Mohiuddin, Md

Abstract Purpose: Immune checkpoint blockade (ICB) induces frequent and durable responses in metastatic deficient DNA mismatch repair (dMMR) colorectal cancer, yet substantial molecular heterogeneity and resistance remain. We sought to identify candidate tumor- and immune-related biomarkers associated with clinical outcomes following anti–PD-1 therapy. Experimental Design: Consecutive patients with metastatic dMMR colorectal cancer (N = 39) treated with anti–PD-1 therapy underwent tumor profiling using a validated immune-enhanced exome and transcriptome platform. Microsatellite instability (MSI) burden was quantified as the percentage of unstable microsatellite loci using MSIsensor-pro. Associations with objective response were evaluated, and progression-free survival (PFS) and overall survival (OS) were analyzed using Cox proportional hazards models. Results: Higher MSI burden was associated with improved objective response (P = 0.018) and survival. The dichotomized MSI level (Q2–4 vs. Q1) was associated with longer PFS [hazard ratio (HR), 0.18; 95% confidence interval (CI), 0.06–0.56; P = 0.003] and OS (HR, 0.20; 95% CI, 0.07–0.58; P = 0.003), with similar results when modeled continuously. MSI burden correlated with neoantigen clonality but not burden (R = 0.53, P = 0.01). Responders exhibited significantly greater T-cell receptor repertoire diversity; both T- and B-cell receptor diversities were associated with survival. Although human leukocyte antigen (HLA) A, HLA-B, and HLA-C expression was not prognostic, the HLA-B*07:02 allele was associated with the best overall response. In contrast, overexpression of immune exhaustion–related genes and cytotoxic T-cell and natural killer cell exhaustion phenotypes were associated with ICB resistance and poorer prognosis. Conclusions: Integrated exome/transcriptome profiling with MSI quantification identified MSI burden and adaptive immune repertoire diversity as potential correlates of response and survival following ICB. These findings suggest a mechanistic link among genomic instability, antigen recognition diversity, and immunotherapy benefit.

Abstract Background: The BRAF(V600E) mutation in colorectal cancer (CRC) is associated with treatment resistance and a poor prognosis. CDK2/9 is frequently activated in human cancers, and we have previously shown that BRAFV600E can upregulate MCL-1, which can be suppressed by the selective CDK2/9 inhibitor fadraciclib. Herein, we determined whether targeting CDK2/9 by fadraciclib can be enhanced by concurrent Bcl-2/Bcl-xL inhibition using LP-118, which minimizes platelet toxicity in patients, compared to the Bcl-2 inhibitor venetoclax. Effects of the drugs on apoptosis, colony formation and tumor growth were studied in a zebrafish model. Methods: We utilized isogenic human RKO (BRAFV600E/V600E/WT) and T29 (BRAFWT/−/−) CRC cell lines in addition to HCT-116 (BRAFWT) and Bax knockout (HCT-116Bax-/-) CRC cells. Cells were treated for 24h with fadraciclib (500nM) plus encorafenib (500nM) in the presence or absence of LP-118 (1µM) or venetoclax (1µM). Apoptosis and cell growth inhibition were assessed using annexin V/PI staining and colony formation assays, respectively. Expression of MCL-1, Bcl-xL, Bcl-2, PARP, and cleaved caspase-3 (Asp175) proteins was analyzed. In a zebrafish tumor xenograft model, the effects of the drugs on caspase-3 cleavage and tumor growth were then evaluated. Results: Fadraciclib suppressed MCL-1 expression, induced apoptosis and significantly inhibited colony formation in all CRC cell lines. However, this effect was enhanced by encorafenib only in RKO (BRAFV600E/V600E/WT) cells. The addition of LP-118 to fadraciclib plus encorafenib potently enhanced apoptosis induction, shown by annexin V and cleavage of PARP, caspase-3, in RKO and HCT-116 cell lines, which was synergistic and Bax dependent. Treatment with LP-118 combined with fadraciclib and encorafenib suppressed both Bcl-xL and MCL-1 expression in RKO cells. The addition of LP-118 to fadraciclib plus encorafenib enhanced apoptosis (annexin V) to a greater extent than did venetoclax. In a zebrafish tumor xenograft model, the addition of LP-118 to fadraciclib plus encorafenib significantly enhanced caspase-3 activation and reduced the tumor xenograft size. Conclusion: LP-118 synergistically enhanced the antitumor activity of fadraciclib plus encorafenib in BRAFV600E human CRC cells, and to a greater extent than did venetoclax. Mechanistically, targeting Bcl-2/Bcl-xL concurrent with inhibition of MCL-1 and CDK2/9 by fadraciclib potently induced apoptosis and suppressed tumor cell growth. These findings suggest a novel and effective therapeutic strategy for BRAFV600E human CRCs. Citation Format: Md Mohiuddin, Vanda Póvoa, Beatriz Sebo, Rita Fior, Frank A. Sinicrope. Novel Bcl-2/Bcl-xL inhibitor, LP-118, enhances apoptosis induction by the CDK2/9 inhibitor, fadraciclib, in BRAF(V600E) human colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4658.

Abstract Background: Mutant BRAF(V600E) is present in 8-12% of human colorectal cancers (CRCs) and is associated with treatment resistance and poor survival. Targeted therapy with inhibitors of BRAF and EGFR is associated with only an incremental survival benefit. Methods: We studied the novel CDK2/CDK9 inhibitor, fadraciclib, alone and in combination with the BRAF inhibitor encorafenib on isogenic CRC cells with two, one, or no BRAFV600E alleles (RKO+/+, A19+/-, T29-/-). Analysis of apoptosis, colony formation, and the cell cycle was performed. The effect of drug treatment on growth of tumor xenografts was determined in a zebrafish model. Results: Fadraciclib induced apoptosis and inhibited colony formation in a gene dose-dependent manner. Its growth inhibitory effect when combined with encorafenib was synergistic. Mechanistically, fadraciclib suppressed the expression of pro-survival MCL-1 and decreased the phosphorylation of RNA polymerase II indicating suppression of RNA transcription. Fadraciclib also impaired Rb phosphorylation and promoted a DNA damage response indicated by the cleavage of PARP, pH2AX (ser139), and activation of p53. Drug treatment was associated with a greater suppression of Rb phosphorylation, cell cycle inhibition, and apoptosis in RKO+/+ versus A19+/- and T29-/- cells. In a zebrafish tumor xenograft model, fadraciclib plus encorafenib significantly reduced the tumor xenograft size concurrent with increased caspase-3 activation. Conclusion: Fadraciclib plus encorafenib potently induced apoptosis and synergistically suppressed tumor cell growth in a gene dose-dependent manner in BRAFV600E CRC cells, and exerted anti-tumor effects in a tumor xenograft model. These data suggest a novel therapeutic strategy in this CRC subtype. Citation Format: Md Mohiuddin, Vanda Póvoa, Rita Fior, Frank A. Sinicrope. Novel CDK2/CDK9 inhibitor fadraciclib targets cell survival and DNA damage pathways and synergizes with encorafenib in human colorectal cancer cells with BRAF(V600E). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1682.