Overexpression of the anti-apoptotic Bcl-2 family proteins is commonly observed in hematological malignancies, including Acute Myeloid Leukemia (AML). Hence, strategies to inhibit Bcl-2 family proteins have been extensively investigated over the years, showing high in vitro and in vivo efficacy.
ABT-199 (Venetoclax) is a BH3-mimetic, selective for Bcl-2, which demonstrated a pronounced antineoplastic activity, receiving FDA approval for the treatment of CLL and AML. However, primary or secondary resistance ensued after prolonged treatment, highlighting the need for a greater understanding of the underlying mechanisms. Among other factors, resistance to Venetoclax appear related to stromal interaction and to the metabolic reprogramming of leukemic blasts. Evidences show that Venetoclax exposure induce a reduction in the oxidative metabolism, and that the simultaneous targeting of metabolism can restore sensitivity to the Bcl-2 inhibitor. A further resistance mechanism has been identified in the cross-talk between Bcl-2 and other signaling pathway, as Venetoclax seems to upregulate Mcl-1 via signaling mediated by ERK.
Given the strict interplay between metabolism and signaling, aim of this study will be to elucidate to what extend both processes concur in the acquisition of BH3-mimetic resistance in AML. We will generate Venetoclax-resistant derived cell lines. The characterization of the metabolic phenotype and the phospho-proteomic profile associated to resistant phenotype will be the start point for the generation of novel BH3 mimetic-based treatment combination strategies able to overcome resistance. Finally, the resulting optimal combination will be tested on AML primary cells.
Results of this study can help to identify additional molecular targets to be pharmacologically addressed in the design of new, more effective therapeutic strategies involving Venetoclax on AML patients.
Despite the remarkable advances in cancer treatment achieved with the development of a wide and still growing spectrum of low molecular weight kinase inhibitors, targeted therapies have displayed some limitations. The main cause of their limited effectiveness is represented by the intrinsic and acquired mechanisms of resistance exhibited by cancer cells against such targeted drugs (von Manstein et al., 2013). The target itself can undergo alterations of its gene structure (i.e. mutation), thus becoming no longer able to interact at the molecular level with the targeted drugs. On the other hand, cancer cells can activate compensatory pathways that allow them to grow and survive independently from the initial target (Masui et al., 2013; McCubrey et al., 2016; Grant, 2008). The recurrence of either pre-existing or acquired resistance mechanisms is also the limitations for the use of BH3 mimetics in cancer therapy. Hence, the need for exploring other strategies in order to avoid the insurgence of these resistance mechanisms. In this perspective, particular attention has been paid to the study of interactions between the numerous STP and the effects induced by the combined use of specific inhibitors of components belonging to intercommunicating pathways. The existing interactions between different pathways may be the cause of appearance of redundant activation phenomena as a result of disruption of specific molecular targets, thus promoting cell survival despite of an effective and specific inhibition of the target itself. This may explain why the inhibition of a single kinase, although effective in vitro, does not turn into a significant antitumor effect when applied to clinical practice and consequently necessitate the simultaneous blockade of multiple molecular targets.
However, combination approaches aimed at disrupting complementary mechanisms require taking into account the mechanistic knowledge of molecular components that drive therapeutic sensitivity and resistance to successful translate the pre-clinical data in effective and innovative therapeutic approaches to AML.
This project aims at characterizing the mechanisms of resistance of a promising drug, Venetoclax, in AML setting, in order to rationally design new combination strategies able to overcome this phenomenon. The translational impact of these new findings can be substantial, as Venetoclax is currently being studied in various clinical trials, and the identification of resistance mechanisms can readily improve the effectiveness of a BH3-mimetics based therapy.