Purpose of review

In this article, we not only review the preclinical and clinical studies of cyclin-dependent kinase (CDK) 4/6 inhibitors in breast cancer, liposarcoma, mantel cell lymphoma, melanoma and germ cell tumors, but also examine promising preclinical data in glioblastoma, renal and ovarian cancer models that may provide directions for future development.

Recent findings

Targeting CDKs has been the focus of considerable basic science and clinical research. The CDK 4/6 inhibitors are a novel class of therapeutics that target the CDK 4/6 kinases that promote transition through the cell cycle. Currently, palbociclib (PD0332991, Pfizer), abemaciclib (LY2835219, Lilly) and ribociclib (LEE011, Novartis) are being investigated in clinical trials. These oral agents offer the hope of clinical efficacy in many tumor types, and have been associated with minimal toxicity. Amplification/overexpression of cyclin D, loss of CDKN2A (p16) and amplification/overexpression of CDK4 are proposed biomarkers of improved response to CDK4/6 inhibition.

Summary

Palbociclib, abemaciclib and ribociclib have demonstrated very promising clinical activity in breast cancer, liposarcoma, mantel cell lymphoma and melanoma. Moreover, CDK4/6 inhibitors have shown promising preclinical activity in glioblastoma, renal and ovarian cancer models that may provide directions for their future clinical development. Further preclinical and clinical research is needed to better understand mechanisms of resistance and develop rational combination therapies with other targeted agents.

Novel treatments that improve outcomes for patients with recurrent or metastatic endometrial cancer (EC) remain an unmet need. Aberrant signaling by fibroblast growth factors (FGFs) and FGF receptors (FGFRs) has been implicated in several human cancers. Activating mutations in FGFR2 have been found in up to 16% of ECs, suggesting an opportunity for targeted therapy. This review summarizes the role of the FGF pathway in angiogenesis and EC, and provides an overview of FGFR-targeted therapies under clinical development for the treatment of EC.

Microarray-based gene expression studies demonstrate that ovarian cancer is both a clinically diverse and molecularly heterogeneous disease compromising subtypes with distinct gene expression patterns that are each associated with statistically significant different clinical outcomes. The information provided by gene expression based assays is promising and deserves incorporation into clinical decision-making. Further studies are needed to determine which subtype signatures are most appropriate to select patients for a given therapy. This process will require the development of standardized molecular diagnostic assays that can be used for retrospective correlative studies and prospective validations of their clinical utility. Recent advances in assay development for FFPE tissues will facilitate accurate and cost-effective classification of ovarian cancer and help move the evolving molecular classification to clinic. The current review will summarize the development of gene expression based assays in ovarian cancer and will describe how the results of studies to date have expanded our appreciation of the heterogeneity of ovarian cancer. We discuss difficulties in the development and validation of molecular classifications in ovarian cancer and we provide future directions how we may be able to soon classify the disease in a manner that might have greater clinical utility.

Antibody-drug conjugates (ADCs) represent a promising new class of cancer therapeutics. Currently more than 60 ADCs are in clinical development, however, only very few trials focus on gynecologic malignancies. In this review, we summarize the most recent advances in ADC drug development with an emphasis on how this progress relates to patients diagnosed with gynecologic malignancies and breast cancer.The cytotoxic payloads of the majority of the ADCs that are currently in clinical trials for gynecologic malignancies or breast cancer are auristatins (MMAE, MMAF), maytansinoids (DM1, DM4), calicheamicin, pyrrolobenzodiazepines and SN-38. Both cleavable and noncleavable linkers are currently being investigated in clinical trials. A number of novel target antigens are currently being validated in ongoing clinical trials including folate receptor alpha, mesothelin, CA-125, NaPi2b, NOTCH3, protein tyrosine kinase-like 7, ephrin-A4, TROP2, CEACAM5, and LAMP1. For most ADCs currently in clinical development, dose-limiting toxicities appear to be unrelated to the targeted antigen but more tightly associated with the payload. Rational drug design involving optimization of the antibody, the linker and the conjugation chemistry is aimed at improving the therapeutic index of new ADCs.Antibody-drug conjugates can increase the efficacy and decrease the toxicity of their payloads in comparison with traditional cyctotoxic agents. A better and quicker translation of recent scientific advances in the field of ADCs into rational clinical trials for patients diagnosed with ovarian, endometrial or cervical cancer could create real improvements in tumor response, survival and quality of life for our patients.