Differential Sensitivities of Fast- and Slow-Cycling Cancer Cells to Inosine Monophosphate Dehydrogenase 2 Inhibition by Mycophenolic Acid

Abstract

As uncontrolled cell proliferation requires nucleotide biosynthesis, inhibiting enzymes that mediate nucleotide biosynthesis constitutes a rational approach to the management of oncological diseases. In practice, however, results of this strategy are mixed and thus elucidation of the mechanisms by which cancer cells evade the effect of nucleotide biosynthesis restriction is urgently needed. Here we explored the notion that intrinsic differences in cancer cell cycle velocity are important in the resistance toward inhibition of inosine monophosphate dehydrogenase (IMPDH) by mycophenolic acid (MPA). In short-term experiments, MPA treatment of fast-growing cancer cells effectively elicited G0/G1 arrest and provoked apoptosis, thus inhibiting cell proliferation and colony formation. Forced expression of a mutated IMPDH2, lacking a binding site for MPA but retaining enzymatic activity, resulted in complete resistance of cancer cells to MPA. In nude mice subcutaneously engrafted with HeLa cells, MPA moderately delayed tumor formation by inhibiting cell proliferation and inducing apoptosis. Importantly, we developed a lentiviral vector-based Tet-on label-retaining system that enables to identify, isolate and functionally characterize slow-cycling or so-called label-retaining cells (LRCs) in vitro and in vivo. We surprisingly found the presence of LRCs in fast-growing tumors. LRCs were superior in colony formation, tumor initiation and resistance to MPA as compared with fast-cycling cells. Thus, the slow-cycling compartment of cancer seems predominantly responsible for resistance to MPA.

Mitochondrial Fusion Via OPA1 and MFN1 Supports Liver Tumor Cell Metabolism and Growth

“…Cell apoptosis analysis was performed by staining cells with Annexin V-FITC and PI as described before [24].…”

What does not kill a tumour may make it stronger:in silicoInsights into Chemotherapeutic Drug Resistance

“…Slow-cycling cells are distinguishable in vitro [13] and Srinivasan et al [67] demonstrated that fast and slow-cycling cells may coexist in a tumour. Many chemotherapeutic drugs, such as cisplatin, attack only cells in a certain phase of the cell cycle by targeting proteins overexpressed in the corresponding phase, leaving other cells unaffected [54,75].…”

“…Rizzo et al [60] demonstrated in vivo in mouse tails that a subpopulation of CSC-like cells indeed may benefit from drug presence when competing for resources with other cell populations. Thus slow-cycling cells have been identified to reinforce tumours, hence to eradicate cancer cell populations containing a subpopulation of slow-cycling cells it is crucial to target both slow-cycling and fast-cycling cells [13]. Intracellular communication is vital for multicellular organisms and cells may communicate with each other using chemical signalling, direct physical contact or, as discussed here, sending and receiving exosomes [66,81].…”

“…Typical chemotherapy drugs target cells in active cell cycle phases, thus quiescent cells parry drug effects [40] and similarly slow-cycling cells are intrinsically more drug resistant than fast cycling cells [13,67] as they are more likely to evade drug attacks. Slow-cycling cells have been linked to cancer stem cell-like (CSC-like) cells [40], they are important drivers for tumours due to their increased drug-survival rate and ability to serve as reserve stem cells [13,67]. CSC-like cells have been depicted to display various traits including being slow-cycling, migratory and non-adhesive [1].…”

Cytoplasmic rods and rings in mycophenolic acid treatment

“…The IMPDH2 isoform is upregulated in a wide range of cancer tissues, associated with disease aggressiveness, and related to poor patient survival. 6 Thus, targeting IMPDH is expected to inhibit cancer by simultaneously blocking nucleotide synthesis and provoking immune response through RR structure induced autoantibodies. Of note, a general feature of many IMPDH inhibitors (e.g.…”