Author ORCID Identifier

Defense Date


Document Type


Degree Name

Doctor of Philosophy


Health Related Sciences

First Advisor

William J Korzun

Second Advisor

Teresa S Nadder

Third Advisor

Melissa J Jamerson

Fourth Advisor

Joseph R Piccotti


Test article CC-325 is a potent oral cereblon (CRBN) modulator that has shown potent G1 to S phase transition 1 (GSPT1) degradation and anti-tumor activity in pre-clinical models. One of the adverse effects associated with CC-325 was dose dependent hypocalcemia, which was determined to be an on-target toxicity.

To investigate the mechanism of hypocalcemia, we conducted a toxicity study in human cereblon (huCRBN) knock-in (KI) mice with CC-325. The huCRBN KI mice are transgenic mice engineered to express human cereblon that is capable of binding to CRBN and degrading GSPT1. Four groups of mice were treated with vehicle (0 mg/kg), CC-325 (50 mg/kg BID), NPS 2143 (120 mg/kg), or CC-325 + NPS 2143. The NPS 2143 is an oral negative allosteric modulator of calcium sensing receptor (CaSR), which upon administration to mice significantly increased plasma ionized calcium (iCa2+) and parathyroid hormone (PTH). Mice treated with CC-325 alone had significant decreases in serum iCa2+ and PTH, while mice treated with NPS 2143 alone as expected had significant increases in serum iCa2+ and PTH. Treatment of mice with CC-325 + NPS 2143 did not reverse the decreases in serum iCa2+ and PTH caused by CC-325, indicating that CC-325 prevents the increase of PTH. To investigate the mechanism of hypocalcemia, we stained parathyroid gland for PTH by immunohistochemistry (IHC) and showed significantly lower PTH in parathyroid with CC-325 treated mice compared to vehicle or NPS 2143 treated mice. To further investigate the cause of low PTH in parathyroid gland in mice treated with CC-325, we stained parathyroid with in-situ hybridization (ISH) probes for PTH mRNA. Results from this analysis showed significantly lower PTH mRNA in parathyroid of CC-325 mice compare to vehicle or NPS 2143 mice, indicating that lower serum PTH in CC-325 treated mice were due to decreased PTH mRNA in Chief cells.

These data collectively indicate that hypocalcemia caused by CC-325 is due to reduction in PTH, which leads to hypocalcemia. Additionally, mice treated with CC-325 are unable to restore normocalcemia because their parathyroid gland did not synthesize sufficient PTH for release into blood stream. Lack of PTH synthesis is caused by diminished level of PTH mRNA in parathyroid gland.

We also measured the level of FGF23 in mice treated with CC-325. Our data indicated that decrease in PTH significantly decreased FGF23 levels even in presence of hyperphosphatemia, indicating that PTH plays a big role in controlling FGF23 during hypoparathyroidism. The cause of decrease in PTH mRNA in parathyroid, whether it is related to lower transcription of PTH mRNA or lack of stability of PTH mRNA, remains to be determined.


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