During the last decade, there has been an increased focus on understanding the factors that influence the chance of success of a drug molecule in development. Recent publications have highlighted that the aromatic ring count of a drug molecule also has an influence on its developability profile. This article reviews both the positive and negative consequences of including aromatic rings in drug molecules based on the recent literature and presents a thorough review of recent publications describing the influence of aromatic ring count on compound developability. These conclusions are analysed alongside their implications for the medicinal chemist. The authors also highlight the limitations of recent analyses; this includes a particular emphasis on the restricted diversity of the compound collections used. Modern medicinal chemists work in a very restricted area of the available drug-like chemical space, although there is evidence that safe compounds can be identified outside of conventional drug-like chemical space. It is true that current evidence implies that drug molecules with > 3 aromatic rings in are undesirable and that heteroaromatics perform better than carboaromatic overall. However, the analyses performed so far have only used compounds designed for oral administration, which were provided from pharmaceutical companies' collections, and were therefore limited in diversity.

A drastic difference exists between the 5-year survival rates of colorectal cancer patients with localized cancer and distal organ metastasis. The liver is the most favorable organ for cancer metastases from the colorectum. Beyond the liver-colon anatomic relationship, emerging evidence highlights the impact of liver immune microenvironment on colorectal liver metastasis. Prior to cancer cell dissemination, hepatocytes secrete multiple factors to recruit or activate immune cells and stromal cells in the liver to form a favorable premetastatic niche. The liver-resident cells including Kupffer cells, hepatic stellate cells, and liver-sinusoidal endothelial cells are co-opted by the recruited cells, such as myeloid-derived suppressor cells and tumor-associated macrophages, to establish an immunosuppressive liver microenvironment suitable for tumor cell colonization and outgrowth. Current treatments including radical surgery, systemic therapy, and localized therapy have only achieved good clinical outcomes in a minority of colorectal cancer patients with liver metastasis, which is further hampered by high recurrence rate. Better understanding of the mechanisms governing the metastasis-prone liver immune microenvironment should open new immuno-oncology avenues for liver metastasis intervention.

Colorectal cancer is the third most common cancer in the world. Despite surgery, up to 50% of patients relapse with incurable disease. First-line chemotherapy uses the topoisomerase 1 (TOP1) poison irinotecan, which triggers cell death by trapping TOP1 on DNA. The removal of TOP1 peptide from TOP1–DNA breaks is conducted by tyrosyl-DNA phosphodiesterase 1 (TDP1). Despite putative roles for TDP1 and TOP1 in colorectal cancer, their role in cellular and clinical responses to TOP1-targeting therapies remains unclear. Here, we show varying expression levels of TOP1 and TDP1 polypeptides in multiple colorectal cancer cell lines and in clinical colorectal cancer samples. TDP1 overexpression or TOP1 depletion is protective. Conversely, TDP1 depletion increases DNA-strand breakage and hypersensitivity to irinotecan in a TOP1-dependent manner, presenting a potential therapeutic opportunity in colorectal cancer. TDP1 protein levels correlate well with mRNA and with TDP1 catalytic activity. However, no correlation is observed between inherent TDP1 or TOP1 levels alone and irinotecan sensitivity, pointing at their limited utility as predictive biomarkers in colorectal cancer. These findings establish TDP1 as a potential therapeutic target for the treatment of colorectal cancer and question the validity of TOP1 or TDP1 on their own as predictive biomarkers for irinotecan response. Mol Cancer Ther; 14(2); 575–85. ©2014 AACR.