Use of tumor necrosis factor receptor 2 (TNFR2)/p75 and TNF-α as an antitumor strategy.

Abstract

e22010 Background: TNF-α has two receptors, TNFR1/p55 and TNFR2/p75, with diverse signaling roles: p55 - predominantly cytotoxic and p75 - prosurvival and proangiogenic. Compared to WT and p55KO/p75KO, growth of tumors in p75 knockout (KO) mice was decreased >50% in Lewis lung carcinoma (LLC) and B16 melanomas (Sasi et al., Oncogene, 2012). This was associated with increased apoptosis and decreased capillary density in tumos. We hypothesized that selective blocking of p75 receptor in tumors may sensitize them to TNF induced apoptosis. Methods: p75 receptor was knockdown (KD) in LLCs using shRNA. LLC and p75KD LLCs were implanted into WT mice flanks. On day 8 post-inoculation, mouse recombinant (mr) TNF (12.5 ng/g/injection) or saline was injected x2 daily for 6 days. Tumor volumes (tV) were measured daily and tumor weights (tW) on day 16. Tumors, tubular bones and spleens were examined by 2 pathologists blindfolded to treatments. Results: Mouse weights remianed stable throughout the study in all groups. There was no difference in tV or tW between LLC minus(-) TNF and p75KD LLC-TNF tumors on day 16 (2 d days after last injection). Compared to 3 control groups, p75KD LLC+TNF showed >2-5-fold decreases in tV (p<0.001, n=8) and tW (p<0.0001, n=8). There was NO difference in tV or tW (p=ns) end of study vs before injections in p75KD LLC+TNF group whereas in 3 control groups tV and tW were increased 2.7-, 4.5- and 3.2-fold (p<0.01, p<0.0002 and p<0.0001). Pathology revealed that 1/3 of tumors in p75KD LLC+TNF group were nearly 100% necrotic. Bone marrow and spleens did not show significant TNF-induced systemic toxic effect. There was an inflammatory response in the BM and spleens of mice with necrotic tumors in +TNF group, reflected by shift of myeloid/erythroid radio in the BM and moderate increases in lymphoid follicles in the spleen. Conclusions: Our results suggest that blocking p75 expression in tumor tissue combined with administration of small exogenous doses of TNF significantly inhibits aggressive LLC tumor growth and induces nearly 100% tumor necrosis in 1/3 of the experimental group in six days, with no detectible systemic toxicity. This may represent new and effective therapy against lung neoplasms and potentially solid tumors of other origin.