Neurotoxic and peripheral neuropathic effects in preclinical and clinical studies of carfilzomib (CFZ), a novel proteasome inhibitor (PI).

Abstract

8135 Background: Treatment-induced peripheral neuropathy (TIPN) is a common, frequently debilitating, therapy-limiting complication in multiple myeloma (MM). Chemotherapies associated with TIPN in MM include thalidomide and bortezomib (BTZ). CFZ, a novel, highly selective PI, is structurally and mechanistically distinct from BTZ. In Ph I-II trials single-agent CFZ is active without dose-limiting PN in pts with relapsed and/or refractory (R/R) MM. Here we compare CFZ and BTZ in a neurotoxicity model and report clinical experience with CFZ in R/R MM. Methods: An in vitro neurotoxicity model established with differentiated SH-SY5Y neuroblastoma cells was used to investigate PI effects on neurite degeneration. A possible mechanism was pursued by bioinformatic and biochemical methods. Data were pooled from 2, ongoing Ph II trials of single-agent CFZ in pts with R/R MM, including neuropathy history, baseline neuropathic symptoms and neurological exam findings, prospective neurological exams, and FACT-GOG/NTx pt survey scores. PN adverse event data were also included. Results: Following 24 hrs of exposure to 10 nM BTZ, SH-SY5Y cells showed 40% reduction in neurite length/cell compared to CFZ- or vehicle-treated cells. Both agents induced equivalent proteasomal inhibition suggesting off-target effects induce neurodegeneration. HtrA2/Omi, a mitochondrial serine protease with a role in neuron survival was identified in databases and confirmed as a target of BTZ (IC50 = 3 nM), but not of CFZ (>10 μ M). At screening, 72% of 135 pts had active Grade (G) 1/2 PN; 81% had a history of TIPN. Pts received a mean of 30.4 CFZ doses (range 2–72) and 17% received >10 mo of therapy. New onset PN or PN worsening from baseline was reported in 16% of pts. There were no reports of G4 PN, missed doses, or treatment discontinuations. Only 1 pt was dose-reduced due to PN. Conclusions: In contrast to BTZ TIPN, CFZ-related PN is uncommon and not dose-limiting. In vitro, BTZ induces neurotoxicity in a proteasome-independent manner and potently inhibits a neuronal cell survival factor, HtrA2. These in vitro and clinical data suggest that severe PN is not a PI class effect. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Onyx Bristol-Myers Squibb, Celgene, Facet, Millennium, Novartis, Onyx Onyx Celgene, Johnson & Johnson, Merck, Millennium, Onyx, Ortho, Takeda Bristol-Myers Squibb, Celgene, Facet, Gloucester Pharmaceuticals, Millennium, Novartis, Onyx