Background: Human breast carcinoma cell lines express high-affinity interleukin-4 receptors (IL-4R). We examined the expression and structure of these receptors on primary and cultured breast carcinoma cell lines and normal breast epithelial cells. We also tested the antitumor activity in vitro and in vivo of a fusion protein comprised of circular permuted IL-4 and truncated Pseudomonas exotoxin, termed IL-4(38-37)-PE38KDEL.
Materials and methods: Eight different primary cell cultures and cell lines of human breast carcinomas were examined for the expression of IL-4R by radiolabeled binding, reverse transcription polymerase chain reaction (RT-PCR) and Northern analyses, and subunit structure by crosslinking studies. The antitumor activity of IL-4 toxin was tested in vitro by cytotoxicity assays and in vivo in a xenograft model in immunodeficient animals.
Results: 125I-IL-4 specifically bound to primary cell cultures and cell lines with a Kd ranging between 0.2 and 1 nM. Breast tumor cells were found to express IL-4R beta and IL-13R alpha' chains, but not IL-2R gamma c chain. These cells were highly sensitive to the cytotoxic effect of IL-4(38-37)-PE38KDEL. The IC50 (concentration inhibiting protein synthesis by 50%) ranged between approximately 0.005-1.5 nM. A normal breast epithelial cell culture was not sensitive to the cytotoxic activity of IL-4(38-37)-PE38KDEL. MDA-MB231 human breast carcinoma cell line formed a rapidly growing tumor in nude mice. Intratumor and intraperitoneal administration of IL-4(38-37)-PE38KDEL caused a dose dependent regression of established tumors. A control toxin, anti-Tac(Fv)-PE38KDEL, targeted to the IL-2 receptor alpha chain did not cause regression of these tumors.
Conclusions: These results suggest that IL-4(38-37)-PE38KDEL may be a useful agent for targeting of IL-4 receptor positive human breast carcinomas and further studies should be performed to explore fully its potential.