The year 2015 marks the 50th anniversary since the discovery of the anticancer potential of cisplatin and it remains just as useful now as it did back then, especially for the treatment of some endocrine-related cancers like ovarian and testicular carcinomas. Since its discovery, five other platin drugs have received approval in various countries. While several new platin drugs are in preclinical development, in the last decade only two new platin drugs have entered clinical trials, LA-12 and dicycloplatin, reflecting a shift in research focus from new drug design to improved formulations of already approved platin drugs. These formulations include their encapsulation with macrocycles to slow and prevent their degradation by proteins and peptides; their attachment to nanoparticles to passively target solid tumours through the enhanced permeability and retention effect and their coordination to important nutrients, proteins, antibodies and aptamers for active tumour targeting. These formulation methods have all shown potential but none have yet yielded a new marketable medicine containing a platin drug. The reasons for this are problems of consistent drug loading, controlling the location and timing of drug release and the inherent toxicity of some of the drug delivery vehicles. In addition to drug delivery, functional genomics is now playing an increasing role in predicting patients' responses to platin chemotherapy and their likelihood of experiencing severe side effects.

Cancers that utilize the alternative lengthening of telomeres (ALT) mechanism for telomere maintenance are often difficult to treat and have a poor prognosis. They are also commonly deficient for expression of ATRX protein, a repressor of ALT activity, and a component of promyelocytic leukemia nuclear bodies (PML NBs) that are required for intrinsic immunity to various viruses. Here, we asked whether ATRX deficiency creates a vulnerability in ALT cancer cells that could be exploited for therapeutic purposes. We showed in a range of cell types that a mutant herpes simplex virus type 1 (HSV-1) lacking ICP0, a protein that degrades PML NB components including ATRX, was ten- to one thousand-fold more effective in infecting ATRX-deficient cells than wild-type ATRX-expressing cells. Infection of co-cultured primary and ATRX-deficient cancer cells revealed that mutant HSV-1 selectively killed ATRX-deficient cells. Sensitivity to mutant HSV-1 infection also correlated inversely with PML protein levels, and we showed that ATRX upregulates PML expression at both the transcriptional and post-transcriptional levels. These data provide a basis for predicting, based on ATRX or PML levels, which tumors will respond to a selective oncolytic herpesvirus.