Dipyridamole interacts with the N-terminal domain of HSP90 and antagonizes the function of the chaperone in multiple cancer cell lines

Reprogramming of pyrimidine nucleotide metabolism supports vigorous cell proliferation of normal and malignant T cells

ABSTRACT

Adult T-cell leukemia/lymphoma (ATL) is triggered by infection with human T-cell lymphotropic virus-1 (HTLV-1). Here, we describe the reprogramming of pyrimidine biosynthesis in both normal T cells and ATL cells through regulation of uridine-cytidine kinase 2 (UCK2), which supports vigorous proliferation. UCK2 catalyzes the monophosphorylation of cytidine/uridine and their analogues during pyrimidine biosynthesis and drug metabolism. We found that UCK2 was overexpressed aberrantly in HTLV-1-infected T cells but not in normal T cells. T-cell activation via T-cell receptor (TCR) signaling induced expression of UCK2 in normal T cells. Somatic alterations and epigenetic modifications in ATL cells activate TCR signaling. Therefore, we believe that expression of UCK2 in HTLV-1-infected cells is induced by dysregulated TCR signaling. Recently, we established azacitidine-resistant (AZA-R) cells showing absent expression of UCK2. AZA-R cells proliferated normally in vitro, whereas UCK2 knockdown inhibited ATL cell growth. Although uridine and cytidine accumulated in AZA-R cells, possibly because of dysfunction of pyrimidine salvage biosynthesis induced by loss of UCK2 expression, the amount of UTP and CTP was almost the same as in parental cells. Furthermore, AZA-R cells were more susceptible to an inhibitor of dihydroorotic acid dehydrogenase, which performs the rate-limiting enzyme of de novo pyrimidine nucleotide biosynthesis, and more resistant to dipyridamole, an inhibitor of pyrimidine salvage biosynthesis, suggesting that AZA-R cells adapt to UCK2 loss by increasing de novo pyrimidine nucleotide biosynthesis. Taken together, the data suggest that fine-tuning pyrimidine biosynthesis supports vigorous cell proliferation of both normal T cells and ATL cells.

Dipyridamole enhances the anti-cancer ability of aspirin against colorectal cancer by inducing apoptosis in an unfolded protein response-dependent manner

PURPOSE

Available evidence indicates that dipyridamole enhances the anti-thrombotic effects of aspirin for the prevention of secondary strokes. Aspirin is a well-known non-steroid anti-inflammatory drug. This anti-inflammatory property has turned aspirin into a potential drug for inflammation-related cancers such as colorectal cancer (CRC). Here, we aimed to explore whether the anti-cancer effect of aspirin against CRC could be improved by combined administration with dipyridamole.

METHODS

Population-based clinical data analysis was conducted to assess a possible therapeutic effect of combined dipyridamole and aspirin treatment in inhibiting CRC compared with either monotherapy. This therapeutic effect was further verified in different CRC mouse models, i.e. an orthotopic xenograft mouse model, an AOM/DSS mouse model, an Apcmin/+ mouse model and a patient derived xenograft (PDX) mouse model. The in vitro effects of the drugs on CRC cells were tested using CCK8 and flow cytometry assays. RNA-Seq, Western blotting, qRT-PCR and flow cytometry were used to identify the underlying molecular mechanisms.

RESULTS

We found that dipyridamole combined with aspirin had a better inhibitory effect on CRC than either monotherapy alone. The enhanced anti-cancer effect of the combined use of dipyridamole with aspirin was found to rely on the induction of an overwhelmed endoplasmic reticulum (ER) stress and subsequent pro-apoptotic unfolded protein response (UPR), which was different from the anti-platelet effect.

CONCLUSIONS

Our data indicate that the anti-cancer effect of aspirin against CRC may be enhanced by combined administration with dipyridamole. In case further clinical studies confirm our findings, these may be repurposed as adjuvant agents.