Combination strategies to overcome drug resistance in FLT+ acute myeloid leukaemia

Inhibition of FLT3-induced signalling in refractory acute myeloid leukaemia

Mutations in FLT3 make this receptor tyrosine kinase overactive. Such mutations found in ∼30 % of the patients who suffer from acute myeloid leukaemia (AML). FLT3 mediates signalling networks that lead to cell proliferation and survival. FLT3 inhibitors are used to treat AML but patients who are treated with them typically become resistant. Such resistance often emerges through secondary mutations which either restore the activity of FLT3 in the presence of drugs or activate a key player in a signalling network such as NRAS. We had developed AML-specific cell lines resistant to two advanced FLT3 inhibitors: gilteritinib and FF-10101. Resistance in these cell lines proceeds though different mechanisms. In this study, we followed on the efficacy of five FLT3 inhibitors (gilteritinib, FF-10101 and three promising inhibitors that are being developed), two pan-PI3K inhibitors (one of which also inhibits mTOR) and two c-KIT inhibitors in order to examine the significance of different signalling cascades in FLT3+-AML. In addition, we used molecular modelling and quantum chemistry calculations to explain why specific FLT3 mutations affect some inhibitors more than others. Two novel FLT3 inhibitors were found to be only weakly affected by resistance mutations against gilteritinib and FF-10101. The efficacy of most FLT3 inhibitors was only weakly (or not at all) affected by the NRAS/G12C activating mutation. Finally, no non-FLT3 inhibitor has shown sufficient efficacy in the cells, suggesting the central role of FLT3 in FLT3-mutated AML.

LncRNA-ANRIL regulates CDKN2A to promote malignant proliferation of Kasumi-1 cells

OBJECTIVE

This study aimed to investigate the regulatory effects of long non-coding RNA-ANRIL on CDKN2A in the cell cycle of Kasumi-1 cells and elucidate the underlying molecular mechanisms.

METHODS

ANRIL and CDKN2A expression levels were quantified using RT-qPCR in peripheral blood samples from acute myeloid leukemia (AML) patients. CDKN2A knockdown efficiency was validated via RT-qPCR, and cell cycle distribution was analyzed using flow cytometry. Cell proliferation assays were conducted with CCK-8 following palbociclib treatment and CDKN2A downregulation. RNA immunoprecipitation (RIP) identified potential ANRIL-associated targets, while western blotting assessed the expression levels of GSK3β/β-catenin/cyclin D1 signaling components and related proteins.

RESULTS

ANRIL and CDKN2A were markedly overexpressed in AML patient samples. Knockdown of ANRIL and CDKN2A led to G1 phase arrest accompanied by reduced CDK2/4/6 and cyclin D1 protein levels, while ANRIL upregulation induced the opposite effect. Palbociclib treatment for 24 h and 48 h elevated the G1 phase cell population and suppressed CDK2/4/6 and cyclin D1 protein expression, demonstrating its ability to counteract ANRIL-driven cell cycle progression. Downregulation of ANRIL and CDKN2A also suppressed the GSK3β/β-catenin signaling pathway, reducing cyclin D1 expression, whereas ANRIL upregulation reactivated this axis. Co-transfection experiments showed that simultaneous cyclin D1 suppression and ANRIL overexpression attenuated ANRIL's stimulatory effects on cell cycle progression. RIP analysis confirmed a physical interaction between ANRIL and CDKN2A. Furthermore, CDKN2A downregulation inhibited cell proliferation and reversed GSK3β/β-catenin/cyclin D1 pathway activation mediated by ANRIL upregulation.

CONCLUSION

ANRIL facilitates Kasumi-1 cell survival by modulating CDKN2A to activate the GSK3β/β-catenin/cyclin D1 signaling pathway.

Inhibition of NLRP3 enhances pro-apoptotic effects of FLT3 inhibition in AML

FLT3 mutations occur in approximately 25% of all acute myeloid leukemia (AML) patients. While several FLT3 inhibitors have received FDA approval, their use is currently limited to combination therapies with chemotherapy, as resistance occurs, and efficacy decreases when the inhibitors are used alone. Given the highly heterogeneous nature of AML, there is an urgent need for novel targeted therapies that address the disease from multiple angles. Recent research has identified the NLRP3 inflammasome as a potential new driver in AML. Here, we investigated the efficacy of different NLRP3 inhibitors in targeting AML cells in vitro. Our findings reveal that NLRP3 inhibition induces cell cycle arrest as well as signs of senescence in multiple AML cell lines. In contrast, NLRP3 inhibition selectively induced apoptosis in FLT3 mutant AML cell lines, but not in FLT3 wild-type AML cells. Moreover, we show that NLRP3 inhibition impairs FLT3 signaling by reducing both FLT3 expression as well as downstream signaling in FLT3 mutant cells. A database analysis revealed a strong positive correlation between FLT3 and NLRP3 in cancer, which was particularly evident in AML patients. Strikingly, the simultaneous inhibition of NLRP3 and FLT3 markedly enhanced apoptosis in FLT3-ITD mutant AML cells, but not in FLT3 wild-type cells. In summary, this study reveals a promising combined therapeutic strategy specifically targeting NLRP3/FLT3-ITD positive AML blasts in vitro, highlighting a potential new avenue for AML treatment.

Recent advancements in biomarkers, therapeutics, and associated challenges in acute myeloid leukemia

Acute myeloid leukemia (AML) is a common type of leukemia that has a high mortality rate. The reasons for high mortality in patients with AML are therapeutic resistance, limited ability to predict duration of response, and likelihood of cancer relapse. Biomarkers, such as leukemic stem cell biomarkers, circulatory biomarkers, measurable residual disease biomarkers, and molecular biomarkers, are used for prognosis, diagnosis, and targeted killing to selectively eliminate AML cells. They also play an indispensable role in providing therapeutic resistance to patients with AML. Therefore, targeting these biomarkers will improve the outcome of AML patients. However, identifying biomarkers that can differentiate between treatment-responsive and non-responsive AML patients remains a challenge. This review discusses recent advancements in AML biomarkers, promising therapeutics, and associated challenges in the treatment of AML.

Understanding mechanisms of resistance to FLT3 inhibitors in adult FLT3-mutated acute myeloid leukemia to guide treatment strategy

The presence of FLT3 mutations, including the most common FLT3-ITD (internal tandem duplications) and FLT3-TKD (tyrosine kinase domain), is associated with an unfavorable prognosis in patients affected by acute myeloid leukemia (AML). In this setting, in recent years, new FLT3 inhibitors have demonstrated efficacy in improving survival and treatment response. Nevertheless, the development of primary and secondary mechanisms of resistance poses a significant obstacle to their efficacy. Understanding these mechanisms is crucial for developing novel therapeutic approaches to overcome resistance and improve the outcomes of patients. In this context, the use of novel FLT3 inhibitors and the combination of different targeted therapies have been studied. This review provides an update on the molecular alterations involved in the resistance to FLT3 inhibitors, and describes how the molecular monitoring may be used to guide treatment strategy in FLT3-mutated AML.

Synergy and antagonism between azacitidine and FLT3 inhibitors

Synergetic interactions between drugs can make a drug combination more effective. Alternatively, they may allow to use lower concentrations and thus avoid toxicities or side effects that not only cause discomfort but might also reduce the overall survival. Here, we studied whether synergy exists between agents that are used for treatment of acute myeloid leukaemia (AML). Azacitidine is a demethylation agent that is used in the treatment of AML patients that are unfit for aggressive chemotherapy. An activating mutation in the FLT3 gene is common in AML patients and in the absence of specific treatment makes prognosis worse. FLT3 inhibitors may be used in such cases. We sought to determine whether combination of azacitidine with a FLT3 inhibitor (gilteritinib, quizartinib, LT-850-166, FN-1501 or FF-10101) displayed synergy or antagonism. To this end, we calculated dose-response matrices of these drug combinations from experiments in human AML cells and subsequently analysed the data using a novel consensus scoring algorithm. The results show that combinations that involved non-covalent FLT3 inhibitors, including the two clinically approved drugs gilteritinib and quizartinib were antagonistic. On the other hand combinations with the covalent inhibitor FF-10101 had some range of concentrations where synergy was observed.