Updated Results of Bortezomib-Naïve Patients in PX-171-004, An Ongoing Open-Label, Phase II Study of Single-Agent Carfilzomib (CFZ) in Patients with Relapsed or Refractory Myeloma (MM).

Carfilzomib (CFZ) is a proteasome inhibitor with unique target selectivity and an irreversible binding mechanism that results in sustained proteasome inhibition. In preclinical studies, CFZ lacks non-proteasome off-target activities associated with bortezomib (BTZ) (Kapur et al, Blood 2008). This may account for observed differences in tolerability with CFZ (e.g. minimal neuropathy and myelosuppression), permitting consecutive day dosing and treatment over an extended period of time. We previously observed higher response rates in multiple myeloma (MM) patients without prior BTZ exposure (BTZ-naïve) compared to those with relapsed disease following BTZ therapy (BTZ-treated). Here we present updated data on the BTZ-naïve cohort from PX-171-004, an ongoing Phase 2 study of single-agent CFZ in MM patients with relapsed or refractory disease following 1–3 prior therapies.

Patients with relapsed or refractory (e.g, < 25% response or disease progression during last treatment) MM were enrolled and stratified into two cohorts: BTZ-naïve and BTZ-treated. CFZ 20 mg/m² IV was administered on Days 1, 2, 8, 9, 15 and 16 every 28 days, for up to 12 cycles. The primary endpoint was Overall Response Rate [≥ Partial Response (PR)] per International Uniform Response Criteria for Multiple Myeloma. Secondary endpoints included Clinical Benefit Response [CBR = ORR + Minor Reponse (MR)] and safety.

Fifty-seven BTZ-naive patients have been enrolled and 56 subjects have received at least one dose of CFZ. Prior therapies included alkylators (81%), stem cell transplant (SCT) (77%), thalidomide (THAL) (67%), lenalidomide (LEN) (42%), and anthracyclines (23%). Ten (18%) patients had received both LEN and THAL and 18 (32%) patients were refractory to their most recent regimen prior to study entry. At baseline, 30 (53%) patients had an ECOG score ≥ 1, 21 (37%) had neuropathy Grade ≥ 1, 12 (21%) had impaired renal function (CrCl < 60 mL/min) and 10 (18%) had diabetes. The mean time from diagnosis was 4 years (range 0.7–24). To date, the mean number of CFZ doses administered was 29.2 (∼5 four-week cycles; range 2–72 doses, 1–12 cycles). Fifty-one patients initiated therapy and were evaluable for response per protocol. The ORR was 45% (23/51 patients) and included 1 CR, 4 VGPR and 18 PR. An additional 9 (18%) patients had MR and 10 (20%) had stable disease (SD) for ≥ 6 weeks. The most common (>25%) adverse events (AEs) were fatigue (59%), nausea (41%), dyspnea (36%), and anemia (29%), and were primarily ≤ Grade 2. Grade 3/4 AEs occurring in ≥ 5% of patients were thrombocytopenia (9%), fatigue (9%), neutropenia (7%), lymphopenia (7%), anemia (5%), pneumonia (5%) and hyperglycemia (5%). One (1.7%) patient had febrile neutropenia. Dose modifications were rarely required. Peripheral neuropathy (PN) of any grade was infrequent (7 patients, 12%) with a single case of Grade 3 PN (2%) in a pt with a history of THAL-induced PN that lasted 41 days. The CFZ dose was reduced and the event resolved to Grade 1 while on CFZ and prior to study discontinuation. Of the12 patients with impaired renal function at baseline, none required dose modifications due to renal AE. Overall, 5 patients have completed the full 12-cycle protocol and another 5 (9%) have completed ≥ 9 cycles; 17 patients (30%) are continuing on study.

The 45% ORR (CBR 63%) is noteworthy for a single-agent regimen in patients with tumor progression despite therapy with novel combinations. CFZ can be safely administered to patients with significant comorbidities (e.g. peripheral neuropathy, leukopenia, renal dysfunction, diabetes) when other anti-myeloma agents may not be well tolerated. Enrollment to PX-171-004 is continuing and, based on the safety profile, subjects are now permitted to dose escalate to 27 mg/m².

Wang:Proteolix: Honoraria, Research Funding. Off Label Use: testing testing. 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. 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. Kukreti:Celgene: Honoraria. Bahlis:Celgene: Honoraria, Speakers Bureau; Ortho Biotech: Honoraria, Speakers Bureau. McDonagh:Proteolix: Research Funding. Belch:Ortho Biotech: Honoraria, Research Funding. Le:Proteolix, Inc.: Employment. Bennett:Proteolix: Employment. Kunkel:Proteolix: Consultancy, Employment. Kauffman:Proteolix, Inc.: Employment. Vij:Proteolix, Inc.: Consultancy, Research Funding.