A small interfering RNA screen of genes involved in DNA repair identifies tumor-specific radiosensitization by POLQ knockdown

The effectiveness of radiotherapy treatment could be significantly improved if tumor cells could be rendered more sensitive to ionizing radiation (IR) without altering the sensitivity of normal tissues. However, many of the key therapeutically exploitable mechanisms that determine intrinsic tumor radiosensitivity are largely unknown. We have conducted a small interfering RNA (siRNA) screen of 200 genes involved in DNA damage repair aimed at identifying genes whose knockdown increased tumor radiosensitivity. Parallel siRNA screens were conducted in irradiated and unirradiated tumor cells (SQ20B) and irradiated normal tissue cells (MRC5). Using gammaH2AX foci at 24 hours after IR, we identified several genes, such as BRCA2, Lig IV, and XRCC5, whose knockdown is known to cause increased cell radiosensitivity, thereby validating the primary screening end point. In addition, we identified POLQ (DNA polymerase ) as a potential tumor-specific target. Subsequent investigations showed that POLQ knockdown resulted in radiosensitization of a panel of tumor cell lines from different primary sites while having little or no effect on normal tissue cell lines. These findings raise the possibility that POLQ inhibition might be used clinically to cause tumor-specific radiosensitization.

Myxopapillary ependymoma with intracranial metastases

We report spontaneous seeding within the subarachnoid space from a myxopapillary ependymoma that progressed despite surgery and radiotherapy treatment.

Competitive oligonucleotide single-base extension combined with mass spectrometric detection for mutation screening

A rapid, robust and widely applicable mutation detection scheme not requiring radioactivity or gel-based detection is introduced. It is a single-tube, competitive oligonucleotide single-base extension (COSBE) reaction using a pair of primers with the 3'-terminal base complementary to either the normal or mutant allele. Upon hybridization and addition of a polymerase and the nucleotide triphosphate corresponding to the next base after the primer, only those primers properly annealed (i.e., no 3'-terminal mismatch) are extended; products are resolved by molecular weight shifts as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (single-scan spectrum acquisition < < 1 s). For the cystic fibrosis delta F508 polymorphism, 28-mer "normal" (N) and 30-mer "mutant" (M) primers generate 29-mer (N + I) or 31-mer (M + 1) products for homozygotes and both for heterozygotes. Since primer and product molecular weights are relatively low (< 10 kDa) and the mass difference between these are at least that of a single approximately 300-Da nucleotide unit, a low-resolution mass spectrometer is suitable for such measurements.