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Therapeutic Development Research for Phenylketonuria (PKU)

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Mild PKU

• BioMarin (http://www.biomarinpharm.com/)
  • Phenoptin™ (BH4): BioMarin initiates Phase 3 Clinical Trial of Phenoptin™ for PKU.
    Novato, CA, April 7, 2005 – BioMarin Pharmaceutical Inc. (Nasdaq and SWX: BMRN) announced today that it has randomized the first patient in its Phase 3 clinical trial of Phenoptin™ (sapropterin hydrochloride), an investigational oral, small molecule therapeutic for the treatment of the genetic disease phenylketonuria (PKU). The company expects to announce data from this trial in the second half of 2005.
    
• List of PKU patients with BH4 responsive mutations studied (from Erlandsen et al., PNAS 101:16903, 2004 [PDF] and Matalon et al., Genet. Med. 6:27-32, 2004 [PDF])
  

  PKU patients with BH4 responsive mutations studied, their location/effect on the PAH structure
  PAH cDNA nucleotide change	PAH mutation	Structural contacts/comments	Metabolic phenotype (homozygotes and functional hemizygotes)	% decrease in L-Phe levels after 24h in patients with BH4-responsive genotypes
  c.117C>G	F39L	In hydrophobic core of RD formed by Leu37, Leu41, Val51, Ile65, Phe79, Leu98, Ile102, Ala104 and Leu106. Substitution to a smaller Leu may change the core structure and destabilize RD.	Mild to classical PKU	F39L/R408W F39L/F55fsdelT F39L/F55fsdelT	44.3 36.1 70.7
  c.194T>C	I65T	In hydrophobic core of RD. Substitution to a more polar Thr may distort the hydrophobic packing in the RD core.	Non-PKU HPA to classical PKU	I65T/R68S I65T/R408W I65T/R408W	23.2 38.2 58.4
  c.204A>T	R68S	H-bonds to Ser67, and stabilizes secondary structure of Rb2. In tetramer model Arg68 is close to Tyr216 from molecule C. Substitution to Ser may disrupt H-bond and dimer/tetramer interactions.	Mild PKU	R68S/R408W R68S/I65T	40.7 23.2
  c.311C>A	H170D	On surface of CD, close to TD and RD. Substitution into an Asp may disrupt a H-bond to Arg241 at the start of Cb1.	Non-PKU HPA	H170D/IVS1nt5g>a	68.2
  C.533A>G	E178G	On surface of CD. Substitution to a small and flexible hydrophobic residue may be very unfavorable, as it can change fold of CD core, which is important for maintaining proper catalytic function.	Non-PKU HPA	E178G/IVS10nt-11g>a	45.8
  c.569T>C	V190A	Close to L-Phe substrate binding site (7.1Å). Important for proper substrate orientation for catalysis.	-	-	-
  c.782G>A	R261Q	In loop between Ca6 and Cb2. Interacts with Gln304 and Thr238 by H-bonds. Close to Tyr417 in tetrameric model. A substitution would disrupt H-bonds to Gln304 and Thr238 which stabilizes the secondary structure in the active site, and potentially interfere with proper dimer/tetramer formation.	Variant PKU to classical PKU	R261Q/R408W R261Q/L308F	17.3 71.9
  c.898C>T	A300S	Close to Thr 238. Not enough room for larger sidechain of Ser. May change polarity in CD core.	Non-PKU HPA	A300S/R408W	58.7
  c.922C>T	L308F	Close to TD Val412 and Tyr414, and CD Ala259 and Glu305. No room for Phe sidechain. Substitution would push TD away. Mutation may interfere with proper dimer/tetramer formation.	-	L308F/R261Q	71.9
  c.937G>A	A313T	Close to TD Ile406 and Pro407. Mutation may interfere with proper dimer/tetramer formation.	Mild PKU	-	-
  c.1117G>A	A373T	Close to Phe402 and Lys320. Mutation may interfere with proper dimer/tetramer formation.	Non-PKU HPA	-	-
  c.1162G>A	V388M	Val388 is located to surface of monomer, close to other monomer of dimmer. Mutation to Met may cause disturbances in dimerization.	Mild to moderate PKU	-	-
  c.1169A>G	E390G	No contacts. On surface, pointing towards molecule B. Substitution to Gly induce local distortions in CD.	Non-PKU HPA	E390G/IVS12nt1g>a	70.2
  c.1219C>T	P407S	Pro may be important for positioning TD helix. Mutation may interfere with proper dimer/tetramer formation.	Non-PKU HPA	P407S/R408W	45.2
  c.1241A>G	Y414C	Stacks between Pro416 (TD) and Phe260 (CD). Important for keeping TD close to CD. Mutation may interfere with proper dimer/tetramer formation.	Non-PKU HPA to variant PKU	Y414C/R408W Y414C/R408W Y414C/IVS7nt5g>a	20.5 26.3 30.1

  

• BH₄ (http://www.bh4.org)
  
• PhenylAde (http://www.medicalfood.com/PhenylAde_tablets.html)

Classical PKU and Enzyme Replacement Therapy

• Enzyme replacement therapeutic for treatment of PKU (under development). Phenylalanine Ammonia Lyase (crystal structure shown below) is under study for modification as a potential enzyme replacement therapy for the treatment of PKU (from Wang et al. Molec. Genet. Metab. 86:134, 2005).

• Mice are currently used in preclinical animal studies and therapeutic development.

• Plasma phenylalanine levels are studied in the mice following administration of potential therapeutics (from Gamez, et. al. Molec. Ther. 11:164, 2005).

• Serum antibody levels after 3 subcutanous bolus injections of 20 kDa linear pegylated PAL formulations (from Gamez, et. al. Molec. Ther. 11:164, 2005).

Last updated 10/28/2005