Arrested Developments: CDK4/6 Inhibitor Resistance and Alterations in the Tumor Immune Microenvironment

CDK4/6 inhibitors dephosphorylate RNF26 to stabilize TSC1 and increase the sensitivity of ccRCC to mTOR inhibitors

BACKGROUND

The combined use of CDK4/6 inhibitors and mTOR inhibitors has achieved some clinical success in ccRCC. Exploring the underlying mechanism of the CDK4/6 pathway in cancer cells and the drug interactions of CDK4/6 inhibitors in combination therapy could help identify new therapeutic strategies for ccRCC. Notably, CDK4/6 inhibitors inactivate the mTOR pathway by increasing the protein levels of TSC1, but the mechanism by which CDK4/6 inhibitors regulate TSC1 is still unclear.

METHODS

Mass spectrometry analysis, coimmunoprecipitation analysis, GST pull-down assays, immunofluorescence assays, Western blot analysis and RT‒qPCR analysis were applied to explore the relationships among CDK4, RNF26 and TSC1. Transwell assays, tube formation assays, CCK-8 assays, colony formation assays and xenograft assays were performed to examine the biological role of RNF26 in renal cancer cells.TCGA-KIRC dataset analysis and RT‒qPCR analysis were used to examine the pathways affected by RNF26 silencing.

RESULTS

CDK4/6 inhibitors stabilized TSC1 in cancer cells. We showed that CDK4 enhances the interaction between TSC1 and RNF26 and that RNF26 activates the mTOR signaling pathway in ccRCC, contributes to ccRCC progression and angiogenesis, and promotes tumorigenesis. We then found that RNF26 functions as an E3 ligase of TSC1 to regulate CDK4-induced TSC1. This finding suggested that RNF26 promotes ccRCC progression and angiogenesis to some extent by negatively regulating TSC1.

CONCLUSION

Our results revealed a novel CDK4/RNF26/TSC1 axis that regulates the anticancer efficacy of CDK4/6 inhibitors and mTOR inhibitors in ccRCC.

A cuproptosis-related lncRNAs signature predicts prognosis and reveals pivotal interactions between immune cells in colon cancer

Copper-mediated cell death presents distinct pathways from established apoptosis processes, suggesting alternative therapeutic approaches for colon cancer. Our research aims to develop a predictive framework utilizing long-noncoding RNAs (lncRNAs) related to cuproptosis to predict colon cancer outcomes while examining immune interactions and intercellular signaling. We obtained colon cancer-related human mRNA expression profiles and clinical information from the Cancer Genome Atlas repository. To isolate lncRNAs involved in cuproptosis, we applied Cox proportional hazards modeling alongside the least absolute shrinkage and selection operator technique. We elucidated the underlying mechanisms by examining the tumor mutational burden, the extent of immune cell penetration, and intercellular communication dynamics. Based on the model, drugs were predicted and validated with cytological experiments. A 13 lncRNA-cuproptosis-associated risk model was constructed. Two colon cancer cell lines were used to validate the predicted representative mRNAs with high correlation coefficients with copper-induced cell death. Survival enhancement in the low-risk cohort was evidenced by the trends in Kaplan-Meier survival estimates. Analysis of immune cell infiltration suggested that survival was induced by the increased infiltration of naïve CD4+ T cells and a reduction of M2 macrophages within the low-risk faction. Decreased infiltration of naïve B cells, resting NK cells, and M0 macrophages was significantly associated with better overall survival. Combined single-cell analysis suggested that CCL5-ACKR1, CCL2-ACKR1, and CCL5-CCR1 pathways play key roles in mediating intercellular dialogues among immune constituents within the neoplastic microhabitat. We identified three drugs with a high sensitivity in the high-risk group. In summary, this discovery establishes the possibility of using 13 cuproptosis-associated lncRNAs as a risk model to assess the prognosis, unravel the immune mechanisms and cell communication, and improve treatment options, which may provide a new idea for treating colon cancer.

Strategy of combining CDK4/6 inhibitors with other therapies and mechanisms of resistance

Cell cycle-dependent protein kinase 4/6 (CDK4/6) is a crucial kinase that regulates the cell cycle, essential for cell division and proliferation. Hence, combining CDK4/6 inhibitors with other anti-tumor drugs is a pivotal clinical strategy. This strategy can efficiently inhibit the growth and division of tumor cells, reduce the side effects, and improve the quality of life of patients by reducing the dosage of combined anticancer drugs. Furthermore, the combination therapy strategy of CDK4/6 inhibitors could ameliorate the drug resistance of combined drugs and overcome the CDK4/6 resistance caused by CDK4/6 inhibitors. Various tumor treatment strategies combined with CDK4/6 inhibitors have entered the clinical trial stage, demonstrating their substantial clinical potential. This study reviews the research progress of CDK4/6 inhibitors from 2018 to 2022, the related resistance mechanism of CDK4/6 inhibitors, and the strategy of combination medication.

Pan-cancer analysis of CDKN2A alterations identifies a subset of gastric cancer with a cold tumor immune microenvironment

BACKGROUND

Although CDKN2A alteration has been explored as a favorable factor for tumorigenesis in pan-cancers, the association between CDKN2A point mutation (MUT) and intragenic deletion (DEL) and response to immune checkpoint inhibitors (ICIs) is still disputed. This study aims to determine the associations of CDKN2A MUT and DEL with overall survival (OS) and response to immune checkpoint inhibitors treatment (ICIs) among pan-cancers and the clinical features of CDKN2A-altered gastric cancer.

METHODS

This study included 45,000 tumor patients that underwent tumor sequencing across 33 cancer types from four cohorts, the MSK-MetTropism, MSK-IMPACT, OrigiMed2020 and TCGA cohorts. Clinical outcomes and genomic factors associated with response to ICIs, including tumor mutational burden, copy number alteration, neoantigen load, microsatellite instability, tumor immune microenvironment and immune-related gene signatures, were collected in pan-cancer. Clinicopathologic features and outcomes were assessed in gastric cancer. Patients were grouped based on the presence of CDKN2A wild type (WT), CDKN2A MUT, CDKN2A DEL and CDKN2A other alteration (ALT).

RESULTS

Our research showed that CDKN2A-MUT patients had shorter survival times than CDKN2A-WT patients in the MSK MetTropism and TCGA cohorts, but longer OS in the MSK-IMPACT cohort with ICIs treatment, particularly in patients having metastatic disease. Similar results were observed among pan-cancer patients with CDKN2A DEL and other ALT. Notably, CDKN2A ALT frequency was positively related to tumor-specific objective response rates to ICIs in MSK MetTropism and OrigiMed 2020. Additionally, individuals with esophageal carcinoma or stomach adenocarcinoma who had CDKN2A MUT had poorer OS than patients from the MSK-IMPACT group, but not those with adenocarcinoma. We also found reduced levels of activated NK cells, T cells CD8 and M2 macrophages in tumor tissue from CDKN2A-MUT or DEL pan-cancer patients compared to CDKN2A-WT patients in TCGA cohort. Gastric cancer scRNA-seq data also showed that CDKN2A-ALT cancer contained less CD8 T cells but more exhausted T cells than CDKN2A-WT cancer. A crucial finding of the pathway analysis was the inhibition of three immune-related pathways in the CDKN2A ALT gastric cancer patients, including the interferon alpha response, inflammatory response, and interferon gamma response.

CONCLUSIONS

This study illustrates the CDKN2A MUT and DEL were associated with a poor outcome across cancers. CDKN2A ALT, on the other hand, have the potential to be used as a biomarker for choosing patients for ICI treatment, notably in esophageal carcinoma and stomach adenocarcinoma.

Identification of naphthalimide-derivatives as novel PBD-targeted polo-like kinase 1 inhibitors with efficacy in drug-resistant lung cancer cells

Targeting polo-box domain (PBD) small molecule for polo-like kinase 1 (PLK1) inhibition is a viable alternative to target kinase domain (KD), which could avoid pan-selectivity and dose-limiting toxicity of ATP-competitive inhibitors. However, their efficacy in these settings is still low and inaccessible to clinical requirement. Herein, we utilized a structure-based high-throughput virtual screen to find novel chemical scaffold capable of inhibiting PLK1 via targeting PBD and identified an initial hit molecule compound 1a. Based on the lead compound 1a, a structural optimization approach was carried out and several series of derivatives with naphthalimide structural motif were synthesized. Compound 4Bb was identified as a new potent PLK1 inhibitor with a KD value of 0.29 μM. 4Bb could target PLK1 PBD to inhibit PLK1 activity and subsequently suppress the interaction of PLK1 with protein regulator of cytokinesis 1 (PRC1), finally leading to mitotic catastrophe in drug-resistant lung cancer cells. Furthermore, 4Bb could undergo nucleophilic substitution with the thiol group of glutathione (GSH) to disturb the redox homeostasis through exhausting GSH. By regulating cell cycle machinery and increasing cellular oxidative stress, 4Bb exhibited potent cytotoxicity to multiple cancer cells and drug-resistant cancer cells. Subcutaneous and oral administration of 4Bb could effectively inhibit the growth of drug-resistant tumors in vivo, doubling the survival time of tumor bearing mice without side effects in normal tissues. Thus, our study offers an orally-available, structurally-novel PLK1 inhibitor for drug-resistant lung cancer therapy.

Identification of CNKSR1 as a biomarker for "cold" tumor microenvironment in lung adenocarcinoma: An integrative analysis based on a novel workflow

Background

Therapies targeting PD1/PD-L1 pathway have revolutionized the treatment of lung cancer. However, anti-PD1/PD-L1 therapies have proven beneficial for only a select group of lung adenocarcinoma (LUAD) patients and generally do not work for immuno-cold tumors characterized by a lack of immune cell infiltration. Identifying novel biomarkers is vital to broad therapeutic options for LUAD patients with no response to anti-PD1/PD-L1 immunotherapies.

Methods

Our study has developed a novel strategy to identify a promising biomarker that addresses the limitations of anti-PD1/PD-L1 immunotherapy in treating immunological cold tumors. We exacted LUAD RNA-seq data from the Cancer Genome Atlas database (TCGA). Using several machine learning methods, we identified the candidate biomarker. Based on the expression level of PD-L1 and the identified biomarker, samples were categorized into four groups. We further used ESTIMATE, ssGSEA, and CIBERSORT algorithms to calculate the immune infiltration level of each group. The results were validated in three independent bulk datasets and one scRNA-seq dataset. Immunohistochemistry (IHC) assessments were performed in clinical samples to further evaluate the coexpression of CNKSR1 and PD-L1, and to compare CD8 + T cell infiltration among groups.

Results

After comprehensive analyses, CNKSR1 was identified as a novel promising biomarker for immuno-cold LUAD. CNKSR1 mRNA expression levels exhibited a negative correlation with both PD-L1 mRNA expression and the extent of immune cell infiltration in LUAD. Besides, in contrast to the significant association between the expression of PD-L1 and the majority of other well-established or widely studied immune checkpoint molecules, a mutually exclusive expression pattern is observed between CNKSR1 and these molecules. The aforementioned results were consistent in validation datasets. The prognostic model built based on the CNKSR1 coexpression module also showed robust predictive performance. Additionally, IHC assessments have confirmed that the coexpression of CNKSR1 and PD-L1 is rare in LUAD samples. Notably, LUADs in the high-CNKSR1 group, characterized by high CNKSR1 but low PD- L1 expression, demonstrated reduced infiltration of CD8+ T cells.

Conclusions

In summary, CNKSR1 emerges as a promising biomarker for immune-cold LUADs, and the study into CNKSR1 modulating T-cell infiltration may lead to the identification of compensatory molecules to enhance the effectiveness of current immunotherapy for LUAD.

Effect of CDK4/6 Inhibitors on Tumor Immune Microenvironment

Cancer is an abnormal proliferation of cells that is stimulated by cyclin-dependent kinases (CDKs) and defective cell cycle regulation. The essential agent that drive the cell cycle, CDK4/6, would be activated by proliferative signals. Activated CDK4/6 results in the phosphorylation of the neuroblastoma protein (RB) and the release of the transcription factor E2F, which promotes the cell cycle progression. CDK4/6 inhibitor (CDK4/6i) has been currently a research focus, which inhibits the CDK4/6-RB-E2F axis, thereby reducing the cell cycle transition from G1 to S phase and mediating the cell cycle arrest. This action helps achieve an anti-tumor effect. Recent research has demonstrated that CDK4/6i, in addition to contributing to cell cycle arrest, is also essential for the interaction between the tumor cells and the host immune system, i.e., activating the immune system, strengthening the tumor antigen presentation, and reducing the number of regulatory T cells (Treg). Additionally, CDK4/6i would elevate the level of PD-L1, an immunosuppressive factor, in tumor cells, and CDK4/6i in combination with anti-PD-L1 therapy would more effectively reduce the tumor growth. Our results showed that CDK4/6i caused autophagy and senescence in tumor cells. Herein, the impact of CDK4/6i on the immune microenvironment of malignant tumors was mainly focused, as well as their interaction with immune checkpoint inhibitors in affecting anti-tumor immunity.

Discovery of Novel Antitumor Small-Molecule Agent with Dual Action of CDK2/p-RB and MDM2/p53

Cell cycle-dependent kinase 2 (CDK2) is located downstream of CDK4/6 in the cell cycle and regulates cell entry into S-phase by binding to Cyclin E and hyper-phosphorylating Rb. Proto-oncogene murine double minute 2 (MDM2) is a key negative regulator of p53, which is highly expressed in tumors and plays an important role in tumorigenesis and progression. In this study, we identified a dual inhibitor of CDK2 and MDM2, III-13, which had good selectivity for inhibiting CDK2 activity and significantly reduced MDM2 expression. In vitro results showed that III-13 inhibited proliferation of a wide range of tumor cells, regardless of whether Cyclin E1 (CCNE1) was overexpressed or not. The results of in vivo experiments showed that III-13 significantly inhibited proliferation of tumor cells and did not affect body weight of mice. The results of the druggability evaluation showed that III-13 was characterized by low bioavailability and poor membrane permeability when orally administered, suggesting the necessity of further structural modifications. Therefore, this study provided a lead compound for antitumor drugs, especially those against CCNE1-amplified tumor proliferation.

LUM as a novel prognostic marker and its correlation with immune infiltration in gastric cancer: a study based on immunohistochemical analysis and bioinformatics

BACKGROUND

Gastric cancer (GC) is considered the sixth highly prevailing malignant neoplasm and is ranked third in terms of cancer mortality rates. To enable an early and efficient diagnosis of GC, it is important to detect the fundamental processes involved in the oncogenesis and progression of gastric malignancy. The understanding of molecular signaling pathways can facilitate the development of more effective therapeutic strategies for GC patients.

METHODS

The screening of genes that exhibited differential expression in early and advanced GC was performed utilizing the Gene Expression Omnibus databases (GSE3438). Based on this, the protein and protein interaction network was constructed to screen for hub genes. The resulting list of hub genes was evaluated with bioinformatic analysis and selected genes were validated the protein expression by immunohistochemistry (IHC). Finally, a competing endogenous RNA network of GC was constructed.

RESULTS

The three genes (ITGB1, LUM, and COL5A2) overexpressed in both early and advanced GC were identified for the first time. Their upregulation has been linked with worse overall survival (OS) time in patients with GC. Only LUM was identified as an independent risk factor for OS among GC patients by means of additional analysis. IHC results demonstrated that the expression of LUM protein was increased in GC tissue, and was positively associated with the pathological T stage. LUM expression can effectively differentiate tumorous tissue from normal tissue (area under the curve = 0.743). The area under 1-, 3-, and 5-year survival relative operating characteristics were greater than 0.6. Biological function enrichment analyses suggested that the genes related to LUM expression were involved in extracellular matrix development-related pathways and enriched in several cancer-related pathways. LUM affects the infiltration degree of cells linked to the immune system in the tumor microenvironment. In GC progression, the AC117386.2/hsa-miR-378c/LUM regulatory axis was also identified.

CONCLUSION

Collectively, a thorough bioinformatics analysis was carried out and an AC117386.2/hsa-miR-378c/LUM regulatory axis in the stomach adenocarcinoma dataset was detected. These findings should serve as a guide for future experimental investigations and warrant confirmation from larger studies.

Neoadjuvant nivolumab + palbociclib + anastrozole for oestrogen receptor-positive/human epidermal growth factor receptor 2-negative primary breast cancer: Results from CheckMate 7A8

BACKGROUND

Preclinical data suggest synergistic activity with the combination of programmed death-1 and cyclin-dependent kinase 4/6 blockade in oestrogen receptor-positive/human epidermal growth factor 2-negative (ER+/HER2-) breast cancer. The noncomparative phase 1b/2 CheckMate 7A8 study (NCT04075604) evaluated neoadjuvant treatment with nivolumab, palbociclib, and anastrozole in patients with ER+/HER2- breast cancer. Here, we report outcomes from the safety run-in phase.

METHODS

Patients with histologically confirmed, untreated ER+/HER2- breast cancer, primary tumour ≥2 cm, ECOG performance status ≤1, and eligible for post-treatment surgery received nivolumab 480 mg intravenously every 4 weeks, palbociclib 125 mg or 100 mg orally once daily for 3 weeks per cycle, and anastrozole 1 mg orally once daily for five 4-week cycles, or until disease progression. The primary endpoint was the proportion of patients with dose-limiting toxicities (DLTs) within 4 weeks of treatment initiation.

RESULTS

At safety data review, 21 patients were treated (palbociclib 125-mg group: n = 9; palbociclib 100-mg group: n = 12). DLTs were reported in 2 (22.2%) and 0 patients in the palbociclib 125-mg and 100-mg groups, respectively. Across both groups, 9 patients discontinued treatment due to toxicity (grade 3/4 hepatic adverse events [n = 6], grade 3 febrile neutropaenia [n = 1], grade 1 pneumonitis [n = 1], and grade 3 rash and grade 2 immune-mediated pneumonitis [n = 1]). Consequently, the study was closed early.

CONCLUSIONS

Neoadjuvant treatment with nivolumab, palbociclib, and anastrozole showed a high incidence of grade 3/4 hepatotoxicity and treatment discontinuation, indicating that this combination should not be further pursued for treatment of primary ER+/HER2- breast cancer.

Subacute cutaneous lupus erythematosus following ribociclib therapy for metastatic breast cancer

INTRODUCTION

Drug-induced subacute cutaneous lupus erythematosus (DI-SCLE) has been associated with drugs with different mechanisms of action, including anti-hypertensives, tumour necrosis factor-α inhibitors and even some chemotherapy medicines. In the last years, a few reports have been described in patients treated with cyclin-dependent kinase (CDK) 4/6 inhibitors, palbociclib and abemaciclib.

CASE REPORT

Here, we describe a case of DI-SCLE in association with ribociclib and exemestane in a woman diagnosed with metastatic breast cancer.

MANAGEMENT AND OUTCOME

Topical mometasone was prescribed for two weeks with complete resolution of lesions, also abemaciclib was substituted for ribociclib, and the patient had stable disease with no relapse of DI-SCLE.

DISCUSSION

To our knowledge, this is the first report of ribociclib-induced SCLE but based on the DI-SCLE reported cases associated others CDK4/6 inhibitors, the role of this family of drugs in dermatopathology must be further investigated.

The RNA-binding protein LRPPRC promotes resistance to CDK4/6 inhibition in lung cancer

Kinase inhibitors against Cyclin Dependent Kinase 4 and 6 (CDK4/6i) are promising cancer therapeutic drugs. However, their effects are limited by primary or acquired resistance in virtually all tumor types. Here, we demonstrate that Leucine Rich Pentatricopeptide Repeat Containing (LRPPRC) controls CDK4/6i response in lung cancer by forming a feedback loop with CDK6. LRPPRC binds to CDK6-mRNA, increasing the stability and expression of CDK6. CDK6 and its downstream E2F Transcription Factor 1 (E2F1), bind to the LRPPRC promoter and elevate LRPPRC transcription. The activation of the LRPPRC-CDK6 loop facilitates cell cycle G1/S transition, oxidative phosphorylation, and cancer stem cell generation. Gossypol acetate (GAA), a gynecological medicine that has been repurposed as a degrader of LRPPRC, enhances the CDK4/6i sensitivity in vitro and in vivo. Our study reveals a mechanism responsible for CDK4/6i resistance and provides an enlightening approach to investigating the combinations of CDK4/6 and LRPPRC inhibitors in cancer therapy.

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.

Phase 2 trial of palbociclib and ganitumab in patients with relapsed Ewing sarcoma

BACKGROUND

Ewing sarcoma (EWS) is an aggressive sarcoma with few treatment options for patients with relapsed disease. Cyclin-dependent kinase 4 (CDK4) is a genomic vulnerability in EWS that is synergistic with IGF-1R inhibition in preclinical studies. We present the results of a phase 2 study combining palbociclib (CDK4/6 inhibitor) with ganitumab (IGF-1R monoclonal antibody) for patients with relapsed EWS.

PATIENTS AND METHODS

This open-label, non-randomized, phase 2 trial enrolled patients ≥12 years with relapsed EWS. All patients had molecular confirmation of EWS and RECIST measurable disease. Patients initially received palbociclib 125 mg orally on Days 1-21 and ganitumab 18 mg/kg intravenously on Days 1 and 15 of a 28-day cycle. The primary endpoints were objective response (complete or partial) per RECIST and toxicity by CTCAE. An exact one-stage design required ≥4 responders out of 15 to evaluate an alternative hypothesis of 40% response rate against a null of 10%. The study was closed following enrollment of the 10th patient due to discontinuation of ganitumab supply.

RESULTS

Ten evaluable patients enrolled [median age 25.7 years (range 12.3-40.1)]. The median duration of therapy was 2.5 months (range 0.9-10.8). There were no complete or partial responders. Three of 10 patients had stable disease for >4 cycles and 2 had stable disease at completion of planned therapy or study closure. Six-month progression-free survival was 30% (95% CI 1.6%-58.4%). Two patients had cycle 1 hematologic dose-limiting toxicities (DLTs) triggering palbociclib dose reduction to 100 mg daily for 21 days. Two subsequent patients had cycle 1 hematologic DLTs at the reduced dose. Eighty percent of patients had grade 3/4 AEs, including neutropenia (n = 8), white blood cell decreased (n = 7), and thrombocytopenia (n = 5). Serum total IGF-1 significantly increased (p = 0.013) and ctDNA decreased during the first cycle.

CONCLUSIONS

This combination lacks adequate therapeutic activity for further study, though a subset of patients had prolonged stable disease.

Dendritic cell therapy augments antitumor immunity triggered by CDK4/6 inhibition and immune checkpoint blockade by unleashing systemic CD4 T-cell responses

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy are a mainstay treatment for hormone receptor-positive breast cancer. While their principal mechanism is inhibition of cancer cell proliferation, preclinical and clinical evidence suggests that CDK4/6i can also promote antitumor T-cell responses. However, this pro-immunogenic property is yet to be successfully harnessed in the clinic, as combining CDK4/6i with immune checkpoint blockade (ICB) has not shown a definitive benefit in patients.

METHOD

We performed an in-depth analysis of the changes in the tumor immune microenvironment and systemic immune modulation associated with CDK4/6i treatment in muring breast cancer models and in patients with breast cancer using high dimensional flow cytometry and RNA sequencing. Gain and loss of function in vivo experiments employing cell transfer and depletion antibody were performed to uncover immune cell populations critical for CDK4/6i-mediated stimulation of antitumor immunity.

RESULTS

We found that loss of dendritic cells (DCs) within the tumor microenvironment resulting from CDK4/6 inhibition in bone marrow progenitors is a major factor limiting antitumor immunity after CDK4/6i and ICB. Consequently, restoration of DC compartment by adoptively transferring ex vivo differentiated DCs to mice treated with CDK4/6i and ICB therapy enabled robust tumor inhibition. Mechanistically, the addition of DCs promoted the induction of tumor-localized and systemic CD4 T-cell responses in mice receiving CDK4/6i-ICB-DC combination therapy, as characterized by enrichment of programmed cell death protein-1-negative T helper (Th)1 and Th2 cells with an activated phenotype. CD4 T-cell depletion abrogated the antitumor benefit of CDK4/6i-ICB-DC combination, with outgrowing tumors displaying an increased proportion of terminally exhausted CD8 T cells.

CONCLUSIONS

Our findings suggest that CDK4/6i-mediated DC suppression limits CD4 T-cell responses essential for the sustained activity of CD8 T cells and tumor inhibition. Furthermore, they imply that restoring DC-CD4 T-cell crosstalk via DC transfer enables effective breast cancer immunity in response to CDK4/6i and ICB treatment.

Multi-View Radiomics Feature Fusion Reveals Distinct Immuno-Oncological Characteristics and Clinical Prognoses in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide, and the pronounced intra- and inter-tumor heterogeneity restricts clinical benefits. Dissecting molecular heterogeneity in HCC is commonly explored by endoscopic biopsy or surgical forceps, but invasive tissue sampling and possible complications limit the broadeer adoption. The radiomics framework is a promising non-invasive strategy for tumor heterogeneity decoding, and the linkage between radiomics and immuno-oncological characteristics is worth further in-depth study. In this study, we extracted multi-view imaging features from contrast-enhanced CT (CE-CT) scans of HCC patients, followed by developing a fused imaging feature subtyping (FIFS) model to identify two distinct radiomics subtypes. We observed two subtypes of patients with distinct texture-dominated radiomics profiles and prognostic outcomes, and the radiomics subtype identified by FIFS model was an independent prognostic factor. The heterogeneity was mainly attributed to inflammatory pathway activity and the tumor immune microenvironment. The predominant radiogenomics association was identified between texture-related features and immune-related pathways by integrating network analysis, and was validated in two independent cohorts. Collectively, this work described the close connections between multi-view radiomics features and immuno-oncological characteristics in HCC, and our integrative radiogenomics analysis strategy may provide clues to non-invasive inflammation-based risk stratification.

Stromal Senescence following Treatment with the CDK4/6 Inhibitor Palbociclib Alters the Lung Metastatic Niche and Increases Metastasis of Drug-Resistant Mammary Cancer Cells

BACKGROUND

CDK4/6 inhibitors (CDKi) have improved disease control in hormone-receptor-positive, HER2-negative metastatic breast cancer, but most patients develop progressive disease.

METHODS

We asked whether host stromal senescence after CDK4/6 inhibition affects metastatic seeding and growth of CDKi-resistant mammary cancer cells by using the p16-INK-ATTAC mouse model of inducible senolysis.

RESULTS

Palbociclib pretreatment of naïve mice increased lung seeding of CDKi-resistant syngeneic mammary cancer cells, and this effect was reversed by depletion of host senescent cells. RNA sequencing analyses of lungs from non-tumor-bearing p16-INK-ATTAC mice identified that palbociclib downregulates immune-related gene sets and gene expression related to leukocyte migration. Concomitant senolysis reversed a portion of these effects, including pathway-level enrichment of TGF-β- and senescence-related signaling. CIBERSORTx analysis revealed that palbociclib alters intra-lung macrophage/monocyte populations. Notably, lung metastases from palbociclib-pretreated mice revealed senescent endothelial cells. Palbociclib-treated endothelial cells exhibit hallmark senescent features in vitro, upregulate genes involved with the senescence-associated secretory phenotype, leukocyte migration, and TGF-β-mediated paracrine senescence and induce tumor cell migration and monocyte trans-endothelial invasion in co-culture.

CONCLUSIONS

These studies shed light on how stromal senescence induced by palbociclib affects lung metastasis, and they describe palbociclib-induced gene expression changes in the normal lung and endothelial cell models that correlate with changes in the tumor microenvironment in the lung metastatic niche.

Deregulated E2F Activity as a Cancer-Cell Specific Therapeutic Tool

The transcription factor E2F, the principal target of the tumor suppressor pRB, plays crucial roles in cell proliferation and tumor suppression. In almost all cancers, pRB function is disabled, and E2F activity is enhanced. To specifically target cancer cells, trials have been undertaken to suppress enhanced E2F activity to restrain cell proliferation or selectively kill cancer cells, utilizing enhanced E2F activity. However, these approaches may also impact normal growing cells, since growth stimulation also inactivates pRB and enhances E2F activity. E2F activated upon the loss of pRB control (deregulated E2F) activates tumor suppressor genes, which are not activated by E2F induced by growth stimulation, inducing cellular senescence or apoptosis to protect cells from tumorigenesis. Deregulated E2F activity is tolerated in cancer cells due to inactivation of the ARF-p53 pathway, thus representing a feature unique to cancer cells. Deregulated E2F activity, which activates tumor suppressor genes, is distinct from enhanced E2F activity, which activates growth-related genes, in that deregulated E2F activity does not depend on the heterodimeric partner DP. Indeed, the ARF promoter, which is specifically activated by deregulated E2F, showed higher cancer-cell specific activity, compared to the E2F1 promoter, which is also activated by E2F induced by growth stimulation. Thus, deregulated E2F activity is an attractive potential therapeutic tool to specifically target cancer cells.

Deciphering the Immunomodulatory Role of Cyclin-Dependent Kinase 4/6 Inhibitors in the Tumor Microenvironment

Cancer is characterized by persistent cell proliferation driven by aberrant cell cycle regulation and stimulation of cyclin-dependent kinases (CDKs). A very intriguing and potential approach for the development of antitumor medicines is the suppression of CDKs that lead to induction of apoptosis and cell cycle arrest. The shift of the cell cycle from the G0/G1 phase to the S phase, which is characterized by active transcription and synthesis, depends on the development of the cyclin D-CDK4/6 complex. A precise balance between anticancer activity and general toxicity is demonstrated by CDK inhibitors, which can specifically block CDK4/6 and control the cell cycle by reducing the G1 to S phase transition. CDK4/6 inhibitors have recently been reported to exhibit significant cell growth inhibition via modulating the tumour microenvironment in cancerous cells. One significant new understanding is that these inhibitors serve important functions in the interaction among tumour cells and the host immune system in addition to being cytostatic. Herein, we discuss the biological significance of CDK4/6 inhibitors in cancer therapeutics, as well as their biological impact on T cells and other important immune cells. Furthermore, we explore the integration of preclinical findings of these pharmaceuticals' ability to enhance antitumor immunity.

PFKFB4 facilitates palbociclib resistance in oestrogen receptor-positive breast cancer by enhancing stemness

BACKGROUND

ER⁺ breast cancer (ER⁺ BC) is the most common subtype of BC. Recently, CDK4/6 inhibitors combined with aromatase inhibitors have been approved by FDA as the first-line therapy for patients with ER⁺ BC, and showed promising therapeutic efficacy in clinical treatment. However, resistance to CDK4/6 inhibitors is frequently observed. A better understanding of the drug resistance mechanism is beneficial to improving therapeutic strategies by identifying optimal combinational treatments.

METHODS

Western blotting, qPCR, flow cytometry and a series of cell experiments were performed to evaluate the phenotype of MCF-7/R cells. RNA sequencing, non-targeted metabolomics, shRNA knockdown and tumour cell-bearing mouse models were used to clarify the drug resistance mechanism.

RESULTS

Here, we found that ER⁺ BC cells have shown an adaptive resistance to palbociclib-induced cell cycle arrest by activating an alternative signal pathway, independent of the CDK4/6-RB signal transduction. Continuing treatment of palbociclib evoked cellular senescence of ER⁺ BC cells. Subsequently, the senescence-like phenotype promoted stemness of ER⁺ BC cells, accompanied by increased chemoresistance and tumour-initiating potential. Based on transcriptome analysis, we found that PFKFB4 played an important role in stemness transformation and drug resistance. A close correlation was determined between PFKFB4 expression by ER⁺ BC cells and cell senescence and stemness. Mechanistically, metabolomic profiling revealed that PFKFB4 reprogramed glucose metabolism and promoted cell stemness by enhancing glycolysis. Strikingly, diminishing PFKFB4 levels improved drug sensitivity and overcame chemoresistance during palbociclib treatment in ER⁺ BC.

CONCLUSIONS

These findings not only demonstrated the novel mechanism underlying which ER⁺ BC cells resisted to palbociclib, but also provided a possible therapeutic strategy in the intervention of ER⁺ BC to overcome drug resistance.

On-treatment derived neutrophil-to-lymphocyte ratio and survival with palbociclib and endocrine treatment: analysis of a multicenter retrospective cohort and the PALOMA-2/3 study with immune correlates

BACKGROUND

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have been established as a standard treatment for hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC); however, predictive biomarkers with translational relevance have not yet been elucidated.

METHODS

Data from postmenopausal women who received the CDK4/6 inhibitor palbociclib and letrozole for HR-positive, HER2-negative ABC from tertiary referral centers were analyzed (N = 221; exploratory cohort). Pre- and on-treatment neutrophil-to-lymphocyte ratio (NLR) and derived NLR (dNLR; neutrophil/[leukocyte-neutrophil]) were correlated with survival outcomes. Data from the PALOMA-2 (NCT01740427) and PALOMA-3 studies (NCT01942135) involving patients treated with endocrine treatment with or without palbociclib were also analyzed (validation cohort). Prospectively enrolled patients (N = 20) were subjected to immunophenotyping with circulating immune cells to explore the biological implications of immune cell dynamics.

RESULTS

In the exploratory cohort, palbociclib administration significantly reduced leukocyte, neutrophil, and lymphocyte counts on day 1 of cycle 2. Although the baseline dNLR was not significantly associated with progression-free survival (PFS), higher on-treatment dNLRs were associated with worse PFS (hazard ratio = 3.337, P < 0.001). In the PALOMA-2 validation cohort, higher on-treatment dNLRs were associated with inferior PFS in patients treated with palbociclib and letrozole (hazard ratio = 1.498, P = 0.009), and reduction in the dNLR after treatment was predictive of a survival benefit (hazard ratio = 1.555, P = 0.026). On-treatment dNLRs were also predictive of PFS following palbociclib and fulvestrant treatment in the PALOMA-3 validation cohort. Using flow cytometry analysis, we found that the CDK4/6 inhibitor prevented T cell exhaustion and diminished myeloid-derived suppressor cell frequency.

CONCLUSIONS

On-treatment dNLR significantly predicted PFS in patients with HR-positive, HER2-negative ABC receiving palbociclib and endocrine treatment. Additionally, we observed putative systemic immune responses elicited by palbociclib, suggesting immunologic changes upon CDK4/6 inhibitor treatment.

Construction of a prognostic assessment model for colon cancer patients based on immune-related genes and exploration of related immune characteristics

Objectives: To establish a novel risk score model that could predict the survival and immune response of patients with colon cancer. Methods: We used The Cancer Genome Atlas (TCGA) database to get mRNA expression profile data, corresponding clinical information and somatic mutation data of patients with colon cancer. Limma R software package and univariate Cox regression were performed to screen out immune-related prognostic genes. GO (Gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) were used for gene function enrichment analysis. The risk scoring model was established by Lasso regression and multivariate Cox regression. CIBERSORT was conducted to estimate 22 types of tumor-infiltrating immune cells and immune cell functions in tumors. Correlation analysis was used to demonstrate the relationship between the risk score and immune escape potential. Results: 679 immune-related genes were selected from 7846 differentially expressed genes (DEGs). GO and KEGG analysis found that immune-related DEGs were mainly enriched in immune response, complement activation, cytokine-cytokine receptor interaction and so on. Finally, we established a 3 immune-related genes risk scoring model, which was the accurate independent predictor of overall survival (OS) in colon cancer. Correlation analysis indicated that there were significant differences in T cell exclusion potential in low-risk and high-risk groups. Conclusion: The immune-related gene risk scoring model could contribute to predicting the clinical outcome of patients with colon cancer.

The future of targeted kinase inhibitors in melanoma

Melanoma is a cancer of the pigment-producing cells of the body and its incidence is rising. Targeted inhibitors that act against kinases in the MAPK pathway are approved for BRAF-mutant metastatic cutaneous melanoma and increase patients' survival. Response to these therapies is limited by drug resistance and is less durable than with immune checkpoint inhibition. Conversely, rare melanoma subtypes have few therapeutic options for advanced disease and MAPK pathway targeting agents show minimal anti-tumor effects. Nevertheless, there is a future for targeted kinase inhibitors in melanoma: in new applications such as adjuvant or neoadjuvant therapy and in novel combinations with immunotherapies or other targeted therapies. Pre-clinical studies continue to identify tumor dependencies and their corresponding actionable drug targets, paving the way for rational targeted kinase inhibitor combinations as a personalized medicine approach for melanoma.

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.

CDK4: a master regulator of the cell cycle and its role in cancer

The cell cycle is regulated in part by cyclins and their associated serine/threonine cyclin-dependent kinases, or CDKs. CDK4, in conjunction with the D-type cyclins, mediates progression through the G₁ phase when the cell prepares to initiate DNA synthesis. Although Cdk4-null mutant mice are viable and cell proliferation is not significantly affected in vitro due to compensatory roles played by other CDKs, this gene plays a key role in mammalian development and cancer. This review discusses the role that CDK4 plays in cell cycle control, normal development and tumorigenesis as well as the current status and utility of approved small molecule CDK4/6 inhibitors that are currently being used as cancer therapeutics.

CDK4/6 inhibitors sensitize gammaherpesvirus-infected tumor cells to T-cell killing by enhancing expression of immune surface molecules

BACKGROUND

The two oncogenic human gammaherpesviruses, Kaposi sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), both downregulate immune surface molecules, such as MHC-I, ICAM-1, and B7-2, enabling them to evade T-cell and natural killer cell immunity. Both also either encode for human cyclin homologues or promote cellular cyclin activity, and this has been shown to be important for proliferation and survival of gammaherpesvirus-induced tumors. CDK4/6 inhibitors, which are approved for certain breast cancers, have been shown to enhance expression of MHC-I in cell lines and murine models of breast cancer, and this was attributed to activation of interferons by endogenous retrovirus elements. However, it was not known if this would occur in gammaherpesvirus-induced tumors in which interferons are already activated.

METHODS

Multiple KSHV/EBV-infected cell lines were treated with CDK4/6 inhibitors. The growth of viable cells and expression of surface markers was assessed. T cell activation stimulated by the treated cells was assayed by a T-cell activation bioassay. Both viral and host gene expression was surveyed using RT-qPCR.

RESULTS

Three CDK4/6 inhibitors, abemaciclib, palbociclib, and ribociclib, inhibited cell growth in KSHV-induced primary effusion lymphoma (PEL) and EBV positive Burkitt's lymphoma (BL) cell lines, and KSHV-infected human umbilical vein endothelial cells (HUVECs). Moreover, CDK4/6 inhibitors increased mRNA and surface expression of MHC-I in all three and prevented downregulation of MHC-I surface expression during lytic replication in KSHV-infected cells. CDK4/6 inhibitors also variably increased mRNA and surface expression of ICAM-1 and B7-2 in the tested lines. Abemaciclib also significantly enhanced T-cell activation induced by treated PEL and BL cells. Certain gammaherpesvirus genes as well as endogenous retrovirus (ERV) 3-1 genes were enhanced by CDK4/6 inhibitors in most PEL and BL lines and this enhancement was associated with expression of gamma interferon-induced genes including MHC-I.

CONCLUSIONS

These observations provide evidence that CDK4/6 inhibitors can induce expression of surface immune markers MHC-I, B7-2, and ICAM-1 in gammaherpesvirus-infected cell lines and induce virus-specific immunity. They can thus thwart virus-induced immune evasion. These effects, along with their direct effects on KSHV- or EBV-induced tumors, provide a rational for the clinical testing of these drugs in these tumors.

CDK6 Immunophenotype Implicates Potential Therapeutic Application of CDK4/6 Inhibitors in Urothelial Carcinoma

Background

Infiltrating bladder urothelial carcinoma is the most common bladder malignancy with limited therapeutic options and poor prognosis. Identifying new therapeutic targets or strategies has important clinical significance. The data from public sources indicate poor prognosis in urothelial carcinoma cases with high CDK6 mRNA levels. Furthermore, studies have shown that CDK6 expression is elevated in urothelial carcinoma tissue compared to the surrounding urothelium, thus presenting a case for performing CDK4/6 inhibitor targeted research in urothelial carcinoma. However, a phase II trial showed that CDK4/6 inhibitors are not effective for advanced urothelial carcinoma, suggesting that case screening is important for targeted therapy.

Objective

Immunohistochemistry (IHC) is simple and easy to perform and can be used to screen urothelial carcinoma cases with high CDK6 expression in clinical practice. The aim of this study was to determine the CDK6 expression threshold for positive cases.

Methods

We evaluated the correlation between the H-score of CDK6 protein expression and survival or CDK6 mRNA level using RNA sequencing. The effects of different CDK4/6 inhibitors were tested on bladder carcinoma cell lines with different CDK6 expression levels.

Results

The H-score, which predicts poor prognosis and reflects a high CDK6 mRNA level, was determined as the selection criterion for positive cases. Furthermore, we found that urothelial carcinoma cell lines with higher CDK6 expression levels displayed greater sensitivity to CDK4/6 inhibitors than cells with lower expression levels.

Conclusions

IHC staining for CDK6 protein in urothelial carcinoma is proposed as a promising screening platform for CDK4/6 inhibitor targeted therapy.

ASF1B is a Promising Prognostic Biomarker and Correlates With Immunotherapy Efficacy in Hepatocellular Carcinoma

Background: Anti-silencing function 1B (ASF1B), a histone H3-H4 chaperone, is crucial for S-phase progression and cell proliferation. Recent studies have shown that ASF1B may be used as a new proliferation marker for cancer prognosis. However, the prognostic value and effect of ASF1B on tumor cells and the immune microenvironment in hepatocellular carcinoma (HCC) remain unclear.

Methods: We analyzed the expression of ASF1B and its prognostic value using The Cancer Genome Atlas (TCGA) database (as a training set) and other databases, and we validated the findings by immunohistochemistry in our clinical database, containing 141 HCC patients (as a validation set). Gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) were performed to probe the tumor-associated biological processes of ASF1B in HCC. The interrelationships between ASF1B expression and tumor immunological characteristics were analyzed by multiple databases. The Imvigor210 cohort was retrieved to assess the ability of ASF1B to predict immunotherapy efficacy.

Results: ASF1B was highly expressed in tumor tissue compared to paracancerous tissue. High ASF1B expression was associated with worse overall survival (OS) and progression-free survival (PFS) in the training set (p = 0.005, p < 0.001) and validation set (p < 0.001, p < 0.001). Multivariate analysis revealed that ASF1B was an independent prognostic factor associated with OS and PFS. GSEA and GSVA suggested that ASF1B was involved in tumor-associated biological processes, including the cell cycle, DNA replication, base excision repair, mismatch repair, RNA degradation, ubiquitin-mediated proteolysis, and nucleotide excision repair. Further analysis revealed that the levels of ASF1B were positively correlated with the immune cells infiltration of B cells, CD8⁺ T cells, CD4⁺ T cells, neutrophils, and dendritic cells. However, ASF1B was positively correlated with Treg cell infiltration and inhibitory immune checkpoints in exhausted T cells. Patients who received anti-PD-L1 immunotherapy with high ASF1B expression had a higher objective response.

Conclusion: The ASF1B level is an independent prognostic factor and may serve as a potential immunotherapeutic target.

Interactions Between Anti-Angiogenic Therapy and Immunotherapy in Glioblastoma

Glioblastoma is the most aggressive brain tumor with a median survival ranging from 6.2 to 16.7 months. The complex interactions between the tumor and the cells of tumor microenvironment leads to tumor evolution which ultimately results in treatment failure. Immunotherapy has shown great potential in the treatment of solid tumors but has been less effective in treating glioblastoma. Failure of immunotherapy in glioblastoma has been attributed to low T-cell infiltration in glioblastoma and dysfunction of the T-cells that are present in the glioblastoma microenvironment. Recent advances in single-cell sequencing have increased our understanding of the transcriptional changes in the tumor microenvironment pre and post-treatment. Another treatment modality targeting the tumor microenvironment that has failed in glioblastoma has been anti-angiogenic therapy such as the VEGF neutralizing antibody bevacizumab, which did not improve survival in randomized clinical trials. Interestingly, the immunosuppressed microenvironment and abnormal vasculature of glioblastoma interact in ways that suggest the potential for synergy between these two therapeutic modalities that have failed individually. Abnormal tumor vasculature has been associated with immune evasion and the creation of an immunosuppressive microenvironment, suggesting that inhibiting pro-angiogenic factors like VEGF can increase infiltration of effector immune cells into the tumor microenvironment. Remodeling of the tumor vasculature by inhibiting VEGFR2 has also been shown to improve the efficacy of PDL1 cancer immunotherapy in mouse models of different cancers. In this review, we discuss the recent developments in our understanding of the glioblastoma tumor microenvironment specially the tumor vasculature and its interactions with the immune cells, and opportunities to target these interactions therapeutically. Combining anti-angiogenic and immunotherapy in glioblastoma has the potential to unlock these therapeutic modalities and impact the survival of patients with this devastating cancer.

Synergistic combination of cytotoxic chemotherapy and cyclin-dependent kinase 4/6 inhibitors in biliary tract cancers

BACKGROUND AND AIMS

Biliary tract cancers (BTCs) are uncommon, but highly lethal, gastrointestinal malignancies. Gemcitabine/cisplatin is a standard-of-care systemic therapy, but has a modest impact on survival and harbors toxicities, including myelosuppression, nephropathy, neuropathy, and ototoxicity. Whereas BTCs are characterized by aberrations activating the cyclinD1/cyclin-dependent kinase (CDK)4/6/CDK inhibitor 2a/retinoblastoma pathway, clinical use of CDK4/6 inhibitors as monotherapy is limited by lack of validated biomarkers, diffident preclinical efficacy, and development of acquired drug resistance. Emerging studies have explored therapeutic strategies to enhance the antitumor efficacy of CDK4/6 inhibitors by the combination with chemotherapy regimens, but their mechanism of action remains elusive.

APPROACH AND RESULTS

Here, we report in vitro and in vivo synergy in BTC models, showing enhanced efficacy, reduced toxicity, and better survival with a combination comprising gemcitabine/cisplatin and CDK4/6 inhibitors. Furthermore, we demonstrated that abemaciclib monotherapy had only modest efficacy attributable to autophagy-induced resistance. Notably, triplet therapy was able to potentiate efficacy through elimination of the autophagic flux. Correspondingly, abemaciclib potentiated ribonucleotide reductase catalytic subunit M1 reduction, resulting in sensitization to gemcitabine.

CONCLUSIONS

As such, these data provide robust preclinical mechanistic evidence of synergy between gemcitabine/cisplatin and CDK4/6 inhibitors and delineate a path forward for translation of these findings to preliminary clinical studies in advanced BTC patients.

Treatment with ribociclib shows favourable immunomodulatory effects in patients with hormone receptor-positive breast cancer-findings from the RIBECCA trial

BACKGROUND

Inhibitors of the cyclin-dependent kinases 4 and 6 (CDK4/6i) have significantly improved clinical outcomes in patients with advanced hormone receptor-positive (HR+) breast cancer and have demonstrated favourable antitumour immune responses in preclinical studies.

METHODS

Here, we investigated peripheral immune responses to ribociclib in patients with metastatic HR+ breast cancer as a preplanned exploratory subanalysis of the RIBECCA trial (NCT03096847). Peripheral blood mononuclear cells were subjected to immune cell profiling, gene expression analysis of immune-related signatures, and deep T cell receptor profiling before treatment started and after 12 weeks of treatment with ribociclib.

RESULTS

Gene expression analysis revealed an upregulation of signatures associated with an activated adaptive immune system and a decrease in immunosuppressive cytokine signalling during treatment with ribociclib. Profiling of peripheral immune cell subpopulations showed a decrease in Treg cell frequencies, which was associated with treatment response. Furthermore, induction of CD4+ naive T cells could be seen, whereas effector and memory T cell populations remained largely unchanged. Correspondingly, T cell repertoire diversity remained mostly unchanged during treatment, although an increase in clonality could be observed in single patients.

CONCLUSIONS

We show that treatment with ribociclib has significant effects on the peripheral innate and adaptive immune response in patients with HR+ breast cancer. Our data suggest that these effects lead to an activation of an already existing immune response rather than a de novo induction and make a strong case for future combination strategies of CDK4/6i with immunotherapies to enhance the adaptive immune response in HR+ breast cancer.

Baseline lymphopenia as prognostic factor in patients with metastatic breast cancer treated with palbociclib

Cyclin-dependent-kinase 4-6 inhibitors (CDK4/6i) have improved the management of hormone receptor (HR)⁺/human epidermal growth factor receptor (HER)2^- metastatic breast cancer (mBC). Currently, there are no valid prognostic factors for response to CDK4/6i. Baseline lymphopenia is reported as a prognostic factor in several types of cancer. The present retrospective study aimed to evaluate the effect of baseline absolute lymphocyte count (ALC) on response to palbociclib. Progression-free survival (PFS) was the primary endpoint. Secondary endpoints were overall survival (OS), best response and safety. A total of 114 patients treated for mBC between 2016 and 2019 were included. Median baseline ALC was 1.4 g/l (range, 0.2-4.3 g/l). A total of 65 (57%) and 49 (43%) patients had baseline ALC values of <1.5 and ≥1.5 g/l, respectively. Patients with baseline lymphopenia exhibited significantly shorter PFS (6 vs. 10 months; P=0.004) and OS (20 vs. 33 months; P=0.02). ALC <1.5 g/l independently predicted worse survival, as indicated by multivariate analysis (P=0.04; hazard ratio, 1.76; 95% confidence interval, 1.02-3.02). Patients with baseline ALC <1.5 g/l had significantly less partial response (14 vs. 22%; P=0.016) and more disease progression (46 vs. 20%; P=0.016) than those with ALC ≥1.5 g/l. ALC is a strong and easy-to-use dosage with prognostic factor for patients with HR⁺/HER2^- mBC treated with palbociclib and endocrine therapy. Lymphopenia may also be a predictive factor of early progression. These data need to be verified in a larger prospective study.

Various Uses of PD1/PD-L1 Inhibitor in Oncology: Opportunities and Challenges

The occurrence and development of cancer are closely related to the immune escape of tumor cells and immune tolerance. Unlike previous surgical, chemotherapy, radiotherapy and targeted therapy, tumor immunotherapy is a therapeutic strategy that uses various means to stimulate and enhance the immune function of the body, and ultimately achieves the goal of controlling tumor cells.With the in-depth understanding of tumor immune escape mechanism and tumor microenvironment, and the in-depth study of tumor immunotherapy, immune checkpoint inhibitors represented by Programmed Death 1/Programmed cell Death-Ligand 1(PD-1/PD-L1) inhibitors are becoming increasingly significant in cancer medication treatment. employ a variety of ways to avoid detection by the immune system, a single strategy is not more effective in overcoming tumor immune evasion and metastasis. Combining different immune agents or other drugs can effectively address situations where immunotherapy is not efficacious, thereby increasing the chances of success and alternative access to alternative immunotherapy. Immune combination therapies for cancer have become a hot topic in cancer treatment today. In this paper, several combination therapeutic modalities of PD1/PD-L1 inhibitors are systematically reviewed. Finally, an analysis and outlook are provided in the context of the recent advances in combination therapy with PD1/PD-L1 inhibitors and the pressing issues in this field.

Real-world benefit of combination palbociclib and endocrine therapy for metastatic breast cancer and correlation with neutropenia

BACKGROUND

Combination CDK4/6 inhibitor and endocrine therapy has been shown to significantly improve progression-free survival (PFS) in patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (mBC). The aim of this retrospective study was to evaluate the real-world benefit of first-line combination therapy in this cohort and to correlate treatment efficacy with neutropenia, a common toxicity of CDK4/6 inhibitors.

METHODS

This study included HR-positive, HER2-negative advanced or mBC patients who were treated with palbociclib plus endocrine therapy, mainly letrozole, between 1 January 2015 and 1 March 2018. Progression-free survival (PFS) was determined using Kaplan-Meier analysis. The predictive value of absolute neutrophil count (ANC) and neutrophil-to-lymphocyte ratio (NLR) for PFS were explored using Cox regression models. Both ANC and NLR were used as a time-dependent variable.

RESULTS

In total, 165 patients were included with median PFS of 24.19 months (95% CI 18.93-NR). Median PFS for patients with bone-only metastases (n = 54) was not reached (95% CI 18.21-NR). Among patients with all other metastases (n = 111), median PFS was 24.19 months (95% CI 16.33-33.82). Lower ANC was correlated with decreased risk of progression (HR 0.84, 95% CI 0.71-0.97, p = 0.008). There was no significant association between NLR and the risk of disease progression (HR 1.07, 95% CI 0.97-1.18, p = 0.203).

CONCLUSION

The effectiveness of palbociclib and endocrine therapy in the treatment of HR-positive, HER2-negative mBC in the real-world setting is similar to the efficacy reported in the PALOMA-2 trial. Patients with lower neutrophil count may have a lower risk of early disease progression.

Prognostic and immunological value of ATP6AP1 in breast cancer: implications for SARS-CoV-2

Abnormal ATPase H+ Transporting Accessory Protein 1 (ATP6AP1) expression may promote carcinogenesis. We investigated the association of ATP6AP1 with breast cancer (BC) and COVID-19. The Oncomine, Gene Expression Profiling Interactive Analysis, Human Protein Atlas and Kaplan-Meier plotter databases were used to evaluate the expression and prognostic value of ATP6AP1 in BC. ATP6AP1 was upregulated in BC tissues, and higher ATP6AP1 expression was associated with poorer outcomes. Data from the Tumor Immune Estimation Resource, Tumor-Immune System Interaction Database and Kaplan-Meier plotter indicated that ATP6AP1 expression correlated with immune infiltration, and that its prognostic effects in BC depended on tumor-infiltrating immune cell subtype levels. Multiple databases were used to evaluate the association of ATP6AP1 with clinicopathological factors, assess the mutation and methylation of ATP6AP1, and analyze gene co-expression and enrichment. The ATP6AP1 promoter was hypomethylated in BC tissues and differentially methylated between different disease stages and subtypes. Data from the Gene Expression Omnibus indicated that ATP6AP1 levels in certain cell types were reduced after SARS-CoV-2 infections. Ultimately, higher ATP6AP1 expression was associated with a poorer prognosis and with higher or lower infiltration of particular immune cells in BC. BC patients may be particularly susceptible to SARS-CoV-2 infections, which may alter their prognoses.

A novel function for cyclin D1 as a transcriptional role in oncogenesis and tumor development by ChIP-Seq and RNA-Seq

Introduction: Aberrations in cell cycle control is defined as one of the hallmarks of cancer, while cyclin D1 is an essential protein to cell cycle which promote G1 phase into S phase, and frequently overexpressed in many human cancers. However, new functions have been identified in transgenic mice models, including the transcription of genome, the development of chromosome instability and DNA repair. In this research, our aim is to find the function of cyclin D1 in transcription in human cancers.

Methods: The correlation of the cyclin D1 expression levels and prognosis of cervical cancer patients were analyzed in tissue microarray (TMA) cohort. We chose C33A as our main research object. Using chromatin immunoprecipitation sequencing (ChIP-seq) coupled with RNA sequencing (RNA-seq), to find out the genes differentially expressed in C33A, cyclin D1 knock-in C33A and cyclin D1 knock-down C33A.

Results: We found that upregulation of cyclin D1 was associated with shorter overall survival (OS) and disease-free survival (DFS). Functionally, we identified 422 genes differentially expressed through analysis of the results of ChIP-seq and RNA-seq. These genes are highly enriched in Gene Ontology categories and involve in diverse cellular functions via KEGG classification, including replication and repair, signal transduction, cell growth and death.

Conclusion: These findings suggested that the expression of cyclin D1 was associated with the prognosis of patients with cervical cancer. Cyclin D1 can serve both to activate and downregulate gene expression as a transcriptional role directly binding with genome DNA, which means that cyclin D1 may be a key protein during oncogenesis and tumor development.

CSNK2B contributes to colorectal cancer cell proliferation by activating the mTOR signaling

The function of Casein kinase 2 beta (CSNK2B) in human malignancies has drawn increasing attention in recent years. However, its role in colorectal cancer (CRC) remains unclear. In the present study, we aimed to explore the expression and biological functions of CSNK2B in CRC. Public gene expression microarray data from online database and immunohistochemistry analysis demonstrated that CSNK2B was highly expressed in CRC tissues than in normal tissues. In vitro and in vivo cellular functional experiments showed that increased CSNK2B expression promoted CRC cell viability and tumorigenesis of CRC. Further western blots and rescue experiments confirmed that CSNK2B promoted CRC cell proliferation mainly by activating the mTOR signaling pathway. These findings identified CSNK2B as a novel oncogene contributing to the development of CRC.

Metabolic modulation by CDK4/6 inhibitor promotes chemokine-mediated recruitment of T cells into mammary tumors

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) delay progression of metastatic breast cancer. However, complete responses are uncommon and tumors eventually relapse. Here, we show that CDK4/6i can enhance efficacy of T cell-based therapies, such as adoptive T cell transfer or T cell-activating antibodies anti-OX40/anti-4-1BB, in murine breast cancer models. This effect is driven by the induction of chemokines CCL5, CXCL9, and CXCL10 in CDK4/6i-treated tumor cells facilitating recruitment of activated CD8+ T cells, but not Tregs, into the tumor. Mechanistically, chemokine induction is associated with metabolic stress that CDK4/6i treatment induces in breast cancer cells. Despite the cell cycle arrest, CDK4/6i-treated cells retain high metabolic activity driven by deregulated PI3K/mTOR pathway. This causes cell hypertrophy and increases mitochondrial content/activity associated with oxidative stress and inflammatory stress response. Our findings uncover a link between tumor metabolic vulnerabilities and anti-tumor immunity and support further development of CDK4/6i and immunotherapy combinations.

Phosphorylation regulates cullin-based ubiquitination in tumorigenesis

Cullin-RING ligases (CRLs) recognize and interact with substrates for ubiquitination and degradation, and can be targeted for disease treatment when the abnormal expression of substrates involves pathologic processes. Phosphorylation, either of substrates or receptors of CRLs, can alter their interaction. Phosphorylation-dependent ubiquitination and proteasome degradation influence various cellular processes and can contribute to the occurrence of various diseases, most often tumorigenesis. These processes have the potential to be used for tumor intervention through the regulation of the activities of related kinases, along with the regulation of the stability of specific oncoproteins and tumor suppressors. This review describes the mechanisms and biological functions of crosstalk between phosphorylation and ubiquitination, and most importantly its influence on tumorigenesis, to provide new directions and strategies for tumor therapy.

How selective are clinical CDK4/6 inhibitors?

Pharmacological inhibition of cyclin-dependent kinase 4/6 (CDK4/6) has emerged as an efficient approach for treating breast cancer, and its clinical potential is expanding to other cancers. CDK4/6 inhibitors were originally believed to act by arresting proliferation in the G1 phase, but it is gradually becoming clear that the cellular response to these compounds is far more complex than this. Multiple context-dependent mechanisms of action are emerging, involving modulation of quiescence, senescence, autophagy, cellular metabolism, and enhanced tumor cell immunogenicity. These mechanisms may be driven by interactions with unexpected targets. We review cellular responses to the Food and Drug Administration-approved CDK4/6 inhibitors palbociclib, ribociclib, and abemaciclib, and summarize available knowledge of other drugs undergoing clinical trials, including data on their off-target landscapes. We emphasize the importance of comprehensively characterizing drugs' selectivity profiles to maximize their clinical efficacy and safety and to facilitate their repurposing to treat additional diseases based on their target spectrum.

Functional imaging of RAS pathway targeting in malignant peripheral nerve sheath tumor cells and xenografts

BACKGROUND

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive form of soft-tissue sarcoma (STS) in children. Despite intensive therapy, relatively few children with metastatic and unresectable disease survive beyond three years. RAS pathway activation is common in MPNST, suggesting MEK pathway inhibition as a targeted therapy, but the impact on clinical outcome has been small to date.

PROCEDURE

We conducted preclinical pharmacokinetic (PK) and pharmacodynamic studies of two MEK inhibitors, trametinib and selumetinib, in two MPNST models and analyzed tumors for intratumor drug levels. We then investigated 3'-deoxy-3'-[¹⁸ F]fluorothymidine (¹⁸ F-FLT) PET imaging followed by ¹⁸ F-FDG PET/CT imaging of MPNST xenografts coupled to short-term or longer-term treatment with selumetinib focusing on PET-based imaging as a biomarker of MEK inhibition.

RESULTS

Trametinib decreased pERK expression in MPNST xenografts but did not prolong survival or decrease Ki67 expression. In contrast, selumetinib prolonged survival of animals bearing MPNST xenografts, and this correlated with decreased pERK and Ki67 staining. PK studies revealed a significantly higher fraction of unbound selumetinib within a responsive MPNST xenograft model. Thymidine uptake, assessed by ¹⁸ F-FLT PET/CT, positively correlated with Ki67 expression in different xenograft models and in response to selumetinib.

CONCLUSION

The ability of MEK inhibitors to control MPNST growth cannot simply be predicted by serum drug levels or drug-induced changes in pERK expression. Tumor cell proliferation assessed by ¹⁸ F-FLT PET imaging might be useful as an early response marker to targeted therapies, including MEK inhibition, where a primary effect is cell-cycle arrest.

Combined CDK2 and CDK4/6 Inhibition Overcomes Palbociclib Resistance in Breast Cancer by Enhancing Senescence

Breast cancer represents the number one global cancer burden in women and the hormone receptor (HR)-positive subtype comprises approximately 70% of breast cancers. Unfortunately, acquired resistance ultimately occurs in almost all cases, even though cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are a highly effective therapy for HR-positive/human epidermal growth factor receptor 2-negative subtype. Here, we investigated mechanisms of resistance to CDK4/6 inhibitor and potential therapeutic strategies using our palbociclib-resistant preclinical model. We observed that cyclin E was significantly overexpressed in palbociclib-resistant cells, and similar association was also confirmed in pleural effusion samples collected from HR-positive breast cancer patients. After confirmation of cyclin E-CDK2 interaction by co-immunoprecipitation, we demonstrated CDK2 inhibition combined with palbociclib synergistically suppressed proliferation of palbociclib-resistant cells and growth of palbociclib-resistant xenograft in mice. We also proved that enhancing C-MYC-mediated senescence is a novel mechanism behind the synergism created by targeting both CDK2 and CDK4/6. Furthermore, the clinical relevance of cyclin E as a therapeutic target was supported by significant association between CCNE1 overexpression and poor prognosis based on large-scale public gene expression data sets in HR-positive breast cancer patients. Therefore, we propose cyclin E-CDK2 signaling as a promising therapeutic target for overcoming cyclin E-associated resistance to CDK4/6 inhibitor.

Mechanisms of CDK4/6 Inhibitor Resistance in Luminal Breast Cancer

As a new-generation CDK inhibitor, a CDK4/6 inhibitor combined with endocrine therapy has been successful in the treatment of advanced estrogen receptor-positive (ER+) breast cancer. Although there has been overall progress in the treatment of cancer, drug resistance is an emerging cause for breast cancer-related death. Overcoming CDK4/6 resistance is an urgent problem. Overactivation of the cyclin-CDK-Rb axis related to uncontrolled cell proliferation is the main cause of CDK4/6 inhibitor resistance; however, the underlying mechanisms need to be clarified further. We review various resistance mechanisms of CDK4/6 inhibitors in luminal breast cancer. The cell signaling pathways involved in therapy resistance are divided into two groups: upstream response mechanisms and downstream bypass mechanisms. Finally, we discuss possible strategies to overcome CDK4/6 inhibitor resistance and identify novel resistance targets for future clinical application.

Non-coding RNA derived from extracellular vesicles in cancer immune escape: Biological functions and potential clinical applications

The tumor microenvironment represents a dynamically composed matrix into which cancer cells and many other cell types are embedded to form organ-like structures. The tumor immune microenvironment (TIME), composed of immune cells, is an inseparable part of the tumor microenvironment. Extracellular vesicles (EVs) participate in the occurrence and development of tumors by delivering various biologically active molecules between cells; their role in cancer immune escape in particular has been widely proven. EVs can carry a wide array of cargo, such as non-coding RNAs (ncRNAs), including miRNAs, lncRNAs, and circRNAs, which are selectively loaded by EVs, secreted, and transported to participate in the proliferation of immune cells. Hence, strategies to specifically target EV-ncRNAs could be attractive therapeutic options. In this review, we summarize the current research on the role of EV-ncRNAs in cancer immune escape, and discuss the latest research on the function and regulation mechanism of EV-ncRNAs in cancer immune escape, highlighting and elucidating the potential clinical applications of EV-ncRNAs, including in diagnosis and immunotherapy.

Advances in cyclin-dependent kinase inhibitors for the treatment of melanoma

Introduction: Despite the recent advances in the treatment of malignant melanoma with immunotherapy and BRAF/MEK targeted agents, advanced disease still beholds a poor prognosis for a significant proportion of patients. Cyclin-dependent kinase (CDK) inhibitors have been investigated as novel melanoma therapeutics throughout a range of phase 1 and 2 trials, as single agents and in combination with established treatments. Areas covered: This article summarizes the rationale for, and development of CDK inhibitors in melanoma, with their evolution from pan-CDK inhibitors to highly specific agents, throughout clinical trials and finally their potential future use. Expert opinion: Whilst CDK inhibitors have been practice changing in breast cancer management, their efficacy is yet to be proven in melanoma. Combination with BRAF/MEK inhibitors has been hindered by dose-limiting toxicities, but their role may yet to be found within the spectrum of biomarker-derived personalized melanoma management. The effect that CDK inhibitors can have as an adjunct to immunotherapy also remains to be seen.

Avelumab: search for combinations of immune checkpoint inhibition with chemotherapy

INTRODUCTION

Immune checkpoint inhibition (ICI) has proved successful for selected tumors and a subpopulation of patients. The human monoclonal IgG1 antibody (mAB) avelumab capable of mediating antibody-dependent cytotoxicity (ADCC) lysis is directed to programmed death ligand-1 (PD-L1) of tumor cells and is tested in trials aiming to improve ICI in combination with chemotherapeutic drugs.

AREAS COVERED

This article presents an overview of the current trials to enhance ICI regimens using avelumab in combination with chemotherapeutics, antiangiogenetic drugs, and immunomodulators. Predictive factors for this kind of immunochemotherapy are discussed.

EXPERT OPINION

Clinical data demonstrate that avelumab shows efficacy in cancer patients against Merkel cell carcinoma (MCC), renal cell carcinoma (RCC), and urothelial cancers as single agent. Furthermore, avelumab in combination with axitinib in RCC increases survival and exhibits activity in combination with docetaxel in urothelial carcinoma. However, several other immunochemotherapy trials for ovarian cancer, gastric cancer, and non-small lung cancer (NSCLC) showed no activity due to factors disfavoring administration of immunotherapy combos.

Using Gene Editing Approaches to Fine-Tune the Immune System

Genome editing technologies not only provide unprecedented opportunities to study basic cellular system functionality but also improve the outcomes of several clinical applications. In this review, we analyze various gene editing techniques used to fine-tune immune systems from a basic research and clinical perspective. We discuss recent advances in the development of programmable nucleases, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeat (CRISPR)-Cas-associated nucleases. We also discuss the use of programmable nucleases and their derivative reagents such as base editing tools to engineer immune cells via gene disruption, insertion, and rewriting of T cells and other immune components, such natural killers (NKs) and hematopoietic stem and progenitor cells (HSPCs). In addition, with regard to chimeric antigen receptors (CARs), we describe how different gene editing tools enable healthy donor cells to be used in CAR T therapy instead of autologous cells without risking graft-versus-host disease or rejection, leading to reduced adoptive cell therapy costs and instant treatment availability for patients. We pay particular attention to the delivery of therapeutic transgenes, such as CARs, to endogenous loci which prevents collateral damage and increases therapeutic effectiveness. Finally, we review creative innovations, including immune system repurposing, that facilitate safe and efficient genome surgery within the framework of clinical cancer immunotherapies.

CDK4/6 Inhibitors in Breast Cancer Treatment: Potential Interactions with Drug, Gene, and Pathophysiological Conditions

Palbociclib, ribociclib, and abemaciclib belong to the third generation of cyclin-dependent kinases inhibitors (CDKis), an established therapeutic class for advanced and metastatic breast cancer. Interindividual variability in the therapeutic response of CDKis has been reported and some individuals may experience increased and unexpected toxicity. This narrative review aims at identifying the factors potentially concurring at this variability for driving the most appropriate and tailored use of CDKis in the clinic. Specifically, concomitant medications, pharmacogenetic profile, and pathophysiological conditions could influence absorption, distribution, metabolism, and elimination pharmacokinetics. A personalized therapeutic approach taking into consideration all factors potentially contributing to an altered pharmacokinetic/pharmacodynamic profile could better drive safe and effective clinical use.