Alpha-momorcharin (alpha-MMC) is a ribosome-inactivating protein (RIP) with excellent cytotoxicity to tumor cells. However, its strong immunogenicity and short plasma half-life limit its clinical applications. To overcome this, we have to PEGylated alpha-MMC using a branched 20 kDa (mPEG) (2)-Lys-NHS. Homogeneous mono-, di- and tri-PEGylated alpha-MMCs were synthesized, purified and characterized. In vitro and in vivo analysis indicated that the serial PEG-conjugates preserved moderate anti-tumor activity with 36% acute toxicity and at most 66% immunogenicity decrease. These results suggested the potential application of alpha-MMC-PEG conjugates as an anti-tumor agent.

PEGylation is effective in reducing the immunogenicity, immunotoxicity, and hepatotoxicity of α-MMC in vivo.

Ribosome-inactivating proteins (RIPs) are a family of enzymes that depurinate rRNA and inhibit protein biosynthesis. Here we report the purification, apoptosis-inducing activity, and polyethylene glycol (PEG) modification of RIP from the bitter melon seeds. The protein has a homogenous N-terminal sequence of NAsp- Val-Ser-Phe-Arg. Moreover, the RIP displayed strong apoptosis-inducing activity and suppressed cancer cell growth. This might be attributed to the activation of caspases-3. To make it available for in vivo application, the immunogenicity of RIP was reduced by chemical modification with 20 kDa (mPEG)(2)-Lys-NHS. The inhibition activity of both PEGylated and non-PEGylated RIP against cancer cells was much stronger than against normal cells, and the antigenicity of PEGylated RIP was reduced significantly. Our results suggested that the PEGylated RIP might be potentially developed as anti-cancer drug.

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To study the tumor specificity and antitumor activity of the replication-competent oncolytic adenovirus TOA02, which is controlled by a modified human telomerase reverse transcriptase (hTERT) promoter and expresses granulocyte macrophage colony-stimulating factor (GM-CSF). The wild-type hTERT promoter was modified, by inserting two E2F-binding sites. The effect of the modified hTERT on the viral yield and cytotoxicity of TOA02 were determined in vitro with a panel of tumor cells and normal cells, to evaluate tumor specificity; the effect on the antitumor efficacy and toxicity of TOA02 were determined in vivo, to evaluate the therapeutic potential of the adenovirus. The TOA02 adenovirus, which contained the modified hTERT promoter, produced a higher yield of virus in telomerase-positive and retinoblastoma-defective human cells, and a lower yield of virus in normal human cells than the wild-type adenovirus. A single injection of TOA02 showed strong antitumor efficacy in nude mice with human head/neck and hepatocellular carcinoma xenografts, and the efficacy further improved when used in combination with chemotherapy and with different routes of administration and regimens. In immunocompetent mice, the addition of GM-CSF produced a stronger antitumor activity and induced more mature dendritic cells and macrophages. The TOA02 adenovirus showed strong tumor-cell selectivity in vitro and antitumor efficacy in mouse models of human head/neck and hepatocellular cancer, suggesting that TOA02 has potential clinical applications for the treatment of solid tumors.