Prognostic impact of resistance to bortezomib and/or lenalidomide in carfilzomib‐based therapies for relapsed/refractory multiple myeloma: The Kyoto Clinical Hematology Study Group, multicenter, pilot, prospective, observational study in Asian patients

Abstract Background Combinatory strategies with carfilzomib (CFZ), a second‐generation proteasome inhibitor, plus dexamethasone (DEX) with or without lenalidomide (LEN) have shown promising efficacy for patients with relapsed/refractory multiple myeloma (RRMM) in pivotal clinical trials. However, their effects on patients who were resistance to bortezomib (BTZ) and/or LEN have not been fully evaluated in a daily practice setting. Aims To evaluate the real‐world efficacy and safety of CFZ‐based treatments; that is, CFZ with LEN plus DEX (KRD therapy) and CFZ with DEX (KD therapy), in Asian patients, we conducted a multicenter pilot prospective observational study in the Kyoto Clinical Hematology Study Group. Methods and Results All 50 patients with RRMM enrolled in this study were treated with CFZ‐based treatments between 2017 and 2019. KRD and KD were administered to 31 and 19 patients, respectively. The overall response rates (ORRs) were 80.6% with KRD and 73.7% with KD. Two‐year progression‐free survival (PFS) and overall survival (OS) were 58.5% and 79.7% with KRD, and 23.1% and 52.6% with KD. By multivariate analysis, refractoriness to BTZ and to LEN were identified as independent unfavorable factors for both PFS and OS. The common non‐hematologic AEs included hypertension (42.0%), fever (24.0%), fatigue (24.0%), and infection (16.0%). No serious heart failure was observed. This study is registered as UMIN000025108. Conclusion This study suggests the need of the development of novel CFZ‐containing strategy which can overcome the refractoriness to BTZ and/or LEN, while both KRD and KD were shown to be mostly feasible in Asian patients in a daily practice setting.

patients, we conducted a multicenter pilot prospective observational study in the Kyoto Clinical Hematology Study Group.
Methods and Results: All 50 patients with RRMM enrolled in this study were treated with CFZ-based treatments between 2017 and 2019. KRD and KD were administered to 31 and 19 patients, respectively. The overall response rates (ORRs) were 80.6% with KRD and 73.7% with KD. Two-year progression-free survival (PFS) and overall survival (OS) were 58.5% and 79.7% with KRD, and 23.1% and 52.6% with KD. By multivariate analysis, refractoriness to BTZ and to LEN were identified as independent unfavorable factors for both PFS and OS. The common non-hematologic AEs included hypertension (42.0%), fever (24.0%), fatigue (24.0%), and infection (16.0%). No serious heart failure was observed. This study is registered as UMIN000025108.
Conclusion: This study suggests the need of the development of novel CFZcontaining strategy which can overcome the refractoriness to BTZ and/or LEN, while both KRD and KD were shown to be mostly feasible in Asian patients in a daily practice setting. Carfilzomib (CFZ) is a second-generation, epoxyketone PI. By binding selectively and irreversibly to the β5 and β5i subunits and inhibiting chymotrypsin-like constitutive proteasome and immunoproteasome activities, CFZ potently induces myeloma cell death, including cells with acquired resistance to bortezomib (BTZ), a first-generation PI, in experimental settings. 4,5 Promising clinical efficacies of CFZ-based therapies have also been reported in relapsed/refractory multiple myeloma (RRMM) in several pivotal clinical trials. In the ASPIRE trial, combinatory treatment of twice weekly CFZ with lenalidomide (LEN) and dexamethasone (DEX) (KRD therapy) was more efficacious than LEN and DEX only (Rd therapy) based on longer progression-free survival (PFS) and overall survival (OS) in patients with RRMM. 6,7 In the ENDEAVOR trial, the superior efficacy of combination therapy of twice weekly CFZ and DEX (KD therapy) versus a combination of BTZ and DEX was also shown in RRMM, even in patients previously exposed to BTZ. 6-10 However, patients refractory to BTZ and/or LEN were excluded in the ASPIRE trial, while those refractory to BTZ were excluded in the ENDEAVOR trial.
Therefore, the efficacies of CFZ-based therapy for RRMM in patients refractory to BTZ and/or LEN remain uncertain.
Information on the prognostic impact of prior resistance to BTZ and/or LEN in KRD therapy is also limited in real-world observational studies, [11][12][13] while such information is mostly lacking for KD therapy.
Because the combination therapies containing BTZ and/or LEN are the standard of care for newly diagnosed MM, the failure of the firstline treatment strongly associates with the resistance to BTZ and/or LEN. Therefore, therapeutic strategies those can overcome the resistance to BTZ and/or LEN are critically important as the salvage treatment for RRMM. Given that prior therapeutic resistance to BTZ and/or LEN may influence the effect of novel CFZ-based therapy, such as KD plus the anti-CD38 MoAb daratumumab, 14

| Study design
Fifty patients with RRMM aged >20 years old who were scheduled to receive CFZ-based therapies (i.e., KRD or KD) at nine centers in the KOTOSG were registered in the study before initiation of treatment from June 2017 to August 2019. The sample size of this study was determined based on the rules of pilot test. [18][19][20] The data cut-off date was March 31, 2021. No randomization was performed for selection of the treatment strategy for each patient, and the treatment modality was selected as KRD or KD at the discretion of a physician. KRD and KD were basically administered following the protocols established in pivotal trials, with dose modification due to AEs and/or a patient's condition permitted at the physician's discretion. Prophylaxis with acyclovir and sulfamethoxazole trimethoprim was recommended. The use of granulocyte-colony stimulating factor (G-CSF) for neutropenia was permitted.
Data were collected using a case report form for patient back- The study was conducted in compliance with the Guidelines for Good Clinical Practice and the Declaration of Helsinki, and the study protocol was approved by local institutional review boards. All patients provided written informed consent at the study enrollment before the initiation of CFZ-based treatment. This study is registered as UMIN000025108.

| Study endpoint
The primary endpoint was overall response rate (ORR). Treatment response was assessed using the IMWG criteria 23 and ORR was defined as the sum of rates of stringent complete response (sCR), CR, very good partial response (VGPR) and PR. The secondary endpoints were PFS, OS, and safety. PFS was defined as the time from the date of treatment initiation to progression or death, and OS as the time from the date of treatment initiation to death. PFS was censored at the end of CFZ-based treatment in patients who proceeded to a planned next treatment. AEs were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) ver. 4.0. Regarding hypertension, grade 2 or higher was defined as clinically significant.

| Statistical analysis
A Fisher exact test was used to compare categorical variables and a Mann-Whitney-U test was used to compare continuous variables between two groups. The Kaplan-Meier method was used for survival analysis, with a log-rank test for comparison of the survival curves.
Prognostic factors were identified using Cox proportional hazards model analysis. The confidence interval (CI) was 95% and p < .05 was considered to be significant. All statistical analyses were performed with EZR ver. 1.37. 24 3 | RESULTS

| Background of patients
The characteristics of the 50 patients are summarized in Table 1 (Table S1). All patients received a twice-weekly CFZ regimen. Of all 50 patients, 2 (4.0%) were still under treatment with CFZ-based therapy at the data cut-off, while 48 had discontinued therapy due to AEs (n = 7, 14.0%), including CVAEs (n = 3); disease progression (n = 18, 36.0%); insufficient response that resulted in a treatment change (n = 5, 10.0%); a preplanned treatment change (n = 13, 26.0%), including proceeding to high-dose chemotherapy with autologous stem cell transplantation (HDT/ASCT), typically after four cycles of KRD or KD (n = 9), and proceeding to LEN maintenance after KRD (n = 4); and other reasons (n = 5, 10.0%) (Table S1). In this cohort, we performed HDT/ASCT after CFZ-based treatments in patients who were fit and under 70 years old.
There was no significant difference in the rate of ORR between in the KRD group and KD group (p = .475) ( 9.3 months, p = .067) ( Figure 1A and Figure S1A).   As the results, the refractoriness to BTZ and the refractoriness to LEN were identified as independent unfavorable risk factors for PFS; and the refractoriness to BTZ, the refractoriness to LEN, and serum β2-mG level were identified as independent unfavorable risk factors for OS ( Table 2).

| Factors associated with survival
The relationship between resistance to BTZ and/or LEN and survival with CFZ-based therapy was next examined in more detail. The patients were divided into four groups: those sensitive to both BTZ and LEN (double-sensitive), refractory to BTZ but not to LEN, refractory to LEN but not to BTZ, and refractory to both BTZ and LEN (double-refractory). Survival outcomes with KRD or KD therapy were compared among the groups. Despite the small number of patients in each group, patients who were double-refractory to BTZ and LEN either significantly had or tended to have a poor prognosis compared with those with single resistance to BTZ or LEN; and the double-sensitive to BTZ and LEN may be a favorable predictor for PFS and OS in both KRD and KD therapy ( Figure 2). In addition, the presence of poor cytogenetic abnormalities, that is, t(4;14) or t(14;16), did not significantly affect PFS and OS in our cohort ( Figure 1H and Figure S1H), while the prognostic impact of del(17p) or 1q abnormality was not evaluable due to missing data.  (Table 3). were 66%, 59% and 37%, respectively, in patients treated with KRD in the ASPIRE trial; and 54%, 70% and 34%, respectively, in patients treated with KD in the ENDEAVOR trial. 6 34 The efficacy in the current study may reflect the findings in these basic and clinical studies, and suggests the importance of insight into drug sensitivity based on prior treatment in selection of CFZ-based therapies compared to other approaches. For instance, it has been reported that addition of daratumumab to KD may improve the outcomes of patients with acquired resistance to LEN. 14 In addition, patients in KRD group showed significantly longer OS than in KD group, and KRD also provided trend for long PFS compared with KD, although not significantly, in this study. These trends seemed to be consistent with previously reported data. 35 With regard to AEs, CFZ has been shown to have less off-target activity against enzymes other than those in the proteasome and immunoproteasome, 36 and this may be associated with the different toxicity profile of CTZ compared with BTZ; for example, the low incidence of PN. [6][7][8][9][10][11][12][13][14] Hematological AEs were most common in our cohort, and there was no significant difference in the frequencies of hematologic AEs with KRD and KD therapy. Regarding nonhematologic AEs, a high frequency of CVAEs has been a critical concern in use of CFZ for myeloma. [6][7][8][9][10][11][12][13] HTN was the most frequent non-hematological AE in our cohort, and HTN over grade 2 occurred more frequently in our patients compared with previous reports. [6][7][8][9][10][11][12][13][37][38][39][40] Arrythmia occurred in 7 patients (14.0%), with all events being grade 1-2, detected on a regular electrocardiogram without symptoms, and requiring no medication. Somewhat surprisingly, only one patient had grade 1 heart failure, giving a much lower rate than that in a previous study of CFZ in an Asian cohort. 41 These results for AEs might be biased by patient selection in our    In conclusion, this study shows that CFZ-based treatment is effective and mostly feasible in Asian patients with RRMM in a realworld clinical setting, however, a prior history of resistance to BTZ and/or LEN may impair for the efficacy and the outcome of CFZbased treatment. This suggests the need of the development of novel CFZ-containing strategy which can overcome the refractoriness to BTZ and/or LEN by, for instance, adding upcoming new agents, such as a monoclonal antibody, an antibody-drug conjugate, selinexor or venetoclax, and also the need of the next prospective study for evaluating efficacies of those strategies with larger sample size.