Thursday, April 10, 2025
4/10/2025
Overcoming therapy resistance in melanoma - PROJECT SUMMARY AND ABSTRACT Rationale: Despite novel chemotherapies have significantly improved the prognosis of melanoma patients, drug resistance occurs inevitably and tumor progression becomes inexorable, presenting an unmet and urgent need for novel therapeutic intervention. Most melanomas harbor oncogenic BRAFV600E and are responsive to the BRAFV600E-specific inhibitor dabrafenib and the MEK inhibitor trametinib; however, patients eventually acquire resistance mainly due to MAPK reactivation and/or the counteraction by phosphoinositide 3-kinase (PI3K). While substantial efforts have been made to mitigate therapy resistance using PI3K inhibitors; there has been a lack of success as no PI3K inhibitors are currently capable of serving for this purpose. PI3K has four functionally divergent catalytic kinases PI3Kα/β/δ/γ. Drugs that block all four kinases or individual PI3Kα/δ/γ have shown clinical benefit, but elicited notable metabolic or immune-related toxicities. Such clinical challenge in drugging PI3Kα/δ/γ has fueled interest in PI3Kβ therapies; however, PI3Kβ ATP competitive inhibitors GSK2636771, TGX-221, and AZD6482 are not clinically effective, notwithstanding their promising preclinical anti-cancer activities. This is perhaps because ATP competitive inhibitors interact with well-conserved residues at motifs pivotal for executing kinase activity in PI3Kα/β/δ/γ, making them not as PI3Kβ-selective as desired. Rising to this challenge, we have recently identified an 18-residue motif dubbed β18 that occurs only in PI3Kβ, but not in PI3Kα/δ/γ. Selectide-18 bearing β18 and a cell- penetrating peptide distorts PI3Kβ complexes, inactivates PI3Kβ, slows down the growth of BRAFV600E melanomas expressing high levels of PI3Kβ and low levels of the PI3K-antagonizing phosphatase PTEN (designated as PI3Kβhyper), and sensitizes therapy-resistant PI3Kβhyper melanoma cells to dabrafenib/trametinib. Our further in-silico analyses have identified Selectide-9, a short version of Selectide-18 which only contains 9 residues derived from the S18 motif, but still retains the same cytotoxic activities as Selectide-18. Hypothesis: We hypothesize that Selectide- 9 selectively degrades and inactivates PI3Kβ, thereby overcoming therapy resistance in PI3Kβhyper melanoma. Specific Aims: We will use approaches established in the PI’s laboratory to test the above hypothesis. In Aim 1, we will test how Selectide-9 degrades and inactivates PI3Kβ selectively using biochemical and imaging techniques. In Aim 2, we will test whether Selectide-9 is superior to ATP competitive inhibitors in overcoming therapy resistance using two human BRAFV600E patient-derived xenograft lines in immunodeficient mice. The WM4701-6673 line has low levels of PI3Kβ and the recurrent/therapy-resistant WM4701-7329 tumor is derived from WM4701-6673 treated with a BRAFV600E inhibitor. We will determine if WM4701-6673 is sensitive, whilst WM4701-7329 is resistant, to dabrafenib and trametinib and if Selectide-9 is more potent than GSK2636771 in restoring the sensitivity to dabrafenib and trametinib. Moreover, we will identify gene signatures defining therapy-resistant PI3Kβhyper melanomas using single-cell RNA sequencing. Impact: Our work will lay the groundwork to support future studies to gain deeper insights into therapy resistance in melanoma and identify an innovative approach to circumventing this resistance.
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