Carfilzomib (CFZ), a Novel Proteasome Inhibitor for Relapsed or Refractory Multiple Myeloma, Is Associated with Minimal Peripheral Neuropathic Effects.

Peripheral neuropathy (PN) is a feature of multiple myeloma (MM) itself as well as a debilitating side effect and major dose-limiting toxicity of thalidomide (THAL) and bortezomib (BTZ) (Chaudry et al, J Peripher Nerv Syst. 2008). Although the mechanism of BTZ-induced PN (BIPN) is unknown, PN may not be a proteasome inhibitor class effect. Carfilzomib (CFZ) is a highly selective proteasome inhibitor with activity in relapsed or refractory MM. CFZ overcomes BTZ-resistance in vitro (Kuhn et al, Blood 2007), lacks the off-target activities of BTZ (Kapur et al, Blood 2008), and does not cause neurotoxicity in long-term chronic (e.g. up to 9 months) animal toxicology studies (Kirk et al, Blood 2008). In Phase I and 1b/2 trials (total n=138), CFZ was not associated with dose-limiting PN. Here we report on the experience of CFZ treatment from two ongoing Phase 2 trials in relapsed or refractory MM.

Patients with relapsed or refractory MM received CFZ, 20 mg/m² IV, Days 1, 2, 8, 9, 15, and 16 in a 28-day cycle for up to 12 cycles on studies PX-171-003 and PX-171-004. Neuropathy history, neurological physical exam and PN-related quality of life data (FACT-GOG/NTx v 4.0 scores) were collected at screening. Prospective neurological exams and subjective reporting of PN using the FACT-GOG/Ntx subscale v.4 questionnaire occurred every 2 cycles until study discontinuation to proactively assess for PN. Adverse Event (AE) data were also collected. AEs reported as ‘neuropathy peripheral', ‘neuropathic pain', ‘neuropathy', and ‘peripheral sensory neuropathy' were included as PN. AE reports of ‘paraesthesias' and ‘dysesthesias' were counted separately.

To date, baseline data are availabel for 136 patients. At screening, 73 (54%) patients had active PN, including 64 (47%) with Grade (G) 1 and 9 (7%) with G2. 111 (82%) patients had a history of PN which was attributed to prior chemotherapy, 86 cases of which were attributed to either THAL or BTZ. THAL was implicated in 57 cases, BTZ in 45 cases, and both THAL and BTZ in 17 cases. For 27 of these patients, PN was the primary reason for THAL or BTZ discontinuation. The mean number of CFZ doses was 27 (4.5 four-week cycles) and 27 (20%) patients completed at least 8 cycles. Peripheral neuropathy AEs (all grades) were reported in 21 (15%) patients; 12 (9%) cases were considered possibly related to CFZ. Grade ≥ 3 PN was reported in only 3 (2%) patients. In one patient, the Grade 3 neuropathy lasted from treatment days 2 to 3 (i.e., < 36 hours) and resolved; the patient continued on CFZ at full dose for 30 days before discontinuing study due to progressive MM. In a second patient, Grade 3 neuropathy occurred on study day 91. The dose was reduced from 20 mg/m² to 15 mg/m², at the same twice-weekly frequency; the PN resolved to G1 and the patient continued on therapy until day 133. The third patient had G3 PN that occurred from days 260-281 and resolved to G1 while still on full dose CFZ. This patient completed the full 12-cycle protocol (∼1 year CFZ treatment). Paraesthesias and dysesthesia were reported in 10 (7%) patients; all were G1 or 2. There were no missed doses or CFZ treatment discontinuations due to PN, paraesthesias or dysesthesias. Comparative FACT-GOG/Ntx subscale scores were availabel for 95 patients. There was no statistically significant change in FACT-GOG/NTx scores from baseline to the end of the study. Neurological exams did not identify any additional peripheral neuropathy beyond those reported as AEs.

In MM patients receiving CFZ therapy, reports of PN, paraesthesias and dysesthesia are generally mild and do not result in missed doses or CFZ discontinuation, allowing long-term treatment and prolonged disease control. These data, along with the experience from other clinical trials, indicate that PN is not a class effect of proteasome inhibitors.

Vij:Proteolix: Consultancy, Research Funding. Wang:Proteolix, Inc.: Research Funding. Stewart:Genzyme, Celgene, Millenium, Proteolix: Honoraria; Takeda, Millenium: Research Funding; Takeda-Millenium, Celgene, Novartis, Amgen: Consultancy. Lonial:Celgene: Consultancy; Millennium: Consultancy, Research Funding; BMS: Consultancy; Novartis: Consultancy; Gloucester: Research Funding. Trudel:Celgene: Honoraria, Speakers Bureau; Ortho Biotech: Honoraria. Jakubowiak:Millennium Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Centocor Ortho Biotech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Exelixis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol-Myers-Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Belch:Ortho Biotech: Honoraria, Research Funding. Bahlis:Celgene: Honoraria, Speakers Bureau; Ortho Biotech: Honoraria, Speakers Bureau. Le:Proteolix, Inc.: Employment. Cruickshank:Proteolix, Inc.: Employment. Bennett:Proteolix: Employment. Molineaux:Proteolix, Inc.: Employment, Equity Ownership. Siegel:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.