Sirnaomics' STP705 shows promise for  the treatment of Cutaneous Squamous Cell Carcinoma In Situ (isSCC), according to interim results of part-one of an ongoing Phase IIb clinical trial.

The majority (78%) of 32 patients with STP705 treatment achieved histological clearance, and one of the three treatment cohorts achieved 89 percent histological clearance. 

STP705 is an siRNA (small interfering RNA) therapeutic that takes advantage of a dual-targeted inhibitory property and polypeptide nanoparticle (PNP)-enhanced delivery to directly knock down both TGF-β1 and COX-2 gene expression.

The two-part, double-blind, randomized, placebo-controlled Phase IIb study is designed to evaluate the safety and efficacy of various doses of STP705, administered as an intralesional injection in subjects with isSCC. In the part-one of the study, we have treated 32 patients with 30 μg/ml, 60 μg/ml and 90 μg/ml of STP705, respectively, and 12 patients with 0 μg/ml placebo weekly. After six-week repeated dosing, we collected tissue samples from the treatment sites followed by histological analysis.

This interim report is specifically for part-one of the study results with a total of 44 patients. Based on our Phase IIb study plan, part-two of this study will include 60 additional subjects who will receive selected doses or placebo for a total of more than 100 subjects. Enrolled subjects will be randomly allocated to receive STP705 or placebo injection once a week for a total of six weeks. In the seventh week, the lesion will be excised.

"The positive clinical readouts of the part-one study of this Phase IIb trial provide a further validation of our STP705 for treatment of non-melanoma skin cancers." says Dr. Patrick Lu, Founder, Chairman of the Board, Executive Director, President and CEO of Sirnaomics, in a news release. "With more clinical results from this study and the cutaneous Basal Cell Carcinoma (BCC) study, we feel more enthusiastic about this novel RNAi cancer therapeutics for treatment of Squamous Cell Carcinoma (SCC), addressing a broader unmet patient need."

"In our study thus far, patients who received various doses of STP705 over six weeks achieved better histological clearance of isSCC excised lesions than the patients who received a placebo," adds Dr. Michael Molyneaux, M.D., Executive Director and Chief Medical Officer of Sirnaomics. "As we move into the latter phase of the clinical trial, we will use this information to determine which doses we deem most effective for treating SCC, which is a type of nonmelanoma skin cancer that affects millions of people in the U.S. Currently, there are only a small number of approved non-surgical treatments that exist for SCC."

This interim report of unblinded results of part-one of the Phase IIb study showed that 25 of 32 subjects with STP705 treatment resulted in a high ratio (78%) of histological clearance. Among three treatment cohorts, the 30 μg treatment group (N = 9) achieved the highest histological clearance (89%), while the 60 μg treatment group (N = 12) achieved 75%, and the 90 μg group (N = 11) achieved 73%, which are clearly higher than the placebo group (N = 12) which achieved 58%. There were no treatment-related AE's or SAE's and Local Skin Response Scores were stable or improved across all treatment groups.

More about STP705

STP705 has received multiple IND approvals from both the U.S. Food and Drug Administration (FDA) and the Chinese National Medical Products Administration (NMPA), including treatments of cholangiocarcinoma, non-melanoma skin cancer and hypertrophic scar. STP705 has also received Orphan Drug Designation for treatment of cholangiocarcinoma (CCA) and primary sclerosing cholangitis (PSC). STP705 is currently in seven clinical trials for different indications: a Phase IIb for squamous cell carcinoma in situ (isSCC), a Phase II for basal cell carcinoma (BCC), a Phase I/II for keloid scarring, a Phase I/II for hypertrophic scar (HTS), a Phase I/II for facial isSCC, a Phase I for liver cancer (basket), and a Phase I for medical aesthetics treatment.