The la autoantigen is a malignancy-associated cell death target that is induced by DNA-damaging drugs

Purpose: To evaluate the La autoantigen as a target for specific monoclonal antibody (mAb) binding in dead cancer cells after use of DNA-damaging chemotherapy. Experimental Design: In vitro studies of La-specific 3139 mAb binding to malignant and normal primary cells with and without cytotoxic drug treatment were done using immunoblotting and flow cytometry. Chromatin-binding studies and immunofluorescence detection of gamma H2AX as a marker of DNA double-stranded breaks together with 3139 binding assays were done to measure DNA damage responses. Incorporation of a transglutaminase 2 (TG2) substrate and TG2 inhibition were studied to measure protein cross-linking in dead cells. Results: La was overexpressed in human cancer cell lines with respect to normal primary cells. Within 3 h of the DNA-damaging stimulus, La became chromatin bound when it colocalized with,gamma H2AX. Later, after the stimulus produced cell death, La-specific 3139 mAb bound specifically and preferentially in the cytoplasm of dead cancer cells. Moreover, 3139 binding to dead cancer cells increased with increasing DNA damage. Both La and 3139 became cross-linked in dead cancer cells via TG2 activity. Conclusion: La autoantigen represents a promising cancer cell death target to determine chemotherapy response because its expression was selectively induced in dead cancer cells after DNA-damaging chemotherapy.