Tailored first-line and second-line CDK4-targeting treatment combinations in mouse models of pancreatic cancer

A stumbling block in pancreatic cancer treatment: drug resistance signaling networks

The primary node molecules in the cell signaling network in cancer tissues are maladjusted and mutated in comparison to normal tissues, which promotes the occurrence and progression of cancer. Pancreatic cancer (PC) is a highly fatal cancer with increasing incidence and low five-year survival rates. Currently, there are several therapies that target cell signaling networks in PC. However, PC is a "cold tumor" with a unique immunosuppressive tumor microenvironment (poor effector T cell infiltration, low antigen specificity), and targeting a single gene or pathway is basically ineffective in clinical practice. Targeted matrix therapy, targeted metabolic therapy, targeted mutant gene therapy, immunosuppressive therapy, cancer vaccines, and other emerging therapies have shown great therapeutic potential, but results have been disappointing. Therefore, we summarize the identified and potential drug-resistant cell signaling networks aimed at overcoming barriers to existing PC therapies.

Temporally resolved proteomics identifies nidogen-2 as a cotarget in pancreatic cancer that modulates fibrosis and therapy response

Pancreatic ductal adenocarcinoma (PDAC) is characterized by increasing fibrosis, which can enhance tumor progression and spread. Here, we undertook an unbiased temporal assessment of the matrisome of the highly metastatic KPC (Pdx1-Cre, LSL-KrasG12D/+, LSL-Trp53R172H/+) and poorly metastatic KPflC (Pdx1-Cre, LSL-KrasG12D/+, Trp53fl/+) genetically engineered mouse models of pancreatic cancer using mass spectrometry proteomics. Our assessment at early-, mid-, and late-stage disease reveals an increased abundance of nidogen-2 (NID2) in the KPC model compared to KPflC, with further validation showing that NID2 is primarily expressed by cancer-associated fibroblasts (CAFs). Using biomechanical assessments, second harmonic generation imaging, and birefringence analysis, we show that NID2 reduction by CRISPR interference (CRISPRi) in CAFs reduces stiffness and matrix remodeling in three-dimensional models, leading to impaired cancer cell invasion. Intravital imaging revealed improved vascular patency in live NID2-depleted tumors, with enhanced response to gemcitabine/Abraxane. In orthotopic models, NID2 CRISPRi tumors had less liver metastasis and increased survival, highlighting NID2 as a potential PDAC cotarget.

Targeting STAT3 potentiates CDK4/6 inhibitors therapy in head and neck squamous cell carcinoma

Anti-CDK4/6 therapy has been employed for the treatment for head and neck squamous cell carcinoma (HNSCC) with CDK4/6 hyperactivation, but the response rate is relatively low. In this study, we first showed that CDK4 and CDK6 was over-expressed and conferred poor prognosis in HNSCC. Moreover, in RB-positive HNSCC, STAT3 signaling was activated induced by CDK4/6 inhibition and STAT3 promotes RB deficiency by upregulation of MYC. Thirdly, the combination of Stattic and CDK4/6 inhibitor results in striking anti-tumor effect in vitro and in Cal27 derived animal models. Additionally, phospho-STAT3 level negatively correlates with RB expression and predicts poor prognosis in patients with HNSCC. Taken together, our findings suggest an unrecognized function of STAT3 confers to CDK4/6 inhibitors resistance and presenting a promising combination strategy for patients with HNSCC.

Palbociclib inhibits the progression of head and neck cancer and improves the Cetuximab response under specific condition in vitro and in vivo

BACKGROUND

In head and neck squamous cell carcinoma (HNSCC) with human papillomavirus (HPV)-negative, deregulation of cell cycle is partly due to inactivation of p16INK4 and overexpression of cyclin D1. Here we investigated the in vitro and in vivo effects of the CDK4/6 inhibitor Palbociclib alone or combined with EGFR inhibitor Cetuximab in HNSCC.

METHODS AND RESULTS

CCK-8, soft agar assay, colony formation assay, wound healing assay and transwell assay, β-galactosidase assay, western blotting, and cell-derived xenografts were used to investigated the in vitro and in vivo activity of drugs. Cell viability and colony formation decreased in a dose-dependent manner in Tu686, AMC-HN8, and Fadu cells under Palbociclib treatment. Palbociclib remarkably inhibited migration, invasion and the expression MMP-9 in HNSCC cells. Palbociclib also induced senescence. Palbociclib caused the dephosphorylation of RB but increased the cyclin D1 level in a dose-dependent manner. Moreover, combination with Cetuximab could significantly prevent the induction of cyclin D1 and activation of EGFR signals from Palbociclib treatment. Nevertheless, only within the range of certain concentrations, a synergistic inhibitory effect on cell growth was observed when combined with Palbociclib and Cetuximab. Although the synergistic effect in Palbociclib/Cetuximab combined therapy was comparable to that in traditional chemotherapeutic regimens (cisplatin/Cetuximab) in Fadu tumor xenograft, the combination therapy was less active than Cetuximab monotherapy in Tu686 tumor xenograft.

CONCLUSION

In HPV-negative HNSCC, CDK4/6 inhibitor shows promising anti-tumor effects, which exhibits a synergistic effect when combined with EGFR inhibitor only in specific drug concentration and mouse model.

Pharmacological modulation of RB1 activity mitigates resistance to neoadjuvant chemotherapy in locally advanced rectal cancer

Resistance to neoadjuvant chemotherapy leads to poor prognosis of locally advanced rectal cancer (LARC), representing an unmet clinical need that demands further exploration of therapeutic strategies to improve clinical outcomes. Here, we identified a noncanonical role of RB1 for modulating chromatin activity that contributes to oxaliplatin resistance in colorectal cancer (CRC). We demonstrate that oxaliplatin induces RB1 phosphorylation, which is associated with the resistance to neoadjuvant oxaliplatin-based chemotherapy in LARC. Inhibition of RB1 phosphorylation by CDK4/6 inhibitor results in vulnerability to oxaliplatin in both intrinsic and acquired chemoresistant CRC. Mechanistically, we show that RB1 modulates chromatin activity through the TEAD4/HDAC1 complex to epigenetically suppress the expression of DNA repair genes. Antagonizing RB1 phosphorylation through CDK4/6 inhibition enforces RB1/TEAD4/HDAC1 repressor activity, leading to DNA repair defects, thus sensitizing oxaliplatin treatment in LARC. Our study identifies a RB1 function in regulating chromatin activity through TEAD4/HDAC1. It also provides the combination of CDK4/6 inhibitor with oxaliplatin as a potential synthetic lethality strategy to mitigate oxaliplatin resistance in LARC, whereby phosphorylated RB1/TEAD4 can serve as potential biomarkers to guide the patient stratification.

CDKs Functional Analysis in Low Proliferating Early-Stage Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly devastating disease with a poor prognosis and growing incidence. In this study, we explored the potential roles of CDK1, CDK2, CDK4, and CDK6 in the progression of early-stage PDAC. Clinicopathologic and mRNA expression data and treatment information of 140 patients identified with stage I/II PDAC who underwent pancreaticoduodenectomy were obtained from the Cancer Genome Atlas data set. Our bioinformatic analysis showed that higher CDK1, CDK2, CDK4, or CDK6 expression was associated with a shorter median survival of the early-stage PDAC patients. Of note, in the low-proliferating pancreatic cancer group, CDKs expressions were significantly associated with proteins functioning in apoptosis, metastasis, immunity, or stemness. Among the low-proliferating PDAC, higher expression of CDK1 was associated with the shorter survival of patients, suggesting that CDK1 may regulate PDAC progression through cell cycle-independent mechanisms. Our experimental data showed that CDK1 knockdown/inhibition significantly suppressed the expression levels of AHR and POU5F1, two critical proteins functioning in cancer cell metastasis and stemness, in low-proliferating, but not in high-proliferating pancreatic cancer cells. In all, our study suggests that CDKs regulate PDAC progression not only through cell proliferation but also through apoptosis, metastasis, immunity, and stemness.

Novel therapeutic strategies in pancreatic cancer: moving beyond cytotoxic chemotherapy

INTRODUCTION

Prognosis of patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) remains disappointing with a 5-year overall survival of only 3-5%. Compared to other cancers, the evolution in standard therapeutic options has been stagnant and polychemotherapy regimens (with well-known toxicity profile and resistance pattern) remain standard of care. Only for patients (5%-7%) with a breast cancer gene (BRCA) pathogenic germline variant, prognosis has improved by the use of olaparib (poly-ADP ribose polymerase (PARP) inhibitor).

AREAS COVERED

This review covers emerging treatment strategies in the management of mPDAC. One of the main topics is the rigid and immunological cold tumor microenvironment (TME) of PDAC and the search for agents that impact this TME and/or engage the immune system. In addition, the use of next-generation sequencing (NGS) has elicited for some patients new targeted therapies directed at alterations in the RTK/RAS/MAPK pathway and the deoxyribonucleic acid (DNA) damage repair pathway. Other evolving treatment strategies are also discussed.

EXPERT OPINION

The search for new, often combination, treatment strategies for mPDAC should be encouraged and implemented in early treatment lines given the significant decline of performance status of patients in later lines. NGS analysis should be used where available, although cost-effectiveness could be debatable.

Role of neoadjuvant therapy for nonmetastatic pancreatic cancer: Current evidence and future perspectives

Pancreatic adenocarcinoma (PDAC) is one of the most common and lethal human cancers worldwide. Surgery followed by adjuvant chemotherapy offers the best chance of a long-term survival for patients with PDAC, although only approximately 20% of the patients have resectable tumors when diagnosed. Neoadjuvant chemotherapy (NACT) is recommended for borderline resectable pancreatic cancer. Several studies have investigated the role of NACT in treating resectable tumors based on the recent advances in PDAC biology, as NACT provides the potential benefit of selecting patients with favorable tumor biology and controls potential micro-metastases in high-risk patients with resectable PDAC. In such challenging cases, new potential tools, such as ct-DNA and molecular targeted therapy, are emerging as novel therapeutic options that may improve old paradigms. This review aims to summarize the current evidence regarding the role of NACT in treating non-metastatic pancreatic cancer while focusing on future perspectives in light of recent evidence.

SETD4 Confers Cancer Stem Cell Chemoresistance in Nonsmall Cell Lung Cancer Patients via the Epigenetic Regulation of Cellular Quiescence

Increasing evidence indicates that quiescent cancer stem cells (CSCs) are a root cause of chemoresistance. SET domain-containing protein 4 (SETD4) epigenetically regulates cell quiescence in breast cancer stem cells (BCSCs), and SETD4-positive BCSCs are chemoradioresistant. However, the role of SETD4 in chemoresistance, tumor progression, and prognosis in nonsmall cell lung cancer (NSCLC) patients is unclear. Here, SETD4-positive cells were identified as quiescent lung cancer stem cells (qLCSCs) since they expressed high levels of ALDH1 and CD133 and low levels of Ki67. SETD4 expression was significantly higher in advanced-stage NSCLC tissues than in early-stage NSCLC tissues and significantly higher in samples from the chemoresistant group than in those from the chemosensitive group. Patients with high SETD4 expression had shorter progression-free survival (PFS) times than those with low SETD4 expression. SETD4 facilitated heterochromatin formation via H4K20me3, thereby leading to cell quiescence. RNA-seq analysis showed upregulation of genes involved in cell proliferation, glucose metabolism, and PI3K-AKT signaling in activated qLCSCs (A-qLCSCs) compared with qLCSCs. In addition, SETD4 overexpression facilitated PTEN-mediated inhibition of the PI3K-mTOR pathway. In summary, SETD4 confers chemoresistance, tumor progression, and a poor prognosis by regulating CSCs in NSCLC patients.

Inhibiting CDK4/6 in pancreatic ductal adenocarcinoma via microRNA-21

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies, with a 5-year survival rate of 5-10 %. The high mortality rate is due to the asymptomatic progression of clinical features in metastatic stages of the disease, which renders standard therapeutic options futile. PDAC is characterised by alterations in several genes that drive carcinogenesis and limit therapeutic response. The two most common genetic aberrations in PDAC are the mutational activation of KRAS and loss of the tumour suppressor CDK inhibitor 2A (CDKN2A), which culminate the activation of the cyclin-dependent kinase 4 and 6 (CDK4/6), that promote G1 cell cycle progression. Therapeutic strategies focusing on the CDK4/6 inhibitors such as palbociclib (PD-0332991) may potentially improve outcomes in this malignancy. MicroRNAs (miRs/miRNAs) are small endogenous non-coding RNA molecules associated with cellular proliferation, invasion, apoptosis, and cell cycle. Primarily, miR-21 promotes cell proliferation and a higher proportion of PDAC cells in the S phase, while knockdown of miR-21 has been linked to cell cycle arrest at the G2/M phase and inhibition of cell proliferation. In this study, using a CRISPR/Cas9 loss-of-function screen, we individually silenced the expression of miR-21 in two PDAC cell lines and in combination with PD-0332991 treatment, we examined the synergetic mechanisms of CDK4/6 inhibitors and miR-21 knockouts (KOs) on cell survival and death. This combination reduced cell proliferation, cell viability, increased apoptosis and G1 arrest in vitro. We further analysed the mitochondrial respiration and glycolysis of PDAC cells; then assessed the protein content of these cells and revealed numerous Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with PD-0332991 treatment and miR-21 knocking out. Our results demonstrate that combined targeting of CDK4/6 and silencing of miR-21 represents a novel therapeutic strategy in PDAC.

Recent advances in targeted therapy for pancreatic adenocarcinoma

Pancreatic adenocarcinoma (PDAC) is a fatal disease with a 5-year survival rate of 8% and a median survival of 6 mo. In PDAC, several mutations in the genes are involved, with Kirsten rat sarcoma oncogene (90%), cyclin-dependent kinase inhibitor 2A (90%), and tumor suppressor 53 (75%–90%) being the most common. Mothers against decapentaplegic homolog 4 represents 50%. In addition, the self-preserving cancer stem cells, dense tumor microenvironment (fibrous accounting for 90% of the tumor volume), and suppressive and relatively depleted immune niche of PDAC are also constitutive and relevant elements of PDAC. Molecular targeted therapy is widely utilized and effective in several solid tumors. In PDAC, targeted therapy has been extensively evaluated; however, survival improvement of this aggressive disease using a targeted strategy has been minimal. There is currently only one United States Food and Drug Administration-approved targeted therapy for PDAC – erlotinib, but the absolute benefit of erlotinib in combination with gemcitabine is also minimal (2 wk). In this review, we summarize current targeted therapies and clinical trials targeting dysregulated signaling pathways and components of the PDAC oncogenic process, analyze possible reasons for the lack of positive results in clinical trials, and suggest ways to improve them. We also discuss emerging trends in targeted therapies for PDAC: combining targeted inhibitors of multiple pathways. The PubMed database and National Center for Biotechnology Information clinical trial website (www.clinicaltrials.gov) were queried to identify completed and published (PubMed) and ongoing (clinicaltrials.gov) clinical trials (from 2003-2022) using the keywords pancreatic cancer and targeted therapy. The PubMed database was also queried to search for information about the pathogenesis and molecular pathways of pancreatic cancer using the keywords pancreatic cancer and molecular pathways.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

CDK4/6 Inhibitors in Pancreatobiliary Cancers: Opportunities and Challenges

Existing treatment strategies for pancreatobiliary malignancies are limited. Nowadays, surgery is the only path to cure these types of cancer, but only a small number of patients present with resectable tumors at the time of diagnosis. The notoriously poor prognosis, lack of diverse treatment options associated with pancreaticobiliary cancers, and their resistance to current therapies reflect the urge for the development of novel therapeutic targets. Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have emerged as an attractive therapeutic strategy in a number of cancers since their approval for treatment in patients with ER+/HER- breast cancer in combination with antiestrogens. In this article, we discuss the therapeutic potential of CDK4/6 inhibitors in pancreatobiliary cancers, notably cholangiocarcinoma and pancreatic ductal adenocarcinoma.

Saikosaponin A enhances Docetaxel efficacy by selectively inducing death of dormant prostate cancer cells through excessive autophagy

Quiescent cancer cells (QCCs), also known as dormant cancer cells, resist and survive chemo- and radiotherapy, resulting in treatment failure and later cancer recurrence when QCCs resume cell cycle progression. However, drugs selectively targeting QCCs are lacking. Saikosaponin A (SSA) derived from Bupleurum DC., is highly potent in eradicating multidrug-resistant prostate QCCs compared with proliferative prostate cancer cells. By further exacerbating the already increased autophagy through inactivation of Akt-mTOR signaling, SSA triggered cell death in QCCs. Contrarily, inhibition of autophagy or activation of Akt signaling pathway prevented SSA-induced cell death. The multicycle of Docetaxel treatments increased the proportion of QCCs, whereas administering SSA at intervals of Docetaxel treatments aggravated cell death in vitro and led to tumor growth arrest and cell death in vivo. In conclusion, SSA is posed as a novel QCCs-eradicating agent by aggravating autophagy in QCCs. In combination with the current therapy, SSA has potential to improve treatment effectiveness and to prevent cancer recurrence.

Applications and mechanisms of the cyclin-dependent kinase 4/6 inhibitor, PD-0332991, in solid tumors

Abnormal CDK4/6-Rb-E2F signal transduction is a common finding in tumors and is a driving factor for the excessive proliferation of various tumor cells. PD-0332991, a highly specific, small molecule inhibitor for CDK4 and 6, has been shown to inhibit tumor growth by abrogating the phosphorylating capacity of CDK4/6 and suppressing Rb phosphorylation. It has been promoted for the treatment of breast cancer and potentially for other tumor types such as liver cancers, lung cancers and sarcomas. Due to the risk of monotherapy resistance, PD-0332991 is commonly used in combination with other drugs. Such combination treatments have proved able to inhibit tumor proliferation more effectively, induce stronger senescence and apoptosis, and enhance the efficiency of immunotherapy. Therefore, tumor cells with senescence induced by PD-0332991 are now used as ideal screening tools of cytolytic drugs with more efficient and thorough anti-tumor properties. With more extensive understandings about the branching points between senescence and apoptosis, it is possible to refine the dosage of PD-0332991. Better characterization of resistant cells, of inhibitors and of adverse effects such as leukopenia are needed to overcome obstacles in the use of PD-0332991. In this review of PD-0332991 research, we hope to provide guidance of transitions from laboratory findings to clinical applications of PD-0332991 and to facilitate PD-0332991-based multi-inhibitor combination therapies for various tumors.

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.

Pharmacologic Targeting of TFIIH Suppresses KRAS-Mutant Pancreatic Ductal Adenocarcinoma and Synergizes with TRAIL

Pancreatic ductal adenocarcinoma (PDAC) typically presents as metastatic disease at diagnosis and remains refractory to treatment. Next-generation sequencing efforts have described the genomic landscape, classified molecular subtypes, and confirmed frequent alterations in major driver genes, with coexistent alterations in KRAS and TP53 correlating with the highest metastatic burden and poorest outcomes. However, translating this information to guide therapy remains a challenge. By integrating genomic analysis with an arrayed RNAi druggable genome screen and drug profiling of a KRAS/TP53 mutant PDAC cell line derived from a patient-derived xenograft (PDCL), we identified numerous targetable vulnerabilities that reveal both known and novel functional aspects of pancreatic cancer biology. A dependence on the general transcription and DNA repair factor TFIIH complex, particularly the XPB subunit and the CAK complex (CDK7/CyclinH/MAT1), was identified and further validated utilizing a panel of genomically subtyped KRAS mutant PDCLs. TFIIH function was inhibited with a covalent inhibitor of CDK7/12/13 (THZ1), a CDK7/CDK9 kinase inhibitor (SNS-032), and a covalent inhibitor of XPB (triptolide), which led to disruption of the protein stability of the RNA polymerase II subunit RPB1. Loss of RPB1 following TFIIH inhibition led to downregulation of key transcriptional effectors of KRAS-mutant signaling and negative regulators of apoptosis, including MCL1, XIAP, and CFLAR, initiating caspase-8 dependent apoptosis. All three drugs exhibited synergy in combination with a multivalent TRAIL, effectively reinforcing mitochondrial-mediated apoptosis. These findings present a novel combination therapy, with direct translational implications for current clinical trials on metastatic pancreatic cancer patients. Significance: This study utilizes functional genetic and pharmacological profiling of KRAS-mutant pancreatic adenocarcinoma to identify therapeutic strategies and finds that TFIIH inhibition synergizes with TRAIL to induce apoptosis in KRAS-driven pancreatic cancer.

Prospects of targeting PI3K/AKT/mTOR pathway in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has one of the worst prognoses among all malignancies. PI3K/AKT/mTOR signaling pathway, a main downstream effector of KRAS is involved in the regulation of key hallmarks of cancer. We here report that whole-genome analyses demonstrate the frequent involvement of aberrant activations of PI3K/AKT/mTOR pathway components in PDAC patients and critically evaluate preclinical and clinical evidence on the application of PI3K/AKT/mTOR pathway targeting agents. Combinations of these agents with chemotherapeutics or other targeted therapies, including the modulators of cyclin-dependent kinases, receptor tyrosine kinases and RAF/MEK/ERK pathway are also examined. Although human genetic studies and preclinical pharmacological investigations have provided strong evidence on the role of PI3K/AKT/mTOR pathway in PDAC, clinical studies in general have not been as promising. Patient stratification seems to be the key missing point and with the advent of biomarker-guided clinical trials, targeting PI3K/AKT/mTOR pathway could provide valuable assets for treatment of pancreatic cancer patients.

Structure-guided design and development of cyclin-dependent kinase 4/6 inhibitors: A review on therapeutic implications

Cyclin-dependent kinase 6 (EC 2.7.11.22) play significant roles in numerous biological processes and triggers cell cycle events. CDK6 controlled the transcriptional regulation. A dysregulated function of CDK6 is linked with the development of progression of multiple tumor types. Thus, it is considered as an effective drug target for cancer therapy. Based on the direct roles of CDK4/6 in tumor development, numerous inhibitors developed as promising anti-cancer agents. CDK4/6 inhibitors regulate the G1 to S transition by preventing Rb phosphorylation and E2F liberation, showing potent anti-cancer activity in several tumors, including HR+/HER2- breast cancer. CDK4/6 inhibitors such as abemaciclib, palbociclib, and ribociclib, control cell cycle, provoke cell senescence, and induces tumor cell disturbance in pre-clinical studies. Here, we discuss the roles of CDK6 in cancer along with the present status of CDK4/6 inhibitors in cancer therapy. We further discussed, how structural features of CDK4/6 could be implicated in the design and development of potential anti-cancer agents. In addition, the therapeutic potential and limitations of available CDK4/6 inhibitors are described in detail. Recent pre-clinical and clinical information for CDK4/6 inhibitors are highlighted. In addition, combination of CDK4/6 inhibitors with other drugs for the therapeutic management of cancer are discussed.

Cyclin-Dependent Kinase 4/6 Inhibitors: A Potential Breakthrough Therapy for Malignancies of Gastrointestinal Tract

Cancer is the leading cause of death worldwide for which effective treatments remain limited. This article aimed to critically review and discuss the potential of targeting cell cycle machineries as a vital tool for cancer treatment. Cyclin dependent kinase (CDK) 4/6 inhibitors were originally approved by the United State Food and Drug Administration (US FDA) for advanced-stage breast cancer treatment. The nearly double-prolonged survival time in patients who received CDK4/6 inhibitors are superior to the conventional chemotherapy or endocrine therapy alone and, thus, these medications have been designated a breakthrough therapy by the US FDA. The requirement of CDK4/6 in the progression of cancer cells, but probably dispensable in normal cells, makes CDK4/6 a popular target for cancer treatment. The effects of CDK4/6 inhibitors in cancer may also involve the tumor microenvironment in which the therapeutic effects are synergistically pronounced. These emerging roles, hence, prompt investigations regarding their therapeutic potential in other cancers, including gastrointestinal cancer. Many preclinical and clinical studies of CDK4/6 inhibitors in gastrointestinal cancers are underway and, as a result, several new potentials are gradually reported. Contrariwise, the primary effect of this drug group is arresting the cell cycle rather than inducing cell death. The efficacy of using CDK4/6 inhibitors as a single regimen in clinical practice is then limited. In this article, the effects of CDK4/6 inhibitors on the progression of gastrointestinal cancers, at both preclinical and clinical levels are reviewed. The future directions for research and the possibility of CDK4/6 inhibitors being "breakthrough therapy" for gastrointestinal cancers are also discussed.

Implementation of a combined CDK inhibition and arginine-deprivation approach to target arginine-auxotrophic glioblastoma multiforme cells

Constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy are hallmarks of Glioblastoma multiforme (GBM). The latter metabolic defect renders tumor cells vulnerable to arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards SpyADI as well as CDK inhibitors (CDKis). To improve therapeutic effects, we here applied a combined approach based on SpyADI and CDKis (dinaciclib, abemaciclib). Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D and effects of this combined SpyADI/CDKi approach were analyzed in-depth. All CDKi/SpyADI combinations yielded synergistic antitumoral effects, especially when given sequentially (SEQ), i.e., CDKi in first-line and most pronounced in the 3D models. SEQ application demonstrated impaired cell proliferation, invasiveness, and viability. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate and extracellular acidification rate after SpyADI/abemaciclib monotherapy or its combination regimens. The combined treatment even induced autophagy in target cells (abemaciclib/SpyADI > dinaciclib/SpyADI). By contrast, the unfolded protein response and p53/p21 induced senescence played a minor role. Transmission electron microscopy confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2 and induced expression changes of genes involved in cellular/cytoskeletal integrity. This study highlights the strong antitumoral potential of a combined arginine deprivation and CDK inhibition approach via complex effects on mitochondrial dysfunction, invasiveness as well as DNA-damage response. This provides a good starting point for further in vitro and in vivo proof-of-concept studies to move forward with this strategy.

Interstitial lung disease in patients treated with Cyclin-Dependent Kinase 4/6 inhibitors: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Cyclin-Dependent Kinase (CDK) 4/6 inhibitors have shown significant clinical activity in cancer patients. However, some concerns regarding rare adverse events (AEs) have occurred including interstitial lung disease (ILD)/pneumonitis, for which data are deficient. The aim of this study was to evaluate the overall incidence and risk of ILD/pneumonitis related to CDK4/6 inhibitors in randomized controlled trials (RCTs).

METHODS

Electronic databases and ClinicalTrials.gov were searched from inception to October 1, 2021 for RCTs reporting the occurrence of LD/pneumonitis in cancer patients treated with CDK4/6 inhibitors. Peto odds ratios (Peto ORs) and 95% confidence intervals (CIs) were used to pool the study.

RESULTS

12 RCTs with a total of 16,060 patients were eligible. The overall incidence of all-grade ILD/pneumonitis was 1.6% (131/8407) in the treatment group compared with 0.7% (50/7349) in the control group. CDK4/6 inhibitors significantly increased the risk of all-grade ILD/pneumonitis with a pooled Peto OR of 2.12 (95% CI [1.57, 2.86], P < 0.00001) with no heterogeneity (I² = 0%, χ² P = 0.98). A higher incidence of grade 3 or higher ILD/pneumonitis was also observed in the treatment group (0.2%, 16/7087) compared with the control group (0.05%, 3/6617) with a Peto OR of 3.22 (95% CI [1.28, 8.09], P = 0.01) with no heterogeneity (I² = 0%, χ² P = 0.62). Two grade 5 pneumonitis were reported in the included studies. Subgroup analyses did not show any significant difference.

CONCLUSIONS

The risk of all-grade and grade 3 or higher ILD/pneumonitis was higher in patients treated with CDK4/6 inhibitors compared to controls. The awareness for these rare AEs in the application of CDK4/6 inhibitors should be enhanced. Further studies are required to validate the mechanisms and the risk factors of ILD/pneumonitis with CDK4/6 inhibitors.

Modulation of Type I Interferon Responses to Influence Tumor-Immune Cross Talk in PDAC

Immunotherapy has revolutionized the treatment of many cancer types. However, pancreatic ductal adenocarcinomas (PDACs) exhibit poor responses to immune checkpoint inhibitors with immunotherapy-based trials not generating convincing clinical activity. PDAC tumors often have low infiltration of tumor CD8+ T cells and a highly immunosuppressive microenvironment. These features classify PDAC as immunologically "cold." However, the presence of tumor T cells is a favorable prognostic feature in PDAC. Intrinsic tumor cell properties govern interactions with the immune system. Alterations in tumor DNA such as genomic instability, high tumor mutation burden, and/or defects in DNA damage repair are associated with responses to both immunotherapy and chemotherapy. Cytotoxic or metabolic stress produced by radiation and/or chemotherapy can act as potent immune triggers and prime immune responses. Damage- or stress-mediated activation of nucleic acid-sensing pathways triggers type I interferon (IFN-I) responses that activate innate immune cells and natural killer cells, promote maturation of dendritic cells, and stimulate adaptive immunity. While PDAC exhibits intrinsic features that have the potential to engage immune cells, particularly following chemotherapy, these immune-sensing mechanisms are ineffective. Understanding where defects in innate immune triggers render the PDAC tumor-immune interface less effective, or how T-cell function is suppressed will help develop more effective treatments and harness the immune system for durable outcomes. This review will focus on the pivotal role played by IFN-I in promoting tumor cell-immune cell cross talk in PDAC. We will discuss how PDAC tumor cells bypass IFN-I signaling pathways and explore how these pathways can be co-opted or re-engaged to enhance the therapeutic outcome.

Diverse and precision therapies open new horizons for patients with advanced pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a common cause of cancer-related death, and most patients are with advanced disease when diagnosed. At present, despite a variety of treatments have been developed for PDAC, few effective treatment options are available; on the other hand, PDAC shows significant resistance to chemoradiotherapy, targeted therapy, and immunotherapy due to its heterogeneous genetic profile, molecular signaling pathways, and complex tumor immune microenvironment. Nevertheless, over the past decades, there have been many new advances in the key theory and understanding of the intrinsic mechanisms and complexity of molecular biology and molecular immunology in pancreatic cancer, based on which more and more diverse new means and reasonable combination strategies for PDAC treatment have been developed and preliminary breakthroughs have been made. With the continuous exploration, from surgical local treatment to comprehensive medical management, the research-diagnosis-management system of pancreatic cancer is improving. This review focused on the variety of treatments for advanced PDAC, including traditional chemotherapy, targeted therapy, immunotherapy, microenvironment matrix regulation as well as the treatment targeting epigenetics, metabolism and cancer stem cells. We pointed out the current research bottlenecks and future exploration directions.

The Impact of Biomarkers in Pancreatic Ductal Adenocarcinoma on Diagnosis, Surveillance and Therapy

Simple Summary

Pancreatic ductal adenocarcinoma is a leading cause of cancer death worldwide. Due to the frequently late diagnosis, early metastasis and high therapy resistance curation is rare and prognosis remains poor overall. To provide early diagnostic and therapeutic predictors, various molecules from blood, tissue and other origin e.g., saliva, urine and stool, have been identified as biomarkers. This review summarizes current trends in biomarkers for diagnosis and therapy of pancreatic ductal adenocarcinoma.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is still difficult to treat due to insufficient methods for early diagnosis and prediction of therapy response. Furthermore, surveillance after curatively intended surgery lacks adequate methods for timely detection of recurrence. Therefore, several molecules have been analyzed as predictors of recurrence or early detection of PDAC. Enhanced understanding of molecular tumorigenesis and treatment response triggered the identification of novel biomarkers as predictors for response to conventional chemotherapy or targeted therapy. In conclusion, progress has been made especially in the prediction of therapy response with biomarkers. The use of molecules for early detection and recurrence of PDAC is still at an early stage, but there are promising approaches in noninvasive biomarkers, composite panels and scores that can already ameliorate the current clinical practice. The present review summarizes the current state of research on biomarkers for diagnosis and therapy of pancreatic 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.

Mutations in key driver genes of pancreatic cancer: molecularly targeted therapies and other clinical implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, with a minimal difference between its incidence rate and mortality rate. Advances in oncology over the past several decades have dramatically improved the overall survival of patients with multiple cancers due to the implementation of new techniques in early diagnosis, therapeutic drugs, and personalized therapy. However, pancreatic cancers remain recalcitrant, with a 5-year relative survival rate of <9%. The lack of measures for early diagnosis, strong resistance to chemotherapy, ineffective adjuvant chemotherapy and the unavailability of molecularly targeted therapy are responsible for the high mortality rate of this notorious disease. Genetically, PDAC progresses as a complex result of the activation of oncogenes and inactivation of tumor suppressors. Although next-generation sequencing has identified numerous new genetic alterations, their clinical implications remain unknown. Classically, oncogenic mutations in genes such as KRAS and loss-of-function mutations in tumor suppressors, such as TP53, CDNK2A, DPC4/SMAD4, and BRCA2, are frequently observed in PDAC. Currently, research on these key driver genes is still the main focus. Therefore, studies assessing the functions of these genes and their potential clinical implications are of paramount importance. In this review, we summarize the biological function of key driver genes and pharmaceutical targets in PDAC. In addition, we conclude the results of molecularly targeted therapies in clinical trials and discuss how to utilize these genetic alterations in further clinical practice.

The Role of CDK4 in the Pathogenesis of Pancreatic Cancer

Pancreatic cancer (PC) continues to have the lowest overall survival and the lack of effective early diagnosis. Cyclin-dependent kinase 4 (CDK4) plays a fundamental role in the orderly progression of the cell cycle, binding to cyclin D to promote the progression through the G1/2 transition. The inhibition of CDK4/6 has therefore gained substantial interest in the hope of new and effective therapeutics in multiple cancers, such as advanced metastatic breast cancer. While the use of these agents is encouraging, their potential is yet to be fully explored. In this study we used the GLOBOCAN database to understand the most recent epidemiology of PC, Human Protein Atlas and KEGG to highlight the role, prevalence, and significance on patient survival of CDK4 in PC. We found that CDK4 cannot be used as prognostic in PC and no significant differences were observed between CDK4 expression and the patient's clinical status, though larger studies, especially concerning CDK4 protein expressions, are required for a more thorough understanding. The use of CDK4/6 inhibitors in PC is still in clinical trials. However, due to only modest improvements observed in the use of single-agent therapies, efforts have focused on combinatorial approaches.

The Diverse Applications of Pancreatic Ductal Adenocarcinoma Organoids

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal solid malignancies. While immortalized cancer cell lines and genetically engineered murine models have increased our understanding of PDAC tumorigenesis, they do not recapitulate inter- and intra-patient heterogeneity. PDAC patient derived organoid (PDO) biobanks have overcome this hurdle, and provide an opportunity for the high throughput screening of potential new therapies. This review provides a summary of the PDAC PDO biobanks established to date, and discusses how they have advanced our understanding of PDAC biology. Looking forward, the development of coculturing techniques for specific immune or stromal cell populations will enable a better understanding of the crosstalk that occurs within the tumor microenvironment, and the impact of this crosstalk on treatment response.

Intravital imaging technology guides FAK-mediated priming in pancreatic cancer precision medicine according to Merlin status

Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic, chemoresistant malignancy and is characterized by a dense, desmoplastic stroma that modulates PDAC progression. Here, we visualized transient manipulation of focal adhesion kinase (FAK), which integrates bidirectional cell-environment signaling, using intravital fluorescence lifetime imaging microscopy of the FAK-based Förster resonance energy transfer biosensor in mouse and patient-derived PDAC models. Parallel real-time quantification of the FUCCI cell cycle reporter guided us to improve PDAC response to standard-of-care chemotherapy at primary and secondary sites. Critically, micropatterned pillar plates and stiffness-tunable matrices were used to pinpoint the contribution of environmental cues to chemosensitization, while fluid flow–induced shear stress assessment, patient-derived matrices, and personalized in vivo models allowed us to deconstruct how FAK inhibition can reduce PDAC spread. Last, stratification of PDAC patient samples via Merlin status revealed a patient subset with poor prognosis that are likely to respond to FAK priming before chemotherapy.

TLR2 activation promotes tumour growth and associates with patient survival and chemotherapy response in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has an extremely poor prognosis, and is plagued by a paucity of targeted treatment options and tumour resistance to chemotherapeutics. The causal link between chronic inflammation and PDAC suggests that molecular regulators of the immune system promote disease pathogenesis and/or therapeutic resistance, yet their identity is unclear. Here, we couple endoscopic ultrasound-guided fine-needle aspiration, which captures tumour biopsies from all stages, with whole transcriptome profiling of PDAC patient primary tumours to reveal enrichment of the innate immune Toll-like receptor 2 (TLR2) molecular pathway. Augmented TLR2 expression associated with a 4-gene "TLR2 activation" signature, and was prognostic for survival and predictive for gemcitabine-based chemoresistance. Furthermore, antibody-mediated anti-TLR2 therapy suppressed the growth of human PDAC tumour xenografts, independent of a functional immune system. Our results support TLR2-based therapeutic targeting for precision medicine in PDAC, with further clinical utility that TLR2 activation is prognostic and predictive for chemoresponsiveness.

The Role of Inherited Pathogenic CDKN2A Variants in Susceptibility to Pancreatic Cancer

ABSTRACT

CDKN2A is cell cycle negative regulator, and the role of CDKN2A in the development of pancreatic ductal adenocarcinoma, which continues to be a lethal cancer, is well-established. Somatic loss of CDKN2A is considered one of the major drivers of pancreatic tumorigenesis. CDKN2A gene is one of the pancreatic cancer susceptibility gene; in addition to melanoma, pathogenic germline CDKN2A variants have been identified in up to 3.3% patients with pancreatic ductal adenocarcinoma depending on family history of disease. Carriers of a known pathogenic germline CDKN2A variant have up to a 12.3-fold increased risk of developing pancreatic cancer. Recently, several studies have demonstrated the benefit of clinical surveillance in patients with pathogenic germline CDKN2A variants. Therefore, identification of patients with a pathogenic germline CDKN2A variant is important for screening of at-risk relatives for pancreatic cancer. It has the potential to lead to the detection of early, potentially curable pancreatic cancer and precursor neoplasms, and reduce mortality. Furthermore, patients with a germline pathogenic CDKN2A variant and somatic loss of CDKN2A may benefit in the future from treatment with targeted therapies, such as a CDK4/6 inhibitor.

NP-ALT, a Liposomal:Peptide Drug, Blocks p27Kip1 Phosphorylation to Induce Oxidative Stress, Necroptosis, and Regression in Therapy-Resistant Breast Cancer Cells

Resistance to cyclin D-CDK4/6 inhibitors (CDK4/6i) represents an unmet clinical need and is frequently caused by compensatory CDK2 activity. Here we describe a novel strategy to prevent CDK4i resistance by using a therapeutic liposomal:peptide formulation, NP-ALT, to inhibit the tyrosine phosphorylation of p27Kip1(CDKN1B), which in turn inhibits both CDK4/6 and CDK2. We find that NP-ALT blocks proliferation in HR+ breast cancer cells, as well as CDK4i-resistant cell types, including triple negative breast cancer (TNBC). The peptide ALT is not as stable in primary mammary epithelium, suggesting that NP-ALT has little effect in nontumor tissues. In HR+ breast cancer cells specifically, NP-ALT treatment induces ROS and RIPK1-dependent necroptosis. Estrogen signaling and ERα appear required. Significantly, NP-ALT induces necroptosis in MCF7 ESR^Y537S cells, which contain an ER gain of function mutation frequently detected in metastatic patients, which renders them resistant to endocrine therapy. Here we show that NP-ALT causes necroptosis and tumor regression in treatment naïve, palbociclib-resistant, and endocrine-resistant BC cells and xenograft models, demonstrating that p27 is a viable therapeutic target to combat drug resistance. IMPLICATIONS: This study reveals that blocking p27 tyrosine phosphorylation inhibits CDK4 and CDK2 activity and induces ROS-dependent necroptosis, suggesting a novel therapeutic option for endocrine and CDK4 inhibitor-resistant HR+ tumors.

Nanotechnology for Boosting Cancer Immunotherapy and Remodeling Tumor Microenvironment: The Horizons in Cancer Treatment

Immunotherapy that harnesses the human immune system to fight cancer has received widespread attention and become a mainstream strategy for cancer treatment. Cancer immunotherapy not only eliminates primary tumors but also treats metastasis and recurrence, representing a major advantage over traditional cancer treatments. Recently with the development of nanotechnology, there exists much work applying nanomaterials to cancer immunotherapy on the basis of their excellent physiochemical properties, such as efficient tissue-specific delivery function, huge specific surface area, and controllable surface chemistry. Consequently, nanotechnology holds significant potential in improving the efficacy of cancer immunotherapy. Nanotechnology-based immunotherapy mainly manifests its inhibitory effect on tumors via two different approaches: one is to produce an effective anti-tumor immune response during tumorigenesis, and the other is to enhance tumor immune defense ability by modulating the immune suppression mechanism in the tumor microenvironment. With the success of tumor immunotherapy, understanding the interaction between the immune system and smart nanomedicine has provided vigorous vitality for the development of cancer treatment. This review highlights the application, progress, and prospect of nanomedicine in the process of tumor immunoediting and also discusses several engineering methods to improve the efficiency of tumor treatment.

Biological Hallmarks and New Therapeutic Approaches for the Treatment of PDAC

Pancreatic Ductal Adenocarcinoma (PDAC) is one of the deadliest solid tumors and is estimated to become a leading cause of cancer-related death in coming years. Despite advances in surgical approaches and the emergence of new chemotherapy options, its poor prognosis has not improved in the last decades. The current treatment for PDAC is the combination of cytotoxic chemotherapy agents. However, PDAC shows resistance to many antineoplastic therapies with rapid progression. Although PDAC represents a heterogeneous disease, there are common alterations including oncogenic mutations of KRAS, and the frequent inactivation of different cell cycle regulators including the CDKN2A tumor suppressor gene. An emerging field of investigation focuses on inhibiting the function of proteins that suppress the immune checkpoint PD-1/PD-L1, with activation of the endogenous immune response. To date, all conventional immunotherapies have been less successful in patients with PDAC compared to other tumors. The need for new targets, associated with an extended molecular analysis of tumor samples could give new pharmacological options for the treatment of PDAC. It is, therefore, important to push for a broader molecular approach in PDAC research. Here, we provide a selected summary of emerging strategy options for targeting PDAC using CDK4/6 inhibitors, RAS inhibitors, and new drug combinations with immune checkpoint agents.

Mechanism of Drug Tolerant Persister Cancer Cells: The Landscape and Clinical Implication for Therapy

A minor population of cancer cells may evade cell death from chemotherapy and targeted therapy by entering a reversible slow proliferation state known as the drug tolerant persister (DTP) state. This DTP state can allow cancer cells to survive drug therapy long enough for additional mechanisms of acquired drug resistance to develop. Thus, cancer persistence is a major obstacle to curing cancers, where insight into the biology of DTP cells and therapeutic strategies targeting this mechanism can have considerable clinical implications. There is emerging evidence that DTP cells adapt to new environments through epigenomic modification, transcriptomic regulation, flexible energy metabolism, and interactions with the tumor microenvironment. Herein, we review and discuss the various proposed mechanisms of cancer persister cells and the molecular features underlying the DTP state, with insights into the potential therapeutic strategies to conquer DTP cells and prevent cancer recurrence or therapeutic failures.

Extracellular Matrices and Cancer-Associated Fibroblasts: Targets for Cancer Diagnosis and Therapy?

Solid cancer progression is dictated by neoplastic cell features and pro-tumoral crosstalks with their microenvironment. Stroma modifications, such as fibroblast activation into cancer-associated fibroblasts (CAFs) and extracellular matrix (ECM) remodeling, are now recognized as critical events for cancer progression and as potential therapeutic or diagnostic targets. The recent appreciation of the key, complex and multiple roles of the ECM in cancer and of the CAF diversity, has revolutionized the field and raised innovative but challenging questions. Here, we rapidly present CAF heterogeneity in link with their specific ECM remodeling features observed in cancer, before developing each of the impacts of such ECM modifications on tumor progression (survival, angiogenesis, pre-metastatic niche, chemoresistance, etc.), and on patient prognosis. Finally, based on preclinical studies and recent results obtained from clinical trials, we highlight key mechanisms or proteins that are, or may be, used as potential therapeutic or diagnostic targets, and we report and discuss benefits, disappointments, or even failures, of recently reported stroma-targeting strategies.

Cancer-Associated Fibroblasts in Pancreatic Ductal Adenocarcinoma Determine Response to SLC7A11 Inhibition

Cancer-associated fibroblasts (CAF) are major contributors to pancreatic ductal adenocarcinoma (PDAC) progression through protumor signaling and the generation of fibrosis, the latter of which creates a physical barrier to drugs. CAF inhibition is thus an ideal component of any therapeutic approach for PDAC. SLC7A11 is a cystine transporter that has been identified as a potential therapeutic target in PDAC cells. However, no prior study has evaluated the role of SLC7A11 in PDAC tumor stroma and its prognostic significance. Here we show that high expression of SLC7A11 in human PDAC tumor stroma, but not tumor cells, is independently prognostic of poorer overall survival. Orthogonal approaches showed that PDAC-derived CAFs are highly dependent on SLC7A11 for cystine uptake and glutathione synthesis and that SLC7A11 inhibition significantly decreases CAF proliferation, reduces their resistance to oxidative stress, and inhibits their ability to remodel collagen and support PDAC cell growth. Importantly, specific ablation of SLC7A11 from the tumor compartment of transgenic mouse PDAC tumors did not affect tumor growth, suggesting the stroma can substantially influence PDAC tumor response to SLC7A11 inhibition. In a mouse orthotopic PDAC model utilizing human PDAC cells and CAFs, stable knockdown of SLC7A11 was required in both cell types to reduce tumor growth, metastatic spread, and intratumoral fibrosis, demonstrating the importance of targeting SLC7A11 in both compartments. Finally, treatment with a nanoparticle gene-silencing drug against SLC7A11, developed by our laboratory, reduced PDAC tumor growth, incidence of metastases, CAF activation, and fibrosis in orthotopic PDAC tumors. Overall, these findings identify an important role of SLC7A11 in PDAC-derived CAFs in supporting tumor growth. SIGNIFICANCE: This study demonstrates that SLC7A11 in PDAC stromal cells is important for the tumor-promoting activity of CAFs and validates a clinically translatable nanomedicine for therapeutic SLC7A11 inhibition in PDAC.

Substrate-biased activity-based probes identify proteases that cleave receptor CDCP1

CUB domain-containing protein 1 (CDCP1) is an oncogenic orphan transmembrane receptor and a promising target for the detection and treatment of cancer. Extracellular proteolysis of CDCP1 by poorly defined mechanisms induces pro-metastatic signaling. We describe a new approach for the rapid identification of proteases responsible for key proteolytic events using a substrate-biased activity-based probe (sbABP) that incorporates a substrate cleavage motif grafted onto a peptidyl diphenyl phosphonate warhead for specific target protease capture, isolation and identification. Using a CDCP1-biased probe, we identify urokinase (uPA) as the master regulator of CDCP1 proteolysis, which acts both by directly cleaving CDCP1 and by activating CDCP1-cleaving plasmin. We show that coexpression of uPA and CDCP1 is strongly predictive of poor disease outcome across multiple cancers and demonstrate that uPA-mediated CDCP1 proteolysis promotes metastasis in disease-relevant preclinical in vivo models. These results highlight CDCP1 cleavage as a potential target to disrupt cancer and establish sbABP technology as a new approach to identify disease-relevant proteases.

Breaking the cycle: Targeting of NDRG1 to inhibit bi-directional oncogenic cross-talk between pancreatic cancer and stroma

Pancreatic cancer (PaCa) is characterized by dense stroma that hinders treatment efficacy, with pancreatic stellate cells (PSCs) being a major contributor to this stromal barrier and PaCa progression. Activated PSCs release hepatocyte growth factor (HGF) and insulin-like growth factor (IGF-1) that induce PaCa proliferation, metastasis and resistance to chemotherapy. We demonstrate for the first time that the metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), is a potent inhibitor of the PaCa-PSC cross-talk, leading to inhibition of HGF and IGF-1 signaling. NDRG1 also potently reduced the key driver of PaCa metastasis, namely GLI1, leading to reduced PSC-mediated cell migration. The novel clinically trialed anticancer agent, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), which upregulates NDRG1, potently de-sensitized PaCa cells to ligands secreted by activated PSCs. DpC and NDRG1 also inhibited the PaCa-mediated activation of PSCs via inhibition of sonic hedgehog (SHH) signaling. In vivo, DpC markedly reduced PaCa tumor growth and metastasis more avidly than the standard chemotherapy for this disease, gemcitabine. Uniquely, DpC was selectively cytotoxic against PaCa cells, while "re-programming" PSCs to an inactive state, decreasing collagen deposition and desmoplasia. Thus, targeting NDRG1 can effectively break the oncogenic cycle of PaCa-PSC bi-directional cross-talk to overcome PaCa desmoplasia and improve therapeutic outcomes.

G2M checkpoint pathway alone is associated with drug response and survival among cell proliferation-related pathways in pancreatic cancer

Given the severe side effects of the treatments and poor survival, prognostic and predictive biomarkers to guide management of pancreatic cancer are in critical need. We hypothesized that cell proliferation-related pathways are associated with drug response and survival in pancreatic cancer. Six Hallmark cell proliferation-related gene sets (G2M Checkpoint, E2F Targets, MYC Targets V1 and V2, Mitotic Spindle, p53 pathway) defined by MSigDB in gene set variant analysis were evaluated in 3 independent cohorts- TCGA-PAAD (n = 176), GSE57495 (n = 63), and GSE62452 (n = 69). G2M and E2F, as well as Mitotic and p53 pathway correlated highly with other gene sets. All pathways were significantly correlated with MKI67 expression and its proliferation score, but none with cytolytic activity and the rate of pathologically complete resection (R0). All pathways were significantly associated with high alteration and expression of KRAS gene except for MYC v1. G2M, E2F, and p53 pathway were significantly associated with high alteration of TP53 gene. Interestingly, different pathways correlated with the AUC of different cancer therapeutics, such as Gemcitabine (Mitotic: r = 0.706 [P = 0.01]), Paclitaxel (MYC v2: r = -0.636 [P < 0.05]), Apatinib (Mitotic: r = -0.556 [P = 0.03]), Palbociclib (E2F: r = 0.675 [P < 0.01]), and Sorafenib (G2M: r = -0.593 [P = 0.03]). Among all six pathways, only G2M was consistently associated with worse patient survival in all three cohorts. In conclusion, each cell proliferation-related pathway was predictive of a unique agent, and the G2M score alone predicts survival in pancreatic cancer.

Agrimol B present in Agrimonia pilosa Ledeb impedes cell cycle progression of cancer cells through G0 state arrest

Cancer recurrence poses a significant challenge. At the cellular level, recurrence takes place as a result of reactivation of dormant cancer cells residing at G₀ phase. The aim of the study was to identify compounds that can trap prostate and lung cancer cells in G₀ phase from a new Chinese herb recipe, Astringent recipe, consisting of Radix Paeoniae Alba, Agrimonia pilosa Ledeb, Fructus Mume, Fritillaria thunbergii Miq., Ganoderma Lucidum Karst, and Astragalus membranaceus (Fisch.) Bunge. Astringent recipe impeded cell cycle progression in prostate and lung cancer cells by rounding them up at G₀ phase by flow cytometric analysis of cancer cells stained with Hoechst 33342 and Pyronin Y, respectively, for DNA and RNA. The anti-cancer efficacy of the recipe was found to be attributable to Agrimonia pilosa Ledeb. Further study established that agrimol B, a polyphenol derived from Agrimonia pilosa Ledeb, contributed to the activity of the herb. The action of agrimol B on the cancer cells was likely derived from its effect on c-MYC, SKP2 and p27 by immunoblotting and immunofluorescence. Oral administration of Agrimonia pilosa Ledeb or agrimol B reduced growth of prostate cancer cell xenograft in animal. In conclusion, Agrimol B can enrich for prostate and lung cancer cells in G₀ state and influence key regulators that govern G₀ status.

Quantifying and visualising the nuances of cellular dynamics in vivo using intravital imaging

Intravital imaging is a powerful technology used to quantify and track dynamic changes in live cells and tissues within an intact environment. The ability to watch cell biology in real-time 'as it happens' has provided novel insight into tissue homeostasis, as well as disease initiation, progression and response to treatment. In this minireview, we highlight recent advances in the field of intravital microscopy, touching upon advances in awake versus anaesthesia-based approaches, as well as the integration of biosensors into intravital imaging. We also discuss current challenges that, in our opinion, need to be overcome to further advance the field of intravital imaging at the single-cell, subcellular and molecular resolution to reveal nuances of cell behaviour that can be targeted in complex disease settings.

Cyclin-dependent kinase inhibitors exert distinct effects on patient-derived 2D and 3D glioblastoma cell culture models

Current therapeutic approaches have met limited clinical success for glioblastoma multiforme (GBM). Since GBM harbors genomic alterations in cyclin-dependent kinases (CDKs), targeting these structures with specific inhibitors (CDKis) is promising. Here, we describe the antitumoral potential of selective CDKi on low-passage GBM 2D- and 3D models, cultured as neurospheres (NSCs) or glioma stem-like cells (GSCs). By applying selective CDK4/6i abemaciclib and palbociclib, and the more global CDK1/2/5/9-i dinaciclib, different effects were seen. Abemaciclib and dinaciclib significantly affected viability in 2D- and 3D models with clearly visible changes in morphology. Palbociclib had weaker and cell line-specific effects. Motility and invasion were highly affected. Abemaciclib and dinaciclib additionally induced senescence. Also, mitochondrial dysfunction and generation of mitochondrial reactive oxygen species (ROS) were seen. While autophagy was predominantly visible after abemaciclib treatment, dinaciclib evoked γ-H2AX-positive double-strand breaks that were boosted by radiation. Notably, dual administration of dinaciclib and abemaciclib yielded synergistic effects in most cases, but the simultaneous combination with standard chemotherapeutic agent temozolomide (TMZ) was antagonistic. RNA-based microarray analysis showed that gene expression was significantly altered by dinaciclib: genes involved in cell-cycle regulation (different CDKs and their cyclins, SMC3), mitosis (PLK1, TTK), transcription regulation (IRX3, MEN1), cell migration/division (BCAR1), and E3 ubiquitination ligases (RBBP6, FBXO32) were downregulated, whereas upregulation was seen in genes mediating chemotaxis (CXCL8, IL6, CCL2), and DNA-damage or stress (EGR1, ARC, GADD45A/B). In a long-term experiment, resistance development was seen in 1/5 cases treated with dinaciclib, but this could be prevented by abemaciclib. Vice versa, adding TMZ abrogated therapeutic effects of dinaciclib and growth was comparable to controls. With this comprehensive analysis, we confirm the therapeutic activity of selective CDKi in GBM. In addition to the careful selection of individual drugs, the timing of each combination partner needs to be considered to prevent resistance.

Small-molecule inhibitors of breast cancer-related targets: Potential therapeutic agents for breast cancer

Despite dramatic advances in cancer research and therapy, breast cancer remains a tricky health problem and represents a top biomedical research priority. Nowadays, breast cancer is still the leading cause of malignancy-related deaths in women, and incidence and mortality rates of it are expected to increase significantly the next years. Currently more and more researchers are interested in the study of breast cancer by its arising in young women. The common treatment options of breast cancer are chemotherapy, immunotherapy, hormone therapy, surgery, and radiotherapy. Most of them require chemical agents, such as PARP inhibitors, CDK4/6 inhibitors, and HER2 inhibitors. Recent studies suggest that some targets or pathways, including BRD4, PLK1, PD-L1, HDAC, and PI3K/AKT/mTOR, are tightly related to the occurrence and development of breast cancer. This article reviews the interplay between these targets and breast cancer and summarizes the progress of current research on small molecule inhibitors of these anti-breast cancer targets. The review aims to provide structural and theoretical basis for designing novel anti-breast cancer agents.

miR-10a as a therapeutic target and predictive biomarker for MDM2 inhibition in acute myeloid leukemia

Pharmacological inhibition of MDM2/4, which activates the critical tumor suppressor p53, has been gaining increasing interest as a strategy for the treatment of acute myeloid leukemia (AML). While clinical trials of MDM2 inhibitors have shown promise, responses have been confined to largely molecularly undefined patients, indicating that new biomarkers and optimized treatment strategies are needed. We previously reported that the microRNA miR-10a is strongly overexpressed in some AML, and demonstrate here that it modulates several key members of the p53/Rb network, including p53 regulator MDM4, Rb regulator RB1CC1, p21 regulator TFAP2C, and p53 itself. The expression of both miR-10a and its downstream targets were strongly predictive of MDM2 inhibitor sensitivity in cell lines, primary AML specimens, and correlated to response in patients treated with both MDM2 inhibitors and cytarabine. Furthermore, miR-10a inhibition induced synergy between MDM2 inhibitor Nutlin-3a and cytarabine in both in vitro and in vivo AML models. Mechanistically this synergism primarily occurs via the p53-mediated activation of cytotoxic apoptosis at the expense of cytoprotective autophagy. Together these findings demonstrate that miR-10a may be useful as both a biomarker to identify patients most likely to respond to cytarabine+MDM2 inhibition and also a druggable target to increase their efficacy.

Targeting DNA Damage Response and Replication Stress in Pancreatic Cancer

BACKGROUND & AIMS

Continuing recalcitrance to therapy cements pancreatic cancer (PC) as the most lethal malignancy, which is set to become the second leading cause of cancer death in our society. The study aim was to investigate the association between DNA damage response (DDR), replication stress, and novel therapeutic response in PC to develop a biomarker-driven therapeutic strategy targeting DDR and replication stress in PC.

METHODS

We interrogated the transcriptome, genome, proteome, and functional characteristics of 61 novel PC patient-derived cell lines to define novel therapeutic strategies targeting DDR and replication stress. Validation was done in patient-derived xenografts and human PC organoids.

RESULTS

Patient-derived cell lines faithfully recapitulate the epithelial component of pancreatic tumors, including previously described molecular subtypes. Biomarkers of DDR deficiency, including a novel signature of homologous recombination deficiency, cosegregates with response to platinum (P < .001) and PARP inhibitor therapy (P < .001) in vitro and in vivo. We generated a novel signature of replication stress that predicts response to ATR (P < .018) and WEE1 inhibitor (P < .029) treatment in both cell lines and human PC organoids. Replication stress was enriched in the squamous subtype of PC (P < .001) but was not associated with DDR deficiency.

CONCLUSIONS

Replication stress and DDR deficiency are independent of each other, creating opportunities for therapy in DDR-proficient PC and after platinum therapy.

Kinome Array Profiling of Patient-Derived Pancreatic Ductal Adenocarcinoma Identifies Differentially Active Protein Tyrosine Kinases

Pancreatic cancer remains one of the most difficult malignancies to treat. Minimal improvements in patient outcomes and persistently abysmal patient survival rates underscore the great need for new treatment strategies. Currently, there is intense interest in therapeutic strategies that target tyrosine protein kinases. Here, we employed kinome arrays and bioinformatic pipelines capable of identifying differentially active protein tyrosine kinases in different patient-derived pancreatic ductal adenocarcinoma (PDAC) cell lines and wild-type pancreatic tissue to investigate the unique kinomic networks of PDAC samples and posit novel target kinases for pancreatic cancer therapy. Consistent with previously described reports, the resultant peptide-based kinome array profiles identified increased protein tyrosine kinase activity in pancreatic cancer for the following kinases: epidermal growth factor receptor (EGFR), fms related receptor tyrosine kinase 4/vascular endothelial growth factor receptor 3 (FLT4/VEGFR-3), insulin receptor (INSR), ephrin receptor A2 (EPHA2), platelet derived growth factor receptor alpha (PDGFRA), SRC proto-oncogene kinase (SRC), and tyrosine kinase non receptor 2 (TNK2). Furthermore, this study identified increased activity for protein tyrosine kinases with limited prior evidence of differential activity in pancreatic cancer. These protein tyrosine kinases include B lymphoid kinase (BLK), Fyn-related kinase (FRK), Lck/Yes-related novel kinase (LYN), FYN proto-oncogene kinase (FYN), lymphocyte cell-specific kinase (LCK), tec protein kinase (TEC), hemopoietic cell kinase (HCK), ABL proto-oncogene 2 kinase (ABL2), discoidin domain receptor 1 kinase (DDR1), and ephrin receptor A8 kinase (EPHA8). Together, these results support the utility of peptide array kinomic analyses in the generation of potential candidate kinases for future pancreatic cancer therapeutic development.