Identification and characterization of riproximin, a new type II ribosome‐inactivating protein with antineoplastic activity from Ximenia americana

Abstract

The aim of this study was to identify and characterize the active component(s) of Ximenia americana plant material used to treat cancer in African traditional medicine. By a combination of preextraction, extraction, ion exchange and affinity chromatography, a mixture of two cytotoxic proteins was isolated. Using degenerated primers designed on the de novo sequence of two tryptic peptides from one of these proteins, a DNA fragment was amplified and the sequence obtained was used to determine the complete cDNA sequence by the RACE method. Sequence analysis and molecular modeling showed that the new protein, riproximin, belongs to the family of type II ribosome inactivating proteins. These results are in good agreement with the ability of riproximin to inhibit protein synthesis in a cell-free system, as well as with the cytotoxicity of riproximin, as demonstrated by its IC50 value of 0.5 pM in MCF7, 1.1 pM in HELA and 0.6 pM in CC531-lacZ cells. To assess the antineoplastic efficacy of the purified riproximin in vivo, the CC531-lacZ colorectal cancer rat metastasis model was used. Significant anticancer activity was found after administration of total dosages of 100 (perorally) and 10 (intraperitoneally) pmol riproximin/kg. These results suggest that riproximin has distinct potential for cancer treatment.

Evaluation of Riproximin Binding Properties Reveals a Novel Mechanism for Cellular Targeting

“…An increase in riproximin cytotoxicity was observed upon neuraminidase treatment for the strongly sialylated MDA-MB-231 cells but not for the sialyl-poor MCF7 (46), the most sensitive cell line within the panel tested (2). This experiment demonstrated a direct relationship between the biological activity of riproximin and the extent of sialylation found on cell surfaces.…”

“…Riproximin specificity for the clustered Tn antigen is remarkable and could explain its tumor specificity described previously (1,2). Prominent targets for riproximin on cancer cells could therefore be the cancer-associated mucins (MUCs).…”

“…Riproximin is a lectin with potent antineoplastic activity in vitro and in vivo (1,2). It was originally identified as the active component of a powdered plant material used in African traditional medicine for treating cancer and has subsequently been isolated from the fruit kernels of Ximenia americana.…”

Riproximin’s activity depends on gene expression and sensitizes PDAC cells to TRAIL

“…1 These proteins consist of two chains, which exhibit complementary properties. 2 The A chain is an rRNA N-glycosidase, which causes depurination of the 28S rRNA in a catalytic manner and thus leads to transcriptional arrest by inhibiting protein synthesis.…”

“…We reasoned that it would be worth investigating 2 , and Martin R Berger the activity of Rpx in PDAC models, because a colorectal cancer liver metastasis model had shown explicit antineoplastic activity. 1 Moreover, the affinity of Rpx for carcinoembryonic antigen (CEA) 5 suggested that neoplasias expressing this glycoprotein might be preferential targets. Therefore, we determined the sensitivity of 17 PDAC cell lines to Rpx and investigated in a newly established PDAC liver metastasis model, whether Rpx has antineoplastic efficacy against PDAC cells growing in rat liver.…”