26 ORAL Phase Ib and pharmacodynamic study of the MEK inhibitor AZD6244 (ARRY-142886) in patients with advanced solid malignancies

Dual inhibition of mitogen-activated protein kinase kinase and mammalian target of rapamycin in differentiated and anaplastic thyroid cancer

CONTEXT

Differentiated thyroid cancer and anaplastic thyroid cancer tumors frequently have activation of the ras/raf /MAPK kinase (MEK)/ERK and phosphatidylinositol 3-kinase (PI-3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathways.

OBJECTIVE

The objective of the study was to investigate the efficacy of MEK and mTOR inhibitors in preclinical thyroid cancer treatment models with defined mutation status.

EXPERIMENTAL DESIGN

The MEK inhibitor AZD6244 (ARRY-142886) and mTOR inhibitor rapamycin were tested separately and in combination in 10 differentiated thyroid cancer and anaplastic thyroid cancer cell lines and in a xenograft model for evidence of pathway inhibition, growth inhibition, apoptosis, and long-range adaptation and resistance.

RESULTS

Seven of 10 tested lines had evidence of significant basal activity of the PI-3K/AKT/mTOR pathway, with elevated phosphorylated AKT and phosphorylated p70 S6 kinase. Activation of ras/RAF/MEK/ERK was equally common in this panel. All 10 lines exhibited better than 60% growth inhibition with combined MEK and mTOR inhibition, including lines with BRAF, Ret-PTC, ras, and PTEN mutations. Rapamycin or AZD6244 alone achieved this threshold in six and two lines, respectively. Dual-pathway inhibition in the Ret-PTC mutant cell line TPC1 caused an intense G(1) arrest in cell culture and reversible cytostatic inhibition in a xenograft model. We did not observe significant feedback up-regulation of AKT activation in either acute or prolonged exposures.

CONCLUSION

These preclinical results support the inclusion of thyroid cancer patients in early-phase clinical trials combining RAS/RAF/MEK/ERK and PI-3K/AKT/mTOR pathway inhibition.

K-ras as a target for lung cancer therapy

K-ras is currently accepted to be the most frequently mutated oncogene in non-small cell lung cancer. In addition, tumors harboring mutant K-ras seem to be refractory to most available systemic therapies, making K-ras an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the putative K-ras-directed therapeutic agents tested have demonstrated clinical activity. However, many of these agents have multiple targets, and their antitumor effects may not be due to K-ras inhibition. To date, no selective, specific inhibitor of the K-ras pathway is available for routine clinical use.

Overcoming resistance to molecularly targeted anticancer therapies: Rational drug combinations based on EGFR and MAPK inhibition for solid tumours and haematologic malignancies

Accumulating evidence suggests that cancer can be envisioned as a "signaling disease", in which alterations in the cellular genome affect the expression and/or function of oncogenes and tumour suppressor genes. This ultimately disrupts the physiologic transmission of biochemical signals that normally regulate cell growth, differentiation and programmed cell death (apoptosis). From a clinical standpoint, signal transduction inhibition as a therapeutic strategy for human malignancies has recently achieved remarkable success. However, as additional drugs move forward into the clinical arena, intrinsic and acquired resistance to "targeted" agents becomes an issue for their clinical utility. One way to overcome resistance to targeted agents is to identify genetic and epigenetic aberrations underlying sensitivity/resistance, thus enabling the selection of patients that will most likely benefit from a specific therapy. Since resistance often ensues as a result of the concomitant activation of multiple, often overlapping, signaling pathways, another possibility is to interfere with multiple, cross-talking pathways involved in growth and survival control in a rational, mechanism-based, fashion. These concepts may be usefully applied, among others, to agents that target two major signal transduction pathways: the one initiated by epidermal growth factor receptor (EGFR) signaling and the one converging on mitogen-activated protein kinase (MAPK) activation. Here, we review the molecular mechanisms of sensitivity/resistance to EGFR inhibitors, as well as the rationale for combining them with other targeted agents, in an attempt to overcome resistance. In the second part of the paper, we review MAPK-targeted agents, focusing on their therapeutic potential in haematologic malignancies, and examine the prospects for combinations of MAPK inhibitors with cytotoxic agents or other signal transduction-targeted agents to obtain synergistic anti-tumour effects.