Inhibition of CDK4/6 Promotes CD8 T-cell Memory Formation

Perfusion drugs for non‑muscle invasive bladder cancer (Review)

The high recurrence rate and poor prognosis of non-muscle invasive bladder cancer (BC) are challenges that need to be urgently addressed. Transurethral cystectomy for bladder tumors is often combined with bladder perfusion therapy, which can effectively reduce the recurrence and progression rates of BC. The present review integrated and analyzed currently available bladder perfusion drugs, mainly including chemotherapeutic agents, immunotherapeutic agents and other adjuvant perfusion drugs. Bacillus Calmette-Guerin (BCG) perfusion was the pioneering immunotherapy for early BC and still ranks high in the selection of perfusion drugs. However, BCG infusion has a high toxicity profile and has been shown to be ineffective in some patients. Due to the limitations of BCG, new bladder perfusion drugs are constantly being developed. Immunotherapeutic agents have opened a whole new chapter in the selection of therapeutic agents for bladder perfusion. The present review explored the mechanism of action, clinical dosage and adverse effects of a variety of bladder perfusion drugs currently in common use, described combined perfusion and compared the effects of certain drugs on BC.

The cell cycle regulator p16 promotes tumor infiltrated CD8+ T cell exhaustion and apoptosis

The therapeutic efficacy of adoptive T cell therapy is largely restricted by reduced viability and dysfunction of CD8+ T cells. Continuous antigen stimulation disrupts the expansion, effector function, and metabolic fitness of CD8+ T cells, leading to their differentiation into an exhausted state within the tumor microenvironment (TME). While the function of the cell cycle negative regulator p16 in senescent cells is well understood, its role in T cell exhaustion remains unclear. In this study, we demonstrated that TCR stimulation of CD8+ T cells rapidly upregulates p16 expression, with its levels positively correlating with TCR affinity. Chronic TCR stimulation further increased p16 expression, leading to CD8+ T cell apoptosis and exhaustion differentiation, without inducing DNA damage or cell senescence. Mechanistic investigations revealed that p16 downregulates mTOR, glycolysis, and oxidative phosphorylation (OXPHOS) associated gene expression, resulting in impaired mitochondrial fitness, reduced T cell viability, and diminished effector function. Furthermore, the deletion of p16 significantly enhances the persistence of CD8+ T cells within tumors and suppresses the terminal exhaustion of tumor-infiltrating T cells. Overall, our findings elucidate how increased p16 expression reshapes T cell intracellular metabolism, drives T cell apoptosis and exhaustion differentiation, and ultimately impairs T cell anti-tumor function.

Exploiting the therapeutic implications of KRAS inhibition on tumor immunity

Over the past decade, RAS oncogenic proteins have transitioned from being deemed undruggable to having two clinically approved drugs, with several more in advanced stages of development. Despite the initial benefit of KRAS-G12C inhibitors for patients with tumors harboring this mutation, the rapid emergence of drug resistance underscores the urgent need to synergize these inhibitors with other therapeutic approaches to improve outcomes. RAS mutant tumor cells can create an immunosuppressive tumor microenvironment (TME), suggesting an increased susceptibility to immunotherapies following RAS inhibition. This provides a rationale for combining RAS inhibitory drugs with immune checkpoint blockade (ICB). However, achieving this synergy in the clinical setting has proven challenging. Here, we explore how understanding the impact of RAS mutant tumor cells on the TME can guide innovative approaches to combining RAS inhibition with immunotherapies, review progress in both pre-clinical and clinical stages, and discuss challenges and future directions.

Cell-cycle inhibition and immune microenvironment in breast cancer treated with ribociclib and letrozole or chemotherapy

In this study, we performed genomic analyses of cell cycle and tumor microenvironment changes during and after ribociclib and letrozole or chemotherapy in the CORALLEEN trial. 106 women with untreated PAM50-defined Luminal B early breast cancers were randomly assigned to receive neoadjuvant ribociclib and letrozole or standard-of-care chemotherapy. Ki67 immunohistochemistry, tumor-infiltrating lymphocytes quantification, and RNA sequencing were obtained from tissue biopsies pre-treatment, on day 14 of treatment, and tumor specimens from surgical resection. Results showed that at surgery, Ki67 and the PAM50 proliferation scores were lower after ribociclib compared to chemotherapy. However, consistent reactivation of tumor cell proliferation from day 14 to surgery was only observed in the ribociclib arm. In tumors with complete cell cycle arrest (CCCA) at surgery, PAM50 proliferation scores were lower in the ribociclib arm compared to chemotherapy (p < 0.001), whereas the opposite was observed with tumor cellularity (p = 0.002). Gene expression signatures (GES) associated with antigen-presenting cells (APCs) and innate immune system activity showed increased expression post-chemotherapy but decreased expression post-ribociclib. Interferon-associated GES had decreased expression with CCCA and increased expression with non-CCCA. Our findings suggest that while both treatment strategies decreased proliferation, the depth and the patterns over time differed by treatment arm. Immunologically, ribociclib was associated with downregulated GES associated with APCs and the innate immune system in Luminal B tumors, contrary to existing preclinical data. Further studies are needed to understand the effect of CDK4/6 inhibition on the tumor cells and microenvironment, an effect which may vary according to tumor subtypes.

Integrative score based on CDK6, PD-L1 and TMB predicts response to platinum-based chemotherapy and PD-1/PD-L1 blockade in muscle-invasive bladder cancer

BACKGROUND

Cyclin-dependent kinase 6 (CDK6) was proved to be an important regulator in the progression of cell cycle and has been a promising therapeutic target in cancer treatment. However, the clinical significance of CDK6 in muscle-invasive bladder cancer (MIBC) remains obscure. Herein, we attempt to explore the clinical relevance of CDK6 and assess the feasibility of the integrative model to predict immune checkpoint blockade (ICB) response.

METHODS

This study enrolled 933 patients with muscle-invasive bladder cancer (MIBC) from Zhongshan Hospital (ZSHS), The Cancer Genome Atlas (TCGA), Chemo, IMvigor210 and UC-GENOME cohorts. Kaplan-Meier survival and Cox regression analyses were performed to assess clinical outcomes based on CDK6 expression.

RESULTS

High CDK6 expression conferred poor prognosis and superior response to platinum-based chemotherapy but inferior response to ICB in MIBC. Furthermore, the integrative model named response score based on CDK6, PD-L1 and TMB could better predict the response to ICB and chemotherapy. Patients with higher response scores were characterised by inflamed immune microenvironment and genomic instability.

CONCLUSIONS

CDK6 expression was correlated with prognosis and therapy response in MIBC. Integration of CDK6, PD-L1 and TMB could better identify patients who were most likely to benefit from ICB and chemotherapy.

PD-1 Blockade Induces Reactivation of Nonproductive T-Cell Responses Characterized by NF-κB Signaling in Patients with Pancreatic Cancer

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) trials have evaluated CTLA-4 and/or PD-(L)1 blockade in patients with advanced disease in which bulky tumor burden and limited time to develop antitumor T cells may have contributed to poor clinical efficacy. Here, we evaluated peripheral blood and tumor T cells from patients with PDAC receiving neoadjuvant chemoradiation plus anti-PD-1 (pembrolizumab) versus chemoradiation alone. We analyzed whether PD-1 blockade successfully reactivated T cells in the blood and/or tumor to determine whether lack of clinical benefit could be explained by lack of reactivated T cells versus other factors.

EXPERIMENTAL DESIGN

We used single-cell transcriptional profiling and TCR clonotype tracking to identify TCR clonotypes from blood that match clonotypes in the tumor.

RESULTS

PD-1 blockade increases the flux of TCR clonotypes entering cell cycle and induces an IFNγ signature like that seen in patients with other GI malignancies who respond to PD-1 blockade. However, these reactivated T cells have a robust signature of NF-κB signaling not seen in cases of PD-1 antibody response. Among paired samples between blood and tumor, several of the newly cycling clonotypes matched activated T-cell clonotypes observed in the tumor.

CONCLUSIONS

Cytotoxic T cells in the blood of patients with PDAC remain sensitive to reinvigoration by PD-1 blockade, and some have tumor-recognizing potential. Although these T cells proliferate and have a signature of IFN exposure, they also upregulate NF-κB signaling, which potentially counteracts the beneficial effects of anti-PD-1 reinvigoration and marks these T cells as non-productive contributors to antitumor immunity. See related commentary by Lander and DeNardo, p. 474.

p21 Prevents the Exhaustion of CD4+ T Cells Within the Antitumor Immune Response Against Colorectal Cancer

BACKGROUND & AIMS

T cells are crucial for the antitumor response against colorectal cancer (CRC). T-cell reactivity to CRC is nevertheless limited by T-cell exhaustion. However, molecular mechanisms regulating T-cell exhaustion are only poorly understood.

METHODS

We investigated the functional role of cyclin-dependent kinase 1a (Cdkn1a or p21) in cluster of differentiation (CD) 4+ T cells using murine CRC models. Furthermore, we evaluated the expression of p21 in patients with stage I to IV CRC. In vitro coculture models were used to understand the effector function of p21-deficient CD4+ T cells.

RESULTS

We observed that the activation of cell cycle regulator p21 is crucial for CD4+ T-cell cytotoxic function and that p21 deficiency in type 1 helper T cells (Th1) leads to increased tumor growth in murine CRC. Similarly, low p21 expression in CD4+ T cells infiltrated into tumors of CRC patients is associated with reduced cancer-related survival. In mouse models of CRC, p21-deficient Th1 cells show signs of exhaustion, where an accumulation of effector/effector memory T cells and CD27/CD28 loss are predominant. Immune reconstitution of tumor-bearing Rag1-/- mice using ex vivo-treated p21-deficient T cells with palbociclib, an inhibitor of cyclin-dependent kinase 4/6, restored cytotoxic function and prevented exhaustion of p21-deficient CD4+ T cells as a possible concept for future immunotherapy of human disease.

CONCLUSIONS

Our data reveal the importance of p21 in controlling the cell cycle and preventing exhaustion of Th1 cells. Furthermore, we unveil the therapeutic potential of cyclin-dependent kinase inhibitors such as palbociclib to reduce T-cell exhaustion for future treatment of patients with colorectal cancer.

CDK4/6 inhibition in hormone receptor-positive/HER2-negative breast cancer: Biological and clinical aspects

A dysregulated cell division, one of the key hallmarks of cancer, results in uncontrolled cellular proliferation. This aberrant process, mediated by a dysregulated cell-cycle machinery and overactivation of cyclin-dependent kinase (CDK) 4 and 6, can potentially promote tumorigenesis. The clinical application of CDK 4/6 inhibitors, developed to inhibit cell-cycle progression, in the treatment regimens of breast cancer (BC) patients is expanding. Currently, three agents, ribociclib, palbociclib, and abemaciclib, are approved for treating patients with hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic BC. In addition, abemaciclib is FDA and EMA-approved for patients with hormone receptor-positive HER2-negative, node-positive, early BC at high risk of recurrence. Emerging data suggest potential anti-tumor effects beyond cell cycle arrest, providing novel insights into the agent's mechanisms of action. As a result, a broader application of the CDK4/6 inhibitors in patients with cancer is achieved, contributing to enhanced optimized treatment in the adjuvant and neoadjuvant settings. Herein, the immunomodulatory activities of CDK4/6 inhibitors, their impact on the cell's metabolic state, and the effect on the decision of the cell to undergo quiescence or senescence are discussed. Moreover, this review provides an update on clinical trial outcomes and the differences in the underlying mechanisms between the distinct CDK4/6 inhibitors.

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.

Prognosis of immunotherapy for non-small cell lung cancer with CDKN2A loss of function

Background

Immunotherapy has been widely used to treat non-small cell lung cancer (NSCLC) but is only effective in 20% of patients. Cyclin-dependent kinase inhibitor 2A (CDKN2A) is an important tumor suppressor gene, and its loss of function (LOF) is quite common in NSCLC. Pre-clinical studies suggest CDKN2A LOF promotes immune evasion; however, the results in relation to NSCLC are controversial, and debate continues as to the effect of CDKN2A LOF on immunotherapy.

Methods

In this study, we collected the data of 49 CDKN2A LOF and 173 CDKN2A wild-type NSCLC consecutive patients treated by any line of immunotherapy. Through immunohistochemical (IHC) and immunofluorescent (IF) staining, we analyzed the CDKN2A predominant transcription protein p16INK4A in the CDKN2A LOF and CDKN2A wild-type NSCLC patients. Using Kaplan-Meier curves, we also examined the relationship between CDKN2A LOF and immunotherapy.

Results

The IHC and IF staining results showed that most CDKN2A LOF patients were p16INK4A negative, while most CDKN2A wild-type patients were p16INK4A positive. In the LOF group, five patients had partial responses, 35 had stable disease, and nine had progressive disease after the first evaluation of immunotherapy. The LOF group had a median progression-free survival (PFS) time of 4.67 months, while the wild-type group had a median PFS time of 8.63 months [hazard ratio (HR): 0.54; 95% confidence interval (CI): 0.38-0.77; P<0.001]. The LOF group had a median overall survival (OS) time of 9.07 months, while the wild-type group had a median OS time of 21.37 months (HR: 0.42; 95% CI: 0.29-0.61; P<0.001).

Conclusions

Our study revealed that CDKN2A LOF NSCLC patients treated with immune checkpoint inhibitor (ICI) mono-therapy or combined therapy had a worse prognosis than those with CDKN2A wild-type NSCLC. However, our study also suggested that ICI could work quite effectively in selective CDKN2A LOF patients.

CAR+ and CAR- T cells share a differentiation trajectory into an NK-like subset after CD19 CAR T cell infusion in patients with B cell malignancies

Chimeric antigen receptor (CAR) T cell therapy is effective in treating B cell malignancies, but factors influencing the persistence of functional CAR+ T cells, such as product composition, patients' lymphodepletion, and immune reconstitution, are not well understood. To shed light on this issue, here we conduct a single-cell multi-omics analysis of transcriptional, clonal, and phenotypic profiles from pre- to 1-month post-infusion of CAR+ and CAR- T cells from patients from a CARTELL study (ACTRN12617001579381) who received a donor-derived 4-1BB CAR product targeting CD19. Following infusion, CAR+ T cells and CAR- T cells shows similar differentiation profiles with clonally expanded populations across heterogeneous phenotypes, demonstrating clonal lineages and phenotypic plasticity. We validate these findings in 31 patients with large B cell lymphoma treated with CD19 CAR T therapy. For these patients, we identify using longitudinal mass-cytometry data an association between NK-like subsets and clinical outcomes at 6 months with both CAR+ and CAR- T cells. These results suggest that non-CAR-derived signals can provide information about patients' immune recovery and be used as correlate of clinically relevant parameters.

DGKα/ζ inhibition lowers the TCR affinity threshold and potentiates antitumor immunity

Diacylglycerol kinases (DGKs) attenuate diacylglycerol (DAG) signaling by converting DAG to phosphatidic acid, thereby suppressing pathways downstream of T cell receptor signaling. Using a dual DGKα/ζ inhibitor (DGKi), tumor-specific CD8 T cells with different affinities (TRP1high and TRP1low), and altered peptide ligands, we demonstrate that inhibition of DGKα/ζ can lower the signaling threshold for T cell priming. TRP1high and TRP1low CD8 T cells produced more effector cytokines in the presence of cognate antigen and DGKi. Effector TRP1high- and TRP1low-mediated cytolysis of tumor cells with low antigen load required antigen recognition, was mediated by interferon-γ, and augmented by DGKi. Adoptive T cell transfer into mice bearing pancreatic or melanoma tumors synergized with single-agent DGKi or DGKi and antiprogrammed cell death protein 1 (PD-1), with increased expansion of low-affinity T cells and increased cytokine production observed in tumors of treated mice. Collectively, our findings highlight DGKα/ζ as therapeutic targets for augmenting tumor-specific CD8 T cell function.

CDK4/6 inhibitor-mediated cell overgrowth triggers osmotic and replication stress to promote senescence

Abnormal increases in cell size are associated with senescence and cell cycle exit. The mechanisms by which overgrowth primes cells to withdraw from the cell cycle remain unknown. We address this question using CDK4/6 inhibitors, which arrest cells in G0/G1 and are licensed to treat advanced HR+/HER2- breast cancer. We demonstrate that CDK4/6-inhibited cells overgrow during G0/G1, causing p38/p53/p21-dependent cell cycle withdrawal. Cell cycle withdrawal is triggered by biphasic p21 induction. The first p21 wave is caused by osmotic stress, leading to p38- and size-dependent accumulation of p21. CDK4/6 inhibitor washout results in some cells entering S-phase. Overgrown cells experience replication stress, resulting in a second p21 wave that promotes cell cycle withdrawal from G2 or the subsequent G1. We propose that the levels of p21 integrate signals from overgrowth-triggered stresses to determine cell fate. This model explains how hypertrophy can drive senescence and why CDK4/6 inhibitors have long-lasting effects in patients.

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.

Myeloid-intrinsic cell cycle-related kinase drives immunosuppression to promote tumorigenesis

Massive expansion of immature and suppressive myeloid cells is a common feature of malignant solid tumors. Over-expression of cyclin-dependent kinase 20, also known as cell cycle-related kinase (CCRK), in hepatocellular carcinoma (HCC) correlates with reduced patient survival and low immunotherapy responsiveness. Beyond tumor-intrinsic oncogenicity, here we demonstrated that CCRK is upregulated in myeloid cells in tumor-bearing mice and in patients with HCC. Intratumoral injection of Ccrk-knockdown myeloid-derived suppressor cells (MDSCs) increased tumor-infiltrating CD8+T cells and suppressed HCC tumorigenicity. Using an indel mutant transgenic model, we showed that Ccrk inactivation in myeloid cells conferred a mature phenotype with elevated IL-12 production, driving Th1 responses and CD8+T cell cytotoxicity to reduce orthotopic tumor growth and prolong survival. Mechanistically, CCRK activates STAT3/E4BP4 signaling in MDSCs to acquire immunosuppressive activity through transcriptional IL-10 induction and IL-12 suppression. Taken together, our findings unravel mechanistic insights into MDSC-mediated immunosuppression and offer a therapeutic kinase-target for cancer immunotherapy.

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.

Efficacy, safety, and biomarker analysis of nivolumab in combination with abemaciclib plus endocrine therapy in patients with HR-positive HER2-negative metastatic breast cancer: a phase II study (WJOG11418B NEWFLAME trial)

BACKGROUND

Hormone receptor (HR)-positive breast cancer is a disease for which no immune checkpoint inhibitors have shown promise as effective therapies. Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors synergistically increased the effectiveness of antiprogrammed cell death protein-1 (anti-PD-1)/programmed death-ligand 1 (PD-L1) antibodies in preclinical studies.

METHODS

This non-randomized, multicohort, phase II study evaluated the efficacy and safety of the anti-PD-1 antibody nivolumab 240 mg administered every 2 weeks in combination with the CDK4/6 inhibitor abemaciclib 150 mg twice daily and either fulvestrant (FUL) or letrozole (LET) as a first-line or second-line treatment for HR-positive HER2-negative metastatic breast cancer. The primary end point was the objective response rate (ORR), and secondary end points were toxicity, progression-free survival, and overall survival. Blood, tissue, and fecal samples were collected at multiple points for correlative studies to evaluate immunity biomarkers.

RESULTS

From June 2019 to early study termination due to safety concerns on July 2020, 17 patients were enrolled (FUL: n=12, LET: n=5). One patient with a prior treatment history in the FUL cohort was excluded. ORRs were 54.5% (6/11) and 40.0% (2/5) in the FUL and LET cohorts, respectively. Treatment-emergent (TE) adverse events (AEs) of grade ≥3 occurred in 11 (92%) and 5 (100%) patients in the FUL and LET cohorts, respectively. The most common grade ≥3 TEAEs were neutropenia (7 (58.3%) and 3 (60.0%) in the FUL and LET cohorts, respectively), followed by alanine aminotransferase elevation (5 (41.6%) and 4 (80.0%)). One treatment-related death from interstitial lung disease occurred in the LET cohort. Ten patients developed liver-related grade ≥3 AEs. Liver biopsy specimens from 3 patients showed hepatitis characterized by focal necrosis with predominant CD8+ lymphocyte infiltration. Marked elevation of tumor necrosis factor-related cytokines and interleukin-11, and a decrease in peripheral regulatory T cells (Tregs), were observed in patients with hepatotoxicity. These findings suggest that treatment-related toxicities were immune-related AEs likely caused by proinflammatory cytokine production and suppression of Treg proliferation due to the addition of abemaciclib to nivolumab therapy.

CONCLUSIONS

Although the combination of nivolumab and abemaciclib was active, it caused severe and prolonged immune-related AEs.

TRIAL REGISTRATION NUMBER

JapicCTI-194782, jRCT2080224706, UMIN000036970.

Drug Repurposing to Circumvent Immune Checkpoint Inhibitor Resistance in Cancer Immunotherapy

Immune checkpoint inhibitors (ICI) have achieved unprecedented clinical success in cancer treatment. However, drug resistance to ICI therapy is a major hurdle that prevents cancer patients from responding to the treatment or having durable disease control. Drug repurposing refers to the application of clinically approved drugs, with characterized pharmacological properties and known adverse effect profiles, to new indications. It has also emerged as a promising strategy to overcome drug resistance. In this review, we summarized the latest research about drug repurposing to overcome ICI resistance. Repurposed drugs work by either exerting immunostimulatory activities or abolishing the immunosuppressive tumor microenvironment (TME). Compared to the de novo drug design strategy, they provide novel and affordable treatment options to enhance cancer immunotherapy that can be readily evaluated in the clinic. Biomarkers are exploited to identify the right patient population to benefit from the repurposed drugs and drug combinations. Phenotypic screening of chemical libraries has been conducted to search for T-cell-modifying drugs. Genomics and integrated bioinformatics analysis, artificial intelligence, machine and deep learning approaches are employed to identify novel modulators of the immunosuppressive TME.

Emerging Therapies for Breast Cancer

The steady, incremental improvements in outcomes for both early-stage and advanced breast cancer patients are, in large part, attributable to the success of novel systemic therapies. In this review, we discuss key conceptual paradigms that have underpinned this success including (1) targeting the driver: the identification and targeting of major oncoproteins in breast cancers; (2) targeting the lineage pathway: inhibition of those pathways that drive normal mammary epithelial cell proliferation that retain importance in cancer; (3) targeting precisely: the application of molecular classifiers to refine therapy selection for specific cancers, and of antibody-drug conjugates to pinpoint tumor and tumor promoting cells for eradication; and (4) exploiting synthetic lethality: leveraging unique vulnerabilities that cancer-specific molecular alterations induce. We describe promising examples of novel therapies that have been discovered within each of these paradigms and suggest how future drug development efforts might benefit from the continued application of these principles.

Investigating potential immune mechanisms of trilaciclib administered prior to chemotherapy in patients with metastatic triple-negative breast cancer

PURPOSE

In a phase II trial in patients with metastatic triple-negative breast cancer (mTNBC; NCT02978716), administering trilaciclib prior to gemcitabine plus carboplatin (GCb) enhanced T-cell activation and improved overall survival versus GCb alone. The survival benefit was more pronounced in patients with higher immune-related gene expression. We assessed immune cell subsets and used molecular profiling to further elucidate effects on antitumor immunity.

METHODS

Patients with mTNBC and ≤ 2 prior chemotherapy regimens for locally recurrent TNBC or mTNBC were randomized 1:1:1 to GCb on days 1 and 8, trilaciclib prior to GCb on days 1 and 8, or trilaciclib alone on days 1 and 8, and prior to GCb on days 2 and 9. Gene expression, immune cell populations, and Tumor Inflammation Signature (TIS) scores were assessed in baseline tumor samples, with flow cytometric analysis and intracellular and surface cytokine staining used to assess immune cell populations and function.

RESULTS

After two cycles, the trilaciclib plus GCb group (n = 68) had fewer total T cells and significantly fewer CD8+ T cells and myeloid-derived suppressor cells compared with baseline, with enhanced T-cell effector function versus GCb alone. No significant differences were observed in patients who received GCb alone (n = 34). Of 58 patients in the trilaciclib plus GCb group with antitumor response data, 27 had an objective response. RNA sequencing revealed a trend toward higher baseline TIS scores among responders versus non‑responders.

CONCLUSION

The results suggest that administering trilaciclib prior to GCb may modulate the composition and response of immune cell subsets to TNBC.

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.

Short-term immune-checkpoint inhibition partially rescues perturbed bone marrow hematopoiesis in mismatch-repair deficient tumors

Wide-spread cancer-related immunosuppression often curtails immune-mediated antitumoral responses. Immune-checkpoint inhibitors (ICIs) have become a state-of-the-art treatment modality for mismatch repair-deficient (dMMR) tumors. Still, the impact of ICI-treatment on bone marrow perturbations is largely unknown. Using anti-PD1 and anti-LAG-3 ICI treatments, we here investigated the effect of bone marrow hematopoiesis in tumor-bearing Msh2loxP/loxP;TgTg(Vil1-cre) mice. The OS under anti-PD1 antibody treatment was 7.0 weeks (vs. 3.3 weeks and 5.0 weeks, control and isotype, respectively). In the anti-LAG-3 antibody group, OS was 13.3 weeks and thus even longer than in the anti-PD1 group (p = 0.13). Both ICIs induced a stable disease and reduced circulating and splenic regulatory T cells. In the bone marrow, a perturbed hematopoiesis was identified in tumor-bearing control mice, which was partially rescued by ICI treatment. In particular, B cell precursors and innate lymphoid progenitors were significantly increased upon anti-LAG-3 therapy to levels seen in tumor-free control mice. Additional normalizing effects of ICI treatment were observed for lin-c-Kit+IRF8+ hematopoietic stem cells, which function as a "master" negative regulator of the formation of polymorphonuclear-myeloid-derived suppressor cell generation. Accompanying immunofluorescence on the TME revealed significantly reduced numbers of CD206+F4/80+ and CD163+ tumor-associated M2 macrophages and CD11b+Gr1+ myeloid-derived suppressor cells especially upon anti-LAG-3 treatment. This study confirms the perturbed hematopoiesis in solid cancer. Anti-LAG-3 treatment partially restores normal hematopoiesis. The interference of anti-LAG-3 with suppressor cell populations in otherwise inaccessible niches renders this ICI very promising for subsequent clinical application.

Picking up speed: cell cycle regulation during effector CD8+ T cell differentiation

Clonal expansion and development of immunological memory are two hallmarks of adaptive immune responses. Resolving the intricate pathways that regulate cell cycle activity and lead to the generation of diverse effector and memory T cell subsets is essential for improving our understanding of protective T cell immunity. A deeper knowledge of cell cycle regulation in T cells also has translational implications for adoptive cell therapies and vaccinations against infectious diseases. Here, we summarize recent evidence for an early diversification of effector and memory CD8⁺ T cell fates and discuss how this process is coupled to discrete changes in division speed. We further review technical advances in lineage tracing and cell cycle analysis and outline how these techniques have shed new light on the population dynamics of CD8⁺ T cell responses, thereby refining our current understanding of the developmental organization of the memory T cell pool.

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.

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.

Targeting protein tyrosine phosphatases for CDK6-induced immunotherapy resistance

Elucidating the mechanisms of resistance to immunotherapy and developing strategies to improve its efficacy are challenging goals. Bioinformatics analysis demonstrates that high CDK6 expression in melanoma is associated with poor progression-free survival of patients receiving single-agent immunotherapy. Depletion of CDK6 or cyclin D3 (but not of CDK4, cyclin D1, or D2) in cells of the tumor microenvironment inhibits tumor growth. CDK6 depletion reshapes the tumor immune microenvironment, and the host anti-tumor effect depends on cyclin D3/CDK6-expressing CD8+ and CD4+ T cells. This occurs by CDK6 phosphorylating and increasing the activities of PTP1B and T cell protein tyrosine phosphatase (TCPTP), which, in turn, decreases tyrosine phosphorylation of CD3ζ, reducing the signal transduction for T cell activation. Administration of a PTP1B and TCPTP inhibitor prove more efficacious than using a CDK6 degrader in enhancing T cell-mediated immunotherapy. Targeting protein tyrosine phosphatases (PTPs) might be an effective strategy for cancer patients who resist immunotherapy treatment.

PD-1 blockade and CDK4/6 inhibition augment nonoverlapping features of T cell activation in cancer

We performed single-cell RNA-sequencing and T cell receptor clonotype tracking of breast and ovarian cancer patients treated with the CDK4/6 inhibitor ribociclib and PD-1 blockade. We highlight evidence of two orthogonal treatment-associated phenomena: expansion of T cell effector populations and promotion of T cell memory formation. Augmentation of the antitumor memory pool by ribociclib boosts the efficacy of subsequent PD-1 blockade in mouse models of melanoma and breast cancer, pointing toward sequential therapy as a potentially safe and synergistic strategy in patients.

Discordant Humoral and T-Cell Response to mRNA SARS-CoV-2 Vaccine and the Risk of Breakthrough Infections in Women with Breast Cancer, Receiving Cyclin-Dependent Kinase 4 and 6 Inhibitors

Few data are available about the immune response to mRNA SARS-CoV-2 vaccines in patients with breast cancer receiving cyclin-dependent kinase 4/6 inhibitors (CDK4/6i). We conducted a prospective, single-center study of patients with breast cancer treated with CDK4/6i who received mRNA-1273 vaccination, as well as a comparative group of healthcare workers. The primary endpoint was to compare the rate and magnitude of humoral and T-cell response after full vaccination. A better neutralizing antibody and anti-S IgG level was observed after vaccination in the subgroup of women receiving CDK4/6i, but a trend toward a reduced CD4 and CD8 T-cell response in the CDK4/6i group was not statistically significant. There were no differences in the rate of COVID-19 after vaccination (19% vs. 12%), but breakthrough infections were observed in those with lower levels of anti-S IgG and neutralizing antibodies after the first dose. A lower rate of CD4 T-cell response was also found in those individuals with breakthrough infections, although a non-significant and similar level of CD8 T-cell response was also observed, regardless of breakthrough infections. The rate of adverse events was higher in patients treated with CDK4/6i, without serious adverse events. In conclusion, there was a robust humoral response, but a blunted T-cell response to mRNA vaccine in women receiving CDK4/6i, suggesting a reduced trend of the adaptative immune response.

Drug-tolerant persister B-cell precursor acute lymphoblastic leukemia cells

Reduced responsiveness of precursor B-acute lymphoblastic leukemia (BCP-ALL) to chemotherapy can be inferred when leukemia cells persist after 28 days of initial treatment. Survival of these long-term persister (LTP) / minimal residual disease (MRD) cells is partly due to bone marrow stromal cells that protect them under conditions of chemotherapy stress. We used RNA-seq to analyse BCP-ALL cells that survived a long-term, 30-day vincristine chemotherapy treatment while in co-culture with bone marrow stromal cells. RNAs of as many as 10% of the protein-encoding genes were differentially expressed. There was substantial overlap with genes associated with MRD cell persistence reported in other studies. The top pathway regulated in the LTP cells was that involving p53, a master regulator of a spectrum of responses relevant to drug resistance and cytotoxic drug exposure including control of autophagy. We tested a select number of genes for contribution to BCP-ALL cell survival using Cas9/CRISPR in a 2-step selection, initially for overall effect on cell fitness, followed by 21 days of exposure to vincristine. Many genes involved in autophagy and lysosomal function were found to contribute to survival both at steady-state and during drug treatment. We also identified MYH9, NCSTN and KIAA2013 as specific genes contributing to fitness of BCP-ALL cells. CD44 was not essential for growth under steady state conditions but was needed for survival of vincristine treatment. Finally, although the drug transporter ABCC1/MRP1 is not overexpressed in BCP-ALL, a functional gene was needed for DTP cells to survive treatment with vincristine. This suggests that addition of possible ABCC1 inhibitors during induction therapy could provide benefit in eradication of minimal residual disease in patients treated with a chemotherapy regimen that includes vincristine.

A Proactive Approach to Prevent Hematopoietic Exhaustion During Cancer Chemotherapy in Older Patients: Temporary Cell-Cycle Arrest

Age is associated with the decline of multiple organ systems. In older patients, hematological toxicities associated with chemotherapy are often dose limiting, impairing dose intensity and treatment efficacy. Contrary to the classical path using growth factors to activate tissue regeneration, a novel strategy is emerging to prevent chemotherapy toxicity that involves temporary cell-cycle arrest of normal cells, such as hematopoietic or epithelial precursors. This proactive approach may allow the sparing of the stem cell reserve of these tissues. Two molecules are included in this new category, trilaciclib and ALRN-6924, which induce cell-cycle arrest by two different pathways. Previous approaches, such as the use of myelopoietic growth factors, were reactive and they might even have accelerated the depletion of stem cells by enhancing the commitment of these elements. Trilaciclib causes cell-cycle arrest by CDK 4/6 inhibition and ALRN-6924 by p53 activation. In a pooled analysis of three randomized phase II studies of patients with small cell lung cancer, trilaciclib prevented neutropenia, thrombocytopenia, and anemia. Similar chemoprotective results were observed with ALRN-6924 in an open-label phase Ib study of patients with p53-mutated small cell lung cancer. Trilaciclib is now approved as a myelopreservation agent in patients with extensive-stage small cell lung cancer. ALRN-6924 is currently in phase Ib clinical development in patients with p53-mutated cancer. In addition to preserving the normal hemopoietic pool, these drugs promise to preserve the stem cell reserve of other normal tissues with high turnover, preventing potentially other dose-limiting toxicities, such as mucositis and diarrhea. An "ex vivo" study provided early evidence that ALRN-6924 may prevent chemotherapy-induced alopecia. By affording protection from multiple toxicities with a single drug, trilaciclib and ALRN-6924 have the potential to transform the current standards of supportive care for oncology patients and may prevent the depletion of tissue stem cells already compromised with age.

Palbociclib impairs the proliferative capacity of activated T cells while retaining their cytotoxic efficacy

The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor palbociclib is an emerging cancer therapeutic that just recently gained Food and Drug Administration approval for treatment of estrogen receptor (ER)-positive, human epidermal growth factor receptor (Her)2-negative breast cancer in combination with the ER degrader fulvestrant. However, CDK4/6 inhibitors are not cancer-specific and may affect also other proliferating cells. Given the importance of T cells in antitumor defense, we studied the influence of palbociclib/fulvestrant on human CD3+ T cells and novel emerging T cell-based cancer immunotherapies. Palbociclib considerably inhibited the proliferation of activated T cells by mediating G0/G1 cell cycle arrest. However, after stopping the drug supply this suppression was fully reversible. In light of combination approaches, we further investigated the effect of palbociclib/fulvestrant on T cell-based immunotherapies by using a CD3-PSCA bispecific antibody or universal chimeric antigen receptor (UniCAR) T cells. Thereby, we observed that palbociclib clearly impaired T cell expansion. This effect resulted in a lower total concentration of interferon-γ and tumor necrosis factor, while palbociclib did not inhibit the average cytokine release per cell. In addition, the cytotoxic potential of the redirected T cells was unaffected by palbociclib and fulvestrant. Overall, these novel findings may have implications for the design of treatment modalities combining CDK4/6 inhibition and T cell-based cancer immunotherapeutic strategies.

CDK4/6 blockade provides an alternative approach for treatment of mismatch-repair deficient tumors

Mismatch repair-deficient (dMMR) tumors show a good response toward immune checkpoint inhibitors (ICI), but developing resistance impairs patients’ outcomes. Here, we compared the therapeutic potential of an α-PD-L1 antibody with the CDK4/6 inhibitor abemaciclib in two preclinical mouse models of dMMR cancer, focusing on immune-modulatory effects of either treatment. Abemaciclib monotherapy significantly prolonged overall survival of Mlh1^−/− and Msh2^{loxP/loxP;TgTg(Vil1-cre)} mice (Mlh1^−/−: 14.5 wks vs. 9.0 wks (α-PD-L1), and 3.5 wks (control); Msh2^{loxP/loxP;TgTg(Vil1-cre)}: 11.7 wks vs. 9.6 wks (α-PD-L1), and 2.0 wks (control)). The combination was not superior to either monotherapy. PET/CT imaging revealed individual response profiles, with best clinical responses seen with abemaciclib mono- and combination therapy. Therapeutic effects were accompanied by increasing numbers of tumor-infiltrating CD4⁺/CD8⁺ T-cells and lower numbers of M2-macrophages. Levels of T cell exhaustion markers and regulatory T cell counts declined. Expression analysis identified higher numbers of dendritic cells and neutrophils within tumors together with high expression of DNA damage repair genes as part of the global stress response. In Mlh1^−/− tumors, abemaciclib suppressed the PI3K/Akt pathway and led to induction of Mxd4/Myc. The immune-modulatory potential of abemaciclib renders this compound ideal for dMMR patients not eligible for ICI treatment.

Repurposing of Commercially Existing Molecular Target Therapies to Boost the Clinical Efficacy of Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) is now standard of care for several metastatic epithelial cancers and prolongs life expectancy for a significant fraction of patients. A hostile tumor microenvironment (TME) induced by intrinsic oncogenic signaling induces an immunosuppressive niche that protects the tumor cells, limiting the durability and efficacy of ICB therapies. Addition of receptor tyrosine kinase inhibitors (RTKi) as potential modulators of an unfavorable local immune environment has resulted in moderate life expectancy improvement. Though the combination strategy of ICB and RTKi has shown significantly better results compared to individual treatment, the benefits and adverse events are additive whereas synergy of benefit would be preferable. There is therefore a need to investigate the potential of inhibitors other than RTKs to reduce malignant cell survival while enhancing anti-tumor immunity. In the last five years, preclinical studies have focused on using small molecule inhibitors targeting cell cycle and DNA damage regulators such as CDK4/6, CHK1 and poly ADP ribosyl polymerase (PARP) to selectively kill tumor cells and enhance cytotoxic immune responses. This review provides a comprehensive overview of the available drugs that attenuate immunosuppression and overcome hostile TME that could be used to boost FDA-approved ICB efficacy in the near future.

New Advances in Supportive Care: Chemoprotective Agents as Novel Opportunities in Geriatric Oncology

PURPOSE OF REVIEW

To explore the effectiveness of trilaciclib and ALRN-6924 in the prevention of cancer chemotherapy-induced toxicity in older patients. New chemoprotective agents are necessary because age is the main risk factor for chemotherapy complications that account largely for the poorer outcome of cancer in the elderly. Trilaciclib and ALRN-6924 cause a reversible block of the proliferation of normal cells through cell cycle arrest (CCA). With this mechanism, they may prevent the toxicity of cycle-active cancer treatment including neutropenia, anemia, thrombocytopenia, lymphopenia, mucositis, and alopecia.

RECENT FINDINGS

Myelopoietic growth factors may prevent neutropenia in the aged, but they may cause severe bone pain, may aggravate thrombocytopenia and anemia, and may cause myelodysplasia and acute leukemia as a late complication. The prevention of thrombocytopenia, anemia, mucositis, and alopecia is unsatisfactory at present. These complications may jeopardize the treatment outcome as they require a reduction of treatment dose/intensity and because many patients find the resulting symptoms intolerable. In three studies of patients with extensive disease small cell lung cancer (ES-SCLC), trilaciclib reduced the severity and duration of neutropenia and thrombocytopenia as well as the need for blood transfusions. In addition, it produced a significant expansion of T-cell clones. Trilaciclib received FDA approval for the prevention of chemotherapy-induced myelosuppression in patients with ES-SCLC. ALRN-6924 is currently studied in phase II study of ES-SCLC. In a phase IB of 38 patients, ALRN-6924 prevented myelosuppression to an extent comparable with trilaciclib. Both drugs proved as effective in patients 65 and older as they were in the younger ones. In an "ex vivo" study, ALRN-6924 protected the epithelial stem cells of hair follicles from taxanes and promised to prevent alopecia. The possibility that CCA of tumor cells may reduce the effectiveness of cycle-active chemotherapy is a major concern. For this reason, the use of trilaciclib, an inhibitor of CDK 4/6, should be limited to tumors with inactivated RB1, and the use of ALRN-6924, an inhibitor of P53, should be limited to tumors with inactivated P53. Chemotherapy-related toxicities limit dose intensity and contribute to significant morbidity and mortality in elderly cancer patients. Trilaciclib and ALRN-6924 are of particular interest to geriatric oncologists because of their novel mechanism of action. Ameliorating chemotherapy-induced toxicities holds the promise of transforming the practice of geriatric oncology by enabling chemotherapeutic regimens that are currently not feasible for this patient population. Specifically, these agents may prevent chemotherapy-induced neutropenia and thrombocytopenia, perhaps the most life-threatening complications of cytotoxic chemotherapy, thereby obviating the need for the use of rescue strategies such as hematopoietic growth factors. In addition, these agents offer the potential for broad tissue protection from other chemotherapy-related toxicities, including mucositis, diarrhea, and alopecia, which historically have been poorly managed. Importantly, by preventing a spectrum of chemotherapy-related toxicities, these agents may permit the administration of chemotherapy at full-dose intensity, prevent functional decline, and grant maintenance of resilience to older cancer patients. As a result, the successful prevention of chemotherapy-induced side effects may not only mitigate the costs of care but also improve patient outcomes and quality of life. Finally, chemoprotective strategies offer the opportunity to apply geriatric principles to clinical trials of cancer treatment. In particular, they may allow the testing of prolongation of "active life expectancy" as a major goal of clinical trials in elderly patients. They may also enable novel and more practical forms of clinical trials. By assessing the risk of chemotherapy-related toxicity with the Chemotherapy Risk Assessment Scale for High Age Patients (CRASH) or the Cancer and Aging Research Group (CARG) instruments, these agents may permit researchers to utilize patients as their own controls and endorse the approval of supportive care drugs based upon the risk profile of individual patients.

A CRISPR Path to Finding Vulnerabilities and Solving Drug Resistance: Targeting the Diverse Cancer Landscape and Its Ecosystem

Cancer is the second leading cause of death globally, with therapeutic resistance being a major cause of treatment failure in the clinic. The dynamic signaling that occurs between tumor cells and the diverse cells of the surrounding tumor microenvironment actively promotes disease progression and therapeutic resistance. Improving the understanding of how tumors evolve following therapy and the molecular mechanisms underpinning de novo or acquired resistance is thus critical for the identification of new targets and for the subsequent development of more effective combination regimens. Simultaneously targeting multiple hallmark capabilities of cancer to circumvent adaptive or evasive resistance may lead to significantly improved treatment response in the clinic. Here, the latest applications of functional genomics tools, such as clustered regularly interspaced short palindromic repeats (CRISPR) editing, to characterize the dynamic cancer resistance mechanisms, from improving the understanding of resistance to classical chemotherapeutics, to deciphering unique mechanisms that regulate tumor responses to new targeted agents and immunotherapies, are discussed. Potential avenues of future research in combating therapeutic resistance, the contribution of tumor-stroma signaling in this setting, and how advanced functional genomics tools can help streamline the identification of key molecular determinants of drug response are explored.

Signaling pathways and targeted therapies in lung squamous cell carcinoma: mechanisms and clinical trials

Lung cancer is the leading cause of cancer-related death across the world. Unlike lung adenocarcinoma, patients with lung squamous cell carcinoma (LSCC) have not benefitted from targeted therapies. Although immunotherapy has significantly improved cancer patients' outcomes, the relatively low response rate and severe adverse events hinder the clinical application of this promising treatment in LSCC. Therefore, it is of vital importance to have a better understanding of the mechanisms underlying the pathogenesis of LSCC as well as the inner connection among different signaling pathways, which will surely provide opportunities for more effective therapeutic interventions for LSCC. In this review, new insights were given about classical signaling pathways which have been proved in other cancer types but not in LSCC, including PI3K signaling pathway, VEGF/VEGFR signaling, and CDK4/6 pathway. Other signaling pathways which may have therapeutic potentials in LSCC were also discussed, including the FGFR1 pathway, EGFR pathway, and KEAP1/NRF2 pathway. Next, chromosome 3q, which harbors two key squamous differentiation markers SOX2 and TP63 is discussed as well as its related potential therapeutic targets. We also provided some progress of LSCC in epigenetic therapies and immune checkpoints blockade (ICB) therapies. Subsequently, we outlined some combination strategies of ICB therapies and other targeted therapies. Finally, prospects and challenges were given related to the exploration and application of novel therapeutic strategies for LSCC.

Redirecting the Neo-Substrate Specificity of Cereblon-Targeting PROTACs to Helios

Immunomodulatory imide drugs (IMiDs), such as thalidomide and its analogues, are some of the most commonly utilized E3 ligase ligands for the development of proteolysis targeting chimeras (PROTACs). While the canonical neo-substrates of IMiDs (i.e., Ikaros and Aiolos) are often considered to be unwanted targets of PROTACs, maintaining the degradation of these neo-substrates also provides the opportunity to synergistically degrade multiple proteins with a single compound. Here, we report the development of ALV-07-082-03, a CDK4/CDK6/Helios triple degrader that consists of palbociclib, an FDA-approved CDK4/6 inhibitor, conjugated to DKY709, a novel IMiD-based Helios degrader. Pharmacological codegradation of CDK4/6 and Helios resulted in potent suppression of downstream signaling and proliferation in cancer cells, as well as enhanced derepression of IL-2 secretion. Thus, not only do we demonstrate the possibility of rationally redirecting the neo-substrate specificity of PROTACs by incorporating alternative molecular glue molecules as E3 ligase ligands but our findings also suggest that cotargeting CDK4/6 and Helios may have synergistic effects.

Mechanisms of tumor resistance to immune checkpoint blockade and combination strategies to overcome resistance

Immune checkpoint blockade (ICB) has rapidly transformed the treatment paradigm for various cancer types. Multiple single or combinations of ICB treatments have been approved by the US Food and Drug Administration, providing more options for patients with advanced cancer. However, most patients could not benefit from these immunotherapies due to primary and acquired drug resistance. Thus, a better understanding of the mechanisms of ICB resistance is urgently needed to improve clinical outcomes. Here, we focused on the changes in the biological functions of CD8⁺ T cells to elucidate the underlying resistance mechanisms of ICB therapies and summarized the advanced coping strategies to increase ICB efficacy. Combinational ICB approaches and individualized immunotherapies require further in-depth investigation to facilitate longer-lasting efficacy and a more excellent safety of ICB in a broader range of patients.

Tissue-adhesive hydrogel for multimodal drug release to immune cells in skin

Both innate and adaptive immune systems play a crucial role in the pathology of skin diseases. To control these cells, there is a need for transdermal drug delivery systems that can target multiple cell populations at independently tunable rates. Herein, we describe a tissue-adhesive hydrogel system that contains particles capable of regulating the release of small molecule drugs at defined rates. Resiquimod (a macrophage-targeting drug) and palbociclib (a T cell-targeting drug) are encapsulated within two types of silicone particles embedded within the hydrogel. We demonstrate that drug release is mediated by the crosslink density of the particles, which is decoupled from the bulk properties of the hydrogel. We show that this system can be used to sustainably polarize macrophages toward an anti-tumor phenotype in vitro and ex vivo, and that the hydrogels can remain attached to skin explants for several days without generating toxicity. The hydrogel system is compatible with standard dermatological procedures and allows transdermal passage of drugs. The multimodal, tunable nature of this system has implications in treating a variety of skin disorders, managing infections, and delivering vaccines. STATEMENT OF SIGNIFICANCE: We describe a tissue-adhesive hydrogel that can regulate the release of drugs in a manner that is decoupled from its bulk properties. The mechanism of drug release is mediated by embedded microparticles with well-defined crosslink densities. The significance of this system is that, by encapsulating different drugs into the particles, it is possible to achieve multimodal drug release. We demonstrate this capability by releasing two immunomodulatory drugs at disparate rates. A drug that targets innate immune cells is released quickly, and a drug that targets adaptive immune cells is released slowly. This programmable system offers a direct means by which cellular responses can be enhanced through independent targeting for a variety of transdermal applications, including cancer treatment and vaccine delivery.

Senescence and cancer - role and therapeutic opportunities

Cellular senescence is a state of stable, terminal cell cycle arrest associated with various macromolecular changes and a hypersecretory, pro-inflammatory phenotype. Entry of cells into senescence can act as a barrier to tumorigenesis and, thus, could in principle constitute a desired outcome for any anticancer therapy. Paradoxically, studies published in the past decade have demonstrated that, in certain conditions and contexts, malignant and non-malignant cells with lastingly persistent senescence can acquire pro-tumorigenic properties. In this Review, we first discuss the major mechanisms involved in the antitumorigenic functions of senescent cells and then consider the cell-intrinsic and cell-extrinsic factors that participate in their switch towards a tumour-promoting role, providing an overview of major translational and emerging clinical findings. Finally, we comprehensively describe various senolytic and senomorphic therapies and their potential to benefit patients with cancer.

The entry of cells into senescence can act as a barrier to tumorigenesis; however, in certain contexts senescent malignant and non-malignant cells can acquire pro-tumorigenic properties. The authors of this Review discuss the cell-intrinsic and cell-extrinsic mechanisms involved in both the antitumorigenic and tumour-promoting roles of senescent cells, and describe the potential of various senolytic and senomorphic therapeutic approaches in oncology.

Cellular senescence is a natural barrier to tumorigenesis; senescent cells are widely detected in premalignant lesions from patients with cancer.

Cellular senescence is induced by anticancer therapy and can contribute to some treatment-related adverse events (TRAEs).

Senescent cells exert both protumorigenic and antitumorigenic effects via cell-autonomous and paracrine mechanisms.

Pharmacological modulation of senescence-associated phenotypes has the potential to improve therapy efficacy and reduce the incidence of TRAEs.

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.

Targeting CDK4 and 6 in Cancer Therapy: Emerging Preclinical Insights Related to Abemaciclib

Pharmacologic inhibitors of cyclin-dependent kinases 4 and 6 (CDK4 and 6) are approved for the treatment of subsets of patients with hormone receptor positive (HR+) breast cancer (BC). In metastatic disease, strategies involving endocrine therapy combined with CDK4 and 6 inhibitors (CDK4 and 6i) improve clinical outcomes in HR+ BCs. CDK4 and 6i prevent retinoblastoma tumor suppressor protein phosphorylation, thereby blocking the transcription of E2F target genes, which in turn inhibits both mitogen and estrogen-mediated cell proliferation. In this review, we summarize preclinical data pertaining to the use of CDK4 and 6i in BC, with a particular focus on several of the unique chemical, pharmacologic, and mechanistic properties of abemaciclib. As research efforts elucidate the novel mechanisms underlying abemaciclib activity, potential new applications are being identified. For example, preclinical studies have demonstrated abemaciclib can exert antitumor activity against multiple tumor types and can cross the blood-brain barrier. Abemaciclib has also demonstrated distinct activity as a monotherapeutic in the treatment of BC. Accordingly, we also discuss how a greater understanding of mechanisms related to CDK4 and 6 blockade highlight abemaciclib's unique in-class properties, and could pave new avenues for enhancing its therapeutic efficacy.

Divide and Conquer: Phenotypic and Temporal Heterogeneity Within CD8+ T Cell Responses

The advent of technologies that can characterize the phenotypes, functions and fates of individual cells has revealed extensive and often unexpected levels of diversity between cells that are nominally of the same subset. CD8⁺ T cells, also known as cytotoxic T lymphocytes (CTLs), are no exception. Investigations of individual CD8⁺ T cells both in vitro and in vivo have highlighted the heterogeneity of cellular responses at the levels of activation, differentiation and function. This review takes a broad perspective on the topic of heterogeneity, outlining different forms of variation that arise during a CD8⁺ T cell response. Specific attention is paid to the impact of T cell receptor (TCR) stimulation strength on heterogeneity. In particular, this review endeavors to highlight connections between variation at different cellular stages, presenting known mechanisms and key open questions about how variation between cells can arise and propagate.

Cyclin-dependent kinase inhibition and its intersection with immunotherapy in breast cancer: more than CDK4/6 inhibition

INTRODUCTION

Cyclin-dependent kinase (CDK) 4/6 inhibitors (CDK4/6i) have had clinical success in treating hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer. Notably, CDK4/6i have expanded to the neoadjuvant setting for early breast cancer and other cancer types and potently synergize with immunotherapy. Other CDKs, including CDK7, CDK9, and CDK12/13, mainly function in transcriptional processes as well as cell cycle regulation, RNA splicing, and DNA damage response. Inhibiting these CDKs aids in suppressing tumors, reversing drug resistance, increasing drug sensitivity, and enhancing anti-tumor immunity in breast cancer.

AREAS COVERED

We reviewed the applications of CDK4/6i, CDK7i, CDK9i and CDK12/13i for various breast cancer subtypes and their potentials for combination with immunotherapy. A literature search of PubMed, Embase, and Web of Science was conducted in April 2022.

EXPERT OPINION

The use of CDK4/6i represents a major milestone in breast cancer treatment. Moreover, transcription-related CDKs play critical roles in tumor development and are promising therapeutic targets for breast cancer. Some relevant clinical studies are underway. More specific and efficient CDKis will undoubtedly be developed and clinically tested. Characterization of their immune-priming effects will promote the development of combination therapies consisting of CDKi and immunotherapy.

Targeting CDK4 and CDK6 in cancer

Cyclin-dependent kinase 4 (CDK4) and CDK6 are critical mediators of cellular transition into S phase and are important for the initiation, growth and survival of many cancer types. Pharmacological inhibitors of CDK4/6 have rapidly become a new standard of care for patients with advanced hormone receptor-positive breast cancer. As expected, CDK4/6 inhibitors arrest sensitive tumour cells in the G1 phase of the cell cycle. However, the effects of CDK4/6 inhibition are far more wide-reaching. New insights into their mechanisms of action have triggered identification of new therapeutic opportunities, including the development of novel combination regimens, expanded application to a broader range of cancers and use as supportive care to ameliorate the toxic effects of other therapies. Exploring these new opportunities in the clinic is an urgent priority, which in many cases has not been adequately addressed. Here, we provide a framework for conceptualizing the activity of CDK4/6 inhibitors in cancer and explain how this framework might shape the future clinical development of these agents. We also discuss the biological underpinnings of CDK4/6 inhibitor resistance, an increasingly common challenge in clinical oncology.

Molecular Characteristics, Oncogenic Roles, and Relevant Immune and Pharmacogenomic Features of EVA1B in Colorectal Cancer

OBJECTIVE

EVA1B, a protein coding gene, is a critical paralog of EVA1A gene. Herein, our study was conducted to investigate the role of EVA1B in colorectal cancer (CRC) progression and prognosis.

METHODS

Pan-cancer analysis was conducted to analyze expression, genetic and epigenetic alterations, and immunological characteristics of EVA1B. Especially, immunological characteristics and mutational landscape were compared between high and low EVA1B expression groups in the combined TCGA-COAD and TCGA-READ datasets. Through random survival forest analysis, an EVA1B-derived genomic model was developed, and its prognostic value was verified in the external datasets (GSE14333, GSE39582, and GSE87211). Drug sensitivity was compared between high- and low-risk subpopulations. A nomogram was conducted through integrating independent factors.

RESULTS

EVA1B expression presented a remarkable upregulation in most cancer types, especially CRC. EVA1B expression was significantly correlated to DNA methyltransferases, DNA mismatch repair genes, m⁶A regulators, TMB, and MSI across pan-cancer. High EVA1B expression indicated an undesirable CRC patients' prognosis. Additionally, its upregulation was correlated to enhanced immune cell infiltration, increased stromal and immune activation, and elevated activities of cancer immunity cycle. Higher frequencies of amplification and deletion were investigated in high EVA1B expression subpopulation. Following verification, the EVA1B-derived genomic model reliably predicted patients' prognosis and drug responses. The nomogram (age, stage, EVA1B-derived risk score) was conducted to quantify an individual's survival probability. Furthermore, our experimental validation based on immunohistochemistry indicated that EVA1B overexpression is correlated with CRC tumorigenesis and poor outcomes in our CRC patients' cohort.

CONCLUSION

Collectively, our findings provided valuable resource for guiding the mechanisms and therapeutic analysis of EVA1B in CRC.

CDC25C as a Predictive Biomarker for Immune Checkpoint Inhibitors in Patients With Lung Adenocarcinoma

The application of immune checkpoint inhibitors (ICIs) in non-small cell lung cancer has significantly improved patient survival. However, most patients fail to respond to ICIs or develop drug resistance during treatment. Therefore, novel biomarkers are needed to predict the efficacy of ICIs or provide clues on how to overcome drug resistance. Here, it was revealed that cell division cycle 25C (CDC25C) expression was upregulated in lung adenocarcinoma (LUAD) compared to that of normal lung tissue in multiple databases. This was further verified by q-PCR. Furthermore, higher CDC25C expression was associated with shorter overall survival and worse pathological stage. Most importantly, a higher CDC25C expression was associated with shorter progression-free survival in LUAD patients treated with nivolumab, suggesting the role of the cell cycle in immunotherapy. In addition, CDC25C expression was significantly associated with immune cell infiltration and immune-related signatures in the LUAD tumor microenvironment. Moreover, CDC25C was differentially expressed and correlated with overall survival in multiple tumors, indicating that CDC25C is a broad-spectrum biomarker. Taken together, our study demonstrates that CDC25C is a prognostic biomarker for LUAD patients, especially for patients treated with ICIs. Our study also provides strong evidence for the role of the cell cycle in ICIs therapy and tumor microenvironment.

Harnessing the immunotherapeutic potential of CDK4/6 inhibitors in melanoma: is timing everything?

CDK4/6 inhibitors (CDK4/6i) were developed as a cancer therapeutic on the basis of their tumor-intrinsic cytostatic potential, but have since demonstrated profound activity as immunomodulatory agents. While currently approved to treat hormone receptor-positive breast cancer, these inhibitors are under investigation in clinical trials as treatments for a range of cancer types, including melanoma. Melanoma is a highly immunogenic cancer, and has always been situated at the forefront of cancer immunotherapy development. Recent revelations into the immunotherapeutic activity of CDK4/6i, therefore, have significant implications for the utility of these agents as melanoma therapies. In recent studies, we and others have proven the immunomodulatory effects of CDK4/6i to be multifaceted and complex. Among the most notable effects, CDK4/6 inhibition induces transcriptional reprogramming in both tumor cells and immune cells to enhance tumor cell immunogenicity, promote an immune-rich tumor microenvironment, and skew T cell differentiation into a stem-like phenotype that is more amenable to immune checkpoint inhibition. However, in some contexts, the specific immunomodulatory effects of CDK4/6i may impinge on anti-tumor immunity. For example, CDK4/6 inhibition restricts optimal T cells expansion, and when used in combination with BRAF/MEK-targeted therapies, depletes immune-potentiating myeloid subsets from the tumor microenvironment. We propose that such effects, both positive and negative, may be mitigated or exacerbated by altering the CDK4/6i dosing regimen. Here, we discuss what the most recent insights mean for clinical trial design, and propose clinical considerations and strategies that may exploit the full immunotherapeutic potential of CDK4/6 inhibitors.

Targeting oncogene and non-oncogene addiction to inflame the tumour microenvironment

Immune checkpoint inhibitors (ICIs) have revolutionized the clinical management of multiple tumours. However, only a few patients respond to ICIs, which has generated considerable interest in the identification of resistance mechanisms. One such mechanism reflects the ability of various oncogenic pathways, as well as stress response pathways required for the survival of transformed cells (a situation commonly referred to as 'non-oncogene addiction'), to support tumour progression not only by providing malignant cells with survival and/or proliferation advantages, but also by establishing immunologically 'cold' tumour microenvironments (TMEs). Thus, both oncogene and non-oncogene addiction stand out as promising targets to robustly inflame the TME and potentially enable superior responses to ICIs.

Cellular mechanisms underlying response and resistance to CDK4/6 inhibitors in the treatment of hormone receptor-positive breast cancer

Pharmacological inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) are now an established standard of care for patients with advanced hormone receptor-positive breast cancer. The canonical mechanism underlying CDK4/6 inhibitor activity is the suppression of phosphorylation of the retinoblastoma tumor suppressor protein, which serves to prevent cancer cell proliferation. Recent data suggest that these agents induce other diverse effects within both tumor and stromal compartments, which serve to explain aspects of their clinical activity. Here, we review these phenomena and discuss how they might be leveraged in the development of novel CDK4/6 inhibitor-containing combination treatments. We also briefly review the various known mechanisms of acquired resistance in the clinical setting.