In vitro to Clinical Translation of Combinatorial Effects of Doxorubicin and Abemaciclib in Rb-Positive Triple Negative Breast Cancer: A Systems-Based Pharmacokinetic/Pharmacodynamic Modeling Approach

Abstract

Background Doxorubicin (DOX) and its pegylated liposomal formulation (L_DOX) are the standard of care for triple-negative breast cancer (TNBC). However, resistance to DOX often occurs, motivating the search for alternative treatment approaches. The retinoblastoma protein (Rb) is a potential pharmacological target for TNBC treatment since its expression has been associated with resistance to DOX-based therapy. Methods DOX (0.01–20 μM) combination with abemaciclib (ABE, 1–6 μM) was evaluated over 72 hours on Rb-positive (MDA-MB-231) and Rb-negative (MDA-MB-468) TNBC cells. Combination indices (CI) for DOX+ABE were calculated using Compusyn software. The TNBC cell viability time-course and fold-change from the control of phosphorylated-Rb (pRb) protein expression were measured with CCK8-kit and enzyme-linked immunosorbent assay. A cell-based pharmacodynamic (PD) model was developed, where pRb protein dynamics drove cell viability response. Clinical pharmacokinetic (PK) models for DOX, L_DOX, and ABE were developed using data extracted from the literature. After scaling cancer cell growth to clinical TNBC tumor growth, the time-to-tumor progression (TTP) was predicted for human dosing regimens of DOX, ABE, and DOX+ABE. Results DOX and ABE combinations were synergistic (CI<1) in MDA-MB-231 and antagonistic (CI>1) in MDA-MB-468. The maximum inhibitory effects (Imax) for both drugs were set to one. The drug concentrations producing 50% of Imax for DOX and ABE were 0.565 and 2.31 μM (MDA-MB-231) and 0.121 and 1.61 μM (MDA-MB-468). The first-orders rate constants of abemaciclib absorption (k a ) and doxorubicin release from L_DOX (k Rel ) were estimated at 0.31 and 0.013 h −1 . Their linear clearances were 21.7 (ABE) and 32.1 L/h (DOX). The estimated TTP for intravenous DOX (75 mg/m2 every 21 days), intravenous L_DOX (50 mg/m 2 every 28 days), and oral ABE (200 mg twice a day) were 125, 31.2, and 8.6 days shorter than drug-free control. The TTP for DOX+ABE and L_DOX+ABE were 312 days and 47.5 days shorter than control, both larger than single-agent DOX, suggesting improved activity with the DOX+ABE combination. Conclusion The developed translational systems-based PK/PD model provides an in vitro-to-clinic modeling platform for DOX+ABE in TNBC. Although model-based simulations suggest improved outcomes with combination over monotherapy, tumor relapse was not prevented with the combination. Hence, DOX+ABE may not be an effective treatment combination for TNBC.

Cyclin‐dependent kinase inhibitors enhance programmed cell death protein 1 immune checkpoint blockade efficacy in triple‐negative breast cancer by affecting the immune microenvironment

“…We hypothesized that CDK inhibitors activate antitumor immunity by downregulating DNMT. However, our study did not thoroughly investigate how CDK inhibitors affect DNA methylation, a direction for future research 7,29‐31 . Reducing DNA methylation levels in tumor cells restores the expression of chemokine genes, thereby promoting chemokine secretion 32 .…”

“…The three CDK inhibitors, ABE, FAD, and SAM, effectively inhibited the proliferation of MDA‐MB‐231 and 4T1 TNBC cells in vitro. CDK inhibitors exert antitumor effects by targeting CDK via classical mechanisms 6,7 . All the three CDK inhibitors blocked the cell cycle by targeting their respective target proteins, exhibiting antitumor activity.…”

“…However, our study did not thoroughly investigate how CDK inhibitors affect DNA methylation, a direction for future research. 7,[29][30][31] Reducing DNA methylation levels in tumor cells restores the expression of chemokine genes, thereby promoting chemokine secretion. 32 Accordingly, we found significant upregulation of Cxcl9, Cxcl10, Cxcl12, and CCL5 in TNBC cells after treatment with CDK inhibitors.…”

“…6 Monotherapy using immune checkpoint inhibitors for breast cancer is unsatisfactory; to ensure efficacy, it is often combined with chemotherapy, sometimes leading to bone marrow suppression and immune function impairment. 7 The IMpassion130 study reported adverse reactions, including leukopenia (76%), neutropenia (58%), and lymphopenia (54%), in the combination group. 8 Immunotherapy efficacy depends on normal immune function; this antagonistic effect limits its effectiveness.…”

“…Approximately 20% of patients with TNBC show positive expression of programmed death‐ligand 1 (PD‐L1), a biomarker for anti‐programmed cell death protein 1 (PD‐1) therapies, indicating a treatment response; this limits the eligible patient population 6 . Monotherapy using immune checkpoint inhibitors for breast cancer is unsatisfactory; to ensure efficacy, it is often combined with chemotherapy, sometimes leading to bone marrow suppression and immune function impairment 7 . The IMpassion130 study reported adverse reactions, including leukopenia (76%), neutropenia (58%), and lymphopenia (54%), in the combination group 8 …”