Efficient in vivo antitumor effect of an immunotoxin based on ribotoxin α-sarcin in nude mice bearing human colorectal cancer xenografts

Abstract

Tagging of RNases, such as the ribotoxin α-sarcin, with the variable domains of antibodies directed to surface antigens that are selectively expressed on tumor cells endows cellular specificity to their cytotoxic action. A recombinant single-chain immunotoxin based on the ribotoxin α-sarcin (IMTXA33αS), produced in the generally regarded as safe (GRAS) yeast Pichia pastoris, has been recently described as a promising candidate for the treatment of colorectal cancer cells expressing the glycoprotein A33 (GPA33) antigen, due to its high specific and effective cytotoxic effect on in vitro assays against targeted cells. Here we report the in vivo antitumor effectiveness of this immunotoxin on nude mice bearing GPA33-positive human colon cancer xenografts. Two sets of independent assays were performed, including three experimental groups: control (PBS) and treatment with two different doses of immunotoxin (50 or 100 μg/ injection) (n = 8). Intraperitoneal administration of IMTXA33αS resulted in significant dose-dependent tumor growth inhibition. In addition, the remaining tumors excised from immunotoxin-treated mice showed absence of the GPA33 antigen and a clear inhibition of angiogenesis and proliferative capacity. No signs of immunotoxin-induced pathological changes were observed from specimens tissues. Overall these results show efficient and selective cytotoxic action on tumor xenografts, combined with the lack of severe side effects, suggesting that IMTXA33αS is a potential therapeutic agent against colorectal cancer.

Fungal proteinaceous compounds with multiple biological activities

“…Hopefully more drugs will be isolated from fungi in the future and exploited to the welfare of mankind. (Orlandi et al, 1988;Rao et al, 2015;Yadav and Batra, 2015) α-sarcin from Aspergillus giganteus AVTWTCLNDQKNPKTNKYETKRLL α-sarcin immunotoxin IMTXA33αS on SW1222 cells (IC 50 = 30 nM) and LIM1215 cells (IC 50 = 70 nM) It inhibited growth of SW1222 in mice (Sacco et al, 1983;Tomé-Amat et al, 2015) …”

“…An α-sarcin immunotoxin IMTXA33αS when injected intraperitoneally undermined the growth of GPA33-positive human colon cancer xenografts in nude mice. The GPA33 antigen was absent from the residual tumors, and angiogenesis and proliferation were suppressed (Tomé-Amat et al 2015). The inhibition of protein biosynthesis in immunotoxin-treated tumors is due to the α-sarcin component.…”

A deimmunised form of the ribotoxin, α-sarcin, lacking CD4+T cell epitopes and its use as an immunotoxin warhead

“…New non-immunogenic toxin warheads need to be developed and tested in order to provide a new generation of targeted immunotoxins for the treatment of malignancies. α-Sarcin is a good candidate toxin warhead since it has been demonstrated to have potent anti-tumour activity both in vitro and in animal models of colorectal cancer (Carreras-Sangrà et al ., 2012; Tomé-Amat et al ., 2015a). In order to improve therapeutic utility, we sought to deimmunise α-sarcin by identifying T cell epitopes within the protein and then removing them by mutagenesis.…”

“…These results suggest that WT and deimmunised variant α-sarcins are able to either separate from the anti-Her2 scFv in the endosomes and effectively penetrate the cell cytoplasm without requirement for a protease cleavage site or, alternatively, it is possible that the whole fusion protein with the G 4 S linker translocates to the cytoplasm and the presence of the anti-Her2 scFv does not affect ribosome binding and cytotoxicity. Similarly, other studies using a scFv to GPA33 fused with WT α-sarcin containing a G 4 S linker effectively killed cells and demonstrated anti-tumour effects in vivo (Carreras-Sangrà et al ., 2012; Tomé-Amat et al ., 2015a). It is possible that different targeting moieties (scFvs) to the same target or to different targets will traffic and process differently when fused with the new deimmunised α-sarcin variants.…”

Characterization of a new toxin from the entomopathogenic fungus Metarhizium anisopliae: the ribotoxin anisoplin

“…In Aspergillus, they seem to be produced during conidia maturation, most probably as a defense mechanism against predators (Brandhorst and Kenealy, 1992). They have been extensively studied ( Lacadena et al, 2007;García-Ortega et al, 2010;Olombrada et al, 2014a,b) with the most recent studies focused on their antitumor properties conjugated as immunotoxins and their toxicity against insects ( Carreras-Sangrá et al, 2012;Olombrada et al, 2013;Tomé-Amat et al, 2015).…”