statistics, Medical Center, University of Freiburg, Freiburg, Germany Correspondence to: Philipp Wolf, e-mail: philipp.wolf@uniklinik-freiburg.de Keywords: prostate cancer, PSMA, immunotoxin, docetaxel, chemotherapy Received: November 26, 2015 Accepted: February 23, 2016 Published: March 9, 2016 ABSTRACT Docetaxel (DOC) is used for the first-line treatment of castration resistant prostate cancer (CPRC). However, the therapeutic effects are limited, only about one half of patients respond to the therapy and severe side effects possibly lead to discontinuation of treatment. Therefore, actual research is focused on the development of new DOC-based combination treatments. In this study we investigated the antitumor effects of a recombinant immunotoxin targeting the prostate specific membrane antigen (PSMA) in combination with DOC in vitro and in vivo . The immunotoxin consists of an anti-PSMA single chain antibody fragment (scFv) as binding and a truncated form of Pseudomonas aeruginosa Exotoxin A (PE40) as toxin domain. The immunotoxin induced apoptosis and specifically reduced the viability of androgen-dependent LNCaP and androgen-independent C4-2 prostate cancer cells. A synergistic cytotoxic activity was observed in combination with DOC with IC 50 values in the low picomolar or even femtomolar range. Moreover, combination treatment resulted in an enhanced antitumor activity in a C4-2 SCID mouse xenograft model. This highlights the immunotoxin as a promising therapeutic agent for a future DOC-based combination therapy of CPRC.