Dose Escalation Using Magnetic Resonance Guided High-Dose-Rate Endorectal Brachytherapy to Enhance Clinical Response after Neoadjuvant Radiotherapy in Rectal Adenocarcinoma

PURPOSE/OBJECTIVE(S)

To assess the proportion of patients with rectal adenocarcinoma achieving clinical complete response after neoadjuvant chemoradiation (NACTRT) and MR guided endorectal brachytherapy boost (MR-ERBT) MATERIALS/METHODS: Patients with rectal cancers (T2-T4/N0-N+) treated with concurrent chemoradiotherapy (50Gy/25# with Capecitabine) between June-2017 to April-2022. Post RT, patients having residual non-circumferential lesions <8cm in length were administered escalated-dose MR-ERBT with Ir192 HDR source. A median dose of 12Gy (8-15Gy) in 3 (2-3) fractions at 3-5 day intervals was delivered using MR-ERBT after external radiation. Data on near complete/complete clinical response (nCR/cCR) rates, local regrowth rates and clinical outcome were collected for analysis.

RESULTS

Of the 145 patients who received MR-ERBT, majority were staged as T3(78.7%) and N1-2 (77.5%) rectal cancers. Median tumor length was 4cm and 123 (85%) of the tumors were located in the lower rectum (0-5cm from anal verge). Seventy-six (52%) patients achieved cCR or nCR (37 cCR, 39 nCR) and were advised observation or watch and wait (WW) management. The 69 patients having partial response were advised surgery. The patients having nCR 16 (29%) underwent resection, of these 10 (62%) had pathological complete response (pCR). The patients with partial or poor response, 57 underwent resection and of these 11 (19%) had pCR, 12 patients refused surgery due to fear of permanent stoma and continued to be on follow up. Of the 79 patients undergoing resection, 36 (45.5%) had sphincter preserving surgeries. At the median follow up of 30 months, local regrowth was seen in 8 (10.5%) of patients on WW and 6 were surgically salvaged while other 2 had synchronous metastatic relapse. Thus, 56 (41%) achieved organ preservation and continued to be on WW management. Twelve (8,2%) patients developed distant metastasis in the entire cohort, 3 in the WW group and 9 in the resected group. There were no pelvic recurrences seen in the resected patients. The disease-free survival at 3 years were (96.1% vs 89% Observation vs. resected (p_0.05) respectively. The overall survival at 3 years were (93% vs 98% Observation vs. resected (p_0.44) respectively. Late rectal toxicity was observed in 16(11%) patients on observation CONCLUSION: Dose Escalated MR-EBRT is an effective and safe method to enhance complete clinical response, thus improving the rate of organ preservation for distal rectal cancers.

OP0097 PROOF-OF-CONCEPT OF FIBROBLAST-TARGETED PHOTODYNAMIC THERAPY IN HUMAN 3D SCLERODERMA SKIN MODEL AND BLEOMYCIN-INDUCED SKIN FIBROSIS IN MICE

Background

Systemic sclerosis (SSc) is a rare, severe auto-immune disease characterized by inflammation, vasculopathy and fibrosis. Activated (myo)fibroblasts are crucial drivers of fibrosis. By exploiting their expression of fibroblast activation protein (FAP) to perform targeted photodynamic therapy (tPDT), we can locoregionally deplete these pathogenic cells.

Objectives

We explored the use of FAP-tPDT to selectively target primary skin fibroblasts from SSc patients, both in 2D and 3D cultures, as well as in biopsies from fibrotic skin lesions in the murine bleomycin-induced skin fibrosis model.

Methods

The FAP targeting monoclonal antibody (clone 28H1) was conjugated with the photosensitizer IRDye700DX. Primary skin fibroblasts were obtained from lesional skin biopsies of SSc patients via spontaneous out-growth and subsequently cultured on plastic or collagen type I. For 2D FAP-tPDT, cells were incubated in buffer with or without the antibody-photosensitizer (Ab-PS) construct, washed after 4 h and exposed to λ = 689 nm light (50 J/cm2 at 280 mW/cm2). Cell viability was measured using CellTiter Glo. For 3D FAP-tPDT, cells were seeded in collagen plugs and underwent the same treatment procedure. Contraction of the plugs was followed over time to determine myofibroblast activity. Skin fibrosis was induced in mice by 3x/week injections of 1.5 IU bleomycin intradermally on the back of the mouse. After 5 weeks the mice were sacrificed and biopsies were taken from affected and not affected skin. These were incubated with or without the FAP targeting Ab-PS construct or a control Ab-PS. After washing, the biopsies were exposed to light, incubated for 1h and subsequently formalin fixed and paraffin embedded. Sections were immuno stained for the presence of cleaved caspase-3.

Results

FAP-tPDT resulted in antibody-dose dependent cytotoxicity in primary skin fibroblasts upon light exposure. Cells not exposed to light or incubated with a control Ab-PS construct did not show this response. FAP-tPDT fully prevented contraction of collagen plugs seeded with primary SSc fibroblasts. Even incubation with a very low dose of antibody (0.4 nM) inhibited contraction in 2 out of 3 donors. In fibrotic skin biopsies from mice with bleomycin-induced skin fibrosis, an upregulation of apoptosis, as evidenced by increased caspase-3 staining (Figure 1), was observed in response to FAP-tPDT. The same treatment on biopsies of control skin did not increase caspase-3 staining, nor did incubation with a control Ab-PS construct or light alone.

Figure 1.

Cleaved caspase-3 staining of biopsies from the skin of mice with bleomycin-induced dermal fibrosis upon treatment with FAP-tPDT. The red arrows indicate the presence of positive fibroblasts.

Conclusion

Here we have shown, for the first time, the potential of FAP-tPDT for the selective targeting of pathogenic fibroblasts and treatment of fibrosis in SSc skin both in relevant patient-derived culture models as well as an in vivo model of fibrosis.

Disclosure of Interests

Daphne Dorst: None declared, Arjan van Caam: None declared, Elly Vitters: None declared, Birgitte Walgreen: None declared, Monique Helsen: None declared, Christian Klein Employee of: CK is an employee of Roche pharmaceutics, Shreya Gudi: None declared, Tirza Wubs: None declared, Jyoti Kumari: None declared, Przemysław Błyszczuk: None declared, Madelon Vonk: None declared, Peter van der Kraan: None declared, Marije Koenders: None declared.

Coronoidectomy, masticatory myotomy and buccal fat pad graft in management of advanced oral submucous fibrosis

The purpose of this study is to evaluate coronoidectomy, masticatory myotomy and buccal fat pad graft in advanced (Stage III-IV) oral sub mucous fibrosis (OSF). 10 patients with clinically and histologically confirmed advanced OSF underwent surgery entailing bilateral coronoidectomy, masticatory muscle myotomy and closure with a pedicled buccal fat pad graft followed by vigorous mouth opening exercises. The result was evaluated using the interincisal distance at maximum mouth opening as the objective outcome measure over a follow up period of 12 months. Results showed a mean interincisal opening of 14.7 mm preoperatively and 32.5 mm at 12 months postoperatively. Relapse was encountered in one patient who did not cooperate with the postoperative exercise regime. Results suggest this regime is effective.

Modulation of GTPase activity of G proteins by fluid shear stress and phospholipid composition

Mechanical forces arising from strain, pressure, and fluid shear stress are sensed by cells through an unidentified mechanoreceptor(s) coupled to intracellular signaling pathways. In vascular endothelial cells, fluid shear stress is transduced via pathway(s) involving heterotrimeric guanine nucleotide-binding proteins (G proteins) by molecular mechanisms that are unknown. In the present study, we investigated the activation of purified G proteins reconstituted into phospholipid vesicles. Vesicles containing G proteins were loaded with [gamma-32P]GTP and subjected to physiological levels of fluid shear stress in a cone-and-plate viscometer. Steady-state GTP hydrolysis was measured as an index of G protein function. Shear stress (0-30 dynes/cm2) activated G proteins in dose-dependent manner (0.48-4.6 pmol/min per microg of protein). Liposomes containing lysophosphatidylcholine (30 mol %) or treated with benzyl alcohol (40 mM), conditions that increase bilayer fluidity, exhibited 3- to 5-fold enhancement of basal GTPase activity. Conversely, incorporation of cholesterol (24 mol %) into liposomes reduced the activation of G proteins by shear. These results demonstrate the ability of the phospholipid bilayer to mediate the shear stress-induced activation of membrane-bound G proteins in the absence of protein receptors and that bilayer physical properties modulate this response.

Activation of G proteins mediates flow-induced prostaglandin E2 production in osteoblasts

Interstitial fluid flow may play a role in load-induced bone remodeling. Previously, we have shown that fluid flow stimulates osteoblast production of cAMP inositol trisphosphate (IP3), and PGE2. Flow-induced increases in cAMP and IP3 were shown to be a result of PG production. Thus, PGE2 production appears to be an important component in fluid flow induced signal transduction. In the present study, we investigated the mechanism of flow-induced PGE2 synthesis. Flow-induced a 20-fold increase in PGE2 production in osteoblasts. Increases were also observed with ALF4-(10mM) (98-fold), an activator of guanidine nucleotide-binding proteins (G proteins), and calcium ionophore A23187 (2 microM) (100-fold) in stationary cells. We then investigated whether flow stimulation is mediated by G proteins and increases in intracellular calcium. Flow-induced PGE2 production was inhibited by the G protein inhibitors GDP beta S (100 microM) and pertussis toxin (1 microgram/ml) by 83% and 72%, respectively. Chelation of extracellular calcium by EGTA (2 mM) and intracellular calcium by quin-2/AM (30 microM) blocked flow stimulation by 87% and 67%, respectively. These results suggest that G proteins and calcium play an important role in mediating mechanochemical signal transduction in osteoblasts.