Prokaryotically and eukaryotically expressed interleukin-24 induces breast cancer growth suppression via activation of apoptosis and inhibition of tumor angiogenesis.

Melanoma differentiation‑associated‑7 (mda‑7)/interleukin‑24 (IL‑24), a unique cytokine‑tumor suppressor, exerts tumor‑selective killing activity in numerous types of cancer cell. Although eukaryotically and prokaryotically expressed recombinant human (rh)IL‑24 proteins have been previously shown to produce potent antitumor effects, to the best of our knowledge, no side‑by‑side study has been conducted that compares the two proteins directly. In the present study, rhIL‑24 protein was expressed in BL21 Escherichia coli transformed with the pET‑21a(+)‑hIL‑24 plasmid by isopropyl‑β‑D‑1‑thiogalactopyranoside induction. Following a denaturing and renaturing process, the soluble rhIL‑24 was purified using a Q‑Sepharose column. rhIL‑24 protein was also expressed in Chinese hamster ovary mammalian cells stably transfected with the pcDNA3‑hIL‑24 plasmid. The in vitro antitumor efficacies of the two treatments were compared using the MDA‑MB‑231 human breast cancer cell line. Furthermore, the therapeutic efficacies of the bacteria‑derived rhIL‑24 protein and the liposome‑coated pcDNA3‑hIL‑24 naked plasmid were evaluated in athymic nude mice with subcutaneously xenografted MDA‑MB‑231 cell tumors. The prokaryotically expressed/purified rhIL‑24 protein and the eukaryotically expressed rhIL‑24 in the cell supernate were revealed to be capable of efficiently suppressing MDA‑MB‑231 tumor growth in vitro. Similarly, the administration of bacteria‑derived rhIL‑24 protein and pcDNA3‑hIL‑24 naked plasmid also provided therapeutic benefits in the treatment of in vivo MDA‑MB‑231 xenografted tumors. The retarded in vitro and in vivo breast cancer growth elicited by rhIL‑24 was closely associated with the upregulation of the ratio of anti‑apoptotic B cell lymphoma 2 (Bcl‑2) to pro‑apoptotic Bcl‑2‑associated X protein (Bax), as well as the activation of caspase‑3 followed by marked induction of apoptosis, and the notable inhibition of tumor angiogenesis. Thus, the results of the present study indicate that prokaryotically expressed rhIL‑24 protein may be an alternate and promising antitumor agent in human breast cancer or other types of cancer.