8-Amino-adenosine is a potential therapeutic agent for multiple myeloma

Abstract

Multiple myeloma (MM) is a malignancy of clonal B-cells that accounts for 10% of all hematologic malignancies. We have shown previously that a novel purine analogue, 8-chloro-adenosine, has significant activity for MM in preclinical studies. Objective: Using MM cell lines, we investigated the molecular mechanism of related congener of adenosine, 8-amino-adenosine (8-NH2-Ado). Methods: We employed biological and biochemical assays in MM cell lines to evaluate the clinical potential of 8-NH2-Ado. Results: In MM cell lines both sensitive and resistant to conventional chemotherapies, 8-NH2-Ado is cytotoxic, with IC50 ranging from 300 nmol/L to 3 μmol/L. A mouse leukemic cell line lacking adenosine kinase activity was resistant to 8-NH2-Ado, indicating that phosphorylation of 8-NH2-Ado to its triphosphate form is required for cytotoxicity. A 4-hour incubation of MM cells with 10 μmol/L analogue resulted in an accumulation of >7 mmol/L 8-NH2-ATP with a parallel decline in the endogenous ATP levels. Accumulation of 8-NH2-ATP was dependent on both exogenous concentration of 8-NH2-Ado and incubation time. The accumulation of 8-NH2-ATP was accompanied by a decrease in both RNA and DNA synthesis. The mechanism of 8-NH2-Ado-mediated cytotoxicity was due to apoptosis as measured by an increase in Annexin V binding, a decrease in mitochondrial membrane potential, an increase in caspase activity, cleavage of caspase substrates, and an increase in cells with a sub-G1 DNA content. Conclusion: Based on these results, we conclude that 8-NH2-Ado may hold great potential as a therapeutic agent for the treatment of MM.

Novel Adenosine-Derived Inhibitors of 70 kDa Heat Shock Protein, Discovered Through Structure-Based Design

“…Compound 4 was also shown to inhibit the growth of human colon tumor 116 (HCT116) cells in a sulforhodamine B (SRB) growth inhibition assay (GI 50 0.05 µM). 16,17 The cytotoxic activity of 4 has been previously reported, 18 but the mismatch between HSP70 FP IC 50 and HCT116 GI 50 , and later PD marker studies (see below), indicated that the cytotoxic mechanism of action of compound 4 must be predominantly through a route other than HSP70 inhibition.…”

8-Aminoadenosine Enhances Radiation-induced Cell Death in Human Lung Carcinoma A549 Cells

“…Several studies have shown that 8-chloroadenosine (8-Cl-Ado) and 8-NH2-Ado have strong hematological toxicity through their ability to inhibit RNA synthesis, and 8-Cl-Ado is currently in a Phase I clinical study for patients with chronic lymphocytic leukemia. [11][12][13][14][15] 8-NH2-Ado was reported to be more potent as shown by induction of apoptosis-related cleavage of poly (ADP-ribose) polymerase compared with 8-Cl-Ado. Furthermore, the intracellular accumulation of 8-NH2-ATP is 38-fold higher than that of 8-Cl-ATP in leukemia cells and leads to greater analogue-mediated declines in the ATP pool and mRNA synthesis.…”

“…Adenosine and 8-NH 2 -Ado are known to be converted to ATP and 8-NH2-ATP by adenosine kinase and other enzymes. 11) If phosphorylation of 8-NH2-Ado is essential to lead the radiosensitization and this phosphorylation reaction is a competitive reaction to the same enzyme for adenosine, addition of exogenous adenosine to the culture medium seems to ameliorate the killing effect of 8-NH2-Ado. Thus, to examine the effect of adenosine on 8-NH2-Ado-induced apoptosis and intracellular ATP level, A549 cells were cotreated with the large amounts (10 μM-500 μM) of adenosine and 10 μM 8-NH2-Ado for 24 h. As shown in Fig.…”

“…15) Furthermore, in multiple myeloma cells exposed to 8-NH2-Ado, it was reported that accumulation of 8-NH2-ATP and depletion of intracelluar ATP occurred and apoptotic cell death was induced by inhibition of not only RNA synthesis but also DNA synthesis. 11) Another report also showed that 8-NH2-Ado induced apoptotic cell death by inhibiting the expression of anti-apoptotic proteins Mcl-1 and XIAP in chronic lymphocytic cells. 12) These observations imply that 8-NH2-Ado has the ability to induce radiosensitization for solid tumors.…”

“…1, was demonstrated to have strong hemato-logical toxicity through its ability to inhibit RNA synthesis. [11][12][13][14][15] This inhibition of RNA synthesis occurred through multiple mechanisms such as exhaustion of the ATP pool needed for RNA constituent and polyadenylation reactions, inhibition of phosphorylation of RNA polymerase II and transcription termination through incorporation of 8-NH2-ATP into RNA at the 3'-terminal position. 15) Furthermore, in multiple myeloma cells exposed to 8-NH2-Ado, it was reported that accumulation of 8-NH2-ATP and depletion of intracelluar ATP occurred and apoptotic cell death was induced by inhibition of not only RNA synthesis but also DNA synthesis.…”