Synergistic Effect of Trifluridine and PARPi Combination in Targeting TP53-Mutated AML
Authors: Parcha Phani Krishna , Shastri Vivek M. , Licht Jonathan D. , Lamba Jatinder K. 
Published: December 2024

Introduction: TP53 encodes the tumor suppressor p53 protein, which is critical in regulating response to DNA damage, and is one of the most commonly mutated genes in human cancer. In acute myeloid leukemia (AML) TP53 has predominantly mutations in the DNA binding domain. TP53-mutated AML has very poor outcome to standard therapy with a median survival of 6-7 months. Additionally, TP53 mutations are found at an approximately 5-fold higher frequency upon exposure to treatment in AML patients without pre-existing mutations. Whether pre-existing or therapy-induced, TP53-mutated AML patients also show a lowered likelihood of measurable residual disease (MRD) negativity, a higher likelihood of relapse, and respond poorly to transplant with shortened survival. So far, no FDA-approved therapies targeting mutated p53 are available. A recent study has shown a very promising impact of using a combination of TAS-102 (LonsurfTM), containing the thymidine analog trifluridine, and PARP inhibitor talazoparib (TalzennaTM) in TP53-mutated colorectal and pancreatic cancer cells (Alruwaili et al, 2024; PMID 38387463). The trifluridine component of TAS-102 is incorporated in the DNA and selectively induces base excision repair mediated single-strand breaks (SSB) in TP53 mutated cells. PARP inhibition by talazoparib abrogates SSB repair, leading to the development of double-strand breaks (DSB). These DSBs accumulate without p53-mediated G1 checkpoint and trigger cell death. The current study was designed with the objective to test the trifluorothymidine and PARPi combination for its effectiveness in TP53-mutated AML.

Methods: Five TP53-mutated AML cell lines: THP-1 (TP53 mutation: p.R174LfsTer3), Kasumi-1 (TP53 mutation: p.R248Q), NOMO-1 (TP53 mutation:p.C242AfsTer5), K-562 (TP53 mutation p.Q136PfsTer13), and HL-60 (TP53 null) and three TP53 wild-type (no known TP53 mutations) AML cell lines OCI-AML2, OCI-AML3, and ML2 cells with treated with varying concentration of single agents (trifluorothymidine-TAS102 or PARPi-talazoparib) for 72 hours before assessing cell viability using CellTiter-Glo® 2.0 Assay. For combination treatments, cells were preincubated with varying concentrations of TAS-102 for 24 hours, followed by adding talazoparib (0 nM, 50 nM, 500 nM, or 1000 nM) for 72 hours before cell viability assays. Fractional inhibitory concentration (FIC) was calculated for each drug as the IC50 value of each drug when used in combination/IC50 of each drug when used alone. The combination index (CI) was calculated as the sum of FICs of the two drugs used in combination, with a CI &lt;1 indicating synergy, CI=1 indicating additivity, and CI &gt;1 indicating antagonism.

Results: TP53-mutant and TP53-WT AML cell lines showed varying sensitivity to TAS102 or talazoparib when exposed as single agents. Combination of TAS102 (triflurothymidine) with talazoparib (PARPi) demonstrated increased chemosensitivity in TP53-mutant but not P53-WT AML cell lines. Isobolograms for this combination showed CI values ranging from 0.16-0.93 for TP53-mutated cells, indicating a synergistic interaction between TAS-102 and talazoparib in TP53-mutant AML. However, CI values for this combination ranged from 1.03-9.30 in cells with TP53-WT cell lines implying antagonism.

Conclusions: These results, for the first time, demonstrate synergism between TAS-102 and talazoparib to specifically target and mediate cytotoxicity in a panel of AML cell lines with TP53 mutations but not those with wildtype TP53. Ongoing studies are focused on testing these in primary patient specimens and PDX mouse models, once validated these results support the potential for using this two-drug combination of FDA-approved drugs for improving outcome in TP53-mutated AML.