StaphTAME

GangaGen’s lead product is a proprietary recombinant protein, P128, for the topical prevention and treatment of Staphylococcal infections, including infection with methicillin-resistant Staphylococcus aureus (MRSA).

Why StaphTAME is needed

Superbugs are an increasing menace both in hospitals and in the community. GangaGen’s StaphTAME (P128 protein) is being developed to prevent or treat serious, and often fatal infection by MRSA, which is a ‘Superbug’, resistant to multiple antibiotics. Legislation at the national level in Europe and the state level in the United States mandating control of Superbugs is becoming more and more common. S.aureus, which over the decades has become resistant to a large number of antibiotics, is one such target of these mandates.

Staphylococcus aureus causes a range of illnesses, from minor skin infections, such as pimples, impetigo, boils, cellulitis, folliculitis, carbuncles, scalded skin syndrome, and abscesses, to life-threatening diseases such as pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock syndrome, bacteremia, and sepsis. Also, it is one of the most common causes of hospital acquired infections (HAIs) and is often the cause of postsurgical wound infection. S.aureus was the first among ten most common pathogens causing device and procedure related Hospital associated infections (HAIs) during 2006-7 as reported by hospitals in the National Healthcare Safety Network (NHSN), USA. Staphylococcal infection especially MRSA, has shown significant rise in the incidence in Asia. The regional Resistance Surveillance (RSS) programme showed that 73% of the clinical S.aureus isolates from two hospitals in Korea were MRSA in 2011. The SENTRY studies in China showed MRSA in 13 to 27.8% of clinical S.aureus isolates from three hospitals in 1998-2001; however rates increased to 50–62% in 2004–2005. The nationwide surveillance study in 2011 showed a mean MRSA incidence rate of 45.8% among all clinical S.aureus isolates. The ANSORP study showed MRSA rates of 38.1% for the Philippines, 57% for Thailand and 74.1% for Vietnam in 2004–2006

Methicillin-resistant Staphylococcus aureus (MRSA) was first described in 1961. Shortly thereafter, outbreaks of MRSA were reported in early 1960s from many places. Since then, MRSA has spread worldwide, and the prevalence of MRSA has exponentially increased in both healthcare and community settings. HAIs infections due to methicillin resistant strains of S.aureus amounted to 60% in ICUs in US during 2003 and more than 90,000 invasive infections were estimated to be MRSA during the 18 month period of 2004 to 2005. A substantial proportion of cases of S.aureus blood infection appear to be of self origin given that they disseminate from the patient’s nose. About 30-50% of the population carries S.aureus in their nares. The number of surgical-site S.aureus infections acquired in the hospital can be reduced by rapid screening and clearing the organism from their nose. This reduces the risk of infection and the resultant hospitalization and treatment costs.

The first case of vancomycin-intermediate-resistant S.aureus (VISA) was identified in 1997, and such strains have now been reported worldwide. More recently, there have been reports of vancomycin resistant S.aureus (VRSA), which is even more alarming, as these isolates demonstrate complete vancomycin resistance.

Linezolid, is one of the few therapeutic options shown to be effective against MRSA. In 2001, one year after linezolid was approved for clinical use, the first Linezolide Resistant Staphylococcus aureus (LRSA) was reported in a US patient. Since then, several cases of LRSA have been reported.

Whereas previously only regarded as an innocuous commensal microorganism on the human skin, Staphylococcus epidermidis is nowadays seen as an important opportunistic pathogen. It is now a frequent cause of nosocomial infections, at a rate about as high as that due to its more virulent cousin Staphylococcus aureus. In particular, S.epidermidis represents the most common source of infections on indwelling medical devices. This likely stems from the fact that S.epidermidis is a permanent and ubiquitous colonizer of human skin, and the resulting high probability of device contamination during insertion. While S.epidermidis infections only rarely develop into life-threatening diseases, their frequency and the fact that they are extremely difficult to treat represent a serious burden for the public health system. The costs related to vascular catheter-related bloodstream infections caused by S.epidermidis amount to an estimated $ 2 billion annually in the United States alone.

Drug-resistant strains among coagulase-negative staphylococci, including S.capitis, S.ureolyticus, S. hemolyticus and S. epidermidis are reported both inside and outside the hospital environment. These represent upcoming challenges as these Staphylococci are capable of causing serious infections.

With the increasing drug resistance among Staphylococci, new classes of antimicrobial agents with different mechanisms of action are urgently required. P128 is effective against MRSA, VISA, VRSA. and antibiotic-resistant Coagulase negative Staphylococcal species.

How We Developed StaphTAME

P128 is a protein and functionally, it is an enzyme. P128 was developed based on a key protein from bacteriophage. When the phage first interacts with a bacterial cell, they damage the cell wall in order to introduce their genetic material into the cell. GangaGen has identified the active portion of the phage protein molecule that causes this damage, and coupled it with another protein sequence that allows rapid and targeted binding to the surface of Staphylococcus. The hybrid molecule is capable of binding to, and damaging the surface of, all strains of S.aureus tested. This damage results in the death of the bacteria.

P128 Structure

The segment shown in red, CHAP, is the enzymatic domain that degrades the bacterial cell wall.It is the cysteine-histidine aminohydrolase / peptidase (CHAP) domain of open reading frame 56 of Phage K; a portion of the tail-associated muralytic enzyme of the phage.

The segment shown in blue, SH3b, confers staphylococcal binding specificity. This is derived from a bacterial anti-staphylococcal protein, known as lysostaphin. Note that P128 is able to kill bacteria that are resistant to killing by full-length lysostaphin itself.

What it does:

P128 is specific to Staphylococcus and kills rapidly leaving other bacteria untouched. Hence, normal microflora and innocuous inhabitant bacterial population remains unaffected unlike the case with many antibiotics which harm normal indigenous bacterial population also.

The P128 protein has been tested in suitable models in vitro against over 200 strains of S.aureus, more than half of which are methicillin-resistant, and has proved capable of killing all of them, none showing resistance to P128. This panel included 56 Japanese, 8 Canadian, 119 Indian isolates and 30 New Jersey strains representative of more than 3000 isolates from across the globe.

Killing of the bacteria is dose-dependent. When the P128 concentration was varied, greater numbers of cells were killed with increasing concentrations of the protein. At concentrations of 2.5 µg/mL and above, the killing rate of P128 was greater than or equal to 99.9%. When the quantity of the applied protein was held constant at 10 µg/mL and the number of cells was increased upto 109/mL, effectively varying the quantity of P128 available per cell, the killing efficacy remained at greater than or equal to 99.99%. The number of remaining viable cells was seen to decrease reaching total clearance when the protein was acting on lower number of cells such as 104/mL.

StaphTAME is efficacious in decolonizing S.aureus in rat nares:

P128 was tested for biological activity in an experimental model of S.aureus nasal colonization in rats. An MRSA strain USA300, that is known to be resistant to the currently in-use antibiotic Mupirocin, was used in these studies. Bacterial cells were instilled in the nares of the animals and allowed to colonize for three days. From the following day, nares were treated twice daily with StaphTAME hydrogel formulation for 3 days. Nasal load of S.aureus was evaluated at the end of the treatment period, as a measure of efficacy of StaphTAME. The bacterial counts recovered from the nares of untreated colonized animals were comparable to the counts recovered from animals that were treated with the Placebo gel. In case of animals treated with Bactroban, a Mupirocin cream formulation, there was no reduction in the number of the instilled USA300 bacteria. In animals that were treated with StaphTAME, four of nine animals (44.4%) had no recoverable MRSA bacteria and could be declared decolonized. In the remaining five animals, the counts recovered were very low, as shown in the figure below.

Way forward:

P128 is a prophylactic for use prior to surgical intervention on patients with chronic dialysis is being progressed.