Treating multiple myeloma cells with panobinostat and FK506 reduced their viability by inhibiting expression of the PPP3CA catalytic subunit of calcineurin, according to researchers.

“The development of new calcineurin-targeted therapies, which inhibit PPP3CA–NF-kappaB signaling by small molecules, is expected to profoundly improve the treatment of multiple myeloma. This will overcome drug resistance and improve osteolytic lesions in a wide range of patients, including those receiving reduced intensity–conditioned allogeneic stem cell transplantation, who may be treated with panobinostat and FK506,” wrote Dr. Yoichi Imai of Tokyo Women’s Medical University in Japan, and his associates (JCI Insight 2016 doi: 10.1172/jci.insight.85061 ). .

Adding panobinostat to bortezomib and dexamethasone has been shown to improve progression-free survival in relapsed and refractory multiple myeloma, the researchers noted. Other studies have linked calcineurin activation to the pathogenesis of T-cell cancers, and calcineurin inhibition seems to be involved in defective B-cell activation, they added.

Eight candidate oncogenes were identified by use of the Gene Expression Omnibus. PPP3CA was expressed at significantly higher levels in multiple myeloma cells from patients with stage III disease compared with those with stage I disease (P = .016). Furthermore, levels of serum lactate dehydrogenase correlated with PPP3CA expression and with poor overall and progression-free survival. Patients with high PPP3CA expression also had high levels of alpha4 integrins, which mediate resistance to bortezomib and conventional chemotherapy, the researchers noted.

When multiple myeloma cells were exposed to either panobinostat or a control agent, PPP3CA dropped in the panobinostat-treated cells. Adding the proteasome inhibitor lactacystin to the mixture counteracted this effect, “supporting the possibility that PPP3CA expression was reduced through protein degradation by panobinostat,” they said.

Levels of PPP3CA expression were lower in multiple myeloma cells that were cotreated with an HDAC inhibitor (panobinostat or ACY-1215) and the immunosuppressive agent FK506 than in multiple myeloma cells that were exposed only to an HDAC inhibitor. In addition, the combination regimen blocked the formation of osteoclasts, which are involved in osteolytic lesions, the researchers noted.

Also, significantly higher PPP3CA expression, which correlated with worse progression-free survival, was noted in bortezomib-resistant patients, compared with bortezomib-sensitive patients.

“The cytotoxic effect exerted by panobinostat on CD20+ cells was subtle, while the addition of FK506 did not increase their viability,” the researchers reported. “Moreover, development of T and B lineage cells was normal in PPP3CA-deficient mice, and panobinostat did not compromise donor lymphocyte reconstitution in a mouse BM transplantation model. These results suggest that calcineurin-targeting therapy exerts an antimyeloma effect without inducing significant side effects in normal lymphoid systems.”

The Japan Society for the Promotion of Science, the Takeda Science Foundation, the International Myeloma Foundation, and the Japan Leukemia Research Fund funded the study. The investigators had no disclosures.