AIM: Type Ⅳ collagenase including MMP-2 and -9 plays an important role in cancer cell invasion and metastasis and is an attractive target for mAb-directed therapy. The immunoreactivity of mAb 3G11, a mAb directed against type Ⅳ collagenase in human colorectal carcinomas, was studied by immuno-histochemical (IHC) staining. mAb 3G11 was conjugated to an antitumor antibiotic lidamycin (LDM). The antitumor activity of 3G11-LDM conjugate against colon carcinoma was investigated in mice.METHODS: ELISA, gelatin zymography, and West blot assay were used for the biological characterization of mAb 3G11. The immunoreactivity of mAb 3G11 with human colorectal carcinomas was detected by IHC staining. The cytotoxicity of LDM and 3G11-LDM conjugate to human colon carcinoma HT-29 cells was examined by clonogenic assay and MTT assay. The therapeutic effect of conjugate 3G11-LDM was evaluated with colon carcinoma 26 in mice.RESULTS: As shown in ELISA, mAb 3G11 reacted specifically with type Ⅳ collagenase, while 3G11-LDM conjugate also recognized specifically its respective antigen. In IHC assay,mAb 3G11 showed positive immunoreactivity in most cases of colorectal carcinoma, and negative immunoreactivity in the adjacent non-malignant tissues. By gelatin zymography,the inhibition effect of mAb 3G11 on the secretion activity of type Ⅳ collagenase was proved. In terms of IC50 values in MTT assay, the cytotoxicity of LDM to human colon carcinoma HT-29 cells was 10 000-fold more potent than that of mitomycin C (MMC) and adriamycin (ADM). 3G11-LDM conjugate also displayed extremely potent cytotoxicity to human colon carcinoma HT-29 cells with an ICs0 value of 5.6×10-19 mol/L. 3G11-LDM conjugate at the doses of 0.05 and 0.1 mg/kg inhibited the growth of colon carcinoma 26 in mice by 70.3 and 81.2%, respectively.CONCLUSION: mAb 3G11 is immunoreactive with human colorectal carcinoma and its conjugate with LDM is highly effective against colon carcinoma in mice.