Increasing Ionic Calcium Inhibits Myeloma Cell Growth and its Progression in Mouse.
Syed Hassan Mehdi¹, Alex Lee², Paul K Lee², Donghoon Yoon¹
¹ Myeloma Center, the University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; ²CBHI (Calcium & Bone Health Institute, Canada), Coquitlam, British Colombia, Canada
Multiple myeloma (MM) is the second most common blood cancer, which forms in plasma cells in the bone marrow. MM-induced bone disease (MMBD) is one of the defining features of MM characterized by bone destruction and increased calcium level. We and others found that proteasome inhibitors (PIs) improve bone formation in MMBD, and a significant population of low-risk MM patients shows mineral deposition1-3. We developed a severe MMBD animal model4 and demonstrated that the bone anabolic agent promotes bone formation and delays MM progression5. Sigma Anti-Bonding Calcium Carbonate (SAC) is a physically modified calcium carbonate with a unique weak bonding. It acts as ionic calcium and significantly increases active ionized calcium in the body. We hypothesized that SAC inhibits the MMBD progression in the 5TGM1-induced MM mouse.
We divided the 8-12-week-old NOD SCID gamma mice into three groups: PBS, the SAC-Treated group before Transplant (TbT), and the SAC-Treated group after Transplant (TaT). SAC was treated via intraperitoneal injection, BID, five days/week. Since myeloma cell engraftment/proliferation in mice occurs within two weeks from systemic injection, we gave two weeks before or after the transplant (TbT or TaT). The 1×106 luciferase-expressing 5TGM1 cells were injected into the mice via the tail vein. Mice were imaged weekly by IVIS imager to assess the myeloma progression and terminated when endpoint criteria were met. Survival curves were plotted, and the median survivals and statical difference between the two groups were tested by the Log-rank test using GraphPad Prism (San Diego, CA). At postmortem, the spine was removed, and ex vivo bone mineral content and bone mineral density were measured using a PIXI-mus bone densitometer with on-board PIXI-mus software (G.E.Lunar, Madison, WI, USA). For histomorphometric analyses, the lumbar vertebrae (L1–L6) from the PBS and SAC-treated mice were scanned using a microCT40 (SCANCO Medical, Bassersdorf, Switzerland). The student’s t-test was conducted using GraphPrism7.
We found that he median survival was 45 days in the PBS group, while 50 days in the TbT group and 49.5 days in the TaT group. The BL image analysis showed that myeloma slowly progressed in both treated group mice, and DEXA results demonstrated that bone mineral density and bone mineral content significantly increased in the spine of SAC-treated mice compared to the control mice. Trabecular thickness and bone volume density (p < 0.05) were significantly increased in the SAC-treated group at the lumbar spine compared to the PBS group.
Although our results showed that two weeks of SAC pretreatment in mice may not be sufficient to affect mouse survival, we demonstrated that the SAC treatment delays mouse myeloma progression in 5TGM1-induced NSG mice by promoting bone formation.
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