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15357163mct140089t-sup-fig_1.pdf (66.13 kB)

Supplementary Figure 1 from In Vitro and In Vivo Activity of the Low-Immunogenic Antimesothelin Immunotoxin RG7787 in Pancreatic Cancer

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posted on 2023-04-03, 14:10 authored by Kevin Hollevoet, Emily Mason-Osann, Xiu-fen Liu, Sabine Imhof-Jung, Gerhard Niederfellner, Ira Pastan

PDF - 66K, A: SYTOX Dead Cell Stains allows to gate out viable cells from a representative dissociated KLM-1 tumor. B: In the subpopulation of viable cells, cell doublets are excluded. C: CD71+ cells (=human KLM-1 tumor cells) are gated out of the subpopulation of viable single cells. D: Based on the Alexa-647 background signal in the CD71+ cells of an untreated tumor (not shown), a gate is set and the percentage of Alexa-647+ cells in an RG7787-Alexa647-treated tumor is determined.

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ARTICLE ABSTRACT

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, and new therapies are needed. RG7787 is a novel low-immunogenic antimesothelin recombinant immunotoxin (RIT), engineered to overcome the limitations of SS1P, a RIT now in clinical trials. In vitro activity was evaluated on five established PDAC cell lines (KLM-1, AsPC-1, BxPC-3, Panc 3.014, and PK-1) and on PDAC cells directly established from a patient tumor (GUMC108). RG7787 had subnanomolar IC50s in most cell lines, and was significantly more active than SS1P in GUMC108, KLM-1, and Panc 3.014 cells. GUMC108 was most sensitive, with RG7787 killing >99% of the cells. In a subcutaneous KLM-1 xenograft mouse model, two cycles of 3 × 2.5 mg/kg RG7787 QOD combined with two cycles of 1 × 50 mg/kg paclitaxel induced near-complete responses, with all tumors regressing below 5 mm3 within 30 days after therapy was initiated (>95% decrease) and no significant growth increase for at least another 3 weeks. RG7787 alone gave limited but significant regressions and paclitaxel by itself arrested tumor growth. Quantifying the uptake of Alexa Fluor 647–labeled RG7787 in tumors showed that the RIT reached only 45% of KLM-1 cells, accounting in part for the limited responses. Paclitaxel did not improve RG7787 uptake, which thus cannot explain the beneficial effect of the combination therapy. In conclusion, RG7787 has high cytotoxic activity on PDAC cell lines as well as on primary patient cells. In vivo, this novel RIT gives durable near-complete tumor responses when combined with paclitaxel. RG7787 merits further evaluation for the treatment of PDAC. Mol Cancer Ther; 13(8); 2040–9. ©2014 AACR.

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