Volasertib Versus Chemotherapy in Platinum-Resistant or -Refractory Ovarian Cancer: A Randomized Phase II Groupe des Investigateurs Nationaux pour l'Etude des Cancers de l'Ovaire Study

Novel Mechanisms of Resistance to Investigational Molecularly Targeted Drugs

Drug resistance is a critical problem inhibiting the effective use of targeted molecular cancer therapies. Investigators have revealed a variety of resistance mechanisms, including alterations in drug targets, activation of pro-survival pathways, and the ineffective induction of cell death. The key alterations driving this resistance are likely condition-dependent, and a detailed analysis would be required to characterize these diverse alterations under a variety of conditions in order to facilitate practical precision medicine for treating individual cancer patients. We have been investigating the molecular mechanisms of anti-cancer drug resistance, and analyzed our original resistant cells against anti-mitotic kinase inhibitors. This study suggests that novel mechanisms reduce cytokinetic dysregulation caused by those inhibitors, and anti-apoptotic activities are associated with resistant phenotypes. These observations suggest that the activation of various bypass mechanisms may allow cancer cells to avoid the selective antiproliferative effect of molecularly targeted drugs, and such bypass activation mechanism would thus be a critical target for designing combination chemotherapy to overcome non-genetic drug resistance.

Cell cycle proteins as promising targets in cancer therapy

Cancer is characterized by uncontrolled tumour cell proliferation resulting from aberrant activity of various cell cycle proteins. Therefore, cell cycle regulators are considered attractive targets in cancer therapy. Intriguingly, animal models demonstrate that some of these proteins are not essential for proliferation of non-transformed cells and development of most tissues. By contrast, many cancers are uniquely dependent on these proteins and hence are selectively sensitive to their inhibition. After decades of research on the physiological functions of cell cycle proteins and their relevance for cancer, this knowledge recently translated into the first approved cancer therapeutic targeting of a direct regulator of the cell cycle. In this Review, we focus on proteins that directly regulate cell cycle progression (such as cyclin-dependent kinases (CDKs)), as well as checkpoint kinases, Aurora kinases and Polo-like kinases (PLKs). We discuss the role of cell cycle proteins in cancer, the rationale for targeting them in cancer treatment and results of clinical trials, as well as the future therapeutic potential of various cell cycle inhibitors.

Clinical Development of Anti-mitotic Drugs in Cancer

Mitosis is one of the most fundamental processes of life by which a mammalian cell divides into two daughter cells. Mitosis has been an attractive target for anticancer therapies since fast proliferation was identified as one of the hallmarks of cancer cells. Despite efforts into developing specific inhibitors for mitotic kinases and kinesins, very few drugs have shown the efficiency of microtubule targeting-agents in cancer cells with paclitaxel being the most successful. A deeper translational research accompanying clinical trials of anti-mitotic drugs will help in identifying potent biomarkers predictive for response. Here, we review the current knowledge of mitosis targeting agents that have been tested so far in the clinics.

Effect of AKT3 expression on MYC- and caspase-8-dependent apoptosis caused by polo-like kinase inhibitors in HCT 116 cells

Polo-like kinase (PLK) is a cell-cycle regulator that is overexpressed in several cancer cell types. Polo-like kinase is considered a novel target for cancer therapies, and several PLK inhibitors (PLKis), including BI 2536, BI 6727, and GSK461364, have been developed. In this study, we established five BI 2536-resistant cell lines from human colorectal cancer HCT 116 cells, to explore the resistance mechanism and identify predictable biomarkers of PLKis. We showed that PLKi-induced caspase-8 activation was attenuated in the BI 2536-resistant cell lines. We also showed that the expression of P-glycoprotein (P-GP) and AKT3 was upregulated, whereas that of MYC was downregulated in some BI 2536-resistant cell lines. Expression of P-GP conferred resistance to PLKis, and PLKi-induced apoptosis was dependent on MYC and caspase-8 in HCT 116 cells. We also showed for the first time that AKT3 suppressed BI 6727-induced caspase-8 activation and conferred resistance to PLKis. Collectively, these results indicate that MYC, caspase-8, P-GP, and AKT3 play critical roles in PLKi-induced apoptosis. Therefore, they are candidate biomarkers of the pharmacological efficacy of PLKis.

Negative trials in ovarian cancer: is there such a thing as too much optimism?

Recently, two clinical trials of novel agents in metastatic ovarian cancer were published: a phase 3 study of nintedanib and a phase 2 study of volasertib. There seemed to be discordance between the results and conclusions in the publication of both these trials. Despite not very optimistic results, the studies concluded optimistically in favor of the new agents under study. Using these examples, we point out the discrepancies and the risks of concluding optimistically based on statistical significance when the actual benefit is minimal. We also appeal against conducting large phase 3 trials that require significant resources without good phase 2 evidence for doing so.

BORA-dependent PLK1 regulation: A new weapon for cancer therapy?

The mitotic kinase polo like kinase 1 (PLK1) is overexpressed in many cancers and its inhibition slows down proliferation and increases apoptosis in cancer cell lines. Understanding how PLK1 is activated is therefore crucial for the development of novel PLK1 inhibitors with anticancer properties. We recently identified a conserved regulatory loop leading to PLK1 activation that involves cyclin-dependent kinase 1 (CDK1).

Therapeutic drug monitoring of 5-fluorouracil

PURPOSE

For over 50 years, 5-FU has played a critical role in the systemic chemotherapy of cancer patients. 5-FU serves as the main backbone of combination chemotherapy for patients with colorectal cancer in both the adjuvant and metastatic disease settings. Herein, we review the current status of 5-FU therapeutic drug monitoring (TDM) and discuss its potential role in the clinical practice setting.

METHOD

PubMed and abstracts from the American Society of Clinical Oncology were searched up through September 2015 for clinical data relating to 5-FU TDM.

RESULTS

5-FU dosing has been typically determined by using body surface area (BSA). However, it is now well established that BSA-based 5-FU dosing is correlated with a wide variation of 5-FU systemic exposure. Pharmacokinetic (PK) studies of 5-FU systemic exposure have shown a wide range of interpatient variation of 5-FU plasma drug levels. Over the past 30 years, increasing efforts have been placed on optimizing 5-FU dosing with the main goals of increasing antitumor efficacy while reducing drug-associated toxicity. There is growing evidence to show that 5-FU dosing based on plasma 5-FU drug level is feasible and that 5-FU TDM can improve clinical outcomes by improving efficacy of 5-FU-based combination regimens and reducing toxicities.

CONCLUSION

Dose adjustment of 5-FU is feasible, and PK-based dosing can significantly improve clinical outcomes by reducing toxicities and improving efficacy.