Recent advances with cyclin-dependent kinase inhibitors: therapeutic agents for breast cancer and their role in immuno-oncology

Introduction: Collaborative interactions between several diverse biological processes govern the onset and progression of breast cancer. These processes include alterations in cellular metabolism, anti-tumor immune responses, DNA damage repair, proliferation, anti-apoptotic signals, autophagy, epithelial-mesenchymal transition, components of the non-coding genome or onco-mIRs, cancer stem cells and cellular invasiveness. The last two decades have revealed that each of these processes are also directly regulated by a component of the cell cycle apparatus, cyclin D1.

Area covered: The current review is provided to update recent developments in the clinical application of cyclin/CDK inhibitors to breast cancer with a focus on the anti-tumor immune response.

Expert opinion: The cyclin D1 gene encodes the regulatory subunit of a proline-directed serine-threonine kinase that phosphorylates several substrates. CDKs possess phosphorylation site selectivity, with the phosphate-acceptor residue preceding a proline. Several important proteins are substrates including all three retinoblastoma proteins, NRF1, GCN5, and FOXM1. Over 280 cyclin D3/CDK6 substrates have b\een identified. Given the diversity of substrates for cyclin/CDKs, and the altered thresholds for substrate phosphorylation that occurs during the cell cycle, it is exciting that small molecular inhibitors targeting cyclin D/CDK activity have encouraging results in specific tumors.     

局灶性脑缺血对细胞周期蛋白D1/CDK4基因表达的影响

目的观察脑缺血后细胞周期蛋白（cyclin）D1和它的酶CDK4基因表达，以及这种表达的改变是否影响神经细胞凋亡。方法成年雄性SD大鼠32只随机分为假手术组（n=4）和实验组（n=28），实验组再进一步分为7个亚组（再灌注2h，6h，12h，1d，3d，7d和14d，每组n=4）。应用线栓法建立SD大鼠大脑中动脉阻塞／再灌注模型．TUNEL法检测神经细胞凋亡。原位杂交检测cyclinD1和CDK4mRNA的表达。结果CyclinD1mRNA和CDK4mRNA的表达与凋亡细胞的区域基本相同。再灌注2h脑组织即开始出现神经细胞凋亡，并于1d分别在皮层区和纹状体区达高峰（分别为72．80±4．66和87．75±0．85）。神经细胞cyclinD1mRNA和CDK4mRNA的表达分别于再灌注2h和6h开始逐渐增强，并于12h和1d达高峰（皮质区分别为94．50±2．75和85．75±3．73，纹状体区分别为88．25±5．06和89．80±2．93）。结论CyclinD1和CDK4选择性地在形态学完整或已经有改变的缺血侧神经元和少突胶质细胞内表达。CyclinD1／CD1（4mRNA表达可能是诱导细胞凋亡的重要因素之一。     

Deregulation of the G1/S-phase control in human testicular germ cell tumours

Deregulated cell cycle and defective genome-integrity checkpoints are among the hallmarks of cancer.Here we summarize our recent studies of key components of the GI/S machinery in normal human spermatogenesis, and their abnormalities in testicular germ cell tumours (TGCTs), with special emphasis on carcinoma in situ lesions (CIS). Our combined immunohistochemical and immunoblotting analyses of normal human adult and fetal testes, CIS, seminomas, embryonal carcinomas, and teratomas, revealed an 'unorthodox' spectrum of defects within the so-called RB pathway in TGCTs. The early aberrations included lack of expression of the retinoblastoma tumour suppressor (pRB) and the CDK inhibitor pl9ink4d, and overexpression of cyclin D2. Progression from CIS to invasive TGCTswas associated with loss of another two CDK inhibitors and tumour suppressors: pl6ink4a and pl8ink4c. We also found the lack of pRB and pl9ink4d in fetal gonocytes, the candidate target cell for all types of TGCTs. These findings, together with the status of the Chk2-p53 DNA-integrity checkpoint, are considered in relation to the origin, biology and pathogenesis of TGCTs, and potential implications of the GI/S defects for the curability of these tumours.     

Inflammatory malignant fibrous histiocytomas and dedifferentiated liposarcomas: histological review, genomic profile, and MDM2 and CDK4 status favour a single entity

Inflammatory malignant fibrous histiocytoma (inflammatory MFH) is a very rare tumour that occurs most often in the retroperitoneum. So far, it has been considered to be a special subtype of MFH. As it is now widely accepted that most retroperitoneal pleomorphic MFHs are dedifferentiated liposarcomas, the present study compared histological features, genomic profile (CGH analysis), and MDM2 and CDK4 status (immunohistochemistry, FISH, and quantitative PCR) in inflammatory MFHs from 12 patients and dedifferentiated liposarcomas that had an inflammatory MFH component from eight patients. Metaphase cytogenetic and FISH analyses were also performed on one inflammatory MFH. Histological review showed areas of well-differentiated liposarcoma in nine inflammatory MFHs. CGH analysis showed 12q13-15 amplification or gain in six of seven inflammatory MFHs and in seven of seven dedifferentiated liposarcomas. Immunohistochemistry showed positivity of tumour cells for MDM2 in every tumour in both groups and for CDK4 in ten and seven inflammatory MFHs and dedifferentiated liposarcomas, respectively. Metaphase cytogenetic and FISH analysis performed on one inflammatory MFH showed the presence of a supernumerary large marker chromosome and ring chromosome with high-level amplification of both MDM2 and CDK4 genes. FISH analysis on paraffin wax-embedded sections showed amplifications of MDM2 and CDK4 in seven of seven inflammatory MFHs and in seven of seven dedifferentiated liposarcomas. Quantitative PCR showed amplification of MDM2 in six and of CDK4 in seven of nine inflammatory MFHs. In conclusion, this study strongly suggests that most so-called inflammatory MFHs are dedifferentiated liposarcomas.     

CDK4-pRB-E2F1通路是Aβ1-40诱导皮层神经元凋亡的可能途径

目的:探讨β淀粉样肽_1-40(beta-amyloidpeptide_1-40, Aβ_1-40)诱导大鼠皮层神经元凋亡的可能分子机制。方法:以40mg/L的Aβ_1-40诱导离体培养的大鼠皮层神经元凋亡, 流式细胞仪及免疫印迹方法检测细胞周期相关的周期依赖性激酶4(CDK4)、磷酸化的视网膜神经胶质瘤蛋白(pRB)水平;RT-PCR技术检测E2F1mRNA表达水平;荧光分光光度计检测半胱氨酸基天冬氨酸特异性蛋白酶3(caspase-3)活力;观察在Aβ_1-40诱导凋亡过程中是否伴随上述指标的变化。结果:①CDK4、磷酸化pRB水平在Aβ_1-40作用后2-4h显著升高;②Aβ_1-40孵育3h后皮层神经元E2F1基因表达上调;③Aβ_1-40作用12-24h后caspase-3活力明显升高。结论:CDK4-pRB-E2F1信号转导通路可能在Aβ_1-40诱导的大鼠皮层神经元凋亡中起主要作用。     

CDK9/CYCLIN T1 expression during normal lymphoid differentiation and malignant transformation

CDK9 is a member of the CDC2-like family of kinases. Its cyclin partners are members of the CYCLIN T family (T1, T2a, and T2b) and CYCLIN K. The CDK9/CYCLIN T1 complex is very important in the differentiation programme of several cell types, controlling specific differentiation pathways. Limited data are available regarding the expression of CDK9/CYCLIN T1 in haematopoietic and lymphoid tissues. The aim of this study was to analyse the expression of the CDK9/CYCLIN T1 complex in lymphoid tissue, in order to assess its role in B- and T-cell differentiation and lymphomagenesis. CDK9/CYCLIN T1 expression was found by immunohistochemistry in precursor B and T cells. In peripheral lymphoid tissues, germinal centre cells and scattered B- and T-cell blasts in interfollicular areas expressed CDK9/CYCLIN T1, while mantle cells, plasma cells, and small resting T-lymphocytes displayed no expression of either molecule. CDK9/CYCLIN T1 expression therefore appears to be related to particular stages of lymphoid differentiation/activation. CDK9 and CYCLIN T1 were highly expressed in lymphomas derived from precursor B and T cells, from germinal centre cells, such as follicular lymphomas, and from activated T cells (ie anaplastic large cell lymphomas). Hodgkin and Reed-Sternberg cells of classical Hodgkin's lymphoma also showed strong nuclear staining. Diffuse large B-cell, Burkitt's lymphomas, and peripheral T-cell lymphomas, among T-cell lymphoproliferative disorders, showed a wide range of values. No expression of CDK9 or CYCLIN T1 was detected in mantle cell and marginal zone lymphomas. However, at the mRNA level, an imbalance in the CDK9/CYCLIN T1 ratio was found in follicular lymphoma and diffuse large B-cell lymphomas with germinal centre phenotype, and in the cell lines of classical Hodgkin's lymphomas, Burkitt's lymphomas, and anaplastic large cell lymphoma, in comparison with reactive lymph nodes. These results suggest that the CDK9/CYCLIN T1 complex may affect the activation and differentiation programme of lymphoid cells. The molecular mechanism through which the CDK9/CYCLIN T1 complex is altered in malignant transformation needs to be elucidated.     

血小板第4因子对辐射损伤小鼠骨髓细胞周期的调控机制

目的：检测小鼠骨髓细胞p53、Cyclin D1及CDK4蛋白表达量的变化，以探讨血小板第4因子（PF4）对急性辐射损伤小鼠骨髓细胞保护作用的机制。方法：雄性BALB／c小鼠随机分为3组，第1组（正常对照组）、第2组（单纯照射组）、第3组（PF4保护组），第3组在照射前26h及20h腹腔注射PF440μg／kg，第2、3组全身一次性5Gy ^60Co-γ射线照射，照射后4h取小鼠骨髓细胞，Western blot检测小鼠骨髓细胞内p53、Cyclin D1、CDK4蛋白量表达的变化。结果：第2组、第3组小鼠骨髓细胞p53蛋白量与第1组相比明显升高，而Cyclin D1、CDK4则明显降低（P〈0．05）；第2组与第3组p53蛋白表达量的表达有明显差异（P〈0．05），而Cyclin D1与CDK4无统计学意义（P〉0．05）。结论：p53蛋白在PF4对急性辐射损伤小鼠骨髓细胞周期调控作用中起一定作用。     

SARS-CoV-2 neutralizing antibodies after first vaccination dose in breast cancer patients receiving CDK4/6 inhibitors

Undoubtedly, the development of COVID-19 vaccines displays a critical step towards ending this devastating pandemic, considering their protective benefits in the general population. Yet, data regarding their efficacy and safety in cancer patients are limited. Herein we provide the initial analysis of immune responses after the first dose of vaccination in 21 breast cancer patients receiving cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors. The levels of neutralizing antibodies post vaccination were similar to the matched healthy controls, whereas no safety issues have been raised. Further exploration is needed to reduce the uncertainty of SARS-CoV-2 immunity among cancer patients under treatment.