Immune effects of CDK4/6 inhibitors in patients with HR+/HER2− metastatic breast cancer: Relief from immunosuppression is associated with clinical response

Pirfenidone inhibits CCL2-mediated Treg chemotaxis induced by palbociclib and fulvestrant in HR+/HER2- breast cancer

In human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer, the most prevalent subtype, the pathological complete response (pCR) rate after neoadjuvant chemotherapy is less than 18 %, and the survival of patients with advanced-stage disease is approximately 34 %, highlighting the critical demand for more potent therapies. Recent research has underscored the substantial therapeutic benefits of the combination of CDK4/6 inhibitors and fulvestrant (Ful) in managing HR+/HER2- breast cancer. These therapeutics not only curtail tumor proliferation but also alter the tumor immune microenvironment, suggesting novel avenues for immunotherapy for this breast cancer subtype. Flow cytometry, PCR, WB, and RNA-seq experiments revealed that the combination of the CDK4/6 inhibitor palbociclib (Pal) with Ful upregulated CCL2 in tumor cells by inducing the SASP and activating the MAPK signaling pathway. CCL2 attracts Tregs to the tumor microenvironment, where it exerts an immunosuppressive effect. By administering the CCL2 inhibitor pirfenidone, we inhibited these effects and enhanced the antitumor efficacy of Pal + Ful. Our research revealed an immunosuppressive effect of CDK4/6 inhibitors and fulvestrant and suggested that CCL2 inhibitors may be a viable approach for treating patients with advanced HR+/HER2- breast cancer.

Precision oncology targeting FGFRs: A systematic review on pre-clinical activity and clinical outcomes of pemigatinib

Fibroblast Growth Factor Receptors (FGFRs) are emerging as key factors involved in tumorigenesis, tumor microenvironment remodeling and acquired resistance to targeted therapies. Pemigatinib is a Tyrosine-Kinase Inhibitor that selectively targets aberrant FGFR1, FGFR2 and FGFR3. Pemigatinib is now approved for advanced-stage cholangiocarcinoma (CCA) but data suggests that other tumor histotypes exhibit FGFR alterations, thus hypothesizing its potential efficacy in other cancer settings. The present systematic review, based on PRISMA guidelines, aims to synthetize and critically interpret the results of all available preclinical and clinical evidence regarding Pemigatinib use in cancer. In April 2024, an extensive search was performed in PubMed, MEDLINE, and Scopus databases using the keyword "Pemigatinib". Twenty-seven studies finally met all inclusion criteria. The promising results emerging from Pemigatinib preclinical and clinical studies pave the way for Pemigatinib extension to multiple solid cancer settings.

Neutrophil-to-lymphocyte ratio at the end of treatment with CDK4/6 inhibitors is an independent prognostic factor for ER-positive HER2-negative advanced breast cancer

PURPOSE

The aim of this study was to elucidate the clinical significance of peripheral blood biomarkers, including absolute lymphocyte count (ALC) and neutrophil-to-lymphocyte ratio (NLR), at the end of treatment (EOT) with CDK4/6 inhibitors abemaciclib and palbociclib in patients with estrogen receptor-positive human epidermal growth factor receptor 2-negative advanced breast cancer.

METHODS

We included 67 patients treated with fulvestrant plus abemaciclib or palbociclib. Overall survival (OS) since the EOT with CDK/4/6 inhibitors was compared in relation to the levels of ALC and NLR. The cut-off values of ALC and NLR were set at 1000/μL and 3, respectively.

RESULTS

Patients with a high ALC at EOT showed significantly longer OS than those with a low ALC (p = 0.0358). Moreover, patients with a low NLR at EOT showed significantly longer OS than those with a high NLR at EOT (p = 0.0044). Looking at the changes of ALC and NLR between baseline and the EOT, patients with a high ALC both at baseline and at the EOT showed significantly longer OS than others (p = 0.0201). Similarly, patients with a low NLR both at baseline and at the EOT showed significantly longer OS after EOT than others (p = 0.0136). Multivariable analysis revealed that the NLR at EOT (low vs. high) and changes in NLR (low at baseline to low at EOT vs. others) were significant and independent prognostic factors for OS after EOT (p = 0.0337, p = 0.0039, respectively).

CONCLUSION

NLR at EOT with CDK4/6 inhibitors is a significant and independent prognostic marker for patients with ER-positive HER2-negative advanced breast cancer.

CD25+FOXP3+CD45RA- regulatory T-cell infiltration as a prognostic biomarker for endometrial carcinoma

BACKGROUND

Regulatory T (Treg) cells reportedly play crucial roles in tumor angiogenesis as well as antitumor immunity. In order to explore their therapeutic potential, we investigated the precise prognostic impact of Treg markers in endometrial carcinoma.

METHODS

We performed multiplexed immunofluorescence and quantitative image analyses of CD25, FOXP3, CTLA4, and CD45RA in tumor specimens from 176 consecutive patients treated at our institution for primary endometrial carcinomas. Bioinformatics analyses were further conducted to corroborate the findings.

RESULTS

High CD25+, FOXP3+, and CD25+FOXP3+CD45RA- stromal cell counts correlated with better overall survival (OS) (p = 0.00019, 0.028 and 0.0012) and MSI-high (p = 0.015, 0.016 and 0.047). High CD45RA+ stromal cell count was associated with superficial myometrial invasion (p = 0.0038). Bioinformatics survival analysis by Kaplan-Meier plotter showed that high CD25, FOXP3, CTLA4, and CD45RA mRNA expressions correlated with better OS (p = 0.046, 0.00042, 0.000044, and 0.0022). Univariate and multivariate analyses with various clinicopathologic prognostic factors indicated that high CD25+ or CD25+FOXP3+CD45RA- stromal cell count was significant and independent for favorable OS (p = 0.0053 and 0.0015). We subsequently analyzed the correlations between the multiplexed immunofluorescence results and treatment-free interval (TFI) after primary chemotherapy in recurrent cases, finding no significant associations. Further analysis revealed that high ratio of CD25+ : CD8+ cell count or CD25+FOXP3+CD45RA- : CD8+ cell count correlated with longer TFI (p = 0.021 and 0.021).

CONCLUSION

The current observations suggest that the balance between CD25+ or CD25+FOXP3+CD45RA- cells and CD8+ cells, corresponding to promoting or inhibiting effect on tumor angiogenesis, affect tumor chemosensitivity leading to prognostic significance. CD25+FOXP3+CD45RA- effector Treg tumor infiltration may serve as a useful prognostic biomarker and a potential target for immunotherapeutic manipulation of tumor chemosensitivity by novel management for advanced/recurrent endometrial carcinomas.

Breaking through therapeutic barriers: Insights into CDK4/6 inhibition resistance in hormone receptor-positive metastatic breast cancer

The therapeutic landscape for hormone receptor-positive (HR+) breast carcinoma has undergone a significant transformation with the advent of cyclin-dependent kinase (CDK)4/6 inhibitors, particularly in combination with endocrine therapy as the primary regimen. However, the evolution of resistance mechanisms in response to CDK4/6 inhibitors in HR+ metastatic breast cancer presents substantial challenges in managing the disease. This review explores the diverse genomic landscape underlying resistance, including disturbances in the cell cycle, deviations in oncogenic signaling pathways, deficiencies in DNA damage response (DDR) mechanisms, and changes in the tumor microenvironment (TME). Additionally, it discusses potential strategies to surmount resistance, including advancements in endocrine therapy, targeted inhibition of cell cycle components, suppression of AKT/mTOR activation, exploration of the FGFR pathway, utilization of antibody-drug conjugates (ADCs), and integration of immune checkpoint inhibitors (ICIs) with endocrine therapy and CDK4/6 inhibitors, providing pathways for enhancing patient outcomes amidst treatment challenges.

Effect of Cyclin-Dependent Kinase 4/6 Inhibitors on Circulating Cells in Patients with Metastatic Breast Cancer

The combination of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) is the standard-of-care for estrogen receptor (ER)-positive, HER2-negative (ER+/HER2- advanced/metastatic breast cancer (mBC). However, the impact of CDK4/6i on circulating immune cells and circulating tumor cells (CTCs) in patients receiving CDK4/6i and ET (CDK4/6i+ET) remains poorly understood. This was a prospective cohort study including 44 patients with ER+/HER2- mBC treated with CDK4/6i+ET in either first or second line. Peripheral blood samples were collected before (baseline) and 3 months (t2) after therapy. Immune cell's subsets were quantified by flow cytometry, and microfluidic-captured CTCs were counted and classified according to the expression of cytokeratin and/or vimentin. Patients were categorized according to response as responders (progression-free survival [PFS] ≥ 6.0 months; 79.1%) and non-responders (PFS < 6.0 months; 20.9%). CDK4/6i+ET resulted in significant changes in the hematological parameters, including decreased hemoglobin levels and increased mean corpuscular volume, as well as reductions in neutrophil, eosinophil, and basophil counts. Specific immune cell subsets, such as early-stage myeloid-derived suppressor cells, central memory CD4+ T cells, and Vδ2+ T cells expressing NKG2D, decreased 3 months after CDK4/6i+ET. Additionally, correlations between the presence of CTCs and immune cell populations were observed, highlighting the interplay between immune dysfunction and tumor dissemination. This study provides insights into the immunomodulatory effects of CDK4/6i+ET, underscoring the importance of considering immune dynamics in the management of ER+/HER2- mBC.

PACE: A Randomized Phase II Study of Fulvestrant, Palbociclib, and Avelumab After Progression on Cyclin-Dependent Kinase 4/6 Inhibitor and Aromatase Inhibitor for Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor-Negative Metastatic Breast Cancer

PURPOSE

Cyclin-dependent kinase (CDK) 4/6 inhibitors (CDK4/6is) are an important component of treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), but it is not known if patients might derive benefit from continuation of CDK4/6i with endocrine therapy beyond initial tumor progression or if the addition of checkpoint inhibitor therapy has value in this setting.

METHODS

The randomized multicenter phase II PACE trial enrolled patients with hormone receptor-positive/HER2- MBC whose disease had progressed on previous CDK4/6i and aromatase inhibitor (AI) therapy. Patients were randomly assigned 1:2:1 to receive fulvestrant (F), fulvestrant plus palbociclib (F + P), or fulvestrant plus palbociclib and avelumab (F + P + A). The primary end point was investigator-assessed progression-free survival (PFS) in patients treated with F versus F + P.

RESULTS

Overall, 220 patients were randomly assigned between September 2017 and February 2022. The median age was 57 years (range, 25-83 years). Most patients were postmenopausal (80.9%), and 40% were originally diagnosed with de novo MBC. Palbociclib was the most common previous CDK4/6i (90.9%). The median PFS was 4.8 months on F and 4.6 months on F + P (hazard ratio [HR], 1.11 [90% CI, 0.79 to 1.55]; P = .62). The median PFS on F + P + A was 8.1 months (HR v F, 0.75 [90% CI, 0.50 to 1.12]; P = .23). The difference in PFS with F + P and F + P + A versus F was greater among patients with baseline ESR1 and PIK3CA alterations.

CONCLUSION

The addition of palbociclib to fulvestrant did not improve PFS versus fulvestrant alone among patients with hormone receptor-positive/HER2- MBC whose disease had progressed on a previous CDK4/6i plus AI. The increased PFS seen with the addition of avelumab warrants further investigation in this patient population.

Nanoparticle-Mediated Immunotherapy in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype with the worst prognosis and highest recurrence rates. The treatment choices are limited due to the scarcity of endocrine and HER2 targets, except for chemotherapy. However, the side effects of chemotherapy restrict its long-term usage. Immunotherapy shows potential as a promising therapeutic strategy, such as inducing immunogenic cell death, immune checkpoint therapy, and immune adjuvant therapy. Nanotechnology offers unique advantages in the field of immunotherapy, such as improved delivery and targeted release of immunotherapeutic agents and enhanced bioavailability of immunomodulators. As well as the potential for combination therapy synergistically enhanced by nanocarriers. Nanoparticles-based combined application of multiple immunotherapies is designed to take the tactics of enhancing immunogenicity and reversing immunosuppression. Moreover, the increasing abundance of biomedical materials holds more promise for the development of this field. This review summarizes the advances in the field of nanoparticle-mediated immunotherapy in terms of both immune strategies for treatment and the development of biomaterials and presents challenges and hopes for the future.

Peripheral immune cells in metastatic breast cancer patients display a systemic immunosuppressed signature consistent with chronic inflammation

Immunotherapies blocking the PD-1/PD-L1 checkpoint show some efficacy in metastatic breast cancer (mBC) but are often hindered by immunosuppressive mechanisms. Understanding these mechanisms is crucial for personalized treatments, with peripheral blood monitoring representing a practical alternative to repeated biopsies. In the present study, we performed a comprehensive mass cytometry analysis of peripheral blood immune cells in 104 patients with HER2 negative mBC and 20 healthy donors (HD). We found that mBC patients had significantly elevated monocyte levels and reduced levels of CD4+ T cells and plasmacytoid dendritic cells, when compared to HD. Furthermore, mBC patients had more effector T cells and regulatory T cells, increased expression of immune checkpoints and other activation/exhaustion markers, and a shift to a Th2/Th17 phenotype. Furthermore, T-cell phenotypes identified by mass cytometry correlated with functionality as assessed by IFN-γ production. Additional analysis indicated that previous chemotherapy and CDK4/6 inhibition impacted the numbers and phenotype of immune cells. From 63 of the patients, fresh tumor samples were analyzed by flow cytometry. Paired PBMC-tumor analysis showed moderate correlations between peripheral CD4+ T and NK cells with their counterparts in tumors. Further, a CD4+ T cell cluster in PBMCs, that co-expressed multiple checkpoint receptors, was negatively associated with CD4+ T cell tumor infiltration. In conclusion, the identified systemic immune signatures indicate an immune-suppressed environment in mBC patients who had progressed/relapsed on standard treatments, and is consistent with ongoing chronic inflammation. These activated immuno-suppressive mechanisms may be investigated as therapeutic targets, and for use as biomarkers of response or treatment resistance.

The combination of IL-2 nanoparticles and Palbociclib enhances the anti-tumor immune response for colon cancer therapy

Immunotherapy of tumors plays a pivotal role in the current treatment of cancer. While interleukin 2 (IL-2) demonstrated its efficacy as an immunotherapeutic drug in the early days, its short blood circulation time poses challenges in maintaining effective therapeutic concentrations. Additionally, IL-2's activation of regulatory T cells can counteract its anti-cancer effects. Therefore, the primary goal of this study was to formulate IL-2-carrying nanoparticles via boron-nitrogen coordination between methoxy poly (ethylene glycol) block poly-[(N-2-hydroxyethyl)-aspartamide]phenylboronic acid (mPEG-b-PHEA-PBA, P-PBA) and poly (L-lysine) (PLL). These nanoparticles are intended to be used in combination with CDK4/6 inhibitors to address the short blood circulation time of IL-2, reduce its immunosuppressive effects, and enhance the overall immune response. The envisaged outcome is a sustained and potent therapeutic effect, offering a novel and promising combination therapy strategy for tumor immunotherapy.

CDK4/6 Inhibition Sensitizes Intracranial Tumors to PD-1 Blockade in Preclinical Models of Brain Metastasis

PURPOSE

Brain metastases are associated with high morbidity and are often resistant to immune checkpoint inhibitors. We evaluated whether CDK4/6 inhibitor (CDKi) abemaciclib can sensitize intracranial tumors to programmed cell death protein 1 (PD-1) inhibition in mouse models of melanoma and breast cancer brain metastasis.

EXPERIMENTAL DESIGN

Treatment response was evaluated in vivo using immunocompetent mouse models of brain metastasis bearing concurrent intracranial and extracranial tumors. Treatment effect on intracranial and extracranial tumor-immune microenvironments (TIME) was evaluated using immunofluorescence, multiplex immunoassays, high-parameter flow cytometry, and T-cell receptor profiling. Mice with humanized immune systems were evaluated using flow cytometry to study the effect of CDKi on human T-cell development.

RESULTS

We found that combining abemaciclib with PD-1 inhibition reduced tumor burden and improved overall survival in mice. The TIME, which differed on the basis of anatomic location of tumors, was altered with CDKi and PD-1 inhibition in an organ-specific manner. Combination abemaciclib and anti-PD-1 treatment increased recruitment and expansion of CD8+ effector T-cell subsets, depleted CD4+ regulatory T (Treg) cells, and reduced levels of immunosuppressive cytokines in intracranial tumors. In immunodeficient mice engrafted with human immune systems, abemaciclib treatment supported development and maintenance of CD8+ T cells and depleted Treg cells.

CONCLUSIONS

Our results highlight the distinct properties of intracranial and extracranial tumors and support clinical investigation of combination CDK4/6 and PD-1 inhibition in patients with brain metastases. See related commentary by Margolin, p. 257.

Targeting T regulatory (Treg) cells in immunotherapy-resistant cancers

Primary or secondary (i.e., acquired) resistance is a common occurrence in cancer patients and is often associated with high numbers of T regulatory (Treg) cells (CD4+CD25+FOXP3+). The approval of ipilimumab and the development of similar pharmacological agents targeting cell surface proteins on Treg cells demonstrates that such intervention may overcome resistance in cancer patients. Hence, the clinical development and subsequent approval of Cytotoxic T Lymphocyte Antigen-4 (CTLA-4) targeting agents can serve as a prototype for similar agents. Such new agents aspire to be highly specific and have a reduced toxicity profile while increasing effector T cell function or effector T/T regulatory (Teff/Treg) ratio. While clinical development with large molecules has shown the greatest advancement, small molecule inhibitors that target immunomodulation are increasingly entering early clinical investigation. These new small molecule inhibitors often target specific intracellular signaling pathways [e.g., phosphoinositide-3-kinase delta (PI3K-δ)] that play an important role in regulating the function of Treg cells. This review will summarize the lessons currently applied to develop novel clinical agents that target Treg cells.

Peripheral blood lymphocytes predict clinical outcomes in hormone receptor-positive HER2-negative advanced breast cancer patients treated with CDK4/6 inhibitors

Background

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) combined with Endocrine Therapy (ET) are the standard treatment for patients with Hormone Receptor-positive/HER2-negative advanced breast cancer (HR+/HER2- aBC).

Objectives

While CDK4/6i are known to reduce several peripheral blood cells, such as neutrophils, lymphocytes and platelets, the impact of these modulations on clinical outcomes is unknown.

Design

A multicenter, retrospective-prospective Italian study.

Methods

We investigated the association between baseline peripheral blood cells, or their early modifications (i.e. 2 weeks after treatment initiation), and the progression-free survival (PFS) of HR+/HER2- aBC patients treated with ETs plus CDK4/6i. Random Forest models were used to select covariates associated with patient PFS among a large list of patient- and tumor-related variables.

Results

We evaluated 638 HR+/HER2- aBC patients treated with ET plus CDK4/6i at six Italian Institutions between January 2017 and May 2021. High baseline lymphocyte counts were independently associated with longer PFS [median PFS (mPFS) 20.1 versus 13.2 months in high versus low lymphocyte patients, respectively; adjusted Hazard Ratio (aHR): 0.78; 95% confidence interval (CI): 0.66-0.92; p = 0.0144]. Moreover, patients experiencing a lower early reduction of lymphocyte counts had significantly longer PFS when compared to patients undergoing higher lymphocyte decrease (mPFS 18.1 versus 14.5 months; aHR: 0.82; 95% CI: 0.73-0.93; p = 0.0037). Patients with high baseline lymphocytes and undergoing a lower reduction, or even an increase, of lymphocyte counts during CDK4/6i therapy experienced the longest PFS, while patients with lower baseline lymphocytes and undergoing a higher decrease of lymphocytes had the lowest PFS (mPFS 21.4 versus 11 months, respectively).

Conclusion

Baseline and on-treatment modifications of peripheral blood lymphocytes have independent prognostic value in HR+/HER2- aBC patients. This study supports the implementation of clinical strategies to boost antitumor immunity in patients with HR+/HER2- aBC treated with ETs plus CDK4/6i.

Immune Cells in the Tumor Microenvironment of Soft Tissue Sarcomas

Soft tissue sarcomas (STSs) are a rare heterogeneous group of malignant neoplasms characterized by their aggressive course and poor response to treatment. This determines the relevance of research aimed at studying the pathogenesis of STSs. By now, it is known that STSs is characterized by complex relationships between the tumor cells and immune cells of the microenvironment. Dynamic interactions between tumor cells and components of the microenvironment enhance adaptation to changing environmental conditions, which provides the high aggressive potential of STSs and resistance to antitumor therapy. Today, active research is being conducted to find effective antitumor drugs and to evaluate the possibility of using therapy with immune cells of STS. The difficulty in assessing the efficacy of new antitumor options is primarily due to the high heterogeneity of this group of malignant neoplasms. Studying the role of immune cells in the microenvironment in the progression STSs and resistance to antitumor therapies will provide the discovery of new biomarkers of the disease and the prediction of response to immunotherapy. In addition, it will help to initially divide patients into subgroups of good and poor response to immunotherapy, thus avoiding wasting precious time in selecting the appropriate antitumor agent.

Profiling regulatory T lymphocytes within the tumor microenvironment of breast cancer via radiomics

OBJECTIVE

To generate an image-driven biomarker (Rad_score) to predict tumor-infiltrating regulatory T lymphocytes (Treg) in breast cancer (BC).

METHODS

Overall, 928 BC patients were enrolled from the Cancer Genome Atlas (TCGA) for survival analysis; MRI (n = 71 and n = 30 in the training and validation sets, respectively) from the Cancer Imaging Archive (TCIA) were retrieved and subjected to repeat least absolute shrinkage and selection operator for feature reduction. The radiomic scores (rad_score) for Treg infiltration estimation were calculated via support vector machine (SVM) and logistic regression (LR) algorithms, and validated on the remaining patients.

RESULTS

Landmark analysis indicated Treg infiltration was a risk factor for BC patients in the first 5 years and after 10 years of diagnosis (p = 0.007 and 0.018, respectively). Altogether, 108 radiomic features were extracted from MRI images, 4 of which remained for model construction. Areas under curves (AUCs) of the SVM model were 0.744 (95% CI 0.622-0.867) and 0.733 (95% CI 0.535-0.931) for training and validation sets, respectively, while for the LR model, AUCs were 0.771 (95% CI 0.657-0.885) and 0.724 (95% CI 0.522-0.926). The calibration curves indicated good agreement between prediction and true value (p > 0.05), and DCA shows the high clinical utility of the radiomic model. Rad_score was significantly correlated with immune inhibitory genes like CTLA4 and PDCD1.

CONCLUSIONS

High Treg infiltration is a risk factor for patients with BC. The Rad_score formulated on radiomic features is a novel tool to predict Treg abundance in the tumor microenvironment.

Broad-spectrum kinome profiling identifies CDK6 upregulation as a driver of lenvatinib resistance in hepatocellular carcinoma

Increasing evidence has demonstrated that drug resistance can be acquired in cancer cells by kinase rewiring, which is an obstacle for efficient cancer therapy. However, it is technically challenging to measure the expression of protein kinases on large scale due to their dynamic range in human proteome. We employ a lysine-targeted sulfonyl fluoride probe, named XO44, which binds to 133 endogenous kinases in intact lenvatinib-resistant hepatocellular carcinoma (HCC) cells. This analysis reveals cyclin-dependent kinase 6 (CDK6) upregulation, which is mediated by ERK/YAP1 signaling cascade. Functional analyses show that CDK6 is crucial in regulation of acquired lenvatinib resistance in HCC via augmentation of liver cancer stem cells with clinical significance. We identify a noncanonical pathway of CDK6 in which it binds and regulates the activity of GSK3β, leading to activation of Wnt/β-catenin signaling. Consistently, CDK6 inhibition by palbociclib or degradation by proteolysis targeting chimeras (PROTACs) is highly synergistic with lenvatinib in vitro. Interestingly, palbociclib not only exerts maximal growth suppressive effect with lenvatinib in lenvatinib-resistant HCC models but also reshapes the tumor immune microenvironment. Together, we unveil CDK6 as a druggable target in lenvatinib-resistant HCC and highlight the use of a chemical biology approach to understand nongenetic resistance mechanisms in cancer.

The Evolving Pathways of the Efficacy of and Resistance to CDK4/6 Inhibitors in Breast Cancer

The approval of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) has remarkably improved the survival outcomes of patients with advanced hormone receptor-positive (HR+) breast cancer (BC), becoming the new standard of care treatment in these patients. Despite the efficacy of this therapeutic combination, intrinsic and acquired resistance inevitably occurs and represents a major clinical challenge. Several mechanisms associated with resistance to CDK4/6i have been identified, including both cell cycle-related and cell cycle-nonspecific mechanisms. This review discusses new insights underlying the mechanisms of action of CDK4/6i, which are more far-reaching than initially thought, and the currently available evidence of the mechanisms of resistance to CDK4/6i in BC. Finally, it highlights possible treatment strategies to improve CDK4/6i efficacy, summarizing the most relevant clinical data on novel combination therapies involving CDK4/6i.

Targeting FGFRs by pemigatinib induces G1 phase cell cycle arrest, cellular stress and upregulation of tumor suppressor microRNAs

BACKGROUND

Fibroblast growth factor receptor (FGFR) gene family alterations are found in several cancers, indicating their importance as potential therapeutic targets. The FGFR-tyrosine kinase inhibitor (TKI) pemigatinib has been introduced in the treatment of advanced cholangiocarcinoma and more recently for relapsed or refractory myeloid/lymphoid neoplasms with FGFR2 and FGFR1 rearrangements, respectively. Several clinical trials are currently investigating the possible combination of pemigatinib with immunotherapy. In this study, we analyzed the biological and molecular effects of pemigatinib on different cancer cell models (lung, bladder, and gastric), which are currently objective of clinical trial investigations.

METHODS

NCI-H1581 lung, KATO III gastric and RT-112 bladder cancer cell lines were evaluated for FGFR expression by qRT-PCR and Western blot. Cell lines were treated with Pem and then characterized for cell proliferation, apoptosis, production of intracellular reactive oxygen species (ROS), and induction of senescence. The expression of microRNAs with tumor suppressor functions was analyzed by qRT-PCR, while modulation of the proteins coded by their target genes was evaluated by Western blot and mRNA. Descriptive statistics was used to analyze the various data and student's t test to compare the analysis of two groups.

RESULTS

Pemigatinib exposure triggered distinct signaling pathways and reduced the proliferative ability of all cancer cells, inducing G1 phase cell cycle arrest and strong intracellular stress resulting in ROS production, senescence and apoptosis. Pemigatinib treatment also caused the upregulation of microRNAs (miR-133b, miR-139, miR-186, miR-195) with tumor suppressor functions, along with the downregulation of validated protein targets with oncogenic roles (c-Myc, c-MET, CDK6, EGFR).

CONCLUSIONS

These results contribute to clarifying the biological effects and molecular mechanisms mediated by the anti-FGFR TKI pemigatinib in distinct tumor settings and support its exploitation for combined therapies.

An increase in tumor-infiltrating lymphocytes after treatment is significantly associated with a poor response to neoadjuvant endocrine therapy for estrogen receptor-positive/HER2-negative breast cancers

BACKGROUND

The reason for the poor prognosis of estrogen receptor (ER) + /human epidermal growth factor receptor 2 (HER2)- breast cancer patients with high levels of tumor-infiltrating lymphocytes (TILs) is poorly understood. The association between TILs and response to neoadjuvant endocrine therapy (NET) was examined.

METHODS

We recruited 170 patients with ER + /HER2- breast cancer who were treated with preoperative endocrine monotherapy. TILs were evaluated before and after NET, and their changes were noted. Furthermore, T cell subtypes were examined using CD8 and FOXP3 immunohistochemical analyses. Neutrophil and lymphocyte counts in the peripheral blood were analyzed with reference to TIL levels or changes. Responders were defined as Ki67 expression levels ≤ 2.7% after treatment.

RESULTS

Post-treatment (p = 0.016), but not pre-treatment (p = 0.464), TIL levels were significantly associated with the response to NET. TIL levels increased significantly after treatment among non-responders (p = 0.001). FOXP3 + T cell counts increased significantly after treatment in patients with increased TILs (p = 0.035), but not in those without increased TILs (p = 0.281). Neutrophil counts decreased significantly after treatment in patients without increased TILs (p = 0.026), but not in patients with increased TILs (p = 0.312).

CONCLUSION

An increase in TILs after NET was significantly associated with a poor response to NET. Given that FOXP3 + T-cell counts increased, and neutrophil counts did not decrease in patients with increased TILs after NET, the induction of an immunosuppressive microenvironment was speculated to play a role in the inferior efficacy. These data might partially indicate the involvement of the immune response in the efficacy of endocrine therapy.

Flow cytometry-assisted quantification of cell cycle arrest in cancer cells treated with CDK4/6 inhibitors

Cyclin-dependent kinase 4 (CDK4) and CDK6 inhibitors (i.e., palbociclib, abemaciclib, and ribociclib) are well known for their capacity to mediate cytostatic effects by promoting cell cycle arrest in the G1 phase, thus inhibiting cancer cell proliferation. Cytostatic effects induced by CDK4/6 inhibitors can be transient or lead to a permanent state of cell cycle arrest, commonly defined as cellular senescence. Induction of senescence is often associated to metabolic modifications and to the acquisition of a senescence-associated secretory phenotype (SASP) by cancer cells, which in turn can promote or limit antitumor immunity (and thus the efficacy of CDK4/6 inhibitors) depending on SASP components. Thus, although accumulating evidence suggests that anti-cancer effects of CDK4/6 inhibitors also depend on the promotion of antitumor immune responses, assessing cell cycle arrest and progression in cells treated with palbociclib remains a key approach for investigating the efficacy of CDK4/6 inhibitors. Here, we describe a method to assess cell cycle distribution simultaneously with active DNA replication by flow cytometry in cultured hormone receptor-positive breast cancer MCF7 cells.

Immunomodulatory effects of CDK4/6 inhibitors

The dysregulation of the cell cycle is one of the hallmarks of cancer. Cyclin-dependent kinase 4 (CDK4) and CDK6 play crucial roles in regulating cell cycle and other cellular functions. CDK4/6 inhibitors have achieved great success in treating breast cancers and are currently being tested extensively in other tumor types as well. Accumulating evidence suggests that CDK4/6 inhibitors exert antitumor effects through immunomodulation aside from cell cycle arrest. Here we outline the immunomodulatory activities of CDK4/6 inhibitors, discuss the immune mechanisms of drug resistance and explore avenues to harness their immunotherapeutic potential when combined with immune checkpoint inhibitors (ICIs) or chimeric antigen receptor (CAR) T-cell therapy to improve the clinical outcomes.

Mechanisms of CD8+ T cell exclusion and dysfunction in cancer resistance to anti-PD-(L)1

CD8⁺ T cells are the front-line defensive cells against cancer. Reduced infiltration and effector function of CD8⁺ T cells occurs in cancer and is contributed to defective immunity and immunotherapy resistance. Exclusion and exhaustion of CD8⁺ T cells are the two key factors associated with reduced durability of immune checkpoint inhibitor (ICI) therapy. Initially activated T cells upon exposure to chronic antigen stimulation or immunosuppressive tumor microenvironment (TME) acquire a hyporesponsive state that progressively lose their effector function. Thus, a key strategy in cancer immunotherapy is to look for factors contributed to defective CD8⁺ T cell infiltration and function. Targeting such factors can define a promising supplementary approach in patients receiving anti-programmed death-1 receptor (PD-1)/anti-programmed death-ligand 1 (PD-L1) therapy. Recently, bispecific antibodies are developed against PD-(L)1 and a dominant factor within TME, representing higher safety profile and exerting more desired outcomes. The focus of this review is to discuss about promoters of deficient infiltration and effector function of CD8⁺ T cells and their addressing in cancer ICI therapy.

Can Patients with HER2-Low Breast Cancer Benefit from Anti-HER2 Therapies? A Review

Breast cancer (BC) poses a severe threat to the health of women worldwide. Currently, different therapeutic regimens are used for BC according to the pathological classification of HER2-positive or HER2-negative. Clinical reports of HER2-low expression indicate that the condition is HER2-negative, which was ineligible for HER2-targeted therapy. In contrast to HER2-zero tumors, however, HER2-low BC is a heterogeneous disease with unique genetic characteristics, prognoses, and different therapeutic responses. Clinical efficacy has been demonstrated by numerous potent and innovative anti-HER2 medications, particularly antibody-drug conjugates (ADCs). Certain ADCs, including T-DXd, have demonstrated good efficacy in some trials either used alone or in conjunction with other medications. To enhance outcomes in individuals with HER2-low BC, immunotherapy and other treatments are frequently combined with HER2-targeted therapy. There are also alternative strategies that target both HER2 and HER3 or other antigenic sites. We hope more individuals with HER2-low BC will benefit from more precise treatment regimens in the future. This article provides a review of existing research and clinical trials.

Managing the immune microenvironment of osteosarcoma: the outlook for osteosarcoma treatment

Osteosarcoma, with poor survival after metastasis, is considered the most common primary bone cancer in adolescents. Notwithstanding the efforts of researchers, its five-year survival rate has only shown limited improvement, suggesting that existing therapeutic strategies are insufficient to meet clinical needs. Notably, immunotherapy has shown certain advantages over traditional tumor treatments in inhibiting metastasis. Therefore, managing the immune microenvironment in osteosarcoma can provide novel and valuable insight into the multifaceted mechanisms underlying the heterogeneity and progression of the disease. Additionally, given the advances in nanomedicine, there exist many advanced nanoplatforms for enhanced osteosarcoma immunotherapy with satisfactory physiochemical characteristics. Here, we review the classification, characteristics, and functions of the key components of the immune microenvironment in osteosarcoma. This review also emphasizes the application, progress, and prospects of osteosarcoma immunotherapy and discusses several nanomedicine-based options to enhance the efficiency of osteosarcoma treatment. Furthermore, we examine the disadvantages of standard treatments and present future perspectives for osteosarcoma immunotherapy.

Tailoring therapies to counter the divergent immune landscapes of breast cancer

Breast cancer remains a significant clinical concern affecting millions of women worldwide. Immunotherapy is a rapidly growing drug class that has revolutionized cancer treatment but remains marginally successful in breast cancer. The success of immunotherapy is dependent on the baseline immune responses as well as removing the brakes off pre-existing anti-tumor immunity. In this review, we summarize the different types of immune microenvironment observed in breast cancer as well as provide approaches to target these different immune subtypes. Such approaches have demonstrated pre-clinical success and are currently under clinical evaluation. The impact of combination of these approaches with already approved chemotherapies and immunotherapies may improve patient outcome and survival.

Clinico-Immunological Effects of a Single-Agent CDK4/6 Inhibitor in Advanced HR+/HER2- Breast Cancer Based on a Window of Opportunity Study

Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6 i), abemaciclib, palbociclib, and ribociclib, have been FDA-approved for the treatment of hormone receptor-positive (HR+), HER2−negative (HER2−) advanced breast cancer (aBC). This targeted therapy has revived hope in those aBC patients who did not respond to standard therapies. Interestingly, when administered as a single agent, CDK4/6 modulated several peripheral blood cells after a short-course treatment of 28 days. However, the impact of these immune effects has yet to be thoroughly investigated. Methods: We administered abemaciclib, palbociclib, and ribociclib monotherapy to 23 patients with HR+/HER2− metastatic breast cancer. The aim is to investigate the impact of on-treatment modifications on peripheral blood cells and their composite scores in patients after a 28-day course of CDK4/6 i alone. Results: In the current study, we observed a significant decrease in neutrophils (p-value < 0.001) for patients treated with abemaciclib, palbociclib, and ribociclib. An overall decrease of Tregs was observed and potentially linked to palbociclib treatment. The neutrophile to lymphocyte (N/L) ratio was also decreased overall and potentially linked to abemaciclib and palbociclib treatment. Platelets were decreased in patients administered with abemaciclib. Notably, the radiometabolic response was available only for those patients treated with ribociclib and abemaciclib, and only those lesions treated with ribociclib reached statistical relevance. Conclusions: Our study strongly supports the notion that CDK4/6 inhibitors induce tumour immune modulation. N/L ratio and platelet levels decreased due to treatment. Future studies should test whether patients would benefit from immunomodulators in association with CDK4/6 agents in a larger clinical trial. Moreover, the CDK4/6-induced immune modulation could also be considered a potential predictive clinical factor in HR+/HER2− advanced breast cancer.

Glycan-Lectin Interactions as Novel Immunosuppression Drivers in Glioblastoma

Despite diagnostic and therapeutic improvements, glioblastoma (GB) remains one of the most threatening brain tumor in adults, underlining the urgent need of new therapeutic targets. Lectins are glycan-binding proteins that regulate several biological processes through the recognition of specific sugar motifs. Lectins and their ligands are found on immune cells, endothelial cells and, also, tumor cells, pointing out a strong correlation among immunity, tumor microenvironment and vascularization. In GB, altered glycans and lectins contribute to tumor progression and immune evasion, shaping the tumor-immune landscape promoting immunosuppressive cell subsets, such as myeloid-derived suppressor cells (MDSCs) and M2-macrophages, and affecting immunoeffector populations, such as CD8⁺ T cells and dendritic cells (DCs). Here, we discuss the latest knowledge on the immune cells, immune related lectin receptors (C-type lectins, Siglecs, galectins) and changes in glycosylation that are involved in immunosuppressive mechanisms in GB, highlighting their interest as possible novel therapeutical targets.