Advancing the understanding of venetoclax in t(11;14)-positive multiple myeloma: a comprehensive review of clinical evidence and future prospects

ABSTRACT

Venetoclax is a selective inhibitor of the anti-apoptotic protein B-cell lymphoma 2 (BCL2), as a targeted therapy for multiple myeloma (MM) patients. It was initially approved by the United States Food and Drug Administration for the treatment of chronic lymphocytic leukemia in April 2016 and later for acute myeloid leukemia in October 2020. However, venetoclax is used as an off-label in a subset group of relapsed and refractory multiple myeloma (RRMM) patients with the presence of translocation t(11;14). Preclinical and clinical studies have highlighted the potential of venetoclax in the management of MM patients, with a specific focus on t(11;14) as a predictive biomarker for initiating venetoclax-based treatment. Later, several studies in RRMM patients that used venetoclax in combination with dexamethasone or/and proteasome inhibitors have shown promising results, in which management guidelines have included venetoclax as one of the options to treat MM patients. Hence, this review focuses on the use of venetoclax in RRMM, clinical efficacy, safety, dosing strategies, and predictive biomarkers for initiating venetoclax. Additionally, we discuss ongoing studies that are investigating different combination of venetoclax regimens in MM patients.

KEYWORDS:

• Venetoclax
• t(11;14)
• multiple myeloma

ABBREVIATION:

• AML, acute myeloid leukemia; BCL2, B-cell lymphoma 2; CAR T-cell, chimeric antigen receptor T-cell; CLL, chronic lymphocytic leukemia; FDA, Food and Drug Administration; IC50, half maximal inhibitory concentration; IL-6: interleukin 6; IMiD, immune-modulators; MM, multiple myeloma; ORR, overall response rate; PFS, progression-free survival; PI, proteasome inhibitor; RRMM, relapsed/refractory multiple myeloma

Introduction

Multiple myeloma (MM) is a type of cancer that arises from plasma cells, which are a type of white blood cells that produce antibodies [1,2]. MM is known to have several cytogenetics abnormalities, such as translocation between chromosomes 11 and 14 [t(11;14)], which results in the overexpression of the cyclin D1 gene. This abnormality is found in approximately 15–20% of all MM cases and is associated with intermediate-risk for survival time [2]. Although several treatments for multiple myeloma have been developed in recent years, such as the development of immunomodulators (IMiDs), anti-CD38, and chimeric antigen receptor (CAR) T-cell therapy, a definitive cure for the disease has not yet been found, and more effective treatment options are necessary.

Venetoclax is a selective inhibitor of the anti-apoptotic protein B-cell lymphoma 2 (BCL2) [1]. Venetoclax mimics BH3 and inhibits the anti-apoptotic protein BCL2 by the interference with the binding of BCL2 to pro-apoptotic BH3-only proteins like BIM (BCL2 Interacting Mediator of cell death), enabling these proteins to activate the apoptotic effectors BAX and BAK (Figure 1). The resultant release of the protein cytochrome c – normally locked inside the mitochondria – activates the apoptosome complex and cause apoptosis in the affected cell [1].

Figure 1. The mechanism of action of venetoclax in MM. In the mitochondria, apoptosis pathway is regulated by the interaction between anti-apoptotic proteins (multiple exist but only BCL2 is indicated in the figure for simplicity) and pro-apoptotic proteins (BAX, BAK, BIM). In some malignant cells, BCL2 protein becomes upregulated, blocking apoptosis. Venetoclax works by inhibiting BCL2 thereby shifting the balance towards the pro-apoptotic effect and ultimately inducing apoptosis. Pro-apoptotic proteins induce apoptosis by releasing the protein complex cytochrome C – a non-specific protease – from the mitochondria. BCL2: B-cell lymphoma 2.

Venetoclax was approved by the United States Food and Drug Administration (FDA) for the treatment of chronic lymphocytic leukemia (CLL) in April 2016 and later for the management of acute myeloid leukemia (AML) patient’s ineligible for intensive chemotherapy in October 2020 [2]. In recent years, preclinical and clinical studies have highlighted the potential of venetoclax as a targeted therapy for MM patients. In this review, we discuss the evidence supporting the use of venetoclax in the management of MM patients, with a specific focus on t(11;14) as a predictive biomarker for initiating venetoclax-based treatment. Moreover, the optimal dosing strategies for venetoclax in the management of MM are also discussed in this review.

Venetoclax in multiple myeloma

Following early studies that demonstrated the benefits of venetoclax in patients with CLL, AML, and non-hodgkin’s lymphoma, interest grew in its potential effects on other hematological malignancies [3–6]. After the discovery of in vitro sensitivity of MM cells with t(11;14) to BCL2 inhibitors, numerous clinical trials, including several phase I and II trials and one phase III trial, were conducted [7–12].

Venetoclax and dexamethasone

The initial interest in using venetoclax for MM stemmed from in vitro data showing that MM cells, particularly those with t(11;14), underwent apoptosis when treated with the BH3 mimetic ABT-737 [13]. Plasma cells typically rely more on MCL1 than BCL2 for anti-apoptosis, due to the effect of IL-6, which influences the binding of BIM [14]. Dexamethasone has been shown to shift the binding of BIM toward BCL2, increasing the sensitivity of venetoclax as explained by Matulis et al. [15]. This synergy was further supported by the findings of a subsequent study showing dexamethasone significantly reduced the half maximal inhibitory concentration (IC50) in all MM patient samples tested [16]. In the most responsive cohort, the IC50 decreased from 40 nanomolar (nM) to 9.5 nM (p < 0.0001), potentially due to corticosteroid-induced reduction of IL-6 levels via anti-inflammatory effects. This might be explained by corticosteroid-induced reduction in IL-6 level through its anti-inflammatory effects (Figure 2).

Figure 2. Synergistic effect of dexamethasone with venetoclax. Release of IL-6 result in an increase in the affinity of BIM (anti-apoptotic protein) towards MCL-1 (another member of the anti-apoptotic proteins) that result in blocking apoptosis independently from BCL-2, which bypass the effect of venetoclax. Dexamethasone is a potent anti-inflammatory agent that inhibits the effect of IL-6, restoring the sensitivity of the malignant plasma cell to venetoclax.

Venetoclax and proteasome inhibitors

One of the major resistance mechanisms to venetoclax is through the upregulation of MCL1 – another member of the BCL2 anti-apoptotic molecules – for inhibiting the apoptosis pathway and thus bypassing the BCL2 inhibition induced by venetoclax [17]. It has been shown that bortezomib downregulates MCL1 by inducing NOXA, which neutralizes MCL1 [18]. This suggests that bortezomib sensitizes malignant plasma cells to venetoclax by shifting the dependence of the malignant plasma cells toward BCL2 (Figure 3).

Figure 3. Bortezomib's role in enhancing venetoclax efficacy. Bortezomib mitigates venetoclax resistance by upregulating NOXA, which binds to and inhibits MCL-1, reinstating the effectiveness of venetoclax.

Clinical evidence supporting synergism of venetoclax combined with dexamethasone

The effect of venetoclax with dexamethasone was demonstrated by two phase I trials conducted by Kumar et al. and Kaufman et al. [7,8]. The Kumar et al. study administered venetoclax as a monotherapy, with dexamethasone added upon progression in relapsed/refractory MM (RRMM) patients, resulting in an overall response rate (ORR) of 40% among patients with t(11;14). However, 60% of t(11;14) MM patients who received venetoclax still did not show a response. Conversely, the study by Kaufman et al. combined venetoclax with dexamethasone in RRMM patients with t(11;14), achieving a 65% ORR [7]. These findings affirm the enhanced efficacy of venetoclax when paired with steroids. An ongoing study is investigating the role of IL-6 in relapsed MM patients with t(11;14) by administering tocilizumab, an IL-6 neutralizing antibody, in combination with venetoclax (NCT05391750).

Clinical evidence supporting synergism of venetoclax combined with proteasome inhibitors (PIs)

Moreau et al conducted a phase I study looking into venetoclax in combination with bortezomib and dexamethasone to treat RRMM patients [9]. Notably, only 14% of the study participants had t(11;14) with reported ORR of 67%. Interestingly, bortezomib-refractory patients exhibited a lower ORR (31%) compared to non-refractory patients (92%). High BCL2 expression also correlated with a better response (94% ORR) compared to low expression (59% ORR). Furthermore, in a phase II trial of RRMM patients conducted by Costa et al., venetoclax was combined with carfilzomib, and an ORR was observed in 80% of patients [10]. Notably, 73% of the study subjects did not have t(11;14), and in this group of patients, 75% showed an ORR, with 56% of the patients had high BCL2 expression. These outcomes suggest that venetoclax's effect may be influenced more by BCL2 biology rather than solely by cytogenetic abnormalities.

BELLINI trial

The first randomized clinical trial on venetoclax in RRMM patients was performed in an unselected population during the BELLINI trial [11]. Subjects were randomized to receive either venetoclax at dose of 800 mg daily with bortezomib and dexamethasone or placebo with bortezomib and dexamethasone. Progression-free survival (PFS) was prolonged in the venetoclax group (VenDD) with a hazard ratio (HR) of 0.63 (95% confidence interval (CI) 0.44–0.9). Despite a minority of patients having t(11;14) (∼10%), however, about 80% of patients had high BCL2 expression on polymerase chain reaction (PCR) test [11]. Contrary to the notion that venetoclax is only active in t(11;14), the study results did show significant PFS benefit even in participants who had no t(11;14). At the interim analysis for overall survival in BELLINI, there were 41 deaths reported among 194 patients in the venetoclax-treated study arm while 11 deaths were reported among 97 patients in the placebo-treated arm. Subgroup analysis has shown that this mortality was seen only in patients without t(11;14) and low BCL2 expression [11]. This increased mortality may be attributable, in part, to the high venetoclax dosage of 800 mg compared to the lower dosing regimen of 400 mg used in other indications such as in AML and CLL [11,13,14]. It is worth noting that unlike AML and CLL, there was no dose ramp-up in the trial, and there were no significant excess events of TLS [11]. Due to the safety results of this study, the FDA ordered partial clinical hold on all venetoclax-related trials in March 2019, then the partial hold was removed on the same year [19].

Evidence from real-world data

Despite the rarity of using venetoclax in the management of MM, real-world data are growing. Basali et al. reported on the administration of venetoclax to 10 patients with RRMM in combination with dexamethasone, a PI or both [20]. All patients exhibited the t(11;14) translocation, and most presented with a complex karyotype. Remarkably, all patients were refractory to bortezomib, 90% to lenalidomide, and 80% to daratumumab. The observed overall survival (OS) was 77%, with an ORR of 78%. While venetoclax dosing began at 400 mg and was intended to escalate to 800 mg, the specific dosages patients received were not quantified. By the end of the study, three patients had died due to various causes: sepsis, declining health status, and disease progression. Another study by Szita et al. reported outcomes from a multiple Hungarian hematology centers for 58 RRMM patients with t(11;14) who started on venetoclax-based combinations [21]. Sixty-three percent began venetoclax-based therapy for refractory disease, while the rest received it as part of a re-induction strategy. The ORR was notably high, at 94% in the refractory group and 100% in the re-induction group. Adverse events were common, affecting almost 97% of patients, with 40% related to infections. However, specific details regarding venetoclax dosing were not provided. In Table 1, we have summarized venetoclax studies and their outcomes.

Table 1. Summarized venetoclax studies and outcome.

Author	Study Design	Regimen	% of t(11;14)	Outcomes	Critique	Interpretation
Kumar [11]	Phase III trial (BELLINI study)	Venetoclax 800 mg + bortezomib + dexamethasone	10%	Improved median PFS (HR, 0.63 95%CI 0.44–0.90)	Higher venetoclax dose was used that could be responsible for the increased infection rates	Venetoclax combination increased modified PFS in RRMM patients and clinical effect was seen even without t(11;14) albeit with high BCL2 expression
				4% fatal infection events
Costa [10]	Phase II dose escalation study	Venetoclax (400 or 800 mg) + carfilzomib + dexamethasone	27%	ORR of 80% in all patients (92% in patients with t(11;14) and 75% in patients without t(11;14), 86% in high BCL2 expression cohort and 65% in low BCL2 expression cohort)	Non-comparative study	No excess infection rates was reported however, antibiotic prophylaxis was used in this study
				One treatment-related death, 92% had >grade 3 adverse events
Kaufman [7,22]	Phase I/II trial	Venetoclax 800 mg + dexamethasone	100%	ORR achieved in 45% of patients	Non-comparative study	55% of patients with t(11;14) did not achieve response, questioning the predictive power of t(11;14)
					Did not assess BCL2 expression
BELLINI trial [11]	Phase III	Venetoclax 800 mg daily with bortezomib and dexamethasone vs placebo with bortezomib and dexamethasone	10%	Median PFS was 22.4 mos with venetoclax vs 11.5 mos with palcebo	Higher doses of venetoclax, no ramp-up dose. More infections and deaths in venetoclax arm	Venetoclax intervention arm increased clinical benefits such as PFS
						A higher incidence of mortality was observed in the venetoclax cohort, largely attributable to a heightened frequency of infections, indicating the necessity of careful patient selection and the use of infection prophylaxis
Basali [20]	Retrospective chart review	Venetoclax + various combinations (Dexamethasone and/or a PI)	100%	ORR achieved in 78%	Very small sample size	Most patients responded to venetoclax-based combination
					No sufficient information on venetoclax actual dosing	3 patients died, 1 of them due to sepsis which raise the concern for ventoclax dosing and safety
					No information on BCL2 expression
Szita [21]	Retrospective chart review	Venetoclax	100%	ORR achieved in 100%	No information on the details of the combined agents	Favorable response to venetoclax
					No information on BCL2 expression
					No information on the dosing of venetoclax

Is t(11;14) an accurate predictive biomarker for response of venetoclax?

The sensitivity of t(11;14) plasma cells to venetoclax can be elucidated through ex vivo studies, which have demonstrated the reliance of plasma cells in MM patients with t(11;14) on BCL2 [16,17,23]. Conversely, plasma cells with different cytogenetic abnormalities in MM appear to depend more on MCL1, rendering them less sensitive to venetoclax, hence indicating a potential impact of t(11;14) on treatment outcomes.

Despite the association of t(11;14) with cyclin D1 overexpression, this does not appear to mechanistically or biologically explain the sensitivity of these cells to venetoclax from a pharmacological perspective [24]. This is supported by a genomic analysis performed by Gupta et al., which showed that the knock out of cyclin D1 in t(11;14) malignant plasma cells from MM patients did not affect the sensitivity to venetoclax. This finding suggest that cyclin D1 overexpression does not have a direct role in determining the sensitivity of t(11;14) plasma cells to venetoclax [25]. This observation is consistent with the known mechanism of action of venetoclax, a BCL2 inhibitor, and the absence of a known biological function for cyclin D1 in the apoptotic pathway regulated by the BCL2 protein family. Additionally, it is important to note that the gene encoding BCL2 is located on chromosome 18q21 and is not clearly known to be genetically affected by t(11;14) [26].

In a recent meta-analysis that assessed clinical trials of venetoclax-based regimens in RRMM patients, showed that other treatments regiments were superior than venetoclax ± dexamethasone treatments in ORR (82% vs 42%, p = .003) [27]. Nevertheless, a subgroup of patients with the t(11;14) translocation and high BCL-2 expression reached an impressive 97% ORR, compared to 78% in those without the translocation. Moreover, patients with elevated BCL2 expression attained an 88% ORR, against a 71% ORR in those with lower expression levels, indicating that venetoclax regimens may be particularly efficacious for patients with the t(11;14) translocation and high BCL2 expression. Currently, there is no standardized quantitative PCR test for BCL2 gene expression, which hinders its application as a routine clinical biomarker to gauge treatment efficacy [28]. Besides t(11;14) positivity, a research group from Columbia University is exploring venetoclax for patients with a B-cell phenotype identified via flow cytometry, drawing on insights from the Emory group's research [28].

Plasma cells harboring t(11;14) as a biologically distinct entity from other myeloma plasma cell subtypes

In a subsequent study by Gupta et al., genomic and epigenetic analyses were performed to investigate the differences between venetoclax-sensitive and -resistant cells [25]. The study revealed that the epigenetic landscape of sensitive cells mirrored that of B-cells, unlike their resistant counterparts. Specifically, B-cell markers such as BATF, CD20, and CD79a were exclusively present in venetoclax-sensitive cells, and their chromatin accessibility patterns more closely resembled those of memory B-cells rather than plasma cells. These insights suggest that MM characterized by t(11;14) may arise from plasma cells that are biologically divergent from those in other cytogenetic MM subgroups.

This phenomenon is similar to that observed in B-cell non-Hodgkin's lymphoma, but differs from normal plasma cell biology and other MM cytogenetic subgroups, providing an explanation for the sensitivity of these cells to venetoclax [25]. Previous clinical trials have shown a significant response to venetoclax in a subset of patients despite the absence of t(11;14), indicating that there may be other genomic and/or biological events that are associated with, but not entirely dependent on, t(11;14) that predict response to venetoclax, such as high BCL2 expression [9–11]. Thus, while venetoclax has potential as a targeted therapy in MM, t(11;14) by itself may not be an adequate sole predictor of therapeutic response. There is a pressing need for further research to pinpoint precise biomarkers that reliably forecast venetoclax sensitivity and to refine patient selection for this treatment.

Although the recommendations of the National Comprehensive Cancer Network (NCCN) guidelines are restricted to use venetoclax only in RRMM patients with t(11;14), it should be emphasized that MM patients without t(11;14), but with high BCL2 expression still may have significant clinical benefit [29]. On the other hand, significant number of MM patients with t(11;14) might be unresponsive to venetoclax and experience increased toxicity without beneficial outcomes. All this highlights the need for better patient selection criteria, potentially incorporating biomarkers like BCL2 expression, to prevent reliance on t(11;14) as a singular predictive marker. Enhancing the precision of patient selection is pivotal to optimizing the therapeutic impact of venetoclax in MM.

Safety profile of venetoclax

Venetoclax warrants certain precautions prior to initiation [17]. Two of the most prominent concerns are tumor lysis syndrome (TLS), and neutropenia. Interestingly, in MM, there is no dose ramp-up, and there are fewer significant instances of tumor lysis syndrome [11]. Additionally, some of the most common adverse reactions to venetoclax, occurring in more than 20% of patients, are diarrhea, nausea, anemia, upper respiratory tract infections, thrombocytopenia, and fatigue [17].

Ongoing studies

Several ongoing studies are investigating different combination of venetoclax regimens in MM patients (Table 2). While it is known that venetoclax combination with proteasome inhibitor (PI)-based and steroid-based regimens enhance the sensitivity of malignant plasma cells to venetoclax, other classes of anti-MM drugs are being investigated. These studies may lead to future comparative analyses to determine the most effective synergistic combinations with venetoclax. Notably, some of these studies include dose-finding phases that may address concerns about the high-dose of venetoclax used in the BELLINI trial (NCT02899052) [11]. However, almost all of these studies primarily rely on t(11;14) as the biological marker for inclusion. Moreover, a new novel BCL2 inhibitor (Lisaftoclax) is under investigation in patients with R/R CLL/SLL as a combination therapy with a BTK inhibitor [30]. Lisaftoclax has shown promising efficacy and favorable safety in earlier studies [31,32]. However, there is no data regarding it is safety and efficacy in MM patients.

Table 2. Summarized ongoing venetoclax studies in MM.

Study design	Arm 1	Arm 2	Outcomes	Key inclusion criteria	Clinical.gov identifier
Phase III (Canova trial)	Venetoclax + dexamethasone	Pomalidomide + dexamethasone	PFS	Relapsed or refractory MM on at least 2 prior lines	NCT03539744
				Positive for t(11;14)
Phase II	Carfilzomib + dexamethasone + venetoclax (dose level1 = 400 mg daily, dose level2 = 800 mg daily)	NA	Safety Response rate	Relapsed or refractory MM	NCT02899052
				Positive t(11;14) on FISH
Phase I/II dose expansion study	Daratumumab + dexamethasone + venetoclax	Daratumumab + dexamethasone + bortezomib	Overall response rate	Relapsed or refractory MM	NCT03314181
				T(11;14) positive on FISH
Phase II	Selinexor + dexamethasone + venetoclax	NA	Overall response rate	Relapsed or refractory MM	NCT05530421
				Positive T(11;14) on FISH
Phase I dose-finding study	Tocilizumab + venetoclax	NA	Maximum tolerated dose	Relapsed or refractory MM	NCT05391750
				On more than 3 previous lines of therapy
				Positive T(11;14) on FISH

Conclusion

In conclusion, MM is a complex malignancy with significant cytogenetic abnormalities, including t(11;14), which leads to overexpression of cyclin D1 gene. Venetoclax has emerged as a promising targeted therapy for MM patients with t(11;14) translocation. Early clinical trials of venetoclax in combination with dexamethasone or proteasome inhibitors have shown promising results in terms of overall response rates in RRMM patients with t(11;14). However, there is a need to explore better combination regimens, and predictive biomarkers (specifically toward BCL2 expression) in future studies. Additionally, further studies are needed to evaluate the optimal and safe dosing of venetoclax in this patient population. Finally, after the biological subset of MM patients that predict response to venetoclax is established and clearly defined, we think that venetoclax needs to be explored further in different settings such as in maintenance phase and in the upfront line.

Disclosure statement

No potential conflict of interest was reported by the author(s).