Phase I dose-escalation trial of checkpoint kinase 1 inhibitor MK-8776 as monotherapy and in combination with gemcitabine in patients with advanced solid tumors

Cyclin-dependent kinase inhibitors for cancer therapy: a patent review (2009 - 2014)

INTRODUCTION

Cell cycle deregulation is a common characteristic of cancer cells. Progression through the cell cycle is controlled by enzymes known as cyclin-dependent kinases (CDKs), whose activity can be upregulated by a wide range of molecular mechanisms. Based on these observations, small molecule CDK inhibitors are being developed as potential cancer therapeutics. Some of these compounds have entered Phase III clinical trials and one of them, palbociclib, recently received accelerated approval from the FDA. However, the complexity of CDK biology and the undesired side effects of the existing inhibitors mean that the hunt for new CDK-targeting drug candidates continues.

AREAS COVERED

This article reviews patent applications related to small molecule CDK inhibitors published between 2009 and 2014.

EXPERT OPINION

Clinical trials with pan-specific inhibitors have generally yielded unambiguously positive outcomes. However, better results have been achieved with highly specific inhibitors of CDK4/CDK6. This may be due to several factors and has generated considerable interest in the discovery of new mono-specific CDK inhibitors. The development of such compounds is challenging because all CDKs have very similar active sites. Aside from this issue of selectivity, another key challenge is the identification of patients who will benefit from specific therapies.

Topotecan synergizes with CHEK1 (CHK1) inhibitor to induce apoptosis in ovarian cancer cells

Background

Topotecan (TPT) is a therapeutic option for women with platinum-resistant or -refractory ovarian cancer. However, the dose-limiting toxicity of TPT is myelosuppression. This led us to seek a combination treatment to augment TPT anti-cancer activity in a cancer-targeted manner. Ovarian serous cancers, a major subtype, show dysregulated DNA repair pathway and often display a high level of CHEK1 (CHK1), a cell cycle regulator and DNA damage sensor. CHEK1 inhibitors are a novel approach to treatment, and have been used as single agents or in combination chemotherapy in many cancers.

Methods

We evaluated the cellular effects of TPT in a panel of high grade serous (HGS) and non-HGS ovarian cancer cells. We then determined IC50s of TPT in the absence and presence of CHEK1 inhibitor, PF477736. Synergism between TPT and PF477736 was calculated based on cellular viability assays. Cytotoxic effect of the combined treatment was compared with apoptotic activities by Caspase3/7 activity assay and Western blotting of cleaved-PARP1 and γH2AX.

Results

Non-HGS ovarian cancer cells were generally more sensitive to TPT treatment compared to HGS ovarian cancer cells. When combined with CHEK1 inhibitor, TPT potently and synergistically inhibited the proliferation of HGS ovarian cancer cells. This dramatic synergism in cellular toxicity was consistent with increases in markers of apoptosis.

Conclusions

Our findings suggest that the addition of CHEK1 inhibitor increases the response of ovarian cancer cells to TPT. Furthermore, reduced dosages of both drugs achieved maximal cytotoxic effects by combining TPT with CHEK1 inhibitor. This strategy would potentially minimize side effects of the drugs for extended clinical benefit.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1231-z) contains supplementary material, which is available to authorized users.