Inducible mismatch repair streamlines forward genetic approaches to target identification of cytotoxic small molecules.

Orphan cytotoxins are small molecules for which the mechanism of action (MoA) is either unknown or ambiguous. Unveiling the mechanism of these compounds may lead to useful tools for biological investigation and new therapeutic leads. In selected cases, the DNA mismatch repair-deficient colorectal cancer cell line, HCT116, has been used as a tool in forward genetic screens to identify compound-resistant mutations, which have ultimately led to target identification. To expand the utility of this approach, we engineered cancer cell lines with inducible mismatch repair deficits, thus providing temporal control over mutagenesis. By screening for compound resistance phenotypes in cells with low or high rates of mutagenesis, we increased both the specificity and sensitivity of identifying resistance mutations. Using this inducible mutagenesis system, we implicate targets for multiple orphan cytotoxins, including a natural product and compounds emerging from a high-throughput screen, thus providing a robust tool for future MoA studies.

Inducible mismatch repair streamlines forward genetic approaches to target identification of cytotoxic small molecules.

Orphan cytotoxins are small molecules for which the mechanism of action (MoA) is either unknown or ambiguous. Unveiling the mechanism of these compounds may lead to useful tools for biological investigation and in some cases, new therapeutic leads. In select cases, the DNA mismatch repair-deficient colorectal cancer cell line, HCT116, has been used as a tool in forward genetic screens to identify compound-resistant mutations, which have ultimately led to target identification. To expand the utility of this approach, we engineered cancer cell lines with inducible mismatch repair deficits, thus providing temporal control over mutagenesis. By screening for compound resistance phenotypes in cells with low or high rates of mutagenesis, we increased both the specificity and sensitivity of identifying resistance mutations. Using this inducible mutagenesis system, we implicate targets for multiple orphan cytotoxins, including a natural product and compounds emerging from a high-throughput screen, thus providing a robust tool for future MoA studies.

Early volume expansion during diarrhea and relative nephroprotection during subsequent hemolytic uremic syndrome.

OBJECTIVES: To determine if interventions during the pre-hemolytic uremic syndrome (HUS) diarrhea phase are associated with maintenance of urine output during HUS. DESIGN: Prospective observational cohort study. SETTINGS: Eleven pediatric hospitals in the United States and Scotland. PARTICIPANTS: Children younger than 18 years with diarrhea-associated HUS (hematocrit level <30% with smear evidence of intravascular erythrocyte destruction), thrombocytopenia (platelet count <150 × 10³/mm³), and impaired renal function (serum creatinine concentration > upper limit of reference range for age). INTERVENTIONS: Intravenous fluid was given within the first 4 days of the onset of diarrhea. OUTCOME MEASURE: Presence or absence of oligoanuria (urine output ≤ 0.5 mL/kg/h for >1 day). RESULTS: The overall oligoanuric rate of the 50 participants was 68%, but was 84% among those who received no intravenous fluids in the first 4 days of illness. The relative risk of oligoanuria when fluids were not given in this interval was 1.6 (95% confidence interval, 1.1-2.4; P = .02). Children with oligoanuric HUS were given less total intravenous fluid (r = -0.32; P = .02) and sodium (r = -0.27; P = .05) in the first 4 days of illness than those without oligoanuria. In multivariable analysis, the most significant covariate was volume infused, but volume and sodium strongly covaried. CONCLUSIONS: Intravenous volume expansion is an underused intervention that could decrease the frequency of oligoanuric renal failure in patients at risk of HUS.