Summary of Clinical Trials with CB-24 (Crotoxin)

Annals of Oncology (full text)

Abstract:

Background
Crotoxin, a neurotoxin from Crotalus durissus terrificus, showed significant anti-tumor activity with intramuscular administration but had notable toxicity. Preclinical data suggested that an intra-patient dose escalation protocol allows for high doses with reduced toxicity.

Methods
Following the study design of Medioni et al. (Abstract CT071, AACR 2018), intra-patient (pt) dose escalation was conducted in 8 pts (5 males, 3 females) with advanced solid tumors without further treatment options: 1 nasal squamous cell carcinoma, 2 glioblastomas, 1 endometrial adenocarcinoma, 1 NSCLC, 1 prostatic carcinoma, 1 ovarian carcinoma, and 1 choroidal melanoma. The objective was to determine maximum tolerated dose (MTD) defined as the dose at which no further dose escalation can be safely achieved for >33% of pts in the group of 12 consecutive pts. Dose escalation occurred three times weekly, followed by a 2-hour observation at the clinic, with increments of 0.08 mg/m2/day at each level every 3-4 days. The initial dose was 0.08 mg/m2/day for 6 pts and 0.20 mg/m2/day for 2 pts. RhythmicTM continuous delivery pumps enabled pts to remain at home. Dose limiting toxicity (DLT) was defined as the inability to escalate the dose twice due to toxicity, permitting treatment continuation at the last tolerated dose.

Results
MTD was not achieved due to the low toxicity of crotoxin. Adverse events related to the crotoxin were mainly Grade (G) 1 and G2. One pt with pre-existing diarrhea, G2 hypomagnesemia, G3 hypokalemia and G2 anemia experienced complete arrhythmia with asymptomatic atrial fibrillation, which was resolved. This event was classified as a possible drug-related Serious Adverse Event, also associated with prior chemotherapy (nivolumab and cisplatin). Three patients showed tumor stability on day 36, and one of them, who began treatment at 0.20 mg/m2/day, reached DLT on day 40 (G3 creatine phosphokinase and G3 alanine aminotransferase) and remained stable at four weeks post-DLT.

Conclusions
Initiating at a higher dose and increasing the speed of dose escalation was safe showing a trend towards clinical benefit. New cohort will begin at 0.20 mg/m2/day using faster escalation, twice a week, to determine MTD.

DOI: 10.1158/1538-7445.AM2018-CT071

Abstract:

Introduction
Crotoxin (CRTX), a potent neurotoxin from the venom of Crotalus durissus terrificus, rattlesnake, upon intramuscular administration has been shown to have broad anti-tumor activity accompanied with significant toxicity. Preclinical animal data suggested that in intra-patient dose escalation protocol the administration of high doses and efficacy can be achieved without toxicity.

Methods
We followed the design of Medioni et al (Contemp. Clinical Trials Comm. 7, 2017: 186-168) in intra-patient dose escalation study to administer CRTX in heavily pre-treated patients (5 males and 1 female) with advanced solid tumors: 1 nasal squamous cell carcinoma, 2 glioblastomas, 1 endometrial adenocarcinoma, 1 NSCLC and 1 prostatic carcinoma. Lightweight RythmicTM pump capable of continuous delivery (no weekend breaks) allowed patients to stay at home. Over 35 days, CRTX dose escalation from 0.08 to 0.64 mg/m2/day was carried on Mondays, Wednesdays and Fridays, followed each time by 2h observation at the clinic. Dose limiting toxicity (DLT) and maximum tolerated dose (MTD) were defined as the inability of dose escalation twice due to toxicity and the dose at which no further dose escalation can be safely achieved for >33% of the pts in the study, respectively.

Results
2/6 patients developed possibly drug-related G1 diplopia and 1/6 pts increased ASAT/ALAT. One patient recruited with pre-existent diarrhoea syndrome with uncontrolled G2 hypomagnesaemia, G3 hypokalaemia and G2 anaemia, developed complete arrhythmia with asymptomatic atrial fibrillation that resolved with amiodarone. Patient was hospitalised for observation and the event was classified as a possible study drug-related SAE as well as related to the digestive syndrome and tubulopathy resulting from previous chemotherapy (nivolumab and platinum salts). Stable disease was observed in 2/6 patients.

Conclusion
No DLT or MTD have been reached. CRTX dose escalation is safe but too slow, doses achieved too low and too late for advanced patients. In a new cohort, CRTX regimen will be continued starting from higher dose with faster dose escalation.

DOI: 10.1158/1538-7445.AM2018-CT070

Abstract:

Introduction
Crotoxin is a bipartite South America rattle snake neurotoxin. It has broad spectrum antitumor activity in vivo in addition to exerting analgesic effects. Prior clinical reports using i.m. injections resulted in local immune reactions with erythema, itching or pain, in addition to anaphylaxis though encouraging responses were recorded. A clinical study was designed incorporating i.v. administration, dose escalation and pre-treatment antihistamine use, aimed at improving dose limiting toxicity (DLT) and local tolerance.

Method
This trial was performed in patients with stage IV cancer with the primary endpoints to assess safety and tolerability, measured by Dose-Limiting Toxicity (DLT) and to define the Maximum Tolerated Dose (MTD). The secondary objectives were to document anti-tumor efficacy, evaluated according to radiological RECIST criteria 1.0 and analgesia. Baseline pain assessments were completed for each patient. Cohort I included 6 patients with advanced solid tumors (no further therapy options), with dose escalation from 0.04 to 0.32 mg/m2/day administered IV by saline drip over 2h daily (Mon to Fri) over 54 days.

Results
One male and 5 females (pts) with prior heavily treated advanced tumors were enrolled: colorectal adenocarcinoma, epithelioid mesothelioma, non-small-cell lung cancer, carcinoma of unknown primary site, invasive breast ductal carcinoma and ovarian papillary adenocarcinoma. Three patients reached the highest target dose level. DLT or MTD were not attained. In Cohort I grade 1 to 2 drug-related events occurred in 3/6 patients: anorexia, diplopia and nystagmus. There were no drug-related serious adverse events. Tumor assessment was performed after 8 weeks of dose escalation (day 54) and all subjects were determined to have progressive disease. At baseline, pain was reported for 5/6 subjects, surveys revealed a diminution of analgesic scores.

Conclusion
Crotoxin i.v. dose escalation protocol allowed administering 0.32 mg/m2/day without unexpected toxicity. Lack of anti-cancer benefit might be related to the long period of 6-8 weeks to reach this dose. A redesign of the protocol to escalate faster and to higher doses, without weekend breaks, is required.

PubMed PMID: 11948110

Abstract:
A Phase I clinical trial was performed on patients with solid tumors refractory to conventional therapy. Crotoxin was administered i.m. for 30 consecutive days at doses ranging from 0.03 to 0.22 mg/m2. Patients entered the study after providing a written informed consent. Although 26 patients were entered only 23 were evaluated. Reversible, nonlimiting neuromuscular toxicity evidenced as diplopia because of pareses of the external ocular muscles was present in 13 patients. It started at doses of 0.18 mg/m2 and lasted from 2 to 6 h. These episodes did not require dose adjustment and disappeared in 1–3 weeks of treatment. Three patients experienced palpebral ptosis, nystagmus (grade 2), and anxiety (grade 2–3) at the dose-limiting toxicity of 0.22 mg/m2. Also, at dose-limiting toxicity, 1 patient showed nystagmus (grade 2) and anxiety (grade 3) without evidence of palpebral ptosis. Transient increases (grades 1–3) in the levels of creatinine kinase, aspartate aminotransferase, and alanine transaminase attributed to crotoxin myotoxicity were observed but returned to normal by the last week of treatment. At 0.21 mg/m2 there was a case of grade-3 anaphylactic reaction on day 31, which required treatment. Hypersensitivity was regarded as an adverse drug-related reaction, and the patient was removed from the protocol. Two patients at different doses (0.12 mg/m2 and 0.22 mg/m2) had sialorrhea. Four patients had asymptomatic transient increase in blood pressure (up to 20 mm Hg) 12 h after the first injection, which lasted 24 h. No treatment was required and toxicity did not reappear. Six patients experienced slight eosinophilia during the first 2 weeks. The maximum tolerated dose was set at 0.21 mg/m2. Objective measurable partial responses (>50% reduction of tumor mass) were noted in 2 patients treated at 0.21 mg/m2 and 1 at 0.12 mg/m2. One patient (at 0.21 mg/m2) presented a complete response on day 110. Crotoxin pharmacokinetics showed rapid absorption from the injection site to blood (t1/2 A = 5.2 ± 0.6 min). Plasma concentration reached a peak (Cmax = 0.79 ± 0.1 ng/ml) at τmax = 19 ± 3 min. The half-life of the distribution (alpha) phase is 22 ± 2 min. Starting at 1.5 h after injection, the decrease in plasma concentration becomes slower, reaching 14 ± 3 pg/ml 24 h after injection. The profile is dominated by the elimination (beta) phase with a half-life of 5.2 ± 0.6 h. Consequently, 24 h after the injection (approximately five half-lives) 97% of the product was eliminated. The area under plasma concentration versus time curve was 0.19 ± 0.05 μg/min/ml. Assuming availability (F) approximately 1, the clearance is CL = 26.3 ± 7 ml/min, and the apparent volume of distribution is Vd = 12 ± 3 liter/kg. The recommended dose for a Phase II study is 0.18 mg/m2.

Costa et al. 17th International Cancer Congress, Rio de Janeiro (Brazil), August 24–28, 1998. Active link unavailable.

Abstract:
Novel therapies targeting the epidermal growth factor receptor (EGFR) could represent a new approach for the treatment of carcinomas. VRCTC-310, a combination of crotoxin and cardiotoxin, is a natural product derived from snake venom fractions with phospholipase A2 activity. Its cytostatic activity appears to be related to its ability to induce tyrosine phosphorylation of EGFR in several cell lines, manifested by disturbances in cell-membrane lipid components, thereby allowing cell destruction. From December 1996 to August 1997, five patients (pts) with histologically confirmed locally advanced cancer (breast cancer, n=3; squamous cell cancer of the hand, n=1; chordoma, n=1) were treated at Bernardo Houssay Hospital (Oncology Unit) with VRCTC-310 at a full dose of 0.014 mg/kg once weekly, inoculated peritumorally and distributed in four injections around the tumor, for no fewer than eight courses. All patients provided written informed consent per local ethics committee requirements. A complete response was observed in three patients (breast cancer, n=2; skin carcinoma of the hand, n=1), and a partial response was recorded in the other two patients. No toxicities were observed except mild local pain at the injection site. We conclude that weekly VRCTC-310 administered subcutaneously via the peritumoral route is an active, well-tolerated, and safe treatment for advanced skin metastatic tumors.

PubMed PMID: 9543697

Abstract:
The authors report their clinical experience with VRCTC-310 in two patients suffering with advanced cancer in which the skin was severely compromised. VRCTC-310 is a combination of the snake venoms crotoxin (CT) and cardiotoxin (CD). The local (peritumoral) treatment with the drug (0.014 mg/kg/week during 6 weeks) provoked the complete disappearance of a relapsed skin squamous cell cancer in one patient. The other patient was an aged woman with local-advanced breast cancer (carcinoma en cuirasse) who was inoculated intra-and-peritumoral with VRCTC-310. After 6 weekly courses (0.014 mg/kg/week) with the drug a > 80% tumor reduction was seen. A 133 days follow-up demonstrated not only an objective complete response of the primary tumor mass, but the disappearance of supraclavicular tumor mass as well a significant reduction in lymphangitis. To our knowledge, this is the first communication about the in vivo antitumoral activity of VRCTC-310 when injected locally to humans. Further studies are now in progress.

PubMed PMID: 9402309

Abstract:
A phase I study was performed to evaluate the maximum tolerated dose (MTD), safety profile and pharmacokinetic data with VRCTC-310, a natural product derived from purified snake venom fractions, with phospholipase A2 activity and inhibitory effects against human and murine tumor cell lines. Fifteen patients with refractory malignancies were entered after providing written informed consent. VRCTC-310 was administered as an intramuscular injection daily for 30 consecutive days. Doses were escalated from 0.0025 to 0.023 mg/kg. Toxicities included local pain at the injection site, eosinophilia, reversible diplopia and palpebral ptosis. Dose escalation was stopped at 0.023 mg/kg, when two patients had developed anaphylactoid reactions. Both cases had high VRCTC-310-specific IgG by EIA. MTD was 0.017 mg/kg and the recommended dose for phase II studies is 0.017 mg/kg. Stabilization was found in six patients.

The above-described early-stage development trials have cumulatively shown exceptional safety indications, particularly in comparison to many approved therapeutics, with trends to efficacy and pain relief (also a significant benefit of the drug).

The Company continues to advance its novel and unique i.v. intra-patient dose escalating protocol. The Company is planning a Phase I to Phase II rollover trial, DLT) Phase II trials to confirm clinical efficacy. This trial will commence in France with the Phase II rollover being expanded to several other countries.