Protein kinase C beta in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a disease with few therapeutic options. Protein kinase C beta (PKCbeta) is involved in important cellular functions. Enzastaurin (LY317615.HCl) is a novel inhibitor of PKC in clinical development. MPM cell lines (7) and patient tumor tissues (24) were evaluated for expression of PKCbeta by immunoblotting and immunohistochemistry, respectively. In-vitro cell growth assays were performed with enzastaurin with or without cisplatin. Cell migration was evaluated with the wound healing assay. Downstream signaling (survival and focal adhesion pathways) was studied by immunoblotting for related molecules in the presence of phorbol ester with or without enzastaurin. Expression for PKCbeta1 was seen in all cases, with a mean integrated optical density of 152.5 (standard deviation=95.47, n=24), whereas PKCbeta2 expression was less intense, with a mean integrated optical density of 11.45 (standard deviation=16.27, n=21). There was a trend toward lower overall survival among patients expressing above-median PKCbeta1 (P=0.064), but not PKCbeta2. Robust expression of PKCbeta1 and low expression of PKCbeta2 were observed in MPM cell lines. Treatment of MPM cell lines with enzastaurin revealed an IC50 of 5 micromol/l, and strong synergism was observed when combined with cisplatin. Wound healing assay revealed that treatment of H2461 cells with enzastaurin reduced migration by 59.2%. Enzastaurin treatment led to disruption of F-actin architecture. Downstream signaling showed reduced phosphorylation of AKT, FAK (focal adhesion kinase), p130Cas, S6 ribosomal protein, and paxillin. PKCbeta1 was expressed in the majority of MPM samples. Enzastaurin has preclinical activity against MPM, and exhibited synergism with cisplatin. PKCbeta inhibition in MPM might be able to reduce the invasiveness of MPM by affecting cytoskeletal function.

[NSCLC: update on second line therapy following ASCO 2007]

Since the year 2000 second line therapy for pre-treated non-small cell lung cancer patients has been established. There are currently two chemotherapeutic agents - docetaxel (Taxotere) and pemetrexed (Alimta) - which have been approved for second line treatment in Austria in addition to the tyrosinkinase-inhibitor erlotinib (Tarceva). In randomised trials these agents have shown a clear advantage over best supportive care in pre-treated patients in terms of overall survival and quality of life. However, these compounds also cause considerable drug-specific toxicities. Therefore there is an urgent need for new treatment options with higher efficacy and a lower burden of toxicity. At ASCO 2007, results of randomised trials were presented concerning new chemotherapeutic agents, such as vinflunine as well as targeting agents such as gefitinib, without affecting outcome. Another trial comparing a standard dose of pemetrexed with a higher dose also showed no improvement in outcome. A comparison of immediate application with delayed application of docetaxel after primary treatment demonstrated improved progression-free survival in selected patients in the immediate study arm but this did not translate to a survival benefit. The results of these trials may add further treatment options to the present portfolio of agents and concepts in this setting and give some optimism for the near future. At present, no changes need to be made in the options for standard second-line treatment of NSCLC in view of the results presented at ASCO 2007.

Enzastaurin

PURPOSE OF REVIEW

Enzastaurin - a novel oral antitumor agent that selectively inhibits protein kinase Cbeta activity - has demonstrated promise in phase I and II trials in various advanced cancers, and is being investigated in multiple hematologic malignancies and solid tumors.

RECENT FINDINGS

Enzastaurin (LY317615) was initially developed as an antiangiogenic cancer therapy. Subsequent preclinical studies showed its antitumor effect by inhibiting tumor proliferation and inducing apoptosis on multiple cancer cell lines as well as xenograft models. Enzastaurin not only inhibits protein kinase Cbeta activity but also suppresses signaling through the phosphoinositide-3 kinase/AKT pathway. Based on the phase I study, 525 mg/day is the recommended dose for oral enzastaurin. It is well tolerated at this dose, with no clinically significant grade 3 or 4 toxicities. A recent phase II study of enzastaurin in patients with relapsed or refractory diffuse large B-cell lymphoma showed enzastaurin to be associated with prolonged freedom from progression. Several preliminary studies showed promising results in patients with various advanced cancers and suggested that enzastaurin can be safely used long term in combination with traditional chemotherapies.

SUMMARY

Enzastaurin is emerging as a promising new antitumor treatment. This review addresses the mechanism of action, development, preclinical studies, and clinical study results with enzastaurin.