Carbon Dots As a Potential Therapeutic Agent for Anemia Treatment in Malignancies

Anemia, characterized by a decreased number of circulating red blood cells (RBCs) and/or hemoglobin, is a major public health problem worldwide. It can be caused by different pathophysiologic processes, prognoses and preventive or therapeutic approaches. As the commonest hematological manifestation of cancer, anemia afflicts 40-64% of patients treated for malignancies and leads to decline in the quality of life, poor tolerance to chemotherapeutic drugs, and shortened survival. However, few agents have been developed to treat this disease in the clinic, especially applying in malignancies. Erythropoietin (EPO) as a common agent is used to treat for a various of anemia. Nevertheless, several reports have showed that it can aggravate the proliferation and metastasis of some cancer cells, including breast cancer and ovarian cancer. Therefore, it is urgent to develop new efficient agents to manage and treat caner-related anemia.

Carbon dots (CDs) as a new class of zero-dimensional carbon nano materials with size less than 10 nm, have shown enormous potentials for biomedical and optoelectronic applications owing to their outstanding characteristics such as good biocompatibility, low cytotoxicity, photostability as well as unique tunable photoluminescence and exceptional physicochemical properties. Herein, we have designed one kind of distinctive CDs with sp2/sp3 carbon and oxygen/nitrogen-based groups via a hydrothermal process, which are efficient to treat anemia without triggering tumor proliferation and migration.

We first showed that the CDs significantly promote the proliferation of erythroid cells, using an in vitro erythroid differentiation system. To explore the mechanisms responsible for increased cell growth, we examined the effects of CDs on cell-cycle progression, and found that CDs led to an increased S phase in conjunction with decreased G1/G0 phase. Interestingly, CDs remarkably increased the rate of erythroblast enucleation, the essential step of human RBCs production, without affecting erythroid progenitor development and terminal erythroid differentiation. We then checked the effect of CDs on erythropoiesis in vivo. Compared with the control group, intraperitoneal injection of CDs in normal mice caused higher percentage of reticulocytes, RBCs and hemoglobin in peripheral blood, which are similar with those of intraperitoneal injection of EPO. To further investigate the functions of CDs on stress erythropoiesis, we performed the phenylhydrazine-induced anemia mice model, and found that CDs, similar with EPO, could quickly rescue the typical anemia phenotypes, such as compensatory splenomegaly, decreased RBCs, reduced hemoglobin and lower hematocrit. Moreover, flow cytology analysis indicated that CDs and EPO led to elevation of orthochromatic erythroblasts and reticulocytes in bone marrow and lower rates of these populations in spleen, implying CDs' potential function to treat anemia. Macrophages have been proved to be important for erythropoiesis and associated with tumorigenesis. Intriguingly, we found that while EPO induced more CD169⁺F4/80⁺ macrophages in bone marrow, treatment of CDs had no influence on macrophages compared with control group. To examine whether the CDs have effects on tumor directly, we tested breast cancer cell line MD-231 and ovarian cancer cell line A2780. When EPO obviously promoted the proliferation and migration of these tumor cells, which is consistent with previous reports, CDs had no discernible effect on the tumor cell growth and migration. Taken together, our study demonstrates that CDs could induce efficient erythropoiesis without affecting tumour growth, representing a promising agent for caner-related anemia.