Mesenchymal stem cells (MSCs) participate in the regeneration of tissue lesions induced by antimetabolite chemotherapy; however, the influence of this class of anti-cancer compounds on the stem cells remains largely unknown.
The survival of MSCs after exposure to 5-fluorouracil (5-FU) and gemcitabine was measured by viability and clonogenic assays. MSC morphology, surface marker expression, adhesion potential, cellular velocity and differentiation potential were determined after antimetabolite treatment. Cell cycle distribution and apoptosis were assessed using flow cytometry, and senescence induction was evaluated by beta-galactosidase staining. Gene expression arrays were used to analyze the expression of enzymes involved in DNA metabolism and multidrug resistance.
Here, we show that human primary bone marrow MSCs are relatively resistant to treatment with the widely used antimetabolite drugs 5-FU and gemcitabine. The stem cells were able to largely retain their functional abilities and defining stem cell traits after antimetabolite exposure. MSCs surface markers were found stably expressed, and the characteristic multi-lineage differentiation potential was maintained irrespective of 5-FU or gemcitabine treatment. High expression levels of enzymes involved in DNA metabolism and multidrug resistance transporters may contribute to the resistance to antimetabolite chemotherapy.
The observed resistance and functional integrity may form the basis for further investigations of MSCs as a potential therapy for antimetabolite-induced tissue damage.
Antimetabolite compounds comprise a large group of substances that inhibit components of the cellular metabolism and are widely used for the treatment of cancers, benign proliferative diseases or autoimmune diseases (Peters et al., 2000; Cipriani et al., 2014; Batista et al., 2010; Green et al., 2014). Many antimetabolite cancer agents exhibit structural similarities to the purine or pyrimidine bases of DNA and act by competitively inhibiting the synthesis of these molecules or their incorporation into nascent DNA strands, thereby blocking DNA replication (Kinsella et al., 1997; Hatse et al., 1999). Due to their efficiency against many cancer types, cytostatic antimetabolites form the largest group of anticancer agents currently in clinical use (Johnston et al., 1996). The prototypical antimetabolite cancer drug, 5-fluorouracil (5-FU) was developed as a pyrimidine analogue and received approval for clinical utilization in the early 1960s; 5-FU has since been introduced intro treatment protocols for breast, skin, head-and-neck, pancreatic, esophageal, gastric, colorectal and anal cancers (O'Connell et al., 1994; Jacobs et al., 1992; Berlin et al., 2002; Cunningham et al., 2006; AlBatran et al., 2016). While the drug's exact mechanism of action is yet to be completely understood, it involves blocking of the enzyme thymidylate synthase, resulting in a lack of phosphorylated deoxythymidine and a toxic accumulation of deoxyuridine (Hatse et al., 1999). Gemcitabine is a newer antimetabolite drug and was approved for clinical use in 1995; it is phosphorylated intracellularly and can then be incorporated into DNA instead of cytidine nucleotides. As it does not lead to DNA strand breaks, its incorporation is masked for physiological DNA repair mechanisms, thus creating commonly irreparable DNA damage (Plunkett et al., 1995). Gemcitabine is used against pancreatic, bladder, non-small cell lung, ovarian and breast cancers (Berlin et al., 2002; Messing et al., 2018; Cardenal et al., 1999). Both 5-FU and gemcitabine have well-known myelosuppressive effects that may result in life-threatening leukopenia or thrombopenia (Okusaka et al., 2006).