Evaluation of Novel S-Allyl Derivatives of 6-Mercapto-Purine against B-CLL: Combining the Effects of Different Compounds in A Single Molecule.

Abstract 3437

Poster Board III-325

Previously, we have shown that Allicin, the highly active compound of freshly crushed garlic, produced by the reaction of the enzyme Alliinase with its substrate Alliin, induced the apoptotic killing of B-CLL cells in vitro. In addition, we also reported that generation of Allicin in situ on the surface of B-CLL cells by targeting Alliinase to the cell surface of the CD20⁺ cells by Rituximab, resulted in the eradication of primary B-CLL in a human-mouse chimeric model, denoting the marked anti-CLL potential of combining these two different molecules, with different mechanism of action, into a single drug entity (Arditti et al., Mol Cancer Ther 2005;4(2)325-331). Indeed, monotherapeutic approaches, even if effective, are usually not sufficient to fully eradicate B-CLL and the most effective therapeutic protocols require the utilization of more than one agent. With this in mind, we took advantage of the high reactivity of Allicin, with SH-containing compounds, and created novel chimeric compounds by the combination of Allicin with 6-Mercapto-Purine (6MP) and 6MP-riboside (6MPR), both SH-containing purine analogs used for decades for the treatment of hematologic malignancies. The resulting novel compounds, S-Allyl-6MP (SA-6MP) and S-Allyl-6MPR (SA-6MPR), were examined against primary B-CLL cells obtained from the peripheral blood of patients at Binnet stage C. In our in vitro assays, Annexin-V staining indicated that SA-6MP acted in a dose dependent manner, inducing the apoptotic death of 37.9% and 95.2% of plated CD19⁺CD5⁺ B-CLL cells (10.9% in untreated cells) incubated for 16 h at 37 °C in the presence of 50 uM or 100 uM, respectively. As expected, the original 6MP compound had no impact on the viability of plated B-CLL cells (9.7% and 8.7%) at doses of up to 150 uM. In preliminary in vivo experiments, we compared the anti-BCLL activity of SA-6MP with that of SA-6MPR and the original 6MP compound on primary B-CLL cells from 5 different patients (Binnet stage C) in a human-SCID/Beige mouse model. Following the engraftment of the human B-CLL cells, mice were treated with i.p. injections of 2.5 mg/kg body weight of SA-6MP, SA-6MPR, or 6MP on a daily basis throughout 7 consecutive days, after which, the engraftment of primary B-CLL cells was examined by the recovery of CD45⁺CD19⁺CD5⁺ from injected mice. An additional group of mice injected with vehicle (1% DMSO) was also examined as a control. In close similarity to our in vitro results, engraftment of primary B-CLL cells was considerably reduced following treatment with SA-6MP (>90% reduction), as compared with treatment with the original 6MP drug. In addition, the chimeric riboside 6MP derivative, SA-6MPR, induced a potent anti-BCLL effect comparable to that of SA-6MP. In summary, our results in vitro and in vivo suggests that combining the pro-apoptotic effects of Allicin with the antiproliferative effects of 6MP or 6MPR is superior to the effect of either of the purine analogs alone. This approach may be evaluated at first instance in B-CLL patients with refractory disease.