Sapphyrins Exhibit Tumor Selectivity and Efficacy in Animal Models of Hematologic Malignancies.

Sapphyrins are pentapyrrolic metal-free expanded porphyrins that localize to tumors. We have previously demonstrated that sapphyrins induce apoptosis in a variety of hematologic tumor cell lines including lymphomas (Ramos, DHL-4, HF-1), leukemias (Jurkat, HL-60), and myelomas (8226/S, 1-310, C2E3, 1-414). Through chemical modification of the parent compound, PCI-2000, a number of derivatives were generated and tested for induction of apoptosis in Ramos cells. PCI-2000 and one of the more potent apoptosis-inducing derivatives, PCI-2050, were injected into CD-1 nude mice bearing Ramos xenografts. Animals were sacrificed 48 hrs after injection and analyzed for drug uptake in the tumor, liver and spleen using flow cytometry. For PCI-2000, the relative uptake was spleen>tumor>liver. For PCI-2050 the relative uptake was tumor>spleen>liver, suggesting that PCI-2050 preferentially localizes in tumors compared to PCI-2000. Tumor cells isolated from PCI-2050 treated animals grew less well in culture and had more apoptotic cells than those derived from PCI-2000 or control animals. Uptake of PCI-2050 into xenograft tumor cells and tumor cell killing was dose dependent. PCI-2050 (10 umol/kg x 2 days in a row) was administered to Ramos xenograft bearing animals that were then monitored for tumor growth. In both minimal tumor (animals treated before tumor was palpable) and established tumor (palpable tumor) models, PCI-2050 reduced tumor growth by 60–75%. Alternative dosing strategies revealed that split dosing (allowing 1 or more days between doses) was more efficacious in tumor control than dosing 2 days in a row. At the doses used in this study, there was no myelosuppression or lymphosuppression, hepatic or renal abnormalities as assessed by complete blood count and comprehensive serum chemistry analysis, respectively. Our work demonstrates that PCI-2050 induces apoptosis in tissue culture and inhibits tumor growth in an animal tumor model while exhibiting minimal toxicity. PCI-2050 and other sapphyrin derivatives will be further evaluated as potential anti-cancer agents.