The new paradigm in the treatment of colorectal cancer: are we hitting the right target?

Screening of potential molecular targets for colorectal cancer therapy

Colorectal cancer is a leading cause of cancer death worldwide. To identify molecular targets for colorectal cancer therapy, we tested small interfering RNAs (siRNAs) against 97 genes whose expression was elevated in human colorectal cancer tissues for the ability to promote apoptosis of human colorectal cancer cells (HT-29 cells). The results indicate that the downregulation of PSMA7 (proteasome subunit, alpha-type, 7) and RAN (ras-related nuclear protein) most efficiently induced apoptosis of HT-29 cells. PSMA7 and RAN were highly expressed in colorectal cancer cell lines compared with normal colon tissues. Furthermore, PSMA7 and RAN were overexpressed in not only colon tumor tissues but also the other tumor tissues. Moreover, in vivo delivery of PSMA7 siRNA and RAN siRNA markedly induced apoptosis in HT-29 xenograft tumors in mice. Thus, silencing of PSMA7 and RAN induces cancer cells to undergo apoptosis, and PSMA7 and RAN might be promising new molecular targets for drug and RNA interference-based therapeutics against colorectal cancer.

Protein kinase Cbeta is an effective target for chemoprevention of colon cancer

Colon cancer develops over a period of 10 to 15 years, providing a window of opportunity for chemoprevention and early intervention. However, few molecular targets for effective colon cancer chemoprevention have been characterized and validated. Protein kinase CbetaII (PKCbetaII) plays a requisite role in the initiation of colon carcinogenesis in a preclinical mouse model by promoting proliferation and increased beta-catenin accumulation. In this study, we test the hypothesis that PKCbetaII is an effective target for colon cancer chemoprevention using enzastaurin (LY317615), a PKCbeta-selective inhibitor, in a mouse model of colon carcinogenesis. We find that enzastaurin potently reduces azoxymethane-induced colon tumor initiation and progression by inhibiting PKCbetaII-mediated tumor cell proliferation and beta-catenin accumulation. Biochemically, enzastaurin reduces expression of the PKCbetaII- and beta-catenin/T-cell factor-regulated genes PKCbetaII, cyclooxygenase II, and vascular endothelial growth factor, three genes implicated in colon carcinogenesis. Our results show that enzastaurin is an effective chemopreventive agent in a mouse model of sporadic colon cancer that significantly reduces both tumor initiation and progression by inhibiting expression of proproliferative genes. Thus, PKCbetaII is an important target for colon cancer chemoprevention and the PKCbeta-selective inhibitor enzastaurin may represent an effective chemopreventive agent in patients at high risk for colon cancer.

Update on clinical data with regimens inhibiting angiogenesis and epidermal growth factor receptor for patients with newly diagnosed metastatic colorectal cancer

As a result of the development of novel chemotherapeutic drugs and targeted biologic agents, the treatment of colon cancer has changed significantly over the past 10 years. Today, we have more active agents to use in colon cancer than ever before. The better understanding underlying the pathogenesis of this disease at the molecular level has allowed us to take advantage of 2 key pathways, the angiogenic and epidermal growth factor (EGF) signaling pathways. The combination of traditional chemotherapy drugs with agents that inhibit these pathways has led to a significant improvement in survival. At present, patients with metastatic colon cancer routinely achieve a median survival time > 2 years. The numerous agents available have made the choice of initial treatment more difficult for a newly diagnosed patient. Herein, we review the 2 main molecular targets of biologic therapy in colon cancer and examine the clinical evidence for regimens that inhibit angiogenesis and EGF receptor alone or in combination for newly diagnosed metastatic colorectal cancer.