Clinical stage oncology company Prescient Therapeutics (ASX: PTX) has announced continued promising data for its targeted therapy PTX-100, after releasing Phase 1b trial data that showed a wealth of positive data – including two complete responses in patients with relapsed and refractory (r/r) Peripheral T-cell Lymphoma (PTCL). This data comes on the heels of a recent announcement by the US Food and Drug Administration (FDA) to grant PTX-100 Orphan Drug Designation for all T-cell lymphomas.  The company is now expanding the trial in preparation for a Phase 2 Accelerated Approval trial.

A complete eradication of cancer is not generally expected in this disease, so it is exceptionally encouraging to see PTX-100 have such positive results in two patients. The overall response rate (ORR) so far of 40% is exceeding the target of >30%.  This calculation does not take into account those patients experiencing stable disease (SD). The Clinical Benefit Rate (CBR) for CTCL, which includes patients with complete and partial response as well as those with durable stable disease, was 60% – compared to the average CBR of 50% for typical CTCL therapies. 

The median progression free survival rate for r/r PTCL patients with current therapies is just 3-4 months.  In total, 7 out of 10 evaluable patients with r/r PTCL and r/r CTCL had durations of responses that exceeded the standard of care. The Phase 1b study had targeted median progression free survival (PFS) rate of 5-6 months – and has so far achieved a mean 8.7 months. This is all the more impressive given that the study is ongoing, and new patients that were recently added, impact this PFS figure.

PTX is now recruiting an additional seven patients to the study in order to build a more robust data package ahead of an upcoming meeting with the FDA later this year. The company is planning a subsequent Phase 2 trial in TCL, which the FDA will hopefully allow to be an Accelerated Approval trial in an Orphan indication. This could pave the way for expedited regulatory approval for PTX-100. 

PTCL is a rare type of non-Hodgkin’s lymphoma that arises in the lymphoid tissues outside of the bone marrow – such as lymph nodes, spleen, gastrointestinal tract and skin. Most PTCLs are aggressive (fast-growing) lymphomas, and there is a high chance of patients relapsing. There are around 5,600 cases per year in the US, and the disease has an average 5-year survival rate of 32%.

Currently available therapies for PTCL are typically characterised by a high occurrence of serious toxicities, low response rates (less than 30%) and a short duration of responses (3-4 months).

The standard protocol for initial treatment of PTCL involves multi-drug chemotherapy regimens such as CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone). However, approximately 68% of PTCL patients relapse after treatment or are refractory (resistant) to conventional chemotherapy. 

Newer ‘breakthrough’ therapies are only given to PTCL patients after prior lines of therapy have failed (which puts patients in the r/r category), at which time the cancer has likely spread throughout the body. One of these therapies is called Folotyn, an injectable chemotherapy drug that stops cancer cells multiplying by preventing the cells from using folic acid to make DNA. It costs US$450,540 per patient, per year –  and comes with a greater than 70% chance of a serious adverse event including anaemia, mucositis and thrombocytopenia (low platelets).

At the time of it’s approval in 2009, Folotyn was the only approved therapy for relapsed or refractory (R/R) PTCL. Perfectly characterising the desperation of the disease’s clinical landscape, which is still very much present today, the drug was given approval based on its overall response rate – not clinical benefits such as an improvement in progression free survival or overall survival (which were not demonstrated). 

Commenting on the state of current therapies, Prescient MD and CEO Steven Yatomi-Clarke said, “I think it is easier to justify a high drug price if the drug works well. But the most expensive cancer therapies are those that don’t work and do more harm than good. We hope PTX-100 will make a real improvement in outcomes for patients who desperately need more effective therapies”.

Mr Yatomi-Clarke, was very excited to see this early clinical data continue unfold so favourably, especially seeing as PTX-100 has maintained its excellent safety profile where other TCL therapies have not.

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