Hohl, Raymond J.

Abstract Introduction: The binding of Programmed Death-Ligand 1 (PD-L1) on the surface of tumor cells to PD-1 on T cells prevents T-cell-mediated anti-cancer immune responses. Immune checkpoint blockades that target the PD-L1/PD-1 interaction have improved survival rates but have several critical limitations. Post-translational modifications (PTMs) of PD-L1, such as glycosylation, are crucial for its stability and engagement with PD-1. Thus, targeting PD-L1 PTMs may be a novel method to improve immune checkpoint blockade efficacy. The mevalonate pathway (MVP) generates various substances involved in PTMs process. Here, we explore the effect of MVP in altering the PTMs of PD-L1 and its impacts on cell surface PD-L1 function. Methods: The triple-negative human breast cancer (TNBC) cell lines MDA-MB-231 and BT549 were treated with the HMG-CoA reductase inhibitor lovastatin (LOV) with or without the addition of IFN-γ and/or MVP intermediates for 48 hours. PD-L1 transcription was evaluated by qPCR. Alterations in PD-L1 size were detected by Western blotting. PD-L1 surface levels were measured by flow cytometry. HMG-CoA reductase (HMGCR) knockdown was performed to validate the non-off-target effect of LOV. The binding of PD-1 protein to the cell surface PD-L1 was measured by PD-1/PD-L1 binding assay. PD-L1 glycosylation levels were measured by Concanavalin A (Con A) lectin binding assay with immunoprecipitated PD-L1 protein. Results: LOV treatment caused a significant molecular weight shift of PD-L1 from approximately 45 kDa to 40 kDa and reduced the cell surface PD-L1 levels. However, PD-L1 transcription was not affected by LOV. HMGCR knockdown produced similar changes, indicating LOV's impact on PD-L1 was not due to off-target effects. The addition of MVP intermediates mevalonate (MEV) or geranylgeraniol, but not farnesol prevented LOV-induced changes in PD-L1 molecular weight and surface levels. Interestingly, the addition of 25-hydroxycholesterol, but not dolichol, partially prevented LOV-induced decreases in PD-L1 surface levels. Geranylgeranyl transferase inhibitor GGTI-286, which prevents protein geranylgeranylation, also altered PD-L1 molecular weight and decreased surface levels. In addition, LOV impaired the binding of PD-1 protein to tumor cells' surface PD-L1, which was reversed by the addition of MVP substrate MEV. Con A lectin-binding of immunoprecipitated PD-L1 showed that the LOV did not reduce the N-glycosylation level of PD-L1. Conclusions: This study reveals the involvement of the MVP in regulating PD-L1 PTMs and highlights the MVP as a potential therapeutic target to modulate PD-L1’s molecular weight and function and improve the efficacy of immunotherapy interventions, presenting a promising avenue for further investigation. Citation Format: Ruoheng Zhang, Emily J. Koubek, Jessie L. Reed, Jeffrey D. Neighbors, Joel M. Reid, Raymond J. Hohl. The role of the mevalonate pathway in post-translational modifications of PD-L1 [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 4265.

Abstract Abstract 287 Purpose: Farnesyltransferases are key cellular enzymes involved in the prenylation of proteins. Prenylated proteins are important for malignant cell growth. The purpose of this phase II study (NCT00082888) was to assess tumor response and toxicity associated with the oral farnesyltransferase inhibitor tipifarnib (R115777, Johnson and Johnson) in patients with relapsed aggressive, indolent, or uncommon lymphoma. The uncommon group included low incidence lymphoma types such as Hodgkin lymphoma (HL) and T-cell non-Hodgkin lymphoma- cutaneous T-cell lymphoma (CTCL) and peripheral T-cell lymphoma (PTCL). Patients and Methods: Patients with relapsed or refractory non-Hodgkin (NHL) or Hodgkin (HL) were eligible if they had measurable disease, performance status ≤2, platelet count ≥75,000 × 10(6)/L, an absolute neutrophil count ≥1000 × 10(6)/L and a creatinine ≤2 × upper limit of normal. Patients initially received tipifarnib 300 mg twice daily, days 1–21 every 28 days. The trial was conducted by the University of Iowa/Mayo Clinic Lymphoma SPORE. Results: Ninety-three patients with lymphoma (42 aggressive, 15 indolent, and 36 uncommon) enrolled in the trial between March 2004 and November 2008. The median age was 62 years (range, 18–91). The median number of prior therapies was 5 (range, 1–17). The overall response rate (ORR) was 20% (19/93) with 6% (6/93) complete responses (CR) and 14% (13/93) partial responses (PR). The ORR was 17%, 7%, and 31% for the aggressive, indolent, and uncommon groups, respectively (Table). Among the 19 responders were 7 diffuse large B-cell lymphoma (DLBCL), 7 T-cell NHL, 1 follicular grade II, and 4 HL. The overall median response duration for the 19 responders was 7.5 months (mean, 12.8; range, 1.8 – 48.1 months). The median response duration was 11.3 months (mean, 10.1; range, 1.8 – 18.5 months), 2 months, and 7.5 months (mean, 15.5; range, 1.9 – 48.1 months) for the aggressive (7), indolent (1), and uncommon (11) groups, respectively. Five patients in the uncommon group are still receiving treatment with a range of treatment duration between 25 – 60+ months. Among the 5 still receiving treatment 4 responded and 1 is stable. The range of response duration is 15.4, 17.7, 43.1, and 48.1 months. These five patients (2 with HL, 1 anaplastic large cell cutaneous, and 2 PTCL) are currently receiving doses of 400 (1), 200 (2), and 100 (2) mg twice daily. The median time to progression for all patients was 3.6 months (95% CI: 2.1 – 4.5 months). The grade 3,4 toxicities observed were primarily fatigue (10%) and reversible myelosuppression with 11% anemia, 37% neutropenia, and 32% thrombocytopenia. Correlative studies demonstrated tipifarnib-induced upregulation of Bim, a marker of tipifarnib action in lymphoma cell lines, in 7 of 9 paired lymphoma biopsies. Conclusions: Tipifarnib has activity in lymphoma, with responses in patients with heavily pretreated DLBCL, HL and T-cell types, but little activity in follicular NHL. This agent has an excellent toxicity profile and targets a novel pathway. Further studies in combination with other agents are warranted for patients with DLBCL, HL or T-cell NHL. Disclosures: No relevant conflicts of interest to declare.

AbstractThe schweinfurthins have potent antiproliferative activity in multiple glioblastoma multiforme (GBM) cell lines; however, the mechanism by which growth is impeded is not fully understood. Previously, we demonstrated that the schweinfurthins reduce the level of key isoprenoid intermediates in the cholesterol biosynthetic pathway. Herein, we describe the effects of the schweinfurthins on cholesterol homeostasis. Intracellular cholesterol levels are greatly reduced in cells incubated with 3‐deoxyschweinfurthin B (3dSB), an analog of the natural product schweinfurthin B. Decreased cholesterol levels are due to decreased cholesterol synthesis and increased cholesterol efflux; both of these cellular actions can be influenced by liver X‐receptor (LXR) activation. The effects of 3dSB on ATP‐binding cassette transporter 1 levels and other LXR targets are similar to that of 25‐hydroxycholesterol, an LXR agonist. Unlike 25‐hydroxycholesterol, 3dSB does not act as a direct agonist for LXR α or β. These data suggest that cholesterol homeostasis plays a significant role in the growth inhibitory activity of the schweinfurthins and may elucidate a mechanism that can be targeted in human cancers such as GBM.

R115777 is a nonpeptidomimetic enzyme-specific inhibitor of farnesyl protein transferase (FT) that was developed as a potential inhibitor of Ras protein signaling, with antitumor activity in preclinical models. This study was a phase 1 trial of orally administered R115777 in 35 adults with poor-risk acute leukemias. Cohorts of patients received R115777 at doses ranging from 100 mg twice daily (bid) to 1200 mg bid for up to 21 days. Dose-limiting toxicity occurred at 1200 mg bid, with central neurotoxicity evidenced by ataxia, confusion, and dysarthria. Non–dose-limiting toxicities included reversible nausea, renal insufficiency, polydipsia, paresthesias, and myelosuppression. R115777 inhibited FT activity at 300 mg bid and farnesylation of FT substrates lamin A and HDJ-2 at 600 mg bid. Extracellular signal-regulated kinase (ERK), an effector enzyme of Ras-mediated signaling, was detected in its phosphorylated (activated) form in 8 (36.4%) of 22 pretreatment marrows and became undetectable in 4 of those 8 after one cycle of treatment. Pharmacokinetics revealed a linear relationship between dose and maximum plasma concentration or area under the curve over 12 hours at all dose levels. Weekly marrow samples demonstrated that R115777 accumulated in bone marrow in a dose-dependent fashion, with large increases in marrow drug levels beginning at 600 mg bid and with sustained levels throughout drug administration. Clinical responses occurred in 10 (29%) of the 34 evaluable patients, including 2 complete remissions. Genomic analyses failed to detect N-ras gene mutations in any of the 35 leukemias. The results of this first clinical trial of a signal transduction inhibitor in patients with acute leukemias suggest that inhibitors of FT may have important clinical antileukemic activity.