A new Chinese study’s findings suggest Adriamycin-based chemotherapy may simulate cancer stem cells (CSCs) through transcription factor signaling activation, but that such signaling is inhibited by statins. Reported in the May 25, 2017, online edition of Stem Cell Reports, the results may be important in designing new osteosarcoma treatment regimens.
A rare but the most commonly diagnosed primary malignancy of growing bones affecting children and adolescents, osteosarcoma is characterized by its highly aggressive nature and metastatic potential.
Adriamycin (doxorubicin) has been used to treat osteosarcoma since the early 1970s. It is currently combined with methotrexate, cisplatin and ifosfamide as standard first-line chemotherapy.
However, despite advances in multidisciplinary management, the osteosarcoma cure rate has not improved significantly since the 1970s, with tumor recurrence and metastasis being common, and drug resistance occurring in most cases.
“Patients with localized osteosarcoma have 65 to 70 percent five-year survival rates, but those who present with metastases have survival rates of just 19 to 30 percent,” corresponding author Meidan Ying, an associate professor in the College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, told BioWorld Today.
For example, 40 to 50 percent of patients develop pulmonary metastases after apparently successful chemotherapy, and drug resistance is almost inevitable. Moreover, while chemotherapy reduces tumor mass, it exerts selective pressure on surviving cells, favoring growth of the most aggressive.
Recent evidence also suggests that tumor microenvironmental stresses such as chemotherapy can lead to enrichment of CSCs, resulting in cancer metastasis, recurrence and drug resistance.
“There is substantial evidence that chemotherapy can lead to CSC enrichment. For example, platinum-based chemotherapy has been shown to induce the enrichment of CSCs in non-small-cell lung cancer and ovarian cancer,” noted Ying.
“The anti-angiogenic agents, sunitinib [Sutent, Pfizer Inc.] and bevacizumab [Avastin, Roche Holding AG] have also been shown to increase breast CSCs via generation of tumor hypoxia. In addition, acquired resistance to epidermal growth factor receptor inhibitors is associated with a manifestation of stem cell-like properties in lung cancer cells,” said Ying, noting that the mechanisms underlying those processes and how to target CSCs are largely unknown.
CSCs are a subpopulation of tumor cells that possess tumor initiation and self-renewal capacity, and the ability to give rise to bulk populations of cancer cells through differentiation.
Moreover, “CSCs exhibit enhanced chemo/radiotherapy resistance, and their survival following cancer treatment is believed to be responsible for tumor recurrence and metastasis,” said Ying.
“Osteosarcoma stem cells (OSCs) are thought to have self-renewal abilities that can drive cancer metastasis, recurrence and drug resistance, so targeting these may provide a novel strategy in the treatment of osteosarcoma,” she explained.
In their new study, researchers led by Ying and Qiaojun He, a professor in the College of Pharmaceutical Sciences, showed that Adriamycin treatment induced a stem-like cell phenotype and promoted metastatic potential in osteosarcoma cells through up-regulation of a transcription factor called Kruppel-like factor 4 (KLF4).
KLF4 is one of the KLF family of transcription factors, which is involved in the regulation of cell proliferation, differentiation, apoptosis and somatic reprogramming.
“We found that Adriamycin could enhance the stemness and metastasis traits of osteosarcoma cells and that this was also associated with up-regulation of KLF-4 protein expression,” explained Ying. In addition, the researchers demonstrated that KLF4 gene knockdown using short interference (siRNA) blocked development of Adriamycin-induced stemness and metastasis capacity.
“The KLF4 knockdown finding suggests KLF4 is critical for development of these phenotypes, so targeting KLF4 may provide a novel therapeutic means to augment the Adriamycin chemosensitivity of osteosarcoma cells,” Ying suggested.
The research team then demonstrated that statins reversed the Adriamycin-induced CSC properties and metastasis by down-regulation of KLF4.
In particular, they showed that Zocor (simvastatin, Merck & Co Inc.) markedly impaired Adriamycin-enhanced tumorigenesis of human osteosarcoma KHOS/NP cells in vivo. The KHOS/NP cell line shows a very high tumorigenesis potential in mice, suggesting that simvastatin might inhibit OSCs.
“Our data show that statins, especially simvastatin, effectively antagonized the osteosarcoma stemness phenotype and metastasis induced by Adriamycin in vitro and in vivo. This provides a rationale for using the combination of statins and Adriamycin to improve treatment of patients with osteosarcoma and possibly other cancers,” co-corresponding author He told BioWorld Today.
“Our findings not only provide a possible mechanism of tumor recurrence in Adriamycin-treated osteosarcoma patients, but also help to optimize a therapeutic strategy to cure osteosarcoma.”
However, much remains to be done in that field, including elucidation of the mechanism of KLF4 in regulating Adriamycin-induced cancer stemness and determining whether the role of KLF-4 in regulating OSC stemness is restricted to Adriamycin.
“We hope through our preclinical investigations to gain a more in-depth understanding of the molecular mechanisms underlying regulation and maintenance of the OSC phenotype and its influence in osteosarcoma,” He said.
“We thereby hope to generate novel strategies for identifying agents for treating osteosarcoma that will influence the next generation of clinical trials, with the ultimate goal of improving survival outcomes.”