Abstract 5506: In vivo activity of the ribonucleoside analogue 8-chloro-adenosine in breast cancer mouse models.
Authors: Stellrecht Christine M. , Shentu Shujun , Ayres Mary L. , Gandhi Varsha 
Published: August 2014

In contrast to deoxyribose or arabinose containing nucleoside analogs that are currently established for cancer therapeutics, 8-chloro-adenosine (8-Cl-Ado) possesses a ribose sugar. This unique nucleoside analog is RNA directed and is in a phase I clinical trial for hematological malignancies. Preclinically, it has been found to be cytotoxic to a number of malignant cell lines. Previously, we demonstrated in the breast cancer cell lines, MCF-7 and BT-474, 8-Cl-Ado accumulates as a triphosphate (8-Cl-ATP) reaching ∼125 and ∼400 μM, respectively, by 6 h of treatment with 10 μM 8-Cl-Ado [Breast Cancer Res Treat 121:355, 2010]. This accumulation was coupled with a parallel decrease in the endogenous cellular ATP pool levels. These changes in nucleotide levels lead to ∼50% inhibition of RNA synthesis. The net effect of these metabolic changes results in a 90% loss of clonogenic survival after a 3 d treatment with 10 μM 8-Cl-Ado. This loss in survival was associated with both apoptotic and autophagic cell death. Cellular pharmacology analyses on CD2F1 mice after i.v. administration of 50 and 100 mg/kg 8-Cl-Ado, revealed 8-Cl-ATP accumulated in the circulating peripheral blood mononuclear cells; within 1 hr of infusion the levels reached ∼350 and ∼1150 μM, respectively [Cancer Chemother Pharmacol 50:85, 2002] which was comparable to the levels seen in BT-474 cells treated with 10 μM for 6 and 72 hr, respectively. To test the in vivo antitumor activity of 8-Cl-Ado in breast cancer, orthotopic xenograft mouse models using both MCF-7 and BT-474 cell lines were evaluated. 8-Cl-Ado was administered i.p. 3 d/wk for 3 wk with a dose range of 25, 50 and 100 mg/kg/d once tumors reached ∼0.4 cm diameter. The MCF-7 xenograft mice showed dose dependent tumor growth inhibition evident after the second dose. In mice with the BT-474 tumors, the 100 mg/kg dose was highly effective as tumor sizes decreased after the first dose of treatment. Furthermore, in several of the mice there was an eventual loss of a palpable tumor. Likewise, the 100 mg/kg 8-Cl-Ado dose had a profound effect on the final tumor volumes in the BT-474 xenograft mice assessed during necropsy and completely eliminated any visible tumors in 9/21 (42.8%) mice assessed during necropsy. Importantly, none of these tested doses (25, 50 and 100 mg/kg/d) resulted in any untoward toxicity which was assessed by infusing various 8-Cl-Ado doses in CD1 mice. The results of the toxicology assessment showed that only repeated high i.v. doses (250 and 350 mg/kg/d for 5 d) showed a persistent nephrotoxicity 32 d after drug administration, while no other pathologic or hematologic toxicities were observed. In conclusion, our data indicates tumoricidal levels of 8-Cl-ATP are readily achieved in vivo without deleterious toxic effects and establishes 8-Cl-Ado in vivo efficacy against 2 breast cancer tumor models. Based on these findings, we plan to test 8-Cl-Ado in the clinic for patients with breast cancer.

Citation Format: Christine M. Stellrecht, Shujun Shentu, Mary L. Ayres, Varsha Gandhi. In vivo activity of the ribonucleoside analogue 8-chloro-adenosine in breast cancer mouse models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5506. doi:10.1158/1538-7445.AM2013-5506