Overcoming Venetoclax Resistance: The Emergence of LP-118 as a Dual Bcl-2 and Bcl-Xl Inhibitor in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL), the most prevalent adult leukemia, is marked by an increase in mature CD19+CD5+ B cells that avoid cell death by boosting the anti-apoptotic protein Bcl-2. Venetoclax, a groundbreaking Bcl-2 inhibitor, has revolutionized CLL treatment. However, resistance to venetoclax can emerge due to mutations near the drug's binding site on Bcl-2 or due to alterations in TP53 or the upregulation of other anti-apoptotic proteins like Bcl-xL.

Our research involved BH3 profiling on primary CLL cells, both untreated and relapsed after venetoclax treatment, to determine the reliance on various anti-apoptotic proteins. We utilized peptides targeting specific proteins and found that many cells depended on Bcl-2, as indicated by their response to BIM and BAD peptides. However, venetoclax-resistant samples showed a shift towards dependency on Bcl-xL.

We then explored LP-118, a novel Bcl-2 inhibitor more potent than venetoclax, which selectively binds to Bcl-xL with reduced platelet toxicity. LP-118 was designed to have an intermediate IC50 for Bcl-xL, positioned between venetoclax and navitoclax, to mitigate platelet-related side effects. Given the common mutation in Bcl-2 or increased Bcl-xL dependency in venetoclax-resistant patients, we hypothesized that inhibiting Bcl-xL could be beneficial.

In an 18-hour incubation experiment, we tested the sensitivity of CLL cells to LP-118, venetoclax, and navitoclax. We discovered that untreated CLL cells were more responsive to LP-118 than the other drugs, and venetoclax-resistant cells were significantly affected by LP-118 but not the other two. Further investigation revealed that LP-118 induced the transformation of the pro-apoptotic protein Bak and the release of cytochrome c, indicating apoptosis.

Experiments with cells containing the Bcl-2 Gly101Val mutation showed that LP-118 was effective with an IC50 of 20 nM, unlike venetoclax. Additionally, LP-118 induced quicker Bak transformation and cytochrome c release in these cells.

In vivo studies using a xenograft model demonstrated that LP-118 significantly reduced tumor growth and improved survival compared to venetoclax. Our findings support the ongoing preclinical and clinical development of LP-118, with a phase 1 clinical trial for patients with relapsed hematologic malignancies soon to commence.