Current tools for the inhibition of microRNA (miR) function are limited to modified antisense oligonucleotides, sponges, and decoy RNA molecules and none have been used to understand miR function during development. CRISPR/Cas mediated deletion of miR sequences within the genome requires multiple chromosomal deletions to remove all functional miR family members due to duplications. Here we report a novel plasmid-based miR inhibitor system (PMIS) that expresses a new RNA molecule, which inhibits miR family members in cells and mice. The PMIS engineered RNA optimal secondary structure, flanking sequences and specific antisense miR oligonucleotide sequence bind the miR in a stable complex to inhibit miR activity. In cells, one PMIS can effectively inhibit miR family members that share the same seed sequence. The PMIS shows no off-target effects or toxicity and is highly specific for miRs sharing identical seed sequences. Transgenic mice expressing both PMIS-miR-17-18 and PMIS-miR-19-92 show similar phenotypes of miR-17-92 knockout mice. Interestingly, mice only expressing PMIS-miR-17-18 have developmental defects distinct from mice only expressing PMIS-miR-19-92 demonstrating usefulness of the PMIS system to dissect different functions of miRs within clusters. Different PMIS miR inhibitors can be linked together to knockdown multiple miRs expressed from different chromosomes. Inhibition of the miR-17-92, miR-106a-363 and miR-106b-25 clusters reveals new mechanisms and developmental defects for these miRs. We report a new tool to dissect the role of miRs in development without genome editing, inhibit miR function in cells and as a potential new therapeutic reagent.

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Purpose: To introduce a feasible interstitial rotating shield brachytherapy (I‐RSBT) system for treating prostate cancer. With I‐RSBT, the radiation sources are surrounded by catheters that contain shields to enable conformal avoidance of healthy tissues, potentially reducing complications relative to conventional high‐dose‐rate brachytherapy (HDR‐BT) techniques. Methods: The I‐RSBT system is based around ten control cartridges with 9.5 mm × 9.5 mm cross sections. Each control cartridge contains a rotational stepper motor, connected to a lead screw, which drives a platinum‐shielded nitinol catheter containing a 37 GBq Gd‐153 source. Gadolinium‐153 is generated by neutron irradiation of europium‐151 or Gd‐152 and is mass‐producible at reasonable cost. For I‐RSBT delivery, the cartridges are arranged in a box‐shaped magazine in a desired delivery pattern and aligned with a template containing implanted 16 gauge interstitial nitinol needles. Each source/catheter travels down a needle in a helical pattern during the dose delivery process. An I‐RSBT delivery using more than ten needles can be accomplished by dividing the treatment into multiple parts, each with a different cartridge arrangement in the magazine. Results: Treatment plans based on Monte Carlo dose calculations and optimized using the linear least squares technique demonstrated I‐RSBT reduced D1% (minimum dose to hottest 1%) for the urethra and rectum by 20% and 10% respectively, relative to conventional HDR‐BT. The prostate D97% was the same for I‐RSBT as for HDR‐BT. The I‐RSBT treatment time for a 20 Gy delivery would be 3 hours with fresh Gd‐153 sources. Since Gd‐153 has substantially lower gamma ray energies than iridium‐192, I‐RSBT treatments can occur in procedure rooms rather than conventional brachytherapy suites, reducing the disadvantage of the longer I‐RSBT delivery times. Conclusions: Treating prostate cancer with I‐RSBT is technically feasible in reasonable treatment times using platinum‐shielded Gd‐153 sources and the proposed delivery system. University of Iowa Research Foundation

Purpose: To construct and experimentally validate a compensator‐based brachytherapy (CBT) prototype system for treating cervical cancer. With CBT, high‐precision 3‐D manufacturing techniques are used to generate a patient‐specific compensator with spatially‐varying thicknesses, through which an electronic brachytherapy (eBT) source travels to deliver conformal radiation dose distributions. Methods: A prototype cylindrical compensator with 8 octants, each with different thicknesses, was designed. Direct Metal Laser Sintering (DMLS) was used to construct Cobalt‐Chromium (CoCr) and Titanium (Ti) compensators, and a 4‐axis CNC milling (4‐D milling) technique was used to construct a Ti compensator. Gafchromic EBT2 films, held by an acrylic quality assurance (QA) phantom, were irradiated to approximately 125 cGy with an eBT source for both shielded and unshielded cases. The dose at each point on the films was calculated using a TG‐43 dose calculation model that was modified to account for the presence of a compensator by ray‐tracing. Results: Both 4‐D milling and DMLS methods achieved 25.4 urn and 20–40 urn spatial accuracy, respectively. Construction time is approximately 10 hours for 4‐D milling and 2 hours for DMLS. The agreement between the expected EBT2 film dose and measured dose was within 10% without a compensator, and within 15% for non‐thickness‐transition area with a compensator. The use of Monte Carlo dose calculations is expected to improve dosimetric accuracy relative to the current TG‐43‐based method. Conclusion: We expect that patient‐specific compensators can be constructed rapidly in clinical situations using DMLS. CBT is a non‐invasive alternative to supplementary interstitial BT that is expected to improve the dose conformity to bulky cervical cancer tumors relative to conventional intracavitary brachytherapy. University of Iowa Research Foundation