19-NOR-26,27-BISHOMO-VITAMIN-D-3 ANALOGS - A UNIQUE CLASS OF POTENT INHIBITORS OF PROLIFERATION OF PROSTATE, BREAST, AND HEMATOPOIETIC CANCER-CELLS

Vitamin D-3 [1,25-dihydroxyvitamin-D-3 (1,25(OH)(2)D-3)] modulates the proliferation and differentiation of many cen types. Analogs of 1,25( OH)(2)D-3 that have greater potency may become adjuvant therapy for br east and prostate cancers, myelodysplastic syndrome, acute myelogenous leukemia in remission and other cell types, especially in the setting of ion; disease burden. A new class of analogs of 1,25(OH)(2)D-3 has been synthesized that has a novel 19-nor moth, as well as incorporatin g many structural elements previously shown to increase potency. These analogs were examined for their effects on prostate cancer tell lines (PC-3, LN-Cap, and DU 145), a human breast fell line (MCF-7), and an acute myeloid leukemia cell line (HL-60). Dose-response clonogenic stu dies showed that each of these analogs had more potent antiproliferati ve activities against the cancer cells than 1,25(OH)(2)D-3, and 1,25-( OH)(2)-16,23Z-diene-26,27-bishomo-19-nor-D-3 (Ro 27-2014) was the most potent analog [10-fold increased activity compared to 1,25(OH)(2)D-3] . Further studies were pet-formed using Ro 27-2014. Pulse-exposure stu dies showed that a 5-day pulse-exposure to Ro 27-2014 (10(-7) M) in li quid culture was adequate to achieve a 50% inhibition of MCF-7 clonal growth in soft agar in the absence of the analog, suggesting that the growth inhibition mediated by the analog was irreversible. Cell cycle analyses using MCF-7 tells showed that Ro 27-2014(10(-7) M for 4 days) induced a significant increase in the number of cells in G(0)-G(1) (7 2.8 +/- 8.9% versus 49.9 +/- 3.5% in control cells), with a concomitan t decrease in the percent trf cells in S phase (13.1 +/- 6.2% versus 3 5.8 +/- 3.5% in control cells). The chief toxicity of ;vitamin D-3 com pounds is hypercalcemia, and therefore, we examined calcemic activity of Ro 27-2014 in mice and found it not to induce hypercalcemia at dose s of 0.05 mu g i.p. three times per week. In contrast, the same dose o f a 19-nor vitamin D-3 compound with 6 fluorines on the side chain (1, 25-(OH)(2)-16-ene-23-yne-26,27-F-6-19-nor-D-3), although also having p otent anticancer activity, caused severe hypercalcemia (18 mg/dl). In summary, 19-nor vitamin D-3 compounds with desaturation and lengthenin g of their side chains result in a series of compounds with a good the rapeutic index, having potent anticancer activity and low toxicity.