ABSTRACT
Background: Moderate hypofractionated radiotherapy (MHRT) has emerged as the preferred treatment modality for localized prostate cancer based on randomized controlled studies regarding efficacy and toxicity using contemporary radiotherapy techniques. In the setting of MHRT, available data on dosimetric parameters and late rectal toxicity are limited. Aim: To present the effects of MHRT on late rectal toxicity while conducting an extensive dosimetric analysis in conjunction with rectoscopy results. Methods: This is a prospective study including patients with intermediate-risk prostate adenocarcinoma. All patients were treated with MHRT 44 Gy in 16 fractions to the seminal vesicles and to the prostate, followed by a sequential boost to the prostate alone of 16.5 Gy in 6 fractions delivered with three-dimensional conformal radiation therapy (3DCRT). Acute and late toxicity were assessed. Endoscopy was performed at baseline, every 3 months post-therapy for the first year, and every 6 months for the year after. The Vienna Rectoscopy Score (VRS) was used to assess rectal mucosal injury related to radiotherapy. Dosimetric analysis for the rectum, rectal wall, and its subsegments (upper, mid, and low 1/3) was performed. Results: Between September 2015 and December 2019, 20 patients enrolled. Grade 1 late gastrointestinal toxicity occurred in 10% of the patients, whereas 5% had a grade ≥2. Twelve months post radiotherapy: 4 (20%) patients had VRS 1; 2 (10%) patients had VRS 2; 1(5%) patient had VRS 3. 24 months post radiotherapy, VRS 1 was observed in 4 patients (20%) and VRS 2 in 3 (15%) patients. The dosimetric analysis demonstrated noticeable variations between the rectum, rectal wall, and rectal wall subsegments. The dosimetric analysis of the rectum, rectal wall, and its mid and low segments with respect to rectoscopy findings showed that the higher dose endpoints V52.17Gy and V56.52Gy are associated with rectal mucosal injury. Conclusions: A thorough delineation of the rectal wall and its subsegments, together with the dosimetric analysis of these structures, may reduce late rectal toxicity. Dosimetric parameters such as V52.17Gy and V56.52Gy were identified to have a significant impact on rectal mucosal injury; additional dose endpoint validation and its relation to late GI toxicity is needed.
ABSTRACT
STAT3, a transcriptional mediator of oncogenic signaling, is constitutively active in ~70% of human cancers. The development of STAT3 inhibitors remains an active area of research as no inhibitors have yet to be approved for the treatment of human cancer. Herein, we revealed that bruceantinol (BOL) is a novel STAT3 inhibitor demonstrating potent antitumor activity in in vitro and in vivo human colorectal cancer (CRC) models. BOL strongly inhibited STAT3 DNA-binding ability (IC50 = 2.4 pM), blocked the constitutive and IL-6-induced STAT3 activation in a dose- and time-dependent manner, and suppressed transcription of STAT3 target genes encoding anti-apoptosis factors (MCL-1, PTTG1, and survivin) and cell-cycle regulators (c-Myc). Structure-activity relationship studies demonstrated that the C15 side chain on BOL affected its ability to bind STAT3. Administration of 4 mg/kg BOL significantly inhibited CRC tumor xenografts [p < 0.001], but no effect was observed in a STAT3-/- tumor model. Additional studies showed that BOL effectively sensitized MEK inhibitors through repression of p-STAT3 and MCL-1 induction, known resistance mechanisms of MEK inhibition. Taken together, our findings suggest BOL is a novel therapeutic STAT3 inhibitor that can be used either alone or in combination with MEK inhibitors for the treatment of human CRC.
