Palbociclib ups PFS in HER2-/ER+ breast cancer

Effective combination therapies in preclinical endocrine resistant breast cancer models harboring ER mutations

Although endocrine therapy is successfully used to treat patients with estrogen receptor (ER) positive breast cancer, a substantial proportion of this population will relapse. Several mechanisms of acquired resistance have been described including activation of the mTOR pathway, increased activity of CDK4 and activating mutations in ER. Using a patient derived xenograft model harboring a common activating ER ligand binding domain mutation (D538G), we evaluated several combinatorial strategies using the selective estrogen receptor degrader (SERD) fulvestrant in combination with chromatin modifying agents, and CDK4/6 and mTOR inhibitors. In this model, fulvestrant binds WT and MT ER, reduces ER protein levels, and downregulated ER target gene expression. Addition of JQ1 or vorinostat to fulvestrant resulted in tumor regression (41% and 22% regression, respectively) though no efficacy was seen when either agent was given alone. Interestingly, although the CDK4/6 inhibitor palbociclib and mTOR inhibitor everolimus were efficacious as monotherapies, long-term delayed tumor growth was only observed when co-administered with fulvestrant. This observation was consistent with a greater inhibition of compensatory signaling when palbociclib and everolimus were co-dosed with fulvestrant. The addition of fulvestrant to JQ1, vorinostat, everolimus and palbociclib also significantly reduced lung metastatic burden as compared to monotherapy. The combination potential of fulvestrant with palbociclib or everolimus were confirmed in an MCF7 CRISPR model harboring the Y537S ER activating mutation. Taken together, these data suggest that fulvestrant may have an important role in the treatment of ER positive breast cancer with acquired ER mutations.

Pathogenesis and heterogeneity of ovarian cancer

PURPOSE OF REVIEW

The most common type of ovarian cancer, high-grade serous ovarian carcinoma (HGSOC), was originally thought to develop from the ovarian surface epithelium. However, recent data suggest that the cells that undergo neoplastic transformation and give rise to the majority of HGSOC are from the fallopian tube. This development has impacted both translational research and clinical practice, revealing new opportunities for early detection, prevention, and treatment of ovarian cancer.

RECENT FINDINGS

Genomic studies indicate that approximately 50% of HGSOC are characterized by mutations in genes involved in the homologous recombination pathway of DNA repair, especially BRCA1 and BRCA2. Clinical trials have demonstrated successful treatment of homologous recombination-defective cancers with poly-ribose polymerase inhibitors through synthetic lethality. Recently, amplification of CCNE1 was found to be another major factor in HGSOC tumorigenesis, accounting for approximately 20% of all cases. Interestingly, amplification of CCNE1 and mutation of homologous recombination repair genes are mutually exclusive in HGSOC.

SUMMARY

The fallopian tube secretory cell is the cell of origin for the majority of ovarian cancers. Although it remains unclear what triggers neoplastic transformation of these cells, certain tumors exhibit loss of BRCA function or amplification of CCNE1. These alterations represent unique therapeutic opportunities in ovarian cancer.

CDK4/6 inhibitors have potent activity in combination with pathway selective therapeutic agents in models of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) has a poor prognosis, in part, due to the therapy-recalcitrant nature of the disease. Loss of the CDK4/6 inhibitor CDKN2A is a signature genetic event in PDA. Therefore, PDA may be amenable to treatment with pharmaceutical CDK4/6 inhibitors. Surprisingly, response to CDK4/6 inhibition was highly variable in PDA models, and associated with differential suppression of gene expression. Mitotic genes were repressed and FOXM1 was uniformly attenuated; however, genes involved in DNA replication were uniquely suppressed in sensitive models. Aberrant induction of Cyclin E1 was associated with resistance, and knockdown demonstrated synergistic suppression of the cell cycle with CDK4/6 inhibition. Combination therapies are likely required for the effective treatment of disease, and drug screening demonstrated additive/antagonistic interactions with CDK4/6 inhibitors. Agents dependent on mitotic progression (taxanes/PLK1 inhibitors) were antagonized by CDK4/6 inhibition, while the response to 5-FU and gemcitabine exhibited drug specific interactions. PI3K/MTOR and MEK inhibitors potently cooperated with CDK4/6 inhibition. These agents were synergistic with CDK4/6 inhibition, blocked the aberrant upregulation of Cyclin E1, and yielded potent inhibition of tumor cell growth. Together, these data identify novel mechanisms of resistance to CDK4/6 inhibitions and provide a roadmap for combination therapies in the treatment of PDA.

Durability of Kinase-Directed Therapies--A Network Perspective on Response and Resistance

Protein kinase-directed cancer therapies yield impressive initial clinical responses, but the benefits are typically transient. Enhancing the durability of clinical response is dependent upon patient selection, using drugs with more effective pharmacology, anticipating mechanisms of drug resistance, and applying concerted drug combinations. Achieving these tenets requires an understanding of the targeted kinase's role in signaling networks, how the network responds to drug perturbation, and patient-to-patient network variations. Protein kinases create sophisticated, malleable signaling networks with fidelity coded into the processes that regulate their presence and function. Robust and reliable signaling is facilitated through network processes (e.g., feedback regulation, and compensatory signaling). The routine use of kinase-directed therapies and advancements in both genomic analysis and tumor cell biology are illuminating the complexity of tumor network biology and its capacity to respond to perturbations. Drug efficacy is attenuated by alterations of the drug target (e.g., steric interference, compensatory activity, and conformational changes), compensatory signaling (bypass mechanisms and phenotype switching), and engagement of other oncogenic capabilities (polygenic disease). Factors influencing anticancer drug response and resistance are examined to define the behavior of kinases in network signaling, mechanisms of drug resistance, drug combinations necessary for durable clinical responses, and strategies to identify mechanisms of drug resistance.

Breakthrough cancer medicine and its impact on novel drug development in China: report of the US Chinese Anti-Cancer Association (USCACA) and Chinese Society of Clinical Oncology (CSCO) Joint Session at the 17th CSCO Annual Meeting

The US Chinese Anti-Cancer Association (USCACA) teamed up with Chinese Society of Clinical Oncology (CSCO) to host a joint session at the17th CSCO Annual Meeting on September 20th, 2014 in Xiamen, China. With a focus on breakthrough cancer medicines, the session featured innovative approaches to evaluate breakthrough agents and established a platform to interactively share successful experiences from case studies of 6 novel agents from both the United States and China. The goal of the session is to inspire scientific and practical considerations for clinical trial design and strategy to expedite cancer drug development in China. A panel discussion further provided in-depth advice on advancing both early and full development of novel cancer medicines in China.

Cell-cycle reprogramming for PI3K inhibition overrides a relapse-specific C481S BTK mutation revealed by longitudinal functional genomics in mantle cell lymphoma

Despite the unprecedented clinical activity of the Bruton tyrosine kinase (BTK) inhibitor ibrutinib in mantle cell lymphoma (MCL), acquired resistance is common. By longitudinal integrative whole-exome and whole-transcriptome sequencing and targeted sequencing, we identified the first relapse-specific C481S mutation at the ibrutinib binding site of BTK in MCL cells at progression following a durable response. This mutation enhanced BTK and AKT activation and tissue-specific proliferation of resistant MCL cells driven by CDK4 activation. It was absent, however, in patients with primary resistance or progression following transient response to ibrutinib, suggesting alternative mechanisms of resistance. Through synergistic induction of PIK3IP1 and inhibition of PI3K-AKT activation, prolonged early G1 arrest induced by PD 0332991 (palbociclib) inhibition of CDK4 sensitized resistant lymphoma cells to ibrutinib killing when BTK was unmutated, and to PI3K inhibitors independent of C481S mutation. These data identify a genomic basis for acquired ibrutinib resistance in MCL and suggest a strategy to override both primary and acquired ibrutinib resistance.

SIGNIFICANCE

We have discovered the first relapse-specific BTK mutation in patients with MCL with acquired resistance, but not primary resistance, to ibrutinib, and demonstrated a rationale for targeting the proliferative resistant MCL cells by inhibiting CDK4 and the cell cycle in combination with ibrutinib in the presence of BTK(WT) or a PI3K inhibitor independent of BTK mutation. As drug resistance remains a major challenge and CDK4 and PI3K are dysregulated at a high frequency in human cancers, targeting CDK4 in genome-based combination therapy represents a novel approach to lymphoma and cancer therapy. Cancer Discov; 4(9); 1022-35. ©2014 AACR. This article is highlighted in the In This Issue feature, p. 973.