Selective potentiation of lometrexol growth inhibition by dipyridamole through cell-specific inhibition of hypoxanthine salvage

Enhanced anticancer activity of combined treatment of imatinib and dipyridamole in solid Ehrlich carcinoma-bearing mice

The current study was designed to evaluate potential enhancement of the anticancer activity of imatinib mesylate (IM) with dipyridamole (DIP) and to investigate the underlying mechanisms of the combined therapy (IM/DIP) to reduce hepatotoxicity of IM in solid Ehrlich carcinoma (SEC)-bearing mice. SEC was induced in female albino mice as a model for experimentally induced breast cancer. Mice were randomly divided into seven groups (n = 10): SEC vehicle, IM₅₀ (50 mg/kg), IM₁₀₀ (100 mg/kg), DIP (35 mg/kg), a combination of IM₅₀/DIP and IM₁₀₀/DIP. On day 28th, mice were sacrificed and blood samples were collected for hematological studies. Biochemical determination of liver markers was evaluated. Glutamic oxaloacetic transaminase (SGOT), glutamic pyruvic transaminase (SGPT) and alkaline phosphatase (ALP) levels were assessed. In addition, MDR-1 gene expression and immunohistochemical staining of BAX and BCL-2 was done. Also, in vitro experiment for determination of IC50 of different treatments and combination index (CI) were assessed in both MCF-7 and HCT-116 cell lines. IM- and/or DIP-treated groups showed a significant reduction in tumor volume, weight, and serum levels of SGOT, SGPT, and AIP compared to vehicle group. In addition, reduction of VEGF, Ki67, and adenosine contents was also reported by treated groups. Also, IM/DIP combination showed lower IC50 than monotherapy. Combination index is less than 1 for IM/DIP combination in both cell lines. DIP as an adjuvant therapy potentiated the cytotoxic effect of IM, ameliorated its hepatic toxicity, and showed synergistic effect with IM in vitro cell lines. Furthermore, the resistance against IM therapy may be overcome by the use of DIP independent on mdr-1 gene expression.

High expression of PRPS1 induces an anti-apoptotic effect in B-ALL cell lines and predicts an adverse prognosis in Chinese children with B-ALL

Phosphoribosyl pyrophosphate synthetase 1 (PRPS1) is closely associated with a number of diseases; however, its influence in B-cell acute lymphoblastic leukemia (B-ALL) and the potential molecular mechanisms involved remain unclear. The present study aimed to evaluate the expression of PRPS1 in Chinese children with B-ALL and to investigate the mechanism of action of PRPS1 in this disease. A Cell Counting Kit-8 (CCK-8) assay was performed to examine the proliferation of B-ALL Sup-B15 and Raji cells, and flow cytometric analysis was conducted to determine the cell cycle distribution and rate of apoptosis. The mRNA and protein expression levels of PRPS1, MYC proto-oncogene, bHLH transcription factor, cyclin E1, B-cell lymphoma-2 (Bcl-2), cyclin dependent kinase 2 and caspase-3 were detected by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. Elevated PRPS1 expression was associated with a high-risk stratification and poor prognosis in patients with B-ALL. Furthermore, overexpression of PRPS1 accelerated the growth of and inhibited apoptosis in Sup-B15 and Raji cells as well as increasing the expression of Bcl-2 to induce an anti-apoptotic effect in B-ALL cell lines. The results of the present study indicate that PRPS1 regulates multiple processes in B-ALL and may be an attractive therapeutic target.

Resistance-modifying agents. 11.(1) Pyrimido[5,4-d]pyrimidine modulators of antitumor drug activity. Synthesis and structure-activity relationships for nucleoside transport inhibition and binding to alpha1-acid glycoprotein

The cardiovascular and antithrombotic agent dipyridamole (DP) has potential therapeutic utility as a modulator of the activity of antimetabolite antitumor agents by virtue of its inhibition of nucleoside transport. However, the activity of DP can be compromised by binding to the acute phase serum protein, alpha(1)-acid glycoprotein (AGP). Analogues of DP were synthesized and evaluated as inhibitors of (3)H-thymidine uptake into L1210 leukamia cells in the presence and absence of 5 mg/mL AGP. Compounds with potency similar to that of DP were identified where the piperidino substituents at the 4,8-positions were replaced by 4'-methoxybenzylamino, 3',4'-dimethoxybenzylamino, or piperonylamino groups. Replacement of the diethanolamino groups at the 2,6-positions of DP by alkylamino or alkoxy substituents was tolerated, although at least one oxygen-bearing function (hydroxyl or alkoxy) was required in the side chain for activity comparable to that of DP. Whereas AGP completely ablated the activity of DP, the majority of the newer compounds synthesized retained significant activity in the presence of excess AGP, although replacement of the piperidino groups at the 4,8-positions by N-methylbenzylamino substituents did, in some cases, restore susceptibility to AGP. Selected compounds have been demonstrated to prevent rescue from antifolate cytotoxicity, mediated by nucleoside salvage.

Resistance-modifying agents. Part 7: 2,6-disubstituted-4,8-dibenzylaminopyrimido[5,4-d]pyrimidines that inhibit nucleoside transport in the presence of alpha1-acid glycoprotein (AGP)

The synthesis and biological evaluation of potent 4,8-dibenzylaminopyrimidopyrimidine nucleoside transport inhibitors, with reduced binding to alpha1-acid glycoprotein, is reported.

Dipyridamole potentiates the in vitro activity of MTA (LY231514) by inhibition of thymidine transport

The novel pyrrolopyrimidine-based antifolate LY231514 (MTA), inhibits multiple folate-requiring enzymes including thymidylate synthase, glycinamide ribonucleotide formyltransferase and dihydrofolate reductase. Both thymidine and hypoxanthine are required to reverse MTA growth inhibition in leukaemia and colon cancer cells. Prevention of MTA growth inhibition by thymidine and/or hypoxanthine was investigated in two human lung (A549, COR L23) and two breast (MCF7, T47D) tumour cell lines, and the effect of the nucleoside/base transport inhibitor dipyridamole (DP) on thymidine and hypoxanthine rescue defined. MTA IC50 values (continuous exposure three population doublings) were: A549-640 nM, COR L23-28 nM, MCF7-52 nM and T47D-46 nM. Thymidine (1 microM) completely prevented growth inhibition at the MTA IC50 in all cell lines. At 10 x IC50, growth inhibition was only partially reversed by thymidine (< or = 10 microM); both thymidine and hypoxanthine (30 microM) being required for complete reversal, reflecting the multi-targeted nature of MTA. Growth inhibition by MTA was not affected by hypoxanthine alone. A non-toxic concentration (1 microM) of DP prevented thymidine/hypoxanthine rescue of MTA indicating that DP may potentiate MTA activity by preventing nucleoside and/or base salvage. Thymidine transport was inhibited by > or = 89% by 1 microM DP in all cell lines, whereas hypoxanthine transport was inhibited only in A549 and MCF7 cells. Therefore, prevention of end-product reversal of MTA-induced growth inhibition by DP can be explained by inhibition of thymidine transport alone.

Nucleoside transporters: molecular biology and implications for therapeutic development

The uptake of nucleosides (or nucleobases) is essential for nucleic acid synthesis in many human cell types and in parasitic organisms that cannot synthesize nucleotides de novo. The transporters responsible are also the route of entry for many cytotoxic nucleoside analogues used in cancer and viral chemotherapy. Moreover, by regulating adenosine concentrations in the vicinity of its cell-surface receptors, nucleoside transporters profoundly affect neurotransmission, vascular tone and other processes. The recent molecular characterization of two families of human nucleoside transporters has provided new insights into the mechanisms of natural nucleoside and drug uptake and into future developments of improved therapies.